Impedance profiling of media with nonparallel layers

The spectral distortion in the received pulse-echo signal, which occurs when planar layers are insonified at some oblique incidence relative to normal, was calculated and experimentally verified. As the spectral distortion contains readily distinguishable features from which the incident angle can be determined, the received signal from an unknown angle can be transformed into the equivalent normally incident pulse. By separately processing echoes from the interfaces of a multilayer medium with nonparallel layers, the acoustic impedance profile may be reconstructed. The distortion has been characterized for both planar and focused circular pistons. Results for both types of pistons are presented