Explain the thermal detectors method of detection of ultrasonic waves.

Thermal detectors method:

It is the most generally used method of detection of ultrasonic waves. In this method, a fine platinum wire is utilized. That wire is moved by the medium. At the position of nodes, due to alternate compressions ad rarefactions, adiabatic changes in temperature takes place. The resistance of the platinum wire changes according to time. It can be detected with the help of Callendar and Garrifith’s bridge arrangement. At that position of the antinodes, the temperature as stayed constant. It will be indicated by the undisturbed balanced position of the bridge.