Abstract: To achieve active health monitoring of plate-like objects,piezoelectric ceramic wafers bonded in the structures are applied for excitation and reception of guided wave modes and proper modes are optimized for identification and evaluation of the defects.According to the theoretical prediction,compared with A₀ mode,S₀ mode in a low frequency range with dominant in-plane displacement and low dispersion is suitable for defect detection in the aluminum plate.The piezoelectric ceramic wafers 11 mm in diameter and 0.4 mm in thickness are used for excitation and reception of S₀ mode at 300 kHz,which is suitable for defect detection in aluminum plates with a thickness of 1 mm.Based on the experimental results,an artificial hole-like defect is machined in the plate for verifying the ability of defect detection using S₀ mode,and the effect of the defect diameter on the amplitudes of received guided wave signals is further analyzed.Experimental results show that Lamb wave modes can be applied for defect detection in the aluminum plate using the pitch-catch method and defect characterization can be achieved based on the amplitudes of the received echoes.