Estimation of Piezoelectric Equivalent Circuit Parameters Using Principle of Least Variance

The estimates of equivalent circuit parameters of a piezoelectric transducer, observed from the admittance circle near resonance in a conventional manner, are improved on two types of lumped-parameter circuits, namely, L- and T-type circuits, which are consistent with Marutake's approximation formula for estimating electromechanical coupling coefficient, using the principle of least variance with regard to the physical quantities observed in more than one resonance mode. First, the electrically observed frequencies of resonance and antiresonance are corrected using the T- and L-type circuits, respectively. Secondly, whether the transducer is actually driven in the L- or T-effect is distinguished using the principle of least variance introduced in this study. Next, the inductance components of the circuit are re-estimated using this principle again, and finally other circuit components are also adjusted in a self-consistent manner.