Walied Moussa - Academia.edu (original) (raw)

Papers by Walied Moussa

Journal of Micromechanics and Microengineering, 2011

A three-axis load detector has been designed and manufactured utilizing four piezoresistive senso... more A three-axis load detector has been designed and manufactured utilizing four piezoresistive sensors on a flexible silicon membrane. The detector was prototyped using bulk microfabrication techniques on a single-crystal silicon wafer and was designed to detect normal and shear loadings applied to the membrane. Finite element analysis and experimental calibration methods have been used to determine the shear and normal

Journal of Micromechanics and Microengineering, 2012

A compact packaging solution for microelectromechanical systems (MEMS) devices is presented. The ... more A compact packaging solution for microelectromechanical systems (MEMS) devices is presented. The 3D-integrated packaging solution was designed for the instrumentation of a spinal screw with a wireless sensor array, but may be adapted for a variety of applications. To achieve the compact package size, an unobtrusive through-silicon via (TSV) design was added to the microfabrication process flow for the MEMS

MEMS, NANO and Smart …, 2004

... YH Shang, W. Finlay*, W. Moussa 2-11 Mechanical Engineering, University of Alberta, Edmonton,... more ... YH Shang, W. Finlay*, W. Moussa 2-11 Mechanical Engineering, University of Alberta, Edmonton, AB, Canada Corresponding author e-mail ... Serdar Deger, KT, Dirk Boehmer, Tanja Schink, Jan Roigas, Andreas H. Wille, Volker Budach, Klaus-Dieter Wernecke, Stefan A. Loening ...

Microsystem Technologies

In this paper an overview of some of the challenges encountered in the fabrication and testing of... more In this paper an overview of some of the challenges encountered in the fabrication and testing of MEMS-based piezoelectric devices is presented. All major steps involved in developing piezoelectric MEMS, with particular focus on energy harvesters, are examined in three main sections: Microfabrication, Packaging and Testing. Although the main focus of this paper are the challenges involved with vibration based piezoelectric energy harvesters, most of these challenges apply to other piezoelectric MEMS devices. Various techniques reported for each individual fabrication step are categorized to provide a summary of required information. This allows new researchers to estimate the overall fabrication process, available resources and equipment to prepare accordingly. In addition, challenges of each technique are pointed out explicitly with solutions from literature and our own research. These challenges are typically overlooked in results-based technical papers. Some of the technical solu...

Journal of Micromechanics and Microengineering

This article describes a preliminary step taken in investigating the potential of vertical comb d... more This article describes a preliminary step taken in investigating the potential of vertical comb drives to be used as force-compensation mechanisms in interfacial force microscopes, by exploring the lower limit of the stiffness of the springs the comb drives can be fabricated with. The stiffness of their springs will affect the sensitivity of the microscope. Six vertical comb drives were fabricated for this study; the dimensions of their spring beams were chosen with the intention of giving them stiffnesses of three different orders of magnitude. During fabrication it was found that etching the tops of some of the teeth down to create the vertical offset between the combs can be done using only photoresist to mask the rest of the teeth. The stiffnesses of the fabricated springs were estimated by applying loads to them and measuring their resulting deflections. Weights were applied to the two comb drives with the stiffest springs. Voltages were also applied to them so as to determine ...

Proceedings International Conference on MEMS, NANO and Smart Systems, 2003

ABSTRACT For pt.I, see ibid., no.3, p.015-021 (2003). The finite element procedure proposed in pa... more ABSTRACT For pt.I, see ibid., no.3, p.015-021 (2003). The finite element procedure proposed in part I was successfully used to model a smart-self-damage control system consisted of SMA wires embedded in a polymeric matrix. A parametric study was performed to investigate the effect of various parameters on the performance of the system. It was found that increasing current density speeds up the recovery process although it adds more heat to the system. Also, it was found that increasing wire diameters although speeds up the recovery process as well, it might cause harmful effects to the system by increasing the difference in CTE forces effect. Increasing number of activated wires was found to be beneficial as it reduces the amount of phase transformation and forces required per wire, and increases system sensitivity to small cracks. It is suggested that convection coefficient not to be too low or to high, and the initial temperature of the system to be as close to the Austenite start temperature as possible. It was also found that SMA wires prestraining have negligible effects if its not too low.

