Ceiling Mountable Passive Infrared Intrusion Detection System

This invention is related to U.S. Pat. No. 4,375,034 and to U.S. utility patent application Ser. No. 454,852, U.S. Pat No. 4,514,631 both the same inventive entity and assigned to the same assignee as herein, and both incorporated herein by reference.

This invention relates to intrusion detection systems and more particularly to a ceiling mountable passive infrared intrusion detection system.

Passive infrared intrusion detection systems are known for sensing the presence of an intruder in a protected space and for providing an output signal representative of intruder detection. Examples of passive infrared intrusion detection systems are shown in U.S. Pat. Nos. 3,036,219; 3,524,180; 3,631,434; 3,703,718; and 3,886,360. It is an object of the present invention to provide a system and a mirror assembly therefor especially suited to ceiling mounting to produce a field of view through which an intruder must pass when moving about the floor area of a protected region, through which an intruder must pass when moving between the ceiling and the floor of the protected area, and through which an intruder must pass when moving on the floor and directly below the mirror assembly.

Briefly, the ceiling mountable passive infrared intrusion detection system of the present invention provides a plurality of radially outwardly extending generally vertical first curtains symmetrically disposed azimuthally, either a generally disc shaped thin second curtain or a first plurality of circumferentially symmetrically disposed finger beams both transverse the vertical curtains, and either a conical third curtain or a second plurality of circumferentially symmetrically disposed finger beams both generally downwardly directed and nested within the field of view of the vertical curtains and of the field of view of the curtain transverse the first curtains. Each of the vertical curtains have a relatively broad field of view in the vertical plane and a relatively narrow field of view in the horizontal plane. The vertical curtains are arranged within a facility being monitored such that an intruder must traverse these curtains when in motion about the floor of the protected area and thereby trigger an intruder alarm. Either the generally disc-shaped thin second curtain or the plural first finger beams extend 360.degree. azimuthally. The generally disc-shaped second curtain, and each of the plural first finger beams are relatively narrow in the vertical direction, and are arranged within a facility being monitored such that an intruder must traverse therethrough when in motion between the ceiling and the floor of the area to be protected and thereby trigger an intruder alarm. Either the generally downwardly directed conical third curtain or the second plurality of finger beams are arranged within a facility being monitored such that an intruder must traverse therethrough when in motion about that region of the floor of the area to be protected defined directly below the detector.

The system includes a mirror assembly having a two-part and split-apart focusing mirror subassembly one element of which is cooperative with each one of an array of adjacent cylindrical mirror facets to provide the field of view of the vertical curtains. The cylindrical mirror facets are symmetrically disposed around 360.degree. of azimuth to provide multiple generally vertical first curtains. A conical mirror is cooperative with the same element of the split focusing mirror assembly to provide the field of view of the generally disc-shaped second curtain. The conical mirror is concentrically disposed outwardly of the array of adjacent cylindrical mirror facets. A second conical mirror concentrically disposed within both the first conical mirror and the cylindrical facet array is cooperative with the other element of the split focusing mirror subassembly to provide the field of view of the generally downwardly directed conical third curtain. In the alternative embodiment, a plurality of planar facets outwardly adjacent a corresponding one of the plural cylindrical facets are cooperative with the first focusing mirror subassembly element to provide the field of view of the first plurality of finger beams. A plurality of second planar facets concentrically disposed within and aligned with corresponding ones of the first plurality of planar facets are cooperative with the other element of the focusing mirror subassembly to provide the second plurality of finger beams that provide a field of view that protects the general region below the detector.

An infrared detector is disposed along the optical axis of the split focusing mirror subassembly and at the foci thereof to provide an electrical signal in response to received radiation from the field of view of the first curtains, from the field of view of either the second curtain or the first plurality of finger beams, and from the field of view of either the generally downwardly directed third curtain or the second plurality of finger beams representative of intruder presence. In the first embodiment, an unbalanced infrared detector is disclosed, and in the second embodiment, a balanced infrared detector is disclosed. The detector signals are electronically processed in both embodiments to provide an output indication of intruder presence when moving about the floor or through the air space of the protected facility.

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a sectional view of a mirror assembly embodying the present invention;

FIG. 2A shows a plan view of the field of view of the mirror assembly of the present invention;

FIG. 2B showns an elevational view of the fields of view of the mirror assembly of the present invention;

FIG. 3A and FIG. 3B are different scale plan views of alternative embodiments of the field forming mirror subassembly of the mirror assembly of the present invention;

FIG. 4A shows an elevational view and FIG. 4B shows a plan view of the detector subassembly of the mirror assembly of the present invention; and

FIG. 5A shows an elevational view and FIG. 5B shows an alternate embodiment of the detector subassembly of the mirror assembly of the present invention.

