Solid Freeform Encapsulation of 1-3-0 PZT Composites

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Two types of encapsulated lead zirconate titanate (PZT) composite hydrophones have been built and tested: a straight walled 1-3-0 PZT composite design and a curved wall 1-3-0 PZT design. The solid freeform fabrication (SFF) technique was used to construct the polymer encapsulation for the two prototype designs.In the 1-3 composites ‘soft’ PZT bars are embedded in a polymer matrix with a surrounding air gap. The polymer encapsulations were fabricated on a SFF stereolithography machine in order to enclose the gap and the PZT. Air gaps between the polymer and the PZT were shown to increase the hydrostatic piezoelectric response (dh) by absorbing the lateral hydrostatic stress. Because of the small percentage of PZT, these composites had a low density (neutral buoyancy), low dielectric constant, and, therefore, a lower dielectric constant, and a corresponding higher hydrostatic voltage coefficient, gh.The curved-wall composite design decoupled the PZT component more effectively from the lateral pressure, and thereby improved upon the direct piezoelectric effect. The large cap surface and the curved-wall further improved the amplification of the mechanical loading on the PZT element. The effective hydrostatic charge coefficient dh, reached about 1100 pC/N which amplified the d33 coefficient, and greatly enhanced the dhgh figure of merit.

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