Liquid Surface Wave Longitudinal Attenuation Of The Optical Research Methods

There are two attenuation in the liquid surface acoustic wave:one is horizontal attenuation along the direction of propagation of liquid surface wave. The other is longitudinal attenuation which is vertical with the direction of propagation of liquid surface wave. horizontal attenuation of liquid surface wave is studied by optical method. Attenuation coefficient is measured under different frequency. Based on this research, longitudinal attenuation of liquid surface wave is studied in this paper. The relation between the liquid surface wave amplitude and exited depth is observed and longitudinal attenuation coefficient is obtained.This paper mainly includes the four parts as follows:The first part introduces surface wave and the liquid surface acoustic wave. Then the research history of liquid surface wave is reviewed. There are many methods to detect liquid. This part summarizes the optical technology and their advantages. Four techniques, including laser diffraction, scanning laser slope, the imaging detector of capillary waves and laser interference, are mainly introduced.The second part deduces the theory of the acoustic-optic effect and surface acoustic-optic effect. Acoustic-optic effect is divided into two classes:Ranman-Nath diffraction and Bragg diffraction, based on different frequency and wavelength. When the light wave and SAW interact in liquid surface, SAW can be as grating. So it will appear acoustic-optic diffraction effectThe third part studies the horizontal damping character of liquid surface wave. It is measured by different kinds under certain condition. Horizontal damping character of liquid surface wave at dozens of hertz is studied by laser interference. Liquid surface wave at hundreds of hertz is studied by laser diffraction. The attenuation coefficient of liquid surface wave is detected.The fourth part studies the longitudinal attenuation of liquid surface wave. In the experiment, Diffraction pattern is observed through changing the exiting depth. Diffraction pattern change with the change of the exiting depth. Based on the diffraction pattern, the rule of liquid surface wave and exiting depth is obtained.This paper is based on the experiment. It mainly studies the longitudinal attenuation of the SAW by the laser diffraction. Liquid surface acoustic wave at 100Hz is produced by the exiting needle. Diffraction pattern is collected at different exiting depth. The relation between the diffraction pattern distribution and the surface acoustic wave amplitude is achieved and this relation is programmed. Then, the dependence of the amplitude on the exited depth is obtained. It is found that the liquid surface waves amplitude decreases exponentially as the exited depth increase based on the least square method.