Magnetic Flux Density Levels Research Articles

Research on the simulation accuracy of static hysteresis loops of electrical steels using an improved simplified LLG equation

For tackling the problem of large errors in simulating the static inner symmetrical minor hysteresis loops through the Simplified Landau-Lifshitz-Gilbert (S-LLG) equation, a modification by improving the grain structure arrangement and introducing additional hysteresis energy function is proposed. With the proposed model, only a unified set of parameters identified by four static hysteresis loops is needed to predict hysteresis loops under arbitrarily different magnetic flux density levels. To verify the global simulation capability of the proposed model, the simulation results of hysteresis loops are compared with the measured data of a grain-oriented (GO) steel. The obtained results show that the model has good simulation ability for hysteresis loops under different magnetic flux densities for both sinusoidal and harmonic excitation conditions.

New measuring system for locating firearm projectiles in the human body based on eddy currents and GMI sensors

Noninvasive magnetic mapping for locating non-ferromagnetic metallic foreign bodies, such as firearm projectiles, has a promising application for guiding accurate surgical removals. The strategy consists of inducing eddy currents in the metallic object by applying an external alternating magnetic field. A secondary magnetic field generated by the induced currents in the foreign body can be detected by a high-sensitivity transducer. Previously proposed systems presented constraints to the measurement capability of the transducer imposed by the primary magnetic field interference on their sensing elements. Overcoming these limitations, this work proposes a new configuration of the system that decouples the excitation and measuring stages, arranging their elements symmetrically to generate a spatial distribution of the field lines in such a way that adequate magnetic flux density levels are produced in the region of the foreign body, with values nearly not-detectable at the sensor location. Thereby, the secondary field generated by the induced eddy currents can be amplified, allowing the detection of smaller fragments located at greater depth distances from the skin. The measuring system concept, the spatial distribution of the primary and secondary magnetic fields, and the new approach’s performance to localize foreign bodies are presented.

A two-phase model for studying the complex interplay between natural convection and magnetic field in aluminum-oxide/water nanofluid

While previous experimental studies revealed the existence of optimal heat transfer performance in natural convection of magnetohydrodynamic (MHD) nanofluid flows, it is believed that this phenomenon is not unique in different levels of magnetic flux density. In order to prove this speculation, we numerically investigate the influence of the magnetic field on steady natural convection of aluminum-oxide (Al2O3) nanofluids inside an enclosure. The MHD flow model without the consideration of nanofluids is well validated against theoretical, numerical, and experimental results. The nanofluid in the present investigation has temperature-dependent physical properties and is modeled by a two-phase mixture considering thermophoresis and Brownian diffusion. While varying the volume fraction of nanoparticles from 0 to 6%, we methodically examine the effect of the Hartmann number on the heat transfer performance through the thermal behavior map in terms of the Hartmann–Rayleigh plane. Depending on the combination of magnetic intensity and buoyancy-induced flow, the nanofluid heat transfer with the addition of various concentrations of nanoparticles can be categorized into two patterns separated by a critical Hartmann number: the presence of a maximum Nusselt number (Type A) and continuously increased heat transfer rates (Type B) over a wide range of the Rayleigh number from 103 to 106 and the Hartmann number from 0 to 300. Described by a piecewise-defined function, the critical Hartmann number is exponentially proportional to the Rayleigh number from 104 to 106 and rises linearly in a logarithmic scale with elevating the Rayleigh number from 103 to 104.

Survey of public exposure to extremely low-frequency magnetic fields in the dwellings

Background: Extremely low-frequency electromagnetic fields (ELF-EMFs) are generated from indoor electrical appliances and wiring. In 2002, the International Agency for Research on Cancer (IARC) classified ELF magnetic fields as possibly carcinogenic to humans (Group 2B). Therefore, the aim of this study as the first ever study conducted in Tehran was to survey the public exposure to ELF magnetic fields in dwellings, in 2018. Methods: In this study, 102 houses were selected using convenience sampling method. The magnetic field was measured based on the IEEE std 644-1994 standard using TES-1393 EMF tester. Spot measurements were done in three different rooms including kitchen, living room, and bedroom of each residential. Results: The average value of measurements taken in dwellings was 0.1 µT. There was a significant difference between total value of magnetic flux density and background level of magnetic flux density among 102 dwellings. There was also a non-significant difference among magnetic fields collected from kitchen, living room, and bedroom. The ELF magnetic fields collected from television and computer in different distances present that MFs decrease rapidly with increasing distance from the source. Conclusion: According to the statistical analysis, the average value of ELF magnetic field in Tehran, Iran, is the same as the recommended value provided by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).

