GB2337170A

GB2337170A - Electromagnetic direction-finders

Info

Publication number: GB2337170A
Application number: GB8028535A
Authority: GB
Inventors: Dennis William George Byatt
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1980-09-09
Filing date: 1980-09-09
Publication date: 1999-11-10
Anticipated expiration: 2000-09-09
Also published as: GB2337170B; GB8028535D0

Abstract

Apparatus for finding the direction of a source of electromagnetic radiation (for example, an enemy infra-red laser) comprises an array 10 of sensors, means 15 casting a shadow 19 on the array when the apparatus is illuminated by the radiation, and means (the connection matrix 16,17,and computing means not shown) for determining the position of that shadow and thereby indicating the direction of the radiation source. Range is determined from two directional determinations.

Description

2337170 SENSOR DEVICES This invention relates to sensor devices, and

concerns in particular such devices suitable for detecting the presence of electromagnetic energy and for indicating the direction of the source thereof.

It is common in modern warfare for a battle unit (a soldier, a gun position, a tank, a 'plane or a ship, for example) to be illuminated by enemy-originating beamed electro magnetic radiation. Thus, a tank or gun position might be targetted by an infra-red laser beam missile-guidance system, or a 'plane or a ship might be scanned by a long-range radar detection system. While there are currently available a number of devices that can detect, and warn of, the use of electromagnetic radiation systems of this general kind there are few is - if any - that can in a simple and practical way indicate as well the direction from which the beamed energy is coming (a datum that may well be of crucial importance to the battle unit concerned). It is the object of the present invention to provide such a simple, practical direction- indicating electromagnetic radiation detector device.

In one aspect, therefore, this invention provides a method for determining the direction of a source of electroragnetic radiation, in which method illumination of the apparatus by the radiation causes a shadow to be cast upon a radiation sensor system, and the position of the shadow is determined and used to indicate the direction of the radiation source.

In a parallel aspect the invention provides apparatus for determining the direction of a source of electromagnetic radiation,Which apparatus comprises a radiation sensor system, means casting a shadow on the sensor system when the apparatus is illuminated by the radiation, and means for determining the position of that shadow and thereby indicating the direction of the radiation source.

The electromagnetic radiation can be of any type, though most likely types are those undetectable by the human eye, specifically infra-red (as used in present-day laser targetting systems) and microwaves(as used in radar systems).

Furthermore, since the apparatus must of necessity be larger than the wavelength of the radiation, and because the apparatus as a whole will usually be quite small (of the order of 10cms across), the radiation will in general have a wavelength of 1cm or less.

The radiation sensor system is an active system giving an output dependant upon the radiation falling upon it, and this output is an electrical output, enabling the source direction indication easily to be computed or considered at a site remote from the sensor system itself. The sensor system itself is conveniently an array of individual sensor elements (sensitive to the radiation to be detected) each providing an output of the required sort.

As so far described the apparatus of the invention may be defined as an electromagnetic-radiation detection and direction-indicating device comprising:

a) an array of individual sensor elements sensitive to the radiation to be detected and giving an electrical output in dependance thereon; b) positioned in front of the array a sighting member part of which is opaque to the radiation to be detected, so that when in operation radiation illuminates the device a shadow of the opaque part is cast onto the sensor array; and c) means for providing from a knowledge of the position of the sighting member and of the thus shadowed and illuminated areas of the sensor array an indication of the direction of the origin of the detected radiation.

Typical sensor elements are pyroelectric devices (those based, for example, on the recently-developed pyro- electric plastics such as polyvinylidene fluoride) and photoelectric devices (those based, for example, on silicon semiconductor elements of the type used or suggested for use in television camera tube targets), though clearly any type of sensor element can be used provided it is sensitive to the radiation concerned and gives a satisfactory output. Indeed, if desired more than one type of sensor element can be used in the same array.

The output of the sensor array determines the position of the shadow cast thereupon by the sighting member (this position determination is effected merely by knowing which element(s) is/are providing the spe7ified output). In the simplest case, where the array is merely a number of spaced detector elements individually wired, this presents no serious problems. In more complex cases, especially where high definition is required, it may be necessary to use a mosaic array - an array of many hundreds of individual detector elements very close together - connected to detector-identifying computing means via a multiplexed network of orthogonal electrode pairs. Devices using one or - other of these two systems are described in more detail hereinafter.

