WO2002065417A1

WO2002065417A1 - Perimeter barrier systems and method of perimeter barrier monitoring

Info

Publication number: WO2002065417A1
Application number: PCT/AU2001/001574
Authority: WO
Inventors: Donald Jaffrey
Original assignee: Future Fibre Technologies Pty Ltd
Priority date: 2001-02-13
Filing date: 2001-12-05
Publication date: 2002-08-22
Also published as: AUPR313701A0

Abstract

A perimeter barrier and method of monitoring a perimeter barrier are disclosed. The perimeter barrier includes posts (12, 14) and rails (16). A taut string (24) is suspended in one of the rails (16) and is tensioned by a spring (28) which is connected to post (12) and to the string (24). An optical fibre is coupled to the string (24) by attachment members (32) so that when the barrier element is disturbed, the taut string vibrates at one of its natural harmonic frequencies and imparts a vibrational movement to the waveguide to change a parameter of the light travelling through the waveguide so the change in parameter can be detected by a detector to provide an indication of the disturbance to the perimeter barrier.

Description

PERIMETER BARRIER SYSTEMS AND METHOD OF PERIMETER BARRIER MONITORING

FIELD OF THE INVENTION

This invention relates to a method and system for monitoring a perimeter barrier against intrusion or tampering utilising fibre optic sensing technology.

The invention constitutes a modification or improvement to that disclosed in our International patent application number PCT/AU00/01332 the contents of which is incorporated into this specification by this reference.

ART BACKGROUND

Our abovementioned International application discloses a method and system in which perimeter barrier elements such as fence sections are spring mounted for limited movement. An optical fibre is connected to the element so that any attempt to break in or tamper with the fence causes the element to move against the bias of the spring which in turn moves the optic fibre so that a change in a parameter of light travelling through the fibre can be detected to provide an indication of an intrusion or tampering. In the abovementioned invention the elements which are spring mounted may comprise an entire fence panel or individual pickets of a fence. In both situations the assembly of the perimeter barrier is made somewhat more difficult in view of the need to spring mount the elements for movement. This therefore increases the complexity of assembling the barrier and therefore the cost of the barrier.

Another possible problem with the system according to our earlier International application is the possibility of an element being moved inadvertently or as a nuisance without any attempt to breach the perimeter barrier, due to the spring mounting of the element. Because of the spring mounting if any person accidentally contacts the perimeter barrier it is likely to cause a movement against the bias of the spring or, people as a nuisance can easily move the elements thereby causing the change in the parameter of the light in the fibre and thereby indicating an attempted breach when no breach has in fact occurred. Thus, in view of the spring mounting accidental or nuisance movement of the fence is quite easy to achieve and this may result in an alarm condition being detected which is not in fact an attempt to breach the perimeter barrier.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is to provide a method and system which alleviates the need to spring mount the barrier elements for limited movement in order to enable detection of an intrusion or an attempt to tamper with the barrier.

The invention may be said to reside in a perimeter barrier systems including; a barrier element; a taut string coupled to the barrier element; a waveguide attached to the taut string and extending along the taut string; a light source for launching light into the waveguide so that light can travel through the waveguide; a detector for detecting light which has traveled through the waveguide; and wherein upon a disturbance of the barrier element the taut string vibrates at one of its natural harmonic frequencies and imparts a vibrational movement to the waveguide to change a parameter of the light traveling through the waveguide so that the change in parameter can be detected by the detector to thereby provide an indication of the disturbance to the perimeter barrier system.

According to the present invention any attempt to breach the perimeter barrier such as an attempt to scale the perimeter barrier will impart energy to the barrier and this will cause a slight movement of the perimeter barrier regardless of the manner in which the perimeter barrier is installed. This movement of the perimeter barrier will cause the taut string to commence to vibrate at one of its natural frequencies, usually the fundamental mode and because the waveguide is connected to the taut string the waveguide will also vibrate with the taut string thereby causing the change in the parameter of light which can be detected by the detector to thereby provide an indication of a breach of the perimeter barrier. Because energy is imparted from the perimeter barrier to the taut string to cause the taut string to vibrate, the perimeter barrier can be solidly erected in accordance with normal techniques such as by securing posts in concrete and securely attaching fence elements such as rails and pickets to the posts. Even with the perimeter barrier mounted or assembled in this manner any attempt to scale the perimeter barrier will still cause a slight movement, notwithstanding the fact that the posts or other members are embedded in concrete, which will be sufficient to cause the taut string to vibrate at one of its natural frequencies to enable an indication of a breach to be provided. However, any accidental contact with the perimeter barrier is unlikely to impart sufficient energy to the perimeter barrier to cause a movement which will create the vibrating movement of the string and therefore no spurious alarm condition will be given. Furthermore, any attempt to trigger an alarm for nuisance value will also be much more difficult to achieve because the perimeter barrier can be erected in a solid fashion thereby making it much more difficult to move the perimeter barrier.

