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Full-Text Articles in Physics

Electromagnetic Materials Characterization Of Ferromagnetic Composites At Microwave Frequencies, Eric Ryan Abram Jan 2007

Electromagnetic Materials Characterization Of Ferromagnetic Composites At Microwave Frequencies, Eric Ryan Abram

Retrospective Theses and Dissertations

No abstract provided.


Critical Behavior Of Thermal Expansion And Magnetostriction In The Vicinity Of The First Order Transition At The Curie Point Of Gd5(Si[Subscript X]Ge[Subscript 1-X])4 , Mangui Han Jan 2004

Critical Behavior Of Thermal Expansion And Magnetostriction In The Vicinity Of The First Order Transition At The Curie Point Of Gd5(Si[Subscript X]Ge[Subscript 1-X])4 , Mangui Han

Retrospective Theses and Dissertations

Thermal expansion (TE) and magnetostriction (MS) measurements have been conducted for Gd5(SixGe1-x)4 with a series of x values to study its critical behavior in the vicinity of transition temperatures.;It was found that the Curie temperature of Gd5(SixGe 1-x)4 for x: 0 ~ 0.5 is dependent on magnetic field, direction of change of temperature (Tc on cooling was lower than Tc on heating), purity of Gd starting material, compositions, material preparation methods, and also can be triggered by the external magnetic field with a different dT/dB rate for different x values. For Gd5(Si1.95Ge ...


Synchrotron Diffraction Studies Of Spontaneous Magnetostriction In Rare Earth Transition Metal Compounds , Ning Yang Jan 2004

Synchrotron Diffraction Studies Of Spontaneous Magnetostriction In Rare Earth Transition Metal Compounds , Ning Yang

Retrospective Theses and Dissertations

Thermal expansion anomalies of R2Fe14B and R 2Fe17Cx (x = 0, 2) (R = Y, Nd, Gd, Tb, Er) stoichiometric compounds are studied with high-energy synchrotron X-ray powder diffraction using Debye-Scherrer geometry in temperature range 10K to 1000K. Large spontaneous magnetostriction up to their Curie temperatures (Tc) is observed. The a-axes show relatively larger invar effects than c-axes in the R 2Fe14B compounds whereas the R2Fe17C x show the contrary anisotropies. The iron sub-lattice is shown to dominate the spontaneous magnetostriction of the compounds. The contribution of the rare earth sublattice is roughly proportional to the spin magnetic moment of the rare ...


Spin Dynamics And Quantum Tunneling In Fe8 Nanomagnet And In Afm Rings By Nmr , Seung-Ho Baek Jan 2004

Spin Dynamics And Quantum Tunneling In Fe8 Nanomagnet And In Afm Rings By Nmr , Seung-Ho Baek

Retrospective Theses and Dissertations

In this thesis, our main interest has been to investigate the spin dynamics and quantum tunneling in single molecule magnets (SMMs). For this we have selected two different classes of SMMs: a ferromagnetic total high spin S = 10 cluster Fe8 and antiferromagnetic (AFM) ring-type clusters. For Fe8, our efforts have been devoted to the investigation of the quantum tunneling of magnetization in the very low temperature region. The most remarkable experimental finding in Fe8 is that the nuclear spin-lattice relaxation rate (1/T1) at low temperatures takes place via strong collision mechanism, and thus it allows to measure directly the ...


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 ...


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 ...


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 ...


Development Of Highly Magnetostrictive Composites For Applications In Magnetomechanical Torque Sensors , Yonghua Chen Jan 1999

Development Of Highly Magnetostrictive Composites For Applications In Magnetomechanical Torque Sensors , Yonghua Chen

Retrospective Theses and Dissertations

The objective of this work was to investigate and develop a new type of magnetomechanical material with high magnetomechanical response and low hysteresis. This material will be used in electronic torque sensors. A major appreciation could be for advanced steering systems in automobiles which will replace the fuel inefficient hydraulic steering systems currently in use;The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles was studied. Both experimental and modeled results showed that the elastic modulus of the matrix is an important factor determining the magnetostriction of the composite. For a series of composites ...


