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This thesis combines four manuscripts of which I am the first author. The first manuscript examines the phase separation process and related process parameters. This article provides detailed experimental results of the delivery and separation process. During the delivery of 40% Liquid-to-Powder-Ratio (LPR) paste, only 62[plus ou moins]3 % of the paste initially present in the 10-mL syringe could be injected. Thereafter, the remaining paste in the syringe was not amendable to injection suggesting the existence of liquid separation. The LPR of the extruded fraction of a 37% LPR paste ranged from 40.9[plus ou moins]2.0 % to 42.7[plus ou moins]2.1 %. On the other hand, a shortage of water content was measured for the paste left in the syringe. Furthermore, this shortage was gradual, ranging from 27.3[plus ou moins]1.9 % at the plunger side to 30.9[plus ou moins]1.6 % at the tip side. In addition, this article presents rheological measurements of the paste showing clearly that the limitation was not related to the viscosity of the paste but rather to the phase separation process. Specifically, the yield stresses were around 66[plus ou moins]2 Pa, 19[plus ou moins]2 Pa, and 8[plus ou moins]0 Pa for 40%, 50%, and 65% LPR suspensions, respectively. For the three studied LPRs, the viscosity rapidly dropped with an increase of shear rate to a level below 10 Pas. The second manuscript examines the possibility that fine particles migrate faster than large particles during injection, hence leading to a so-called size separation. This size separation process can be expected from the scientific literature, but had not been investigated prior to my study. In a way, the size separation is very similar to the phase separation process. An electrohydraulic system was used to control the delivery process. The result of this second study, showed no evidence of size separation. It was therefore concluded that the main mechanism underlying the limited injectability is the liquid phase filtration through the porous particles bed of the paste. The third manuscript examines the role of powder porosity ([epsilon]) and permeability. For that purpose, an electronically assisted device was used to measure the powder permeability. In this study, three powders were examined for comparison and better understanding. In addition, the powder permeability was correlated with the paste injectability. Adding 3 wt% of a fine nanosized powder to the [bêta]-TCP powder decreased the mixture permeability at a porosity of [varepsilon] = 67.5% from 6.4.10[exposant]-13 m[exposant]2 to 5.6.10[exposant]-13 m[exposant]2 and increased the injected volume fraction from 70.8[plus ou moins]1.9 % to 84.5[plus ou moins]0.9 %. The results showed clear evidence that the injectability can be improved by admixing different powders. However, permeability was not a strong predictor of the liquid separation phenomenon. The last manuscript provides a practical solution to reduce phase separation occurrence. For that purpose an ultrasonication process was suggested and applied during the delivery process to improve injectability. Specifically, sonicating the paste reduced agglomeration, decreased paste viscosity due to the shear thinning and therefore reduced phase separation. The result of the ultrasound assisted delivery was remarkably effective since it has been able to fully deliver highly concentrated paste, with minimal force exerted by hand. For instance, the injectable volume fraction of a 40% LPR paste injected with a 5-mL syringe increased significantly from 71.3[plus ou moins]0.5 % to 99.1[plus ou moins]0.9 % using 150 microns ultrasonic amplitude at a 20 kHz frequency. This chapter provides clear evidence that an electromechanical approach can be used to improve the injectability of a calcium phosphate paste. This thesis addresses an important limitation of calcium phosphate cements, namely phase separation during injection. This thesis also provides a scientific understanding and a practical solution for this problem. The electromechanical solution proposed here is one out of several possible solutions. Future work may focus on building numerical tools to help in the design of the powder and to understand the link between powder properties, rheology, syringe geometry and phase separation."--Résumé abrégé par UMI

Arrays of microelectrodes were used to apply forces to dielectric (soda lime glass) spheres in a thin (200 micrometer thick) layer of a dielectric liquid polymer (EOPN 8021). The microelectrodes were fabricated using standard photolithographic methods of evaporating and electroplating gold onto a glass substrate. The objective is to use the electric body forces in the sphere and the electric surface tractions on the sphere to position the spheres in a microscale pattern, in this case a square array in-plane. Three sizes of spheres were used: 30, 90, and 170 microns in diameter. The 30 micron spheres formed clusters associated with the regions of highest electric energy density, whereas single 90 micron spheres were located at the regions of highest electric energy density. The 170 micron spheres generally did not form patterns. The experiments indicated that free charges, either in the volume of the sphere and/or on the sphere surface, significantly influence the motion of the sphere. A finite element analysis was performed to study the electro-fluid mechanics. The liquid velocity and streamlines were plotted, and the force resultants due to the liquid acting on the sphere were calculated. Also, the electric body force and surface tractions resultants were calculated. In general, the forces on the sphere and the liquid velocity are in agreement with the experimental results.