Referring now to FIG. 1, there is shown a sectional view of a novel mirror assembly illustrating a ceiling mountable passive infrared intrusion detection system in accordance with the invention. The mirror assembly includes a split focusing mirror generally designated 10, an infrared detector 12 disposed along the optical axis of the split mirror 10 and at the common-foci thereof, a circular array of adjacent cylindrical mirror facets 15 each oriented to provide a predetermined first field of view and to cooperate with the mirror assembly 10 to direct infrared radiation within the associated field of view to the cooperative portion of the mirror assembly 10 and thence to detector 12, a first conical mirror 16 oriented to provide a predetermined second field of view and to cooperate with mirror assembly 10 to direct infrared radiation within the second field of view to the cooperative portion of the mirror assembly 10 and thence to the detector 12, and a second conical mirror 17 oriented to provide a predetermined third field of view and to cooperative with the mirror assembly 10 to direct infrared radiation within the third field of view to the cooperative portion of the mirror assembly 10 and thence to the detector 12. Preferably, the mirrors 15 have their cylindrical axes orthogonal to the optical axis of the mirror assembly 10, and the mirrors 16, 17 have their longitudinal axes coincident with the optical axis of the mirror assembly 10. The detector 12 is operative to provide electrical signals in response to received infrared radiation that are electroncially processed in well-known manner to provide an output indication of intruder presence about the floor and in the air space of a protected facility.

In typical use, the mirror assembly is oriented with the optical axis of the mirror assembly 10 and the longitudinal axes of the mirrors 16, 17 vertical and the axes of the mirrors 15 horizontal. The cylindrical mirror facets 15 allow each of the associated fields of view to be relatively narrow in the horizontal plane, as shown in FIG. 2A, and relatively large in the vertical plane, as shown in FIG. 2B. The horizontal field of view or divergence angle designated "B" (FIG. 2A) is controlled by the focal length of the cooperating element of the split focusing mirror assembly 10. The curvature and arclength of the cylindrical miror facets 15 are determined in relation to the curvature of the cooperative focusing mirror assembly element to provide the intended vertical field of view or vertical divergence angle designated "A" (FIG. 2B). The front and rear edges of the cylindrical mirror facets 15 determine the limits or extent of the vertical field of view. The forward edge delimits the lower boundary of the field of view, while the uppper boundary of this field of view is determined by the rearward edge. In the illustrated embodiment, a vertical divergence angle of about 50.degree. typically is provided, while a horizontal divergence angle of about 5.degree. typically is provided. As illustrated in FIG. 3A, twelve such adjacent cylindrical mirror facets 15 are symmetrically arranged circumferentially about 360.degree. of azimuth to provide the twelve first curtains 18 (FIGS. 2A, 2B) having a generally vertical field of view (FIG. 2B). The field of view of the generally vertical first curtains in the illustrated embodiments extends from about 15.degree. to about 65.degree. below the horizontal. The ange of the first curtains depends on the focal length of the cooperative element of the mirror assembly 10 and upon the size of the detector 12. Typically, the focal length and element size are selected to image a human-size target at at nominal range. As a result, the area to be protected is fully protected agains intruder translation about the floor of the protected space. Although twelve circumferentially symmetrically disposed cylindrical mirror segments are specifically illustrated, a greater or a lesser number of symmetrically or non-symmetrically arranged mirrors can be employed as well without departing from the inventive concept.

The conical mirror 16 allows the field of view of the second curtain to be generally disc-shaped and to extend 360.degree. azimuthally as shown at 20 in FIG. 2A, and to be relatively narrow in elevation as shown at 21 in FIG. 2B. The extent of elevational variation, the so-called drop-through angle designated "C" (FIG. 2B), is determined by the focal length of the coopertive element of the mirror assembly 10 and the size of the detector 12. Typically, a 2.5.degree. drop-through angle is obtained in the illustrated embodiment. As a result of the second field of view provided by the conical mirror 16, the area to be protected is fully protected against intruder translation between the ceiling and the floor of the protected area.

The conical mirror 17 allows the field of view of the third curtain to be generally cone-shaped, and it is disposed centrally within the several mirrors 15, 16 in such a way as to provide a generally downwardly directed zone of protection 22 (FIGS. 2A, 2B) disposed centrally within the several vertical curtains 18. The angle of the cone-shaped zone 22 designated "D" is determined by the focal length of the cooperative element of the mirror assembly 10 and the size of the detector 12. Typically, about a 3.5 angle is obtained in the illustrated embodiment. As a result of the third field of view provided by the conical mirror 17, the area directly below the detector is fully protected against intruder translation on the floor of the area to be protected.

