Magnetic Flux Measurements Research Articles

Mitigation of Unbalanced Magnetic Pull in Synchronous Machines With Rotating Exciters

A magnetization system with active compensation of unbalanced magnetic pull for synchronous machines with rotating exciters is demonstrated. The system used switched power electronics and a digital control system to control the currents in four rotor pole groups, each consisting of 3 poles. It was mounted on the shaft of a synchronous machine, providing an interface between a permanent magnet outer-pole brushless exciter and the segmented field winding. Measurements of magnetic flux density on each pole face and current control made it possible to control the airgap magnetic flux density to balance the machine magnetically, thus removing flux density space harmonics in the airgap and also the unbalanced magnetic pull. The construction of the system is presented along with results from experiments and simulations. Tests were performed with the stator winding both in series and with two parallel circuits. Approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {80\%}$</tex-math></inline-formula> reduction of static forces and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {60\%}$</tex-math></inline-formula> reduction of dynamic forces between the stator and rotor were observed when the system was running.

Magnetic Stress Sensing System for Nondestructive Stress Testing of Structural Steel and Steel Truss Components Based on Existing Magnetism.

To detect the stress of steel structures and members using the existing magnetism, a magnetic stress sensing system integrating a magnetic flux induction coil, a magnetic flux measurement device, a loaded device, and data acquisition software was developed. The magnetic coupling test research was carried out for different grades of structural building and bridge steel specimens to establish the magnetic stress flux mathematical model, and the fitting equation of the magnetic flux changes with the positions of different sections of specimens was analyzed. Furthermore, a practical formula for stress detection was obtained through the experiments. Meanwhile, on these bases, the typical steel truss structure model of a Bailey beam was designed and manufactured under different working conditions, nondestructive online stress testing was carried out, and the stress of the model structure and its members was measured by strain and magnetic flux tests to obtain the curves of the test results for the stress–strain and magnetic stress flux, respectively. The results of these two methods are in good agreement with each other. The stress of the steel truss model structure was analyzed and calculated using the finite element method. The results agreed well with the experimental results from the magnetic stress sensing system—the maximum error was about 5%, which meets the requirements of engineering applications.

Magnetic flux density measurements from narrow grain boundaries produced in sintered permanent magnets.

This review examines methods of magnetic flux density measurements from the narrow grain boundary (GB) regions, the thickness of which is of the order of nanometers, produced in Nd-Fe-B-based sintered magnets. Despite of the complex crystallographic microstructure and the significant stray magnetic field of the sintered magnet, recent progress in electron holography allowed for the determination of the intrinsic magnetic flux density due to the GB which is embedded in the polycrystalline thin-foil. The methods appear to be useful as well for intensive studies about interface magnetism in a variety of systems.

Triaxial Magnetic Flux Emanation in Response to Uniaxial Electric Field in Magnetoelectric Composite Cylinder Structure

Magnetoelectricity in bulk strain‐mediated multiferroic composites has been growing in attention for sensor and actuator applications. For actuator applications, where electric to magnetic coupling is utilized, the magnetoelectric composite alters the magnetic field which it is within resulting in full‐field spatial and directional changes to the magnetic flux. To grasp a better understanding of the full‐field magnetic behavior of a magnetoelectric composite with a complex geometry, multiple magnetic flux measurements in different locations and directions are taken to unveil interesting behaviors and phenomena such as modality and postfabrication material property modification. Remarkably, a significant multidirectional magnetic flux is measured at a distance away from the composite which can be harnessed to improve the efficiency of multiferroic actuators. In addition, the intensity and directionality of the magnetic flux is highly tunable by modifying the frequency and bias magnetic field depending on the need for the application.

