wearable thermo-electric generators
Researchers demonstrated proof-of-concept wearable thermo-electric generators that can harvest energy from body heat to power bio-sensors for measuring heart rate and other factors.
The modular generators could inkjet printed on flexible substrates, including fabric, and manufactured using inexpensive roll-to-roll techniques.
“The attraction of thermoelectric generators is heat all around us,” said Akanksha Menon from Georgia Institute of Technology. We are working on how to produce electricity with heat from the body.
Getting enough thermal energy from a small contact area on the skin increases the challenge, and internal resistance in the device ultimately limits the power output.
p-type and n-type polymers
To overcome that, researchers designed a device with thousands of dots composed of alternating p-type and n-type polymers in a closely-packed layout. The pattern converts more heat due to large packing densities enabled by inkjet printers. By placing the polymer dots closer together, the interconnect length decreases, which in turn lowers the total resistance and results in a higher power output from the device.
The new circuit fractally symmetric design allows the modules to cut along boundaries between symmetric areas to provide the voltage and power needed for a specific application. That eliminates the need for power converters that add complexity and take power away from the system.
“This is valuable in the context of wearables, where you want as few components as possible,” said Menon. “We think this could be a really interesting way to expand the use of thermoelectric for wearable devices.”
So far, the devices printed on ordinary paper. But, the researchers begun exploring the use of fabrics. Both, paper and fabric are flexible, but the fabric easily integrated into clothing.
With the novel design, the researchers expect to get enough electricity to power small sensors, in the range of microwatts to milliwatts. That would be enough for simple heart rate sensors, but not more complex devices like fitness trackers or smartphones.
The generators might also useful to supplement batteries, allowing devices to operate for longer periods of time.
This class of polymer material is a low-cost and abundant thermo-electric material that would have an inherently low thermal conductivity. The organic electronics community has made tremendous advances in understanding electronic and optical properties of polymer-based materials.
More information: [Journal of Applied Physics]