Cylindrical Permanent Magnet Research Articles

Magnetic field modeling and validation for a spherical actuator with cylindrical permanent magnets

A permanent magnet spherical actuator is an electromagnetic device characterized by achieving multi-degree-of-freedom rotations in one driving unit. Analytical magnetic field modeling of the rotor array is needed for the design, performance analysis and optimization of the spherical actuator. This paper presents an analytical method to formulate the complex magnetic field distribution of rotor array with cylindrical permanent magnets in 3D spherical space. This method combines the current model by toroidal functions and transformation method, thus the magnetic field can be calculated efficiently with reasonable accuracy in order for further design optimization and real-time control. The analytical magnetic model of the permanent magnet rotor array is validated with the numerical finite element method by Ansoft Maxwell and experimental measurement.

Impulse Magnetized Magnetic Screws

This paper is an investigation in the performance of two types of magnetic screws (MSs). The first is the magnet to magnet and consists of permanent magnet (PM) nut and PM screw and the second is a magnet to reluctance and consists of PM nut and a double-start reluctance screw. It is argued that for cost sensitive and long stoke applications, a magnet-to-reluctance MS may be the preferred option. It is also shown that capacitor discharge magnetization techniques can be employed for imprinting helical magnetization distributions on cylindrical PMs, significantly reducing the complexity and facilitating the practical realization of MS systems.

Velocity-Dependent Lorentz Force Evaluation: A Simulation Study

A velocity-dependent Lorentz force evaluation is proposed to improve the defect depth estimation. Data sets of a specimen with stacked aluminum sheets and a cylindrical permanent magnet, with different defect shapes, depths, and two velocities, simulated by the finite-element method, are investigated. Shifts and amplitude changes of Lorentz force perturbation signals at a high velocity ( $v=10\,\,\text{m}$ /s) in comparison to a low velocity ( $v=0.1$ m/s) can be used to determine the defect depth.

A novel and reproducible release mechanism for a drug-delivery system in the gastrointestinal tract.

To establish a reliable, reproducible and accurate release of the drug in the gastrointestinal tract, a novel release mechanism for a controllable drug-delivery system has been investigated. The release mechanism, consisting of a one-way valve for drug release, a drug chamber, two axially magnetized cylindrical permanent magnets and a multi-layer solenoid coil, is hosted in the capsule-shaped shell with diameter 11mm and length 30mm. To actuate the coil piston, the two static magnetic fields produced by the two magnets are aligned along the same axis, having the same magnitude, but opposite directions. Based on the principle of the electromagnetic force and the Bernoulli equation, the actuating force can be expressed as a function of the coil stroke and the excitation current, which was modeled and experimentally verified. Thus the actuating force can be controlled by adjusting the activated period and intensity of the coil, resulting in the reproducible release with different doses and mean rates. Then, a prototype of the drug-delivery system has been developed, which consists of a drug-delivery capsule, a radio frequency transmission module, an interface circuit, and an instruction setting and triggering platform. All the drug release parameters, including the release mode, times, dose and mean flow rate, can be set by the platform. The experiment verifies that the drug-delivery capsule can deliver a predetermined dose with different flow rates and dip angles of the capsule. The relative error of the releasing dose becomes larger with increasing releasing rate and decreasing releasing dose.

Torque Ripple Optimization of a Novel Cylindrical Arc Permanent Magnet Synchronous Motor Used in a Large Telescope

This paper proposes the use of a novel cylindrical arc permanent magnet synchronous motor (CAPMSM) in a large telescope, which requires high positioning accuracy and low torque ripple. A 2D finite element method was used to analyze the cogging torque of the CAPMSM. The CAPMSM can be an alternative for a rotating motor to realize direct drive. A new method is proposed to separate the cogging torque, Tcog, into the torque, Tslot, generated by the slotted effect and the end torque, Tend, generated by the end effect. The average torque and the torque ripple are optimized considering stator center angle, the angle between two adjacent stators and the unequal thickness of a Halbach permanent magnet. The torque ripple decreased from 31.73% to 1.17%, which can satisfy the requirement of tracking accuracy for large telescopes.

