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Foiling Counterfeiters With Nanotech Tiny tags can prove authenticity P.32

Soon, Your Body Can Be A Display Think tattoo, but full-color and live-motion P.38

Kenya’s Low-Key Farming Boom Off-grid solar and microcredit: a dynamic duo P.44

How Inovio’s Kate Broderick Is Helping to Reinvent the Vaccine

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VOLUME 58 / ISSUE 6

The Hidden Authenticators

JUNE 2021

Tiny, near-invisible mechanical resonators can help to combat the sale of counterfeit goods. By Roozbeh Tabrizian & Swarup Bhunia

Put Down That Smartphone: The Display Is on Your Skin

Vaccines Go Electric

A new COVID-19 vaccine relies on a handheld gadget to zap DNA into cells. By Emily Waltz

The last frontier in wearable electronics is about to be crossed. By Takao Someya

Off-Grid Solar’s Killer App

Solar-powered irrigation boosts crop yields and neutralizes the threat of droughts in Africa. By Peter Fairley NEWS Weaponized Drones (p.6) Lithium-ion Prices (p.10) EV Reluctance Motors (p.11) HANDS ON RISC V makes for a very modern home-brew CPU.

CROSSTALK 20 Numbers Don’t Lie (p.20) Internet of Everything (p.22) Macro & Micro (p.23) PAST FORWARD A Story of Silicon THE INSTITUTE

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Wireless Smart Bandage

Its sensors measure body temperature and the strain being put on skin.

ON THE COVER AND THIS PAGE [RIGHT]: Photo by Spencer Lowell

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BACK STORY

Big Plans in Kenya

EEE Spectrum contributing editor Peter Fairley is accustomed to traveling the world in pursuit of a good story. For Spectrum, he’s reported on billion-dollar power-grid projects in China, Germany, and Libya, among other places. For “Off-Grid Solar’s Killer App” [p. 44], Fairley’s focus was on the opposite end of electricity generation: places where the main power grid is unlikely to arrive anytime soon. To report it, he flew from his home in Canada’s British Columbia to Kenya. Fairley knew that Kenya had embraced off-grid solar power early on and with great success. And he knew there was a new phase of that story to tell about productivity. Landing in Nairobi, Fairley headed straight to an international conference on off-grid solar, where panelists and exhibitors described solar-powered electric cookers, refrigerators, grain processors, and irrigation pumps. “I became convinced that solar water pumping in particular could have a massive impact,” Fairley says. Despite an abundance of groundwater in much of sub-Saharan Africa, farmers rarely rely on irrigation and are at the mercy of frequent droughts. With irrigation, productivity soars and incomes stabilize. He quickly got in touch with one of the leaders in this sector, SunCulture, and the company connected him with several of its farming customers. To visit the farms, Fairley bought a ticket on a matatu, a minibus, which took him to the equatorial town of Nanyuki. “As soon as you leave the main road, the power grid quickly falls away,” Fairley says. On each farm, he spotted several vintages of discarded solar equipment. “Solar panels, batteries, and lights have been around for a while, but only recently have these systems become robust and capable of lifting water,” he notes. Fairley was struck by the sense of optimism among the farmers he met. “They want to expand what they can do with solar. They all have big plans.”

PETER FAIRLEY

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CONTRIBUTORS

 NATASHA BAJEMA EDITOR IN CHIEF Susan Hassler, s.hassler@ieee.org EXECUTIVE EDITOR Glenn Zorpette, g.zorpette@ieee.org EDITORIAL DIRECTOR, DIGITAL Harry Goldstein, h.goldstein@ieee.org MANAGING EDITOR Elizabeth A. Bretz, e.bretz@ieee.org SENIOR ART DIRECTOR Mark Montgomery, m.montgomery@ieee.org PRODUCT MANAGER, DIGITAL Erico Guizzo, e.guizzo@ieee.org SENIOR EDITORS Evan Ackerman (Digital), ackerman.e@ieee.org Stephen Cass (Special Projects), cass.s@ieee.org Jean Kumagai, j.kumagai@ieee.org Samuel K. Moore, s.k.moore@ieee.org Tekla S. Perry, t.perry@ieee.org Philip E. Ross, p.ross@ieee.org David Schneider, d.a.schneider@ieee.org Eliza Strickland, e.strickland@ieee.org DEPUTY ART DIRECTOR Brandon Palacio, b.palacio@ieee.org PHOTOGRAPHY DIRECTOR Randi Klett, randi.klett@ieee.org ONLINE ART DIRECTOR Erik Vrielink, e.vrielink@ieee.org NEWS MANAGER Mark Anderson, m.k.anderson@ieee.org ASSOCIATE EDITORS Willie D. Jones (Digital), w.jones@ieee.org Michael Koziol, m.koziol@ieee.org SENIOR COPY EDITOR Joseph N. Levine, j.levine@ieee.org COPY EDITOR Michele Kogon, m.kogon@ieee.org EDITORIAL RESEARCHER Alan Gardner, a.gardner@ieee.org ADMINISTRATIVE ASSISTANT Ramona L. Foster, r.foster@ieee.org CONTRIBUTING EDITORS Robert N. Charette, Steven Cherry, Charles Q. Choi, Peter Fairley, Maria Gallucci, W. Wayt Gibbs, Mark Harris, Jeremy Hsu, Allison Marsh, Prachi Patel, Megan Scudellari, Lawrence Ulrich, Emily Waltz EDITOR IN CHIEF, THE INSTITUTE Kathy Pretz, k.pretz@ieee.org ASSISTANT EDITOR, THE INSTITUTE Joanna Goodrich, j.goodrich@ieee.org DIRECTOR, PERIODICALS PRODUCTION SERVICES Peter Tuohy MULTIMEDIA PRODUCTION SPECIALIST Michael Spector ASSOCIATE ART DIRECTOR, PUBLICATIONS Gail A. Schnitzer ADVERTISING PRODUCTION +1 732 562 6334 ADVERTISING PRODUCTION MANAGER Felicia Spagnoli, f.spagnoli@ieee.org SENIOR ADVERTISING PRODUCTION COORDINATOR Nicole Evans Gyimah, n.gyimah@ieee.org EDITORIAL ADVISORY BOARD, IEEE SPECTRUM Susan Hassler, Chair; David C. Brock, Robert N. Charette, Ronald F. DeMara, Shahin Farshchi, Lawrence O. Hall, Jason K. Hui, Leah Jamieson, Mary Lou Jepsen, Deepa Kundur, Peter Luh, Michel Maharbiz, Somdeb Majumdar, Allison Marsh, Carmen Menoni, Sofia Olhede, Wen Tong, Maurizio Vecchione EDITORIAL ADVISORY BOARD, THE INSTITUTE Kathy Pretz, Chair; Qusi Alqarqaz, Philip Chen, Shashank Gaur, Lawrence O. Hall, Susan Hassler, Peter Luh, Cecilia Metra, San Murugesan, Mirela Sechi Annoni Notare, Joel Trussell, Hon K. Tsang, Chenyang Xu MANAGING DIRECTOR, PUBLICATIONS Steven Heffner EDITORIAL CORRESPONDENCE IEEE Spectrum, 3 Park Ave., 17th Floor, New York, NY 10016-5997 TEL: +1 212 419 7555 FAX: +1 212 419 7570 BUREAU Palo Alto, Calif.; Tekla S. Perry +1 650 752 6661 DIRECTOR, BUSINESS DEVELOPMENT, MEDIA & ADVERTISING Mark David, m.david@ieee.org ADVERTISING INQUIRIES Naylor Association Solutions, Erik Henson +1 352 333 3443, ehenson@naylor.com REPRINT SALES +1 212 221 9595, ext. 319

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Bajema is director of the Converging Risks Lab at the Council on Strategic Risks, in Washington, D.C. Over more than two decades, she has held long-term assignments in the U.S. Department of Defense and the Department of Energy. Today, she says, sophisticated commercial drones demand new thinking about strategic risks. In this issue [p. 6], Bajema examines the devious ways drones can be weaponized.

 TAKAO SOMEYA Someya is dean and professor at the University of Tokyo’s graduate school of engineering and chief scientist and team leader at RIKEN, a private research institute founded in 1917. His research focuses on stretchable and flexible organic electronics and their use in health care and robotics, including the skin displays he describes in this issue [p. 38]. Someya says he looks forward to using these devices to silently communicate with family members by sending emojis.

 ROOZBEH TABRIZIAN Tabrizian and Swarup Bhunia, both on the faculty of the electrical and computer engineering department at the University of Florida, write in this issue about their work turning nanoscale resonators into tiny, invisible tags that can be used to distinguish authentic goods from counterfeits [p. 32]. “We were trying to make resonators for another project, and we were seeing a lot of spurious resonance peaks,” says Tabrizian. “For this project, we’re actually using those spurious peaks.”

 EMILY WALTZ IEEE Spectrum contributing editor Waltz has been a key part of our coverage of the COVID-19 pandemic. In this issue, the Nashville-based journalist writes about a new type of vaccine that requires an electric gadget for its administration [p. 24]. The pandemic has unleashed innovation that will endure beyond this crisis, Waltz says: “Even if a company’s COVID-19 vaccine isn’t wildly successful, it can use this opportunity to validate its whole platform.”

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Smartphones, smart homes, smart...healthcare? RFID tags are used across many industries, but when it comes to healthcare, there is a major design challenge: size. If wearable RFID tags are too big and bulky, they could cause patient discomfort. Or, if the tag is for a biomedical implant, it has to be smaller than a grain of rice! Design engineers can optimize the size of an RFID tag for its intended purpose using RF simulation. learn more comsol.blog/biomed-RFID-tags

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NATIONAL SECURITY

Weaponized Drones: Know Your Enemy Uncanny agility may be the real danger BY NATASHA BAJEMA

or all the amazement that swarms of consumer-grade drones provoke—flying in choreographed clusters to form logos, pictures, and even QR codes in the sky—they’re also a subject of some strategic concern among national security experts. Drone swarms, one analyst says, are the new WMD (weapon of mass destruction); “slaughterbots” are the new nightmare technology, says another; one prominent media account describes “sinister” flocks of “really creepy” drones buzzing residents in rural areas and raising fears of mass surveillance, or worse. Of course, drones by themselves are not new. However, what is new is that rogue states, terrorist groups, and other malevolent actors around the world are seeking weapons that can do less damage but can still rival a WMD in effect. During the Cold War, strategic analysts surmised that states would want WMDs for widespread destruction. Yet in the last three decades, several states have used chemical agents—canonical WMDs—in peacetime for assassination of individuals. North Korean dictator Kim Jong Un is thought to have assassinated his half brother with VX nerve agent in 2017. A year later, Russia was suspected to have used a Novichok chemical agent in Salisbury, England, in a failed assassination attempt of a former Russian spy and his daughter. The U.S. intelligence community has recently linked the Russian gov-

6 SPECTRUM.IEEE.ORG JUNE 2021

Azerbaijan recently used its Turkish Bayraktar TB2 unmanned combat aerial vehicles (UCAVs) to great effect in its conflict with Armenia.

ernment to the attempted assassination of Russian dissident Aleksei Navalny in 2020 with a Novichok agent. Geopolitical actors have shifted their desired outcomes because they’re already getting the strategic impact they want at lower levels of destruction. Think of this as a new category of armament similar to WMD—also scalable, as the chemical agents above have been used for more targeted killings, but more accessible and with similar strate-

gic impact. Call this new category, as it were, weapons of mass agility (WMA). For the above reasons among others, nefarious states and violent nonstate actors may be increasingly attracted to WMAs. So strategists need to be aware of this trend to counter its threat. Weaponized consumer drones, for instance, have the potential to spark fear among the general public. “Really creepy” was used in response to those drones that hovered but did nothing, at

BAYKAR/ANADOLU AGENCY/GETTY IMAGES

JUNE 2021

least that anyone could discover. What might public reactions be if this consumer technology was used for more malevolent ends? In that sense, weaponized commercial drones might therefore factor into the strategic calculations of national and international leaders in similar ways as cyber, biological, and chemical weapons. In March 2021, online publication The War Zone revealed the results of an extensive investigation of drone flybys around naval ships. In July 2019, the

U.S. Navy documented the presence of a drone swarm near the USS Kidd destroyer several times over a period of a few days. As many as six drones engaged in complex maneuvers in low visibility conditions, buzzing the destroyer, which was traveling at more than 29 kilometers per hour (18 miles per hour). The drone activity unleashed an internal investigation involving the Navy, FBI, and U.S. Coast Guard and receiving attention from the Chief of Naval Operations.

The War Zone uncovered details of the strange events through FOIA requests of the Navy’s deck logs and internal communications and reconstructed the scenarios using ship location data. No viable explanation for the drones could be uncovered. Simple math illustrates the potential of drones against a destroyer. It costs the U.S. Navy as much as US $936 million to build a single Arleigh Burke–class destroyer. Meanwhile, a Turkish Bayraktar TB2, the unmanned combat aerial vehicle (UCAV) most recently used to great effect by Azerbaijan in its conflict with Armenia, carries a payload of 150 kilograms of laser-guided munitions. The TB2 costs only somewhere between $1 million and $2 million each. Assuming the higher end for each weapons system, a country could acquire 468 UCAVs for the price of a single guided-missile destroyer. When recalling the al-Qaida-led suicide bomber attack against the USS Cole destroyer in 2000, it doesn’t require a great stretch of the imagination to see the strategic advantage in smaller, cheaper, smarter systems over exquisitely designed and expensive platforms such as fighter jets, aircraft carriers, and destroyers. It took only a small boat laden with about 180 to 320 kg of C4 explosives to blast a large hole in the Cole, killing 17 sailors and injuring 37 more. Though the vessel was not destroyed by the attack, it was removed from service for nearly three years for repair. A Ford-class aircraft carrier costing $12.8 billion per ship offers up an even more lucrative target than a destroyer. Although consumer drones remain far less capable than military-grade UCAVs, their payload, performance, and autonomous capabilities are growing quickly. The impact of drones also extends far beyond their prospects for causing damage to expensive military targets. The potential of consumer or commercial drones harming world leaders became immediately evident when a protester hovered one close to German chancellor Angela Merkel at a campaign rally in 2013. Leveraging their agility, coun-

JUNE 2021 SPECTRUM.IEEE.ORG 7

NEWS

This article is an adaptation of a recent report the author wrote for the Council on Strategic Risks, “Weapons of Mass Agility: A New Threat Framework for Mass Effects in the 21st Century.”