We discuss the effect of elastic deformations on the electronic properties of atomically thin materials, with a focus on bilayer graphene and MoS2 membranes. In these materials distortions of the lattice translate into fictitious gauge fields in the electronic Dirac Hamiltonian that are explicitly derived here for arbitrary elastic deformations, including in-plane as well as flexural (out-of-plane) distortions. We consider bilayer graphene, where a constant fictitious gauge field causes a dramatic reconstruction of the low energy trigonally warped electronic spectrum inducing topological transitions in the Fermi surface. We then present results of ballistic transport in trigonally warped bilayer graphene with and without strain, with particular focus on noise and the Fano factor. With the inclusion of trigonal warping the Fano factor at the Dirac point is still F = 1/3, but the range of energies which show pseudo diffusive transport increases by orders of magnitude compared to the results stemming out of a parabolic spectrum and the applied strain acts to increase this energy range further. We also consider arbitrary deformations of another two-dimensional membrane, MoS2. Distortions of this lattice also lead to a fictitious gauge field arising within the Dirac Hamiltonian, but with a distinct structure than seen in graphene. We present the full form of the fictitious gauge fields that arise in MoS2. Using the fictitious gauge fields we study the coupling between electronic and mechanical degrees of freedom, in particular the coupling between electrons and excited vibrational modes, or vibrons. To understand whether these effects may have a strong influence on electronic transport in MoS2 we calculate the dimensionless electron-vibron coupling constant for all vibron modes relevant for electronic transport. We find that electron-vibron coupling constant is highly sample specific and that the longitudinal stretching mode is the vibron with the dominant coupling. This however reaches maximum values which are lower than those observed in carbon nanostructures.

Design and analysis of polysilicon and single crystal silicon gyroscopes have been carried out. Variations in suspension design have been explored. Designs that utilize in-plane and out-of-plane sensing are studied. Damping plays an important role in determining the sense response. Reduction in damping directly affects sensor performance. The various damping mechanisms that are prevalent in gyroscopes are studied. Perforations on the proof mass are observed to significantly reduce the damping in the device when operated in air. The effects of perforation geometry and density have been analyzed. The analysis results show that there is a two orders of magnitude reduction in damping of thick gyroscope structures with optimized perforation design. Equivalent circuit lumped parameter models have been developed to analyze gyroscope performance. The simulation results of these models have been compared with results obtained from SABER, a MEMS specific system level design tool from Coventorware. The lumped parameter models are observed to produce faster simulation results with an accuracy comparable to that of Coventorware Three gyroscopes specific to the PolyMUMPS fabrication process have been designed and their performance analyzed. Two of the designs sense motion out-of-plane and the other senses motion in-plane. Results of the simulation show that for a given damping, the gyro design with in-plane modes gives a resolution of 4º/s. The out-of-plane gyroscopes have two variations in suspension. The hammock suspension resolves a rate of 25º/s in a 200 Hz bandwidth while the design with folded beam suspension resolves a rate of 2º/s in a 12 Hz bandwidth. A single crystal silicon in-plane gyroscope has been designed with vertical electrodes to sense Coriolis motion. This design gives an order of magnitude higher Capacitance change for a given rotation in comparison to conventional comb-finger design. The effects of process induced residual stress on the characteristic frequencies of the polysilicon gyroscopes are also studied. The in-plane gyroscope is found to be robust to stress variations. Analysis results indicate that the tuning fork gyroscope with the hammock suspension is the most susceptible to compressive residual stress, with a significant drop in sensitivity at high stress values.

