Novel sensors for monitoring acoustic cavitation

This paper describes a novel acoustic sensor of potential application in monitoring cavitation occurring within ultrasonic cleaning vessels. The sensors, fabricated in the form of hollow cylinders, are manufactured from a thin (110 μm) piezoelectric polymer whose acoustic bandwidth (10 MHz) is sufficient to detect the high-frequency signals generated by cavitating bubble collapse. One of the key characteristics of the sensors is their spatial resolution: acoustic signals detected at high frequencies originate from bubble events occurring within the hollow cylinder itself. To isolate these, the cavitation sensors are encapsulated in a 4 mm thick layer of a specially-developed acoustical absorber acting as a shield to bubble events occurring outside of the sensor volume. The construction of the new sensor is described, and early results of its response in the acoustic field of an ultrasonic cleaning vessel are presented