bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Retraction on Three-Stream Injector Pulsatile Atomization for Air–Water Systems
Authors: Strasser Wayne , Battaglia Francine
Published: April 2016

Although coaxial airblast primary atomization has been studied for decades, relatively little attention has been given to three-stream designs; this is especially true for transonic self-pulsating injectors. Herein, the effects of nozzle geometry, grid resolution, modulation, and gas flow rate on the acoustics and spray character within an industrial scale system were investigated computationally using axisymmetric (AS) and three-dimensional (3D) models. Metrics included stream pressure pulsations, spray lift-off, spray angle, and primary droplet length scale, along with the spectral alignment among these parameters. Strong interactions existed between geometry and inner gas (IG) feed rate. Additionally, inner nozzle retraction and outer stream meeting angle were intimately coupled. Particular attention was given to develop correlations for various metrics versus retraction; one such example is that injector flow capacity was found to be linearly proportional to retraction. Higher IG flows were found to widen sprays, bringing the spray in closer to the nozzle face, and reducing droplet length scales. Substantial forced modulation of the IG at its dominant tone did not strongly affect many metrics. Incompressible 3D results were similar to some of the AS results, which affirmed the predictive power by running AS simulations as surrogates. Lastly, normalized droplet size versus normalized distance from the injector followed a strikingly similar trend as that found from prior two-fluid air-slurry calibration work.
Factors Affecting Spherical Nano-Indentation of Thin Film/Substrate Systems
Authors: Hossain A. , Mian A.
Published: April 2016

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.
Residual Stresses in Laser Micro-Joints of Dissimilar Materials
Authors: Mayeed Mohammed S. , Newaz Golam
Published: April 2016

Detailed analyses of thermal residual stress profiles due to laser micro-joining of several dissimilar material combinations, titanium (Ti) and polyimide (PI) [1], titanium coated glass (Gl) and polyimide [2], and glass and silicon (Si), are vital for the long-term applications of bio-implants and opto-electronics. In these studies, comprehensive three dimensional (3D) transient simulations for thermal and thermal stress analyses of transmission laser micro-joining of dissimilar materials have been performed by using the finite element (FE) code ABAQUS, along with moving Gaussian or super Gaussian laser heat source. The laser beam moving at a certain velocity, passes through the transparent material (e.g. PI or Gl), gets absorbed by the absorbing material (e.g. Ti or Si), and eventually softens/melts the interfacial materials to form the bond. Computational results have been compared with experiments in terms of temperatures and bond widths, and good comparisons have been observed in all combinations. Then the computational model has been used to optimize the process parameters and after this residual stress profiles of the laser-micro-joints have been calculated using the temperature profiles obtained from the thermal analyses as the systems cool down to room temperature. According to the various stress profiles, none of the stresses cross the tensile or the compressive strengths in cases of all the dissimilar material combinations at room temperature. A critical discussion has been included comparing the thermal residual stresses generated in the three combinations of dissimilar materials being used in these studies. A conclusion has been made on the formation processes of these stresses in laser micro-joining processes of dissimilar materials. This report will help to estimate the expected residual stresses in the laser micro-joining processes of dissimilar materials and will shed insight on how to select a better dissimilar material combination for a laser precision joining process.
A Modified Optimal Design of a Vibration Absorber for Ground Motion Isolation
Authors: Issa Jimmy S.
Published: April 2016

Recently, a new vibration absorber setup was proposed where the absorber is placed between the dynamic system and its moving support. The problem was solved and design guidelines were proposed using the classical absorber design technique. In this work, the unique optimal absorber parameters are determined with the aim of minimizing the maximum of the primary system amplitude. For a given stiffness ratio of the system, the optimal mass and damping ratios are obtained analytically using an optimization method based on invariant points of the objective function. Similar to the case of the classical vibration absorber setup, these points are independent of the system damping ratio. It is shown that a trade-off relationship exists between these points, therefore the optimal mass ratio is determined first by a proper placement of the invariant points. Two suboptimal damping ratios are determined by forcing one of the two peaks of the objective function to coincide with one of the invariant points. Then, the optimal damping ratio is obtained from the average of the two suboptimal damping ratios. This approximate analytical solution is validated through comparison with the exact optimal parameters which were calculated numerically using two different numerical optimization methods. The first is based on the genetic algorithm technique and the second on the downhill simplex method. The optimal parameters are plotted and several examples are considered where the objective function is plotted in its approximate and exact optimal shapes.
Variational Methods for Phononic Band-Structure Evaluation
Authors: Srivastava Ankit
Published: April 2016