The advent of synchronized wide-area frequency measurements obtained from frequency disturbance recorders and phasor measurement units has presented the power industry with special opportunities to study power system dynamics. I propose the use of wide-area frequency measurements in identifying system disturbances based on power system post-event modal properties. In this work, power system dynamics are examined from an internal system energy viewpoint. Since an electric power system is composed of coupled rotating machines (large generators) which have air gap magnetic fields that are essentially static, or quasi-static, the power system may be modeled as a system with energy stored in quasi-static magnetic fields. The magnetic fields in the machines do change with time but may be modeled as static as far as wave propagation is concerned. The dynamic model that I develop treats this magnetic energy specifically as potential energy. Each rotating machine also contains an inertia due to the mass and motion of its rotor train and so each machine contains a rotational kinetic energy. Thus the internal system energy for a power system dynamic model may be considered to be contained in potential (magnetic) and kinetic (rotating mass) energies. This notion of internal energy lends itself to the use of a state-space model where each system state is associated with either a kinetic energy or a potential energy. An n-machine system would have a total of 2n states and would thus be a 2n-th order system. For many power system disturbances, I postulate that a linearized version of this model may be used to examine system natural response in terms of frequency and phasor measurements. The disturbances that I will investigate include generator and line outages. For any particular outage, the power system exhibits a very specific natural response in terms of its kinetic and potential energies. Kinetic energy in the system is directly related to each specific machine's rotational speed. I propose that the kinetic energy corresponds directly with bus frequencies through a linear transformation. Likewise magnetic field energy in each machine corresponds directly with a torque angle. The potential energy in the system thus corresponds directly with bus angles through a linear transformation. The primary focus of this work is on frequency deviation modal characteristics – specifically damped oscillation frequencies, mode shapes, and damping ratios. This work presents how specific disturbances on a power system will lead to specific oscillation frequencies in the deviation quantities and that these oscillation frequencies may be used to identify the disturbance. The idea of disturbance identification stems out of previous work done in locating disturbances by using a distributed parameter (DP) model of an electric power system. This DP model, which assumes a wave-like motion of frequency and phase quantities, was used to locate disturbances via a triangulation method. This present work, instead of using a DP model of the power system, assumes lumped parameters and focuses on disturbance identification strictly via modal characteristics – particularly oscillation frequency in the frequency deviations. This model is not concerned with geographic location but focuses on system topology, loading, and machine mass as lumped parameters. Advantages of disturbance identification include mainly reliability enhancements but can also be used in marketing applications. The state-space model used to realize this theory is verified via simulation using small, "academic" systems which should prove useful in classroom settings. Additionally the model is verified on a larger test system in order prove its validity and potential usefulness on large power systems. / Ph. D.

This thesis describes the development of a framework for computational modelling of electromechanics in the mouse, with the purpose of being able to integrate cellular and tissue scale observations in the mouse and investigate physiological hypotheses. Specifically, the framework is applied to interpret electromechanical coupling mechanisms and the progression of heart failure in genetically modified mice. Chapter 1 introduces the field of computational biology and provides context for the topics to be investigated. Chapter 2 reviews the biological background and mathematical bases for electromechanical models, as well as their limitations. In Chapter 3, a set of efficient computational methods for coupled cardiac electromechanics was developed. Among these are a modified Newton method combined with a solution predictor which achieves a 98% reduction in computational time for mechanics problems. In Chapter 4, this computational framework is extended to a multiscale electromechanical model of the mouse. This electromechanical model includes our novel cardiac cellular contraction model for mice, which is able to reproduce murine contraction dynamics at body temperature and high pacing frequencies, and provides a novel explanation for the biphasic force-calcium relation seen in cardiac myocytes. Furthermore, our electromechanical model of the left ventricle of the mouse makes novel predictions on the importance of strong velocity-dependent coupling mechanisms in generating a plateau phase of ventricular pressure transients during ejection. In Chapter 5, the framework was applied to investigate the progression of heart failure in genetically modified 'Serca2 knockout' mice, which have a major disruption in mechanisms governing calcium regulation in cardiac myocytes. Our modelling framework was instrumental in showing for the first time the incompatibility between previously measured cellular calcium transients and ventricular ejection. We were then able to integrate new experimental data collected in response to these observations to show the importance of beta-adrenergic stimulation in the progression of heart failure in these knockout mice. Chapter 6 presents the conclusions and discusses possibilities for future work.

Cardiac motion is a highly complex and integrated process of vital importance as it sustains the primary function of the heart, that is pumping blood. Cardiac tissue microstructure, in particular the alignment of myocytes (also referred to as fibre direction) and their lateral organisation into laminae (or sheets), has been shown by both experimental and computational research to play an important role in the determination of cardiac motion patterns. However, current models of cardiac electromechanics, although already embedding structural information in the models equations, are not yet able to fully reproduce the connection between structural dynamics and cardiac deformation. The aim of this thesis was to develop an electromechanical modelling framework to investigate the impact of tissue structure on cardiac motion, focussing on left ventricular contraction in rat. The computational studies carried out were complemented with a preliminary validation study based on experimental data of tissue structure rearrangement during contraction from diffusion tensor MRI.

