Tile Permanent Magnets Research Articles

Torsional mode magnetostrictive patch transducer with TPSMs for liquid-filled pipes inspection

T (0,1) mode guided waves have no axial or radial vibration displacement. Therefore, the energy leakage is small in liquid-filled pipes, which is suitable for detecting the axial defects of the liquid-filled pipes. Fe–Co materials with high magnetostriction coefficient is fabricated. Its magnetic properties are tested. The size and distribution of static magnetic fields generated by different permanent magnets are verified by simulation. A new torsional mode guided wave magnetostrictive patch transducer with tile-shaped permanent magnets for defect detection of the liquid-filled pipes is proposed. The detection effect of the transducer on the liquid-filled pipes under different pressures is tested through experiments. The proposed transducer consists of four tile-shaped permanent magnets, eight triangular yokes, a coil, and two magnetostrictive patches. Four groups of tile permanent magnets are symmetrically distributed around the patch according to the polarity. Magnetic yokes are installed at both ends of each group of tile permanent magnets. The experiment verified that the magnetostrictive patch transducer realize the excitation and reception of guided wave signals in the magnetostrictive patches. The amplitude and signal-to-noise ratio of echo signals is improved. The position of pipe defects is determined according to the propagation time of guided wave. The influence of different pressures in the liquid-filled pipes on the amplitude of guided wave is verified.

Optimum Injected Harmonics Into Magnet Shape in Multiphase Surface-Mounted PM Machine for Maximum Output Torque

Harmonics can be injected into the permanent magnet (PM) shape to maximize the output torque in five-phase machines. The optimal harmonics of different orders for maximum torque is mathematically derived and validated by the finite element (FE) method in this paper. The output torque of the five-phase machine with sinusoidal shape can be improved by 12.5% by injecting the optimal third harmonic. Meanwhile, 3.2% further more torque improvement can be obtained with the optimal third and fifth harmonics injected. However, the output torque barely change with the seventh harmonic injection. The torque ripple of the machines with shaped PMs is much lower than the machines with conventional tile PM. The electromagnetic performance for all the machines including back electromotive force, average torque, torque ripple, etc., are compared. Finally, the five-phase machine with third and fifth harmonics injection into the rotors is prototyped to verify the analytical and FE analyses.

A THREE DIMENSIONAL ANALYTICAL CALCULATION OF THE AIR-GAP MAGNETIC FIELD AND TORQUE OF COAXIAL MAGNETIC GEARS

In order to solve the defects that the end-efiect of magnetic fleld is ignored in two dimension (2-D) analytical method or 2-D flnite element method (FEM); meanwhile, mass computer resource and time for parametric design or optimization are wasted in three dimension (3-D) FEM, a concise and e-cient 3-D analytical approach is put forward for the calculation of the air-gap magnetic fleld and torque of coaxial magnetic gears. Based on the cylindrical coordinates where a coaxial magnetic gear is in, the equivalent current model and vector magnetic potential equation of permanent magnets in high speed permanent magnetic ring are constituted. By superposed magnetic ∞ux density of every tile permanent magnets on high speed permanent magnetic ring in cylindrical coordinates, a air-gap magnetic fleld 3-D analytical formula is set up without ferromagnetic pole-pieces; in the interest of modulated air-gap magnetic fleld 3-D analytical formula with ferromagnetic pole-pieces, three types boundary conditions using state equations of contact surfaces between ferromagnetic pole-pieces and air-gap are established by a thorough analysis of the modulate mechanism of ferromagnetic pole-pieces. Finally, magnets of the low speed permanent magnetic ring are reduced to a distribution of equivalent current, which experience the Lorentz force in modulated magnetic fleld of high speed permanent magnetic ring for torque calculation. The integrals in all aforementioned calculation are axial, so the end-efiect is embodied in above analytical model and more precise than 2-D analytical method or 2-D FEM. As the calculation results, the formula is accurate but faster than the 3-D FEM. The analytical model is suited for programmable calculation and that will make the structural and parametric design or optimization of coaxial magnetic gears simple and timesaving.

