RF METAL DETECTOR AND ELECTRONIC ARTICLE SURVEILLANCE SYSTEM USING SAME

• US 20130169466A1
• Filed: 08/23/2011
• Published: 07/04/2013
• Est. Priority Date: 08/25/2010
• Status: Active Grant

• Current Assignee: Clairvoyant Technology, Inc.
• Original Assignee: Clairvoyant Technology LLC
• Inventors: Frederick, Thomas J.
• Granted Patent: US 9,171,440 B2
• Time in Patent Office: Days
• US Class Current: 342/22
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: G01S 13/56 for presence detection presence detection using near field arrangements G01V3/00, e.g. G01V3/08, G01V3/12; burglar, theft or intruder alarms with electrical actuation G08B13/22 - G08B13/26
• CPC Class Codes: G01S 13/86 Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
• CPC Class Codes: G01S 13/887 for detection of concealed objects, e.g. contraband or weapons
• CPC Class Codes: G08B 13/2402 Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting mechanical aspects of the tags, e.g. related to locking E05B73/0017; RFID readers G06K7/00; RFID tags G06K19/00; access control systems G07C9/00; anti-theft control in point of sale systems G07G3/003; security seals G09F3/03
• CPC Class Codes: G08B 13/2448 Tag with at least dual detection means, e.g. combined inductive and ferromagnetic tags, dual frequencies within a single technology, tampering detection or signalling means on the tag
• 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 radio frequency (RF) metal detector and an electronic article surveillance (EAS) system are disclosed. The RF metal detector in example embodiments transmits an RF signal. A receiver measures the power and phase of the signal as reflected from metallic objects in an interrogation zone. The RF metal detector can be deployed in a combined system that performs multiple functions. For example, the RF metal detector can be integrated with an EAS system that also sends RFID commands and receives RFID responses. In some embodiments the metal detector can discriminate between moving metal objects and stationary metal objects, and/or discriminate between objects in the interrogation zone and objects outside the interrogation zone. An antenna or antennas can be connected in a mono-static or bi-static configuration and the phase and power signals can be either DC-coupled or AC-coupled into the system through a mixer.

Claims

1. A metal detector comprising:

a transmitter to transmit a continuous wave incident radio frequency (RF) signal;

a receiver to receive a reflected RF signal; and

a processor connected to the transmitter and the receiver, wherein the processor is operable to detect metal objects by processing at least a portion of the reflected RF signal.

2. The metal detector of claim 1 further comprising an antenna connected to the transmitter and the receiver.

3. The metal detector of claim 2 wherein the antenna further comprises a plurality of antennas.

4. The metal detector of claim 2 wherein the processor is further operable to discriminate between moving metal objects and stationary metal objects using phase and power measurements of the reflected RF signal received by the plurality of antennas over time.

5. The metal detector of claim 3 wherein the plurality of antennas can be arranged on different sides of an interrogation zone and the processor is operable to use the plurality of antennas when so arranged to discriminate between objects in the interrogation zone and objects outside the interrogation zone.

6. The metal detector of claim 2 further comprising a coupler disposed between the plurality of antennas and the transmitter and the receiver to enable the plurality of antennas to be used for both sending the continuous wave incident RF signal and receiving the reflected RF signal.

7. The metal detector of claim 3 wherein some of the antennas are connected to the receiver and other of the antennas are connected to the transmitter.

8. The metal detector of claim 1 further comprising:

a mixer connected to the receiver;

an analog-to-digital converter connected to the processor; and

a lowpass filter connected between the mixer and the analog-to-digital converter to DC couple the reflected RF signal to the analog-to-digital converter.

9. The metal detector of claim 1 further comprising:

a mixer connected to the receiver;

an analog-to-digital converter connected to the processor; and

a bandpass filter connected between the mixer and the analog-to-digital converter to AC couple the reflected RF signal to the analog-to-digital converter; and

wherein the transmitter is further operable to modulate the continuous wave incident RF signal with a low-correlation signal.

