Communications: electrical – Systems – Call station
Patent
1975-02-20
1976-11-02
Trafton, David L.
Communications: electrical
Systems
Call station
324 41, 340258R, G08B 1324
Patent
active
039900657
ABSTRACT:
Apparatus and method for detecting the presence, in an inspection area, of a marker tag having preselected properties. Transfer of articles from a protected area can be monitored by coupling a marker tag with each article and by including an inspection area in all transfer paths. In a theft detection system, the coupled marker tag can be removed or made inoperative in some manner for authorized withdrawal of an article from the protected area.
The marker tag is comprised of a small, thin strip of magnetic material. A time-varying magnetic field is provided for interacting with a marker tag located in the inspection area. The magnetic field, which includes components having frequencies f.sub.1 and f.sub.2, has a time-dependent spatial orientation which permits interaction with a marker tag having an arbitrary orientation in the inspection area. The magnetic field components of frequency f.sub.2 produce changes in the magnetic properties of the marker tag, resulting in the generation of a signal having components of frequencies f.sub.1 .+-.2f.sub.2.
When the magnitude and phase of the signal having the component f.sub.1 + 2f.sub.2 falls within a range of values of magnitude and phase peculiar to the marker tag, an alarm is activated by signal detection apparatus. The restricted nature of the signals producing an alarm effectively distinguishes a marker tag from signals produced by other objects in the inspection area.
REFERENCES:
patent: 3707711 (1972-12-01), Cole et al.
patent: 3747086 (1973-07-01), Peterson
patent: 3765007 (1973-10-01), Elder
patent: 3820104 (1974-06-01), Fearon
patent: 3838409 (1974-09-01), Minasy et al.
Auger Robert
Holzinger Carl S.
Purinton Edwin C.
Barbee Joe E.
Briody Thomas A.
Streeter William J.
The Magnavox Company
Trafton David L.
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