Signal-powered frequency-dividing transponder

5,517,179

08/443,477

May 18, 1995

A batteryless, portable frequency divider, such as used in presence detection systems for article surveillance or as used for article-location determination, includes a series LC resonant circuit connected directed across a parallel LC resonant circuit. One circuit is resonant at a first frequency and the other circuit is resonant at a second frequency that is a plural-integer-divided quotient of the first frequency. In one class of embodiments, either or both of the series and parallel resonant circuits includes a variable capacitance element, such as a varactor, in which the capacitance varies in accordance with the voltage across the variable capacitance element. The variation of the capacitance of the variable capacitance element in response to variations in energy in the higher-frequency resonant circuit resulting from receipt electromagnetic radiation at the first frequency causes the lower-frequency resonant circuit to transmit electromagnetic radiation at the second frequency. In another class of embodiments, the parallel circuit is resonant at the higher first frequency and the series circuit is resonant at the frequency-divided second frequency; the frequency divider includes a three-terminal semiconductor switching device having a control terminal, a reference terminal, and a controlled terminal, which is connected directly across both resonant circuits and between the inductance and the capacitance of the series resonant circuit and which switches on and off in response to variations in energy in the parallel resonant circuit resulting from the parallel resonant circuit receiving electromagnetic radiation at the first frequency to cause the series resonant circuit to transmit electromagnetic radiation at the second frequency.

Charlot, Jr., Lincoln H. (St. Petersburg, FL)

XLINK Enterprises, Inc. (St. Petersburg, FL)

I claim

1. A batteryless, portable frequency divider, comprising

a first resonant circuit including an inductance and a capacitance that is resonant at a first frequency for receiving electromagnetic radiation at a first frequency; and

a second resonant circuit including an inductance and a capacitance that is resonant at a second frequency that is 1/n the first frequency for transmitting electromagnetic energy at the second frequency, wherein "n" is an integer greater than one;

wherein one of the resonant circuits is a series resonant circuit and the other of the resonant circuits is a parallel resonant circuit;

wherein the one resonant circuit is connected directly across the other resonant circuit; and

wherein the frequency divider includes an element for causing the second resonant circuit to transmit electromagnetic radiation at the second frequency in response to variations in energy in the first resonant circuit's resulting from the first resonant circuit receiving electromagnetic radiation at the first frequency.

2. A batteryless, portable frequency divider according to claim 1, wherein the capacitance of one or both of the resonant circuits is a variable capacitance element in which the capacitance varies in accordance with the voltage across the variable capacitance element; and

wherein variation of the capacitance of the variable capacitance element in response to variations in energy in the first resonant circuit resulting from the first resonant circuit's receiving electromagnetic radiation at the first frequency causes the second resonant circuit to transmit electromagnetic radiation at the second frequency.

3. A frequency divider according to claim 2, wherein "n" is two.

4. A batteryless, portable frequency divider according to claim 1, comprising

a three-terminal semiconductor switching device having a control terminal, a reference terminal, and a controlled terminal;

wherein the first resonant circuit is a parallel resonant circuit and the second resonant circuit is a series resonant circuit; and

wherein the semiconductor switching device is connected directly across both resonant circuits and between the inductance and the capacitance of the series resonant circuit and switches on and off in response to variations in energy in the parallel resonant circuit resulting from the parallel resonant circuit's receiving electromagnetic radiation at the first frequency to cause the series resonant circuit to transmit electromagnetic radiation at the second frequency.

5. A frequency divider according to claim 4, wherein "n" is two.

6. A frequency divider according to claim 5, wherein the semiconductor switching device has its control terminal connected to a terminal common to the parallel resonant circuit and the capacitance of the series resonant circuit, its reference terminal connected to a terminal common to the parallel resonant circuit and the inductance of the series resonant circuit and its controlled terminal connected between the capacitance and the inductance of the series resonant circuit so that the inductance of the series resonant circuit is shunted during forward-biased half-cycles of the energy in the second resonant circuit, with the controlled terminal being reverse biased with respect to the reference terminal during alternate cycles so that no shunting then occurs, thereby enabling frequency division.

7. A frequency divider according to claim 5, wherein the semiconductor switching device has its controlled terminal connected to a terminal common to the parallel resonant circuit and the capacitance of the series resonant circuit, its reference terminal connected to a terminal common to the parallel resonant circuit and the inductance of the series resonant circuit and its control terminal connected between the capacitance and the inductance of the series resonant circuit so that the parallel resonant circuit is shunted during forward-biased half-cycles of the energy in the second resonant circuit, with the control terminal being reverse biased with respect to the reference terminal during alternate cycles so that no shunting then occurs, thereby enabling frequency division.

8. A tag for attachment to an article to be detected within a surveillance zone of an electronic article surveillance system, comprising

a frequency-dividing transponder for detecting electromagnetic radiation of a first predetermined frequency and responding to said detection by transmitting electromagnetic radiation of a second predetermined frequency that is a plural-integer-divided quotient of the first predetermined frequency;

a container for housing the transponder and

means for use in attaching the container to the article to be detected;

wherein the transponder comprises

wherein the frequency-dividing transponder includes an element that is responsive to variations in energy in the first resonant circuit resulting from the first resonant circuit's receiving electromagnetic radiation at the first frequency for causing the second resonant circuit to transmit electromagnetic radiation at the second frequency.

9. A tag according to claim 8, wherein the capacitance of one or both of the resonant circuits is a variable capacitance element in which the capacitance varies in accordance with the voltage across the variable capacitance element; and

10. A tag according to claim 9, wherein "n" is two.

11. A tag according to claim 8, comprising

a three-terminal semiconductor switching device having a control terminal a reference terminal, and a controlled terminal;

12. A tag according to claim 11, wherein "n" is two.

13. A tag according to claim 8, wherein the means for use in attaching the container include a clutch mechanism for receiving a pin in order to attach the container to the article to be detected.

14. A tag for attachment to a buried article to enable the buried article to be located by detecting the presence of said tag, comprising

a frequency-dividing transponder for detecting electromagnetic radiation of a first predetermined frequency and responding to said detection by transmitting electromagnetic radiation of a second predetermined frequency that is a plural-integer-divided quotient of the first predetermined frequency; and

a sealed container housing the transponder to protect the transponder from moisture;

15. A tag according to claim 14, wherein the capacitance of one or both of the resonant circuits is a variable capacitance element in which the capacitance varies in accordance with the voltage across the variable capacitance element; and

16. A tag according to claim 15, wherein "n" is two.

17. A tag according to claim 14, comprising

a three-terminal semiconductor switching device having a control terminal, a reference terminal, and a controlled terminal

18. A tag according to claim 17, wherein "n" is two.

19. A tag according to claim 14, wherein the article is attached to a buried conduit.

20. A tag according to claim 14, further comprising means for attaching the container to a conduit.

340/572; 363/157; 363/158; 363/163

G08B 13187

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