Variation Of Magnetic Flux Research Articles

A novel energy absorber based on magnetorheological gel

In this work, a novel magnetorheological energy absorber (MREA) was designed by using magnetorheological gel (MRG) as the damping medium. The proposed MREA had tunable piston gap distances and variable inner magnetic flux density distribution. The piston gap distance could be varied from 7–2 mm and the magnetic flux density at the gap increased from 120–860 mT, respectively. Under both low velocity compression and high speed impact, the damping could be divided into three parts. In the impact test, the velocity of a drop hammer could be reduced from to 3.4–0 m s−1 within a very short time (13 ms) and distance (17 mm). The maximum damping force of the MREA reached to as high as 8 kN. The damping force could also be adjusted by changing the current input. Under a 2 A current, the energy absorption ratio increased about 23% (from 4.13–5.07 J mm−1).

27 August 2001 substorm: Preonset phenomena, two main onsets, field‐aligned current systems, and plasma flow channels in the ionosphere and in the magnetosphere

AbstractWe supplement the results of the 27 August 2001 substorm studied earlier in the series of papers. Described is the plasma flow in the nightside ionosphere from the near‐polar region from the polar cap to the auroral oval during the substorm preonset phase and two expansion onsets, EO1 and EO2, produced by reconnection in the closed tail (magnetic reconnection (MR1) and in the open tail lobes (MR2), respectively. We discuss the location of the MR2 region (is it near, middle, and/or distant tail?) and the EO2 trigger mechanism. The upward substorm current wedge field‐aligned current (FAC) and the downward FAC in the polar cap dusk sector that were both produced by different types of magnetosphere‐ionosphere feedback instability are found to provide the main contribution to the system of FACs during EO1 and EO2. Also, we obtain the estimates for the EO1 and EO2 power and energy. Addressed are the variations in the tail lobe magnetic flux and their (variations) association with EO2. In addition, we describe a 3‐D system of mesoscale cells, each of which involves a plasma vortex and a local FAC maximum. The cells of this system in the inner magnetosphere and in the tail lobes intensify one after other within 2 min interval. At last, we substantiate the assumption that the fast plasma flow recorded by the Cluster satellites 7 min prior to EO1 was a bursty bulk flow from the most distant tail.

Innovations on Design of 6x4 and 6x6 Switched Reluctance Generators for Increasing the Efficiency

This paper aims to present innovations in design of a Switched Reluctance Generator in settings 6×4 and 6×6. A specific methodology for generators design is proposed, based on the study of magnetic saturation and mutual inductances influences. These studies, when compared to classical methodology design, indicate the need for modifications on structure and dimensions of these converters with the intention to increase the efficiency. The proposed modifications cause a significant increment on magnetic saturation and mutual inductances at excitation period. This saturation increasing decreases the magnetic flux variation, causing the reduction of required torque to spin the generator rotor. So, the decrease of this required torque provokes the increasing efficiency. A bench test is built to validate the simulations results.

Magnetic Signals of High-Temperature Superconductor Bulk During the Levitation Force Measurement Process

In order to study the commonly neglected magnetic field information in the course of levitation force measurement process in a superconducting maglev system, a multipoint magnetic field measurement platform was employed to acquire magnetic signals of a bulk high- $$T_{c}$$ superconductor on both the top and the bottom surface. Working conditions including field cooling (FC) and zero field cooling were investigated for these vertical down and up motions above a permanent magnet guideway performed on a HTS maglev measurement system. We have discussed the magnetic flux variation process based on the Bean model. A magnetic hysteresis effect similar to the levitation force hysteresis loop of the bulk superconductor was displayed and analyzed in this paper. What is more valuable, there exists some available magnetic flux on the top surface of the bulk superconductor, and the proportion is as high as 62.42% in the FC condition, which provides an experimental hint to design the superconductor bulk and the applied field for practical use in a more efficient way. In particular, this work reveals real-time magnetic flux variation of the bulk superconductor in the levitation application, which is the other important information in contrast to the macroscopic levitation and guidance force investigations in previous studies, and it enriches the existing research methods. The results are significant for understanding the magnetic characteristic of superconductors, and they can contribute to optimize the present HTS maglev system design.

