18 Notebook
BY TIM SLAVIN
A TEG Talk
TOBIAS FAUCHER, DAVID GRIFFITHS, UNSPLASH
Technology, its history, and its frequently surprising applications are an endless source of fascination for me. Recently, I read an article about powering phones by body temperature. How does that work? I did some online digging. I learned electricity can be generated from a difference in temperature between two parts of the same piece of metal. It’s called TEG. Typing the phrase, define TEG, into a search engine yielded my first result: a teg is a two-year-old sheep. Hmm. Clearly, I needed to refine my search terms. "Define TEG electronics" turned up the correct result from Wikipedia. “A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat flux (temperature differences) directly into electrical energy through a phenomenon called the Seebeck Effect (a form of thermoelectric effect).” Solid state device? What’s that? Britannica.com tells me: “...electronic device in which electricity flows through solid semiconductor crystals (silicon, gallium arsenide, germanium) rather than through vacuum tubes.” So, a TEG creates electricity from the temperature difference between two parts of a metal piece treated with solid semiconductor crystals like silicon or gallium arsenide. One side measures body heat. The other side measures something cooler, like air temperature. Yet I found no mention of this capability in a Science Advances journal on TEG technology. The closest I came was: “A record-high open-circuit voltage among flexible TEGs is achieved, reaching 1 V/cm2 at a temperature difference of 95 K.” Do you know what that means? Neither did I. Although I guessed 1 V/cm2 means 1 volt of electricity per square cm of the material. However, I found the mention of 95K interesting. K could stand for kelvin. (kelvin is a scale for measuring temperature.) Could it be 95 degrees kelvin? When I searched define 95K, the search engine treated 95K as 95 thousand IOPS or input/output operations per second. I tried again, with define 95K temperature solid state device. That got me lots of articles about solid state drives, (another topic entirely) and the effects of too-high temperatures. Then, In an aha! moment, I noticed my search term used 95K, not the 95 K (with space in between). I wanted to learn more about the Kelvin temperature scale, so I searched: define Kelvin temperature. I learned that kelvin is the base unit of temperature in the International System of Units (SI). It uses the symbol K (uppercase) as in 95 K. Kelvin measures temperature from absolute zero, where molecules stop moving. There are no negative numbers in kelvin and there are no degrees. However, a kelvin unit does correspond to a degree in Celsius. Then, it made sense. Reading the Science Advances journal article about this amazing super-duper discovery of stretchy material that can sustain an electrical connection using body heat, it appears the researchers did use the kelvin scale in their research. Next question. Can I buy a TEG at a store along with the usual electronic cables and plugs? My research said: “not yet.” Powering a phone requires a steady source of electricity: a problem for us fidgety humans who can’t stay still enough to maintain a constant electrical connection...UNLESS you use a material that stretches and re-forms as people move. For now, a TEG can power a cell phone in theory, but not in reality. But keep an eye out for it in the next 5-10 years. Won’t that be fun to wear a bracelet that wirelessly charges your phone? I found out more than I bargained for in my research on body temperature and phone charging. I also learned that the words you use in your searches matter and can take you places you never expected. b
