Pole Gap Research Articles

Dynamic model of high-speed maglev train-guideway bridge system with a nonlinear suspension controller

To improve the anti-interference ability of maglev trains, a dynamic model of the high-speed maglev train with a nonlinear suspension controller for the guideway system is proposed in this paper. Based on the nonlinear characteristics of the magnetic suspension system, a nonlinear decoupling controller is designed using the feedback linearization theory. Then, a high-speed maglev train model is refined with a guideway coupling system, consisting of a maglev train simulated as a multi-body dynamics model with 537 degrees of freedom and a spatial finite element model of the guideway. Taking the Shanghai high-speed maglev train as an example, the correctness of the computational model is verified by comparing the modeling results with field measurement data, and the control effectiveness of the nonlinear controllers and the traditional PD controllers is compared considering different train speeds and disturbance forces. The results show that the suspension gap under the decoupling control is smaller than that under the PD control during the train operations. Under the same disturbance force, the decoupling control exhibits better control performance than the PD control. The variation amplitudes of the magnetic pole gaps are generally linearly related to the disturbance force.

Cryogenic calibration for Hall probes

Cryogenic calibration for Hall probes

First beam extraction from a superconducting azimuthally varying field cyclotron for proton therapy

First beam extraction from a superconducting azimuthally varying field cyclotron for proton therapy

Investigation of Spherical Al2O3 Magnetic Abrasive Prepared by Novel Method for Finishing of the Inner Surface of Cobalt-Chromium Alloy Cardiovascular Stents Tube.

In this investigation, spherical Al2O3 magnetic abrasive particles (MAPs) were used to polish the inner surface of ultra-fine long cobalt-chromium alloy cardiovascular stent tubes. The magnetic abrasives were prepared by combining plasma molten metal powder and hard abrasives, and the magnetic abrasives prepared by this new method are characterized by high sphericity, narrow particle size distribution range, long life, and good economic value. Firstly, the spherical Al2O3 magnetic abrasives were prepared by the new method; secondly, the polishing machine for the inner surface of the ultra-fine long cardiovascular stent tubes was developed; finally, the influence laws of spindle speed, magnetic pole speed, MAP filling quantities, the magnetic pole gap on the surface roughness (Ra), and the removal thickness (RT) of tubes were investigated. The results showed that the prepared Al2O3 magnetic abrasives were spherical in shape, and their superficial layer was tightly bound with Al2O3 hard abrasives with sharp cutting; the use of spherical Al2O3 magnetic abrasives could achieve the polishing of the inner surface of ultra-fine cobalt-chromium alloy cardiovascular bracket tubes, and after processing, the inner surface roughness (Ra) of the tubes decreased from 0.337 µm to 0.09 µm and had an RT of 5.106 µm.

Design and Prototyping of Biaxial Flexible Support Table for Fine Positioning Through Controlled Magnetic Attraction Forces

High-precision positioning can be obtained by reducing sliding friction and securing support rigidity. A prototype of a biaxial positioning table with non-contact drive by magnetic force and flexible mechanism support was developed to meet these requirements. The magnetic poles of a permanent magnet and an electromagnet were placed opposite to each other with an appropriate gap between them, and the attraction force between the two poles was used as the actuator for fine feed. The table was supported with a flexible mechanism composed of metal (A2017) beams with notches and elastic hinges assembled into a square frame shape. The permanent magnets were commercial neodymium magnets, and the electromagnets were self-made of S45C core bars. Two types of attraction force, maximum and minimum, were set depending on the number of neodymium magnets and the magnetic pole gap. The relationship between the applied current and attraction force for each type was calibrated using an electronic balance. Upon increasing and decreasing the applied current to the electromagnets, a linear relationship was shown between them. The relationship between the attraction force and the X- and Y-axes displacements was simulated by finite element analysis. Based on both results, the relationship between the applied current and displacement was estimated. The fine-feed experiment was conducted in both directions of the X- and Y-axes by applying current to electromagnets in a stepwise sequence. The displacements of total strokes in the long-stroke feed on applying the maximum attraction force were 340 μm and 315 μm for the X-axis and 160 μm and 133 μm for the Y-axis. These values are 2.0–2.8 times larger than the estimated displacement. Additionally, 3%–12% of the other axes interference occurred between the X- and Y-axes. In the high resolution feed applying the minimum attraction force, the displacement per step was 75 nm and 78 nm for the X-axis and 35 nm and 39 nm for the Y-axis. Cooperative feed with a combination of long stroke and high resolution was verified to be feasible.

