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1978 full-text articles. Page 1 of 55.

Computational Eddy-Current Probe Model For Composites, Metals And Semiconductors, L. David Sabbagh, John R. Bowler, Harold A. Sabbagh 2017 Sabbagh Associates, Inc.

Computational Eddy-Current Probe Model For Composites, Metals And Semiconductors, L. David Sabbagh, John R. Bowler, Harold A. Sabbagh

John R. Bowler

A comprehensive computer code for research and design studies in electromagnetic NDE is now at an advanced stage of development. It has the capability of predicting the impedance characteristics of fully three-dimensional eddy-current probes in the presence of metals, semiconductors and advanced composites. By using a combination of the conjugate gradient method applied to a matrix and fast Fourier transform techniques, the resulting algorithm is both efficient in CPU time and has modest storage requirements. The theoretical model was presented in [1].


Eddy Current Probe Impedances Due To Interaction With Advanced Composites, John R. Bowler, Harold A. Sabbagh, L. David Sabbagh 2017 Sabbagh Associates, Inc.

Eddy Current Probe Impedances Due To Interaction With Advanced Composites, John R. Bowler, Harold A. Sabbagh, L. David Sabbagh

John R. Bowler

Electromagnetic fields in uniaxial conductors have been studied in order to examine the induced current distributions excited by external alternating current sources. The problem is motivated by the need to evaluate eddy current testing techniques for the inspection of composites such as graphite-epoxy or boron-epoxy. In particular it is important to understand how eddy currents behave in anisotropic materials, especially uniaxial conductors in which the conductivity in the axial direction may be several hundred times greater than the transverse conductivity [1].


Prediction And Analysis Of Transient Eddy-Current Probe Signals, J. R. Bowler 2017 University of Surrey

Prediction And Analysis Of Transient Eddy-Current Probe Signals, J. R. Bowler

John R. Bowler

In eddy-current nondestructive evaluation, the electromagnetic field is usually excited by a probe carrying a time-harmonic current and flaw information inferred from the amplitude and phase of the probe signal. In principle, transient excitation of eddy-currents would seem to offer great advantages since the probe response contains the equivalent information of a spectrum of frequencies. This paper explores a number of basic transient solutions due to normal air-cored coils and shows how the induced emf in a coil is related to its coupling coefficient.


Inversion Of Eddy Current Probe Impedance Data For Crack Reconstruction, John Bowler, D. J. Harrison, S. J. Norton 2017 University of Surrey

Inversion Of Eddy Current Probe Impedance Data For Crack Reconstruction, John Bowler, D. J. Harrison, S. J. Norton

John R. Bowler

The aim of eddy current inversion is to reconstruct an unknown flaw from probe signals measured as a function of probe position and frequency or time. In seeking the solution of an inverse problem, one can take advantage of an ability to solve forward problems by using predictions of probe signals calculated with a tentative estimate of the flaw. A well known inversion strategy adopted here for eddy current inversion, is that of varying the flaw estimate iteratively until the disparity between predicted and observed probe signals is minimized. Then the model flaw which gives the optimum predictions of the ...


Eddy Current Field Theory For A Flawed Conducting Half-Space, John R. Bowler 2017 University of Surrey

Eddy Current Field Theory For A Flawed Conducting Half-Space, John R. Bowler

John R. Bowler

By using dyadic Green’s functions the electromagnetic field in an unflawed conducting half-space can be found for a general alternating current source distribution. A crack in the conductor gives rise to a secondary source which may be represented as a surface distribution of current dipoles. An integral equation for the secondary source distribution is derived and the dipole density evaluated numerically for a rectangular subsurface crack.


Eddy-Current Probe Interaction With Subsurface Cracks, John R. Bowler 2017 University of Surrey

Eddy-Current Probe Interaction With Subsurface Cracks, John R. Bowler

John R. Bowler

Electric current will flow around on open crack in a conductor and give rise to very abrupt variations in the field. If the crack has a negligible opening it acts as a surface barrier where the field is virtually discontinuous. Effectively the crack is then equivalent to a layer of current dipoles with the dipole orientation normal to the surface and pointing upstream. An integral equation for the dipole density has been derived for an idealised subsurface crack using the Green’s function method [1]. Numerical solutions have been found by assuming a piecewise constant dipole density and satisfying boundary ...


