Nonlinear mechanical behavior of piezocomposites for ultrasonic transducers

A comparative study is carried out between the nonlinear behavior of a comp osite and the piezoceramic used to obtain it. This characterization is nece ssary for using the composite in power transducer applications. A study of the losses and the resonator stiffness variations has also been done. Both these effects, as well. as the possibility of the frequency hysteresis, sho w different behavior in the composites, since the increases in the ceramics are different from those in the composites. In this study two measurement methods are used: principally the motional impedance increase with the moti onal current measurements. The results obtained are normalized in order to make them independent of the resonator size, and thus make the comparison b etween the composite and the ceramic easier. The figure of the mechanical l oss tangent tan delta(m) versus the mean strain [S] shows that the losses c an be greater in the ceramic than in the composite for soft ceramics. The d ependence behavior of the losses and stiffness variations versus the mean s train is studied for both resonators. (C) 2000 Elsevier Science B.V. All ri ghts reserved.