Sharif Digital Repository

In the past few decades piezoelectric materials have gained extensive applications in electromechanical devices and smart composite materials. Composite piezoelectric materials posses better piezoelectric effects as compared with the homogeneous piezoelectric materials. A special type of composite piezoelectric materials is multiphase spherical ensemble. Consider a set of (N + 1)-phase concentric spherical piezoelectric ensemble consisting of a core region encased by a sequence of nested spherical layers. Each phase is spherically isotropic, the polling direction of it, is radially oriented and it is also functionally graded piezoelectric material (FGPM) in the radial direction. This paper... 

The propagation behavior of Love wave in functionally graded magneto-electro-elastic half-spaces with a quadratic variation is addressed. The magneto-electromechanical coupling factor, the dispersion relations, electric potential, magnetic potential and displacement are obtained analytically for both magneto-electrically open and short conditions. The effect of gradient coefficient on phase velocity, group velocity and magneto-electromechanical coupling factor are plotted and discussed. Research on the wave propagation in magneto-electro-elastic materials is still very limited. This work provides us with a theoretical foundation to design and practically apply SAW devices with high... 

The axisymmetric contact problem of a rigid inclusion embedded in the piezoelectric biomaterial frictionless interface subjected to simultaneous far-field compression and electric displacement is addressed. With the aid of a robust technique, the coupled governing integral equations of this mixed boundary-value problem are reduced to decoupled Fredholm integral equations with a constraint equation. A useful limiting case for the contact problem of transversely isotropic bimaterials is addressed. The present solution is analytically in agreement with the existing solution for an isotropic bimaterial. Selected numerical results of interest to engineering applications including the radius of... 

Studying the behavior of piezoelectric materials containing self-assembled quantum wires and quantum dots is of great interest. This work is devoted to analytical and exact determination of the electro-elastic fields associated to quantum wires and quantum dots in piezoelectric mediums. The present work accounts for: (1) different shapes and orientations of quantum wires and quantum dots, (2) different types of anisotropy, and (3) high concentrations of quantum wires and quantum dots, that is, the corresponding interaction is considered properly. The presented solution is valid for general anisotropy and different shapes of quantum wires and quantum dots. In this work, periodic and... 

Smart materials and structures are among the research fields that have been expanded significantly in recent years. At a glance, a smart structure consists of sensors and actuators in which the recorded data are used to control the structural response against the applied lateral loadings, utilizing a specific control algorithm. In this regard, the Piezo-electric materials are widely used both as sensors and actuators in smart structures. In this thesis, the dynamic behavior of a simply supported Euler-Bernoulli beam that beside the effect of moving load or mass is subjected to support excitation is evaluated and the dynamic response of its mid-span is determined. Then, an extensive... 

In this research, a functionally graded microbeam bonded with piezoelectric layers is analyzed under electric force. Static and dynamic instability due to the electric actuation is studied because of its importance in micro electro mechanical systems, especially in micro switches. In order to prevent pull-in instability, two piezoelectric layers are used as sensor and actuator. A charge amplifier is used to supply input voltage of the actuator from the output of the sensor layer. Using Hamilton's principle and Euler-Bernoulli theory, equation of motion of the system is obtained. It is shown that the load type (distributed or concentrated) applied to the microbeam from the piezoelectric... 

A large number of bridges in Iran are deteriorating under long and heavy traffic loadings, while getting closer to the end of their design life time. Therefore, many of them have been exhibiting various problems such as excessive vibration or large deflection under the normal service loadings. So, mitigating traffic-induced bridge vibration and damages is necessary to extend their efficient period of serviceability. On the other hand, application of active and passive control devices in structural retrofitting have absorbed the attention of many engineers and researchers. In this work, the performance of an active control system made of piezoelectric actuators is investigated in reducing the... 

The analytical treatment of fracture analysis of a rigid disk inhomogeneity embedded in a piezoelectric medium is addressed. By virtue of the potential functions introduced by Ding for piezoelectric materials, the governing equations corresponding to this mixed boundary value problem are written as a set of triple integral equations. With the aid of some mathematical techniques, the obtained integral equations are reduced to a Fredholm integral equation and solved by a well-known numerical method. Some numerical results for the stress intensity factors at the tip of the penny-shaped crack are presented. The limiting case of an isotropic solid considered by Selvadurai is used for... 

The electro-elastic fields of nano-sized piezoelectric structures are considered based on the non-classical continuum theory. Nowadays because of increasing the application of piezoelectric materials in nano technology and exclusive properties of this kind of materials, they can use as the ingredients of electromechanical systems. Therefore, the determination of induced electro-mechanical fields is important. In this study the constitutive equations based on non-classical continuum theory and general anisotropy for the elastic, piezoelectric and dielectric tensors are considered, and the electromechanical fields are determined using the micromechanical method. Furthermore, the size effects... 

During the past decade, micromachining technology has become available to fabricate micron-sized mechanical parts. The miniaturization of almost all types of devices and systems is arguably a greater opportunity for commercial profit and beneficial technological advances (e.g., micromechanical, microfluidic, microthermal, micromagnetic, microoptical and microchemical). However, instead of the traditional evolutionary engineering effort to reduce size and power while simultaneously increasing the performance of such a diverse set of systems, the field of microelectromechanical systems (MEMS) represents an effort to radically transform the scale, performance and cost of these systems by... 

Imaging using ultrasonic waves is one of the common non-invasive diagnostic methods which have gained a lot of attention in recent years. The imaging resolution depends mainly on the center frequency of the ultrasonic transducer. High frequency ultrasonic imaging is mainly used in intravascular, skin and eye diseases and also in small animal studies. The main Goal of this thesis is to design two high frequency ultrasound imaging probes (between 10 to 50 MHz) which millimetric dimensions which can be used to image skin, eye or intravascular systems. In this thesis after discussing the science of high frequency ultrasound and reviewing the importance papers and books on the subject, two... 

The propagation of anti-plane surface waves in an inhomogeneous magneto-electro-elastic MEE) half-space with 6mm symmetry is studied. By virtue of both direct and indirect methods, the dispersion relations corresponding to two general cases of material properties variation are obtained. In the first case, it is assumed that all material properties involving MEE properties and density vary similarly in depth. Whereas, the second case considers different variations for MEE properties and density. The non-dispersive shear surface wave velocities pertinent to homogeneous MEE media under eight different surface electromagnetic boundary conditions are obtained as the limiting cases of the current...