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Electromagnetics and Photonics

Iowa State University

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Articles 1 - 30 of 130

Full-Text Articles in Physics

Intelligent Metasurfaces With Continuously Tunable Local Surface Impedance For Multiple Reconfigurable Functions, Fu Liu, Odysseas Tsilipakos, Alexandros Pitilakis, Anna C. Tasolamprou, Mohammad Sajjad Mirmoosa, Nikolaos V. Kantartzis, Do-Hoon Kwon, Maria Kafesaki, Costas M. Soukoulis, Sergei A. Tretyakov Apr 2019

Intelligent Metasurfaces With Continuously Tunable Local Surface Impedance For Multiple Reconfigurable Functions, Fu Liu, Odysseas Tsilipakos, Alexandros Pitilakis, Anna C. Tasolamprou, Mohammad Sajjad Mirmoosa, Nikolaos V. Kantartzis, Do-Hoon Kwon, Maria Kafesaki, Costas M. Soukoulis, Sergei A. Tretyakov

Ames Laboratory Accepted Manuscripts

Electromagnetic metasurfaces can be characterized as intelligent if they are able to perform multiple tunable functions, with the desired response being controlled by a computer influencing the individual electromagnetic properties of each metasurface inclusion. In this paper, we present an example of an intelligent metasurface that operates in the reflection mode in the microwave frequency range. We numerically show that, without changing the main body of the metasurface, we can achieve tunable perfect absorption and tunable anomalous reflection. The tunability features can be implemented using mixed-signal integrated circuits (ICs), which can independently vary both the resistance and reactance, offering complete ...


Tailoring Bandgap Of Perovskite Batio3 By Transition Metals Co-Doping For Visible-Light Photoelectrical Applications: A First-Principles Study, Fan Yang, Liang Yang, Changzhi Ai, Pengcheng Xie, Shiwei Lin, Cai-Zhuang Wang, Xihong Lu Jun 2018

Tailoring Bandgap Of Perovskite Batio3 By Transition Metals Co-Doping For Visible-Light Photoelectrical Applications: A First-Principles Study, Fan Yang, Liang Yang, Changzhi Ai, Pengcheng Xie, Shiwei Lin, Cai-Zhuang Wang, Xihong Lu

Ames Laboratory Accepted Manuscripts

The physical and chemical properties of V-M″ and Nb-M″ (M″ is 3d or 4d transition metal) co-doped BaTiO3were studied by first-principles calculation based on density functional theory. Our calculation results show that V-M″ co-doping is more favorable than Nb-M″ co-doping in terms of narrowing the bandgap and increasing the visible-light absorption. In pure BaTiO3, the bandgap depends on the energy levels of the Ti 3d and O 2p states. The appropriate co-doping can effectively manipulate the bandgap by introducing new energy levels interacting with those of the pure BaTiO3. The optimal co-doping effect comes from the ...


Antimatched Electromagnetic Metasurfaces For Broadband Arbitrary Phase Manipulation In Reflection, Odysseas Tsilipakos, Thomas Koschny, Costas M. Soukoulis Jan 2018

Antimatched Electromagnetic Metasurfaces For Broadband Arbitrary Phase Manipulation In Reflection, Odysseas Tsilipakos, Thomas Koschny, Costas M. Soukoulis

Ames Laboratory Accepted Manuscripts

Metasurfaces impart phase discontinuities on impinging electromagnetic waves that are typically limited to 0–2π. Here, we demonstrate that multiresonant metasurfaces can break free from this limitation and supply arbitrarily large, tunable time delays over ultrawide bandwidths. As such, ultrathin metasurfaces can act as the equivalent of thick bulk structures by emulating the multiple geometric resonances of three-dimensional systems that originate from phase accumulation with effective material resonances implemented on the surface itself via suitable subwavelength meta-atoms. We describe a constructive procedure for defining the required sheet admittivities of such metasurfaces. Importantly, the proposed approach provides an exactly linear phase ...


