Dual antenna coil transponder system

• US 20050087599A1
• Filed: 11/01/2002
• Published: 04/28/2005
• Est. Priority Date: 11/02/2001
• Status: Active Grant

• Current Assignee: Avid Identification Systems, Inc. (Avid Technology Incorporated)
• Original Assignee: Avid Identification Systems, Inc. (Avid Technology Incorporated)
• Inventors: Ward, William H., Ward, Timothy Jon
• Granted Patent: US 7,347,379 B2
• Time in Patent Office: Days
• US Class Current: 235/451
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: G08B 13/2477 Antenna or antenna activator circuit
• CPC Class Codes: H01Q 1/2208 associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems methods or arrangements for sensing record carriers, e.g. for reading patterns G06K7/00; record carrier for use with machines and with at least a part designed to carry digital markings G06K19/00
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

The present invention relates to a dual antenna coil identification system, and more particularly, to an interrogator or reader for inductively coupling to a transponder and thereby extract data from the transponder. The magnetic field required to energize a transponder is generated by currents flowing through two essentially identical but opposite phased antenna coils arranged near the area where tags are to be read.

Claims

1. An interrogator for a radio frequency identification device comprising,

an antenna driver circuit;

a first antenna;

a second antenna; and

a splitter circuit communicatively coupled to said antenna driver circuit such that said splitter circuit splits a drive current generated by said antenna driver circuit into substantially similar first and second antenna currents directed to said first and second antennas, respectively.

4. The interrogator according to an of claims 1 to 3 further comprising a difference current detector communicatively coupled to said splitter to obtain a signal derived from a field differential between the first antenna as compared to the second antenna.

5. The interrogator according to any of claims 1 to 3 wherein the difference current detector is a differential transformer.

6. The interrogator according to any of claims 1 to 3 further comprising a receiver to receive the signal derived from the field differential and a decoder to process the signal to obtain encoded information.

7. The interrogator according to any of claims 1 to 3 where the receiver further includes an auto-nulling circuit to null any offset between current in the first antenna and the second antenna.

8. The interrogator according to any of claims 1 to 3 wherein said splitter further includes an antenna balance circuit to adjust the first and second antennas so that the driving signals to the first and second antennas are substantially equivalent.

9. The interrogator according to any of claims 1 to 3 further comprising an auto-tuning circuitry to tune the drive current provided to the first and second antennas to a desired resonance.

2. An interrogator comprising,

an antenna driver circuit;

a splitter circuit communicatively coupled to the antenna driver circuit to receive a drive signal and split the drive signal into balanced drive signals;

a first antenna communicatively coupled to the splitter circuit to receive said first balanced drive signal;

a second antenna communicatively coupled to the splitter circuit to receive said second balanced drive signal; and

a receiver communicatively coupled to the first and second antennas to receive and decode a transponder signal obtained by said first and second antennas.

3. A field effect detector/interrogator to detect a variations in an electro magnetic field comprising;

an antenna driver;

a first antenna;

a second antenna; and

a splitter circuit communicatively coupled to said antenna driver such that said splitter splits a drive current signal generated by said antenna driver into a substantially similar first and second antenna drive signals directed to said first and second antennas respectively; and

a difference current detector communicatively coupled to said splitter to measure any differential currents imposed on the first and second antennas.