Sound velocity measurements in thin films

The authors have developed a novel technique for measuring the phase velocity of elastic waves in self-supporting thin films. One edge of the film is fixed to an interdigital transducer (IDT) acting as a transmitter, while another IDT, the receiver, moves freely above the film. The coupling between the receiver and the film is made through a liquid bond. This allows a continuous variation of the path length, and the resulting change in phase and amplitude of the received continuous-wave (CW) signal permits a simultaneous and accurate measurement of the phase velocities of the different vibrational modes present in the foil.