Anisotropic Magnetization And Transport Properties Of Ragsb₂ (R=Y, La-Nd, Sm, Gd-Tm) , Kenneth Duane Myers Jan 1999

Anisotropic Magnetization And Transport Properties Of Ragsb₂ (R=Y, La-Nd, Sm, Gd-Tm) , Kenneth Duane Myers

Retrospective Theses and Dissertations

Anisotropic measurements of the magnetic and transport properties have been performed on high quality single crystals of the RAgSb2 series of compounds with R = Y, La-Nd, Sm, Gd-Tm. For all of these compounds except for ErAgSb2 and TmAgSb2, strong magnetic anisotropy created by CEF splitting of the Hund's rule ground state confines the moments to the basal plane. Additional anisotropy within the basal plane is also observed in DyAgSb2, leading to a series of metamagnetic transitions. Detailed analysis of the saturated moment and critical fields allows a determination of the net distribution of magnetic moments within each phase. The ...


Design, Fabrication And Analysis Of A Terfenol-D Based Magnetostrictive External Cavity Diode Laser Sensor With An Advanced Signal Processing Capability , Wing Chiu Chung Jan 1999

Design, Fabrication And Analysis Of A Terfenol-D Based Magnetostrictive External Cavity Diode Laser Sensor With An Advanced Signal Processing Capability , Wing Chiu Chung

Retrospective Theses and Dissertations

Miniature magnetometer is desired in many applications, such as undersea surveillance, buried landmine detection, vehicle tracking and guidance and personal dosimetry. This dissertation reports the fabrication, and characterization of a miniature magnetometer, which utilizes the highly magnetostrictive material, Terfenol-D and an ultra-short external cavity diode laser sensor. A thin slice of the magneto strictive material, biased by an open magnetic circuit, is configured as an external reflector modulating the effective modal reflectivity of the diode laser cavity in response to an ac magnetic field. The detection limit of the sensor are being investigated and the principle of the device is ...


Nonlinear And Hysteretic Magnetomechanical Model For Magnetostrictive Transducers , Marcelo Jorge Dapino Jan 1999

Nonlinear And Hysteretic Magnetomechanical Model For Magnetostrictive Transducers , Marcelo Jorge Dapino

Retrospective Theses and Dissertations

The growing interest on magnetostrictive materials for generation of strains and forces in smart structure systems motivates the development of increasingly accurate models of the performance of these materials as used in transducers. The proposed magnetomechanical model provides a characterization of the material magnetization as well as the strain and force output by a transducer in response to quasistatic applied magnetic fields. The model is built in three steps. In the first, the mean field model for ferromagnetic hysteresis originally developed by Jiles and Atherton is used to compute the magnetization arising from the application of magnetic fields. While this ...


Measurements And Modeling Of The Effects Of An Orthogonal Bias Field On Properties Of Isotropic Magnetic Materials , Ying Bi Jan 1998

Measurements And Modeling Of The Effects Of An Orthogonal Bias Field On Properties Of Isotropic Magnetic Materials , Ying Bi

Retrospective Theses and Dissertations

The effects of the orthogonal bias field were investigated systematically in this study. The measurements on various magnetic materials under different experimental conditions showed that the orthogonal bias field rotated the hysteresis loop reducing permeability and reduced its enclosed area. As a result, permeability, hysteresis loss, coercivity and remanence decreased with increasing orthogonal bias field. The experimental results indicated that the orthogonal field reduced hysteresis loss by increasing the component of reversible domain rotation magnetization;In the present study, the Jiles-Atherton model has been expanded to include the effect of an orthogonal bias field. Based on the experimental observation, a ...


