GB1564457A - Infrared intrusion detectors - Google Patents

Description

(54) IMPROVEMENTS IN INFRARED INTRUSION DETECTORS (71) We, CERBERUS LIMITED, a Swiss company of alte Landstrasse 411, CH-8708 Maennedorf, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an improved infrared instrusion detector of the type comprising a number of reflective surfaces which focus infrared radiation arriving from different separate receiving regions upon a common radiation receiver.

With the aid of detectors of this type the presence of an object, for instance an intruder or a burglar in a protected room or area is determined by detecting the infrared radiation radiated by the object. The radiation in question can be the inherent radiation of the individual, in the range between 5 ,xm and 20 jim preferably between 7 jim and 14 jim. However, instead there can alternatively be provided a source of infrared radiation and means for evaluating the radiation reflected by the object or the individual. This arrangement provides the advantage that it enables the use of radiation in the near infrared range above 1 jtm, where most optical components, such as lenses and so forth do not yet exhibit any appreciable infrared absorption.When utilizing the inherent radiation of the individual it is necessary, on the other hand, to carefully select the optical components employed in order to maintain the infrared absorption as small as possible.

Coverage of the protected room or area by a number of separate viewing fields or receiving regions with intermediately situated dark zones or fields has been found to be particularly advantageous, in order to be able to detect even the slightest movements of an individual who otherwise would not appreciably alter the total amount of radiation received. With suitable coverage of the space, suitable to the field of application, it is possible to achieve the result that even slight movements of the intruder cause a boundary between a receiving region and a dark zone to be traversed so that a pulselike signal or an alternating voltage signal appears at the output of the radiation receiver and can easily be detected by means of a conventional evaluation circuit and utilized for triggering an alarm signal.Different patterns of receiving area have already been proposed, for instance the coverage or subdivision of a room by means of a large number of receiving rays possessing small aperture angles, by receiving strips or circular- or conical-shaped receiving regions.

However, with state of the art arrangements of the aforementioned type the reflector surfaces are arranged such that the different receiving rays or receiving strips intersect in front of or at the front of the intrusion detector. This has the advantage that the reflection angle at the individual reflector surfaces can be maintained just slightly less than 90". Thus even with a relatively poor optically corrected surface good focusing can be obtained at the radiation receiver and a small aperture angle of the received rays or regions. Since such intrusion detectors can also be equipped with simple spherical reflectors, attempts have already been made on numerous occasions to employ them in practice.However, it has been found to be extremely disadvan tageous that at the area of the intersecting receiving region, i.e. at the near or close region directly in front of the entrance aperture of the detector, the sensitivity is greater by many times than at the remote region, i.e. at a greater spacing from the entrance aperture side. Therefore, such devices tend to yield false alarms when insects or other living organisms are present in their close region. Also, the closure disc which is a]most always used with such devices, and serves to protect or camouflage the device, can result in triggering of a false alarm.This closure disc is generally constructed such that it is only permeable to radiation in the wavelength range of the radiation to which the detector is sensitive, for instance between 7 wsm and 14 pm. Radiation of other wavelengths is absorbed and heats the closure disc, which consequently again transmits its intrinsic infrared radiation towards the radiation receiver. In the presence of pronounced disturbing radiation in other wavelength ranges, it is therefore possible for a false alarm to be triggered. Additionally, for this reason it is often not possible to utilize the full sensitivity of such intrusion detectors.

Prior art intrusion detectors of this type are also associated with the drawback that they are extremely susceptible to false alarms and in many instances possess inadequate sensitivity especially in remote regions of the protected space.

Hence it is a primary object of the present invention to provide a new and improved construction of infrared radiation detector which is not associated with the aforementioned drawbacks and limitations of the prior art proposals.

Another important object of the present invention aims at overcoming the previously discussed drawbacks and providing a burglary detector which is little susceptible to false alarms and possesses good sensitivity, yet having a relatively small increase in sensitivity as the detector is approached.

