In this paper, we will present the experimental results of the microwave properties of BaTiO3 and BaTiO3-Pt composites. These composites materials were designed to increase the effective dielectric constant at microwave frequency. Three different platinum volume fractions were used, 3, 5 and 10%, to make BaTiO3-Pt composites, in addition to a pure BaTiO3 material. To characterize the BaTiO3-Pt composites, microwave measurements were conducted using the waveguide transmission measurements. The experimental results verify that it is possible to increase the dielectric constant using the conductor loading method.
KEYWORDS: Actuators, Ferroelectric materials, Ceramics, Dielectrics, Systems modeling, Data modeling, Composites, Capacitance, Control systems, Particles
The elastic behavior of porous piezo-laminates actuators is developed using modified classical lamination theory (CLT). The curvature is obtained for porous piezoelectric laminate with functionally graded microstructure (FGM) under applied voltage throughout its thickness. The porous FGM system consists of multi porous piezoelectric layers where the porosity gradient increases in the thickness direction. The porous FGM actuator is fabricated by co-sintering powder compacts of PZT and stearic acid in air. The electroelastic properties of each layer in the FGM systems were measured and used as input data in the analytical model to predict the FGM actuator curvature. Two optimization techniques are employed to enhance the performance of the porous FGM actuators: (1) Thickness of each layer in the porous FGM actuator, (2) Number of layer in the porous FGM actuator. The thickness of each layer in the FGM system is made to vary in a linear or non-linear manner by changing the FGM thickness exponent. Two, three, and five layer porous FGM systems are investigated to obtain the maximum curvature. The analytical predictions are found to agree well with the experimental measurements.
The mechanical behavior of a cylindrical, finger-like shaped, piezoelectric actuator with Functionally Graded Microstructure (FGM) was modeled by our analytical model and FEM. Different layers or lamina of different piezoelectric volume fraction in a polymer matrix were stacked to create FGM. Although the bimorph plate exhibit reasonably high out-of-plane displacement, induced stress field remains very high limiting its long life use. FGM piezoelectric plates have been developed to increase the out-of-plane displacement while reducing the stresses where the electro-elastic properties are graded through the plate thickness. Finger-like shape piezo actuators are developed where the properties are graded in the radial direction. FGM piezoelectric type actuator showed promising results in that the deflections to any direction can be obtained by manipulating the magnitude and direction of the applied electric field. Analytical modeling in computing the deflection of the finger-like actuator and stress field induced in each lamina was developed and compared to FEM modeling. The theory of cylindrical FGM is based on lamination theory in which the coordinate system is changed from the rectangular to cylindrical one and from infinite to finite plate.
A new type of piezoelectric actuator has been developed by combining two piezoelectric Functionally Gradient Material (FGM) composite laminates into a bimorph to produce an actuator with large out of plane displacements while having reduced mid-plane stresses. This combination of high displacement with reduced stress keeps the benefit of the bimorph while reducing one of its drawbacks. These properties are varied symmetrically about the mid-plane of the actuator with the entire actuator being poled in one direction through the thickness of the device. These deices are produced by stacking individual layers of piezoelectric fibers in a modified epoxy matrix with varying fiber volume fraction form layer to layer thereby leading to varying material properties through the thickness of the composite. The focus of this work has been to use the finite element method to first predict the material properties for individual piezoelectric fiber based layers using a symmetrical unit cell model, which allowed the inter-layer and intra-layer volume fractions to be varied independently reflecting the rectangular packing of fibers present in the actual devices. And, then to predict the behavior of the actual composite devices using these predicted properties.
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