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ABSTRACT: This paper presents a microelectromechanical system (MEMS) capacitive microphone fabricated by using a combination of surface and bulk micromachining techniques equipped with favorable integrated complementary metal-oxide semiconductor capability. Through the proposed equivalent circuit model for the packaged microphone, optimal diaphragm diameter, diaphragm thickness, backplate height, air gap, front chamber volume, back chamber height, and acoustic hole fraction have been determined by analyzing and simulating the capacitive microphone. Consequently, this design model can optimize choice of materials, microphone size, and microphone performance. All parameters for the analysis have been experimentally measured for the microphone. To verify our analysis, the microphone sensitivity has been experimentally measured by pulse electroacoustics with the software SOUND CHECK in an anechoic box. The simulation and experimental results for sensitivity of the microphone follow each other within a range of 2 dB. Moreover, the measured specifications indicate that the packaged microphone has notably high sensitivity ( -42±3 dB V / Pa at 1 kHz), low power consumption (≪250 μ A ) , high S/N ratio (≫55) , and low distortion (≪0.5%) .
Journal of Applied Physics 11/2008; · 2.17 Impact Factor
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ABSTRACT: The piezoelectric/piezomagnetic composite, PZT/Ni0.284Zn0.549Cu0.183Fe1.984O4, was fabricated by the mixed oxide method. The phase assemblage, piezoelectric strain constant and saturation magnetization were investigated. The results indicate that the PZT phase is compatible with Ni0.284Zn0.549Cu0.183Fe1.984O4 phase, and dense diphasic ceramic composites were obtained. It is found that piezoelectric strain constant decreases exponentially as the amount of doped piezomagnetic materials in the composite increases. Correspondingly, saturation magnetization of the composite also decreases with the increasing weight fraction of piezoelectric materials. Three reasons cause the results. First, the grain growth of piezomagnetic phase at the co-sintering temperature reduces grain size and continuity of the piezoelectric phase. Second, the pore size and porosity in composite increase dramatically with increasing amount of piezomagnetic phase. Third, the low resistivity of the composite prevents the poling process and reduces the piezoelectric strain constant. The tailoring of microstructure to achieve a high performance piezoelectric/piezomagnetic composite is proposed based on the analysis.
Journal of Materials Science 03/2005; 40(8):1979-1985. · 2.02 Impact Factor
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ABSTRACT: This study presents overall failure criteria for an infinite anisotropic solid containing multiple flaws subjected to a set of uniform applied loads. Based on the inclusion method, flaws are treated as elliptical inclusions where their elastic moduli are considered to be zero. The explicit expression of elastic fields is obtained for a cubic crystal multiply flawed solid through the use of the Mori-Tanaka mean field theory. The resulting expression is further utilized to find an interaction energy function between the applied loads and flaws. With this energy function, the energy release rates and critical stresses are acquired separately in a closed form for Mode I, II, and III. The closed forms for energy release rates and critical stresses reveal that they are a function of the aspect ratio and the volume fraction of flaws, the modes of the loading, and the material properties. As an illustrated numerical example, the energy release rates and the critical stresses that vary with both the aspect ratio and the volume fraction of the flaws in a cubic crystal material are discussed.
Journal of Materials Science 09/1999; 34(19):4665-4670. · 2.02 Impact Factor
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ABSTRACT: The magneto-electro-elastic Eshelby tensors that represent the stress, electric displacement, and magnetic induction in an inclusion resulting from the constraint of the surrounding matrix of piezomagnetic-piezoelectric composites are presented. The tensors provide the basis for analysis of the magneto-electro-elastic response of the composites and have numerous applications such as to the study of defects, overall properties of multiphase composites, and fracture mechanics, etc. For a three-dimensional transversely isotropic piezoelectric/piezomagnetic composite containing spheriodal inclusions, the number of nonzero Eshelby tensors is 41 while among them only 17 are independent. These independent tensors can be divided into three categories. The first category consists of those tensors related to the elastic response, the second involves those related to the piezomagnetic response, while the third includes elastic and magnetic interactive terms. Moreover, the magneto-electro-elastic Eshelby tensors are obtained in the closed forms when both constituents of the composite are transversely isotropic and shapes of the inclusion are elliptic, rod shaped, penny shaped, and ribbon like. © 1998 American Institute of Physics.
