WO1995021430A1

WO1995021430A1 - A security system

Info

Publication number: WO1995021430A1
Application number: PCT/EP1995/000442
Authority: WO
Inventors: Mathias Maria Jozef Pantus
Original assignee: Aritech B.V.
Priority date: 1994-02-07
Filing date: 1995-02-07
Publication date: 1995-08-10
Also published as: NL9400188A

Abstract

A security system provided with an active sensor comprising at least one source for emitting electromagnetic light in a room to be guarded and at least one detector for detecting electromagnetic light striking thereon, and with an alarm for generating an alarm signal in dependence on a detection signal being delivered by the at least one detector, whereby the security system comprises at least one label provided in the room to be guarded, which directs incident electromagnetic light emanating from the at least one source in modified form to the at least one detector, whereby the at least one detector delivers a detection signal in case of a typical change in the electromagnetic light striking thereon.

Description

A SECURITY SYSTEM

The invention relates to a security system provided with an active sensor comprising at least one source for emitting electromagnetic light in a room to be guarded and at least one detector for detecting reflected electromagnetic light striking thereon, and with an alarm for generating an alarm signal in dependence on a detection signal being delivered by said at least one detector.

Security systems are widely known.

WO-A-9212503 discloses a security system for monitoring the position of valuable objects in a room. Any displacement of the objects is detected by means of two electromagnetically coupled resonant circuits, which are subjected to their own frequency induced by an electromagnetic wave generator. The coupling of these resonant circuits is monitored by a receiver device. Upon displacement one of the circuits being fixed to the object is moved relative to the other as a consequence of which the coupling gets weaker which is detected by the receiver device that provides an alarm. This known security system is however not suitable for detecting the presence of a burglar in a room who will probably be encouraged to steel non-monitored objects. When several objects are monitored by this known security system troublesome electromagnetic interference will occur, unless separate radiofrequency channels are used. Besides, false alarms may be generated when, for example a radio is tuned to the radiofrequency used by the known security system. The above interference will be caused by the radio preselection filter resonance and/or the spurious emission as caused by the radio local oscillator.

An electromagnetic anti-burglar system is known from BE-A-479091 consisting of one or more electromagnetic radio wave transmitters and one or more corresponding receivers for receiving direct or indirect (reflected) waves. The receivers detect a modification of the radiation field resulting from the presence of a burglar. This known burglar system does however not directly monitor the displacement of objects in a room.

GB-A-2 258 577 discloses a vehicle navigation system wherein polarized radio waves are radiated. Beacons are provided to modify the reflected waves thereby retro reflecting only the horizontally polarized radiation while the vertically polarized radiation is more weakly reflected. The vehicle navigation system includes means responsive to the radiation of the magnitude of the reflected signal components to detect beacon reflection and to determine angular beacon position.

All of the above-mentioned systems can be disturbed, influenced or even blinded by introducing an external radio wave source in the room to be monitored. Furthermore they all need a radio license which is costly and troublesome.

A security system of the kind acknowledged in the first part of claim 1 is known from European Patent Application No. 0 255 812 in the name of Elkron S.p.A. The security system described therein utilizes, in a manner known per se, a passive infrared sensor, whereby infrared light emanating from an object in a room to be guarded is directed - via an input of a passive infrared sensor - to a detector, for example in the form of a pyroelectric element, by optical means. Said optical means may for example be a mirror or a Fresnel lens. An intruder in the room to be guarded is detected because the pyro-electric element detects a change in the amount of incident infrared light, which is caused by an intruder, and consequently an alarm is activated, which generates an alarm signal. In order to optimize the operation of the known security system, the aforesaid European patent application proposes to combine the infrared sensor with an active (radio¬ frequency) sensor having a working frequency in the ultrahigh frequency range. With the known security system an alarm signal is generated only when both the passive infrared sensor and the radio-frequency sensor detect - independently of each other - an intruder in a room to be guarded. Whilst the detection operation of the passive infrared sensor is already roughly indicated above, the detection operation of the active (radio-frequency) sensor is in broad outline as follows: An intruder in a room to be guarded, in which radio waves are radiated, causes a disturbance of the radio-frequency wave range (as a result of the Doppler effect) , which disturbance is detected by the radio-frequency sensor and which results in the generation of an alarm signal.