Nonlinear Response Of Superconductors To Alternating Fields And Currents , Jason R. Mcdonald Jan 1997

Nonlinear Response Of Superconductors To Alternating Fields And Currents , Jason R. Mcdonald

Retrospective Theses and Dissertations

Nonlinearities caused by vortex pinning and weak links in superconductors are considered. The effects of vortex pinning will be treated in both the parallel and perpendicular geometries using the critical state model. The results for the parallel geometry will be used to calculate the nonlinear surface impedance of a hard type-II superconductor. The results for the perpendicular geometry will be used to treat harmonic generation (HG) and intermodulation distortion (IM) in superconducting transmission lines and resonators. Nonlinearites due to weak links will be modelled using both the resistively shunted junction model (RSJ) for small junctions, and the damped sine-Gordon equation ...


Two-Dimensional Pancake Vortices In A Finite Stack Of Magnetically Coupled Thin Superconducting Films , Thomas Lim Pe Jan 1997

Two-Dimensional Pancake Vortices In A Finite Stack Of Magnetically Coupled Thin Superconducting Films , Thomas Lim Pe

Retrospective Theses and Dissertations

This dissertation investigates the structure and behavior of two-dimensional (2D) pancake vortices in a stack of N Josephson-decoupled superconducting thin films under a magnetic field applied prependicular to the layers. This system of magnetically coupled superconducting films is proposed as a model for the multilayered high-Tc superconductors. Starting with the properties of one pancake vortex located in any of the N superconducting layers, an analytical expression is derived for the magnetic coupling force between pairs of 2D pancake vortex lattices residing in different layers, each having the same lattice structure, but displaced (not rotated) relative to each other. Using this ...


Design, Analysis, And Modeling Of Giant Magnetostrictuve Transducers , Frederick Theodore Calkins Jan 1997

Design, Analysis, And Modeling Of Giant Magnetostrictuve Transducers , Frederick Theodore Calkins

Retrospective Theses and Dissertations

The increased use of giant magnetostrictive, Terfenol-D transducers in a wide variety of applications has led to a need for greater understanding of the materials performance. This dissertation attempts to add to the Terfenol-D transducer body of knowledge by providing an in-depth analysis and modeling of an experimental transducer. A description of the magnetostriction process related to Terfenol-D includes a discussion of material properties, production methods, and the effect of mechanical stress, magnetization, and temperature on the material performance. The understanding of the Terfenol-D material performance provides the basis for an analysis of the performance of a Terfenol-D transducer. Issues ...


Signal Processing And Image Restoration Techniques For Two-Dimensional Eddy Current Nondestructive Evaluation , Bing Wang Jan 1997

Signal Processing And Image Restoration Techniques For Two-Dimensional Eddy Current Nondestructive Evaluation , Bing Wang

Retrospective Theses and Dissertations

This dissertation presents a comprehensive study on the forward modeling methods, signal processing techniques, and image restoration techniques for two-dimensional eddy current nondestructive evaluation. The basic physical forward method adopted in this study is the volume integral method. We have applied this model to the eddy current modeling problem for half space geometry and thin plate geometry. To reduce the computational complexity of the volume integral method, we have developed a wavelet expansion method which utilizes the multiresolution compression capability of the wavelet basis to greatly reduce the amount of computation with small loss in accuracy. To further improve the ...


Increasing The Efficiency Of A Piezoelectric Aluminum Nitride Microstrip Resonator By Utilizing High Temperature Superconductors , Edward David Goff Jan 1995

Increasing The Efficiency Of A Piezoelectric Aluminum Nitride Microstrip Resonator By Utilizing High Temperature Superconductors , Edward David Goff

Retrospective Theses and Dissertations

High temperature superconductors have potential applications in the field of microwave devices and circuits. To utilize these materials in such a way as to increase the efficiency of these microwave devices would be beneficial for high efficiency/low noise applications. This dissertation accomplishes the following goals: (1) The design and fabrication of an initial device that increases the quality factor, Q, and therefore the efficiency of a high frequency thin film resonator which uses superconducting metal as the device's electrode, (2) the measurement and characterization of this device, (3) the theoretical calculation and predicted performance of this device, and ...


