Pickup Coil Research Articles

An analytical solution for vertical coils near a multi-layered metallic pipe in Pulsed Eddy Current Testing

Analytical model for Pulsed Eddy Current Testing (PECT) of a multi-layered metallic pipe has not been solved, which limits the development of PECT technology. In this paper, the analytical model for vertical coils near a multi-layered metallic pipe is proposed. However, the analytical solution is hard to solve due to the large number of undetermined coefficients. Combined with the global matrix method, an improved transfer matrix across a conductor is established, which overcomes unsolvable problem in the traditional transfer matrix method. The induced voltage of pickup coil calculated based on the analytical model is verified by Finite Element Method (FEM) and experiments. Furthermore, the influence of several working conditions of pipelines on the PECT signal is studied based on the analytical model, providing guidance for engineering applications.

A hybrid spiral-bobbin eddy current testing probe for detection of crack of arbitrary orientation in steam generator tubes

ABSTRACT This paper presents a new hybrid spiral-bobbin probe (S-bobbin probe) of transmitting-receiving (TR) mode for efficient eddy current testing (ECT) of steam generator tubes in nuclear power plants. The new probe of novel configuration can solve the major drawback of the conventional bobbin type ECT probe, i.e., insensitive to circumferential cracks. The excitation coil of the new probe consists of 2 coil segments of spiral geometry and 2 coil segments of half circle geometry which are sequentially connected to form a full coil loop. To acquire defect signal of low lift-off noise, the TR probe mode is adopted and the shape of the pick-up coil is selected the same as that of the excitation coil. As the S-bobbin probe can induce eddy currents in two different directions, it can detect cracks in SG tubes of arbitrary orientations. In order to demonstrate the validity and efficiency of the new S-bobbin probe, simulations and experiments were carried out with a prototype S-bobbin probe and tube specimens with circumferential or axial artificial cracks. The simulation and experimental results agree well, and both of them reveal that a crack in any direction can be properly detected and evaluated by using the new probe.

Transient voltages and energy balance in REBCO insulated magnet: experimental and numerical studies

Different means are investigated today to protect a rare earth–barium–copper oxide (REBCO) coil against local thermal runaway, what is commonly called a ‘Quench’. Metal Insulated Coil or No-Insulated coil have been successfully introduced. However, these protections method may show other issues and are limited in terms of dynamics, making them impractical for fast applications. We successfully tested early detection of dissipative voltage followed by current dumping as a method to protect REBCO insulated test coils, even with engineering current density in the kA mm−2 range. Pick up coils can be used to compensate inductive coil voltage. In previous works we highlighted the presence of transient voltage due to the hysteretic current distribution in REBCO tape width, which can complicate the detection. We then developed a numerical electromagnetic model that reproduce the transient behavior of REBCO coils. Here we study a small REBCO coil instrumented with three different pick-up coils, including a co-wound pick-up whose coupling is close to perfect. The post processing and analysis of the simulation results makes it possible to identify in the transient coil voltage the contribution due to transient losses and coil inductance variation. The resulting evaluation of the REBCO coil inductance and its variations is validated by analysis of the pick-up coil signals. From a practical point of view, this work shows the possibility to have very sensitive early detection of thermal runaway if the threshold is adjusted based on the expected coil compensated voltage drift. The interest of using isolated high-strength co-wound reinforcement tape as pick-up coil is also highlighted.

Improving spatial resolution of scanning SQUID microscopy with an on-chip design

Scanning superconducting quantum interference device (sSQUID) microscopy is currently one of the most effective methods for direct and sensitive magnetic flux imaging on the mesoscopic scale. A SQUID-on-chip (SOC) design allows integration of field coils for susceptometry in a gradiometer setup which is very desirable for measuring magnetic responses of quantum matter. However, the spatial resolution of such a design has largely been limited to micrometers due to the difficulty in approaching the sample. Here, we used electron beam lithography technology in the fabrication of the 3D nano-bridge-based SQUID devices to prepare pick-up coils with diameters down to 150 nm. Furthermore, we integrated the deep silicon etching process in order to minimize the distance between the pick-up coil and the wafer edge. Combined with a tuning-fork-based scanning head, the sharpness of the etched chip edge enables a precision of 5 nm in height control. By scanning measurements on niobium chessboard samples using these improved SQUID devices, we demonstrate sub-micron spatial resolutions in both magnetometry and susceptometry, significantly better than our previous generations of nano-SQUIDs. Such improvement in spatial resolution of SOC is a valuable progress for magnetic imaging of quantum materials and devices in various modes.

External Dynamic InTerference Estimation and Removal (EDITER) for low field MRI.