In July 2019, a swarm of drones buzzed the guided-missile destroyer USS Kidd.

8 SPECTRUM.IEEE.ORG JUNE 2021

ENERGY STORAGE

The Sun Shines on Hydrogen Energy Solar-to-hydrogen conversion process sees dramatic efficiency gains BY MARIA GALLUCCI

onverting sunlight into They also used an aqueous methahydrogen is a seemingly nol solution instead of water, which ideal way to address the allowed them to focus only on the world’s energy challenges. hydrogen component and reduce The process doesn’t directly involve the complexity of the reaction. fossil fuels or create any greenhouse By itself, BaTaO₂N can hardly gas emissions. The resulting hydro- “evolve” hydrogen gas from the solugen can power fuel-cell systems in tion. So, using their new method, the vehicles, ships, and trains; it can feed Shinshu team “loaded” the powder into the electrical grid or be used to granules with a p latinum-based make chemicals and steel. For now, cocatalyst to improve the chemical though, that clean-energy vision activity. exists mainly in the lab. As a result, the materials evolved Recently, Japanese research- hydrogen about 100 times more ers said they’ve made an import- efficiently than BaTaO₂N that’s ant step toward producing vast been loaded with platinum using amounts of hydrogen using solar conventional methods, according energy. The team from Shinshu to the group’s paper in the journal University, in Matsumoto, stud- Nature Communications. ies light-absorbing materials to Takashi Hisatomi, a coauthor split the hydrogen and oxygen of the study, said the results are molecules in water. Now they’ve a “remarkable finding” in this developed a two-step method that research field. Hisatomi is a prois dramatically more efficient at fessor with Shinshu’s Research generating hydrogen from a photo Initiative for Supra-Materials, and catalytic reaction. he has studied BaTaO₂N for nearly The researchers began with a decade. “This is personally very barium tantalum oxynitride exciting for me,” he said of the (BaTaO₂N), a semiconductor mate- 100‑fold improvement. rial that can absorb light at up to Solar energy experts have called 650 nanometers (a visible wave- efforts to make hydrogen more length at the orange end of red). easily or efficiently a “holy grail The powdery substance serves as quest.” When used in fuel-cellthe photocatalyst, harnessing solar powered vehicles or buildings, the energy needed to drive the reaction. odorless gas doesn’t produce emis-

MASS COMMUNICATION SPECIALIST SEAMAN SANG KIM/U.S. NAVY

tries have often used UCAVs to deliver lethal strikes on specific targets, most recently by the Moroccan armed forces to kill the leaders of a separatist group. In 2018, an unidentified nonstate actor used two explosive-bearing commercial drones in the attempted assassination of Venezuelan president Nicolas Maduro. The most consequential WMAs could potentially rise to the level of a WMD, by causing mass casualties and destruction. Possible attacks include using autonomous drone swarms against a soft target like a stadium full of people or dispersing drones bearing biological or chemical agents over a large area. Since the perils of WMD have been around for decades, though, such scenarios are unfortunately not new. And since malevolent actors may still be able to achieve their desired strategic impact at lower levels of destruction with WMAs, these actions may continue to be low probability. However, the close calls and early salvos of maliciously targeted commercial drones have so far provided only a hint of what is to come. Technologists and engineers who work on drones need to be aware when they develop applications that might be weaponized and exploited for deadly effect. And policymakers and military strategists need to be equally vigilant in defending against a highly agile new threat that, while its use has, gratefully, been limited to date, its potential for danger will continue to increase as commercial, off-the-shelf drone technologies mature and proliferate.

SHINSHU UNIVERSITY

sions or air pollution—just a little heat and water. However, nearly all hydrogen today is made using industrial processes that involve natural gas or coal—all of which ultimately pump more emissions into the atmosphere. A handful of facilities can make “green” hydrogen using renewable electricity to split water molecules, but the process itself is energy intensive. If scientists can make hydrogen directly from the sun’s energy, they could bypass this expensive and polluting step. In Belgium, a team at Katholieke Universiteit Leuven (KU Leuven) is developing solar panels that collect moisture in the air, then use chemical and biological components to split water directly on the surface. The researchers envision putting these panels on top of houses, allowing people to heat their homes with hydrogen gas made on-site. Separately, a group of Israeli and Italian scientists is advancing methods to extract as much hydrogen as possible from solar-to-chemical energy conversion. The team has developed rod-shaped nanoparticles, tipped with platinum spheres, that prevent hydrogen and oxygen from recombining after the molecules are separated. At Shinshu, the researchers sought to improve the efficiency of the BaTaO₂N photocatalyst by depositing the platinum-based cocatalyst. But the conventional methods for doing so weren’t initially effective, Hisatomi said. For instance, in the impregnation- reduction process, a surface is filled with a solution containing metal precursors and then subjected to elevated temperatures, which evaporate the solvent and leave behind the metal catalysts. When the Shinshu team applied fine particles of platinum to the BaTaO₂N granules, the particles tended to aggregate, restricting the electronic interaction between the materials. Another method, called photo

Japanese researchers are developing a two-step method to load platinum onto barium tantalum oxynitride to harness solar energy to extract hydrogen gas out of water.

deposition, resulted in weak contact between the BaTaO₂N and cocatalyst, in turn weakening the interaction. So the researchers combined these two methods. First, they deposited only a small amount of the cocatalyst using the impregnation-reduction process, and that prevented the particles from aggregating. Then they applied a second layer using photodeposition; this time, the fine particles grew on the widely dispersed “seeds” planted in the first step. Zheng Wang and Ying Luo conducted the investigation, under the supervision of Kazunari Domen and Katsuya Teshima, respectively. Although the study involved an aqueous methanol solution, not water, the team confirmed that the newly developed platinum-loaded BaTaO₂N can split the

Converting sunlight into hydrogen is a clean-energy innovation that to date has been relegated to the lab bench. New photocatalytic research represents a significant step toward the field’s “holy grail quest.”

hydrogen and oxygen molecules in water more efficiently than earlier BaTaO₂N versions, when combined with another photocatalyst that drives the oxygen evolution process. Hisatomi said the team is considering printing the powdery photocatalyst on a panel-type reactor. He and his colleagues have already built such a device using another material, aluminum-doped strontium titanate, which has the same crystal structure as BaTaO₂N but absorbs lights at different wavelengths. The 1-square-meter panel reactor is filled with a 1-millimeter-deep layer of water. When exposed to sunlight, the chemical reaction rapidly releases gas bubbles. A related research effort aims to develop membranes that can keep the hydrogen and oxygen bubbles separated. Still, despite the 100-fold efficiency jump, BaTaO₂N isn’t quite ready for prime-time hydrogen production. “We still need a similar jump in improvement of the efficiency to make this technology practically useful,” Hisatomi said. As researchers continue improving the photocatalyst, they’ll also begin applying the two-step approach to other types of materials. “We don’t know which material will become the best in the end,” he added.

JUNE 2021 SPECTRUM.IEEE.ORG 9

NEWS

SOURCES: ZIEGLER & TRANCIK/ENERGY & ENVIRONMENTAL SCIENCE/HARVARD DATAVERSE

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BATTERIES

The Tech That Crushed the Cost of Energy Storage And why it’s only going to continue BY RAHUL RAO

ehind clean energy today is a sharp, continuing drop in photo voltaic solar-cell prices. And behind the scenes, the prices of lithium-ion batteries are plummeting just as quickly. Between 1991 and 2018, the average price of the batteries that power mobile phones, fuel electric cars, and underpin green energy storage fell more than thirtyfold, according to work by

10 SPECTRUM.IEEE.ORG JUNE 2021

Micah Ziegler and Jessika Trancik at the Massachusetts Institute of Technology. Engineers and energy-policy plan ners benefit from knowing future battery prices, but unlike solar prices, they aren’t always readily available. Lithium-ion bat teries tend to be manufactured or bought in bulk by large companies. “Those contracts aren’t necessarily public doc uments,” says Ziegler. That’s partly why

2020

2030

the drivers for the price decline are, for Ziegler and Trancik, an open area of research. Ziegler and Trancik published their comprehensive survey of studies of lithium-ion battery prices in a recent issue of the journal Energy & Environmental Science. Batteries today, the researchers say, have mass-production scales and energy densities unthinkable 30 years ago. Economies of scale and technological improvements appear set to drive storage costs further, approaching the $100 per kilowatt-hour threshold. At about that level, the energy costs for EVs will reach parity with those for gasoline-powered vehicles, according to Bloomberg New Energy Finance. Of course, as battery production increases, so does the pressure to drive down prices. Battery recycling has also reduced the need to mine for new mate rials, according to Annick Anctil, a sus tainability researcher at Michigan State

University. And lithium-ion batteries and solar cells often coexist: “As we’re installing a lot more solar,” Anctil says, “we’re also more interested in putting [in] more storage for it.” The first commercially available lithium-ion battery was released by Sony and Asahi Kasei in 1991. It was cylindrical, like many batteries today, but other shapes have emerged since then. “I think an important aspect of this work is that we differentiated the trends for all types of lithium-ion cells

97%

Price decline of lithium-ion batteries, scaled by energy capacity, since their 1991 commercial introduction

MOTORS

Will Reluctance Drive EVs’ Next Big Move? This tech began as motors for HVAC systems; cars are next BY PHILIP E. ROSS

TURNTIDE TECHNOLOGIES

urntide Technologies, a startup backed by Bill Gates and Amazon, originally pitched its new version of an old electric motor for use in rooftop HVAC systems. Now the company is going after bigger game: electric vehicles. CEO Ryan Morris mentioned the plan in an interview with CNN in early

Originally developed in 1838, the switched reluctance motor continues to be improved to the present day.

April. Now Eric Meyerson, vice president for marketing, is putting a little flesh on those bones. “We are...focusing on commercial vehicles, not consumer passenger cars,” he tells IEEE Spectrum. A full announcement was expected at around press time. Turntide says its switched reluctance motor’s inherent efficiency, together with

from those specifically for cylindrical cells,” says Ziegler. Prismatic lithium-ion batteries tuck the battery inside a flat-pack casing, allowing them to be easily stacked. They’re commonly found in mobile phones and in electric vehicles, although Tesla has long used cylindrical batteries. Pouch batteries first arrived in the world in the mid-1990s, and replaced the hard shell of their counterparts with a flexible, lightweight “pouch” that looks like the packaging of an astronaut meal.

the adaptiveness of its variable-speed capability, provides average energy savings of 64 percent, enough to pay back a customer’s investment in less than three years. Among the dozen or so companies using the motor in rooftop systems are BMW and Amazon. If anything like such savings can be achieved in other applications, the gains could be astounding. Motors consume more than 40 percent of all the electricity generated in the world. The switched reluctance motor was invented way back in 1838. Current in each set of windings on the poles of the stator—the stationary part—induces a temporary magnetic field on the poles of the rotor—the moving counterpart. Switching the current causes the rotor poles to be pulled toward whichever stator poles they happen to be approaching. “Reluctance is the resistance to movement of magnetic flux,” says Piyush Desai, the inventor of Turntide’s motor and the company’s cofounder. “It’s good and bad, like rolling resistance to your car—you need it for your car to move, but you have to overcome it. You want a little but not too much!” The design has few parts, and all three phases of the motor are independent, so if one fails you can still run the motor in a limp-home mode. That makes it rugged and reliable, perfect for such mission-critical applications as airliner generators, big vehicles used in mining operations, and the cooling towers of nuclear power plants. But the motor never gained wider acceptance because it proved hard to control, and this resulted in a lot of noise and vibration.

JUNE 2021 SPECTRUM.IEEE.ORG 11

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began by putting sensors in the machine to track the movements of the rotor; that way, they could determine just when to turn the switch on or off. The knowledge they gained allowed them to devise a sensorless algorithm. What would the world do with a cheap motor that needs no exotic material, consumes energy sparingly, requires little maintenance, lasts long, and doesn’t make too much noise? It would beat a path to the door of whoever is selling it.

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Some of Desai’s improvements involve sheer mechanics. “I came up with a simple idea: increase the number of rotor poles,” he says. “That gives you more space on the stator for more copper winding.” (It can’t be done with a small number of rotor poles because those poles must work within stator poles having a certain angular spread, or pole arc.) The idea succeeded from the very beginning, but making it practical took a lot of work, mostly in software. Turntide engineers

magine being able to read an entire book in a single second, but only receiving the pages individually over the course of a minute. This is analogous to the woes of a supercomputer. Supercomputer processors can handle whopping amounts of data per second, but the flow of data between the processor and computer subsystems is not nearly as efficient, creating a data-transfer bottleneck. To address this issue, one group of researchers has devised a system design, involving reconfigurable networks, called FLEET—which could potentially speed up the

transfer of data 100-fold. (The acronym stands for Fast Lanes for Expedited Execution at 10 Terabits.) FLEET’s initial design, as part of a “DARPA-hard” project, is described in a study published in a recent issue of the journal IEEE Internet Computing. Network interface cards are critical hardware components that link computers to networks, facilitating the transfer of data. However, these components currently lag far behind computer processors in terms of how fast they can handle data. “Processors and optical net-

works operate at terabits per second (Tb/s), “The connections can be but [current] network interfaces used to modified before or during transfer data in and out typically operate execution to match different in gigabit-per-second ranges,” explains devices over time,” says one Seth Robertson, chief research scientist research scientist develwith Peraton Labs (previously Perspecta oping a new reconfigurable Labs) who has been coleading the design supercomputer interconnect of FLEET. system, called FLEET Part of his team’s solution is the development of Optical Network Interface Cards (O-NICs), which can be peripatetic Grand Staircase in the Harry plugged into existing computer hardware. Potter series’s Hogwarts School. “ImagWhereas traditional network interface ine Hogwarts staircases if they always cards typically have one port, the newly appeared just as you needed to walk designed O-NICs have two ports and someplace new,” he says. can support data transfer among many To support reconfigurability, the different kinds of computer subcom- researchers have designed a new softponents. The O-NICs are connected to ware planner that determines the best optical switches, which allow the system configuration and adjusts the flow of to quickly reconfigure the flow of data data accordingly. “On the software side, as needed. a planner that can actually make use “The connections can be modified of this flexibility is essential to realbefore or during execution to match dif- izing the performance improvements ferent devices over time,” explains Fred we expect,” Douglis emphasizes. “The Douglis, a chief research scientist with wide range of topologies can result in Peraton and coprincipal investigator many tens of terabits of data in flight at of FLEET. He likens the concept to the a given moment.”

