Surveillance system for preventing pilferage

SWEDEN ¢ 12) PUBLICATIONS

IBJp ») ₈₂Q2184-1 (193 SE (51) International Class ⁴ G08B

13/22 (41) (22) (243

Patent Office (86) (86) (44) Application outsourced and the outsourcing document published

The application for general application The patent application was submitted on Lopdag

Stamansokan number

International filing day '' filing date for European patent application (30)

88-02-08

82- 10-08

82-04 <J6

82-04-OG on

POSTING 453 540 as the Swedish inaugural search

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Π ejroposfc patertf application

81-04-07 US 251933 (70

Applicant

Corporation, Deerfield (721

Inventor (74) (54)

Agent

Designation of such a device useful (56) (57)

18) is comprised of a leading prayers tear

Sensormatic Electronics

Beach Fla US

E 0. Eskandry. J N. Weaver. Pompano Beach, Boca Raton Fla AWAPATENT AB Monitoring device and aggregates

Published publications: -

Summary:

A microstrip antenna (17, floor mat (10), the latter grid (20) laminating an intermediate layer of dielectric material to form a capacitor) .The microstrip antenna is coupled to a microwave energy source (13) for transmitting a microwave signal through A low frequency signal is applied to the capacitor section of the mat for direct capacitive coupling through the body of a pedestrian to one of the pedestrian possibly carried over the surveillance marking device.

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The present invention relates to an apparatus for snatching control. More specifically, it relates to an apparatus for detecting the presence of a gossip element in an unauthorized area.

For the purpose of controlling snattery, it has previously been proposed that specially designed marking devices “be affixed to goods to be protected, which marking devices must be inactivated or removed for permissible removal of the goods from the controlled area. US Patent No. 3,895,368 discloses an apparatus in which a microwave signal generator emits an electromagnetic wave in a monitored area to establish a first field. A pulse or frequency modulated low frequency generator was used to apply ₅ A voltage on a discontinuous conductor to establish a second field, which is electrostatic in nature, throughout the space. The presence in the space of a miniaturized, passive, receiver-re-emitter for electromagnetic waves in the form of a semiconductor diode coupled to a dipole antenna provides the re-emitting of the low-frequency component nodulated on the microwave component such as carrier. The input side of a receiver system is tuned to the microwave frequency signal. A coincidence circuit activates an alarm circuit whenever the detected signal coincides with the original modulation envelope applied to the low frequency generator. The patent application states that in general, the discontinuous conductor may be extended over the protected area passage and that an earthed conductor may be located on the floor to provide a return path for the electrostatic signals, if necessary. In a preferred embodiment described in the patent, sockets are located on opposite sides of the passage to be protected, which sockets contain

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foil elements for establishing the electrostatic field. In a particular example, the foil elements are mentioned as being 10x10 cm in size and driven by a signal with an effective value of 245 V.

However, it has been found that, since the radiators of the electrostatic field are located in the side sockets above the floor level, it is difficult to confine the electric field to exactly the area that one wishes to control between the sockets. When the radiated energy 10 extends beyond the desired limits, this is referred to as the boundary crossing. Crossing the border is not desirable, as it reduces the floor space adjacent to the controlled passage where labeled goods can be legitimately located or can be transported by someone without triggering an alarm.

Swedish patent application 8103576-8 discloses an apparatus of the type described in the aforementioned patent, in which apparatus the cross-border as a result of the inability to limit the electrostatic field to the desired space has, if not eliminated, been greatly reduced. A floor mat, consisting of a conductive grid, which is laminated to a conductive sheet with a layer of dielectric material therebetween to form a capacitor, is arranged between the bases which contain means for radiating a microwave signal through a monitoring area. A low-frequency signal is applied to the capacitor mat for direct capacitive coupling through the body of a pedestrian to one of the optionally supported marking devices. Although the use of the carpet reduces the boundary crossing problem, it still leaves the pedestal as an essential component of the passage or hallway. These plinths are particularly reprehensible when it is desired to control a narrow passageway or when it is desired to avoid the introduction of any obstacle into the path of those entering or leaving the area to be controlled, the present invention provides an apparatus of the type described above. , which device eliminates

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453 540 sockets without reducing the efficiency of the monitoring system. According to the invention, a monitoring device is provided for detecting the presence in a controlled space of a miniaturized receiver-repeater for electromagnetic waves with signal mixing capability, which device in combination comprises means for propagating through the space an electromagnetic microwave signal, a source of low signal, an electrode coupled to the source for low frequency signals for placement along the path of the receiver re-radiator through the space for direct capacitive coupling to the receiver re-radiator, whenever the latter is present in the space, to the space detecting signal detecting means for receiving signals from this, the low frequency signals, only when received as a modulation on a carrier signal, the frequency of which exhibits a predetermined relationship to the frequency of the microwave signals, and means coupled to the detection means to provide an alarm in response to the detection of the signals related to the low frequency signals, and the device is characterized in that the means for propagating a signal through a microstrip antenna having a signal propagation signal propagated through the space and signal supply device.