Point-of-care MRI requires operation outside of Faraday shielded rooms normally used to block image-degrading electromagnetic interference (EMI). To address this, we introduce the EDITER method (External Dynamic InTerference Estimation and Removal), an external sensor-based method to retrospectively remove image artifacts from time-varying external interference sources. The method acquires data from multiple EMI detectors (tuned receive coils as well as untuned electrodes placed on the body) simultaneously with the primary MR coil during and between image data acquisition. We calculate impulse response functions dynamically that map the data from the detectors to the time varying artifacts then remove the transformed detected EMI from the MR data. Performance of the EDITER algorithm was assessed in phantom and in vivo imaging experiments in an 80mT portable brain MRI in a controlled EMI environment and with an open 47.5mT MRI scanner in an uncontrolled EMI setting. In the controlled setting, the effectiveness of the EDITER technique was demonstrated for specific types of introduced EMI sources with up to a 97% reduction of structured EMI and up to 76% reduction of broadband EMI in phantom experiments. In the uncontrolled EMI experiments, we demonstrate EMI reductions of up to 99% using an electrode and pick-up coil in vivo. We demonstrate up to a nine-fold improvement in image SNR with the method. The EDITER technique is a flexible and robust method to improve image quality in portable MRI systems with minimal passive shielding and could reduce the reliance of MRI on shielded rooms and allow for truly portable MRI.

Simulation based study of magnetic velocity induction system by using Analysis System Electromagnetics Suite.

The magnetic velocity induction system (MAVIS) is commonly used for velocimetry in shock compression experiment. Due to some discrepancies, the variation in induced voltage amplitude is ambiguous, which makes the simulation of this experiment particularly significant. In this work, we have designed a MAVIS, which was used to determine the induced voltage amplitude and flyer velocity. We built a three-dimensional model of MAVIS and performed the simulations using the Analysis System Electromagnetics Suite. Additionally, we performed some experiments and compared the results of both studies on the basis of flyer thickness, radius, and velocity. It was established that the flyer velocity influenced the induced electromotive force (EMF) in the pick-up coils. The increase in flyer radius led to the increase in the induced EMF. The cut-off radius for flyers was also discussed in detail by computing the lowest induced EMFs at discrete flyer velocities and radii. Due to the eddy current loss, experimental data laid slightly lower than simulations. The simulation data have proved its accuracy within the experimental error range. Thus, it can be applied as an economical framework to calculate projectile velocity precisely, regardless of its geometry, and to estimate the trigger level of the oscilloscope before performing the experiments. In order to enhance the quality of induced voltage, we also proposed a new designconsisting of three pick-up coils. This redesigned MAVIS contributed significantly in signal narrowing as well as controlled the loss in amplitude peaks that reduced the experimental uncertainty in flyer velocity <0.4%.

Self-Oscillating Boost Converter of Wiegand Pulse Voltage for Self-Powered Modules

This paper introduces a new method of electricity generation using a Wiegand sensor. The Wiegand sensor consists of a magnetic wire and a pickup coil wound around it. This sensor generates a pulse voltage of approximately 5 V and 20 µs width as an induced voltage in the pickup coil. The aim of this study is to generate a DC voltage of 5 V from the sensor, which is expected to be used as a power source in self-powered devices and battery-less modules. We report on the design and verification of a self-oscillating boost converter circuit in this paper. A DC voltage obtained by rectifying and smoothing the pulse voltage generated from the Wiegand sensor was boosted by the circuit. A stable DC output voltage in the order of 5 V for use as a power supply in electronics modules was successfully obtained. A quantitative analysis of the power generated by the Wiegand sensor revealed a suitable voltage-current range for application in self-powered devices and battery-less modules.

Control of a wireless sensor using the pulse sequence for prospective motion correction in brain MRI.

To synchronize and pass information between a wireless motion-tracking device and a pulse sequence and show how this can be used to implement customizable navigator interleaving schemes that are part of the pulse sequence design. The device tracks motion by sampling the voltages induced in 3 orthogonal pickup coils by the changing gradient fields. These coils were modified to also detect RF-transmit events using a 3D RF-detection circuit. The device could then detect and decode a set RF signatures while ignoring excitations in the parent pulse sequence. A set of unique RF signatures were then paired with a collection of navigators and used to trigger readouts on the wireless device synchronous to the pulse sequence execution. Navigator interleaving schemes were then demonstrated in 3D RF-spoiled gradient echo, T1 -FLAIR (fluid-attenuated inversion recovery) PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction), and T2 -FLAIR PROPELLER pulse sequences. Excitations in the parent pulse sequences were successfully rejected and the RF signatures successfully decoded. For the 3D gradient echo sequence, distortions were removed by interleaving flipped polarity navigators and taking the difference between consecutive readouts. The impact on scan duration was reduced by 54% by breaking up the navigators into smaller parts. Successful motion correction was performed using the PROPELLER pulse sequences in 3 Tesla and 1.5 Tesla MRI scanners without modifications to the device hardware or software. The proposed RF signature-based triggering scheme enables complex interactions between the pulse sequence and a wireless device. Thus, enabling prospective motion correction that is repeatable, versatile, and minimally invasive with respect to hardware setup.

