Design of a dual-band Janus transducer based on modal coupling analysis and zero-pole control

Longitudinal transducers, such as Tonpilz and Janus structures, are widely utilized in underwater acoustics due to their simple design and ease of array integration. To achieve broadband responses, prior studies have explored modal coupling strategies to excite multiple vibration modes, resulting in dual-resonance and multi-resonance transducers. However, the physical mechanisms behind null-response phenomena in multimodal coupling remain poorly understood, with current explanations relying on parameter scans and numerical simulations that lack predictive accuracy for system null locations. This paper employs pole-zero theory and "spring-mass" models to analyze null-response arising from modal coupling in multi-resonance transducers. Key relationships between modal coupling, system poles, and zeros are established, extending to multi-subsystem cases. A modular design methodology is proposed to control zero locations and optimize energy concentration in specified frequency bands, enabling effective multi-band transducer design. To validate the methodology, a tri-resonance dual-band Janus transducer (DBJT) was developed and tested. The DBJT enhances fundamental resonance while minimizing broadband response fluctuations, making it suitable for underwater detection and acoustic communication applications.