Sharif Digital Repository

Micro and nano electromechanical systems technology has experienced lots of progress in recent years. These systems are widely used in sensors and actuators due to their small size low weight and low energy consumption. Electrostatically actuation is one of the simplest and most prevalent methods of actuation and sensing in these systems. Electrostatically actuated micro and nanobeams are used in many devices such as micro and nano switches, resonators, signal filters, tunable capacitors, pressure and mass sensors, etc. Experimental results and measurements have shown that classical theories contain error in prediction of static and dynamic ... 

Nowadays, Specific applications of micro-mirrors in MEMS industry as actuartors have been found. In optical networks, these instruments are used to transfer data between optical fibers as an optical switch. According to the high desired precision for the relevant applications, many different aspects should be considered in controlling of these systems. Some of these criteria include: high speed response, overshoot elimination, minimal energy consumption by regulating the system inputs, minimal vibration, consideration of system uncertainities and some unmeasurable state variable, and system rubostness against environmental disturbances. In this research by addressing all of these... 

The use of carbon nanotubes in Nano-switches is the new technology employed in NEMS. Nano-switches can also perform as a micro-switch where nano-switches have longer life time, consume lower power and have smaller size with respect to micro-switches. As the dimensions get smaller, continuous models lose their accuracy and molecular methods should be utilized. Non local theory, is attempting to change the responses of continuum models assuaging them to the molecular results. In the current project, non local theory is used to rewrite the governing equations of nano tubes motion and the results are compared with the classical results. In this modeling, the axial force and the mid-plane... 

In recent decades, micro-electromechanical systems – MEMS – havefound extensive applications in applied science and engineering. One of the most popular MEMS actuatorsis micro Scratch Drive Actuator (SDA), which can be used in various applications, for instance: precision positioning, micro-chip displacement and rotating micromotors. Their outstanding capabilities such as: high controllability, precise step displacement, vast transportation domain and large force relative to their small size, have made them popular among researchers. Recently, a new generation of SDA is introduced, known as Bounce-back Scratch Drive Actuator or BSDA, which is fundamentally different in motion generation from... 

This paper presents a novel method for satellite attitude determination, using Electrostatically Suspended gyroscope (ESG). In this method, two superconducting rings rotated around a spherical rotor, which causes a variable flux in rings. So according to faraday’s law of induction, a voltage will be induced in the rings. Using this voltage and a kalman filter, attitude of satellite will be determined. ESG works precisely, when the rotor is maintain at the center of gyroscope cavity, between three pairs of circular electrode, so a backstepping control algorithm will be designed In order to this purpose. The performance of attitude determination using this ESG and designed control algorithm is... 

The important role of MEMS devices in optical system has initiated the development of a new class of MEMS called Micro-Opto-Electro-Mechanical systems (MEOMS), which mainly includes micromirrors and torsional microactuators. These devices have found variety of application in optical switches, display, micro scanning mirrors, optical cross-connects interferometry, spectroscopy, aberration correction and biomedical imaging. In this project, the dynamic behavior of electrostatic micromirrors under the effect of intermolecular surface forces and squeezed film damping are studied. The prior art published in the literature have mainly used pure torsion models. In a pure torsion, just the torsion... 

This research is concerned with the study of the static, dynamic, vibration and instability of an electrostatically actuated microbeam gyroscope considering geometric nonlinearities and electrostatic fringing fields. A vibrating microbeam gyroscope consists of a beam with a rigid (proof) mass attached to it and undergoes coupled flexural-flexural vibrations coupled with base rotation. The primary oscillation is generated in drive direction of the microbeam gyroscope by a pair of DC and AC voltages on the mass. The secondary oscillation occurring in the sense direction is induced by the Coriolis coupling caused by the input angular rate of the beam along its axis. In this case gyroscope acts... 

The need for better characterization systems (electron microscopes) and high resolution lithography systems, have made electron beams systems an interesting choice for research and development. In fact, all of the above applications require ideal electron beams (beams with minimum energy spread, maximum current density, and minimum spotsize), and electron-optic lenses (simple lenses with minimum aberration). In this research, theoretical aspects of electron emission and lens systems are reviewed. Field emission array (FEA) electron guns are introduced as electron sources with minimum energy spread, and a new simulation method is presented in order to minimize the complexity, and reduce the... 

In recent decades, the important role of MEMS devices in optical systems has initiated the development of a new class of MEMS called Micro-Opto-Electro-Mechanical Systems (MOEMS), which torsional micromirror is one of these systems. Among variety kinds of micromirrors the dual axis micromirror has hopefully application such as high quality projection display, free-space fiber optical (FSO) communications and endoscopic optical coherence topography. Dual axis micromirror could play a key role in FSO applications such as satellite-to-satellite separated by hundreds of kilometers, as where. In medical applications, micromirror must could be able to rotates θ_x and θ_y.about two axis x and... 

At a unit in zirconium production plant under the supervision of Soure Co. nuclear grade zirconium is produced. In the process it is required that hafnium get separated from Zirconium. Zirconium and hafnium separation are performed by nitric acid (4N) and hydrochloric acid (4N). This isolation environment is considerably corrosive and damaging for the equipment. Powder coating is one of the solutions to deal with the corrosion. To do so, electrostatic powder coating method was used for ECTFE polymer. After the coating, according to spark test, roughness analysis, thickness, elasticity and adhesion; temperature and time of the spraying and the spraying of top coating was determined. In... 