2004 International Conference on MEMS, NANO and Smart Systems (ICMENS'04), 2004

The behavior of a Capacitive Micro Strain Gauge, CMSG, consisting of two parallel plates embedded... more The behavior of a Capacitive Micro Strain Gauge, CMSG, consisting of two parallel plates embedded in a dielectric media, is investigated analytically and numerically. Of the particular interests to this study is the application of the Capacitive Micro Strain Gauge in on-a-chip systems for biomedical and industrial health monitoring. A combination of analytical and numerical approaches is presented to extract

2010 IEEE International Ultrasonics Symposium, 2010

Capacitive micromachined ultrasound transducers (CMUTs) offer many potential advantages over piez... more Capacitive micromachined ultrasound transducers (CMUTs) offer many potential advantages over piezoelectric transducers, but have not yet seen widespread implementation. Possible reasons for this may include key issues of (1) long-term device reliability and (2) electrical safety issues associated with relatively high voltage electrodes on device surfaces which could present an electrical safety hazard to patients. A double SOI CMUT design

International Conference on MEMS, NANO, and Smart Systems, 2005

The modeling and simulation of fabricated 3D hybrid hydrogel microvalve using a commercial FE pac... more The modeling and simulation of fabricated 3D hybrid hydrogel microvalve using a commercial FE package is presented in this paper. A PDMS diaphragm is deflected to 197.5 μm. A stimulated hydrogel volume swelled to 465% of its original volume. Results of the finite element analysis are reported and a comparison to the fabricated model results is made.

Medical Imaging 2005: Ultrasonic Imaging and Signal Processing, 2005

Transducers based on piezoelectric crystals dominate the biomedical ultrasonic imaging field. How... more Transducers based on piezoelectric crystals dominate the biomedical ultrasonic imaging field. However, fabrication difficulties for piezoelectric transducers limit their usage for complex imaging modalities such as 2D imaging, high frequency imaging, and forward looking intravascular imaging. Capacitive micromachined ultrasonic transducers (CMUTs) have been proposed to overcome these limitations and they offer competitive advantages in terms of bandwidth and dynamic range. Further, the ease of fabrication enables manufacturing of complex array geometries. A CMUT transducer is composed of many electrostatically actuated membranes. Earlier analysis of these devices concentrated on an equivalent circuit approach, which assumed the motion of the membrane was approximated by a parallel plate capacitor. Finite element analysis is required for more accurate results. In this paper, we present the finite element model developed to evaluate the performance of the CMUTs. The model is composed of a membrane radiating into immersion medium. Electrostatic actuation is added on using electromechanical elements. Symmetry boundary conditions are imposed around the sidewalls of the finite element mesh, so that the model reflects the properties of a cell driven with the same phase as its neighboring membranes in an infinitely large array. Absorbing boundaries are implemented one wavelength away from the membrane to avoid reflections from the end of the finite element mesh. Using the model, we optimized the membrane radius, membrane thickness and gap height. Our optimized designed yielded a center frequency of 13 MHz with hundred percent bandwidth. A maximum output pressure of 20 kPascal per volt was obtained.

2005 International Conference on MEMS,NANO and Smart Systems, 2005

An electrokinetic model for microfluidic flow has been developed. The effects of surface waviness... more An electrokinetic model for microfluidic flow has been developed. The effects of surface waviness of the channel wall on a pressure-driven flow have been investigated. Current analysis considers a cylindrical microchannel of finite length, having two reservoirs at ends. Poisson-Nernst-Planck and Navier-Stokes equations constitute the electrokinetic model. Significant influence of the concentration boundary condition, at the reservoir exit plane, on the solution was observed. Solvent flux and channel length are two determining factors for the concentration distribution along the channel length. The effects of frequency and amplitude of the surface waviness were also investigated. Any irregularity in channel wall causes higher concentration and potential gradients across the channel.

2005 International Conference on MEMS,NANO and Smart Systems, 2005

The influence of thermal effects on the reliability of RF MEMS switches is investigated in this p... more The influence of thermal effects on the reliability of RF MEMS switches is investigated in this paper. Low power consumption and capacity to handle high power at very high frequency elevate the scope of RF MEMS in the field of satellite and mobile communication technology immensely. The reliability of these switches are still under consideration as they fail due to thermal stresses developed during operation. A significant temperature rise occurs while transmitting high power at high frequency. In this paper, we introduced design parameters and investigated their influence to improve the switch's resistance to acute thermal stresses. A three dimensional finite element model of RF MEMS switch was simulated. A current density model and a thermal model were coupled to calculate the current density, heat loss and temperature rise within the domain. The maximum frequency and power range that the switch can handle before buckling failure were estimated.