Eddy-current array-probe technique for imaging near-surface and deep-lying delaminations in multidirectional carbon fiber composites

An eddy-current array-probe method was proposed to visualize delamination occurring within multidirectional carbon fiber-reinforced plastics. First, samples with a near-surface delamination were scanned by a coil array probe comprising a single driver coil and multiple pickup coils, and the detectability of the delamination was evaluated by the signal-to-noise ratio. An appropriate selection of the image phase and the distance between the driver and pickup coils enabled detection of the delamination suppressing the signal variation in the non-defective region. Furthermore, the experimental results suggested that the distance between the driver coil and the most sensitive pickup coil correlated with the delamination size. Second, the array-probe technique was used to detect a delamination located at various depths. The detectability of the delamination was found to be strongly affected by the rotation angle of the array probe. The optimum probe rotation angle depended on the depth of the delamination, indicating that a delamination occurring in deeper regions can be visualized by setting an appropriate probe rotation angle.

Matteucci Effect and Single Domain Wall Propagation in Bistable Microwire under Applied Torsion

Systematic experimental results on the Matteucci effect in torsioned magnetostrictive FeSiB microwire are introduced, observed during the propagation of a single domain wall (DW) under the action of axial driving magnetic field, Hdr. These data are discussed, reviewing current bibliography models and proposing new perspectives. The unidirectional DW velocity is quantified by voltage induced in tiny pickup coils along the microwire. The Matteucci electromotive force (emf) induced between the microwire's ends is associated with depinning and annihilation of the DW, introducing a new method to measure DW velocity. The emf amplitude is proportional to the DW velocity and the time derivative of the azimuthal magnetization, tailored by applied torsion. The data confirm the existence of net values of azimuthal magnetization and spontaneous torsion induced during fabrication. The clockwise/counterclockwise applied torsion dependence of Matteucci emf and DW velocity are experimentally determined for parallel and antiparallel Hdr. Asymmetric behaviors are observed for both, the sense of applied torsion and the direction of Hdr. The experimental data are discussed in terms of the magnetoelastic anisotropy introduced by torsion. Through analysis of the DW dynamics, such asymmetric behaviors are interpreted as a magnetochiral effect derived from the change of chirality of the propagating wall.

Dosimetry of pulsed magnetic field towards attaining bacteriostatic effect on Enterococcus faecalis: Implications for endodontic therapy.

To examine in a laboratory setting the efficacy of moderate to high strength magnetic fields, as a potential bacteriostatic stimulus, against Enterococcus faecalis, one of the causative agents for infection during root canal treatments. Four different strengths (1, 2, 3 and 4T) of the pulsed magnetic field (PMF) were applied in thirty repetitions to bacterial suspension. A pickup coil setup was used to measure the electromotive force induced inside the bacterial suspensions. The optical density (OD) was monitored over time (for 16h 40min) during the post-treatment period to assess bacterial growth. Along with the change in OD values, live/dead assay, membrane depolarization study, atomic force microscopy (AFM), scanning electron microscopy (SEM) and reactive oxygen species (ROS) assay on selected samples were studied to evaluate the effect of PMFs. All results were analysed using one-way ANOVA followed by post hoc Tukey test and considered significant at p<.05. Regression analysis (at a confidence of 95%, α=0.05) was performed on the bacterial growth and membrane depolarization studies to determine progressive changes of the outcomes. The peak value of the induced electromotive force was recorded as 0.25V, for the 4T magnetic field pulse with a pulse width of 16ms. There was a significant arrest of bacterial cell growth after an exposure to PMFs of 1T, 3T and 4T (ANOVA score: F (4, 495) =395.180 at p=.05). The image-based qualitative results of the live/dead assay using fluorescence microscopy techniques indicated that an exposure to higher PMFs (3T/ 4T) induced a bacteriostatic effect in a longer post-exposure timescale. Evidence of altered membrane potential within the 2h of exposure to 4T PMF was supported by the incidence of elevated ROS. For the ROS assay, a significant difference occurred for 4T exposed samples (ANOVA score: calculated F (1, 3) =20.2749 at p=.05). SEM and AFM observations corroborated with the outcomes, by portraying significant membrane damage. In a laboratory setting, PMFs with higher magnitudes (3T and 4T) were capable of inducing bacteriostatic effects on E.faecalis.