In this paper we present comparative results regarding the computational efficiency, speed, and versatility of three fundamental variational schemes for phononic band-structure calculation: a. traditional Rayleigh quotient where the displacement field is varied, b. inverse Rayleigh quotient where the stress field is varied, and c. mixed-method where both the displacement and the stress fields are varied. We show that the variational principles can be used for the fast evaluation of various phononic properties such as the dispersion relation, equi-frequency contours, and the density of states.
Large-Scale Model of Flip-Chip Joining Defects
Authors: Sylvestre Julien , Samson Maud , Duchesne Éric , Langlois-Demers Dominique
Published: April 2016

A numerical model is developed for the flip chip reflow process, including many significant aspects of the joining dynamics: thermal expansion of the device and substrate; temperature-dependent substrate warpage; random variations of the solder volume with position; and global device position above the substrate. A detailed micro-model of each interconnect captures the transition from two contacting solder bumps to a single continuous solder interconnect, using a random wetting delay parameterized by the surface energy of the bumps relative to an energy scale. The model is shown to correctly fit measurements of the device position during the reflow process, and is used to study the occurrence of non-wet and bridge defects. The effects of spatial variations in the solder volume distribution on these defects is studied in details for an actual device with 12 504 interconnections, using an effective data reduction technique.
Verification of the Vibration Characteristics of a Reciprocating Compressor in Operation and the Proposal of the Model Parameters Estimation Method
Authors: Mori Yoshifumi , Saito Takashi , Fujita Katsuhide
Published: April 2016

Vibration characteristics of a reciprocating compressor are discussed. To investigate the frequency characteristics in the operation of unhealthy and healthy, we employed the proposed model, which includes stiffness characters about both the connecting and the sliding parts. Expressing the motion of the reciprocating compressor as a rigid body model with eleven degrees of freedom, we numerically investigated the frequency characteristics in operation and the natural vibration characteristics based on a locally linearized method. To examine the frequency characteristics, we carried out vibration tests using a small experimental machine and the eigenvalue analysis based on the proposed model. Comparing the analytical results with experimental results, we found that the proposed model could simulate the fundamental frequency characteristics in operation and the natural modes. Eigenvalue analysis shows that the natural frequencies and modes for a reciprocating compressor depend upon the angle of the crankshaft. In the proposed model, it can express the dominant frequencies occurring during operation and the natural vibration characteristics.
Improvement of Thermal Conductivity of Electroplated Copper Thin-Film Interconnections by Controlling Their Micro Texture
Authors: Rittinon Pornvitoo , Suzuki Ken , Miura Hideo
Published: April 2016

Copper thin films are indispensable for the interconnections in the advanced electronic products, such as TSV (Trough Silicon Via), fine bumps, and thin-film interconnections in various devices and interposers. However, it has been reported that both electrical and mechanical properties of the films vary drastically comparing with those of conventional bulk copper. The main reason for the variation can be attributed to the fluctuation of the crystallinity of grain boundaries in the films. Porous or sparse grain boundaries show very high resistivity and brittle fracture characteristic in the films. Thus, the thermal conductivity of the electroplated copper thin films should be varied drastically depending on their micro texture based on the Wiedemann-Franz’s law. Since the copper interconnections are used not only for the electrical conduction but also for the thermal conduction, it is very important to quantitatively evaluate the crystallinity of the polycrystalline thin-film materials and clarify the relationship between the crystallinity and thermal properties of the films. The crystallinity of the interconnections were quantitatively evaluated using an electron back-scatter diffraction method. It was found that the porous grain boundaries which contain a significant amount of vacancies increase the local electrical resistance in the interconnections, and thus, cause the local high Joule heating. Such porous grain boundaries can be eliminated by control the crystallinity of the seed layer material on which the electroplated copper thin film is electroplated.
Improvement of the Long-Term Reliability of TSV Interconnections Used in Three-Dimensional Stacked Modules
Authors: Miura Hideo , Suzuki Ken
Published: April 2016

The long-term reliability of inerconnectons of three-dimensional integrated modules was investigated from the view point of crystallographic quality of the interconnection. The dgradation process of the interconnections was dominated mainly by the diffusion of copper atoms along grain boundaries in a polycrystalline thin-film and the diffusion constant was found to vary drastically depending on the crystallinity of the copper interconnections. The crystallinity of the interconnections changed seriously as a strong function of the mismatch in the lattice constant between copper and the seed layer material used for electroplating of the copper interconnections. The crystallinity of the electroplated interconnections was evaluated quantitatively by using an electron back-scatter diffraction method. Both the quality of grains and grain boundaries in the copper interconnections varied drastically as a function of electroplating conditions and their thermal hystory after the electroplating. The most important factors for the long-term reliability was the initial quality of the interconnection just after the electroplating.
Simulation of Impaction Between Liquid Droplet and Solid Particles Based on SPH Method
Authors: Meng Shuai , Wang Qian , Yang Rui
Published: April 2016

