Abstract:
An infrared motion detector including at least one infra-red radiation sensor, at least one radiation reflecting surface, operative to direct radiation impinging thereon towards the at least one infra-red radiation sensor and at least one coating layer, coating the at least one radiation reflective surface, which is substantially reflective to far infra-red radiation and which strongly absorbs at least one of visible light and near infra-red radiation, wherein the at least one coating layer includes black nickel.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is hereby made to U.S. Provisional Patent Application Ser. No. 60/834,367, filed Jul. 27, 2006, entitled PASSIVE INFRA-RED DETECTORS, the contents of which is hereby incorporated by reference and priority of which are hereby claimed pursuant to 37 CFR 1.78(a) (4) and (5)(i). 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to passive infrared detectors generally. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to passive infrared motion detectors used for detection of motion of human targets moving in a spatial region monitored by the detector, by sensing far infrared radiation emanating from the targets. Such detectors contain an optical system, such as a reflective mirror device, which directs and focuses the infrared radiation from one or more detection fields-of-view or zones thereof. The detection fields-of-view or zones monitor the spatial region and pass through an infrared transparent window into the detector housing and onto one or more infrared radiation sensors, located within the motion detector. 
         [0004]    The design of the optical system is usually based on the use of one or more optical elements, such as mirror segments, arranged in one or more rows, each row including one or more segments. The segments within the rows are arranged with their optical axes spread azimuthally in a plane, generally parallel to the horizontal, or inclined with respect to the horizontal. 
         [0005]    Each of the segments is arranged to focus infrared energy emanating from a pre-defined detection zone onto an infrared radiation sensor such as a pyroelectric sensor, which is common to one or more segments. The combined detection zones of the multiple optical elements or segments, constitute the field-of-view of the detector, which is defined as the detection region covered by the detector or the “coverage” of the detector. 
         [0006]    The mirrors are normally formed of plastic base such as Acrylonitrile Butadiene Styrene (ABS), preferably by injection molding or vacuum forming and are then coated with bright nickel or bright chrome as known in the art. 
         [0007]    In such detectors, incoming infrared radiation enters the detector through an infrared transparent window in the detector housing and is reflected by the mirror segments to focus onto a pyroelectric sensor. The window is provided to prevent insects and other spurious matter from entering the detector. 
         [0008]    A person moving through the field-of-view of the detector emits far infrared radiation having wavelength of 7-14 μm and causes the generation of a signal output from the infrared radiation sensor. This signal caused by a moving person is defined to be a “desired signal”. Signal processing circuitry of the detector detects and processes the desired signal and activates an alarm signal output when certain criteria are met. 
         [0009]    Infrared motion sensors of the type described hereinabove are typically subjected to various sources of “undesired” radiation during their operation, such as radiation emitted by strong light sources. Furthermore, motion sensors using mirrored optics are generally unprotected from various undesired wavelengths of incoming radiation. 
         [0010]    As a result, the “undesired” radiation reaches the mirror surface and is then reflected and focused onto the infra-red radiation sensor causing generation of “undesired signals”, which may cause false alarms and/or other inaccurate detection events. 
         [0011]    Sunlight, as well as tungsten/halogen lamps, such as automobile headlights, produces one type of undesired radiation that is known to promote false alarms in infrared motion sensors. These radiation sources emit strong radiation in both the visible and the near infrared spectrum. Accordingly, compliance testing of infrared motion sensors in various countries often involves the use of a halogen light source at fairly intense levels (e.g., 2000 to 6000 lux) to determine the immunity of the motion sensor to this type of radiation. 
         [0012]    Various solutions have been provided to minimize the effect of these undesired radiations. 
         [0013]    The following published patent documents and other publications are believed to represent the current state of the art: 
         [0014]    U.S. Pat. Nos.: 3,949,259; 4,199,218; 4,245,217; 4,321,594; 4,342,987; 5,424,718; 5,712,622; 5,608,220 and 6,822,788. 
