Generation and Reception of Second Harmonic Waves by Using a focused Beam in the Pulse-Echo Mode

When a nonlinear parameter is measured by the pulse echo method, the second harmonic component reflected at the stress free boundary (R = - 1) is generally very small, makin g measurement difficult. However, when the beam is concentrated at the reflection surface, phase change occurs and the magnitude of the second harmonic after reflection increases. Therefore, when measuring nonlinear parameters in a solid, it is advantageous to generate a focused beam by using pulse reflection. In this study, beam focusing is induced by using constructive interference by diffraction, in accordance with the widely used Fresnel zone plate theory, instead of using acoustical lenses, which are heavy and difficult to use. The theoretical study was carried out through simulation in order to optimize the design and production of a beam-focusing ultrasonic transducer.