La croissance formidable des dispositifs sans fils et autonomes (réseaux de capteurs, objets connectés…) voit actuellement son développement limité par les batteries qui présente une durée de vie limitée et ainsi soulève des problèmes de maintenance. Afin de palier à cette limitation, l’utilisation de l’énergie directement disponible dans l’environnement immédiat du dispositif, conduisant au concept de « récupération d’énergie », est une voie fortement explorée depuis une dizaine d’années. Ainsi, l’objectif de cette thèse a été de développer de nouvelles techniques et/ou d’utiliser de nouveaux principes de conversion afin de proposer des alternatives aux techniques de récupération d’énergie classiques. Dans un premier temps, l’optimisation de récupérateurs électrostatiques a été étudiée. Les performances de ces systèmes étant fortement liées à la variation de capacité, une structure fractale, permettant un accroissement important des surfaces en regard entre deux électrodes (et donc de la capacité) lorsque ces dernières sont proches, a été proposée et modélisée. Il est ainsi montrer un accroissement significatif des possibilités de récupération d’énergie ; ces dernières étant étroitement liées à l’amplitude de vibration du système. Le second axe de recherche de cette thèse s’est attelé à développer un modèle haut niveau simple mais précis pour les structure utilisant des polymères électrostrictifs fonctionnant en flexion. Une analyse énergétique a permis de mettre en place un modèle électromécanique masse-ressort-amortisseur couplé avec une source de courant contrôlée par les excitations mécaniques et électriques du système, permettant ainsi une conception plus aisée du microgénérateur. Enfin, la dernière partie de cette thèse s’est intéressée à la conversion d’énergie thermique utilisant la variation de perméabilité des matériaux ferromagnétiques, ouvrant de nouvelles possibilités de conversion de l’énergie. En particulier, une technique simple et autonome consiste à créer un champ magnétique de polarisation à l’aide d’un aimant, permettant une variation du flux magnétique lors d’un changement de température, qui peut être converti sous forme électrique à l’aide d’un bobinage. / This thesis has been devoted to electrostatic mechanical energy harvesting based on capacitors inspired by fractal geometry, to mechanical energy harvesting based on beams with electrostrictive polymers, and to thermal energy harvesting based on ferromagnetic materials. For electrostatic energy harvesting without electrets, interdigitated capacitors are usually applied as in-plane overlap varying and in-plane gap closing electrostatic generators. In consideration of the limit of aspect ratio for fingers in the capacitor, we would like to improve the capacitor configuration by taking advantage of self-similarity patterns. The concept is to gradually add fingers of smaller widths between original ones to form a mountain-shape capacitor. According to the different width ranges of capacitors, they are classified as of different orders whose performances vary with the vibration amplitude. Harvested energy over one cycle for capacitors of order 1, 2 and 3 has been demonstrated by theoretical and FEM results. In application, the order of capacitor needs to be properly chosen to maximize the harvested energy. Electrostrictive polymer (polyurethane) has been utilized along with a beam to perform mechanical energy harvesting. Two models have been analyzed: clamped-free beam with a polymer film attached at the clamped end, clamped-free bimorph beam. The simple model for electrostrictive devices under flexural solicitation is set up on the base of analysis of energy conversion and it shows that the electrostrictive system can be reduced to a simple spring-mass-damper system with a quadratic dependence with the applied voltage on the mechanical side and to a current source controlled by the applied voltage with a capacitive internal impedance on the electrical side. Experiments based on the clamped-free beam with a polymer film attached to the clamped end have been carried out to evaluate the mechanical to electrical conversion. The thermal energy generator is based on a ferromagnetic material, a magnet and a coil. As the magnetic permeability of ferromagnetic materials encounters drastic variation around the Curie temperature, the concept of the generator is to take advantage of the permeability variation caused by temperature decrease to generate sharp variation in magnetic flux which induces a current in the coil. According to theoretical results, the generated current is closely related to the temperature variation and the variation velocity. Experiments have been carried out on Ni30Fe of which the Curie temperature is 55 ºC. When the temperature decreases from 20.5 ºC to -42.4 ºC, the maximum power is about 4×10^(-7)W with the load to be 2 Ω.

