Halbach Magnet Array Research Articles

Efficiency Improvement of Permanent Magnet BLDC Motors for Electric Vehicles

A permanent magnet Brushless DC (BLDC) motor has been designed with different rotor configurations based on the arrangement of the permanent magnets. Rotor configurations strongly affect the torque and efficiency performance of permanent magnet electric motors. In this paper, different rotor configurations of the permanent magnet BLDC motor with parallel the Halbach array permanent magnet were compared and evaluated. Many applications of electric drives or air-crafts have recently preferred the surface-mounted permanent magnet design due to its ease of construction and maintenance. The finite element technique has been used for the analysis and comparison of different geometry parameters and rotor magnet configurations to improve efficiency and torque performance. A comprehensive design of a three-phase permanent magnet BLDC 35kW motor is presented and simulations were conducted to evaluate its design. The skewing rotor and Halbach magnet array are applied to the permanent surface-mounted magnet on the BLDC motor for eliminating torque ripples. In order to observe the skewing rotor effect, the rotor lamination layers were skewed with different angles and Halbach sinusoidal arrays. The determined skewing angle, the eliminated theoretically cogging torque, and the back electromotive force harmonics were also analyzed.

Towards self-powered technique in underwater robots via a high-efficiency electromagnetic transducer with circularly abrupt magnetic flux density change

In this article, we present a high-efficiency electromagnetic transducer harvesting kinetic energy from the ocean current for self-powered technique in underwater robots to tackle the electric energy replenishment problem. A circular magnet array with alternating magnet arrangement was employed for providing a sudden change in magnetic flux density. A gear train was introduced into the compact design to greatly increase the rotation speed of the rotor. The finite element method is used to simulate and compare the magnetic flux density distributions and the induced voltages in the coil under different magnet arrays (conventional Halbach magnet array and proposed alternating one) with different magnet dimensions and numbers. The finite element method analysis shows that the alternating array displays a much larger changing magnetic flux density rate resulting in high induced electromotive forces. The experimental results based on a fabricated prototype indicate that the transducer yields maximum average output power of about 0.51 W with an energy conversion efficiency of 30.91% under the water flow speed of 0.64 m/s with a load resistance of 1 kΩ. We also investigated the capability of the transducer for self-powered applications in underwater robots. The transducer charged a 20 mF capacitor from 0 V to 29 V in 50 s. Also, the prototype charged a lithium battery embedded inside an underwater robot by 75% within 400 s. This study, with a broad application prospect, can advance the future development of self-powered underwater robotic systems.

Stability control of permanent magnet and electromagnetic hybrid Halbach array electrodynamic suspension system

Purpose The purpose of the paper is to study the stability control of permanent magnet (PM) and electromagnetic hybrid Halbach array electrodynamic suspension (EDS) system because of the poor suspension stability caused by the well-known under-damped nature of PM EDS system. The adjustment control is realized by PM and electromagnetic hybrid Halbach array, which is composed by winding active normal conductor coils on PM surface. Design/methodology/approach The three-dimensional (3-D) electromagnetic force analytical expression of PM and electromagnetic hybrid Halbach array EDS system for a nonmagnetic conductive plate is derived. And the accuracy of the derived equations is verified by a 3-D finite-element model (FEM). Basing on the 3-D levitation force expression, an acceleration feedback suspension controller is designed to suppress the vibration of PM EDS system, and the suspension stability of the system under the track and load disturbance was simulated and analyzed. Findings The 3-D electromagnetic force comparison of analytical model and FEM are in good agreement, which verifies the correctness of the analytical expression. The simulation results show that the acceleration feedback suspension controller can make the system have good suspension stability under the external disturbance. So it proved that the PM and electromagnetic hybrid Halbach array EDS system can overcome the poor suspension stability caused by the under-damped nature of PM EDS system through the designed acceleration feedback suspension controller. Originality/value This paper designed an acceleration feedback suspension controller to suppress the vibration of PM and electromagnetic hybrid Halbach array EDS system under external disturbance, basing on the derived levitation force analytical expression. And the simulation results show that the acceleration feedback suspension controller can make the system have good suspension stability under the external disturbance.

An ultra-stable 1.5T permanent magnet assembly for qubit experiments at cryogenic temperatures.