Experimental and numerical analysis of the magnetophoresis of magnetic nanoparticles under the influence of cylindrical permanent magnet

Abstract Dye-tracing and concentration-measuring experiments are carried out to investigate the magnetophoresis of magnetic nanoparticles (MNP) in the presence of an external cylindrical permanent magnet. The magnetophoresis of MNP, inducing an obvious forced-convective flowing of the carrier fluid, which can be observed by visualizing flowing of carrier fluid, results in a temporal and spatial variation of particle concentration. Moreover, in order to get insight into the physical mechanisms of magnetophoresis of MNP, a coupled particle-fluid analysis, in which the non-linear drift-diffusion differential equation is incorporated into the Navier-Stokes equation, is adopted to discuss the influence of particle-fluid interaction on the variation of particle concentration and the kinetics of carrier fluid. It is worth noting that the equivalent current source (ECS) method is adopted to obtain a closed-form field analysis, which provides exactly prediction of the Kelvin force and enables magnetophoretic analysis more efficient. In dye-tracing experiments, an obvious vortex can be observed as the methylene blue moves with the convection of carrier fluid. Furthermore, this phenomenon is also predicted by using the coupled particle-fluid model. A comparison between the experimental and numerical results shows that the hydrodynamic interactions between MNP and carrier fluid plays an important role in inducing forced-convective flowing of carrier fluid and enhancing the magnetophoresis of MNP. Furthermore, these results also denote that the coupled particle-fluid model provides a more efficient and accurate method in investigating the magnetophoresis of MNP.

A Novel 6-D Tracking Method by Fusion of 5-D Magnetic Tracking and 3-D Inertial Sensing

Pose tracking based on a permanent magnet is not limited by line of sight. In general, a high-remanence and axially magnetized cylindrical permanent magnet is utilized as the magnetic source, which is regarded as a magnetic dipole model. However, this magnetic tracking approach cannot estimate the rotation information along the direction of the magnetic moment. Thus, only 3-D linear motion and 2-D rotational motion of the magnet can be tracked. On the other hand, inertial sensors provide effective 3-D orientation tracking. In this paper, an inertial measurement unit was attached on the surface of a permanent magnet. Then, the tracking information of these two modes was fused based on the adaptive weighted fusion algorithm. Experiments show that the full 6-D pose is acquired with an improved orientation accuracy, where the average orientation errors for $\alpha $ , $\beta $ , and $\gamma $ , obtained by the fusion algorithm, were 0.81°, 0.93°, and 1.26°, respectively. This paper is helpful to those who want to accurately track the full 6-D pose of an object.

Quantitative Approach to the Magnetic Force of a Cylindrical Permanent Magnet Acting on a Ferromagnetic Object

Quantitative Approach to the Magnetic Force of a Cylindrical Permanent Magnet Acting on a Ferromagnetic Object

Quantitative Approach to the Magnetic Force of a Cylindrical Permanent Magnet Acting on a Ferromagnetic Object

Quantitative Approach to the Magnetic Force of a Cylindrical Permanent Magnet Acting on a Ferromagnetic Object

Optimal Design of Permanent Magnet Linear Generator and Its Application in a Wave Energy Conversion System

The emerging global wave energy industry has great potential to contribute to the world’s energy needs. However, one of the key challenges in designing a wave energy converter (WEC) is the wave energy generator. Thus, this paper focuses on the optimal design of a cylindrical permanent magnet linear generator (CPMLG), which is used for the wave energy conversion system. To reduce the end effect and enhance the magnetic field performance of the CPMLG, the level-set method is applied to the design of the topology and size for the generator. In the paper, the objective air gap magnetic field is given by the mathematical analysis method and appropriate measuring points are predetermined. The measuring points can fully reflect the distribution characteristics of the air gap magnetic field. Then, topology evolution on the permanent magnet (PM) and yoke based on the level-set method are performed. The level set function corresponding to the initial shape of the PM is constructed. The algorithm is programmed and computed iteratively using the discrete time and space variables. Finally, the performances of the CPMLG with the updated PM and width of yoke are analyzed by ANSYS Maxwell. Results show that the magnetic field distortion and the unbalance of three-phase electromotive force (EMF) of the CPMLG is reduced by the optimization of the level-set method. It has also been verified that the designed CPMLG with the level-set method could be used for WEC at different wave conditions.

Levitation Force Computation of HTS/PM System Based on <inline-formula> <tex-math notation="LaTeX">$H$ </tex-math> </inline-formula>-Formulation

The levitation system containing high-temperature superconductor (HTS) has great advantages in various applications, but the highly nonlinear properties of HTS limit its practical applications. In this paper, a method to analyze the electromagnetic behaviors of the levitation system which includes HTS bulk and permanent magnets (PMs) is presented. The method is based on the finite-element method combining with ${H}$ -formulation, which is applicable for 2-D axial symmetric problems that include HTS materials. To deal with the nonlinear properties of HTS bulks, its electric field–current density ( E–J ) relationship is considered here. In order to verify the validity and accuracy of the method, a simple HTS/PM system model is established which includes a cylindrical HTS bulk and PM. The axial levitation force of the model is computed considering the nonlinear properties of HTS bulk. Moreover, the corresponding experimental results of the system are also obtained and compared with the related simulation results. The comparison shows that the experimental and corresponding simulation results match well.