Fluid damping arising from squeeze film flow of air or some inert gas trapped between an oscillating micro mechanical structure, such as a beam or a plate, and a fixed substrate often dominates the other energy dissipation mechanisms in silicon based MEM devices. As a consequence, it has maximum effect on the resonant response or dynamic response of the device. Unfortunately, modelling of the squeeze film flow in most MEMS devices is quite complex because of several factors unique to MEMS structures. In this thesis, we set out to study the effect of these factors on squeeze film flow. First we list these factors and study each of them in the context of a particular application, using experimental measurements, extensive numerical simulations, and analytical modelling for all chosen factors. We consider five important factors. The most important factor perhaps is the effect of rarefaction that is dominant when a device is vacuum packed with low to moderate vacuum, typical for MEMS packaging. The second problem is to investigate and model the effect of perforations which are usually provided for efficient etching of the sacrificial layer during fabrication of the suspended structures. The third problem is to consider the effect of non-uniform deflection of the structure such as those in MEMS cantilever beams and model its effect on the squeeze film. The fourth effect studied is the influence of different boundary conditions such as simple, fully open and partially closed boundaries around the vibrating structure on the characteristics of the squeeze film flow. The fifth problem undertaken is to analyze the effect of high operating frequencies on the squeeze film damping. In the first problem, the rarefaction effect is studied by performing experiments under varying pressures. Depending on the ambient pressure or the size of the gap between the vibrating and the fixed structure, the fluid flow may fall in any of the flow regimes, ranging from continuum flow to molecular flow, and giving a wide range of dissipation. The relevant fluid flow characteristics are determined by the Knudsen number, which is the ratio of the mean free path of the gas molecule to the characteristic flow length of the device. This number is very small for continuum flow and reasonably big for molecular flow. Here, we study the effect of fluid pressure on the squeeze film damping by carrying out experiments on a MEMS device that consists of a double gimbaled torsional resonator. Such devices are commonly used in optical cross-connects and switches. We vary fluid pressure to make the Knudsen number go through the entire range of continuum flow, slip flow, transition flow, and molecular flow. We experimentally determine the quality factor of the torsional resonator at different air pressures ranging from 760 torr to 0.001 torr. The variation of this pressure over six orders of magnitude ensures the required rarefaction to range over all flow conditions. Finally, we get the variation of the quality factor with pressure. The result indicates that the quality factor, Q, follows a power law, Q P-r, with different values of the exponent r in different flow regimes. To numerically model the effect of rarefaction, we propose the use of effective viscosity in Navier-Stokes equation. This concept is validated with analytical results for a simple case. It is then compared with the experimental results presented in this thesis. The study shows that the effective viscosity concept can be used effectively even for the molecular regime if the air-gap to length ratio is sufficiently small (h0/L < 0.01). However, as this ratio increases, the range of validity decreases. Next, a semianalytical approach is presented to model the rarefaction effect in double-gimballed MEMS torsion mirror. In this device, the air gap thickness is 80 µm which is comparable to the lateral dimension 400 µm of the oscillating plate and thus giving the air-gap to length ratio of 0.2. As the ratio 0.2 is much greater than 0.01, the conventional Reynolds equation cannot be used to compute the squeeze film damping. Consequently, we find the effective length of an equivalent simple mirror corresponding to the motion about the two axes of the mirror such that the Reynolds equation still holds. After finding the effective length, we model the rarefaction effect by incorporating effective viscosity which is based on different models including the one proposed in this paper. Then we compare the analytical solution with the experimental result and find that the proposed model not only captures the rarefaction effect in the slip, transition and molecular regimes but also couples well with the non-fluid damping in the intrinsic regime. For the second problem, several analytical models exist for evaluating squeeze film damping in rigid rectangular perforated MEMS structures. These models vary in their treatment of losses through perforations and squeezed film, in their assumptions of compressibility, rarefaction and inertia, and their treatment of various second order corrections. We present a model that improves upon previously reported models by incorporating more accurate losses through holes proposed by Veijola and treating boundary cells and interior cells differently as proposed by Mohite et al. The proposed model is governed by a modified Reynolds equation that includes compressibility and rarefaction effect. This equation is linearized and transformed to the standard two-dimensional diffusion equation using a simple mapping function. The analytical solution is then obtained using Green’s function. The solution thus obtained adds an additional term Γ to the damping and spring force expressions derived by Blech for compressible squeeze flow through non-perforated plates. This additional term contains several parameters