Multiphysics Analysis Of Electrochemical And Electromagnetic System Addressing Lithium-Ion Battery And Permanent Magnet Motor, Abhishek Sarkar Jan 2018

Multiphysics Analysis Of Electrochemical And Electromagnetic System Addressing Lithium-Ion Battery And Permanent Magnet Motor, Abhishek Sarkar

Graduate Theses and Dissertations

Lithium-ion batteries are the leading energy storage technology in the electronic-driven society. With the need for portable, long-life electronics the demand for lithium batteries has escalated over the decade. Lithium-ion batteries show remarkable electrochemical characteristics, including but not limited to, long cycle-life, high cut-off voltages and high energy-density. However, lithium-ion cells are problematic to design due to their inherent thermal and/or mechanical instability. The objective of the current research framework is to establish the criteria causing thermo-mechanical failure of the battery systems, material properties effecting the performance, and model cycle-life degradation due to electrolyte loss by solid electrolyte interface ...


Calibration Of Air-Coupled Transducers For Absolute Nonlinear Ultrasonic Measurements, Nicholas Selby, David Torello, Jin-Yeon Kim, Laurence J. Jacobs Jan 2016

Calibration Of Air-Coupled Transducers For Absolute Nonlinear Ultrasonic Measurements, Nicholas Selby, David Torello, Jin-Yeon Kim, Laurence J. Jacobs

Review of Progress in Quantitative Nondestructive Evaluation

We describe a novel calibration technique of air-coupled transducers for nonlinear ultrasonic measurements through homogenous, isotropic media. Our calibration technique combines laser interferometrywith a model-based approach to derive a relationship between received force at the transducer face and the measured output voltage. Conventional nonlinear ultrasonic measurement techniques have relied upon contact receiving transducers that are heavily influenced by contact conditions (e.g. inconsistent coupling) and laser interferometers that are prohibitively expensive and rely on a mirror-finished surface or complicated optics. Air-coupled transducers are significantly less expensive than laser interferometers and are robust relative to surface conditions, but current calibration techniques ...


Electromagnetic Modelling Of An Eddy-Current Position Sensor In For Use In A Fast Reactor, Tao Wu, John Bowler Jan 2016

Electromagnetic Modelling Of An Eddy-Current Position Sensor In For Use In A Fast Reactor, Tao Wu, John Bowler

Review of Progress in Quantitative Nondestructive Evaluation

In this article, we proposed a novel theoretical electromagnetic model of an eddy current probe used as a position sensor with respect to a tube in a fast reactor under standby conditions while immersed in a liquid metal coolant. In these circumstances the coil position cannot be guided by optical aids but electromagnetic sensing can be used. Initially, we derived analytical expressions for the quasi-static time-harmonic electromagnetic field of a circular current filament via the transverse magnetic potential expressed in terms of a single layer potential. This is then used to deduce the field of a circular sensor coil near ...


Pseudo-Pulse-Echo Mode Focused Rayleigh Wave Emats For High Resolution Imaging Of Surface-Breaking Defects, C. B. Thring, Y. Fan, R. S. Edwards Jan 2016

Pseudo-Pulse-Echo Mode Focused Rayleigh Wave Emats For High Resolution Imaging Of Surface-Breaking Defects, C. B. Thring, Y. Fan, R. S. Edwards

Review of Progress in Quantitative Nondestructive Evaluation

Electromagnetic Acoustic Transducers (EMATs) are useful in Non-Destructive Testing as they can be used at lift-off on hot, moving, and rusted surfaces while being relatively inexpensive and robust. Generation of ultrasound using EMATs is relatively inefficient, however, the amplitude of the signal at a defect can be greatly improved with the use of focusing. A focused Rayleigh wave EMAT has been designed, characterized, and used to size a range of surface breaking defects in aluminum. The EMAT has improved spatial resolution compared to unfocused designs and generates a strong signal (giving up to 30 dB SNR) at the focal point ...


Limited View Guided Wave Tomography Based On Full Waveform Inversion, Jing Rao, Madis Ratassepp, Zheng Fan Jan 2016

Limited View Guided Wave Tomography Based On Full Waveform Inversion, Jing Rao, Madis Ratassepp, Zheng Fan

Review of Progress in Quantitative Nondestructive Evaluation

Guided wave tomography offers good potential to estimate the remnant thicknesses of corrosion patches without scanning an ultrasonic transducer along the surface. It uses the dispersion characteristics of guided waves, and reconstructs the thickness map by the inversion of ultrasonic signals captured by a transducer array around the inspection area. A guided wave tomography method based on full waveform inversion (FWI) was developed for the corrosion mapping, which uses a numerical forward model to predict the scattering of guided wave through corrosion defects, and an iterative inverse model to reconstruct the corrosion profile.

