Characterization of Giant Magnetostrictive Materials Using Three Complex Material Parameters by Particle Swarm Optimization

Complex material parameters that can represent the losses of giant magnetostrictive materials (GMMs) are the key parameters for high-power transducer design and performance analysis. Since the GMMs work under pre-stress conditions and their performance is highly sensitive to pre-stress, the complex parameters of a GMM are preferably characterized in a specific pre-stress condition. In this study, an optimized characterization method for GMMs is proposed using three complex material parameters. Firstly, a lumped parameter model is improved for a longitudinal transducer by incorporating three material losses. Then, the structural damping and contact damping are experimentally measured and applied to confine the parametric variance ranges. Using the improved lumped parameter model, the real parts of the three key material parameters are characterized by fitting the experimental impedance data while the imaginary parts are separately extracted by the phase data. The global sensitivity analysis that accounts for the interaction effects of the multiple parameter variances shows that the proposed method outperforms the classical method as the sensitivities of all the six key parameters to both impedance and phase fitness functions are all high, which implies that the extracted material complex parameters are credible. In addition, the stability and credibility of the proposed parameter characterization is further corroborated by the results of ten random characterizations.

Finite-size-effect on a very large length scale in NBT-based lead-free piezoelectrics

[Formula: see text][Formula: see text]TiO3-based lead-free piezoelectrics are considered for potential replacement of the lead-based commercial piezoceramics in high-power transducer applications. We have examined the role of grain size in influencing the structural-polar inhomogeneity of stoichiometric and off-stoichiometric [Formula: see text][Formula: see text]TiO3 (NBT), and its morphotropic-phase-boundary (MPB) derivative 0.94[Formula: see text][Formula: see text]TiO3-0.06BaTiO3 (NBT-6BT). Our study reveals that size effect comes into play in these systems on a very large length scale (on the scale of microns) considerably affecting its global structure and properties.