A Closed-Form Integration Method For State-Space Time-Domain Analysis Of Electronic Circuits And Systems , Bruce Alan Alspaugh Jan 1994

A Closed-Form Integration Method For State-Space Time-Domain Analysis Of Electronic Circuits And Systems , Bruce Alan Alspaugh

Retrospective Theses and Dissertations

While most traditional circuit simulation programs such as SPICE rely upon numerical integration techniques to perform transient analysis, this dissertation presents an alternative approach that relies on closed-form integration. Traditional numerical approaches offer no hope of finding an analytical solution, even if it is known that the solutions will be in a simple functional form. By using closed-form methods, the computer can find the exact analytical solution to the network and completely avoid problems associated with numerical approximations, determining appropriate integration step sizes, stiff systems of differential equations, or accumulated global error. Computer run time is independent of the amount ...


Magnetization Studies Of Oxides Related To The High Temperature Cuprate Superconductors , Zhaorong Wang Jan 1994

Magnetization Studies Of Oxides Related To The High Temperature Cuprate Superconductors , Zhaorong Wang

Retrospective Theses and Dissertations

An Oxford Instruments Faraday magnetometer, capable of operating in the temperature range between 1.5 K and 1000 K, and magnetic field range between 0 T to 8 T, with a sensitivity of 3x10[superscript]-8 cm[superscript]3G, was assembled and calibrated. The pumping station which supported this magnetometer was designed and built. Software for reducing the raw data and generating calibration files was written. The magnetic properties of several oxides related to the high temperature cuprate superconductors BaCuO[subscript]2+x, La[subscript]2CuO[subscript]4, Sr[subscript]2IrO[subscript]4, Sr[subscript]2RhO[subscript]4, Sr[subscript ...


Sub-Micron Scale Conduction Processes On Clean Surfaces , Kevin R. Kimberlin Jan 1994

Sub-Micron Scale Conduction Processes On Clean Surfaces , Kevin R. Kimberlin

Retrospective Theses and Dissertations

Fundamental electrical conductance measurement has been studied in-situ in two dimensions in the Ag/Si(111) system as a function of the incident adatom flux rate with a four probe technique. A conductance study in a three dimensional conical structure was also carried out with field emission techniques. Field emission is now well established and has been used in this case to characterize a novel geometry for use in flat panel displays to replace cathode ray tube monitors. For the two dimensional study on Ag/Si(111), the origin of conduction is still unclear, as both transport by means of ...


Effects Of Randomly Rough Surfaces On Ultrasonic Inspection , Mehmet Bilgen Jan 1993

Effects Of Randomly Rough Surfaces On Ultrasonic Inspection , Mehmet Bilgen

Retrospective Theses and Dissertations

Surface finish of an industrial part affects its ultrasonic inspection and consequently the surfaces are often machined smooth before the evaluation. Ultrasonic inspection through smooth surfaces has been well studied and understood. A theoretical basis has been established for the characterization of interior cracks, voids and inclusions, and vast amount of literature exists. However, much less is known about quantitative ultrasonic inspection of such flaws in parts with rough surfaces, e.g. machine marks or "as-cast" surfaces. A question arises "When can an industrial part with randomly rough surfaces be inspected robustly using ultrasound?" This dissertation is aimed at answering ...


Frequency Conversion Analysis Of Noise In Heterojunction Bipolar Transistor Oscillators Including Periodically Modulated Noise Sources , Bradley Allen Kramer Jan 1993

Frequency Conversion Analysis Of Noise In Heterojunction Bipolar Transistor Oscillators Including Periodically Modulated Noise Sources , Bradley Allen Kramer

Retrospective Theses and Dissertations

A procedure which may be used to analyze the noise characteristics of HBT oscillators is presented. A large signal model of a HBT is developed based largely on the Gummel-Poon transistor model. A new base-emitter diffusion capacitance model is also generated which shows improved accuracy over conventional bipolar transistor models in characterizing HBTs. The large signal characteristics of the oscillator are then established using a time domain simulator. Conversion matrix theory is applied to the large signal model to generate an equivalent linear oscillator model which accounts for all of the frequency conversion effects which occur due to circuit nonlinearities ...


