Courants de Foucault

On appelle courants de Foucault (Eddy currents) les courants électriques créés dans une masse conductrice, soit par la variation au cours du temps d'un champ magnétique extérieur traversant ce milieu (le flux du champ à travers le milieu), soit par un déplacement de cette masse dans un champ magnétique. Ils sont une conséquence de l'induction électromagnétique. Les courants de Foucault sont responsables d'une partie des pertes (dites pertes par courants de Foucault) dans les circuits magnétiques des machines électriques alternatives et des transformateurs. C'est la raison pour laquelle les circuits magnétiques sont constitués de tôles feuilletées afin de limiter ces courants et les pertes par effet Joule qui en découlent, ce qui améliore le rendement global des transformateurs. Historique Ce phénomène a été découvert par le physicien français Léon Foucault en 1851, de qui il tire son nom. Principe vignette|Le feuilletage permet de réduire les pertes par coura

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Electric motor

An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric

Transformateur électrique

Un transformateur électrique (parfois abrégé en « transfo ») est une machine électrique permettant de modifier la tension efficace délivrée par une source d'énergie électrique alternative, une transfo

Induction électromagnétique

L'induction électromagnétique est un phénomène physique conduisant à l'apparition d'une force électromotrice dans un conducteur électrique soumis à un flux de champ magnétique variable. Cette force é

Characterization of Surface Cracks Through The Local Magnetic Field Induced by Eddy Currents

Hannes Bleuler, David Florian Hippert, Pavel Kejik, Roland Moser, Marco Picasso, Gilles Raphaël Santi

It is important to reliably characterize cracks in metallic mechanical parts in order to assess the serenity of damage due to fatigue. The most important parameter for this is the crack depth. This is notoriously difficult with standard Eddy current techniques. We show here that this can be achieved by measuring the local magnetic field induced by Eddy currents flowing around the crack. This is done by using a high-density array of micro-Hall sensors integrated in a single CMOS chip with a spatial resolution of 10 mu m. We present the dependence of the signal on varying crack depths, liftoff and yaw angle. Finally, we study the response of the sensor to cracks in a DC magnetic field, i.e. the flux leakage due to the presence of a crack. This is especially relevant to cases where cracks appear predominantly close to edges with complex geometries for which it is difficult to induce clean Eddy currents.

Ios Press2014

Chargement

The High-Resolution Magnetic Camera: A Novel Sensor for Eddy Current Testing

Hannes Bleuler, David Florian Hippert, Pavel Kejik, Roland Moser, Marco Picasso, Gilles Raphaël Santi

Eddy current techniques are often used to detect and, in some advanced applications, to characterize fatigue surface-breaking cracks appearing in mechanical parts. One of the major difficulties in this approach is to reliably separate the crack contribution to the signal from the others (liftoff, edge effects, material property variations). This is particularly prominent in weld inspection. We present here a novel sensor consisting in an array of 200 micro-Hall sensors on a CMOS chip aligned over a length of 2 mm with a 10 mu m pitch. This sensor, which we call a "high-resolution magnetic camera", gives a direct measurement of the perturbation of the local magnetic field caused by the modification of the Eddy currents flow due to the surface-breaking crack. We show that using this technique, a crack has a very distinctive signature which can be easily distinguished from all other contributions. Finite element simulations are used to understand the signal response of different cracks. In addition, this system can perform "micro-magnetoscopy" on magnetic materials by giving a fine picture of the local variations of the magnetic field caused by the presence of a defect.

Ios Press2014

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Image analysis technique applied to lock-exchange gravity currents

Claudia Adduce, Helena Isabel Dos Santos Nogueira

An image analysis technique is used to estimate the two-dimensional instantaneous density field of unsteady gravity currents produced by full-depth lock-release of saline water. An experiment reproducing a gravity current was performed in a 3.0 m long, 0.20 m wide and 0.30 m deep Perspex flume with horizontal smooth bed and recorded with a 25 Hz CCD video camera under controlled light conditions. Using dye concentration as a tracer, a calibration procedure was established for each pixel in the image relating the amount of dye uniformly distributed in the tank and the greyscale values in the corresponding images. The results are evaluated and corrected by applying the mass conservation principle within the experimental tank. The procedure is a simple way to assess the time-varying density distribution within the gravity current, allowing the investigation of gravity current dynamics and mixing processes.

Institute of Physics2013

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PHYS-423: Plasma I

Following an introduction of the main plasma properties, the fundamental concepts of the fluid and kinetic theory of plasmas are introduced. Applications concerning laboratory, space, and astrophysical plasmas are discussed throughout the course.

PHYS-201(d): General physics: electromagnetism

The topics covered by the course are concepts of fluid mechanics, waves, and electromagnetism.

ME-424: Mecatronics

Mécatronique, Systèmes dynamiques, Commande, Electronique, Informatique temps réel.