We’ve gotten to the point where technology is small enough that it can be incorporated into wearable devices, such as bio-sensors and wireless data transmitters. Unfortunately, they still require power, and rechargeable batteries and other power sources tend to be bulky, on the heavy side, and usually require a recharge before the day is over. To mitigate those issues, researchers from the University of Massachusetts have designed an all-fabric thermal generator that taps body heat to power those wearable devices.
Enter the thermoelectric effect- in theory; the body heat can produce power by tapping into the difference between body temperature and the surrounding ambient air via thermocouple- thus creating a voltage when there is a different temperature on each side. Researchers have shown that small amounts of power can be produced throughout a day (eight hours or so), but the materials to harvest it are inefficient, or worse, toxic.
According to materials chemist Trisha Andrew, she and her researchers have solved those issues- “What we have developed is a way to inexpensively vapor-print biocompatible, flexible and lightweight polymer films made of everyday, abundant materials onto cotton fabrics that have high enough thermoelectric properties to yield fairly high thermal voltage, enough to power a small device.”
More specifically, the team capitalized on wool and cotton’s low heat transport properties and created a thermopile made from a conductive p-doped poly (PEDOT-C), vapor-printed it onto the wool/cotton fabric, and weaved it into a wearable band capable of generating 20-millivolts when worn on the hand. The researchers tested the fabrics durability by laundering and rubbing the fabric repeatedly, and found it didn’t lose any conductivity. In fact, they did find that a looser weave of PEDOT-C fabric produced a higher conductivity, over a tightly knit design.
As you might image, early applications include powering wearable medical devices, such as heart rate or glucose monitors, however, the wearable generator will not directly power them as its too variable as a current source. Instead, it’s better suited as a trickle-charger for a battery that powers the devices.