Probe Coil Research Articles

Simulation Analysis of Eddy Current Testing Parameters for Surface and Subsurface Defect Detection of Aviation Aluminum Alloy Plate

In the process of eddy current testing (ECT) of surface and subsurface defects of aviation aluminum alloy plates, the setting of parameters is important to the test results. Inappropriate test parameters can cause false detection or even missed detection of defects. To address this problem, the effects of probe type, coil size, and excitation frequency on the accurate identification and quantitative evaluation of surface and subsurface defect detection were studied and analyzed in this study to determine the best testing parameters. The experimental results show that the absolute probe with an outer radius of 3.3 mm has better detection performance for aviation aluminum alloy plate defects. There are different optimal excitation frequency ranges for the surface and subsurface defects. An excitation frequency of 80 kHz to 90 kHz can be used for the detection of unknown defects.

Bdot probe and Rogowski coil cross-calibration and sensor fusion in pulsed direct current capacitor discharges.

Bdot probes and Rogowski coils are used in the measurement of transient magnetic fields and currents, respectively. They both share the mechanism of creating an induced electromotive force response via Faraday's law, which scales linearly with the pulsed magnetic field. High power capacitor direct current (DC) discharge systems release a single pulse of current that is both very high and very fast (≲1 ms). To capture these transient data and characterize these systems, high current tolerant and fast response time sensors are required. While these measuring devices have been well studied and utilized for almost 100 years, a comprehensive and detailed description of the custom design, calibration, and sensor fusion application of these tools for use in various pulsed DC capacitor value discharges is largely missing in the literature. Using robust analytical calculations, finite element analyses, and empirical methods, we have developed a sensor fusion protocol for current and magnetic field probes (with relative errors of ±13% and ±15%, respectively) for use in any geometry of high speed pulsed DC current calibrated capacitor discharge systems. This paper comprehensively outlines the design and sensor fusion methodologies that allow for the deployment of in-house built Bdot probes and Rogowski coils to a wide range of pulsed DC systems and demonstrates their use in a characteristic plasma environment.

Radially Periodic Metasurface Lenses for Magnetic Field Collimation in Resonant Wireless Power Transfer Applications

In this paper, a new procedure and topology of magnetic metasurface lens are proposed for improving the performance of Resonant Wireless Power Transfer systems. Firstly, three subwave-length unit cells are optimized in order to get negative magnetic permeability in the same frequency, each one with a different refractive index, and they are experimentally characterized. Then, the Transformation Optics technique is applied in order to find the unit cell arrangements which lead to the magnetic field focusing in a given direction. For this purpose, two coordinate transformations are proposed, and the effective electric permittivity and permeability that generate these profiles are calculated. It is shown from simulations and measurements that the refractive index gradient produced by the radial disposition of the unit cells can lead to a magnetic field manipulation similar to the optical converging and diverging lenses. Both metamaterials lenses are built, and the calculation of the magnetic flux density as a function of the measured induced voltage in a probe coil verifies their effects on the magnetic field. Finally, their performance in a resonant wireless power transfer system is tested, and improvements in terms of efficiency and range are presented. The proposed design method and the lenses that were developed demonstrate that metasurface lenses can improve efficiency without reducing the range, once these lenses are positioned close to the transmitter coil. Besides that, this method can reduce the losses due to misalignment between coils once the field can be collimated in a specific direction.

In Situ Real-Time Quantitative Determination in Electrochemical Nuclear Magnetic Resonance Spectroscopy

For the purpose of acquiring highly sensitive and differential spectra in in situ electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy, uniform distributions of amplitudes and phases of radio frequency (RF) fields in the sample are needed for consistent flip angles of all nuclei under scrutiny. However, intrinsic electromagnetic incompatibility exists between such requirements with electric properties of the conductive material in an electrolytic cell, including metallic electrodes and ionic electrolytes. This proposed work presents the adverse repercussions of gradually varying electrolyte conductivity, which is strongly associated with the change of ion concentrations in a real-time electrochemical reaction, on spatial distributions of RF field amplitude and phase in the detective zone of an NMR probe coil. To compensate for such a non-linear trend of the spatial dependent distribution, we eliminate different excitation effects of the RF field on the build-in external standard and the electrolyte both situated in nearly the same detection area, as well as promote the greater accuracy of quantitative determination of reactant concentrations. The reliability and effectiveness of the improved in situ EC-qNMR (quantitative NMR) method are confirmed by the real-time monitoring of the electrochemical advanced oxidation process for phenol, in which instant concentrations of reactants and products are detected simultaneously to verify the degradation reaction scheme of phenol.

