Acoustic reflectivity enhancement using higher-order nonlinear reflection mode

Acoustic wave reflection is studied for sharp nonlinear inhomogeneities embedded into nonlinear medium with similar linear characteristics. The higher-order nonlinear reflection mode is used to increase the reflectivity of such inclusions “invisible” in a linearly reflected field. For YZ-LiNbO₃ the discontinuity in nonlinear properties was measured to be the most dramatic for the SAW third harmonic generated in the area of the contact acoustic nonlinearity (simulating a closed crack) and acousto-electronic nonlinearity (piezoelectric-semiconductor structure). The experiments revealed from 3 to 4 orders of magnitude increase in reflectivity of the nonlinear inhomogeneities for the third-order nonlinear reflection mode