Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1975-07-02
1977-07-26
Corcoran, Robert J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
235 617B, 235 6111D, 235 6112M, 340149A, G01R 3312
Patent
active
040385965
ABSTRACT:
Apparatus to examine a magnetic storage layer expected to contain a magnetic watermark includes means to magnetize the layer with a unidirectional field of a selected strength without saturating it and means to detect any distinct region of magnetic remanence. The apparatus may further include means to record the resultant remanence levels (or their ratio) for such a region and another part of the layer, means to magnetize the layer with a unidirectional field of a different selected strength, means to detect any then-existing such distinct region or regions, means to measure the remanence levels (or their ratio) for the then-existing such region and another part of the layer, and means to compare the measured and recorded levels (or their ratios) and indicate from the result of the comparison whether or not this represents a layer having a magnetic watermark of regions of distinctly aligned anisotropic magnetic particles. The use of different amounts of magnetization will produce different ratios of remanence in a layer having such a watermark but not in an homogenous layer.
REFERENCES:
patent: 2254933 (1941-09-01), Bryce
patent: 3627934 (1971-12-01), Riddle
patent: 3702133 (1972-11-01), Vibert et al.
patent: 3873975 (1975-03-01), Miklos et al.
patent: 3927393 (1975-12-01), Fayling
Corcoran Robert J.
E M I Limited
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