According to the present invention there is provided an infrared radiation intruder detector comprising within a housing a radiation receiver and a plurality of reflector surfaces arranged to focus radiation arriving from different receiving regions upon the radiation receiver, said reflector surfaces being arranged and aligned such that each region in which radiation received from one direction intersects radiation received from another direction, is located behind the surface of the detector housing through which the radiation enters, as viewed in the direction of irradiation.

To this end the angle of inclination of the reflector surfaces, in comparison to the angle of incidence at the receiver reflector, must fall within certain angular ranges, as will be discussed more fully hereinafter.

In order to obtain good focusing upon the radiation receiver, notwithstanding the smaller angle of reflection at the reflector surfaces in comparison with heretofore known detectors, in a further extension of the invention the reflector surfaces externally of the axis of the device are formed as eccentric sections of a paraboloid of revolution. According to a further embodiment of the invention, possessing the additional advantages of ease in accommodation of the system to predetermined fields of application and ready adjustment, the different reflector surfaces are constructed as parts of the same cylindrical surface, which are separated from one another, perpendicular to the cylinder axis, by non-reflecting, preferably displaceable, strips.

The invention will be better understood from the following detailed description given with reference to the accompanying drawings wherein: Figure 1 illustrates a first exemplary embodiment of a reflector arrangement of an infrared intrusion detector according to the invention; Figure 2 illustrates a second embodiment of reflector arrangement of an intrusion detector; Figure 3 illustrates a third embodiment of reflector arrangement of an intrusion detector; Figures 4, 5 and 6 respectively show different embodiments of intrusion detectors equipped with different types of reflectors; and Figure 7 illustrates a still further construction of a reflector employing a doublycurved reflector surface.

Referring now to the drawings, the arrangement illustrated in Figure 1 shows a housing G which is provided at its front side or face with an infrared filter B which is transmissive for the wavelength band to be evaluated. Within the housing G there are arranged three reflectors, Rl, R2, R3 such that radiation arriving from different directions El, E2 and E3 can be focused by respective ones of the reflectors upon a radiation receiver F arranged at a common focal point of the reflectors. Instead of using only three reflectors it is to be understood that a larger number of reflectors can be provided, depending upon the desired number of preferred directions of reception. Also it is possible to dispense with a reflector located on the axis of the device.Furthermore, instead of the illustrated coplanar arrangement of reflectors, producing a linear arrangement of receiving directions, a threedimensional arrangement can be selected.

The alignment of the reflectors R1, R2, R3 also can be such that the preferred directions of reception form a raster or grid, for instance as disclosed in co-pending application No. 25304/77 (Serial No.1,561,407).

In the embodiment of Figure 1 the reflectors Rl and Ra located externally of the central or longitudinal axis E of the device.

are inclined towards the longitudinal axis E2 in such a manner that the angle /3 of the primary normal or perpendicular of the reflector surfaces is greater than the angle of incidence a of the radiation incident upon the receiver F. Consequently regions S in which radiation received from one direction intersects radiation received from a different direction-viewed in the direction of irradiation-are all located with respect to one another between the radiation receiver F and the intermediate reflector R2. Consequently, any infrared radiation, which emanates from points directly in front of the closure disc or filter B, or from the closure disc itself, is prevented from being reflected by a number of reflectors onto the radiation receiver F.The increase in sensitivity in regions adjacent the detector, in comparison to the remote sensitivity, can be thus reduced to that amount which cannot be avoided for other reasons, and any triggering of false alarms by small living organisms located in front of or upon the closure discs or owing to temperature radiation of the disc B itself can be largely prevented.

Heating of the closure disc or filter B by the ambient radiation can be still further reduced by means of a diaphragm SB comprising a solid body formed of a good thermally-conductive material and located in front of the housing G. The body is provided with openings or bores through which preferably only radiation emanating from the contemplated receiving directions E1, E2 and E3 can enter the detector, whereas radiation coming from other directions is largely absorbed. A further improvement can be obtained if there is arranged in front of the radiation receiver F a further filter element advantageously possessing the same properties as the filter or closure disc B. In this way the infrared self-radiation of the closure disc B is selectively absorbed by the further filter element.