Analytical model of a T-core coil above a multi-layer conductor with hidden hole using the TREE method for nondestructive evaluation

PurposeIn eddy current nondestructive testing, a probe with a ferrite core such as an E-core coil is usually used to detect and locate defects such as cracks and corrosion in conductive material. However, the E-core coil has some disadvantages, such as large volume and difficulty in the process of winding the coils. This paper aims to present a novel T-core probe and its analytical model used for evaluating hidden holes in a multi- layer conductor.Design/methodology/approachBy using a cylindrical coordinate system, the solution domain is truncated in the radial direction. The magnetic vector potential of each region excited by a filamentary coil is derived, and the expansion coefficients of the solutions are obtained by matching the boundary and interface conditions between the regions. By using the truncated region eigenfunction expansion method, the final expression in closed form for the impedance of the multi-turn coil is worked out, and the impedance calculation is performed in Mathematica. For frequencies ranging from 100 Hz to 100 kHz, both the impedance changes of the T-core coil above the multi-layer conductor without a hidden hole and in the absence of the layered conductor were calculated, and the influence of a hidden hole in the multi-layer conducting structure on the impedance change was investigated.FindingsThe correctness of the analytical model of the T-core coil was verified by the finite element method and experiments. The proposed T-core coil has higher sensitivity than an air-core coil, and similar sensitivity and smaller size than an E-core coil.Originality/valueA new T-core coil probe and its accurate theoretical model for defect evaluation of conductor were presented; probe and analytical model can be used in probe design, detection process simulation or can be directly used in defect evaluation of multi-layer conductor.

Progress Towards a Higher Sensitivity 13C-Optimized 1.5 mm HTS NMR Probe.

Nuclear magnetic resonance (NMR) probes using thin-film high temperature superconducting (HTS) resonators offer high sensitivity and are particularly suitable for small-sample applications. We are developing an improved 1.5 mm HTS NMR probe designed for operation at 14.1 T and optimized for 13C detection. The total sample volume is about 35 μL and the active sample volume is 20 μL. The probe employs HTS resonators for 13C and 1H transmission and detection and the 2H lock. We examine the interactions of multiple superconducting resonators and normal metal tuning loops on coil resonance frequency and probe sensitivity. We test a recently introduced 13C resonator design, engineered to significantly increase 13C detection sensitivity over previous all-HTS probes. At zero field, we observe a 13C quality factor of 6000 which is several times higher than previous resonators. In this work the coil design considerations and probe build-out procedure are discussed.

Methodology: non-invasive monitoring system based on standing wave ratio for detecting water content variations in plants

BackgroundWater content variation during plant growth is one of the most important monitoring parameters in plant studies. Conventional parameters (such as dry weight) are unreliable; thus, the development of rapid, accurate methods that will allow the monitoring of water content variation in live plants is necessary. In this study, we aimed to develop a non-invasive, radiofrequency-based monitoring system to rapidly and accurately detect water content variation in live plants. The changes in standing wave ratio (SWR) caused by the presence of stem water and magnetic particles in the stem water flow were used as the basis of plant monitoring systems.ResultsThe SWR of a coil probe was used to develop a non-invasive monitoring system to detect water content variation in live plants. When water was added to the live experimental plants with or without illumination under drought conditions, noticeable SWR changes at various frequencies were observed. When a fixed frequency (1.611 GHz) was applied to a single experimental plant (Radermachera sinica), a more comprehensive monitoring, such as water content variation within the plant and the effect of illumination on water content, was achieved.ConclusionsOur study demonstrated that the SWR of a coil probe could be used as a real-time, non-invasive, non-destructive parameter for detecting water content variation and practical vital activity in live plants. Our non-invasive monitoring method based on SWR may also be applied to various plant studies.

First results from the NORTH tokamak

NORTH is a small-sized tokamak located at the Technical University of Denmark. It can be operated both as a spherical tokamak and a simple magnetized torus (SMT). Here we show first experimental results. We discuss the setup of the device, including the layout of the vacuum vessel, the magnetic field coils, the power supply systems, the heating sources, diagnostics, and the control system. We present measurements in discharges that have been heated by electron cyclotron resonance heating at the fundamental resonance. The waves have been injected both from the low-field side and the high-field side, and rich fluctuation spectra in Langmuir probe and Rogowski coil signals are presented during the different plasma phases. Finally, we discuss research plans and further installations to be made on NORTH.

