Magnetic Field Produced by a Tile Permanent Magnet Whose Polarization is both Uniform and Tangential

pages 1-20International audienceThis 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. 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. To our knowledge, this calculation appears for the first time in the literature

Time-varying non linear modeling of electrodynamic loudspeakers

International audienceThis paper deals with the time-varying nonlinear analytical modeling of the electrodynamic loudspeaker. We propose a model which takes into account the variations of Small signal parameters. The six Small signal parameters ($R_{e}$, $L_{e}$, $Bl$, $R_{ms}$, $M_{ms}$, $C_{ms}$) depend on both time and input current. The electrodynamic loudspeaker is characterized by the electrical impedance which, precisely measured, allows us to construct polynomial functions for each Small signal parameter. By using this analytical model, we propose to compare two identical electrodynamic loudspeakers. One of them is supposed to be run in and the other one is not. The experimental methodology is based on a precise measurement. In all the paper, the time scale is assumed to be much longer than one period of the harmonic excitation

Experimental measurement of the nonlinearities of electrodynamic microphones

International audienceThis paper presents an experimental way of characterizing the nonlinearities of electrodynamic microphones used as acoustical sources. This functioning occurs for reciprocal calibration techniques. For this purpose, its electrical impedance is measured with a Wayne Kerr wedge which has an excellent precision. Moreover, it can be noted that the Thiele and Small model is used to characterize its electrical impedance. Furthermore, an experimental method based on Simplex algorithm allows us to construct polynomial laws which describe the dependence of the Thiele and Small parameters with the input voltage. The nonlinear variations obtained allow us to determine the nonlinear differential equation of the electrodynamic microphone. Then, this equation is solved numerically in order to confirm the accuracy of the polynomial laws obtained by the Simplex algorithm. The distortions are measured with a laser Doppler velocimeter and compared with the ones obtained by the numerical solving of the nonlinear differential equation. The experimental displacement spectrum is consistent with the theoretical one

Mechanical properties of ferrofluid applications: centering effect and capacity of a seal

International audienceThis paper presents three dimensional study of a ferrofluid seal, its centering effect and its static capacity. Thus, a method based on a potential energy criterion has been put forward to study the seal shape. But such a use of ferrofluid seals is interesting only if the magnetic field created by the permanent magnets saturates totally the ferrofluid. Two cylindrical structures consisting of two and three outer ring permanent magnets with an inner non-magnetic cylinder are considered. The calculation of the magnetic pressure of the ferrofluid seal is analytically established

Permanent Magnet Couplings: Field and Torque Three-Dimensional Expressions Based on the Coulombian Model

International audienceThis paper presents three-dimensional expressions for the optimization of permanent-magnet couplings. First, we give a fully analytical expression of the azimuthal field created by one arc-shaped permanent magnet radially polarized which takes into account its magnetic pole volume density. Such an expression has a very low computational cost and is exact for all points in space. Then, we propose two semi-analytical expressions of the azimuthal force and the torque exerted between two arc-shaped permanent magnets. These expressions are valid for thick or thin arc-shaped permanent magnets. Furthermore, this approach allows us to realize easily parametric studies and optimizations. The analytical approach taken in this paper, based on the Coulombian model, is a good alternative compared to the finite element method generally used to study such configurations

Etude analytique des systèmes magnétomécaniques sans fer (application au haut-parleur guidé par joints de ferrofluide)

Cette thèse a pour objet la modélisation analytique des systèmes à aimants permanents. Leurs caractérisations supposent la détermination du champ magnétique qu'ils produisent et des énergies spécifiques mises en jeu. Nous exposons dans cette thèse les expressions analytiques du champ magnétique créé par des anneaux et des tuiles d'aimantations radiale, ariale, transversale, orthoradiale et uniforme. Ces modèles sont utilisés pour l'étude d'une nouvelle structure de haut-parleur sans fer. Ce nouveau transducteur utilise des joints de ferrofluide pour assurer le guidage d'un piston émissif produisant des ondes acoustiques.This thesis deals with the analytical modeling of permanent magnet systems. Such devices are generally characterized by the magnetic field they produce. We present the analytical expressions of the magnetic field produced by ring and tile permanent magnets with radial, arial, orthoradial and uniform polarizations. Our analytical models are used for the study of a new kind of ironless loudspeaker. This new actuator uses ferrofluid seals so as to guide an emissive piston generating acoustic waves.LE MANS-BU Sciences (721812109) / SudocSudocFranceF