The development of FLEET is still in its early stages. The initial design of the O-NICs and software planner was achieved in the first year of an expected four-year project. But once the work is complete, the team anticipates that the new network interface will reach speeds of 12 Tb/s based on the current, fifth generation, of PCIe (an interface standard that connects interface network cards and other high-performance peripheral devices) and could reach higher speeds with newer generations of PCIe. Importantly, Robertson notes that FLEET will depend almost entirely on off-the-shelf components, with the exception of the newly designed O-NICs, meaning FLEET can be easily integrated into existing computer systems. “Once we can prove [FLEET] meets its performance targets, we’d like to work to standardize its interfaces and see traditional hardware vendors make this highly adaptable networking topology widely available,” says Robertson, noting that his team plans to opensource the software.

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JUNE 2021 SPECTRUM.IEEE.ORG 13

THE BIG PICTURE

Red Planet Selfie NASA’s Mars 2020 Perseverance rover takes a “rover selfie,” albeit with a twist. For the first time, in this image taken 6 April 2021, a rover captured not only itself but a buddy— the tiny helicopter Ingenuity, which made the trip in Perseverance’s belly. What looks like a single wide-angle shot is actually 62 individual images stitched together, according to Vandi Verma, the mission’s chief engineer for robotic operations. The pictures were taken with the rover’s WATSON (for Wide Angle Topographic Sensor for Operations and eNgineering) camera, situated at the end of the rover’s robotic arm. The arm ultimately doesn’t appear because the stitched-together images overlap in those areas, giving the impression of a floating camera. When not being used for selfies, WATSON takes highly detailed photographs of the Martian surface to identify possible spots of interest for Perseverance’s scientific instruments. PHOTO: JPL-CALTECH/MSSS/NASA

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JUNE 2021 SPECTRUM.IEEE.ORG 15

TECH TO TINKER WITH

The Pineapple One is a complete computer with input/ output, memory, and a homebrew 32-bit RISC-V CPU.

Build Your Own RISC-V CPU Even homebrew processors can use hot new tech BY FILIP SZKANDERA

16 SPECTRUM.IEEE.ORG JUNE 2021

t’s a certain kind of itch that drives people to voluntarily build their own CPU. We start thinking about the papered-over gap in our understanding, the one that lurks between how logic gates and flip-flops work individually and how machine code controls a fully assembled processor. What exactly happens in the magic zone where hardwired circuits start dancing to software’s ever-changing tune?

Illustrations by James Provost

JUNE 2021

The modular nature of the RISC-V design let me build the Pineapple One as a stack of individually testable 10-by-10-centimeter PCBs with different functions [clockwise, from top left]: VGA driver; RAM; transport layer; shifter; ALU; register file; control unit; program counter; ROM.

It turns out this itch afflicts enough people that there are commercial kits for makers who want to put a CPU together to see (or hear) it tick, and the Web is littered with home-brewed 4-bit and 8-bit CPUs with architectures that would be familiar to an engineer from the 1970s. I should know—I made one myself. But then I began to wonder: Could I build my own CPU featuring some of the latest technology? Could I design my own fully

compliant 32-bit RISC-V central processing unit? RISC-V is an open-source architecture that’s about 11 years old, and is now starting to make inroads in a world dominated by the x86 and ARM CPU architectures. I was alerted to the possibilities of RISC-V by the work of Robert Baruch, who started a similar project about two years ago but hasn’t yet completed his processor, in part because he had to keep redesigning com-

ponents he’d built early on to meet the needs of an evolving design. Instead, I started out by building my complete design—which I dubbed Pineapple One—in Logisim Evolution, a logic-circuit simulator. After consulting the official RISC-V manual and the first edition of David Patterson and John Hennessy’s book Computer Organization and Design, RISC-V Edition (Elsevier, 2017), and pushing Logisim to its outer

JUNE 2021 SPECTRUM.IEEE.ORG 17

HANDS ON

While there are provisions for instructions that can range in length between 16 bits and a theoretically unlimited number, here are the fixed 32-bit formats of the four core types of RISC-V instructions. Some instructions combine an opcode with additional functional fields to define behavior, while others allow multiple source registers to be combined with so-called immediate data, with the results placed in the destination register.

limits, I had a working simulation of ineapple One that met the requirements P of a basic RISC-V CPU in six months. In implementing the RISC-V architecture, I was amazed at how much more sense the architecture made compared to the conventional complex instruction set I’d used in my earlier home-brew CPU. Redundancies had been eliminated, and the processor’s registers—the scratchpads that store the CPU’s working memory—were more flexible. Another big advantage was that RISC-V is a well-documented modular design, so I knew just what each block had to do. My goal was to design each block in my own way, but make sure it performed in compliance with the RISC-V standards. (This dictated that my CPU be 32-bit, as RISC-V instructions are at least that long by definition.)

Physically, the Pineapple One is distributed over a vertical stack of eight square printed circuit boards that are about 10 centimeters on a side, plus a card that handles a VGA display interface. It uses over 230 integrated circuits, mostly from the 74HCT series of logic chips. My biggest challenge was implementing a barrel shifter—a circuit that can shift around the bits in a register by a controllable amount. I first tried a fast implementation that would require over 80 components, but try as I might, I couldn’t get it to fit onto my PCBs. So instead I went with a low-component approach that essentially suspends the operation of the rest of the CPU until my shifter finishes cranking away. Due to the Pineapple One’s long traces, as compared to a single-chip CPU, I also struggled to manage parasitic capacitance and impedance, which meant debugging some really strange behaviors.

Home-brew CPUs made out of basic logic chips are fun to build, but they’re rarely more than toys. Filip Szkandera built a 32-bit CPU that’s RISC-V compliant. 18 SPECTRUM.IEEE.ORG JUNE 2021

I tested each individual board by using an Arduino microcontroller to simulate inputs from the rest of the computer, and to monitor outputs for correctness. I 3D-printed a nice case to hold the entire stack of PCBs and input/ output connectors, so that it’s possible to hook up a keyboard and VGA display directly to the Pineapple One. There are four general-purpose I/O ports—two 8-bit inputs and two outputs. My friend Jan Vykydal helped me set up a RISC-V-compliant compiler to work properly, so I wrote some system software and demo programs in C. The compiler produces machine code, and I use a Python script that takes the code and flashes it to the CPU’s memory. Even though Pineapple One runs at only 500 kilohertz, that’s still fast enough to play a simple computer game like Snake in real time, and the 512 kilobytes of program memory and 512 kB of RAM are ample. Ultimately, I would like to upgrade the processor a little bit so it can run more-complex programs. I’d also like to add more expansion boards, such as a sound card. You can find schematics and a bill of materials on Hackaday, but ultimately it would be great to offer it as a kit to others interested in understanding contemporary CPU design. n

SHARING THE EXPERIENCES OF WORKING ENGINEERS

S.B. Divya How a working engineer writes some of the best science fiction around BY DANIEL P. DERN

SERGEANT CREATIVE

ngineers often find themselves of the trouble spots are, socially, for in the role of turning ideas that labor, economics, humanity, and ethics,” used to be science fiction into says Divya. All the engineering aspects reality. So it’s natural that some “were things I had studied or done at my of them turn the flow of ideas in the other jobs.” And she has some tips for other direction, and become authors of science engineers attuned to the sci-fi possibilfiction. One such engineer-turned-writer ities of their work. is Divya Srinivasan Breed, who writes her As well as being a writer, Divya has science fiction as S.B. Divya, and whose worked as an EE for 20 years. “My B.S. stories have been nominated for Hugo from Caltech is in computation and neural and Nebula awards. systems, and my UC San Diego master’s “In my novella Runtime (2016), my in engineering is in signal processing and main character was putting together exo- communications. My jobs have involved skeletons, hacking firmware, people were everything from pattern-recognition embedding chips in their bodies…. And work—including g etting two patents— my novel Machinehood (2021) reflects and signal processing to AI and machine my understanding of where we are today learning, including designing [physical]and where we are headed in terms of layer signal processing at Marvell machine intelligence, and where some Semiconductor and developing and

JUNE 2021

implementing the AI engine for the SleepWatch app for iOS.” “I began reading science fiction around age 10,” recalls Divya. “Around 13 or 14, I became more interested in physics and astrophysics, but I’ve also always been interested in metaphysics—philosophy of the mind, existence, the universe...the big questions.” As an undergrad at Caltech, “when I came across the computational neuroscience department, I thought it was great because it integrated all these different disciplines—physics, electrical engineering, and biology,” she says. “Having a broad cross-subject undergrad major has helped me in doing research for my science fiction, because I am pretty comfortable looking at space science, geophysics, and various forms of biology. As an SF writer, my strength is to draw on that breadth of subject matter and be able to integrate it into a fully realized fictional world.” Divya isn’t of course the only engineer to turn to writing science fiction: Cheryl Rydbom, Vernor Vinge, and Andy Weir are some other examples of those who have turned their hand to the page. Divya has two core recommendations for those seeking to join their ranks: First, “don’t forget the story part of it. It’s easy to lose yourself in the fun of inventing cool new technology and new areas of science, but as an author of fiction, you’re there to tell a story.” Second, “make use of the things you know. Whether it’s the tech or the science itself, or about working in that area, your experience and knowledge bring perspectives that other people don’t have.” And Divya has some general career advice: “I made a change in my major as an undergraduate, shifted again in graduate school, made another career shift 15 years later. Leave your doors open, keep your mind open to possibilities. Don’t confine yourself to one thing, particularly early in life—especially given the rapid pace at which technologies change.” What’s next? “I’m working on another novel,” says Divya. “It has AIs, but it’s a far-future novel more concerned with the posthuman descendants of humanity. And, at some point, [I’ll be] doing more engineering.”

JUNE 2021 SPECTRUM.IEEE.ORG 19

OPINION, INSIGHT, AND ANALYSIS

Fugitive Emissions Natural gas produces lower carbon emissions than the coal it replaces, but we have to find ways to minimize the leakage of methane

it comes up inside a production steel pipe, natural gas is usually a mixture of the lightest alkanes, which are hydrocarbons of the CnH2n+2 series. Methane (CH4) dominates (between 85 and 95 percent), followed by ethane (C2H6, typically 2 to 7 percent by volume), small amounts of propane (C3H8), butane (C4H10), and pentane (C5H12), and traces of carbon dioxide, hydrogen sulfide, and other gases. Gas processing removes most of these things before the final product, about 95 percent methane, reaches consumers. Natural gas is abundant, low-cost, convenient, and reliably transported, with low emissions and high combustion efficiency. Natural-gas-fired heating furnaces have maximum efficiencies of 95 to 97 percent, and combined-cycle gas turbines now achieve overall efficiency slightly in excess of 60 percent. Of course, burning gas generates carbon dioxide, but the ratio of energy to carbon is excellent: Burning a gigajoule of natural gas produces 56 kilograms of carbon dioxide, about 40 percent less than the 95 kg emitted by bituminous coal. This makes gas the obvious replacement for coal. In the United States, this transition has been unfolding for two decades. Gas-fueled capacity increased by 192 gigawatts from 2000 to 2005 and by an additional 69 GW from 2006 through the end of 2020. Meanwhile, the 82 GW of coal-fired capacity that U.S. utilities removed from 2012 to 2020 is projected to be augmented by another 34 GW by 2030, totaling 116 GW—more than a third of the former peak rating. So far, so green. But methane is itself a very potent greenhouse gas, packing from 84 to 87 times as much global warming potential as an equal quantity of carbon dioxide when measured over 20 years (and 28 to 36 times as much over 100 years). And some of it leaks out. In 2018, a study of the

20 SPECTRUM.IEEE.ORG JUNE 2021

98%

of gas consumed today has a lower life-cycle emissions intensity than coal when used for power or heat

U.S. oil and natural-gas supply chain found that those emissions were about 60 percent higher than the Environmental Protection Agency had estimated. Such fugitive emissions, as they are called, are thought to be equivalent to 2.3 percent of gross U.S. gas production. Headlines decried natural gas as unnatural, painting it blacker than coal. Bill McKibben concluded, with the rhetorical restraint befitting the country’s leading climate catastrophist, that turning from coal to natural gas is “as if we proudly announced that we kicked our OxyContin habit by taking up heroin instead.” Without doubt, methane leakages during extraction, processing, and transportation do diminish the overall beneficial impact of using more natural gas, but they do not erase it, and they can be substantially reduced. In its detailed 2020 assessment of life-cycle emissions resulting from natural-gas and coal supply, the International Energy Agency concluded that “an estimated 98 percent of gas consumed today has a lower life-cycle emissions intensity than coal when used for power or heat.” Moreover, a 2019 assessment found that about three-quarters of today’s methane emissions from the oil and gas industry can be controlled by deploying known technical fixes—and, most significantly, that about 40 percent of those emissions could be avoided at no net cost. Even the most efficacious drugs have undesirable side effects; even the best technical fixes have downsides. To think that the supposedly greenest alternatives, photovoltaics and wind turbines, produce no fossil-fuel footprint and bring only benefits is to ignore reality. So too does the uninformed judgment about the evils of natural gas: It is not a perfect choice—nothing is—but its benefits surpass its drawbacks, and they could be raised even further. n