The actual electrical connections carrying the output from the sensor elements may be of any kind appropriate.

For example, they may be metal wires, metal foil (laid down by evaporation, and possibly transparent). or the presentlypreferred transparent tin oxide-type conductive strips.

The sensor array may, in the simplest case, be a linear array, but advantageously it is at least planar (so that it can be used to detect both the azimuth and the elevation of the source). Moreover, the array can be flat (as a straight line, or a flat plane), thus having a front face with a "view" of somewhat less than 180 0, or it can be_ a hemi-sphere curved (as a circle, a cylinder,,6r - most preferably - a sphere), thus having a curved front face with a view of 0 hmi-spherical up to 360 Devices using planar,,&ng spherical arrays respectively are described in more detail hereinafter; in the case of spherical devices, however, it may here be said that if the sensor elements are essentially opaque then they naturally face inwardly of the sphere and are conveniently small relative both to the spacing of adjacent elements and to the size of the shadow-casting member, whereas if the elements are essentially transparent (and can react to radiation from either side) then their relative size and the way they face is not so significant.

In front of the sensor array is the shadow-casting sighting member. As will be appreciated, the sighting member can either cast a large shadow adjacent to or surrounding a much smaller unshadowed area (as would an aperture or transparent window in the middle of an opaque screen) or - and more preferably - it can cast a small shadow adjacent to or surroundedbya much larger unshadowed area is (as would an opaque patch in the middle of a transparent window). Devices of this latter variety are described in more detail hereinafter, but here it is convenient to say that the shadow-casting member is preferably an opaque disc or a hemi- spherical in a transparent window (for use with a flat planar/sensor array) or an opaque spherewit-hin a larger transparent sphere (for use with a spherical sensor array).

The device of the invention includes means for providing an indication of the radiation source's direction, this being based upon a knowledge of the geometry of the device (the position of the sighting member relative to the sensor array, and the position of the shadow cast by the sighting member on the sensor array). Though other solutions are possible, presentday advances in computing 6 - technology effectively ii.emand that the means be a microprocessor; suitably pre-programmed the microprocessor will calculate the required direction from the two sets of position data (relative to a third reference datum line either on the device itself or like a compass - external thereto). The use of a microprocessor is particularly convenient when dealing with high definition devices and/or devices with a 360 0 solid angle view.

The device of the invention is intended primarily for use as an incident radiation beam direction finder., two or more of the devices may, however, be of use as a range finding device - and in yet another aspect this invention provides apparatus fordetermining the range of a source of electromagnetic energy, which apparatus comprises at least two of the direct ion-de termin ing apparatus of the invention mounted in spaced relation, there being provided in addition means for determining from the direction data the range of the source.

Range finding devices using two sets of bearing data are in themselves very well known, and so from that point of view the range finding device of the invention need not be described in an: great detail. Indeed, it suffices to say that two source-locating devices are adequate, that the further they are apart the more accurate the range finder becomes, and that the calculation of the range from the directional data is again best preferred by a suitably pre- programmed microprocessor.

The invention is now described, though only by way of illustration, with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic perspective see-through view of one embodiment of the radiation source direction-finding apparatus of the invention; Figure 2 is a diagrammatic cross-sectional view of another embodiment; Figure 3a is a representation of a complete system utilising yet another embodiment; and Figure 3b is a detail of the detector array used in the embodiment of Figure 3a.

The apparatus of Figure 1 comprises a planar rectangular array (generally.10) of a very large number of is individual sensor elements (as 11) - for clarity, only a few are shown - located on the inner surface of the back wall (12) of a box-like container (13). The front wall (14) of the container 13 is transparent (to the radiation to be detected), and carries at its centre point a sighting member disc (15) which is opaque (to the radiation to be detected). All the container walls except the front wall 14 are opaque, though for convenience they have been shown in see-through fashion, as though they were transparent.

