GB2468547A

GB2468547A - Acoustic apparatus for disrupting material

Info

Publication number: GB2468547A
Application number: GB0904453A
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: GB0904453D0

Abstract

A method and apparatus for remotely applying pressure to a target 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. The method and apparatus have particular application to technologies for removing surface layers of material from bulk material, such as surface layers of concrete from structures, or unstable rock from a rock face. The focussing element may be moved or rotated to target a different area of the target.

Description

ACOUSTIC APPARATUS FOR DISRUPTING MATERIAL

BACKGROUND

Technical Field of the Invention

The system relates to technologies for decommissioning nuclear facilities such as nuclear power stations, particularly dismantling contaminated concrete structures.

The system also finds application in the area of mining offering a means for testing the stability of rock formations and dislodging unstable material at range to enhance safety.

Nuclear power stations have a limited lifespan of between 30 and 60 years and eventually must be decommissioned and demolished before they become unsafe.

Due to the unpopularity of nuclear power with local populations it is politically expedient to replace old facilities with new ones upon the same site. A major problem is demolishing the buildings safely as they become contaminated with radioactive materials such as Uranium Oxide, Strontium-90, Caesium 137 and Cobalt 60. As a result of this contamination all the building materials must be treated as radioactive waste, and so huge volumes of waste are generated, all requiring storage for long periods of time. Another problem inherent in nuclear decommissioning is that of the suppression of dust in any demolition. All dust could potentially be radioactive and so cannot be allowed into the atmosphere for fear of inhalation by nearby residents. A cost saving and safer alternative is that of scabbling. Scabbling is a process by which a thin layer of building material, such as masonry or concrete, is removed from the structure without affecting its overall integrity. The radioactive contaminants will only penetrate a few millimetres into the building, so by removing a layer of concrete several millimetres deep from the inside and carefully collecting all the dust and debris produced, it becomes possible to fully decontaminate the building whilst producing a fraction of the volume of radioactive waste for subsequent storage. Once decontaminated the nuclear power station can then be demolished conventionally, without fear of dust contamination or undue s hazard to workers and the local population. Scabbling is done conventionally using mechanical devices operated manually, but this is not possible in radioactive environments, and so remote controlled robots must be employed. Much research has been devoted to employing long range energy transfer devices such as lasers and microwaves for remote scabbling. However such devices whilst offering the io benefits of operation at range often have high capital and running costs, and can be too delicate for operation in difficult environments.

The issue of nuclear decommissioning is a very significant global problem and the US Department of Energy estimates it may cost up to I Trillion dollars to make safe all the aging nuclear facilities worldwide over the next half century. The UK's Nuclear Decommissioning Authority estimates that it will cost over �7OBn to deal with the existing UK sites alone. Therefore any technique that could offer a cost effective and robust remote scabbling solution would have an immediate impact.

The use of explosives in commercial mining operations is well known and has been widespread since the Nineteenth Century. Used in both surface and sub-surface mining, controlled explosions are used to break up ore deposits for subsequent extraction as well as to aid the removal of bedrock in reaching such deposits. Such explosives are usually placed by hand in pre-drilled holes in the rock, and carefully positioned in arrays to provide a controlled blast to the rock face. Two issues remain problematic in mining when using explosives. The first is placing the charges in regions where the rock structure is unstable. This is particularly problematic in quarries or open cast mining, where the desired blasting points may be well above ground level and where the miners could be at risk of injury in placing charges if the rock face crumbles whilst they are upon or near it. Furthermore post-blasting the remaining rock face may be unstable presenting a hazard to miners and machinery extracting ore below. A device for remotely testing the stability of an elevated rock face or for bringing down unstable rock formations at range could offer significant safety benefits for the mining industry worldwide.

Description of Related Art

In the field of nuclear decommissioning scabbling the top layer of concrete from the inside of a contaminated radioactive structure represents a potential method to achieve successfully decontamination whilst minimising the volume of radioactive waste generated. Conventional scabbling techniques used in the construction industry employ mechanical devices which scrape away the top layer of the building material using, for example grinders or rotating abrasive elements. Such devices are is manually operated making them unsuitable for use in dangerous radioactive environments. Furthermore such devices would be unsuitable for scabbling the surfaces of nuclear installations as such installations often have highly complex and large scale dimensions and so would be difficult to access.

