Visualizing detecting low-frequency underwater acoustic signals by means of optical diffraction

Abstract

A novel and simple technique based on the light diffraction effect for visualization of low-frequency underwater acoustic waves (LFUAWs) in real time has been developed in this paper. A cylindrical object has been put on the surface of the water. A low-frequency underwater longitudinal wave can be generated into a water surface transversal capillary wave around the cylinder by our technique. Modulating the phase of a laser beam reflected from a water surface by surface acoustic waves (SAWs) realizes the acousto-optic effect. Then, a steady and visible diffraction pattern is experimentally observed. A physical model of the SAW is established to verify the feasibility of our technique. An analytical expression of wavelength, wave amplitude, and excitation frequency has been derived to study the physical properties of LFUAWs, and it explains the experimental phenomenon very well. As a result, the technique is effective, easy, and practical for visualizing LFUAWs and has significance for applications.

Detection of Water Surface Acoustic Waves Using Sinusoidal Phase Modulation Interferometer and Prenormalized PGC-Arctan Algorithm

“…Currently, the optical detection methods of such weak water surface waves are mainly divided into optical intensity modulation method [3], light scattering method [4], laser Doppler interference method [5][6][7][8], and optical diffraction method [9][10][11]. Some of these detection methods have been applied to the detection of physical properties of media, such as in the study of surface tension, viscosity of medium, and molecular motion; some have been used in the detection of underwater acoustic information.…”