Furthermore, the fact that the waveguide is caused to vibrate with the taut string at the natural frequency of the taut string also results in a well defined and controllable set of characteristics which are produced when an attempted breach of the perimeter barrier occurs . For example, the frequency of vibration, the attenuation or decay rate of the vibration and other characteristics of a string vibrating at one of its natural harmonic frequencies, enables easy detection of a change in parameter of the light which can be indicative of an attempted breach, as distinct from any low energy events such as slight movement of the fence element which may be caused by accidental contact, natural settling of the perimeter barrier after assembly or the like which will not be sufficient to cause the string to vibrate and therefore move the waveguide.

In the preferred embodiment of the invention the barrier element comprises a fence including at least two posts securely mounted in the ground, the posts supporting a fence section.

Preferably the fence section includes at least one horizontal or inclined rail and a plurality of pickets.

Preferably at least one of the rails is hollow and the taut string and waveguide are arranged within the hollow rail.

In one embodiment of the invention the taut string can be tensioned by connecting the string to a spring at least one end, the spring being connected to the perimeter barrier.

Preferably the spring is connected to one of the posts by a hook .

Preferably the other end of the string is also connected to a post of the perimeter barrier by a hook.

Preferably the waveguide comprises an optical fibre and the optical fibre is connected to the taut string by a plurality of attachments so that the fibre takes up a shallow curved configuration between the attachments.

In one embodiment of the invention the light source and detector are arranged at opposite ends of the optical fibre. However, in other embodiments the detector and light source can be arranged at a common end and the other end of the fibre can be mirrored so that light which is launched from the light source travels through the optical fibre and is reflected from the mirror to travel back along the fibre for detection by the detector.

The invention may also be said to reside in a method of monitoring a perimeter barrier including the steps of; connecting a taut string to the perimeter barrier; connecting a waveguide to the taut string, launching light into the waveguide; and detecting light which has traveled through the waveguide, whereby any attempt to breach the perimeter barrier will cause the taut string to vibrate at one of its natural frequencies thereby moving the waveguide with the taut string so as to change the parameter of light travelling through the waveguide and so that the detector can detect the change in parameter and thereby provide an indication of an attempted breach of the perimeter barrier.

Preferably the method includes providing at least one hollow rail and arranging the taut string and waveguide within the hollow rail.

Preferably the spring is connected to the barrier by a hook.

Preferably the other end of the string is also connected to the perimeter barrier by a hook.

Preferably the waveguide comprises an optic fibre and the optic fibre is connected to the taut string by a plurality of attachments so that the fibre takes up a shallow curved configuration between the attachments.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will be described, by way of example, with reference to the accompanying drawings in which;

Figure 1 is a view of a perimeter barrier embodying the invention; and

Figure 2 is a view of the barrier of Figure 1 with some of the componentary omitted for ease of illustration and explanation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to Figure 1 a perimeter barrier 10 is shown which is in the form of a fence comprising posts 12 and 14 which are mounted in a conventional fashion usually by digging a post hole and concreting the posts 12 and 14 into the ground. Obviously, the perimeter barrier will include a larger number of posts 12 and 14. A fence rail 16 is connected between the posts 12 and 14 by welding, brackets, bolts or any other suitable manner. The fence rail 16 is preferably formed from hollow metal tube of, for example, square or rectangular cross-section. A lower fence rail 16' can be arranged below the upper rail 16.

A plurality of pickets 18 in the form of metal rods or tubes of generally circular cross-section are connected to the rails 16 and 16' by welding, bolting or the like so as- to be securing connected to the rails 16 and 16'.

Thus, the fence structure according to the preferred embodiment of the invention is solidly assembled in a generally conventional fashion by mounting posts in concrete and attaching rails 16 and 16' and pickets 18 to the posts.

The posts 12 and 14 are provided with hooks 20 and 22 respectively which suspend a taut string 24. The string 24 can be formed from any suitable material such as wire, nylon, or any other suitable elastic material. In the preferred embodiment of the invention end 16a of the taut string 24 is connected to the hook 22 whereas end 16b is connected to a spring 28 which in turn is connected to the hook 20. The spring 28 maintains the string 24 taut and the tension of the string 24 can be adjusted by selecting a spring 28 of the required stiffness.

Each pair of posts 12 and 14 which make up the entire perimeter will provided with a taut string 24 in the manner shown in Figure 1. However, a single string could pass through posts 12 and 14 and occupy the space between a plurality of the pairs of posts 12 and 14.

As is best shown in Figure 2 a waveguide in the form of an optical fibre 30 is connected to the taut spring 24 by cable attachments 32.

