Piezoelectric transducer design and impedance tuning for concurrent ultrasonic power and data transfer

Abstract

Ultrasonic waves can be used to transfer power and data to low power electronic devices placed in inaccessible locations such as the human body, deep in the ocean, or in metallic enclosures. The upstream communication from the device can be transmitted using a minimal power by modulating the impedance of a piezoelectric transducer to switch between absorbing incident ultrasonic waves and completely reflecting it. The absorbed ultrasonic power in this configuration is supplied to an energy harvesting circuit for powering the device. Piezoelectric transducers are commonly optimized either for power applications only (narrow bandwidth and high sensitivity) or data applications only (broadband and low sensitivity). This work explores piezoelectric transducer design for simultaneous power and data transfer using acoustic and electrical impedance matching. A broadband transducer is designed to receive uninterrupted ultrasonic power at 1.3 MHz while transmitting upstream data at a different frequency band with a bandwidth of 300 kHz. The factors affecting power/signal reflection due to impedance mismatch are analyzed analytically, and an approach for simultaneous acoustic and electrical impedance matching is introduced to maximize the bandwidth and sensitivity. Several air-backed underwater transducers with different matching layers are fabricated, and their electrical and acoustic reflection as well as their electrical impedance are experimentally measured and compared to analytical predictions. A circuit for maximizing the bandwidth and sensitivity of the transducer for data transfer is then tested experimentally. Another circuit for achieving uninterrupted simultaneous power and data transfer using a single transducer is also implemented and tested.