The phenomenon of impaction between liquid droplets and solid particles is involved in many scientific problems and engineering applications, such as impaction between sprayed droplet and solid particles in limestone injection desulfurization system and the collision between a droplet of the liquid to be granulated and a seed particle in fluidized bed spray granulation process. There are a lot of factors affected this phenomenon: droplet and particle size, momentum of both liquid droplet and solid particles, materials, surface conditions of the solid particles and so on. However the experimental or numerical researches have been done mostly pay attention to Specific application or process, so the impaction phenomenon has not been through studied, for example how different factors affected the impaction process with its effect on different applications. This paper focuses on the basic issue of interaction between droplet and solid particles. Three main factors were considered: ratio of diameter between the droplet and solid particle, relative velocity and the surface tension (including the contact angle between droplet and solid particle). All the study is based on simulation using SPH (smoothed particle hydrodynamics) method, and the surface tension is simulated by particle-particle interaction.
Effect of Ply Stacking Sequence on Structural Response of Symmetric Composite Laminates
Authors: Rahman Mosfequr , Absar Saheem , Aktaruzzaman F. N. U. , Rahman Abdur , Hossain N. M. Awlad
Published: April 2016

In this work, the effect of ply stacking sequence on the structural response of multi-ply unidirectional fiber-reinforced composite laminates was evaluated using finite element analysis. The objective of this study was to develop a computational model to analyze the stress response of individual plies in a composite laminate for a given stacking sequence. A laminated composite plate structure under tensile loading was modeled in ANSYS. Stress profiles of the individual plies were obtained for each lamina. An Epoxy matrix with both unidirectional Graphite and Kevlar fibers was considered for the model. Three dimensional sectioned shell elements (SHELL181) were used for meshing the model. Several sets of stacking sequences were implemented, symmetrical to the mid-plane of the laminate. Symmetric stacking configurations of 6 layers stacked in ply angles of [0/45/-45]s, [0/60/-60]s, [0/45/90]s, and an 8-layered arrangement of [0/45/60/90]s were modeled for the analysis. The layer thickness was maintained at 0.1 mm. The results were compared against an analytical model based on the generalized Hooke’s law for orthotropic materials and classical laminate theory. A numerical formulation of the analytical model was implemented in MATLAB to evaluate the constitutive equations for each lamina. The stress distributions obtained using finite element analysis have shown good agreement with the analytical models in some of the cases.
Finite Element Analysis of a Hobie 16 Mast and Possible Alternatives for Improvement
Authors: Rahman Mosfequr , Calloway Bryan , Sullivan Eric , Darley Matthew , Hanson Anthony , Hare Collin , Mian Ahsan
Published: April 2016

Hobie Cat is one of the most popular sailboat production companies to ever exist, and the Hobie 16 is the most popular boat in the Hobie Cat line-up. The key to Hobie’s success was largely in part to advancements in strong and lightweight materials. This advancement allowed Hobie to achieve record breaking performance in their particular class of boat. The mast of the Hobie 16 is one of the heavier pieces of the craft. The overall mass and center of mass is greatly affected by this component, which begs to question if there may possibly be room for improvement. A sailboat mast is defined as a tall vertical spar, sometimes sectioned, that rises from the keel or deck of a sailing vessel to support the sails and the standing and running rigging. Sailboat masts are long, slender structures. They must be designed to be able to hold the thrust loads that are acting on them from the sails which will differ based on wind conditions. A mast must also be made of a material that will allow it to go through the varying environmental conditions without fatiguing. When designing a sailboat mast a few of the main goals are to have a low center of gravity, be light weight, and also aerodynamically efficient.

During this research a Hobie 16 mast design was taken as a baseline design for testing. The current mast on the market weighs between 50–60 lbs. While this is not extremely heavy, the center of gravity is approximately 13.5 feet from the end of the mast. This high center of gravity makes it tough to raise and lower the mast when launching the boat. One important objective in this work is to create a mast that will be easier for the user to raise and lower without sacrificing the structural integrity of the mast. Three masts have been created in solid modeling software, and their performance characteristics have been tested using finite element analysis software ANSYS. Two of the designs are original works, while one is a copy of the original Hobie Cat design. The original design was analyzed, providing baseline data for which to compare the new designs with. In addition to the new designs, all designs have been constructed from three different materials as Aluminum Alloy 6061, Aluminum Alloy 7075 and Acrylic. This allows for comparison of designs and possible new materials. After an in depth analysis of all masts, the recommendation is made that Hobie 16 users would benefit greatly from the use of a tapered mast made of aluminum alloy 7075.
Finite Element Analysis Conversion Factors for Natural Vibrations of Beams
Authors: Cosby Austin , Gutierrez-Miravete Ernesto
Published: April 2016

