Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1981-09-04
1983-11-01
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
340522, G08B 1324
Patent
active
044132549
ABSTRACT:
A surveillance marker has a semiconductor connected between arms of a dipole antenna, one arm being of non-ferrous conductive material and the other of high permeability low coercivity material such as permalloy. Higher coercivity magnetizable pieces are disposed adjacent the low coercivity arm, and all is sandwiched between paper or other insulating layers. The marker is detected by a combination of RF field and low frequency magnetic field generating and receiving units that energize a master alarm only when both units simultaneously detect the marker signals. Magnetizing the higher coercivity pieces suppresses a signal that would otherwise be reradiated by the marker from the high permeability arm thereby rendering the marker undetectable.
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patent: 3983552 (1976-09-01), Bakeman, Jr. et al.
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patent: 4195286 (1980-03-01), Galvin
patent: 4209776 (1980-06-01), Frederick
patent: 4309697 (1982-01-01), Weaver
Pinneo George G.
Weaver Jon N.
Sensormatic Electronics Corporation
Swann III Glen R.
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