Shear resonance mode decoupling to determine the characteristic matrix of piezoceramics for 3-D modelling

The determination of the characteristic frequencies of an electromechanical resonance is not enough data to obtain material properties of piezoceramics, including all losses, from complex impedance measurements. Besides, values of impedance around resonance and antiresonance frequencies are also required to determine the material losses. Uncoupled resonances are needed for this purpose. The shear plates used for the material characterization present unavoidable mode coupling of the shear mode and other modes of the plate. A study of the evolution of the complex material coefficients as the coupling of modes evolves with the change in the aspect ratio (lateral dimension/thickness) of the plate is presented here. These are obtained by Alemany et al. software. A soft commercial PZT ceramic was used in this study and a number of shear plates amenable to material characterization were obtained in the range of aspect ratios below 15. The validity of the material properties for 3-D modelling of piezoceramics is assessed by means of Finite Element Analysis (FEA), which shows that uncoupled resonances are virtually pure thickness driven shear modes.