Magnetic Flux Measurements Research Articles

Comprehensive Analysis of Magnetic Flux Density and RF-EMF Exposure in Electric Buses: A Case Study from Samsun, Turkey.

This study investigates magnetic flux density (B) and radiofrequency electromagnetic field (RF-EMF) measurements on electric buses operating in Samsun, Turkey, focusing on two bus routes (called E1 and E4) during the morning and evening hours. Measurements were taken under diverse operational conditions, including acceleration, cruising, and braking, at locations of peak passenger density. Along the E1 route, the magnetic field intensity varied significantly based on the bus position, road slope, and passenger load, with notable increases during braking. In contrast, the E4 route showed a lower magnetic field intensity and RF-EMF values due to its straighter trajectory and reduced operational stops. The highest RF-EMF measurement recorded was 6.01 V/m, which is below the maximum levels established by the ICNIRP guidelines. In 11 out of the 12 different band-selective RF-EMF measurements, the highest contribution came from the downlink band of the base stations, while in only one measurement, the highest contribution originated from the uplink bands of the base stations. All data were subject to the Anderson-Darling test, confirming the generalized extreme value distribution as the best fit for both B and RF-EMF measurements. Additionally, the study assessed B levels inside and outside the bus during charging, revealing heightened readings near the pantograph. These findings significantly contribute to our understanding of electromagnetic field exposure in electric bus environments, highlighting potential health implications and informing the development of targeted mitigation strategies.

Low-Power Magnetic Displacement Sensor Based on RISC-V Embedded System.

With the emergence of RISC-V architecture in embedded devices, its inherent low-power features have propelled its extensive adoption across various industrial settings. Displacement sensors leveraging Hall sensors and magnetic flux measurement present notable benefits including cost-effectiveness and compact design. This study undertakes the porting of Hall sensors onto RISC-V architecture embedded devices, validating their functionality within displacement sensors. Empirical investigations substantiate that the ported system consistently delivers comparable outcomes to those obtained from x86 architecture systems employing PM-MFM methods, affirming its reliability and performance in practical applications.

Modeling a Solenoid Driver with Nonlinear Inductive Load Using Circuit Simulation and Magnetic Flux Measurement

This paper describes the procedure for creating a electronic simulation model of a solenoid power electronic driver with a nonlinear inductive load. Furthermore, it discusses the electromagnetic interaction between the driver and the load example electromagnetic valve. The consideration of nonlinear effects in the power electronic components MOSFET and diode is particularly important to distinguish their effects from the nonlinear behaviour of the inductive load.

Performance analysis of acoustically actuated magnetoelectric antennas via equivalent circuit method

Acoustically actuated magnetoelectric (ME) antennas based on resonant magnetoelectric coupling within ferromagnetic/piezoelectric ME laminated composites have recently been considered as a promising solution for antenna miniaturization. However, its radiation performance has been theoretically overestimated, since the negative effects on performances due to the magnetization saturation and the nonlinear mechanical behavior that occur from high-field driving have not been paid enough attention. This work presents a unique equivalent-circuit-based numerical method to analyze the near-field resonance radiation performances of ME antennas driven by high electric fields. In this method, we establish an equivalent circuit of the converse magnetoelectric effect for a ME laminated composite to describe the operating principle of acoustically actuated electromagnetic radiation. The equivalent parameters related to resonance characteristics are determined by fitting the circuit model to the data from frequency response measurements of the near-field magnetic flux density. The validity of the model is verified by comparing the theoretical predictions with the experimental results, in the view of the volume fraction dependence of the mechanical resonance-related radiation characteristics of the fabricated ME composites. Based on the proposed model, the influence of driving voltage amplitude on near-field radiation performances is further analyzed by experimental fitting to the model, and the potential limiting factors of ME antennas are discussed according to the driving-amplitude dependence of parameters obtained from the fit. This work provides an effective and engineering-friendly approach to predict the evolution of ME antenna performances, leading a way to improve the performance limit for resonant magnetoelectric coupling.

