ELECTRONIC ARTICLE SURVEILLANCE SYSTEM WITH METAL DETECTION CAPABILITY AND METHOD THEREFOR

• US 20100001872A1
• Filed: 06/26/2009
• Published: 01/07/2010
• Est. Priority Date: 07/07/2008
• Status: Active Grant

• Current Assignee: Sensormatic Electronics LLC (Johnson Controls International plc)
• Original Assignee: Sensormatic Electronics Corporation (Johnson Controls International plc)
• Inventors: NARLOW, Douglas A., SOTO, Manuel A., LIAN, Ming-Ren
• Granted Patent: US 8,704,638 B2
• Time in Patent Office: Days
• US Class Current: 340/661
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• CPC Class Codes: G08B 13/248 EAS system combined with another detection technology, e.g. dual EAS and video or other presence detection system

Abstract

A method for detecting metal using an electronic article surveillance (“EAS”) system. The EAS system includes a transmitter and a receiver. An EAS interrogation signal is transmitted to establish the interrogation zone. The EAS interrogation signal is used to detect EAS markers and metal objects within the interrogation zone. The EAS signal is received and a metal object present in the interrogation zone is detected during a metal detection cycle. The metal object is detected based upon perturbations in the received EAS interrogation signal. The metal detection cycle is periodically interspersed with at least one EAS detection cycle.

Claims

1. A method for detecting metal using an electronic article surveillance (“

EAS”

) system, the EAS system including a transmitter and a receiver, the method comprising;

transmitting an EAS interrogation signal, the EAS interrogation signal establishing an interrogation zone and being used to detect EAS markers and metal objects within the interrogation zone;

receiving the EAS signal; and

detecting a metal object present in the interrogation zone during a metal detection cycle based upon perturbations in the received EAS interrogation signal, the metal detection cycle periodically interspersed with at least one EAS detection cycle.

2. The method of claim 1, further comprising detecting an EAS marker signal during the at least one EAS detection cycle.

3. The method of claim 2, wherein the metal detection cycle includes a metal detection window during which both the transmitter and the receiver are operating.

4. The method of claim 3, wherein the at least one EAS detection cycle includes:

a transmission window, during which the transmitter is operating and the receiver is not operating; and

a receive window, during which the receiver is operating and the transmitter is not operating.

5. The method of claim 1, wherein detecting a metal object includes:

determining a first voltage of the received EAS interrogation signal when a metal object is not in proximity to the EAS system;

comparing a second voltage of the received EAS interrogation signal to the first voltage; and

responsive to determining that the second voltage is less than the first voltage, determining that the metal object is present.

6. The method of claim 5, wherein the second voltage is less than the first voltage by at least a predetermined threshold.

7. The method of claim 1, wherein responsive to detecting the metal object present in the interrogation zone, the method further comprises triggering an alarm.

8. The method of claim 7, further comprising:

determining whether the metal object is magnetic; and

responsive to determining the metal object is magnetic, suppressing the alarm.

9. A system for electronic article surveillance (“

EAS”

) comprising;

a transmitter operable to transmit an EAS interrogation signal, the EAS interrogation signal establishing an interrogation zone and being used to detect EAS markers and metal objects within the interrogation zone;

a receiver operable to receive the EAS interrogation signal; and

a metal detector operable to detect a metal object in proximity to the EAS system during a metal detection cycle based upon perturbations in the received EAS interrogation signal, the metal detection cycle periodically interspersed with at least one EAS detection cycle.

10. The system of claim 9, further comprising a controller electrically connected to the transmitter, to the receiver and to the metal detector, the controller operable to detect an EAS marker signal during the at least one EAS detection cycle.

11. The system of claim 10, wherein the metal detection cycle includes a metal detection window during which both the transmitter and the receiver are operating.

12. The system of claim 11, wherein the at least one EAS detection cycle includes:

a transmission window, during which the transmitter is operating and the receiver is not operating; and

a receive window, during which the receiver is operating and the transmitter is not operating.

13. The system of claim 9, wherein the metal detector detects the metal object by:

determining a first voltage of the received EAS interrogation signal when a metal object is not in proximity to the EAS system;

comparing a second voltage of the received EAS interrogation signal to the first voltage; and

responsive to determining that the second voltage is less than the first voltage, determining that the metal object is present.

14. The system of claim 13, wherein the second voltage is less than the first voltage by at least a predetermined threshold.

15. The system of claim 9, further comprising an alarm, wherein responsive to detecting the metal object present in the interrogation zone the metal detector is further operable to trigger the alarm.

16. The system of claim 15, further comprising a magnetic material detector operable to:

determine whether the metal object is magnetic; and

responsive to determining the metal object is magnetic, suppress the alarm.

17. The system of claim 9, wherein the receiver includes:

two receiving antennas; and

a differential amplifier having two input connection and an output connection, each input connection electrically coupled to a corresponding one of the receiving antennas;

the metal object is detected by determining that a voltage of the output connection exceeds a predetermined threshold.

18. A metal detection system comprising:

a transmitter operable to generate an electromagnetic signal during a transmission window, the electromagnetic signal establishing an interrogation zone and being used to detect electronic article surveillance (“

EAS”

) markers and metal objects within the interrogation zone;

a receiver operable to detect a signal received from an EAS marker during a detection window; and

a metal detector operable to detect a metal object in proximity to the interrogation zone during the transmission window based upon perturbations in the electromagnetic signal created by the metal object.

19. The system of claim 18, wherein the metal detector detects the metal object by:

determining a first voltage of the received electromagnetic signal when a metal object is not in proximity to the interrogation zone;

comparing a second voltage of the received electromagnetic signal to the first voltage; and

responsive to determining that the second voltage is less than the first voltage, determining that the metal object is present.

20. The system of claim 19, further comprising:

an alarm, wherein responsive to detecting the metal object present in the interrogation zone the metal detector is further operable to trigger the alarm; and

a magnetic field detector operable to determine whether the metal object is magnetic, and responsive to determining that the metal object is magnetic, the metal detector is further operable to suppress the alarm.