Strength Of Permanent Magnet Research Articles

Basic Research on a Magnetic Refrigeration System for Cooling to Liquid Hydrogen Temperature

Magnetic refrigeration technology is expected to be a highly efficient process at a temperature of around 20 K, which is the hydrogen liquefaction temperature. In magnetic refrigeration, a magnetic field change is applied to a magnetocaloric material (MCM) to obtain a magnetocaloric effect. In addition, since the greater the magnetic field change, the better the cooling characteristics, the magnetic field strength of permanent magnets is insufficient, and the use of superconducting coils that can generate strong magnetic fields with low power consumption is essential. We are researching and developing a static magnetic refrigeration system (SMRS) that does not have moving parts to obtain magnetic field changes, and generates them by altering the energizing current to the coil. The key to devising this system is an AC loss of the superconducting coil. In this study, we measured the AC loss under energization conditions of multiple palm-sized REBCO coils at liquid nitrogen temperature, and calculated the efficiency of the SMRS by improving the accuracy of the analysis method for evaluating the AC loss, based on the results. We report the results and discuss the technical feasibility of SMRS.

Multi-material topology optimization of permanent magnet synchronous motors

This paper presents a multi-material topology optimization for the design of permanent magnet synchronous motors (PMSMs). Specifically, structural shapes of permanent magnet (PM) and iron core in a PMSM rotor are simultaneously designed together with the orientation of PM magnetization. For a co-design of PM and iron core, relative permeability and residual magnetic flux density are interpolated by the three-field density approach based on the Helmholtz filtering and regularized Heaviside step function. Here, the Helmholtz filtering aims to attain smooth border in design results, and the Heaviside function enables us to acquire a clear border (i.e. zero-one design) without intermediate densities. The optimization goal is set as maximizing the average torque of PMSMs. The average torque is calculated by Maxwell stress tensor (MST) method considering a maximum torque per ampere (MTPA) control. To validate the effectiveness of the proposed multi-material topology optimization approach, a PMSM rotor with 4 poles and 12 slots is designed. In addition, design results at various settings of input current amplitude and PM strength are compared and discussed. When the input current is stronger than the PM strength, rotor PM and iron core are designed for utilizing both PM and reluctance torque components like V-shape interior PMSMs. On the other hand, in the case of stronger PM strength, PM is designed near the air-gap, which utilizes only PM torque component like surface PMSMs.

Experimental investigation of energy harvesting from sloshing phenomenon: Comparison of Newtonian and non-Newtonian fluids

In the present work, energy harvesting from sloshing of Newtonian and non-Newtonian fluids has been studied experimentally. The most important features of this study are: proposing a new method for energy harvesting, comparing the performance of Newtonian and non-Newtonian fluids in energy harvesting, determining the impact and contribution of each input parameter in the results and driving a relationship for the obtained data in terms of input parameters. Power law index of fluids, frequency of excitations, electrical resistance, strength of permanent magnets and non-dimensional fluid height in the container have been used as input parameters. Effect of input parameters on peak to peak voltage, root mean square voltage and electrical power have been investigated. Also, the effect of input parameters was statistically investigated using analysis of variance (ANOVA) and finally an empirical-mathematical model was developed for harvested voltages and electrical power. Results showed that strength of the permanent magnets and the frequency of excitations had higher influence on the output parameters with respect to the other input parameters. For example, the contribution percentage of B and f on the harvested electrical power were 28.63% and 22.67%, respectively. Obtained results also indicated that the harvested voltages and electrical power were higher for Newtonian fluid than dilatant and pseudoplastic liquids. Harvested electrical power was increased by increasing the strength of permanent magnet and decreasing electrical resistance. Another important finding is reaching the output parameters to their maximum level at near the resonance frequency of the system. Highest measured parameters were 650 mV, 94.96 mV and 41.52 μW for Vpp, Vrms and P, respectively.

