Abstract
Numerous formulae have been given for the calculation of the electromechanical coupling factor of piezoelectric disks in terms of the resonant and anti-resonant frequencies. These formulae, which are derived either on the basis of an analysis of the mechanical motions of a disk, or by considering the equivalent electrical circuit give widely divergent values of coupling factor.
It is shown that when an equivalent circuit which takes account of the overtones is used, the corresponding value of coupling factor obtained is in agreement with that of the mechanical analysis.
Curves, and a nomogram are given to enable coupling factor to be quickly calculated from the equations of the mechanical analysis without approximation.