ABSTRACT This article describes a preliminary step taken in investigating the potential of vertic... more ABSTRACT 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 the force-voltage relationship for their comb design. Since the other four comb drives had the same comb design, the stiffnesses of their springs could be estimated from the displacements of their movable combs when voltages were applied to them.
Journal of Computational and Theoretical Nanoscience
ABSTRACT This paper presents a numerical model to externally induce deformation of a micro fiber ... more ABSTRACT This paper presents a numerical model to externally induce deformation of a micro fiber introduced inside a human lung pathway. The fiber contains ferromagnetic nano particles and has a cross-section of 0.4 × 0.22 μm and length of 20 μm. The fiber heating is achieved by applying an external high frequency magnetic field (2.6 kA/m, 1.0 MHz) to induce eddy currents in the ferromagnetic materials. Prediction of the thermal bending of the fiber requires a complicated multi-physics numerical modeling process. This finite element model is constructed in this paper to calculate the electromagnetic energy dissipation within the fiber. The deposited energy is coupled to a heat-transfer model to calculate the temperature rise. The distribution of temperature inside the fiber then allows prediction of fiber deformation. A tip displacement is up to 2.2 μm is achieved in the structural phase of the analysis. This is the first attempt to use thermal heating induced by a high frequency oscillatory magnetic field to cause deformation of a foreign Nano Electro-Mechanical-System (NEMS) in the human lunge aerosol system.
In the last two decades, multiple cracks are often found in aging aerospace and mechanical struct... more In the last two decades, multiple cracks are often found in aging aerospace and mechanical structures. The interaction and coalescence of multiple cracks may significantly affect the service lives of these aging structures. Knowledge of the behavior of interacting cracks is still limited. The calculation of the crack-tip stress intensity factor, SIF, along the interacting crack fronts is considered a major contribution for the application of any linear fracture mechanics model to investigate the growth life of these cracks. In this paper, a parametric study is presented for two parallel surface cracks in an infinite plate subjected to remote tension or to pure bending loads. This study focuses on constructing a finite element (FE) model that combines the submodeling technique with its ability to generate crack submodels of different lengths and depths, and a mesh generator that can build up a mesh grid based on the size, depth, and orientation of the interacting crack sub-models. The stress intensity factors for these cracks are calculated as a function of the crack front position, depth, shape, and plate thickness. In this paper, the values of the studied crack depth to length ratio, a/c, are 0.33, 0.5, 0.67, and 1.0. Where possible, a comparison of the 3-D with 2-D results is also considered.
Computer Methods in Biomechanics and Biomedical Engineering, Jun 6, 2008
Finite element analysis was implemented in three stages to design a piezoresistive, micro-electro... more Finite element analysis was implemented in three stages to design a piezoresistive, micro-electro-mechanical systems sensor array consisting of four-terminal sensors placed on deformable silicon diaphragms. This sensor array was used to retrofit the Contrel-Dubousset instrumentation in order to capture forces and moments applied by surgeons in real time during scoliosis correction surgery. Outputs from the sensor array have been designed to be compatible with a low-power wireless data transmission system that is currently being developed with a collaborating team in the biomedical industry. The designed sensor array is capable of resolving forces of up to 1000 N and moments of up to 4000 N mm in three dimensions during surgery. A process flow to produce the first prototyped version of this micro sensor with known performance characteristics is presented and tested. Acceptable correlation was found between the performance of the manufactured prototypes, numerical simulation and similar documented devices.
2005 International Conference on Mems Nano and Smart Systems, Jul 24, 2005
The use of finite element analysis to simulate the performance of a piezoresistive sensor is a te... more The use of finite element analysis to simulate the performance of a piezoresistive sensor is a technique that potentially allows for more efficient design and revision of MEMS devices. By comparing the performance of a FEA pressure sensor to that of an actual device as manufactured allows the capabilities of current simulation software in this field to be examined.
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.
The Canadian Journal of Chemical Engineering, Feb 1, 2006
... S., JC Chen and M. Elimelech, Coupled Model of Concentration Polarization and Pore Transport... more ... S., JC Chen and M. Elimelech, Coupled Model of Concentration Polarization and Pore Transport in Crossflow Nanofiltration, AICHE J. 47 ... Quddus, N., S. Bhattacharjee and W. Moussa, An Electrostatic-Peristaltic Colloidal Micropump: A Finite Elemental Analysis, J. Comput. ...