       SUMMARY OF THE INVENTION 
       [0015]    The objective of the present invention is to provide a passive infra-red detector based on a reflecting mirror device, which is substantially immune to false alarms caused by undesired radiation in both the visible and the near infra-red spectrum, substantially without loosing its sensitivity to the desired far infra-red radiation having wavelengths of 7-14 μm. 
         [0016]    For accomplishing this objective the reflecting surfaces of the mirror device are coated preferably with a selective absorbing material, such as black nickel. Black nickel strongly absorbs visible light and near infrared radiation having wavelengths shorter than 2 μm. At the same time the black nickel coating is substantially reflective to far infrared radiation, having wavelengths of 7-14 μm, thereby acting as a selective filter. 
         [0017]    When compared to mirror devices coated with bright nickel or bright chrome as known in the art, mirror devices coated with black nickel are found to reflect far infra-red radiation substantially at the same level as bright nickel or bright chrome but at the same time to reduce the “undesired signals” caused by visible light and near infra-red radiation by 80%-90% compared to mirror devices coated with bright nickel or bright chrome. 
         [0018]    Another preferred coating is the black chrome coating which provides similar selective filtering properties as black nickel. Black nickel and black chrome coatings are provided by a simple electroplating process, similar to processes used for bright nickel and bright chrome coatings of the mirrors known in the art. Furthermore, mirror devices coated with black nickel and black chrome are resistant to environmental conditions and therefore do not need to be coated with any protective coating such as other selective coatings. 
         [0019]    The reflectivity to far infrared radiation and the absorbance of visible light and near infrared radiation of a mirror device coated with black nickel or black chrome may vary with the thickness of the coating. The preferred thickness may vary in the range of 0.2 to 10 micron depending on the type of electroplating bath and other plating parameters such as temperature, current, PH and the like. Furthermore, when varying the coating thickness of the black nickel, it is seen that at a certain thickness, the reflectivity of the far infra-red radiation of a mirror coated with black nickel was better, compared to the same mirror, coated with bright nickel or bright chrome as known in the art, without losing its absorbance to visible light and near infra-red radiation. 
         [0020]    There are other coatings that may be used together with or instead of black nickel or black chrome such as black copper, black zinc, black cobalt or iron oxide. 
         [0021]    There is thus provided in accordance with a preferred embodiment of the present invention an infrared motion detector including at least one infra-red radiation sensor, at least one radiation reflecting surface, operative to direct radiation impinging thereon towards the at least one infra-red radiation sensor and at least one coating layer, coating the at least one radiation reflective surface, which is substantially reflective to far infra-red radiation and which strongly absorbs at least one of visible light and near infra-red radiation, wherein the at least one coating layer includes black nickel. 
         [0022]    In accordance with a preferred embodiment of the present invention the at least one coating layer includes black chrome. Preferably, the at least one coating layer includes at least one of black copper, black zinc, black cobalt and iron oxide. Additionally or alternatively, the at least one coating layer is deposited onto a reflective coating layer. 
         [0023]    In accordance with another preferred embodiment of the present invention the reflective coating layer includes at least one of nickel, chrome, silver, aluminum, copper, steel, and gold. Preferably, the reflective coating layer is a highly reflective bright coating layer. Additionally or alternatively, the at least one coating layer has a thickness in the range of 0.2 and 10 microns. 
         [0024]    In accordance with yet another preferred embodiment of the present invention the at least one infrared radiation sensor is a pyroelectric sensor. Preferably, the far infrared radiation has wavelengths in the range of 7-14 μm. Additionally or alternatively, the visible light and the near infrared radiation have wavelengths below 2 μm. 
         [0025]    In accordance with still another preferred embodiment of the present invention the infrared motion detector also includes at least one intermediate radiation reflective surface located along the optical path of the radiation impinging on the at least one radiation reflective surface and operative to direct the radiation along the optical path toward the at least one infrared sensor. Preferably, the at least one intermediate radiation reflective surface is coated by the at least one coating layer. Alternatively, the at least one radiation reflective surface is not coated by the at least one coating layer. 