In this study, the FWI method is ...


Compton Imaging Tomography For Nondestructive Evaluation Of Spacecraft Thermal Protection Systems, Volodymyr Romanov, Eric Burke, Victor Grubsky Jan 2016

Compton Imaging Tomography For Nondestructive Evaluation Of Spacecraft Thermal Protection Systems, Volodymyr Romanov, Eric Burke, Victor Grubsky

Review of Progress in Quantitative Nondestructive Evaluation

Novel nondestructive evaluation (NDE) systems based on a recently pioneered Compton Imaging Tomography (CIT) technique [1-4] are currently being developed by Physical Optics Corporation (POC). CIT provides high-resolution, three-dimensional, Compton scattered X-ray imaging of the internal structure of evaluated objects, using a set of acquired two-dimensional, Compton scattered X-ray images of consecutive cross sections of these objects. Unlike conventional computerized tomography, CIT requires only one-sided access to objects, has no limitation on the dimensions and geometry of such objects, and can be applied to large, multilayer, nonuniform objects. Also, CIT does not require any contact with objects during its application ...


Photonic Molecules For Subwavelength Light Confinement Design And Applications, Aditya Jain Jan 2016

Photonic Molecules For Subwavelength Light Confinement Design And Applications, Aditya Jain

Graduate Theses and Dissertations

Similar to the confinement of an electron in a potential well, photons can be spatially confined inside a high index resonator. This confinement can be used to create efficient strong light matter interaction, all optical logic, single photon generation among many other possibilities, provided the resonators possess a small physical volume and low photon decay rate simultaneously. In this thesis, we present two resonator designs, that are 30 times smaller than the wavelength of light in a single direction and exhibit large quality factors. Thereafter, we proceed with three different applications of these resonators.

First application is to slow down ...


Influence Of Mn Concentration On Magnetic Topological Insulator Mnxbi2−Xte3 Thin-Film Hall-Effect Sensor, Ravi L. Hadimani, S. Gupta, S. M. Harstad, Vitalij K. Pecharsky, David C. Jiles Nov 2015

Influence Of Mn Concentration On Magnetic Topological Insulator Mnxbi2−Xte3 Thin-Film Hall-Effect Sensor, Ravi L. Hadimani, S. Gupta, S. M. Harstad, Vitalij K. Pecharsky, David C. Jiles

Ames Laboratory Publications

Hall-effect (HE) sensors based on high-quality Mn-doped Bi2Te3 topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi2Te3. The sensors with low Mn concentrations, MnxBi2-xTe3, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almost eight times as high as ...


Magnetic Interaction And Electronic Transport In La0.4bi0.6mn0.5ti0.5o3 Manganite, Vijaylakshmi Dayal, Punith Kumar V., Ravi L. Hadimani, E. A. Balfour, H. Fu, David C. Jiles May 2015

Magnetic Interaction And Electronic Transport In La0.4bi0.6mn0.5ti0.5o3 Manganite, Vijaylakshmi Dayal, Punith Kumar V., Ravi L. Hadimani, E. A. Balfour, H. Fu, David C. Jiles

Electrical and Computer Engineering Publications

We report magnetic interactions and electronic transport properties in La0.4Bi0.6Mn0.5Ti0.5O3 perovskite manganite synthesized using solid-state route. After characterizing the samples structurally, the systematic investigations of magnetic and electrical transport behaviors have been undertaken. It has been observed that at low temperatures near TC, the sample is magnetically frustrated leading to the second-order magnetic transition. A justification for the observed magnetic behavior has been explained based on Arrott's plot study. The resistivity as a function of temperature in the absence and the presence of applied magnetic field suggests semiconducting nature of the sample. The conduction of ...


