Harvesting body heat to power biosensors
ATLANTA: Using flexible conducting polymers and novel circuitry patterns printed on paper, researchers have demonstrated wearable thermoelectric generators that can harvest energy from body heat to power simple biosensors.
These biosensors can be used to measure heart rate, respiration or other factors.
Because of their symmetrical fractal wiring patterns, the devices can be cut to the size needed to provide the voltage and power requirements for specific applications. The modular generators could be inkjet printed on flexible substrates, including fabric, and manufactured using inexpensive roll-to-roll techniques.
“The attraction of thermoelectric generators is that there is heat all around us,” said Akanksha Menon, a doctoral student in the Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. “If we can harness a little bit of that heat and turn it into electricity inexpensively, there is great value. We are working on how to produce electricity with heat from the body.”
The research, supported by PepsiCo, Inc. and the Air Force Office of Scientific Research, was reported online in the Journal of Applied Physics.
Thermoelectric generators, which convert thermal energy directly into electricity, have been available for decades, but
The attraction of thermoelectric generators is that there is heat all around us. If we can harness a little bit of that heat and turn it into electricity inexpensively, there is great value. Akanksha Menon, doctoral student
standard designs use inflexible inorganic materials that are too toxic for use in wearable devices. Power output depends on the temperature differential that can be created between two sides of the generators, which makes depending on body heat challenging. 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.
To overcome that, Menon and collaborators in the laboratory of Assistant Professor Shannon Yee designed a device with thousands of dots composed of alternating p-type and n-type polymers in a closely-packed layout. Their pattern converts more heat per unit area 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.
“Instead of connecting the polymer dots with a traditional serpentine wiring pattern, we are using wiring patterns based on space filling curves, such as the Hilbert pattern – a continuous space-filling curve,” said Kiarash Gordiz, a co-author who worked on the project while he was a doctoral student at Georgia Tech. “The advantage here is that Hilbert patterns allow for surface conformation and self-localisation, which provides a more uniform temperature across the device.” — Newswise