As shown in the Figure, the apparatus is being illuminated by a beam of radiation (represented by the arrows) from an unseen source to the left of the Figure as viewed - thus, to the left of and above the apparatus datum line (18). This radiation passes through the container's transparent front face 14, except where it meets the opaque disc 15, and so illuminates all the sensor elements 11 except those in the shadow (19) case by the opaque disc 15 (and those, to the left (as viewed) of the line 20, which are shadowed by the opaque left side (21) of the container).

The sensor array 10 has output connections represented by the matrix of horizontal and vertical (as shown) lines (as 16 and 17). Standard methods may be used to determine whether any particular sensor element 11 is giving an output or not; the electronic apparatus involved (not shown in the drawing) is itself associated with computing apparatus (also not shown) which, fed with information as to which sensor elements 11 are giving outputs, and knowing the position and direction'of the datum line 18, can compute the direction of the source of the illuminating radiation.

Figure 2 represents a sectional view through the middle of a spherical device of the invention having a regular array of two types (infra-red and visible light) of individual sensor elements arranged on its inner surface. The Figure shows a device with a transparent shell (20) on the inner surface of which are arranged the sensor elements (as 21a, 21b)(each with its output connections illustrated by the line (as 22) projecting therefrom). Mounted (by means not shown) in the centre of the spherical shell 20 is the sighting member, an opaque sphere (23). The individual sensor elements 21 used in this embodiment are themselves opaque; they are mounted facing inwardly of the shell 20, and are small relative both to the spacing between adjacent elements 21 and the size of the opaque sphere 23, so that radiation passes between them and they themselves cast noappreciable shadow.

In this Figure radiation (represented by the arrows) is being beamed at the device from an unseen source to the left (as viewed). The sensor elements to the left of the terminator line (24) all effectively face away from the source and are so all in shadow; those to the right face towards the source, and so are illuminated, except for those in the shadow cast by the opaque sphere 23. As with the device of Figure 1, the outputs are fed (by means not shown) to apparatus (also not shown) which determines which elements are giving which output, and uses the information to compute the direction of the illuminating radiation.

The system represented by Figure 3A comprises a hemispherical detector array (30) connected, via suitable amplifiers and other electronic components (as 31, 32) to a visual display unit (33). The detector array 30 comprises a bowl-shaped array of two sorts of detector element (shown in more detail in Figure 3B), one of which (34) is a silicon- is based element for detecting visible and near visible radiation, while the other of which (35) is a polyvinylidene fluoride element for detecting infra-red radiation, and the two types of element are regularly interspersed one with the other over the array surface. The bowl-shaped array 30 is faced with a flat window (36 - here shown spaced from the array) transparent to the radiation to be detected, and the window has an opaque circular patch (37) at its centre. In operation, and when the array is illuminated from the front, the patch 37 casts a circular'shadow (38) upon the detector array. From the position of this shadow the various electronic components of the system compute the direction of the incident radiation, and cause this information to be displayed upon the visual display unit 33.

- 10 CLAXE: - 1. Apparatus for determining the direction of a source of electromagnetic radiation, which apparatus comprises a radiation sensor system, means casting a shadow on the sensor system when the apparatus is illuminated by the radiation, and means for determining the position of that shadow and thereby indicating the direction of the radiation source. 2. Apparatus as claimed in claim 1, wherein the radiation sensor system includes an array of individual sensor elements each providing an output of the required sort. 3. Apparatus as claimed in claim 2 which is an electromagnetic-radiation detection and directionindicating device, and which comprises:

a) an array of individual sensor elements sensitive to the radiation to be detected and giving an electrical output in dependance thereon; b) positioned in front of the array, a sighting member part of which is opaque to the radiation to be detected, so that when in operation radiation illuminates the device a shadow of the opaque part is cast onto the and c) sensor array; means for providing from a knowledge of the position of the sighting member and of the thus shadowed and illuminated areas of the sensor array an indication of the direction 11 - of the origin of the detected radiation. 4. Apparatus as claimed in claim 3, wherein the radiation sensor system is sensitive to infra-red radiation. 5. Apparatus as claimed in claim 4, wherein the elements of the sensor element array are based on polyvinylidene fluoride. 6. Apparatus as claimed in any of claims 3 to 5, wherein the sensor element array is connectbd to detector-identifying computing means via a multiplexed. network of orthogonal electrode pairs. 7. Apparatus as claimed in any of claims 3 to 6, wherein the sensor element array is at least planar. 8. Apparatus as claimed in claim 7, wherein the sensor element array is hemi-spherical or spherical. 9. Apparatus as claimed in any of claims 3 to 8, wherein the shadow-casting sighting member casts a small shadow adjacent to or surrounded by a much larger unshadowed area.

