GB2468546A

GB2468546A - Apparatus for remotely applying sound pressure to a target

Info

Publication number: GB2468546A
Application number: GB0904452A
Authority: GB
Inventors: Matthew Henry; William O'neill
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-03-13
Filing date: 2009-03-13
Publication date: 2010-09-15
Also published as: GB0904452D0

Abstract

Apparatus 301 for remotely applying sound pressure to a target (such as a landmine 307 or airborne missile) comprises a sound energy source 303, for generating compression waves 304 in air, and a focussing element 302 arranged to focus the compression waves 304 to a convergence point 305 remote from the apparatus 301. Sound pressure at the convergence point 305 is sufficient to disrupt, destroy or perturb matter located in the region of the convergence point 305 (e.g. to explode a landmine 307).

Description

ACOUSTIC APPARATUS AND METHOD OF OPERATION

BACKGROUND

Technical Field of the Invention

The system relates to technologies for clearing land mines and other ordinance, particularly for clearing explosive devices which are triggered by pressure. The system also finds application in the area of repelling incoming missiles, mortars and other such airborne ordinance.

The United Nations (UN) and the International Campaign to Ban Landmines (ICBL) estimate that there are between 70 and 110 million unexploded anti-personnel landmines (APLs) in the ground at the time of writing. In 2007 there were 5426 confirmed landmine victims with the estimated number three or even four times greater, of these nearly 90% are civilian and around half of them are children. APLs are designed to maim rather than to kill to cause maximum logistical difficulties for opposing armed forces in warfare. In practice this means that landmine victims are is likely have at least one foot totally destroyed with children suffering more severe injuries due to their small size. If they survive, a landmine victim will be crippled for life. As most landmine victims are from developing countries they may struggle to get the medical care and support they need, and will most likely become a burden to their already impoverished family and community. Consequently the fear of 2o landmines can devastate entire communities who can be denied access to needs as basic as clean water or arable farmland.

Anti-personnel landmines are designed to be as difficult to detect as possible by enemy forces. They are usually made of plastic, with minimal metallic components to inhibit detection by metal detectors. The International Mine Action Standards (IMAS) state that humanitarian demining must achieve a minimum of 99.6% success rate.

The only method that can achieve this stringent target is manual demining, in which a trained individual meticulously excavates the mined area in front of them. The deminer will use a prodder, a trowel, a brush and a highly sensitive short-range metal detector to clear the ground ahead. Such work is dangerous and painstakingly slow. The largest global demining organisation, The HALO Trust, states that a single deminer can clear between 10 and 50 square meters of mined ground per day depending upon terrain conditions and contamination. The of use dogs and ic mechanical devices to aid manual demining is widespread, however both methods have a significant failure rate and so cannot be used for demining by themselves, as they can miss APLs. A worst case scenario is to declare a mined area clear, and give it back to the local populous, but have missed one. Therefore only the rigour of manual demining is considered sufficient for humanitarian clearance.

A key problem for demining is the wide variety of APLs in use. Estimates suggest that there may be as many as 700 different designs deployed since World War One.

The one common element for antipersonneI blast mines is that they are all activated by pressure -specifically that of a person standing upon them. Such pressure will cause the device to detonate, and APLs are typically set to detonate when a mass of greater than 5kg is applied to them, minimising accidental detonation by wildlife. Any device that could help increase the speed and reduce the hazard of demining whilst still meeting the stringent IMAS targets would be of great value.

A related problem to landmines is that presented by cluster munitions. Such devices release small bomblets' over a wide area. Such weapons are area effect devices and intended to maximise the area of damage achieved by a single munition.

Unfortunately cluster bombs have a relatively high failure rate, which even the US government estimates to be as much as 20%. The UN estimates that there may be as many as one million unexploded bomblets in Southern Lebanon following the conflict between Israel and Hezbollah in 2006. Such unexploded bomblets should have detonated on impact and are often unstable and can explode spontaneously or if triggered by vibration or shock. In order to assist subsequent clearance efforts the United States paint their bomblets yellow. Unfortunately this has lead to children mistaking them for toys with catastrophic results. Whilst not deliberately hidden like landmines, unexploded cluster munition present a significant hazard to the civilian population. Furthermore being fragmentation weapons the potential for fatal injuries is greater than that for landmines. Any device that could improve the speed and safety of clearing them would be of major benefit.

Improvised Explosive Devices (lEDs) are a hazard to armed forces operating in countries such as Iraq and Afghanistan and have caused thousands of casualties amongst coalition forces since 2003. According to the Washington Post 63% of all US casualties in Iraq have been due to lEDs. These devices are often manufactured from household materials or parts of used or scrap ordinance and are predominately used to attack military patrols by insurgents or paramilitary forces. lEDs are most often employed to attack vehicles and are usually hidden within rubbish along roads, disguised as rocks or dug into the roads themselves. Such weapons are primarily command controlled, meaning that they are triggered by an insurgent to cause maximum damage to a passing vehicle. Such trigger mechanisms may include using mobile phones to remotely activate the detonator. The US government has spent in the region of $l7Bn since 2006 on blast resistant vehicles to mitigate this problem.

However blast resistant vehicles are not perfect and casualties are still significant. A further device to minimise the impact of such improvised weapons would be of great value.

The goal of an effective defence against incoming missiles, even low technology ones such as mortars or rockets, remains elusive. Much publicised technologies such as the US Patriot anti-missile system have failed to stop even home made rockets, such as those launched by HAMAS at Israel from the Gaza strip in 2008.

