Presence of ultrasonic waves can be detected by using any one of the following methods: 1. Quartz crystal method This method of detecting ultrasonic waves is based on the principle of piezoelectric effect. When one pair of opposite faces of the quartz crystal is exposed to ultrasonic waves, in the other pair of opposite faces, charges get developed as shown in figure. These changes are amplified and detected using suitable electronic circuits. 2. Thermal detection method Principle When the ultrasonic waves are propagated through a medium, the temperature of the medium changes due to alternate compressions and rarefactions. In the case of stationery waves, there is a change in the temperature at nodes and no change in temperature at antinodes. Based on this principle, by sensing the change in temperature using suitable components, the ultrasonic waves can be detected. It is the most commonly used method to detect ultrasonic waves. In this method, a fine platinum wire ...