US3740742A

US3740742A - Method and apparatus for actuating an electric circuit

Info

Publication number: US3740742A
Application number: US00142132A
Authority: US
Inventors: T Thompson; J Griffith
Original assignee: T Thompson; J Griffith
Current assignee: 3M Co
Priority date: 1971-05-11
Filing date: 1971-05-11
Publication date: 1973-06-19
Anticipated expiration: 1990-06-19

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.

Description

nite

States Patent 1191 Thompson et al.

1111 3,740,742 1 1 June 19,- 1973 METHOD AND APPARATUS FOR 1 ACTUATING AN ELECTRIC CIRCUIT [76] Inventors: Thomas F. Thompson, 3660 Harlow Road, Eugene, Oreg. 9740]; Joseph W. Griffith, 8705 S. W. White Court, Portland, Oreg. 97225 22 Filed: May 11, 1971 21 Appl. No.: 142,132

Related U.S. Application Data [63] Continuation-impart of Ser. No. 879,080, Nov. 24, 1969, abandoned, which is a continuation-in-part of Ser. No. 797,053, Feb. 6, 1969, abandoned.

[52] U.S. Cl 340/280, 340/258 C, 340/408,

' I 340/224, 343/6.8 R [51] Int. Cl. G08b 13/24 [58] Field of Search 340/280, 258 D, 258 B,

340/258 C, 408, 224, 152 T; 325/29, 8; 128/21 A; 343/68 R [56] References Cited 7/1959 Gille 343/68 R 3,218,638 11/1965 Honig 340/224 2,774,060 12/1956 Thompson..... 340/280 2,818,732 1/1958 Bennett 340/224 3,582,931 6/1971 Nawrocki... 340/258 3,493,955 2/1970 Mi'nasy Primary Examiner-D0na1d J. Yusko Assistant ExaminerGlen R. Swarm, III Attorney-Oliver D. Olson [5 7] 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.

20 Claims, 15 Drawing Figures CLIPPER CLlPPER ,L ALARM PAIENTEB JUN! 91975 SHEET 3 BF 3 AMPL. BIAS TIMING SIGNALS I E238 '272 l I E J in FIG. I4 270 SCHMIDT I TRIGGER f I 250 i 264 266 BIAS 252 TIMING SIGNALS SCHMIDT I TRIGGER ALARM COINCIDENCE AMPL- GATE I I 2 NED THOMAS F. THOMPSON REFE E E JOSEPH w GRIFFITH FIG.

INV NTQRS. BY

AGENT METHOD AND APPARATUS FOR ACTUATING AN ELECTRIC CIRCUIT CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION This invention relates to the actuation of electric ciredits, and more particularly to a novel method and apparatus for actuating an" electric circuit from a remote position. Specially, this invention relates to a method and apparatus for detecting stolen merchandise.

Various methods and devices have been employed heretofore to effect actuation of an electric circuit from a remote position. Among these is the method and apparatus disclosed in applicants earlier U.S. Pat. No..

2,774,060 over which the present invention represents an improvement. The method and apparatus of applicants earlier patent has many functions, including the detection of stolen merchandise, and involves the use of a tuned resonant circuit which, when placed in the field of an oscillator causes the oscillator to produce a change in potentialzwhich may be utilized to actuate an electric circuit. v i

Although apparatus of the type disclosed in applicants earlier patent is quite effective for the purposes intended, its effectiveness is somewhat limited by the shielding effects of extraneous objects placed in proximity to, the tunedcircuit, thereby limiting the effective range of operation of the apparatus.

Other methods and devices of the class described are generally characterized by being operable with a multiplicity of magnetic or electrically conductive objects of various shapes and sizes. Although such methods and apparatus may find utility in the actuation of certain types of electric circuits,they are of no value forvthe purpose of detecting stolen merchandise.

SUMMARY OF THE INVENTION In its basic concept the present invention involves the activation ofa tuned-electric energy absorbing and radiating device-by an intermittently generated field of electrostatic, electromagnetic or radio frequency radiant energy, whereby when the energy field is cut off the decaying electric signal from thetuned device is radiated to a receiver. The receiver electric signal functions to activate an electric circuit.

It is by virtue of the foregoing basic concept that the principal objective of the present invention is achieved, namely to overcome the disadvantages of prior methods and apparatus as described hereinbefore.

Another important object of the present invention is to provide apparatus of the class described in which the tuned device is a passive tuned resonant LC circuit in which means is provided for disabling the tuned resonant circuit after it has served its purpose.