Due to the hazard posed to any operator entering a radioactive structure any scabbling device should ideafly be remote controlled. One such device is the Pentek WaliWalker, manufactured by Pentek mc, of Pennsylvania, USA and described in US patent 5408407. This apparatus is suspended between two high strength cables attached to computer controlled winches mounted above the apparatus. By adjusting the lengths of each cable it is possible to move the suspended WallWalker to any point within the range of the cables. It is possible to mount a concrete scabbling device upon the WalIWalker allowing the remote decontamination of a radioactively contaminated surface. A significant problem however is that the controlling winches and WaliWalker must be mounted upon the desired surface before scabbling can take place. This will have to be done manually and so the engineers will be exposed to radiation during the installation of the system. This problem will be exacerbated where the area to be scabbled is elevated, and so greater time will be required to complete the installation resulting in greater exposure. Furthermore the WallWalker has a limited area of operation, so once the scabbling is completed the device will need to be moved to the next location, again resulting in radioactive exposure to the Whilst the WallWalker offers an improvement in safety for workers engaged in nuclear decommissioning, by reducing their radiological exposure time by comparison with conventional manual scabbling operations, it does not eliminate it altogether, and so workers would still be subject to high doses of radiation. A better alternative would be to use a device which is remote controlled and can scabble concrete at range and over a wide variety of complex surfaces. Therefore the scabbling process could be entirely automated and so no worker would need to enter the structure thus minimising hazard. Two approaches have been investigated, the first using a robot-mounted high power microwave system, described in Japanese patent 3002595, Yukio and Hideo, and the second using a robot-mounted high power laser system described in European Patent 0653762A1, Li and Steen. Both approaches have been tested at length and do offer advantages in that a controlled burst of electromagnetic energy can be applied to a concrete surface resulting in a precision scabbling process at range. Unfortunately the practical implementation of such systems and the capital and running costs can prove prohibitive. Microwave devices for example require operation at relatively close range, limiting their effectiveness in scabbling large structures. Furthermore they are sensitive to environmental conditions and can be disabled by dust, making them insufficiently robust for large scale scabbling, as they would require regular maintenance which in itself presents a hazard if contaminated with radioactive material. Laser devices can be operated at greater ranges and when employing fibre delivery and the latest fibre laser designs represent a better alternative for true remote scabbling. Unfortunately such lasers have very high capital and running costs. Furthermore they too are highly sensitive to dust contamination, particularly on optical surfaces, which can cause catastrophic damage to the optical system. In addition lasers require very precise control of their focal positions to ensure consistent scabbling, which is problematic when scabbling over large complex surfaces at range.

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 nuclear decommissioning it is possible to use this high pressure focus to ablate away the top surface of a building material such as concrete. Therefore it is possible to use the sonic cannon to scabble off the radioactively contaminated top surface of a building at long range minimising the volume of radioactive waste generated and enhancing operator safety during decommissioning.

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.

The apparatus enables the pressure impulse on the target to be precisely controlled in order to ensure consistent scabbling over long term operation. The effective range will be many metres, and potentially up to hundreds of metres,. making the device suitable for scabbling large and complex structures. Unlike laser or microwave systems the tolerance of operation of the apparatus should be wide making the scabbling process robust and consistent. Furthermore, the components of the system may be relatively simple and highly robust, therefore the need for maintenance should be minimised as the system can withstand challenging environments and should be insensitive to dust. The system will also be easy to automate and mount upon a remotely controlled vehicle. Furthermore, in implementations using no consumable elements, the cost of ownership and the need for maintenance is reduced. The scabbling process described is relatively rapid and will have a relatively low capital cost and cost of ownership making it a highly cost effective solution for nuclear decommissioning.

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; S 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 for use in nuclear decommissioning; Fig. 4 shows a schematic of the material removal mechanism for the first io embodiment.