The objective of this paper is to present results of a study designed to determine conversion factors to allow designers and analysts calculate natural frequencies of vibrating prismatic beams of arbitrary dimensions using simpler beam elements instead of expensive 3D solid elements. Prismatic beams subject to the most commonly encountered boundary conditions were modeled using beam elements and solid elements. The resulting natural frequencies were calculated and validated and the corresponding conversion factors were determined.
A Parameter Study of Micromachined Seesaw Type Microphone
Authors: Han Sangil , Kim Byungki
Published: April 2016

A seesaw type microphone has been characterized to study its feasibility for sound source localization. A microphone system design is based on an unique eardrum structure of Ormia ochracea whose two ears are mechanically coupled. In the design of the microphone mimicking the fly, a torsional stiffness of a hinge and a damping constant of diaphragm receiving a sound wave are believed to be the major factors to determine its directivity. To study their effect on the responses, the microphones are designed to have different levels of parameters, i.e. torsional hinge lengths and damping hole sizes. An experimental effort to analyze displacement signals from both sides of ears/diaphragm in microphone is made in this paper. Corresponding possible optimized structures of microphone to localize a sound source are suggested.
Model Reduction for the Electrostatically Actuated Silicon Diaphragm Based on Modal-Type Dynamic Condensation
Authors: Lin X. Z. , Hu Z. M. , Huang J. M.
Published: April 2016

A method for constructing reduced-order models (ROM) of an electrostatically actuated clamped silicon diaphragm is presented. This reduced-order model is constructed by using basis the spatially dependent eigen-functions. A commercial finite element package is firstly used to form the system mass and stiffness matrices representing the model. These matrices are then manipulated in MATLAB™ and reduced using modal type dynamic condensation. The eigen-value problem is then solved for the reduced mass and stiffness matrices and subset of the modes are used to producing low-order but highly accurate models of electrostatically actuated diaphragm. The reduced-order model can accounts for general residual stress and strain hardening and allows for any other electric driving signal simulations. Once the ROM has been generated, it can be reused to simulate the quasi-state and dynamics behaviors of the device over a range of different electric driving waveforms. The calculated results show that the resulting ROM can capture the static/dynamic behaviors of the device very well. The simulation results also show good agreement with the fully meshed dynamic models simulation results, thus the efficiency and accuracy of the modeling technology are valid.
A Combined Perfectly Matching Layer and Infinite Element Formulation for Unbounded Wave Problems in the Frequency Domain
Authors: Pettigrew Joseph S. , Mulholland Anthony J. , Cipolla Jeffrey L. , Mould John , Banks Robert
Published: April 2016

In this paper, Berenger’s Perfectly Matching Layer (PML) and Bettess’ Infinite Element (IE) scheme are combined to create a new type of element for unbounded acoustic wave problems. An assessment of this new element formulation is made through its use in the calculation of the acoustic modal response of a spherical radiator in the frequency domain. The performance of the PML+IE approach is contrasted with the IE only methodology by comparing them to the exact solution of this test problem in terms of the surface inertia and resistance in the near field. The results are encouraging and the PML+IE approach shows a marked improvement in performance, particularly at lower frequencies.
Assessment of Surface-Based Aeroacoustic Noise From Blades of a Vertical-Axis Wind Turbine
Authors: Williams Robert , Rocha Joana , Matida Edgar , Nitzsche Fred
Published: April 2016

Surface-based sources of aerodynamically-generated noise for the 17-m troposkien shape vertical-axis wind turbine are predicted using Farassat’s Formulation 1A of the Ffowcs Williams-Hawkings equation. By discretizing the three-dimensional turbine blades over the height of the turbine into constant-radius sections, the blades were aerodynamically modeled in two-dimensions in the horizontal plane by an unsteady panel method to obtain results for surface pressures and velocities. The acoustic pressure generated by the blades throughout their rotations was determined by the combination of loading and thickness noise sources on the surface of the blade sections in the time-domain. The simulation results were compared to experimental results for the acoustic pressure power spectral density. The sound pressure level around the turbine was found to have a slight dipole radiation pattern, caused primarily by the loading acoustic pressure on the blades.
Cavity Resonance Biomedical Sensor
Authors: Lucklum Ralf , Zubtsov Mikhail , Arango Simon Villa
Published: April 2016

We report on first steps towards a phononic crystal sensor for biomedical applications. Phononic crystals and metamaterials allow for unprecedented control of sound propagation. The classical ultrasonic sensors, acoustic microsensors and MEMS resonator sensors face severe limitations when applying them to small volume liquid analytes. Phononic crystal sensors are a new concept following the route of photonic crystal sensors. Basically, the material of interest, here a liquid analyte confined in a cavity of a phononic crystal having a solid matrix constitutes one component of the phononic crystal. In an application as chemical sensor the value of interest, let’s say the concentration of a toxic compound in liquid, is related to acoustic properties of the liquid in the cavity. A change in the concentration causes measurable changes in the properties of the phononic crystal. Transmission or reflection coefficients are appropriate parameters for measurement. Specifically, a resonance induced well separated transmission peak within the band gap is the most favorable feature. The sensor scheme therefore relies on the determination of the frequency of maximum transmission as measure of concentration.