Robust Reconstruction of the Void Fraction from Noisy Magnetic Flux Density Using Invertible Neural Networks.

Electrolysis stands as a pivotal method for environmentally sustainable hydrogen production. However, the formation of gas bubbles during the electrolysis process poses significant challenges by impeding the electrochemical reactions, diminishing cell efficiency, and dramatically increasing energy consumption. Furthermore, the inherent difficulty in detecting these bubbles arises from the non-transparency of the wall of electrolysis cells. Additionally, these gas bubbles induce alterations in the conductivity of the electrolyte, leading to corresponding fluctuations in the magnetic flux density outside of the electrolysis cell, which can be measured by externally placed magnetic sensors. By solving the inverse problem of the Biot-Savart Law, we can estimate the conductivity distribution as well as the void fraction within the cell. In this work, we study different approaches to solve the inverse problem including Invertible Neural Networks (INNs) and Tikhonov regularization. Our experiments demonstrate that INNs are much more robust to solving the inverse problem than Tikhonov regularization when the level of noise in the magnetic flux density measurements is not known or changes over space and time.

Detection of blood coagulation in an extracorporeal circuit using magnetic and absorbance properties

In extracorporeal circulation, intra-circuit blood coagulation can lead to serious problems. However, intra-circuit coagulation cannot be monitored in real-time and is only intermittently monitored by measuring the activated clotting time (ACT). As blood clotting progresses in a circuit, the color of the blood turns from bright red to dark red. And, changes in blood coagulation can be detected using devices with optical sensors because the absorbance is likely to change as blood coagulates. However, the absorbance may also increase when oxygen partial pressure is altered by artificial lungs. Thus, there is a need for a device that is not affected by blood oxygenation. Therefore, we used a magnet and a flux meter to assess changes in the magnetic force with blood coagulation. Thus, there is a need for a device that is not affected by blood oxygenation. Therefore, we used a magnet and a flux meter to assess changes in the magnetic force with blood coagulation. Measurements were made at different flux intensities to capture the magnetic flux changes during blood coagulation. Blood (100 ml) was stored in a beaker. Calcium chloride (CaCl2: 0.2 ml) was then added to the beaker to promote coagulation. Blood from the beaker was drawn into a syringe and set in the magnetic flux measurement fixture, and a magnet was fixed on top of the syringe for 24 min. The flux meter readings increased as the blood coagulated. The results suggest that it is possible to capture magnetic flux density changes during the process of blood coagulation. From the above may lead to the development of a device that monitors coagulation in extracorporeal circuits in real time by monitoring two aspects of the coagulation process: absorbance and magnetic flux density.

3D magnetic flux density measurement with reduced sampling and high accuracy using visual localization and adaptive mesh generation

3D magnetic flux density measurement with reduced sampling and high accuracy using visual localization and adaptive mesh generation

Optimization of the equilibrium magnetic sensor set for the SPARC tokamak

Accurate reconstruction of the plasma equilibrium is imperative for successful operation of the SPARC tokamak. In order to assess the expected reconstruction accuracy throughout the duration of design-point discharges, the EFIT equilibrium reconstruction code was deployed for SPARC. Reconstructions from SPARC baseline scenarios were compared with free-boundary equilibria generated by FreeGS, Toksys, and the Tokamak Simulation Code. The key geometric areas of interest, where design constraints are imposed, included: the inner and outer midplane gaps, the X-point locations, as well as the strike point locations. Successful reconstructions of various reference discharges, using deviations in these key geometric quantities as metrics, were calculated from synthetic signals considering an optimized equilibrium magnetic sensor set. The optimization process for this sensor set combined a scan of randomized sensor placement with a linear perturbation analysis to determine critical sensor locations, while simultaneously conforming to design constraints on the sensor placement. This optimized set was also successful in performing equilibrium reconstructions with the addition of error to synthetic measurements of magnetic flux and magnetic field, as well as contributions from eddy currents in conducting structures. These methods represent a workflow of optimization and validation that balances the engineering constraints of sensor placement with achieving sufficient reconstruction fidelity for science and operations missions for SPARC.