Figure 2 illustrates an embodiment wherein the points of intersection S are shifted rearwardly behind the rear wall of the housing G by appropriately inclining the reflector Rl and Ra. This is realized by making the intersection angle ,ss of the respective normal or perpendicular at the centre of area of each reflector surface with the longitudinal axis E2 of the device is chosen to be smaller than one half of the angle a at which radiation is incident upon the receiver F. An advantage of this embodiment, apart from the aforementioned feature, is that the intersection points S are shifted quite far rearwardly and the susceptibility to false alarms and the sensitivity variation can be further reduced.A certain drawback exists, however, in that here the angle of reflection must be considerably smaller than 90 , requiring better optical correction of the reflection surfaces, or larger aperture angles of the individual receiving regions must be tolerated, which, however, in many practical instances, is desired in any case. In the embodiment of Figure 2 there are provided, as a further improvement, lamella or webshaped diaphragms SB, composed of spacedapart lamellae or webs 22 arranged in front of the reflector assembly and disposed so as to limit the entrance angles of received radiation.

In the embodiment shown in Figure 3 the eccentric reflector surfaces R, and Ra are rearwardly inclined, so that the normal at the centre of area intersects the longitudinal axis E of the device at a point behind the reflector and the angle ,ss becomes greater than 90". In this case an intersection point S of the receiving directions which is located behind the front of the device is always obtained. With this embodiment there can be realized receiving directions which cover an entire 1800 field, so that an intrusion detector thus arranged due to its panoramic sensitivity is particularly suitable for use as a ceiling alarm which can be mounted at the centre of the room.In this case it is advantageous to also construct the side portions of the housing G as infrared filters B.

Since it is not possible to obtain good focusing upon the receiver F from the lateral receiving directions E1 and E3, due to the obtuse angle of reflection when using spherical mirrors, it is advantageous to construct the lateral reflectors R1 and Ra as markedly eccentric sections of a paraboloid of revolution, the axis of which is aligned essentially parallel to the particular preferred direction of reception.This is shown in the case of R1 by paraboloid P, of which the axis Pa is parallel to the preferred direction Ea. In this way a considerable improvement can be realized and also with lateral radiation incidence a sharper boundary can be obtained between the regions of preferred reception or viewing fields and the intermediately situated non-preferred or dark zones or fields than was possible with the heretofore known infrared radiation intrusion detectors employing spherical mirrors.

In summation it can be stated that the characteristic feature, namely that the intersection points of the individual directions of preferred reception, viewed in the radiation direction, are located behind the front of the detector, or behind the radiation receiver usually arranged at this region, is realized in that the angle of inclination of each eccentric reflector defined by, the intersection angle /3 of the normal at its centre of area with the longitudinal axis of the device, is chosen such that it lies outside of the region between the angle of incidence a at the receiver and one half of this angle lea/2. With heretofore known constructions the normal angle ,ss was selected such that it assumed a value between the angle of incidence a and one half of this angle lay/2, resulting in the intersection point of the receiving directions coming to lie in front of the radiation receiver F.

Figure 4 illustrates an intrusion detector in which a reflector arrangement of the type shown in Figure 1 or Figure 2 is employed.

A generally vat- or trough-shaped reflector support 5 is rotatably and pivotably arranged by means of a bracket 4 upon a support plate 2 within a housing 1, which is covered at the front by a filter 3 (represented as being wholly transparent) which is pervious to infrared radiation. The reflector support 5 is arranged such that the device axis can be adjusted in accordance with the specific application. In the trough-shaped reflector support 5 there are mounted five or more reflector elements R, R2, Ra etc. Forwardly of the front opening an infrared radiation receiver 6 is secured, by means of an attachment bracket, in such a manner that it is located approximately at the focal points of all the reflector surfaces.The terminals of the radiation receiver 6 are connected with any conventional evaluation circuit A known to the art and arranged internally of the housing 1 and-which circuit, upon a sudden change in the radiation or a rapidly fluctuating irradiation of the radiation receiver 6, triggers an alarm signal.