A furtherimportant object of this invention is the provision of a novel tuned resonant circuit construction for use with the method and apparatus.

The foregoing and other objects and advantages of the present invention will appear-from the following detailed description, taken in connection with the accompanying drawings of-the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic electrical diagram, partly in block form, illustrating the method and one form of apparatus of the present invention.

FIG. 2 is a graphic representation of a plurality of waveforms of electric signals illustrating the operation of the apparatus of FIG. 1.

FIG. 3 is a plan view'of a merchandise tag having concealed therein, and illustrated by broken lines, a tuned resonant circuit embodying features of the present invention.

FIG. 4 is a fragmentary sectional view on a magnified scale taken on the line 44 in FIG. 3.

FIG. 5 is a schematic representation of means for disabling the tuned resonant circuit illustrated in FIGS. 3 and 4.

FIG. 6 is a schematic electrical diagram, partly in block form, illustrating the method and a second form of apparatus of the present invention.

FIG. 7 is a graphic representation of a plurality of waveforms of electric signals illustrating the operation of the apparatus of FIG. 6. 7

FIG. 8 is a schematic electrical diagram, partly in block form, illustrating the method and a third form of apparatus of the present invention.

FIG. 9 is a schematic electrical diagram, partly in block form, illustrating a still further modified form of apparatus embodying the features of this invention.

FIG. 10 is aplan view of an identification card having incorporated therewith means by which to activate the apparatus shown in FIG. 9.

FIG. 11 is a schematic diagram of another form of tuned resonant circuit concealed in a tag illustrated by brokenlines and embodying features of this invention.

FIGS. 12 and 13 are schematic representations of further modified forms of tuned resonant circuits embodying features of this invention.

FIG. 14 is a schematic electrical diagram, partly in block form, illustrating a still further modified form of apparatus embodying the features of this invention.

FIG. 15 is a schematic electrical diagram in block form illustrating a modification of the receiving component of the apparatus of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 of the drawings there is illustrated a pair of electrically conductive plates 10 and 12. These plates are separated a distance sufficient to define a space between them operable to receive at least one energy absorbing and radiating device, such as tuned resonant circuit 14. Thus, the plates may be spaced apart on opposite sides of a conveyor on which merchandise may travel. The spacing between plates alternatively may define an aisle in a department store or the like through which the customers must pass. As a still further alternative, the plates may be positioned adjacent the opposite walls of a room, whereby to activate all of the tuned resonant circuits carried by articles of merchandise contained in the room.

One of the plates 10 is connected to the positive terminal of a source 16 of direct current. The negative terminal of the source is connected to the plate of the switching tube 18, the cathode of which is grounded. The control grid of the tube is connected through the capacitor 20 to the output of the clipper circuit 22,

many types of which are well known in the art. The input of the clipper circuit is connected across the secondary winding 24 of the transformer 26. One end of this secondary winding is connected to ground. The primary winding 28 is connected to a source of alternating current, conveniently the 60 cycle, 110 volt conventional household source.

The other electrostatic plate 12 is connected to the negative terminal of the source 30 of direct current. The positive terminal of the supply source is connected to the cathode of the switching tube 32, the plate of which is connected to ground. The control grid of the tube is connected through the capacitor 34 to the output of the clipper circuit 36 the input of which is connected across the ungrounded secondary winding 38 of the transformer 26.

The positive electrostatic plate also is connected to the plate of the switching tube 40. The negative plate 12 is connected through the adjustable potentiometer 42 to the cathode of the switching tube 40. This cathode also is connected to one terminal of the source 44 of direct current. The other terminal of the supply source and the control grid of the switching tube 40 are connected through the capacitor 46 to the output of the clipper circuit 48. Although one clipper circuit may be sufficient, it is preferred that two or more clipper circuits be employed to provide the desired signal waveform described hereinafter. Thus, the input of the clipper circuit 48 is connected to the output of the associated clipper circuit 50 the input of which is connected across the secondary winding 52 of the transformer 26. The grounded end of this winding is the same as that of winding 24.

The secondary winding 54 of the transformer 26 is connected across the input of the clipper circuit 56 the output of which is connected to the radio frequency receiver 58 to effect activation of the latter. For example, the clipper output may be connected to provide bias voltage for the first r.f. stage of the receiver. The receiver antenna 60 functions to receive a corresponding radio frequency signal from a tuned resonant circuit 14, as described hereinafter, whereby to activate an alarm L or other electric load connected to an appropriate output of the receiver. For example, the load may be in an electric circuit controlled by a relay, the coil of which is connected through a rectifier to the output of the if stage of the receiver.

