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

Calculation Method of Permanent Magnet Pickups for Electric Guitars

International audienceThis paper first presents the structures of permanent magnet pickups for electric guitar and the considered device: string, magnet, coil. It then describes a method to calculate the induced electromotive force (EMF) in the pickup coil when the string moves. The method of calculation links the EMF in the pickup coil with the flux cut by the string when it moves. The EMF is of course nonlinear. The harmonics of the EMF can be calculated. This is a first step towards the final aim that will consist in studying the frequency spectrum of the electrical signal given by the pickup, which is quite complicated, in order to link the magnetic structure and the string movement with the musical effect. Analytical calculations using the coulombian model of magnets are used to evaluate the magnetic field created by the magnet and the electromotive force in the pickup coil

Magnetic Field Created by Tile Permanent Magnets

International audienceThis paper presents the 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

Ironless loudspeakers

International audienceWe note the drawbacks of classical loudspeaker motors: the inductance varies with the coil's position, there is a reluctant effect and Eddy currents appear because of the iron in the motor. We then present ironless structures of loudspeaker motors to eliminate these drawbacks. These structures are studied with the use of Coulomb's model of permanent magnets, which affords analytical calculations. Thus the design can be optimized to create a uniform, high level induction in the space where the coil moves