ABSTRACT
Performing any operation with ultrasonic waves means transmitting them from one medium to another where the measurement or actuation is to be performed. This chapter considers reflection and transmission at normal incidence for liquid–liquid interfaces. It allows readers to concentrate on basic concepts such as acoustic mismatch, standing waves, and layered media in the simplest mathematical description and the most important applications area. The traveling or progressive waves treated in bulk media thus far are characterized by the propagation of a disturbance (phase) and the propagation of energy. The input impedance of a layer sandwiched between two different media can be calculated by a direct extension of the reflection coefficient for a single interface.
