bluuebunny/crossref_metadata_2025 huggingface dataset:
AC Electrokinetic Pumps for Micro/NanoFluidics
Authors: Wu Junqing , Soni Gaurav , Wang Dazhi , Meinhart Carl D.
Published: April 2008

We have developed micropumps for microfluidics that use AC electric fields to drive aqueous fluid motion through micro channels. These pumps operate at relatively low voltages (~5–10Vrms), and high frequencies (~100kHz). They have several distinct advantages over the DC electrokinetic pumps. The low voltages make the pumps well suited for a wide variety of biosensor and “Lab-on-a-Chip” applications (e.g. PCR chip for DNA amplification). The high frequencies minimize electrolysis, so that bubbles do not form on the electrode surfaces, and do not contaminate the working fluid. The pumps can also be used as active valves or precision micro-dispensers.
Multiple Parting Surfaces for Sand Casting
Authors: Ramaswami Hemant , Anand Sam
Published: April 2008

Multiple parting surfaces are frequently used in sand casting, die casting and injection molding processes. However, most research in this area has focused on die casting and injection molding. Parting surfaces for die casting and injection molding are relatively easier to compute compared to sand casting because their orientations and shapes are less restricted. In sand casting, the parting surfaces have to be parallel to each other and perfectly flat to permit the use of flasks with more than two pieces. The concepts of visibility and object illumination can be used to divide an object into two parts using a single parting surface. These methods, however, cannot be directly used for multiple parting surfaces. In this paper, a methodology to generate multiple parting surfaces for sand casting is described. The method uses Gauss maps to identify potential casting directions, and global accessibility cones to determine which faces can be cast in the same part of the pattern. The pattern is sliced using parallel planes such that each slice can be withdrawn from the mold in at least one direction. After the object is sliced, the number of parting surfaces is reduced by combining adjacent middle sections depending on their accessible directions.
Finite Element Estimation of the Residual Stresses in Roller-Straightened Rail
Authors: Talamini Brandon , Gordon Jeff , Perlman A. Benjamin
Published: April 2008

The purpose of this paper is to develop models to accurately predict the residual stresses due to the roller straightening of railroad rails. Several aspects of residual stress creation in rail due to roller straightening are addressed. The effect of the characteristics of the loads applied by the roller-straightener on the stress profile is examined. In addition, the analysis attempts to discern the relative influence of bending and contact on the residual stresses. The last goal is to determine how the heat treatment of rail alters the predicted roller-straightening residual stress field. The loads for the simulation are estimated from available data. To identify the most credible values, a baseline loading case is defined and modeled. These straightening loads are parameterized by considering alternative loading scenarios. Residual stresses and deformations are calculated using these loads. To separate the effects of bending and contact on the residual stress induced by the roller loads, each credible load case is analyzed with two models. One is a 2-dimensional generalized plane strain (GPS) model that accounts only for the flexural stresses. The other is a fully 3-dimensional analysis that includes roll-on-rail contact to make estimates of the true residual stress field. Comparison of the residual stress results from both models reveals the relative influence of local roll-rail contact and bending on the final profile. Comparison of the 2- and 3-dimensional residual stress results reveals that the magnitude of the contact loads is a decisive influence on the stress field, even in portions of the rail web located far from the contact interface. Therefore, it is critical to obtain accurate estimates of the straightening loads to make accurate roller straightening residual stress estimates. Heat treatment of the rail prior to roller straightening primarily affects the longitudinal residual stress in the web, causing a positive shift in the stress values.
A Nonlinear Six Degree-of-Freedom Axle and Body Combination Roll Model for Heavy Trucks’ Directional Stability
Authors: Rajapakse Nuraj I. , Happawana Gemunu S.
Published: April 2008

Six degrees of freedom nonlinear suspension roll model of a heavy truck axle unit is presented. The model includes the effects of nonlinear tire damping, road inclination angle, and variation of suspension angles. The roll model parametric analysis provides the influence of various geometric truck parameters that are important to the designer in stability viewpoint. Many of the important parameters such as nonlinear tire coefficients, road and suspension inclination angles, and some of their limiting values for stability are also discussed to facilitate the selection of proper actuators and sensors for automation. The dynamic stability of the axle unit is illustrated using parameters dependent phase portraits. These phase portraits provide qualitative information on truck’s directional stability.
Plate Heat Exchanger Adsorber for a Regenerative Adsorption Heat Pump
Authors: Lambert Michael A. , Jones Benjamin J.
Published: April 2008

