The characteristics of a high-strength millihertz seismic sound source

Acoustic waves propagating at ultra-low frequencies contain information that corresponds to earthquake, explosion, and tsunami, and find applications in ocean exploration, disaster alerting, In ocean environments, the noise in the ultra-low frequency range, from 0.001 Hz to 1 Hz, is predominantly seismic noise. Consequently, the sound source in this frequency range is referred to as a seismic sound source in underwater acoustic studies. This work aims at tacking the longstanding challenge of realizing the ultra-low frequency seismic sound source at millihertz frequency using the nonlinear interaction process between high-frequency acoustic waves and electromagnetically forced fluid. The author produces acoustic waves in the ultra-low frequency range from 0.001 Hz to 1 Hz using the seismic sound source. A novel theoretical framework is developed to guide the realization of the seismic sound source. The strength of the generated ultra-low frequency acoustic waves increases as the acoustic frequency decreases. Laboratory experiments identify the effects of built-in assumptions and simplifications in theoretical studies. Efforts are made to determine the operation boundaries of the proposed seismic sound source. The research outcomes have the potential to surpass the limitations of existing sound generation methods and pave the way for ultra-low frequency acoustic communications and seabed explorations.