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

Physics Commons

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

Iowa State University

Electrical and Computer Engineering

Keyword
Publication Year
Publication
Publication Type

Articles 1 - 30 of 191

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 ...


Ultrafast Nonlinear Transparency Driven At A Telecom Wavelength In An Organic Semiconductor System, Joong-Mok Park, Di Cheng, Aaron Patz, Liang Luo, Fadzai Fungura, Ruth Shinar, Kai-Ming Ho, Joseph Shinar, Jigang Wang Feb 2019

Ultrafast Nonlinear Transparency Driven At A Telecom Wavelength In An Organic Semiconductor System, Joong-Mok Park, Di Cheng, Aaron Patz, Liang Luo, Fadzai Fungura, Ruth Shinar, Kai-Ming Ho, Joseph Shinar, Jigang Wang

Ames Laboratory Accepted Manuscripts

Ultrafast laser-induced transparency is demonstrated using femtosecond (fs) pump-probe experiments in the organic P3HT:PCBM (donor:acceptor) blend structure. For above band gap pumping, ultrafast transient signals strongly depend on the probe photon energy. Most intriguingly, for below band gap pumping at 0.95 eV, or 1.3 µm at a telecom wavelength, a huge transmission increase up to 30% only during the laser pulse ∼100 fs is observed as a pump-driven, quasi-instantaneous suppression of absorption for the high photon-energy energy probe beam. We attribute the observed laser-driven transparency to dynamic Franz-Keldysh effect, at least one order of magnitude stronger ...


Spatial–Temporal Spectroscopy Characterizations And Electronic Structure Of Methylammonium Perovskites, Zhaoyu Liu, K. C. Bhamu, Liang Luo, Satvik Shah, Joong-Mok Park, Di Cheng, Men Long, Rana Biswas, F. Fungara, Ruth Shinar, Joseph Shinar, Javier Vela, Jigang Wang Jul 2018

Spatial–Temporal Spectroscopy Characterizations And Electronic Structure Of Methylammonium Perovskites, Zhaoyu Liu, K. C. Bhamu, Liang Luo, Satvik Shah, Joong-Mok Park, Di Cheng, Men Long, Rana Biswas, F. Fungara, Ruth Shinar, Joseph Shinar, Javier Vela, Jigang Wang

Chemistry Publications

Using time-resolved laser-scanning confocal microscopy and ultrafast optical pump/THz probe spectroscopy, we measure photoluminescence and THz-conductivity in perovskite micro-crystals and films. Photoluminescence quenching and lifetime variations occur from local heterogeneity. Ultrafast THz-spectra measure sharp quantum transitions from excitonic Rydberg states, providing weakly bound excitons with a binding energy of ~13.5 meV at low temperatures. Ab-initio electronic structure calculations give a direct band gap of 1.64 eV, a dielectric constant ~18, heavy electrons, and light holes, resulting in weakly bound excitons, consistent with the binding energies from experiment. The complementary spectroscopy and simulations reveal fundamental insights into perovskite ...


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 ...


Biodetection And Biointerface Based On Nanostructured Aluminum Oxide (Nao): From Fluorescence Enhancement To Ms Effect On Single Neural Cells, Xiangchen Che Jan 2018

Biodetection And Biointerface Based On Nanostructured Aluminum Oxide (Nao): From Fluorescence Enhancement To Ms Effect On Single Neural Cells, Xiangchen Che

Graduate Theses and Dissertations

Anodic aluminum oxide (AAO) has been investigated and utilized in numerous products for almost a century. But the rapidly increasing interest in nanoscale materials and their outstanding properties has propelled nanoporous AAO to be used as a substrate for sensors and biosensors. Fluorescence-based biosensors are one type of optical biosensors which are very popular for detecting a variety of targets (DNA, RNA, glucose, enzyme, bacteria, etc.). The recent discovery of AAO fluorescence enhancement effect makes AAO more attractive since it has the great potential to be used in biosensing field to improve the sensor sensitivity. However, the mechanism of the ...


Periodically Patterned Structures For Nanoplasmonic And Biomedical Applications, Akshit Peer Jan 2017

Periodically Patterned Structures For Nanoplasmonic And Biomedical Applications, Akshit Peer

Graduate Theses and Dissertations

Periodically patterned nanostructures have imparted profound impact on diverse scientific disciplines. In physics, chemistry, and materials science, artificially engineered photonic crystals have demonstrated an unprecedented ability to control the propagation of photons through light concentration and diffraction. The field of photonic crystals has led to many technical advances in fabricating periodically patterned nanostructures in dielectric/metallic materials and controlling the light-matter interactions at the nanoscale. In the field of biomaterials, it is of great interest to apply our knowledge base of photonic materials and explore how such periodically patterned structures control diverse biological functions by varying the available surface area ...


