Patent ID: 9063190
Filing Date: 2015-06-23
Classification: G01R

Abstract:
1. A non-contact magnetic sensor for non-destructively determining magnetic property degradation in a ferromagnetic sheet material sample by providing sensitive indications of salient hysteresis features of the ferromagnetic material, comprising: permanent magnet means spaced closely adjacent to and a known distance from one surface of said sample, said magnet being polarized normal to said one surface and presenting a constant polarity to said surface; at least one active field sensor means positioned along the surface of said sample opposite from said one surface, at a fixed position relative to said sample and at a known distance from said opposite surface; said permanent magnet means and said at least one surface being mounted for and capable of relative back and forth reciprocating motion along a fixed line of travel whereby no point on said at least one surface is permitted to pass the magnet means more than once without changing direction, said field sensor means being positioned along and at the center of the line of travel, said one surface being generally flat or gently curved in the direction of motion; and said field sensor means having a sensing axis oriented to sense longitudinal fields arising from said magnet and from the gradient of magnetization arising in said sample; whereby said magnetic field H(x) at said field sensor means for a number of corresponding magnet distances x from the field sensor means along the line of travel for both directions of back and forth movement between the magnet means and said at least one surface can be sensed for each direction of movement, a directional difference, D(x), between H(x) at distance x in each direction calculated and D(x) plotted against x (D(x) signature) for determining information indicative of hysteresis properties of said ferromagnetic sheet material sample.