Effects of thermal treatment and temperature on domain wall dynamics in magnetic microwire

Investigation of the influence of thermal treatment and temperature on domain wall (DW) dynamics in bi-stable magnetic microwire with strong unidirectional effect on DW propagation is presented. Measurements of remanent magnetic flux allowed to use in our consideration the force acting on the DW during propagation instead of applied driving field. Then the DW damping coefficient was determined for two values of force acting on the propagating DW for the same sample, but under different conditions (effects of annealing and temperature). Experimental and model temperature dependences of normalized damping coefficient were compared. The theoretical model used takes into account possible changes in DW length caused by mechanical stress and applied force. Experimental and model dependences are in qualitative agreement and show that changes in mechanical stress with temperature are the dominant mechanism responsible for changes in damping coefficient with temperature. Additional analysis shows that the ratio between spin relaxation and eddy current damping is not a constant parameter, but probably increases with increasing DW velocity (applied field).

A Fast Magnetic Flux Density Measurement Method With Skip-Echo Acquired Turbo Spin Echo (SATE).

The measurements of magnetic flux density ( Bz) needed in magnetic resonance electrical impedance tomography (MREIT) and magnetic resonance current density imaging (MRCDI) techniques often utilize spin echo (SE)-based sequences for data acquisition. The low imaging speed of SE-based methods significantly hampers the clinical applications of MREIT and MRCDI. Here, we propose a new sequence for substantially accelerating the acquisition of Bz measurements. A skip-echo acquired turbo spin echo (SATE) imaging sequence based on the conventional turbo spin echo (TSE) technique was proposed by adding a skip-echo module in front of the TSE acquisition module. The skip-echo module consisted of a series of refocusing pulses without acquisition. In SATE, amplitude-modulated crusher gradients were used to remove the stimulated echo pathways, and the radiofrequency (RF) pulse shape was specially selected to preserve more signals. In efficiency evaluation experiments performed on a spherical gel phantom, we demonstrated that SATE had improved measurement efficiency compared to the conventional TSE sequence via skipping one echo before acquiring signals. The accuracy of the Bz measurements by SATE was validated against those by the multi-echo injection current nonlinear encoding (ME-ICNE) method, while SATE was able to accelerate the data acquisition up to 10-fold. Volumetric coverage of Bz maps obtained in the phantom, pork, and human calf illustrated that SATE can reliably measure volumetric Bz distributions within clinically acceptable time. The proposed SATE sequence provides a fast and effective approach for volumetric coverage of Bz measurements, greatly facilitating the clinical applications of MREIT and MRCDI techniques.

Single Stretch Wire and vibrating wire measurement system for characterization of multipole accelerator magnets

A stretch wire magnetometer is a versatile instrument and can be treated as the primary standard of magnetic qualification of accelerator magnets. Bhabha Atomic Research Centre has developed a Stretch wire magnetic measurement system to cater to the requirements of magnetic measurements on accelerator magnets. This bench also includes a vibrating wire system. The scheme used in this instrument for measurements of magnetic flux ensures drift compensations after each scan. This feature along with post-signal processing gives an accuracy of homogeneity measurements comparable to that of a rotating coil magnetometer. Unlike conventional stretch wire systems, wire moves in the r-z plane (along r-axis) at different azimuthal angles. This provides the opportunity for drift compensation at each scan. This has immensely enhanced the measurement accuracy of non-homogeneity of integral fields to less than 3 units. The same is cross-verified with a rotating coil system. The comparison between rotating coil and stretch wire is presented. The Paper gives the step-wise procedure for the measurement of key performance indicators of an accelerator magnet. This paper brings out salient features of the system along with design and calibration results.

