EAS system with alternating on/off transmitter operation and loop antenna

• US 5,327,118 A
• Filed: 09/08/1993
• Issued: 07/05/1994
• Est. Priority Date: 10/28/1992
• Status: Expired due to Term

• Current Assignee: Sensormatic Electronics LLC (Johnson Controls International plc)
• Original Assignee: Sensormatic Electronics Corporation (Johnson Controls International plc)
• Inventors: Morin, Sylvie R., Watkins, Harry E., Drucker, Frank
• Primary Examiner(s): SWANN III, GLEN R
• Application Number:
  US08/118,015
• Time in Patent Office: 300 Days
• Field of Search: 340/572, 340/571
• US Class Current: 340/572.7
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22
• CPC Class Codes: G08B 13/2488 Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver

Abstract

In an EAS system a transmitter alternately drives first and second antennas with the same coded message signal in its entirety. The antennas, in turn, transmit first and second signals each containing the coded message signal into respective first and second partially overlapping parts of an interrogation zone. Also disclosed is an antenna structure comprised of a plurality of loops extending one after the other and successive ones of which are of opposite phase. One of the loops circumscribes an area which is smaller than each of the other loops to realize reduced coupling to adjacent structures.

Claims

1. An EAS system for transmitting signals into and receiving signals from an interrogation zone comprising;

a first antenna, said first antenna when driven transmitting signals into a first part of said interrogation zone, said first part of said zone being less than said entire zone;

a second antenna, said second antenna when driven transmitting signals into a second part of said interrogation zone, said second part of said interrogation zone being less than said entire interrogation zone and partially overlapping with said first part of said interrogation zone;

and means for developing coded message signals and for alternatively driving said first and second antennas with the same coded message signal in its entirety, whereby said first and second antennas transmit first and second signals containing the same entire coded message signal into said first and second parts, respectively, of said interrogation zone.

2. An EAS tag in accordance with claim 1 further comprising:

a tag which is able to respond to each of the coded message signals and take on action based on that coded message signal.

3. An EAS system in accordance with claim 2 wherein:

each of said coded message signals contains an identifying preamble and a command;

and said tag is adapted to recognize said identifying preamble and to perform the action specified by said command.

4. An EAS system in accordance with claim 1 wherein:

said means includes;

a transmitter for developing said coded message signals;

a switch for selectively connecting said transmitter to said first and second antennas; and

control means for controlling said transmitter and said switch such that said transmitter generates a particular coded message signal and said switch alternately connects said transmitter to said first antenna and said second antenna so as to alternately drive said first and second antennas with said particular coded message signal.

5. An EAS system in accordance with claim 1 wherein:

said first and second antennas are situated on opposite sides of said interrogation zone.

6. An EAS system in accordance with claim 5 wherein:

said first and second parts of said interrogation zone overlap in a region which is centrally between said first and second antennas.

7. A method for use with an EAS system in which signals are transmitted into and received from an interrogation zone comprising;

providing a first antenna, said first antenna when driven transmitting signals into a first part of said interrogation zone, said first part of said zone being less than said entire zone;

providing a second antenna, said second antenna when driven transmitting signals into a second part of said interrogation zone, said second part of said interrogation zone being less than said entire interrogation zone and partially overlapping with said first part of said interrogation zone;

and developing coded message signals and alternately driving said first and second antennas with the same coded message signal in its entirety, whereby said first and second antennas transmit first and second signals containing the same entire coded message signal into said first and second parts, respectively, of said interrogation zone.