A research team at the University of Massachusetts Amherst has developed a fabric which harvests body heat to produce levels of electricity high enough to power small wearable devices. Published in Advanced Materials Technologies, the fabric concept takes advantage of the ‘thermoelectric’ effect, whereby a material at differing temperatures produces electric voltages which, in this case, can be harnessed. Materials chemist Trisha Andrew and her Ph.D. student Linden Allison vapour-printed biocompatible, flexible and lightweight polymer films onto cotton fabrics to yield thermal voltages which can power an accompanying smart device.

Cotton was used as the fabric substrate due to the naturally low heat transport properties of wool which enabled the team to create a thermoelectric garment that can maintain a temperature gradient across an electronic device known as a thermopile, which converts heat into electrical energy over long periods of time. “Essentially, we capitalized on the basic insulating property of fabrics to solve a long-standing problem in the device community,” Andrew said. “We believe this work will be interesting to device engineers who seek to explore new energy sources for wearable electronics and designers interested in creating smart garments.”

To create a thermopile capable of transferring heat into electricity, the research team vapour-printed a p-doped poly (PEDOT-Cl) coating onto the textile substrate. This smart fabric was applied as a wrist band after it was established that the wrist, palms and upper arms radiated the most heat and therefore would provide the most energy to convert. The durability of the PEDOT-CI coating was then assessed through various laundering methods. According to Andrew’s team, the coating “did not crack, delaminate or mechanically wash away upon being laundered or abraded, confirming the mechanical ruggedness of the vapour-printed PEDOT-CI.”

Concluding, Andrew and Allison note, “We show that the reactive vapour coating process creates mechanically-rugged fabric thermopiles. Further, we describe best practices for naturally integrating thermopiles into garments, which allow for significant temperature gradients to be maintained across the thermopile despite continuous wear.” This work was supported by the National Science Foundation and by the David and Lucille Packard Foundation.