The state of the art in regenerative adsorption (solid-vapor) heat pumps achieved to date is a maximum Coefficient of Performance for Cooling (COPC) of 1.1 with 70% regeneration of waste heat. A number of configurations for the heat exchanger within the adsorbent bed have been investigated, including concentric tube, shell and tube, serpentine flat pipe, spiral flat pipe, and single-pass plate type. However, to date, compact (or multiple pass plate) heat exchangers for use with adsorbent beds have not been studied. This investigation explains the challenges involved in this application, and describes the design and analysis of three configurations of a compact heat exchanger for use with solid adsorbent. The prinicipal figure of merit affecting both coefficient of performance, COPC, and specific cooling power, SCP (W cooling per kg adsorbent), is defined as NTU divided by the ratio of non-adsorbent (“dead”) to adsorbent (“live”) thermal masses. The best of the three configurations consists of thin adsorbent (zeolite) tiles epoxied to the heat exchanger plates (sheets) with screen wire pin fins in the oil passages to enhance heat transfer.
Hydrodynamics of Cerebrospinal Fluid in Spinal Canal With Chiari Malformation and Syringomyelia
Authors: Kalata Wojciech , Martin Bryn , Oshinski John , Loth Francis
Published: April 2008

Magnetic resonance imaging (MRI) is has great potential as a tool for diagnosis of neurological diseases such as Chiari malformation (CM) and syringomyelia (SM). Its extended capability to obtain in-vivo velocities of blood or cerebrospinal fluid (CSF) allowed engineers to perform studies with engineering analysis applications such as computational fluid dynamics and physical modeling. Recently, a new MR technique called balanced steady-state free procession (bSSFP) cine imaging was developed for analysis of geometrical changes during the cardiac cycle due to compliance [1]. This study used MRI utilities to investigate hydrodynamic environment of CSF in the sub-cranial subarachnoid space (SAS). A model was constructed to simulate fluid dynamics of CSF in SAS. This model will allow investigation of detailed pressure and velocity using laser Doppler anemometry and pressure transducers. The MRI data from patient, healthy volunteers, the flow model were compared.
Microchannel Experimental Structure for Measuring Temperature Fields During Convective Boiling
Authors: Kramer Theresa A. , Flynn Roger D. , Fogg David W. , Wang Evelyn N. , Hidrovo Carlos H. , Goodson Kenneth E. , Prasher Ravi S. , Chau David S. , Narasimhan Sridhar
Published: April 2008

This work designs and fabricates a microchannel structure for measurement of wall temperature fields in two-phase flow. The microchannel with hydraulic diameter of 100 micrometers is etched into a suspended beam of silicon with three independently heated regions and integrated doped silicon resistors sensitive to channel temperature. Doped silicon resistors are also sensitive to strain in the silicon caused by pressure transients in the channel, so sensors are designed with two different orientations and thus two different piezoresistive coefficients to allow decoupling of pressure and temperature effects. Use of a 400 micrometer wide suspended beam reduces side-wall conduction compared to a bulk sample and provides better opportunities to measure the influence of flow regimes on heat transfer coefficients in future work. Use of the central heater reduces fluid preheating in the inlet plenum. The measured temperature distributions at flowrates up to 0.25 ml/min with heat fluxes into the silicon beam up to 78 W/cm2 show initial capabilities of the structure.
Analytical Model Development and Model Reduction for Electromechanical Brake System
Authors: Kwak Jaeho , Yao Bin , Bajaj Anil
Published: April 2008

This paper presents a detailed analytical model development which can describe the dynamic behavior of the electromechanical brake-by-wire (BBW) system over the entire operating range. The complete model has 10 degree-of-freedom (DOF) and includes essential nonlinearities such as gear backlashes, Coulomb frictions, and disk gap clearance. Such a full model is reduced to 6 degree-of-freedom model in SIMULINK for simulation study of the effectiveness and the achievable performance of different hardware and controller designs, an invaluable tool in the early design stage of a product. Simulation results show that the model is able to reproduce various nonlinear characteristics including typical structural hysteresis as shown in real brake assembly. The linearized version of the full nonlinear model is then obtained for its modal properties to understand the modes that are critical to the low frequency dynamics of the overall system. The results of the modal analyses are subsequently utilized to obtain two simplified models, one for non-contact mode and the other for the contact mode of operation. The concepts of two simplified models well capture the dynamic characteristics of the system over the frequencies of interest and are being used in the controller (e.g., clamping force control) and estimator (e.g., gap clearance estimation) designs that are under investigation.
The Thermal Conductance of Indium-Filled Contacts at Cryogenic Temperatures
Authors: Phelan Patrick E. , Zhang Meng
Published: April 2008

Indium foil is often used to increase the thermal contact conductance hc of junctions at cryogenic temperatures, yet relatively few experimental data on hc at subambient temperatures are available. Here, experimental measurements of hc at a copper/copper junction containing a 25.4-μm-thick indium foil are reported. The average sample temperature ranged from 40 to 180 K, and the contact pressures ranged from 0.2 to 20 MPa. Although it was originally anticipated that increasing the contact pressure would lead to increasing hc, the observed hc showed little or no dependence on contact pressure. This was attributed to the severe nonflatness of the copper surfaces. Comparison between the measured hc, and that calculated from existing “flat” and “nonflat” theories indicated better agreement with the “nonflat” model, although the model still predicted that hc should depend on pressure.
Single High Aspect Ratio Pillar Support Structures: Multi-Scale Chip Integrated Conformal Structures
Authors: Northen M. T. , Turner K. L.
Published: April 2008

