Using flexible conducting polymers and novel circuitry patterns printed on paper, researchers in Dr. Yee’s laboratory have demonstrated proof-of-concept wearable thermoelectric generators that can harvest energy from body heat to power simple biosensors for measuring heart rate, respiration, or other factors.

Dr. Shannon Yee
Dr. Shannon Yee

Tech Briefs: What are the goals of your project?

Dr. Shannon Yee: My group has recently been looking at polymer-based thermoelectric (TE) materials to serve as the semiconductor elements for wearable TEs. Since one of the big problems is the interconnects between the different TE elements, we decided to tackle that first, and we found new interconnect patterns that could enable us to build many different TE devices.

We’ve been looking at the well-studied Hilbert curve mathematical framework, with which we can create fractal-like geometries where sub-modules are repeated geometrically throughout the main module. Because the sub-modules are independent of each other, any localized fluctuations in temperature are confined to that one sub-module; they won’t propagate across the entire device. Also, since series and parallel modules can be printed over large fabric areas, you could literally come with a pair of scissors and cut the module to create the current and voltage you need for your application. We’re also looking at classic knitting patterns to see how, using TE yarn, we can knit a module directly into a shirt.

Tech Briefs: What practical uses do you envision?

Dr. Yee: Imagine we have these modules integrated into TE textiles, and you have the textiles against your body. You could generate electrical power from your body heat. In reality, however, that is a very small amount of electricity. Without really large areas of clothing, it wouldn’t be enough to power your cellphone. There is only enough power for small sensors; for example, a heart monitor. Potentially, one could embed a bio-monitor in the fabric and connect the TE with a couple of wires.

Tech Briefs: The distance from the shirt to the body varies as you move.

Dr. Yee: That’s where the fractal geometry comes in. As you move, different parts of the module are going to be hotter than others. Self-contained sub-modules are a means of dealing with that. Typically, we can keep the voltage constant by using a voltage regulator — these are very common, very small components. There are also other electronic devices you can add such as bootstrap converters that allow you to step up the voltage or current.

Tech Briefs: What about other applications?

Dr. Yee: What I think is more exciting than generating electricity is the ability to run these in reverse and achieve cooling. You could hook up a battery to your shirt and it can produce a cool sensation. I see that as a better option — a shirt that acts as your personal thermostat. If we can enable personal cooling, we may be able to widen the envelope that a room thermostat has to meet. We don’t even have to change the core temperature of your body. Your metabolism does a fantastic job of that. We just have to make people feel comfortable. If we can do that with less energy, we have a huge savings in energy usage, which will help reduce global warming, mostly from reduction in refrigeration, refrigerant leaks, and the equivalent CO2 emissions from generating electricity to power air conditioning.


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This article first appeared in the February, 2018 issue of Tech Briefs Magazine.

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