05218189 is referenced by 139 patents and cites 18 patents.

A tag for identifying an item to which it is attached includes an inductance connected in parallel with a capacitance. The capacitance includes a plurality of individual capacitors, each of a predetermined different capacitance. The individual capacitors are connected to the inductance to establish a resonant circuit having a predetermined resonant frequency. At least one of the capacitors includes a dimple for shorting the capacitor when the tag is exposed to electromagnetic energy at the predetermined resonant frequency. The shorted capacitor establishes a second resonant frequency which may be used to identify which capacitor has become shorted. A binary "1" is assigned to either the shorted capacitor or the non shorted capacitor and a binary "0" is assigned to the capacitors which are not assigned a binary "1", the binary "1"s and "0"s combining to establish a numeric code uniquely associated with the tag.

Title
Binary encoded multiple frequency RF indentification tag
Application Number
7/756419
Publication Number
5218189
Application Date
September 9, 1991
Publication Date
June 8, 1993
Inventor
Donald W Hutchison
Wilmington
DE, US
Agent
Panitch Schwarze Jacobs & Nadel
Assignee
Checkpoint Systems
NJ, US
IPC
G06K 19/067
G06K 7/00
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