Coil Axis Research Articles

Pulsed Eddy Current Nondestructive Testing for Defect Evaluation and Imaging of Automotive Lightweight Alloy Materials

Rapid and accurate damage detection of magnesium-aluminum alloy, which is an important material for automotive lightweight, is of great significance. Pulsed eddy current (PEC) is an effective electromagnetic nondestructive testing and evaluation (NDT&E) technique for metal materials. Metal loss evaluation and imaging are one of the most important steps in quality control and maintenance of key components of automobiles. A PEC method based on a rectangular excitation coil and an axial parallel pickup coil is proposed and investigated for the purpose of metal loss evaluation and imaging. Metal loss type of defects with different sections is designed and detected using line scanning technique and C-scan imaging in two scanning directions. Experimental results have illustrated that metal loss depth can be estimated effectively by the peak amplitude of PEC A-scan response. Then, the quantification information of metal loss depth is preliminarily obtained based on the linear fitting equation. Consequently, metal loss evaluation is realized by line scanning peak waves and C-scan pseudo 3D images. At last, the sensitivity comparison shows that the metal loss can be detected in both directions. The proposed method is an effective approach to evaluate the image surface-breaking metal loss in automotive lightweight alloy materials.

Modeling of inductive coil geometry for gap position measurement

Finite element modelling of high frequency inductive coils and metal plates was used to investigate the impedance response to a narrow gap between the plates. The model was used to predict distance sensitivity for both coil-to-gap and coil-to-plate. Different coil axis orientations, along and across the gap and normal to the plate, were modeled, as well as different coil lengths. The model can be used to predict the working range and select orientation and geometry of inductive seam tracking probes with zero gap capability for precision laser beam welding. Different materials, thicknesses and frequencies can be used.

Position adjustment method and distance estimation method of magnetic field supply and detection unit for magnetic hyperthermia

In magnetic hyperthermia, the temperature and localization of a ferromagnetic implant in a tumor region is vital in determining the effectiveness of therapeutic heating. We have developed a noninvasive wireless temperature measurement method by utilizing the magnetic permeability property of a ferromagnetic implant with low Curie temperature (FILCT) that varies with the temperature. In clinical settings, when the FILCT is injected into a tumor region, the position of the FILCT is expected to deviate from the central axis of the heating coil (drive coil). When it deviates, the magnetic flux density applied to the FILCT decreases, thus causing difficulty in detecting the temperature of FILCT via a pickup coil and heating of the FILCT at a constant treatment temperature. Therefore, to adjust the magnetic field supply and detection (MFSD) unit to be directly above the FILCT, we propose a position adjustment method by referring to three voltages induced in three pickup coils symmetrically installed inside the drive coil. By using the average value of the three voltages, we also propose a method to estimate the distance between the MFSD unit and the FILCT, which is required for wireless thermometry and determination of the optimal energy applied. The proposed methods are experimentally examined by a verification system.

Simulation, design, and test of an elliptical surface coil for magnetic resonance imaging and spectroscopy

AbstractThe simplest design of surface coils for magnetic resonance imaging (MRI) applications is circular and square loops, both producing a magnetic field perpendicular to the coil plane in the central region‐of‐interest (ROI), with an amplitude that decreases along the coil axis. However, a surface coil constituted by a loop with different geometry could be necessary when particular field‐of‐views (FOVs) are desired, especially for performing imaging in an elongated region. This can be achieved by using an elliptical loop, which can guarantee a wide longitudinal FOV and a good penetration in deep sample regions. This work proposes the application of a method for elliptical coil Signal‐to‐Noise Ratio (SNR) estimation previously developed for circular and square loop design, in which coil inductance and resistance are analytically calculated and the magnetic field pattern is estimated using the magnetostatic approach, while the sample‐induced resistance is calculated with the vector potential calculation method. In the second part of the paper, we propose the simulation and the design of a transmit/receive elliptical coil for MRI in mice with a 3T clinical scanner. We also evaluated the coil performance in a preliminary magnetic resonance spectroscopy (MRS) study in phantom.