Furthermore a major problem for western forces has been insurgents firing mortars into coalition bases from portable man-mounted launchers. These attacks are generally made from areas of high population density and so retaliatory action is not possible without causing unacceptable casualties to civilians. Also any such action would be ineffective as a mobile mortar can be set-up, fired and taken down in a matter of seconds -so the paramilitary can escape before the target force can respond. Thousands of military personnel have been seriously injured or killed by the shelling of their bases in Iraq and Afghanistan. Any device that could provide an effective defence against even low technology missiles like mortars or rockets would be most useful.

Description of Related Art

In the field of humanitarian demining and military mine clearance, many technical or mechanised solutions have been put forward to assist in either detecting or destroying Iandmines. Virtually none have been successfully deployed in practice due to the stringent standards required in demining to ensure that all APLs are ultimately destroyed regardless of terrain, environmental conditions or mine type.

One of the few examples actually employed is that of mechanical demining, in which an armoured vehicle is driven over a mine field in order to cause any mines therein to detonate harmlessly. The vehicle will typically employ an armoured front section which is brought into contact with the ground in order to transfer pressure on to any landmines that may be present, causing them to detonate. There are a number of different designs in use depending on application. Humanitarian demining organisations sometimes employ modified agricultural vehicles or industrial bulldozers with rotating armoured sieves or simply armoured buckets on the end of hydraulic arms. These vehicles dig up the top layer of soil and the APLs either detonate on contact or are contained within the sieve or bucket. For military purposes mine ploughs are sometimes employed mounted on the front of a tank to quickly create a mine free corridor through a minefield. The plough is driven through the topsoil and any landmines present are either pushed to one side or detonate harmlessly on contact.

However the classic and most widely used vehicle for mechanical demining is the flail tank. Flail tanks have been in use since the Second World War for mine clearance operations. The design is simple. A heavily armoured tank has a rotating drum mounted on the front. Attached to this drum are many chains with weights attached to the end. As the drum rotates the weighted chains beat the ground in front of the tank as it drives forward. Consequently any anti-personnel mines present are detonated when the chains impact upon the soil above them.

Despite being in use for more than 60 years, the design of flail tanks are still being improved and refined in the modern era. An enhanced form of flail design intended to ensure more consistent pressure distribution upon the mine field is described in US20050235815A1 Shankhfa and Kushwaha; and a shock absorbing design intended to allow the use of smaller more economic tanks is described in US6619177 Norwegian Demining Consortium.

However, flail tanks have serious shortcomings which prevent them being used as a successful replacement for manual demining. The primary problem is the failure rate in mine detonation. The Geneva International Centre for Humanitarian Demining reports that clearance rates can be as low as 50 to 60%, far below the 99.6% S required by IMAS standards. Furthermore there are landmines which are designed to be resistant to shock such as the Italian MAT/6 to inhibit the use of flail tanks or explosive mine clearance techniques. Therefore flail tanks cannot be used for humanitarian demining by themselves they can only be used to augment manual demining.

Flail tanks can also fling unexploded landmines into adjacent areas, contaminating safe land and recontaminating previously cleared areas.

A further significant problem is that flail tanks are vulnerable to anti-tank mines.

Whilst an anti-personnel mine has insufficient explosive yield to damage an armoured vehicle, anti-tanks mines are designed to penetrate armour. Therefore if a flail tank detonates one it is likely that the tank will be severely damaged, possibly destroyed and any crew killed or injured.

Finally the high capital and running costs of flail tanks can prove prohibitive for use by the charitable Non-Government Organisations (NGOs) that undertake the majority of demining worldwide.

The problems described above apply to all other designs of mechanical demining equipment.

SUMMARY OF THE SYSTEM

The invention is set out in the claims.

In overview, a design for a sonic cannon is described which creates a local region of high pressure at a target some distance from the device. A high energy sound source, for example, a high output loudspeaker is directed on to a focussing element (e.g. a curved surface, for example, an off-axis parabolic reflector) which focuses the acoustic compression wave to a convergence point aimed on to a target remote from the apparatus. By focussing a powerful sound wave into a small area it is possible to create very high pressures at the point of focus. By moving the reflector and sound source it is possible to change the position of the focus quickly thus allowing the high pressure region to be positioned on any desired target area. In the field of Iandmine remediation it is possible to use this high pressure focus to mimic the footfall of a soldier in a mine field causing any landmines present to detonate. Thus it is possible to cause the controlled detonation of pressure activated landmines and other explosive devices at long range enabling safer and faster demining than previously possible.

The sound energy source may comprise any sound energy source that provides sufficient sound energy to achieve the effect sought and may, for instance, comprise a high energy loud speaker, a directional hailing device, a directional acoustic device, a parametric acoustic array, a piston acting within a cylinder, a plasma arc cavitation device or the like. As all anti-personnel blast mines are pressure activated, the proposed device is likely to be insensitive to the wide variation in APL designs.

By controlling the sound pressure level output of the acoustic source it will be possible to mimic the pressure profile upon a mine of the footfall of an adult at focus.

This will allow the system to be effective against landmines that are designed to be shock or blast resistant. By scanning the position of the focus (also referred to as a convergence point) back and forth across a minefield it will be possible to quickly expose every square millimetre of the contaminated terrain to the high pressure region, thus ensuring that all APLs present detonate harmlessly and that the area is cleared of mines quickly. The envisaged system may be automated and therefore could be run by remote control further reducing the hazard to personnel as the S operator could control the machine from a distance. Furthermore, as the component parts of the system are relatively simple and robust any such device should be suitable for use even in difficult terrain and environmental conditions. The proposed apparatus also has the benefit of not requiring any consumable parts, which will minimise running costs and increase the ease of transportation. The system is also unlikely to damage the soil, unlike other proposed demining technologies which employ thermal or explosive strategies, thus allowing the reclaimed land to be used immediately for farming. A significant problem in demining is the presence of vegetation, which must typically be cleared before demining, either manually or by a cutting machine, both processes which risk accidental detonations and injury. The proposed system is likely to flatten or remove all the vegetation in the target area in a preparatory first pass or passes. The demining may be achieved at the same time as the clearance of the vegetation and the vegetation clearance then allows an operator to survey the area cleared for other objects of interest e.g. remaining cluster bomb!ets etc. Finally it should be possible to clear a mined area much more rapidly than manual demining using this technique. Therefore the proposed system should be cost effective.

