Open Access. Powered by Scholars. Published by Universities.®

Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

Faculty Publications

Discipline
Institution
Keyword
Publication Year
File Type

Articles 2731 - 2760 of 3294

Full-Text Articles in Engineering

Water Transport In Polymer Electrolyte Membrane Electrolyzers Used To Recycle Anhydrous Hcl: I. Characterization Of Diffusion And Electro-Osmotic Drag, Sathya Motupally, Aaron J. Becker, John W. Weidner Jan 2002

Water Transport In Polymer Electrolyte Membrane Electrolyzers Used To Recycle Anhydrous Hcl: I. Characterization Of Diffusion And Electro-Osmotic Drag, Sathya Motupally, Aaron J. Becker, John W. Weidner

Faculty Publications

In this paper, diffusion and electro-osmotic drag of water across Nafion® membranes in the presence of HCl are characterized. For all the measurements, one side of the Nafion membrane was in contact with liquid water and the other side with gaseous anhydrous HCl. To characterize diffusion of water, the open-circuit flux of water across a catalyst-coated Nafion 115 membrane was measured as a function of HCl flow rate and temperature at a constant cell pressure of 1 atm. Due to the nature of varying driving force for diffusion as a function of HCl flow rate, the experimental data was analyzed …

Go to article

Development Of A Novel Co Tolerant Proton Exchange Membrane Fuel Cell Anode, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang Jan 2002

Development Of A Novel Co Tolerant Proton Exchange Membrane Fuel Cell Anode, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang

Faculty Publications

Typically Pt is alloyed with metals such as Ru, Sn, or Mo to provide a more CO-tolerant, high-performance proton exchange membrane fuel cell (PEMFC) anode. In this work, a layer of carbon-supported Ru is placed between the Pt catalyst and the anode flow field to form a filter. When oxygen is added to the fuel stream, it was predicted that the slow H2 kinetics of Ru in this filter would become an advantage compared to Pt and Pt:Ru alloy anodes, allowing a greater percentage of O2 to oxidize adsorbed CO to CO2. With an anode feed …

Go to article

Studies On Capacity Fade Of Spinel-Based Li-Ion Batteries, Ramadass Premanand, Anand Durairajan, Bala Haran, Ralph E. White, Branko N. Popov Jan 2002

Studies On Capacity Fade Of Spinel-Based Li-Ion Batteries, Ramadass Premanand, Anand Durairajan, Bala Haran, Ralph E. White, Branko N. Popov

Faculty Publications

The performance of Cell-Batt® Li-ion cells using nonstoichiometric spinel as the positive electrode material has been studied at different charging rates. The capacity of the cell was optimized based on varying the charging current and the end potential. Subsequent to this, the capacity fade of these batteries was studied at different charge currents. During cycling, cells were opened at intermittent cycles and extensive material and electrochemical characterization was done on the active material at both electrodes. For all charge currents, the resistance of both the electrodes does not vary significantly with cycling. This result is in contrast with cells …

Go to article

Modeling The Effects Of Ion Association On Alternating Current Impedance Of Solid Polymer Electrolytes, Changqing Lin, Ralph E. White, Harry J. Ploehn Jan 2002

Modeling The Effects Of Ion Association On Alternating Current Impedance Of Solid Polymer Electrolytes, Changqing Lin, Ralph E. White, Harry J. Ploehn

Faculty Publications

This work presents a rigorous continuum model describing the transport of ions and associated ion pairs in solid polymer electrolytes subjected to small amplitude alternating current (ac) excitation. The model treats ion association as a reversible reaction among ions and ion pairs. Dimensionless governing equations are developed from component mass balances, flux equations based on dilute solution theory, and the Poisson equation. Assuming reversible electrode reactions and electroneutrality, the model equations have an analytical solution. Further simplifications are possible in limiting cases (weak and strong association, zero and infinite frequency excitation), giving expressions consistent with previously published models. We use …

Go to article

Trusted Autonomy, Michael N. Huhns, Duncan A. Buell Jan 2002

Trusted Autonomy, Michael N. Huhns, Duncan A. Buell

Faculty Publications

We describe how agents are the right building blocks for constructing trustworthy systems. Robust software and trusted autonomy represent the future for agent technology and software engineering.

