Sharif Digital Repository

Vibration analysis of micro-structures has been a major topic in recent years. Among them micro-plates play an important role in micro- and nano-electromechanical systems (MEMS and NEMS), e.g. micropumps, micromirrors, and microresonators. Some experimental observations revealed the size-dependent mechanical behavior in micro-scaled structures. Because of the incapability of the classical continuum theory to interpret the experimentally-detected small-scale effects in mechanical behavior of micro-scaled systems, non-classical theories should be used to deal with micron and sub-micron structures. Couple stress theory is one of the non-classical theories with only one length scale parameter. A... 

Nowadays the combination of mechanical and electronic systems in small scales is gaining attention. Micro electro-mechanical systems are widely used in various industries such as car manufacturing and electronic chips. In these devices, the most important and useful mechanical structures are beams and plates. Therefore, investigating the mechanical properties of these structures in very small scales (micro and nano) is of great importance. Decreasing the size to these scales leads to the dependence of the behavior of these structures to size. Accordingly, some theories for prediction of these behaviors have been presented, one of which is the strain gradient theory. This theory is used in... 

Nano/Microelectromechanical systems have generated a great impact on industry and technology. There are many applications for these systems in micropumps, airbag accelerometers and inkjet printer heads. In theses systems mechanical and electrical fields are involved with each other, and complexities due to this involvement has prevented the scientific society from an effective tool for analysis of this systems in computational point of view. So the objective of this project is to use the Extended Kantorovich method to solve the equations of microplate deformation due to electrostatic actuation. This method is based on variational principals and it uses an initial guess function which doesn’t... 

In this project, a size-dependent formulation is presented for mechanical analyses of inhomogeneous micro-plates based on the modified couple stress theory. The modified couple stress theory as a non-classical continuum theory has the ability to consider the small size effects in the mechanical behavior of the structures.The material properties are supposed arbitrarily to vary through the thickness of the plate. The governing differential equations of motion are derived for functionally graded plates utilizing variational approach. Based on the derived formulation, the static and free-vibration behaviors as well as buckling analysis of a rectangular functionally graded micro-plate are... 

Based on the modified couple stress and Mindlin plate theories, a Levy type solution is presented for bending and vibration analysis of rectangular isotropic micro plates with simple supports at opposite edges and different boundary conditions at the other two ones. Modified couple stress theory is taken into account to capture the size effect and the governing equations are derived using Hamilton's principle, and solved by Levy solution and space-state method. The results are verified with the existing ones in the literature. As a benchmark, additional tables for vertical deflections and free vibrations of plate with various boundary conditions are presented  

Due to the features like small dimensions, low manufacturing cost and low power consumption, micro-electromechanical systems (MEMS) are widely utilized in engineering applications. Many experimental investigations have indicated that the mechanical behavior of constructive microelements of these systems isn’t predictable by classical continuum theory. Therefore, to analyze the behavior of microelements, the non-classical continuum theories which can capture size effects should be utilized. On the other hand, various experimental observations have confirmed that thermoelastic damping (TED) is a dominant source of energy dissipation in microelements, in contrast to the non-small parts and... 

Micro electromechanical systems (MEMS) such as sensors and actuators are gaining more popularity in recent years. These systems have different application in automation, medicine and other industries. Mechanical structures are governed by electrical systems in MEMS devices and this is one of the challenges of MEMS studies. Usually these systems made by one deformable beam or plate over a fixed substrate. Due to applied voltage between substrate and deformable plate or beam, the deformable plate deflects toward the fixed substrate. The voltage at which the system becomes unstableis called pull-in voltage. Pull-in voltage is the most important characteristics of MEMS beyond which pull-in takes...