Apparatus and method for metal detection using radio frequency reflection

• US 9,171,440 B2
• Filed: 08/23/2011
• Issued: 10/27/2015
• Est. Priority Date: 08/25/2010
• Status: Active Grant

• Current Assignee: Clairvoyant Technology, Inc.
• Original Assignee: Clairvoyant Technology LLC
• Inventors: Frederick, Thomas J.
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US13/813,464
• Publication Number:
  US 20130169466A1
• Time in Patent Office: 1,526 Days
• Field of Search: 324326-329
• US Class Current: 1/1
• 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 system comprising:

a receiver to receive a returned RF signal including a carrier signal reflected from a metal object;

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 to extract modulated RFID responses from the returned RF signal to detect an RFID tag, and detect metal objects by measuring at least one parameter of the carrier signal in the returned RF signal.

2. The system of claim 1 further comprising a digital-to-analog converter connected to the processor to control modulation of the incident RF signal with the RFID commands.

3. The system of claim 1 further comprising an antenna connected to at least one of the transmitter and the receiver.

4. The system of claim 3 wherein the at least one parameter includes phase and power of the carrier signal.

5. The system of claim 3 wherein the antenna fluffier comprises a plurality of antennas.

6. The system o claim 5 wherein the processor uses the plurality of antennas when arranged on different sides of an interrogation zone with the plurality of antennas arranged in different sides to discriminate betwen objects in the interrogation zone and objects outside the interrogation zone.

7. The system of claim 5 wherein some of the antennas are connected to the receiver and other of the antennas are connected to the transmitter.

8. The system of claim 3 wherein the processor discriminates between moving metal objects and stationary metal objects by measuring phase and/or power over time.

9. The system of claim 8 wherein the processor measures the phase and/or power during an RFID receive slot.

10. The system of claim 3 further comprising a couplet disposed between the antenna and the transmitter and the receiver to enable the antenna to he used for both sending the incident RF signal and receiving the returned RF signal.

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

transmitting an incident radio frequency (RF) signal;

modulating the incident RF signal with an RFID command;

extracting an RFID response from the returned RF signal;

measuring a phase and a power of a carrier signal of 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.

12. The method of claim 11 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 the metal object has been detected.

13. The method of claim 12 wherein the making of the exit determination comprises making the exit determination using a plurality of antennas sensing the returned RF signal.

14. Apparatus comprising:

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

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

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

means for measuring a phase and a power of a carrier signal of 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.

15. The apparatus of claim 14 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.

16. The apparatus of claim 15 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 connected to the means for measuring.