Preparation of a high-T c superconducting magnetic flux transformer with a 100 mm bore coil and static magnetic field transfer at 77 K

Herein, superconducting magnetic flux transformers with pickup coils of diameter 100 mm were prepared using a commercial RE123 high critical temperature (high-T c ) superconductive tape. A superconducting flux transformer requires a closed circuit containing a superconductive joint, which is difficult to prepare for a cuprate high-T c superconductor. Using the cut-and-wind method, seamless and large-bore coils were equipped to the flux transformer; these features are advantageous for non-destructive estimation and geological magnetic survey. The magnetic flux transfer of the applied static field caused by the spontaneously induced superconductive shield current at the liquid nitrogen temperature was confirmed, and the efficiency in the static field transfer, depending on the inductance of the coils in the flux transformer, was estimated.

Contribution to the study of the domain wall shape in bistable microwires

Magnetic domain wall in bistable glass-coated microwires is subject of the study in this paper. The domain wall between axial domains in these microwires is not a standard 180° domain wall. It is the source of a stray field, so the shape of the induced signal due to the domain wall passing through the pick-up coil is influenced by the domain wall geometry as well as by the presence of the stray field accompanying the moving wall. The present work considers the possibility of the moving domain wall having a stable conical-like shape with the apex pointing ahead. Based on this configuration, the signal induced in the pick-up coil is modelled. It is shown that the shape of the obtained model signal can explain the typical signals observed in experiments.

Angle Magnetization Rotation Method for Characterizing Co-Rich Amorphous Ferromagnetic Microwires

A low-frequency model of the magnetization reversal of a microwire is developed for those cases when the microwire magnetization response can go beyond the linear approximation. The analysis of the influence of external magnetic fields on the process of magnetization reversal of the microwire, including the hysteresis mode, was performed. The characteristic dependences of the amplitude of the electromotive force, U2f, arising in the pick-up coil wound around the microwire are obtained. It was established that, in the region of relatively small-acting circular and longitudinal magnetic fields, the U2f signal could have a region with the opposite sign. An extended small-angle magnetization rotation method was used to verify the proposed model and test glass-coated, amorphous, Co-rich microwires. During the experiments, the amplitude of the second harmonic, U2f, arising in the pick-up coil when an alternating electric current with the frequency f flows through the microwire, was measured as a function of the applied longitudinal magnetic field at various mechanical tensile stresses. The effective anisotropy field, the magnetostriction constant, and the residual quenching stress of the investigated microwires were determined by comparing the theoretical and experimental data.

Observation of antichiral edge states in a circuit lattice

We constructed an electrical circuit to realize a modified Haldane lattice exhibiting the unusual phenomenon of antichiral edge states. The circuit consists of a network of inductors and capacitors with interconnections reproducing the effects of a magnetic vector potential. The next nearest neighbor hoppings are configured differently from the standard Haldane model, and as predicted by earlier theoretical studies, this gives rise to antichiral edge states that propagate in the same direction on opposite edges and co-exist with bulk states at the same frequency. Using pickup coils to measure the voltage distributions in the circuit, we experimentally verify the key features of the modified Haldane lattice, including the group velocities of the antichiral edge states.

Mechanical Behavior of the Shielded HL-LHC Beam Screen During a Magnet Quench

In the framework of the High-Luminosity Large Hadron Collider (HL-LHC) project, larger and shielded beam screens will be installed in the beam pipe of the superconducting magnets of the insertion next to the ATLAS and CMS detectors. The beam screen is a complex assembly that guarantees the vacuum requirements while shielding the magnet cold mass from the induced heat loads. Such an assembly has to withstand high intensity electromagnetic forces induced during magnet quenches. The mechanical stability was verified in a dedicated quench test campaign performed at the magnet test station of CERN. Strain gauges, custom-made probes, and optical fibers were installed in the beam screen to measure deformations during a quench. Magnetic field measurements were also carried out by means of pick-up coils mounted within the assembly. The main outcomes of this work are the elastic behaviour of the beam screen after 52 quenches and a satisfactory agreement between measurements and simulations.

