A sweater embedded with a coil filled with liquid metal can wirelessly charge wearable or portable electronic devices, including medical sensors, movement trackers and smartphones.
Wireless charging technology is growing in popularity, and it has the potential to be听built into clothing to charge small听electronics devices while they are being worn. However, this potential has yet to be realised because a wireless charger produces electromagnetic radiation that may damage human tissue after prolonged听exposure over such a close range.
at the University of Tokyo in Japan and his colleagues have now designed a wireless charging system called MeanderCoil++ that doesn鈥檛 produce high levels of electromagnetic radiation.
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They injected a conductive liquid metal alloy called Galinstan into a silicone tube. They then bent this tube and stitched it into a sweater. In more detail, the tube passes around the chest in a horizontal loop before doubling back on itself in an S-shape bend beneath the armpits and passing around the chest in another horizontal loop, and so on, snaking down the torso.
They also inserted capacitors 鈥� devices that store energy 鈥� at certain points along the tube. This effectively broke the system into a series of shorter coils, which also reduces the strength of the radiation it generates.
The sweater can be hooked up to a small power supply tucked into one of its pockets. Then, as current flows through the sweater, it generates low levels of electromagnetic radiation. Electronic devices with inbuilt 鈥渞eceiver coils鈥� can transform the radiation back into electricity to charge their batteries. The MeanderCoil++ can provide up to 10 watts of charging power, about the same rate as a mobile phone charger.
Takahashi and his colleagues presented the work at the in New Orleans on 3 May.
鈥淢y vision is to drive multiple wearable devices on the body for a long time to realise advanced medical care and advanced activity recognition,鈥� says Takahashi.
But there are still some problems to solve before the system is ready for the commercial market. While the liquid metal is useful for its high conductivity, low toxicity and flexibility, it could be messy if it leaks from its containing tube.
The fabrication process for the charging sweater is also currently time-consuming; it takes hours for Takahashi to weave the conductive tube and metal into the fabric. Future designs will focus on automating the process, he says.
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