Journal of Applied Physics 06/1998; · 2.17 Impact Factor
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ABSTRACT: An inverse analysis method is proposed to simulate the A-scan ultrasonic nondestructive testing by means of back-propagation neural networks and computational mechanics. Both direct problem and inverse problem are considered in this study. In the direct problem, the frequency responses of a cracked medium subjected to an impact loading are calculated by the computational mechanics combining the finite element method with the boundary integral equation. The transient responses are obtained using fast Fourier transform. In the inverse problem, the back-propagation neural networks are trained by the characteristic parameters extracted from the various surface responses obtained from the direct problem. These surface responses carry a great deal of information about the structure of the medium with or without cracks. The trained neural networks are then utilized for the classification and identification of the crack in the medium to determine the type, location, and length of the crack.
Computer Methods in Applied Mechanics and Engineering.
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ABSTRACT: Explicit formulae are presented to assess the optimized fiber volume fraction for maximum magnetoelectric coupling effect exhibiting in the composite with piezomagnetic matrix reinforced by piezoelectric continuous fibers. The formulae consist of the analytical expressions for the effective properties of the composite and the magneto-electro-elastic Eshelby tensors. With these expressions, the closed-form solution for the magnetoelectric coupling effect, which is a new property existing in the piezoelectric–piezomagnetic composite even though neither of the individual phases exhibits such a property, is acquired. Furthermore, by taking the derivative of the close form for magnetoelectric coupling effect with respect to the fiber volume fraction as zero yields the optimized volume fraction of fibers analytically. The optimized fiber volume fraction shows that it is a function of the elastic properties of constituents, but not a function of the magnetic and electric properties.
International Journal of Engineering Science.
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Jin H. Huang
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ABSTRACT: This paper presents a micromechanics approach for examining the dynamic response of a laminated composite plate composed of randomly oriented fibres in each layer. The fibre orientation is described by a three-parameter probability density function to simulate a bias distribution. By utilizing the Mori–Tanaka mean-field theory, the effective elastic moduli of each lamina are assessed explicitly as a function of phase properties, volume fraction, orientation angles and fibre shape. Three special cases for fibre orientation have been discussed and the closed-form elastic moduli have been obtained. The resulting moduli are further applied to analyze the dynamic behaviour of laminated plates. Numerical examinations for a plate made of four layers of E-glass/epoxy fibre-reinforced laminates have been given. It is showed that the natural frequency for every fibre aspect ratio continually increases with respect to the extension of the fibre volume fraction and a higher aspect ratio leads to a higher natural frequency. Analysis results also indicate that the natural frequencies of the case in which all fibres are aligned and parallel to one direction are higher than those of the cases in which fibres are uniformly lying on a plane and a space.
Composites Part A Applied Science and Manufacturing 32(11):1573-1582. · 2.69 Impact Factor
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ABSTRACT: The post-buckling response of the functionally graded materials plate, subjected to thermal and mechanical loadings, is obtained analytically, using fast converging finite double Chebyshev polynomials. A functionally graded plate made of aluminum and alumina is considered for different kinds of boundary conditions. The volume fraction of the material constituents follows a simple power law distribution. The mathematical formulation is based on the first-order shear deformation theory and von-Karman nonlinear kinematics. Numerical results indicate that the critical temperature and buckling loads decrease with increase in volume fraction exponent of the FGM plate. It is observed that effect of the volume fraction exponent k up to 2 on the buckling and post-buckling response of the plate is more significant. The effects of plate aspect ratio on the post-buckling response of the plate for different volume fraction of the constituents of the materials are presented. It is observed that the buckling load and post-buckling response of the FGM plate is almost same for a plate aspect ratio more than or equal to 3.
Composite Structures.
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ABSTRACT: A first-order shear deformation theory is presented for studying the fully coupled response characteristics of hybrid composite and piezoelectric plates. The plates consist of a combination of fiber-reinforced composite laminates and piezoelectric layers and the response quantities of the plates are coupled by the mechanical field and the electric field. The theory, based on the three-dimensional linear piezoelectricity, assumes that the fundamental unknowns such as the displacement components and the electric potential can be expanded through the plate thickness coordinate. The governing equations are obtained in terms of the displacement and electric potential coefficients. Numerical studies of single piezoelectric layer plate and a nine-layered hybrid plate show that the proposed method is accurate to predict the response quantities for both mechanical and electric loading cases.
International Journal of Engineering Science.