Analytical Design of Permanent Magnet Radial Couplings

This paper presents a three-dimensional analytical approach for computing the torque transmitted by synchronous radial couplings with radially polarized tile permanent magnets. An expression is given as a finite sum of elliptic functions, which has no underlying simplificating assumptions. Such an expression allows parametric studies and optimizations of coupling structures. It is applied first to the study of conventional radial couplings. Then, structures with “short pitch” magnets are considered and compared with conventional ones. Eventually, special designs are presented, as the ones dedicated to screwing applications, for instance, which require creating an asymmetrical torque.

MAGNETIC FIELD CREATED BY A UNIFORMLY MAGNETIZED TILE PERMANENT MAGNET

This paper presents a general analytical formulation for calculating the three-dimensional magnetic fleld distribution produced by Halbach structures with radial or axial polarization directions. Our model allows us to study tile permanent magnets of various magnetization directions and dimensions. The three magnetic fleld components are expressed in terms of analytical and semi-analytical parts using only one numerical integration. Consequently, the computational cost of our model is lower than 1s for calculating the magnetic fleld in any point of space. All our expressions have been checked with previous analytical models published in the literature. Then, we present two optimized permanent magnet structures generating sinusoidal radial flelds.

Magnetic Field Created by Tile Permanent Magnets

This paper presents an analytical calculation of the three components of the magnetic field created by tile permanent magnets whose magnetization is either radial or axial. The calculations are based on the Coulombian model of permanent magnets. The magnetic field is directly calculated, without the magnetic potential. Both axial and radial magnetization of the tiles are considered. The expressions obtained give the magnetic field in all the space. Such analytical expressions are very useful for the design and optimization of many industrial applications.

Torque in permanent magnet couplings: Comparison of uniform and radial magnetization

We present a three-dimensional study of the torque transmitted between tile permanent magnets uniformly magnetized. All this study is based on the Coulombian model. The torque is calculated semianalytically by considering all the surface densities that appear on the tiles. In addition, no simplifying assumptions are done in the expressions given in this paper. Consequently, the evaluation of the torque is very accurate and allows us to show the drawbacks of using tile permanent magnets uniformly magnetized instead of using tile permanent magnets radially magnetized. Such an approach is useful because it allows us to realize easily parametric studies.

DISCUSSION ABOUT THE MAGNETIC FIELD PRODUCED BY CYLINDRICAL HALBACH STRUCTURES

This paper uses a three-dimensional analytical approach based on the Coulombian model for studying the magnetic field produced by cylindrical Halbach structures. Such structures, commonly used in magnetic couplings or in electrical machines, are composed of tile permanent magnets with rotating magnetizations. Such assemblies of tile permanent magnets allow one to easily optimize the radial field shape in the air gap of electrical machines. In addition, Halbach structures can be used in magnetic couplings for improving the torque transmitted between the two rotors. Analytical studies dealing with the optimization of such structures generally use a two- dimensional analytical approach for calculating either the magnetic field produced by tile permanent magnets or the forces exerted between them. These two-dimensional expressions are useful because they have a very low computational cost. However, their accuracy depends greatly on the structure dimensions. We propose in this paper to use a three-dimensional analytical model based on the Coulombian model for determining the exact shape of the magnetic field produced by a Halbach structure. Such an approach also allows one to determine the demagnetizing magnetic field inside the tile permanent magnets. This element of information is important for the design of tile permanent magnets. In addition, we show that some effects cannot be predicted with the linearized analytical model. This implies that a linearized dimensional optimization is not accurate. This study has been carried out without any simplifying assumptions. Therefore, the calculations of the three magnetic field components are exact for all points in space, whatever the magnet dimensions. We can say that such a three-dimensional analytical approach is a good alternative to a finite element one because it has a lower computational cost and is more accurate.

