Acoustic vibrations for versatile wireless power transfer

We present an overview of prior/recent work done at the US Army Combat Capabilities Command—Army Research Laboratory on using acoustic waves for wireless power transfer (WPT). In the past we have demonstrated through-air ultrasonic phased array power beaming, through-metal longer distance transfer using Lamb waves, and power/data transfer to embedded sensor nodes. Acoustic WPT has the advantage of not being shielded by metal, and can achieve higher efficiencies than inductive WPT at larger distances. Part of our recent work is on developing a through-metal acoustic WPT based wireless UAV recharging platform. For the first time, we have demonstrated a self-detachable acoustic WPT receiver, using the switchable magnetic force from electro-permanent-magnets to attach a receiver transducer onto a steel platform to receive power (a transmitter is bonded on the other side of the platform), without the need of any liquid couplant. The magnetic force enhances the mechanical mode coupling, while allowing the receiver to attach/detach freely from the platform. AC-AC power efficiency up to 63% was achieved, and with the appropriate power electronics and matching network, an overall DC-DC efficiency of 44% was achieved when charging a 3-cell LiPo UAV battery with 4.6 W, with higher power levels achievable.