A flat-type piezoelectric ceramic ultrasonic transmitter was successfully fabricated for application in acoustic devices with cone-free diaphragms. The transmitter, possessing a center frequency of 40.6 kHz, exhibited a higher displacement characteristic for a multilayer type compared with a single layer type. Surface roughness treatment of an Al elastic diaphragm influenced a slight increase (1.1 dB) in the sound pressure level (SPL) at 10 Vrms due to the enlarged surface area. The fabricated multilayer piezoelectric ceramic ultrasonic transmitter showed increasing SPL with increasing input voltage, with a maximum SPL of approximately 123.6 dB at 10 Vrms. This implies a doubly increased SPL density of 3.6 dB/mm3, superior to that of a commercial open-type transmitter with a cone.
