High sensitivity magnetic viewer using anhysteretic transfer for

Details High sensitivity magnetic viewer using anhysteretic transfer for High sensitivity magnetic viewer using anhysteretic transfer for

1994-11-30

1996-10-15

Snow, Walter E.

Electricity: measuring and testing

Magnetic

With means to create magnetic field to test material

324260, G01N 2772, G01R 3312

Patent

active

055657729

ABSTRACT:
A magneto-optic layer of bismuth-garnet deposited on a thin transparent substrate is utilized in viewing very low amplitude magnetic field patterns. When subjected to a magnetic field perpendicular to the layer, the layer lowers its magnetic energy by breaking up into a series of reversed domains called meander patterns. As the magnetic fields to be viewed are too low in amplitude, (approximately equal to, or less than 1 Oe), to directly modify the meander pattern, the magneto-optic layer is excited with an AC magnetic field of more than 100 Oe which is then slowly reduced to zero; (a small DC bias field is simultaneously applied to control the background of the viewed field, and to cancel the earth's field). This causes the anhysteretic transfer of the pattern of the low amplitude field onto the magneto-optic layer, with the resultant meander pattern replicating the low amplitude field pattern. By the Faraday effect, the domains of the magneto-optic layer rotate the plane of polarization of a linearly polarized light beam traversing the layer, and when viewed through crossed polarizers the meander pattern is readily visible.

REFERENCES:
patent: 3612665 (1971-10-01), Vassiliou
patent: 4403226 (1983-09-01), Gaudioso
patent: 4621192 (1986-11-01), Duthoit et al.
patent: 4755752 (1988-07-01), Fitzpatrick

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