Measurement of Small Values of Electromechanical-Coupling Coefficient in Piezoelectric Transducers

The electromechanical-coupling coefficient of a piezoelectric transducer k is usually derived from the difference between resonance and antiresonance frequencies for a particular mode. However, if the mechanical Q of the transducer Qm is low, i.e., k2Qm < 2, this relationship breaks down. The region k <20% and 100 <Qm <1000 has been analyzed and the resulting formulas processed by computer. The final data are presented in graphical form, making it possible to derive accurate values of k and Q from observations of the magnitudes and frequencies of the impedance maximum and minimum.