電気的磁極反転形可変界磁PMモータの提案と原理実証

This paper presents a variable magnetic flux PM motor in which space harmonic power is utilized for the magnetic flux weakening, automatically. The stator has a toroidally-concentrated winding structure, and the torque generation surfaces are composed of three air-gaps, which are single radial-gaps and double axial-gaps. The radial-gap rotor is a consist-magnetized PM rotor, and the axial-gap rotor is a self-excited wound-field rotor. These rotors are coaxially fastened with opposite magnetic pole position. The magnetomotive force of axial-gap rotor can automatically retrieve space harmonic power, which is inevitably generated by a concentrated winding structure. A mechanical design of the prototype is revealed, and the operation principle of the automated-magnetic flux weakening is clarified through the mathematical approach. Then, the operation principle of the electrified reversal magnetic pole is experimentally demonstrated, and the effects of the proposed variable magnetic flux technique are verified using the prototype machine in terms of the adjustable speed drive characteristics and the variable magnetic flux range.

The count of losses by eddy currents in the windings of electric motors with hollow anchor

Given the rationale of taking into account losses on eddy currents in the windings of a low-inertia DC motors with offered magnetoelectric systems. Increased in recent years, the power of these motors (through the use of highly coercive magnets permanent) caused an increase in the volume of copper in the air gap and the magnetic induction values. All this has values given rise to significant eddy currents in the windings made in the air gap, and hence the necessity of taking into account losses from these currents. The experimentally obtained dependence of the losses on eddy currents on the frequency of rotation for a DC motor with a hollow anchor with a power of 350 watts. The magnitude of these losses can reach 30% of the nominal power of the motor. Described mechanism of occurrence of losses. Eddy currents occur in areas with variable magnetic flux and cause the appearance of force, which is directed toward the velocity vector and inhibits the anchor. The directions of these currents, the vectors of magnetic induction, magnetic field and force acting on the conductor winding and a braking anchor. The proposed methods reduce losses: crushing contours of eddy currents and achieve uniform distribution of magnetic induction in the interpolar space of the motor. Shows their strengths and weaknesses. The crushing circuits of windings occur surge currents. To eliminate the losses on the surge currents it is necessary to apply a transposition of the conductors. Given a refined formula for finding the losses on eddy currents in the armature winding, the conductors of which is made in the form of a harness of several wires. Formula has shown a good convergence with experimental data.

簡易可変界磁モータの試作と評価

簡易可変界磁モータの試作と評価

マルチギャップ形可変界磁PMモータの磁極相対角に対する駆動特性の実機検証

This paper presents a variable magnetic flux PM motor in which space harmonic power is utilized for weakening the magnetic flux, automatically. The stator has a toroidally-concentrated winding structure, and the torque generation surfaces are composed of three air-gaps, including one single radial gap and two axial gaps. The radial-gap rotor is a constant-magnetized PM rotor and the axial-gap rotors are self-excited wound-field rotors. These rotors are coaxially fastened with opposite magnetic pole positions. The magnetomotive force of axial-gap rotor can automatically retrieve space harmonic power, which is inevitably generated by the concentrated winding structure. In this study, the effect of relative angle of the magnetic pole between the radial-gap rotor and the axial-gap rotors on the drive performance, e.g., current phase-vs.-torque characteristics, adjustable speed drive characteristics, and variable-magnetic-flux range, are experimentally demonstrated with a prototype machine.

Nanofiber-based brush-distributed sensor for detecting heavy metal ions

A brush-distributed metal oxidation sensing nanostructure is developed by growing zinc oxide (ZnO) nanorods on electrospun titanium dioxide (TiO2) nanofibers to improve ions adsorption of lead and copper. A pair of inductive plane coils are designed to measure inductive variation induced by the adsorbed ion concentration. The brush-distributed ZnO–TiO2 nanofibers are fabricated by using electrospinning and hydrothermal methods that are deposited on the PVDF-formed nanofiber membrane to enhance copper and lead ions adsorption efficiency. The sensitivity has been promoted based on the van der Waals force and produced hydroxyl from grown surface nanorods. The TiO2 structure was examined by checking XRD patterns. These diffraction peaks are indexed as the (101), (004), (200), and (105) of anatase TiO2 and are consistent with the standard data (JCPDS No. 78-2486). The circular coils are designed and simulated using the finite element method to sense metal ions by measuring concentration-dependent magnetic flux variation. The developed ZnO–TiO2 ion sensing composites include the following advantages: simple fabrication process, low cost, high selectivity, highly effective adsorption, specific surface area and porosity, rapid response, and good repeatability and reproducibility.

