Inversion Of Eddy Current Probe Impedance Data For Crack Reconstruction, 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, 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, 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, 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, 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, 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 ...

Highly Directional Receiver And Source Antennas Using Photonic Band Gap Crystals, 2017 Iowa State University

#### 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

*Gary Tuttle*

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.

Ferromagnetism Of Magnetically Doped Topological Insulators In Crxbi2− Xte3 Thin Films, 2017 Iowa State University

#### 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

*Gary Tuttle*

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 ...

Implementation Of Range Autofocus For Sar Radar Imaging, 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.

Development Of Intermediate Band Solar Cell Through Ingan Quantum Well Structures, 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, In_{x}Ga_{1-x}N 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.

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

Comparing Multiple Turbulence Restoration Algorithms Performance On Noisy Anisoplanatic Imagery, 2017 Air Force Research Laboratory

#### Comparing Multiple Turbulence Restoration Algorithms Performance On Noisy Anisoplanatic Imagery, Michael Armand Rucci, Russell C. Hardie, Alexander J. Dapore

*Electrical and Computer Engineering Faculty Publications*

In this paper, we compare the performance of multiple turbulence mitigation algorithms to restore imagery degraded by atmospheric turbulence and camera noise. In order to quantify and compare algorithm performance, imaging scenes were simulated by applying noise and varying levels of turbulence. For the simulation, a Monte-Carlo wave optics approach is used to simulate the spatially and temporally varying turbulence in an image sequence. A Poisson-Gaussian noise mixture model is then used to add noise to the observed turbulence image set. These degraded image sets are processed with three separate restoration algorithms: Lucky Look imaging, bispectral speckle imaging, and a ...

On The Simulation And Mitigation Of Anisoplanatic Optical Turbulence For Long Range Imaging, 2017 University of Dayton

#### On The Simulation And Mitigation Of Anisoplanatic Optical Turbulence For Long Range Imaging, Russell C. Hardie, Daniel A. Lemaster

*Electrical and Computer Engineering Faculty Publications*

We describe a numerical wave propagation method for simulating long range imaging of an extended scene under anisoplanatic conditions. Our approach computes an array of point spread functions (PSFs) for a 2D grid on the object plane. The PSFs are then used in a spatially varying weighted sum operation, with an ideal image, to produce a simulated image with realistic optical turbulence degradation. To validate the simulation we compare simulated outputs with the theoretical anisoplanatic tilt correlation and differential tilt variance. This is in addition to comparing the long- and short-exposure PSFs, and isoplanatic angle. Our validation analysis shows an ...

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

Three Dimensional Modeling Of The Dc Potential Drop Method Using Finite Element And Boundary Element Analysis, 2017 Iowa State University

#### Three Dimensional Modeling Of The Dc Potential Drop Method Using Finite Element And Boundary Element Analysis, S. Nath, Thomas J. Rudolphi, W. Lord

*Thomas Rudolphi*

Finite element (FE) and boundary element (BE) methods of numerical analysis have been utilized in the solution of numerous electromagnetic nondestructive evaluation (NDE) phenomena. Investigations using these methods have been undertaken by Lord [1, 2, 3], Palanisamy [4], Atherton [5], Beissner [6], Burais [7] and others.

Simulation Of Anisoplanatic Imaging Through Optical Turbulence Using Numerical Wave Propagation With New Validation Analysis, 2017 University of Dayton

#### Simulation Of Anisoplanatic Imaging Through Optical Turbulence Using Numerical Wave Propagation With New Validation Analysis, Russell C. Hardie, Jonathan D. Power, Daniel A. Lemaster, Douglas R. Droege, Szymon Gladysz, Santasri Bose-Pillai

*Electrical and Computer Engineering Faculty Publications*

We present a numerical wave propagation method for simulating imaging of an extended scene under anisoplanatic conditions. While isoplanatic simulation is relatively common, few tools are specifically designed for simulating the imaging of extended scenes under anisoplanatic conditions. We provide a complete description of the proposed simulation tool, including the wave propagation method used. Our approach computes an array of point spread functions (PSFs) for a two-dimensional grid on the object plane. The PSFs are then used in a spatially varying weighted sum operation, with an ideal image, to produce a simulated image with realistic optical turbulence degradation. The degradation ...