This paper describes the realization of the integration of micro and nanoscale conformal structures. A new dry processing technique is used to create structures supported by a single high aspect ratio pillar support (SHARPS), creating submicron single crystal silicon features, with tight geometric control, attached to much larger (10–200μm) silicon dioxide platforms. The platforms have lithographically defined two dimensional shapes. The curvature of the platforms is adjusted through metal deposition and subsequent processing. The flexibility of the structures allows them to conform to meso and microscale roughness. To account for nanoscale conformance stochastic arrays of vertically aligned titania nanofibers are created on the platform surface. The application of the system as a passive microadhesive is investigated using a nanoindenter. Results show that the titania nano fiber surface offers significant increase in adhesion over smooth silicon dioxide or titanium surfaces. However when used in conjunction with the SHARPS structures the fibers are too stiff to allow for conformance to the surface prior to larger scale conformation, thus the combination does not increase the overall adhesion.
Adiabatic Effectiveness Measurements and Predictions of Leakage Flows Along a Blade Endwall
Authors: Ranson W. W. , Thole K. A. , Cunha F. J.
Published: April 2008

Traditional cooling schemes have been developed to cool turbine blades using high-pressure compressor air that bypasses the combustor. This high pressure forces cooling air into the hot main gas path through seal slots. While parasitic leakages can provide a cooling benefit, they also represent aerodynamic losses. The results from the combined experimental and computational studies reported in this paper address the cooling benefit from leakage flows that occur along the platform of a first stage turbine blade. A scaled-up, blade geometry with an upstream slot, a mid-passage slot, and a downstream slot was tested in a linear cascade placed in a low speed wind tunnel. Results show that the leakage flow through the mid-passage gap provides only a small cooling benefit to the platform. There is little to no benefit to the blade platform that results by increasing the coolant flow through the mid-passage gap. Unlike the mid-passage gap, leakage flow from the upstream slot provides good cooling to the platform surface, particularly in certain regions of the platform. Relatively good agreement was observed between the computational and experimental results although computations overpredicted the cooling.
Laser-Based Fabrication of Polymer Micro-Fluidic Devices
Authors: Kim Joohan , Xu Xianfan
Published: April 2008

Micro-fluidic devices have many applications such as clinical diagnostics, drug delivery, and microelectronics cooling. So far, most micro-fluidic devices are fabricated using the well established photo-lithography process. In this paper, we present laser-based techniques for fabricating polymer micro-fluidic devices. Advantages using polymers as a material for micro-fluidic applications are discussed. A UV excimer laser and a femtosecond laser are used to machine polymer micro-fluidic structures directly. This direct machining process suits the need of rapid prototyping, as in many applications changes from the original design are often required. As examples, two polymer micro-systems are developed: a micro-check valve and a micro diffuser pump. Further, a micro stamping process for rapid replication is also developed. A photoetchable glass-ceramic stamp is utilized for this process and several polymer-micro devices are fabricated using this process.
Velocity Measurements Inside a Hemodialysis Graft In Vitro Model
Authors: Smith David S. , Loth Francis , Bassiouny Hisham S. , Fischer Paul , Grogan Jennifer K. , Lee Sang-Wook
Published: April 2008

Arteriovenous (AV) grafts, which provide an access site for hemodialysis, typically produce a high flow rate environment with pressure and velocity fluctuations; high and low wall shear stress, and vibration. Laser Doppler anemometry (LDA) was performed at Reynolds number (Re) 1200 on an in vitro model, which was constructed from computerized tomography (CT) images of a perfusion fixed plastic cast of a canine venous anastomosis. The results obtained were compared to numerical results and to results previously obtained with idealized in vitro models. This study showed the importance of an accurate geometry in characterizing the flow environment inside an AV graft. Good agreement between the computational fluid dynamics (CFD) and LDA was observed although differences were clearly present.
Variable Transmission Compliance With an MR Damper
Authors: Westervelt E. R. , Schmiedeler J. P. , Washington G.
Published: April 2008

This paper presents a novel transmission design that consists of a parallel combination of an MR damper and a compliant element together acting in series with an actuator. By adjusting the magnetic field to vary the amount of damping, the transmission can be switched between compliant and effectively rigid modes. Transmission compliance between an actuator and its load has several benefits: It enables (1) storage of elastic energy to improve efficiency, (2) filtering of shocks acting on the load that would otherwise be transmitted to the actuator, and (3) facilitation of force control by converting it to a position control problem. Despite these benefits, the design objective for most robotic systems remains to minimize transmission compliance to improve transmission bandwidth, improving the ability to control the position of the load with high precision. With the new transmission presented in this paper, compliance becomes a tunable quantity allowing joint stiffness to be optimized based upon the task requirements.
Direct Synthesis and Self-Assembly of Silicon Nanowires
Authors: Englander Ongi , Christensen Dane , Kim Jongbaeg , Lin Liwei
Published: April 2008

