Electroactive composites consisting of a ferroelectric ceramic in a polymer matrix have gained much interest as compliant electromechanical or pyroelectric sensors. Of the various theoretical models developed to understand the dielectric and electroactive properties of composites, the majority are based on a cube of unit dimensions representing the matrix with fractional inclusions representing the ceramic. Composite properties are dictated by the choice of constituent materials along with the intra-and inter-connectivity of the separate phases. A ceramic powder randomly dispersed in a polymer matrix is referred to as having 0-3 connectivity, i.e. the ceramic phase possesses no intra-connectivity throughout the composite in the x y, and z directions, whereas the polymer possesses full intraconnectivity in these directions. For thin composite films, where the ceramic grain size is comparable to the film thickness, or for composites with high ceramic volume content, the degree of ceramic c o~e~t i v i t y throughout the composite thickness will be enhanced over thick or low ceramic content composites, thus implying an amount of 1-3 connectivity within the composite. In order to investigate the properties of such composites, a cube model has been applied that deals with mixed 0-3 and 1-3 connectivity composites. This paper reports on the experimental and theoretical characterization of two different mixed connectivity composites, one with a polar polymer matrix and another with a nonpolar matrix.
~ODUCTIOIIOIOhe field of piezoelectric and pyroelectric com-T posites has grown from the need to combine the desirable properties of the existing electroactive materials to form new materials that exhibit enhanced properties over their single-phase counterparts. Fer-
Piezoelectric composites, consisting of a ferroelectric ceramic powder of calcium‐modified lead titanate dispersed in two different polymer matrices, viz. from vinylidene fluoride trifluoroethylene and an epoxy, have been fabricated. The composites show a mixed connectivity structure, and the results of electromechanical characterization are given. Thin films of these materials have been incorporated into surface mounted acoustic emission sensors and their frequency response and ability to detect plate waves, generated by a simulated acoustic emission source, has been examined. In situ transducers embedded into glass‐reinforced laminate plates have also been examined and have been shown suitable for acoustic emission sensors.
Aberdeen Proving Ground, Maryland 21 005-5069Mixed connectivity composites consisting of a ferroelectric ceramic powder of calcium modified lead titanate dispersed in a polymer matrix have been fabricated into piezoelectric bimorph sensors. The piezoelectric, dielectric and electromechanical coupling coefficients of these sensors have been measured and a full characterization of the electromechanical properties are reported. The suitability of these bimorph transducers as in-situ acoustic emission sensors, embedded into glassepoxy laminate plate like structures, has been investigated. A comparison of the performance of these sensors to those of previously investigated monomorph sensors fabricated from the same material has been made. SCIENCE, MARCH 1999, V d . 39, No. 3
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POLYMER ENGINEERING AND
Two different mixed connectivity composites, consisting of a ferroelectric ceramic powder of calcium modified lead titanate ( m a ) dispersed in a polymer matrix, have been fabricated and their ferroelectric properties have been investigated. Hysteresis measurements have been conducted on composites of FTCa with a polar polymer of polyvinylidene trifluoroethylene (P(VDF-TrFE)) and PTCa with a thermosetting epoxy resin to determine the coercive fields and remanent polarization of the two different composites. The composites show noticeable differences in their behavior during poling along with the values of their piezoelectric coefficients, with the composite of €TCa/P(VDF-'IYFE) showing enhanced piezoelectric activity over that of FTCa/epoxy. This paper reports on the polarkation properties and the microstructural nature of the composites.
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