Modal response coupling mechanism in multi-element coupled transducers.

Multi-element coupled transducers (MCTs) effectively reduce their operating frequency through acoustic interactions among closely spaced elements. However, their narrow bandwidth significantly limits practical applications. This study investigates an MCT comprising three axially aligned bender transducers with identical characteristics. A theoretical underwater acoustic radiation model was developed to analyze far-field pressure distributions. Modal superposition theory was employed to examine the coupling mechanisms among multiple vibration modes. By optimizing the amplitude and phase relationships of the excitations applied to individual elements, positive modal coupling was achieved, significantly broadening the operational bandwidth of the MCT. A prototype consisting of three bender transducers was fabricated, and its transmitting voltage response (TVR) was experimentally evaluated. The results demonstrated a maximum TVR of 131.2 dB within the frequency range of 460-1002 Hz, with an in-band fluctuation of 12.4 dB. Compared to conventional uniform-amplitude and in-phase excitation methods, the fluctuation amplitude was reduced by approximately 12.3 dB. This work provides theoretical insights and practical guidance for designing low-frequency broadband underwater acoustic transducers.