Characterizing the performance of eddy current probes using photoinductive field-mapping: a numerical approach

Nondestructive evaluation (NDE) method has been applied to analyze the configura- tions of coil probes and the characteristics of discontinuities in the few years, especially the ef- fects of probe tilt are paid attention to gradually. However, the probe tilt has been recognized as the one reason of producing noise in eddy current testing (ECT), such as the flaw manual scan- ning or the manufacture of probes with the irregular orientation coil. The inability to calibrate the tilt coil of probe makes it impossible to accurately inspect the surface cracks. Based on the above, we should found the applicable method to examine the structures of probe and demonstrate that it has the feasibility on investigating of probe with tilted coil. The photoinductive (PI) method is a novel inspection technique for detecting surface cracks. This paper shows how the PI technique can be utilized to analyze the effects of tilted coil of probe. The numerical multiphysics simula- tions of the PI imaging was performed with two dimensional finite element method (2D FEM) to characterize the variations of magnetic field and probe's impedance on a conductive metal foil. As anticipated, the proposed model shows that the PI imaging signals can reveal the construction of the probe. The FEM simulation results of tilted coils are showed and discussed. The effects of PI signals with different excited frequencies of the coil are also examined and analyzed. The simulation results demonstrate that not only the PI method is appropriate for investigating the structures of probe, but also how the tilt probe can affect the reliability of an eddy current in- spection.

Research on pulsed eddy current automatic detection technology for weld defects of pressure vessel cylinder

In order to solve the problems of low detection efficiency, high labor intensity and poor working environment of large pressure vessel cylinder, the pulsed eddy current (PEC) nondestructive testing technology is used to detect the defects in the welding seam of the cylinder. The PEC sensor composed of rectangular probe coil and Hall sensor is installed on the mobile inspection platform to test two simulated cylinder weld samples. Results show that the signal curve of sample 1 without defect is gentle and without mutation, while the signal of sample 2 with defect has three mutation signals. Then, the X-ray testing method is used to detect the sample, radiograph confirmed that there are no defects on sample 1 and three porosity defects in sample 2. Through the comparison and analysis of the above two kinds of detection results, the feasibility of the detection method for weld subsurface defects is verified.

Magnetic Field Measurements of First Pre-series Full-Length 4.2 m Quadrupole MQXFA03 Using PCB Rotating Coils for the Hi-Lumi LHC Project

The U.S. Hi-Lumi LHC Accelerator Upgrade Project (AUP) and CERN have joined efforts to develop high field quadrupoles for the Hi-Lumi LHC upgrade. The US national laboratories in the AUP project will deliver 10 magnets and each cryostat has two 4.2 m high gradient quadrupoles in it. These magnets are made of Nb3Sn conductors, with large aperture (150 mm) and integrated gradient of 556.9 T. This paper reports on magnetic measurements performed during the vertical test at Brookhaven National Laboratory (BNL) in 2019-2020. A warm measurement Z-Scan (+/-15 A) with 42 Z-positions before cool-down was performed at BNL. The results were directly compared to field data measured at LBNL during magnet assembly. Measured harmonics and magnetic center offsets (ΔX and ΔY) have provided timely and informative diagnostics on the magnet structure's shape at both warm and cold temperatures. A new centering fixture was designed and added to better center the warm bore tube which contains the rotating coil probe. After the quench training to 16.47 kA was achieved, a complete set of cold measurements (Z-Scan at 16.47 kA and I-Scan from 960 A to 16.47 kA and back to 960 A) was made. Periodic axial variation of allowed and nonallowed harmonics was observed which is related to the coil radial and/or mid-plane variations along the magnet axis. Overall, the average harmonics in the straight section are within the required field boundaries.

