Sharif Digital Repository

In this study, influences of intermolecular forces on dynamic pull-in instability of electrostatically actuated beams are investigated. Effects of midplane stretching, electrostatic actuation, fringing fields and intermolecular forces are considered. The boundary conditions of the beams are clamped-free and clamped-clamped. A finite element model is developed to discretize the governing equations and Newmark time discretization is then employed to solve the discretized equations. The results indicate that by increasing the Casimir and van der Waals effects, the effect of inertia on pull-in values considerably increases  

In this study, homotopy analysis method is used to derive analytic solutions to predict dynamic pull-in instability of electrostatically-actuated microsystems. The model considers midplane stretching, initial stress, distributed electrostatic force and fringing fields effect. Influences of different parameters on dynamic pull-in instability are investigated. Results are in good agreement with numerical and experimental findings. © 2009 Elsevier Ltd. All rights reserved  

Developing a transient fully-meshed model of coupled-domain microsystems is of paramount importance not only for accurate simulation and design but also for creating more accurate low-order or macro dynamic models. So in this paper, a complete nonlinear finite element model for coupled-domain MEMS devices considering electrostatic and squeeze film effects is presented. For this purpose, we use the Galerkin weighted-residual technique for developing the finite element model that capture the original microsystem's nonlinear behaviors, such as the structural dynamics, the squeeze-film damping, the electrostatic actuation and the geometric nonlinearity caused by inherent residual stresses. In... 

This paper presents a model to analyze contact phenomenon in microsystems, actuated by ramp voltages, which has applications in frequency sweeping. First-order shear deformation theory is used to model dynamical system using finite element method, while finite difference method is applied to model squeeze film damping. The model is validated by static pull-in results. The presented hybrid FEM-FDM model is utilized to compute values of contact time and dynamic behavior. Considering this model, effects of different geometrical and mechanical parameters on contact time are studied. The influence of imposing the additional reverse voltage on dynamic characteristics of the system is also... 

In this study, dynamic pull-in instability and snap-through buckling of initially curved microbeams are investigated. The microbeams are actuated by suddenly applied electrostatic force. A finite element model is developed to discretize the governing equations and Newmark time discretization is employed to solve the discretized equations. The static pull-in behavior is investigated to validate the model. The results of the finite element model are compared with finite difference solutions and their convergence is examined. In addition, the influence of different parameters on dynamic pull-in instability and snap-through buckling is explored  

This paper presents a model to analyze contact phenomenon in microsystems actuated by ramp voltages, which has applications in frequency sweeping. First-order shear deformation theory is used to model dynamical system using finite element method, while finite difference method is applied to model squeeze film damping. The model is validated by static pull-in results. The presented hybrid FEMFDM model is utilized to compute values of contact time and dynamic behavior. Considering this model, effects of different geometrical and mechanical parameters on contact time are studied. The influence of imposing the additional reverse voltage on dynamic characteristics of the system is also... 

In this study, nonlinear oscillations of microbeams, actuated by suddenly applied electrostatic force, are investigated. Effects of electrostatic actuation, residual stress, midplane stretching and fringing fields are considered in modeling. Galerkin's decomposition method is utilized to convert the governing nonlinear partial differential equation to a nonlinear ordinary differential equation. Homotopy analysis method is used to find semi-analytic solutions to the vibrations of microbeams. Convergence regions of the solution series are determined. Influences of increasing the voltage and midplane stretching on the frequency of vibrations are also studied. Results are in good agreement with... 

In this study, influences of intermolecular forces on the dynamic pull-in instability of electrostatically actuated beams are investigated. The effects of midplane stretching, electrostatic actuation, fringing fields, and intermolecular forces are considered. The boundary conditions of the beams are clamped-free and clamped-clamped. A finite-element model is developed to discretize the governing equations, and Newmark time discretization is then employed to solve the discretized equations. The static pull-in instability is investigated to validate the model. Finally, dynamic pull-in instability of cantilevers and double-clamped beams are studied considering the Casimir and van der Waals... 

In this study, the homotopy analysis method (HAM) is used to study dynamic pull-in instability in microbeams considering different sources of nonlinearity. Electrostatic actuation, fringing field effect and midplane stretching causes strong nonlinearity in microbeams. In order to investigate dynamic pull-in behavior, using Galerkin's decomposition method, the nonlinear partial differential equation of motion is reduced to a single nonlinear ordinary differential equation. The obtained equation is solved analytically in time domain using HAM. The problem is studied by two separate manners: direct use of HAM and indirect use of HAM in conjunction with He's Modified Lindstedt- Poincaré Method.... 

In this study, dynamic pull-in instability and snap-through buckling of initially curved microbeams are investigated. The microbeams are actuated by suddenly applied electrostatic force. A finite element model is developed to discretize the governing equations, and Newmark time discretization is employed to solve the discretized equations. The static pull-in behavior is investigated to validate the model. The results of the finite element model are compared with finite difference solutions and their convergence is examined. In addition, the influence of different parameters on dynamic pull-in instability and snap-through buckling is explored  

Different methods have been utilized to improve ultra-thin-film silicon solar cells, one of which is the proposed plasmonic structure. The output efficiency of this structure compared to smaller thicknesses needs to be studied and researched. In this paper, an ultra-thin structure of a silicon cell with two nanoparticles in the neighborhood tangential to the beginning and end of the cell has been made by considering a very small radius for these two nanoparticles in two inner surfaces, which causes a significant increase in current due to the plasmonic surface effects of the nanoparticles. The results indicate that, compared to the smaller volume of metal in the proposed structure, it causes... 

