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Wearable Patch Designed for Personal Warmth, Cooling

Heating-cooling patch

Thermoelectric armband with, right to left, heating and cooling patch, control circuits, and battery pack. (Univ of California, San Diego)

17 May 2019. An electronic wearable device worn as a patch is designed to act like a personal heating or cooling system in uncomfortable ambient temperatures. An engineering team from University of California in San Diego describes the personalized thermoelectric device in today’s issue of the journal Science Advances.

Most people today have few options for keeping comfortable when encountering uncomfortably high or low temperatures, other than adding or discarding layers of clothing, or adjusting central heating or air conditioning systems. Making adjustments in central heat or cooling to accommodate a few people can be wasteful, and in electric vehicles, adjusting cabin temperatures can affect the vehicle’s range. According data cited by the authors, climate control systems in vehicles can drain as much as 40 percent of an electric vehicle’s battery power.

Researchers from the lab of engineering professor Renkun Chen at UC-San Diego are seeking devices that provide more comfort options to people in changing ambient temperatures. Chen’s thermal energy materials and physics, or Temp lab studies nanoscale structured materials and devices that readily transfer heat and energy, helping provide individuals more personal comfort.

Many devices on the market today aiming to provide personal heating or cooling use fluids, fans, or complex electronics requiring considerable power, which are bulky, impractical, or not convenient in many instances. Chen and colleagues, however, propose a different approach: a wearable device with materials designed to transfer heat toward or away from the individual.

The team’s thermoelectric device uses a material known as bismuth telluride, known to efficiently transfer heat. The device places a series of short bismuth telluride pillars on thin copper electrodes between flexible, soft rubbery sheets. The sheets are made from commercial Ecoflex plastic, combined with powdered aluminum nitride, another material with high thermal conductivity. The device is powered by thin coin-type batteries connected by copper-wire springs, enclosed with flexible control circuits in a stretchable material.

A thermoelectric unit is configured as a 5-centimeter square patch, using 0.2 watts of power. When the device is turned on, it transfers heat from one side of the patch to the other, sending heat along the bismuth telluride pillars. “To do cooling,” says Chen in a university statement, “we have the current pump heat from the skin side to the layer facing outside. To do heating, we just reverse the current so heat pumps in the other direction.”

The researchers tested the thermoelectric device under simulated conditions in the lab, then configured into a wearable system, encasing the device in a mesh fabric and worn as an armband by a volunteer. The device kept the volunteer’s arm at a constant temperature of 90 degrees F (about 32 C), while the air temperature varied from 72 to 97 degrees. Physical activity by the volunteer causing the body temperature to rise triggered more cooling by the device. The unit’s heat transfers were also captured with infrared camera images.

The team estimates 144 of the units could be assembled into a vest or stitched into garments, supplemented with a lightweight battery pack that can operate for 6 hours. Wearing these themoelectric devices, say the authors, could return enormous savings in cooling large areas for relatively few people. “If there are just a handful of occupants in that room,” notes Chen “you are essentially consuming thousands of watts per person for cooling. A device like the patch could drastically cut down on cooling bills.”

The university filed for a provisional patent on the technology with Chen and first author Sahngki Hong as inventors. The project is financed in part by a grant from a university start-up fund.

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