         [0026]    In accordance with a further preferred embodiment of the present invention the at least one radiation reflective surface includes a focusing mirror for far infrared radiation. Preferably, the at least one intermediate radiation reflective surface includes a non-focusing mirror for far infrared radiation. Additionally or alternatively, the at least one intermediate radiation reflective surface provides optical power for far infrared radiation. 
         [0027]    In accordance with a still further preferred embodiment of the present invention, the at least one intermediate radiation reflective surface is formed of a substrate base made of ABS (Acrylonitrile Butadiene Styrene). Preferably, the at least one radiation reflective surface is formed of a substrate base made of ABS (Acrylonitrile Butadiene Styrene). 
         [0028]    There is also provided in accordance with another preferred embodiment of the present invention a radiation reflector for use in motion detectors, to direct far infrared radiation towards an infrared radiation sensor, including at least one radiation reflective surface and at least one coating layer coating the radiation reflective surface which is substantially reflective to far infra-red radiation and which strongly absorbs at least one of visible light and near infra-red radiation, wherein the at least one coating layer includes black nickel. 
         [0029]    In accordance with a preferred embodiment of the present invention the at least one coating layer includes black chrome. Preferably, the at least one coating layer includes at least one of black copper, black zinc, black cobalt and iron oxide. Additionally or alternatively, the at least one coating layer is deposited onto a reflective coating layer. 
         [0030]    In accordance with another preferred embodiment of the present invention the reflective coating layer includes at least one of nickel, chrome, silver, aluminum, copper, steel, and gold. Preferably, the reflective coating layer is a highly reflective bright coating layer. Additionally or alternatively, the at least one coating layer has a thickness in the range of 0.2 and 10 microns. 
         [0031]    In accordance with yet another preferred embodiment of the present invention the far infrared radiation has wavelengths in the range of 7-14 μm. Preferably, the visible light and the near infrared radiation have wavelengths below 2 μm. Additionally or alternatively, the at least one radiation reflective surface includes a multi-segmented mirror. 
         [0032]    In accordance with still another preferred embodiment of the present invention the at least one radiation reflective surface includes a focusing mirror for far infrared radiation. Alternatively, the at least one radiation reflective surface includes a non-focusing mirror for far infrared radiation. Preferably, the at least one radiation reflective surface is formed of a substrate base made of ABS (Acrylonitrile Butadiene Styrene). 
         [0033]    There is further provided in accordance with a further preferred embodiment of the present invention a radiation reflector, for use in motion detectors, to direct far infrared radiation towards an infrared radiation sensor, the radiation reflector including a substrate base made of a plastic material, a first layer of electroless conductive coating plated over at least part of the substrate base and a second layer including black nickel electroplated over the first layer. 
         [0034]    In accordance with a preferred embodiment of the present invention the first layer includes electroless nickel or electroless copper. Preferably, the first layer includes a bright finish. Additionally or alternatively, the second layer includes black chrome electroplated over the first layer. 
         [0035]    In accordance with another preferred embodiment of the present invention the second layer includes at least one of black copper, black zinc, black cobalt and iron oxide electroplated over the first layer. Preferably, the second layer has a thickness in the range of 0.2 and 10 microns. 
         [0036]    In accordance with yet another preferred embodiment of the present invention the radiation reflector also includes an additional layer including bright acid copper electroplated over the first layer, and wherein the second layer is electroplated over the additional layer. Alternatively, the radiation reflector also includes an additional layer including bright nickel electroplated over the first layer, and wherein the second layer is electroplated over the additional layer. 
         [0037]    As a further alternative, the radiation reflector also includes a first additional layer including bright acid copper electroplated over the first layer and a second additional layer including bright nickel electroplated over the first additional layer, wherein the second layer is electroplated over the second additional layer. Preferably, the second additional layer includes at least one of chrome, silver, aluminum, copper, steel, and gold, having bright finish electroplated over the second layer. 