Acoustically Driven Integrated Microstrip Antennas And Electromagnetic Radiation From Piezoelectric Devices , Charles Forrest Campbell Jan 1993

Acoustically Driven Integrated Microstrip Antennas And Electromagnetic Radiation From Piezoelectric Devices , Charles Forrest Campbell

Retrospective Theses and Dissertations

For a receiver system to be considered integrated, the antenna and electronics need to be fabricated on a single semiconductor wafer. To avoid EMI problems, the circuitry must somehow be shielded from the environment where the antenna resides. The required shielding may be accomplished by separating the antenna on one side of the wafer from the electronics on the other side with a conducting ground plane. Energy may be acoustically coupled from the antenna to the circuitry through the ground plane via thin film piezoelectric transducers on either side of the wafer. The radiating side of the wafer would then ...


Theory Of Eddy Current Inspection Of Layered Metals , Erol Uzal Jan 1992

Theory Of Eddy Current Inspection Of Layered Metals , Erol Uzal

Retrospective Theses and Dissertations

Some forward and inverse problems related to layer sizing in eddy current nondestructive evaluation (NDE) were examined and experimental tests were done. An air-core or ferrite-core eddy current probe coil above a half space is considered. The half space's conductivity changes only as a function of depth, but otherwise it is arbitrary. A numerical method for the computation of coil impedance based on the exact solution of Cheng, Dodd and Deeds (International Jour. of Nondestructive Testing, 3, 109-130,1971) is described. Also, for a specific conductivity profile involving the hyperbolic tangent function, the exact solution for the impedance is ...


Diffusion Effects In Eddy Current Nondestructive Evaluation, Paul Andrew Stucky Jan 1991

Diffusion Effects In Eddy Current Nondestructive Evaluation, Paul Andrew Stucky

Retrospective Theses and Dissertations

No abstract provided.


Auger Effect On The Output Power Of Ingaasp Dh Lasers , Mani Mina Jan 1989

Auger Effect On The Output Power Of Ingaasp Dh Lasers , Mani Mina

Retrospective Theses and Dissertations

A model has been developed for CW operation of InGaAsP Double-heterostructure (DH) lasers considering Auger recombination as the major source of nonradiative recombination inside the active region. The model uses a two dimensional temperature distribution solution inside of the active layer of stripe geometry InGaAsP DH lasers to get better average value for the active region temperature. Then, utilizing Haug's model of threshold current density for lasing, together with Asada and Suematsu's model for the external differential quantum efficiency, the light output power P[subscript]L as a function of the injection current I is obtained;The developed ...


Binding Energies Of The Light Hyperfragments , James Thomas Jones Jr. Jan 1956

Binding Energies Of The Light Hyperfragments , James Thomas Jones Jr.

Retrospective Theses and Dissertations

No abstract provided.


Magnetic Properties Of Neodymium And Dysprosium Single Crystals , Donald Ray Behrendt Jan 1956

Magnetic Properties Of Neodymium And Dysprosium Single Crystals , Donald Ray Behrendt

Retrospective Theses and Dissertations

No abstract provided.


Magnetic Properties Of Gd-La And Gd-Y Alloys , Wilbur Collins Thoburn Jan 1956

Magnetic Properties Of Gd-La And Gd-Y Alloys , Wilbur Collins Thoburn

Retrospective Theses and Dissertations

No abstract provided.


Ferromagnetic-Antiferromagnetic Phase Transitions , Thomas James Hendrickson Jan 1956

Ferromagnetic-Antiferromagnetic Phase Transitions , Thomas James Hendrickson

Retrospective Theses and Dissertations

No abstract provided.