Low-field magnetic analysis for sigma phase embrittlement monitoring in thermally aged 22Cr duplex stainless steel

The aim of this study is to evaluate a new nondestructive method designated as Low-Field Magnetic Analysis (LFMA) based on the measurement of magnetic flux density for monitoring sigma (σ) phase precipitation in duplex stainless steel (DSS). In addition, the effect of isothermal aging treatment at 800 °C on the metallurgical degradation of UNS S31803 DSS was investigated. It was found a change in the volume fraction of α-Fe/γ-Fe phases due to α-Fe (ferromagnetic phase) eutectoid decomposition to precipitate sigma and secondary austenite (paramagnetic phases). A significant and gradual reduction of saturation magnetization was observed with the increase of thermal treatment time, indicating a decrease in the quantity of α-Fe phase. Two magnetic methods were used to verify the evolution of the σ phase: M−H measurements at 300 K using a commercial magnetometer and LFMA testing. Both methods were sensitive to small percentages of σ phase in the microstructure. Furthermore, our developed technique presents accurate results for low magnetic fields with high sensitivity and reliability.

Low Frequency Magnetic Fields Emitted by High-Power Charging Systems

The new generation of fast charging systems faces a formidable technological challenge, aiming to drastically reduce the time needed to recharge an electric vehicle as a way to tackle the range anxiety issue. To achieve this, high power (up to 350 kW) is transferred from the grid to the vehicle, leading to potentially high values of low frequency magnetic fields. This study presents the results of measurements of magnetic flux density (B-field) emitted by two different high power charging systems. The electric vehicle used for the recharge was able to digest up to 83 kW of delivered power. The test procedure was designed to identify the locations where the maximum B-field levels were recorded and to measure the exposure indices according to reference levels for general public exposure defined in the Council Recommendation 1999/519/EC. Measurements in close proximity to the power cabinets during the recharge revealed that, at some points, exposure indices were higher than 100%, leading to the identification of a distance from the system components at which the value was lower than the reference level. In the worst case, this distance was 31 cm.

Vibration problem solution of high-capacity hydropower units

This paper proposes hydro generator vibration observations under various conditions and solution of a problem of high vibration in upper guide bearing of 110MW hydro generator. Among the test, which were carried out to identify vibration origin of hydro generating unit were: voltage drop tests, magnetic flux measurements, interferric gap measurements, turbine pressure pulsation measurements, etc. It was shown, that among other possible reasons, correct balancing, including pivot bearing adjustment was the most efficient measure to eliminate vibration in start-up modes of hydro power unit. According to the results of conducted step-by-step defect analysis, the corresponding recommendations were provided for service and maintenance regarding the generation unit No2 of Sangtuda-2 Hydro Power Plant, Tajikistan.

Magnetic particle inspection and EMF Directive 2013/35/EU

EMF Directive 2013/35/EU [1] was transposed into legislation in EU member states in 2016. In the UK, the Health and Safety Executive (HSE) produced the Control of Electromagnetic Fields at Work (CEMFAW) Regulations 2016 [2] . It is the first piece of legislation in the UK that is specific to electromagnetic fields (EMFs) and requires all employers to perform an EMF risk assessment. For many this is a relatively easy process, as most workplaces do not contain equipment capable of producing high fields. However, any piece of equipment that uses a high level of electrical current is capable of generating a high magnetic field and, in the case of magnetic particle inspection (MPI), it is an intended output. As the operator is often required to stand close to the generated field, exposure levels can be relatively high. Magnetic flux density measurements have shown that the action levels (ALs) used as the basis for exposure assessment can be exceeded. In some instances this can be mitigated by some instruction or training, while in others it may be necessary to prove compliance with exposure limit values (ELVs). Proving compliance with ELVs is more complicated than proving compliance with ALs. It is by no means impossible, however, as computer modelling can be employed. The regulations also list categories of worker considered to be at particular risk. Pregnant workers and workers with active medical devices, such as pacemakers, or passive implants, for example artificial joints, pins, plates, screws or stents, are all considered to be at particular risk. To perform a risk assessment for such workers, reference levels contained in EU Council Recommendation 1999/519/EC [3] are used. These are much more stringent than ALs and compliance is more difficult, but a pragmatic approach can be employed to achieve a successful outcome. Fundamentally, the purpose of the regulations is not to place obstacles in the way of industry but to make employers and equipment manufacturers aware of their obligations and the possible routes that can be taken to achieve compliance.

