Wristband that turns body heat into electricity can power an LED

A wearable wristband containing a thermoelectric generator (TEG) can convert body heat into enough electricity to power an LED. In future, the technology might be able to power smartwatches and end the necessity for traditional charging hardware.

“Energy supply is always a major issue, and this could help alleviate the energy crisis,” says Qian Zhang of the Harbin Institute of Technology, China, one of the co-authors of the paper, who has worked on TEGs for more than 15 years.

TEGs are used in a variety of applications, but are often rigid – something Zhang and her colleagues sought to resolve. They layered a magnesium and bismuth material – the TEG materials – between polyurethane and a flexible electrode, enabling the wristband to wrap around a human arm.

The result is a wristband 115 millimetres long and slightly under 30mm wide. It uses the difference between your temperature of human skin and ambient room temperature to create power.

At its peak, these devices has the capacity to generate 20.6 microwatts per square centimetre – more than enough to light an LED from the wristband. “The environmental temperature affects performance a whole lot,” says Zhang. Winter is way better, she adds, because ambient temperatures are lower and the difference with body’s temperature is greater.

Read more: Smart glove computes what you’re holding from its weight and shape

Tests show the device could be wrapped around an arm and unwrapped again more than 10,000 times without any significant change in performance. Wearers don’t experience any undesireable effects when wearing the wristband.

“I love the thought of harvesting power from the human body, instead of needing to use batteries,” says Rolf Hut, a maker considering wearables who works at Delft University of Technology in holland. “Given just how many LEDs I love to use in my projects, I really do wonder just how much you can ‘withdraw’ from a human before it becomes uncomfortable.”

The researchers desire to improve performance by increasing how big is the TEG on the wristband and integrating a voltage converter to permit it to power larger electronics – though they explain that doing so will demand increasing the size of the complete device.

Journal reference: Cell Reports Physical Science , DOI: 10.1016/j.xcrp.2021.100412

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