Characterization of complex material parameters for a piezoelectric ceramic disk in thickness extensional mode using a global optimization approach

The characteristics of piezoelectric materials are governed by three key parameters: piezoelectric, elastic, and dielectric constants, as well as their associated losses. This study introduces a global optimization method for determining the complex material parameters of piezoelectric ceramic disk resonators operating in the thickness extensional mode. The global minimum of the average relative error is identified by evaluating all local minima derived from multiple randomly selected initial conditions using the Levenberg – Marquardt algorithm. Using experimentally obtained admittance spectra, we fitted the material parameters using both the proposed global optimization technique and conventional nonlinear fitting functions in MATLAB. The results indicate that the proposed algorithm achieves higher fitting accuracy than the MATLAB functions, particularly when spurious peaks are present in the admittance spectra. Furthermore, the global optimization method exhibits lower sensitivity to initial parameter estimates, while the MATLAB functions demonstrate a strong dependence on initial values.