Awlad Hossain

Four-Terminal Square Piezoresistive Sensors for MEMS Pressure Sensing

The sensitivity of four-terminal piezoresistive sensors commonly referred to as van der Pauw (VDP) structure is investigated. The VDP sensor is considered to be fabricated on (100) silicon due to its potential application in MEMS (microelectromechanical systems) pressure sensors. The sensitivity of the VDP sensor may be affected by misalignment during the etching/diffusion process, the nonuniformity of piezoresistive coefficients through the sensor thickness, and pad size with respect to the sensor size. For this particular analysis, the effect of VDP stress sensitivity on variations in pad sizes and through-the-thickness -coefficient variation are studied as the effect of misalignment has already been investigated by researchers. Two three-dimensional (3D) finite element analysis (FEA) models are first developed for both traditional VDP resistance and equivalent four-wire bridge measurements. Then, the FEA models are validated with the closed form analytical solutions for point contacts (“zero” pad size) under different biaxial loads. Once the FEA models are validated, additional simulations are conducted to understand the influence of different parameters on the voltage measurements for an equivalent four-wire bridge configuration. It is observed that pad size and through-the-thickness nonuniformity in piezoresistive constants adversely affect the sensor sensitivity.

Teaching an Undergraduate Dynamics Course for Mechanical “Engineering Technology” Students: Successful Implementation for Students Learning

Applied mechanics is a branch of the physical sciences that describes the response of bodies (solids and fluids) or systems of bodies to external forces. It deals with the basic concepts of force, moment and its effects on the bodies at rest or in motion. It helps engineers or engineering students to understand how different bodies behave under the application of different types of loads. Mechanics can be broadly divided into two branches as called Statics and Dynamics. Statics deals with the bodies at rest whereas dynamics involves studies related to bodies in motion. In particular, the major emphasis of a dynamics course is to provide the details of the principles of applied mechanics or physics with the studies of motion of objects caused by forces or torques. It is an important course to develop a method of stripping a problem to its essentials and solving it in a logical, organized manner. In our institution, we offer a one-quarter long Dynamics class for Mechanical Engineering Technology (MET) curriculum. This course teaches several topics of solving dynamics problems that belong to Kinematics in Rectilinear & Angular Motions, Plane Motion, Kinetics, Work & Energy, and Impulse & Momentum. This course is designed for the MET students, who are more “hands-on” and have mathematical knowledge up to Calculus II. However, the prerequisite of this course is Tech Statics, not Calculus II. On the other hand, the prerequisites of Tech Statics are Physics and Pre-Cal-II. Therefore, MET students enrolled in Dynamics course solve problems using algebra rather than using calculus. As a whole, this course becomes challenging to convey different concepts of dynamics to our students within 10 weeks’ time frame. To facilitate the overall learning, the course instructors solve different interesting realistic dynamics problems, besides solving the conventional problems from the text book. Solving these realistic dynamics problem helps our students to enhance their conceptual understanding, and motivate them to pursue further in subsequent chapters. The paper presents in details several interesting problems related to different chapters and how they are linked to convey the targeted message related to course objectives. The paper also presents how different topics taught in this class fulfill the targeted course objectives, which are mapped with ABET Engineering Technology criteria. While a course in Dynamics could be a common offering in many universities, the authors of this paper presents the pedagogical approaches undertaken to successfully teach or implement the course objectives to the undergraduate engineering technology students.Copyright

Teaching an Undergraduate Introductory Finite Element Analysis Course: Successful Implementation for Students Learning

In our institution, we offer a one-quarter long finite element analysis (FEA) class for Mechanical Engineering curriculum. This course teaches computational methods to solve engineering problems using the state of art FEA software ANSYS. The coursework involves teaching fundamental mathematical theories to build the concept, analyzing simple structural problems using matrix algebra, and then solving a wide variety of engineering problems dealing with statics, dynamics, heat transfer and others. Students enrolled in this class solve varieties of problem by analytical approach, finite element approach using matrix algebra, using APDL (ANSYS Parametric Design Language) and ANSYS Workbench. As we are in quarter system, it is challenging to solve additional multidisciplinary complex engineering problems in regular class lectures. Therefore, students enrolled in this class are required to conduct a project solvable by student version of ANSYS within very short time. The project must have adequate engineering complexity conveying interesting knowledge or technical concepts to the entire class. Students have to prepare a brief written report, and share what they have learned with the entire class giving an oral presentation. While a course in FEA could be a common offering in many universities, the author of this paper presents the pedagogical approaches undertaken to successfully implement the course objectives to the undergraduate engineering students. The topics and techniques applied to teach different concepts of FEA to enhance students learning outcomes are addressed in this paper.Copyright

