United States Patent 3711848

A system for detecting the unauthorized removal of protected articles from a designated area comprising a harmonic generator circuit made up of a semiconductor diode chip and a pair of antennas adapted to receive a radio frequency signal at a first frequency and transmit a second radio frequency signal at a second, relatively higher frequency. Transmitting and receiving means are positioned adjacent an exit area for actuating the circuit and an alarm when protected articles approach the area, and means are provided for deactivating the circuit when the protected article is legitimately purchased. The generator circuit can be manufactured at very low cost thereby permitting, when a legitimate sale is made, permanent deactivation of the circuit without removing or otherwise handling the tag or label carrying the circuit.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
340/572.3, 340/572.7, 343/701, 343/720
International Classes:
G08B13/24; (IPC1-7): G08B21/00
Field of Search:
340/280,258 325
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US Patent References:

Primary Examiner:
Caldwell, John W.
Assistant Examiner:
Slobasky, Michael
I claim

1. A system for detecting the unauthorized removal of protected articles from a predetermined area comprising

2. The system of claim 1 wherein said second radio frequency level is approximately twice the frequency of said first frequency level, and the output power of said power signal source is approximately ten times the output power of the transmitted radio frequency signal of said receiving and transmitting unit.

3. The system of claim 2 wherein said receiving and transmitting unit comprises a transmitter including a source of high frequency energy, a filter, and a transmitter antenna, and a receiver comprising a receiving antenna, a band pass filter, a receiver adapted to receive signals of predetermined frequency approximately double the frequency of the signals emitted by said transmitter, and alarm means actuated by said receiver in response to the penetration of a protected article which has not been deactivated into the area of said transmitter.

4. The system of claim 1 wherein said first and second antennas each include a relatively pointed leading end portion adapted to contact and be electrically connected to the cathode and anode, respectively, of said diode chip.


The present invention relates generally to theft detection apparatus and more particularly to a method of and apparatus for detecting the passage of articles past predetermined check points and signaling such passage so that the person or persons surreptitiously removing such articles from the premises can be apprehended.

Shoplifting has long posed a considerable problem to retail business establishments, with the magnitude of such problem growing yearly. Numerous methods have been tried in order to reduce the loss caused by shoplifting, including various systems of personnel surveillance and, more recently, by means of electrical and mechanical theft detection devices or systems. The use of personnel to detect and apprehend shoplifters has obvious shortcomings. The use of floor walkers, security guards and the like constitutes a considerable business expense, oftentimes exceeding the amount saved as a result of reduced pilferage. In addition, the presence of security personnel is often at the sacrifice of the good will of the business for whom such personnel are hired, with the loss of good will being considerably magnified where customers thought to be shoplifters are mistakenly apprehended.

The provision of an electrical or mechanical theft detection system does of course obviate the above noted problem with respect to security personnel, but these systems have in the past not proven entirely satisfactory for a number of reasons. Systems representative of the prior art include U.S. Pat. Nos. 2,774,060; 3,493,955; and 3,500,373. The detection device disclosed in U.S. Pat. No. 2,774,060 for example, requires that the tag or label mounting the detection circuit be removed by the cashier, which adds to the checkout time, a source of possible customer dissatisfaction, as well as permitting removal of the tag or label by an individual who wishes to pass such article undetected through the checkout point.

Although permanent attachment of the detection device to the protected articles is suggested in the prior art, reference being made to U.S. Pat. No. 3,493,955, the method disclosed therein of deactivation and subsequent activation is not entirely satisfactory. Furthermore, in previous systems employing devices which may be permanently attached to the goods, the size and/or cost of the device are inhibiting factors against the use of such devices on a widespread basis.


With the above in mind, a primary object of the present invention is to provide a harmonic generator circuit which is simple and reliable and which will function to actuate an alarm circuit or the like when articles have surreptitiously passed a predetermined checkpoint such as the cashier's checkout area.

