A stepped plate transducer as an ultrasonic loudspeaker

Research on the ultrasonic loudspeaker has been under way since Mary Beth Bennett and Blackstock verified the existence of parametric array phenomenon in air experimentally. Although several transducers that make use of piezoelectric films have been proposed, an ultrasonic loudspeaker system is not developed enough to be practical due to its high cost and high power consumption. In the 1970s, Gallego-Juarez et al. developed an ultrasonic transducer exploiting flexural modes of circular radiating plate, which shows highly efficient and directional performance. The feasibility of this type of transducer as ultrasonic loudspeakers, however, has not been investigated. Thus, a transducer with a stepped radiating plate of 283 mm diameter and a resonance at 40 kHz was designed, manufactured, and tested. In order to maximize the pressure radiated, piezoelectric ceramics were placed at the nodal point of the structure. The features of the transducer manufactured are over 130 dB of maximum primary wave at resonance on the acoustic axis, half-power beamwidth of primary ultrasound less than 10 deg, 40 to 60 dB of secondary waves from 1.5 to 20 kHz at 1m, and half-power beamwidth of secondary sound less than 10 deg.