Resonant circuit tuning system with dynamic impedance matching

• US 20070296593A1
• Filed: 06/27/2006
• Published: 12/27/2007
• Est. Priority Date: 06/27/2006
• Status: Active Grant

• Current Assignee: Sensormatic Electronics LLC (Johnson Controls International plc)
• Original Assignee: Sensormatic Electronics LLC (Johnson Controls International plc)
• Inventors: Hall, Stewart E., Herring, Richard
• Granted Patent: US 7,570,220 B2
• Time in Patent Office: Days
• US Class Current: 340/572.7
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G08B 13/2477 Antenna or antenna activator circuit

Abstract

A resonant circuit tuning system and a method for tuning are provided. The resonant circuit tuning system may include a resonant circuit having a first capacitive element in series between a transmitter and an antenna coil and a second capacitive element in parallel with the transmitter and the antenna coil. At least one of the first capacitive element and second capacitive element may be configured to be varied. The resonant circuit tuning system also may include a controller for controlling a variable value of at least one of the first and second capacitive elements.

Claims

1. A resonant circuit tuning system comprising:

a resonant circuit having a first capacitive element in series between a transmitter and an antenna coil and a second capacitive element in parallel with the transmitter and the antenna coil, at least one of the first capacitive element and second capacitive element configured to be varied; and

a controller for controlling a variable value of at least one of the first and second capacitive elements.

2. A resonant circuit tuning system in accordance with claim 1 further comprising a variable inductive element connected in one of (i) a series arrangement with the antenna and (ii) magnetically coupled to the antenna.

3. A resonant circuit tuning system in accordance with claim 2 wherein the controller is configured to control at least one of the variable capacitive element and variable inductive element to adjust at least one of a resonant frequency and a resonant impedance of the resonant circuit.

4. A resonant circuit tuning system in accordance with claim 1 wherein the resonant circuit is configured in one of a series and a parallel arrangement.

5. A resonant circuit tuning system in accordance with claim 1 wherein the controller is configured to dynamically adjust at least one of the first capacitive element and second capacitive element based on a sensed current.

6. A resonant circuit tuning system in accordance with claim 1 wherein at least one of the first capacitive element and second capacitive element comprises a variable capacitor and the controller is configured to adjust a capacitance ratio.

7. A resonant circuit tuning system in accordance with claim 1 wherein the resonant circuit is configured to operate in connection with at least one of an Electronic Article Surveillance (EAS) system and a Radio Frequency Identification (RFID) system.

8. A transmitting antenna comprising:

a plurality of coils defining a transmission portion; and

a resonant tuning portion having at least one variable capacitive element and at least one variable inductive element together configured to control at least one of a resonant frequency and a resonant impedance of the transmission portion, the variable capacitive element in one of a series arrangement and parallel arrangement with a transmitter and the plurality of coils, and the inductive element in one of a series arrangement and magnetically coupled to the plurality of coils.

9. A transmitting antenna in accordance with claim 8 further comprising a controller configured to dynamically control the resonant tuning portion.

10. A transmitting antenna in accordance with claim 8 wherein the resonant tuning portion comprises a sensing point to sense at least one of a current and voltage of the plurality of coils.

11. A transmitting antenna in accordance with claim 8 wherein a first variable capacitive element is in series between the transmitter and the plurality of coils and a second variable capacitive element is in parallel with the plurality of coils.

12. A transmitting antenna in accordance with claim 8 further comprising a fixed value capacitive element in series between the transmitter and the plurality of coils and the at least one variable capacitive element is in parallel with the plurality of coils.

13. A transmitting antenna in accordance with claim 8 further comprising a controller configured to independently control one of a frequency shift and an impedance shift of the resonant tuning portion.

14. A transmitting antenna in accordance with claim 8 further comprising a controller configured to control both a frequency shift and an impedance shift of the resonant tuning portion.

15. A transmitting antenna in accordance with claim 8 wherein the resonant tuning portion is configured to operate in connection with at least one of an Electronic Article Surveillance (EAS) system and a Radio Frequency Identification (RFID) system.

16. A method for resonant tuning, the method comprising:

sensing at least one of a current and voltage of an antenna coil; and

adjusting a variable capacitive element of a resonant circuit tuning system to vary a resonant impedance of the coil based on the sensing, the variable capacitive element in one of a series arrangement and parallel arrangement with a transmitter and the antenna coil.

17. A method in accordance with claim 16 wherein the adjusting is performed dynamically.

18. A method in accordance with claim 16 further comprising adjusting a variable inductive element of a resonant circuit tuning system to vary a resonant frequency of the coil, the variable inductive element in one of a series arrangement and magnetically coupled to the antenna coil.

19. A method in accordance with claim 16 further comprising determining whether the antenna coil is within a tolerance based on the sensing.

20. A method in accordance with claim 16 wherein the adjusting is performed based on an environmental affect.