A parametric resonance based capacitive ultrasonic transducer for wireless power transfer in air

Abstract

Capacitive ultrasonic transducers have been in use for many years for various applications such as medical imaging, wireless power, sensing, and nondestructive testing. Typically, capacitive transducers require a DC bias or electret in order to operate efficiently and with high sensitivity. This makes them less desirable for applications such as wireless power transfer or energy harvesting, where a passive piezoelectric transducer may be preferred. Recently, it was shown that the requirement of a DC bias can be overcome by driving the capacitive transducer into parametric resonance using ultrasound (Surappa et al., Appl. Phys. Lett. 111(4), 043503). In this work, we present the operation of the first ever biasless, chargeless capacitive parametric ultrasonic transducer (CPUT) in air and demonstrate the utility of such a system for acoustic power transfer and sensing. Experiments performed in air show that the CPUT has an open-circuit sensitivity of more than 100 mV/Pa and is able to recover 31 µW at a distance of 10 cm from a 50 kHz ultrasonic source in the absence of a DC bias.