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Contactless ultrasonic power transmission (UPT) through a metal barrier has become an exciting field of research, as metal barriers prevent the use of electromagnetic wireless power transfer due to Faraday shielding effects. In this paper, we demonstrate power transfer through a metal wall with the use of ultrasonic waves generated from a piezoelectric transducer. Accurate characterization and modeling of the transducer and investigation of the influence of the acoustic properties of the transmitting medium are instrumental for the performance prediction and optimal design of an ultrasonic power link. In this work, we applied the KLM model for the emitting and receiving transducers, with respect to the transmitting medium and model for both the emission and reception function. A practical UPT system was built by mechanically coupling and co-axially aligning two composite transducers on opposite sides of a transmitting medium wall. The optimal transmission performance of the ultrasonic power link through thickness-stretch vibrations of the wall together with two piezoelectric transducers working in TE mode was determined. Eventually, the operating frequency and ohmic loading condition for maximum power transmission were obtained for two different media, aluminium and polyoxymethylene (POM), with contrasting specific acoustic impedances. The results showed that the measured optimal electric loads and operating frequency for maximum power transfer agreed well with the theoretical predictions. [ABSTRACT FROM AUTHOR]

Ultrasonic power transfer (UPT) is a promising method for wireless power transfer technology for low-power medical applications. Most portable or wearable medical devices are battery-powered. Batteries cannot be used for a long time and require periodic charging or replacement. UPT is a candidate technology for solving this problem. In this work, a 40-KHz ultrasound transducer was used to design a new prototype for supplying power to a wearable heart rate sensor for medical application. The implemented system consists of a power unit and heart rate measurement unit. The power unit includes an ultrasonic transmitter and receiver, rectifier, boost converter and super-capacitors. The heart rate measurement unit comprises measurement and monitoring circuits. UPT-based transfer power and efficiency were achieved using 1-, 4- and 8-Farad (F) super-capacitors. At 4 F, the system achieved 69.4% transfer efficiency and 0.318 mW power at 4 cm. In addition, 97% heart rate measurement accuracy was achieved relative to the benchmark device. The heart rate measurements were validated with statistical analysis. Our results show that this work outperforms previous works in terms of transfer power and efficiency with a 4-cm gap between the ultrasound transmitter and receiver. [ABSTRACT FROM AUTHOR]