Nonspecular sound reflection and phase conjugation

A strong back reflection is observed at certain angles of incidence of sound waves at a limited plate or shell in a liquid. This reflection is termed nonspecular reflection. It arises whenever the condition for coincidence or spatial resonance in a plate is satisfied, i.e., in other words, when the velocity of the incident wave trace coincides with the propagation velocity of any free wave in a plate or shell. If the surface of a plate or shell performs forced vibrations at the frequency doubled in comparison with the frequency of the incident wave, back reflection is observed at any incidence angle. This phenomenon is termed phase conjugation. It is caused by nonlinear interaction of an incident wave with the vibrations of a plate or shell. Fundamentals of nonspecular reflection and phase conjugation are given, i.e., theoretical concepts and some experimental data. The generality and differences of the phenomena of nonspecular reflection and phase conjugation are discussed as well as their importance for...