Manufacturing and Control of a Variable Magnetic Flux Motor Prototype with a Mechanical Adjustment Method

SUMMARYA new structure and control method for a variable magnetic flux motor (VMFM) is proposed to achieve a high‐efficiency electric vehicle (EV) motor drive under a wide range of conditions. A VFMF prototype that was designed by considering the loss was manufactured and evaluated in an experiment. The prototype demonstrated low iron loss and sufficient max torque. Thus, the prototype can provide a high‐efficiency drive with low output, which is frequently the case for EVs. Map control enables a wide phase angle for the vector‐control drive of the VMFM under a changing magnetic flux. Thus, the VMFM provides a high‐efficiency drive under a wide range of conditions.

An orientable search coil

We provide a design for a low cost orientable search coil that can be used to investigate the variation of magnetic flux with angle. This experiment is one of the required practical activities in the current A level physics specification for the AQA examination board in the UK. We demonstrate its performance and suggest other suitable investigations that can be undertaken.

Magneto-optical imaging and analysis of magnetic field micro-distributions with the aid of biased indicator films

Magneto-optical imaging films (MOIFs) were used for the study of magnetic stray field distributions above topographically and thermomagnetically patterned permanent magnet films and other miniature elements that could be used in magnetic micro-systems. Calibrated external bias fields were applied to the samples in situ to simplify the graduation procedure, to expand the measurement range and to minimize the measurement errors. Both uniaxial and planar MOIF were used to make quantitative measurements. A scheme for the fast reconstruction of magnetic serial sections of non-uniform field profiles is proposed. The usefulness of biased MOIF imaging is illustrated by a number of specific examples, such as mechanical hole-drilling adapted to the case of magnetic analysis, dynamic range expansion beyond the limits set by MOIF saturation, rendering surface magnetic flux variations at the microscale and in the presence of strong background.

Analytical and experimental free vibration analysis of multi-layer MR-fluid circular plates under varying magnetic flux

Free vibration characteristics of sandwich annular circular plates comprising magneto-rheological (MR) fluid as the core layer are evaluated analytically and experimentally. An analytical model of the sandwich annular plate was formulated using Ritz method based on the classical plate theory. The numerical analyses were performed to study the free vibration responses of the sandwich plate in terms of resonant frequencies and loss factors considering variations in the magnetic flux and boundary conditions. The experiments were conducted on a free-free sandwich circular plate comprising two PETG (Polyethylene Terephthalate Glycol) face layers constraining the MR fluid core layer. A hollow-core electromagnet was developed for inducing variable magnetic flux over the structure. The free vibration properties of the sandwich plate were measured using MEscop VES modal analyzer. The measured data were analyzed to determine natural frequencies of the MR sandwich plate under different levels of the magnetic flux, which were subsequently used to examine validity of the analytical model. Furthermore, the effects of plate parameters on the natural frequencies and damping of the structure were investigated. The results suggested that increasing the flexibility of the face layers yields more pronounced effect of magnetic flux on the structure stiffness properties.

機械調整式可変界磁モータの試作と制御

SUMMARY A new structure and control method for a variable magnetic flux motor (VMFM) is proposed to achieve a high-efficiency electric vehicle (EV) motor drive under a wide range of conditions. A VFMF prototype that was designed by considering the loss was manufactured and evaluated in an experiment. The prototype demonstrated low iron loss and sufficient max torque. Thus, the prototype can provide a high-efficiency drive with low output, which is frequently the case for EVs. Map control enables a wide phase angle for the vector-control drive of the VMFM under a changing magnetic flux. Thus, the VMFM provides a high-efficiency drive under a wide range of conditions.

3-D Effects of Rotor Step-Skews in Permanent Magnet-Assisted Synchronous Reluctance Machines

Permanent magnet assisted synchronous reluctance machines (PMA SynRM), stemming from the combination of synchronous reluctance and interior PM machine topologies, have recently gained increasing popularity as a viable candidate for electric vehicle traction applications due to concerns regarding the price volatility of rare-earth magnet materials. Their attractiveness can be attributed to their distinct torque production mechanism, which essentially relies on the reluctance torque component enabling the use of less expensive ferrites or bonded NdFeB magnet solutions. A drawback often associated with this machine topology is high torque ripple emanating from its intrinsically high salient nature [1]. Among several machine design techniques available to mitigate the high torque ripple, rotor step-skew is known to be one of the most effective and frequently incorporated solutions. When a step-skew is performed, it causes variation of magnetic flux density along the axial (skew) direction, and thus influences the machine's electromagnetic behavior [2]. Numerous methods are available in literature to account for the effects of skew using (either) 2D or 3D numerical finite element analysis (FEA), analytical, or semi-analytical approaches, the trade-off in each case being computational time versus accuracy. Due to the prohibitive computational time and numerical memory costs of 3D FEA, the prediction of a skewed machine's electromagnetic performance typically relies on 2D domain-based techniques, such as multi-slice 2D FEA [3] or more computationally efficient semi-analytical techniques [2] exhibiting comparable accuracy. A common limitation associated with these techniques is their inability to capture certain 3D phenomena, namely the end-effects and axial interaction between skewed steps, since they explicitly rely on the 2D domain [4]. The significance of such 3D effects is influenced by the axial length to airgap diameter ratio (viz. end-effect), the number of skewed steps, the skew angle and the structure of the machine topology under consideration. The quantification, and most importantly experimental verification, of the 3D effects associated with skewed PMA SynRMs has received limited attention in literature to date.