This study focuses on investigating the design parameters of lateral Electrostatic Comb-Drive act... more This study focuses on investigating the design parameters of lateral Electrostatic Comb-Drive actuators, where the effect of these parameters on the actuation performance is explored using Finite Element Analysis (FEA). This level of analysis is essential to the design process of system-on-a-chip MEMS applications, where a Comb-Drive can represent the main source of actuation within the chip system. Of particular interest to this study, is the application of the electrostatic Comb- Drive motor as a fluidic pump in on-a-chip systems used for drug delivery or in cooling of microprocessors used in space vehicles. The commercial FE package ANSYS is utilized to construct a robust comb-drive model and solve its multiphysics interaction problem using the Direct Coupled-Field Analysis. In this model, the thickness, gab and overlap between the Comb fingers are varied. The design of this model is also modulated to account for the change in the number of Comb fingers and the applied driving vo...

Journal of Pressure Vessel Technology-transactions of The Asme - J PRESSURE VESSEL TECHNOL, 1999

Smart Materials and Structures, 2007

In this paper, a finite element procedure is presented to model a SMA-based damage control system... more In this paper, a finite element procedure is presented to model a SMA-based damage control system that is applied to monitor and reduce the degradation in the bonding material of bonded composite patches used to maintain aerospace structure frames. A parametric study was performed to investigate the effect of various design parameters on the performance of the damage control system. Also, increasing the number of activated wires was found to reduce the amount of phase transformation and forces required per wire, which can increase the system sensitivity to small cracks. It is suggested that the difference between the initial temperature of the system and the austenite start temperature is minimized to achieve faster damage recovery. Furthermore, it was found that, by increasing the SMA wire diameter at constant power input, heat loss by conduction at the surface of the wires becomes the dominant effect on the recovery process; therefore, more time is needed to recover the crack as the wires' diameters are increased. Finally, the modulus of elasticity of the matrix material for the bonding is found to have a major effect on the damage recovery process.

Sensors, 2009

In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using ... more In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using three dimensional (3D) coupled multiphysics finite element (FE) analysis. The coupled field analysis involved three consecutive multiphysics interactions. The first interaction is characterized as a two-way sequential electromagnetic (EM)-thermal field coupling. The second interaction represented a one-way sequential thermal-structural field coupling. The third interaction portrayed a two-way sequential structural-electrostatic field coupling. An automated substructuring algorithm was utilized to reduce the computational cost of the complicated coupled multiphysics FE analysis. The results of the substructured FE model with coupled field analysis is shown to be in good agreement with the outcome of previously published experimental and numerical studies. The current numerical results indicate that the pull-in voltage and the buckling temperature of the RF switch are functions of the microfabrication residual stress state, the switch operational frequency and the surrounding packaging temperature. Furthermore, the current results point out that by introducing proper mechanical approaches such as corrugated switches and through-holes in the switch membrane, it is possible to achieve reliable pull-in voltages, at various operating temperatures. The performed analysis also shows that by controlling the mean and gradient residual stresses, generated during microfabrication, in conjunction with the proposed mechanical approaches, the power handling capability of RF MEMS switches can be increased, at a wide range of operational frequencies. These design features of RF MEMS switches are of particular importance in

Sensors, 2008

In this article, we report on the new design of a miniaturized strain microsensor. The proposed s... more In this article, we report on the new design of a miniaturized strain microsensor. The proposed sensor utilizes the piezoresistive properties of doped single crystal silicon. Employing the Micro Electro Mechanical Systems (MEMS) technology, high sensor sensitivities and resolutions have been achieved. The current sensor design employs different levels of signal amplifications. These amplifications include geometric, material and electronic levels. The sensor and the electronic circuits can be integrated on a single chip, and packaged as a small functional unit. The sensor converts input strain to resistance change, which can be transformed to bridge imbalance voltage. An analog output that demonstrates high sensitivity (0.03mV/µε), high absolute resolution (1µε) and low power consumption (100µA) with a maximum range of ±4000µε has been reported. These performance characteristics have been achieved with high signal stability over a wide temperature range (±50 o C), which introduces the proposed MEMS strain sensor as a strong candidate for wireless strain sensing applications under harsh environmental conditions. Moreover, this sensor has been designed, verified and can be easily modified to measure other values such as force, torque…etc. In this work, the sensor design is achieved using Finite Element Method (FEM) with the application of the piezoresistivity theory. This design process and the microfabrication process flow to prototype the design have been presented. Sensors 2008, 8 2643

