A new wearable patch could provide personalized cooling and heating at home, work, or on the go. The soft, stretchy patch cools or warms a user’s skin to a comfortable temperature and keeps it there as the ambient temperature changes. It is powered by a flexible, stretchable battery pack and can be embedded in clothing. Wearing it could help save energy on air conditioning and heating.
The patch is flexible, lightweight, and can be easily integrated into clothing. It 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. It could be placed on areas that tend to warm up or cool down faster than the rest of the body, such as the back, neck, feet, or arms.
It consists of small pillars of thermoelectric materials (made of bismuth telluride alloys) that are soldered to thin copper electrode strips and sandwiched between two elastomer sheets that are specially engineered to conduct heat while being soft and stretchy. The sheets were created by mixing a rubber material called Ecoflex with aluminum nitride powder, a material with high thermal conductivity.
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 made of an array of coin cells all connected by spring-shaped copper wires and embedded in a stretchable material. The system also includes a stretchable circuit board. One patch measures 5 × 5 centimeters in size and uses up to 0.2 Watts of power. It would take 144 patches to create a cooling vest. This would use about 26 Watts to keep an individual cool on an average hot day (during extreme heat, estimated power use would climb up to 80 Watts, which is about how much a laptop uses). By comparison, a conventional air conditioning system uses tens of kilowatts to cool down an entire office.
A prototype of the patch was embedded into a mesh armband and tested 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 °F. It kept the tester’s skin at that temperature as the ambient temperature varied between 71.6 and 96.8 °F.
The ultimate goal is to combine multiple patches together to create smart clothing that can be worn for personalized cooling and heating. Soft electronic devices were designed that can stretch, bend, and twist without compromising their electronic functions.