MAGNETIC FIELD PRODUCED BY A TILE PERMANENT MAGNET WHOSE POLARIZATION IS BOTH UNIFORM AND TANGENTIAL

This paper presents the exact 3D calculation of the magnetic field produced by a tile permanent magnet whose polarization is both tangential and uniform. Such a calculation is useful for optimizing magnetic couplings or for calculating the magnetic field produced by alternate magnet structures. For example, our 3D expressions can be used for calculating the magnetic field produced by a Halbach structure. All our expressions are determined by using the coulombian model. This exact analytical approach has always proved its accuracy and its usefulness. As a consequence, the tile permanent magnet considered is represented by using the fictitious magnetic pole densities that are located on the faces of the magnet. In addition, no simplifying assumptions are taken into account for calculating the three magnetic field components. Moreover, it is emphasized that the magnetic field expressions are fully three-dimensional. Consequently, the expressions obtained are valid inside and outside of the tile permanent magnet, whatever its dimensions. Such an approach allows us to realize easily parametric studies.

ANALYTICAL EXPRESSION OF THE MAGNETIC FIELD CREATED BY TILE PERMANENT MAGNETS TANGENTIALLY MAGNETIZED AND RADIALS CURRENT IN MASSIVE DISKS

In this paper, we present new expressions for calculating the magnetic field produced by either tile permanent magnets tangentially magnetized or by radial currents in massive disks. These expressions are fully analytical, that is, we do not use any special functions for calculating them. In addition, they are three-dimensional and can be used for calculating the magnetic field for all regular points in space. The expressions commonly used for calculating the magnetic field produced by radial currents in massive disks are often based on elliptic integrals or semi-analytical forms. We propose in this paper an alternative analytical method that can also be used for tile permanent magnets. Indeed, by using the analogy between the coulombian model and the amperian current model, radial currents in massive disks can be represented by using the fictitious magnetic pole densities that are located on two faces of a tile permanent magnet tangentially magnetized. The two representations are equivalent and thus, the shape of magnetic field produced is the same for all points in space, with a smaller value in the case of it is produced by radial currents in massive disks. Such expressions can be used for realizing easily parametric studies.

MODELLING AN IRONLESS LOUDSPEAKER BY USING THREE-DIMENSIONAL ANALYTICAL APPROACHES

MODELLING AN IRONLESS LOUDSPEAKER BYUSING THREE-DIMENSIONAL ANALYTICALAPPROACHESR. Ravaud and G. LemarquandLaboratoire d'Acoustique de l'Universite du Maine, UMR CNRS 6613Avenue Olivier Messiaen, 72085 Le Mans, Franceguy.lemarquand@univ-lemans.frAbstract |This paper presents some improved three-dimensionalexpressions of the magnetic ¯eld created by tile permanent magnetsuniformly and radially magnetized for the design of ironlessloudspeaker structures. All the expressions determined have beenreduced to compact forms. We use these expressions for theoptimization of ironless loudspeaker structures in which the radial¯eld must be radially uniform. Indeed, as ring permanent magnetsradially magnetized are rather di±cult to manufacture, these magnetsare replaced by assemblies of tile permanent magnets radiallyand uniformly magnetized. We present an example of ironlessloudspeaker structure that has been optimized with our three-dimensional approaches.1. INTRODUCTIONTile permanent magnets can be used for manufacturing ring permanentmagnets radially magnetized by stacking them together. Such a wayof manufacturing a ring is commonly realized because ring permanentmagnets radially magnetized are di±cult to fabricate. Consequently,this alternative method consists in using tile permanent magnetsuniformly magnetized. However, they do not exhibit the sameproperties as tiles radially magnetized and can lower the quality ofthe radial ¯eld created by the permanent magnet structure.Manyauthorshavestudiedthe¯eldcreatedbyring[1]-[6], cylinder[7]-[9], tile permanent magnets [10]-[12] or by disk conductors [13]-[15]. All these analytical methods have enabled authors to study thesti®ness or the force between permanent magnets for magnetic bearings[16][17] or couplings [18][19]. More generally, optimizations can becarried out with analytical or semi-analytical approaches [20]-[22]. An