A further object of the present invention is to provide such a harmonic generator circuit which is both relatively small in size and inexpensive to manufacture. In accordance with the invention, the circuit is embodied in a relatively small tag or label which can be conveniently embedded or concealed within articles desired to be protected. In view of the substantially reduced cost of manufacture of each tag or label, the same can be left concealed or hidden in such articles when the same are purchased, and simply deactivated at the checkout point to prevent actuation of the alarm which would otherwise occur when the purchaser leaves the store.

A further object of the present invention is to provide a harmonic generator circuit which operates at relatively high frequency thereby precluding inadvertent actuation of the circuit by unprotected metallic articles passing through the checkout area.

A still further object of the present invention is to provide a new method of manufacture of the harmonic generator circuit, in which a continuous strip of longitudinally spaced circuits can be formed, assembled and thereafter cut into predetermined lengths.

A further object of the present invention is to provide a generator circuit which is readily adaptable to other areas of surveillance in addition to the environment disclosed. In view of the size, reliability and low manufacturing cost, the invention can be used as well in the surveillance of personnel to detect the passage of unauthorized persons through predesignated areas.

These and other objects will become apparent to those skilled in the art as the following description proceeds, in particular reference to the application drawings, in which:


FIG. 1 is a perspective view illustrating a doorway having mounted on either side thereof a transmitting and receiving unit for detecting the presence of protected articles which have surreptitiously passed the cashier checkout counter;

FIG. 2 is a perspective view showing a typical checkout counter, having associated therewith means for deactivating protected articles which have been legitimately purchased;

FIG. 3 is a sectional view through a tag or label constructed in accordance with the present invention, taken on line 3--3 of FIG. 4;

FIG. 4 is a plan view of the tag or label of FIG. 3;

FIG. 5 is a diagrammatic view of the transmitter unit used in the present invention;

FIG. 6 is a diagrammatic view of the receiver and alarm circuit used in accordance with the present invention;

FIG. 7 is a diagrammatic view of the deactivation circuit constructed in accordance with the present invention;

FIG. 8a is a plan view of a diode chip constructed in accordance with the present invention;

FIG. 8b is a side elevational view of the diode chip;

FIGS. 9-13 comprise top plan views of various forms of antennas which can be used in combination with the diode chip 28 to form the harmonic generator circuit;

FIG. 14 comprises a longitudinal sectional view taken on line 14--14 of FIG. 15 showing the top half of a tape member or the like carrying a metalized antenna pattern on the bottom side thereof;

FIG. 15 is a bottom plan view of the tape shown in FIG. 14;

FIG. 16 is a longitudinal sectional view taken on line 16--16 of FIG. 17, showing a mating tape member carrying a metalized antenna pattern on the bottom thereof for subsequent association with the member shown in FIG. 14;

FIG. 17 is a bottom plan view of the tape member of FIG. 16;

FIG. 18 is an isolated, reduced view of the diode chip constructed in accordance with the present invention;

FIG. 19 is a longitudinal sectional view taken through the assembled harmonic generator circuit of the invention, and

FIG. 20 is a top plan view of the assembly of FIG. 19.


Referring now in more detail to the drawings, wherein like parts are indicated by like reference numerals, and initially to FIGS. 1 and 2, there is illustrated therein a typical environment in which the present invention may be used to advantage. These figures are intended to depict a typical checkout and exit arrangement in a department store or the like, with the exit being indicated by door 25 on either side of which is mounted a transmitter and receiver unit 26, the construction of which is shown diagrammatically in FIGS. 5 and 6 and which will be discussed in detail when specific reference is made to these figures.

FIG. 2 illustrates a typical checkout area, comprising checkout counter C and cash register 37. Disposed laterally of the counter at the exit end thereof are deactivating units 38 and 39 between which the protected articles purchased in an authorized manner can be passed for deactivation of the harmonic generator circuit.