BRIEF DESCRIPTION OF THE DRAWINGS

The forgoing objects described herein may be better understood with reference to the following drawings, which are intended for example purposes only.

Fig. I is a schematic of the core elements of one embodiment of a system; Fig. 2A and 2B show cross-sections of parabolic and off-axis parabolic reflective surfaces; Fig. 3 shows a schematic of the first embodiment of the system in use for landmine remediation; Fig. 4 shows a graph illustrating the examples of incident pressure over time upon an area to best mimic the footfall of a soldier; Fig. 5 shows a plan view of the proposed system sweeping a mined area; Fig. 6 is a schematic illustrating how the focussed compression waves may be overlapped in decontaminating a mined area; Fig. 7 is a schematic of a piston as an alternative mechanism to generate a high energy compression wave; Fig. 8 is a schematic of a high energy compression wave created using an electrical arc generator; is Fig. 9A and 9B show two alternative reflector configurations for focussing a spherical compression wave; Fig.1O shows a second embodiment of the present system wherein the focussed sound wave is used to disturb a suspected unexploded munition; Fig. 11 shows a third embodiment in which the focussed compression wave is used to mitigate the effect of any hidden munition; Fig. 12 shows a fourth embodiment wherein the focussed acoustic wave is used to destabilise, deflect or destroy an incoming aerial munition;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In overview, a sonic cannon is described which creates a local region of high s pressure at a target some distance from the device. A high energy sound source, for example, a high output loudspeaker, is directed on to a curved surface, for example, an off-axis parabolic reflector, which focuses the acoustic compression wave on to a target remote from the apparatus. By focussing a powerful sound wave into a small area it is possible to create very high pressures at the point of focus. By moving the reflector and sound source it is possible to change the position of the focus quickly thus allowing the high pressure region to be positioned on any desired target area. In the field of landmine remediation it is possible to use this high pressure focus to mimic the footfall of a soldier in a mine field causing any landmines present to detonate. Thus it is possible to cause the controlled detonation of pressure activated landmines and other explosive devices at long range enabling safer and faster demining than previously possible.

In one embodiment, apparatus for remotely disrupting, destroying or perturbing matter comprises a sound energy source, for generating compression waves in air, and a focussing element arranged to focus the compression waves to a convergence point remote from the apparatus, wherein the sound pressure at the convergence point is sufficient to disrupt, destroy or perturb matter located in the region of the convergence point. Thus the normal or regular state of the matter is altered. A corresponding method is also described.

This can be further understood with reference to the core embodiment of the present system shown in Fig. 1. A high energy sound source 101 generates an acoustic compression wave 103 which is directed towards a focussing element 102. In this embodiment, the focussing element 102 comprises a concave reflective surface 102.

S It may be expedient to use a waveguide ill to maximise the sonic energy transfer towards the reflector 102 depending upon the frequency of the acoustic wave generated by the sound source 101. A preferred geometry of the waveguide 111 may be cylindrical but other geometries may also be preferable depending on the nature of the acoustic compression wave 103. The concave surface of the focussing element 102 reflects the sound wave along the axis 109 focussing itto a minimum diameter at point 104. The distance from the centre point of the reflector 108 to the focal point 104 can selected through careful design of the radius of curvature of the reflector 102 and the control of the incident compression wave 103. Thus the effective focal length of the sonic cannon shown in Fig. I can be tailored for a given application.

To vary the focal position 104 of the sonic cannon to impinge on a given target a number of axes of motion may be provided. Such axes may include angular motion about the centre point 108 of the reflector, linear motion 106 parallel to the axis of the incident sonic wave 103 and rotational motion 107 about the axis 110. By combining such axes of motion it should be possible to control the position of the focus 104 to intersect with any desired target. A further requirement may be a rotation of the entire apparatus about point 108, ensuring that the angle between axes 109 and 110 is preserved whilst the focal position 104 is adjusted.

As the skilled reader will understand it may be advantageous to employ additional axes of motion to better control the focal position relative to the proposed apparatus dependent upon the specific application.

In a further embodiment a focussing reflector 102 which is deformable is used and which can have its radius of curvature altered during the course of operation to adjust both the focal distance between points 108 and 104 and the diameter of the sound wave at the point of focus 104.

The focal range between the apparatus centre point 108 and the convergent point of the compression wave 104 is between Im and 10,000m, or more preferably between 5mand2000m.

The focal diameter of the converging acoustic wave at point 104 is between 0.1mm and 2000mm, or more preferably between 0.5mm and 250mm.

The high energy sound source 101 creates longitudinal compression waves of sufficient intensity to result in pressure levels at the point of focus 104 of between 600 Pascals and 2000 Mega Pascals, or more preferably between 2000 Pascals and 63 Mega Pascals. Measured in decibels this would correspond to a range between 150dB and 280dB, or more preferably between 160dB and 250dB, presuming a standard reference sound pressure level of 20dB or 20 micro Pascals absolute pressure.

The high energy sound source 101 would generate acoustic waves of the frequency range between 1 Hz to 40 kHz, or more preferably between 500Hz to 40 kHz.