Although the resonant circuit 14 may be provided in a variety of forms well known in the art, the construction illustrated in FIGS. 3 and 4 is preferred. In this construction the resonant circuit is concealed between

laminated sheets

62 and 64 of paper, or other electrically non-conductive material, as follows: On the inside face of one sheet 62 there is formed an open loop 66 of electrically conductive metal such as copper, silver, etc. This may be provided by the well known technique of printed circuitry. On the inner side of the other sheet 64 there is similarly formed an arcuate segment 68 of the electrically conductive material. This segment is positioned on the sheet so that when the latter is superimposed over the first mentioned sheet 62, the arcuate segment 68 overlaps one end portion of the open loop 66. lnterposed between these overlapped portions is a film 70 of electrical insulation material. This may be provided in the form of a small plate bonded to one of the overlapping portions, or it may be in the form of a liquid material, such as thermoplastic resin, painted or otherwise deposited over the surface of one of the overlapping portions.

The arcuate segment 68 of electrically conductive material may be of sufficient length to overlap the opposite end of the open loop 66 to provide electrical conductivity therebetween when the two sheets are bonded together in superimposed relation. However, in the embodiment illustrated, the arcuate segment terminates short of the opposite end of the loop and electrical connection is provided by a length of lead or other electrically conductive fusible material 72. This length of fusible material preferably is of small cross section, such as a thread, and it may be formed as an extension of the arcuate segment, as illustrated, or as an extension of the opposite end of the open loop. In either case it functions as a fusible electrical connection between the arcuate segment and the end of the open loop opposite the overlapped portions.

The fusible connection serves the additional function of enabling the destruction of the tuned resonant circuit after it has served its purpose. Thus, referring to FIG. 5, when it is desired to destroy the tuned circuit it is placed in the field of the output coil 74 of an oscillator 76 which provides sufficient current to melt the fusible connection.

The L-C tuned circuit 14 is designed to provide a Q factor of sufficient magnitude as to effect appropriate activation of the receiver output circuit. Although the Q factor may vary over a considerable range, depending in part upon the sensitivity of the receiver, a Q factor of about 80 is satisfactory. Improvement of the Q factor of the tuned circuit may be achieved by depositing particles 78 (FIG. 3) of polyiron or other suitable material within the loop 66 prior to bonding the two

sheets

62 and 64 together.

Having formed the

segments

66 and 68 of the tuned circuit on the inner surfaces of the sheets, the latter are bonded together in superimposed relation, by means of a suitable adhesive, with the overlapped portions properly oriented and with the insulating layer between them. The completed tag is thin and flexible and may be used in the manner of a conventional price tag upon which appropriate pricing information may be printed.

The dimensions of the tuned circuit, and hence of the confining tag, may be varied over a considerable range, as desired. For example, the tuned circuit may be designed to have a resonant frequency of 10 megacycles, whereby the diameter of the loop will be about one-half inch. This may provide a tag of about three-quarters inch square.

The resonant frequency of the tuned circuit also may be selected from a wide range of radio frequencies most suitable for the use intended. The lower the frequency the larger the dimensions of the tuned circuit becomes but the lesser are the shielding effects imposed by extraneous objects. Thus, very low or very high radio frequencies may be employed for certain uses. For use with merchandise price tags a frequency of about 10 megacycles is quite satisfactory, although other frequencies may be employed.

In the operation of the apparatus illustrated in FIG. 1 let it be assumed that the electrostatic plates 10 and 12 are positioned on opposite sides of an aisle, downstream of a cashiers counter to which customers are directed. The receiver antenna 60 also is positioned downstream from the cashiers counter. Let it also be assumed that each piece of merchandise in the store has attached to it one of the tags concealing a tuned resonant circuit l4. The tag may be concealed within the merchandise, or it may take the form of a price tag attached in a visible place to the merchandise.

As a customer passes through the aisle and completes his purchases with the cashier, the cashiereither removes the tag from each piece of merchandise, or subjects the tuned circuit 14 to destruction by placing it in the field of the oscillator coil 74. Conveniently, this coil may be placed under the surface of the cashiers counter so that the tuned circuit will be destroyed merely by placing the merchandise on the counter. In either case the customer then may exit along the aisle between the electrostatic plates and 12 and past the receiver antenna 60 without incident.

Assume now that a person has concealed an article of merchandise with the intent of stealing it. Having completed his purchase of other articles at the cashier counter, he proceeds to exit from the aisle by passing between the plates 10 and 12 and by the receiver antenna 60. The apparatus then operates as follows:

The electrostatic plates 10 and 12 are charged positively and negatively, respectively, as indicated in FIG. 1, on an intermittent time cycle determined by the frequency of the alternating current supply to the primary winding 28 of the transformer. The waveform 80 (FIG.