MAGNETIC FIELD IN MRI YOKELESS DEVICES: ANALYTICAL APPROACH

This paper presents a three-dimensional analytical expressions for studying the static magnetic fleld produced by Magnetic Resonance Imaging structures. This medical imaging technique uses a very high and uniform magnetic fleld produced by ring permanent magnets with rotating polarizations. However, the manufacturing of such ring permanent magnets is di-cult to realize. Consequently, such ring permanent magnets are replaced by assemblies of tile permanent magnets uniformly magnetized. Unfortunately, the magnetic fleld produced by these tile permanent magnets uniformly magnetized is both less important and less uniform than the one produced by an idealized ring permanent magnet. We propose in this paper to study the in∞uence of the number of tile permanent magnets used on the magnetic fleld properties.

COMPARISON OF THE COULOMBIAN AND AMPERIAN CURRENT MODELS FOR CALCULATING THE MAGNETIC FIELD PRODUCED BY RADIALLY MAGNETIZED ARC-SHAPED PERMANENT MAGNETS

This paper presents some improved analytical expressions of the magnetic fleld produced by arc-shaped permanent magnets whose polarization is radial with the amperian current model. First, we show that the radial component of the magnetic fleld produced by a ring permanent magnet whose polarization is radial can be expressed in terms of elliptic integrals. Such an expression is useful for optimization purposes. We also present a semi-analytical expression of the axial component produced by the same conflguration. For this component, we discuss the terms that are di-cult to integrate analytically and compare our expression with the one established by Furlani (1). In the second part of this paper, we use the amperian current model for calculating the magnetic fleld produced by a tile permanent magnet radially magnetized. This method was in fact still employed by Furlani for calculating the magnetic fleld produced by radially polarized cylinders. We show that it is possible to obtain a fully analytical expression of the radial component based on elliptic integrals. In addition, we show that the amperian current model allows us to obtain a fully analytical expression of the azimuthal component. All the expressions determined in this paper are compared with the ones established by Furlani (1) or in previous works carried out by the authors.

MAGNETIC COUPLINGS WITH CYLINDRICAL AND PLANE AIR GAPS: INFLUENCE OF THE MAGNET POLARIZATION DIRECTION.

This paper presents a comparison of cylindrical and plane air gap magnetic couplings in which the tile permanent magnet polarizations can be either radial or tangential or axial. The expressions of the torque transmitted between the two rotors of each coupling are determined by using the colombian approach. All the calculations are performed without any simplifying assumptions. Consequently, the expressions obtained are accurate and enable a fast comparison between the structures presented in this paper.

THE THREE EXACT COMPONENTS OF THE MAGNETIC FIELD CREATED BY A RADIALLY MAGNETIZED TILE PERMANENT MAGNET

This paper presents the exact analytical formulation of the three components of the magnetic field created by a radially magnetized tile permanent magnet. These expressions take both the magnetic pole surface densities and the magnetic pole volume density into account. So, this means that the tile magnet curvature is completely taken into account. Moreover, the magnetic field can be calculated exactly in any point of the space, should it be outside the tile magnet or inside it. Consequently, we have obtained an accurate 3D magnetic field as no simplifying assumptions have been used for calculating these three magnetic components. Thus, this result is really interesting. Furthermore, the azimuthal component of the field can be determined without any special functions. In consequence, its computational cost is very low which is useful for optimization purposes. Besides, all the other expressions obtained are based on elliptic functions or special functions whose numerical calculation is fast and robust and this allows us to realize parametric studies easily. Eventually, we show the interest of this formulation by applying it to one example: the calculation and the optimization of alternate magnetization magnet devices. Such devices are commonly used in various application fields: sensors, motors, couplings, etc. The point is that the total field is calculated by using the superposition theorem and summing the contribution to the field of each tile magnet in any point of the space. This approach is a good alternative to a finite element method because the calculation of the magnetic field is done without any simplifying assumption.