A triple-resonant Janus-Helmholtz transducer.

The Janus-Helmholtz (JH) transducer is an underwater acoustic device that utilizes longitudinal resonance (LR) and liquid cavity resonance (LCR) to produce low-frequency, broadband acoustic emissions. However, attempts to enhance coupling with the flexural resonance (FR) of the radiation head have demonstrated that effective interaction between FR and LCR remains unachieved, thereby constraining the operational bandwidth of the JH transducer. This study addresses this limitation by proposing a sound field model for the JH transducer under flexural vibration and elucidates the inherent physical constraints. By exploiting the vibration characteristics of FR, two oscillating structures are introduced into the JH transducer. The effects of oscillating structures on resonant frequency and emission performance are evaluated using the finite element method. It is shown that the resonant frequency and the associated sound field can be manipulated through mass effects and the interference principles of coherent sound waves. A prototype of the proposed JH transducer is fabricated, and experimental validation supports both theoretical predictions and finite element simulations. This research achieves successful coupling among LR, LCR, and FR, significantly extending the operational bandwidth of JH transducer. These findings provide new insights into the control of resonant frequency and sound field in free-flooded transducer designs.