We rigorously analyze the dispersion function and the curvature of the dispersion surface of a photonic crystal to explore the fundamental limit of its angular sensitivities. With insight gained from group theory, we fi nd that symmetry indu

GVD (group velocity dispersion)

Lamb波的频散曲线是进行超声Lamb波无损检测的重要依据。本程序对Rayleigh2Lamb方程进行了分析，给出了无限大板中Lamb波频散曲线的数值计算方法，通过Matlab软件对求解过程进行编程，绘制出Lamb波在铝板中传播的相速度和群速度曲线，并通过试验进行了验证对推广应用Lamb波进行无损检测具有实际意义。(The dispersion curve of Lamb wave is an important basis for non-destructive testing of ultr