Ultra-Low-Frequency Acoustic Dual-Resonance System for Marine Geology and Subsea Energy Detection

Low-frequency underwater acoustic sources face a fundamental trade-off between miniaturization and output power, which severely constrains their use in marine geological exploration. To address this limitation, this work proposes a dual-resonant underwater low-frequency transducer based on the coupling of a bubble resonator and a Helmholtz resonator The device delivers controllable output waveforms at low frequencies with high pressure intensity. A research framework integrating theoretical modeling, numerical simulation, and experimental verification is established. On the theoretical side, a lumped-parameter model was developed by use of electroacoustic analogy; an equivalent relationship between volume pulsations and radiated sound pressure was formulated on the basis of monopole theory. MATLAB parameter fitting was then used to quantify the effects of key parameters on the resonance frequency and sound pressure level was quantified, while COMSOL simulations served to screen and optimize the dimensions of the prototype. On the experimental side, the bubble resonant cavity was structurally optimized, the tensile properties of the diaphragm were characterized, and mechanisms for air circulation and flow regulation were designed. Particularly, a high-pressure gas source driving a highly elastic diaphragm replaced the traditional blower-driven excitation, which miniaturized the pneumatic acoustic source while preserving broadband controllable output. Measurement in an anechoic tank and in a lake showed that the prototype produced a SPL exceeding 180 dB at its designed natural frequency of 20 Hz. This study offers a practical technical route toward compact, high-sound-intensity artificial seismic sources is of considerable engineering value for underwater low-frequency acoustic propagation and marine geological exploration.