The focusing mirror assembly 10 is split into component elements 10', 10" cooperative with field forming mirror assembly elements 15, 16 and 17 to provide the fields of view of the first, second and third curtains. The elements 10', 10" each have a different focal length, and are axially spaced apart along the longitudinal axis of the detector assembly to provide an aperture therebetween that allows IR energy present generally below the assembly to be incident on the detector 12. Because the field of view of the third curtain fully provides coverage of the protected facility below the detector, the optical aperture of the mirrors 15, 16 is thereby freed to be utilized to provide a downrange detection sensitivity, via the plural first curtains, that otherwise would not be possible. The present invention therewith achieves a more efficient distribution of the system optical aperture. The conical mirrors 16, 17 bring optical energy present in the second and third curtains to the detector 12 in such a way that the energy is "smeared" due to the curvature of the mirrors 16, 17. A detector assembly of the so-called unbalanced type suitable for use with the "smeared" energy pattern provided by the field-forming conical mirrors 16, 17 is generally designated at 24 in FIGS. 4A, 4B. The detector 24 includes inner and outer equal-area infrared detectors 25, 26 mounted in a housing 27 having an infrared transparent window 28 such that infrared energy received thereby is incident only on the central detector 25. The "smeared" energy pattern of the IR energy received via the conical field-forming mirrors 16, 17 that is incident on the unbalanced detector assembly 24 thereby provides a signal indication of intruder presence.

Referring now to FIG. 3B, generally designated at 29 is an alternate embodiment of the field-forming mirror assembly of the present invention. The assembly 29 like the assembly illustrated in FIG. 3A has plural cylindrical facets 15 defining a corresponding one of the fields of view of the generally vertical curtains 18 (FIGS. 2A, 2B). The assembly 29 differs therefrom insofar as a first plurality of planar mirror facets 30 replace the conical mirror 16, and a second plurality of planar mirror facets 31 replace the conical mirror 17. The first and second pluralities of planar facets 30, 31 are circumferentially spaced symmetrically about the field forming mirror assembly 29 and are individually cooperative with a corresponding element 10', 10" of the split focusing mirror assembly 10 (FIG. 1) to provide an associated one of first and second pluralities of circumferentially symmetrically oriented finger beams. While any number of facets 30, 31 can be employed, in the illustrated embodiment forty-eight such facets have been found to be sufficient to provide an effectively continuous coverage of the field of view provided by the second and third curtains of the embodiment of the field forming mirror assembly of the FIG. 3A embodiment. The energy pattern of the facets 30, 31 is not-smeared at the detector 12 as is the case for the conical mirrors of the first embodiment, so that a so-called balanced detector can be employed therewith.

The balanced detector subassembly of the present invention is shown in FIGS. 5A, 5B and includes an inner infrared sensitive element 32 and an outer infrared sensitive element 34 concentric therewith and of equal area. The elements 32 and 34 are formed on a pyroelectric substrate 36. As shown in FIG. 5A a housing 27 having a window 28 is provided such that both the central sub-element 32 and the sub-element 34 are in external radiation receiving relationship. Any suitable pyroelectric substrate can be utilized such as thickness poled ceramic PZT, lithium tantalate, and polyvinylidene flouride, among others. As shown in FIG. 1, the detector 12 in both embodiments is preferably mounted in a recess provided therefor to help protect it from unwanted radiation and air turbulence. It should b noted that the detector can be otherwise mounted in a position intended to receive infrared radiation without departing from the inventive conecpt.

The shape of the cylindrical mirrors can be varied to control the system aperture to vary the system sensitivity across the viewing fields. For example, the cylindrical mirrors can be structured or shaped to provide lower sensitivity to objects near the detector and higher sensitivity to objects further removed from the detector. A smaller cylindrical surface area provides a smaller aperture and therfore lower sensitivity. While the image at the detector is distorted by the cylindrical mirrors, such distortion is not of any material detriment to system performance, since intruder detection is based upon the change in received radiation due to a moving intruder entering or leaving corresponding ones of the fields of view rather than precise imaging of the intruder onto the detector. The elements of the split focusing mirror assembly preferably are spherical segments.

The invention thus provides a ceiling mountable passive infrared intrusion detection system in which one or more first solid curtains of protection are provided to achieve an area of survelliance which cannot readily be compromised or circumvented by an intruder in translation about the floor area whether by crawling or by jumping, in which a second curtain of protection transverse the one or more first curtains is provided to achieve an area of survelliance which cannot be readily compromised or circumvented by an intruder whether dropping into the area to be protected such as through an unauthorized hole in the ceiling of the protected area or scaling upwardly to the ceiling such as on a rope, and in which a third curtain of protection is provided to protect intruder motion directly below the mirror assembly. The optical aperture can be easily controlled by shaping of the cylindrical mirror surfaces. Uniform detection sensitivity is obtained irrespective of the range of an intruder.

It will be appreciated that many modifications of the presently disclosed invention can be effected without departing from the scope of the appended claims.