Orientation effect in helical coils with smooth and rib-roughened wall: Toward improved gas heaters for supercritical carbon dioxide Rankine cycles

Helical coils have gained increasingly interest in the field of supercritical carbon dioxide (SCCO2) Rankine cycles during the last decade due to the compact structure and high heat transfer rate. Past studies mainly focused on effects of operating conditions and the gravitational buoyancy, and are not sufficient to fully understand the behavior of SCCO2 helically coiled gas heaters. Influence of some other key factors, such as the coil orientations and internal wall roughness, on overall performance has been seldom reported and is still unclear to date. In this work we filled this gap with a solid-to-fluid conjugate heat transfer model where supercritical flow turbulence is solved by the Shear-Stress Transport k-ω equations. The orientation effect on performance of helical coils was revealed with the coil axis arranged in horizontal, vertically upward and downward directions, respectively. Results demonstrate that the criterion of Bo < 10−5 for negligible buoyancy effect was applicable to coils with dimensionless curvature δ = 0.01–0.1. The Orientation effect only emerged when the buoyancy effect became significant with Bo > 10−5. Deterioration and enhancement of heat transfer occurred alternatively in horizontal coils. The overall performance of horizontal coils was much worse than vertical coils, among which the downward orientation was slightly better than the upward one. The increase of δ barely improved the performance of horizontal coils. Instead, at larger δ the intensive fluctuation in heat transfer coefficients was more frequent due to the more drastic change of the flow direction. The location and extent of local impairment also varied with the inlet arrangement. Finally, the passive compound enhancement technique of helical coils in conjunction with internal helical-rib roughness was found to be very effective in mixed convection of SCCO2, especially in the horizontal coils.

Radiofrequency fields in MAS solid state NMR probes

We present a detailed analysis of the radiofrequency (RF) field over full volume of a rotor that is generated in a solenoid coil. On top of the usually considered static distribution of amplitudes along the coil axis we describe dynamic radial RF inhomogeneities induced by sample rotation. During magic angle spinning (MAS), the mechanical rotation of the sample about the magic angle, a spin packet travels through areas of different RF fields and experiences periodical modulations of both the RF amplitude and the phase. These modulations become particularly severe at the end regions of the coil where the relative RF amplitude varies up to ±25% and the RF phase changes within ±30°. Using extensive numerical simulations we demonstrate effects of RF inhomogeneity on pulse calibration and for the ramped CP experiment performed at a wide range of MAS rates. In addition, we review various methods to map RF fields using a B0 gradient along the sample (rotor axis) for imaging purposes. Under such a gradient, a nutation experiment provides directly the RF amplitude distribution, a cross polarization experiment images the correlation of the RF fields on the two channels according to the Hartmann-Hahn matching condition, while a spin-lock experiment allows to calibrate the RF amplitude employing the rotary resonance recoupling condition.Knowledge of the RF field distribution in a coil provides key to understand its effects on performance of a pulse sequence at the spectrometer and enables to set robustness requirements in the experimental design.

Calculations of the parameters of the single-layer solenoidal inductor of finite length surrounded by a lossy dielectric medium

The expressions for estimating the spatial distributions of a quasi-static and rotational electric field are obtained for the near-field zone of single-layer solenoidal coils (inductors) surrounded by a medium with complex permittivity. Calculations are performed at field frequencies substantially lower than the self-resonance frequency. The environment conductance is taken into account, and its influence on the effective inductance, self-capacitance, and ohmic resistance of the inductor is established. It is demonstrated that capacitive currents can flow only between turns that are symmetrically arranged with respect to the central plane perpendicular to the coil axis.