A remote lab for measuring, visualizing and analysing the field of a cylindrical permanent magnet

Qualitative experiments such as visualizing magnetostatic fields with iron filings are often carried out in primary and secondary school, while quantitative evaluations of permanent magnetic fields are often left aside. This also applies to most lectures at university despite the fact that the topic would fit quite well into a lecture on electrodynamics. Gaining a quantitative picture of permanent magnetic fields is a rather difficult task. Calculating such fields often requires numerical methods and measuring them a very sensitive apparatus. However, as magnetic fields are invisible, properties of these fields have to be determined in order to visualize them quantitatively. A remote laboratory was developed to be used in teaching at the Ludwig-Maximilians-Universität München. It combines exact measurements and theoretical predictions for the field of a cylindrical permanent magnet. Furthermore, multiple representations of the measurements and possibilities of analysis are offered. The laboratory is accessible via https://www.didaktik.physik.uni-muenchen.de/sims/magneticfield/.

Promotion of toluene degradation in negative DC corona discharge by magnetic field

Enhancement of the efficiency, energy yield (EY) and COx selectivity of volatile organic compound (VOC) removal by negative DC corona discharge through application of a magnetic field was demonstrated. Experimental studies were carried out in a wire-to-cylinder type reactor composed of an aluminum cylinder with 20 mm inner diameter and a nickel-chrome wire with 0.5 mm diameter located at its axis. Toluene was chosen as the VOC agent. During the experiments, the outer aluminum tube was connected to a high DC voltage, while the central wire was grounded. The stationary magnetic field was supplied by cylindrical permanent magnets producing a magnetic field along the axis. Experimental results demonstrated that the magnetic field could efficiently increase the discharge current, the efficiency of toluene removal, EY, COx selectivity and the production of O3 and NOx. In addition, the above quantities were obviously improved with the increase of magnetic induction strength and magnetic field cover length. For example, at a discharge voltage of 10.6 kV, the removal efficiency value was 79.3% at 0 mT but increased to 85.5% and 91.5% when the magnetic induction strength was increased to 54 mT and 145 mT respectively. The analysis of the outlet gas through GC-MS indicated that the organic byproducts primarily consisted of formic acid, acetic acid, maleic anhydride and benzaldehyde. A possible pathway for toluene degradation was proposed based on these byproducts.

A Novel Three-Dimensional Electromagnetic Digital Actuator With 12 Discrete Positions

This paper presents a three-dimensional (3-D) digital electromagnetic actuator able to reach 12 discrete positions distributed in a 3-D space. The mobile part of this actuator includes a cuboid permanent magnet fixed in a hexagonal casing. The mobile part is able to reach six discrete positions in xy -plane at level z $_1$ and the remaining six discrete positions at level z $_2$ . The switching of the mobile part in xy -plane is achieved by injecting currents in the fixed planar wires situated beneath it. The actuator design integrates a coil to switch the mobile part between two predefined levels in z -axis. To maintain the mobile part at a discrete position without energy consumption, six fixed cylindrical permanent magnets are placed around the mobile part. To design the actuator, a model has been developed and is presented in this paper. Rapid prototyping approach (laser cutting) is used to fabricate the actuator prototype. The maximum and the minimum strokes in xy -plane are between 0.5 to 1.0 mm while along z -axis the actuator is able to perform a stroke of 1.0 mm. Experiments have been conducted on the prototype to validate the proposed design and the 3-D actuation. The performance characterization has been conduced and the experimental and the simulated results have been compared.

Driving frequency dependent wave modes of point-focusing electromagnetic acoustic transducers.

This article presents a driving frequency dependent wave mode of point-focusing electromagnetic acoustic transducers (PF-EMATs), which is composed of a cylindrical permanent magnet and a concentric meander line (CML) coil with a varying spacing interval for concentring the ultrasound waves to a point. A finite element model is established to simulate the incentive and propagation process of ultrasonic waves so that the focusing characteristic, such as displacement, amplitude profile, and focal offset, can be obtained, allowing for investigation into the driving frequency dependence of wave modes. In addition, the universality of driving frequency dependent wave modes is well demonstrated. Furthermore, the relationship between the focusing performance of the developed PF-EMAT and the coil parameters, inner radius RC and number of turns NC of the CML coil, is explored. Finally, the experimental results show good agreement with the simulated results and indicate that the presented driving frequency dependent wave modes of PF-EMATs employing CML coils could manipulate the wave modes by carefully controlling the driving frequency.

