Low-frequency sound transmission through rough bubbly air–water interface at the sea surface

Abstract

Transmission of a sound generated by a localized point source in the air through a realistic sea surface is studied by the use of the Kirchhoff-Helmholtz integral. An earlier approach had been based on the Kirchhoff-Helmholtz integral which only considered the effects of rough surface. In the current study, not only the effect of the rough surface is taken into account but also the effects of subsurface bubbles are included in modeling the real phenomenon more accurately. In order to include the effects of subsurface bubble population, the classic relations of the Kirchhoff-Helmholtz integral are reformulated. Accordingly, a three-phase region of air, water, and bubbly water at the sea surface is analyzed, and the rough interface of bubbly water-air is discretized. Through considering an element area A i , the transmission coefficient T i , incident angle h li , transmitted angle h 3i , and local surface acoustical roughness R i are investigated for each individual element. Also, the effects of subsurface bubbles, transmission change as a function of frequency f, wind speed W, incident angle h, source/receiver position ratio (D/H), surface acoustical roughness, and subsurface bubble population are examined. Results of the modified Kirchhoff-Helmholtz integral method display good agreement against available experimental data.

A Bionic MEMS Electronic Stethoscope With Double-Sided Diaphragm Packaging

“…For DMES, the media on both sides of the reflection interface are silicone oil and air, and due to the diaphragm's silicone oil impermeability and sound transmission ability, which form a water-air interface. The water-air interface is called a "pressure release" or "soft" surface for the underwater sound as it is usually an almost perfect reflector of acoustic waves [18]- [19]. For SMES, these two media are silicone oil and shell material.…”

“…, s u is the peak value of the collected heart sound signal, n u is the peak value of the collected noise signal, the noise signal is the static noise of the stethoscope without a heart sound signal. The heart sound waveforms are shown in Figures 17,18,and 19. Table IV shows the results calculated by the formula.…”