An analytical model and a finite element based numerical model is presented to study the effects of fiber shape on the complete elastic, dielectric, and piezoelectric properties of a general 1–3 long-fiber “longitudinal” and “transverse” composite with elastically anisotropic and piezoelectrically active constituents. Six classes of piezoelectric composites, each with several prismatic and nonprismatic shaped fibers, in two widely different ceramic and polymer matrices are considered. It is demonstrated that (i) while the longitudinal material properties are insensitive to changes in the shape of the fiber phase, the transverse properties display a strong dependence on the shape of the fiber phase, particularly for the polymer-matrix composites; (ii) while the figures of merit such as the longitudinal piezoelectric coupling constant and the acoustic impedance do not demonstrate significant fiber shape effects, the transverse sensing ability of the polymer-matrix transverse composite is significantly influenced by the fiber shape with the composites with prolate shaped fibers providing the highest piezoelectric voltage constant.

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Building an interface between a nano-scale system and the larger-scale world is of utmost importance in implementing and testing the system utility. By taking advantage of the enzyme function at the nano-scale, our group is developing functional contact lenses integrating electronic biosensors that can detect and report the level of glucose on the surface of the eye. In order to verify the functionality of the contact lenses we have developed a physiologically accurate mechanical model of a human eye which allows sensor characterization under thin-film conditions, in a controlled chemical environment. The polymer eye model replicates the geometry of an eye, the blinking motion of an eyelid, as well as the tear fluid input and output microchannels. Liquid used in the experiments was prepared to closely mimic the chemical and mechanical properties of biological tear fluid.

A finite element model is developed to characterize the complete electromechanical response of piezoelectric composite materials with hollow fibers and to obtain a quantitative assessment of the relative effects of the introduction of porosity and a piezoelectric second phase in a piezoelectric matrix material. Fifteen characteristic composites are identified for each of the two model ceramic-based and polymer-based matrix systems ͑i.e., barium titanate and polyvinylidine difluoride͒ by systematically varying the volume fractions of porosity and the second phase ͑i.e., lead zirconate titanate͒. It is demonstrated that the fundamental properties and the piezoelectric figures of merit of the piezoelectric composites generally exhibit greater sensitivity to the presence of porosity in the electroelastically stiffer ceramic-based systems while the piezoelectrically active second phase has a dominant influence in the electroelastically compliant polymer-based systems.Piezoelectric materials with their unique electromechanical coupling characteristics have been recognized for their potential utility in many electromechanical device applications. 1 Toward optimizing their electrical and mechanical characteristics, several approaches toward modifying the structure of monolithic piezoelectric materials have been identified. By following an additive approach, wherein solid piezoelectrically active fibers are introduced within a compliant polymeric matrix, piezoelectric ͑solid fiber͒ composites with enhanced mechanical flexibility can be obtained. 2-9 By adopting a subtractive approach, wherein porosity is introduced within a solid piezoelectric material, porous piezoelectric materials with enhanced piezoelectric characteristics ͑i.e., improved piezoelectric coupling and reduced acoustic impedance͒ can be designed. [10][11][12][13][14][15][16][17][18][19] While the additive and subtractive approaches allow for the modification of a piezoelectric material in one dimension each, a few preliminary studies have examined the combined effects of additive and subtractive approaches wherein a second piezoelectric phase and porosity are introduced simultaneously within a matrix material to create composites with hollow fibers. 20 However, a comprehensive study that captures the complete electromechanical response of piezoelectric composites with hollow fibers is not yet available. Hence, the objectives of the present study are ͑i͒ to systematically characterize the elastic, dielectric, and piezoelectric properties of piezoelectric systems with hollow fibers and ͑ii͒ to assess the relative impact of porosity and the second piezoelectric phase on the effective performance characteristics of piezoelectric composites.In general, the complete electromechanical response of a piezoelectric material is captured by the coupled constitutive relationships which, in the linear elastic domain, are represented in a matrix format as 21 ͑1͒where ͓C E ͔ 6ϫ6 is the elasticity matrix, ͓e͔ 3ϫ6 the piezoelectric matrix, and ͓K ͔ 3ϫ3 the dielectric matri...