Vibrating ring gyroscopes (VRG) as MEMS devices are employed to micro scale systems for determination of the rotation rate and rotation speed of them. It is experimentally approved that micro scale structures behaves differently in comparison to macro scale systems, Therefore higher order continuum theories are required for modeling and analysis of these systems. In addition to that there is no comprehensive investigation on the dynamic performance of ring gyroscopes in the literature, In view of this in the present research the static and dynamic analysis of vibrating ring gyroscopes based on the strain gradient theory and the proposed finite element model of the gyroscope is performed. The... 

Electro Static discharge (ESD) in ICs can damage them. To prevent ICs from being damaged by ESD, protection circuits must be used. These protection circuits can be either designed on chip or on PCBs, to be more protective, both can be used. In this thesis, 8 kV ESD protection circuits according to human body model (HBM) in high voltage 0.18 um CMOS technology has been designed. In this thesis, in addition to study of electro static discharge phenomenon and its protection circuits, we have designed high voltage pads which are protected against 8 kV electro static discharge according to human body model. Finally these pads have been used in automotive ICs. In this thesis, firs we have... 

The important role of MEMS devices in optical systems has initiated the development of a new class of MEMS called Micro-Opto-Electro-Mechanical Systems (MOEMS), which mainly includes nano/micromirrors and torsional nano/microactuators. These devices have found variety of applications in optical switches, displays, micro scanning mirrors, optical cross-connects, interferometery, spectroscopy, aberration correction and biomedical imaging. In this project, the static and dynamic behavior of electrostatic nano/micromirrors under the effect of intermolecular surface forces and squeezed film damping are studied. The prior art published in the literature have mainly used pure torsion models. In a... 

Due to tremendous growth in usage of electron beams in different applications like VLSI, welding, chemical processes, Polymer industry and medical applications, precise study of these beams is of great importance. One of the most important parameters in studying electron beams characteristics is the phenomenon and effect of space charge. Although in most methods of analyzing electron optical systems, this effect is neglected, however in high density beams, this effect is bold. Space charge effect is due to interaction and electrostatic repulsion force between each of the electrons in the beam, which results in a change in shape and also divergence of beam. It is worth to mention that in... 

Researches in last decades have shown that biological cell’s functionality is related to the way of their deformation in response to forces and stresses exerted on the cell. Therefore designing microsensors with easy and economical applicationswhich are capable for determining cell mechanical properties seems to be logical. In this project using an electrostatically actuated microbeam with both clamped ends equipped with an indenter at midpoint to transmit force on the cell, proposed as a technique to apply axial load on the cell. Inthis research by implementation of approximated methods for solving nonlinear algebraic and differential equations, governing on microbeam deflection, it has... 

Today, the material selection process plays an important role in all engineering design branches. Generally, in transition from concept design to detail design, designers and engineers need to find specific materials to optimize performance of the systems. There are introduced nearly 80000 engineering materials up to now, i.e. metallic alloys, composite materials, plastics, ceramics, glass and etc. These large amounts of materials and the wide range of manufacturing processes causes engineers always seek new material selection methods. In material selection it’s require to consider advantages, restrictions, necessities of method and this phenomenon appear because of design problem that... 

Systems that are electrostatically actuated have found a vast role in MEMS application. This technology is used in optical systems, sensors, micro switches, and deformable mirrors. Raising the use of these systems in fields that needs better performance highlighted the need to accurate study of dynamics and control of electrostatic actuated systems in micro scale. This work is dedicated to design of an estimation and control system for a micro-beam that is actuated by electrostatic. After a comprehensive survey on pervious works that are done on dynamic, applications, fabrication and control of these systems dynamic of the system is fully derived. The environmental factors like fringing... 

Poly vinylidene fluoride (PVDF) as a fluorine polymer with acceptable thermal, chemical and physical property attractive create attention in membrane technology for water treatment application. However, with differential surface free energy between PVDF and water (∆G_s=30 mJ/m^2) PVDF polymer is divided as a hydrophobic materials, that is one of the basic problem for PVDF polymer. Due to its hydrophobicity the water molecules repulsion away from hydrophobic PVDF membrane surface as a spontaneous process with an entropy increasing and therefore pollutant molecules with hydrophobic functional group have tendency to adsorb onto membrane surface and dominate the boundary layer. In recent years... 

Charged particle lenses perform two types of operations. One purpose of lenses is to confine a beam, or maintain a constant or slowly varying radius. This is important in high-energy accelerators where particles must travel long distances through a small bore.A second function of lenses is to focus beams or compress them to the smallest possible radius. If the particles are initially parallel to the axis, a linear field lens aims them at a common point. Focusing leads to high particle flux or a highly localized beam spot. Focusing is important for applications such as scanning electron microscopy, ion microprobes, and ion-beam-induced inertial fusion. All modern lenses, have fully metal... 

Here we have used CFD to simulate the flow field around a DBD plasma active controller for flow control. Enhanced Electrostatic model is applied to model the plasma actuator, by solution of two elliptic equations to find electric field and charge density in whole flow field. So, it provided the body force by neglecting the magnetic forces in Lorentz equation. The body force is added to the momentum equation as a source term. A commercial software FLUENT is used for this simulation. To validate the algorithm, flow over a flat plate using DBD actuator is solved and results are compared with experimental and numerical results. Flow control around a cylinder with Reynolds number of 18,000 is...