Go to article

Weaving A Computing Fabric, Michael N. Huhns, Larry M. Stevens, John W. Keele, Jim E. Wray, Warren M. Snelling, Greg P. Harhay, Randy R. Bradley Jan 2002

Weaving A Computing Fabric, Michael N. Huhns, Larry M. Stevens, John W. Keele, Jim E. Wray, Warren M. Snelling, Greg P. Harhay, Randy R. Bradley

Faculty Publications

As sources of information relevant to a particular domain proliferate, we need a methodology for locating, aggregating, relating, fusing, reconciling, and presenting information to users. Interoperability thus must occur not only among the information, but also among the different software applications that process it. Given the large number of potential sources and applications, interoperability becomes an extremely large problem for which manual solutions are impractical. A combination of software agents and ontologies can supply the necessary methodology for interoperability.

Go to article

Agents As Web Services, Michael N. Huhns Jan 2002

Agents As Web Services, Michael N. Huhns

Faculty Publications

Web services are extremely flexible. Most advantageously, a developer of Web services need not know who or what will use the services being provided. The paper discusses current standards for Web services, directory services and the Semantic Web. It considers how agents extend Web services in several important ways.

Go to article

Robust Software, Michael N. Huhns, Vance T. Holderfield Jan 2002

Robust Software, Michael N. Huhns, Vance T. Holderfield

Faculty Publications

Agents offer a convenient level of granularity at which to add redundancy a key factor in developing robust software. Blindly adding code introduces more errors, makes the system more complex, and renders it harder to understand. However, adding more code can make software better, if it is added in the right way. As this article describes, the key concepts appear to be redundancy and the appropriate granularity.

Go to article

Agent Societies: Magnitude And Duration, Michael N. Huhns Jan 2002

Agent Societies: Magnitude And Duration, Michael N. Huhns

Faculty Publications

If you only need agents to search the Web for cheap CDs, scalability is not an issue. The Web can support numerous agents if each acts independently. In short order, however, billions of embedded agents that sense their environment and interact with us and other agents will fill our world, making the human environment friendlier and more efficient. These agents will need not only scalable infrastructures and communication services, but also scalable social services encompassing ethics and laws. Research projects are under way around the world to develop and deploy such services. The author takes a look at the critical …

Go to article

Making Agents Secure On The Semantic Web, Csilla Farkas, Michael N. Huhns Jan 2002

Making Agents Secure On The Semantic Web, Csilla Farkas, Michael N. Huhns

Faculty Publications

Agents were designed to collaborate and share information. While highly desirable for interoperability, this feature is scary from the security perspective. Illegal inferences, supported by semantic Web technology and ontologies, might enable users to access unauthorized information. In addition to semantic associations and replicated data with different sensitivity, malicious agents could also exploit statistical inferences. Although each agent in a system might behave in a desired and secure way, their combined knowledge could be used to disclose sensitive data. The research community must therefore develop and implement techniques that allow control over released data. To answer the questions related to …

Go to article

Estimation Of Diffusion Coefficient Of Lithium In Carbon Using Ac Impedance Technique, Qingzhi Guo, Venkat R. Subramanian, John W. Weidner, Ralph E. White Jan 2002

Estimation Of Diffusion Coefficient Of Lithium In Carbon Using Ac Impedance Technique, Qingzhi Guo, Venkat R. Subramanian, John W. Weidner, Ralph E. White

Faculty Publications

The validity of estimating the solid phase diffusion coefficient, Ds, of a lithium intercalation electrode from impedance measurement by a modified electrochemical impedance spectroscopy (EIS) method is studied. A macroscopic porous electrode model and concentrated electrolyte theory are used to simulate the synthetic impedance data. The modified EIS method is applied for estimating Ds. The influence of parameters such as the exchange current density, radius of active material particle, solid phase conductivity, porosity, volume fraction of inert material, and thickness of the porous carbon intercalation electrode, the solution phase diffusion coefficient, and transference number, on the …

Go to article

Using Sputter Deposition To Increase Co Tolerance In A Proton-Exchange Membrane Fuel Cell, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Narender Rana, Stephan Grunow, Timothy C. Stoner, Alain E. Kaloyeros Jan 2002