Langmuir, 2003

A numerical solution of the nonlinear Poisson-Boltzmann equation based on finite element approxim... more A numerical solution of the nonlinear Poisson-Boltzmann equation based on finite element approximation is developed to assess the interaction force between two identical spherical particles located inside a straight cylindrical capillary. The interaction forces for constant potential and constant charge particle surfaces are calculated for different surface potentials on the cylinder wall, various particle sizes, and different cylinder radii. The interaction force between the spheres was affected significantly by the proximity of the charged cylinder wall, particularly for constant surface potential particles. The influence of the cylinder wall on the particle-particle interaction force was most pronounced when the particle radius was comparable to the cylinder radius. The results suggest that when the cylinder and the particle surfaces are like-charged (bearing the same sign of the charge or surface potential), the electrostatic repulsion between the two spherical colloids is considerably suppressed. Conversely, the interparticle repulsion is more pronounced when the cylinder wall is oppositely charged with respect to the particles. The possibility of inducing a force modulation between two charged particles by altering the surface potential of the confining cylindrical wall appears to be viable on the basis of these simulations.

Journal of Micromechanics and Microengineering, 2010

In this paper, the design of MEMS piezoresistive strain sensor is described. ANSYS®, finite eleme... more In this paper, the design of MEMS piezoresistive strain sensor is described. ANSYS®, finite element analysis (FEA) software, was used as a tool to model the performance of the silicon-based sensor. The incorporation of stress concentration regions (SCRs), to localize stresses, was explored in detail. This methodology employs the structural design of the sensor silicon carrier. Therefore, the induced strain

Journal of Pressure Vessel Technology-transactions of The Asme - J PRESSURE VESSEL TECHNOL, 1999

Journal of Micromechanics and Microengineering, 2011

A three-axis load detector has been designed and manufactured utilizing four piezoresistive senso... more A three-axis load detector has been designed and manufactured utilizing four piezoresistive sensors on a flexible silicon membrane. The detector was prototyped using bulk microfabrication techniques on a single-crystal silicon wafer and was designed to detect normal and shear loadings applied to the membrane. Finite element analysis and experimental calibration methods have been used to determine the shear and normal

Journal of Micromechanics and Microengineering, 2012

A compact packaging solution for microelectromechanical systems (MEMS) devices is presented. The ... more A compact packaging solution for microelectromechanical systems (MEMS) devices is presented. The 3D-integrated packaging solution was designed for the instrumentation of a spinal screw with a wireless sensor array, but may be adapted for a variety of applications. To achieve the compact package size, an unobtrusive through-silicon via (TSV) design was added to the microfabrication process flow for the MEMS

MEMS, NANO and Smart …, 2004

... YH Shang, W. Finlay*, W. Moussa 2-11 Mechanical Engineering, University of Alberta, Edmonton,... more ... YH Shang, W. Finlay*, W. Moussa 2-11 Mechanical Engineering, University of Alberta, Edmonton, AB, Canada Corresponding author e-mail ... Serdar Deger, KT, Dirk Boehmer, Tanja Schink, Jan Roigas, Andreas H. Wille, Volker Budach, Klaus-Dieter Wernecke, Stefan A. Loening ...

Microsystem Technologies

In this paper an overview of some of the challenges encountered in the fabrication and testing of... more In this paper an overview of some of the challenges encountered in the fabrication and testing of MEMS-based piezoelectric devices is presented. All major steps involved in developing piezoelectric MEMS, with particular focus on energy harvesters, are examined in three main sections: Microfabrication, Packaging and Testing. Although the main focus of this paper are the challenges involved with vibration based piezoelectric energy harvesters, most of these challenges apply to other piezoelectric MEMS devices. Various techniques reported for each individual fabrication step are categorized to provide a summary of required information. This allows new researchers to estimate the overall fabrication process, available resources and equipment to prepare accordingly. In addition, challenges of each technique are pointed out explicitly with solutions from literature and our own research. These challenges are typically overlooked in results-based technical papers. Some of the technical solu...