A Linear Eddy Current Speed Sensor With a Perpendicular Coils Configuration

This paper presents a new linear eddy current speed sensor with rectangular-shaped coils. The excitation coil and the pick-up coil have a perpendicular configuration without a magnetic yoke. The proposed sensor is shorter than the previous designs. The sensor works for a conductive moving target; in this paper we present calculations and an experimental verification for solid iron and aluminum moving part materials. A novel 3D analytical method is presented for the description and for the design of an eddy current speed sensor that is fast and has high precision. The source fields and the reaction fields caused by induced eddy currents are separated in our 3D analytical method, which facilitates an enhanced investigation of the features of the speed sensor. Evaluations of the effects of the moving part material and of coil lift off on the performance of the speed sensor are made with the use of a 3D analytical method. Measurements are performed for an eddy current speed sensor at different speeds up to 11.65 m/s and at different frequencies with a novel analytical model in terms of the induced voltage in the pickup coil versus speed. Simplicity and high precision are the main advantages of the proposed speed sensor. The achieved linearity error is 0.47% (measured) up to 11.6 m/s, and 0.43% (calculated) up to 117 m/s (420 km/h).

Design of a Rectangular Pickup Coil Fabricated on a PCB Using WBG Power Semiconductor in Discrete Package

Power semiconductors based on wide bandgap (WBG) devices are capable of fast switching and have low on-resistance. Accordingly, a fast sensor with a higher bandwidth is required for circuit inspection based on switch current measurements. Thus, it is necessary to have a current sensor in the printed circuit board (PCB) circuit for diagnosis and protection of the surface mount device (SMD) type circuit system. Accordingly, a pickup coil with the advantages of a high degree of sensor configuration freedom, wide bandwidth, and low cost can be a good alternative. This study analyzes the influence of coil shape and parameters on sensor design as a guideline for embedding a pickup coil in an SMD-type PCB circuit of a WBG power semiconductor-based, half-bridge structure. The mutual inductance and self-inductance values of the coil are considered large variables in the design of a sensor coil for simultaneously maintaining high bandwidth and sensor sensitivity. Therefore, magnetic and frequency response analyses were conducted to verify the correlation with inductance, the influence of coupling capacitance, and the influence of the magnetic field formation via the current flowing through the external trace inside the PCB. The coil model is verified and discussed through simulation and double pulse tests.

Measurement of plasma current in Damavand tokamak using magnetic probes assembly as a discrete Rogowski coil

In this paper, the pickup coils assembly in vacuum vessel of Damavand tokamak is used as a discrete Rogowski coil. An important advantage of this approach is the insensitivity of discrete Rogowski coil to magnetic fields created by the external excitation and equilibrium coils. Three interpolation methods are compared to evaluate the magnetic field between pickup coils with experimental data. The lowest error for estimating current is obtained by piecewise quadratic interpolation method. Moreover, the sensitivity to magnetic noise of this approach is investigated by introducing statistical error. According to the results, this array can measure plasma current with considerably better accuracy than a continuous external Rogowski coil.

A Novel Method for Thickness Measurement in Conducting Materials by Apparent Conductivity Calculation Through Transient Eddy Current NDE

This paper describes a novel method for thickness measurement in conducting material by combining the measurement of the decaying induced eddy current and its associated apparent conductivity calculation. In conventional frequency domain NDE (Non-destructive Evaluation), the skin depth is the limiting factor due to the single frequency excitation. In contrast, with a pulsed excitation, the induced eddy currents decay with time and the decay of the eddy current consists of continuum of frequencies and hence the entire thickness of the conducting material could be investigated in a single shot. The time at which the decay of the eddy current is maximum is called diffusion time “tm” and the corresponding calculated value of apparent electrical conductivity “σmapp” both of which can be directly correlated to the thickness of the material. Since the induction of the eddy current and its associated secondary magnetic field measured by using suitable magnetic sensors [hz α (σ/t)3/2 for B-field and Vz α (σ3/2/t5/2) for an induction coil] is directly related to the conductivity of the materials, one can calculate the apparent conductivity σapp(t) as a function of decay time. Apparent conductivity calculations have been made for aluminum plates based on the thin conducting sheet model in which the applied magnetic field is uniform throughout the thickness. Subsequently, transient measurements have been performed with stacks of aluminum plates by using pickup coils in the form of an absolute as well as differential configuration. From this, it has been shown that the square root of the ratio of the maximum diffusion time, tm and the corresponding apparent conductivity, σmapp called as maximum diffusion depth, δm which is proportional to the plate thickness. The diffusion depth is a parameter derived from standard electromagnetic equations which is analogous to the skin depth in the frequency domain. In this work, induction coil sensors of both types have been used to measure the transients, and the other instruments such as transmitter, transmitter controller and data acquisition system used for this work are the same ones used for TDEM (time domain electro-magnetic) based geophysical applications.