Fig. 5 shows a graph illustrating various examples of incident pressure over time upon an area to achieve optimised scabbling; Fig. 6 is a schematic of a piston as an alternative mechanism to generate a high energy compression wave; is Fig. 7 is a schematic of a high energy compression wave created using an electrical arc generator; Fig. 8A and 8B show two alternative reflector configurations for focussing a spherical compression wave; Fig. 9 shows a second embodiment of the present system wherein the focussed sound wave is used to perturb a rock face

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In overview, 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 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 nuclear decommissioning it is possible to use this high pressure focus to ablate away the surface of a building material such as concrete. Therefore it is possible to use the sonic cannon to scabble off the radioactively contaminated top surface of a building at long range minimising the volume of radioactive waste generated and enhancing operator safety during decommissioning.

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.

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 it to 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 105 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 5m and 2000m.

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 is 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 by a single 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 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 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 I Om 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 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 proposed system is shown in Fig. 3 wherein the apparatus is used for nuclear decommissioning. A remote controlled vehicle 301 upon which a sonic cannon is mounted is positioned within a radioactive building. A high energy sound source 302 directs a compression wave into a concave reflector 303 which focuses it to a point 305 upon the surface of a concrete building 304. The incident pressure wave and resulting recoil pressure causes the top layer to be ablated. The resulting debris, particulates and dust 307 are extracted and stored by a remote controlled extraction device 308. Therefore the top layer of the surface is selectively removed 306. By moving the focal point 305 back and forth across the target structure it is possible to ablate away the top layer from a desired area. This process is known as scabbling. The proposed system may be applicable to any form of building decontamination, for example where the contaminants are chemical or biological in nature as well as fissile by-products. Furthermore it may be applicable to any form of building material that can be ablated, for example masonry or brickwork as well as concrete.

The envisaged vehicle 301 is robust, rugged and remote controlled. The sonic cannon could be mounted upon any suitable remotely controlled mechanised vehicle including for example, an agricultural vehicle, a vehicle used in civil engineering such as an excavator or bulldozer, a High Mobility Multi-purpose Wheeled Vehicle (HMMWV or Humvee) or a Land Rover.

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 305 is always on the surface of the io structure 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. Other forms of telemetry may be beneficial and a person skilled in the art would be able to add them accordingly.

Fig. 4 shows the process mechanism for scabbling concrete in which the compression wave 402 is focussed on to the surface 403. The pressure wave and resulting recoil pressure causes the top surface layer to crack 404 and then break up into fragments 405 and dust and particulates 406 which are ablated from the bulk structure 401. The resulting waste is sucked 407 into a remote controlled extraction unit 408 which stores this radioactive debris for later safe disposal.

An advantage to the proposed system is the ability to precisely control the pressure impulse applied to the target area. This will allow the pressure gradient to be carefully optimised to ensure successful and consistent scabbling of the target structure resulting in efficient decontamination. Fig. 5 shows a graph of pressure against time for a given area with example curves showing the level of control and variation possible over the incident compression wave. The sharp pressure impulse 501 shown as a solid line shows a high intensity regime for scabbling. The dashed line 502 may be representative of a lower intensity regime of operation. Profiles showing more gradual applications of pressure over time are the dotted line 505 which shows a trapezoid impulse and the dotted and dashed line 504 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. Thus it will be possible to readily tailor the nature of the incident compression wave energy profile to best suit the target material and optimise the scabbling process on a case by case basis or dynamically during a scabbling procedure.

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 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 (PM) 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 io resulting compression wave will be the speed of sound which is approximately 343m1s 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. 6 in which a piston 601 mounted in a housing 602 is driven by an external force to a position 603 rapidly compressing the air within the housing creating a propagating compression wave 605 from the aperture 607. By moving the piston back and forth across a range of travel 606 it is possible to create a controlled high energy compression wave. Varying the diameter of the aperture 607 may allow control of the pressure level and diameter of the compression wave 605. 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. 7 in which a high voltage electrical source 701 provides a charge across two opposing electrodes 702 that produces an electrical arc discharge between them 703. 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 704 that propagates outwards through the atmosphere from the axis between the electrodes 702. 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 8A a schematic cross-section is seen along the axis of the electrodes which produce an expanding plasma 802 inducing a spherical compression wave 803. The centre of the plasma is positioned at the focus of a conventional parabolic reflector 801 which then reflects the expanding compression wave to form a plane wave 804 which is directed on to a subsequent off-axis parabolic reflector 805 which then focuses the compression wave to a point 806. An alternative configuration is shown in Fig. 8B where the plasma 807 is centred at one of the two focal positions of an elliptical reflector 809. The expanding compression wave 808 is reflected and converges 810 on to the second focal point 811 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 a robust low profile tracked vehicle operated by remote control, designed in part for mining operations.

