Magnetic Circuit Configuration Research Articles

Experimental Studies of Magnetic Fluid Seals and Their Influence on Rolling Bearings

There are many seals designed for rolling bearings. One interesting perspective is the application of magnetic fluid seals for this purpose, because they are an alternative to commonly-used solutions and combine the advantages of contactless seals (e.g. labyrinths) and contact seals (e.g. rubber lip seals), therefore they have low resistance moment and high tightness. This publication describes rolling bearings and a magnetic fluid seal system in terms of the maximum sealing pressure, which was compared to the results of numerical simulations, and the influence of the magnetic field on the bearing torque was also investigated. The tests were carried out for various types of seal stage shapes. Different magnetic circuit configurations have been considered i.e. the main magnetic flux passing through the seals or rolling bearings (steel or ceramic). Studies have shown that a magnetic field increases the torque in the bearing and magnetic fluid seals may reduce the torque because part of the magnetic flux passes through the seal elements. This result is important because it shows that it

Theoretical modeling and experimental verification of the motor design for a 500 g micro moving-coil linear compressor operating at 90–140 Hz

This paper presents the theoretical modeling and experimental verification of the motor design for a micro moving-coil dual-opposed linear compressor operating at 90–140 Hz. A three-dimensional model is built to study the characteristics of its magnetic field and then the magnetic circuit configuration is optimized theoretically. The non-uniform distribution of magnetic field will have an important effect on the direction of the motor force, thereby decreasing the efficiency. Based on theoretical analyses, a 500 g micro linear compressor is built and then coupled with a given micro pulse tube cold finger to test the performance. Experimental results show that the developed compressor achieves an average motor efficiency of 78.6%, and a cooling power of 1.2 W at 77 K is acquired with an electric input power of 60 W. The experimental results of both linear motor and the cooler system are compared with the theoretical ones and good agreements can be observed.

Magnetoelectric effect induced by eddy current generated vibration in permanent magnets/PZT composites

This letter proposed a series of magnetoelectric (ME) composites consisting of permanent magnets (PM) and Pb(Zr,Ti)O3(PZT) ceramic plate. The Magneto-mechanical system based on the interaction between eddy currents and PM was utilized to replace the magnetostrictive material in conventional ME composites. The ME voltage coefficients of PM/PZT ME composites along the thickness direction were measured, which were equivalent to that of Terfenol-D based ME composites along the length direction. The ME effect of π-type, L-type and Z-type PM/PZT ME composites were investigated and showed that the ME voltage coefficients can be tuned by the properties of PM and the structure of ME composites with different magnetic circuit configurations.

Design and simulation of a combined serpentine t-shape magnetorheological brake

A magnetorheological brake (MRB) is a device to dissipate rotational energy using magnetorheological fluids (MRF). MRB can change its braking torque quickly in response to external magnetic field strength. The brake is rotational, utilizing the MRF in shear mode. In this study, the geometrical design of the MRB, magnetic circuit and MRF flow path is addressed. Mathematical models are presented that describe the braking torque of the MRB. A novel prototype is introduced combining T-shape rotor model with serpentine flux magnetic circuit configuration. The rotor member is selected to direct the flux concentration at that location. Serpentine flux configuration is selected to achieve higher torque without increasing the size of MRB by activated more surface area of MRF with the magnetic flux. The finite element method is used to evaluate the magnetic flux density in MRB using FEMM 4.2. FEMM results showed that this novel design could provide sufficient magnetic flux along MRF flow path. Finally, the influence of input current to the MRB on braking torque is investigated. It is found that the braking torque in MRB increases with the increase of the input current. The prototype is formulated as foot-drop prevention orthotic. The MRB would be further integrated into ankle-foot orthoses for post-stroke patients. The design is formulated as a preliminary geometrical design, aiming to obtain the minimum required braking torque.