A drawback of the known security system is that it does not provide a solution for the following problem: Since the operation c the passive infrared sensor is based on the detection of infrared light, that is heat radiation having a wavelength in the order of in particular about 6 - 18 μm, which emanates from an intruder in a room to be guarded, and since only very few materials transmit such infrared light well (nearly all materials block, absorb and/or reflect this type of light) , the detection of the known security system can be easily sabotaged by placing m.. erials which tranεrit this type of infrared light well or. and/or near the detector of the passive infrared sensor. When for example at least one part of the input of the passive infrared sensor is blocked by materials such as paper, glass, paint, cardboard or plastic, the quality of the security offered by the known security system is seriously affected. This affecting (sabotaging) of the quality of the known security system can sometimes even be effectuated without this being visible to the user of the security system, whereby in particular the placing of a sheet of glass in front of the detector of the passive infrared sensor may be thought of, or the application of a correspondingly colored paint on the input of the passive infrared sensor. A further drawback of the security system known from European Patent Application No. 0 255 812 is that it is a complex and relatively costly system, in particular because two separate sensors are used, and that an alarm signal is generated only when both the passive infrared sensor and the active (radio-frequency) sensor detect an intruder in a room to be guarded, so that no alarm signal is generated when one of the sensors does not (optimally) function.

The object of the present invention is to provide a simple and inexpensive security system, which makes it possible to detect sabotaging thereof.

In order to accomplish this objective a security system of the kind referred to in the introduction is characterized in that said security system comprises at least one label provided in the room to be guarded, which directs incident electromagnetic radiation emanating from said at least one source in modified form to said at least one detector, whereby said at least one detector delivers a detection signal in case of a typical change in the electromagnetic radiation striking thereon. In principle the label, for example in the form of a card or a sticker, may be provided at a random location within the room to be guarded.

Possibly the label, which may or may not be visible, is integrated in an object within the room to be guarded. It is to be preferred to place several labels within said room, and that in such a manner that a path of rays between the source, the detector and the label will be influenced directly or indirectly (that is, for example interrupted or shifted) . The labels may for example be provided on valuable objects, such as works of art and the like, and beside doors or windows. When an intruder interrupts the path of rays between for example the source, the detector and the label upon entering the room to be guarded, the radiation striking on the detector is "typically" changed, as regards its amplitude in this case, which, upon delivery of a detection signal, results in the alarm being activated. An alarm signal is also generated when for example an intruder moves a work of art provided with a label in the room to be guarded, since in this case the incident radiation on the detector changes typically, for example as regards its polarization or frequency. In a preferred embodiment the security system according to the invention is characterized in that said at least one detector delivers a detection signal in case of a change in at least one wave characteristic (phase, amplitude, polarization, energy (density) and/or frequency (Doppler) ) of the electromagnetic radiation. The detector preferably delivers a detection signal when the electromagnetic radiation striking thereon corresponds with a signal value below a predetermined level (lower threshold) or above a predetermined level (upper threshold) , as will be explained ir. tore detail hereafter with reference to the Figures.

It is noted that it is not necessary for all of the electromagnetic radiation striking on the detector to emanate from the label, it may also originate in part from external influences (sources) . In order to prevent external influences that may be present from causing a typical change in the electromagnetic radiation striking on the detector, one embodiment of a security system according to the invention is characterized in that said at least one source emits characteristic electromagnetic radiation in the room to be guarded. The source emits electromagnetic radiation, for example, which cannot be generated by external influences that may be present, for example because such radiation does not occur in nature.

Another embodiment of a security system according to the invention is characterized in that said at least one detector is selective for electromagnetic radiation emanating from said at least one source, which is directed to said at least one detector by said at least one label. In this way the aforesaid phenomenon of external sources is likewise avoided, since the detector is not responsive to electromagnetic radiation emanating from external sources.

Another embodiment of a security system according to the invention is characterized in that said at least one label reflects incident electromagnetic radiation emanating from said at least one source to said at least one detector. Preferably the label is a so-called retroreflector. A retroreflector is a reflector which is for example built up of a large number of small prismas, so that light reaching the reflector at a random angle is reflected at the same angle and in the same direction as it came from.

Another embodiment of a security system according to the invention is characterized in that said at least one label transmits electromagnetic radiation to said at least one detector, said electromagnetic radiation corresponding with the incident electromagnetic radiation on said at least one label emanating from said at least one source. In this case the label constitutes an active transmitter.

Another embodiment of a security system according to the invention is characterized in that said at least one label modifies at least one wave characteristic (phase, amplitude, polarization, energy (density) and/or frequency) of the electromagnetic radiation emanating from said at least one source.

The invention will be explained in more detail hereafter with reference to Figures illustrated in a drawing, in which:

Figure 1 diagrammatically shows a room to be guarded, in which a security system according to the invention is present; Figures 2 - 10 illustrate in more detail the principle of operation of the security system of Figure 1; and

Figures 11-15 show several practical applications of the security system of Figure 1.

