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Articles 1 - 12 of 12

Full-Text Articles in Physics

Examination Of Focused Beam Propagation Through A Finite Non-Reciprocal Planar Chiral Slab Using Complex Fresnel Coefficients And Dual Transforms, Monish Ranjan Chatterjee, Sumit Nema, Partha P. Banerjee Oct 2003

Examination Of Focused Beam Propagation Through A Finite Non-Reciprocal Planar Chiral Slab Using Complex Fresnel Coefficients And Dual Transforms, Monish Ranjan Chatterjee, Sumit Nema, Partha P. Banerjee

Electrical and Computer Engineering Faculty Publications

Recently, uniform plane wave propagation across a nonchiral-chiral interface was examined via the development of appropriate Fresnel coefficients. In this extension, propagation of focused uniform and profiled beams through a finite, planar nonreciprocal chiral slab is investigated using complex Fresnel coefficients via angular plane wave decomposition and dual transforms.


Revisiting The Fresnel Coefficients For Uniform Plane Wave Propagation Across A Nonchiral, Reciprocal And Chiral, Nonreciprocal Interface, Monish Ranjan Chatterjee, Sumit Nema Aug 2003

Revisiting The Fresnel Coefficients For Uniform Plane Wave Propagation Across A Nonchiral, Reciprocal And Chiral, Nonreciprocal Interface, Monish Ranjan Chatterjee, Sumit Nema

Electrical and Computer Engineering Faculty Publications

The problem of EM wave propagation in non-reciprocal chiral media has been studied by several investigators. In a recent approach, a dual-transform technique has been developed to study the problem of such propagation under paraxial and slow-envelope variation conditions.

In this paper, we first outline some of the results obtained using the dual transform technique for arbitrary boundary conditions within the left boundary of a semi-infinite, non-reciprocal chiral medium for a uniform plane wave, and a fundamental Gaussian-profiled beam. Next, we explore the problem of a uniform EM wave incident at an oblique angle at an interface between a reciprocal ...


Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho Jul 2003

Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, Rana Biswas, Gary L. Tuttle, Ekmel Ozbay, Burak Temelkuran, Mihail Sigalas, Kai-Ming Ho

Iowa State University Patents

A directional antenna made with photonic band gap structures has been presented. The directional antenna is formed with two photonic band gap structures oriented back to back and separated from each other by a distance to form a resonant cavity between the photonic band gap structures. An antenna element is placed in the resonant cavity. The resonant frequency of the cavity is tuned by adjusting the distance between the photonic band gap structures. The resonant cavity can be asymmetrical or symmetrical.


Design Of High-Magnetic Field Gradient Sources For Controlling Magnetically Induced Flow Of Ferrofluids In Microfluidic Systems, W. He, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar May 2003

Design Of High-Magnetic Field Gradient Sources For Controlling Magnetically Induced Flow Of Ferrofluids In Microfluidic Systems, W. He, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar

Ames Laboratory Publications

The use of miniature electromagnets for ferrofluid-actuated liquid dispensing into microfluidic channels has been investigated by numerical simulations using the finite element method and measurements of fluid displacement and flow rate. The simulations illustrate the effect of structural and geometrical parameters of single and paired solenoid coils on the magnetic force experienced by the ferrofluid. Dual solenoids were used for extended fluid displacement. Ferrofluid positioning and flow rates were controlled also by using a solenoid with an iron core. The experimental measurements of fluidflow in capillaries were used to validate the modeling calculations. The results can be used as a ...


Microelectromagnetic Ferrofluid-Based Actuator, Y. Melikhov, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar May 2003

Microelectromagnetic Ferrofluid-Based Actuator, Y. Melikhov, S. J. Lee, David C. Jiles, D. H. Schmidt, Marc D. Porter, Ruth Shinar

Ames Laboratory Publications

Computer simulations were used to investigate the performance of a microscale ferrofluid-based magnetic actuator developed for liquid dispensing in microfluidic channels. The actuation was based on the movement of a ferrofluid plug in a magnetic field gradient generated by on-chip effectively infinite parallel conductors. The movement, positioning, and retaining of ferrofluid plugs with different lengths at various locations along a microfluidic channel were investigated for two cases. In case (a), the magnetic field gradient was generated by a single conductor; when the ferrofluid reached its equilibrium position, the current was switched off and the nearest neighbor conductor was energized. A ...


In Situ Applied Field Imaging Of A Magnetic Tunnel Junction Using Magnetic Force Microscopy, J. S. Leib, Chester C.H. Lo, John E. Snyder, David C. Jiles May 2003

In Situ Applied Field Imaging Of A Magnetic Tunnel Junction Using Magnetic Force Microscopy, J. S. Leib, Chester C.H. Lo, John E. Snyder, David C. Jiles

Materials Science and Engineering Publications

Knowledge of domain behavior in magnetic tunnel junctions is an essential component, together with knowledge of the electron band structure, for understanding their magnetoelectronic properties. To this purpose, the magnetization reversal processes of a multilayertunnel junction of structure substrate/NiFe/AlOx/FeCo/CrPtMn/Al of tapered half-ellipsoid shape have been imaged using a magnetic force microscope(MFM) within situ applied magnetic fields. Stripe domains through both the stack and free layers observed at zero applied field were erased by a ∼100 Oe field applied to the left followed by applying a small field to the right. Magnetic domain structure ...