Comparative Study of Fault-Tolerant Switched-Flux Permanent-Magnet Machines

The fault-tolerant capabilities are compared in this paper for the conventional double-layer switched-flux permanent-magnet machine and its single-layer counterparts, i.e., C-core, E-core, and modular. The comparison includes the interturn short-circuit and irreversible demagnetization faults. A combination of Simulink and finite element models is used in the study. Based on the predictions, it is found that the modular topology produces the lowest short-circuit current and also has the best demagnetization withstand capability while the conventional one produces the highest short-circuit current and has the worst demagnetization withstand capability. The frozen permeability method is employed to separate the flux produced by armature current and magnets, and the results showed that, besides the influence of short-circuit current, the available magnet volume and magnetic circuit configuration play an important role in the demagnetization process. It is also found that removing half of the magnets, such as using C-core, E-core, and modular topologies, generally improves the demagnetization withstand capability and also increases the torque per magnet volume. Measured results are also presented to validate the short-circuit current predictions and magnet demagnetization.

Rediscovery of permanent magnet flux-switching machines applied in EV/HEVs: Summary of new topologies and control strategies

Substantial efforts are currently underway around the world to develop environmentally friendly transportation, of which the development of electric vehicles plays a key role. Stator-permanent magnet (PM) machines have attracted wide attention due to the robust rotor structure and comparable performance in terms of normal permanent magnet synchronous machines (PMSM) having magnets in the rotor. In particular, the flux-switching machines feature a particular magnetic circuit configuration that favors Dy-free magnets in terms of demagnetization risk, and as a result, the cost of the motor can be reduced considerably. With focus on applications in electric vehicles (EVs) and hybrid electric vehicles (HEVs), this paper reviews the latest developments of PM flux switching machines, with particular emphasis on the novel machine topologies and control strategies.

An omnidirectional shear-horizontal guided wave EMAT for a metallic plate

We propose a new electromagnetic acoustic transducer (EMAT) for generation and measurement of omnidirectional shear-horizontal (SH) guided waves in metallic plates. The proposed EMAT requires a magnetic circuit configuration that allows omnidirectional SH wave transduction. It consists of a pair of ring-type permanent magnets that supply static magnetic fluxes and a specially wound coil that induces eddy currents. The Lorentz force acting along the circumferential direction is induced by the vertical static magnetic flux and the radial eddy current in a plate, resulting in omnidirectional SH wave generation. To maximize the transducer output at given excitation frequencies, optimal EMAT configurations are determined by numerical simulations and validated by experiments. The omnidirectivity of the proposed EMAT is also confirmed by the simulations and experiments.

Optimization of magnetic circuit configuration for GDI injector based on MOSA algorithm

GDI (Gasoline Direct injection) injector is one of the most important components in GDI engine, which requires high precision and dynamic response. The magnetic circuit configuration as the key part of GDI injector which decides the magnetic force, dynamic response, energy loss and temperature rising. All these factors directly or indirectly impact on the GDI injector comprehensive performance. The aim of this investigation is to optimize the magnetic circuit configuration and improve the comprehensive performance for GDI injector. The specific factors that influence the optimum operation of the GDI injector have been analyzed based on physical theories. MOSA (Multi Objective Simulated Annealing) algorithm is used to implement the multi-objective parameters optimization for the magnetic circuit configuration. To validate the optimization results the multi-physical fields coupling simulation based on Finite Element Method (FEM) is used, and the simulation results were validated by experiments. Compared the initial configuration to the optimized one, the comprehensive performances have great improvement after optimization. The results indicate that the methods can be used to GDI injector concept design and performances prediction. The essence of the GDI injector is an ultra-high-speed and giant force solenoid valve which required high frequency response,high power density and downsizing. Simultaneously, when GDI injector work- ing, multi-physical fields coupling effect on magnetic circuit cause the coupling mechanism is compli- cate to reveal. Since 1970s, with the rapid development of mathematics and computer sciences, a lot of new algorithm and new number simulation methods were utilized in industry. With the development of the electronic technology, electronic fuel injector have chance to be used in combustion engine. But now, the environmental regulations are much more stringent conventional design methodology cannot satisfy the requirements of combustion engine for high efficiencyand clean emission. Therefore, quicker dynamic response, higher power density and smaller size GDI injectors are necessary. That means new methods should be used to improve the comprehensive performance essentially.

Loss Calculation and Thermal Analysis of Surface-Mounted PM Motor and Interior PM Motor

The difference of rotor magnetic circuit configuration will directly affect the magnetic field distribution, losses and temperature rises of motor. A few papers have been published on the performance comparison of different rotor configurations [1-3]. However, few papers compare losses and temperature rises in various regions of motor with different rotor configurations. In this paper, the performances of a surface-mounted permanent magnet (SPM) motor and a series-parallel hybrid magnetization interior permanent magnet (IPM) motor are researched, the airgap flux density, losses and temperature rise of two machines with the same stator size, airgap length, armature core length, winding construction, material, permanent magnet consumption, armature current, and speed are compared.