2) illustrates the in-phase outputs of the

clipper circuits

22 and 36, and when the voltage reaches the level indicated by' the dash line

82'the switching tubes

18 and 32 are caused to conduct. Such conduction functions to complete the electric circuits of the direct current sup ply

sources

16 and 30, whereby to apply the corresponding charges'to the plates 10 and 12. The time interval T of conduction of the switching tubes is governed by the frequency of the alternating current supply at the primary winding, and this conveniently may be 60 cycles per second as mentioned hereinbefore.

The waveform 84- represents the output of the final clipper unit 48. This waveform is in phase opposition to waveform 80 by virtue of the opposed ground connections of windings 24 and 52. When the potential reaches the level indicated by the dash line 86 the switching tube 40 is caused to conduct. Conduction of this tube functions to provide an electrical short between the plates 10 and 12, thereby accelerating their discharge and collapse of the electrostatic field. The potentiometer 42 is adjusted to provide complete collapse of the electrostatic field in the time interval T between cutoff of conduction of the switching tubes 18,

32 and the attainment of maximumconduction of the switching tube 40. This time interval is chosen to represent one-half cycle of the resonant frequency of the tuned circuit 14.

The waveform 88 represents the output of the clipper 56. This waveform is in phase with waveform 84. When the potential reaches the level indicated by the dash line 90 the receiver 58 is activated. The time interval T between conduction of the switching tube 40 .and activation of the receiver provides sufficient time delay to insure against reception by the receiver of false signals due to collapsing of the electrostatic field and to insure reception by the receiver only of the signal radiated by the tuned circuit 14.

The damped waveform 92 represents the decaying radio frequency signal radiated by the tuned circuit. The decay of this signal commences upon complete collapse of the electrostatic field and, depending upon the Q factor of the tuned circuit, continues for a time T following activation of the receiver. The decaying signal following activation of the receiver activates the output circuit of the receiver to provide an electric signal to activate the alarm L. The alarm may be in the form of a lamp, a buzzer, a camera actuator and/or any other device suitable for the purpose intended.

Referring now to the embodiment illustrated in FIG. 6: The pair of electrostatic plates 10 and 12 previously described are replaced by electrically conductive coils and 102 to provide an electromagnetic field between them. In the preferred embodiment illustrated,

each of the coils of the pair consists of two'or more coils connected together in parallel to provide a very low Q factor.

In manner similar to the electrostatic plates, the pair of coils are spaced apart to define between them a space in which one or more tuned resonant circuits 14 may be placed for excitation on an intermittent cycle.

The coils are connected at one end to ground and at the other end to one terminal of a source 104 of direct current. The other terminal of the supply source is connected to the plate of the switching tube 106. The control grid of the tube is connected through the capacitor 108 to the output of the clipper circuit 110.'The input of the clipper unit is connected across the secondary winding 112 of the transformer 114 the primary winding 116 of whichis connected to a suitable source of alternating current as, for example, conventional 60 cycle household current. The other secondary winding 118 of the transformer is connected across the input of the clipper circuit 120 the output of which is connected to the receiver 122 for activating the latter on an intermittent cycle, 180 out of the phase with activation of the switching tube 106. As in the embodiment previously described, this is achieved by grounding the secondary windings 112 and 118 at opposite ends, as illustrated. The antenna 124 of the receiver functions to receive the signal radiated by the tuned resonant circuit 14 to effect activation of an alarm L.

Referring now to P16. 7, the waveform represents the output of the clipper circuit 110. When the potential reaches the level indicated by the dash line 132, the switching tube 106 is caused to conduct, thereby completing the electric circuit of the direct current supply 104 and energizing the coils 100 and 102 for the time interval T of conduction. The waveform 134 represents the output of the clipper circuit 120. When the potential reaches the level indicated by the dash line 136, the receiver 122 is activated for the time interval T The interval T of time between cutoff of conduction of the switching tube 106 and activation of the receiver 122 provides suff cient time delay to insure complete collapse of the electromagnetic field and thus insure reception by the receiver only of the decaying signal 92 radiated by the tuned circuit 14, as explained hereinbefore.

