1382gilchrist[1]

NanoFET

Scalable Flat-Panel Nanoparticle Propulsion Technology for Space Exploration in the 21st Century Brian Gilchrist University of Michigan Ann Arbor, Michigan 2006 NIAC Annual Meeting Tucson, AZ October 18, 2006

NanoFET

Project Participants

• Extraction & Acceleration of Nanoparticles; Systems & Mission Design – Faculty Brian Gilchrist, Electrical Engineering & Space Systems Alec Gallimore, Aerospace Engineering & Applied Physics Michael Keidar, Aerospace Engineering – Students Thomas Liu, Aerospace Engineering Louis Musinski, Electrical Engineering Prashant Patel, Aerospace Engineering

• Storage & Transport of Nanoparticles – Faculty Mark Burns, Chemical & Biomedical Engineering Michael Solomon, Chemical Engineering & Macromolecular Science and Engineering Joanna Mirecki-Millunchick, Materials Science and Engineering – Students Deshpremy Mukhija, Chemical Engineering Kyung Sung, Chemical Engineering 2

NanoFET

Presentation Outline

• Electric propulsion systems • What is nanoFET? • Potential nanoFET advantages • Work-to-date – Particle charging, transport, extraction, and acceleration – Liquid surface instability

Acknowledgments • NASA Institute for Advanced Concepts • Matthew Forsyth & Bailo Ngom, University of Michigan • Robb Gillespie, University of Michigan

• Phase II work plan – Particle extraction and acceleration – Particle storage and transport – Systems and mission analysis 3

NanoFET

Electric Propulsion Systems

• The acceleration of charged gases or particles for propulsion by electrical heating and/or by electric and magnetic body forces • Advantages – High specific impulse possible – Low propellant cost compared to chemical rockets

1 q I sp = 2Vo

g 0 m p

T 2 mp =

P Vo q

1 2

1 2

• Disadvantages – Limited specific impulse range – Low efficiency when operating at low specific impulses – Charge exchange collisions (CEX) and hollow cathodes limit thruster lifetime

Source: PEPL

4

NanoFET

What is nanoFET?

• nanoparticle Field Extraction Thruster • Scalable arrays of micronsized emitters

Use MEMS/NEMS structures for propellant feed & acceleration

– thousands to millions of emitters possible – integrated MEMS/NEMS units

• In situ propellant manufacture?

45-nm dia. x 500-nm length

Source: N. Behan

– electrostatic charging and acceleration – great flexibility in controlling charge-to-mass ratio to tune performance

Use nanoparticles of various geometries and materials as propellant Source: Philips Electronics

• Nanoparticle propellant

100-nm dia.

5

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Dielectric Liquid Configuration

• Low vapor pressure, dielectric liquid transports nanoparticles of specific geometry to extraction zones • Biased MEMS gate structures produce charging & accelerating electric fields • Charge neutralization can be achieved by other emitters operating at opposite polarity

Nanoparticle Accelerating Gate Dielectric Spacer

Dielectric Liquid Reservoir

Conducting & no liquid options possible

Charging Electrode 6

VN NanoFET

ur E

~1 Îźm

Conductor Conducting Grid

Dielectric

Conductor Conducting Grid

V2

Dielectric

ur E

V1

Charged Nanoparticles

Conductor Conducting Grid

Dielectric

Conductor Conducting Grid

ur E V0 Uncharged Nanoparticles

Liquid Reservoir

Liquid Flow

Liquid Flow

Stages of emitter operation 1. Transport to extraction zone via recirculating flow in microfluidic channel 2. Charging by contact with charging electrode 3. Lift-off from charging electrode & transit through liquid 4. Extraction from liquid surface 5. Acceleration through biased gate structures & ejection from emitter

Conducting Plate

7

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nanoFET Advantages

• Decouples propulsion system design from spacecraft design – Geometrically scalable with power level – Plug-and-play approach

• Affords broader set of missions and mission phases with single engine type – Variable specific impulse over large range – High thrust-to-power with high efficiencies

• Both mission enhancing and mission enabling – Eliminates lifetime-limiting factors of existing EP systems – Lowers thruster specific mass