The invention will be described in more detail below with reference to the accompanying drawings. Fig. 1 is a perspective view of an installation according to the present invention. Fig. 2 is a view of a floor mat containing both the direct capacitive coupling electrode to the receiver-re-radiator and the microstrip antenna, for use in the installation of Fig. 1. Fig. 3 is a block diagram of a typical circuit useful in conjunction with the mat of Fig. 2 in the installation of Fig. 1.

Referring now to Fig. 1, a typical installation consisting of a food assembly 10 is located on the floor within a hallway or passage 11 and connected by a concealed

453 5,453,540 cable 12 to a hidden electronic control box 13, which in turn is connected by means of a cable 14 to an alarm sensor 15. The sensor 15 is located in a place where it can be observed by security personnel. In the illustrated example, it is shown mounted on the wall 11 of the corridor. The aisle 11 can, for example, constitute the passage at the exit from a retail shop to ensure that goods sold are not removed from the warehouse space without a * permit. Alternatively, it can be placed anywhere within the store to control unauthorized movement of goods from one sales area to another. Obviously, the device can be used anywhere and in conjunction with any type of operation where it is desired to detect unauthorized transport of articles from one place to another.

As shown in Figure 1, the mat 10 covers the hallway 11, where a pedestrian must walk when passing through the controlled space. If the individual shown were to carry a concealed item marked with a receiver-re-radiator of the above-mentioned type, the system would give alarm. The operation will be essentially that described in the aforementioned patent application, wherein the hidden conductive grating electrode 20 in the floor mat 10 generates an electrostatic field which is transmitted to the receiver-re-radiator via the pedestrian body. However, in accordance with the present invention, the electromagnetic microwave signal is propagated through the space to be controlled by activating the microstrip antenna elements 17 and 18, which are also hidden in the mat 10.

The details of the mat 10 will now be described with reference to Fig. 2. As can be seen from that figure, the mat 10 consists of a conductive ground plane sheet 19, an electrode layer 20 formed as an open grid, and a layer of dielectric material 21 laminated between the grid 20 and the conductive sheet 19. An edge of the grid electrode 20 and underlying dielectric layers 21 are cut or provided with a notch 22. The two band conductor members

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453 540 and 18 of the microstrip antenna are located mainly in the plane of the grid 20 and are inserted into the space enclosed by the notch edge 22 but are distinct from this edge. If the band conductor elements 17 and 18 are formed on a surface of a conventional circuit board, the underside of which is provided with a continuous conductive layer, the entire circuit board assembly may be inserted into the space provided by the aforementioned notches, as shown in Fig. 2. However, the conductive layer on the back of the circuit board is preferably insulated from the sheet 19 to ensure that unwanted crosstalk is avoided from the electrostatic field radiator. Alternatively, the dielectric layer 21 may be coherent over the entire rectangular area of ​​the mat and the strip conductor elements 17 and 18 may be formed thereon by any suitable method.

In this case, the underlying section of the sheet should be separated and isolated from the remainder of the sheet 19 to provide an insulated microstrip ground plane on the antenna. Fig. 2 also shows a rectangular three-sided protective electrode 23 arranged around the band conductor elements 17 and 18 at a distance from them as well as from the edge 22 of the grid 20.

Fig. 2, to which reference is still made, also shows that the band conductor elements 17 and 18 are each provided with signal supply terminals 24 and 25. By appropriately positioning the feed points in a known manner relative to the edge of the corresponding band conductor element, the correct phase for circular polarization of the emitted energy is achieved. Such a radiation pattern is desirable in the practice of the present invention.

The two connection points themes 24 and 25 are connected in parallel to the inner conductor 26 of a shielded cable 27 for receiving microwave energy therefrom. The shield 28 of the cable 27 shall be connected to the ground plane of the antenna, that is, the conductive layer on the back of the circuit board, if such construction is employed, or the insulated conductive section of the sheet 19 mentioned above. This ground plane should also be in some timely manner

453 540 connected to the protective electrode 23.

A typical mat can be constructed as follows.

On a thin, rectangular aluminum sheet down to a size of about 75x90 cn, a 3.2 rom thick layer of a dielectric ABS plastic material is laminated. To this, a thin rectangular grid section, which serves as the grid electrode 20, is attached. Along one of the longer edges of the rectangular structure so formed, the grating is cut to provide the notch with the edge

22, while the dielectric ABS material is cut away to form a rectangular cavity of about 15x30 cm, into which is inserted a circuit board formed on a 1.6 mm thick G-10 fiberglass. The exposed conductive surface of the circuit board is formed in the manner shown in Fig. 2, while the lower surface has the same extent as the insert element. Suitable dielectric spacers are preferably inserted between the circuit board and the aluminum sheet 19 so that the strip or band conductor elements 17 and 18 and the protective strip 23 lie in approximately the same plane as the grid 20. Alternatively, thinner sheets of dielectric material may be placed both below and above the circuit board to insulate it. later from sheet 19 and providing it with a smooth upper surface for pedestrian traffic. The assembly thus prepared is sealed with a covering or enclosing layer of polyurethane material to encapsulate it and protect it from damage by moisture and the like. A layer of elastomeric material of any known composition with the ability to withstand wear as well as constitute a good insulator covers and conceals the active parts of the mat.

