New Designs and Analytical Modeling of Piezoceramic Polymer Composites

摘要

In this program, a dynamic model has been developed which yields nearly exactsolution to the field quantities in a 2-2 piezocomposite and in some special 1-3 piezocomposite. In the model, we avoided the approximations made in the earlier works and hence, can address the dynamic response of piezocomposites, such as the frequency of various modes, the mode coupling, the electromechanical coupling factor, the vibration profiles of composites under different external driving conditions and medium, etc. in a realistic and consistent manner. Especially, the model can directly address the issue of the effect of the thickness of a composite plate on the ultrasonic response of a composite transducer. For example, it is shown that for a composite plate, as long as the thickness resonance is below that of the lowest lateral mode, there is always a frequency near the thickness resonance where the vibration of profile of a composite is uniform. The effect of the aspect ratio is on the frequency bandwidth in which the polymer and ceramic vibrate in unison. The prediction based on the model on the lateral modes is also far beyond the earlier models and is in excellent accord with the experimental observation. The input acoustic impedance of a piezocomposite was also analyzed and experimentally investigated since it is related to the design of the matching and backing. From the results, it is shown that the thickness of the matching layer should be less than the conventional lambda/4. The effect of the acoustic loss of the polymer matrix is treated and it is shown that it has a strong effect on the dispersion curves in a composite, especially on the modes related to the lateral periodic structure.