Sharif Digital Repository

Micro grippers are essential tools for manipulation of objects in micron size. An electrostatic micro stepper-motor is used for actuating a proposed gripper mechanism and performance of this gripper is compared with the previous ones. The characteristic of the proposed mechanism is analyzed by simulation and it is shown that the designed gripper has the capability of doing manipulation in micron dimension with an acceptable performance  

In this paper, the classical and nonlocal elasticity are applied to investigate the deflection and instability of electrostatically actuated carbon nanotubes. The results are presented for different geometries and boundary conditions. They reveal that increasing radius and gap and decreasing length confine to increasing pull-in voltages of the carbon nanotubes. The results prove that application of the nonlocal elasticity theorem leads to stiffer structures with higher pull-in voltages. Thus, in order to obtain more accurate results about the mechanical and electromechanical behaviors of the carbon nanotubes, one should apply the nonclassical elasticity theories such as that applied in this... 

The paper deals with studying the deflection and pull-in voltages of the carbon nanotubes under electrostatic actuation with various dimensions and boundary conditions. The size-dependent behaviors of the carbon nanotubes (CNTs) are considered via application of the strain gradient theory. The results obtained from the strain gradient theory are compared to those estimated using the classical elasticity. The outcomes reveal that the classical elasticity theory underestimates the pull-in voltages of the carbon nanotubes and strain gradient theorem results in stiffer nano-structures with higher pull-in voltages. Increasing of the deflection due to the higher voltages increases the differences... 

We present a wideband tunable optical cavity based on electrostatic actuation. Over 60nm shift in wavelength is achieved by applying less than 1 Volt corresponds to a mechanical displacement of 30nm  

The paper deals with the investigation of nonlinear static and dynamic behaviors of electrostatically actuated carbon nanotubes with different geometries and boundary conditions. The deflection and pull-in properties are studied in detail in the presence of DC and combined DC+AC electrostatic voltages accompanying the interatomic interactions. The considered nano system can be applied in a wide range of nanoelectronics devices such as nano switches, nano resonators, nano transistors, nano capacitors and random access memories. Moreover, a useful mathematical model of the nano sensor application of the studied nano system to sense the stiffness of the nano particles is presented  

In this study tracking problem of tip of a micro cantilever, actuated by electrostatic, is investigated. Dynamic model of the system is a PDE. Using electrostatic actuation introduced significant nonlinearity in dynamic model of the system. Control goals are achieved by means of backstepping for SI and feedback linearization for MI system. Performance of control system is inspected for some assumptions and simplifications. The results are in according to numerical simulations  

Modified couple stress theory is a size-dependent theorem capturing the micro/nanoscale effects influencing the mechanical behaviors of the micro- and nanostructures. In this paper, it is applied to investigate the nonlinear vibration of carbon nanotubes under step DC voltage. The vibration, natural frequencies and dynamic pull-in characteristics of the carbon nanotubes are studied in detail. Moreover, the effects of various boundary conditions and geometries are scrutinized on the dynamic characteristics. The results reveal that application of this theory leads to the higher values of the natural frequencies and dynamic pull-in voltages  

The paper presents size-dependant mechanical behaviors of carbon nanotubes under electrostatic actuation using modified couple stress theory. The behaviors of the carbon nanotubes with different geometries and boundary conditions are studied in detail. The results reveal that application of this theory results in higher pull-in voltages for both cantilever and doubly clamped boundary conditions  

The paper deals with scrutinizing the vibration and dynamic pull-in behaviours of carbon nanotubes with different dimensions and boundary conditions. The strain gradient theory as a nonclassical elasticity theorem is applied in this research to compensate the limitations of the classical theories in predicting the mechanical behaviours of the micro- and nanostructures in general and carbon nanotubes, in particular under electrostatic actuation. The results reveal that the mechanical properties of carbon nanotube (CNTs) computed using the strain gradient theory differ significantly with those obtained from the classical theory. The strain gradient theory leads to higher stiffness and pull-in... 

In this paper the static deflection and pull-in instability of electrostatically actuated microcantilevers is investigated based on the strain gradient theory. The equation of motion and boundary conditions are derived using Hamilton's principle and solved numerically. It is shown that the strain gradient theory predicts size dependent normalized static deflection and pull-in voltage for the microbeam while according to the classical theory the normalized behavior of the microbeam is independent of its size. The results of strain gradient theory are compared with those of classical and modified couple stress theories and also experimental observations. According to this comparison, the... 

