Magnetic detector for security document
US6257488A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 2, 1999 |
| Grant date | Jul 10, 2001 |
| Priority date | — |
| Expiry date | Jul 2, 2019 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG07D7/04
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
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 have such a long and thin form that their demagnetization factor N is smaller than 1/250, they have a diameter smaller than 30 micrometer, and they a magnetic saturation field greater than 100 A/m. Apparatus includes an emitter which emits an electromagnetic source signal of one or more particular base frequencies to the substrate (e.g., so that any magnetic elongated particles present go into a non-linear part of a B-H curve for at least part of cycle of the source signal). Apparatus also includes a detector that detects an electromagnetic detection signal emanating from the substrate for examining the detection signal for the presence of particular higher harmonics of the base frequencies or of any linear combination of the base frequencies or of the harmonics, particular higher harmonics being indicative of the presence of the magnetic elongated particles.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.