10. The metal detector of claim 3 further comprising:

a mixer connected to the receiver;

an analog-to-digital converter connected to the processor; and

a lowpass filter connected between the mixer and the analog-to-digital converter to DC couple the reflected RF signal to the analog-to-digital converter.

11. The metal detector of claim 3 further comprising:

a mixer connected to the receiver;

an analog-to-digital converter connected to the processor; and

a bandpass filter connected between the mixer and the analog-to-digital converter to AC couple the reflected RF signal to the analog-to-digital converter; and

wherein the transmitter is further operable to modulate the incident RF signal with a low-correlation signal.

12. A system comprising:

a receiver to receive a returned RF signal;

a transmitter to transmit an incident radio frequency (RF) signal modulated with radio frequency identification (RFID) commands; and

a processor connected to the transmitter and the receiver, wherein the processor is operable to both detect metal objects and determine RFID responses by processing at least a portion of the returned RF signal.

13. The system of claim 12 further comprising a digital-to-analog converter to modulate the incident RF signal with the RFID commands.

14. The system of claim 12 further comprising an antenna connected to the transmitter and the receiver.

15. The system of claim 14 wherein the processor detects metal objects by measuring phase and power of the returned RF signal during an RFID receive slot.

16. The system of claim 14 wherein the antenna further comprises a plurality of antennas.

17. The system of claim 14 wherein the processor is further operable to discriminate between moving metal objects and stationary metal objects using phase and power measurements of the returned RF signal received by the plurality of antennas over time.

18. The system of claim 17 wherein the processor makes the phase and power measurements during an RFID receive slot.

19. The system of claim 16 wherein the plurality of antennas can be arranged on different sides of an interrogation zone and the processor is operable to use the plurality of antennas when so arranged to discriminate between objects in the interrogation zone and objects outside the interrogation zone.

20. The system of claim 14 further comprising a coupler disposed between the plurality of antennas and the transmitter and the receiver to enable the plurality of antennas to be used for both sending the incident RF signal and receiving the returned RF signal.

21. The system of claim 16 wherein some of the antennas are connected to the receiver and other of the antennas are connected to the transmitter.

22. A method of detecting objects using radio frequencies, the method comprising:

transmitting an incident radio frequency (RF) signal;

measuring a phase and a power in a returned RF signal;

comparing the phase and the power over time to entry criteria;

making an entry determination as to when the phase and the power over time meet the entry criteria for a specified period of time; and

signaling that a metal object has been detected based on the determination.

23. The method of claim 22 further comprising making an exit determination as to whether the power meets an exit criteria for an additional period of time prior to the signaling that a metal object has been detected.

24. The method of claim 23 further comprising:

modulating the incident RF signal with an RFID command; and

extracting an RFID response from the returned RF signal.

25. The method of claim 23 wherein the making of the exit determination comprises making the exit determination for a plurality of antennas sensing the returned RF signal.

26. The method of claim 25 further comprising:

modulating the incident RF signal with an RFID command; and

extracting an RFID response from the returned RF signal.

27. Apparatus comprising:

means for transmitting an incident radio frequency (RF) signal;

means for measuring a phase and a power in a returned RF signal;

means for comparing the phase and the power over time to entry criteria;

means for determining when the phase and the power over time meet the entry criteria for a specified period of time; and

means for signaling that a metal object has been detected, the means for signaling being responsive to the means for determining.

28. The apparatus of claim 27 further comprising means for evaluating whether the power meets an exit criteria for an additional period of time, wherein the means for signaling is further responsive to the means for evaluating.

29. The apparatus of claim 28 further comprising:

means for modulating the incident RF signal with an RFID command; and

means for extracting an RFID response from the returned RF signal.

30. The apparatus of claim 28 wherein the means for determining and the means for evaluating are operably responsive to the returned RF signal as sensed at a plurality of antennas.

31. The apparatus of claim 30 further comprising:

means for modulating the incident RF signal with an RFID command; and

means for determining an RFID response from the returned RF signal.