This paper studies the effect of Casimir force on the pull-in instability of electrostatically actuated torsional nano/micro actuators. Dependence of the actuator's pull-in angle and pull-in voltage on several design parameters are investigated and it is found that Casimir force can considerably reduce the stability limits of the torsional actuators. Nonlinear equilibrium equation is solved numerically and analytically using straight forward perturbation expansion method. It is observed that a fourth-order perturbation approximation can precisely model the behavior of a torsional actuator. The results of this paper can be used for safe and stable design of torsional nano/micro actuators  

This paper deals with investigation of fluid flow on static and dynamic behaviors of carbon nanotubes under electrostatic actuation. The effects of various fluid parameters including fluid viscosity, velocity, pressure and mass ratio on the deflection and pull-in behaviors of the cantilever and doubly clamped carbon nanotubes are studied. Furthermore, the effects of temperature variation on the static and dynamic pull-in voltages of the doubly clamped carbon nanotubes are reported. The results reveal that altering the fluid parameters significantly changes the mechanical and pull-in behaviors. Hence, the proposed system can be applied properly as a nano fluidic sensor to sense the various... 

The paper presents the effects of fluid flow on the static and dynamic properties of carbon nanotubes that convey a viscous fluid. The mathematical model is based on the modified couple stress theory. The effects of various fluid parameters and boundary conditions on the pull-in voltages are investigated in detail. The applicability of the proposed system as nanovalves or nanosensors in nanoscale fluidic systems is elaborated. The results confirm that the nanoscale system studied in this paper can be properly applied for these purposes  

This paper analyzes the deflection and pull-in behaviors of cantilever and doubly clamped carbon nanotubes (CNTs) under electrostatic actuation using the homotopy perturbation method. The effects of electrostatic force and interatomic interactions on the deflection and pull-in instabilities of CNTs with different lengths, diameters, and boundary conditions are investigated in detail. The results reveal that larger diameters and shorter lengths result in higher pull-in voltages. Moreover, CNTs with doubly clamped boundary conditions, in comparison with cantilever boundary conditions, are more resistant to pull-in  

This paper is concerned with the study of the oscillatory behavior of an electrostatically actuated microcantilever gyroscope with a proof mass attached to its free end. In mathematical modeling, the effects of different nonlinearities such as electrostatic forces, fringing field, inertial terms and geometric nonlinearities are considered. The microgyroscope is subjected to bending oscillations around the static deflection coupled with base rotation. The primary oscillation is generated in drive direction of the microgyroscope by a pair of DC and AC voltages on the tip mass. The secondary oscillation occurring in the sense direction is induced by the Coriolis coupling caused by the input... 

The objective of this work is to create an analytical framework to study the static pull-in and also equilibrium behavior in electrostatically actuated torsional micromirrors. First the equation governing the static behavior of electrostatic torsion micromirrors is derived and normalized. Perturbation method, the method of straight forward expansion is utilized to find the pull-in angle of the mirror. Comparison of the presented results with numerical ones available in the literature shows that the proposed second order perturbation expansion gives very precise approximations for the pull-in angle of the mirror. Then straightforward perturbation expansion method is used again to analytically... 

Micro/nano gyroscopes which can measure angular rate or angle are types of merging gyroscope technology with MEMS/NEMS technology. They have extensively used in many fields of engineering, such as automotive, aerospace, robotics and consumer electronics. There are many studies of a variety of gyroscopes with various drive and detect methods and different resonator structures in last years. In case of electrostatically actuated and detected beam micro/nano-gyroscopes, DC voltages are applied in driving and sensing directions and AC voltage is utilized in driving direction in order to excite drive oscillation. The intermolecular surface forces are especially significant when the gyroscopes are... 

Vibratory micromachined gyroscopes use suspending mechanical parts to measure rotation. They have no gyratory component that require bearings, and for this reason they can be easily miniaturized and batch production using micromachining methods. They operate based on the energy interchange between two modes of structural vibration. The objective of this paper is to study the oscillatory behavior of an electrostatically actuated vibrating microcantilever gyroscope with proof mass at its end. In the modelling, the effects of different nonlinearities, fringing field and base rotation are considered. The microgyroscope is subjected to coupled bending oscillations around the static deflection... 

In MEMS gyroscopes, it is essential to use matched resonance frequencies of the drive and sense vibrational modes for improving the sensitivity. For this end, the natural frequencies can be tuned by voltages. In this study, a new model is utilized to determine the natural frequencies of the doubly clamped beam microgyroscope. In the model, nonlinear electrostatic forces, fringing fields and mid-plane stretching of thebeam are considered. The system is actuated and sensed by electrostatic force and its natural frequencies and stiffness are detuned by DC voltages. The oscillatory problem of the gyroscope is analytically solved versus DC voltages for different design parameters. Copyright  

Micro-electro-mechanical systems (MEMS) such as sensors and actuators are rapidly gaining popularity in a variety of industrial applications. Usually these systems are constructed by a cantilever beam or plate along with a fixed substrate. The movable beam or plate deflects due to applied voltage between the plates. Pull-in voltage and contact time are the most important characteristic of these systems. Allowing the substrate to be movable in vertical direction pull-in voltage in comparison with the fixed substrate is expected to be much smaller. In this paper the pull-in voltage and the point at which pull-in takes place for a fully clamped microplate is evaluated. The nonlinear...