Development of Electron Paramagnetic Resonance Magnet System for In Vivo Tooth Dosimetry

As part of a homebuilt continuous wave electron paramagnetic resonance (EPR) spectrometer operating at 1.2 GHz, a magnet system for in vivo tooth dosimetry was developed. The magnet was designed by adopting NdFeB permanent magnet (PM) for the main magnetic field generation. For each pole of the magnet, 32 cylindrical PMs were arranged in 2 axially aligned ring arrays. The pole gap was 18 cm, which was wide enough for a human head breadth. The measured magnetic field was compared with the magnetic field distribution calculated in a finite element method (FEM) simulation. EPR spectra of intact human teeth irradiated 5 and 30 Gy were measured for the performance test with the developed magnet system and spectrometer. The measured mean magnetic flux density was estimated to be 44.45 mT with homogeneity of 1,600 ppm in a 2 cm diameter of the spherical volume of the XY plane, which was comparable to the FEM simulation results. The sweep coefficient of the magnetic field sweep coil was 0.35 mT per Ampere in both the measurement and FEM simulation. With ±9 A current, the sweep range was 5.7 mT, which was sufficiently wide to measure the tooth radiation-induced signal (RIS) and reference material. The peak-to-peak amplitude of the measured modulation field was 0.38 mT at the center of the magnet. With the developed magnet fully integrated into an EPR system, the EPR spectra of 5 and 30 Gy irradiated teeth were successfully acquired. The developed magnet system showed sufficiently acceptable performance in terms of magnetic flux density and homogeneity. The EPR spectrum of tooth RIS could be measured ex vivo. The RIS of 5 and 30 Gy irradiated teeth was clearly distinguishable from intact human teeth.

Investigation of end effect in integrated permanent magnetic damper for cylinder block–valve plate pair in axial piston pump

The present work develops an integrated permanent magnetic damper (IPMD) to apply magnetic torque on a cylinder block, which makes it possible to suppress eccentric wear of the cylinder block–valve plate pair in an axial piston pump. Then, the structure and working principle of the IPMD are described. According to the relationship between the axial and the radial magnetic pole gap, the corresponding end flux tube models are established. Based on the principle of micro-displacement, the axial magnetic force and torque output by IPMD are derived. After separating from the relevant structures inside the pump, to ensure the effectiveness of the results, the test method of IPMD independent of the axial piston pump is provided. To make a more comprehensive analysis of the magnetic bearing characteristics, the prototype of IPMD is manufactured and tested. The influence of the end effect of IPMD on the residual hydraulic torque under different discharge pressures is studied. The results verified the correctness of the theoretical analysis, which have important guiding significance to improve the reliability of the cylinder block–valve plate pair in the axial piston pump.

A portable magnet for radiation biology and dosimetry studies in magnetic fields.

In the current and rapidly evolving era of real-time MRI-guided radiotherapy, our radiation biology and dosimetry knowledge is being tested in a novel way. This paper presents the successful design and implementation of a portable device used to generate strong localized magnetic fields. These are ideally suited for small-scale experiments that mimic the magnetic field environment inside an MRI-linac system, or more broadly MRI-guided particle therapy aswell. A portable permanent magnet-based device employing an adjustable steel yoke and magnetic field focusing cones has been designed, constructed, and tested. The apparatus utilizes two banks of Nd Fe B permanent magnets totaling around 50 kg in mass to generate a strong magnetic field throughout a small volume between two pole tips. The yoke design allows adjustment of the pole tip gap and exchanging of the focusing cones. Further to this, beam portal holes are present in the yoke and focusing cones, allowing for radiation beams of up to 5 5 cm to pass through the region of high magnetic field between the focusing cone tips. Finite element magnetic modeling was performed to design and characterize the performance of the device. Automated physical measurements of the magnetic field components at various locations were measured to confirm the performance. The adjustable pole gap and interchangeable cones allows rapid changing of the experimental set-up to allow different styles of measurements to beperformed. A mostly uniform magnetic field of 1.2 T can be achieved over a volume of at least 3 3 3 cm . This can be reduced in strength to 0.3 T but increased in volume to 10 10 10 cm via removal of the cone tips and/or adjustment of the steel yoke. Although small, these volumes are sufficient to house radiation detectors, cell culture dishes, and various phantom arrangements targeted at examining small radiation field dosimetry inside magnetic field strengths that can be changed with ease. Most important is the ability to align the magnetic field both perpendicular to, or inline with, the radiation beam. To date, the system has been successfully used to conduct published research in the areas of radiation detector performance, lung phantom dosimetry, and how small clinical electron beams behave in these strong magneticfields. A portable, relatively inexpensive, and simple to operate device has successfully been constructed and used for performing radiation oncology studies around the theme of MRI-guided radiotherapy. This can be in either inline and perpendicular magnetic fields of up to 1.2 T with x-ray and particlebeams.