Pulsed Eddy-Current Measurements For The Characterization Of Thin Layers And Surface Treatments, M. J. Johnson, John R. Bowler 2017 Iowa State University

Pulsed Eddy-Current Measurements For The Characterization Of Thin Layers And Surface Treatments, M. J. Johnson, John R. Bowler

John R. Bowler

By using a transient excitation, eddy-current probes exhibit a diffuse pulse-echo response in the presence of stratified conductors. The response has been investigated in order to evaluate pulsed eddy-current signals due to a single conducting layer over a uniform substrate of dissimilar conductivity. The aim of the investigation is to assess the feasibility of measuring the thickness and quality of surface treatments including the diffusion of aluminum into nickel parts and the case hardening of steel components.


Prediction Of Eddy-Current Probe Impedance Due To Surface Cracks In Ferromagnetic Steels, N. Harfield, John R. Bowler 2017 University of Surrey

Prediction Of Eddy-Current Probe Impedance Due To Surface Cracks In Ferromagnetic Steels, N. Harfield, John R. Bowler

John R. Bowler

Ferromagnetic steels usually have a high value of relative permeability which means that, for frequencies commonly used in eddy-current non-destructive evaluation, the electromagnetic skin-depth is typically much smaller than the depth of a crack. This behavior allows the use of approximate, thin-skin theories to describe the interaction between induced eddy-currents and surface-breaking cracks in steel. Thin-skin approximations are also appropriate for use with non-magnetic materials at sufficiently high frequency. Auld et al [1] treated the high-frequency, surface-crack problem in aluminium using a magnetic scalar potential formulation. The surface impedance boundary condition was applied to the field on the crack faces ...


Measurement And Calculation Of Transient Eddy-Currents In Layered Structures, John R. Bowler, D. J. Harrison 2017 University of Surrey

Measurement And Calculation Of Transient Eddy-Currents In Layered Structures, John R. Bowler, D. J. Harrison

John R. Bowler

In transient eddy-current inspection, an electromagnetic field pulse is excited in a conductor by causing a step change in the current through a coil. As this pulse propagates into the material, it is broadened by dispersion and scattered by discontinuities in the conductivity and permeability of the conductor. Subsurface defects cause part of the pulse to be scattered back to the surface of the conductor where it can be observed as a transient signal in the time domain, either as an EMF across the coil, or by direct measurement of the magnetic field using, for example, a Hall sensor. The ...


Implementation Of Range Autofocus For Sar Radar Imaging, Nicholas J. Testin, Philip Davis 2017 Kennesaw State University

Implementation Of Range Autofocus For Sar Radar Imaging, Nicholas J. Testin, Philip Davis

Honors College Capstones and Theses

The range calculation for an FMCW radar depends on accurate linear modulation. In some circumstances, linear modulation may not be available and must be corrected for. This paper describes an autofocus technique used to correct for phase error due to non-linearities in the components of a FMCW radar. Also described here is the algorithm used in calculating the phase error and application of the phase correction with triangle modulation. Known errors were calculated at certain distances and applied to correcting the phase of data taken at similar distances. The results given were generated using a SAR working outside linear ranges.


Smart Feedback Control For Fiber-Optics Acoustic Emission Sensor System, Xiangyu Luo 2017 University of Nebraska-Lincoln

Smart Feedback Control For Fiber-Optics Acoustic Emission Sensor System, Xiangyu Luo

Theses, Dissertations, and Student Research from Electrical & Computer Engineering

Optical fiber sensors for ultrasonic detection have become a subject of much research in recent years. In this thesis, a fiber-optic acoustic emission (AE) sensor system that is capable of performing AE detection, even when the sensor is experiencing large quasi-static strains, is first described. The system consists of a smart selection of a wavelength notch to which a distributed feedback (DFB) laser is locked for high sensitivity AE signal demodulation. A smart feedback control unit for the DFB laser, which is the focus of this thesis, is designed and investigated. The smart control ensures that the AE signal is ...