Factors Affecting Spherical Nano-Indentation of Thin Film/Substrate Systems

Great interests have been made over the last few years in the development of techniques to measure the mechanical properties of many engineering materials at the nano scale. In nano-indentation, a hard tip with known mechanical properties is pressed into a sample whose properties are unknown. The load, indentation depth and deformed area resulting from this test are then used to determine the desired mechanical properties, such as hardness and modulus. In this study, the computer-based finite element analysis (FEA) method is used to investigate factors effecting nano-indentation to ensure reliable measurement of thin film properties. First, the FEA method is used to predict the mechanical response of bulk aluminum (Al) using a spherical indenter. The numerical prediction is then compared with existing published results to validate the FEA modeling scheme. Once the model is validated, additional numerical analyses are conducted to investigate the response of Al-film deposited on different substrate materials. New mathematical formulations are proposed to determine the film modulus from nano-indentation test. The film modulus obtained from the new and existing mathematical formulations are also compared. Results obtained from this research can be used to characterize the mechanical properties of soft biological materials such as biofilm or tissue scaffolds.Copyright

Dynamic Analysis of a Microscale Cricket Filiform Hair Socket

Filiform hairs of crickets are of great interest to engineers because of their highly sensitive response to low velocity air currents. In this study, the cercal sensory system of a common house cricket has been analyzed. The sensory system consists of two antennae like appendages called cerci that are situated at the rear of the cricket’s abdomen. Each cercus is covered with 500–750 flow sensitive hairs that are embedded in a complex viscoelastic socket that acts as a spring -dashpot system and guides the movement of the hair. When the hair deflects due to the drag force induced on its length by a moving air-current, the spiking activity of the neuron and the combined spiking activity of all hairs are extracted by the cercal sensory system. The hair has been experimentally studied by few researchers though its characteristics are not fully understood. The socket structure has not been analyzed experimentally or theoretically from a mechanical standpoint. Therefore, this study aims to understand the socket’s behavior and its interaction with the filiform hair by conducting static analysis. First, a 3D Finite Element Analysis (FEA) model, representing hair and hair-socket, has been developed. Then the static analysis is conducted utilizing the appropriate load and boundary conditions based on the physical conditions that an insect experiences. These numerical analyses aid to understand the deformation mechanism the hair and hair-socket system. The operating principles of the hair and hair-socket could be used for the design of highly responsive MEMS devices such as fluid flow sensors or micro-manipulators.Copyright

Finite Element Analysis of Polyurethane Based Composite Shafts Under Different Boundary Conditions

Depending on the type of matrix materials, composites can be broadly divided into three different major classifications: Organic-matrix composites (OMC), metal-matrix composites (MMC), and ceramic-matrix composites (CMC). OMC can be further sub-classified into polymer-matrix composites (PMC) and carbon-matrix composites or carbon-carbon composites. In this paper the main objective is to focus on polyurethane based PMC composites. Polyurethane is one of the widely used polymer matrix materials. It has diversified applications, easily available and cheap. In this computational study a composite shaft with a core made of matrix material completely wrapped around by a woven fiber cloth with a very strong bonding between core and fibers is considered. Three different types of woven fibers: fiber glass, Kevlar 49, and carbon fibers, are considered. A woven fabric is the interlocking or weaving of two unidirectional fibers. This configuration is often used to produce curve surfaces because of the ease with which it could be placed on and conform to curved surfaces. Authors had fabricated these three composites in their in-house laboratory. They had also experimentally measured the mechanical properties of these composites using 3-point bending test which already been published.In this current study finite element analyses has been performed for the modeling of the static response of these three different polyurethane based composite shafts as fiber glass reinforced polyurethane epoxy, carbon fiber reinforced polyurethane epoxy, and Kevlar fibers reinforced polyurethane epoxy for three different boundary conditions. These three boundary conditions are simply supported, cantilever, both end fixed types with bending loads applied at the middle for simply supported case and distributed load along the length of the shaft for the last two types of boundary conditions. A three dimensional model of the composite beam has been implemented in this study using SolidWorks. A finite element commercial software ANSYS is used to investigate the stress response and deformation behavior of the model geometry for these three polyurethane based composite shafts for these three boundary conditions. A twenty node three dimensional element has been implemented for the finite element formulation of the modeled geometry such that it is applicable for the analysis of a layered composite structure, while providing support for linear, large rotation, and large strain nonlinear loading conditions. Convergence has also been ensured for various mash configurations in this work.Copyright