A further embodiment of the present system is to use multiple high energy sound sources directed on to a single focussing reflector to increase the maximum pressure level achievable at the focus. A further extension to this embodiment would be to use multiple sound sources and multiple reflectors wherein the focal points from the various reflectors all intersect at the target and, by employing phase matching, constructive interference will result in a higher pressure level than could be achieved byasingle unit.

The focussing element 102 serves to focus the incident sound wave to a minimum focus (also known as a minimum focal diameter) where the converging beam comes to a convergence point 104. A simple curved surface with a specific radius of curvature may be sufficient to achieve the desired pressure level at focus. Fig. 2A io shows an alternative preferred design which may offer enhanced focussing through the use of a parabolic reflector. A parabolic reflector may be described in cross section by the equation y2 = 4ax where the point of focus is along the x-axis at a distance a' from the origin. This is shown in Fig. 2A where the curve 201 is the surface of the parabolic reflector, which reflects all incident plane waves 202 is travelling perpendicular towards the y-axis through different paths 203 to a common focus 204, which is a specific distance 205 from the origin, corresponding to distance a', the effective focal length. The advantage of a parabolic reflector is that it focuses all incident plane waves to a common point thus achieving the smallest possible focus diameter. Thus a parabolic reflector could be employed to focus the sonic compression wave in this system.

To achieve a useful focal distance 205 the parabolic surface 201 of the parabolic reflector has an effective focal length 205 of lOm but a resulting diameter of over 28m. Fig. 2B shows a preferred design for a reflective surface, an off-axis parabolic reflector. In this instance an arc 206 is taken from a larger parabolic curve 207, described by the equation above. This surface 206 is described as an off-axis parabola, shown by a solid line, which is a fragment of a full parabola, shown by the dotted line 207. The surface 206 reflects all incident plane waves travelling perpendicular towards the y-axis 208 and focuses them to a point 210. The key difference is that the effective focal length of the off-axis parabola 206 is the distance between its centre and the focus point 210 shown by line 209 not that shown as 205 in Fig. 2A. Therefore an off-axis parabolic reflector 206 being a small fragment of a much larger parabola 207 can be used to achieve much longer effective focal lengths from a correspondingly smaller diameter reflector. Nonetheless the achievable minimum focal diameter should be the same or close to that for a full io parabolic reflector. This preferred embodiment of a focussing reflector is therefore a more practical approach for the proposed system and in the example shown in Fig. 2B the diameter of the off-axis parabolic reflector is 2.1 m with an effective focal length of 11.3m.

A first embodiment of the present system is illustrated in Fig. 3 wherein the apparatus is employed for landmine remediation. The focussed acoustic device is mounted upon an armoured tracked vehicle 301 which is capable of traversing difficult terrain. The high energy sound source 303 is directed into an off-axis parabolic reflector 302, which directs the sound waves 304 to a focal point 305. The focal point is positioned upon the surface of the terrain which is contaminated by landmines. The compression wave results in a very high pressure region at the point of focus. The recoil pressure generated propagates through the ground 306 from the point of focus 305 intersecting with any landmines 307 hidden nearby in the ground.

By controlling the output of the high energy sound source 303 it is possible to control the pressure incident upon the soil at the focus 305 and therefore mimic the footfall of a soldier. In doing so any pressure-activated anti-personnel mines present will be triggered and detonate harmlessly. By adjusting the position of the focus 305 to sweep the area it will be possible to detonate all the mines hidden or buried in the

minefield 308.

The distance of the point of focus 305 will be a minimum of a few metres from the vehicle 301, with a desired range of between 5 and 2000m, depending on local conditions. Therefore any mine that is detonated will be far enough away from the vehicle to prevent any possibility of injury to the operator or the vehicle itself. In a preferred embodiment the vehicle would be remotely controlled to increase the safety of the operator, who could control it at a range of I Os or 1 OOs of metres further from the minefield. This would be particularly beneficial in the event that the apparatus caused the detonation of a fragmentation munition with an area effect.

The envisaged vehicle 301 is armoured and tracked for maximum robustness and safety in dangerous environments. However the sonic cannon could be mounted upon any suitable mechanised vehicle including for example, an agricultural vehicle, an excavator or bulldozer, a mine-resistant vehicle, a High Mobility Multi-purpose Wheeled Vehicle (HMMVVV or Humvee) or a Land Rover. Furthermore the device could be mounted upon any aerial platform, including an aeroplane or a helicopter either piloted or remotely controlled. In addition the device could potentially be mounted upon a water based platform, for example a boat or ship, possibly moored offshore from a mined beach or nearby contaminated area.

In an embodiment the typical pressure profile of an adult's footfall upon the ground is mimicked. Modern anti-personnel landmines can be designed to be resistant to a sudden shock or high pressure impulse, for example the Italian VS-I.6. This makes them resistant to mine clearance techniques such as flail tanks or the use of explosive devices like Bangalore Torpedoes or their modern equivalent such as the Giant Viper employed by the British Army. Fig. 4 shows a graph of pressure against time for a given area. The sharp pressure impulse 401 shown as a solid line may be representative of an explosive compression wave. The dashed line 402 may be representative of a high impact device such as a flail tank. It is not possible to precisely control the pressure gradient applied to the target area using such techniques. However by controlling the output of the sound source used in the present system it will be possible to carefully control the incident pressure profile at the focus as desired. Example profiles are the dotted line 405 which shows a trapezoid impulse and the dotted and dashed line 404 which shows a curved impulse. Controlling the output of the high energy sound source over time will be possible using computer control, and there will be a high degree of flexibility in the nature of the profiles created. An explosive demining device would produce a pressure wave with a lifetime of a few milliseconds or less. A mechanical demining device would produce a pressure wave with a lifetime of lOOs of milliseconds or less, is whereas a human footfall may vary from lOOs of milliseconds to seconds depending on whether running or walking. Therefore by controlling the amplitude of the compression wave over time it will be possible to closely mimic the footfall of an adult ensuring that all anti-personnel mines detonate reliably regardless of design.

