05055659 is referenced by 150 patents and cites 13 patents.

A system for reading from and for writing data into electronic tags which may be associated with objects which are moving with respect to an interrogator, or may be located in fixed positions in the path of a moving interrogator. The interrogator, which is stationary if the tag is moving, sends a continuous RF signal to the remote tag. The tag backscatter-modulates the received RF signal with data temporarily or permanently stored in the tag, including, for example, data associated with the object to which the tag is attached, for example, its identity or contents. The system of this invention uses a very efficient encoding technique for the data which is backscatter-modulated by the tag and received by the interrogator. The backscatter-modulated signals are made up of signals of first and second frequencies f.sub.1 and 2f.sub.1, respectively, where the second frequency 2f.sub.1 is twice the first frequency f.sub.1, and where one of the two binary bits ONE and ZERO is represented by one-half period of a signal of the first frequency followed by one period of the second frequency, and the other of the two binary bits is represented by one period of a signal of the second frequency followed by one-half period of a signal of the first frequency. The signals also contain FRAME MARKERS made up of five periods of frequency 2f.sub.1 followed by one-half period of frequency f.sub.1.

Title
High speed system for reading and writing data from and into remote tags
Application Number
7/475729
Publication Number
5055659
Application Date
February 6, 1990
Publication Date
October 8, 1991
Inventor
Michael A Wolf
Los Alamos
NM, US
Donald F Speirs
San Juan
NM, US
Peter L Hendrick
Los Alamos
NM, US
Agent
Roger S Borovoy
Assignee
Amtech Technology
NM, US
IPC
G06K 7/10
G01S 13/76
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