A model is proposed to predict the electroelastic moduli of 0-3 connectivity piezo-composites from which parameters such as longitudinal wave velocity and thickness mode coupling factor can be deduced. The composite, a polymer loaded with ceramic particles, is represented by a unit cell, and a matrix manipulation is shown to be a practical way to perform a generalization of the series and parallel analysis used for 2-2 connectivity composites. The anisotropy of the ceramic phase is taken into account, and its effect on the properties of the composite is shown. The model is then used to optimize composite performance and to choose the two constituents through comparison of results obtained using several commercial polymers and ceramics.

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Porous ceramics are of interest for ultrasonic transducer applications. Porosity allows to decrease acoustical impedance, thus improving transfer of acoustical energy to water or biological tissues. For underwater applications, the d h g h figure of merit can also be improved as compared to dense materials. In the case of high frequency transducers, namely for high resolution medical imaging, thick film technology can be used. The active films are generally porous and this porosity must be controlled. An unpoled porous PZT substrate is also shown to be an interesting solution since it can be used in a screen-printing process and as a backing for the transducer. This paper describes the fabrication process to obtain such materials, presents microstructure analysis as well as functional properties of materials. Modelling is also performed and results are compared to measurements. Finally, transducer issues are addressed through modelling and design of several configurations. The key parameters are identified and their effect on transducer performance is discussed. A comparison with dense materials is performed and results are discussed to highlight in which cases porous piezoceramics can improve transducer performance, and improvements are quantified.

A model previously developed for pure 0-3 connectivity piezocomposites has been extended to 3-3 connectivity. This matrix method allows the prediction of the effective electroelastic moduli of a piezocomposite according to its connectivity. It is used to optimize composite performance by choosing the optimal constituents for each phase. A simple combination of the results for 0-3 and 3-3 connectivities allows the effective proportion of 3-3 connectivity to be defined in highly loaded 0-3 piezocomposites. This theoretical analysis has been used to evaluate effective proportions of 3-3 connectivity in five composite samples. The values obtained are shown to be a function of the ceramic volume fraction and fabrication process. The results of this study were used to optimize the fabrication process.

The results of the evaluation of different effective parameters of 0-3 and 1-3 piezoactive composites are reported. For this, a matrix method previously developed for 2-2 connectivity is used and its application extended to 1-3 and 0-3 connectivities. Simulations are made with three perovskite-type ferroelectric ceramics and a vinylidene fluoride/trifluoroethylene piezoelectric polymer. Comparisons are shown and discussed between the different compositions, connectivities and other models and calculation methods. Particular attention is focused on factors leading to the appearance of extreme, discontinuity points and other features of effective parameters which are functions of volume concentrations of components (phases).