Analysis of material removal of Inconel 718 cylinder using magnetic abrasive finishing process assisted with chemical etching

Analysis of material removal of Inconel 718 cylinder using magnetic abrasive finishing process assisted with chemical etching

Dynamic Modeling and Parametric Analysis of the Magnetic Stiffness on a Radial Heteropolar Rotor Magnetic Bearing (RMB)

This paper presents both the dynamic modelling and the study of the variation of certain physical parameters (pole area, gap and base current) that change the magnetic stiffness of a radial heteropolar Rotor Magnetic Bearing (RMB) aiming at the analysis of the magnitude of its control current for three different equilibrium points. The RMB is modelled as a fully uncoupled symmetric active 8-pole magnetic bearing. The analysis is performed using spectral cubes for a better visualisation of the posed problem. The saturation analysis of the RMB is also performed. At last, it is shown that a control current with the same magnitude as the base current is reached with minimum pole area and air gap s0 = 528 um.

On the question of using solid electrodes in the electrolysis of cryolite-alumina melts. Part 3. Electric field distribution on the electrodes

The aim of this work is to identify the theoretical limitations of molten salts electrolysis using solid electrodes to overcome these limitations in practice. We applied the theory of electric field distribution on the electrodes in aqueous solutions to predict the distribution of current density and potential on the polycrystalline surface of electrodes in molten salts. By combining the theoretical background of the current density distribution with the basic laws of potential formation on the surface of the electrodes, we determined and validated the sequence of numerical studies of electrolytic processes in the pole gap. The application of the method allowed the characteristics of the current concentration edge effect at the periphery of smooth electrodes and the distribution of current density and potential on the heterogeneous electrode surface to be determined. The functional relationship and development of the electrolysis parameters on the smooth and rough surfaces of electrodes were established by the different scenario simulations of their interaction. It was shown that it is possible to reduce the nonuniformity of the current and potential distribution on the initially rough surface of electrodes with an increase in the cathode polarisation, alumina concentration optimisation and melt circulation. It is, nonetheless, evident that with prolonged electrolysis, physical and chemical inhomogeneity can develop, nullifying all attempts to stabilise the process. We theoretically established a relationship between the edge effect and roughness and the distribution of the current density and potential on solid electrodes, which can act as a primary and generalising reason for their increased consumption, passivation and electrolytic process destabilisation in standard and low-melting electrolytes. This functional relationship can form a basis for developing the methods of flattening the electric field distribution over the anodes and cathodes area and, therefore, stabilising the electrolytic process. Literature overview, laboratory tests and theoretical calculations allowed the organising principle of a stable electrolytic process to be formulated -the combined application of elliptical electrodes and the electrochemical micro-borating of the cathodes. Practical verification of this assumption is one direction for further theoretical and laboratory research.

An integrated magnetic resonance plant imager for mobile use in greenhouse and field

An integrated magnetic resonance plant imager for mobile use in greenhouse and field

Novel design of hydrodynamic–magnetic compound support for cylinder block–valve plate in axial piston pump

An innovative hydrodynamic–magnetic compound support (HMCS) is proposed for the cylinder block–valve plate pair of the axial piston pump. Compared with the traditional design method, the magnetic structure provides a fixed magnetic torque to balance the residual torque, which causes eccentric wear on the valve plate and keeps the compression coefficient constant. First, the structure and principle of the HMCS are introduced, the magnetic model is established together with relative hydraulic models, and the influence of the permanent magnet length on the magnetic force is obtained. By studying the magnetic moment, the optimal structure of the magnetic pole is determined. Next, the 3D finite element method is used to simulate the magnetic forces under different pole gaps. After that, a reasonable magnetic pole gap and flux density distribution are determined. To obtain the influence mechanism of the HMCS on the cylinder block, the changing law of the track radii of hydraulic forces and average difference in the track radii are analyzed. Finally, the trend of the resultant torque of the cylinder block under multiple working conditions is analyzed. The results show that the HMCS can balance the residual torque acting on the valve plate, which is beneficial in preventing the occurrence of eccentric wear of the valve plate.

Electric drive of the generator of the diesel-electric tractor DET-250M2 on the basis of a Field Regulated Reluctance Machine

The diesel electric tractor DET-250M2 was the first tractor in the USSR with an all-electric transmission. This tractor usually works in agriculture as a cultivator and a bulldozer. However, it is often used in the railway sector, in industry, in large construction projects. Since the tractor’s electrical installation developed in the 1950s on the basis of DC collector machines is now obsolete, difficult to maintain, it was decided to upgrade the traction electric drive. The article presents the calculations of an electric machine: optimization of the rotor geometry, selection of the optimal ratio of the pole and interpolar gap, selection of the optimal number of poles of the machine, selection of the current shape, type of rotor. As an electric machine, a FRRM, which characterized by high overload capacity, a wide range of work in terms of torque and speed, was selected.