Figure 1 shows a room to be guarded, which is provided with a security system according to the invention, said security system comprising an active sensor 1 (TX-RX) with a source for emitting electromagnetic radiation into the room to be guarded, a detector for detecting electromagnetic radiation striking thereon, and several labels 2 - 7. The labels 2 - 7, which are provided on a painting, near a door 10 and beside a window 9 in Figure 1, modify incident electromagnetic radiation emanating from the source, as regards its polarization, for example, and reflect the modified electromagnetic radiation to the detector. The detector activates an alaz-m, when the amplitude of electromagnetic radiation striking thereon is changed as regards its polarization, for example when the polarization pattern changes, for example from circular to elliptic or linear. In other words, an alarm signal is generated when the detector detects electromagnetic radiation with which a signal value below and preferably also above a predetermined signal (amplitude) value corresponds. All this will be explained in more detail with reference to Figures 2 - 5.

Figures 2 - 5 show four graphs placed one above the other on the left and four graphs placed one above the other on the right, in which graphs a detection signal value is plotted against time, wherein the four graphs on the left relate to detection signal A and the four graphs on the right relate to detection signal B. The detection signals A and B correspond with signal values which have been measured in a certain polarization direction. The detection signals A and B are different from each other in that detection signal A only emanates from the surrounding space, that is from background radiation (a characteristic feature of labels 2 - 7 is that they absorb electromagnetic radiation having polarization A) , whilst detection signal B emanates from the surrounding space and from radiation reflected by labels 2 - 7 (labels 2 - 7 only reflect incident electromagnetic radiation having polarization B) .

Figure 2 shows a situation wherein the security system according to the invention is in operating condition, but does not detect intruders (condition of rest) .

Figure 3 relates to a situation in which the painting provided with label 2 is being removed, so that the amount of electromagnetic radiation having polarization B which strikes on the detector is changed, resulting in an alarm signal being generated. The amplitude of detection signal A does not change, of course, because said detection signal only emanates from the surrounding space and consequently is not influenced by a change in the amount of light having polarization B which is reflected by the labels 2 - 7. The same Figure 3 applies to the case where an intruder opens the door 10 or breaks the window-pane 9 upon entering the room to be guarded, as a result of which the path of rays between the source, the detector and the respective label located near the door 10 or the window 9 being interrupted. Also in these cases an alarm signal is generated, because also here a change in the amount of light having polarization B which is reflected by labels 2 - 7 is detected. A likewise situation occurs when a sticker 11 provided behind a painting is "released" when the painting is removed by an intruder. Accordingly, the amplitude of detection signal A does not change, whereas the amplitude of detection signal B increases instead of decreases (figure 3) .

Figure 4 refers to the situation where an intruder introduces an element corresponding with a label into the room to be guarded, so that the detection signal values A and B are higher than those in the condition of rest of Figure 2. After all, this element will reflect electromagnetic radiation having polarization A as well as electromagnetic radiation having polarization B. Again an alarm will be generated. The fact of the matter is that the detector activates the alarm, also when the electromagnetic radiation striking thereon corresponds with a detection signal value above a predetermined amplitude level. When furniture, glass vases and the like are introduced into the room to be guarded, or moved therein, this may lead to increased detection signal values A and B in comparison with those in the condition of rest (Figure 2) .

Figure 5 relates to the situation where the amplitude of the electromagnetic radiation striking on the detector is changed as regards ". larizations A and B (characteristic features) , without an intruder crossing the path of rays between the source, the detector and one of the labels, but where the intruder does cause a change in the total amount of electromagnetic radiation having polarizations A and B being reflected to the detector, for example by sneaking into the room to be guarded. An alarm will be generated. A similar effect occurs when insects, or animals in general, come within reach of the detector.

Figures 6-10 again show four graphs placed one above the other on the left and four graphs placed one above the other on the right, in which graphs a detection signal value is plotted against time, wherein the four graphs on the left relate to detection signal A and the four graphs on the right relate to detection signal B. The detection signals A and B correspond with signal values which have been measured in a certain polarization direction. As in figures 2-5 the detection signals A and B are different from each other in that detection signal A only emanates from the surrounding space, that is from background radiation (a characteristic feature of labels or tag 2 - 7 is that they absorb electromagnetic radiation having polarization A) , whilst detection signal B emanates from the surrounding space and from radiation reflected by labels or tag 2 - 7 (labels 2 - 7 only reflect incident electromagnetic radiation having polarization B) .

