For measuring thin oil-film thickness distribution in the mechanical equipments,the measurement of thin oil-film thickness distribution by using ultrasonic technique was theoretically studied. Based on the related theory of the a-coustic propagation in three layers of media and considered the boundary conditions,a spring model of reflection coeffi-cient was constructed to simulate the propagation of oblique incidence ultrasound in three layers of media on condition that the oil-film thickness was far less than the wavelength. The functional relationship between reflection coefficient and the stiffness of the oil-film can be obtained from this model. The oil-film thickness can be got from the stiffness. The influence of the incident angle,frequency and the oil-film thickness on the reflection coefficient was studied. Each reflection coeffi-cient measured corresponds to the thickness of a point on the oil-film,and the oil-film thickness distributions can be extrac-ted from these reflection coefficients via this model.% 为了测量机械设备中的薄油膜厚度分布，对超声测量薄油膜厚度分布的方法进行了理论研究。基于声波在三层介质中传播的相关理论，对中间层油膜厚度远小于油膜中入射声波波长的情况，结合具体边界条件，建立斜入射时超声波在三层介质中传播的反射系数弹簧模型，获得反射系数和油膜刚度的函数关系，进而由刚度获得油膜厚度；分析超声波入射频率、入射角度和油膜厚度对反射系数的影响规律，通过测量油膜中各点的反射系数即可获得相应点的油膜厚度，实现油膜厚度分布的测量。
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