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

A comparative nonlinear characterization is carried out between the nonline ar behavior of a composite and the piezoceramic used to obtain it. This stu dy is necessary for using the composite in power transducer applications, a s in the Non Destructive Testing (NDT) by ultrasonic waves at high frequenc ies (300 kHz-800 kHz). Measurements of the losses and the resonator stiffne ss variations have also been done. Both these effects, as well as the possi bility of the frequency hysteresis; show different behavior in the composit es, since the increases in the ceramics are different from those in the com posites. In this study two measure methods are used; principally the motion al impedance increase with the motional current measurements. The results o btained are normalized in order to make them independent of the resonator s ize, and thus make the comparison between the composite and the ceramic eas ier. 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 t he 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.