Figure 6 illustrates a situation wherein the security system according to the invention is in operating condition, whereby a person is moving close to the detector (phototracer) not covering or masking a label or tag 2. The amplitudes of detection signals A and B have a corresponding shape, because the person moving close to the detector reflects electromagnetic radiation having polarization A as well as electromagnetic radiation having polarization B. In fact, the situations of figures 5 and 6 refer to the same electromagnetic phenomenon.

Figure 7 refers to a situation in which someone moves close to the detector (phototracer) accidentally masking or covering a label or tag 2. Only the amount of electromagnetic radiation having polarization B striking on the detector is changed, resulting in alarm signal being generated. The amplitude of detection signal A does not change, for this detection signal only emanates from the surrounding space and consequently is not influenced by a change in the amount of light having polarization B (caused by masking the label 2) which is reflected by the labels 2 - 7.

Figure 8 shows a situation where an intruder moves close to a label or tag 2 accidentally masking this label. For reasons already explained, the amplitude of detection signal A does not change but the amplitude of detection signal B does, for the amount of electromagnetic radiation having polarization B striking on the detector is changed (caused by masking the tag) .

Figure 9 shows the effects of aging of one of two light sources, which may be a infrared light source. The one light source emitting electromagnetic radiation having polarization A ages (left graph) , whereas the other light source emitting electromagnetic radiation having polarization B shows no aging effects- (right graph) . Figure 10 shows a situation wherein an external white light influence of 10.000 lux is detected. It shows that such light will only slightly influence the signal levels A and B. However it does not effect the proper functioning of the security system.

In the above description of figures 1-10, the change of amplitude of electromagnetic radiation refers to polarization, but could of course also relate to frequency, phase, amplitude ect. as mentioned earlier.

Figure 11 shows a painting 12 and a vase 13 protected by an element 14 provided with a label or tag according to the invention. The element 14 is attached to the wall 15 or under the table top 16. When displacing the painting 12 or the vase 13 the amount of electromagnetic radiation having a certain characteristic (for example; polarization, frequency etcetera) striking on the detector is changed, due to the fact that the label on the element 14 only reflects incident electromagnetic radiation having polarization B, resulting in an alarm.

Figures 12 and 13 refer to a security system according to the invention, wherein several labels forming a strip are used to guard the entrance of a door (figure 12) or to guard the excess to a valuable object, for example a vase 13 (figure 13) .

Figure 14 shows an arrangement of two columns 17 and 18. Each column 17,18 is provided with its own sensor 1, and with label/material which covers at least a part of the outside of the columns 17,18. Additional labels, not shown, could be provided elsewhere in the room as shown. The one column now monitors the other and vice versa, and both of them monitor their surrounding, thus providing optimum security and protection.

Figures 15a and 15b show a top view and a cross sectional view respectively, of a corner and wall part of a room, and the corresponding dotted area of protection by the sensor 1.

ONFir?MATION COPY

Claims

1. A security system provided with an active sensor comprising at least one source for emitting electromagnetic light in a room at least having objects to be guarded and provided with at least one detector for detecting reflected electromagnetic light striking thereon, and with an alarm for generating an alarm signal in dependence on a detection signal being delivered by said at least one detector, characterized in that said security system comprises at least one modified light reflecting label provided in the room to be guarded, which directs incident electromagnetic radiation emanating from said at least one source in modified form to said at least one detector, whereby said at least one detector delivers a detection signal in case of a typical change in at least the modified electromagnetic radiation striking thereon.

2. A security system according to claim 1, characterized in that said at least one detector delivers a detection signal in case of a change in at least one wave characteristic (phase, amplitude, polarization, energy (density) and/or frequency) of the electromagnetic light.

3. A security system according to claim 1 or 2, characterized in that said at least one source emits characteristic electromagnetic light in the room to be guarded.

4. A security system according to claim 1, 2 or 3, characterized in that said at least one detector is selective for electromagnetic light emanating from said at least one source, which is directed to said at least one detector by said at least one label.

CONFIRM AVON COPY

5. A security system according to any one of the preceding claims, characterized in that said at least one label reflects incident electromagnetic light emanating from said at least one source to said at least one detector.

6. A security system according to any one of the preceding claims, characterized in that said at least one label actively transmits electromagnetic light to said at least one detector, said electromagnetic light corresponding with the electromagnetic light emanating from said at least one source, which strikes on said at least one label.

7. A security system according to any one of the preceding claims, characterized in that said at least one label modifies at least one wave characteristic (phase, amplitude, polarization, energy (density) and/or frequency) of the electromagnetic light emanating from said at least one source.