NUMBERS DON’T LIE BY VACLAV SMIL

ADDITIONS AND CLOSURES OF ELECTRICITY-GENERATING POWER PLANTS NATURAL GAS

40 THE TORCH PASSES We get ever more generation capacity from natural gas and ever less from coal.

MEGAWATTS ADDED (thousands)

MEGAWATTS LOST (thousands)

COAL

2000 SOURCES: U.S. EIA, UNIVERSITY OF WYOMING

2010

2020

2030

JUNE 2021 SPECTRUM.IEEE.ORG 21

CROSSTALK

INTERNET OF EVERYTHING BY STACEY HIGGINBOTHAM

Forget Bitcoin Project CHIP’s security ledger is a better use for blockchain technology

ryptocurrencies and nonfungible tokens (NFTs) may be all the rage right now, but they’re overshadowing better uses for blockchain and other distributed-ledger technologies. Rather than using them to disrupt financial systems or the art world, distributed ledgers can be used to create trust among Internet of Things devices, which is essential for any successful IoT network. Trust among devices can enable scenarios like an autonomous security robot checking the security clearances of drones flying overhead, or a self-checkout register at a grocery store that flags recalled meat when someone tries to buy it. Unfortunately, these use cases exist in primarily theoretical or pilot stages, while flashy crypto applications garner the most attention. But finally, an upcoming smart-home standard is using blockchain to create trust among devices. The new standard, put forth by the Project Connected Home over IP (CHIP) working group in the Zigbee Alliance, an organization develop� ing the ZigBee wireless standards, focuses on improving IoT-device compatibility. That includes making sure devices from different manufacturers can securely interact with one another. Project CHIP’s ledger is one of the first scaled-out blockchain efforts outside of cryptocurrency launches. CHIP’s standard describes a blockchain-based ledger that contains each CHIP-certified device, its manufacturer, and facts about that device, such as the current version of its software and whether or not it has received a particular update. The standard also includes other basic security features such as encryption among devices. The creation of this CHIP Compliance Ledger will let anyone with access to the ledger automatically monitor the status of all connected devices

22 SPECTRUM.IEEE.ORG JUNE 2021

Rather than using them to disrupt financial systems or the art world, distributed ledgers can be used to create trust among IoT devices.

listed. People living in smart homes with hundreds of sensors, devices, and connected appliances could then use a service provider to keep everything up to date. The ledger also allows manufacturers such as Amazon, Apple, or Whirlpool to monitor the security of their own devices automatically. What’s great about this blockchain approach is that it eliminates the need for users to track and monitor the security of all their devices. Depending on how the ledger is set up, it could also alert people to device vulnerabilities. The ledger could even be used to automatically quarantine those vulnerable devices. CHIP hasn’t shared a lot of details on the ledger yet, but it’s unlikely that it will use a difficult, energy-intensive proof-of-work approach to verify a change to the ledger. Cryptocurrencies like Bitcoin and Ethereum currently use such approaches, with the downside that they make the currencies extremely energy hungry. But because smart devices are already designed to merely sip battery power, CHIP’s ledger will hopefully require less-taxing proofs to add to or change the ledger. While CHIP’s ledger may not be as flashy as an NFT selling for over US $60 million, it’s an important step toward a more useful approach to distributed ledgers. A device’s ability to establish its bona fides and list its software patches over its lifetime is invaluable for device security. If the companies participating in Project CHIP can show the world that its blockchain approach can certify and secure millions of smart-home devices, then we can expect to see more efforts to scale up distributed ledgers. Those efforts may not be meme-worthy, but it will be a relief to have more machines that trust one another.

Photo-illustration by Lincoln Agnew

MACRO & MICRO BY MARK PESCE

An Overdue Revolution It took a pandemic for remote working to go viral

have a friend who lives on a farm and for years had connected to the Internet through a slow and prone-to-fail DSL (Digital Subscriber Line) link. He was okay living without Netflix, but as an attorney, he would have sorely liked to teleconference with clients, particularly after COVID-19 arrived. So he desperately needed a better Internet connection for his rural abode. Starlink, Elon Musk’s new satellite-based broad�band service, fit the bill, so he signed up for its public beta test. Imagine how many people will follow in his footsteps when Starlink becomes fully operational. The pandemic appears to have reversed the migration toward urban centers that has been going on since the start of the Industrial Revolution. People are now fleeing cities like San Francisco while rewriting the rules of office work. After all, why maintain expensive homes in or near a city when you can work from anywhere, via satellite? The magnitude of the change that many people made over the last year cannot be overempha-

Photo-illustration by Edmon de Haro

Why maintain expensive homes in or near a city when you can work from anywhere, via satellite?

sized. Within hours of the planet effectively s hutting down in mid-March 2020, many i nformation-based businesses resumed operations, more or less unaffected. An entire population of office workers continued to carry out their daily tasks without skipping a beat. That is nothing less than miraculous. How could so many manage so painlessly to achieve this transformation? More than three decades ago, I earned my living at Shiva Corporation writing firmware for “dial-up” modems, peripherals that allowed anyone to connect a computer to an office network from anywhere with a telephone line. That and other forms of portable office technology introduced over the years—everything from the Apple II to the latest smartphone—provide people the chance to work from anywhere, even (at least in our imaginations) from underneath a cabana on some tropical beach. The potential always lay within reach, yet most of us were unable to grasp it because work had always been performed under the watchful eye of the boss. Decades ago, economists predicted that the massive investment in office technologies would lead to sharp increases in productivity. Yet, those gains never appeared. It seems that established business practices undermined those productivity gains, so we saw few benefits from all that gear until those practices changed, as they did very suddenly last year. At that point, the value of those years of investment in work-from-anywhere technologies fully revealed itself. Had the pandemic come along 30 years ago, the business world truly would have come to a stop as we withdrew into our homes. With very few personal computers around, fewer still with modems, and no Internet services to speak of, we would have struggled to connect with one another via landlines. Home schooling would have been conducted via mimeograph and mail drops. Office work would have been Xeroxed, carted home, and written out in pen. Over the last generation, office workers have gained powerful tools for boosting productivity, but they hadn’t taken full advantage of them. It was like having a chainsaw available but using only a stone ax—simply because we’d always used one. But now that many of us have found a new way to work, one supported by incredible tools for remote collaboration, our offices and our work habits will never be the same.

JUNE 2021 SPECTRUM.IEEE.ORG 23

Vaccines Go Electric A HANDHELD GADGET COULD USHER IN A NEW ERA OF VACCINES

BY EMILY WALTZ PHOTOGRAPHY BY SPENCER LOWELL

24 SPECTRUM.IEEE.ORG JUNE 2021

Inovio’s device uses a technique called electroporation to sneak a DNA vaccine into cells. Kate Broderick, Inovio’s senior vice president of R&D, has been working on this technique for years, but the pandemic provided both motivation and funding to accelerate development.

T TOOK A GLOBAL PANDEMIC to accomplish one of the most significant advances in the history of vaccinology: widespread, commercial deployment of vaccines derived from nucleic acids. As of this writing, hundreds of millions of people have been vaccinated against SARS-CoV-2, the virus that causes COVID-19. And most of those shots have been the Pfizer-BioNTech and Moderna offerings, which are both of a type known as an mRNA (messenger RNA) vaccine. Conceived decades ago but released to the public for the first time during the pandemic, mRNA vaccines so far are living up to their promise. Both the Pfizer and Moderna vaccines have proven to be about 95 percent effective against the novel coronavirus. In addition, this kind of vaccine can be tweaked with relative ease to target new variants of a virus, and its production does not rely on items that can be difficult to produce quickly in enormous quantities. And yet, a couple

of drawbacks of mRNA vaccines have also been widely noted over the past six months: They depend on deep-freeze supply chains and storage, and they can produce significant side effects such as fever, chills, and muscle aches. So hopes remain high for another kind of nucleic-acid vaccine, one that makes use of DNA rather than mRNA. DNA-based vaccines have most of the advantages of mRNA vaccines, yet they produce no significant side effects—and, crucially, they don’t need to be refrigerated. These attributes could make these vaccines a boon to rural and low-resource regions. “If we really have to vaccinate 7 billion people, we might just need every possible technology,” says Margaret Liu, chairman of the board of the International Society for Vaccines. DNA vaccines come with a major challenge, however. When administered with an ordinary hypodermic needle, they’ve conferred only weak immunity, at best, in many human studies. But if a

small, ambitious Pennsylvania company backed by the U.S. Department of Defense succeeds in its clinical trials, DNA vaccines—enabled by a new delivery technology—could soon join the fight against COVID-19, and a host of other viral illnesses. The company, Inovio Pharmaceuticals, is using a technique known as electroporation, in which an electrical pulse applied to the skin briefly opens channels in cells to allow the vaccine to enter. After a standard vaccine injection, Inovio’s electroporation device, which looks like an electric toothbrush, is held against the skin. At the press of a button, a weak electric field pulses into the arm, opening channels into the cells. The tool gives DNA vaccines the boost they need to work in humans—or so the company says. It’s an engineering solution to a biological problem. With its overseas warfighters in mind, the U.S. Department of Defense (DOD) has backed Inovio’s approach

with a US $71 million contract to scale up the manufacturing of its electroporation device, and an undisclosed sum to cover phase 2 and 3 studies of the company’s COVID-19 vaccine. And the Bill and Melinda Gates Foundation gave the company $5 million as part of an effort to increase equitable access to COVID-19 vaccines. Inovio is now finishing phase 2 studies that are testing the vaccine’s efficacy on relatively small groups in the United States and China, and those results are imminent. In the meantime, the company has ramped up manufacturing with a plan to supply hundreds of millions of COVID-19 vaccine doses to the global population, should the vaccine prove successful. But here’s the rub: The electroporation tool is essential to Inovio’s vaccine, but it also adds a layer of complication. It’s both an enabler and a handicap. Inovio must manufacture not only the vaccine but also the device and its dis-

posable tips. Any vaccination site planning to administer Inovio’s vaccine will need not only the device but also people who know how to use it. The public will have to develop trust in a new apparatus. And all of this will have to happen during a pandemic and a frenzied vaccine rollout characterized by rampant misinformation and, in some quarters, an unwillingness to be vaccinated. Given that backdrop, the idea of complicating mass vaccinations with an electric device has drawn skepticism. “This is not standard methodology for giving vaccines,” notes John Moore, an immunologist at Weill Cornell Medicine, in New York City. The technique might work, but “how practical it is is another question entirely,” he says. Neither the skeptics nor tough questions from regulators have deterred Inovio. Nor has the fact that, despite more than a decade of research and development in other disease areas, the company has yet to bring a DNA vaccine

to market. These are hardly normal times. The coronavirus has propelled many other novel technologies, medicines, and vaccines into the mainstream, and in the process has created massive business success stories. Inovio is betting that its technology will make it into that elite group of pandemic-era winners.

ucleic-acid-based vaccines have captivated scientists for decades because they can be quickly designed and easily manufactured. These vaccines are typically made with either DNA, the double- stranded molecule that carries the genetic code for living organisms, or messenger RNA (mRNA), a single-stranded molecule that is complementary to DNA and carries instructions from DNA for synthesizing proteins. DNA and mRNA vaccines can be thought of as blueprints that instruct a cell to produce a specific protein from the virus that will trigger an immune response. In making a nucleic-acid vaccine, scientists first sequence the virus’s genome. Next, they figure out which of its proteins is the most important and most recognizable by the human immune system. Then they manufacture either DNA or mRNA that codes for the production of that protein and formulate it into a vaccine. That genetic material gets injected into the body, where nearby cells take it in and start following their new instructions for making a viral protein. To the immune system, this looks like a viral infection, and it mounts a response. Now, should the real virus ever appear, the immune system is primed and ready to attack. Altering the design of a nucleic-acid vaccine is as easy as plugging in a new code. That’s incredibly important when facing a virus that mutates frequently. Indeed, several highly contagious variants of SARS-CoV-2, the virus that

Inovio’s vaccine contains a snippet of DNA that codes for the production of a coronavirus protein. If the body is exposed to a real virus later, the immune system will recognize that protein and mount a defense. The DNA is first amplified in bacterial cells [left] and then purified [right].

JUNE 2021 SPECTRUM.IEEE.ORG 27

The newest Inovio device, the Cellectra 3PSP, is currently manufactured at Inovio’s facility in San Diego. The handheld Cellectra delivers about a hundred doses on a single battery charge. Its electrodes administer a series of electrical pulses that cause nearby cells to open channels through which the vaccine can enter.

causes COVID-19, have already emerged globally, and scientists have warned that the currently available vaccines may be less effective against some of them. Despite the allure of nucleic-acid vaccines, none had been approved for commercial use in humans by medical regulators prior to the pandemic. In fact, most nucleic-acid-based vaccines hadn’t made it past midstage clinical trials. The problem: Human cells don’t readily take in foreign DNA or mRNA. After injection, much of the vaccine would remain inert in the body and eventually break down, without prompting much of an immune response. Developers of mRNA vaccines recently resolved the issue by packaging the vaccine with chemicals. In one approach,

28 SPECTRUM.IEEE.ORG JUNE 2021

researchers encapsulate mRNA within fat droplets called lipid nanoparticles, which fuse with the cell membrane and help the vaccine get inside. Companies such as BioNTech, Moderna, and CureVac were in the midst of testing various mRNA vaccines against other viruses when the COVID-19 pandemic hit. Market pressure and billions of dollars from governments helped companies finish the job, and quickly. The mRNA vaccine from BioNTech, through a collaboration with Pfizer, was first to market in the United States and Europe, followed swiftly by the one from Moderna. But the delivery strategies used for mRNA vaccines haven’t worked out for DNA vaccines. That challenge has led to

an outpouring of creative development and the eventual adoption of an electrical engineering approach.

he first human studies of DNA vaccines, which began in the mid-1990s, “were a complete flop,” says Kate Broderick, senior vice president of R&D at Inovio. The vaccine just didn’t prompt much of an immune response. “It was a big surprise and disappointment,” adds Jeffrey Ulmer, who was head of preclinical R&D at the pharma giant GSK until last year and is now an industry consultant. “Despite very good data in a wide variety of animal models for a wide variety of different disease targets, it just did not seem to translate into humans,” he says.

