Abstract: To solve the contact defect(such as cracks,delaminations) detection in structures,a nonlinear acoustic technique for detection of contact defects in plates using sparsely distributed sensors was developed associating guided waves with vibro-modulation techniques.The low frequency vibration varies the interface area within the contact defect; therefore the amplitude and phase of high frequency guided waves reflected from the contact defect will be modulated. Due to the exiting of contact defects,there is obvious low frequency component in the time-frequency distribution of modulated guided wave series.Furthermore the nonlinear responses at frequency of vibration are extracted out and used for defect imaging.It is shown that the nonlinear guided wave imaging method based on vibration modulation can effectively characterize and locate the nonlinear contact defects.