Flat-panel nanoFET architecture can be scaled for microsats to flagship missions Acceleration System

Gimbal Structure Prime Power PPU

10 kW 1 kW 10 W <1 W Particle Storage (Variable Depth)

Nanoparticle Emitters

Leveraging single engine type across broad range of missions lowers time for propulsion system development, testing, and qualification and thus cost

8

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Compact & Scalable Design 3 cm

Individual nanoFET Emitters 2 Îźm

Emitter Array

Emission Sites

25 Îźm

Plug-and-play technology provides design flexibility, simplifies system integration, and lowers thruster specific mass 9

Large Isp Range Diameter [nm] 5 1 1 1

High efficiency

Specific Impulse (s)

With single engine type: â&#x20AC;˘ High Isp cruise to reduce propellant cost â&#x20AC;˘ Low Isp mode for greater thrust capability

Thrust-to-Power (mN/kW)

Internal Efficiency

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Height [nm] 100 100 3500 400

Isp range [s] 100-500 500-2000 2000-10000 800-4000

High thrust-topower

Specific Impulse (s)

Wertz, 1999 10

• Variable-Isp engines – Consume less propellant than constant-Isp engines – Can optimize thrust profile in real time to accommodate missions with unplanned or unknown maneuvers – Enables propellant-time trade to be conducted

Normalized propellant cost

Greater Mission Flexibility Using Variable Isp

NanoFET

Variable Isp

Min Variable Isp

• Benefits

Max Variable Isp

Isp range (s)

– Wider margin to accommodate off-nominal mission scenarios – Improved capability for dynamic retasking and flight time adjustment

Constant Isp

Optimal constant Isp

Transfer time (min)

11

NanoFET

Summary of Work-to-Date

• Assessed significance of nanoFET as a propulsion system for space missions • Addressed fundamental physics questions regarding nanoFET’s feasibility – Demonstrated regime for particle extraction prior to liquid surface instability using scaled-up proof-ofconcept tests – Modeled nanoFET’s projected performance with decreased particle sizes

ln (4 A ) q (tex ) A2 exp

ln mp l ln (4 A ) l A

12

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Proof-of-Concept Experiments

• Understand how nanoFET works at scaled-up dimensions • Validate models of particle behavior and liquid surface instability • Experiments – Particle charging, transport, & lift-off – Particle extraction through liquid surface – Particle acceleration & ejection using multi-grid structure – Threshold for liquid surface instability

v E

Accelerating Grid

VN

Accelerating Grid

V2

Dielectric Accelerating Grid

V1

Dielectric

Charged Nanoparticle

v E

V0

Extraction Grid

Liquid Reservoir

Charging Grid

13

Particle Charging, Transport, and Lift-Off

NanoFET

• Demonstrate charging and transport of conducting particles in dielectric liquid with high electric fields • Particles: aluminum – Cylinders (300-μm dia. by 2.5-mm length – Spheres (800-μm dia.)

• Liquid: 100-cSt silicone oil

Experimental Setup: Liquid filled electrode gap with conducting particles Electrode

V

E-Fields

Gap Filled w/ Silicone Oil Conducting Particles

Electrode

Spherical Particles

Cylindrical Particles

5 mm 14

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Particle Extraction & Acceleration Through Grid Particle charged on charging electrode Experimental Setup:

V2

E-Fields

Grid 2

Grid 2 Grid 1

Grid 1 E-Fields

V1

Particle

Liquid Surface

Conducting Particle

Charging Electrode

Charging Electrode

2 mm 15

Particle Extraction & Acceleration Through Grid

NanoFET

Particle extracted through liquid surface Charged particle is transported to and extracted through liquid surface by intense electric fields

(

)

dv dt = q(t)El + Fbuoyant W D Fsurface

mp + Kml

t q (t ) = q0 exp

l

, =

l

Grid 2

Grid 1

Particle

Charging Electrode

Liquid Surface

2 mm

Particle appears to shift to left due to diffraction through test apparatus 16

NanoFET

Particle Extraction & Acceleration Through Grid Particle ejected from dual grid structure Grid 2

Particle is accelerated through the dual gird structure and finally ejected to provide thrust

Grid 1

Particle Liquid Surface

Charging Electrode

2 mm 17

NanoFET

1.