The direct synthesis and self-assembly of silicon nanowires to yield a two-terminal, nano-to-micro integrated system has been demonstrated. The process takes advantage of localized heating to initiate and sustain a bottom up nanowire synthesis mechanism. As soon as the nanowire synthesis process is complete, the integrated system is ready for characterization of mechanical and electrical properties as well as functionalization for sensing applications. The process is CMOS compatible and eliminates the nano-to-micro contact formation process that is currently required of traditional processes.
Modeling of Fiber Bragg Grating Sensor Response Due to Combined Effects
Authors: Prabhugoud Mohanraj , Peters Kara
Published: April 2008

This article presents a finite element formulation for the calculation of the spectral response of a fiber Bragg grating sensor embedded in a host material system. The formulation is based on a 3D element for which the propagation constant is calculated from the optical and geometric properties in the plane perpendicular to light propagation, after which the optical transfer matrix is calculated. The effects of axial strain, transverse strain, fiber curvature and shear loading are implemented into the formulation. This novel approach permits the prediction of the sensor response when the sensor is embedded in a complicated material system for which analytical or approximative solutions do not accurately predict the strain state in the sensor. A numerical example of a relatively simple sensor geometry is presented to verify the formulation. The integration of the proposed sensor finite element formulation into a classical structural mechanics finite element program to perform the complete analysis is also discussed.
Silicon Microarray Pin With Selective Hydrophobic Coating
Authors: Tsai Jane Gin Fai , Kim Chang-Jin , Chen Zugen , Nelson Stanley
Published: April 2008

We have recently demonstrated the viability of silicon microarray pins, taking advantage of lithographic and batch processing of silicon micromachining in comparison with conventional and serial processing currently used for commercial pins. The reduced spot size (< 50% in diameter, i.e., > 4X in array density), however, made such undesirable needs as preprinting more pronounced. Preprinting, a common practice in microarray printing, drains out the excess liquid formed outside the liquid channel during dipping. In this paper, we describe how surface wettability can be controlled and report its dramatic effect on the printing performance, for the first time. By making the exterior surfaces hydrophobic and the interior surface hydrophilic, the excess liquid outside the liquid channel is eliminated, and the advantages of silicon-micromachined pins are fully exercised.
Galvanic Cell Formation During MEMS Release Processes: Implications for Sub-Micron Device Fabrication
Authors: Miller David C. , Gall Kenneth A. , Stoldt Conrad R.
Published: April 2008

The addition of a noble metallization layer to doped polysilicon results in the formation of a galvanic cell when the composite is submerged in aqueous hydrofluoric acid. A corrosion current created by the galvanic cell promotes the electrochemical etching of silicon in contact with the acidic solution. Here, we demonstrate the galvanic corrosion of phosphorus-doped polysilicon when a gold metallization layer is used. As a consequence of galvanic corrosion, a number of significant changes to the polysilicon structural layers are observed including a finite polysilicon etch rate, an increase in electrical resistance (both ohmic and non-ohmic), a change in curvature (i.e. mechanical shape), and a decrease in mechanical resonant frequency. The observed change in electrical and mechanical performance on micromechanical structures necessitates more careful consideration of the post-processing procedures, as well as the choice of device metallization layer. The physical impact of corrosion becomes even more significant as device scale is decreased.
Limiting Performance of High Throughput Continuous Flow Micro-PCR
Authors: Chen Pin-Chuan , Hashimoto Masahiko , Mitchell Michael W. , Nikitopoulos Dimitris E. , Soper Steven A. , Murphy Michael C.
Published: April 2008

Continuous flow polymerase chain reaction (CFPCR) devices are compact reactors suitable for microfabrication and the rapid amplification of target DNAs. For a given reactor design, the amplification time can be reduced simply by increasing the flow velocity through the isothermal zones of the device; for flow velocities near the design value, the PCR cocktail reaches thermal equilibrium at each zone quickly, so that near ideal temperature profiles can be obtained. However, at high flow velocities there are penalties of an increased pressure drop and a reduced residence time in each temperature zone for the DNA/reagent mixture, potentially affecting amplification efficiency. This study was carried out to evaluate the thermal and biochemical effects of high flow velocities in a spiral, 20 cycle CFPCR device. Finite element analysis (FEA) was used to determine the steady-state temperature distribution along the micro-channel and the temperature of the DNA/reagent mixture in each temperature zone as a function of linear velocity. The critical transition was between the denaturation (95°C) and renaturation (55°C-68°C) zones; above 6 mm/s the fluid in a passively-cooled channel could not be reduced to the desired temperature and the duration of the temperature transition between zones increased with increased velocity. The amplification performance of the CFPCR as a function of linear velocity was assessed using 500 and 997 base pair (bp) fragments from λ-DNA. Amplifications at velocities ranging from 1 mm/s to 20 mm/s were investigated. Alternative design of PCR was investigated. Shuttle PCR has a single straight channel and a DNA plug, driven by electrokinetic flow, will move forward and backward in the microchannel to achieve the repetitive thermal cycles. Thermal performance, independent insulated temperature blocks, and molecular and thermal diffusion were evaluated.
A MEMS Tunable Capacitor Based on Plastically Deformed Vertical Comb Sets
Authors: Kim Jongbaeg , Lin Liwei
Published: April 2008