Nano-Indentation for Characterizing Mechanical Properties of Soft Materials

We have attempted to apply the computer-based finite element analysis (FEA) method to accurately measure the mechanical properties (e.g., hardness and elasticity) of a soft material by an indentation test. First, an axisymmetric model has been developed using commercially available FEA code ANSYS. The FEA model consisted of a thin Al-film resting on Si-substrate. A spherical indenter has been used to indent the Al-film, which traveled a predefined depth during the loading and unloading cycles. First, numerical simulations were conducted to get the force vs. displacement plot, which was later used to determine the modulus of elasticity and hardness of Al-film. The effects of substrate modulus and indentation depth were thoroughly investigated to determine the modulus and hardness of Al-film. The effect of friction, considered at the interface of indenter and Al-film, was found to offer minimum impact for relatively small indentation depth. The induced force on the Al-film by the indenter has been found to be higher with increasing indentation depth when friction was considered. However the contact stiffness, represented by the slope of the unloading curve, has been found almost the same with and without considering friction. The variation of substrate modulus has been found to be ineffective to capture the Al-film modulus for relatively small indentation depth. However for higher indentation depth, the substrate modulus has been found to offer profound effect to capture the film modulus. The hardness of the Al-film has also been found to be relatively unaffected with variation of substrate modulus. However, the hardness of the Al-film has been found to be higher with friction for relatively high indentation depth. Results obtained from this preliminary research are important to continue further investigation and to characterize the mechanical properties of other soft-materials, e.g., biofilms to minimize its detrimental effects and utilize its favorable aspects in industrial and biomedical applications.Copyright

Characterize Dynamic Response of Cantilevers Submerged in Viscous Fluids

Miniaturized devices are essential to precisely determine the rheological properties of viscous fluid when the available sample volume is inadequate. In this paper, we have attempted to apply the finite element analysis (FEA) method to characterize the dynamic response of a mini cantilever beam to measure the rheological properties of viscous fluid. First, the dynamic response of a mini cantilever beam, partially submerged in viscous fluid, is experimentally measured, and then compared with corresponding FEA solutions. Once the FEA model is validated, further numerical analysis is conducted to investigate how the modal response would change with changing density and viscosity associated with different viscous fluids. The numerical simulations are also repeated with changing the dip-length to investigate the sensitivity analysis. It seems from numerical results that the resonant frequency, Q-factor, time constant and depth of penetration of acoustic wave are dominantly influenced by viscosity of submerged liquid. Results obtained from this study can be used to design the optimized MEMS based test set up for measuring the rheological properties of viscous fluid.Copyright

Numerical Analysis to Predict Dynamic Response of Mini Cantilever Beam Submerged in Viscous Fluids

This research employed the finite element analysis (FEA) method to predict the dynamic response of a mini cantilever beam partially submerged in viscous media. First, the FEA method was validated by comparing the numerical results with corresponding experiments. Then, extensive numerical analyses were performed to investigate the variation of modal response in terms of resonant frequency and Q-factor with changing fluid viscosity and density. The resonant frequency of the beam was found to be reduced with increasing the fluid viscosity and density. The Q-factor was also reduced with increasing fluid viscosity. However, it did not changed significantly by changing fluid density. Numerical analyses were also repeated with varying the depth of beam (one-third, two-third and full) submerged in viscous media. The beam was found to be the most sensitive to respond in resonant frequency and Q-factor when submerged by one-third in viscous media. Results obtained from this numerical study can be used to design the optimized MEMS based test set up for measuring the rheological properties of viscous fluid.Copyright