Gd5(Si,Ge)4 Thin Film Displaying Large Magnetocaloric And Strain Effects Due To Magnetostructural Transition, Ravi L. Hadimani, Joao H. B. Silva, Andre M. Pereira, Devo L. Schlagel, Thomas A. Lograsso, Yang Ren, David C. Jiles, Joao P. Araújo Jan 2015

Gd5(Si,Ge)4 Thin Film Displaying Large Magnetocaloric And Strain Effects Due To Magnetostructural Transition, Ravi L. Hadimani, Joao H. B. Silva, Andre M. Pereira, Devo L. Schlagel, Thomas A. Lograsso, Yang Ren, David C. Jiles, Joao P. Araújo

Ames Laboratory Publications

Magnetic refrigeration based on the magnetocaloric effect is one of the best alternatives to compete with vapor-compression technology. Despite being already in its technology transfer stage, there is still room for optimization, namely, on the magnetic responses of the magnetocaloric material. In parallel, the demand for different magnetostrictive materials has been greatly enhanced due to the wide and innovative range of technologies that emerged in the last years (from structural evaluation to straintronics fields). In particular, the Gd5(Six Ge1−x)4 compounds are a family of well-known alloys that present both giant magnetocaloric and colossal magnetostriction effects. Despite their ...


New Developments In Magneto-Optic Interferometric Switching, John William Pritchard Jan 2015

New Developments In Magneto-Optic Interferometric Switching, John William Pritchard

Graduate Theses and Dissertations

In the next few decades, it is likely that high bandwidth wireless and optical technologies will be placed in the spotlight as the dominant avenues for communication all over the world. It is arguable that this is currently the case, and that the expectation for higher data transfer speeds, more secure and reliable transmission, and longer communication range is on an exponential rise. Thus, much effort and emphasis is being put on these technologies to advance as quickly as possible.

For optical systems, the majority of research has been focused on the realization of all-optical transmission, that is, transmission such ...


Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles Jan 2015

Second Order Phase Transition Temperature Of Single Crystals Of Gd5si1.3ge2.7 And Gd5si1.4ge2.6, Ravi L. Hadimani, Yevgen Melikhov, Deborah L. Schlagel, Thomas A. Lograsso, Kevin W. Dennis, R. William Mccallum, David C. Jiles

Electrical and Computer Engineering Publications

Gd5(Six Ge 1−x)4 has mixed phases in the composition range 0.32 < x < 0.41, which have not been widely studied. In this paper, we have synthesized and indexed single crystal samples of Gd5Si1.3 Ge 2.7 and Gd5Si1.4 Ge 2.6. We have investigated the first order and second orderphase transition temperatures of these samples using magnetic moment vs. temperature andmagnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the “hidden” second order phase transition temperature of the orthorhombic II phase.


Deep Brain Transcranial Magnetic Stimulation Using Variable “Halo Coil” System, Y. Meng, Ravi L. Hadimani, Lawrence J. Crowther, Z. Xu, J. Qu Jan 2015

Deep Brain Transcranial Magnetic Stimulation Using Variable “Halo Coil” System, Y. Meng, Ravi L. Hadimani, Lawrence J. Crowther, Z. Xu, J. Qu

Electrical and Computer Engineering Publications

Transcranial Magnetic Stimulation has the potential to treat various neurological disorders non-invasively and safely. The “Halo coil” configuration can stimulate deeper regions of the brainwith lower surface to deep-brain field ratio compared to other coil configurations. The existing “Halo coil” configuration is fixed and is limited in varying the site of stimulation in the brain. We have developed a new system based on the current “Halo coil” design along with a graphicaluser interface system that enables the larger coil to rotate along the transverse plane. The new system can also enable vertical movement of larger coil. Thus, this adjustable “Halo ...


Analysis Of Ringing Effects Due To Magnetic Core Materials In Pulsed Nuclear Magnetic Resonance Circuits, Neelam G. Prabhu Gaunkar, N. R. Y. Bouda, Ikenna C. Nlebedim, Ravi L. Hadimani, I. Bulu, K. Ganesan, Y. Q. Song, Mani Mina, David C. Jiles Jan 2015

Analysis Of Ringing Effects Due To Magnetic Core Materials In Pulsed Nuclear Magnetic Resonance Circuits, Neelam G. Prabhu Gaunkar, N. R. Y. Bouda, Ikenna C. Nlebedim, Ravi L. Hadimani, I. Bulu, K. Ganesan, Y. Q. Song, Mani Mina, David C. Jiles

