Design and fabrication of an ultrasonic speaker with thickness mode piezoceramic transducers

Until now, most ultrasonic speakers have utilized piezoelectric buzzer-like radial mode transducers, which necessitates a complicated signal processing circuit to overcome the narrow frequency bandwidth of the transducers. We designed an ultrasonic speaker with thickness mode piezoceramic transducers, and fabricated an ultrasonic speaker system working at a frequency of 650 kHz. The design method of an individual in-air piezoceramic transducer is presented, followed by the design of the parallel combination of many transducers that are used to make the speaker. The performance of the speaker was measured experimentally to verify its unique features; i.e. a high directivity and a wide frequency bandwidth. The ultrasonic speaker developed in this study preserved all the unique features of an ultrasonic speaker without the use of complicated electronic signal processing circuits by virtue of the broadband frequency characteristics of thickness mode piezoelectric transducers.