2.

Surface Instability & Taylor Cone Formation Electric field acts to pull free charge to liquid surface Cones form as a result of balancing surface tension and electric forces Electric field breaks cone off and accelerates charged liquid droplets

3.

1. Charges are pulled to surface

2. E-field pulls liquid up, surface tension pulls down

Electrode

3. Charged droplets are pulled off surface

Electrode

Electrode

E-Fields

V

V Electrode

V Electrode

Electrode

18

Surface Instability Threshold

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â&#x20AC;˘ Charged liquid droplet emission degrades nanoFETâ&#x20AC;&#x2122;s performance by decreasing efficiency and controllability of charge-to-mass ratio â&#x20AC;˘ Does regime exist where particles are extracted without charged droplets?...

1 4

E0,min

â&#x20AC;˘ â&#x20AC;˘

â&#x20AC;˘

Spheres: â&#x20AC;&#x201C; 800 m dia.

Cylinders â&#x20AC;&#x201C; 300 m dia. by 1.5 mm length Gap = 12.7 mm

2

4 g 0 l 0 = 1 + 2

0

l

1 2

Experimentally demonstrated regime where particles are extracted prior to liquid surface instabilities!

19

Phase II Work Plan

NanoFET

•

•

•

Increase physical understanding of particle charging, extraction, and acceleration as particle size is reduced from sub-millimeter scale down to micro- and nanometer scales Develop quantitative understanding of micro- and nanoparticle storage and transport to extraction zone Provide assessment of mission scenarios whose capabilities would be enabled or expanded by nanoFET

20

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Phase II: Nanoparticle Extraction & Acceleration

• How will particle extraction through liquid surface change as particle dimension decreases?

– How does liquid wetting on the particle change?

– What about liquid surface instability threshold under flow and zero-g conditions?

• How do particle charging properties change as size is reduced?

– Does particle conductivity change when particle size is reduced to only several hundred atoms or less?

– How will reducing contact area between particle and charging electrode affect charging process?

• Can common liquid and particles useful for extraction, transport, and storage be identified?

21

NanoFET

• •

• •

Planned Experimental Work Verify accuracy and reliability of charge acquired by particles Extend particle charging, transport, and extraction experiments down to micro- and ultimately down to nano-scale Verify particle extraction behavior under vacuum is the same as in atmosphere Determine feasibility of particle charging, transport, and extraction from slightly conducting liquid Test prototype extractor & integrated feed system 22

Theoretical Work Refinements

NanoFET

• Electrohydrodynamic behavior and instability thresholds in zero-g • Particle effects at nanoscales • Particle extraction through liquid surface

Fluid level at specific test 4

– Particle wetting – Field enhancement effects

• Space charge current limitations due to viscous liquid 9 q Vl 2 j = l 8 dl 3

D v

1. Particle extraction (experiment) 2. Particle extraction (theory) 3. Feasible design space (theory) 4. Taylor cone formation (experiment and theory) 23

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MEMS Gate Prototype Isometric

Top

1 cm Single-layer gate integrated with CNT substrate for field emission

Array of emission channels (2-Îźm diameter, 5-Îźm hole-to-hole spacing) 24

NanoFET

Phase II: Nanoparticle Storage & Transport

â&#x20AC;˘ Under what conditions can nanoparticles be stored at high density and yet be transported as individual particles? â&#x20AC;˘ What are practical and future limits to nanoparticle fluxes when delivered in circulating channel networks? â&#x20AC;˘ How do nanoparticle properties, including size, shape, and material properties, affect transport and storage properties?