Variable-Reluctance Permanent Magnet Resolver Design Guidelines

This article presents the design considerations and geometrical optimization of a variable-reluctance permanent magnet resolver (VRPM resolver). The above-mentioned resolver utilizes permanent magnets (PMs) and magnetic flux measurement units (MFMUs) instead of excitation windings and signal windings. The operating principle of the VRPM resolver is presented, and the geometric and magnetic properties of its various components that influence the accuracy are identified. To study the performance of the resolver, the magnetic equivalent circuit (MEC) model is utilized to ensure both calculation speed and accuracy, while taking saturation and nonlinear <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${B}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> curve effects into account. The developed analytical model is coupled with a multiobjective optimization solver to conduct repetitive simulations and attain an optimal design for the studied VRPM resolver. The objective of the optimization process is to achieve the minimum position error, while simultaneously improving the computational time. Time-stepping finite-element analysis (TSFEA) is used to validate and measure the performance in detail. Finally, experimental tests on a prototyped VRPM resolver are employed to verify the simulation results.

Magnetic flux density analysis of magnetic spring in energy harvester by Hall-Effect sensors and 2D magnetostatic FE model

The paper investigates the magnetic properties and design of energy harvester system including the magnetic spring and vibration generator. The magnetic flux density measurements were conducted by means of Hall-Effect magnetic sensors mounted on the magnetic spring. The amplitude of variable component of the magnetic flux density in the magnetic spring depends on the vibrations frequency resembled by vibration generator. In the magnetic spring, two resonant frequencies at 86 Hz and 110 Hz are identified and the reached maximum amplitude value of magnetic flux density is ∼1mT. To confirm the usefulness of the manufactured magnetic spring, the calculation of the magnetic flux density in 2D axis-symmetric model of vibration generator and magnetic spring has been carried out using the Ansys Maxwell. The results of the simulation are in accordance with the measurements. Through simulation analysis and laboratory measurement tests, a better understanding of the properties of magnetic springs prototype has been achieved.

An Electromagnetic Design of Slotless Variable Reluctance PM-Resolver

This paper proposes a novel design of the variable reluctance permanent magnet (VRPM) resolvers. It utilizes a slotless stator to reduce the resolver volume. The proposed design overcomes the complex structure of windings by replacing them with magnetic flux measurement units (MFMU). The new design eliminates the computationally-expensive demodulation process of output signals by relying on none-modulated signals. An analytical model based on the nonlinear magnetic equivalent circuit (MEC) method is used to extract the output signals of the proposed resolver design. The accuracy of applied analytical model is verified against the time-stepping finite-element method (TSFEM). An optimization is implemented to best improve the resolver performance by saturating the stator ribs targeting a minimum possible PM volume. The design aims high flux density of iron to make the resolver robust against external distortions, but at the same time, the flux density of core is kept within the linear region of the B-H curve to avoid saturation. TSFEM is used to further analyze the performance of the optimal slotless VRPM-Resolver in details. The simulation results are verified by experimental tests on a prototyped resolver design.

A multi-wavelength view of the multiple activity cycles of ϵ Eridani

ϵ Eridani is a highly active young K2 star with an activity cycle of about 3 yr established using Ca II H&amp; K line index measurements (SMWO). This relatively short cycle has been demonstrated to be consistent with X-ray and magnetic flux measurements. Recent work suggested a change in the cyclic behaviour. Here, we report new X-ray flux and SMWO measurements and also include SMWO measurements from the historical Mount Wilson program. This results in an observational time baseline of over 50 yr for the SMWO data and of over 7 yr in X-rays. Moreover, we include Ca II infrared triplet (IRT) index measurements (SCa IRT) from 2013 to 2022 in our study. With the extended X-ray data set, we can now detect the short cycle for the first time using a periodogram analysis. Near-simultaneous SMWO data and X-ray fluxes, which are offset by 20 days at most, are moderately strongly correlated when only the lowest activity state (concerning short-term variability) is considered in both diagnostics. In the SMWO data, we find strong evidence for a much longer cycle of about 34 yr and an 11-yr cycle instead of the formerly proposed 12-yr cycle in addition to the known 3-yr cycle. The superposition of the three periods naturally explains the recent drop in SMWO measurements. The two shorter cycles are also detected in the SCa IRT data, although the activity cycles exhibit lower amplitudes in the SCa IRT than in the SMWO data. Finally, the rotation period of ϵ Eri can be found more frequently in the SMWO as well as in the SCa IRT data for times near the minimum of the long cycle. This may be explained by a scenario in which the filling factor for magnetically active regions near cycle maximum is too high to allow for notable short-term variations.