Fig. 5 shows a plan view of the system in use for landmine remediation. An armoured tracked vehicle 501 has a sonic cannon mounted upon it. The reflector is positioned in a rotary turret 502 which directs the converging sound wave 503 to a minimum 504. By adjusting the position of the turret and other unseen previously described axes of motion it is possible to scan the high pressure focus 504 across the total target area 506, wherein the shaded area 505 represents the section already scanned. In doing so it is possible to expose 100% of the contaminated region 506 to a high energy compression wave ensuring that any APLs present are detonated harmlessly at range and so safely demining the area.

A preferred embodiment of this system employs automated onboard telemetry to ensure consistent, reliable demining, with in-built analysis and safety systems. Such telemetry could include, for example, a laser interferometer or triangulation device to ensure that the focal position of the sound wave 504 is always on the surface of the ground regardless of topographic variation. Diagnostics could also include a vision system to ensure that the focal position is correctly positioned on the target surface and that the focus is of the predicted dimensions to ensure that sufficient pressure is achieved therein. It could include integral pressure sensors to ensure that the output from the high energy sound source is consistent and within acceptable parameters for successful demining. Remote telemetry may also be used to determine the pressure achieved at the focus. It would further be advantageous to incorporate a Global Positioning System (GPS) so that the exact co-ordinates of the demined areas can be recorded and mapped. Other forms of telemetry may be beneficial and a person skilled in the art would be able to add them accordingly.

To maximise the likelihood of the proposed system successfully detonating 100% of all APLs present in a given area, in an embodiment each pressure pulse that impinges at the focus is overlapped to ensure that no mine is missed. Fig. 6 shows a plan view of such an overlap as the focal position is rastered back and forth across the scanned area. The incident compression wave 601 is focussed to a point 604, which is scanned in two orthogonal axes 603 and 605 to build up the demined area 602. In this example each pressure pulse is overlapped by 50% so that every area of the contaminated terrain experiences Iwo pulses to ensure that any mine present is detonated. The overlap may be varied to ensure that each area of ground is exposed to three, four or even more effective footfalls to ensure that every last mine is detonated.

The high energy sound source is capable of producing a powerful compression wave that can subsequently be focussed by a focussing element such as a reflective concave surface. An appropriate sound source would be an LRAD 1000 manufactured by the American Technology Company (ATC) of San Diego in California which can produce a sound pressure level of 151dB at a range of Im from the device from an 840mm diameter surface with a full divergence angle of 30 degrees at 2kHz. Other sound sources made by ATC could also be appropriate. An io alternative sound source could be a Hyperspike HS6O manufactured by the Ultra USSI Corporation of Columbia City, Illinois, which is rated to produce a peak output of 168dB over a frequency range of I -10 kHz. Other sound sources made by Ultra USSI could also be appropriate. Another alternative sound source could be a Parametric Acoustic Array (PAA) made at Massachusetts Institute of Technology (MIT) cited in US patent application no. 20060225509A1 with an output of 160 to 170dB. Furthermore a group of conventional loudspeakers could potentially be combined to produce a sound wave of sufficient intensity, for example two PD743 loudspeakers manufactured by JBL Professional of Northridge, California can produce 144dB.

All of the above sources produce a sonic output. This means the velocity of the resulting compression wave will be the speed of sound which is approximately 343m/s at sea level at 20 degrees ambient temperature. This may limit the ultimate pressure level achievable at focus, and potentially limit the effective range of the device. Alternative sound sources may allow the creation of a supersonic or even hypersonic compression wave ultimately offering much higher pressures at the point of focus or a greater effective focal range. One such source is illustrated in Fig. 7 in which a piston 701 mounted in a housing 702 is driven by an external force to a position 703 rapidly compressing the air within the housing creating a propagating compression wave 705 from the aperture 707. By moving the piston back and forth across a range of travel 706 it is possible to create a controlled high energy compression wave. Varying the diameter of the aperture 707 may allow control of the pressure level and diameter of the compression wave 705. The piston could be driven either from a crankshaft from a combustion engine or an electric motor.

A further embodiment of a high energy compression wave source is shown in Fig. 8 io in which a high voltage electrical source 801 provides a charge across two opposing electrodes 802 that produces an electrical arc discharge between them 803. This arc creates a high energy plasma in the air between the electrodes which is a region of high pressure that expands rapidly. As the plasma expands it creates a powerful spherical compression wave 804 that propagates outwards through the atmosphere is from the axis between the electrodes 802. The plasma can be generated in only a few nanoseconds if desired so the rate of expansion can be extremely fast creating a correspondingly powerful supersonic or even hypersonic compression wave.

A spherical compression wave requires different focussing techniques to that of a directional sonic source. In figure 9A a schematic cross-section is seen along the axis of the electrodes which produce an expanding plasma 902 inducing a spherical compression wave 903. The centre of the plasma is positioned at the focus of a conventional parabolic reflector 901 which then reflects the expanding compression wave to form a plane wave 904 which is directed on to a subsequent off-axis parabolic reflector 905 which then focuses the compression wave to a point 906. An alternative configuration is shown in Fig. 9B where the plasma 907 is centred at one of the two focal positions of an elliptical reflector 909. The expanding compression wave 908 is reflected and converges 910 on to the second focal point 911 of the elliptical surface geometry of the reflector.

For all the cited sonic devices and the plasma arc source an electrical source will be necessary. The LRAD 1000, for example, requires 480W at peak consumption from a 90-24OVAC source at 50Hz. A suitable diesel generator might be a Hyundai DHY2500L which produces a maximum power output of 2kW from a compact source employing a 211cc engine. However the vehicle used to mount the sonic cannon may well have in-built electrical output sufficient to power the compression wave source and actuators required to move the apparatus to adjust the focal position along with any telemetry.