         [0038]    There is additionally provided in. accordance with an additional preferred embodiment of the present invention a method for reducing false alarms in passive infrared motion detectors employing at least one radiation reflective surface in order to direct far infrared radiation impinging thereon towards an infrared radiation sensor, the method including coating the radiation reflective surface by at least one coating layer including black nickel, which at least one coating layer is substantially reflective to far infra-red radiation and which strongly absorbs at least one of visible light and near infra-red radiation. 
         [0039]    In accordance with a preferred embodiment of the present invention, the coating includes coating the at least one radiation reflective surface by at least one coating layer including black chrome. Preferably, the coating includes coating the at least one radiation reflective surface with at least one of black copper, black zinc, black cobalt and iron oxide. Additionally or alternatively, the coating includes coating the at least one radiation reflective surface such that the coating layer has a thickness in the range of 0.2 and 10 microns. 
         [0040]    In accordance with another preferred embodiment of the present invention the coating the at least one radiation reflective surface includes electroless plating of nickel onto the at least one radiation reflective surface, bright acid copper plating of the at least one radiation reflective surface, bright nickel plating of the at least one radiation reflective surface and black nickel plating of the at least one radiation reflective surface. Alternatively, the coating the at least one radiation reflective surface includes electroless plating of nickel onto the at least one radiation reflective surface, bright acid copper plating of the at least one radiation reflective surface and black nickel plating of the at least one radiation reflective surface. 
         [0041]    As a further alternative, the coating the at least one radiation reflective surface includes electroless plating of nickel onto the at least one radiation reflective surface, and black nickel plating of the at least one radiation reflective surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0042]    The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
           [0043]      FIG. 1  is a simplified illustration of a detector constructed and operative in accordance with a preferred embodiment of the present invention; 
           [0044]      FIGS. 2A and 2B  are simplified sectional illustrations of the detector of  FIG. 1  in two alternative configurations, taken along the lines II-II in  FIG. 1 ; 
           [0045]      FIG. 3  is a simplified illustration of a detector constructed and operative in accordance with another preferred embodiment of the present invention; and 
           [0046]      FIGS. 4A and 4B  are simplified sectional illustrations of the detector of  FIG. 3  in two alternative configurations, taken along the lines IV-IV in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0047]    Reference is now made to  FIG. 1 , which is a simplified pictorial illustration of a mirror-based detector constructed and operative in accordance with a preferred embodiment of the present invention, and to  FIGS. 2A and 2B , which are simplified sectional illustrations of the detector of  FIG. 1  in two alternative configurations. 
         [0048]    As seen in  FIG. 1 , the detector typically includes a mirror having fourteen mirror segments, each defining a corresponding detection zone of the detector. The mirror segments are arranged in a mutually concave arrangement in two rows. 
         [0049]    As seen in the illustrated embodiment, a sensor  10  is associated with mirror segments  12 ,  14 ,  16 ,  18 ,  20 ,  22  and  24  in a top row and with mirror segments  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  in a bottom row. Each of the mirror segments is operative to focus radiation from its corresponding detection zone onto the sensor  10 . The mirror segments  12 ,  14 ,  16 ,  18 ,  20 ,  22  and  24  preferably are arranged in a concave arrangement in a circular arc within a housing element  50 . Similarly, mirror segments  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  preferably are arranged in a concave arrangement in a circular arc within housing element  50 . 
         [0050]    The housing element  50  defines an aperture  52  adjacent which is preferably located a window  54  having a circular cross-section. Window  54  preferably is made of a thin material transparent to infrared radiation, such as HDPE, Silicon, Germanium or any other suitable material. Alternatively, other appropriate window shapes may be used. 
         [0051]    Sensor  10  preferably comprises a dual element pyroelectric sensor, such as an LHi-968 sensor, commercially available from Perkin-Elmer of Freemont, Calif., USA. 
