Ultrasonic Wireless Power Transfer in Metal Structures using Frequency-Steerable Acoustic Transducers and Impedance Matching

Ultrasonic Wireless Power Transfer (UWPT) has been widely investigated in recent years as a promising solution for powering inaccessible sensor nodes in structural health monitoring (SHM) applications without affecting materials' in-tegrity and overcoming metal shielding effect. In this work, the Frequency-Steerable Acoustic Transducer (FSAT) has been considered as an innovative device for ultrasonic guided waves-based energy transmission thanks to its directional properties. Power transmission and conversion from ultrasonic waves have been investigated, along with techniques exploiting impedance matching to ensure maximum power transfer and sufficient voltage at the receiver side. More specifically, FSAT's output impedance is measured and two impedance-matching networks are proposed and characterized: a parallel-connected inductor and a magnetic transformer. Experimental results conducted on a 1 mm thick aluminum plate with two FSATs bonded at a 50 cm distance pointed out a maximum received power value of 164 μW at 83 kHz, with a 23 V peak-to-peak voltage in transmission. The received power and voltage are sufficient to energize a low-end MCU and micropower management circuits on a sensor node.