Promising applications like biomedical sensors, point-of-care diagnostics or fast screening introduce further engineering challenges, specifically when considering a disposable element containing the analyte. The three key challenges are the strong restriction coming from limitations to approved materials for the analyte container, geometric dimensions in the mm-range common in hospital or point-of-care environment and acoustic coupling between sensor platform and analyte container.
Comparative Study of Analytical Models to Predict Warpage in Microelectronics Packages
Authors: Singh Charandeep , Kim Yeonsung , Park Seungbae
Published: April 2016

Warpage is a critical concern in the microelectronics industry for several decades. It is a root cause of failures during manufacturing processes such as open solder joints. Also the excessive warpage generates the delamination and die cracking which degrade the package reliability. Thus, the accurate estimation of package warpage is one of the important factors to improve the package reliability. The purpose of this study is to select the best analytical model for prediction of warpage of microelectronic packages. This paper compares the warpage prediction from corrected Suhir’s theory and classical laminate theory. Both analytical models can provide quick warpage estimation when package is subjected to thermal loading. The warpage evaluation was performed based on both analytical models and compared with the experimental result. Also a finite element analysis (FEA) was performed and the result was compared with analytical models. The digital image correlation (DIC) technique was employed to observe the real-time out-of-plane deformation of the test sample exposed to temperature loading. Three layer test vehicle having the die, underfill, and aluminum plate was assembled for this study. Underfill material properties were characterized with DIC and dynamic mechanical analysis (DMA). The result indicates that Laminate theory provides the better prediction of warpage when underfill layer thickness is comparable with die and substrate layer thickness. This study helps to design more reliable components with design parameters being optimized in early stage of the development using analytical solutions.
Characterization of Creep Behavior of Actual Lead-Free Solder Joint for Modeling
Authors: Lee Hohyung , Liu Ruiyang , Park Seungbae , Kwak Jae
Published: April 2016

Creep deformation on solder plays important role in life time of an electronic package. Traditionally, mechanical properties of solders have been tested using bulk solder samples. However, mechanical behaviors of bulk solder and actual solder ball exhibit huge discrepancy due to the different size of the micro structure and existence of inter metallic layers. In this reason, to acquire reliable creep behavior of the solder joint, the actual solder ball need to be tested. In this study, 2D digital image correlation (DIC) technique with microcopy is used to investigate the creep behavior of the actual BGA solder balls from the packages. The full field displacement data of the cross sectioned solder ball are generated while various constant loading is applied at different isothermal temperature. From the full field displacement data, constant creep rates of the actual BGA solder ball are obtained. Using the constants from the experiment, finite element analysis is performed to validate the experiment results by comparing the displacement of the DIC experiment results and FEA modeling.
Static Modeling of a Bi-Axial Micro-Mirror With Sidewall Electrodes
Authors: Towfighian Shahrzad , Ozdogan Mehmet
Published: April 2016

The static modeling of a bi-axial torsional micro-mirror with sidewall electrodes is investigated. The mirror and sidewall electrodes experience different voltages. As a result of the potential difference, the mirror rotates about x and y axes with the torques generated from electrostatic forces by the sidewall and bottom electrodes. The rotations about two axes are made possible using a gimbal frame and serpentine springs. An analytical model is presented that is a simplified model of a previous study based on independent excitation of the two rotation angles. The simplified model enables prediction of the rotation angles with good accuracy and faster computation time.
A Modeling Study of the Effect of Underfill Materials on Solder Joint Thermal Fatigue of Ball Grid Array Package
Authors: Wang Wei , Nguyen Tung
Published: April 2016