For ease of illustration the optical waveguide 30 is not shown in Figure 1 and the rails 16 and 16' and pickets 18 are not shown in Figure 2. However, it will be apparent from a consideration of Figure 1 that the taut string 24 and the optical fibre 30 are arranged within the upper hollow fence rail 16 and therefore are concealed from view.

The optical fibre 30 passes through the posts 12 and 14 and will extend into adjacent horizontal rails (not shown) and be attached to taut strings 24 in those rails. Thus, a single fibre 30 can extend the entire length of the perimeter barrier if required.

A light source such as a pigtailed light source 50 is provided for launching light into the fibre 30. The source 50 can be connected to the fibre 30 by suitable fibre leads and couplers if required.

A detector 60 such as a photodetector is arranged at the other end of the fibre 30 for detecting light which has passed through the fibre 30. However, in other embodiments the detector 60 can be provided at the same end of the fibre 30 as the light source 50 and the other end of the fibre 30 can be mirrored so that light which is launched into the fibre is reflected off the mirror and travels back along the fibre to the detector 60.

As in the disclosure in our previously mentioned International patent application, the detection technique employed in the invention may be in the form of an optic modalmetric interferometer and the detector 60 includes modalmetric intβrferometeric processing capability. Any attempt to scale the perimeter barrier 10 shown in Figure 1 will cause a movement of the perimeter barrier 10 notwithstanding the fact that the posts 12 and 14 are embedded in concrete. This movement will be caused by an impart of energy due to the weight of a person attempting to climb over the fence or when leaping from the fence. This transfer of energy to the fence causes some slight movement of the posts 12 and 14 together with the accompanying rails 16 and 16' and pickets 18 notwithstanding the fact that posts 12 and 14 are embedded in concrete. This imparting of energy to the fence section shown in Figure 1 will cause the taut spring 24 to vibrate at one of its natural frequencies, and usually its fundamental mode, thereby converting a wide range of fence movements into a simple vibration of the taut string 24 with a well defined and controllable set of characteristics such as frequency of vibration, attenuation or decay rate etc. The spring vibrations are transmitted to the optical fibre 30 via the connections 32 and the optical signal pattern detected by the detector 60 is altered by the vibration of the string 24 and the loosely connected optical fibre 30.

However, if the fence is merely accidentally bumped this is unlikely to impart enough energy into the fence to cause the taut string 24 to vibrate at one of its natural frequencies. Furtherstill, any attempt to move the fence 10 for nuisance value to trigger an alarm is likely to take considerably more effort than in the arrangements according to our previously mentioned International application because of the fact that the pickets in the present fence section can be solidly attached rather than spring mounted as in the earlier International application. Furtherstill, because the nature of vibration of the taut string 24 will generally always be the same the characteristic change in a property of the light can be more easily defined to only establish an alarm in an event of an actual intrusion or significant tampering which is likely to cause a vibration of the taut string 24, as distinct from any other movement of the fibre 30 such as by slight settling of the fence, expansion or contraction etc.

In the preferred embodiment of the invention the string 24 is preferably formed from a multistranded high tensile steel wire coated with zinc or cadmium to inhibit corrosion. The spring constant of the spring 28 is selected to facilitate the formation of suitable vibrations in the string 24 and factors which affect this include the mass-unit length of the combined string and optical fibre 30, the manner and spacing of the attachment of the fibre 30 to the string 24, the free length of the string 24, the degree in the slack in the fibre 30 between attachment points 32 and the type and diameter of fibre used for the optical fibre 30.

In the preferred embodiment of the invention the movements of the string and fibre cable may not be synchronous. One triggers the other, but they have different dynamics. It is designed that the fibre cable flop around with the largest possible amplitude to give the strongest signal. If it tightly pinned to the taught cable at close spacings, it is effectively forced to vibrate with the same frequency and amplitudes as the string, but since the combined mass is much larger, the amplitude is smaller. If the cable to strings connections are fewer and free loops somewhat larger, the fibre cable absorbs more of the energy of the vibrating string and manifests this as lower frequency, larger amplitude vibrations. There is then further interaction between these two vibrating bodies and hence it gets complicated, but effectively they dampen each other after the first few major vibrations of each.

If the connections between cable and string are few and - li ¬

very loose, there is insufficient mechanical coupling between them and the fibre cable vibrates very little. Hence the system must preferably be optimised for each combination of wire, spring, length and cable mass.

In other embodiments rather than using hooks 20 and 22 to attach the string 24 to the posts 12 and 14 screws, brackets or other fasteners could also be used. Furthermore, rather than connect the string 24 directly to the posts 12 and 14 the string 24 could be connected to the rail 16 which in turn is connected to the posts 12 and 14. Preferably the optic fibre 30 comprises a single, multimode fibre. However, a single mode fibre could also be used.