A suitable vehicle upon which to mount the sonic cannon might be the MVD Mini-Dozer manufactured by the DOK-ING Ltd company of Croatia, which is an armoured low profile tracked vehicle operated by remote control, designed in part for mine clearance.

For the material used for the focussing reflector a low acoustic absorption coefficient is desirable to maximise reflection. Less than 0.01 is typical for a polished hard surface. The material must be sufficiently dense to inhibit energy losses through vibration, for example, a stone such as granite, an aggregate such as concrete, or a metallic such as aluminium. Hardened plastic or electroplated plastics to minimise the weight of the reflector may be used. The material must be capable of being formed into a complex geometry such as that for an off-axis parabolic reflector by an industrial manufacturing process. The criteria for a successful reflector are twofold, to minimise energy loss from the reflection of the compression wave, and to create the desired focal diameter at the desired focal range from the apparatus.

The proposed system is intended to allow effective mine clearance rapidly and at range, making for safer and faster demining. Furthermore, all anti-personnel blast mines are pressure activated and the proposed device should therefore be insensitive to the wide variation in APL designs. By controlling the sound pressure level output of the acoustic source it should be possible to mimic at the focus point the pressure profile upon a mine of the footfall of an adult. This will allow the system to be effective against landmines that are designed to be shock or blast resistant. By scanning the position of the focus back and forth across a minefield it will be possible to quickly expose every part of the contaminated terrain to the high pressure region, thus ensuring that all APLs present detonate harmlessly and that the area is cleared of mines quickly. The envisaged system is automated and therefore could be run by remote control further reducing the hazard to personnel as the operator could control the machine from a distance. Being a ranged device the proposed apparatus will not be at risk from anti-tank mines within the mine field. Furthermore, the component parts of the system are relatively simple and robust making any such device suitable for use even in difficult terrain and environmental conditions. The proposed apparatus also has the benefit of not requiring any consumable parts, which will minimise running costs and increase the ease of transportation. The proposed system is unlikely to damage the soil, unlike other proposed demining technologies which employ thermal or explosive strategies, thus allowing the reclaimed land to be used immediately for farming. A significant problem in demining is the presence of vegetation, which must typically be cleared before demining, either manually or by a cutting machine, both processes which risk accidental detonations and injury. The system should flatten or remove all the vegetation in the target area in a preparatory first pass or passes. Finally it should be possible to clear a mined area much more rapidly than manual demining using this technique but to the same International Mine Action Standards. Therefore the proposed system will be cost effective.

S In a further embodiment the proposed system can be used to help in the clearance of Explosive Remnants of War (ERW) for example unexploded cluster munitions.

Such devices are not hidden and can often be identified visually at range. US cluster munitions are painted yeflow to aid visual identification. However unexploded munitions can be unstable and potentially detonate if disturbed causing serious injury or death to those nearby. Fig. 10 shows the proposed use of the system in which a vehicle mounted sonic cannon 1001 directs a converging compression wave 1002 to a focus 1004 upon a suspected cluster munition 1003 found in, for example, woodland 1005. By applying a high pressure pulse to the suspected bomblet it is possible to induce detonation if the munition is unstable and shock sensitive. If it is detonates it will do so harmlessly as the area would be evacuated prior to clearance and the sonic cannon is at range. If the suspected munition does not detonate even after repeated strong impulses it may be reasonably assumed that it is not unstable, and therefore may be safely approached and disposed of at short range using conventional means. In a preferred embodiment the apparatus 1001 will be remotely controlled by the operator so they can be further away from any potential detonation.

This is particularly important as cluster munitions and unexploded ordinance are usually fragmentation devices and can have an effective range of tens or hundreds of metres. Thus this proposed embodiment could act as an aid to make ERW clearance safer and faster.

In a further embodiment the proposed system could be used to mitigate the effect of Improvised Explosive Devices (tEDs) used to ambush coalition troops, for example patrols or convoys upon roads in hostile territory. Fig. 11 shows a vehicle mounted sonic cannon 1101 driving down a road 1102 possibly at the head of a column or convoy of vehicles. The turret mounted reflector 1103 directs the converging compression wave 1104 to a focus 1106 which is swept back and forth across the road and surroundings 1107 as the vehicle advances. lEDs are commonly disguised as rocks, hidden within debris and rubbish littering the sides of roads 1105 or buried within the road surface or its surrounds. Whilst not usually pressure activated, by sweeping the terrain in front of the convoy with a high pressure acoustic wave it is likely that any hidden lED may be disturbed, inverted or damaged which either renders it inoperable or minimises its effect on detonation. The incident pressure wave may also move debris to expose an lED allowing the convoy of vehicles to stop before they get within its range. Therefore employing the proposed sonic cannon at the head of a convoy may reduce the incidence of casualties caused by lEDs. A further advantage is that an approaching high energy sound source would encourage local people to leave the area as the ambient sound level rises to uncomfortable levels. This should clear the area of non-combatants without causing injury to them thus making it harder for insurgents or paramilitaries to hide in crowds by the roadside.

In a further embodiment the proposed system could be used in the field of missile defence, potentially mitigating the effect of incoming aerial munitions. Fig. 12 shows a vehicle mounted sonic cannon 1201 directing the converging compression wave 1202 to a focus 1207 which intersects with the known trajectory 1203 of an incoming aerial munition 1204 such as a rocket, shell or mortar. The trajectory of the missile must be determined in advance by a tracking device such as a RADAR station 1205 sweeping an area 1206. The speed of sound can be low compared to that of an aerial munition which can be supersonic. Therefore the position of the focus of the incident compression wave 1207 must be placed on the known trajectory of the rocket or mortar 1203 in advance so that the munition intersects with the high pressure focal region. Aerial munitions are sensitive to gusts of wind and other atmospheric pressure variations and are usually spin or fin stabilised to compensate.