Journal of Micromechanics and Microengineering

This article describes a preliminary step taken in investigating the potential of vertical comb d... more This article describes a preliminary step taken in investigating the potential of vertical comb drives to be used as force-compensation mechanisms in interfacial force microscopes, by exploring the lower limit of the stiffness of the springs the comb drives can be fabricated with. The stiffness of their springs will affect the sensitivity of the microscope. Six vertical comb drives were fabricated for this study; the dimensions of their spring beams were chosen with the intention of giving them stiffnesses of three different orders of magnitude. During fabrication it was found that etching the tops of some of the teeth down to create the vertical offset between the combs can be done using only photoresist to mask the rest of the teeth. The stiffnesses of the fabricated springs were estimated by applying loads to them and measuring their resulting deflections. Weights were applied to the two comb drives with the stiffest springs. Voltages were also applied to them so as to determine ...

Proceedings International Conference on MEMS, NANO and Smart Systems, 2003

ABSTRACT For pt.I, see ibid., no.3, p.015-021 (2003). The finite element procedure proposed in pa... more ABSTRACT For pt.I, see ibid., no.3, p.015-021 (2003). The finite element procedure proposed in part I was successfully used to model a smart-self-damage control system consisted of SMA wires embedded in a polymeric matrix. A parametric study was performed to investigate the effect of various parameters on the performance of the system. It was found that increasing current density speeds up the recovery process although it adds more heat to the system. Also, it was found that increasing wire diameters although speeds up the recovery process as well, it might cause harmful effects to the system by increasing the difference in CTE forces effect. Increasing number of activated wires was found to be beneficial as it reduces the amount of phase transformation and forces required per wire, and increases system sensitivity to small cracks. It is suggested that convection coefficient not to be too low or to high, and the initial temperature of the system to be as close to the Austenite start temperature as possible. It was also found that SMA wires prestraining have negligible effects if its not too low.

2004 International Conference on MEMS, NANO and Smart Systems (ICMENS'04), 2004

The behavior of a Capacitive Micro Strain Gauge, CMSG, consisting of two parallel plates embedded... more The behavior of a Capacitive Micro Strain Gauge, CMSG, consisting of two parallel plates embedded in a dielectric media, is investigated analytically and numerically. Of the particular interests to this study is the application of the Capacitive Micro Strain Gauge in on-a-chip systems for biomedical and industrial health monitoring. A combination of analytical and numerical approaches is presented to extract

2010 IEEE International Ultrasonics Symposium, 2010

Capacitive micromachined ultrasound transducers (CMUTs) offer many potential advantages over piez... more Capacitive micromachined ultrasound transducers (CMUTs) offer many potential advantages over piezoelectric transducers, but have not yet seen widespread implementation. Possible reasons for this may include key issues of (1) long-term device reliability and (2) electrical safety issues associated with relatively high voltage electrodes on device surfaces which could present an electrical safety hazard to patients. A double SOI CMUT design

International Conference on MEMS, NANO, and Smart Systems, 2005

The modeling and simulation of fabricated 3D hybrid hydrogel microvalve using a commercial FE pac... more The modeling and simulation of fabricated 3D hybrid hydrogel microvalve using a commercial FE package is presented in this paper. A PDMS diaphragm is deflected to 197.5 μm. A stimulated hydrogel volume swelled to 465% of its original volume. Results of the finite element analysis are reported and a comparison to the fabricated model results is made.