Metamaterial-Core Probes for Nondestructive Eddy Current Testing

Eddy current testing (ECT) is one of the most important techniques in nondestructive evaluation. A higher probe sensitivity is always pursued in ECT. To improve the probe sensitivity, the near electrical resonance signal enhancement (NERSE) technique was recently proposed. In the NERSE technique, a coaxial cable connecting with the probe coil is introduced to provide a capacitance for the electrical resonance. However, the long coaxial cable is awkward and inconvenient in engineering applications, restraining the usability of such probes. Metamaterials (MTMs) are novel artificial electromagnetic media and have been proved to be effective in manipulating the impedance of a solenoid coil. In other words, in principle, MTMs can be used in the same way as that a coaxial cable in NERSE in ECT. Based on this argument, low-frequency magnetic MTMs are introduced as the probe cores to provide a new approach to achieve the electrical resonance for the NERSE technique. A promising feature of the proposed approach is that the detecting signals and sensitivity are significantly increased due to the extraordinary electromagnetic properties of the MTM. The most salient features of an MTM core over a ferrite core are: 1) effective permeability of the MTM core will vary sharply from a high positive to a high negative values when crossing the resonance frequency, resulting in not only a high magnetic flux density in the tested material but also an extremely large variation of the normalized impedance which is very essential in identifying a crack and 2) electromagnetic properties of an MTM will increase with the increase of frequency, whereas those of a ferrite material usually degrade sharply with the increase of frequency. To demonstrate the advantages of the proposed new probe, comprehensive numerical and experimental studies are conducted, and the results have shown the high performance of the proposed probe. In addition, the proposed MTM-core probe also exhibits a diverse versatility and convenience in engineering applications as compared with the existing NERSE technique.

The Chinese Mars ROVER Fluxgate Magnetometers

The Mars Rover Magnetometers (RoMAG) will implement the first mobile magnetic field measurements on the surface of Mars. Two identical tri-axial fluxgate magnetometer sensors are mounted at the top and bottom of the mast of rover, respectively. The technology of Helmholtz compensation coil probe and digital closed-loop feedback circuit is utilized to realize high precision measurement. Each magnetometer measures the vector magnetic field with a resolution of 0.01 nT in the range of $\pm65000~\text{nT}$ . The sample rate is up to 32 Hz and the noise is $0.01~\text{nT}/\surd\text{Hz}$ @1 Hz. A rover magnetic compensation procedure was conducted to remove the most important magnetic disturbances. Mobile magnetic field measurements on the Martian surface would obtain fine-scale crust field and provide information about its remnant magnetization and any possible intrinsic magnetic field. It would help us to further understand Martian internal structure, coupling processes of solar wind-magnetosphere-ionosphere.

Research on Detection Mechanism of Weld Defects of Carbon Steel Plate Based on Orthogonal Axial Eddy Current Probe.

The uneven surface of the weld seam makes eddy current testing more susceptible to the lift-off effect of the probe. Therefore, the defect of carbon steel plate welds has always been a difficult problem in eddy current testing. This study aimed to design a new type of eddy current orthogonal axial probe and establish the finite element simulation model of the probe. The effect of the probe structure, coil turns, and coil size on the detection sensitivity was simulated. Further, a designed orthogonal axial probe was used to conduct a systematic experiment on the weld of carbon steel specimens, and the 0.2 mm width and 1 mm depth of weld defects of carbon steel plates were effectively detected. The experimental results showed that the new orthogonal axial eddy current probe effectively suppressed the unevenness effect of the weld surface on the lift-off effect during the detection process.

1H detection of heteronuclear dipolar oscillations with water suppression in single crystal peptide and oriented protein samples

Oriented sample solid-state NMR is a complementary approach to protein structure determination with the distinct advantage that it can be applied to supramolecular assemblies, such as viruses and membrane proteins, under near-native conditions, which generally include high levels of hydration as found in living systems. Thus, in order to perform 1H detected versions of multi-dimensional experiments water suppression techniques must be integrated into the pulse sequences. For example, 1H-windowed detection of 1H-15N dipolar couplings enable multi-dimensional NMR experiments to be performed. Here we show that the addition of a solvent suppression pulse during the z-filter interval greatly improves the sensitivity of the experiments by suppressing the 1H signals from water present. This is demonstrated here with a crystal sample submerged in water and then extended to proteins. The combination of solvent-suppressed 1H detected PISEMO and the use of a strip shield-solenoid coil probe configuration provides a two-fold sensitivity enhancement in both the crystal sample and Pf1 coat protein sample compared to the 15N direct detection method. Here we also examine protein NMR line-widths and sensitivity enhancements in the context of window detected separated local field experiments for protein samples.