Supplementary comparison of national standard instruments in the field of magnetic flux density and magnetic flux measurements by sensing coils

Main textThe COOMET.EM-S26 (1715) supplementary comparison of national standard instruments in the field of magnetic flux density and magnetic flux measurements by sensing coils has been organized within the CCEM framework to test the abilities of the metrology institutes to measure magnetic flux density and magnetic flux.Five NMIs participated in the supplementary comparison COOMET.EM-S26 (1715). Ural Research Institute for Metrology (UNIIM) (since 2020 it has been called Affiliated Branch of D.I. Mendeleev Institute for Metrology (VNIIM-UNIIM)), Russian Federation, acted as the coordinating laboratory of the comparison.The comparison on DC magnetic flux density and magnetic flux was carried out through the measurement of the coil constant of transfer standard coils. In general, very good agreement of the results has been observed.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A Displacement Sensing Method Based on Permanent Magnet and Magnetic Flux Measurement.

This paper proposes a displacement sensing method based on magnetic flux measurement. A bridge-structured magnetic circuit, formed by permanent magnets and two ferromagnetic cores, is designed and discussed. The analyses of the equivalent magnetic circuit and three-dimensional finite element simulations showed that the magnetic flux density changes linearly with the reciprocal of the sum of a constant and the displacement. A prototype sensor of the bridge structure is developed that consists of four permanent magnets as excitation, a Hall sensor as reception, and two ferromagnetic cores as the connection. Experiments have validated the feasibility of this method. The measured results show a good linearity between the sensor’s output and the reciprocal of the sum of a constant and the displacement, with a correlation coefficient greater than 0.9995 across different measurement ranges. Additionally, the measured results significantly indicate that the proposed sensor is compatible with different ferromagnetic materials with a worst-case error of less than 5%. The proposed sensor has the advantages of low cost and good linearity; however, the test object is limited to ferromagnetic materials.

Measurement and Calculation of Magnetic Flux Density During Mold Electromagnetic Stirring on a Continuous Casting Bloom Mold

Measurement and Calculation of Magnetic Flux Density During Mold Electromagnetic Stirring on a Continuous Casting Bloom Mold

Exposure to magnetic fields and childhood leukemia: a systematic review and meta-analysis of case-control and cohort studies.