Using Sputter Deposition To Increase Co Tolerance In A Proton-Exchange Membrane Fuel Cell, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Narender Rana, Stephan Grunow, Timothy C. Stoner, Alain E. Kaloyeros

Faculty Publications

Placing a layer of Ru atop a Pt anode increases the carbon monoxide tolerance of proton-exchange membrane fuel cells when oxygen is added to the fuel stream. Sputter-deposited Ru filter anodes composed of a single Ru layer and three Ru layers separated by Nafion-carbon ink, respectively, were compared to Pt, Pt:Ru alloy, and an ink-based Ru filter anodes. The amount of Pt in each anode was 0.15 mg/cm2 and the amount of Ru in each Ru-containing anode was 0.080 mg/cm2. For an anode feed consisting of hydrogen, 200 ppm CO, and 2% O2 (in the form …

Go to article

Increasing Proton Exchange Membrane Fuel Cell Catalyst Effectiveness Through Sputter Deposition, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Timothy Stoner, Narender Rana Jan 2002

Increasing Proton Exchange Membrane Fuel Cell Catalyst Effectiveness Through Sputter Deposition, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Timothy Stoner, Narender Rana

Faculty Publications

Sputter deposition has been investigated as a tool for manufacturing proton-exchange membrane fuel cell (PEMFC) electrodes with improved performance and catalyst utilization vs. ink-based electrodes. Sputter-depositing a single layer of Pt on the gas diffusion layer provided better performance (0.28 A/cm2 at 0.6 V) than sputtering the Pt directly onto a Nafion membrane (0.065 A/cm2 at 0.6 V) and equaled the performance of the baseline for an equivalent Pt loading. Sputter-depositing alternating layers of Pt and Nafion-carbon ink (NCI) onto the membrane did not increase the performance over the baseline as measured in amperes per centimeter squared due …

Go to article

Simulating Shape Changes During Electrodeposition: Primary And Secondary Current Distribution, Venkat R. Subramanian, Ralph E. White Jan 2002

Simulating Shape Changes During Electrodeposition: Primary And Secondary Current Distribution, Venkat R. Subramanian, Ralph E. White

Faculty Publications

A technique based on the analytical method of lines is presented for predicting shape changes during electrodeposition. The technique is presented for both primary and secondary current distributions. The method presented does not require iterations for nonlinear Butler-Volmer boundary conditions or changing electrode shapes. The technique is based on a semianalytical method developed earlier for predicting current distributions in electrochemical cells. This technique is attractive because it provides a symbolic solution for the Laplace equation, and hence requires less computation time to perform case studies.

Go to article

Electrochemical Filtering Of Co From Fuel-Cell Reformate, Balasubramanian Lakshmanan, Wayne Huang, John W. Weidner Jan 2002

Electrochemical Filtering Of Co From Fuel-Cell Reformate, Balasubramanian Lakshmanan, Wayne Huang, John W. Weidner

Faculty Publications

A proton exchange membrane fuel cell was used as a flow reactor for continuous preferential oxidation of CO over H2 from 1.0% CO in H2 under pulse-potential control. By varying the pulse profile ~e.g., on-time, off-time, pulse potential! the CO and H2 oxidation currents were varied independently. The improvement in faradaic selectivity between CO and H2 oxidation results from the promotion of CO adsorption during the off ~i.e., open-circuit! portion of the pulse. Therefore, during the on portion CO oxidation was preferred while the surface was covered with CO.

Go to article

Anodic Behavior Of Ti In Koh Solutions: Ellipsometric And Micro-Raman Spectroscopy Studies, A. Prusi, Lj. Arsov, Bala Haran, Branko N. Popov Jan 2002

Anodic Behavior Of Ti In Koh Solutions: Ellipsometric And Micro-Raman Spectroscopy Studies, A. Prusi, Lj. Arsov, Bala Haran, Branko N. Popov

Faculty Publications

Anodic formation of oxide films on titanium surfaces, in various concentrations of aqueous KOH solutions, have been studied using ellipsometry and micro-Raman spectroscopy. By in situ ellipsometric measurements the coefficient of film thickness growth and indexes of refraction of anodic oxide films have been determined. The voltage at which the oxide film breaks down is strongly dependent on the KOH concentration. Further, the solution concentration strongly influences the potential at which the oxide film is transformed from the amorphous state to crystalline form. Using micro-Raman spectroscopy four crystalline forms of titanium oxides, namely, anatase, brookite, corundum, and rutile, have been …

