METHOD AND APPARATUS FOR ACTUATING AN ELECTRIC CIRCUIT

• US 3,740,742 A
• Filed: 05/11/1971
• Issued: 06/19/1973
• Est. Priority Date: 05/11/1971
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: Joseph W. Griffith, Thomas F. Thompson
• Inventors: Thompson, Thomas F., Griffith, Joseph W.
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): Swann, III, Glen R.
• Application Number:
  US05/142,132
• Time in Patent Office: 770 Days
• Field of Search: 340/280,258D,258B,258C,408,224,152T 325/29,8 128/2.1A 343/6.8R
• US Class Current: 340/572.3
• CPC Class Codes: G08B 13/2414 using inductive tags
• CPC Class Codes: G08B 13/2471 Antenna signal processing by receiver or emitter
• CPC Class Codes: G08B 13/2477 Antenna or antenna activator circuit

Abstract

A field of electrostatic, electromagnetic or high frequency radiant energy is provided on a predetermined intermittent cycle in a confined space through which persons are directed. A tuned resonant circuit, concealed on merchandise being carried through the space, is activated by the energy field. During the time interval when the energy field is cut off, the decaying electric signal from the tuned resonant circuit is radiated to a receiver. The received electric signal functions to activate an alarm.

Claims

1. Apparatus for activating an electric circuit, comprising a. resonant electrical energy absorbing and radiating means tuned to a predetermined frequency and operable upon cut-off of an electric energy field in which it is located to radiate a decaying electric signal at its tuned frequency, b. a radio frequency transmitter and a source of intermittent electric potential connected to the transmitter for intermittently activating the latter for producing an intermittent electric energy field in a predetermined space through which the energy absorbing and radiating means may pass, the transmitter being characterized by having no residual stored energy after a time, following cut-off of the energy field, less than the decay time of the decaying signal, c. electric signal detector means responsive only to said decaying electric signal to produce an electric output signal, the detector means being characterized by having no residual stored energy after a time, following cut-off of the energy field, less than the decay time of said decaying signal, and d. means for connecting said output signal to an electric circuit to be activated.

2. The apparatus of claim 1 wherein the resonant electrical energy absorbing and radiating means comprises a passive LC tuned resonant circuit.

3. The apparatus of claim 2 wherein the tuned resonant circuit is confined between sheets of dielectric material forming a flat laminated tag.

4. The apparatus of claim 2 wherein the tuned resonant circuit comprises two inductively coupled tuned resonant circuits, one tuned to the frequency of the detector means and the other tuned to a different frequency, and wherein the transmitter produces a radio frequency signal tuned to the same frequency as said other tuned circuit.

5. The apparatus of claim 1 for Activating an electric circuit for detecting stolen merchandise, wherein the resonant electrical energy absorbing and radiating means is attached to the merchandise.

6. The apparatus of claim 1 wherein the radio frequency transmitter includes an oscillator having a reference electrode controlled by low impedance resonant means tuned to a predetermined frequency, and energy absorbing means is associated with the resonant means for reducing its effective Q.

7. The apparatus of claim 6 wherein the resonant means comprises a series tuned LC circuit, and the energy absorbing means comprises resistance means arranged in shunt with the inductance of said LC circuit.

8. The apparatus of claim 1 including electric timing signal means interconnecting the radio frequency transmitter and the detector means and operable to render the detector means incapable of producing said output electric signal when the transmitter is turned on.

9. The apparatus of claim 1 wherein the radio frequency transmitter is tuned to the same frequency as the energy absorbing and radiating means, and the apparatus includes timer means synchronizing the transmitter and detector means for activating the detector means only during the time said transmitter is cut off.

10. The apparatus of claim 1 wherein the electric signal detector means includes an amplifier having a reference electrode controlled by low impedance resonant means tuned to the frequency of the decaying signal of the resonant electrical energy absorbing and radiating means, and energy absorbing means is associated with the resonant means for reducing its effective Q.

11. The apparatus of claim 10 wherein the resonant means comprises a series tuned LC circuit, and the energy absorbing means comprises resistance means arranged in shunt with the inductance of said LC circuit.

12. The apparatus of claim 1 wherein the radio frequency transmitter has a cut-off time equal to about one-half cycle of the resonant frequency of the energy absorbing and radiating means.

