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以[001]_c和[011]_c极化的铌锌酸铅-钛酸铅晶体为研究对象,利用子波理论对其无限大自由薄层中传播的Lamb波的色散及模式交叉特性进行了研究.发现只有[001]_c极化的晶体中的对称与反对称模式Lamb波之间出现了多次交叉,并且变化规律与铌镁酸铅-钛酸铅的情形相同.Lamb波的A_0和S_0模式的交叉是由准纵向剪切波慢度曲线的多值关系引起的,此时其x_3方向的波数在一定范围内存在一对非纯虚数的复共轭根.利用此结论推导出A_0和S_0模式交叉时弹性常数需要满足的条件,为判断正交、四方对称性晶体中Lamb波的A_0和S_0模式是否交叉提供了一种直观、简便的方法.
Taking the [001] _c and [011] _c polarization of lead niobate-lead titanate crystals as the research object, the dispersion and mode-crossing characteristics of Lamb wave propagating in an infinitely thin free layer were investigated by using wavelet theory It is found that only the symmetrical and antisymmetric Lamb waves in [001] _c polarized crystals cross several times, and the changing rule is the same as that of lead magnesium niobate-lead titanate. The A_0 and The intersection of S_0 mode is caused by the multi-valued relationship of the slow wave curve of quasi-longitudinal shear wave, in which case the wave number in the direction of x_3 has a complex conjugate root with a non-pure imaginary number in a certain range. Using this conclusion, A_0 And S_0 mode, the elastic constants need to be satisfied, which provides an intuitive and convenient method for judging whether the modes A_0 and S_0 of Lamb waves intersect in the orthorhombic and tetragonal symmetry crystal.