Flip Chip Ball Grid Array packages (FCBGA) have been widely used in microelectronic industry in integrated circuit (IC) packages. Due to the intrinsic mismatch of the coefficient of thermal expansion (CTE) between silicon chip and Printed Circuit Board (PCB) material, solder joint fatigue failure due to thermal cycling becomes the most important concern for this technology. Underfill materials have been widely used as a solution to improving solder joint fatigue life. It is of importance to understand the effect of underfill material properties on the solder joint fatigue life. In this study, finite element method (FEM) was employed to study the effect of underfill materials on solder joint low cycle fatigue life in thermal cycling. ANSYS code was used to calculate the inelastic energy density generated in temperature cycling. The viscoplastic model was used for the solder to consider the inelastic and time dependent behavior under thermal cycling. By using the FEM model, the underfill material properties, the Young’s modulus and CTE were examined to study their effects on the solder joint fatigue life. It was found that the improvement of solder fatigue life could be achieved only when the CTE was low. This improvement could be strengthened by large Young’s modulus to increase the solder strength. In contrast, a large CTE underfill material could deepen the solder joint fatigue damage. This worsening effect became more significant as the Young’s modulus became larger. This study could serve as a foundation for understanding the mechanism of solder joint fatigue in the presence of underfill materials and provide guidance to choose appropriate underfill materials to improve BGA solder joint thermal fatigue in temperature cycling.
Biofilm Streamer Formation in a Microfluidic Porous Media Mimic
Authors: Hassanpourfard Mahtab , Valiei Amin , Thundat Thomas , Liu Yang , Kumar Aloke
Published: April 2016

Several bacterial species possess the ability to attach to surfaces and colonize themselves in thin films called biofilms. Biofilms that grow in porous media are relevant to several industrial and environmental processes such as wastewater treatment and CO2 sequestration. We used Pseudomonas fluorescens, a gram negative aerobic biofilm forming bacteria, to investigate biofilm formation in a microfluidic porous media mimic device. The microfluidic device consists of an array of micro-posts, which were fabricated using soft-lithography. Subsequently, biofilm formation in this device was investigated as a function of time and the formation of filamentous biofilms known as streamers was observed. Furthermore, we used computational fluid mechanics simulation to better understanding of the streamer formation.
Scalable Nanomanufacturing of Metasurfaces Using Nanosphere Photolithography
Authors: Wilson Jacob S. , Liyanage Wipula P. R. , Gegel Michelle L. , Nath Manashi , Kinzel Edward C.
Published: April 2016

We report on using Nanosphere Photolithography (NPL) for submicron patterning of Frequency Selective Surfaces (FSS). NPL is a combination of two techniques; colloidal nanolithography — where nanospheres form a self-assembled hexagonal close-packed (HCP) array when dispensed on a surface, and photonic jets — which are created when light is incident onto a microsphere in contact with a surface. NPL creates a mask-free HCP hole array in the photoresist. This pattern can be used with evaporation and lift-off to create an array of antenna elements, constituting the FSS. Alternatively, electrodeposition techniques can be used to deposit the metal elements. The later is particularly appealing as it lends itself to reel-to-reel fabrication techniques. Finally, we demonstrate that geometries other than simple hole arrays can be patterned in the photoresist by exposing the microsphere array with off normal incidence light.
A Portable Analytical System for Colorimetric Detection of Metal Ions in Water
Authors: Zhao Chen , Zhong Guowei , Kim Da-Eun , Liu Jinxia , Liu Xinyu
Published: April 2016

Heavy metal ions released into various water environments have severe impact on both human beings and aqueous environments, and excess amount of lead and aluminum ions pose high risks to human health and could cause life-threatened diseases. The existence of metal ions in drinking water contributes most to the daily intake by humans, and thus it urges to develop a rapid, low-cost and sensitive method for detection of heavy metal ions. In this research, we develop a portable analytical system for metal ion detection in water by combining a powerful gold nanoparticle (AuNP) based colorimetric method with lab-on-a-chip technology. We utilize single-step assays involving surface functionalized AuNPs for colorimetric detection of lead (Pb2+) and aluminum (Al3+) ions in water with low limit of detection (LOD) and high sensitivity. We demonstrate that this portable system provides LODs of 30 ppb for Pb2+ and 89 ppb for Al3+, both comparable to bench-top analytical spectrometers. The system permits metal ion detections in a more economical and convenient fashion, and is particularly useful for water quality monitoring in remote and/or resource-poor settings.
A Discrete Model for an Electrostatically Driven Micro-Hydraulic Actuator
Authors: Shiari Behrouz , Sadeghi Mahdi M. , Darvishian Ali , Najafi Khalil
Published: April 2016

High-force, large-deflection actuators are critical for devices such as valves and pumps used in micro-fluidic systems. The major technical impediment in improving the performance of the micro-actuators lies in the lack of understanding the physical phenomena and their interactions of electric, mechanical, and fluidic fields for performing their intended functions. Because of the complexity of the actuator, the fully coupled numerical analysis such as finite element analysis is extremely expensive.

Here, we introduce a discrete model of an Electrostatic Micro-Hydraulic (EMH) actuator. The model considers all dynamic forces which are involved in a time operation of the hydraulic actuator cell and covers three major physics: electrostatic, mechanical and fluidic. The physics have been coupled together to investigate the dynamic of the device.