Novel Biomarker Assays Based On Photothermal Effects And Nanophotonics, Yunfei Zhao Jan 2017

Novel Biomarker Assays Based On Photothermal Effects And Nanophotonics, Yunfei Zhao

Graduate Theses and Dissertations

The early diagnosis of some chronic and severe diseases such as cancer, tuberculosis, etc. has been a long-sought goal of the medicine community. Traditional diagnostic tools such as X-ray and fecal blood tests cannot detect the disease before the focus or tumor have grown to an appreciable size or before the number of pathogens or tumor cells has reached a considerable amount in body fluids. These drawbacks could significantly delay the diagnosis. To detect and diagnose such diseases at an early stage, people have sought to detect the biomarkers related to certain physical conditions so that the anomalies caused by ...


Tailoring Nanoscale Morphology Of Polymer: Fullerene Blends Using Electrostatic Field, Moneim Elshobaki, Ryan S. Gebhardt, John Carr, William Lindemann, Wenjie Wang, Eric Grieser, Swaminathan Venkatesan, Evan Ngo, Ujjal Bhattacharjee, Joseph Strzalka, Zhang Jiang, Qiquan Qiao, Jacob W. Petrich, David Vaknin, Sumit Chaudhary Jan 2017

Tailoring Nanoscale Morphology Of Polymer: Fullerene Blends Using Electrostatic Field, Moneim Elshobaki, Ryan S. Gebhardt, John Carr, William Lindemann, Wenjie Wang, Eric Grieser, Swaminathan Venkatesan, Evan Ngo, Ujjal Bhattacharjee, Joseph Strzalka, Zhang Jiang, Qiquan Qiao, Jacob W. Petrich, David Vaknin, Sumit Chaudhary

Chemistry Publications

To tailor the nanomorphology in polymer/fullerene blends, we study the effect of electrostatic field (E-field) on the solidification of poly(3-hexylthiophene-2, 5-diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) bulk heterojunction (BHJ). In addition to control; wet P3HT:PC60BM thin films were exposed to E-field of Van de Graaff (VDG) generator at three different directions—horizontal (H), tilted (T), and vertical (V)—relative to the plane of the substrate. Surface and bulk characterizations of the field-treated BHJs affirmed that fullerene molecules can easily penetrate the spaghetti-like P3HT and move up and down following the E-field. Using E-field treatment ...


Organic Solar Cells: Degradation Processes And Approaches To Enhance Performance, Fadzai Fungura Jan 2016

Organic Solar Cells: Degradation Processes And Approaches To Enhance Performance, Fadzai Fungura

Graduate Theses and Dissertations

Organic solar cells (OSCs) have attracted a lot of attention due to their potential as flexible, lightweight, and low-cost renewable energy sources. Significant improvements have been made in increasing the devices’ power conversion efficiency (PCE) and extensive efforts to understand degradation mechanisms and increase OSCs’ lifetimes are ongoing. OSCs with higher than 10% efficiency have been reported. Enhanced stability and efficiency of inverted poly(3-hexylthiophene) (P3HT) solar cells with Cesium (Cs) halides were achieved by spin-coating Bphen (4,7-di(phenyl)-1,10-phenanthroline) on the halide layer and adding an ~100nm polystyrene beads layer on the blank side of the OSC ...


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 ...


An Annular Array Mpt For Enhanced Generation Of Omnidirectional Sh Waves In A Plate, Chung Il Park, Hong Min Seung, Jun Kyu Lee, Yoon Young Kim Jan 2016

An Annular Array Mpt For Enhanced Generation Of Omnidirectional Sh Waves In A Plate, Chung Il Park, Hong Min Seung, Jun Kyu Lee, Yoon Young Kim

Review of Progress in Quantitative Nondestructive Evaluation

If guided wave transducers are fabricated in an annular array type, the excitation and measurement of target guided wave modes could be considerably enhanced (see, e.g., [1]). Accordingly, various annular array transducers have been developed, including those generating omnidirectional Lamb waves in a plate. Here, we newly consider an annular array type MPT (magnetostrictive patch transducer) to generate enhanced SH (shear-horizontal) waves in a plate. This annular array MPT is based on our earlier development of an omnidirectional SH wave MPT [2]. For wave field analysis by the annular array SH wave MPT, the strain response in a plate ...


Characterization Of An Electrodynamic Flexural Transducer For Air-Coupled Ultrasonics, Tobias J. R. Eriksson, Yichao Fan, Sivaram Nishal Ramadas, Steve Dixon Jan 2016

Characterization Of An Electrodynamic Flexural Transducer For Air-Coupled Ultrasonics, Tobias J. R. Eriksson, Yichao Fan, Sivaram Nishal Ramadas, Steve Dixon

Review of Progress in Quantitative Nondestructive Evaluation

Air-coupled ultrasonics (ACU) has had an increasing importance in non-destructive evaluation (NDE), particularly for inspection of composite materials for example in the aerospace industry [1]. The main problem for ACU is the large impedance mismatch between piezoelectric ceramics and air, and a lack of suitable materials for impedance matching [2]. Many different solutions to this problem have led to a range of transducer technologies and designs, e.g. composite transducers and capacitive micromachined ultrasonic transducers (CMUTs). In previous work by the authors three designs of a novel ACU transducer, combining electromagnetic coupling and flexural mode vibrations, so called electrodynamic flexural ...


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 ...