Finite element analysis of combined magnetoelectric- electrodynamic vibration energy converter

In this paper we report on the design and optimization of a novel combined vibration energy harvester based on the use of electrodynamic and magnetoelectric (ME) principles to increase the energy outcome of an electrodynamic harvester without significantly increasing its size. Thereby the most important aspect is the dependence of magnetic flux variation on design parameters, as is it is the decisive effect for energy conversion. Magnetic circuit form and magnetization are optimized for maximizing energy outcome. We conclude that better magnetic flux variation is reached for a magnetic circuit formed with two magnets stacked one within the other using the same magnetization. Results illustrate that the use of combined converter enables to enhance the performance of simple electrodynamic or ME converter.

Innovative NDT Technique Based on Ferrofluids for Detection of Surface Cracks

An innovative NDT technique is proposed for surface inspection of materials not necessarily magnetic or conductive, based on local magnetic field variations due to ferrofluid deposited in the cracks. The feasibility of the technique is assessed preliminarily, based on signal detectability without applied external magnetic field, and under applied DC fields. The signals (local magnetic flux density variations) are quantified analytically, experimentally and numerically. The model agrees well with the tests, showing that the signal increases with the applied field strength, up to the saturation magnetization of the ferrofluid, and decreases with the distance to the crack longitudinal axis, and thus it can provide useful estimations of the signal. The proposed technique, requiring application of external fields to magnetize the ferrofluid to enhance the signal, seems promising: the model suggests that signals associated to cracks significantly smaller than surface cracks in a target application like aircraft skin panel inspection NASA STD-5009 are easily detectable with commercial magnetometers.

Fundamentals of Electrodynamic Technique of Numerical Designing of Helical High-Explosive Magnetic Generators

Presented are the fundamentals of a consistently electrodynamic 2-D technique of designing helical explosive magnetic generators by numerical simulation on the basis of nonuniform equation for the vector potential with a priori set right-side term. The technique is demonstrated by solving a 1-D problem. A model 2-D problem a closed coil over a tube is analyzed. A coil current rupture is simulated. Concepts of vacuum inductance and free magnetic flux are discussed. Magnetic flux losses in the skin layer and free magnetic flux variation are calculated for an instant compression of an electric contour. A 2-D nonstationary problem a closed coil over a tube is solved. A critical mode of the generator operation is analyzed. A technique is described for solving a problem multiturn helix over a tube .

Design of nested Halbach cylinder arrays for magnetic refrigeration applications

We present an experimentally validated analytical procedure to design nested Halbach cylinder arrays for magnetic cooling applications. The procedure aims at maximizing the magnetic flux density variation in the core of the array for a given set of design parameters, namely the inner diameter of the internal magnet, the air gap between the magnet cylinders, the number of segments of each magnet and the remanent flux density of the Nd2Fe14B magnet grade. The design procedure was assisted and verified by 3-D numerical modeling using a commercial software package. An important aspect of the optimal design is to maintain an uniform axial distribution of the magnetic flux density in the region of the inner gap occupied by the active magnetocaloric regenerator. An optimal nested Halbach cylinder array was manufactured and experimentally evaluated for the magnetic flux density in the inner gap. The analytically calculated magnetic flux density variation agreed to within 5.6% with the experimental value for the center point of the magnet gap.

Measurement of lift-off using the relative variation of magnetic flux in pulsed eddy current testing

Measurement of lift-off can be used to assess the thermal insulation thickness and it has the potential to reduce the lift-off effect in pulsed eddy current testing. In this paper, first, the relative variation of magnetic flux is proposed as a feature for the measurement of lift-off. And then, how to directly obtain the key parameters of the feature from the testing signals is provided. At last, the validity of the feature is verified by simulations and experiments, respectively. The results show that the feature is suitable when the lift-off is tens of millimeters and the plate is ferromagnetic.