In other embodiments, rather than form the perimeter barrier in the form of a fence, the barrier could be in the form of a wall with the string attached to the wall at a suitable location between two attachment points such as hooks and springs of the type previously described. The string and optical fibre could be concealed or simply located on an internal side of the wall so as to be out of view of any person attempting to climb over the wall. The nature of the wall or any other perimeter barrier which is used should be such that upon an attempt to climb over the wall or significant tampering of the wall will cause a slight movement of the wall which will impart the vibrational movement of the string in the manner previously described. In other arrangements the pickets shown in the drawings may be replaced by a mesh panel or sheet metal or similar barriers.

Furtherstill, the arrangement of the rail need not be horizontal and the rail can be arranged at an incline with the string and spring also arranged at the same incline without any significant change in operation of the preferred embodiment of the invention. The preferred embodiment of the invention provides the following advantages; a single string 24 is used for each fence section as shown in Figure 1 and this eliminates the need for a number of compression springs, and associated components which are required in the arrangement according to our previously mentioned International application; the required components required are relatively cheap, freely available and assembly and installation time of the fence 10 is reduced. the optical fibre 30 can be installed in the upper rail 16 and this is preferred because the degree of movement of the fence section 10 if someone attempts to scale the fence will probably be higher at the upper portions of the fence rather than lower portions of the fence, and the ability to locate the sensing section in the upper rail avoids the need for additional installation work at ground level; the fence pickets need not run through the rails and therefore cheaper fence designs are possible; the fibre 30 and string 24 can be contained within the rail 16 and are thus rendered insensitive to common environmental "affects" such as wind, rain, hail, vehicle noise, small animals etc and only movements which shake the fence structure trigger a vibration in the string 24; a fraction of the stored energy in the moving fence is focused into a set of vibrations in a string 24 of much lower mass, thus enhancing the amplitude of its movement. Thus, small fence movements become larger in amplitude vibrations of the fibre 30; the frequency of vibration is a characteristic of the string 24, not the environment or the fence and hence is relatively fixed. This can be used to advantage to simplify signal analysis and can lead to lower cost signal processors . Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.

Claims

1. A perimeter barrier systems including; a barrier element; a taut string coupled to the barrier element; a waveguide attached to the taut string and extending along the taut string; a light source for launching light into the waveguide so that light can travel through the waveguide; a detector for detecting light which has travelled through the waveguide; and wherein upon a disturbance of the barrier element the taut string vibrates at one of its natural harmonic frequencies and imparts a vibrational movement to the waveguide to change a parameter of the light travelling through the waveguide so that the change in parameter can be detected by the detector to thereby provide an indication of the disturbance to the perimeter barrier system.

2. The system of claim 1 wherein the barrier element comprises a fence including at least two posts securely mounted in the ground, the posts supporting a fence section.

3. The system of claim 2 wherein the fence section includes at least one horizontal or inclined rail and a plurality of pickets.

4. The system of claim 3 wherein at least one of the rails is hollow and the taut string and waveguide are arranged within the hollow rail.

5. The system of claim 1 wherein the taut string is tensioned by connecting the string to a spring at least one end, the spring being connected to the perimeter barrier.

6. The system of claim 5 wherein the spring is connected to one of the posts by a hook.

7. The system of claim 6 wherein the other end of the string is also connected to a post of the perimeter barrier by a hook.

8. The system of claim 1 wherein the waveguide comprises an optical fibre and the optical fibre is connected to the taut string by a plurality of attachments so that the fibre takes up a shallow curved configuration between the attachments.

9. The system of claim 1 wherein the light source and detector are arranged at opposite ends of the optical fibre.

10. The system of claim 1 wherein the detector and light source can be arranged at a common end and the other end of the fibre is mirrored so that light which is launched from the light source travels through the optical fibre and is reflected from the mirror to travel back along the fibre for detection by the detector.

11. A method of monitoring a perimeter barrier including the steps of; connecting a taut string to the perimeter barrier; connecting a waveguide to the taut string, launching light into the waveguide; and detecting light which has travelled through the waveguide, whereby any attempt to breach the perimeter barrier will cause the taut string to vibrate at one of its natural frequencies thereby moving the waveguide with the taut string so as to change the parameter of light travelling through the waveguide and so that the detector can detect the change in parameter and thereby provide an indication of an attempted breach of the perimeter barrier.

12. The method of claim 11 wherein the method includes providing at least one hollow rail and arranging the taut string and waveguide within the hollow rail.

13. The method of claim 11 wherein the taut string is tensioned by connecting the string to a spring at least one end, the spring being connected to the perimeter barrier.

14. The method of claim 11 wherein the spring is connected to the barrier by a hook.

15. The method of claim 14 wherein the other end of the string is also connected to the perimeter barrier by a hook.

16. The method of claim 11 wherein the waveguide comprises an optic fibre and the optic fibre is connected to the taut string by a plurality of attachments so that the fibre takes up a shallow curved configuration between the attachments.