We report microfabricated tunable capacitors based on plastically deformed vertical comb sets using a batch process. The arrangement of cascaded comb finger sets and the uniqueness of the angular vertical comb actuators enable large tuning ratio with a small angular displacement. The capacitors are made of 50μm-thick single-crystal silicon on SOI wafer and actuated by self-aligned vertical comb-sets giving a tuning ratio of 4.93 from 0.194 to 0.96pF with a tuning voltage of 100 Volts. As such, this tunable capacitor could find applications in RF communication such as parametric amplifiers, harmonic frequency generators and voltage-controlled oscillators.
An Antagonistic Flexural Unit Cell for Design of Shape Morphing Structures
Authors: Sofla Aarash Y. N. , Elzey Dana M. , Wadley Haydn N. G.
Published: April 2008

An antagonistic flexural unit cell (AFC) concept for the design and fabrication of novel 2-D and 3-D lightweight shape morphing structures is introduced. A fully reversible flexural shape changing cell utilizing opposing one-way shape memory alloy (SMA) actuators is shown to require no spring-like bias elements. The SMA actuating elements are arranged such that the actuation (contraction) of one of them stretches the other one in the cell, preparing it to be actuated later to reverse a flexural displacement. This antagonistic operation allows fully reversed cyclic operation. The focus of this paper is an assessment of performance at the single cell level. The cell logically provides four possible configurations in different stages of its cycle. Two of them are of particular interest because they provide two different fixed shapes for the cell that can be maintained without the continuous supply of external energy. The final deformations of the cell and equilibrium stresses in the SMA elements depend on the amount of stored shape memory strain in each element, external forces and cell geometry. A model is developed, which allows a full characterization of the AFC. The model is used to study NiTi SMA-based AFCs and the results are therefore directly applicable to the design of shape morphing structures using such unit cells.
Disposable Polydimethylsiloxane/Silicon Hybrid Chips for Protein Detection
Authors: Li Shifeng , Fozdar David , Shao Dongbing , Chen Shaochen , Floriano Pierre N. , Christodoulides Nicolaos , Ali Mehnaaz F. , Dharshan Priya , McDevitt John T. , Neikirk Dean
Published: April 2008

This paper presents disposable protein analysis chips with single and multiple chambers - constructed from poly (dimethylsiloxane) (PDMS) and silicon. The chips are composed of a multilayer stack of PDMS layers that sandwich a silicon microchip. This inner silicon chip features an etched array of microcavities hosting agarose beads. The sample is introduced into the fluid network in the top PDMS layer where it is directed to the bead chamber. After reaction of the analyte with the probe beads, signal generated on the beads is captured with a CCD camera, digitally processed, and analyzed. An established bead-based fluorescent assay for C-reactive protein (CRP) was used here to characterize these hybrid chips. The detection limit of the single chamber protein chip was found to be 1ng/mL. Additionally, using the back pressure compensation method, the signals from each of the four-chamber chip were found to be within 10% of each other. Moreover, the fabrication of the multiple-chamber chip may increase throughput and multiplex assay capacity.
Forced Response of Translating Media With Variable Length and Tension: Application to High-Speed Elevators
Authors: Zhu W. D. , Chen Y.
Published: April 2008

The lateral response of vertically translating media with variable length and tension, subjected to general initial conditions and external excitation, are determined. The translating media are modeled as a taut string and tensioned beams with pinned and fixed boundaries. In each model a rigid body is attached to the lower end of the medium and has a prescribed displacement along the horizontal direction. The rate of change of the energy of the translating medium is analyzed from the control volume and system viewpoints. The models are used to predict the forced response of a moving cable in a high-speed elevator. Three spatial discretization schemes are used to calculate the response and shown to yield the same results. The convergence of the solution for each model is investigated. The approximate solution for the string model with constant tension is compared with its exact solution from the wave method.
Numerical Modeling of Unidirectional Stratified Flow Between Parallel Plates
Authors: Yap Y. F. , Chai J. C. , Toh K. C. , Wong T. N. , Lam Y. C.
Published: April 2008

