The elastic plate waves are classified to shear horizontal(SH) wave and Lamb wave which have more than one mode depending on the ratio of the thickness of plate to wavelength of shear wave. Lamb wave was excited by breaking pencil lead and glass capillary on the surface and edge of glass plate, unidirectional and (0°/90°) bidirectional carbon fibre reinforced plastic (CFRP) plates. The lowest symmetric and antisymmetric mode were identified by the power spectrum analysis and the sense of amplitude of the received signal on top and bottom surfaces. The group velocities of these modes were obtained by measuring the delay time of the signals received in two transducer placed different positions. Young's and shear moduli of the fibre direction and normal to fibre direction in unidirectional and (0°/90°) bidirectional CFRP plates and of glass plate were determined with the group velocities. In unidirectional and (0°/90°) bidirectional CFRP plates, the slowness curves of the lowest symmetric and antisymmetric modes in Lamb wave were obtained with the angular dependence of the group velocity and the anisotropy of unidirectional and (0°/90°) bidirectional CFRP plates had better seen in the slowness curve of the lowest symmetric mode.
