Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1990-01-11
1991-10-01
Snow, Walter E.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324213, 324238, 356237, 359282, G01N 2782, G01N 2121, G02F 109
Patent
active
050537040
ABSTRACT:
A device for the direct visualization of surface and near surface cracks, voids, flows, discontinuities, etc. in a target material. A magnetic garnet epitaxial film is deposited on either side, or both sides, of a non-magnetic substrate. A reflective material is provided adjacent to the epitaxial film, and the substrate with its associated layers is placed over a sheet of current carrying material and this sheet is placed over the target material. A bias magnetic field is then applied to the substrate together with its epitaxial film. Polarized light is transmitted onto the substrate with its associated layers and is reflected through the epitaxial layer and back out of the substrate. The existing magnetization, within the epitaxial film, interacts with nearby magnetic fields associated with eddy currents flowing adjacent to flaws in the target material, such that the domain structure of the epitaxial film is altered. The altered domain structure induces a rotation of the plane of polarization of the incident projected light. When viewed through a polarizing material disposed on the top epitaxial layer, the rotation of the reflected light renders the magnetic field variations associated with the flaws directly visible. Accordingly, surface and near surface flows within a skin depth, or slightly greater, of the electromagnetic fields associated with the currents in the current carrying sheet, are optically detected when eddy currents flow in the target material.
REFERENCES:
patent: 4355278 (1982-10-01), Burns et al.
patent: 4625167 (1986-11-01), Fitzpatrick
PRi Instrumentation, Inc.
Snow Walter E.
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