Non-contact modal testing by the electromagnetic acoustic principle: Applications to bending and torsional vibrations of metallic pipes

This work aims to investigate a possibility of non-contact vibration modal testing for bending and torsional motions of cylindrical bodies such as pipes. Here, a transducer operated by the electromagnetic acoustic coupling principle is newly devised. Depending on vibration modes, bending or torsional, different magnetic circuit configurations are employed to fabricate the transducer. The main characteristic of the proposed transducer is non-contact vibration generation in a test specimen without any mechanical movement of the actuating unit. It can be also used as a non-contact sensing unit if necessary. The validity and the performance of the proposed non-contact modal testing method are checked with several experiments.

Pitting corrosion in low carbon steel influenced by remanent magnetization

A new type of experiment is performed using a closed magnetic circuit configuration in order to study the influence of the magnetic field on pitting corrosion in low carbon pipeline steel. The statistical assessment of the pitting corrosion data shows that the magnetic field in the material under test reduces the extreme pit depths and also the average depth of the pit population. It is proposed that reduction in pit depth under the influence of remanent magnetization can be explained based on the behavior of the paramagnetic corrosion products under the influence of the magnetic field gradient produced inside pits.

Development of Compact Transverse Flux Motor with a New Magnetic Circuit Configuration

Development of Compact Transverse Flux Motor with a New Magnetic Circuit Configuration

Direct current electromagnets with constant traction characteristic

Electromagnets have the advantages of low cost, simple construction and ruggedness. In some applications, an electromagnet with the constant (or quasi-constant) traction characteristic is desirable for getting good controllability. In order to design a derect current electromagnet with constant traction characteristic, two basic questions including what kinds of magnetic circuit configuration are adoptable and what conditions should be satisfied must be considered. Focusing on solving the two problems, two kinds of cylindrical electromagnets are proposed and the corresponding conditions in the analytical function expressed by the related geometric dimensions of the electromagnet are also derived, based on the simplified equivalent magnetic circuit method as well as the analysis of the total permeance. Besides, the effects of the main parameters on the traction are discussed. The conclusions obtained by the analytical formulas may be used to provide a primary design, which then may be further improved by electromagnetic field numerical methods and/or by experiments. The comparison between the results calculated by the analytical formulas and by ANSOFT software is fairly good and it validates that the proposed method and the conclusions are simply suitable for the developing and designing of direct current electromagnets with constant traction.

Optimization of magnetic separator circuit configurations

Magnetic separators are commonly used as an effective and low-cost method to concentrate paramagnetic or ferromagnetic minerals. These versatile separators are often used in multistage circuit configurations to further improve concentrate recovery and/or grade. Although these circuits are generally very efficient, field studies suggest that the layout of multistage circuits can be less than ideal for many industrial operations. To illustrate this shortcoming, a theoretical analysis was conducted to compare different circuit configurations for magnetic separators. The resulting knowledge base was used to establish generic engineering guidelines for the layout of multistage circuits. The potential improvements in separation efficiency that may be realized through the application of these guidelines were demonstrated using a simple case study.

Application of 60 mm φ superconducting bulk magnet to magnetron sputtering

We constructed the planar magnetron sputtering apparatus using a c-axis oriented single-domain Sm123 bulk superconductor with 60 mm in diameter as a very powerful magnet in place of an ordinary Nd–Fe–B magnet. A high magnetic field of 4.2 T at the surface of the superconductor coupled with a high target voltage of maximum 6 kV enabled us to discharge even at pressure of 1 × 10 −3 Pa. A target-to-substrate distance of 300 mm was successfully employed under low pressures of 10 −2–10 −3 Pa to make the deposition of almost contamination-free films feasible. The simulation software (JMAG) was used to optimize the magnetic circuit configurations. The simulations could reproduce well the distribution of the magnetic field above the target measured by a three-axial Hall sensor. The discharging characteristics of Cu, Ni and Fe targets in the pressure range over 10 −1–10 −3 Pa were studied under different target voltages. The deposition rates of 0.063 nm/s (or 38 Å/min) and 0.013 nm/s (or 8 Å/min) were achieved for Cu and Fe targets with 3 mm in thickness, respectively, under the Ar pressure of 6.6 × 10 −2 Pa (or 4.9 × 10 −4 Torr).