Magnetic fields are a standard tool in the toolbox of every physicist and are required for the characterization of materials, as well as the polarization of spins in nuclear magnetic resonance or electron paramagnetic resonance experiments. Quite often, a static magnetic field of sufficiently large, but fixed, magnitude is suitable for these tasks. Here, we present a permanent magnet assembly that can achieve magnetic field strengths of up to 1.5T over an air gap length of 7mm. The assembly is based on a Halbach array of neodymium magnets, with the inclusion of the soft magnetic material Supermendur to boost the magnetic field strength inside the air gap. We present the design, simulation, and characterization of the permanent magnet assembly, measuring an outstanding magnetic field stability with a drift rate of |D| < 2.8 ppb/h. Our measurements demonstrate that this assembly can be used for spin qubit experiments inside a dilution refrigerator, successfully replacing the more expensive and bulky superconducting solenoids.

Optimization of the Magnetic Field Produced by Frustum Permanent Magnets for Single Magnet and Planar Halbach Array Configurations

The potential benefits of frustum-shaped magnets over cuboidal magnets have been seldom studied. This article compares these magnet shapes by optimizing frustum geometry for both a single magnet and a multi-magnet planar Halbach array to produce a desirable field. This field is compared to the equivalent field for optimized cuboidal magnets and differences quantified. A single magnet is considered, where the field strength above the center of a magnet is maximized. If the field is measured close to the magnet surface, an optimized frustum magnet can produce a field stronger than an optimized cuboidal magnet. If the field is measured further from the magnet, there is little benefit in using a frustum magnet over a cuboid. In addition, a planar magnet array is considered, in which the field strength and how closely the field resembled a sinusoidal profile are maximized. In this case, no significant benefit is observed using frustum magnets over cuboidal magnets.

Analytical Optimization of Electrodynamic Suspension for Ultrahigh-Speed Ground Transportation

Electrodynamic suspension with a permanent magnet Halbach array is suitable for ultrahigh-speed vacuum pipeline transportation. The optimization of a Halbach array is helpful to save cost and increase carrying capacity. Intricate analytical expressions of electromagnetic forces or time-consuming numerical simulation show inherent defects in the structural optimization. To solve the abovementioned problem, this article develops an analytical optimization by two stages. First, a brief approximate analytical expression of electromagnetic forces is established by omitting high-order harmonic components for both the scalar magnetic potential and vector magnetic potential. Second, the lift-to-weight ratio is taken as the optimization index, and the optimal wavelength-to-gap ratio and thickness-to-gap ratios are put forward by seeking extreme values. The numerical simulation is conducted to verify the validation of the analytical optimization, and the result shows that the optimal structural parameters are highly reliable. An experimental rotatory device for electrodynamic suspension with optimal sizes for a Halbach array is built to verify the validation of the analytical expressions of electromagnetic forces.

Analysis of different cylindrical magnet and coil configurations for electromagnetic vibration energy harvesters

Electromagnetic vibration energy harvesting is a relatively new technology that transforms kinetic energy from mechanical vibrations into electrical energy, allowing the substitution of batteries or cables for powering ultra-low-power devices like wireless sensor networks for structural health monitoring. For this aim, different magnet and coil configurations have been proposed for the design of these harvesters by several researchers. In this paper, four cylindrical “Magnet in-line coil” configurations with back steel, which include a typical single-magnet, a double-magnet array, and two proposed cylindrical Halbach magnet arrays of three and five magnets, are analyzed using the finite element method and compared in terms of their magnetic flux linkage and transduction factor. The numerical simulations are conducted in all cases with the same materials properties, coil parameters, and geometrical boundaries, the latter consisting of the total cross-sectional area of the magnets and the coil, the air gaps, and the total volume of the transducer mechanism. Furthermore, the design that provides the best performance is analyzed with two different coil configurations. It is finally found that the proposed cylindrical Halbach magnet array with three magnets and one-center coil presents the best results, reaching an average transduction factor of 95.83 Vs/m and a normalized power density of 19.72 mW/cm3g2.