Post-operative complications can be attributed to technical aspects of surgery, yet no studies ha... more Post-operative complications can be attributed to technical aspects of surgery, yet no studies have investigated the mechanics behind commonly used incisions for total laryngopharyngectomies (TLP). This procedure, seen in head and neck cancer patients, necessitates free tissue transfer to construct a neo-pharynx, creating an inherently greater risk of complications. We sought to investigate the impact of neck incision location on these post-operative complications for TLP using finite element analysis (FEA). A nonlinear hyperelastic 2-D finite element model was used to evaluate the stress and strain along the incision line of two separate neck incision models commonly used for TLP: low-neck apron (LNA) incisions that incorporate the patient׳s tracheostoma and mid-neck apron (MNA) incisions that do not communicate with the tracheostoma. A constant displacement was applied to the incision to simulate normal neck extension experienced during the post-operative phase. Each neck incision...
The effect of convective relaxation is investigated on the electroosmotic flow in a slit microcha... more The effect of convective relaxation is investigated on the electroosmotic flow in a slit microchannel where one wall is charged and the other is uncharged. Two cases are considered, namely, moving charged wall with a stationary uncharged wall, and stationary charged wall with a moving uncharged wall. Analytical solutions obtained assuming Poisson-Boltzmann approximation for the two cases provide identical results. However, numerical solutions obtained for the two cases by solving the Poisson, Nernst-Planck, and Navier-Stokes equations show the variations of velocity profiles and shear stresses at the charged channel wall. The convective relaxation term, (i n u ), in the Nernst-Planck equations for ion transport, which renders the coupling between the Navier-Stokes and the Poisson equations, is dependent on motion of the charged wall. This implies that at the Poisson-Nernst-Planck level, the two cases are not identical and the solutions are not interchangeable. A similar situation exists in the calculation of the electrophoretic mobility of a charged particle, where the particle is considered stationary and fluid velocity evaluated at the far field is conceived as the particle mobility. This raises questions regarding the soundness of calculating the electrophoretic mobility of a charged particle using a particle fixed frame of reference.
The design of a stress sensor for a scoliosis surgery application is presented. Designed specific... more The design of a stress sensor for a scoliosis surgery application is presented. Designed specifically for detecting forces and moments placed on spinal hooks and screws used in scoliosis correction, the sensor is less 2mm in the largest dimension and less than 0.5mm in thickness. The operative range is approximately 1000MPa in shear and normal stress directions. Preliminary FEA simulation of a piezoresistive sensor incorporating these design constraints demonstrates that different output signals are produced as the sensor is subjected to shear and normal stresses. When the separate signal patterns from several sensors are combined, the hooks and screws will be able to resolve forces and moments in three dimensions.
Piezoresistive sensors designed with the help of coupled-field analysis give physicians real-time... more Piezoresistive sensors designed with the help of coupled-field analysis give physicians real-time feedback on applied loads during corrective spinal surgery.
Proceedings International Conference on MEMS, NANO and Smart Systems, 2003
ABSTRACT In this paper, we introduce a finite element procedure for modeling of shape memory allo... more ABSTRACT In this paper, we introduce a finite element procedure for modeling of shape memory alloy components used in smart structures' applications. The procedure addressed in this paper is based on sequential solution of two main finite-element procedures then combining them together after each iteration. The procedure is set up to be extensible to any geometrical shape and any SMA constitutive model. It is also proved capable of capturing different characteristics of the system as required such as structural and thermal non-linearity, variable SMA material properties and the ability to model coupled electrical, thermal and structural loading and boundary conditions. The procedure was applied to model an SMA wire and the results for the wire was compared with corresponding numerical and experimental results from literature for different loading cases and at different boundary conditions, the results showed very good agreement with both experimental and numerical results.
This paper presents the methodology and challenges experienced in the microfabrication, packaging... more This paper presents the methodology and challenges experienced in the microfabrication, packaging, and integration of a fixed-fixed folded spring piezoelectric energy harvester. A variety of challenges were overcome in the fabrication of the energy harvesters, such as the diagnosis and rectification of sol-gel PZT film quality and adhesion issues. A packaging and integration methodology was developed to allow for the characterizing the harvesters under a base vibration. The conditioning circuitry developed allowed for a complete energy harvesting system, consisting a harvester, a voltage doubler, a voltage regulator and a NiMH battery. A feasibility study was undertaken with the designed conditioning circuitry to determine the effect of the input parameters on the overall performance of the circuit. It was found that the maximum efficiency does not correlate to the maximum charging current supplied to the battery. The efficiency and charging current must be balanced to achieve a high output and a reasonable output current. The development of the complete energy harvesting system allows for the direct integration of the energy harvesting technology into existing power management schemes for wireless sensing.