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.

is Thus the sonic cannon may be used to scabble off the radioactively contaminated top surface of a building at long range minimising the volume of radioactive waste generated and enhancing operator safety during nuclear decommissioning. In some embodiments, the pressure impulse on the target can be precisely controlled in order to ensure consistent scabbling over long term operation. The effective range may be many metres, and potentially up to hundreds of metres, making the device suitable for scabbling large and complex structures. Unlike laser or microwave systems the wide tolerance of operation achievable with the apparatus makes the scabbling process robust and consistent. Furthermore, the components of the system may be relatively simple and highly robust, therefore the need for maintenance should be minimised as the system is able to withstand challenging environments and should be insensitive to dust. A system as described should also be easy to automate and mount upon a remotely controlled vehicle. Furthermore when implemented with no consumable elements cost of ownership and the need for maintenance may be minimised. The system allows for a rapid scabbling process and with relatively low capital cost and cost of ownership making it a highly cost effective solution for nuclear decommissioning.

In a further embodiment the proposed system can be used in the field of commercial mining to enhance safety. Fig. 9 shows a schematic representation of one embodiment. A sonic cannon 901 directs a high energy compression wave 902 to a io convergence point 903 upon the surface of a suspected unstable rock face 904. If the rock face 904 is unstable the high energy pressure impulse will cause the unstable portions to be dislodged and fall harmlessly to the ground. If this does not happen then it may reasonably be inferred that the rock face is stable enough to be approached by miners and machinery safely in order to continue with mining the bulk ore 905. This approach could be used at any time for ranged safety testing in a quarry or open cast mine should a rock face be thought unstable. When blast mining it is necessary to place the explosive charges carefully upon the rock face, often by drilling holes into which the explosives are positioned. This may be done manually as the process is technically rigorous and requires precision placement. If the rock face to be blasted is unstable or prone to collapse then there is the risk of injury or death to the explosives engineer placing the charges, particularly if the charges are to be placed at a significant elevation up the rock face. Thus by employing this embodiment as described it would be possible to first test the stability of the rock before placing charges. Furthermore after blast mining has taken place there may be ambiguity about the stability of the remaining rock face. By testing its stability with the sonic cannon and bringing down any loose material at range the hazard to approaching miners or equipment can be minimised.

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 S 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 removing a surface layer of material from bulk material, 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 remove a surface layer of material from the bulk material.
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 in order to remove a quantity of material.
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 Ito 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 remove a surface layer of material from the bulk material, 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 remove a surface layer of material from the bulk material, 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 io 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 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).51. A method of remotely removing a surface layer of material from bulk material, comprising the steps of; i) identifying a starting target point on the surface of the material, 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 remove a surface layer of material from bulk material, 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, is wherein the sound pressure at the target point is sufficient to remove a surface layer of material from bulk material, vi) repeating steps iv) and v).52. A method of remotely ablating concrete from the surface of a structure, comprising the steps of; i) identifying a starting target point on the surface of the structure, 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 remove concrete from the surface of the structure, 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 remove concrete from the surface of the structure, vi) repeating steps iv) and v).53. A method of remotely stabilising a rock face, comprising the steps of; i) identifying a starting target point on the rock face, 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 remove unstable rock from the rock face, iv) identifying a further target point within the area, v) generating at least one compression wave using the sound energy source io and focussing the at least one compression wave onto the further target point, wherein the sound pressure at the target point is sufficient to remove unstable rock from the rock face, vi) repeating steps iv) and v).54. A method or apparatus as herein described or illustrated in the accompanying figures.