Intensive Study of Skin Effect in Eddy Current Testing With Pancake Coil

Skin depth is an important parameter that quantifies depth of inspection of eddy current (EC) nondestructive testing. The formula which states that the skin depth is inversely proportional to the square root of the product of frequency, permeability, and conductivity has been widely used for calculating skin depth for many decades. It has been noticed that the true skin depth is less than that obtained by the formula when the EC is excited by the ac current in a pancake coil. In-depth and convincible explanation of this discrepancy has not been published. This paper studies this problem by finite-element analysis and concludes that the difference is due to two reasons. One is that the EC associated with pancake coil diffuses with increasing depth, whereas there is no diffusion effect of EC associated with uniform plane field which is the assumption of the conventional formula. The other reason is that the ECs induced by wire segments symmetric about the coil axis cancel each other and the cancellation becomes more severe with increasing depth due to the diffusion of EC. This paper also investigates the influence of each of coil parameters on skin depth. Then, a new formula for estimating skin depth is proposed.

Mechanical Support of the NHMFL 32 T Superconducting Magnet

The HTS insert for the 32 T superconducting magnet is comprised of two dry wound, double pancake REBCO coils of different lengths, nested within an LTS outsert. The high fields present within the HTS coils create large axial compression forces and significant radial expansion. The mechanical solutions implemented to account for the effects of axial and radial coil movement are described. These solutions are applied throughout many of the mechanical subsystems in and between the HTS coils, including electrical terminations, electrical bussing, external reinforcing of the windings, and suspension of the HTS coils within the outsert. Experiences from the assembly in preparation for the initial operation of the magnet are also shared.

Note: Evaluation of magnetometry data acquired from elongated samples.

We document and validate an analytic expression for the flux integral characterizing the response (or sensitivity) of a magnetometer equipped with second-order axial gradiometer coils to long, thin, uniformly magnetized samples. We then demonstrate an application inspired by this analysis, in which magnetometric sensitivity to weak magnetic signatures is readily and appreciably enhanced by increasing the sample volume (and hence the quantity of analyte) well beyond conventional limits.

Studies of magnetic properties when functionalized Fe3O4-antiCRP are associated with human C-reactive proteins for magnetic bio-sensing

In this work, a highly balanced ac susceptometer was designed and implemented for magnetic immunoassays for sensing human C-reactive proteins (CRP). It is known that CRPs are used mainly as a biomarker for inflammation or acute diseases. Monitoring CRP values in blood can help medical doctors understand disease progression or the effectiveness of treatments. We characterize magnetic properties of the ac susceptometer as the human CRPs are associated with Fe3O4-antiCRP. In the design, the pickup coil and the excitation coil are positioned side-by-side with their coil axis parallel and separated at a distance of ∼1.5cm. The pick-up coil consists of two coils wound in opposite direction with a compensation coil to improve balance. We use the Fe3O4-antiCRP-CRP magnetic clusters as the bio-target and study the effects of magnetic clustering on the changes of magnetization. The magnetic clusters are CRPs conjugated onto the Fe3O4-antiCRP and can be observed directly with SEM. The Fe3O4-antiCRP is the anti-C-reactive protein (antiCRP) coated onto dextran-coated magnetic nanoparticles (MNPs), also called the bio-functionalized magnetic nanoparticles (BMNs).

Assessment of Vascular Stent Heating with Repetitive Transcranial Magnetic Stimulation

A high proportion of patients with stroke do not qualify for repetitive transcranial magnetic stimulation (rTMS) clinical studies due to the presence of metallic stents. The ultimate concern is that any metal could become heated due to eddy currents. However, to date, no clinical safety data are available regarding the risk of metallic stents heating with rTMS. We tested the safety of common rTMS protocols (1 Hz and 10 Hz) with stents used commonly in stroke, nitinol and elgiloy. In our method, stents were tested in gelled saline at 2 different locations: at the center and at the lobe of the coil. In addition, at each location, stent heating was evaluated in 3 different orientations: parallel to the long axis of coil, parallel to the short axis of the coil, and perpendicular to the plane of the coil. We found that stents did not heat to more than 1°C with either 1 Hz rTMS or 10 Hz rTMS in any configuration or orientation. Heating in general was greater at the lobe when the stent was oriented perpendicularly. Our study represents a new method for ex vivo quantification of stent heating. We have found that heating of stents was well below the Food and Drug Administration standards of 2°C. Thus, our study paves the way for in vivo testing of rTMS (≤10 Hz) in the presence of implanted magnetic resonance imaging-compatible stents in animal studies. When planning human safety studies though, geometry, orientation, and location relative to the coil would be important to consider as well.