Demagnetizing effects in electromagnet measurements of Nd-Fe-B specimens with end gaps

Demagnetizing effects in electromagnet measurements of Nd-Fe-B specimens with end gaps

The Effect of Variation in the Number of Pole and Air Gap on Torque Density on Radial Magnetic Spur Gear with Magnetic Block

Magnetic gear is an alternative to mechanical gear, where the magnetic gear has the advantages of no noise, minimum vibration, no maintenance required, increased reliability, overload protection capability, no physical contact between gears, and the resulting torque density is still below the mechanical gear torque density. In this research, the variation of the number of poles and air gap in the amount of torque density produced was carried out. The permanent magnet material used is Neodymium type with a gear ratio of 1:2. In the variation of the number of poles used by pairs of 4 and 8 poles, 8 and 16 poles, 10 and 20 poles, and 12 and 24 poles, in the variation of the air gap used, namely 1 mm, 1.2 mm, 1.3 mm, 1.4 mm and 1.5 mm. Magnetic gear performance can be seen through analysis simulation with the 3D finite element method using Finite Elements Software. The type of simulation used is the magnetostatic analysis method at the processing stage and the transient analysis method at the post-processing stage. From the simulation results, it is concluded that the greater the number of poles, the greater the torque density produced, and the closer the air gap distance will result in a greater torque density. The effect of the number of poles on the torque density is more significant than the effect of the air gap.

Demagnetizing Field Caused by Specimen End Gaps in Electromagnet Measurements of Permanent Magnet Materials

The midplane and volume-averaged demagnetizing factors, N mid and Nvol, for a uniformly magnetized cylinder of length l s and radius r s clamped in the pole gap of an electromagnet with end gaps of total length d s are calculated as functions of d s /l s and l s /(2r s ) and used for converting the measured magnetization-field curves of an Alnico specimen for different values of d s . The maximum d s /l s allowed for permanent magnet measurements stated in IEC and ASTM standards are discussed.

Research on key technologies in ±1100 kV ultra‐high voltage DC transmission

Based on completely mastering ±800 kV transmission technologies, the first ±1100 kV direct current (DC) transmission demonstration project is being constructed in China. Combining theoretical analysis and a large number of experiments, the margin of switching overvoltage in converter stations, the configuration scheme and performance of lightning arresters, the shielding angles of ground lines under different geographical conditions, and the maximum air gap of lines have been determined. The switching impulse flashover characteristics of equipotential sphere and typical rod‐plane air gaps are also provided. The external insulation is designed differently for light, medium, and heavy pollution areas. For the ±1100 kV project, if the 8 × 1250 mm2 conductors are applied, the pole gap is 26 m and the height of the line is 25 m, all the electromagnetic parameters will meet the requirement of international electromagnetic standards. The key design points of ±1100 kV converter transformers, smoothing reactors, converter valves, and wall bushings are researched and the 75 mH smoothing reactors, ±1100 kV/5000 A converter valves, and ±1100 kV/5523 A wall bushings are successfully made. The optimised hierarchical connection modes and coordination control measure of the ±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.

A 0.5-T pure-in-plane-field magnetizing holder for in-situ Lorentz microscopy

A 0.5-T pure-in-plane-field magnetizing holder for in-situ Lorentz microscopy

Magnetic field distortion and particle optics in quadrupole magnets when placed close to dipole magnets

The field quality of quadrupole magnets (QPMs) in the ring is affected when accompanied by various corrector dipole magnets (CDMs). Variations of integrated quadrupole field strength in presence of CDMs are measured at various field excitations and by varying the distance between the magnets, using a rotating coil. Experimental results are compared with the results obtained from 3D simulations for better understanding of the results. Possibility of studying the interference effect by scanning the field with a Hall probe is explored. Dependence of field interference on the distance between magnets, pole gap and the steel length are studied. Based on these experimental results the basic cause of such field distortion is discussed. Effects of the adjacent magnets on the higher order multipoles of QPMs are also measured. After knowing the field distortion and having the detailed fringe field data, the trajectory of the charged particle while passing through a QPM is found by solving the differential equations in the first order approximation. The fringe field is utilised to solve the particle trajectory equations and to calculate various lens parameters. The equivalent hard edge models are derived and compared with the conventional hard edge approximation. Presence of the CDM may break the magnetic field symmetry of a QPM. Appropriate technique is developed to treat this asymmetric field and convert this into equivalent hard edge models to be used as input of any existing beam dynamics code. The effect of such field modification of QPM in presence of adjacent magnet in the ring and the variation of different optical parameters are reported.