Primena mera za smanjenje nivoa magnetske indukcije u stanu iznad transformatorske stanice naponskog nivoa 10/0,4 kV

The paper analyzes the levels of magnetic flux density in the apartment located above the 10/0.4 kV distribution transformer station. During the first magnetic field testing, it was concluded that in the case of the rated load of the transformers, increased values of magnetic flux density would occur in the apartment. The main sources of magnetic field in the apartment were the busbars and cable lines connecting the transformers and the 0.4 kV distribution cabinets. For that reason it is proposed to apply measures to reduce the levels of magnetic flux density, which are described in detail in the paper. After implementing the proposed measures, magnetic field testing in the apartment was repeated. The paper presents magnetic field testing results before and after the application of the measures and gives a conclusion regarding the effectiveness of the applied measures as well as regarding the compliance of the levels of magnetic flux density with the exposure limit prescribed by the current national regulations.

Temperature dependency of magnetorheological fluids’ properties under varying strain amplitude and rate

The temperature dependencies of the rheological and viscoelastic properties of magnetorheological (MR) fluids were investigated experimentally using a rotary rheometer. The shear flow and oscillatory shear strain experiments were conducted over a wide temperature range (−5 to 50 °C) for different levels of magnetic flux density, and strain amplitude and rate. The temperature effect is also investigated considering three different MR fluids with varying solid particles concentration. The measured shear stress-strain data were used to evaluate the effects of temperature and magnetic field on the pre- and post-yield properties of the MR fluids. The acquired data under harmonic strain excitations swept in the 0.005–100% strain amplitude and different levels of steady temperatures in the −5 °C to 50 °C range were analyzed to identify storage and loss moduli as functions of the temperature, shear strain amplitude and frequency. The results suggested strong influence of temperature on the mechanical properties of the fluids in the absence of the magnetic field, especially at temperatures below 10 °C. The magnetic field, however, constituted the dominant effect. In the presence of a magnetic field, the temperature effect could be observed only at low strain levels. The temperature dependency of the mechanical properties also varied considerably with the iron particle fraction of the MR fluid. The critical strain amplitude also increased with increasing magnetic field density, while the linear storage modulus approached saturation with magnetic flux density above 0.2 T.

HIGH VOLTAGE POWER LINES MAGNETIC FIELD SYSTEM OF ACTIVE SHIELDING WITH COMPENSATION COIL DIFFERENT SPATIAL ARRANGEMENT

Aim. The synthesis of single-circuit system of active shielding of magnetic field, generated by group of high voltage power lines, with different spatial arrangement of shielding coil. Methodology. The synthesis is based on the decision of a multi-criteria stochastic game, in which the vector payoff is calculated on the basis of the Maxwell equations solutions in the quasi-stationary approximation. The game decision is based on the stochastic multiagent optimization algorithms by multiswarm particles. The initial parameters for the synthesis of active shielding system are the location of the high voltage power lines with respect to the shielding space, geometry and number of shielding coils, operating currents, as well as the size of the shielding space and normative value magnetic flux density, which should be achieved as a result of shielding. The objective of the synthesis of the active shielding system is to determine their number, configuration, spatial arrangement, wiring diagrams and shielding coils currents, setting algorithm of the control systems as well as the resulting of the magnetic flux density value at the points of the shielding space. Results. Three variant of single-circuit robust system of active shielding with different spatial arrangement of shielding coil synthesis results for reduction of a magnetic field generated by group of high voltage power lines is given. The possibility of a significant reduction in the level of magnetic flux density of the magnetic field source within and reducing the sensitivity of the system to uncertainty of the plant parameters is given. Originality. For the first time carried out the synthesis, theoretical and experimental research of the robust system of active shielding of magnetic field generated by group of high voltage power lines with different spatial arrangement of compensation coil. Practical value. Practical recommendations from the point of view of the practical implementation on reasonable choice of the spatial arrangement of shielding coil of robust single-circuit system of active shielding of the magnetic field generated by the group of high voltage power lines is given.