The problem was getting the DNA, which is a big molecule, to penetrate not only through the cell’s outer layers but also through the cell’s nuclear membrane into the nucleus. Unlike an mRNA vaccine, which can function in parts of the cell outside the nucleus, a DNA vaccine can function only inside the nucleus. Some researchers reasoned that DNA vaccines worked well in small animals because the injection needle created pressure that damaged many surrounding cells, allowing DNA molecules to enter. But in the larger bodies of humans, the needle generates relatively little pressure, and fewer cells take in the vaccine. So scientists began experimenting with more physical ways to deliver vaccines and increase cellular uptake. “It’s common sense: Instead of saying ‘Please, open a little window and let me get in,’ you have a violent approach where you break the door,” says Shan Lu, an i mmunologist at the University of Massachusetts Medical School. To that end, researchers engineered all sorts of creative methods to physically force vaccines into the body. They tried sonoporation, which uses sound waves to permeate a cell’s outer layer, and pressurized injections, whereby a piston

pushed by a sudden release of energy delivers a narrow, high-pressure stream of liquid. They experimented with micro shock waves, in which a spark generated by electrodes causes a microexplosion, sending a wave of energy that forces a vaccine through the skin without a needle. They tried gene guns that propel DNA-coated gold particles into cells and microneedles that were laced with vaccine and engineered into skin patches. Among all these contenders, electroporation stood out as particularly promising. “Electroporation was arguably the technology that allowed DNA vaccines to really reemerge as a technology that could be deployed,” says Amy Jenkins, a biological technologies program manager at the U.S. military’s research arm, DARPA, which has invested in both mRNA- and DNA-based vaccines. Researchers have used electroporation routinely for decades to transfer genetic material into cells in the lab. Doctors have also used a high-voltage version of electroporation to break up cancerous masses in humans as part of a surgical technique. So adapting it to vaccines wasn’t a radical step. Inovio’s newest electroporation device, the Cellectra 3PSP, is handheld

and battery operated. It can deliver about a hundred doses on a single charge and has a life-span of about 5,000 uses, due to battery limitations. Each use requires a disposable tip. As with more conventional vaccines, the injection site is the upper arm. Vaccination starts with an intradermal injection of the vaccine dose—a shot that’s only skin deep. Then, the tip of the Cellectra device is pressed against the skin, directly over the location of the shot. Electrodes about 3 milli meters in length administer a series of four square-wave electrical pulses that last 42 milliseconds each, at 0.2 amperes. The recipient feels a brief twinge, similar to the level of pain people experience from a flu shot, according to a clinical study by Inovio. Recipients rated it at an average of about 2.5 on a 0-to-10 pain scale—although the feeling is said to be like a buzzing sensation, rather than the prick and pressure of a shot. The pulses cause nearby cells to temporarily open channels through which the vaccine can enter. As soon as the electrical pulses finish, those channels close. “Now this DNA molecule is trapped inside the cells,” says Inovio’s Broderick. The DNA then “acts like a code, so your cells become a factory for producing the

JUNE 2021 SPECTRUM.IEEE.ORG 29

vaccine,” she explains. Electroporation is generally 10 to 100 times as efficient at provoking an immune response as the same DNA vaccine given by a conventional needle injection alone, says Lu of the University of Massachusetts. Over the last decade, Inovio’s DNA vaccines have been tested against HIV, Ebola, MERS, Lassa fever, and human papillomavirus (HPV), each delivered with some form of electroporation. In total, more than 3,000 people have received one of Inovio’s electroporated medicines, largely through phase 1 and 2 studies, Broderick says. In a phase 1 study involving 40 volunteers, Inovio’s COVID-19 vaccine, which is given in two doses, proved safe and generated an immune response. The results don’t tell us much about how well the vaccine will protect against COVID19 in real life. That will be clearer following the completion of a phase 2 study of 400 volunteers in the United States, which is currently underway. The company is also conducting a phase 2 study of 640 volunteers in China, where it has partnered with biotech company Advaccine Biopharmaceuticals Suzhou Co. to commercialize the vaccine. During the pandemic, some vaccine developers have been linking the different phases of their clinical trials in an effort to speed up the process. But Inovio can’t start on a phase 3 trial in the United States yet—first it has to answer questions from the U.S. Food and Drug Administration about the Cellectra 3PSP device. In September, the FDA notified Inovio of a partial “clinical hold” on trials, a tactic the agency uses when its reviewers find issues with safety or product quality that have not been addressed by the drug developer. Inovio’s vaccine comes with a separate novel device, so that requires additional, independent oversight by the FDA’s device reviewers, says Dennis Klinman, a former senior reviewer of vaccines at the FDA, and now a consultant. The additional device oversight is likely the reason for the clinical hold, he says. Inovio says it plans to answer the FDA’s questions using data from the phase 2 study, but it would not disclose the specifics of the agency’s queries. “It was nothing about the safety or the use of the device in the clinic,” Broderick says. “It’s more logistical areas for us to clarify.” In addition to Inovio, at least three other companies—Genexine, Takis, and

30 SPECTRUM.IEEE.ORG JUNE 2021

In Inovio’s two-step process, the DNA vaccine is first administered via a syringe. Then the Cellectra device is pressed against the skin for electroporation of the cells.

OncoSec—are conducting human s tudies of an electroporated DNA vaccine against COVID-19. Other companies, such as Ichor Medical Systems and IGEA Clinical Biophysics, have developed electroporation devices that they license to pharma companies for DNA vaccine delivery against other diseases. Not everyone thinks electroporation is the solution for DNA vaccines, however. Some groups continue to work on a lternative delivery methods, hoping the surge of interest from the pandemic will push their strategies over the finish line too.

ntroducing a new, unfamiliar device to the vaccination process, particularly during a pandemic, undoubtedly brings logistical challenges. The devices must be mass produced

and delivered, which will add to the cost of the vaccine. Medical personnel must be trained to operate the Cellectra. The extra step (the zap after the shot) adds time to each vaccination. Considering that people have been lining up by the thousands in miles-long car lines to get their COVID-19 vaccines, these inconveniences are not trivial. “I don’t know that [Inovio’s vaccine] is going to get used” during this pandemic, says Moore, the immunologist at Weill Cornell. “It’s not among the most potent, and it’s among the most inconvenient to deliver, so in the end people will vote with their feet—or their arms, as it may be,” he says. Liu of the International Society for Vaccines adds: “We don’t even have enough people trained in the U.S. to give enough syringe injections.” Complicating things with a new

device and new administration method “is going to be hard to do,” she says. And then there’s the issue of consumer acceptance of an unfamiliar device that zaps the skin. “I think the device presents a much larger problem, not from a logistical perspective but from a marketing perspective,” says Bruce Goodwin, who currently leads research on enabling biotechnologies at the U.S. DOD’s Joint Program Executive Office for Chemical, Biological, Radiological, and Nuclear Defense (JPEO–CBRND). “A device that [looks] basically [like] a mix between a sonicator and a stun gun isn’t necessarily the kind of PR people are looking to put out there unless there’s no other choice.” On the other hand, the COVID-19 vaccines available right now can’t reach large swaths of the world. Pfizer’s and Moderna’s vaccines initially had to be

transported and stored in freezers at about –80 °C and –25 °C, respectively. (In February, Pfizer revised its storage guidelines to allow for storage at –25 °C for up to two weeks.) The COVID-19 vaccines developed by Johnson & Johnson, AstraZeneca, and Novavax as well as those deployed in China and Russia don’t need ultracold freezers, but they all need refrigeration. In many poor and remote parts of the world, this complicated supply chain of refrigerators or freezers simply doesn’t exist. Even in more developed and urbanized countries, stories of mishaps abound. Poor temperature control spoiled 12,000 doses en route to Michigan. An unplugged freezer killed 2,000 doses at a hospital in Massachusetts. Widespread power outages in Texas halted deliveries and left officials scrambling to administer thousands of doses before they went bad. A vaccine that can be stored at room temperature would avoid these pitfalls and “greatly facilitate distribution of the vaccine globally,” says Ulmer, the former GSK researcher. “It’s a big advantage.” Inovio’s vaccine is stable for a year at room temperatures of about 19 °C to 25 °C, and for at least a month in hot climates, according to the company. Pfizer’s and Moderna’s mRNA vaccines also tend to trigger flulike side effects, such as fever, chills, headache, muscle pain, nausea, and fatigue. Some of those reactions have been incredibly strong, says Barbara Felber, a senior investigator in the vaccine branch of the National Cancer Institute. For example, within hours of getting an mRNA COVID19 vaccine, Felber’s 25-year-old son was trembling and shivering head to toe while wearing all the blankets in his apartment. “He had such a bad reaction that we were on the phone with him all night,” Felber says. Of course, most people don’t have this kind of reaction, she adds, and the side effects are transient. “It is better to have [side effects] than to get infected by SARS-CoV-2,” she stresses. The United States’ Centers for Disease Control and Prevention (CDC) tracks adverse events of COVID-19 vaccines via a smartphone-based tool called V-safe, which recipients can use to self-report their symptoms. About 25 percent of people who have participated have reported fevers, and 42 percent have reported headaches after

taking the second dose of the Pfizer vaccine. “I have not heard of anybody who got a DNA injection with electroporation who had any of these types of side effects,” Felber says. For Inovio’s DNA vaccine, the only side effect is that momentary buzzing twinge at the injection site, says Broderick, the company’s R&D head.

he upsides of DNA vaccines, plus the ease of manufacturing and its low cost per dose, were enough to convince the DOD to invest heavily in Inovio early in the pandemic. In June 2020 the agency awarded $71 million to scale up the manufacturing of the Cellectra device for COVID19 vaccines. The DOD will also pay for phase 2 and 3 studies of Inovio’s clinical trials, says Nicole Dorsey, director of technology selection and evaluation at the DOD’s JPEO-CBRND, which oversees the funding. “The electroporation device is probably the less appealing part of a DNA vaccine,” but deploying it is a lot easier than maintaining cold-chain transportation overseas, she says. The logistics of a new device seem quite manageable for the military. “Trying to roll out these [Cellectra] 3PSP devices for 300 million people at every Walgreens on every corner—man, it’s a logistical problem that probably just isn’t soluble,” says Chris Earnhart, chief technology officer of the enabling biotechnologies program at JPEO-CBRND. “In the DOD’s case, it’s easily soluble, because we have a very specific population and the numbers are just lower.” Even if Inovio’s technology and vaccines don’t get adopted in the civilian world during this pandemic, they may prove useful in the long run. “The investments we’re making now are related to the COVID response, but in a lot of ways, we’re also preparing for the next event,” says Earnhart. “That could be a bio warfare event, or it could be another endemic outbreak.” And perhaps it’s time for a tech upgrade. Inovio’s Broderick notes that people first began administering medicine via syringe around 1650, when goose quills were used for needles. “It’s actually a really antiquated modality,” she says. “At a time when we carry more computing power around in our pockets than what went to the moon, we should be open to newer technologies for vaccine delivery.” n

JUNE 2021 SPECTRUM.IEEE.ORG 31

THE HIDDEN AUTHENTICATORS

32 SPECTRUM.IEEE.ORG JUNE 2021

Tiny mechanical resonators produced the same way microchips are made [left] can serve to authenticate various goods. Being just a few micrometers across and transparent, these tags are essentially invisible.

Nanometer-scale electromechanical tags could thwart counterfeiters BY ROOZBEH TABRIZIAN & SWARUP BHUNIA

JUNE 2021 SPECTRUM.IEEE.ORG 33

What’s the largest criminal enterprise in the world? Narcotics? Gambling? Human trafficking? • Nope. The biggest racket is the production and trade of counterfeit goods, which is expected to exceed US $1 trillion next year. You’ve probably suffered from it more than once yourself, purchasing on Amazon or eBay what you thought was a brand-name item only to discover that it was an inferior-quality counterfeit.

34 SPECTRUM.IEEE.ORG JUNE 2021

TOTAL GLOBAL COUNTERFEITING, AS A PERCENTAGE OF WORLD TRADE 2016 3.4% 2013 2.5%

scanned. That, their tiny size, and the nature of their constituents, make these tags largely immune to physical tampering or cloning. And they cost just a few pennies each at most. Unseen NEMS tags could become a powerful weapon in the global battle against counterfeit products, even counterfeit bills. Intrigued? Here’s a description of the physical principles on which these devices are based and a brief overview of what would be involved in their production and operation.

Y VALUE OF FAKE EXPORTS, BILLIONS OF US DOLLARS n Electrical machinery and electronics n Jewelry n Optical, photographic, and medical apparatus

138

49.8 26.7

SOURCE: RESEARCHAND MARKETS.COM

ou can think of an RF NEMS tag as a tiny sandwich. The slices of bread are two 50-nanometer-thick conductive layers of indium tin oxide, a material commonly used to make transparent electrodes, such as those for the touch screen on your phone. The filling is a 100-nm-thick piezoelectric film composed of a scandium-doped aluminum nitride, which is similarly transparent. With lithographic techniques similar to those used to fabricate integrated circuits, we etch a pattern in the sandwich that includes a ring in the middle suspended by four slender arms. That design leaves the circular surface free to vibrate. The material making up the piezoelectric film is, of course, subject to the piezoelectric effect: When mechanically deformed, the material generates an electric voltage across it. More important here is that such materials also experience what is known as the converse piezoelectric effect—an applied voltage induces mechanical deformation. We take advantage of that phenomenon to induce oscillations in the flexible part of the tag. To accomplish this, we use lithography to fabricate a coil on the perimeter of the tag. This coil is connected at one end to the top conductive layer and on the other end to the bottom conductive layer. Subjecting the tag to an oscillating magnetic field creates an oscillating voltage across the piezoelectric layer, as dictated by Faraday’s law of electromagnetic induction. The resulting mechanical deformation of the piezo film in turn causes the flexible parts of the tag to vibrate.