In the embodiment illustrated in HO. 8 the electrostatic plates of FIG. 1 and the electromagnetic coils of FIG. 6 are replaced by transmitter and receiver antennas and 142, respectively, spaced apart sufficiently to provide the desired energy field for activating one or more tuned resonant circuits 14. The transmitting antenna is associated with a transmitter 144, the input of which is connected to the output of the clipper circuit 146. The input of the clipper circuit is connected across the secondary winding 148 of the transformer 150, the primary winding 152 of which is connected to a suitable source of electric potential, as explained hereinbefore. The receiving antenna 142 is associated with a receiver 154 the input of which is connected to the output of the clipper circuit 156 having its input connected across the secondary winding 158 of the transformer 150. As in the previous embodiments, these transformer secondary windings are grounded at opposite ends so that the output waveforms from the clipper circuits activate the transmitter and receiver during different portions of the cycle, substantially in the manner illustrated by the waveforms of FIG. 7. Accordingly, a portion of the decaying signal 92 radiated by the tuned circuit 14 after the transmitter has been cut off is received by the receiver to activate an alarm L. It will be understood that the transmitter and the receiver are designed to operate on the same frequency as the resonant frequency of the tuned circuit 14.

FIG. 9 illustrates a further modified form of apparatus wherein three

receivers

160, 162 and 164 each are tuned to a different frequency for association with a correspondingly tuned

resonant circuit

166, 168 and 170, respectively, as is illustrated on the card 172 in FIG. 10. The outputs of the receivers are connected one to each of the relay coils 174, 176 and 178, respectively, the switch contacts 180, 182 and 184 of which are arranged in series in the electric circuit of a device L to be actuated. Accordingly, it will be apparent that in order to actuate the device all three tuned circuits must be present at one instant within the field of the antennas of the three receivers.

The apparatus of FIG. 9 may be employed for the detection of stolen merchandise, as well as for many other purposes. For example, it may be adapted for use in actuating a door lock, such as in private clubs, defense plants, parking lots and various other places where privacy or secrecy is to be maintained. For this purpose each person authorized to enter a restricted area is provided with an identification card or membership card, such as the card 172 illustrated in FIG. 10. As a matter of additional security, such cards may be changed from time to time to add or subtract tuned circuits, or to change the frequency characteristics thereof, in order to render previously issued cards obsolete. It will be understood, of course, that the receivers also will be adjusted to correspond to the frequencies of the tuned circuits in the newly issued cards.

In the embodiments previously described both the source of electric energy field and the receiver necessarily must have the characteristic that once they are turned off they must have no residual stored energy during the time of radiation of the decaying signal from the tuned circuit 14 or other energy absorbing and radiating device. Further, the source of intermittent electrical energy field must have the characteristic of cutting off in a time substantially less than the time during which the decaying signal is being radiated. The embodiments of FIGS. 14 and illustrate specific apparatus providing these characteristics.

Referring first to FIG. 14, the transistor 220 and transformer 222 represent an oscillator. One winding 224 of the transformer is connected to the transmitting antenna 226, a second winding 228 connects a source of direct current potential to the collector of the transistor, and the third winding 230 connects the base of the transistor to a source 232 of electric timing signals through an amplifier 234 and bias circuit 236. The timing signals may be provided by means of a conventional pulse generator, or other well known form of device providing timing signals, in the manner of the transformer and clipper arrangement described hereinbefore.

The desired frequency of oscillation of the transmit ter is established by providing a tuned reference elecv trode. In the embodiment illustrated this is provided by a low impedance resonant device 238 in the form of the series arrangement of inductor 240 and capacitor 242 connecting thetransistor emitter to ground. The inductor and/or capacitor are adjustable in order to establish the desired frequency of transmission providing the intermittent electric energy field.

Means is provided for insuring that the transmitter will be cutoff in a time substantially less than the time during which the decaying signal of the energy absorbing and radiating device 14 is being radiated. For this purpose, the capacitor 242 or, preferably, the inductor 240 is shunted by a resistor 244 of an appropriate value capable of reducing the effective Q of the series tuned circuit, i.e., reducing the energy storing capability of the inductor to a very low value. In this regard, at all frequencies other than that determined by the LC circuit, the impedance of the emitter circuit is high and therefore it has a high degenerative capability for all such other frequencies. However, at the frequency established by the LC circuit, the series impedance is low and the emitter is essentially at ground potential. Accordingly, any signal appearing on the base of transistor, by virtue of the transformer, becomes amplified.

In a typical application, the direct current resistance of the inductor 240 is, for example about 0.1 ohm, but at a frequency of for example megacycles it is about 10,000 ohms, and the series tuned impedance of the LC circuit at the resonant frequency is about 0.1 ohm. A shunting resistor 244 of about 200 ohms provides satisfactory results.