Unidirectional stratified flow of two fluids between two parallel plates is modeled using the Level-Set method. A localized mass correction term is used to ensure mass conservation at every axial cross section. The mass correction term is based on the mass flowrates. Results for various combinations of density, viscosity and mass flowrate ratios are presented. Available fully-developed exact solutions for unidirectional stratified flow are used to validate the numerical simulations. The evolutions of the interface in the developing region are also captured and compared well with “exact” solutions.
Mechanical Fastener Designs for Use in the Microassembly of 3D Microstructures
Authors: Dechev Nikolai , Mills James K. , Cleghorn William L.
Published: April 2008

This paper describes micro-mechanical fastener designs used to create joints between surface micromachined micro-parts. This is part of ongoing research to develop a general microassembly system capable of assembling various types of microstructures. The microassembly system is based on sequential robotic operations and the use of a microgripper. Two new joint designs referred to as ‘key-lock’ joints and ‘inter-lock’ joints are introduced. Key-lock joints are created by the insertion of a ‘key’ on one micro-part, into a mating slot on another micro-part. By translating the first micro-part within the other, after the key is inserted, it becomes locked into position. Inter-lock joints are created by the perpendicular insertion of one micro-part with a slit, into another micro-part with a slit. The slits create an interference fit and are permanent once the micro-parts are joined. The design of these joints and the experimental results are detailed. In addition, ongoing work involving recent ‘snap-lock’ joint fastener designs is described. This includes an example of a 3D micro-transformer and a stacked microstructure. These various micro-mechanical fasteners demonstrate a number of ways in which micro-parts can be assembled into 3D microstructures.
Development of a Silicon Carbide Micro Four-Point Probe
Authors: Choudhury Arnab , Hesketh Peter J.
Published: April 2008

The process development and fabrication of a cantilever-based micro four-point probe (MFPP) is presented. This device will allow for characterization of film resistance with micrometer-scaled resolution. The proble is designed for deployment on a commercial AFM. The cantilevers are made of amorphous silicon carbide (a-SiC) and the probe body using SU8. The probe consists of two sets of cantilevers, with integrated tips, on parallel planes 8.68 μm apart. This allows the probe to contact the surface in a square array and perform a van der Pauw type measurement. Studies to characterize, pattern and dope the a-SiC have been performed to utilize silicon carbide as both the cantilever structural material as well the conductive element in the sensor. The MFPP has been fabricated and some preliminary tests have been performed.
A Novel Approach to Improving the Available Power Output of Piezoelectric Ultrasonic Motors
Authors: Tieck R. M. , Carman G. P.
Published: April 2008

Piezoelectric actuators have attractive operating properties because they do not generate electromagnetic fields and are not affected by them, and their power output characteristics scale linearly with decreasing size. These actuators have not seen widespread industrial use, however, because they have shown a limited power output. This work presents the initial efforts to increase the available power output of the Piezoelectric Ultrasonic Motor (PUSM). Commercially available PUSMs are limited by the small friction forces generated at the rotor/stator interface. Small friction is generated because current PUMs use rubber or polyimides on the rotor to create as the contact with the stator. Traditionally, PUSM contact material has consisted of rubber or reinforced polyimides. The authors intend to replace the traditional contact layer with a compliant super-elastic Nickel-Titanium (NiTi) thin film shape memory alloy (SMA) layer to increase the available power output by increasing the friction forces at the rotor/stator interface, without significantly increasing the size or weight of the actuator. The unmodified motors were baselined tested, modified, tested and the results compared. Recommendations are made with regard to the results of the modified baseline testing and possible implementation of micromachined ‘teeth’ configurations.
Estimating Thermal Contact Resistance Using Sensitivity Analysis
Authors: Gill Jennifer , Divo Eduardo , Kassab Alain J.
Published: April 2008

Characterization of the thermal contact resistance is important in modeling of multi-component thermal systems which feature mechanically mated surfaces. Thermal resistance is phenomenologically quite complex and depends on many parameters including surface characteristics of the interfacial region and contact pressure. In general, the contact resistance varies as a function of pressure and is non-uniform along the interface. A two dimensional model problem is solved analytically for a known contact resistance between two mated surfaces. The results from the analytical solution are compared with a boundary element solution to the same problem, thus verifying the implementation of the boundary element method code. An inverse problem is formulated to estimate the variation of the contact resistance by using a boundary element method to determine sensitivity coefficients for specific temperature measurement points in the geometry. Temperature measured at these discrete locations can be processed to yield the contact resistance between the two mating surfaces using a simple matrix inversion technique. The inversion process is sensitive to noise and requires using a regularization technique to obtain physically possible results. The regularization technique is then extended to a genetic algorithm for performing the inverse analysis. Numerical simulations are carried out to demonstrate the approach. Random noise is used to simulate the effect of input uncertainties in measured temperatures at the sensors.
Design of a Multi-Axis SMA Actuator Arrays Using Segmented Binary Control
Authors: Cho Kyu-Jin , Asada H. Harry
Published: April 2008

