Wearable patches that can be your personalised ACs, heaters

Summers are here. And what one probably looks out for is -- cooling! What can be better than a device that provides personalised cooling as well as heating anytime, anywhere?

The device, as published in the journal -- Science Advances -- is powered by a flexible, stretchable battery pack and is so suitable that it can be embedded in clothing. As an add-on feature, researchers say wearing it could help save energy on air conditioning and heating.

The soft, stretchy wearable patch cools or warms a user's skin to a comfortable temperature and keeps it there as the ambient temperature changes.

"This type of device can improve your personal thermal comfort -- whether you are commuting on a hot day or feeling too cold in your office," says Prof Renkun Chen, University of California.

"If wearing this device can make you feel comfortable within a wider temperature range, you won't need to turn down the thermostat as much in the summer or crank up the heat as much in the winter," adds Prof Chen.

The patch is made of thermoelectric alloys -- materials that use electricity to create a temperature difference and vice versa --sandwiched between stretchy elastomer sheets. The device physically cools or heats the skin to a temperature that the wearer chooses.

"You could place this on spots that tend to warm up or cool down faster than the rest of the body such as the back, neck, feet or arms, in order to stay comfortable when it gets too hot or cold," says the study's first author Sahngki Hong.

To check for the effectiveness of the device, researchers embedded a prototype of the patch into a mesh armband and tested it on a male subject. Tests were performed in a temperature-controlled environment.

In two minutes, the patch cooled the tester's skin to a set temperature of 89.6 degrees Fahrenheit. It kept the tester's skin at that temperature as the ambient temperature was varied between 71.6 and 96.8 degrees Fahrenheit.

The ultimate goal is to combine multiple patches together to create full smart clothing that can be worn for personalised cooling and heating.

The technology behind is that the patch uses an electric current to move heat from one elastomer sheet to the other. As the current flows across the bismuth telluride pillars, it drives heat along with it, causing one side of the patch to heat up and the other to cool down.

The patch is powered by a flexible battery pack. It is made of an array of coin cells all connected by spring-shaped copper wires and embedded in a stretchable material.

"To do the cooling, we have the current pump heat from the skin side to the layer facing outside," Chen explains. "To do heating, we just reverse the current so heat pumps in the other direction," Chen adds.