PREVIOUS PAGES AND RIGHT: UNIVERSITY OF FLORIDA

It’s an all-too-common ploy, and legitimate manufacturing companies and distributors suffer mightily as a result of it. But the danger runs much deeper than getting ripped off when you were seeking a bargain. When purchasing pharmaceuticals, for example, you’d be putting your health in jeopardy if you didn’t receive the bona fide medicine that was prescribed. Yet for much of the world, getting duped in this way when purchasing medicine is sadly the norm. Even people in developed nations are susceptible to being treated with fake or substandard medicines. Counterfeit electronics are also a threat, because they can reduce the reliability of safety-critical systems and can make even ordinary consumer electronics dangerous. Cellphones and e-cigarettes, for example, have been known to blow up in the user’s face because of the counterfeit batteries inside them. It would be no exaggeration to liken the proliferation of counterfeit goods to an infection of the global economic system—a pandemic of a different sort, one that has grown 100-fold over the past two decades, according to the International AntiCounterfeiting Coalition. So it’s no wonder that many people in industry have long been working on ways to battle this scourge. The traditional strategy to thwart counterfeiters is to apply some sort of authentication marker to the genuine article. These efforts include the display of Universal Product Codes (UPC) and Quick Response (QR) patterns, and sometimes the inclusion of radio-frequency identification (RFID) tags. But UPC and QR codes must be apparent so that they are accessible for optical scanning. This makes them susceptible to removal, cloning, and reapplication to counterfeit products. RFID tags aren’t as easy to clone, but they typically require relatively large antennas, which makes it hard to label an item imperceptibly with them. And depending on what they are used for, they can be too costly. We’ve come up with a different solution, one based on radio-frequency (RF) nanoelectromechanical systems (NEMS). Like RFID tags, our RF NEMS devices don’t have to be visible to be

This vibration will become most intense when the frequency of excitation matches the natural frequency of the tiny mechanical oscillator. This is simple resonance, the phenomenon that allows an opera singer’s voice to shatter a wine glass when the right note is hit (and if the singer tries really, really hard). It’s also what famously triggered the collapse of the Broughton suspension bridge near Manchester, England, in 1831, when 74 members of the 60th Rifle Corps marched across it with their footsteps landing in time with the natural mechanical resonance of the bridge. (After that incident, British soldiers were instructed to break step when they marched across bridges!) In our case, the relevant excitation is the oscillation of the magnetic field applied by a scanner, which induces the highest amplitude vibration when it matches the frequency of mechanical resonance of the flexible part of the tag. In truth, the situation is more complicated than this. The flexible portion of the tag doesn’t have just one resonant frequency—it has many. It’s like the membrane on a drum, which can oscillate in various ways. The left side might go up as the right side goes down, and vice versa. Or the middle might be rising as the perimeter shifts downward. Indeed, there are all sorts of ways that the membrane of a drum deforms when it is struck. And each of those oscillation patterns has its own resonant frequency. We designed our nanometer-scale tags to vibrate like tiny drumheads, with many possible modes of oscillation. The tags are so tiny—just a few micro meters across—that their vibrations take place at radio frequencies in the range of 80 to 90 megahertz. At this scale, more than the geometry of the tag matters: the vagaries of manufacturing also come into play. For example, the thickness of the sandwich, which is nominally around 200 nm, will vary slightly from place to place. The diameter and the circularity of the ring-shaped portion are also not going to be identical from sample to sample. These subtle manufacturing variations will affect the mechanical properties of the device, including its resonant frequencies. In addition, at this scale the materials used to make the device are not perfectly homogeneous. In particular, in the piezoelectric layer there are intrinsic variations in the crystal structure. Because of the ample amount of scandium doping, conical clusters of cubic crystals form randomly within the matrix of hexagonal crystals that make up the aluminum nitride grains. The random positioning of those tiny cones creates significant differences in the resonances that arise in seemingly identical tags. Random variations like these can give rise to troublesome defects in the manufacture of some microelectronic devices. Here, though, random variation is not a bug—it’s a feature! It allows each tag that is fabricated to serve as a unique marker. That is, while the resonances exhibited by a tag are controlled in a general way by its geometry, the

These electron micrographs show some of the tags the authors have fabricated, which can take various forms. The preferred geometry [top] is a circular tag containing a piezoelectric ring suspended by four beams. It includes a coil [lighter shade], which connects with electrode layers on the top and bottom of the ring. Voltages induced in this coil by an external scanner set up mechanical oscillations in the ring.

JUNE 2021 SPECTRUM.IEEE.ORG 35

CATCH THE WAVE

exact frequencies, amplitudes, and sharpness of each of its resonances are the result of random variations. That makes each of these items unique and prevents a tag from being cloned, counterfeited, or otherwise manufactured in a way that would reproduce all the properties of the resonances seen in the original. An RF NEMS tag is an example of what security experts call a physical unclonable function. For discretely labeling something like a batch of medicine to document its provenance and prove its authenticity, it’s just what the doctor ordered.

ou might be wondering at this point how we can detect and characterize the unique characteristics of the oscillations taking place within these tiny tags. One way, in principle, would be to put the device under a vibrometer microscope and look at it move. While that’s possible—and we’ve done it in the course of our laboratory studies—this strategy wouldn’t be practical or effective in commercial applications. But it turns out that measuring the resonances of these tags isn’t at all difficult. That’s because the electronic scanner that excites vibrations in the tag has to supply the energy that maintains those vibra-

36 SPECTRUM.IEEE.ORG JUNE 2021

“More than 2 billion different binary signatures are possible– enough to uniquely tag just about any product.”

tions. And it’s straightforward for the electronic scanner to determine the frequencies at which energy is being sapped in this way. The scanner we are using at the moment is just a standard piece of electronic test equipment called a network analyzer. (The word network here refers to the network of electrical components—resistors, capacitors, and inductors—in the circuit being tested, not to a computer network like the Internet.) The sensor we attach to the network analyzer is just a tiny coil, which is positioned within a couple of millimeters of the tag. With this gear, we can readily measure the unique resonances of an individual tag. We record that signature by measuring how much the various resonant-frequency peaks are offset from those of an ideal tag of the relevant geometry. We translate each of those frequency offsets into a binary number and string all those bits together to construct a digital signature unique to each tag. The scheme that we are currently using produces 31-bit-long identifiers, which means that more than 2 billion different binary signatures are possible— enough to uniquely tag just about any product you can think of that might need to be authenticated. Relying on subtle physical properties of a tag to define its unique signature prevents cloning, but it

Illustration by James Provost

TOP IMAGE: UNIVERSITY OF FLORIDA

The authors directly measured the surface topography of a tag using a digital holographic microscope, which is able to scan reflective surfaces and precisely measure their heights [right]. The authors also modeled various modes of oscillation of the flexible parts of such a tag [bottom]. Each mode has a characteristic resonant frequency, which varies with both the geometry of the tag and its physical composition.

FREQUENCY

ENCODING

1101

AMPLITUDE

A tag is characterized by the differences between its measured resonant frequencies [dips in red line] and the corresponding frequencies for an ideal tag [dips in dark gray line]. These differences are encoded as short binary strings, padded to a standard length, with one bit signifying whether the frequency offset is positive or negative [right]. Concatenated, these strings provide a unique digital fingerprint for the tag [bottom].

1001101 0001101

UNIVERSITY OF FLORIDA

0000111

0001101100110100001111101010

does raise a different concern: Those properties could change. For example, in a humid environment, a tag might adsorb some moisture from the air, which would change the properties of its resonances. That possibility is easy enough to protect against by covering the tag with a thin protective layer, say of some transparent polymer, which can be done without interfering with the tag’s vibrations. But we also need to recognize that the frequencies of its resonances will vary as the tag changes temperature. We can get around that complication, though. Instead of characterizing a tag according to the absolute frequency of its oscillation modes, we instead measure the relationships between the frequencies of different resonances, which all shift in frequency by similar relative amounts when the temperature of the tag changes. This procedure ensures that the measured characteristics will translate to the same 31-bit number, whether the tag is hot or cold. We’ve tested this strategy over quite a large temperature range (from 0 to 200 °C) and have found it to be quite robust.

1101010

he RF network analyzer we’re using as a scanner is a pricey piece of equipment, and the tiny coil sensor attached to it needs to be placed right up against the tag. While in some applications the location of the tag on the product could be standardized (say, for authenticating credit cards), in other situations the person scanning a product might have no idea where on the item the tag is positioned. So we are working now to create a smaller, cheaper scanning unit, one with a sensor that doesn’t have to be positioned right on top of the tag. We are also exploring the feasibility of modifying the resonances of a tag after it is fabricated. That possibility arises from a bit of serendipity in our research. You see, the material we chose for the

“Governments might one day adopt nanomechanical tags to authenticate paper money.”

Frequency offset (binary value) Padding bits

Sign bit (positive)

Sign bit (negative)

piezoelectric layer in our tags is kind of unusual. Piezoelectric devices, like some of the filters in our cellphones, are commonly made from aluminum nitride. But the material we adopted includes large amounts of scandium dopant, which enhances its piezoelectric properties. Unknown to us when we decided to use this more exotic formulation was a second quality it imparts: It makes the material into a ferroelectric, meaning that it can be electrically polarized by applying a voltage to it, and that polarization remains even after the applied voltage is removed. That’s relevant to our application, because the polarization of the material influences its electrical and mechanical properties. Imparting a particular polarization pattern on a tag, which could be done after it is manufactured, would alter the frequencies of its resonances and their relative amplitudes. This approach offers a strategy by which low-volume manufacturers, or even end users, could “burn” a signature into these tags. Our research on RF NEMS tags has been funded in part by Discover Financial Services, the company behind the popular Discover credit card. But the applications of the tiny tags we’ve been working on will surely be of interest to many other types of companies as well. Even governments might one day adopt nanomechanical tags to authenticate paper money. Just how broadly useful these tags will be depends, of course, on how successful we are in engineering a handheld scanner—which might even be a simple add-on for a smartphone—and whether our surmise is correct that these tags can be customized after manufacture. But we are certainly excited to be exploring all these possibilities as we take our first tentative steps toward commercialization of a technology that might one day help to stymie the world’s most widespread form of criminal activity. n

JUNE 2021 SPECTRUM.IEEE.ORG 37

PUT DOWN THAT SMARTPHONE: The Display Is on Your Skin

The screen is the last frontier in stretchable, bendable, bodyconforming electronics B y takao S omeya

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relaxes in the afternoon after finishing lunch. A square sheet of thin rubber clings to the back of her hand. Like a poultice, it stretches and then wrinkles as she flexes her fingers. • As she reaches for her teacup, the square lights up with a message: “TAKE YOUR BLOOD PRESSURE MEDICINE.” She smiles, remembering how she used to struggle and often fail to remember, even though her smartphone had been programmed to send her such alerts. But now, thanks to that business-card-size patch on her hand, she hasn’t missed a single dose. Indeed, her blood-pressure value, which she can now see on the display, is well within a healthy range. • Stretchy, thin, bright, waterresistant displays that stick to skin without adhesives are going to start appearing in coming years. They’ll be on the hands and arms of not just the elderly but also on those of athletes, travelers, hipsters, and early adopters. They’re going to unobtrusively update runners and cyclists on heart rate and hydration needs, ultraviolet exposure, and even show maps of the route ahead. They’ll be used to send secret messages between friends and lovers. The fashion-forward will undoubtedly flash messages and vital stats at each other at parties and festivals. Such a display might even share emotional cues with observers, suggesting that you are interested, anxious, available, or excited. Depending on the setting, it might foster friendship, deeper communication, or splendid isolation. 40 SPECTRUM.IEEE.ORG JUNE 2021

For the elderly or infirm, these displays could show electrocardiogram waveforms, collecting the data from wireless electrodes placed elsewhere on the body. They could also alert someone who is hard of hearing to an incoming phone call or a knock on the door. The locations where we place these thin, flexible, stretchable displays won’t be limited to skin; the displays will be equally easy to apply to the curved surfaces of clothes and other objects. Their color, brightness, or patterns could change in response to your activity or in reaction to the world around you. Thanks to the emergence of thin and flexible circuitry capable of twisting, bending, and stretching, people are already affixing semiconductor circuits to their skin, wrapping them around the curved surfaces of a hand, an arm, a calf, or a torso. The first generation of these stretchy wearables are sensors that are measuring vital signs in hospitals and elsewhere. And Gatorade, the sports-drink company, released a flexible sweat-monitoring patch earlier this year. But to get useful information from these sensors, users still have to take out their smartphones or consult a nearby computer. Smartwatches aim to make getting this information less cumbersome, but some people find them clunky, and the tiny displays can be hard to read. Displays have long been a pothole on the road to wearable devices, one that many researchers have been trying to fill, including my group in the University of Tokyo’s Organic Transistor Lab at the school of engineering. Conventional display technology is hard to make flexible. While televisions that roll up and smartphones that fold are finally available, they’re really expensive. And they can roll or fold in only one direction; they can’t twist or stretch.

PREVIOUS PAGES AND ABOVE: YOSHIAKI TSUTSUI/UNIVERSITY OF TOKYO

AN ELDERLY WOMAN, LIVING ALONE IN A SMALL MOUNTAIN VILLAGE,

Now, truly flexible, bright displays are finally close to fruition, poised to feed us the information we need, no phone required. My group has developed and demonstrated several versions of such a skin display. And Dai Nippon Printing Co. is working to bring our skin-display technology to market, likely getting there within the next three years.