Design, development and characterization of tunable Permanent Magnet Quadrupole for Drift Tube Linac

Bhabha Atomic Research Centre, Trombay is developing LEHIPA (Low Energy High Intensity Proton Accelerator) as pre-injector for 1 GeV proton accelerator for proposed ADSS (Accelerator Driven Sub-critical reactor System). LEHIPA is 20 MeV, 30 mA room temperature accelerator and consists of RFQ (Radio Frequency Quadrupole) and DTL (Drift Tube Linac) as major accelerating structures. The RF (Radio Frequency) design of DT (Drift Tube) of DTL aimed at maximizing the shunt impedance; this demands the size (transverse) of DTs to be minimal. The width of the DT is governed by the β of the particle and trade-off between transit time factor and effective accelerating voltage in the DT gap. The availability of limited volume in DTs for housing magnetic quadrupole has motivated the use of permanent magnets for generating the quadrupole field, as they have high magnetic energy density when compared to conventional electromagnets. With usage of permanent magnets, joule heating is eliminated, this helps in limiting the heat load. DTL has copious microwave heat with heat flux as large as 10 W/cm2 at certain locations. The beam dynamics requires uniformity of integral magnetic field gradient of PMQ (Permanent Magnet Quadrupole) to be better than ±0.5% with nominal value of 2.05 T. Further the drift tubes which houses these PMQs have microwave heat generation on outer surface which ranges from 5 kW to 8 kW depending on the size of the DT. This heat is required to be removed, not doing so would result in resonant frequency detuning in DTL cavity and enhanced temperature would deteriorate the strength of permanent magnets of the PMQ, thereby compromising their focal length. The drift tube has hydraulic circuit for microwave heat removal. This paper describes the magnetic design of the PMQ using Sm2Co17 rare earth permanent magnets. Paper discusses the magnetic design for optimizing integral magnetic field gradient (integral Gdl) uniformity. A novel magnetic field tuning technique is used for tuning the integral magnetic field gradient to required value. Comprehensive magnetic tuning and characterization scheme is presented which relates the measured magnetic moment of the permanent magnets, un-tuned integral Gdl and pole length to the required integral Gdl. Based on this scheme thirty six PMQ embedded drift tubes have been developed. Paper also details the results of characterization of twenty PMQs which forms part of 10 MeV to 15 MeV DTL. The scheme used for tuning integral magnetic field gradient is universal and can be implemented in similar permanent magnets quadrupoles and other permanent magnet based systems.

Topology optimization for three-dimensional design of segmented permanent magnet arrays

This paper proposes a topology optimization formulation for the three-dimensional (3-D) design of segmented permanent magnet (PM) arrays. Specifically, the proposed formulation aims to find an optimal 3-D structural topology of PM segments and their discrete magnetization directions. To achieve this, a design variable is defined in the vector form of a Cartesian coordinate system. The magnitude of the design variable vector determines a PM density, and the directional cosines of the vector determine PM magnetization directions. To acquire a segmented PM design with discrete magnetization directions, a PM strength penalization scheme is proposed. In this scheme, a PM strength is controlled using a minimum distance function between a magnetization direction and target discrete directions. Here, the minimum distance function is approximated using the p-norm for sensitivity calculation. To validate the effectiveness of the proposed formulation, three design examples are provided. In the first example, a two-dimensional (2-D) dipole Halbach cylinder is designed to confirm that the proposed formulation can be applied for a 2-D design problem. The second example aims to design 3-D dipole PM arrays with a cuboid cavity. In the third example, a 3-D PM arrays are designed for maximizing the magnetic force acting on a soft ferromagnetic material.

A Comprehensive Study on Transverse Flux Motor for Direct Drive Low-Speed Spacecraft Applications

Transverse flux motor (TFM) has been proven to be the ideal choice for high-torque direct drive applications, thanks to its higher specific torque density than the conventional radial flux machine. This article investigates the suitability of using TFM as the drive motor for precise position control based spacecraft applications, where mass and power reduction are the everlasting demands. Comparative configuration studies have been carried out to find the suitable type of permanent magnet motor for this application. Surface mounted TFM (SM-TFM) outweighs its competitors with lower power requirement and higher average torque, but with increased ripple content. Parametric studies of SM-TFM have been carried out to arrive at an optimal design of variables. To further increase the torque density, flux concentrated (FC) configurations of TFM have been analyzed. Average electromagnetic torque of FC and claw pole type TFM is higher than SM-TFM, with corresponding increase in the cogging torque. Electromagnetic simulation is carried out using Maxwell 3-D simulation software. Two variants of SM-TFMs are realized and the design is evaluated. Effect of Number of poles, material annealing, and strength of permanent magnet on the developed torque of SM-TFM are experimentally validated in the realized motor.