Electrical and Computer Engineering Publications

This work presents investigations and detailed analysis of ringing in a non-resonant pulsednuclear magnetic resonance (NMR) circuit. Ringing is a commonly observed phenomenon in high power switching circuits. The oscillations described as ringing impede measurements in pulsed NMR systems. It is therefore desirable that those oscillations decay fast. It is often assumed that one of the causes behind ringing is the role of the magnetic core used in theantenna (acting as an inductive load). We will demonstrate that an LRC subcircuit is also set-up due to the inductive load and needs to be considered due to its parasitic effects. It ...


Thermal Effects On The Magnetic Properties Of Titanium Modified Cobalt Ferrite, Ikenna C. Nlebedim, David C. Jiles Jan 2015

Thermal Effects On The Magnetic Properties Of Titanium Modified Cobalt Ferrite, Ikenna C. Nlebedim, David C. Jiles

Electrical and Computer Engineering Publications

The temperature dependence of the magnetic properties of titanium modified cobalt ferrite is presented. The change of maximum magnetization obtained at H ≈ 2.4 MA/m between any two temperatures increases systematically with composition, which is desirable for applications in devices. Variation in magnetocrystalline anisotropy and coercivity were different from previous studies on cation substituted cobalt ferrite. At lower concentrations, the effect of lower thermal energy dominated the effect of non-magnetic cation substitutions in controlling the anisotropy.The reverse was the case at higher concentrations. The temperature dependence of coercivity is dominated by the contribution of magnetocrystalline anisotropy to coercivity ...


Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles Jan 2015

Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, Yan Ni, Z. Zhang, Ikenna C. Nlebedim, M. Ravi Hadimani, Gary L. Tuttle, David C. Jiles

Electrical and Computer Engineering Publications

We investigated the effect of magnetic doping on magnetic and transport properties of Bi2Te3thin films. CrxBi2−xTe3 thin films with x = 0.03, 0.14, and 0.29 were grown epitaxially on mica substrate with low surface roughness (∼0.4 nm). It is found that Cr is an electron acceptor in Bi2Te3 and increases the magnetization of CrxBi2−xTe3. When x = 0.14 and 0.29,ferromagnetism appears in CrxBi2−xTe3 thin films, where anomalous Hall effect and weak localization of magnetoconductance were observed. The Curie temperature, coercivity, and remnant Hall resistance of thin films increase with increasing Cr concentration ...


Influence Of Ga-Concentration On The Electrical And Magnetic Properties Of Magnetoelectric Cogaxfe2− Xo4/Batio3 Composite, Yan Ni, Zhen Zhang, Cajetan I. Nlebedim, David C. Jiles Jan 2015

Influence Of Ga-Concentration On The Electrical And Magnetic Properties Of Magnetoelectric Cogaxfe2− Xo4/Batio3 Composite, Yan Ni, Zhen Zhang, Cajetan I. Nlebedim, David C. Jiles

Electrical and Computer Engineering Publications

Multiferroic materials exhibit magnetoelectric (ME) coupling and promise new device applications including magnetic sensors, generators, and filters. An effective method for developing ME materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, the electrical and magnetic properties of Ga doped magnetoelectric CoGaxFe2−xO4/BaTiO3composite are studied systematically. It is found that Ga doping improves the sensitivity of magnetoelastic response and stabilizes the magnetic phase of the composites. More importantly, Ga doping reduces the electrical conductivity of composite, as well as the dielectric loss. An enhancement of the ...


Growth And Characterization Of Pt-Protected Gd5si4 Thin Films, Ravi L. Hadimani, Yaroslav Mudryk, Timothy E. Prost, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., David C. Jiles Jan 2014

Growth And Characterization Of Pt-Protected Gd5si4 Thin Films, Ravi L. Hadimani, Yaroslav Mudryk, Timothy E. Prost, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., David C. Jiles

Electrical and Computer Engineering Publications

Successful growth and characterization of thin films of giant magnetocaloric Gd5(SixGe1−x)4were reported in the literature with limited success. The inherent difficulty in producing this complex material makes it difficult to characterize all the phases present in the thin films of this material. Therefore, thin film of binary compound of Gd5Si4 was deposited by pulsed laser deposition. It was then covered with platinum on the top of the film to protect against any oxidation when the film was exposed to ambient conditions. The average film thickness wasmeasured to be approximately 350 nm using a scanning electron microscopy, and ...