While the first taking this approach. For example, the applications of Rogers Research Group at Northwestwearable displays ern University, a team from Imec and will likely be to communicate TNO in the Netherlands, and health and wellness researchers at the VTT Technical information, the Research Centre of Finland are also possibilities are endless. looking at using arrays of LEDs as part of stretchable displays. NOT ALL TYPES of displays can be made stretchable. In a We recently produced our liquid-crystal display, for example, light shines from behind a set second-generation full-color skin display using commercially of electrodes with a layer of liquid crystals between them. Turning available micro-LEDs. In these displays, a 1.5-square-millimeter electric current on and off changes the orientation of the liquid package makes up a picture element, or pixel; each contains one crystals and therefore the light’s polarization, allowing it to either red, one green, and one blue LED. Because these devices are conpass through a polarizing filter to the viewer or structed using standard semiconductor manbe blocked by the filter. Stretching the LCD ufacturing techniques, the individual LEDs and changes the thickness of the liquid-crystal layer, the packaging that surrounds them are hard. Displays have altering the alignment of the crystals. But the LEDs are tiny, and we mount them on long been a Displays based on organic LEDs (OLEDs) a rubber sheet and connect them with stretchpothole on the have no such limitation. These OLED displays able wiring, creating a very flexible display. road to wearable are indeed printable onto thin, flexible subThese micro-LED packages are arranged devices. strates. Today’s rollable displays take advanin a 12-by-12 array. Unstretched, the pixel tage of that capability. To date, however, no packages are spaced 2.5 mm apart, so the one has yet commercialized an OLED display entire display is about 46 mm square (about that can stretch and bend in multiple directions, although 1.8 inches square), and it’s just 2 mm thick. We can bend and Samsung has reportedly been working on one. In our labora- twist it freely and stretch it to as much as 130 percent of its tory, we did produce a prototype low-resolution OLED display. original length, expanding the distance between the pixels from Still, it will take researchers a considerable amount of time to 2.5 to 3.25 mm. Stretching distorts the picture somewhat, but develop a stretchy, long-lasting material that can also be used text is still legible, and the display has proved resistant to wear to protect devices against oxygen and water vapor. and tear from stretching. So my group has been working mainly with inorganic LEDs To make this stretchable display, we start with a very thin in the form of micro-LED displays. We are not the only ones plastic substrate. We then use screen printing to define the

JUNE 2021 SPECTRUM.IEEE.ORG 41

wiring that connects the pixels into a circuit. For this wiring, these external components and bring them into our flexible we use silver paste—a resin containing silver flakes. When dry, package before our device can be commercialized. This will this silver paste is elastic, conducting electricity even as it present some challenges. expands and contracts. After printing our circuitry, we solder the micro-LED chips to it, using a standard surface mounter used commercially to CHALLENGE NO. 1 is how to power these displays for a attach chips to circuit boards. We then laminate the plastic week or more at a time without bulky batteries. Researchers film onto a silicone-rubber substrate that has been pre- are working hard to improve power sources for wearables. stretched on a frame. When we remove the completed device Stretchable solar cells exist and are already reaching effifrom the frame—now a sheet with multiple layers that include ciencies of more than 12 percent, generating about 10 milli the LED packages, the silver wires, the thin plastic film, and watts per square centimeter outdoors. Still, getting sufficient the silicone substrate—it buckles. It’s in this crinkled, con- power out of them to power a display presents a big chaltracted form that it is applied to someone’s skin. It adheres lenge, one that will certainly involve developing display without adhesive, thanks to natural characteristics of the controllers and wireless radios that use much less power silicone material. than those available today. So that’s our display: micro-LEDs conAt the same time, we’ll want to drive nected by printed silver wiring attached to a more pixels. We know that an array of 144 I believe skin prestretched silicone substrate. Right now, pixels, while usable for displaying text, isn’t displays can get we put the electronics—the controller, the optimal. But for now, we are limited by the us to a future wireless radio, and the batteries—in a sepasize of commercially available LEDs. of technologies rate hard package that is connected by wires Fortunately, micro-LEDs have uses beyond that are gentle, to the display. For testing, we put the flexible skin displays, and their manufacturers are kind, and spread display on the user’s hand and strap the pushing hard to make them smaller every warmth, not just other electronics to the wrist, like a watch. year. Skin displays will undoubtedly benefit information. Obviously, we will have to reduce the size of from that progress.

42 SPECTRUM.IEEE.ORG JUNE 2021

LEFT: DAI NIPPON PRINTING CO.; RIGHT: YOSHIAKI TSUTSUI/UNIVERSITY OF TOKYO

Mounting conventional micro-LEDs on a rubber sheet and connecting them with stretchable wiring creates a display that can bend, twist, and stretch to as much as 130 percent of its original length [left]; University of Tokyo professor Takao Someya [right] hopes skin displays will allow family members to quietly communicate their feelings to one another.

UNIVERSITY OF TOKYO

We also need to improve durability. Right now, our displays can withstand 10,000 stretch cycles in mechanical tests. But we imagine that for many applications, people will wear our displays much of the day, and day after day. So we need to do much better—say, a million stretch cycles. How did we get that number? Consider that a year has 525,600 minutes, and then consider how often someone extends or flexes his hand, and you see how durable a skin display must be. However, there is a trade-off between durability and the degree of burden the display places on the skin. When we use a harder, more durable material, the display becomes less comfortable to wear. We need to do more research to pinpoint the sweet spot between durability and comfort. And, of course, resolving broad issues common to many wearables—including ethics, privacy, and regulations specific to medical instruments—will also be very important to the future of skin displays, particularly those that display biometric information. Based on our work so far, we don’t expect any of these difficulties to be a showstopper. On the contrary, we expect to solve many of these challenges in the very near future. A SKIN DISPLAY isn’t much use unless it has interesting data to communicate to its wearer. To gather this data, we turn to skin-conforming sensors, capable of detecting signals from the heart, brain, skin, muscles, and other organs. The key part of these sensors is the electrode. To make flexible electrodes, we start with a mesh of nanofibers made of a water-soluble polyvinyl alcohol, a substance commonly used in adhesives and contact lenses. We then use vapor deposition to add a conductive layer of gold, 70- to 100-nm thick, to this mesh. To attach this electrode to a person’s skin, we position it and then spray the sensor with water. The water dissolves some of the nanofibers, making them sticky. The electrode then easily adheres to the skin, conforming to curvilinear surfaces as small as sweat pores or the ridges of a fingerprint pattern. It operates even when stretched to 130 percent of its length— about the stretch of the skin on a knuckle when it bends. Because the nanomesh allows water vapor to pass, these sensors are hypoallergenic, and can be worn on the skin continuously for a week without discomfort. Users usually forget they even have them on. Wearable electrodes are not completely new; wearable EKG monitors have for some time been marketed to athletes. But these are bulky devices and

they’re anything but breathable, making them impractical for long-term use. So far, we’ve used our stretchy electrode to monitor muscle activity for electromyogram recording, and it has performed as well as conventional electrodes do. We can similarly create sensors that monitor the activity of the heart or brain from a position on the chest or head.

This flexible electrode starts with a mesh of nanofibers, upon which the author and his team deposited a conductive layer of gold. Here, the researchers use it to monitor muscle activity; it still operates even when stretched by a bending finger.

WHEN WE ATTACH a skin-conforming sensor to a display, we can create a continuous, easily accessible flow of biometric information. But the applications of skin displays go well beyond health and wellness. Skin displays improve accessibility to information, making them particularly useful when you’ve got both hands busy and are on the move. For example, you could read a recipe while cooking without worrying about drying your hands to consult a smartphone. Or you could consult an instruction manual—at home or in a factory—without putting down a tool you’re using. And the applications in sports seem limitless. I already mentioned runners and cyclists, and the utility there is obvious. Other outdoors enthusiasts will also find uses. Consider skydivers, white-water kayakers, and skiers, who could check the output of a helmet-mounted action camera by stealing glances at their arms or hands. A fisherman could consult a fish finder without putting down his pole or risking his smartphone in a chest-deep stream. And because skin displays will flex when they are struck instead of breaking, they will be useful even in contact sports. Tragically, roughly a dozen young American football players perish every year from heatstroke or heart problems. Either condition could be detected in many cases before it became fatal. Finally, I believe skin displays can get us to a future of technologies that are gentle, kind, and spread warmth, not just information. Let’s go back to that elderly woman I described earlier. She’s now resting in her living room after dinner. Because she lives alone, there is no one to talk to. Only the sound coming from the TV breaks the silence. Then she notices something flashing unexpectedly on the display attached to the back of her hand. It’s the image of a heart, and it’s from a grandson who lives in a city far away. It’s just a little red heart, but she feels as though she’s actually hearing her grandson’s voice saying, “I love you, Grandma!” She puts her other hand over the display, holding that heart for a moment. This is what I wish for the future of electronics—devices that not only transmit data but also feelings. n

JUNE 2021 SPECTRUM.IEEE.ORG 43

Solar pumps, batteries, and microcredit are triggering an African agricultural renaissance

Kenya has the highest penetration of off-grid solar systems in Africa. Farmers in the region are gaining access to a number of solar-powered devices, including irrigation pumps, egg incubators, grain processors, and refrigerators.

K E N YA Matanya

Nairobi

OFF-GRID SOLAR’S KILLER APP B y PETER FAI RL EY it’s a baking-hot February day in Matanya, a village that straddles the equator, a few hours’ drive north of Nairobi. Smiling broadly, Patrick Gicheru is sowing carrots in layers of soil and compost at his 0.8-hectare farm and recalling a profitable crop of peppers that recently came from the same field. Tomatoes maturing on another plot should be ready for market in a month. “Tomatoes are going for about 80 shillings per kilo,” he says. He estimates the crop will fetch him roughly 10,000 Kenyan shillings— a little over US $93—every week for nearly three months. • This year’s tomato harvest alone will nearly pay for the technology that’s underpinning Gicheru’s success: a solar-powered water pump. A model of simplicity, it consists of a 310-watt photovoltaic panel, a 440-watt-hour lithium-ion battery pack, and a controller that supports his 3,000-liter-per-hour direct-current pump as well as a few LED lights, a mobile phone charger, and a flat-screen TV. • In February 2020, when I visited Gicheru, the small farmer had zero control over the COVID-19 pandemic that was spreading toward Kenya, or the historic locust invasion devouring fields throughout East Africa. But the solar pump he acquired in 2019 was tapping a stable supply of groundwater, boosting his yields and growing seasons, and neutralizing the waves of drought that have afflicted sub-Saharan Africa since time immemorial. • Before acquiring his solar system, Gicheru—like the vast majority of Kenya’s

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access to capital. “If we can figure out how to make these farmers’ incomes predictable and dependable, we can then give them access to commercial capital markets, and then we create an entirely new consumer market, and then we can sell into that consumer market,” says Ibrahim. That’s a big dream, but it’s one that Ibrahim, Nichols, and many others now believe is within reach.

unculture grew out of an idea that Ibrahim and Nichols hatched in 2011, when both were still college students in New York City. Seeing the rise in off-grid solar technology, they discussed building a solar business around enhancing the productivity of small farmers. They submitted their idea to a business-plan competition at New York University,

More than 43 million small farmers in sub-Saharan Africa live above aquifers but lack the means to tap the water. And so they remain vulnerable to crop failures, even though water might be literally meters away.

where Ibrahim was majoring in business. Nichols had studied mechanical engineering at Stevens Institute of Technology and moved on to economics at Baruch College. Their proposal won the competition’s “audience choice” award that year. By the end of 2012, they had moved to Kenya and were setting up the firm. Nairobi, Kenya’s capital, was a natural choice. A growing tech hub there had earned the city of 5 million its Silicon Savannah moniker. The city is also the epicenter of Africa’s off-grid solar sector, and Kenya has the highest penetration

of off-grid solar systems in Africa. There was also a personal connection: Ibrahim is the son of a Kenyan mother and a Tanzanian father. Still, it took several years for Nichols and Ibrahim’s solar-irrigation plan to gain traction. Incumbent players in the water-pumping business didn’t take solar seriously, and investors doubted that small farmers would be able to afford it. “Everybody thought we were nuts. Nobody wanted to fund us,” recalls Nichols. Eight years and four major design iterations later, SunCulture is selling a robust system for about $950—less than onefifth the price of its first product. The package combines solar-energy equipment with a pump and four LED lights and supports an optional TV. The pump is designed to tap water from as deep as 30 meters and irrigate a 0.4-hectare plot. Nichols says the company’s key hardware breakthrough was to include a battery. Most solar pumping systems, including SunCulture’s early offerings, employ a water-storage tank that can be filled only when the sun is strong enough to run the pump. Nixing the tank and adding a battery instead created a stable power supply that customers could use to pump and irrigate on their own schedules. The battery can also charge in the early morning and late afternoon when the sunlight is too weak to run the pump directly. SunCulture’s partners supply the batteries, photovoltaic panels, and screw pumps driven by high-efficiency brushless DC motors. The company’s core intellectual property lies in the printed circuit board for its integrated controller, communications, and battery base unit, designed by the company’s senior electrical engineer Bogdan Patlun and his Ukraine-based team. SunCulture uses a pay-as-you-go financing model, which has become popular in the off-grid solar sector. Rather than paying the full price up front, farmers put down a small deposit and then make monthly payments over several years. Gicheru put down 8,900 shillings for his system (about $83) and is paying the remainder over 2.5 years at a rate of 3,900 shillings per month. It’s a low-risk scheme for SunCulture because its elec-

Patrick Gicheru [top] has an off-grid solar system from SunCulture that includes a photovoltaic panel, lithium-ion battery pack, water pump, LED lights, and flat-screen TV. Nearby, Monicah Riitho [middle] likes her solar-powered drip irrigation system. Alex Gitau [bottom right], a SunCulture field engineer, says customer data is training algorithms to give farmers advice on irrigation, fertilizers, and crops.