Analysis of different cylindrical magnet and coil configurations for electromagnetic vibration energy harvesters

Electromagnetic vibration energy harvesting is a relatively new technology that transforms kinetic energy from mechanical vibrations into electrical energy, allowing the substitution of batteries or cables for powering ultra-low-power devices like wireless sensor networks for structural health monitoring. For this aim, different magnet and coil configurations have been proposed for the design of these harvesters by several researchers. In this paper, four cylindrical “Magnet in-line coil” configurations with back steel, which include a typical single-magnet, a double-magnet array, and two proposed cylindrical Halbach magnet arrays of three and five magnets, are analyzed using the finite element method and compared in terms of their magnetic flux linkage and transduction factor. The numerical simulations are conducted in all cases with the same materials properties, coil parameters, and geometrical boundaries, the latter consisting of the total cross-sectional area of the magnets and the coil, the air gaps, and the total volume of the transducer mechanism. Furthermore, the design that provides the best performance is analyzed with two different coil configurations. It is finally found that the proposed cylindrical Halbach magnet array with three magnets and one-center coil presents the best results, reaching an average transduction factor of 95.83 Vs/m and a normalized power density of 19.72 mW/cm3g2.

Improved Configuration of Halbach Magnets with a Homogeneous Magnetic Field for Portable NMR Device

Halbach array magnets are widely used in portable nuclear magnetic resonance (NMR) devices that the homogeneity of the magnetic field generated by the array affects the imaging quality. In this paper, we propose some improvements to the construction of the Halbach magnets to enhance magnetic field uniformity. Using a Halbach array model comprising 16 magnets, all the calculations are based on 3D finite element method (FEM) analysis and optimized using the particle swarm optimization (PSO) algorithm. Comparisons of the results are shown to support the observations that the optimized and improved constructions can generate a more homogeneous magnetic field.

General Analytical Optimization Model of Surface-Inset Electrical Machines With Even-/Odd-Segment Halbach

General analytical optimization model has been proposed for brushless surface-inset permanent magnet (PM) machines having even-/odd-segment Halbach array. The air-gap magnetic fields have been analytically obtained by solving the matrix equations of subdomain model. For the maximum air-gap magnetic field, electromotive force (EMF), and electromagnetic torque of the even-/odd-segment Halbach, the optimal pole-arc ratio of each magnet segment, and/or the optimal magnetization angle of each side-magnet have been analytically determined. Taking 16-pole/21-slot surface-inset machines with three-/four-segment Halbach magnet array as examples, the predicted results show that the globally optimized electromagnetic torques of Halbach surface-inset machine are significantly enhanced. Analytically predicted results have been validated by a finite-element (FE) technique.

Characterizing Halbach EMAT Configurations for SH0 Ultrasonic Waves.

Electromagnetic acoustic transducers (EMATs) can efficiently generate the shear horizontal (SH) guided wave modes. In this article, the Halbach magnet array pattern is explored as an alternate to the conventional periodic permanent magnet (PPM) structure. The magnetic field strength of a Halbach array is significantly higher on one side of the structure while it is weak on the opposite side of the array. This magnetic field distribution enables Halbach EMATs to generate ultrasonic waves with relatively large amplitude. To observe this phenomenon, this study compares the amplitude generated from multiple single-row Halbach EMATs with single-row PPM EMAT configurations using finite-element-based simulation models for SH0 ultrasonic wave generation. This article then presents the ultrasonic wave fields generated by various double-row Halbach EMAT configurations using finite-element-based simulation models and experimentally validated for guided fundamental SH0 mode generated in an aluminum plate specimen. It is observed that distinct ultrasonic guided wave beam patterns be associated and predicted for different double-row Halbach EMAT configurations.

Design and performance analysis of wave linear generator with parallel mechanism

Abstract. Considering the irregularity of wave motion, a wave energy converter (WEC) based on 6-UCU parallel mechanism has been investigated. A buoy connected to moving platform is used to harvest wave energy. Each chain is equipped with the linear generator of the same structure, which can convert the absorbed wave energy into electrical energy. Based on the inverse kinematics analysis of parallel mechanism, the position of the parallel mechanism is solved by using the space closed-loop vector method; the relative motion of stator and translator is obtained. Through electromagnetic numerical simulations, the influences of linear generator parameters such as magnetization mode, air gap, and yoke shape on electromagnetic performance were evaluated. Numerical results show axial magnetization and Halbach magnet array can increase magnetic flux intensity more than radial mode. Furthermore, the rule of electromagnetic resistance is discussed with the change of the speed amplitude and the angle frequency. For a case, dynamic differential equation of the whole system is established. The conversion rate of wave energy is derived.

