Ultrasonics can be produced by means of (i) Galton’s Whistle (ii) Magnetostriction Generator (ii) Piezoelectric Generator or Oscillator.
Galton’s Whistle. It contains of essentially a short cylindrical pipe blown in the form of an annular nozzle. The distance of nozzle from the edge of pipe can be varied by turning a micrometer screw. By suitable adjustment of this distance and the pressure of air blast, the pipe is set into resonant viberation at a frequency depending on length and diameter of pipe. The Galton’s Whistle method can be used to produce ultrasonic waves of low frequency upto 100kHz.
I will discuss the other methods in next articles.