FFC NMR Relaxometer with Magnetic Flux Density Control

This paper describes an innovative solution for the power supply of a fast field cycling (FFC) nuclear magnetic resonance (NMR) spectrometer considering its low power consumption, portability and low cost. In FFC cores, the magnetic flux density must be controlled in order to perform magnetic flux density cycles with short transients, while maintaining the magnetic flux density levels with high accuracy and homogeneity. Typical solutions in the FFC NMR literature use current control to get the required magnetic flux density cycles, which correspond to an indirect magnetic flux density control. The main feature of this new relaxometer is the direct control of the magnetic flux density instead of the magnet current, in contrast with other equipment available in the market. This feature is a great progress because it improves the performance. With this solution it is possible to compensate magnetic field disturbances and parasitic magnetic fields guaranteeing, among other possibilities, a field control below the earth magnetic field. Experimental results validating the developed solution and illustrating the real operation of this type of equipment are shown.

An experimental assessment of rotor superconducting stack demagnetization in a liquid nitrogen environment

Stacks of high-temperature superconducting tape have proved to trap in laboratory conditions levels of magnetic flux density one order of magnitude above actual state-of-the-art permanent magnets. Their simple manufacturing, high mechanical properties and intrinsic resistance to sudden quench greatly facilitate their utilization in industrial applications, amongst them, as a source of magnetic flux density in the rotor of electrical machines. For this to happen, the currents induced in the superconducting layers of the stack must not be disturbed during operation. This work studies in experimental conditions the demagnetization of a stack rotating in the airgap of an electrical motor under slot and winding-induced cross-field components, whose values are estimated via conventional 2D finite element analysis. The results are congruent with previous laboratory studies and show small long-term demagnetization rates that may allow operation for time spans longer than initially established.

Characterization of the Performance and Catalytic Activity of Lysozyme from Chicken Egg Submitted to Permanent Magnetic Field

The application of magnetic field is being tested as a way to intensify enzymatic processes. However, studies on the magnetic treatment of enzymes is still scarce and limited and only considers a few enzymes. Also, most of the literature studies evaluate only the catalytic activity of the target enzyme. In this context, this work aims to evaluate the effects of a permanent magnetic field and the operational conditions on the catalytic activity, secondary and tertiary enzyme structure, and particle size of the egg white lysozyme. The magnetic flux density and the pH showed positive significant effects (p < 0.1) on enzyme activity. The application of the magnetic field in the higher levels of magnetic flux density (1.34 T), pH (13), and ionic strength (50 mM of NaCl) resulted in a 3-fold increase in enzyme activity when compared to the native enzyme and was 56% higher than the control sample at the same pH and ionic strength conditions but without magnetic field. The characterization results, based on fluor...

Noise analysis in fast magnetic resonance electrical impedance tomography (MREIT) based on spoiled multi gradient echo (SPMGE) pulse sequence

Magnetic resonance electrical impedance tomography (MREIT) is a promising non-invasive method to visualize a static cross-sectional conductivity and/or current density image by injecting low frequency currents. MREIT measures one component of the magnetic flux density caused by the injected current using a magnetic resonance (MR) scanner. For practical in vivo implementations of MREIT, especially for soft biological tissues where the MR signal rapidly decays, it is crucial to develop a technique for optimizing the magnetic flux density signal by the injected current while maintaining spatial-resolution and contrast. We design an MREIT pulse sequence by applying a spoiled multi-gradient-echo pulse sequence (SPMGE) to the injected current nonlinear encoding (ICNE), which fully injects the current at the end of the read-out gradient. The applied ICNE-SPMGE pulse sequence maximizes the duration of injected current almost up to a repetition time by measuring multiple magnetic flux density data. We analyze the noise level of measured magnetic flux density with respect to the pulse width of injection current and relaxation time. In due consideration of the ICNE-SPMGE pulse sequence, using a reference information of values in a local region of interest by a short pre-scan data, we predict the noise level of magnetic flux density to be measured for arbitrary repetition time TR. Results from phantom experiment demonstrate that the proposed method can predict the noise level of magnetic flux density for an appropriate TR = 40 ms using a reference scan for TR = 75 ms. The predicted noise level was compared with the noise level of directly measured magnetic flux density data.