13. Apparatus for activating an electric circuit, comprising:

a. a loop of electrically conductive material forming a passive LC circuit, a portion of the loop comprising a material of lower melting point capable of being melted under the influence of a current density field, the LC circuit being tuned to a predetermined frequency and operable upon cut-off of an electric energy field in which it is located to radiate a decaying electric signal at its tuned frequency, b. electric field generating means for producing an intermittent electric energy field in a predetermined space through which the LC tuned resonant circuit may pass, the generating means being characterized by having no residual stored energy after a time, following cut-off of the energy field, less than the decay time of said decaying signal, c. electric signal detector means responsive only to said decaying electric signal to produce an electric output signal, the detector means being characterized by having a residual stored energy after a time, following cut-off of the energy field, less than the decay time of said decaying signal, and d. means for connecting said output signal to an electric circuit to be activated.

14. The apparatus of claim 13 wherein the lower melting material divides the loop into a closed loop portion and an open loop portion which defines the LC circuit.

15. The apparatus of claim 13 including means producing a current density field capable of melting said material of lower melting point.

16. Apparatus for activating an electric circuit, comprising:

a. resonant electrical energy absorbing and radiating means tuned to a predetermined frequency and operable upon cut-off of an electric energy field in which it is located to radiate a decaying electric signal at its tuned frequency, b. electric field generating means comprising a pair of spaced electrostatic plates and a source of intermittent electric potential connected to the Plates for intermittently charging the plates in opposite polarities, for producing an intermittent electric energy field in a predetermined space through which the energy absorbing and radiating means may pass, the generating means being characterized by having no residual stored energy after a time, following cut-off of the energy field, less than the decay time of said decaying signal, c. electric signal detector means responsive only to said decaying electric signal to produce an electric output signal, the detector means being characterized by having no residual stored energy after a time, following cut-off of the energy field, less than the decay time of said decaying signal, and d. means for connecting said output signal to an electric circuit to be activated.

17. The apparatus of claim 16 including electric shorting switch means connected across the plates and operable to interconnect the plates when the latter are not being charged, whereby to accelerate discharge of the plates and collapsing of the electrostatic field.

18. Apparatus of activating an electric circuit, comprising:

a. resonant electrical energy absorbing a radiating means tuned to a predetermined frequency and operable upon cut-off of an electric energy field in which it is located to radiate a decaying electric signal at its tuned frequency, b. electric field generating means for producing an intermittent electrostatic field in a predetermined space through which the energy absorbing and radiating means may pass, the electrostatic field having a collapse time of about one-half cycle of the resonant frequency of the energy absorbing and radiating means, the generating means being characterized by having no residual stored energy after a time, following cut-off of the energy field, less than the decay time of said decaying signal, c. electric signal detector means responsive only to said decaying electric signal to produce an electric output signal, the detector means being characterized by having no residual stored energy after a time, following cut-off of the energy field, less than the decay time of said decaying signal, d. means for activating the detector means only during the time said field is cut off, and e. means for connecting said output signal to an electric circuit to be activated.

19. Apparatus for activating an electric circuit, comprising:

a. resonant electrical energy absorbing and radiating means tuned to a predetermined frequency and operable upon cut-off of an electric energy field in which it is located to radiate a decaying electric signal at its tuned frequency, b. electric field generating means comprising a pair of spaced electromagnetic coils and a source of intermittent electric potential connected to the coils for intermittently energizing said coils, for producing an intermittent electric energy field in a predetermined space through which the energy absorbing and radiating means may pass, the generating means being characterized by having no residual stored energy after a time, following cut off of the energy field, less than the decay time of said decaying signal, c. electric signal detector means responsive only to said decaying electric signal to produce an electric output signal, the detector means being characterized by having no residual stored energy after a time, following cut-off of the energy field, less than the decay time of said decaying signal, and d. means for connecting output signal to an electric circuit to be activated.

20. The method of actuating an electric circuit for detecting stolen merchandise, comprising:

a. producing an intermittent electric energy field in a predetermined space through which customers are required to pass, b. attaching to said merchandise for introduction into said space a resonant electrical energy absorbing and radiating device tuned to a predetermined frequency and operable upon cut-off of said field to radiate a decaying electric signal at its tuned frequency, c. cutting off said energy field in a time less than the decay time of said decaying electric signal, d. detecting only said decaying electric signal to produce an output electric signal, e. utilizing said output electric signal to actuate an electric circuit, and f. subjecting the energy absorbing and radiating device to a radiant energy field sufficient to destroy its resonating characteristics prior to passage of the merchandise through said space, when said merchandise has been purchased by a customer.