         [0052]    As seen with particular clarity in  FIG. 2A , it is a particular feature of the present invention that mirror segments  12 ,  14 ,  16 ,  18 ,  20 ,  22  and  24  are coated with a coating layer  57 , which is selectively substantially reflective to far infra-red radiation, having wavelengths of 7-14 μm and strongly absorbs visible light and near infra-red radiation having wavelengths shorter than 2 μm. Preferably, the coating layer  57  is formed of black nickel or black chrome. Additionally or alternatively coating layer  57  can also include black copper, black zinc, black cobalt or iron oxide. The coating preferably has a thickness between 0.2 and 10 microns. Preferably, mirror segments  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  ( FIG. 1 ) are also coated with a coating layer similar to coating layer  57 . 
         [0053]    In an alternative configuration, as shown in  FIG. 2B , the selective layer  57  of  FIG. 2A  is replaced by a first coating layer  58 , formed of black nickel, and preferably having a thickness between 0.2 and 10 microns, deposited onto a reflective coating layer  59 , preferably formed of bright nickel. Additionally or alternatively the first coating layer  58  may include black chrome, black copper, black zinc, black cobalt or iron oxide, and the reflective coating layer  59  may be formed of chrome, silver, aluminum, copper, steel or gold, preferably having a bright finish. 
         [0054]    In accordance with a preferred embodiment of the present invention, the mirror segments  12 ,  14 ,  16 ,  18 ,  20 ,  22 ,  24 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44  are formed of a substrate base preferably made of a plastic material, such as Acrylonitrile Butadiene Styrene (ABS), or any other suitable material, preferably by injection molding, vacuum forming, or by any other suitable process. 
         [0055]    The mirror segments are then coated or electroplated, preferably by forming a black nickel coating, which functions as first coating layer  58 , over bright nickel, which functions as reflective coating layer  59 , as shown in  FIG. 2B . Reflective coating layer  59  is formed by plating the plastic substrate base with a first conductive layer, such as by electroless nickel plating, followed by electroplating a second layer of bright acid copper over the first conductive layer, further followed by electroplating a third layer of bright nickel over the second layer. This is followed by electroplating a layer of black nickel over the bright nickel third layer, which layer of black nickel functions as first coating layer  58 . 
         [0056]    Alternatively, the bright nickel third layer may be obviated, and the layer of black nickel may be formed directly over the bright acid copper second layer. 
         [0057]    As a further alternative, the bright acid copper layer may also be obviated, and the layer of black nickel may be formed directly over the first conductive layer. Preferably, the first conductive layer is formed by electroless nickel plating or electroless copper, preferably having a bright finish. 
         [0058]    Reference is now made to  FIG. 3 , which is a simplified pictorial illustration of a mirror-based detector constructed and operative in accordance with another preferred embodiment of the present invention, and to  FIGS. 4A and 4B , which are simplified sectional illustrations of the detector of  FIG. 3  in two alternative configurations. 
         [0059]    As seen in  FIGS. 3-4B , the detector. typically includes. a mirror having fourteen mirror segments, each defining a corresponding detection zone of the detector. The mirror segments are arranged in a mutually concave arrangement in two rows. 
         [0060]    As seen in the illustrated embodiment, a sensor, preferably a pyroelectric sensor  60 , is associated with mirror segments  62 ,  64 ,  66 ,  68 ,  70 ,  72  and  74  in a top row and with mirror segments  76 ,  78 ,  80 ,  82 ,  84 ,  86  and  88  in a bottom row. Each of the mirror segments is operative to focus radiation from its corresponding detection zone onto the sensor  60  via at least one intermediate reflecting surface  90 . The mirror segments  62 ,  64 ,  66 ,  68 ,  70 ,  72  and  74  preferably are arranged in a concave arrangement in a circular arc within a housing element  92 . Similarly, mirror segments  76 ,  78 ,  80 ,  82 ,  84 ,  86  and  88  preferably are arranged in a concave arrangement in a circular arc within housing element  92 . 