The discrete dynamic model developed in this work may be used for simple yet accurate predictions of dynamic performance of such actuators, and is preferable to more complicated and very expensive coupled numerical models. The analysis relies on physics-based equations and can be modified to accommodate different chamber geometries, different material properties and different working fluids. Results from the analytical model compare favorably with experimental measurements.
Validation of Material Constants for Low-Cycle Fatigue Modeling
Authors: Nguyen Quang , Park Seungbae , Nguyen Tung
Published: April 2016

In our previous paper [1], four material constants required for Low-Cycle Fatigue under drop impact modeling in ABAQUS were obtained. This study aimed to validate that technique using conventional JEDEC drop test results. Several test boards were subjected to drop test at 3000G/0.28ms, close to the most severe condition of JEDEC Standard. During repetitive drops, the overall electrical resistance of daisy-chained solder joints of each package on the test board was monitored to detect the failure. Weibull distribution were obtained for edge and center package. The numerical model was then built in ABAQUS Low-cycle Fatigue, the set of constant obtained from previous study [1] was used as a reference source for the model. Fatigue life of the package extracted from the numerical model was compared with experiment results. The validation was finally reported.
Experimental, Numerical and Analytical Investigation of Thermal Resistance in High Brightness LED Arrays
Authors: Shirazy Mahmood R. S. , D’Arcy-Lepage Andréane , Gilbert Michel , Richard Samuel , Fréchette Luc G.
Published: April 2016

Thermal performance of a commercial LED array module has been studied by experimental, numerical and analytical approaches to find the dominant thermal resistance in the thermal circuit. The light quality, lifetime and reliability of the LED modules depend strongly on the junction temperature which can be obtained and modified by a suitable thermal resistance model. Analytical models for the first level packaging (Die) and second level packaging (PCB and heat sink) have been developed with special attention to the thermal spreading resistance. Numerical modeling has been performed using commercial finite element software (COMSOL) and the results are in good agreement with the analytical models. An LED array module has also been studied experimentally by measuring the temperature field in the PCB and heat sink using thermocouples and infrared thermography. The results of the experimental part are used to validate the numerical and analytical models. It is shown that more than 50% of the total thermal resistance is caused by the heat sink while the PCB and LED package each share 25% of the total thermal resistance.
Effect of Imperfections on Fused Silica Shell Resonators
Authors: Darvishian Ali , Shiari Behrouz , Cho Jae Yoong , Najafi Khalil
Published: April 2016

Axisymmetric shell resonators have been attractive candidates for high performance MEMS vibratory gyroscopes because of their high quality factor, low sensitivity to environmental vibrations and electrostatic tuning capability. Fused silica shell resonators made by blow torch molding with high quality factor could perform as high performance MEMS gyroscopes. Despite such advantageous features, the performance of these shell resonators is limited by geometric imperfections that occur during fabrication. This paper investigates effect of geometric asymmetries such as height and radius imperfections, notch, and mass imbalance in the rim of gyroscopes on the split in natural frequencies of the n=2 wineglass modes. Numerical simulation shows that perfect fused silica shell has 13929 Hz natural resonance frequencies without any frequency split. Analysis of imperfect shell reveals that frequency split is very sensitive to edge geometric imperfection and mass imbalance in the rim. On the other hand, Δf is not very sensitive to the notch in the rim of shell and height imperfection less than 40μm.
Investigation of Thermoelastic Loss Mechanism in Shell Resonators
Authors: Darvishian Ali , Shiari Behrouz , Cho Jae Yoong , Nagourney Tal , Najafi Khalil
Published: April 2016

Maximizing quality (Q) factor is key to enhancing the performance of micro mechanical resonators, which are used in a wide range of applications such as gyroscopes, filters, and clocks. There are several energy loss mechanisms commonly associated with micro resonators including anchor loss through the substrate, squeeze film damping, thermoelastic dissipation (TED), and surface loss. This work focuses on the thermoelastic loss as one of the major energy dissipation mechanisms of micro shell resonators.