The left-hand side of the auroral hiss emission observed by Galileo has a frequency time profile shaped very similar to the funnel shape observed in the Earth's auroral region. This close similarity indicates that we can use the theory of whistler-mode propagation near the resonance cone to locate the emission source. The general characteristics of the whistler mode are discussed. Then the position of the emission source is investigated using a geometrical method that takes into account the trajectory of Galileo. Initially a point source is assumed. Then the possibility of a sheet source aligned along the magnetic field lines which are tangent to the surface of Io is investigated. Both types... 

In addition to perfectly steering the output concentration of a process network to an exogenous set-point, a desired synthetically implemented biological controller should be able to robustly maintain this regulated output in the face of the extrinsic disturbances and inherent uncertainties due to an evervarying environment besides the imprecise modeling. Such an ability, which is called robust perfect adaptation (RPA), can be achieved by integral feedback control (IFC). Answering how IFC is (biochemically) constructible in generally unknown synthetic networks has been a research focus in the community. One of these answers, which has been well investigated previously, is to utilize a simple... 

Vibrations of electrostatically-Actuated microbeams are investigated. Effects of electrostatic actuation, axial stress and midplane stretching are considered in the model. Galerkin's decomposition method is utilized to convert the governing nonlinear partial differential equation to a nonlinear ordinary differential equation. Homotopy perturbation method (i.e. a special and simpler case of homotopy analysis method) is utilized to find analytic expressions for natural frequencies of predeformed microbeam. Effects of increasing the voltage, midplane stretching, axial force and higher modes contribution on natural frequency are also studied. The anayltical results are in good agreement with the... 

In this paper, primary resonance of a double-clamped microbeam has been investigated. The Microbeam is predeformed by a DC electrostatic force and then driven to vibrate by an AC harmonic electrostatic force. Effects of midplane stretching, axial loads and damping are considered in modeling. Galerkin's approximation is utilized to convert the nonlinear partial differential equation of motion to a nonlinear ordinary differential equation. Afterward, a combination of homotopy perturbation method and the method of multiple scales are utilized to find analytic solutions to the steady-state motion of the microbeam, far from pull-in. The effects of different design parameters on dynamic behavior... 

In this study, static pull-in instability of electrostatically-actuated microbridges and microcantilevers is investigated considering different nonlinear effects. Galerkin's decomposition method is utilized to convert the nonlinear differential equations of motion to nonlinear integro-algebraic equations. Afterward, analytic solutions to static deflections of the microbeams are obtained using the homotopy perturbation method. Results are in excellent agreement with those presented in the literature  

In this paper, primary resonance of a double-clamped microbeam has been investigated. The Microbeam is predeformed by a DC electrostatic force and then driven to vibrate by an AC harmonic electrostatic force. Effects of midplane stretching, axial loads and damping are considered in modeling. Galerkin's approximation is utilized to convert the nonlinear partial differential equation of motion to a nonlinear ordinary differential equation. Afterward, a combination of homotopy perturbation method and the method of multiple scales are utilized to find analytic solutions to the steady-state motion of the microbeam, far from pull-in. The effects of different design parameters on dynamic behavior... 

In this paper, dynamic behavior and pull-in phenomenon of electrically actuated rectangular micro plates under the effect of squeeze-film damping and nonlinear electrostatic force is studied. Finite element method is implemented in order to drive weak formulations of linear and nonlinear micro plate equations of motion based on classical plate theory (CPT) (for thin microplates with moderate nonlinearity) and squeeze-film damping based on Reynolds nonlinear equation. Finally, an efficient reduced-order model contingent on singular value decomposition method (SVD) is used to study dynamic pull-in phenomenon. This model is constructed by the global basis functions achieved from a few runs of... 

This paper presents a model to analyze pull-in phenomenon and dynamics of multi layer microplates using coupled finite element and finite difference methods. Firstorder shear deformation theory is used to model dynamical system using finite element method, while Finite difference method is applied to solve the nonlinear Reynolds equation of squeeze film damping. Using this model, Pull-in analysis of single layer and multi layer microplates are studied. The results of pull-in analysis are in good agreement with literature. Validating our model by pull-in results, an algorithm is presented to study dynamics of microplates. These simulations have many applications in designing multi layer... 

As the number of distributed energy resources (DERs) increases, so would their influences on the power systems. Toward managing the intermittent nature of DERs, and providing market participation capability, the concept of virtual power plant (VPP) has been developed in the smart grid era. This paper proposes a novel offering strategy method for a VPP consisting of wind power generation along with storage capacity and flexible demand. In the proposed method, two different sources of uncertainty are addressed: stochastic method, applied in dealing with market price uncertainty, and information-gap decision theory (IGDT), incorporated in the offering model counting for wind power production...