Method and apparatus for producing electromagnetic surveillance fields
US4795995A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 22, 1986 |
| Grant date | Jan 3, 1989 |
| Priority date | — |
| Expiry date | Sep 22, 2006 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B13/2488
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
A system for producing alternating electromagnetic fields for use in theft detection and surveillance systems, including an arrangement of field-generating inductance coils for disposition on opposite sides of a passage to be monitored by the electromagnetic field produced by such coils. In a preferred such arrangement, upper and lower coils are used on each side of the passage and such coils are mutually distinct from one another and separately energizeable so as to generate separate components of a resulting composite electromagnetic field. The upper and lower coils in each such set are preferably disposed in coplanar alignment with one another but have at least portions of one coil overlapping portions of the other, so as to enhance uniformity in the resulting electromagnetic field. The array of separately-energizeable coils provides for resultant flux vector variation in the magnetic field along three mutually orthogonal axes as a function of coil drive excitation phase variation. The specification further discloses preferred coil-drive circuitry for accomplishing such purposes.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.