It may be possible to create a region in the path of its trajectory 1203 which has a pressure level equivalent to that found in Hurricane force winds or even greater.

Therefore the incident pressure wave causes the incoming rocket or mortar to be deflected from its target, or become destabilised and fall short. Alternatively the high energy impulse may cause sufficient shock to detonate the munition in mid-air. In either eventuality the incoming aerial weapon will have had its destructive capability reduced or mitigated altogether.

It is to be understood that various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present system is not intended to be limited to the embodiment shown and such modifications and variations also fall within the spirit and scope of the appended claims.

Claims

CLAIMS1. Apparatus for remotely perturbing matter, the apparatus comprising; a sound energy source for generating compression waves in air, and a focussing element arranged to focus the compression waves to a convergence point remote from the apparatus, wherein the sound pressure at the convergence point is sufficient to perturb matter at the convergence point.
2. Apparatus for remotely detonating pressure-activated explosive devices, such as land mines, the apparatus comprising; a sound energy source for generating compression waves in air, and a focussing element arranged to focus the compression waves to a convergence point remote from the apparatus, wherein the sound pressure at the convergence point is sufficient to detonate a pressure-activated explosive device located in the region of the convergence point.
3. Apparatus in accordance with claim I or claim 2, further comprising a sound source controller, wherein the sound source controller is adapted to control the power output of the sound source to vary the sound pressure at the convergence point.
4. Apparatus in accordance with claim 3, wherein the sound source controller is adapted to control the output of the sound source in accordance with a predefined time-dependent profile stored in a memory element.
5. Apparatus in accordance with claim 4, wherein the predefined time-dependent profile in the memory element is configured to produce a time-dependent sound pressure at the convergence point which mimics the footfall of a person.
6. Apparatus in accordance with any preceding claim, further comprising at least one steering part for controlling the position of the convergence point relative to the apparatus.
7. Apparatus in accordance with claim 6, wherein the at least one steering part comprises components for moving the focussing element relative to the sound energy source.
8. Apparatus in accordance with claim 7, wherein the at least one steering part is arranged to move the focussing element along a propagating axis, the propagating axis defined as the axis along which the compression waves leave the sound energy source.
9. Apparatus in accordance with claim 7 or 8, wherein the at least one steering part is arranged to rotate the focussing element about the propagating axis
10. Apparatus in accordance with claim 7, 8 or 9, wherein the at least one steering part is arranged to tilt the focussing element in relation to the propagating axis.
11. Apparatus in accordance with claim 7, 8 or 9, wherein the at least one steering part is arranged to move the focussing element and sound energy source together.
12. Apparatus in accordance with any preceding claim, wherein the focussing part includes a reflecting surface for reflecting the compression waves generated by the sound energy source.
13. Apparatus in accordance with claim 12, wherein the reflecting surface is concave to focus the compression waves.
14. Apparatus in accordance with claim 13, wherein the concave reflecting surface is parabolic.
15. Apparatus in accordance with claim 14, wherein the parabolic concave reflecting surface is an off-axis parabola.
16. Apparatus in accordance with any preceding claim, wherein the focussing element is fabricated from a material selected to minimise the energy lost through absorption of the compression waves by the focussing element.
17. Apparatus in accordance with claim 16, wherein the focussing element is fabricated from a rigid material.
18. Apparatus in accordance with claim 16 or 17, wherein the focussing element has a polished reflective surface.
19. Apparatus in accordance with claim 16, 17 or 18, wherein the material is selected from a list comprising stone, concrete, steel, iron, aluminium or plastic.
20. Apparatus in accordance with claims I to 16, wherein the focussing element is deformable.
21. Apparatus in accordance with claims I to 16, wherein the focussing element is refractive.
22. Apparatus in accordance with any preceding claim, wherein a waveguide is provided between the sound energy source and the focussing element.
23. Apparatus in accordance with claim 22, wherein the waveguide is tubular.
24. Apparatus in accordance with any preceding claim, wherein the convergence point has an effective footprint within which the sound pressure is sufficient to trigger the detonation of a land mine, and wherein the effective footprint has a diameter in the range 0.5mm to 250mm.
25. Apparatus in accordance with any preceding claim, wherein the convergence point has an effective footprint within which the sound pressure is sufficient to trigger the detonation of a land mine, and wherein the effective footprint has a diameter in the range 0.1mm to 2000mm.
26. Apparatus in accordance with any preceding claim, wherein the distance between the apparatus and the convergence point is in the range 5m to 2000m.
27. Apparatus in accordance with any preceding claim, wherein the distance between the apparatus and the convergence point is in the range Im to 10,000m.
28. Apparatus in accordance with any preceding claim, wherein the sound pressure level at the convergence point is in the range 2,000 Pascals to 63 Mega Pascals.
29. Apparatus in accordance with any preceding claim, wherein the sound pressure level at the convergence point is in the range 600 Pascals to 2,000 Mega Pascals.
30. Apparatus in accordance with any preceding claim, wherein the frequency of the sound produced by the sound energy source is 500 Hz to 40 kHz.
31. Apparatus in accordance with any preceding claim, wherein the frequency of the sound produced by the sound energy source is 1 Hz to 40 kHz.
