Abstract: To detect cracks in plate-like structures without any baseline data, a method to obtain Lamb wave transfer impedance from piezoelectric transducers (PZT) was proposed. First, the damage feature signals which contained converted Lamb wave modes were extracted and classified from two sets of parallel PZT components. Subsequently, transfer impedances of the feature signals were obtained in the frequency domain, and the existence of cracks was determined by comparing the energy associated with the transfer impedances. To analyze the applicability of the proposed method, crack-induced Lamb wave mode conversion and effects of PZT polarization characteristics on the relative phase among each mode were studied using the finite element method (FEM). Further, experiments on aluminum plates verified the effectiveness of this method. This research shows that the proposed crack detection method has strong robustness and applicability, as it is not sensitive to the optimal excitation frequency and the sampling time of signals.