Modes of Vibration of Piezo-Electric Crystals

(a) A crystal is made to oscillate by subjecting it to the action of an air wave produced at a considerable distance from the crystal by a jet of air escaping from a small tube. The piezo-electric charge developed on the surface of the crystal as a result of the oscillation is mapped out by means of a tuned amplifier, and the vibration is analyzed into a fundamental and many overtones. For crystals that are long in one dimension, the overtones are nearly exact harmonics. (b) Exciting the crystal electrically by means of two tubes and especially designed electrodes, any harmonic up to the tenth can be produced. The crystal usually has only one mode of vibration for each pair of electrodes.