Phenomenological Modelling Of First Order Phase Transitions In Magnetic Systems, Yevgen Melikhov, Ravi L. Hadimani, Arun Raghunathan Jan 2014

Phenomenological Modelling Of First Order Phase Transitions In Magnetic Systems, Yevgen Melikhov, Ravi L. Hadimani, Arun Raghunathan

Electrical and Computer Engineering Publications

First order phase transitions may occur in several magnetic systems, with two structural phases having different magnetic properties each and a structural transition between them. Here, a novel physics based phenomenological model of such systems is proposed, in which magnetization is represented by the volumetric amounts of ferromagnetism (described by extended Jiles-Atherton theory) and paramagnetism (described by the Curie-Weiss law) in respective phases. An identification procedure to extract material parameters from experimental data is proposed. The proposed phenomenological approach was successfully applied to magnetocaloric Gd5(Six Ge 1−x)4 system and also has the potential to describe the behavior ...


Enhancement Of Magnetocaloric Effect In The Gd2al Phase By Co Alloying, Z. Y. Huang, H. Fu, Ravi L. Hadimani, E. Agurgo Balfour, S. N. Dembele, B. H. Teng, David C. Jiles Jan 2014

Enhancement Of Magnetocaloric Effect In The Gd2al Phase By Co Alloying, Z. Y. Huang, H. Fu, Ravi L. Hadimani, E. Agurgo Balfour, S. N. Dembele, B. H. Teng, David C. Jiles

Electrical and Computer Engineering Publications

To understand the effect of Co doping on the magnetic entropy changes in Gd2 Al phase, a series of Gd2AlCox alloys with 0 ≤ x ≤ 0.6 were synthesized by arc-melting and the crystal structure was analyzed by XRD. The magnetic properties were investigated, and the entropychanges were calculated for a magnetic field change of 50 kOe. All the as-cast alloys dopedwith Co exhibited greater magnetic entropy changes than the original binary Gd2 Al phase. The main reasons attributed to this are the increase of ferromagnetic interaction indicated by the disappearance of cusp and sharp drop in magnetization and the reduction ...


Structural, Magnetic, And Magnetoelastic Properties Of Magnesium Substituted Cobalt Ferrite, Cajetan Ikenna Nlebedim, Ravi L. Hadimani, Ruslan Prozorov, David C. Jiles Jan 2013

Structural, Magnetic, And Magnetoelastic Properties Of Magnesium Substituted Cobalt Ferrite, Cajetan Ikenna Nlebedim, Ravi L. Hadimani, Ruslan Prozorov, David C. Jiles

Electrical and Computer Engineering Publications

The effects of substituting Mg on the structural, magnetic, and magnetostrictive properties ofcobalt ferrite have been investigated. Comparable values of lattice parameter were obtained for the Mg-substituted samples. Saturation magnetization continuously decreased with increase inMg concentration. Peak-to-peak magnetostriction amplitude and strain sensitivity had a similar dependence on Mg concentration.


Non-Metallic Metamaterials: Modelling, Design, And Fabrication Tolerances Analysis, Yang Li Jan 2012

Non-Metallic Metamaterials: Modelling, Design, And Fabrication Tolerances Analysis, Yang Li

Graduate Theses and Dissertations

Metamaterials are artificial materials, consisting of sub-wavelength building blocks, which can show anomalous and exotic electromagnetic responses. Metal-based metamaterials, as the first experimentally implemented metamaterials, have achieved significant progress in theory, fabrication, and characterization over a broad frequency range from microwave to visible. To

alleviate the drawbacks of metal-based metamaterials, such as conductive loss and anisotropy, non-metallic metamaterials have been proposed and developed rapidly in the last decade. This thesis focuses on the analytical modeling and fabrication-tolerance analysis of non-metallic metamaterials consisting of an array of magnetodielectric spheres. Here, the term "magnetodielectric" refers, generally, to materials with relative permittivity and ...


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 ...


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.