Medical Imaging 2005: Ultrasonic Imaging and Signal Processing, 2005

Transducers based on piezoelectric crystals dominate the biomedical ultrasonic imaging field. How... more Transducers based on piezoelectric crystals dominate the biomedical ultrasonic imaging field. However, fabrication difficulties for piezoelectric transducers limit their usage for complex imaging modalities such as 2D imaging, high frequency imaging, and forward looking intravascular imaging. Capacitive micromachined ultrasonic transducers (CMUTs) have been proposed to overcome these limitations and they offer competitive advantages in terms of bandwidth and dynamic range. Further, the ease of fabrication enables manufacturing of complex array geometries. A CMUT transducer is composed of many electrostatically actuated membranes. Earlier analysis of these devices concentrated on an equivalent circuit approach, which assumed the motion of the membrane was approximated by a parallel plate capacitor. Finite element analysis is required for more accurate results. In this paper, we present the finite element model developed to evaluate the performance of the CMUTs. The model is composed of a membrane radiating into immersion medium. Electrostatic actuation is added on using electromechanical elements. Symmetry boundary conditions are imposed around the sidewalls of the finite element mesh, so that the model reflects the properties of a cell driven with the same phase as its neighboring membranes in an infinitely large array. Absorbing boundaries are implemented one wavelength away from the membrane to avoid reflections from the end of the finite element mesh. Using the model, we optimized the membrane radius, membrane thickness and gap height. Our optimized designed yielded a center frequency of 13 MHz with hundred percent bandwidth. A maximum output pressure of 20 kPascal per volt was obtained.

2005 International Conference on MEMS,NANO and Smart Systems, 2005

An electrokinetic model for microfluidic flow has been developed. The effects of surface waviness... more An electrokinetic model for microfluidic flow has been developed. The effects of surface waviness of the channel wall on a pressure-driven flow have been investigated. Current analysis considers a cylindrical microchannel of finite length, having two reservoirs at ends. Poisson-Nernst-Planck and Navier-Stokes equations constitute the electrokinetic model. Significant influence of the concentration boundary condition, at the reservoir exit plane, on the solution was observed. Solvent flux and channel length are two determining factors for the concentration distribution along the channel length. The effects of frequency and amplitude of the surface waviness were also investigated. Any irregularity in channel wall causes higher concentration and potential gradients across the channel.

2005 International Conference on MEMS,NANO and Smart Systems, 2005

The influence of thermal effects on the reliability of RF MEMS switches is investigated in this p... more The influence of thermal effects on the reliability of RF MEMS switches is investigated in this paper. Low power consumption and capacity to handle high power at very high frequency elevate the scope of RF MEMS in the field of satellite and mobile communication technology immensely. The reliability of these switches are still under consideration as they fail due to thermal stresses developed during operation. A significant temperature rise occurs while transmitting high power at high frequency. In this paper, we introduced design parameters and investigated their influence to improve the switch's resistance to acute thermal stresses. A three dimensional finite element model of RF MEMS switch was simulated. A current density model and a thermal model were coupled to calculate the current density, heat loss and temperature rise within the domain. The maximum frequency and power range that the switch can handle before buckling failure were estimated.

This study focuses on investigating the design parameters of lateral Electrostatic Comb-Drive act... more This study focuses on investigating the design parameters of lateral Electrostatic Comb-Drive actuators, where the effect of these parameters on the actuation performance is explored using Finite Element Analysis (FEA). This level of analysis is essential to the design process of system-on-a-chip MEMS applications, where a Comb-Drive can represent the main source of actuation within the chip system. Of particular interest to this study, is the application of the electrostatic Comb- Drive motor as a fluidic pump in on-a-chip systems used for drug delivery or in cooling of microprocessors used in space vehicles. The commercial FE package ANSYS is utilized to construct a robust comb-drive model and solve its multiphysics interaction problem using the Direct Coupled-Field Analysis. In this model, the thickness, gab and overlap between the Comb fingers are varied. The design of this model is also modulated to account for the change in the number of Comb fingers and the applied driving vo...

Journal of Pressure Vessel Technology-transactions of The Asme - J PRESSURE VESSEL TECHNOL, 1999

Smart Materials and Structures, 2007

In this paper, a finite element procedure is presented to model a SMA-based damage control system... more In this paper, a finite element procedure is presented to model a SMA-based damage control system that is applied to monitor and reduce the degradation in the bonding material of bonded composite patches used to maintain aerospace structure frames. A parametric study was performed to investigate the effect of various design parameters on the performance of the damage control system. Also, increasing the number of activated wires was found to reduce the amount of phase transformation and forces required per wire, which can increase the system sensitivity to small cracks. It is suggested that the difference between the initial temperature of the system and the austenite start temperature is minimized to achieve faster damage recovery. Furthermore, it was found that, by increasing the SMA wire diameter at constant power input, heat loss by conduction at the surface of the wires becomes the dominant effect on the recovery process; therefore, more time is needed to recover the crack as the wires' diameters are increased. Finally, the modulus of elasticity of the matrix material for the bonding is found to have a major effect on the damage recovery process.

