According to Trisha Andrew, a materials chemist at the University of Massachusetts, many wearable biosensors, data transmitters and similar personalized health monitoring devices are rapidly evolving and are now becoming more and more miniaturized. But they require a lot of energy, and the power supply is usually cumbersome. Now, she and her PhD student, Linden Allison, say they have developed a fabric that collects heat from the body and powers small wearable microelectronic devices such as activity trackers.
But they point out that the special materials currently needed are either very expensive, either toxic or inefficient. Andrew said: “We have developed a low-cost steam printing method that prints biocompatible, flexible and lightweight polymer films on cotton fabrics that have high enough thermoelectric properties to produce equivalent The high thermal voltage is enough to drive a small device.”
In this work, the researchers used the natural low heat transfer characteristics of wool and cotton to create a thermoelectric garment that maintains the temperature difference. The temperature gradient passes through an electronic device called a thermopile that converts heat into electrical energy even during prolonged continuous wear.
She and Allison conclude: “In essence, we use the basic insulation properties of fabrics to solve a long-standing problem in the equipment world.” “We believe in equipment engineers who are looking to develop new energy sources for wearable electronics and are interested in developing intelligence. For the designer of the clothing, this work will be very interesting.”
Specifically, the fabric they created was a conductive polymer called persistent p-doped poly(3,4-ethyldioxythiophene) (PEDOT-Cl), which was printed by steam in a compact structure and A medium-tissue form of commercial cotton fabric. They then integrated the thermopile into a specially designed wearable band that produced a thermal voltage greater than 20 millivolts when worn on the hand.
The researchers tested the durability of the PEDOT-CI coating by rubbing or washing the coated fabric. The coating properties were evaluated by scanning electron micrographs. The results showed that the coating “was not cracked or delaminated after washing or scratching, thus confirming the mechanical robustness of the vapour printed PEDOT-CI”.
They measured the surface conductivity of the coating with a custom probe and found that the looser tissue cotton exhibited higher conductivity than the compact tissue material. They added that the conductivity of the two fabrics “has remained essentially unchanged after rubbing and cleaning.”
The study found that they determined that the volunteers had the most heat from the wrists, palms, and upper arms, so Andrew and Allison made flexible thermo-mechanical knit bands that could be worn in these areas. The exposed bands in the air were insulated… Depending on the thickness of the yarn, only the uncoated side of the thermometer can contact the skin to reduce the risk of an allergic reaction to PEDOT-CI.
The researchers noted that sweat significantly increased the thermal voltage output of the extension arms, which is not surprising, as they observed that wet cotton is a better thermal conductor than dry fabrics. They can also arbitrarily turn off heat transfer by inserting a reflective plastic layer between the wearer’s skin and the strap.
In general, they say, “we show that the reactive steam coating process creates a mechanically strong fabric temperature difference” that has a “significantly high thermoelectric power factor” in low-temperature differences compared to conventionally produced equipment. “In addition, we have found that the best practice is to naturally integrate the thermometer into the garment, which allows for a significant temperature gradient across the thermometer despite continued wear.”