Dead cell phones are the problem of the 21st-century. Walk into any coffee shop or airport and every outlet in sight will be plugged with chargers. However, what if you never had to worry about charging your phone again, because your charger was your own body heat.
It's a future that could become a reality through the work of University of Colorado Boulder Aerospace Engineering Sciences assistant professor Sanghamitra Neogi, who has received a $700,000 grant from the Defense Advanced Research Projects Agency (DARPA) to investigate thermoelectric materials, which convert heat into electricity.
A New Take
"This is cutting-edge research," says Neogi, who is the single principle investigator for the grant. "Normally DARPA gives funding because they want a finished project, but this project is being done at a much earlier stage. It's high risk, but high gain."
Thermoelectric generators have been around a long time; NASA has used them for decades on space probes as a long-lived power source that can reliably convert heat into electricity without any moving parts.
The devices work using a principle discovered almost 200 years ago by German physicist Thomas Seebeck and French physicist Jean Peltier: when two different kinds of metal are joined in two places, forming a closed loop, and one junction has a higher temperature than the other, a small electric current will flow through the loop.
Unfortunately, they haven’t been widely adopted for public use because they are typically very expensive, inefficient, or worse, use materials that are toxic to humans.
“I’m looking at materials that are cheaper and non-toxic, silicon and germanium,” says Neogi.
Both are used extensively in the production of high-speed integrated circuits, solar panels, and other commercial and industrial applications, so they’re easy to find and inexpensive, but don't expect to see Neogi conducting experiments in a lab with test tubes and beakers. Her work is with a keyboard and mouse, using advanced computer models to evaluate what happens inside sandwiched layers of nanoscopic silicon and germanium.
“The current models always assume the layers are perfect, exactly like they’re supposed to be, but nothing is perfect. I’m trying to take the imperfections into account. How do those defects in the layers impact efficiency and what can we do about it?” Neogi says.
The research is extremely complex and requires a supercomputer to do the computations. CU Boulder has one, but it may not be enough to carry out all the work and Neogi recently acquired time on a National Science Foundation supercomputer in Texas as an additional resource.
What makes it so complicated?
Atomic, Subatomic, and Quantum Particles
"I’ll have 2,000,000 atoms, and I want to know what each one is doing after every time step," she says.
With the research at such a small size, it’s no surprise she's looking at equally tiny increments of time. Her time steps are in picoseconds, one trillionth of a second.
"I want to know the position, velocity, and force between these atoms for each time step, and I'm going to look at one million time steps," she says.
Tunneling down further, Neogi will also be investigating electrons and phonons, a quantum particle.
“If we can manipulate what happens between the layers, where the germanium and silicon interface with each other, it could change the way materials science works,” she says. "This is an area that's less understood. I'm fascinated by it.”
DARPA sees a variety of potential applications for the research. In addition to turning body heat into electricity, it could also lead to new solutions to the problem of excess heat generated by electronics – an issue easily recognized by anyone who has tried to actually use a laptop computer on their lap and ended up with burned thighs. If new thermoelectric devices could convert that heat into electricity, devices currently requiring large fans, vents, and heat sinks to reduce their high temperatures could be completely reimagined.
"We could fabricate novel devices with smaller size, weight, and power (SWaP) that will be broadly applicable," Neogi says. “That’s the long term goal.”
The three year grant runs through September 2019.