THEORETICAL MODELING OF RESONANT MODES OF COMPOSITE ULTRASONIC TRANSDUCERS

Although a great deal of effort has been devoted to the modeling of co mposite piezoelectric materials, most of the earlier works are based o n the assumption that the structure of the composite relative to the w avelength is very fine, Such approximation cannot address the complete dynamic behavior of composites, In order to understand the overall ch aracteristics of composite ultrasonic transducers, a dynamic model was developed, in which the acoustic waves propagating in 2-2 composites along the thickness direction were analyzed by solving the coupled ela stic equations of the constituent phases, By neglecting the boundary c onditions of the free surfaces and simply taking the resonator thickne ss as half a wavelength, the resonant modes of the composite transduce rs as functions of aspect ratio of the ceramic plate elements and volu me fraction of ceramic phase can be calculated from this model, The th eoretical dispersion curves for the thickness mode and the lateral per iodical mode agree with the experimental results, The vibration distri bution in the ceramic and polymer phases at the resonant frequency as a function of the composite thickness as well as the volume fraction o f the ceramic phase are obtained, and through the discussion of the vi bration field the variation rule of the resonant frequency is well exp lained. For the resonant frequency the results of the isostrain model, the stopband resonance model, and the T-matrix model are consistent w ith the predictions made by this model under the special condition of very fine structure.