Go to article

Study Of Sn-Coated Graphite As Anode Material For Secondary Lithium-Ion Batteries, Basker Veeraraghavan, Anand Durairajan, Bala Haran, Branko N. Popov, Ronald Guidotti Jan 2002

Study Of Sn-Coated Graphite As Anode Material For Secondary Lithium-Ion Batteries, Basker Veeraraghavan, Anand Durairajan, Bala Haran, Branko N. Popov, Ronald Guidotti

Faculty Publications

Tin-graphite composites have been developed as an alternate anode material for Li-ion batteries using an autocatalytic deposition technique. The specific discharge capacity, coulombic efficiency, rate capability behavior, and cycle life of Sn-C composites has been studied using a variety of electrochemical methods. The amount of tin loading and the heating temperature have a significant effect on the composite performance. The synthesis conditions and Sn loading on graphite have been optimized to obtain the maximum reversible capacity for the composite electrode. Heating the composite converts it from amorphous to crystalline form. Apart from higher capacity, Sn-graphite composites possesses higher coulombic efficiency, …

Go to article

Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn Jan 2002

Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn

Faculty Publications

This work presents a mathematical model for charge/discharge of electrochemical capacitors that explicitly accounts for particle-packing effects in a composite electrochemical capacitor consisting of hydrous RuO2 nanoparticles dispersed within porous activated carbon. The model is also used to investigate the effect of nonuniform distributions of salt in the electrolyte phase of the electrode in the context of dilute solution theory. We use the model to compare the performance of capacitors with electrodes made from different activated carbons and to investigate the effects of varying carbon content and discharge current density. Even at low discharge current density, concentration polarization in …

Go to article

Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn Jan 2002

Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn

Faculty Publications

This work presents a mathematical model for charge/discharge of electrochemical capacitors that explicitly accounts for particle-packing effects in a composite electrochemical capacitor consisting of hydrous RuO2 nanoparticles dispersed within porous activated carbon. The model is also used to investigate the effect of nonuniform distributions of salt in the electrolyte phase of the electrode in the context of dilute solution theory. We use the model to compare the performance of capacitors with electrodes made from different activated carbons and to investigate the effects of varying carbon content and discharge current density. Even at low discharge current density, concentration polarization in …

Go to article

Surface Micromachined Force Gauges: Uncertainty And Reliability, Jonathan W. Wittwer, Troy Gomm, Larry L. Howell Jan 2002

Surface Micromachined Force Gauges: Uncertainty And Reliability, Jonathan W. Wittwer, Troy Gomm, Larry L. Howell

Faculty Publications

Surface micromachining of micro-electro-mechanical systems (MEMS), like all other fabrication processes, has inherent variation that leads to uncertain material and dimensional parameters. By considering the effects of these variations during the design of micro force gauges, the gauge uncertainty and reliability can be estimated. Without means of calibrating micro gauges, these effects are often significant when compared to experimental repeatability. The general force gauge model described in this paper can be used to measure a wide range of forces, and simple design changes can lead to improved accuracy in measurement. A method of probabilistic design is described that is not …

Go to article

Evaluation Of A Compound Probability Model With Tower-Mounted Scatterometer Data, David G. Long, Benjamin E. Barrowes Jan 2002

Evaluation Of A Compound Probability Model With Tower-Mounted Scatterometer Data, David G. Long, Benjamin E. Barrowes

Faculty Publications

Six months of data from the YSCAT94 experiment conducted at the CCIW WAVES research platform on Lake Ontario, Canada, are analyzed to evaluate a compound probability model. YSCAT was an ultrawideband small footprint (ap 1 m) microwave scatterometer that operated at frequencies of 2-18 GHz, incidence angles from 0° to 60°, both h-pol and v-pol, and which tracked the wind using simultaneous weather measurements. The probability distribution function of the measured instantaneous backscattered amplitude (p(a)) is compared to theoretical distributions developed from-the composite model and a simple wave spectrum. Model parameters of the resulting Rayleigh/generalized lognormal distribution probability density function …

