عنوان مقاله [English]
Microelectromechanical systems (MEMS) are used in many fields of industry like automotive, aerospace and medical instruments. Among the various ways to operate the MEMS devices, the electrostatic actuator is the common mechanism, due to simplicity and fast response. Previous experiments have shown that the mechanical behavior of devices, which their sizes are in order of micron and submicron, are dependent to size dependency. They also have illustrated that by decreasing the dimension of structures, the size dependent effect is highlighted. In this case, the classical theories are not capable to predict the size dependent effects and mechanical behavior of the microstructures properly. Therefore, nonclassical theories such as modified couple stress and strain gradient theories have been introduced. It was shown that the modified couple stress theory can accurately predict the size dependent behavior of microstructures. There are some influences observed in the MEMS, that they have notable effects on the mechanical behavior of microswitches, such as fringing fields and large deflection. When the air gap is larger than the electrode's width of microswitches, the impacts of fringing fields and geometric nonlinearity significantly affect the mechanical behavior of the system. Therefore, neglecting the abovementioned effects leads to errors in the instability prediction of microswitches. Most of microswitches consist of a microcantilever with a proof mass and a fixed substrate which there is an air gap between them. By applying voltage to the system, the microcantilever starts to deflect into the fixed substrate. In this paper, pull-in instability and
deflection of MEMS switches are investigated based on the size dependent model. The nonlinear model is introduced by considering modified couple stress theory and fringing field effects as well as geometric nonlinearity. Utilizing the minimum total potential energy principle, the static equation of motion is derived in framework of the nonclassical theory. The effects of various parameters on static pull-in instability are studied and errors of considering the linear model or classical theories is calculated. The results show that the presented model is capable to predict the displacement and pull-in instability of the microswitches.