Thermal Voltages of a Quartz Crystal

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Abstract
The thermal charges and voltages which arise in a piezoelectric material because of its heat energy have been computed. The calculations were made for a quartz bar, and include also some of the effects of the measuring circuit. Measurements of the thermal noise voltage of a quartz bar having a natural frequency of 36.6 kc/sec. were made with a specially shielded and filtered amplifier. Completely successful separation of the thermal voltage from the first-stage tube noises was not achieved. However, fairly good agreement between measured and computed crystal thermal voltage was obtained with one amplifier when it was adjusted to have a high input impedance. Measurement of the thermal voltage appears to offer a means of securing rough values of piezoelectric coefficients at room temperature and higher.