A new approach of designing and controlling a multi-axis actuator system using segmented binary control (SBC) is presented. In SBC, Shape Memory Alloy (SMA) actuator wire is divided into multiple segments and their thermal states are controlled in a binary manner using thermoelectric modules. Two-dimensional array architecture for multi-axis SMA actuators is created using SBC. Similar to the biological muscle network, multi-axis SMA actuator wires can be combined flexibly with a two-dimensional segmentation method in order to activate multiple links of a skeletal robot structure in a coordinated manner. Ten-axis actuator is built using this method. Thermoelectric modules are laid on a substrate made of PCB board and SMA actuators are placed in between two substrate layers with a gap to allow the movement of the actuators. The actuator creates coordinated gross motion as well as independent fine movements with reduced number of control loops. The new actuator architecture will provide a novel actuator system forming a network of array actuators connected to a vast number of bone-like linkages.
Effect of Phonon Dispersion on Transport Properties of Single-Crystalline Dielectrics
Authors: Asheghi Mehdi , Liu Wenjun , Goodson K. E.
Published: April 2008

Thermal conductivity modeling using the Debye approximation can significantly reduce the complexity involved in the evaluation of thermal conductivity integral. Nevertheless, there are several compelling reasons (e.g., inconsistency between the estimations of the density of states used for heat capacity and thermal conductivity) that motivate more detailed modeling of the phonon dispersion in silicon or other diamond-like dielectrics. This manuscript presents closed-form expressions for the dispersion of the longitudinal and transverse modes in diamond-like dielectrics, which are then used to estimate the isotopic scattering rate, phonon spectrum and specific heat. The combinations of the above parameters are then used to predict the thermal conductivity of the bulk silicon and germanium with orders of magnitude variation in the mass fluctuation of isotopes and for the temperature range 2 to 1000 K. While this approach offers an elegant and consistent account of the phonon dispersion in diamond-like materials, however, provides no additional insight into the relative contributions of the longitudinal and transverse phonons to the heat transport.
Thermal Detection of Embedded Tumors Using Infrared Imaging
Authors: Mital Manu , Scott E. P.
Published: April 2008

Breast cancer is the most common cancer among women. Statistics released by American Cancer Society (1999) show that every 1 in every 8 women in the United States is likely to get breast cancer during her lifetime. Thermography, also known as thermal or infrared imaging, is a procedure to determine if an abnormality is present in the breast tissue temperature distribution, which may indicate the presence of an embedded tumor. In the year 1982, United States Food and Drug Administration (FDA) approved thermography as an adjunct method of detecting breast cancer, which could be combined with other established techniques like mammography. Although thermography is currently used to indicate the presence of an abnormality, there are no standard protocols to interpret the abnormal thermal images and determine the size and location of an embedded tumor. This research explores the relationship between the physical characteristics of an embedded tumor and the resulting temperature distributions on the skin surface. Experiments were conducted using a resistance heater that was embedded in agar in order to simulate the heat produced by a tumor in the biological tissue. The resulting temperature distribution on the surface was imaged using an infrared camera. In order to estimate the location and heat generation rate of the source from these temperature distributions, a genetic algorithm was used as the estimation method. The genetic algorithm utilizes a finite difference scheme for the direct solution of Pennes bioheat equation. It was determined that a genetic algorithm based approach is well suited for the estimation problem and that thermography can prove to be a valuable tool in locating tumors if combined with such an algorithm.
Effect of Mechanical and Thermal Cycling on Shape Memory Properties of High Temperature Cu-Al-Ni Single Crystals
Authors: Kannarpady Ganesh K. , Bhattacharyya A.
Published: April 2008

With a view towards applications as actuators, the effect of mechanical cycling followed by thermal cycling on 1.5 mm diameter Cu-13.3%Al-4%Ni (by weight) single crystal wires with high stress-free transformation temperatures: Mf = 96°C, Ms = 105.5°C, As = 111.6°C and Af = 115.8°C (determined by the method of tangents) have been studied at different ambient temperatures in the range 25–125°C. The tests are carried out in an Instron machine with an environmental chamber. Stress cycling at a given ambient temperature was carried out for an overall strain of 9% until the stress-strain curves became fairly repeatable. A total of 35 stress cycles were needed to span the ambient temperature range, 25–125°C. The material showed an excellent retention of the shape memory effect in the range of 25–100°C (this is below the Af = 115.8°C of the as-received sample), excellent pseudoelasticity at 125°C, and no irreversible plastic deformation. A net downward shift of transformation temperatures by about 5°C did occur over the first 11 cycles. This was followed by a reversal of the downward shift and the transformation temperatures stabilized by the 35th cycle close to those of the as-received sample. The stabilized temperatures were: Mf = 95°C, Ms = 106.5°C, As = 110°C and Af = 118.5°C (method of tangents). However, the transformation occurred over a wider temperature range as compared to that of the as-received sample, especially during the austenite to martensite transformation on cooling. These features point to the possibility of the Cu-13.3%Al-4%Ni single crystal as a highly competitive candidate for actuator applications.
Effects of “Finiteness” on Wave Propagation and Vibration in Elastic Periodic Structures
Authors: Hussein Mahmoud I. , Hulbert Gregory M. , Scott Richard A.
Published: April 2008