related to perforations and rarefaction. Setting Γ = 0, one recovers Blech’s formulas. We benchmark all the models against experimental results obtained for a typical perforated MEMS structure with geometric parameters (e.g., perforation geometry, air gap, plate thickness) that fall well within the acceptable range of parameters for these models (with the sole exception of Blech’s model that does not include perforations but is included for historical reasons). We compare the results and discuss the sources of errors. We show that the proposed model gives the best result by predicting the damping constant within 10% of the experimental value. The approximate limit of maximum frequencies under which the formulas give reasonable results is also discussed. In the third problem, we study the effect of elastic modeshape during vibration on the squeeze film flow. We present an analytical model that gives the values of squeeze film damping and spring coefficients for MEMS cantilever resonators taking into account the effect of flexural modes of the resonator. We use the exact modeshapes of a 2D cantilever plate to solve for pressure in the squeeze film and then derive the equivalent damping and spring coefficient relations from the back force calculations. The relations thus obtained can be used for any flexural mode of vibration of the resonators. We validate the analytical formulas by comparing the results with numerical simulations carried out using coupled finite element analysis in ANSYS, as well as experimentally measured values from MEMS cantilever resonators of various sizes and vibrating in different modes. The analytically predicted values of damping are, in the worst case, within less than 10% of the values obtained experimentally or numerically. We also compare the results with previously reported analytical formulas based on approximate flexural modeshapes and show that the proposed model gives much better estimates of the squeeze film damping. From the analytical model presented here, we find that the squeeze film damping drops by 84% from the first mode to the second mode in a cantilever resonator, thus improving the quality factor by a factor of six to seven. This result has significant implications in using cantilever resonators for mass detection where a significant increase in quality factor is obtained only by using vacuum. In the fourth and fifth problem, the effects of partially blocked boundary condition and high operating frequencies on squeeze films are studied in a MEMS torsion mirror with different boundary conditions. For the structures with narrow air-gap, Reynolds equation is used for calculating squeeze film damping, generally with zero pressure boundary conditions on the side walls. This procedure, however, fails to give satisfactory results for structures under two important conditions: (a) for an air-gap thickness comparable to the lateral dimensions of the micro structure, and (b) for non-trivial pressure boundary conditions such as fully open boundaries on an extended substrate or partially blocked boundaries that provide side clearance to the fluid flow. Several formulas exist to account for simple boundary conditions. In practice, however, there are many micromechanical structures, such as torsional MEMS structures, that have non-trivial boundary conditions arising from partially blocked boundaries. The most common example is the double-gimballed MEMS torsion mirror of rectangular, circular, or hexagonal shape. Such boundaries usually have clearance parameters that can vary due to fabrication. These parameters, however, can also be used as design parameters if we understand their role on the dynamics of the structure. We take a MEMS torsion mirror as an example device that has large air-gap and partially blocked boundaries due to static frames. Next we model the same structure in ANSYS and carry out CFD (computational fluid dynamics) analysis to evaluate the stiffness constant K, the damping constant C, as well as the quality factor Q due to the squeeze film. We compare the computational results with experimental results and show that without taking care of the partially blocked boundaries properly in the computational model, we get unacceptably large errors. Subsequently, we use the CFD calculations to study the effect of two important boundary parameters, the side clearance c, and the flow length s, that specify the partial blocking. We show the sensitivity of K and C on these boundary design parameters. The results clearly show that the effect of these parameters on K and C is substantial, especially when the frequency of excitation becomes close to resonant frequency of the oscillating fluid and high enough for inertial and compressibility effects to be significant. Later, we present a compact model to capture the effect of side boundaries on the squeeze film damping in a simple rectangular torsional structure with two sides open and two sides closed. The analytical model matches well with the numerical results. However, the proposed analytical model is limited to low operating frequencies such that the inertial effect is negligible. The emphasis of this work has been towards developing a comprehensive understanding of different significant factors on the squeeze film damping in MEMS devices. We have proposed various ways of modelling these effects, both numerically as well as analytically, and shown the efficacy of these models by comparing their predictive results with experimental results. In particular, we think that the proposed analytical models can help MEMS device designers by providing quick estimates of damping while incorporating complex effects in the squeeze film flow. The contents of the thesis may also be of interest to researchers working in the area of microfluidics and nanofluidics.