It is here mentioned that the reflector element Rl, R2 etc. can be constructed as spherical mirrors or paraboloids of revolution, there being formed a number of linearly arranged discrete receiving directions with small aperture angles. In the event stripshaped receiving regions are desired, then this is possible by constructing the reflector surfaces as doubly-curved surfaces having different principal radii of curvature, and the radiation receiver is mounted at the focal point of the horizontal section. With such a construction vertically arranged, stripshaped receiving regions having relatively small horizontal aperture angles can be obtained.

Such an arrangement has been shown in Figure 7 wherein the therein depicted reflector surface Ra constitutes as aspherical double-curved surface having two different main radii of curvature and main focal length. The vertical section V and the horizontal section H are each constructed as a parabola or circular arc, and the focal point Fl of the horizontal section H is different than the focal point Fa of the vertical section V. The radiation detector S is arranged approximately at the focal point F1 of the horizontal section H. As a result, the receiving or viewing field E2 associated with the reflector surface Ra is focused or bundled relatively well horizontally, on the other hand, exhibits a rather large vertical aperture angle 7.

In the case of the radiation detector illustrated in Figure 5, the components of which correspond to the embodiment of Figure 4, the spreading of the point-shaped receiving directions into strip-shaped receiving regions E" E2, Ea, Ei and E1 is achieved by constructing the front side 7 of the housing as a cylindrical lens. Simple spherical reflectors or reflectors formed as paraboloids of revolution may also be used and the use of complicated and expensive reflectors having different primary radii of curvature can be dispensed with. The cylindrical lens 7 may be constructed as an echelon lens, for instance a Fresnel lens, so that its thickness and infrared absorption can be kept small.This is particularly desirable for use in a passive infrared detector for the detection of the self or intrinsic radiation of persons which occurs in the far infrared region. In this regard it is advantageous to form the cylindrical lens from a suitable infrared permeable plastic instead of from glass.

Regarding the intruder detector illustrated in Figure 6 there are used, instead of spherical or paraboloidal reflectors, substantially cylindrical reflector elements or components Rl, R2, Ra and R4 which are separated from one another by radiation-absorbing dark zones D1, D2 and Da. It is particularly advantageous to construct the reflector 8 upon which there are placed displaceable radiation-absorbing strips D1, D2 and Da. These radiation-absorbing strips may, for instance, be in the form of blackened metal strips which can be manually positioned in the desired locations and then fixed by cementing or the like, preferably so as to be capable of displacement if required.The radiationabsorbing strips are further advantageously mounted perpendicularly with respect to the cylinder axis, but also can be arranged to extend to an inclination thereto. The radiation receiver 6 once again is arranged at the focal line of the cylinder 8. There is thus formed a number of receiving regions E" E2, Ea and E. which are linearly arranged above one another and exhibit a very small horizontal aperture angle, but a large vertical aperture angle.What is of particular advantage in this case is that the receiving regions can be easily and conveniently adjusted and accommodated to the operating conditions by appropriate positioning of the radiationabsorbing strips Dl, D2 and Da. Since in this embodiment the normal angle /3=0, the intersection locations of the receiving regions in this case also are located behind the reflectors, so that here also the susceptibility to triggering false alarms and the increase of the near sensitivity can be kept small.