ABSTRACT This article describes a preliminary step taken in investigating the potential of vertic... more ABSTRACT 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 the force-voltage relationship for their comb design. Since the other four comb drives had the same comb design, the stiffnesses of their springs could be estimated from the displacements of their movable combs when voltages were applied to them.
Journal of Computational and Theoretical Nanoscience
ABSTRACT This paper presents a numerical model to externally induce deformation of a micro fiber ... more ABSTRACT This paper presents a numerical model to externally induce deformation of a micro fiber introduced inside a human lung pathway. The fiber contains ferromagnetic nano particles and has a cross-section of 0.4 × 0.22 μm and length of 20 μm. The fiber heating is achieved by applying an external high frequency magnetic field (2.6 kA/m, 1.0 MHz) to induce eddy currents in the ferromagnetic materials. Prediction of the thermal bending of the fiber requires a complicated multi-physics numerical modeling process. This finite element model is constructed in this paper to calculate the electromagnetic energy dissipation within the fiber. The deposited energy is coupled to a heat-transfer model to calculate the temperature rise. The distribution of temperature inside the fiber then allows prediction of fiber deformation. A tip displacement is up to 2.2 μm is achieved in the structural phase of the analysis. This is the first attempt to use thermal heating induced by a high frequency oscillatory magnetic field to cause deformation of a foreign Nano Electro-Mechanical-System (NEMS) in the human lunge aerosol system.
In the last two decades, multiple cracks are often found in aging aerospace and mechanical struct... more In the last two decades, multiple cracks are often found in aging aerospace and mechanical structures. The interaction and coalescence of multiple cracks may significantly affect the service lives of these aging structures. Knowledge of the behavior of interacting cracks is still limited. The calculation of the crack-tip stress intensity factor, SIF, along the interacting crack fronts is considered a major contribution for the application of any linear fracture mechanics model to investigate the growth life of these cracks. In this paper, a parametric study is presented for two parallel surface cracks in an infinite plate subjected to remote tension or to pure bending loads. This study focuses on constructing a finite element (FE) model that combines the submodeling technique with its ability to generate crack submodels of different lengths and depths, and a mesh generator that can build up a mesh grid based on the size, depth, and orientation of the interacting crack sub-models. The stress intensity factors for these cracks are calculated as a function of the crack front position, depth, shape, and plate thickness. In this paper, the values of the studied crack depth to length ratio, a/c, are 0.33, 0.5, 0.67, and 1.0. Where possible, a comparison of the 3-D with 2-D results is also considered.
Computer Methods in Biomechanics and Biomedical Engineering, Jun 6, 2008
Finite element analysis was implemented in three stages to design a piezoresistive, micro-electro... more Finite element analysis was implemented in three stages to design a piezoresistive, micro-electro-mechanical systems sensor array consisting of four-terminal sensors placed on deformable silicon diaphragms. This sensor array was used to retrofit the Contrel-Dubousset instrumentation in order to capture forces and moments applied by surgeons in real time during scoliosis correction surgery. Outputs from the sensor array have been designed to be compatible with a low-power wireless data transmission system that is currently being developed with a collaborating team in the biomedical industry. The designed sensor array is capable of resolving forces of up to 1000 N and moments of up to 4000 N mm in three dimensions during surgery. A process flow to produce the first prototyped version of this micro sensor with known performance characteristics is presented and tested. Acceptable correlation was found between the performance of the manufactured prototypes, numerical simulation and similar documented devices.
2005 International Conference on Mems Nano and Smart Systems, Jul 24, 2005
The use of finite element analysis to simulate the performance of a piezoresistive sensor is a te... more The use of finite element analysis to simulate the performance of a piezoresistive sensor is a technique that potentially allows for more efficient design and revision of MEMS devices. By comparing the performance of a FEA pressure sensor to that of an actual device as manufactured allows the capabilities of current simulation software in this field to be examined.
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.
The Canadian Journal of Chemical Engineering, Feb 1, 2006
... S., JC Chen and M. Elimelech, Coupled Model of Concentration Polarization and Pore Transport... more ... S., JC Chen and M. Elimelech, Coupled Model of Concentration Polarization and Pore Transport in Crossflow Nanofiltration, AICHE J. 47 ... Quddus, N., S. Bhattacharjee and W. Moussa, An Electrostatic-Peristaltic Colloidal Micropump: A Finite Elemental Analysis, J. Comput. ...
