Modern wearable devices have allowed for a wide array of smart technologies to become mobile, including health tracking, receiving notifications, and much more. But due to their small battery size, they often run out of charge within a day or two, thus requiring frequent charging. This problem is what inspired a group of students from the University of Tokyo to create the Meander Coil++ project with the goal of enabling watt-scale wireless power transmission while also remaining safe.

Meander Coil++ differs from other wireless charging solutions in that it consists of a single shirt that has a series of tubes filled with liquid metal running horizontally through it. By applying an electric current, the large coil then creates a magnetic field and can induce current in the device to be charged. Because of this unique design, the researchers were able to achieve an efficiency of 41% for AC-to-AC transfers and a maximum power of 52W.

The coil’s design also relies on a 6.78MHz resonance frequency for power transfer, and this must be maintained no matter how the user is positioned. For this task, an Arduino Nano was combined with a bank of capacitors and relays which toggle on or off based on the values from the current monitoring module.

You can check out the team’s paper here for more details on Meander Coil++ and watch their CHI 22 presentation below, which features application examples such as charging a smartphone, a neck fan, a smartwatch, multiple LEDs, and even a Nano 33 BLE for activity and humidity monitoring.