In addition to the use of the measures described above, the heating of the closure or filter disc 3 by the ambient radiation and the disturbances thus resulting can be reduced if the front or outer surface of the closure disc or lens is constructed to be selectively reflective, and specifically for as large as possible a wavelength range outside of the evaluated band, within which the filter must exhibit as high as possible a transmissivity. A further improvement can be realized by mounting in front of the front of the housing or in front of the closure or filter disc 3, diaphragms which screen or absorb radiation emanating from directions other than the intended receiving regions, as already mentioned in the description of Figures 1 and 2.These diaphragms can be advantageously constructed to be of strip or honeycomb form and/or to consist of a good absorbing blackened material having high specific heat and good thermal conductivity. For instance they may be formed of thick-walled or solid, black anodized aluminium so that good storage and dissipation of the incident radiation energy results.

WHAT WE CLAIM IS:- 1. An infrared radiation intruder detector comprising within a housing a radiation receiver and a plurality of reflector surfaces arranged to focus radiation arriving from different receiving regions upon the radiation receiver, said reflector surfaces being arranged and aligned such that each region in which radiation received from one direction intersects radiation received from another direction, is located behind the surface of the detector housing through which the radiation enters, as viewed in the direction of irradiation.

2. A detector in accordance with claim 1, wherein particular ones of said reflector surfaces do not lie in a longitudinal axis of the detector and aligned such that the angle formed by their principal normals with said longitudinal axis lies outside the angular range between the angle of incidence which the radiation arriving at the radiation receiver forms with said longitudinal axis and one half of said angle of incidence.

3. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces comprises a paraboloid of revolution.

4. A detector in accordance with claim 3 as dependent upon claim 2, wherein said reflector surfaces not lying on said axis comprise eccentric sections of paraboloids of revolution, the respective axes of which are aligned essentially parallel to the respective receiving direction.

5. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces comprises a double-curved surface possessing different principal radii of curvature and the radiation receiver is arranged substantially at the focal point of a principal section of the associated individual reflector surfaces.

6. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces is a substantially spherical surface and a cylindrical lens is arranged at the front of the detector housing.

7. A detector in accordance with claim 6, wherein the cylindrical lens is an echelon lens.

8. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces is a substantially paraboloidal surface and a cylindrical lens is arranged at the front of the detector.

9. A detector in accordance with claim 7, wherein said cylindrical lens is an echelon lens.

10. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces is a substantially cylindrical surface.

11. A detector in accordance with claim 1 or 2, wherein said reflector surfaces comprise portions of a common cylindrical surface, separated by radiation-absorbing strips mounted upon said cylindrical surface, the radiation receiver being arranged at the focal line of said cylinder surface.

12. A detector in accordance with claim 11, wherein said radiation absorbing strips are displaceable upon said surface.

13. A detector in accordance with any one of the preceding claims and further including a filter arranged at the front of the detector.

14. A detector in accordance with claim 13, wherein said filter is permeable to infrared radiation in a predetermined spectral range.

15. A detector in accordance with claim 13, wherein said filter has a front face such that radiation of a wavelength falling outside of a predetermined infrared-throughpass range is at least partially reflected.

16. A detector in accordance with any one of claims 1 to 15 and further including diaphragm means having openings and arranged forwardly of the front of the detector housing and aligned such that the openings thereof only permit passage of radiation emanating from predetermined receiving directions.

17. A detector in accordance with claim 16, wherein said diaphragm means contains radiation absorbing surfaces.

18. A detector in accordance with claim 16, wherein the diaphragm means comprise strips.

19. A detector in accordance with claim 16, wherein the diaphragm means is essentially of honeycomb form.

20. A detector in accordance with claim 16, wherein the diaphragm means comprise bores provided in a thermally highly conductive solid body member.

21. A detector in accordance with claim 13 and further including an additional filter with equivalent properties as said filter arranged at the front of the detector, said additional filter being arranged in front of the radiation receiver.

22. A detector in accordance with any one of the preceding claims wherein the intersection locations of the receiving regions are disposed behind the radiation receiver.