Electric Potential And Electric Field Imaging With Applications, E. R. Generazio Jan 2016

Electric Potential And Electric Field Imaging With Applications, E. R. Generazio

Review of Progress in Quantitative Nondestructive Evaluation

The technology and techniques for remote quantitative imaging of electrostatic potentials and electrostatic fields in and around objects and in free space is presented. Electric field imaging (EFI) technology may be applied to characterize intrinsic or existing electric potentials and electric fields, or an externally generated electrostatic field may be used for “illuminating” volumes to be inspected with EFI. The baseline sensor technology, electric field sensor (e-sensor), and its construction, optional electric field generation (quasi-static generator), and current e-sensor enhancements (ephemeral e-sensor) are discussed. Demonstrations for structural, electronic, human, and memory applications are shown. This new EFI capability is demonstrated ...


Elastic Wave Fields Generated By Shear Horizontal Piezoelectric Fiber Patch (Sh-Pfp) Transducers: Parameter Study By Modelling And Laser Vibrometric Measurements, Bernd Köhler, Tobias Gaul, Frank Schubert, Uwe Lieske Jan 2016

Elastic Wave Fields Generated By Shear Horizontal Piezoelectric Fiber Patch (Sh-Pfp) Transducers: Parameter Study By Modelling And Laser Vibrometric Measurements, Bernd Köhler, Tobias Gaul, Frank Schubert, Uwe Lieske

Review of Progress in Quantitative Nondestructive Evaluation

Recently, a novel lightweight and thin piezoelectric transducer was proposed [1-3]. It generates in-plane surface tractions and thus shear horizontal elastic waves in both bulk materials and waveguides. The paper describes the principle of operation of this Shear Horizontal Piezoelectric Fiber Patch (SH-PFP). In continuation of the previous work, several variants of the SH-PFP are studied. The generated wavefield is characterized bywavefield snapshots and directivity functions. Both numerical simulation and measurements by 3D Laser Vibrometry are performed and the results are compared, showing a good agreement. We discuss possible further developments of the SH-PFP transducer to allow 1D directivity and ...


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 ...


Understanding The Photostability Of Perovskite Solar Cell, Pranav Hemanta Joshi Jan 2016

Understanding The Photostability Of Perovskite Solar Cell, Pranav Hemanta Joshi

Graduate Theses and Dissertations

Global climate change and increasing energy demands have led to a greater focus on cheaper photovoltaic energy solutions. Perovskite solar cells and organic solar cells have emerged as promising technologies for alternative cheaper photovoltaics.

Perovskite solar cells have shown unprecedentedly rapid improvement in power conversion efficiency, from 3% in 2009 to more than 21% today. High absorption coefficient, long diffusion lengths, low exciton binding energy, low defect density and easy of fabrication has made perovskites near ideal material for economical and efficient photovoltaics.

However, stability of perovskite and organic solar cells, especially photostability is still not well understood. In this ...


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 ...


Table-Like Magnetocaloric Effect In Gd56ni15al27zr2 Alloy And Its Field Independence Feature, E. Agurgo Balfour, Z. Ma, F. Hu, Ravi L. Hadimani, David C. Jiles, L. Wang, Y. Luo, S. F. Wang Jan 2015

Table-Like Magnetocaloric Effect In Gd56ni15al27zr2 Alloy And Its Field Independence Feature, E. Agurgo Balfour, Z. Ma, F. Hu, Ravi L. Hadimani, David C. Jiles, L. Wang, Y. Luo, S. F. Wang

Ames Laboratory Publications

In order to obtain “table-like” magnetocaloric effect (MCE), multiple-phase Gd56Ni15Al27Zr2 alloy was prepared by arc-melting followed by suck-casting method. Powder x-ray diffraction and calorimetric measurements reveal that the sample contains both glassy and crystalline phases. The fraction of the glassy phase is about 62%, estimated from the heat enthalpy of the crystallization. The crystalline phases, Gd2Al and GdNiAl further broadened the relatively wider magnetic entropy change (−ΔSM) peak of the amorphous phase, which resulted in the table-like MCE over a maximum temperature range of 52.5 K to 77.5 K. The plateau feature of the MCE was found to ...


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 ...


Study Of Electronic Characteristics Of Heterojunction With Intrinsic Thin-Layer Devices And Defect Density Profile Of Nanocrystalline Silicon Germanium Devices, Watson Paul Mulder Jan 2015

Study Of Electronic Characteristics Of Heterojunction With Intrinsic Thin-Layer Devices And Defect Density Profile Of Nanocrystalline Silicon Germanium Devices, Watson Paul Mulder

Graduate Theses and Dissertations

Heterojunction with Intrinsic Thin-layer (HIT) solar cells are an important photovoltaic technology, recently reaching record power conversion efficiencies. HIT cells hold advantages over the conventional crystalline Si solar cells, such as their fabrication at lower temperatures and their shorter fabrication time. It is important to understand the electronic characteristics and transport properties of HIT cells to continue to improve their efficiencies. The fundamental measurements of a HIT solar cell with an innovative n+/p/p+ structure are presented. We also report on a series of these HIT cells fabricated on wafers with different doping concentrations, observing the relationship between doping ...


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 ...