Means other than the shunting resistor 244, such as a ferrite bead, may be associated with the LC circuit for absorbing energy from the circuit and thereby reducing its effective Q.

The source of intermittent electric energy field may be obtained by means other than the transmitter previously described. For example, it may be a pulse transmitter providing a single spike of energy, or a saturable reactor, or any other type of device providing the amplification and phase shift requirements for an oscillator.

The LC circuit previously described is but one of many other suitable forms of series tuned devices capable of use for purposes of this invention. Crystals, mechanical filters and other low impedance resonant devices are examples. In any event, the source of intermittent electric energy field must be characterized by the absence of residual stored energy when turned off, as previously explained.

The receiver component of the apparatus illustrated in FIG. 14 is a selective energy detector synchronized with the operation of the transmitter by means of timing signals from the timer 232. These signals are fed through a bias circuit 246 and the winding 248 of an untuned transformer 250 ofa receiving antenna 252, to the base of amplifier transistor 254. The emitter of the transistor is connected to ground through a low impedance resonant device 256, again in the form of the series arrangement of inductor 258 and capacitor 260, in manner similar to the series tuned LC circuit previously described, with the inductor being shunted by the resistor 262. Thus, the low impedance series tuned LC circuit functions as part of the reference for the receiver amplifier at all frequencies other than the frequency established by the LC circuit. At this selected frequency, which is the same as the frequency of the decaying signal from the energy absorbing and radiating device, the emitter is held at a particular potential and therefore any signal of that selected frequency appearing at the base or control electrode is amplified.

Thus, the receiver component also is characterized by having no residual stored energy after a time, following cut-off of the energy field, substantially less than the decay time of the energy absorbing and radiating device 14.

The output signal from the receiver component may be utilized in any manner desired. In the embodiment illustrated, this output signal is applied to a Schmidt trigger circuit 264, silicone controlled rectifier, or other suitable device, the output of which functions to activate an alarm 266.

It will be apparent that the transistors previously described may be replaced by vacuum tubes, if desired. For example, the plateof a vacuum tube may be connected through the transformer winding 228' to a source of direct current potential, the control grid may be connected to the transformer winding 230 through the parallel arrangement of a capacitor and resistor, and the cathode may be connected to ground through the series tuned reference device 238.

With reference to the synchronized wave forms illustrated in FIG. 14, it will be understood that while the transmitter is turned on, by virtue of the positive timing signals 268, the receiver component is turned off by virtue of the negative timing signals 270. Similarly, after the transmitter has been turned off, during the interval between adjacent signals 268, the receiver component is turned on by the positive signals 272 for receiving the decaying signal radiating from the energy absorbing and radiating device.

Although the passivetuned resonant LC circuit 14 described hereinbefore is the preferred form of energy absorbing and radiating device, because of its simplicity, economy and'capability of being provided in the form of a substantially two dimensional tag, it will be understood that other forms of energy absorbing and radiating devices may be employed for applications in which the foregoing advantages are not required.

In the. receiver component illustrated in FIG. 14, there is shown a capacitor 274 across the antenna transformer winding 248. This capacitor may be a physical element, or it may represent stray capacitance. ln any event, it is desirable to shunt the winding 'with a resistor 276 in order to spoil the Q of the tuned circuit, in order for the receiver to have no residual stored energy, as previously explained.

FIG. 15 illustrates a modified form of receiver component for use in the apparatus of FIG. 14. As in the previous embodiment, the receiver includes an untuned high impedance amplifier 278 connected to the receivingantenna 252 and having its reference electrode connected to'ground through a low impedance resonant reference device 256. However, the output of the amplifier is fed to a coincidence gate 280, forming a part of the receiver, to which also is fed the timing signals from the timer 232. These timing signals function to operate the gate synthronously with the transmitter so as to select between the transmitter signal from the transmitter antenna 226 and the decaying signals from the energy absorbing and radiating device 14. Thus, during the time that the transmitter is on the timing signals to the coincidence gate disables the latter so that the transmitter signal received by the receiving antenna 252 and amplified by the amplifier, are not passed through to the Schmidt trigger 264 to cause activation of the alarm 266. However, during the time the transmitter is shut off, the timing signals function to enable the gate 280 to pass through to the Schmidt trigger the amplified decaying signal received by the receiving antenna 252 from the energy absorbing and radiating device 14.

As an alternative, through less efficient and therefore less desirable procedure by which to provide a conventional receiver with the characteristic of having no residual stored energy, means such as a diode or other electrically actuated switch may be arranged to shunt or open a tuned resonant antenna circuit, as by timing signals, during the period of time that the transmitter is turned on.