Sensors, 2009

In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using ... more In this paper, the reliability of capacitive shunt RF MEMS switches have been investigated using three dimensional (3D) coupled multiphysics finite element (FE) analysis. The coupled field analysis involved three consecutive multiphysics interactions. The first interaction is characterized as a two-way sequential electromagnetic (EM)-thermal field coupling. The second interaction represented a one-way sequential thermal-structural field coupling. The third interaction portrayed a two-way sequential structural-electrostatic field coupling. An automated substructuring algorithm was utilized to reduce the computational cost of the complicated coupled multiphysics FE analysis. The results of the substructured FE model with coupled field analysis is shown to be in good agreement with the outcome of previously published experimental and numerical studies. The current numerical results indicate that the pull-in voltage and the buckling temperature of the RF switch are functions of the microfabrication residual stress state, the switch operational frequency and the surrounding packaging temperature. Furthermore, the current results point out that by introducing proper mechanical approaches such as corrugated switches and through-holes in the switch membrane, it is possible to achieve reliable pull-in voltages, at various operating temperatures. The performed analysis also shows that by controlling the mean and gradient residual stresses, generated during microfabrication, in conjunction with the proposed mechanical approaches, the power handling capability of RF MEMS switches can be increased, at a wide range of operational frequencies. These design features of RF MEMS switches are of particular importance in

Sensors, 2008

In this article, we report on the new design of a miniaturized strain microsensor. The proposed s... more In this article, we report on the new design of a miniaturized strain microsensor. The proposed sensor utilizes the piezoresistive properties of doped single crystal silicon. Employing the Micro Electro Mechanical Systems (MEMS) technology, high sensor sensitivities and resolutions have been achieved. The current sensor design employs different levels of signal amplifications. These amplifications include geometric, material and electronic levels. The sensor and the electronic circuits can be integrated on a single chip, and packaged as a small functional unit. The sensor converts input strain to resistance change, which can be transformed to bridge imbalance voltage. An analog output that demonstrates high sensitivity (0.03mV/µε), high absolute resolution (1µε) and low power consumption (100µA) with a maximum range of ±4000µε has been reported. These performance characteristics have been achieved with high signal stability over a wide temperature range (±50 o C), which introduces the proposed MEMS strain sensor as a strong candidate for wireless strain sensing applications under harsh environmental conditions. Moreover, this sensor has been designed, verified and can be easily modified to measure other values such as force, torque…etc. In this work, the sensor design is achieved using Finite Element Method (FEM) with the application of the piezoresistivity theory. This design process and the microfabrication process flow to prototype the design have been presented. Sensors 2008, 8 2643

Langmuir, 2003

A numerical solution of the nonlinear Poisson-Boltzmann equation based on finite element approxim... more A numerical solution of the nonlinear Poisson-Boltzmann equation based on finite element approximation is developed to assess the interaction force between two identical spherical particles located inside a straight cylindrical capillary. The interaction forces for constant potential and constant charge particle surfaces are calculated for different surface potentials on the cylinder wall, various particle sizes, and different cylinder radii. The interaction force between the spheres was affected significantly by the proximity of the charged cylinder wall, particularly for constant surface potential particles. The influence of the cylinder wall on the particle-particle interaction force was most pronounced when the particle radius was comparable to the cylinder radius. The results suggest that when the cylinder and the particle surfaces are like-charged (bearing the same sign of the charge or surface potential), the electrostatic repulsion between the two spherical colloids is considerably suppressed. Conversely, the interparticle repulsion is more pronounced when the cylinder wall is oppositely charged with respect to the particles. The possibility of inducing a force modulation between two charged particles by altering the surface potential of the confining cylindrical wall appears to be viable on the basis of these simulations.

Journal of Micromechanics and Microengineering, 2010

In this paper, the design of MEMS piezoresistive strain sensor is described. ANSYS®, finite eleme... more In this paper, the design of MEMS piezoresistive strain sensor is described. ANSYS®, finite element analysis (FEA) software, was used as a tool to model the performance of the silicon-based sensor. The incorporation of stress concentration regions (SCRs), to localize stresses, was explored in detail. This methodology employs the structural design of the sensor silicon carrier. Therefore, the induced strain

Journal of Pressure Vessel Technology-transactions of The Asme - J PRESSURE VESSEL TECHNOL, 1999