The elastomeric layer may, as desired, be bonded or not bonded to the remainder of the mat. The shielded cable 27 may be attached in some suitable manner around the periphery of the mat to a suitable starting point for connection to the electronic control box 13. A separate, shielded cable 29 is connected to the ground plane and the grid 20 in the manner described in the above-mentioned patent application.

Referring now to Fig. 3, the control circuits are shown.

453 540 located in the electronic control box 13. These circuits may consist of a crystal controlled oscillator 30, which feeds a hybrid coupler or circuit 31, which in turn feeds the microstrip antenna elements 17 and 18 via a low frequency barrier filter 32 and a bandpass filter 33 of 915 MHz. the shielded cable 27. In the present example, the output of the crystal controlled oscillator 30 has a frequency of 916 MHz and activates the microstrip antenna elements to propagate through the space to be controlled an electromagnetic microwave signal. When a receiver-re-radiator not shown is present in the space irradiated by the microstrip antenna, which includes the elements 17 and 18, the receiver-re-radiator will be interconnected by the energy radiated from the antenna and a re-radiated component of the radiated signal will be received by the same antenna 17 and 18 and fed back to the hybrid coupler 31. Incoming signals reaching the hybrid coupler 31 will exit over the output path 34 to an input to a mixer 35 which, at a second input, is provided with signals from the crystal controlled oscillator 30 at the transmitted frequency of 915 MHz. The mixer 35 has an output 36 which feeds a signal to a receiver 37 for the 160 kHz frequency, which receiver in turn has an output 38 coupled via a signal processor 25 to an alarm 40.

As described in the aforementioned patent application, it is necessary that a low frequency signal be modulated on the microwave carrier signal in order for the alarm circuit to be activated. For this purpose, a low frequency signal source is also provided in the present device, which in the present example is shown as consisting of a generator 41 for the frequency 160 kHz, the output of which generator is connected via the cable 29 to the capacitor part of the mat 10. The generator 41 may be constructed in a manner well known in the art and provided with suitable means, such as those set forth in the aforementioned patent application, for impedance matching and resonant tuning of the load circuit which includes the capacitor formed by the grid 20 and the ground plane 19.

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In other words, when a tag device (receiver-re-emitter) is present in the controlled space, the carrier signal received from the antenna elements 17 and 18 is modulated by the signal taught by the grid 20 of the mat 10. A signal of frequency 160 kHz comes in other words to be modulated on the carrier signal at the frequency of 915 MHz to be detected by the receiver 37. Further modulation or variation of the monitoring signals may be included in the system for facilitating • false alarm printing. However, such modifications do not form part of the present invention and need not be described. With continued reference to Fig. 3, it is clear to those skilled in the art that the latch filter 32 and bandpass filter 33 are utilized to ensure that a clean 915 MHz signal is fed to the cable 27 free of any crosstalk containing signals at 160 kHz.

. It is also clear that the shielded cables 27 and 29 may be integrated into a single cable assembly 12 for easy installation.

After describing the presently preferred embodiment of the present invention, it should be understood by those skilled in the art that a variety of design modifications are possible. The 160 kHz generator 41 can be replaced by the components described in the aforementioned patent application, which operate at 80 kHz and rely on the receiver device's radiator for doubling the frequency and returning a modulation component at 160 kHz. The number of microstrip antenna elements can be increased or decreased as desired and their location in the floor mat construction can be varied depending on where you want to concentrate the radiated field pattern. As shown in Fig. 1, it is presently preferred that the antenna elements be placed at the edge of the mat, the edge being closest to the exit from the area to be checked, so that the boundary crossing is minimized into areas where goods for sale can legitimately be placed. In case a wider passage is to be checked can be further

453 540 carpets are used and operated in parallel. The hybrid coupler may have multi-port construction, each of its outputs feeding a separate mat via separate filters. Although a rectangular mat has been illustrated, a variety of polygon configurations can be utilized. If desired, the microstrip antenna substrate can be inserted inside the edge of the mat such that the circuit board is surrounded on all four sides of the material in the dielectric layer -1. In this case, the protective electrode 23 should also be four-sided to completely enclose the antenna elements. The thickness of the circuit board can be varied in known manner from the above mentioned dimension of 1.6 mm.

The general design and design of the microstrip antennas seems to be well known. They do not need to be designed as pentagons. Further information can be obtained from Microstrip Antennas ”by IJ Bahl and P. Bhartia, published by Artech House. However, the example of a pentagon antenna described therein is characterized by a bandwidth of 1%, while the monitoring systems herein intended preferably operate with microwave antennas having a bandwidth of 2-3%. Such bandwidth is achieved by using a dielectric material with larger losses between the elements 17 and 18 and the ground plane associated with them. In order to produce a satisfactory mat for use in the intended monitoring system, the load imposed by the overlying elastomeric layer, which strives to lower the resonant frequency of the microwave antenna, must also be considered. The design must therefore take this load into account. It has been found desirable to align the construction of the antenna itself for a 5-10 MHz higher frequency than the intended operating frequency.

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