Ultrasonic Production in engineering physics 2 classroom free notes download
The rod is permanently magnetized in the beginning by passing direct current. The battery is switched on and hence current is produced by the transistor. This current is passed through the coil L, which causes a corresponding change in the magnetization of the rod. Now, the rod starts vibrating due to magnetostriction effect.
When a coil is wounded over a vibrating rod, then e.m.f. will be induced in the coil called as converse magnetostriction effect. Due to this effect an e.m.f. is
induced in the coil L1. The induced e.m.f. is fed to the base of the transistor, which act as a feed back continuously. In this way the current in the transistor is
built up and the vibrations of the rod is maintained. The frequency of the oscillatory circuit is adjusted by the condenser C and when this frequency is equal to the frequency of the vibrating rod, resonance occurs. At resonance, the rod vibrates longitudinally with larger amplitude producing ultrasonic waves of high frequency along both ends of the rod.