Post-operative complications can be attributed to technical aspects of surgery, yet no studies ha... more Post-operative complications can be attributed to technical aspects of surgery, yet no studies have investigated the mechanics behind commonly used incisions for total laryngopharyngectomies (TLP). This procedure, seen in head and neck cancer patients, necessitates free tissue transfer to construct a neo-pharynx, creating an inherently greater risk of complications. We sought to investigate the impact of neck incision location on these post-operative complications for TLP using finite element analysis (FEA). A nonlinear hyperelastic 2-D finite element model was used to evaluate the stress and strain along the incision line of two separate neck incision models commonly used for TLP: low-neck apron (LNA) incisions that incorporate the patient׳s tracheostoma and mid-neck apron (MNA) incisions that do not communicate with the tracheostoma. A constant displacement was applied to the incision to simulate normal neck extension experienced during the post-operative phase. Each neck incision...
The effect of convective relaxation is investigated on the electroosmotic flow in a slit microcha... more The effect of convective relaxation is investigated on the electroosmotic flow in a slit microchannel where one wall is charged and the other is uncharged. Two cases are considered, namely, moving charged wall with a stationary uncharged wall, and stationary charged wall with a moving uncharged wall. Analytical solutions obtained assuming Poisson-Boltzmann approximation for the two cases provide identical results. However, numerical solutions obtained for the two cases by solving the Poisson, Nernst-Planck, and Navier-Stokes equations show the variations of velocity profiles and shear stresses at the charged channel wall. The convective relaxation term, (i n u ), in the Nernst-Planck equations for ion transport, which renders the coupling between the Navier-Stokes and the Poisson equations, is dependent on motion of the charged wall. This implies that at the Poisson-Nernst-Planck level, the two cases are not identical and the solutions are not interchangeable. A similar situation exists in the calculation of the electrophoretic mobility of a charged particle, where the particle is considered stationary and fluid velocity evaluated at the far field is conceived as the particle mobility. This raises questions regarding the soundness of calculating the electrophoretic mobility of a charged particle using a particle fixed frame of reference.
The design of a stress sensor for a scoliosis surgery application is presented. Designed specific... more The design of a stress sensor for a scoliosis surgery application is presented. Designed specifically for detecting forces and moments placed on spinal hooks and screws used in scoliosis correction, the sensor is less 2mm in the largest dimension and less than 0.5mm in thickness. The operative range is approximately 1000MPa in shear and normal stress directions. Preliminary FEA simulation of a piezoresistive sensor incorporating these design constraints demonstrates that different output signals are produced as the sensor is subjected to shear and normal stresses. When the separate signal patterns from several sensors are combined, the hooks and screws will be able to resolve forces and moments in three dimensions.
Piezoresistive sensors designed with the help of coupled-field analysis give physicians real-time... more Piezoresistive sensors designed with the help of coupled-field analysis give physicians real-time feedback on applied loads during corrective spinal surgery.
Proceedings International Conference on MEMS, NANO and Smart Systems, 2003
ABSTRACT In this paper, we introduce a finite element procedure for modeling of shape memory allo... more ABSTRACT In this paper, we introduce a finite element procedure for modeling of shape memory alloy components used in smart structures' applications. The procedure addressed in this paper is based on sequential solution of two main finite-element procedures then combining them together after each iteration. The procedure is set up to be extensible to any geometrical shape and any SMA constitutive model. It is also proved capable of capturing different characteristics of the system as required such as structural and thermal non-linearity, variable SMA material properties and the ability to model coupled electrical, thermal and structural loading and boundary conditions. The procedure was applied to model an SMA wire and the results for the wire was compared with corresponding numerical and experimental results from literature for different loading cases and at different boundary conditions, the results showed very good agreement with both experimental and numerical results.
This paper presents the methodology and challenges experienced in the microfabrication, packaging... more This paper presents the methodology and challenges experienced in the microfabrication, packaging, and integration of a fixed-fixed folded spring piezoelectric energy harvester. A variety of challenges were overcome in the fabrication of the energy harvesters, such as the diagnosis and rectification of sol-gel PZT film quality and adhesion issues. A packaging and integration methodology was developed to allow for the characterizing the harvesters under a base vibration. The conditioning circuitry developed allowed for a complete energy harvesting system, consisting a harvester, a voltage doubler, a voltage regulator and a NiMH battery. A feasibility study was undertaken with the designed conditioning circuitry to determine the effect of the input parameters on the overall performance of the circuit. It was found that the maximum efficiency does not correlate to the maximum charging current supplied to the battery. The efficiency and charging current must be balanced to achieve a high output and a reasonable output current. The development of the complete energy harvesting system allows for the direct integration of the energy harvesting technology into existing power management schemes for wireless sensing.
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Papers by Walied Moussa