Magnetic flux density measurements from grain boundary phase in 0.1 at% Ga-doped Nd–Fe–B sintered magnet

The magnetism of a narrow (~1.6 nm) grain boundary phase produced in a 0.1 at% Ga-doped Nd–Fe–B sintered magnet was examined using electron holography. The magnetic flux density was determined to be 0.8 ± 0.1 T, which was smaller than that for a commercial magnet free from Ga doping (~1.0 T). The presence of a ferromagnetic grain boundary phase reasonably explained the functionality of the 0.1 at% Ga-doped system, such as the improvement in the squareness of the demagnetization curve. The observations provide useful information for deeper understanding of the coercivity mechanism in Ga-doped Nd–Fe–B sintered magnets.

Crosstalk analysis and Current Measurement Correction in Circular 3D Magnetic Sensors Arrays

The circular array of magnetic sensors is a research hotspot in the field of power electronics, especially for the measurement of direct current(DC). The high linearity, large dynamic range, small size and low power consumption of circular magnetic sensors arrays for current measurement are an improvement over the current sensors utilizing a ferromagnetic core. However, due to the absence of core magnetization, the external magnetic field can easily enter the magnetic sensors, which will affect the measurement accuracy. Therefore, this paper focuses on the influence of the interference field from the conductor positioned outside the circular array and proposes a model of the target conductor penetrating the circular array with the interference conductor outside the circular array. This model is used to analyze the influence of relevant parameters of the interference conductor and the target conductor on the crosstalk error. An interference-rejecting method of circular 3D magnetic sensor arrays is proposed, which establishes the model of magnetic flux density measurement to calculate the target conductor current. The simulation results show theoretically that the method can greatly reduce the crosstalk error and correct current measurement. 3-D tunnel magnetoresistance (TMR) chip is selected as the magnetic sensors of the circular array in the laboratory experiment, and the experiment errors can be reduced to around 1%. The simulation and experiment results verify that the interference-rejecting method can correct measurement results and improve the accuracy of the target current.

A Stacked Autoencoder Neural Network Algorithm for Breast Cancer Diagnosis With Magnetic Detection Electrical Impedance Tomography

Magnetic detection electrical impedance tomography (MDEIT) is a novel imaging technique that aims to reconstruct the conductivity distribution with electrical current injection and the external magnetic flux density measurement by magnetic sensors. Aiming at improving the resolution and accuracy of MDEIT and providing an efficient imaging method for breast cancer diagnosis, a new algorithm based on stacked auto-encoder (SAE) neural network is proposed. Both numerical simulation and phantom experiments are done to verify its feasibility. In the numerical simulation, an amount of sample data with different conductivity distribution are calculated. Then a neural network model is established and trained by training these samples. Finally, the conductivity distribution of an imaging target with the anomaly location can be reconstructed by the network model. The reconstruction result of the SAE algorithm is compared with the reconstruction results of the traditional sensitivity matrix (SM) algorithm and the back propagation (BP) neural network algorithm. Under the noise of 30dB, the relative errors of BP algorithm, SM algorithm and SAE algorithm are 137.19%, 24.90% and 15.28% respectively. Result shows by the SAE algorithm, the location of anomalies is reconstructed more accurately, the conductivity value is more closely to the real one and the anti-noise performance is more robust. At last, a breast phantom experiment by self-made platforms is completed to verify the application feasibility of the new algorithm. The relative reconstruction error of conductivity by proposed SAE algorithm can be reduced to 14.56%. The results show that by SAE algorithm, MDEIT can be a promising approach in clinical diagnosis of breast cancer, and it also provide more potential application prospect for the extensive application of MDEIT.

Stress Testing of Steel Suspender of Arch Bridge Model Based on Induced Magnetic Flux Method