Development Of Intermediate Band Solar Cell Through Ingan Quantum Well Structures, Kelly McKenzie 2017 University of Arkansas, Fayetteville

Development Of Intermediate Band Solar Cell Through Ingan Quantum Well Structures, Kelly Mckenzie

Electrical Engineering Undergraduate Honors Theses

In the search for high-efficiency solar cells, InxGa1-xN has come under scrutiny as a unique material with high potential. This is due to characteristics including an easily tunable bandgap, large range of potential bandgap values, and high heat resistance. However, one factor limiting its adaptation is the high density of crystal defects. In this thesis, the qualities of InGaN are discussed and the intermediate band solar cell structure is introduced. Additionally, the growth and characterization of two sets of InGaN-based solar cell devices are reported and evaluated.


Rural Broadband Mobile Communications: Spectrum Occupancy And Propagation Modeling In Western Montana, Erin Wiles 2017 Montana Tech

Rural Broadband Mobile Communications: Spectrum Occupancy And Propagation Modeling In Western Montana, Erin Wiles

Graduate Theses & Non-Theses

Fixed and mobile spectrum monitoring stations were implemented to study the spectrum range from 174 to 1000 MHz in rural and remote locations within the mountains of western Montana, USA. The measurements show that the majority of this spectrum range is underused and suitable for spectrum sharing. This work identifies available channels of 5-MHz bandwidth to test a remote mobile broadband network. Both TV broadcast stations and a cellular base station were modelled to test signal propagation and interference scenarios.


Performance Evaluation Of The Fbg Sensing Device And Comparison With Piezoelectric Sensors For Acoustic Emission Detection, Chuang Zhang, Leonard J. Bond 2017 Hebei University of Technology

Performance Evaluation Of The Fbg Sensing Device And Comparison With Piezoelectric Sensors For Acoustic Emission Detection, Chuang Zhang, Leonard J. Bond

Leonard J. Bond

In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. As the most mature technique in fiber-optic field, Fiber Bragg Grating (FBG) sensors have emerged as a reliable, in situ and nondestructive tool for monitoring and diagnostics in large-scale structure. Main objectives of this work are to evaluate and compare the acoustic emission (AE) sensing characteristics simultaneously with FBG sensor array and piezoelectric (PZ) sensors. The pencil-lead-break (PLB) test, ball dropping test and the excitation from the PZ transducer are treated as the AE source which conducted on the platy and ...


Chiral Light Intrinsically Couples To Extrinsic/Pseudo-Chiral Metasurfaces Made Of Tilted Gold Nanowires, Alessandro Belardini, Marco Centini, Grigore Leahu, David C. Hooper, Roberto Li Voti, Eugenio Fazio, Joseph W. Haus, Andrew Sarangan, Ventsislav K. Valev, Concita Sibilia 2017 Sapienza Università di Roma

Chiral Light Intrinsically Couples To Extrinsic/Pseudo-Chiral Metasurfaces Made Of Tilted Gold Nanowires, Alessandro Belardini, Marco Centini, Grigore Leahu, David C. Hooper, Roberto Li Voti, Eugenio Fazio, Joseph W. Haus, Andrew Sarangan, Ventsislav K. Valev, Concita Sibilia

Andrew Sarangan

Extrinsic or pseudo-chiral (meta)surfaces have an achiral structure, yet they can give rise to circular dichroism when the experiment itself becomes chiral. Although these surfaces are known to yield differences in reflected and transmitted circularly polarized light, the exact mechanism of the interaction has never been directly demonstrated. Here we present a comprehensive linear and nonlinear optical investigation of a metasurface composed of tilted gold nanowires. In the linear regime, we directly demonstrate the selective absorption of circularly polarised light depending on the orientation of the metasurface. In the nonlinear regime, we demonstrate for the first time how second ...


Chiral Light Intrinsically Couples To Extrinsic/Pseudo-Chiral Metasurfaces Made Of Tilted Gold Nanowires, Alessandro Belardini, Marco Centini, Grigore Leahu, David C. Hooper, Roberto Li Voti, Eugenio Fazio, Joseph W. Haus, Andrew Sarangan, Ventsislav K. Valev, Concita Sibilia 2017 Sapienza Università di Roma

Chiral Light Intrinsically Couples To Extrinsic/Pseudo-Chiral Metasurfaces Made Of Tilted Gold Nanowires, Alessandro Belardini, Marco Centini, Grigore Leahu, David C. Hooper, Roberto Li Voti, Eugenio Fazio, Joseph W. Haus, Andrew Sarangan, Ventsislav K. Valev, Concita Sibilia

Joseph W Haus

Extrinsic or pseudo-chiral (meta)surfaces have an achiral structure, yet they can give rise to circular dichroism when the experiment itself becomes chiral. Although these surfaces are known to yield differences in reflected and transmitted circularly polarized light, the exact mechanism of the interaction has never been directly demonstrated. Here we present a comprehensive linear and nonlinear optical investigation of a metasurface composed of tilted gold nanowires. In the linear regime, we directly demonstrate the selective absorption of circularly polarised light depending on the orientation of the metasurface. In the nonlinear regime, we demonstrate for the first time how second ...


