Imaging Surface Displacements of Piezoelectric Composites
Studies over the last ten years have shown that composite piezoelectrics can have a significant advantage over monolithic materials for a number of applications, especially in transducers used in medical imaging. In conventional ceramics the Poisson effect lowers the thickness mode displacement that can occur in wide specimens at high frequencies. This effect is sometimes referred to as self pinning. In one specific type of composite (type 1–3) the proper incorporation of an array of rods made from a piezoelectric ceramic such as PZT in an inactive matrix such as epoxy will form a composite piezoelectric with much lower self pinning than occurs in a monolithic ceramic. For medical applications composite transducer materials may consist of rods as small as 100 microns across and separated by about 25 microns. For lower frequency applications, the rods may be as large as 1.0 mm and be separated by 4.0 mm or more. Characteristics of piezoelectric composite materials and the conventions used in naming them are described in a review article by Smith .
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