Axial-Flux PM Machines With Variable Air Gap

Laminated soft magnetic steel is very often used to manufacture the stator cores of axial-flux PM machines. However, as the magnetic flux typically has main components parallel to the lamination plane, different magnetic flux density levels may occur over the radial direction: High flux densities near the saturation level are found at the inner radius, while the laminations at the outer radius are used inefficiently. To obtain a leveled magnetic flux density, this paper introduces a radially varying air gap: At the inner radius, the air gap is increased, while at the outer radius, the air gap remains unchanged. This results in equal flux densities in the different lamination layers. As the total flux in the stator cores is decreased due to the variable air gap, the permanent-magnet thickness should be increased to compensate for this. The effect of a variable air gap is tested for both a low-grade non-oriented and a high-grade grain-oriented material. For both materials, the redistribution of the magnetic flux due to the variable air gap results in a significant decrease of the iron losses. In the presented prototype machine, the iron losses are reduced up to 8% by introducing a variable air gap. Finally, a prototype machine is constructed using an efficient manufacturing procedure to construct the laminated magnetic stator cores with variable air gap.

Harvesting Energy From Magnetic Fields to Power Condition Monitoring Sensors

Condition monitoring is playing an increasingly important role within electrical power networks, where its use can help to reduce maintenance costs, improve supply reliability, and permit increased utilization of equipment capacity by providing a measure of actual operating conditions as an alternative to relying on more stringent “worst case scenario” assumptions. In this context, energy harvesting may have a role to play in that it offers the possibility of realizing autonomous, self-powering sensors that communicate their data wirelessly. In the vicinity of electrical transmission and distribution equipment, alternating magnetic fields at the power frequency offer a potential source of energy that does not require hard-wiring or batteries. There are many potentially useful locations for sensors where the level of magnetic flux density may be sufficient to provide enough power for a low-power wireless sensor node. This paper describes a free-standing inductive harvester for use in positions where there is an ambient magnetic field due to conductors that are remote and/or inaccessible. Using data from surveys of magnetic flux density levels at two substations, optimum core and coil designs for the harvester are obtained through theoretical analyses and experiments. A demonstrator is then constructed in which a wireless sensor becomes self-powering when immersed in a 50-Hz magnetic field. Laboratory results show that this system can deliver a useful average power of 300 μW when placed in a magnetic flux density of 18 μ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Trms</i> .

Estudio del efecto de la estimulación magnética de semillas de leucaena Leucocephala (Lam.) de Wit

Se presenta los resultados de la tercera fase de los experimentos de estimulación magnética estática de semillas de Leucaena leucocephala (Lam.) de Wit; trabajo dirigido al mejoramiento de metodologías físicas técnicamente viables, y que se puedan extrapolar a la recuperación de especies vegetales silvestres con potencial de uso. Se realizaron experimentos factoriales utilizando niveles de densidad de flujo magnético (B) de 30; 62,5; 125; 200 y 250 mT, tiempos de exposición entre 0,5 y 60 minutos, número de exposiciones magnéticas 1 y 4 veces, y tiempo transcurrido entre cada una de estas: 24 horas y 7 días. Constatando que en algunas dosis, el campo magnético genera una influencia positiva sobre el desarrollo de las plántulas de Leucaena, principalmente afectando la longitud de la raíz, la masa foliar, el porcentaje de nitrógeno y proteína foliar. Los resultados muestran que B tiene mayor influencia que el tiempo de exposición en el tratamiento de semillas para esta especie. La mejor respuesta se dio a 30 mT, y se vislumbra que la acción de la estimulación magnética sobre esta especie presenta un comportamiento acumulativo.

Effect of the plate surface characteristics and gap height on yield stresses of a magnetorheological fluid