Go to article

Using Transition Probability Geostatistics With Modflow, Norman L. Jones, J. R. Walker, S. F. Carle Jan 2002

Using Transition Probability Geostatistics With Modflow, Norman L. Jones, J. R. Walker, S. F. Carle

Faculty Publications

This paper describes a technique for applying the transition probability geostatistics method for stochastic simulation to a MODFLOW model. Transition probability geostatistics has several advantages over traditional indicator kriging methods, including a simpler and more intuitive framework for interpreting geological relationships and the ability to simulate juxtapositional tendencies such s fining-upwards sequences. The indicator arrays generated by the transition probability simulation are converted to layer elevation and thickness arrays for use with the new Hydrogeologic Unit Flow (HUF) package in MODFLOW 2000. This makes it possible to preserve complex heterogeneity while using reasonably sized grids.

Go to article

Spectral Integration Of Microstructure And Design, Brent L. Adams, B. Henrie, M. Lyon, H. Garmestani, Surya R. Kalidindi Jan 2002

Spectral Integration Of Microstructure And Design, Brent L. Adams, B. Henrie, M. Lyon, H. Garmestani, Surya R. Kalidindi

Faculty Publications

Support of the Army Research Office is greatly appreciated. Mechanical design can be conducted in a framework where consideration of microstructure as a continuous design variable is facilitated by the use of a Fourier space. Selection of the mechanical framework for the problem (e.g., mechanical constitutive model and homogenization relations) dictates the dimensionality of the pertinent microstructure representation. Microstructure is comprised of basic elements that belong to the local state space. Local state includes crystallographic phase and orientation, and other parameters such as composition. The local state space is transformed into an isomorphic set in Fourier space. The universe of …

Go to article

Reliability Of Programmable Input/Output Pins In The Presence Of Configuration Upsets, Paul S. Graham, Nathaniel Rollins, Michael J. Wirthlin, Michael P. Caffrey Jan 2002

Reliability Of Programmable Input/Output Pins In The Presence Of Configuration Upsets, Paul S. Graham, Nathaniel Rollins, Michael J. Wirthlin, Michael P. Caffrey

Faculty Publications

Sponsorship: Los Alamos National Laboratories (LA-UR-02-3163). Field programmable gate arrays (FPGAs) are an attractive alternative for space-based remote sensing applications. However, SRAM-based FPGAs are sensitive to radiation induced single-event upsets within the configuration memory. Such configuration upsets may change the logic, routing, and operating modes of a user FPGA design. Upsets within the configuration of an I/O block are especially troublesome as they may impact the operation of other system components. This paper will evaluate the operation of the I/O block within the Xilinx Virtex FPGA in the presence of configuration memory upsets and introduce techniques for detecting and repairing …

Go to article

Localization Of Carriers And Polarization Effects In Quaternary Alingan Multiple Quantum Wells, E. Kuokstis, J. Zhang, M.-Y. Ryu, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur Dec 2001

Localization Of Carriers And Polarization Effects In Quaternary Alingan Multiple Quantum Wells, E. Kuokstis, J. Zhang, M.-Y. Ryu, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur

Faculty Publications

We report on observing a long-wavelength band in low-temperature photoluminescence(PL)spectrum of quaternary Al0.22In0.02Ga0.76N/Al0.38In0.01Ga0.61N multiple quantum wells(MQWs), which were grown over sapphire substrates by a pulsed atomic-layer epitaxy technique. By comparing the excitation-power density and temperature dependence of the PLspectra of MQWs and bulk quaternary AlInGaN layers, we show this emission band to arise from the carrier and/or exciton localization at the quantum well interface disorders. PL data for other radiative transitions in MQWs indicate that excitation-dependent spectra position is determined by screening of the built-in electric field.