Referring now to FIGS. 3 and 4, a tag or label 27 has embedded therein the harmonic generator circuit of the present invention, which comprises a diode chip 28 and metal antennas commonly designated at 29. The diode chip may comprise a conventional point-contact diode but preferably comprises a Schottky diode, the characteristics of which are well known in the art. As will be explained in more detail when specific reference is made to FIGS. 14-20, the anode and cathode of the semi-conductor diode chip 28 are connected respectively to the antennas 29. The circuit can be embedded or encased in the tag or label 27 in a known manner which forms no part of the present invention. It will further be understood that the form of carrier for the circuit will normally depend upon the ultimate desired use of the circuit, with the tag 27 representing a typical use where the circuit can be conveniently concealed in articles to be protected.

The harmonic generator circuit just described is capable of receiving a radio signal at one selected frequency, which will be called Fo, and transmitting a radio signal at twice this frequency, 2Fo. Although the particular frequency employed is not critical, preferably high frequency ranges are employed in order to preclude false actuation of the system by unprotected metallic articles passing through the checkpoints. A typical operating frequency, for example, would be Fo at 912 megacycles, so that the generator circuit transmits a radio signal at 2Fo or 1824 megacycles. It will be understood that these frequencies are exemplary, and that other frequency ranges could also be satisfactorily employed.

Referring to FIG. 5 and 6, each of the transmitter and receiver units 26 comprises a transmitter circuit shown in FIG. 5 and a receiver circuit shown in FIG. 6. The transmitter circuit includes a high frequency generating source 30, a filter 31, and a transmitting antenna 32. Each of these components is commercially available and per se forms no part of the present invention.

The high frequency source 30 delivers a continuous, non-modulated radio frequency signal through the filter 31 to the transmitting antenna 32 which provides radiation of the radio frequency signal at the selected frequency Fo in the direction of the doorway 25. The filter 31 functions in the usual manner to assure passage of signals of such predetermined frequency and to suppress higher harmonics of such frequency.

Referring to FIG. 6, the receiving circuit comprises a directional receiving antenna 33, a band pass filter 34, a receiver 35, and alarm means 36, which can comprise a flashing light, bell, or other audible or visual alarm. In a manner well-known in the art, the band pass filter 34 will only pass radio signals within predetermined frequency limits, with the limits being selected in the present instance to include the frequency 2Fo, 1824 megacycles. Satisfactory limits for the band pass filter can be, for example, between 1775 and 1875 megacycles, and it will be understood that the receiver 35 is sharply tuned only to signals in this range. The receiving of signals in this range by the receiver 35 actuates the alarm 36 thereby indicating passage through the doorway 25 of articles that are protected and that have not been processed through the checkout counter as authorized. All of the components 33-36 are similarly conventional and commercially available.

Referring to FIG. 7, there is illustrated therein the power circuit for deactivating the harmonic generator circuit as protected articles are processed through the checkout counter after legitimate sale. The power circuit includes antennas 38 and 39 and generating means 40 coupled therewith for providing a power signal. The frequency of the power signal is selected to be approximately Fo, and the power output is approximately 10 watts, substantially higher than the power output of the high frequency source 30, which is preferably at or less than 1 watt.

When a protected article is processed subsequent to a legitimate sale, the sales clerk passes the protected article or package through the electromagnetic field between the antennas 38 and 39. The relatively high output of the power source 40 functions to burn out and thus permanently deactivate the tag or label 27 associated with the article whereby the article may freely pass through the doorway 25 without actuation of the units 26 as the merchandise leaves the store. The electromagnetic energy radiated by the antenna 38 will be absorbed by the antenna 39 thereby preventing radiation outside the system.

Referring to FIGS. 8a and 8b, the semiconductor diode chip 28 includes an anode 42 formed on the top of the diode chip and a cathode 43 which forms the bottom of the diode chip.

