Measurement of Small Values of Electromechanical Coupling Coefficient in Piezoelectric Transducers

The electromechanical coupling coefficient k is usually derived from the difference between resonance and antiresonance frequencies fR and fA of a particular mode obtained from observations of the maximum and minimum values of electrical impedance. A simple relationship between fR, fA, and k exists only when the mechanical Q is infinite and the electrical losses negligible. This relationship breaks down when k2Q<2, a region which is important since the minor modes of barium-titanate transducers may have Q values of several hundreds and k<10%. For example, it has been found that, with 4