In this article, the effects of material properties, thickness, conductive coating and operating temperature on the Q-factor of micro shell resonators are investigated. Numerical simulation shows shell resonators have higher Q-factors when they are operating at lower temperatures. Although, the magnitude of the simulated Q-factors of an uncoated bare resonator made from fused silica is more than 70 million and so it is too high to have a remarkable effect on the total Q-factor, our study shows that even a thin layer of some conductive coatings like gold on the surface of a bare shell reduces Q-factor significantly. The sensitivity of the coated shell resonator design to the TED phenomenon provides useful information for the development of new micro shell resonators with improved performance and Q-factors.
High Strain-Rate Constitutive Behavior of SAC305 Solder During Operation at High Temperature
Authors: Lall Pradeep , Zhang Di , Yadav Vikas
Published: April 2016

Leadfree solders have been used as interconnects in electronic packaging, due to its environmental friendly chemical property. However, those materials may experience high strain rates when subjected to shock and vibration. Consequently, failure will occur to electronics in those situations. Therefore, knowing the material properties of lead-free solders are extremely important, but research on mechanical behaviors of those solder alloys at high strain rates are scarce. Anand’s viscoplastic constitutive model has been widely used to describe the inelastic deformation behavior of solders in electronic components under thermo-mechanical deformation. However, Anand’s model constants for the transient dynamic strain rates are scarce. In this paper, the nine material parameters to fit the Anand viscoplastic model at high strain rates have been presented. In order to develop the constants for this model, uniaxial tensile tests at several strain rates and temperatures have been completed. A constant strain rate impact hammer which enables attaining strain rates around 1 to 100 per sec has been employed to implement tensile tests and a small thermal chamber is applied to control testing temperature. High speed cameras operating at 70,000 fps have been used to capture images of specimen and then digital image correlation method is used to calculate tensile strain. Uniaxial stress-strain curves have been plotted over a wide range of strain rates (ε̇ = 10, 35, 50, 75 /sec) and temperatures (T = 25, 50, 75, 100, 125°C). Anand viscoplasticity constants have been calculated by nonlinear fitting procedures. In addition, the accuracy of the extracted Anand constants has been evaluated by comparing the model prediction and experimental data.
Sound Transmission Loss Through a Corrugated-Core Sandwich Panel With Integrated Acoustic Resonators
Authors: Schiller Noah H. , Allen Albert R. , Zalewski Bart F. , Beck Benjamin S.
Published: April 2016

The goal of this study is to better understand the effect of structurally integrated resonators on the transmission loss of a sandwich panel. The sandwich panel has facesheets over a corrugated core, which creates long aligned chambers that run parallel to the facesheets. When ports are introduced through the facesheet, the long chambers within the core can be used as low-frequency acoustic resonators. By integrating the resonators within the structure they contribute to the static load bearing capability of the panel while also attenuating noise. An analytical model of a panel with embedded resonators is derived and compared with numerical simulations. Predictions show that acoustic resonators can significantly improve the transmission loss of the sandwich panel around the natural frequency of the resonators. In one configuration with 0.813 m long internal chambers, the diffuse field transmission loss is improved by more than 22 dB around 104 Hz. The benefit is achieved with no added mass or volume relative to the baseline structure. The embedded resonators are effective because they radiate sound out-of-phase with the structure. This results in destructive interference, which leads to less transmitted sound power.
Vibration Vulnerability of Rod Baffle Type Heat Exchanger: Case Study Badak LNG MCR Aftercooler
Authors: Hutagalung Frilo Fitrasali
Published: April 2016

Badak LNG plant utilizes Multi Component Refrigerant (MCR) as cooling medium for natural gas liquefaction. In the process system, a heat exchanger is serving as compressor aftercooler that cools down this MCR (gas with mostly Methane and Ethane) by means of sea cooling water. This particular heat exchanger is constructed with Rod-Baffle design with Titanium tubes. The design also incorporates a vapour belt at shell inlet/outlet that is functioned as flow distributor.

Badak LNG has 8 plants called process trains; with each process train has one MCR aftercooler. The aftercooler at each train has difference in terms of vapour belt design.

During plant operations, vibration problem has repetitively occurred in all MCR aftercooler and caused tube leaks. However, a computational fluid dynamics study revealed that the fluid velocity was low enough to generate tube vibrations. However, Rod-Baffle design uses single support direction per baffle. With 4 axis of support (X+, X-, Y+, Y-), one direction support will repeat at the 5th support, 10th support, and so on.

Calculation was then made to confirm the effect if one of the baffle failed to support. This condition will increase the length between baffle by 2 times. Consequently, the fluid critical velocity will decrease by 4 times.

This approach was then compared with the fluid velocity pattern inside the exchanger shell. It concludes that the fluid velocity is above its critical velocity. Thus, the exchanger is vulnerable to vibrations.

Each MCR aftercooler has different vulnerability to vibrations due to vapour belt different designs. The study has concluded the comparison of vulnerability of the exchangers. Exchanger A has 25.9 % tubes having tubes vulnerable to vibrations, while Exchanger F (with different vapour belt design) has only 1.92 % tubes vulnerable to vibrations. With 2000 tubes quantity, the effect to process conditions is significantly different between exchangers.

This paper concludes that design of vapour belt can significantly improve the reliability of Rod-Baffle type heat exchanger.