Modal excitation and variable-band operation of piezoelectric tonpilz transducers

This paper addresses the limitations of traditional tonpilz transducers (TTs), which typically operate within a single frequency band, by proposing a modal-excitation method for piezoelectric TTs to achieve variable-band operation with a single device. First, the vibration equation of a thin piezoelectric rod is solved in modal space to determine the excitation characteristics of its different modes. This method allows selective excitation of a single mode in the piezoelectric rod by applying a voltage distribution that matches the stress distribution of that mode. Next, the strain distributions corresponding to different modes of the transducer are calculated. Then, the voltage distributions needed to excite different-order modes are determined. By applying these voltage distributions to the transducer, single-mode excitation is achieved, enabling variable-band operation without altering the transducer's physical structure. Under single-mode excitation, the transducer exhibits a stronger response and improved electroacoustic efficiency compared to traditional uniform excitation. Finally, a modal-excitation TT was designed and experimentally validated. The results demonstrate that the transducer successfully excited the first through third modes individually, achieving variable-band operation. The transmitting voltage responses of the first three orders were measured at 143, 146, and 150 dB, respectively, with corresponding electroacoustic efficiencies of 31%, 34%, and 32%.