Twelve‐slot two‐saliency variable reluctance resolver with non‐overlapping signal windings and axial flux excitation

In this study, a new 12-slot two-saliency variable reluctance (VR) resolver with simple non-overlapping windings is proposed. The excitation winding in the proposed resolver is replaced with one axial coil that is perpendicular to the signal windings. Both distributed and non-overlapping concentric windings with uniform coil turns are used. The rotor has two upper and lower saliencies located in front of each other. The shape and width of each saliency are determined based on the optimisation. Compared with conventional 12-slot VR resolvers, the proposed resolver has a simpler rotor structure and the advantages of two-saliency resolvers against eccentricity, absolute output position, and higher accuracy. The operation principle of the proposed resolver is analytically shown. Then, a three-dimensional time-stepping finite-element method (FEM) is used for the design, analysis, and optimisation of the proposed sensor. After optimisation, a prototype of the most accurate resolver is built. The good agreement obtained between the FEM and the practical results verifies the design and optimisation process.

Proton probing of laser-driven EM pulses travelling in helical coils

The ultrafast charge dynamics following the interaction of an ultra-intense laser pulse with a foil target leads to the launch of an ultra-short, intense electromagnetic (EM) pulse along a wire connected to the target. Due to the strong electric field (of the order of $\text{GV m}^{-1}$ ) associated to such laser-driven EM pulses, these can be exploited in a travelling-wave helical geometry for controlling and optimizing the parameters of laser accelerated proton beams. The propagation of the EM pulse along a helical path was studied by employing a proton probing technique. The pulse-carrying coil was probed along two orthogonal directions, transverse and parallel to the coil axis. The temporal profile of the pulse obtained from the transverse probing of the coil is in agreement with the previous measurements obtained in a planar geometry. The data obtained from the longitudinal probing of the coil shows a clear evidence of an energy dependent reduction of the proton beam divergence, which underpins the mechanism behind selective guiding of laser-driven ions by the helical coil targets.

Superconducting Magnet with a Minimal Steel Yoke for the Future Circular Collider Detector

The conceptual design study of a Future Circular hadron-hadron Collider (FCC-hh) with a center-of-mass energy of the order of 100 TeV, assumed to be constructed in a new tunnel of 80–100 km circumference, includes the determination of the basic requirements for its detectors. A superconducting solenoid magnet of a 12-m-diameter inner bore with a central magnetic flux density of 6 T, in combination with two superconducting dipole magnets and two conventional toroid magnets, is proposed for an FCC-hh experimental setup. The coil of 23.468 m length has seven 3.35-m-long modules included into one cryostat. The steel yoke with a mass of 22.6 kt consists of two barrel layers of 0.5 m radial thickness and a 0.7-m-thick nose disk and four 0.6-m-thick endcap disks each side. The outer diameter of the yoke is 17.7 m. The full length of the magnetic system is 62.6 m. The air gaps between the endcap disks provide for the installation of muon chambers up to an absolute pseudorapidity of about 2.7. The superconducting dipole magnets provide measurement of charged particle momenta in the absolute pseudorapidity region greater than 3. The conventional forward muon spectrometer allows muon identification in the absolute pseudorapidity region from 2.7 to 5. The magnet is modeled with the program TOSCA from Cobham CTS Limited. The total current in the superconducting solenoid coil is 123 MA turns; the stored energy is 41.8 GJ. The axial force acting on each endcap is 450 MN. The stray field is 13.7 mT at a radius of 50 m from the coil axis and 5.2 mT at a radius of 100 m. Many other parameters are presented and discussed.