23. A detector in accordance with any one of claims 1 to 21, wherein the intersec

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (24)

**WARNING** start of CLMS field may overlap end of DESC **. screen or absorb radiation emanating from directions other than the intended receiving regions, as already mentioned in the description of Figures 1 and 2. These diaphragms can be advantageously constructed to be of strip or honeycomb form and/or to consist of a good absorbing blackened material having high specific heat and good thermal conductivity. For instance they may be formed of thick-walled or solid, black anodized aluminium so that good storage and dissipation of the incident radiation energy results. WHAT WE CLAIM IS:-

1. An infrared radiation intruder detector comprising within a housing a radiation receiver and a plurality of reflector surfaces arranged to focus radiation arriving from different receiving regions upon the radiation receiver, said reflector surfaces being arranged and aligned such that each region in which radiation received from one direction intersects radiation received from another direction, is located behind the surface of the detector housing through which the radiation enters, as viewed in the direction of irradiation.

2. A detector in accordance with claim 1, wherein particular ones of said reflector surfaces do not lie in a longitudinal axis of the detector and aligned such that the angle formed by their principal normals with said longitudinal axis lies outside the angular range between the angle of incidence which the radiation arriving at the radiation receiver forms with said longitudinal axis and one half of said angle of incidence.

3. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces comprises a paraboloid of revolution.

4. A detector in accordance with claim 3 as dependent upon claim 2, wherein said reflector surfaces not lying on said axis comprise eccentric sections of paraboloids of revolution, the respective axes of which are aligned essentially parallel to the respective receiving direction.

5. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces comprises a double-curved surface possessing different principal radii of curvature and the radiation receiver is arranged substantially at the focal point of a principal section of the associated individual reflector surfaces.

6. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces is a substantially spherical surface and a cylindrical lens is arranged at the front of the detector housing.

7. A detector in accordance with claim 6, wherein the cylindrical lens is an echelon lens.

8. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces is a substantially paraboloidal surface and a cylindrical lens is arranged at the front of the detector.

9. A detector in accordance with claim 7, wherein said cylindrical lens is an echelon lens.

10. A detector in accordance with claim 1 or 2, wherein each of said reflector surfaces is a substantially cylindrical surface.

11. A detector in accordance with claim 1 or 2, wherein said reflector surfaces comprise portions of a common cylindrical surface, separated by radiation-absorbing strips mounted upon said cylindrical surface, the radiation receiver being arranged at the focal line of said cylinder surface.

12. A detector in accordance with claim 11, wherein said radiation absorbing strips are displaceable upon said surface.

13. A detector in accordance with any one of the preceding claims and further including a filter arranged at the front of the detector.

14. A detector in accordance with claim 13, wherein said filter is permeable to infrared radiation in a predetermined spectral range.

15. A detector in accordance with claim 13, wherein said filter has a front face such that radiation of a wavelength falling outside of a predetermined infrared-throughpass range is at least partially reflected.

16. A detector in accordance with any one of claims 1 to 15 and further including diaphragm means having openings and arranged forwardly of the front of the detector housing and aligned such that the openings thereof only permit passage of radiation emanating from predetermined receiving directions.

17. A detector in accordance with claim 16, wherein said diaphragm means contains radiation absorbing surfaces.

18. A detector in accordance with claim 16, wherein the diaphragm means comprise strips.

19. A detector in accordance with claim 16, wherein the diaphragm means is essentially of honeycomb form.

20. A detector in accordance with claim 16, wherein the diaphragm means comprise bores provided in a thermally highly conductive solid body member.

21. A detector in accordance with claim 13 and further including an additional filter with equivalent properties as said filter arranged at the front of the detector, said additional filter being arranged in front of the radiation receiver.

22. A detector in accordance with any one of the preceding claims wherein the intersection locations of the receiving regions are disposed behind the radiation receiver.

23. A detector in accordance with any one of claims 1 to 21, wherein the intersec

tion location of the receiving regions are located behind the reflector surfaces.

24. An infrared intruder detector substantially as herein described with reference to the accompanying drawings.