FIG. 11 illustrates another form of tuned resonant circuit usable with the various forms of apparatus described hereinbefore. In this embodiment two tuned resonant circuits are arranged to be inductively coupled to each other and preferably concealed in a tag 200 as in the manner previously described. Each tunedcircuit may be constructed in the manner of the tuned circuit illustrated in FIGS. 3 and 4. One of the tuned circuits comprises an open loop of electrically conductive metal forming cell 202 and capacitance 204. When employed with the apparatus of FIG. 8, it is tuned to the frequency of the transmitter 144. The other tuned circuit comprises an open loop forming coil 206 and capacitance 208 and it is tuned to the frequency of the receiver 154' which, for this purpose, is different from the frequency of the transmitter. Although these frequeneies may be harmonics, it is preferred that they not be, so as to insure against possible erroneous activation of the receiver.

It is well known that when the

tuned circuit

202, 204 is activated to oscillation, the closely coupled

circuit

206, 208 will oscillate at the same frequency as the

tuned circuit

202, 204. Then, if the flux energizing the

circuit

202, 204 is cut off, both

resonant circuits

202, 204 and 206, 208 will oscillate with a decaying wave at their own natural frequencies.

Accordingly, let it be assumed for purpose of explanation that the transmitter 144 and tuned

circuit

202, 204 are tuned to the frequency of megacycles and that the receiver and

tuned circuit

206, 208 are tuned to a frequency of megacycles. Thus, when the tag 200 isplaced in the radiation field of the transmitter antenna and the

tuned circuit

202, 204 is excited during the time that the transmitter 144 is energized, the

tuned circuit

206, 208 also will oscillate at the frequency of 100 megacycles. Then, when the transmitter 144 is cut off, by operation of the clipper 146, the

tuned circuit

202, 204 will transmit a damped wave at 100 megacycles and the tuned circuit 206,208 will transmit a damped wave at its natural frequency of 120 megacycles. Since the receiver 154 is tuned to the frequency of 120 megacycles, it will receive only the damped wave from the tuned circuit 206,208.

Since the receiver 154 receives only the damped wave transmitted by the tuned

circuit

206, 208 and is not activated by the transmitter 144 or tuned

circuit

202, 204, it will be apparent that the receiver may be operated continuously. Accordingly, the clipper circuit 156 in FIG. 8 may be omitted.

When the tuned resonant circuit of FIG. 11 is employed with the type of apparatus illustrated in FIGS. 1 and 6, it is necessary merely that the time of complete collapse of the electromagnetic or electrostatic field be adjusted, as by a potentiometer 42 in FIG. 1, to onehalf cycle of the resonant frequency of the tuned

circuit

202, 204. Thus, during the time interval that the energy field is being radiated, both tuned

circuits

202, 204, and 206, 208 resonate at the frequency of the

circuit

202, 204. When the energy field is cut off, both tuned circuits resonate at their own frequencies and therefore the damped wave from

tuned circuit

206, 208 is radiated for reception by the receiver, which may be operated continuously.

In this latter regard, it will be understood that since the tuned resonant circuit 14 is activated by the apparatus of FIGS. 1 and 6 by adjusting the field collapse time to substantially one-half cycle of the resonant frequency of the tuned circuit 14, it is desirable that the associated receiver 58 or 122 be activated only during the time the field is cut off, in order to insure against possible false activation of the receiver during collapse of the field.

FIGS. 12 and 13 illustrate still further forms of tuned resonant circuits which may be concealed in tags, and which are usable with the various forms of apparatus described hereinbefore. In FIG. 12 a printed circuit or other suitable form of electrically conductive metal is arranged to form a pair of interconnected inductive loops 210 and 212. A length of electrically conductive fusible material 214 bridges the metal between the loops 210 and 212, whereby to close the loop 210 and to complete the loop 212 which terminates at its spaced-apart ends in a capacitor 216. Loop 212 and capacitor 216 thus form an L-C circuit which is arranged to resonate at the same frequency as

receiver

58, 122 or 154.

Destruction of the tuned resonant circuit is accomplished by placing it in a strong magnetic field of, for example, conventional 60 cycle household alternating current. This causes a strong current to flow in the closed loop 210, resulting in melting of the fusible link 214. In this regard, since the impedance of the closed loop 210 at 60 cycles is substantially its direct current resistance, the current circulating in the loop is much higher, for a given wattage, than it would be at higher frequencies.

