Characterization of a parametric resonance based capacitive ultrasonic transducer in air for acoustic power transfer and sensing

Abstract

Capacitive transducers typically require a DC bias or a pre-charged electret to operate, rendering them non-ideal for applications such as energy harvesting and wireless power transfer. Parametric resonance based capacitive transducers offer an alternative to traditional capacitive transducers as they can be operated without the need for a bias voltage or a pre-charged electret. In this paper, we experimentally validate a 1D lumped parameter model and characterize a CPUT operating in air at 50 kHz for ultrasonic power transfer and sensing applications. This particular CPUT is able to recover 40.5 μW of power at an efficiency of 0.32% without any DC bias when excited by a 50 kHz piezoelectric transducer. The application of the CPUT as a highly sensitive acoustic sensor is explored by making use of active electrical circuits that reduce the resistance of the system. Finally, the capability of the CPUT as a highly directional acoustic sensor is presented with the electrostatic transducer demonstrating a directivity of ±1° when operated as a CPUT as compared to ±13° when operated as a conventional biased receiver. These results set the stage for the application of CPUT as a multi-functional acoustic transducer.