Variable frequency RF electronic surveillance system
US4531117A · kind A · utility
50Cited by
7References
44Claims
0Family size
Assignee
Inventors
Key dates
| Filing date | Jul 5, 1983 |
| Grant date | Jul 23, 1985 |
| Priority date | — |
| Expiry date | Jul 5, 2003 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B13/2488
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
An electronic article surveillance system is disclosed, having a transmitter means for producing in an interrogation zone sequences containing a plurality of discrete different radio frequencies thereby causing a circuit present within the zone to resonate at its resonant frequency in response to energy absorbed at at least three different frequencies. A receiver means is provided to cause an alarm in the event of detection of three such resonances over two successive sequences.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.