Upon melting of the link 214 the inductance of the open loop 212 is added to loop 210. The combination of this increased inductance with the capacitance 216 provides a tuned circuit which resonates at a lower frequency than previously provided by coil 212 and capacitor 216. Thus, although the-resonant circuit is destroyed effectively for use with the receivers previously mentioned, it may be rc-used at the lower resonant frequency in association with the similarly tuned receiver.

If it is desired to have the destroyed circuit re-usable at a frequency higher than that of coil 212 and capacitor 216, the arrangement illustrated in FIG. 13 may be provided. In this embodiment the fusible link 214 is made a part of the capacitor 216. Thus, upon melting of the link the capacitance of the capacitor 216 is lowered, whereby the resonant frequency of coil 212 and capacitor 216 is increased.

The various forms of apparatus described hereinbefore also may be employed to control the distribution of articles on a moving conveyor selectively to branch conveyors. For example, all articles intended for distribution to one location may be identified by attachment of tags having tuned circuits of the same resonant frequency, while other articles intended for distribution to another location may be identified with tags having tuned circuits of a different resonant frequency. Separate receivers, each corresponding in frequency to a different one of the tuned circuits, thus may function to actuate appropriate equipment to divert the articles on the main conveyor to the appropriate branch conveyors. Such an arrangement has many practical forms of use in commerce and industry. One such use is the selective distribution of luggage at air terminals.

It will be apparent to those skilled in the art that various changes may be made in the size, shape, arrangement, number, types and values of parts described hereinbefore. For example, the number of stages of clipper circuits may be varied to provide the waveform characteristics desired. The clipper circuits providing the substantially square waveforms illustrated may be replaced with sawtooth generators to provide sawtooth waveforms, or with various other well known circuits providing other desired waveforms. The vacuum tube circuitry illustrated may be replaced by transistor circuitry in well known manner.

Activation of the receiver for reception of the damped signal from the tuned resonant circuit has been exemplified hereinbefore by connection of the output of clipper 56 to provide bias voltage for the first r.f. stage of the receiver. Another procedure is to connect the clipper output to a shorting tube, in the manner of shorting tube 40, which is connected across the input resonant circuit of the receiver. In this case the secondary winding 54 is grounded at its upper end, in phase opposition to winding 52, and the receiver is operated continuously but is not activated for reception of the tuned circuit signal except after collapse of the electrostatic (FIG. 1), or electromagnetic (FIG. 6) field, or after cut off of the transmitter (FIG. 8).

The foregoing and other changes may be made without departing from the spirit of this invention.

Having now described our invention and the manner in which it may be used, we claim:

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 signalto 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 forreducing 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 claiml including electric timing 7 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. i 9. The apparatus of claim 1 wherein the radio frequency transmitter is tuned to the samefrequency 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.

sity 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,

0. 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 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 hasa 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: v

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 denportion 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 inter: mittent 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,

vd. 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 sig nal 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 charace. means for connecting said output signal to an electric circuit to be activated.

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 terized by having no residual stored energy after a 5 output signal, the detector means being charactertime, following cut-off of the energy field, less than ized by having no residual stored energy after a the decay time of said decaying signal, time, following cut-off of the energy field, less than electric signal detector means responsive only to the decay time of said decaying signal, and

said decaying electric signal to produce an electric (1. means for connecting output signal to an electric output signal, the detector means being charactercircuit to be activated.

ized by having no residual stored energy after a 20. The method of actuating an electric circuit for time, following cut-off of the energy field, less than detecting stolen merchandise, comprising:

the decay time of said decaying signal, a. producing an intermittent electric energy field in d. means for activating the detector means only dura predetermined space through which customers ing the time said field is cut off, and are required to pass,

b. attaching to said merchandise for introduction into said space a resonant electrical energy absorbing 19. Apparatus for activating an electric circuit, comprising:

a. resonant electrical energy absorbing and radiating 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 fremeans 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,

quency,

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 prob. electric field generating means comprising a pair duce an output electric signal,

of spaced electromagnetic coils and a source of ine. utilizing said output electric signal to actuate an termittent electric potential connected to the coils electric circuit, and for intermittently energizing said coils, for producf. subjecting the energy absorbing and radiating deing an intermittent electric energy field in a predevice to a radiant energy field sufficient to destroy termined space through which the energy absorbits resonating characteristics prior to passage of the ing and radiating means may pass, the generating merchandise through said space, when said mermeans being characterized by having no residual chandise has been purchased by a customer. stored energy after a time, following cut off of the

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.

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.

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.

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.

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.

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.

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.