Design of a New 1D Halbach Magnet Array with Good Sinusoidal Magnetic Field by Analyzing the Curved Surface.

In the linear and planar motors, the 1D Halbach magnet array is extensively used. The sinusoidal property of the magnetic field deteriorates by analyzing the magnetic field at a small air gap. Therefore, a new 1D Halbach magnet array is proposed, in which the permanent magnet with a curved surface is applied. Based on the superposition of principle and Fourier series, the magnetic flux density distribution is derived. The optimized curved surface is obtained and fitted by a polynomial. The sinusoidal magnetic field is verified by comparing it with the magnetic flux density of the finite element model. Through the analysis of different dimensions of the permanent magnet array, the optimization result has good applicability. The force ripple can be significantly reduced by the new magnet array. The effect on the mass and air gap is investigated compared with a conventional magnet array with rectangular permanent magnets. In conclusion, the new magnet array design has the scalability to be extended to various sizes of motor and is especially suitable for small air gap applications.

Analysis of Dual-Armature Flux Reversal Permanent Magnet Machines With Halbach Array Magnets

In this paper, a novel dual-armature (DA) flux reversal permanent magnet (PM) machine with halbach array magnets in the stator slot opening is proposed, which is abbreviated as DA-Halbach machine. Besides the stator armature windings, another set of windings is added in the rotor slots to further enhance torque performance via fully utilizing the rotor space. The influences of major geometric parameters on torque performance are investigated. Both DA-Halbach machine and conventional Halbach machine are optimized with the goal of maximum torque under the same copper loss using finite element (FE) method. The electromagnetic performance of two optimized machines are compared, the results show that the proposed DA-Halbach has larger torque and smaller torque ripple than conventional Halbach machine. When compared with surface-mounted PM machines, the proposed DA-Halbach machine still show better torque performance.

The Reduction of Force Component Produced by Short Sides by Analyzing the Corner of Coil in Planar Motor with Halbach Magnet Array

The planar motor with moving-magnet is purely levitated by the stator coils. The forces produced by coils are calculated with the analytical model of magnet array and coil surface model for applying to the real time control. Take the coil and the Halbach magnet array which is at 45 degree with the long side of coil for analysis. The force component produced by short sides can be eliminated for conveniently controlling when the length of coil takes certain dimension. In practice, the force component produced by short sides is small but not zero. There are two reasons, one is the higher harmonics and the other is the corner segments of coil. The force integral expressions of coil corner segments are given by the Lorenz force law. Then the forces numerically calculated with harmonic model and coil full model are verified by comparing with the magnetic surface charge model and finite element model. In order to reduce the force component produced by short sides, the different corners of coil are analyzed. Comparing the forces of different corners of coil, the force component produced by short sides can be significantly reduced with slightly change of the other force components.

Conceptual Design of Electrodynamic Wheels Based on HTS Halbach Array Magnets

Maglev technologies have been extensively studied for modern transport systems; however, their main applications are limited to transportation systems with fixed tracks. On-road vehicles could have a broader outlook if combined with maglev technologies, for which electrodynamic wheels (EDWs) have provided a possible solution. Conventional EDWs are designed based on permanent magnets (PMs), which generate limited thrust and lift forces while having a low power density. In order to enhance the feasibility of EDWs in maglev vehicles, a novel design of EDWs based on high-temperature superconducting (HTS) Halbach array magnets (HAMs) has been proposed in this paper. The suggested design is made of the second generation (2G) superconducting coils, which have been modeled with the A-formulation and T-formulation based finite element methods. Simulation results show that the proposed HTS HAM EDW can generate higher thrust and lift forces, improve the magnetic flux density distribution in the airgap, and greatly reduce the weight of the magnets compared with the conventional design. This paper provides a possibility for future on-road maglev vehicles.