Wide Angle Achromatic Prism Beam Steering For Infrared Countermeasures Applications, Bradley D. Duncan, Philip J. Bos, Vassili Sergan Apr 2003

Wide Angle Achromatic Prism Beam Steering For Infrared Countermeasures Applications, Bradley D. Duncan, Philip J. Bos, Vassili Sergan

Electro-Optics and Photonics Faculty Publications

The design and analysis of achromatic doublet prisms for use in laser beam steering is presented. The geometric relationships describing the maximum steering angle are given, as are discussions of first- and second-order dispersion reduction. Infrared (IR) material alternatives and optimum IR material characteristics for wide-angle achromatic prism beam steering are also investigated. Sixteen materials in 120 different combinations have been examined to date. For midwave IR applications it is shown that the minimum dispersion currently achievable across the full 2 to 5 μm spectrum is 1.7816 mrad at an average maximum steering angle of 45 deg. This is ...


Index-Matched Boundary Techniques For The Elimination Of Acoustical Resonances, Jack H. Parker, Bradley D. Duncan Feb 2003

Index-Matched Boundary Techniques For The Elimination Of Acoustical Resonances, Jack H. Parker, Bradley D. Duncan

Electro-Optics and Photonics Faculty Publications

We extend the principle of optical index of refraction to apply the concept of acoustical index for transverse acoustical wave propagation in strings. The relationship between acoustical index and mass density of the acoustic material is developed. With this theoretical link established, classic index-matching techniques are explored at acoustical boundaries. Proper selection of boundary interface segments leads to the elimination of resonant vibrationalmodes that occur in rigidly supported strings, while maintaining the nonresonant vibration response.


Digital Image Processing, Russell C. Hardie, Majeed M. Hayat Jan 2003

Digital Image Processing, Russell C. Hardie, Majeed M. Hayat

Electrical and Computer Engineering Faculty Publications

In recent years, digital images and digital image processing have become part of everyday life. This growth has been primarily fueled by advances in digital computers and the advent and growth of the Internet. Furthermore, commercially available digital cameras, scanners, and other equipment for acquiring, storing, and displaying digital imagery have become very inexpensive and increasingly powerful. An excellent treatment of digital images and digital image processing can be found in Ref. [1]. A digital image is simply a two-dimensional array of finite-precision numerical values called picture elements (or pixels). Thus a digital image is a spatially discrete (or discrete-space ...


Development And Modeling Of Iron-Gallium Alloys , Rick Allen Kellogg Jan 2003

Development And Modeling Of Iron-Gallium Alloys , Rick Allen Kellogg

Retrospective Theses and Dissertations

Alloys of iron substituted with non-magnetic gallium (Galfenol) appear promising as mechanically robust actuator/sensing materials. They offer desirable properties including tensile strengths and magnetostrictive strains, respectively, on the order of 100 MPa and 100 x 10-6. To advance the understanding of these materials, this dissertation examines the alloys' magnetic and mechanical response as a function of applied magnetic field, mechanical stress, temperature, stoichiometry and crystallographic morphology. Characterizations of the alloys' single-crystal magneto strictive, elastic and plastic properties are used to facilitate the development and modeling of polycrystalline forms of the material having preferred crystallographic orientations (i.e. texture). The ...


A New Forward-Backward Sweeping Parabolized Navier-Stokes Algorithm With Application To Magnetohydrodynamic Flows , Hiromasa Kato Jan 2003

A New Forward-Backward Sweeping Parabolized Navier-Stokes Algorithm With Application To Magnetohydrodynamic Flows , Hiromasa Kato

Retrospective Theses and Dissertations

A new forward-backward sweeping parabolized Navier-Stokes algorithm has been developed to efficiently compute supersonic/hypersonic flowfields with embedded separated regions. The algorithm splits the streamwise flux vector using the Steger-Warming method and employs multiple forward/backward sweeps of the flowfield in order to duplicate the results that would be obtained with the complete Navier-Stokes equations. The forward/backward sweeping of the flowfield significantly reduces the number of iterations required over previous iterative parabolized Navier-Stokes algorithms. Once a separated flow region is computed, the algorithm returns to the usual forward-space-marching mode until the next separated flow region is encountered. The new ...


Spin Dynamics In Molecular Nanomagnets At Intermediate Temperatures: An Nmr And [Mu]Sr Investigation , Daniele Procissi Jan 2003

Spin Dynamics In Molecular Nanomagnets At Intermediate Temperatures: An Nmr And [Mu]Sr Investigation , Daniele Procissi

Retrospective Theses and Dissertations

Solid lattices of weakly coupled magnetic molecules provide an unique opportunity to study magnetism at a nanoscale level. Each non interacting molecule in the lattice represents a single nanomagnet composed of only a few magnetic moments. These magnetic moments are coupled to each other via exchange interaction. The overall magnetic properties of molecules are entirely ascribed to these few magnetic moments. In order to investigate the spin dynamics of these systems as a function of temperature and external magnetic field we performed an extensive experimental investigation using nuclear magnetic resonance (NMR) and muon rotation spectroscopy (muSR) techniques. The aim of ...