Metal Artifact Reduction MRI for Sagittal Balance Evaluation of Total Ankle Arthroplasty

Category: Ankle Arthritis Introduction/Purpose: Surgical restoration of the anatomical relationship between talus and tibia is considered crucial for longevity of total ankle arthroplasty (TAA). Weight-bearing (WB) radiographs are the current standard for evaluating the sagittal balance alignment, which are, however, prone to rotational misalignment and potentially altered measurements. Metal artifact reduction sequence (MARS) MRI is a cross-sectional technique that minimizes implant-induced artifacts and affords the visualization of bone-implant interfaces and periprosthetic bone without distortions. Although not weight-bearing, MARS MRI offers the ability to align the image plane to the true sagittal axis of the talar implant and anatomically correct measurements. Therefore, the purpose of this study was to compare sagittal balance alignment measurements on MARS MR images and standard WB radiographs in patients with TAA. Methods: In this IRB-approved, prospective study, 23 subjects [10 men/13 women, age 60(41-73) years; 13(3-24) months post- op] underwent MARS MRI and standard lateral WB radiographs. Standardized MARS MR images were obtained in alignment to the sagittal talar component axis and use of a boot-shaped MRI coil. Maximum-intensity-projection MR images that resemble lateral radiographs were created to bring anatomic landmarks, such as lateral talar process, talonavicular joint line, talar implant, tibial shaft, and posterior talus into one single image. Three board-certified foot ankle surgeons performed sagittal balance alignment measurements twice in an independent, random and blinded fashion. The second set of measurements was obtained 1 months after the first assessment. In accordance with published measurements, lateral talar station (LTS), tibial axis-to-talus (T-T) ratio, and normalized tibial axis-to-lateral-process (T-L) distance were measured. Pearson correlation coefficient (r), Concordance-Correlation-Coefficient (CCC) and Intraclass-Correlation-Coefficient (ICC) were used for statistical analysis. Bonferroni-corrected p-values ≤ 0.01 were considered significant. Results: The intra-observer agreement was excellent for radiographic (CCC = 0.93 - 0.97) and MRI (CCC = 0.90 - 0.97) measurements. Inter-observer agreements were good-to-excellent with overall higher agreements for MRI (ICC = 0.76 - 0.93) than for radiography (ICC = 0.58 - 0.95) measurements. There was statistically significant inter-method correlation between radiographic and MRI measurements including LTS (r=0.83, p &lt; 0.001), T-T ratio (r=0.86, p &lt; 0.001) and normalized T-L distance (r=0.72, p &lt; 0.001). The T-T ratios of radiographs and MRI were statistically not different (p=0.36), whereas LTS and normalized T-L distance were significantly lower on MR images when compared with radiographs (p &lt; 0.001). Conclusion: Sagittal balance measurements performed on standardized weight-bearing radiographs and standardized MARS MR images demonstrate substantial correlation and similarity. Given its high inter- and intra-observer agreement, MARS MRI may be helpful for the evaluation of sagittal balance following TAA.

Comparison between circular and square loops for low‐frequency magnetic resonance applications: theoretical performance estimation

AbstractRadiofrequency receiver coils in magnetic resonance (MR) systems are used to pick up the signals emitted by the nuclei with high signal‐to‐noise ratio (SNR) in a small region of sensitivity. The quality of obtained images strongly depends upon the correct choice of the coils geometry and size. The simplest design of such coils is circular and square loops, both producing in the central region‐of‐interest a magnetic field perpendicular to the coil plane, with an amplitude that decreases along the coil axis. This work reviews a method for coil SNR model development employing an equivalent electric circuit and applies it for circular and square loop design. Coil inductance and resistance were analitically calculated by taking into account for the conductors cross‐geometry and the magnetic field pattern was estimated using Biot–Savart law, while the sample‐induced resistance was calculated with a method employing a quasi‐static approach. Coil performance prediction permitted to compare circular and square loops and demonstrated that when a simple relationship between loops size is satisfied, the performance of both coils resulted to be very similar in terms of SNR. Since the theoretical approach formulation is largely detailed, this article could be interesting for graduate students and researchers working in the field of MR coil design and development.