The dynamics of finite elastic periodically layered structures is compared to that of the constituent periodic media. The focus is on both the frequency behavior and the spatial response. Through simulations of harmonically induced wave motion within a finite number of unit cells, the frequency band structure and attenuation characteristics of infinite and finite periodic systems are shown to conform under certain conditions. It is concluded that only one or two unit cells of a periodic material are required for “frequency bandness” to carry through to a finite structure, and only three to four unit cells are necessary for significant wave attenuation to take place when the structure is excited at a stop-band frequency. Furthermore, vibration analyses are conducted on a bounded fully periodic structure. The natural frequency spread is shown to conform with the frequency band layout of the infinite periodic material, and the steady-state forced response is observed to exhibit mode localization patterns that resemble those of the infinite periodic medium. These results could be used for setting guidelines for the design of periodic structures for vibration isolation and frequency filtering.
Optimal Damping Wave Vibration Control of Coupled Bending-Torsion Composite Beams
Authors: Mei C. , Tan C. A.
Published: April 2008

In this paper, an active vibration controller, designed from a wave standpoint, for suppressing coupled bending-torsion vibrations in fiber-reinforced composite beam structures is presented. Vibration control for composite structures is by far a more critical task than for their metallic counterparts because composite materials are generally much lighter and hence are more prone to unwanted vibrations. Moreover, as a result of the directional nature of fiber-reinforced composites, the vibration modes are coupled, rendering the vibration analysis and control of these structures complex. Employing a wave-based approach, vibrations are described as superposition of waves propagating through the structure. Active controllers are designed to optimally dissipate the energy of incoming vibration waves. Particularly, damping-type controllers, based on measurements of the transverse deflection and/or the torsional rotation, are obtained. These controllers are simple in form and easily implementable. Numerical examples are presented and it is shown that the wave-based active controller design is effective in suppressing vibration in materially coupled composite structures.
Experimental Study of a Gas-Liquid Cylindrical Cyclone Separator Performance
Authors: Mele´ndez-Rami´rez Antonio J. , Reyes-Gutie´rrez Miguel A. , Rojas-Solo´rzano Luis R. , Mari´n-Moreno Juan C. , Colmenares Jose´
Published: April 2008

New data of the experimental performance of a Gas-Liquid Cylindrical Cyclone (GLCC) separator are presented. The data were collected using a 2 3/4” (0.07m) ID GLCC model working with an air-glycerin mixture. The inlet liquid flow rate, the inlet gas flow rate, the tangential liquid velocity inside the separator body and the gas carry under were measured for an operation regime without liquid carry over. The influence of the first three parameters over the gas carry under was established. Results show the separator efficiency is mainly affected by the inlet gas flow rate for the explored conditions with slug flow at the GLCC entrance.
Design and Analysis of a Nano-Probe of the AFM Based on the Small/Large Deflection Theory
Authors: Lin Chun-Te , Liao Wei-Chuan , Chen Jen-Yi , Su Hui-Chi , Chiang Kuo-Ning
Published: April 2008

The atomic force microscope (AFM) is a newly developed high resolution microscopy technique which is capable of measuring of nano-scale pattern, nanofabrication, data storage and material analysis in the mechanical, chemical and biological fields. The nano-probe is the most critical component of the AFM, and it consists of three parts: a sharp tip, a cantilever beam and a supporting base. The tip must be sharp enough to measure the surface topography with a high resolution. The cantilever beam must have the appropriate spring constant and resonant frequency for the type of operation selected. The supporting base must be of a suitable size for loading into the probe head. Therefore, depending on the various applications, the nano-probe structures used in the AFM should must meet the following criteria: (1) good tip sharpness with a small radius apex, (2) small spring constant and (3) high resonant frequency. This research will propose the design rule for three types of nano-probes, including the rectangular-shaped, V-shaped and chamfer V-shaped nano-probe for the AFM using the finite element method. The fundamental mechanical parameters of a nano-probe for an AFM are its spring constant, its resonant frequency and its physical dimensions. Research of the relevant literatures indicates that numerous researchers only consider the small deflection theory when analyzing the above-mentioned physical properties of the nano-probe. However, the small deflection theory is suitable only when the behavior of nonlinear geometry has not taken place in the structure. But, the applications of the nano-probe are increasing at a rapid rate, and the geometric dimensions or physical properties of nano-probe are changing from the traditional applications. The measuring of the red corpuscle requires a small size probe, but the ultra-high resolution topography is demanding an ever increasing applied force. The phenomenon of nonlinear geometry is occurring in the structure at present, and as a result the small deflection theory is no longer suitable for analyzing the nano-probe. This research introduces the large deflection theory in the finite element method (FEM) to investigate the geometrical size and the physical properties of the nano-probe.