Effects of the plate material, surface roughness and measuring gap height on static and dynamic yield stresses of a magnetorheological (MR) fluid were investigated with a commercial plate–plate magnetorheometer. Magnetic and non-magnetic plates with smooth (Ra ∼ 0.3 μm) and rough (Ra ∼ 10 μm) surface finishes were used. It was shown by Hall probe measurements and finite element simulations that the use of magnetic plates or higher gap heights increases the level of magnetic flux density and changes the shape of the radial flux density profile. The yield stress increase caused by these factors was determined and subtracted from the measured values in order to examine only the effect of the wall characteristics or the gap height. Roughening of the surfaces offered a significant increase in the yield stresses for non-magnetic plates. With magnetic plates the yield stresses were higher to start with, but roughening did not increase them further. A significant part of the difference in measured stresses between rough non-magnetic and magnetic plates was caused by changes in magnetic flux density rather than by better contact of the particles to the plate surfaces. In a similar manner, an increase in gap height from 0.25 to 1.00 mm can lead to over 20% increase in measured stresses due to changes in the flux density profile. When these changes were compensated the dynamic yield stresses generally remained independent of the gap height, even in the cases where it was obvious that the wall slip was present. This suggests that with MR fluids the wall slip cannot be reliably detected by comparison of flow curves measured at different gap heights.

Robust design of NMR magnet through worst case analysis

Magnets for Nuclear Magnetic Resonance applications are designed to provide high level of magnetic flux density in a testing volume with the greatest level of field homogeneity. Anyway, the manufacturing and assembly tolerances cause unavoidable uniformity degradation, that is usually counteracted by correction coils. The measurement of the magnetic field is the final verification of the complex design and fabrication process of a magnetic system, aimed also at defining currents in correction coils to improve uniformity. Anyway, when seeking high accuracy, it is necessary to assess the effect on final uniformity of uncertainties in the measurement technique. In this paper, an approach is presented to assess impact of measurement error bars on final device performance, based on Worst Case Analysis, guaranteeing quick computational time.

Exposure to extremely low frequency magnetic fields in an urban area

Magnetic field levels were studied in an urban area--the city of Cáceres (Spain). The study included systematic spot measurements throughout the city, an analysis of the temporal variation of the magnetic field, and the incorporation of the data into a geographic information system. The levels detected were at most 7.3% of the ICNIRP reference levels, and the highest fields were found in the oldest neighborhoods. Considered overall, the ELF magnetic flux density levels determined in the present study were between those found in residential and in working environments. Knowledge of the levels of such fields in urban areas is therefore fundamental in evaluating the population's overall exposure, especially for people who work outdoors.

Design of a Superferric Dipole Magnet With High Field Quality in the Aperture

A project to design and construct a new international accelerator was proposed by GSI (Darmstadt, Germany). This project includes the design of several new facilities. One of them is a collector ring (CR). The magnets of the CR operate at constant field (DC), but the level of this field varies for different operational tasks. The magnet system of the CR includes 24 deflecting dipole magnets. The maximum operating field in the aperture is 1.6 T, with a deflection angle of 15 degree, and a bending radius of 8.125 m. The most important requirement for this dipole is a high field uniformity (better than /spl plusmn/0.01% over a volume of 380 mm /spl times/ 150 mm). This requirement must be met for all levels of magnetic flux density in the aperture. Several magnet designs have been investigated including window frame and H-type versions with normal and superconducting coils. The best economical and technical parameters were obtained for a superferric H-type magnet with a wide air filter in the pole. The field homogeneity requirements were fulfilled in such a magnet for field range of 0.2-1.63 T. The effects of the field distortion in the end parts of the magnet, as well as influence of the end plates on the field quality, were also investigated.

Prediction Model for Radiated Magnetic Field at Industrial Frequency Due to Randomly Placed Conductors Pairs

The statistical analysis of the magnetic flux density due to sinusoidal steady-state 50 Hz (or 60 Hz) currents in conductor pair randomly placed inside a conduit is carried out by means of a suitable developed computation model. From the statistics of the field, an equivalent deterministic model is derived. This model allows one to estimate the magnetic flux density levels without knowing the exact position of the conductors. The results are compared with those measured in two laboratory experimental setups.

Improvement of MRI magnet design through sensitivity analysis

Superconducting magnets for MRI are designed to provide high level of magnetic flux density in a wide testing volume with the greatest level of field homogeneity. The design of such magnets is usually performed using optimization techniques able to tune the geometrical parameters of the magnets, taking also into account constructional issues and dimensions and packaging factors of the wires for each coil and, in addition, technical and physical constraints, such as the critical current of the superconductor to prevent the quench phenomenon. Unfortunately due to manufacturing tolerances, the actual geometrical parameters of the magnet differ from the design ones, affecting the field homogeneity. In this paper the effects of the manufacturing tolerances on the field homogeneity are investigated for an MRI magnet by means of a statistical Monte Carlo analysis.