32. Apparatus in accordance with any preceding claim, wherein the sound energy source and the focussing element are mounted on a vehicle.33 Apparatus in accordance with claim 32, wherein the vehicle is armoured.34. Apparatus in accordance with claim 32 or 33, wherein the vehicle is remote controlled.35. Apparatus in accordance with claim 32 to 34, wherein the vehicle is an aircraft.36. Apparatus in accordance with claim 32, wherein the vehicle is an unpowered trailer suitable for being towed by a powered vehicle.37. Apparatus in accordance with any preceding claim, wherein a plurality of sound energy sources are provided.38. Apparatus in accordance with any preceding claim, wherein a plurality of focussing elements are provided.39. Apparatus in accordance with any preceding claim, wherein a monitor is provided to measure the output sound levels of the sound energy source.40. Apparatus in accordance with any preceding claim, wherein remote telemetry is provided to measure the air pressure at the convergence point.41. Apparatus in accordance with any preceding claim, wherein a navigational system is provided to determine and record the absolute position of the convergence point.42. Apparatus in accordance with any preceding claim, wherein a laser interferometer is provided in order to measure the distance between the apparatus and the convergence point.43. Apparatus in accordance with any preceding claim, wherein a triangulation device is provided to measure the distance between the apparatus and the convergence point.44. Apparatus in accordance with any preceding claim, wherein the sound energy source is selected from a loud speaker, a directional hailing device, a directional acoustic device.45. Apparatus in accordance with any preceding claim, wherein the sound energy source is a parametric acoustic array.46. Apparatus in accordance with any preceding claim, wherein the sound energy source is a piston acting within a cylinder.47. Apparatus in accordance with any preceding claim, wherein the sound energy source comprises an arc cavitation device.48. Apparatus in accordance with claim 47, wherein the arc cavitation device comprises electrodes for producing an arc, and a reflective surface, wherein the is reflective surface is parabolic and wherein the arc is generated at the focus of the parabolic reflective surface.49. Apparatus in accordance with any of claims I to 6, wherein the sound energy source is an arc cavitation device comprising electrodes for producing an arc, and wherein the focussing element comprises a reflective surface, wherein the reflective surface is elliptical and wherein the arc is generated at the focus of the elliptical reflective surface, such that a pressure wave produced by the arc cavitation device is focussed to a convergence point by reflection from the elliptical reflective surface.50. A method of remotely detonating a pressure-actuated land mine buried beneath the surface of an area of land, comprising the steps of; generating at least one compression wave in air using a sound energy source, focussing the at least one compression wave at a point on the surface of the land, wherein the pressure generated at the surface of the land is sufficient to trigger detonation of a land mine.51. A method of clearing an area of buried pressure-actuated land mines, comprising the steps of; 1) identifying a starting target point within the area, ii) generating at least one compression wave in air using a sound energy source, iii) focussing the at least one compression wave onto the target point, wherein the sound pressure at the target point is sufficient to trigger the detonation of a land mine if buried at the target point, iv) identifying a further target point within the area, v) generating at least one compression wave using the sound energy source and focussing the at least one compression wave onto the further target point, wherein the sound pressure at the target point is sufficient to trigger the detonation of a land mine if buried at the further target point, vi) repeating steps iv) and v).52. A method of clearing land mines in accordance with claim 51, wherein a plurality of compression waves are generated, such that the sound pressure profile at the target point is varied.53. A method of clearing land mines in accordance with claim 52, wherein the sound pressure profile of the target point mimics the footfall of a person.54. A method of clearing land mines in accordance with claim 50, wherein the focussed compression waves at the target point have an effective footprint within which the sound pressure is sufficient to trigger the detonation of a land mine, and wherein the target points are selected so that the effective footprints overlap.55. A method of clearing land mines in accordance with claims 51 or 52, wherein the pattern of target points is a raster scan of the area to be cleared.56. A method of perturbing a visible explosive device, comprising the steps of; generating at least one compression wave in air using a sound energy source, focussing the at least one compression wave onto the explosive device, wherein the sound pressure generated at the explosive device is sufficient to disturb the explosive device.57. A method of perturbing a visible explosive device in accordance with claim 56, wherein the sound pressure generated at the explosive device is sufficient to detonate the explosive device.58. A method of perturbing a hidden explosive device, comprising the steps of; generating at least one compression wave in air using a sound energy source, focussing the at least one compression wave onto a suspect point where an explosive device is suspected to be hidden, wherein the sound pressure generated S at the suspect point is sufficient to disturb or detonate the explosive device.59. A method of perturbing an airborne explosive device, comprising the steps of; generating at least one compression wave in air using a sound energy source, focussing the at least one compression wave in the region of the explosive device, wherein the sound pressure generated at the explosive device is sufficient to destabilise or deflect the airborne explosive device from its course.60. A method of perturbing an airborne explosive device in accordance with claim 59, wherein the sound pressure generated at the explosive device is sufficient to detonate the explosive device.61. A method of interrupting the flight of an airborne explosive device, comprising the steps of; monitoring a zone using radar, detecting an airborne explosive device, calculating the flight path of the airborne device and an expected position of the airborne device, generating at least one compression wave in air using a sound energy source, focussing the at least one compression wave at the expected position of the explosive device, wherein the sound pressure generated at the explosive device is sufficient to deflect, destabilise or detonate the airborne explosive device.62. A method of remotely perturbing matter, comprising the steps of; i) identifying a starting target point on the surface of the matter, ii) generating at least one compression wave in air using a sound energy source, iii) focussing the at least one compression wave onto the target point, wherein the sound pressure at the target point is sufficient to perturb the matter, iv) identifying a further target point within the area, v) generating at least one compression wave using the sound energy source and focussing the at least one compression wave onto the further target point, wherein the sound pressure at the target point is sufficient to perturb the matter, vi) repeating steps iv) and v).63. A method or apparatus as herein described or illustrated in the accompanying figures.