Finite element modelling of magnetostrictive devices: investigations for the design of the magnetic circuit

Giant magnetostriction of materials such as Terfenol-D rods has potential applications for electromagnetic devices. However, many magnetic problems have yet to be solved. For instance, Terfenol-D has a low relative permeability of about 4 which is responsible for leakage flux and makes it difficult to correctly route both static and dynamic flux in the rods. Thus, to ensure homogeneous magnetic field along the rod, one has to compensate for the flux leakage at the rod ends. To that purpose an extensive computer modelling effort has been performed, on a basic actuator configuration. The Finite Element Method (FEM) has been used to analyse different magnetic circuit configurations. The leakage flux is quantified by the finite element computations. It leads to low magnetic coupling factor and, as a consequence, to low efficiency. Results for different configurations are compared and lead to an optimized design of the magnetic circuits including magnetostrictive rods.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Linear AC magnetic circuit theory

A theory is presented for linear, AC magnetic circuits. The theory develops real and imaginary reluctance terms, which are used in the same manner as real and imaginary impedance terms in linear, AC electrical circuit theory. The reluctance terms can be manipulated through coil-coupled resistances and capacitances. The theory is applied to a parallel magnetic-circuit configuration to show the limits of applicability for the particular materials from which the circuit is constructed. >

Optimum Magnetic Circuit Configurations for Permanent Magnet Aerospace Generators

In the design of high-speed low-power electrical generators for unmanned aircraft and spacecraft, maximization of specific output (power/weight) is of prime importance. Several magnetic circuit configurations (radial-field, axial-field, flux-squeezing, homopolar) have been proposed, and in this paper the relative merits of these configurations are subjected to a quantitative investigation over the speed range 10 000-100 000 rev/min and power range 250 W-10 kW. The advantages of incorporating new high energy-density magnetic materials are described. Part 1 deals with establishing an equivalent circuit for permanent-magnet generators. For each configuration the equivalent circuit parameters are related to the physical dimensions of the generator components and an optimization procedure produces a minimum volume design at discrete output powers and operating speeds. The technique is illustrated by a quantitative comparison of the specific outputs of conventional radial-field generators with samarium cobalt and alnico magnets. In Part II the specific outputs of conventional, flux-squeezing, and claw-rotor magnetic circuit configurations are compared. The flux-squeezing configuration is shown to produce the highest specifilc output for small sizes whereas the conventional configuration is best at large sizes. For all sizes the claw-rotor configuration is significantly inferior. In Part I1l the power densities available from axial-field and flux-switching magnetic circuit configurations are maximized, over the power range 0.25-10 kW and speed range 10 000-100 000 rpm, and compared to the results of Parts I & II. For the axial-field configuration the power density is always less than that of the conventional and flux-squeezing radial-field configurations.

Optimum magnetic circuit design for small DC servometers based on numerical analyses

AbstractFor the purpose of miniaturization of DC servomotors with slotted armatures of the side‐leg type, a numerical analysis is made, taking into account magnetic circuit configurations and materials i;the magnetization characteristics of each section are obtained and the optimum circuit design conditions are specified.For a side‐leg type structure using the rare‐earth magnet, the numerical analysis is made using the difference method and the circuit is divided into main and leakage portions. The design approach is to deal first with the main circuit, in which magnetic saturation is considered, and then to consider the leakage circuit, with the operating points of the magnet made equal. The structure as related to leakage permeance is specified quantitatively. For the armature tooth section constituting the main circuit is analyzed, considering saturation, and the flux density distribution together with the magnetic potential drops as the air‐gap flux increases, are obtained for each section. Based upon these analytical results, the optimum circuit design conditions to yield the maximum power rate‐to‐weight ratio are demonstrated and the relation between material and performance limitations are given.

Design analysis for a solenoid blood pump actuator.

An analysis of a solenoid suitable for direct actuation of a physiological blood pump is carried out in this paper. A general theoretical study of the electromechanical energy conversion process in the solenoid is presented, as well as a discussion of the characteristics of the magnetic circuit configuration. A computer program is described which is based on these results and is used to optimize the solenoid design with respect to conversion efficiency.