Mathematical model to determine the dimensions of superconducting cylindrical coils with a given central field – the case study for MgB2 conductors with isotropic Ic(B) characteristic

In this work, we present a mathematical model which enables to design cylindrical coils with a given central field, made of the superconducting conductor with isotropic Ic(B) characteristic. The model results in a computer code that enables to find out the coil dimensions, and to calculate the coil parameters such as critical current, maximum field in the winding and field non-uniformity on the coil axis. The Ic(B) characteristic of the conductor is represented by the set of data measured in discrete points. This approach allows us to express the Ic(B) as a function linearized in parts. Then, it is possible to involve the central field of the coil, coil dimensions, and parameters of the conductor, including its Ic(B) characteristic, in one equation which can be solved using ordinary numerical non-linear methods. Since the coil dimensions and conductor parameters are mutually linked in one equation with respect to a given coil central field, it is possible to analyze an influence of one parameter on the other one. The model was applied to three commercially available MgB2/Ni/Cu conductors produced by Columbus Superconductors. The results of simulations with the Ic(B) data at 20K illustrate that there exists a set of winding geometries that generate a required central field, changing from a disc shape to long thin solenoid. Further, we analyze how the thickness of stabilizing copper influences the coil dimensions, overall conductor length, coil critical current, maximum field in the winding. An influence of the safety coefficient in operating current on coil dimensions and other above mentioned parameters is studied as well. Finally, we compare the coil dimensions, overall conductor length as well as coil critical current and maximum field in the winding if the value of required central field changes between 1 and 3 T.

Novel Rotating Current Probe With GMR Array Sensors for Steam Generate Tube Inspection

This paper presents a novel probe design that uses a rotating current excitation scheme and giant magnetoresi-stance (GMR) sensors for steam generator tube inspection. Rotating eddy currents in the tube wall under test is induced using a pair of axial and circumferential excitation coils. A circumferential array of GMR sensors measures the radial component of the magnetic field. The perturbation in eddy current flow caused by a defect produces a radial component field that is measured by the GMR sensors. A C-scan image of the induced magnetic field obtained with the axial motion of probe shows defect location and orientation. The probe is sensitive to both the axial and circumferential defects and offers the advantages of high sensitivity over a wide frequency range. A finite-element model was developed to mimic the underlying physical process and predict the output images of defects with different orientations and sizes. A prototype unit consisting of excitation coils and GMR sensor array along with a data acquisition system was developed and tested. A steam generator tube sample with machined axial and circumferential notches was inspected using the prototype probe. Experimental results demonstrating the feasibility of the concept are presented.

Cold Mass Support System for the MSU Superconducting Cyclotron Gas-Stopper Magnet

The cyclotron gas-stopper magnet at Michigan State University consists of two superconducting coils, each in its own cryostat. The two cryostats are mounted in the two warm iron poles of a sector cyclotron magnet used to control the orbit of heavy ions as the particle energy is being removed by circulating the ions through helium gas. Because the two poles of the magnet must be separated to install the gas chamber and beam extraction system, the magnet coils cannot be connected together. As a result, the magnet cold mass support system must carry the forces pushing the magnet into the iron pole as well as any decentering forces that occur from coil placement errors. The cold mass support system for each magnet coil consists of six compression supports that support magnet forces in the axial direction. In addition, there are three radial supports to center the coil axis coaxial with the axis of the iron poles. This paper presents an analysis of the superconducting magnet cold mass support system, which must be designed to have a spring constant that is higher than the magnet force constant at the full design current for the magnet.