One of the design goals for those developing wearable technology is to create comfortable clothing that also include a power source for various small devices people are increasingly using to monitor health and fitness.
A team at the University of Massachusetts Amherst (UMass) said they’ve achieved this aim with a new fabric that can harvest body heat to power small wearable microelectronics.
|Materials chemists led by Trisha Andrew at the University of Massachusetts Amherst have developed a fabric that can harvest body heat to power small wearable microelectronics such as activity trackers. (Image source: UMass Amherst/Andrew Lab)|
Looking to User Friendly
While many wearable biosensors, data transmitters, and similar wearable technology for personalized health monitoring have now been “creatively miniaturized,” they still require a lot of energy, said materials chemist Trisha Andrew at the University of Massachusetts Amherst in a UMass news release. This typically would mean a battery or wires to an external power source, which are bulky and uncomfortable, however, and don’t lend themselves to user-friendly designs, she said.
To solve this issue, Andrew and graduate student Linden Allison took advantage of the naturally low heat-transport properties of wool and cotton to create thermoelectric garments that can maintain a temperature gradient across an electronic device known as a thermopile. This device converts heat to electrical energy even over long periods of continuous wear, she said.
“Essentially, we capitalized on the basic insulating property of fabrics to solve a long-standing problem in the device community,” Andrew said. The work can help inform device engineers as they seek to design new energy sources for wearable electronics, as well as designers interested in creating smart garments, she said.
Indeed, while researchers have developed fabrics that can harvest electricity for wearable devices, what’s yet unproven is their electrical, mechanical, and thermal stability over time, Andrew said.
Power From Body Heat
The work of the UMass team is based on the theory that body heat can produce power by taking advantage of the difference between body temperature and ambient cooler air, which results in a “thermoelectric” effect. In this way, materials with high electrical conductivity and low thermal conductivity can move electrical charge from a warm region toward a cooler one.
Research already has demonstrated that some materials can harvest small amounts of power from a human body over an eight-hour workday, Andrew acknowledged. However, the materials used in these examples thus far have either been very expensive, toxic, or inefficient.
“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,” she explained.
Specifically, researchers created their all-fabric thermopile by vapor-printing a conducing polymer, PEDOT-Cl, onto two forms of commercially cotton fabric—one tight-weave and one medium-weave. They then integrated this thermopile into a specially designed, wearable band that generates thermo-voltages greater than 20 millivolts when worn on a person’s hand and can be used as a power source.
The team described their work in a paper in the journal Advanced Materials Technologies. Researchers tested the durability of the polymer-coated fabrics by laundering them in warm water and assessing performance by scanning electron micrograph. Tests showed that the coating “did not crack, delaminate, or mechanically wash away upon being laundered or abraded, confirming the mechanical ruggedness of the vapor-printed PEDOT-Cl,” researchers wrote in their paper.
The team also detailed how they measured the surface electrical conductivity of the coatings using a custom-built probe, finding that the looser-weave cotton demonstrated higher conductivity than the tighter-weave material. The conductivities of both fabrics “remained largely unchanged after rubbing and laundering,” researchers wrote.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.