46 SPECTRUM.IEEE.ORG JUNE 2021

PREVIOUS PAGES: SUNCULTURE

small farmers—relied exclusively on rainfall. He also raised cattle back then and lost many to dry spells. He describes life with solar-powered irrigation as a new era: “It has really transformed our lives. At the end of the day, I can be able to put food on the table. I’m also employing people, so I can help them put food on the table. So I thank God. I’m happy.” It’s a transformation that, if widely replicated, could radically improve the livelihoods of millions of people across Africa. According to a 2020 report from the International Finance Corp., an arm of the World Bank, more than 43 million small farmers in sub-Saharan Africa aren’t connected to the power grid. Many of these farmers, like Gicheru, live above near-surface aquifers, yet they lack the means to tap the water. As a result, they remain vulnerable to crop failures, even though water might be literally meters away. As struggling farmers give up their land and flee to the cities, the migration drives the continent’s unchecked urbanization and dependence on food imports. “Despite having the very tools for their escape from poverty—which are water, land, and sun—they’re the most underserved people in the world,” says Samir Ibrahim. He’s the CEO and cofounder of Nairobi-based SunCulture, which is now Africa’s leading solar-irrigation developer. Gicheru is one of the company’s satisfied customers. Ibrahim and Charles Nichols, SunCulture’s cofounder and until recently its chief technology officer, have been perfecting their technology since starting the company in 2012. Now they say they’re ready to scale up. Plummeting solar and battery prices have slashed hardware costs. New digital financing tools are making it easier for farmers to buy in. And innovative farming techniques promise to minimize water consumption—a crucial safeguard to ensure that the solar-irrigation boom they aim to unleash doesn’t run dry. The potential upside of solar irrigation could be huge, Ibrahim says. Solar pumps for small farmers could be a $1 billion market in Kenya alone, he notes. What’s more, they could spark a virtuous cycle of rising productivity and

PETER FAIRLEY

JUNE 2021 SPECTRUM.IEEE.ORG 47

48 SPECTRUM.IEEE.ORG JUNE 2021

It’s no wonder then that SunCulture is picking up some big backers, such as France’s state-owned power company, Electricité de France, which provides power in some remote, rural overseas regions and provinces. And no surprise, either, that SunCulture is also picking up some competition.

o keep its momentum going, SunCulture is working hard to ensure its approach is sustainable, by looking for ways to cut the amount of water its farmers use. In 2012, a continent-wide survey by U.K. researchers shone a spotlight on Africa’s abundant and shallow aquifers,

At off-grid solar provider SunCulture’s branch office in Matanya, about 200 kilometers north of Nairobi, Dolly Kathure demonstrates the company’s smart controller. The pay-as-you-go system is affordable for small farmers; the controller allows SunCulture to remotely disable the equipment if a customer stops paying.

which were found even in semiarid areas that receive little rainfall. Subsequent research on groundwater management across sub-Saharan Africa found that tapping these aquifers reduced crop failures and boosted rural incomes. However, the researchers also identified “moderate” impacts on water tables after just five years of small-scale irrigation, with declines of up to 4 meters over 40 percent of the study area in east Africa. An insight into aquifer limits—and one way to avoid exceeding them—is on display at the farmstead of Monicah Riitho, about 2 kilometers from Patrick Gicheru’s farm. Riitho cultivates a bounty of fruits, vegetables, and grains on her 1.2-hectare parcel. Like Gicheru, the mother of four says she’s better off thanks to her SunCulture pump. But every day she turns it on, the water level in her 21-meter borehole drops out of reach after about 3 hours of use. The water level always recovers overnight, and Riitho discounts the risk of it being permanently depleted. “The underground water is large,” she says. Still, conserving it is crucial to her plan to expand: “I just have this one source of water, so I have to use the water economically.” Riitho is testing a water-saving solution: a drip irrigation line that is irrigating her plot of cabbage, spinach, and potatoes, putting out only enough water to moisten the soil near the plants’ roots. A plastic drip line may sound low tech for 2021, but driving one with a minimum of electricity requires some finesse. SunCulture has 15 of its customers testing such drip lines, which are designed for low-pressure activation. The key to such a setup is precise control of the water pressure in the line. “You don’t want to put out much pressure beyond the activation point because that energy just gets lost,” says Nichols. “But it can’t be any lower than the activation point because then no water comes out.” The solution is a feedback loop in the pump’s motor controller that detects current deviations around the line’s activation pressure and stops increasing the flow when the deviations exceed certain limits. It’s a fuzzylogic approach that researchers at the MIT Global Engineering and Research (GEAR) Lab are developing for SunCulture. “If the algorithm is tweaked by the GEAR Lab folks, we can just push

PETER FAIRLEY

tronics let the company remotely disable the equipment if a customer stops paying. By SunCulture’s estimates, its “pay-asyou-grow” financing puts the company’s system within reach of the majority of Kenya’s 2 million small farmers who have access to water. Those who choose to invest quickly see returns, according to a recent report by Dalberg Global Development Advisors, a consultancy headquartered in Geneva. Dalberg estimates that on small farms, solar irrigation improves yields by two to four times and incomes by two to six times. As a result, the report projects that 103,000 solar water pumps will be sold in Kenya over the next five years, up from fewer than 10,000 per year in 2019 and 2020. “The business case for irrigation is very strong,” says Dalberg senior manager Michael Tweed. The off-grid solar business needs products like SunCulture’s pumps to free it from a productivity slump. The sector initially took off in the early 2000s by combining small commodity PV panels, batteries, and LED lights, creating a package that replaced comparatively costly—and dirty—kerosene lamps. Systems quickly expanded to include cellphone charging, which in turn boosted access to mobile banking, messaging, and the Internet. But over the past decade or so, the most popular new capabilities that off-grid solar has added are televisions and fans. The focus on such lifestyle upgrades, as pleasant as they are for the owners, has prompted some economists to question the development impact of off-grid solar. “It’s hard to imagine that watching TV or running a fan would actually make you significantly more productive, and therefore they don’t break you out of the poverty track,” says Johannes Urpelainen, who runs the Initiative for Sustainable Energy Policy at Johns Hopkins University, in Baltimore. “They don’t really solve the main problem.” Solar irrigation, by contrast, demonstrably pulls people up. In a recent update to SunCulture’s supporters, Ibrahim touted solar pumping’s impact during the COVID-19 pandemic. He cited a survey by impact measurement firm 60 Decibels, in which 88 percent of Kenyan farmers said they were worse off financially due to the pandemic. In stark contrast, Ibrahim noted, 81 percent of SunCulture’s clients increased their farming revenue.

BRITISH GEOLOGICAL SURVEY

it out to all of the devices in the next day or two,” says Nichols. The drip line is working for Riitho, who intends to expand the line to another part of her land. She can do that with no money down by refinancing her solar pump, adding an additional 5 months of payments. “It is worth it,” she declares. The drip lines are a small example of the modern techniques that began sweeping developed-world farms decades ago. Now, SunCulture is expanding into precision agriculture. Gicheru, for example, is one of five customers testing the company’s next value-enhancing digital innovation: combining data from soil sensors and hyperlocal weather forecasting to generate agronomic advice. Soil sensors connect to the battery base unit via Bluetooth, and their readings of moisture, temperature, and conductivity—a proxy for pH—are then uploaded to SunCulture via cellular. Alex Gitau, SunCulture’s field engineer in Nanyuki, the closest town to Matanya, says the data will initially be used to advise farmers on irrigation timing and volume. Eventually, he says, smart algorithms will inform fertilizer applications and crop selection. Farmers spend a lot of time and effort tracking down such advice. With the SunCulture agronomy system, “the farmer doesn’t need to go to Nanyuki to go from one agronomist to another, or look for an agricultural extension officer to come to his farm,” Gitau says. “He can get that help from our device.” For now, SunCulture’s expert system is a work in progress. The hardware is ready, thanks to the use of a tiny amplifier designed by Patlun’s team to overcome Bluetooth connectivity glitches that the sensors were having. But Nichols says they need more agronomic and mathematics expertise to convert their data into reliable advice. “You need a top-5percent person, and, as of yet, we’ve been unsuccessful in recruiting someone to provide that firepower,” he says. (Nichols, meanwhile, recently moved on from SunCulture to follow a newfound passion for blockchain-enabled networks.)

f ibrahim and the SunCulture team have their way, solar irrigation will set off a whole chain of developments that will amplify off-grid solar power’s economic impact. SunCulture is one of several firms, for

Shallow aquifers [dark blue] are abundant in much of sub-Saharan Africa, even in areas that receive little rainfall, a 2012 study by the British Geological Survey revealed. Solar-powered water pumps allow small farmers to tap into the groundwater.

example, testing energy-efficient electric pressure cookers, which are expected to take off in the next year or two, as solarpanel and battery costs continue to fall, boosting the amount of electricity that an off-grid solar system can supply. Other appliances nearing a breakthrough include egg incubators, grain processors, and refrigerators. Gicheru’s wish list for his solar system includes electric fencing against herd-raiding hyenas and remote video surveillance. He says security cameras would provide a sense of safety to women in Matanya, and he’d welcome them to help deter thieves. “Once the tomatoes start to ripen, people will come around here,” he says. This yearning for electric enhancements is attracting competitors, such as Mwezi, an England-based distributor that markets off-grid technology in the agricultural basin around Lake Victoria, in western Kenya. Mwezi recently began test-marketing egg incubators and a 400-watt hammer mill for grinding corn from Nairobi-based Agsol. Mike Sherry, Mwezi’s founder and director, says both devices are affordable, thanks to a financing platform from San Francisco–based Angaza, which specializes in pay-asyou-go account management. Sherry, like SunCulture’s principals, sees a proliferation of solar-powered devices having an impact well beyond any immediate productivity gains. For one thing, they help farmers build collateral and a credit history. While Monicah

Riitho plans to refinance her solar pump to purchase more drip lines, such refinancing could be used to purchase just about anything—goods, insurance, or education. For that reason, Sherry says, “We’re not a solar company. We’re a lastmile retailer.” Ibrahim has a similar vision for SunCulture, but he says realizing it will require many more years unless public investment expands. Subsidies could accelerate the uptake of solar irrigation, following the model of rural electrification elsewhere. A 2020 study from Duke University found that countries that successfully electrified during the last half century did so by subsidizing 70 to 100 percent of the cost of rural grid connections (much as the United States did starting in the 1930s). Kenya’s government is upping its support for off-grid solar via a World Bank– financed program that targets 14 counties where 1.2 million households have no access to electricity. The program includes a $40 million investment in stand-alone solar systems and solar water pumps. Dalberg, the Geneva-based consultancy, endorses even greater support for solar irrigation. Without subsidies, Kenya’s solar-pumping market will experience gradual growth, a 2020 Dalberg policy paper projects. But a 9.6-billion-shilling ($90 million) government investment over five years to cover half the installed cost of solar water pumps would nearly triple the pace of installation, amounting to an additional 274,000 solar water pumps by 2025. Small farmers’ income would rise by a cumulative 622 billion shillings. When these subsidies are combined with other policy interventions, the proportion of Kenya’s arable land under irrigation would rise from 3 percent to as much as 22 percent, while food imports would fall by the end of the decade. Monicah Riitho’s farm is already part of that future. She sells her produce to the small shops and restaurants in town and to neighbors. As she chases off the cow that’s pushed through a rotten fence to help itself to some greens, it’s clear there’s more tasks than time. But Riitho says she has no complaints. Solar irrigation is about being her own boss. “I’m on my own, and I’m happy because I’m working daily for my children. I have no worries.” n

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Post-Doctoral Fellow Missouri University of Science and Technology Rolla, Missouri https://ece.mst.edu/ The Departments of Electrical and Computer Engineering (ECE) and Mechanical and Aerospace Engineering (MAE) at the Missouri University of Science and Technology (Missouri S&T) in Rolla, Missouri are seeking outstanding applicants for a Post-Doctoral Fellow level in the area of power systems, power electronics, or battery modeling, estimation, and control. Preference will be given to applicants who can contribute to any the research needs of the project, “Enabling Extreme Fast Charging with Energy Storage.” Specific needs include medium-voltage (12.47 kV) converter design, analysis, and testing; embedded systems development; power system operations; lithiumion battery modeling, estimation, and control; and system integration. Applicants must hold a Ph.D. in electrical engineering, mechanical engineering, or a closely related field. Successful candidates will be expected to have strong commitments to (a) contributing to departmental and college research efforts, (b) having a high degree of synergism and collaborating on research within the Missouri S&T power electronics and battery laboratories, (c) service in the applicant’s professional community and our institution, and (d) increasing the diversity of both the student body and faculty. Applicants should have demonstrated excellence in performing funded research and increasing diversity. Candidates from national labs or industry with a strong research record coupled with academic experience are encouraged to apply as well. Interested candidates should electronically submit their application consisting of: 1) a cover letter, 2) a current curriculum vitae, 3) a research statement, 4) a diversity statement, and 5) complete contact information for at least four references to Missouri S&T’s Human Resources Office at: http://hr.mst.edu/careers/academic/ using Reference Number #00073560. Acceptable electronic formats are PDF and MS Word. Applications will be reviewed as they are received and the review of applications will continue until the position is filled. For full consideration, applicants must apply by June 30, 2021. For more information prior to submitting an application, please contact the Search Committee Chair, Dr. Jonathan Kimball, at: kimballjw@mst.edu. Missouri S&T is an AA/EEO employer and does not discriminate on the basis of race, color, religion, national origin, sex, sexual orientation, gender identity, gender expression, age, disability or status as a protected veteran. Females, minorities, and persons with disabilities are encouraged to apply. Missouri S&T seeks to meet the needs of dual-career couples. The university participates in E-Verify. For more information on E-Verify, please contact DHS at: 1-888-464-4218.

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JUNE 2021 SPECTRUM.IEEE.ORG 67

HISTORY IN AN OBJECT

BY ALLISON MARSH

The furnace at the bottom of this crystal puller heated a sample of silicon, and then a hydraulic lift gently pulled upward, forming a single crystal of pure silicon.

In 1964, four years after earning a master’s degree in materials science from Stanford, Robert E. Lorenzini decided to go into business for himself. He bought motors, gear heads, and other spare parts from an auction and then built his own furnace for growing single crystals of silicon, to feed the burgeoning semiconductor industry. Inspired by the quick-change efficiencies of race-car pit crews, Lorenzini designed his new furnace so that workers could efficiently take it apart, harvest the crystal, and reload it to start growing the next crystal. Downtime, he knew, meant lost profits. Customers for his silicon wafers included IBM, RCA, and Texas Instruments. FOR MORE ON THE HISTORY OF SILICON- GROWING FURNACES, SEE spectrum.ieee. org/pastforward-jun2021

68 SPECTRUM.IEEE.ORG JUNE 2021

SCIENCE HISTORY INSTITUTE

Crystal History

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