Portable through-metal ultrasonic power transfer using a dry-coupled detachable transmitter

Abstract

Ultrasonic waves can be used to transfer power and data efficiently through metallic enclosures when feedthroughs are not practical due to structural or electromagnetic shielding considerations. Previous implementations of ultrasonic power transfer (UPT) used a piezoelectric transducer permanently bonded to the metal for efficient ultrasonic coupling. For portable operation, it is essential to have a detachable transmitter (charger) that is only attached to the enclosure while transferring power. This requirement presents several design challenges; notably, detachable ultrasonic coupling typically relies on liquid or gel couplant, which may become inconvenient or less robust during repeated attachment and detachment. Thus, this work develops a dry-coupled detachable UPT system to transfer power efficiently through a metallic enclosure without the need for a liquid couplant. Low attenuation soft elastomers are experimentally tested with a magnetic setup to evaluate their dry-coupled efficiency. Samples with different materials and thicknesses are experimentally tested to select the best configuration for dry ultrasonic coupling. The softest elastomer tested yielded the best ultrasonic efficiency (AC-to-AC) of 68% at 1 MHz. A full DC-to-DC portable (battery-operated) UPT system was then developed and experimentally characterized. The system was capable of delivering up to 3 W of DC power to a resistive load with a total efficiency of 50%.