25

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Microfluidic Feed System Profs. M. Solomon, M. Burns, & J. Mirecki-Millunchick

High density packing for low parasitic liquid mass

University of Michigan

Controlled displacement of individual particles

On-demand release of individual particles 26

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Particle Control: Metering in Fluidic Channels

side view

valve

Particle properties: NIST polystyrene: 21±0.4 μm 10 μL of 0.01 wt% 2-valve PDMS device

fluid channel

Vanapalli, Sung, Mukhija 27

NanoFET

Particle Control: Transport in Fluidic Channels

1)

90 m

2)

90 m

3)

Sung, Vanapalli, Mukhija

90 m

Multi-channel pressure actuation used to move particles along complex trajectories (~ 20 Îźm particles) 28

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Reservoir for Particle Storage & Transport

• Transport 20 μm particles from storage area reservoir to thruster • Seek high reservoir loadings to minimize parasitic mass

Sung, Mukhija, Vanapalli 29

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Shape Effects on Particle Transport

Poly(methyl methacrylate) (PMMA) rods (length ~ 10 Îźm) with narrow polydispersity

PMMA rod (aspect ratio ~ 5) transport in fluidic channels Mukhija, Vanapalli, Sung 30

NanoFET

Phase II: nanoFET Systems & Mission Analysis – Particle & liquid properties – Geometric configurations – Current density limits

• System efficiency – Liquid drag & charge exchange – Particle impingement on gate – Beam defocusing

• Case studies of missions using nanoFET – Coupling between propulsion and power systems – Remote sensing near gravitational bodies – Variable-Isp to accommodate off-nominal conditions

Normalized Extraction Electric Field

• Performance optimization 3.0

r = 15 μm

2.5

At constant liquid thickness

r = 75 μm

2.0 r = 150 μm

1.5 1.0 0.5 0.0 1

10

100

Aspect Ratio

Low extraction electric field achieved by: high aspect ratio & reduced liquid thickness 31

NanoFET

Other nanoFET Applications Source: National Cancer Institute

Biomedical • targeted drug delivery to cells • cell tagging for diagnostics & tracking • cutting/dissection tool • subdermal implantation

nanoFET

More than just propulsion!

Cancer Cell

Material Substrate

Materials processing • implanting charged particles (doping & printing) • etching

32

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Conclusions

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Backup Slides

34

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1.

2.

3.

4.

Particle Charging, Transport, & Lift-Off Particle in contact with bottom electrode in presence of electric field becomes charged Resulting Coulomb force on charged particle transports particle to top electrode At top electrode, particle becomes charged with opposite polarity but same magnitude Coulomb force pulls particle back down to bottom electrode and process repeats

1. Charged on bottom electrode (-)

2. Transported to top electrode

Electrode

V Electrode

l 2 l El = 2l ln 1 r 4. Transported to bottom electrode

Electrode

V Electrode

qcyl,vert

3. Charged on top electrode (+)

Electrode

V

qsph

2 3 2 = r l El 3

Electrode

V Electrode

Electrode

35

NanoFET

Particle Extraction Through Liquid Surface Experimental Setup: Partially liquid filled electrode gap with conducting particles

• Demonstrate – Use intense electric field to overcome surface tension forces and extract particles from liquid

Electrode E-Fields in Air gap

• Particles: aluminum – Spheres (800 and 1600 μm dia.)

– Cylinders (300 μm dia. by 1.0 - 3.0 mm length)

• Liquid: 100 cSt silicone oil

V

Air gap

d Silicone Oil

E-Fields in liquid gap

Conducting Particles

dl

Electrode

36

NanoFET

Particle Extraction Through Liquid Surface

1

Liquid Surface

Cylindrical particles in oscillation – – – – –

Steel Electrodes

Particles 2

•

Liquid Surface

Steel Electrodes

diameter = 300 m length = 1.5 mm gap = 12.7 mm liquid height = 5 mm V ~ 14 kV

3

Particles

Liquid Surface

Steel Bottom Electrodes

Electrode

Particles

Particles 37

NanoFET

Particle Extraction Through Liquid Surface

1

Liquid Surface

Steel Electrodes

•

Required electric fields for particle extraction depends on – –

Particle size/shape Electric field strength

Particles 2

Liquid Surface

Steel Electrodes

3

Particles

Liquid Surface

Steel Bottom Electrodes

Electrode

Particles

Particles 38