Modeling and experimental investigation of an AA-sized electromagnetic generator for harvesting energy from human motion

Human body mechanical motion is considered as an ideal energy resource for portable or wearable devices. This paper presents an AA-sized electromagnetic energy harvester to convert the motion of human limbs motion into electrical energy. A cylindrical permanent magnet is freely moved in a 3D-printed tube wholly wrapped with coils. The outer dimensions of the device are 14 mm in diameter and 44 mm in height. Based on Faraday’s law a theoretical model was derived and the device size was optimized. The influence of the magnet and coil dimensions on the output power was analyzed by theoretical calculations and proved by experiment following. The optimized dimensions from two separate methods agrees well with each other. When the harvester prototypes are driven by hand shaking at 5 Hz, the average output power reaches to 63.9 mW with power density of 9.42 mW cm−3, which is 51% larger than that of the conventional tube electromagnetic energy harvester. While when the harvester is worn on ankle, a power of 4.2 mW can be obtained even at normal walking frequency of 1 Hz, corresponding to a power density of 0.62 mW cm−3, which is considerably higher compared with other devices of human energy harvesting. Furthermore, the new developed device is simple without needing any restoring spring and is easy to be fabricated.

Loss Calculation, Thermal Analysis, and Measurement of Magnetically Suspended PM Machine

Temperature rise caused by losses is a key issue for a high-speed machine. This paper deals with loss calculation and thermal analysis of a high-speed magnetically suspended PM machine (MSPMM) with an actual power of 33 kW and rotation speed of 55 332 r/min. The temperature distribution based on the finite element method is obtained by accounting for various losses, which consist of air friction losses, copper losses, and iron losses of a radial magnetic bearing, a combined radial/axial magnetic bearing, and high-speed permanent magnet machine (PMM). A back-to-back test setup with two MSPMM is fabricated for verifying the calculation results. The predicted maximum temperature of rotor is located in the center of the cylindrical permanent magnet, and the value is 143 °C. Except for the rotor, the estimated maximum temperature of the stator parts is located in tooth tips of the motor stator core, the value is 92 °C, and the error between the predicted temperature and the measured one is 9.3%. Total measured losses are 1644.4 W, the estimated total losses are 1536.7 W, the error is 6.5%, and the efficiency of the machine under test is 94.6%. The loss calculation and thermal analysis results are verified by the measured ones.

A High-Speed Magnetoelectric High-Power Generator

The efficiency of increasing the power of a magnetoelectric generator (MEG) was investigated in the RMXprt module of the Ansoft Maxwell software package. The MEG under study has four poles. Its magnetic system consists of cylindrical permanent magnets equally spaced over the rotor diameter. The magnetization of the rotor permanent magnets has a radial direction. To determine the thermal state of the MEG, the Solid Works Flow Simulation software package was used. An estimation of efficiency of using the Halbach magnet system in high-speed magnetoelectric energy converters is presented. The influence of the ratio of the rotor pole arc to the pole pitch was investigated, and as a result of the studies it was found that decreasing the pole arc makes it possible to reduce a total harmonic distortion (THD), but a current density increases and short-circuit current decreases. Therefore, when using this method, it is necessary fully to determine all of these parameters. The research results were used as a basis for design of a high-speed liquid-cooled MEG with 450-kW power and a 50 000-rpm rotor speed.

Ultra-precision finishing of optical mold by magnetorheological polishing using a cylindrical permanent magnet

A magnetorheological polishing was proposed to be used for optical glass mold finishing, aiming at suppressing middle spatial frequency errors from ultra-precision grinding while improving surface roughness. A small polishing head, with a cylindrical permanent magnet enveloped by a nonmagnetic outer shell, was also developed. Polishing experiments were performed on concave aspheric tungsten carbide molds. The results demonstrated the developed magnetorheological polishing successfully suppressed the middle spatial frequency errors on the optical mold by decreasing amplitude to 1 nm, while improving overall surface finish to 1 nm in Ra.

Designing High-Accuracy Permanent Magnets for Low-Power Magnetic Resonance Imaging

We present a highly scalable and versatile family of dipole magnet designs suitable for high-resolution magnetic resonance imaging (MRI), constructed entirely from cylindrical permanent magnet rods of two distinct radii. The multiplicity, $N$ , of the main set of rods (which dominate the generated field) can vary from 10 to 26. For each such $N$ , we present several designs that produce magnetic fields uniform to better than 100 parts per million (ppm) over spherical regions of radius half that of the bore. This design family includes peak fields ranging from 0.15 to 0.50 T, adjustable by changing $N$ , with the best accuracy obtained for $N=14$ with a peak field of 0.32 T. With optional correction rods that start out in a zero field configuration, these designs can be tuned to compensate for manufacturing errors simply by adjusting the rotations of these rods. Most of the 100 ppm accuracy radius can thereby be recovered, even in realistic imperfect configurations. We specifically present dimensions for full-body MRI with a standard bore (clearance) diameter of 70 cm, but this family of designs can be scaled uniformly to produce high-uniformity magnetic fields for applications at any length scale.