FIGS. 9-13 illustrate various shaped antennas 41 which extend to either side of the diode chip 28 and are electrically connected respectively to the cathode 43 and anode 42. In these figures, the circuit is shown embedded in the tag 27. The diode chip 28 is preferably of a preselected polarity, and the shape or design of the particular antenna 41 employed is based on which antenna design will perform the best in view of the polarity of the electromagnetic field radiated by the transmitter antenna 32.

There is illustrated in FIGS. 14-20 the preferred method of manufacturing the harmonic generator circuit in accordance with the present invention. Referring to FIGS. 14 and 15, a tape member 44 has a thin metalized antenna pattern 45 formed thereon which comprises one-half of the antenna assembly. It will be noted that the antenna pattern 45 is pointed at one end as shown at 48. The tape 44 can be constructed of any suitable material, with the underside of the tape containing the metalized antenna section being preferably coated with glue, and the exterior surface of the tape being preferably coated with vinyl or similar plastic material.

FIGS. 16 and 17 are generally similar to FIGS. 14 and 15, with the underside of the tape member 46 being formed with a similar metalized section 47 having a pointed end portion 49, the direction of which is opposite to the direction of the pointed end 48 of the metalized section 45 of the tape 44. The tape 46 is also preferably provided with glue on the underside thereof carrying the metalized antenna section and vinyl on the opposite, exposed side.

Referring to FIGS. 19 and 20, the tape members 44 and 46 are shown superimposed, with the faces thereof carrying the antenna sections being in contact. As will be seen from the centerline passing from top to bottom through these several figures, the pointed end regions 48 and 49 of the antenna sections overlap and are designed to extend respectively over and under the diode chip 28 which is positioned therebetween in the manufacturing process. The electrical contact between the cathode and anode of the diode chip 28 and the antenna sections 48 and 49 is preferably by pressure, effected during the assemblying of the circuit. During such assembly, the glued material on the contacting sides of the tapes 44 and 46 can be activated so as to firmly bond the tape members together as shown in cross section in FIG. 19. The assembly thus constitutes a completely embedded diode chip and electrically connected antenna sections, with the exposed surfaces of the tape being vinyl coated and thus highly resistant to the typical environments to which the circuit is subjected.

As above indicated, the size of the harmonic generator circuit assembly can be varied and is to a large degree controlled by the length of the antenna portions. In the assembly illustrated in FIGS. 19 and 20, the length of the assembly is approximately two inches, the width is approximately one-half inch, and the thickness is approximately twenty-thousandth of one inch. It will thus be seen that the assembly can be concealed without difficulty in clothing, for example. Where higher frequencies are employed, the length of the assembly can be made even shorter, thereby further enhancing concealment of the assembly.

The manner in which the harmonic generator circuit of the present invention functions should be apparent from the above description. To briefly summarize, protected articles, that is articles on or in which the assembly is carried, are normally processed through the checkout counter C, and articles that are so protected are passed between the antennas 38 and 39 after legitimate purchase. The power signal produced by the power source 40 functions to permanently deactivate the assembly thereby permitting passage of the protected article through the doorway 25 when the customer leaves the store.

When a customer attempts to leave the premises through door 25 with a protected article that has not been paid for and deactivated, the article enters the radiation pattern of the transmitter antenna in the units 26. The harmonic generator circuit in the tag or label 27 will transmit a signal at approximately 1824 megacycles. The radio signal at such higher frequency will be received by the receiver 35 which in turn will actuate the alarm 36, thereby alerting store personnel of the theft.

It will thus be seen that the objects of the present invention have been accomplished. There has been provided a harmonic generator circuit which is extremely simple in construction and highly reliable in use. The construction of the device itself, coupled with the unique method of manufacturing the same, permits manufacture at very low cost thereby allowing deactivation of the device at the checkout counter, concealment of the device without removal of the same at the checkout counter, a decided disadvantage with prior art assemblies of this general type. In lieu of removal, the device can simply be activated in the disclosed manner and the assembly left in its concealed position. The operating frequencies are such that inadvertent actuation by metallic articles is virtually precluded.