Patent ID: 6257488
Filing Date: 2001-07-10
Classification: G06K,G07D,G07F

Abstract:
A detection apparatus for detecting the presence of magnetic elongated particles in a substrate, the base material of the substrate having magnetic properties substantially differing from the corresponding magnetic properties of the elongated particles, the elongated particles having such a long and thin form that their demagnetization factor N is smaller than 1/250, having a diameter smaller than 30 micrometer and having a magnetic saturation field greater than 100 A/m, said apparatus comprising:a) means for emitting a source signal of one or more base frequencies to said substrate;b) means for detecting a detection signal emanating from said substrate; andc) a signal processor for examining the detection signal for the presence of any particular higher harmonics of said base frequencies or of any linear combination of said base frequencies or of said harmonics, said particular higher harmonics being indicative of the presence of said magnetic elongated particles.