Role Of Antenna Modes And Field Enhancement In Second Harmonic Generation From Dipole Nanoantennas, Domenico de Ceglia, Maria Antonietta Vincenti, Costantino De Angelis, Andrea Locatelli, Joseph W. Haus, Michael Scalora 2017 Charles M. Bowden Research Center

Role Of Antenna Modes And Field Enhancement In Second Harmonic Generation From Dipole Nanoantennas, Domenico De Ceglia, Maria Antonietta Vincenti, Costantino De Angelis, Andrea Locatelli, Joseph W. Haus, Michael Scalora

Joseph W Haus

We study optical second harmonic generation from metallic dipole antennas with narrow gaps. Enhancement of the fundamental-frequency field in the gap region plays a marginal role on conversion efficiency. In the symmetric configuration, i.e., with the gap located at the center of the antenna axis, reducing gap size induces a significant red-shift of the maximum conversion efficiency peak. Either enhancement or inhibition of second-harmonic emission may be observed as gap size is decreased, depending on the antenna mode excited at the harmonic frequency. The second-harmonic signal is extremely sensitive to the asymmetry introduced by gap’s displacements with respect ...


Design Of Radio-Frequency Arrays For Ultra-High Field Mri, Ian R O Connell 2017 The University of Western Ontario

Design Of Radio-Frequency Arrays For Ultra-High Field Mri, Ian R O Connell

Electronic Thesis and Dissertation Repository

Magnetic Resonance Imaging (MRI) is an indispensable, non-invasive diagnostic tool for the assessment of disease and function. As an investigational device, MRI has found routine use in both basic science research and medicine for both human and non-human subjects.

Due to the potential increase in spatial resolution, signal-to-noise ratio (SNR), and the ability to exploit novel tissue contrasts, the main magnetic field strength of human MRI scanners has steadily increased since inception. Beginning in the early 1980’s, 0.15 T human MRI scanners have steadily risen in main magnetic field strength with ultra-high field (UHF) 8 T MRI systems ...


Topography Measurements Using An Airborne Ka-Band Fmcw Interferometric Synthetic Aperture Radar, Kan Fu 2017 University of Massachusetts - Amherst

Topography Measurements Using An Airborne Ka-Band Fmcw Interferometric Synthetic Aperture Radar, Kan Fu

Doctoral Dissertations May 2014 - current

Radar interferometry at millimeter-wave frequencies has the ability of topography measurement of different types of terrain, such as water surfaces and tree canopies. A Ka-band interferometric radar was mounted on an airborne platform, and flown over the Connecticut river region in western Massachusetts near Amherst on June 11, 2012. More than 20 Gigabytes of raw data was recorded. This dissertation outline presents the results of the data processing, which includes (1) the estimation and removal of the embedded high frequency phase error in the raw data; (2) the synthetic aperture processing; (3) the interferometric processing. The digital elevation model (DEM ...


Hybrid Parallelization Of The Nasa Gemini Electromagnetic Modeling Tool, Buxton L. Johnson Sr. 2017 University of Kentucky

Hybrid Parallelization Of The Nasa Gemini Electromagnetic Modeling Tool, Buxton L. Johnson Sr.

Theses and Dissertations--Electrical and Computer Engineering

Understanding, predicting, and controlling electromagnetic field interactions on and between complex RF platforms requires high fidelity computational electromagnetic (CEM) simulation. The primary CEM tool within NASA is GEMINI, an integral equation based method-of-moments (MoM) code for frequency domain electromagnetic modeling. However, GEMINI is currently limited in the size and complexity of problems that can be effectively handled. To extend GEMINI’S CEM capabilities beyond those currently available, primary research is devoted to integrating the MFDlib library developed at the University of Kentucky with GEMINI for efficient filling, factorization, and solution of large electromagnetic problems formulated using integral equation methods. A ...


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