液体表面波纵向衰减的光学研究方法

【作者】 李能能；

【导师】 苗润才；

【作者基本信息】 陕西师范大学 ， 光学， 2011， 硕士

【摘要】 液体表面波存在有两种衰减：一种是沿液体表面波传播方向的横向衰减,另一种是垂直液体表面波传播方向的纵向衰减。我们曾用光学的方法研究了液体表面波的横向衰减特性,并测量了不同频率下的衰减系数。基于这一研究,本文主要研究了液体表面波的纵向衰减特性,得出了液体表面波振幅随激发深度的变化规律,并进一步得到液体表面波的纵向衰减系数。全文主要由以下四个部分组成：第一部分介绍了表面声波,并详细介绍了液体表面波；回顾了液体表面波的研究历史；综述了液体表面波的光学检测技术及其优点,并重点介绍了四种光学检测技术：液体表面波的激光衍射检测技术、低频液体表面波的激光斜率扫描检测技术、液体表面波的激光成像检测技术、低频液体表面波的激光干涉检测技术。第二部分对声光效应及表面声光效应的理论进行了推导分析。根据声波的频率(或波长)高低和光波(波长)相对声场的入射角度及二者之间相互作用的长度,将声光衍射效应分为两类：拉曼-奈斯(Ranman-Nath)衍射和布拉格(Bragg)衍射。光波和表面声波相互作用时,液体表面波对光波而言可看成是表面波光栅。光波通过这种特殊的光栅时就会发生声光衍射作用。第三部分研究了液体表面波的横向衰减特性。对于不同频率范围内的液体表面波,采用不同的方法进行研究。用激光干涉法研究频率为几十赫兹的液体表面波横向衰减特性,用激光衍射法研究频率为几百赫兹的液体表面波横向衰减特性。最后,测量了液体表面波随传播距离衰减的横向衰减系数。第四部分研究了液体表面波的纵向衰减特性。实验中通过改变液体表面波激发器的深度观察衍射图样的变化。结果发现随着激发深度的增加,衍射图样呈现出规律的变化,然后对不同激发深度处的衍射图样分析,得出了液体表面波振幅随激发深度变化的规律。本文主要以实验为主,采用激光衍射法,重点研究了液体表面波的纵向衰减特性。用探针式激发器激发液体表面,产生频率为100Hz的液体表面波,通过改变激发深度并采集不同激发深度处对应的衍射图样,再根据衍射图样分布与液体表面波之间的关系以及计算机编程,用最小二乘法拟合,得到表面波振幅与激发深度的关系。结果发现：液体表面波振幅随激发深度的增加而逐渐减小,并呈指数规律衰减。更多还原

【Abstract】 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.更多还原