Research on torque of based hydraulic rotary hole cleaning tool on Halbach permanent magnet array

The hydraulic rotary hole cleaning tool does not require a drill string to provide torque, so it is compatible with downhole motors in the sliding phase of directional drilling. It facilitates efficient cutting cleaning, especially in the directional interval and horizontal interval. The magnet array structure must be optimized to enhance the magnetic torque transmission capacity and thus increase the output power of this tool. Magnetic field analysis was conducted in this study using Laplace and Poisson equations. A mathematical model was established to calculate the magnetic torque transmitted by the hydraulic rotary hole cleaning tool. The effects of various magnetic field and tool design parameters on the magnetic torque transmission capacity were compared among different permanent magnet array structures. The negative-positive Halbach magnet array structure shows enhanced magnetic torque transmission capacity compared to the traditional radial magnet array structure; it achieves a better excitation magnetic field direction of the permanent magnets on the magnetic shafts and an increased magnetic flux density within the tool housing. The suggested tool housing thickness under the field operation safety requirement is 9–10 mm. The optimum tool design features include a negative-positive Halbach magnet array structure, 100% magnet field coverage within the tool housing and a permanent magnet thickness range of 9.5–10.5 mm. The maximum magnet torque transmission capacity can be obtained within these parameters. The proposed magnetic torque transmission capacity model was compared against laboratory experiment data to prove that it is reliable and precise enough to optimize existing hydraulic rotary hole cleaning tools with the negative-positive Halbach magnet array structures.

Improving the field homogeneity of fixed- and variable-diameter discrete Halbach magnet arrays for MRI via optimization of the angular magnetization distribution

The aim of this work was to maximize the homogeneity of fixed- or variable-diameter Halbach array of discrete magnets by optimizing the angular rotation of individual magnets within each ring of the array. Numerical simulations have been performed for magnet arrays with various length:radius ratios (L/R) using a dipole-approximation model. These simulations used an uninformed random-search algorithm, with the initial state corresponding to the classical Halbach dipole configuration. Two different classes of systems were studied, one with magnet rings of constant radius, and the other in which the radius of the rings was allowed to vary to increase the homogeneity. Simulation results showed that for a fixed-diameter array optimization of the angular orientation of individual magnets increased the homogeneity by ~17% for very short magnets, with the improvement dropping to ~5% for L/R values greater than ~3:1, where the homogeneity was measured over a region-of-interest equal to one-half the diameter of the magnet array. An empirical formula was derived which allows easy estimation of the required magnetization angles for any L/R. For a 23-ring variable diameter magnet with L/R of ~4:1 the optimization procedure produces an increase in homogeneity of ~18%.

Design of coaxial magnetic gear utilising a novel permanent magnet Halbach array structure

Mechanical gears are constrained due to wear and tear and call for lubrication. A magnetic gear, utilising permanent magnet (PM) arrays, facilitates the mechanical gear roles. It can withstand high-speeds and large loads with zero friction. The magnetic gear is more efficacious on account of the least noise, performance, overload protection, and physical isolation between parts than conventional mechanical gears. The quantity of PMs in magnetic structures plays a principal role in its total price, which necessitates optimal arrangements for PMs. Halbach array provides a bigger torque density according to its one-sided flux. In this research, proposing a novel Halbach array structure, leads to intensification in the one-sided flux in a much sinusoidally waveform that consequently increases the magnetic torque. These all lead to gain higher torques in constant volumes of magnets. Besides, the magnetic torque ripple and the modulators’ losses are decremented. The new model is based on the variation of the magnetisation angles of the adjacent permanent magnet blocks, in the array. Various states of the magnetisation angles in the array are optimised based on a heuristic method. This is studied in the whole trigonometric range for magnetisation angles characteristics. The prototype is fabricated based on the optimised magnetic gear design and complies with the results.

Analysis of Superconducting Synchronous Motors With Halbach Array Field Excitation

This article evaluates the novel design approach of a 3 MW partially superconducting synchronous machine for electric aircraft propulsion. Its special feature is the application of an electromagnetic Halbach array for the field excitation to reduce the back yoke weight and thereby increase the overall output power density. The electromagnetic Halbach array is obtained by reproducing a permanent magnet Halbach array with high-temperature superconducting coils. The arrangement is further optimized, and its field characteristics are compared to a conventional superconducting field winding design. Even though the Halbach array has a higher space and superconductor consumption, it shows better characteristics concerning the intensity of inside and outside magnetic field. Applied in a superconducting motor, the Halbach array field winding achieves a back yoke thickness reduction of up to 85% and a back yoke weight reduction of up to 78% compared to reference models. The gravimetric power density is increased by up to 30% at the expense of volumetric power density. In exchange for a back yoke weight reduction, other components, such as field winding and cryostat, become heavier.