Saturday, December 18, 2010

Eddy current Theory

Eddy current theory is based on electromagnetic induction. That means, a variable magnetic field can induce an electric current on a conductor which is separate to the source of the magnetic field, and also vice versa, which is an electric current generates a magnetic field. Similar theory is used for the magnetic particles inspection as well.
Electromagnetic induction is used in many applications such as, Transformers, Electric motors, Generators, etc...



In the field of Non destructive testing (NDT), we manipulate with this theory which I mentioned above, and try to find surface defects or/and shallow internal defects of ferromagnetic materials.

Thursday, December 2, 2010

Eddy current method (ET)

Short research about the history of eddy current
The first person to observe current eddies was François Arago (1786-1853), the 25th president of France, Who was also a mathematician, physicist and astronomer.1824 He discovered what has been called rotatory magnetism, and the fact that most bodies could be magnetized; these discoveries were completed and explained by Michael Faraday (1791-1867).
In 1834, Heinrich Lenz stated the principle that defines how the properties of the test objects are communicated back to the test system. Lenz's law states that the direction of current flow in the test object will be such that its magnetic field will oppose the magnetic field that caused the current flow in the test object. This means, in practice, the eddy currents communicate with the test coil by developing secondary flux that cancels a portion of the coil's flux equivalent to the magnitude and phase of the flux developed by the eddy currents.
 
Léon Foucault (1819-1868)

However, the first person who really discovered eddy current (or Foucault current)