Inductive coupling is the most common approach to wireless power transfer and is used, for instance, in the small wireless charging systems of smartphones. Recently, researchers have been looking to adapt this technology to other applications. One such example is its use in the wireless autonomous microsystem that featured on the cover of our March 2020 issue (image, left). The paper was from Feng Zhu, Oliver Schmidt and colleagues, and was entitled ‘A flexible microsystem capable of controlled motion and actuation by wireless power transfer’ (Nat. Electron. 3, 172–180; 2020). The researchers created a micrometre-scale platform containing rolled-up microcatalytic engines that were powered through a wireless inductive link and could be used to propel and steer the devices. Enough power could be transferred to also power small electronic devices integrated into the platform and a micro-arm that could be used for grasping tasks.
Transferring power between devices on a person — for wearable technologies or electronic medical devices for example — is challenging. Inductive approaches typically work over short distances, while far-field radiofrequency methods require line of sight between devices. Additionally, body movement can detune coupled circuits that need to remain in fixed positions. Work published in our July 2021 issue reported an approach to overcome this by using the human body as the transmission medium. The paper was from Jerald Yoo and colleagues, and was entitled ‘Body-coupled power transmission and energy harvesting’ (Nat. Electron. 4, 530–538; 2021). The approach used capacitive coupling between the body, the devices and the environment, and could be used to transfer power from a device on a person’s head to one on their ankle — a distance of about 160 cm.
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