         [0061]    The sensor  60  may be located at any suitable location within the housing  92 . The at least one intermediate reflecting surface  90 , here shown as a single intermediate reflecting surface, is located along optical paths defined by mirror segments  62 ,  64 ,  66 ,  68 ,  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84 ,  86  and  88  at a location suitable for redirecting radiation from the mirror segments to pyroelectric sensor  60 . 
         [0062]    In the illustrated embodiment of  FIGS. 3-4B , the sensor  60  is shown mounted at an aperture  93  in mirror segment  68 . It is appreciated that alternatively, the sensor  60  may be located rearward of the aperture, and in such a case may be mounted on a circuit board (not shown) which also mounts the mirror segments. In such a case, intermediate reflecting surface  90  may require some optical power. 
         [0063]    The housing element  92  defines aperture  94  adjacent which is preferably located a window  95 , having a circular cross-section. Window  95  preferably is made of a thin material transparent to infrared radiation, such as HDPE, Silicon, Germanium or any other suitable material. Alternatively, other appropriate window shapes, such as a flat window, may be used. 
         [0064]    Sensor  60  preferably comprises a dual element pyroelectric sensor, such as an LHi-968 sensor, commercially available from Perkin-Elmer of Freemont, Calif., USA. 
         [0065]    As seen with particular clarity in  FIG. 4A , it is a particular feature of the present invention that mirror segments  62 ,  64 ,  66 ,  68 ,  70 ,  72  and  74  are coated by a coating layer  97 , which is selectively substantially reflective to far infra-red radiation, having wavelengths of 7-14 μm, and strongly absorbs visible light and near infra-red radiation, having wavelengths shorter than 2 μm. Preferably, the coating layer  97  is formed of black nickel or black chrome. Alternatively, coating layer  97  can be formed of black copper, black zinc, black cobalt or iron oxide. The coating preferably has a thickness between 0.2 and 10 microns. Additionally, mirror segments  76 ,  78 ,  80 ,  82 ,  84 ,  86  and  88  and/or intermediate reflecting surface  90  may also be coated by coating layer  97 . In accordance with a preferred embodiment of the present invention, which provides an enhanced radiation selectivity effect, the mirror segments  62 ,  64 ,  66 ,  68 ,  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84 ,  86  and  88  and one or more intermediate reflecting surfaces, such as intermediate reflecting surface  90 , are coated by coating layer  97 . 
         [0066]    It is appreciated that not all the mirror segments and/or intermediate reflecting surfaces need necessarily be coated with coating layer  97 . One may choose to coat only some of the segments or intermediate reflecting surfaces with coating layer  97 , such that the segments or intermediate reflecting surfaces which are not coated have a bright reflective coating. 
         [0067]    In an alternative configuration, as shown in  FIG. 4B , the selective layer  97  of  FIG. 4A  is replaced by a first coating layer  98 , formed of black nickel, and preferably having a thickness between 0.2 and 10 microns, deposited onto a reflective coating layer  99 , preferably formed of bright nickel. Additionally or alternatively, the first coating layer  98  may include black chrome, black copper, black zinc, black cobalt or iron oxide, and the reflective coating layer  99  may be formed of chrome, silver, aluminum, copper, steel or gold, preferably having a bright finish. 
         [0068]    In accordance with a preferred embodiment of the present invention, the mirror segments  62 ,  64 ,  66 ,  68 ,  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84 ,  86  and  88 , as well as the intermediate reflecting surface  90 , are formed of a substrate base preferably made of a plastic material such as ABS or of any other suitable material, preferably by injection molding, vacuum forming, or by any other suitable process. The mirror segments, as well as the intermediate reflecting surface  90 , are then coated or electroplated preferably by one of the processes described hereinabove with respect to  FIGS. 1-2B . 
         [0069]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove as well as modifications and variations thereof as would occur to a person of skill in the art upon reading the foregoing specification and which are not in the prior art.