WO1984004986A1

WO1984004986A1 - A multi-laser security curtain

Info

Publication number: WO1984004986A1
Application number: PCT/AU1984/000100
Authority: WO
Inventors: John Leonard Hughes
Original assignee: Hughes Technology Pty Ltd
Priority date: 1983-06-03
Filing date: 1984-06-04
Publication date: 1984-12-20

Abstract

A laser curtain security system having a hollow pole (1) placed centrally of a substantially circular optical detector array (9) which is located on the surface where objects to be secured (13, 14) are situated. The hollow pole (1) contains a laser beam generator (2) and a beam expanding telescope (3) which propagates a "doughnut" shaped cross section laser beam (4) to conical mirrors (5, 7) which reflect the laser beam (4) into an inner and outer laser beam curtain (6, 8). The detector array (9) is connected to alarm circuits. The laser beam may be coded and more than two curtains may be generated. Goods may be protected on dry land, under water and in space.

Description

A MULTI-LASER SECURITY CURTAIN

This invention relates to a system which provides security protection for objects including aircraft, ships, motor vehicles, railway carriages and containers, consisting of a centralised pole from the upper portion of which several conical laser beams emmanate in a downward direction so that they strike the ground in a concentric circular pattern around the base of the pole to irradiate a circularly symmetric array of narrow band, optically filtered, optical detectors. As an intruder passes over the detector array, its shadow falls on a portion of the optical detectors within the detector array causing a change in the electrical current emitted by said detectors, more than one of which have to be shadowed in order to set off the alarm. In order to achieve the highest possible false alarm threshold for my invention it is necessary to use multiple laser beam curtains otherwise a single moth penetrating a single beam curtain near the top of the pole would cast a large shadow on the ground over the detector array and set off the alarm. By spacing the multi-layer laser beam curtains by distances greater than the dimensions of the largest birds likely to be flying in the vicinity of the pole, the circuits corresponding to two layers of the curtain cannot be activated since a laser beam will always illuminate the optical detector array on the ground. On the other hand, the alarm should not go off if a bird flew over the detector array near ground level and to avoid this the optical detectors have also to be arranged in multiple rows.

Prior art laser security systems have utilized single or multiple laser beams, rather than multiple laser curtains. The prior art systems were activated when the intruder cut the beam and affected the current flow in the optical detectors mounted as part of a laser fence. My invention differs from prior art systems in that it provides a conical, multilayered umbrella of light which covers the objects to be secured so that any sizable intruder penetrating any part of the curtain sets off the alarm.

It is an aim of my invention to secure a large conical volume containing valuable objects by generating a multilayer umbrella of light which irradiate a concentric array of optically filtered, optical detector array.

It is also the aim of my invention to provide the highest possible false alarm threshold by allowing the passage of small moving objects such as moths, birds and small animals. It is a further aim of my invention to indicate the exact location along the perimeter of the secured area that the intruder enters. Yet a further aim of my invention is to transmit a code along the laser beam so that it becomes difficult to interfere with optical parameters of the high curtain by applying an external source of light to the optical detector array. It is also an aim of my inveniton to protect goods on dry land, under water and in space.

A better understanding of my invention may be obtained by consideration of the accompanying diagrams which are not meant to limit the scope of my invention in any way. Figure 1 depicts a overall form of my invention with the central, hollow pole with the laser beam generator mounted in its base and emitting a "doughnut" mode laser beam with a hollow centre. The beam then propagates up the pole to be reflected at the top into multiple cones which propagate downwards to the ground to illuminate the detector arrays circumscribing the objects to be secured. Figure 2 depicts the relative position of the central pole and the optical detector array together wih the central alarm and power supply systems which could be included with the boundaries of the invention if required for added security. Figure 3 depicts a technique used to generate three conical laser curtains from one "doughnut" laser beam at the top of the pole. In Figure 1, numeral 1 indicates the central pole whilst numeral 2 indicates the laser beam generator. Numeral 3 indicates the beam expanding telescope whilst numeral 4 indicates the doughnut" shaped cross-section laser beam propagating up the inside of the pole 1. Numeral 5 indicates a semitransparent conical section which converts a portion of the "doughnut" shaped incident beam 4 into the inner umbrella curtain 6. Numeral 7 indicates the conical mirror at the top of pole l which reflects the remaining "doughnut" beam 4 into the outer umbrella indicated by numeral 8.

On striking the ground beams 6 and 8 also irradiate the detector array indicated by numeral 9, said array being protected by a shield indicated by numeral 10. Connecting leads indicated by mumerals ll and 12 respectively, connect detector array 11 and laser generator 2 to the control and alarm centres not shown. The goods to be secured are a truck indicated by numeral 13 and the containers indicated by numeral 14.

In Figure 2, pole 1 is at the centre of detector array 9 with leads 11 and 12 connecting to laser beam code generator indicated by numeral 15, which also feeds into the control unit indicated by numeral 16. Numeral 17 indicates the power supply and decoding unit for the photodetector array 9 whilst numeral 18 indicates the alarm unit.

In Figure 3, top of pole 1 has optics 5 and 7 mounted to produce three laser curtains from incident beam 4. Numeral 19 indicates the third curtain, each curtain being generated at appropriate angles relative to each other so as to provide optimum illumination of detector array 9.

My invention has application in a wide range of industries, including the transport, construction and defence industries. The laser beams used to generate the multilayer light curtains in my invention should be in a region of the electromagnetic spectrum which is least sensitive to the eyes of insects and birds so as to minimise the false alarms that could result from the presence of large amounts of such intruders in the light curtains if the laser wavelength was highly attractive to the insect or bird intruder. My invention can also accommodate continuously variable angles between the light curtain layers so that a scanning of the detector arrays becomes effective. In this way more information regarding the movement of any intruder can be obtained.

The height of the central pole of my invention must be enough for the security curtain to pass over the objects to be secured. For example, in the case of a large aircraft the pole would have to be about 100 ft tall and diameter of the detector array several hundred feet. For a wide distribution of objects to be secured, several poles may be required to provide adequate protection. From the safety viewpoint, the laser beam generator at the base of the pole could produce powerful laser beams which, if viewed directly would be very harmful to the eye. However, when spread out into a light curtain the laser intensity is dramatically reduced via the spreading effect so that when it reaches the detector array on the ground it is well within safety standards.

Claims

The claims defining the invention are as follows: (1) A laser multi-light curtain security system consisting of a hollow pole, positioned at the centre of a circular optical detector array placed on the surface on which the objects to be secured are situated, the said hollow pole containing a laser beam generator and beam collimating optics, said laser beam propagating up said pole at the top section of which is placed a series of partially reflecting, conically shaped beam reflectors and above which is positioned a totally reflecting conically shaped mirror, said optical light curtain which propagates downwards to illuminate the optical detector array, both laser beam generator and optical detector being connected to control and alarm units.

(2) A system as claimed in claim 1 where the laser curtain beams are coded.

(3) A system as claimed in claim 1 where the angles of the light curtains relative to each other are variable .

(4) A system as claimed in claim 1 where the laser beam generator emits a high intensity beam at the base of the pole but is spread into a low intensity, eye safe curtain of light by the time it illuminates the detector array. (5) A system as claimed in claim 1 where the wavelength of the transmitted laser. curtains is least sensitive to insects and birds.