To establish an online nondestructive stress testing method for arch bridge suspender based on the principle of magnetic coupling, the magnetic mechanical property of Q345qD steel is explored taking an arch bridge model structure with Q345qD steel suspender as the research object. Under the action of magnetic field excited by a coil, the test of the coupling relationship between stress and excitation flux is carried out. The theoretical model of stress‐magnetic flux is simplified to better meet the requirements of engineering applications. The excitation device, magnetic flux measurement device, stress‐magnetic flux data analysis program, and so on are developed, and the magnetic coupling stress detection system is integrated. The test model structure of a steel arch bridge with suspenders of Q345qD alloy steel is designed and made; under the different load conditions, the stresses of the suspenders are tested and studied. The relationships between induced magnetic flux and technical magnetized voltage, test load of model structure, and different stress conditions of the suspenders are analyzed; with the induction magnetic flux as the parameter, the stress‐magnetic flux coupling model is established. The test results based on the stress‐magnetic flux coupling model are compared with those of the traditional stress‐strain test in a linear elastic range; it shows that the two testing methods are in good agreement with each other, and the maximum error is less than 5%. Meanwhile, with the increase in the load on the suspender, the tension stress increases and the induced magnetic flux decreases, showing a good linear relationship. The conclusions drawn from the research can provide important reference for health monitoring of suspenders of arch bridges.

Integrator Drift Compensation of Magnetic Flux Transducers by Feed-Forward Correction.

Integrator drift is a problem strongly felt in different measurement fields, often detrimental even for short-term applications. An analytical method for modelling and feed-forward correcting drift in magnetic flux measurements was developed analytically and tested experimentally. A case study is reported on the proof of principle as a novel kind of quasi-DC field marker of the 5-ppm Nuclear Magnetic Resonance (NMR) transducer Metrolab PT2026, applied to the Extra Low ENergy Antiproton (ELENA) ring and the Proton Synchrotron Booster (PSB) at CERN. In some particle accelerators, such as in ELENA, the resulting feed-forward correction guarantees 1 T field stability over 120-s long magnetic cycle on a plateau of 50 mT, reducing by three orders of magnitude the field error caused by the integrator drift with respect to the state of the art.

Local magnetic flux density measurements for temperature control of transient and non-homogeneous processing of steels

Measuring temperatures during high-temperature processing of steels is usually limited to surface measurements that cannot directly assess the internal temperature distribution. Here, we demonstrate the feasibility of using a magnetic flux density measurement system to assess transient and non-homogeneous temperature fields in a modern high-strength steel, within the intercritical temperature range where microstructural evolution defines their key mechanical properties. The system accurately detects the Curie temperature and distinguishes temperature change rates within the processed volume. The magnetic measurements are also sensitive to the volume above Curie temperature and its shape, as revealed when integrated with thermal computational simulations. The electromagnetic signal provides real-time qualitative and quantitative information relevant to the metallurgical conditions enabling future intelligent control systems for the production and processing of steels. Contactless measurements of temperature-dependent electromagnetic properties can enable through-thickness temperature monitoring solutions, opening up opportunities for non-destructive full-field imaging of steels during thermal and thermomechanical processing.

Machine Perception Based on Eddy Current for Physical Field Reconstruction of Conductivity and Hidden Geometrical Features

This paper presents a new machine perception method based on eddy-current (EC) effects to reconstruct physical fields (EC field, electrical-conductivity field, and hidden geometrical features) of a nonferrous material commonly encountered in intelligent manufacturing using one-time finite magnetic flux density (MFD) measurements. An analytical model for EC testing system with conductor discretization is established and expressed in state-space representation. Two improvements (physical constraints and adaptive element refinement) are developed and integrated into the system model. The measurement models of physical fields using discrete MFD measurements are linearly established, reducing the physical field reconstruction to a linear inverse problem for solving using the Tikhonov regularization method. The EC-based machine perception is numerically illustrated by reconstructing the EC density field, conductivity field, and hidden geometrical features of aluminum plates. Additionally, the effects of element refinement, physical constraints, and sensor configurations on the reconstruction results are analyzed numerically. Using an experimental prototype consisting of an air-cored electromagnet and a two-dimensional (2-D) array of magnetic sensors with associated electronics, the effectiveness of the machine perception method and the accuracy of the reconstructed physical field are demonstrated experimentally.

Development of a High-Performance Magnetic Field Sensor and Its Application to a Magnetic Field Visualization System Using the Augmented Reality Technique

Two- or three-dimensional visualization of magnetic flux density distribution around sources is quite informative for understanding the field environment intuitively. Measurement of magnetic flux density, as well as positioning of measuring points in space, has to be performed in a short time because temporal variation in the source current results in different field environments. It is also valuable to obtain the frequency spectrum of the magnetic field simultaneously at the time of field measurement, especially for sources generating high-frequency components like inverter-driven equipment. This paper develops a high-performance magnetic field sensor which satisfies the above requirements. And, as an application of it, the magnetic field visualization system using the augmented reality (AR) technique is proposed by combining two sensors: one is a magnetic field sensor described above, and the other is a Kinect sensor which has a skeleton tracking function as position determination.

