Nonlinear characterization of resonant piezocomposites 1-3 for NDT ultrasonic transducers

A comparative nonlinear characterization is carried out between the nonlinear behavior of a composite and the piezoceramic used to obtain it. This study is necessary for using the composite in power transducer applications, as in the Non Destructive Testing (NDT) by ultrasonic waves at high frequencies (300 kHz-800 kHz). Measurements of the losses and the resonator stiffness variations have also been done. Both these effects, as well as the possibility of the frequency hysteresis; show different behavior in the composites, since the increases in the ceramics are different from those in the composites. In this study two measure methods are used; principally the motional impedance increase with the motional current measurements. The results obtained are normalized in order to make them independent of the resonator size, and thus make the comparison between the composite and the ceramic easier. The figure of the mechanical loss tangent tg delta(m) versus the mean strain [S] shows that the losses can be greater in the ceramic than in the composite for soft ceramics. The dependence behavior of the losses versus the mean strain shows that hard composite transducers have lower losses and higher strains than the soft ones. However, these losses in hard composites are higher than those in the bulk ceramic transducers.