Measurement of Electrical Conductivity Degree of some Metallic Conductors by Using the LC Circuit

Metallic conductors have different degrees of their electrical conductivity. The aim of this research is to measure the electrical conductivity degree for some metallic conductors by measuring the induced voltage in a coil probe, which moves inside the metallic conductor sample tube. When a low frequency of alternating current flows through the LC circuit, it will pass through the solenoid and will generate a magnetic field, which will be reduced due to the presence of the metallic sample tube. The magnetic flux strength generated inside the solenoid determine the electrical conductivity (σ ) of this metallic tube by measuring the EM force induced on the solenoid in the presence the sample tube and without it. Measurements are conducted on two sample models (zinc and aluminum). Test results shows deviation of 10 % compared with the reference values ​​.

Study on the Impedance Change of Rectangular Coil Perpendicular to Conductive Cylinder

Cover meter is widely used to monitor the reinforced structures, and the response of the cover meter probe coil is used to locate the rebar, evaluate the diameter and cover depth of the rebar embedded in concrete. In order to analyze and optimize the performance of the cover meter, the analytical solution to the response of the probe is of great importance. Based on the theory of the second order vector potential (SOVP), the integral solutions to the coil coefficient and the impedance change of the rectangular coil are achieved when the normal direction of the coil is perpendicular to the axis of the conductive cylinder. The theoretical and experimental results are in excellent agreement induced not only by nonmagnetic materials but also by magnetic materials. The impedance changes of the rectangular coil and the circular coil with same sectional area are compared theoretically, as a consequence, the rectangular coil can help to find the direction of the rebar embedded in concrete. The allowed frequency of the coil is also discussed. These integral solutions to the impedance change of the rectangular coil can help the cover meter designers to optimize the coil parameters and the exciting frequency conveniently.

Research on the detection of curved ferromagnetic materials by flexible eddy current array sensor based on ldc1614

Flexible eddy current array nondestructive testing technology has the advantages of large single scanning area and fast scanning speed in the defect detection of conductive materials, so it becomes a common research hotspot of sensor and nondestructive testing technology. The performance of the array probe on the sensor is an important factor to determine the performance of the sensor, and the detection circuit and excitation mode are another important factor. In this paper, the array coils with different parameters are simulated and analyzed, and the resonant detection circuit based on ldc1614c digital inductance conversion chip is used to detect the high permeability materials on curved surface. Through the digital imaging technology, the defect image of the tested material is obtained to verify the selection of the probe coil and the reliability of the detection circuit.

Generation and Diagnostics of Pulse Plasma Flows

Pulsed plasma accelerators are widely used for the production of high-temperature pulsed plasma flows for fundamental and practical applications. The basic parameters of pulsed plasma accelerators are the characteristics of the external electric and magnetic circuits, as well as the structural and energy properties of the plasma flow. This work aims to characterize an IPU-30 pulsed plasma accelerator. The triple Langmuir probe method, calorimetric plasma energy density measurements, Rogowski coil, and high-speed visible imaging with a Phantom VEO710S fast camera are used to diagnose the pulsed plasma obtained in the IPU-30. The local plasma parameters such as electron temperature and density, the energy density of the pulsed plasma flow, pulsed plasma current, and also discharge current are experimentally obtained at different discharge voltages and air pressure in the chamber. The typical waveforms of the triple probe and Rogowski coil are presented in the form of oscillograms. The images of plasma formation in the discharge gap are obtained and the velocity of a pulsed plasma flow is measured.

Estimation of Unknown Parameters of the Equivalent Electrical Model During an Eddy Current Test

This article presents a method to estimate unknown parameters in an eddy current detection system: the magnetic coupling coefficient $k$ between the probe coil and the surface of a conductive sample and also a constant $C$ dependent on the material and geometrical properties of the conductive target. These parameters are defined from the analysis of the electrical equivalent model of the measurement system. Thereby, the liftoff from an ECT probe can be estimated during a scanning procedure by estimating $k$ . The presented method depends on the input impedance of the inductive probe stimulated by a power source with an appropriate range of frequencies. The self-inductance as well the intrinsic resistance of the probe needs to be measured in advance. While the input impedance is monitored, the magnetic coupling coefficient $k$ and constant $C$ are continuously estimated with a recursive least squares method. A theoretical analysis is presented and supported by experiments conducted with three different conductive metal samples: aluminum, copper, and brass. The results presented good agreement with the reference and estimated parameters $C$ and $k$ as well as the liftoff between the probe and the conductive target.