Development of EMA transducer for inspection of pipelines

Electromagnetic acoustic transducers (EMATs) have potential for In-line inspection (ILI) of pipelines compare to other Nondestructive evaluation (NDE) methods, since EMAT doesn’t need to contact and/or coupling material and can detect defects in outside of pipelines. However, improvement of transduction efficiency of EMATs is needed to secure integrity of the pipelines. To improve performance of EMAT, optimization of major parameters, such as strength of permanent magnet, shape of coil, configuration of static and dynamic magnetic fields is required. Thus, in this paper, investigation of transduction efficiency with variation of major parameters are performed by comparison of generated ultrasonic signals. Based on the investigation results, EMATs for ILI of pipelines are designed and fabricated with optimized Periodic solenoid array (PSA) types of meander-line sensor, static magnetic field, and then, performance of the developed EMATs are evaluated by detecting defects in the gas pipelines mounted in the one-bed testing system.

Topology optimization for design of segmented permanent magnet arrays with ferromagnetic materials

This paper presents multi-material topology optimization for the co-design of permanent magnet segments and iron material. Specifically, a co-design methodology is proposed to find an optimal border of permanent magnet segments, a pattern of magnetization directions, and an iron shape. A material interpolation scheme is proposed for material property representation among air, permanent magnet, and iron materials. In this scheme, the permanent magnet strength and permeability are controlled by density design variables, and permanent magnet magnetization directions are controlled by angle design variables. In addition, a scheme to penalize intermediate magnetization direction is proposed to achieve segmented permanent magnet arrays with discrete magnetization directions. In this scheme, permanent magnet strength is controlled depending on magnetization direction, and consequently the final permanent magnet design converges into permanent magnet segments having target discrete directions. To validate the effectiveness of the proposed approach, three design examples are provided. The examples include the design of a dipole Halbach cylinder, magnetic system with arbitrarily-shaped cavity, and multi-objective problem resembling a magnetic refrigeration device.

Cogging Torque Reduction Techniques for Spoke-type IPMSM

A spoke-type interior permanent magnet synchronous motor (IPMSM) is extending its tentacles in industrial arena due to good flux-weakening capability and high power density. In many of the application, high strength of permanent magnet causes the undesirable effects of high cogging torque that can aggravate performance of the motor. High cogging torque is significantly produced by IPMSM due to the similar length and the effectiveness of the magnetic air-gap. The address of this study is to analyze and compare the cogging torque effect and performance of four common techniques for cogging torque reduction such as skewing, notching, pole pairing and rotor pole pairing. With the aid of 3-D finite element analysis (FEA) by JMAG software, a 6S-4P Spoke-type IPMSM with various rotor-PM configurations has been designed. As a result, the cogging torque effect reduced up to 69.5% for skewing technique, followed by 31.96%, 29.6%, and 17.53% by pole pairing, axial pole pairing and notching techniques respectively.

Analysis of Permanent Magnet Demagnetization Effect Outer-rotor Hybrid Excitation Flux Switching Motor

This paper addresses the irreversible permanent magnet (PM) demagnetization analysis of hybrid excitation flux switching motor (HEFSM) with outer-rotor configuration. PM demagnetization cause the PM strength used in the motor significantly reduces and hence contributes less torque performance. The study is focused on thermal analysis and conducted at various temperature up to as high as 180 degrees Celsius which has a tendency to be demagnetized. Therefore, PM demagnetization is among a critical issue and influences the choice of the applied motor. The analysis is carried out based on finite element method (FEM) and percentage of PM demagnetization is then calculated. Finally, based on simulated and calculated results the final design outer-rotor HEFSM has only 0.85 percent PM demagnetization at very high temperature and obviously the is no PM demagnetization at normal operating conditions.