10. Apparatus as claimed in claim 9, wherein the shadowcasting sighting member is an opaque disc in a transparent window. 11. Apparatus as claimed in any of claims 3 to 10, wherein the means for providing an indication of the direction of the radiation source, based upon a - 12 knowledge of the geometry of the device, is a suitably pre-programmed microprocessor.

12. Apparatus for determining the direction of a source of electromagnetic radiation as claimed in any of the preceding claims and substantially as described hereinbefore.

13. Apparatus for determining the range of a source of electromagnetic energy, which apparatus comprises at least two of the direction-determining apparatus as claimed in any of the preceding claims mounted in spaced relation,', there being provided in addition means for determining from the direction data the range of the source.

1 ,7 --- '61 1., Amendments to the claims have been filed as follows is a) 1. Apparatus for determining the direction of a source of electromagnetic radiation, which apparatus comprises a radiation sensor system-, means casting a shadow on the sensor system when the apparatus is illuminated by the radiation, and means for determining the position of that shadow and thereby indicating the direction of the radiation source.

2. Apparatus as claimed in claim 1, wherein the radiation sensor system includes an array of individual sensor elements each providing an output of the required sort.

3. Apparatus as claimed in claim 2 which is an electromagnetic-radiation detection and direction indicating device, and which comprises:

c) an array of individual sensor elements sensitive to the radiation to be detected and giving an electrical output in dependance thereon; b) positioned in front of the array, a sighting member part of which is opaque to the radiation to be detected, so that when in operation radiation illuminates the device a shadow of the opaque part is cast onto the sensor array; and means forproviding from a knowledge of the position of the sighting member and of the thus shadowed and illuminated areas of the sensor array an indication of the direction i4_ of the origin of the detected radiation. 4. Apparatus as claimed in claim 3, wherein the radiation sensor system is sensitive to infra-red radiation.

5. Apparatus as claimed in claim 4, wherein the elements of the sensor element array are based on polyvinylidene fluoride. 6. Apparatus as claimed in any of claims 3 to 5, wherein the sensor element array is connected to detector-identifying computing means via a multiplexed network of orthogonal electrode pairs.

7. Apparatus as claimed in any of claims 3 to 6, wherein the sensor element array is at least two-dimensional.

8. Apparatus as claimed in claim 7, wherein the sensor element array is hemi-spherical or spherical.

9. Apparatus as claimed in any of claims 3 to 8, wherein the shadow-casting sighting member casts a small shadow adjacent to or surrounded by a much larger unshadowed area. 10. Apparatus as claimed in claim 9, wherein the shadow- casting sighting member is an opaque disc in a transparent window. 11. Apparatus as claimed in any of claims 3 to 10, wherein the means for providing an indication of the direction of the radiation source, based upon a 15, knowledge of the geometry of the device, is a suitably pre-programmed microprocessor. 12. Apparatus for determining the direction of a source of electromagnetic radiation as claimed in any of the preceding claims and substantially as described hereinbefore. 13. Apparatus for determining the range of a source of electromagnetic energy, which apparatus comprises at least two of the direction-determining apparatus as claimed in any of the preceding claims mounted in spaced relation, there being provided in addition means for determining from the direction data the range of the source.

14. A method for determining the direction of a source of electromagnetic radiation, in which method illumination of the apparatus by the radiation causes a shadow to be cast upon a radiation sensor system, and the position of the shadow is determined and used to indicate the direction of the radiation source.

15. A method as claimed in claim 14, wherein there is used the apparatus of any of claims 1 to 131. 16. A method as claimed in either of claims 14 and and substantially as described hereinbefore.