The association between childhood leukemia and extremely low frequency magnetic fields (ELF-MF) generated by power lines and various electric appliances has been studied extensively during the past 40years. However, the conditions under which ELF-MF represent a risk factor for leukemia are still unclear. Therefore, we have performed a systematic review and meta-analysis to clarify the relation between ELF-MF from several sources and childhood leukemia. We have systematically searched Medline, Scopus, Cochrane Database of Systematic Review and DARE to identify each article that has examined the relationship between ELF-MF and childhood leukemia. We have performed a global meta-analysis that takes into account the different measures used to assess magnetic field exposure: magnetic flux density measurements (<0.2µT vs. >0.2µT), distances between the child's home and power lines (>200m vs. <200m) and wire codings (low current configuration vs. high current configuration). Moreover, meta-analyses either based on magnetic flux densities, on proximity to power lines or on wire codings have been performed. The association between electric appliances and childhood leukemia has also been examined. Of the 863 references identified, 38 studies have been included in our systematic review. Our global meta-analysis indicated an association between childhood leukemia and ELF-MF (21 studies, pooled OR=1.26; 95% CI 1.06-1.49), an association mainly explained by the studies conducted before 2000 (earlier studies: pooled OR=1.51; 95% CI 1.26-1.80 vs. later studies: pooled OR=1.04; 95% CI 0.84-1.29). Our meta-analyses based only on magnetic field measurements indicated that the magnetic flux density threshold associated with childhood leukemia is higher than 0.4µT (12 studies, >0.4µT: pooled OR=1.37; 95% CI 1.05-1.80; acute lymphoblastic leukemia alone: seven studies, >0.4µT: pooled OR=1.88; 95% CI 1.31-2.70). Lower magnetic fields were not associated with leukemia (12 studies, 0.1-0.2µT: pooled OR=1.04; 95% CI 0.88-1.24; 0.2-0.4µT: pooled OR=1.07; 95% CI 0.87-1.30). Our meta-analyses based only on distances (five studies) showed that the pooled ORs for living within 50m and 200m of power lines were 1.11 (95% CI 0.81-1.52) and 0.98 (95% CI 0.85-1.12), respectively. The pooled OR for living within 50m of power lines and acute lymphoblastic leukemia analyzed separately was 1.44 (95% CI 0.72-2.88). Our meta-analyses based only on wire codings (five studies) indicated that the pooled OR for the very high current configuration (VHCC) was 1.23 (95% CI 0.72-2.10). Finally, the risk of childhood leukemia was increased after exposure to electric blankets (four studies, pooled OR=2.75; 95% CI 1.71-4.42) and, to a lesser extent, electric clocks (four studies, pooled OR=1.27; 95% CI 1.01-1.60). Our results suggest that ELF-MF higher than 0.4µT can increase the risk of developing leukemia in children, probably acute lymphoblastic leukemia. Prolonged exposure to electric appliances that generate magnetic fields higher than 0.4µT like electric blankets is associated with a greater risk of childhood leukemia.

On the automatic detection of enacted compulsive hand washing using commercially available wearable devices

BackgroundCompulsive hand washing is one of the most frequent compulsions and includes highly ritualized, repetitive hand motions. Developing an algorithm that can automatically detect compulsive washing with off-the-shelf wearable devices is a first step toward developing more sophisticated sensor-based assessments and micro-interventions that might ultimately supplement cognitive behavioral therapy for obsessive-compulsive disorder (OCD). ObjectiveThe main objective was to establish whether enacted compulsive hand washing can be distinguished from routine hand washing. This distinction will inform future research on the development of an algorithm that can automatically detect compulsive hand washing. MethodTwenty-one participants were trained individually to wash their hands according to 1 of 5 scripted hand-washing procedures that were based on descriptions of pathological compulsive washes and additionally to wash their hands as they usually would, while wearing a smartwatch. Washes were video recorded to obtain validation data. To generate a baseline model, we opted to extract well-known features only (mean and variance of each sensor axis). We tested four classification models: linear support vector machine (SVM), SVM with radial basis functions, random forest (RF), and naive Bayes (NB). Leave-one-subject-out cross-validation was applied to gather F1, specificity, and sensitivity scores. ResultsThe best-performing parameters were a classification window duration of 10 s, with a mean-variance feature set calculated from quaternions, rate of turn, and magnetic flux measurements. The detection performance varied with the particular enacted compulsive hand wash (F1 range: 0.65–0.87). Overall, enacted compulsive and routine hand washing could be distinguished with an F1 score of 79% (user independent), a sensitivity of 84%, and a specificity of 30%. ConclusionsOur analysis of the sensor data demonstrates that enacted compulsive hand washing could be distinguished from routine hand washing with acceptable sensitivity. However, specificity was low. This study is a starting point for a series of follow-ups, including the application in individuals diagnosed with OCD.