Topology optimization of Halbach magnet arrays using isoparametric projection

Topology optimization using isoparametric projection for the design of permanent magnet patterns in Halbach arrays is proposed. Based on isoparametric shape functions used in the finite element analysis, the permanent magnet strength and magnetization directions in a Halbach array are simultaneously optimized for a given design goal. To achieve fabrication feasibility of a designed Halbach magnet array, two design schemes are combined with the isoparametric projection method. First, a penalization scheme is proposed for designing the permanent magnets to have discrete magnetization direction angles. Second, an extrusion scheme is proposed for the shape regularization of the permanent magnet segments. As a result, the method systematically finds the optimal permanent magnet patterns of a Halbach array considering manufacturing feasibility. In two numerical examples, a circular shaped permanent magnet Halbach array is designed to minimize the magnitude of the magnetic flux density and to maximize the upward direction magnetic flux density inside the magnet array. Logical extension of the method to the design of permanent magnet arrays in linear actuators is provided, where the design goal is to maximize the actuator magnetic force.

Measurement of Set Fibre-Concrete Homogeneity in Finished Steel Fibre-Concrete Structure of Segmental Tunnel Lining

A new test method of set fibre concrete homogeneity in finished steel fibre-concrete structure is described in this contribution. The method is based on measurements of the changes in magnetic field strength of permanent magnets which are induced by a change of wire distribution in steel fibre-concrete structure. It is evident from the method described in this contribution that the test is characterized as a local failure test using small diameter core drill. It is a semi-destructive method. Its application in practice does not affect safety and reliability of steel fibre-concrete structures.Additionally to the method described, an example of its application for the assessment of fibre concrete homogeneity of the segmental tunnel lining parts is described. The results of partial measurements give both information about fibre concrete homogeneity in a segment and a number and a selection of points for homogeneity measurements which are subject to the size and the production method of such segment.

Calculation Methods and Effects of End-Winding Inductance and Permanent-Magnet End Flux on Performance Prediction of Nonoverlap Winding Permanent-Magnet Machines

Due to the short end windings of nonoverlap winding permanent-magnet (PM) machines, the end-winding inductance component is generally ignored in the design. In most cases, the end-flux fringing effects in PMs are also not taken into account. It is shown in this paper that these end effects have a significant influence on the performance parameters of the machine. In this paper, several nonoverlap winding PM machines are considered with respect to the effects of end-winding inductance and PM end-flux fringing. A number of calculation methods for the per-phase end-winding inductance of the machines are compared. A new simple analytical calculation method is proposed, which is shown to give a relatively good prediction of the end-winding inductance compared with 3-D finite-element (FE) results. It is proposed in this paper that the PM strength should be reduced by a certain fringing factor to take the end-flux fringing effects into account in the 2-D FE analysis. Practical measurements are also presented to validate the FE calculations and to give an indication on the effects that are caused by the end-winding inductance and the PM end-flux fringing.

Line‐start permanent magnet motors: proper design for pole‐changing starting method

Pole-changing of line-start permanent magnet (LSPM) motors at start-up eliminates all their drawbacks such as poor starting torque, vibration at start-up and synchronisation problems. In addition, by using this method almost all the inherent limitations in the design parameters of line-start motors such as rotor resistance, permanent magnet strength and mechanical stress influenced by pulsating torques are alleviated. Therefore there is no need to compromise between the motor parameters. In this study, the design procedure of these motors is investigated and a high-performance motor based on the pole-changing starting-method is designed and fabricated. Next, the possibility and advantages of replacing laminated cage-bar rotors with solid rotors are investigated for pole-changing LSPM motors. Then, simulations are done by the two-dimensional finite element method and finally, the experimental results are presented. The good agreement between simulation and experimental results validates the theoretical method and also the new design.