Go to article

Ultraviolet Light-Emitting Diodes At 340 Nm Using Quaternary Alingan Multiple Quantum Wells, V. Adivarahan, A. Chitnis, J. P. Zhang, M. Shatalov, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur Dec 2001

Ultraviolet Light-Emitting Diodes At 340 Nm Using Quaternary Alingan Multiple Quantum Wells, V. Adivarahan, A. Chitnis, J. P. Zhang, M. Shatalov, J. W. Yang, Grigory Simin, M. Asif Khan, R. Gaska, M. S. Shur

Faculty Publications

An ultraviolet light-emitting diode with peak emission wavelength at 340 nm is reported. The active layers of the device were comprised of quaternary AlInGaN/AlInGaN multiple quantum wells, which were deposited over sapphire substrates using a pulsed atomic-layer epitaxy process that allows precise control of the composition and thickness. A comparative study of devices over sapphire and SiC substrates was done to determine the influence of the epilayer design on the performance parameters and the role of substrate absorption.

Go to article

Greenland Snow Accumulation Estimates From Satellite Radar Scatterometer Data, Mark R. Drinkwater, David G. Long, Andrew W. Bingham Dec 2001

Greenland Snow Accumulation Estimates From Satellite Radar Scatterometer Data, Mark R. Drinkwater, David G. Long, Andrew W. Bingham

Faculty Publications

Data collected by the C band ERS-2 wind scatterometer (EScat), the Ku band ADEOS-1 NASA scatterometer (NSCAT), and the Ku band SeaWinds on QuikScat (QSCAT) satellite instruments are used to illustrate spatiotemporal variability in snow accumulation on the Greenland ice sheet. Microwave radar backscatter images of Greenland are derived using the scatterometer image reconstruction (SIR) method at 3-day intervals over the periods 1991–1998 and 1996–1997 for EScat and NSCAT, respectively. The backscatter coefficient σ° normalized to 40° incidence, A, and gradient in backscatter, B, in the range 20°–60° are compared with historical snow accumulation data and recent measurements …

Go to article

A Dipolar Coupling Based Strategy For Simultaneous Resonance Assignment And Structure Determination Of Protein Backbones, Fang Tian, Homayoun Valafar, James H. Prestegard Nov 2001

A Dipolar Coupling Based Strategy For Simultaneous Resonance Assignment And Structure Determination Of Protein Backbones, Fang Tian, Homayoun Valafar, James H. Prestegard

Faculty Publications

A new approach for simultaneous protein backbone resonance assignment and structure determination by NMR is introduced. This approach relies on recent advances in high-resolution NMR spectroscopy that allow observation of anisotropic interactions, such as dipolar couplings, from proteins partially aligned in field ordered media. Residual dipolar couplings are used for both geometric information and a filter in the assembly of residues in a sequential manner. Experimental data were collected in less than one week on a small redox protein, rubredoxin, that was 15N enriched but not enriched above 1% natural abundance in 13C. Given the acceleration possible with partial 13C …

Go to article

Ortho-Planar Linear-Motion Springs, John J. Parise, Larry L. Howell, Spencer P. Magleby Nov 2001

Ortho-Planar Linear-Motion Springs, John J. Parise, Larry L. Howell, Spencer P. Magleby

Faculty Publications

This paper presents an ortho-planar spring design that operates by raising or lowering its platform relative to the base with no rotation. The compact nature of the design, and its non-rotating motion, eliminates the problem of rotation against adjoining surfaces and is less sensitive to variation in assemblies than many current compact springs. Nomenclature is presented to identify different configurations, mathematical equations are provided that accurately model the force-defection relationships, and a pneumatic valve positioner application is demonstrated.

Go to article

Stacked Subwavelength Gratings As Circular Polarization Filters, Gregory P. Nordin, P. C. Deguzman Nov 2001

Stacked Subwavelength Gratings As Circular Polarization Filters, Gregory P. Nordin, P. C. Deguzman

Faculty Publications

We have stacked subwavelength gratings (SWGs) on a single substrate to create a compact, integrated circular polarization filter. The SWGs consist of a wire grid polarizer and a broadband form-birefringent quarter-wave plate (QWP). Rigorous coupled-wave analysis was used to design the QWP for operation over the 3.5-5.0 m wavelength range. The fabricated silicon broadband QWP exhibited a phase retardance of 82-97° across this wavelength range. Two stacked structures are presented, each with a different wire grid polarizer fabricated on an organic planarization layer (SU-8) that is deposited on a QWP grating. Transmittance measurements of the first structure when illuminated with …

Go to article

First Prev Next Last