提出低频多模式超声兰姆波定征方法来估计超薄层状单向纤维增强复合材料的密度、厚度、弹性常数等参数。这里“超薄”的概念是指材料厚度h远小于材料中的声波波长λ，导致在时域上材料前后界面的各次回波信号相互混迭。分析了沿平行和垂直于纤维两个方向上，在超薄层状单向纤维增强复合材料中传播的低频兰姆波色散特性，提出在最小二乘意义下以材料色散曲线为基础的反向算法对材料参数进行了估计。文中分析了影响估计准确性的各种因素，研究了该方法对材料参数的灵敏度及其在误差传递中的意义。结合超声漏兰姆波频域分析方法，并使用超声耦合剂耦合方式和一对中心频率为2MHz的宽带纵波换能器，实验结果证实，该方法能够准确估计h<0.05 λ的单向玻璃纤维增强双酚A型聚砜（PSF）复合材料的材料参数。
A low-frequency multi-mode ultrasonic Lamb wave method suitable for characterizing thickness, density and elastic stiffness tensors of the ultra-thin uni-direction fiber-reinforced composite layer is presented. The “ultra-thin” there means that the thickness of the plate is only a fraction of the ultrasound wavelength. The dispersion properties of the low frequency Lamb wave propagating along and parallel to the fiber direction are derived, which is the basis of the characterization method. In conjunction with the method of least squares, the secant algorithm is used to estimate the parameters of the ultra-thin fiber-reinforced composite layer. The reasons for evaluation error of the parameters and the sensitivity of all methods for different parameters are analyzed. Using the ultrasound coupler and a pair of broadband longitudinal wave transducers with 2 MHz center frequency, one can successfully estimate the parameters of the ultra-thin GF/PSF composite layer by combination with employing the leaky guided wave frequency-domain analysis method.
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