Wearable device changes temperature to hide wearer's body heat

A wearable device developed by the University of California at San Diego has a surface that quickly cools down or heats up to match ambient temperatures, camouflaging the wearer's body heat. The wireless device can be embedded into fabric.
A wearable device developed by the University of California at San Diego has a surface that quickly cools down or heats up to match ambient temperatures, camouflaging the wearer's body heat. The wireless device can be embedded into fabric, such as an armband. (University of California San Diego)

Researchers at the University of California San Diego have developed a wearable technology that can hide its wearer from heat-detecting sensors such as night vision goggles, even when the ambient temperature changes. The technology can quickly adapt to temperature changes, keeping the wearer comfortable.

The proof-of-concept device has a surface that quickly cools down or heats up to match ambient temperatures, camouflaging the wearer's body heat. The surface can go from 10 to 38ºC (50 to 100.4ºF) in less than a minute. Meanwhile, the inside remains at the same temperature as human skin, making it comfortable for the wearer. The wireless device can be embedded into fabric, such as an armband. A more advanced version could be worn as a jacket.

The research team, led by UC San Diego mechanical and aerospace engineering professor Renkun Chen, detailed their work in a recent issue of the journal Advanced Functional Materials.

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At the technology's core are materials that can create heating or cooling effects when the ambient temperature changes, and flexible electronics that can be embedded into clothing. The outside layer of the device is driven by a technology that Chen and colleagues detailed in a paper in Science Advances in May 2019. It is made of thermoelectric alloys—materials that use electricity to create a temperature difference—sandwiched between stretchy elastomer sheets. It is powered by a battery and controlled by a wireless circuit board.

The researchers built the device using a phase-changing material that's similar to wax but with more complex properties. The material melts at 30ºC (86º F), the same temperature as the surface temperature of human skin. If the temperature on the outside of the device is higher than that, the material will melt and stabilize, insulating the wearer; if colder, it will slowly solidify, still acting as an insulating layer.

The researchers hope to scale up the technology, creating a jacket with the technology built in. Under current conditions, the garment would weigh 2 kilograms (about 4.5 lb.), be about 5 mm thick and only function for one hour. The team will be looking to find lighter, thinner materials so the garment could weigh two or three times less.

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