SAL-biased MR heads stabilized by canted permanent magnets

The design and fabrication of anisotropic magnetoresistance (AMR) heads biased with a soft-adjacent layer (SAL), stabilized by canted permanent magnet (PM), have been investigated. MR linear response to AC writer current was observed. The response of bias point to DC writer current in overlaid head stronger than abutted head indicates that this MR response to writer is at two side-wings in overlaid head while at the track edges in abutted head. This MR response to writer current can be minimized for narrow track recording by adjusting magnetization angle and strength of PM, which is confirmed by full track scan and micro-track profiles.

Micromagnetic Simulation of Hard Bias Field Effects on Submicron Spin Valve Heads

The three-dimensional micromagnetic simulations of submicron spin valve (SV) heads are presented. At such sensor widths, the amplitude of SV head output is reduced. An effective way to improve this reduction is to weaken the longitudinal bias field from permanent magnets. Results of simulations reveal that the magnetizations of the pinned layer near the air bearing surface rotate irregularly below a critical permanent magnet strength at a positive external medium field. This irregular rotation causes hysteresis of transfer curve. The critical permanent magnet strength decreases linearly with an increase in the reciprocal of the square of the sensor width. At the optimum permanent magnet strength, the amplitude of the sensor with 0.3 μm wide is almost the same as that of the sensor with 1.0 μm wide. It is important to evaluate the domain stability of the pinned layer when designing a SV head with submicron sensor widths.

Spin-valve heads utilizing antiferromagnetic NiO layers

Spin-valve heads utilizing antiferromagnetic NiO layers as the pinning layers were investigated. Advantages of using NiO are (1) superior corrosion resistance, (2) relatively high blocking temperature and (3) reduction in the heat generation due to current shunting. Spin-valve films of a structure of NiO/NiFe/Cu/NiFe show large /spl Delta//spl rho///spl rho/ (approximately 4%) and good sensitivity. Thin Co layers inserted between NiFe and Cu improve both /spl Delta//spl rho///spl rho/ and the thermal stability. To explore the feasibility of spin-valves with NiO, unshielded sensors with hard bias structure having longitudinally magnetized permanent magnets were fabricated. Irregular response in the transfer curves can be suppressed when the permanent magnet strength M/sub r/t is 0.5 memu/cm/sup 2/ or more. The linear response region of the spin-valve sensor was optimized by adjusting the thickness of the pinned layers and the sensor height. Finally, by incorporating these results a shielded spin-valve head with a track width of 2.4 /spl mu/m, a gap length of 0.3 /spl mu/m and a sensor height of 0.7 /spl mu/m was fabricated The response was noise-free and the output obtained with a small sense current of 0.41 mA was approximately 1 mVp-p, demonstrating a high sensitivity of a spin-valve head utilizing NiO.

Instability evaluation for permanent magnet biased magnetoresistive heads

We have used micromagnetic modeling to study instability of permanent magnet biased magnetoresistive heads. A new approach based on the dependence of reproducing characteristics on initial magnetization is proposed to examine the instability of both AMR and spin-valve heads. When the permanent magnet strength is smaller than a critical value, the output voltage of an AMR head depends on the initial magnetization, which results in instability. The critical permanent magnet strength gradually increases as shield-to-shield separation decreases. The critical value for spin-valve heads is smaller than that for AMR heads, because the pinned layer under a large exchange field does not change its magnetization at all.

A sectioned spheroid model for cylindrical permanent magnets

A model is proposed for approximating the field strength of permanent magnets. The model has only one adjustable parameter rather than the usual two, and implies a specific pole distribution within the magnet. Calculations and measurements of axial field are compared for six small Alnico magnets of various sizes, with agreement generally within a few percent. The model assumes a distribution of magnetic poles on part of the surface of a uniformly magnetized spheroid, that segment of the surface which lies inside a cylinder of the size of the magnet. The aspect ratio of the spheroid is an adjustable parameter that permits a good fit of calculated and measured data. The calculated internal fields due to the assumed pole distributions support the concept that isolated cylindrical magnets may partially demagnetize near the end faces.

Test for Change of Pole Strength of Permanent Magnet

Test for Change of Pole Strength of Permanent Magnet