![]() ![]() Such relaxation can be represented with complex piezoelectric coefficients or by a piezoelectric loss tangent. Piezoelectric relaxation has been observed in many materials, including ceramics, composites, and bone. Examples of piezoelectric materials include quartz, Rochelle salt, and lead titanate zirconate ceramics. ![]() Not all materials are piezoelectric only those materials lacking a center of symmetry on the atomic scale can be piezoelectric. In piezoelectric materials stress and strain are coupled to electrical field and polarization. Piezoelectricity is a coupled field effect as is thermoelasticity. Including a positive out-of-phase piezoelectric modulus results in reduced values of the predicted loss, which constitutes an improvement over earlier theories which predict losses exceeding measured losses by a factor greater than two. This loss depends on specimen geometry as a result of differences in effects related to the electrical boundary conditions. The piezoelectric contribution to the mechanical loss tangent of a piezoelectric solid is derived from its complex piezoelectric and dielectric coefficients. Shape dependent damping in piezoelectric solids, Rod Lakes, IEEE Trans. In making the detector for these studies, I have used the well known concept of negative capacitance in feedback circuits. ![]() and Saha, S., "A non-contacting electromagnetic device for the determination of in vivo properties of bone." Medical Instrumentation, 12 (2), 106-109, (1978). S., "A non-invasive technique for detecting stress waves in bone using the piezoelectric effect," IEEE Transactions on Biomedical Engineering, BME-24, 508-512, (1977). ![]()
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