On the evaluation of global laser-induced effects on a medical Ti-6Al-4Valloy by non-destructive techniques

ABSTRACTTi6Al4V ELI alloy is widely used for the fabrication of a wide range of load-bearing implants. Surface modification by laser shock processing (LSP) has demonstrated the capability to generate roughness of clinical interest, being the control of the surface and subsurface microstructural changes relevant to the intended applications. This work is aimed to compare the induced effects by scanning electron microscopy (SEM) and thermoelectric power (TEP) techniques to sense the subtle material variations such as local texture, increased dislocation density, hardening and residual stresses degree in a non-destructive way. For comparative purposes, synchrotron radiation X-ray diffraction (SR-XRD) experiments were also carried out to determine the residual stress state, The magnetic flux density (MFD) measurements demonstrate that the non-contact technique is very sensitive to the compressive residual stresses with increasing the severity of the laser treatment parameters, while the TEP contacting results are closely related to grain size, cracks, anisotropy, and work hardening.

Self-Sensing Estimation of Mechanical Stress in Magnetostrictive Actuators

Magnetostrictive actuators show interesting performances related to high-precision actuation with high-energy density, which focused the interest of research in the past years. Nevertheless, the output deformation is related to the current and the applied stress, through a complex multi-input multi-output (MIMO) hysteresis process. As a consequence, a reliable and accurate control task cannot neglect the stress monitoring. Such task, if performed by an ad hoc stress sensor, e.g., a load cell, will face with the sensor’s placement in the device, resulting in an increase in cost, complexity, and bulkiness of the system. This issue can be circumvent if the current and magnetic flux measurements, available in the control chain, are exploited. To this aim, a novel self-sensing approach to deliver real-time estimation of the stress is presented in this paper, involving some recent results of a thermodynamic compatible MIMO model of hysteresis for magnetostrictive materials.

Heat and Mass Transport in a Vapor‐Dominated Hydrothermal Area in Yellowstone National Park, USA: Inferences From Magnetic, Electrical, Electromagnetic, Subsurface Temperature, and Diffuse CO2 Flux Measurements

AbstractVapor‐dominated hydrothermal systems are characterized by localized and elevated heat and gas flux. In these systems, steam and gas ascend from a boiling water reservoir, steam condenses beneath a low‐permeability cap layer, and liquid water descends, driven by gravity (“heat pipe” model). We combine magnetic, electromagnetic, and geoelectrical methods and CO2 flux and subsurface temperature measurements in the Solfatara Plateau Thermal Area in the Yellowstone Caldera to address several fundamental questions: (1) What are the structural and/or lithological controls on heat and mass transport in vapor‐dominated areas? (2) What is the geometry and size of convecting multiphase thermal plumes? (3) Are thermal plumes associated with subsurface rock alteration and demagnetization? Magnetic and electromagnetic data inversions suggest an asymmetric 50‐ to 100‐m thick basin of glacial deposits with the thickest part adjacent to the margin of a rhyolite flow. The 3‐D electrical conductivity model in the glacial basin reveals a narrow vertical conductor interpreted as a focused multiphase plume, which coincides at the ground surface with the heat and CO2 flux maxima. The magnetic data suggest that destruction of magnetic minerals due to rock alteration associated with the hydrothermal plume occurs mainly near the ground surface. We propose a model where the buoyant multiphase plume forms in response to decompression, boiling, and phase separation of pressurized thermal groundwater that discharges from the brecciated base of a rhyolite flow into the basin of glacial deposits. Results from multiphase groundwater flow and heat transport numerical simulations corroborate the first‐order characteristics of this model.

A Novel Test Method for Real-time Magnetic Flux Measurement of Power Transformers

Optimizing magnetic flux distribution in iron cores is very important in the transformer design. It can affect whether the iron cores of transformers are saturated or not in severe con ...