Patent Number: 
Section: claims

1. A method of using cavitation in producing a localised compression of gas comprising:providing a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is in contact with a depression in a surface, wherein the depression is shaped so as to at least partially receive the pocket of gas; andapplying a static pressure to the non-gaseous medium, wherein the static pressure has an average value greater than atmospheric pressure such that the applied static pressure causes the pocket of gas in contact with the depression to collapse via mechanisms of cavitation, wherein the collapse of the pocket of gas causes a jet of the non-gaseous medium to form that traverses the pocket of gas towards and impacts against a surface of the depression, and wherein the surface of the depression is arranged to receive the jet impact such that at least some of the gas from the original pocket of gas is trapped by the impacting jet against the surface of the depression, wherein the gas trapped by the impacting jet against the surface of the depression is compressed responsive to the mechanisms of cavitation, wherein the mechanisms of cavitation are enhanced by the applied static pressure. 2. A method as claimed in claim 1, wherein the static pressure is applied over a timescale greater than 1 ms. 3. A method as claimed in claim 1, wherein the average value of the static pressure is at least 2 bar. 4. A method as claimed in claim 1, comprising controlling the level of the static pressure to form a transverse jet having a desired speed. 5. A method as claimed in claim 1, wherein the static pressure applied to the non-gaseous medium is varied over time. 6. A method as claimed in claim 5, wherein the variation in the static pressure is provided by a standing pressure wave or pressure variation applied to the non-gaseous medium. 7. A method as claimed in claim 6, wherein the frequency of the standing wave or pressure variation is greater than 10 Hz. 8. A method as claimed in claim 1, wherein a single shot pressure wave or shockwave is additionally applied to the non-gaseous medium. 9. A method as claimed in claim 1, comprising providing the pocket of gas within the non-gaseous medium. 10. A method as claimed in claim 9, comprising allowing or causing the pocket of gas to expand within the non-gaseous medium. 11. A method as claimed in claim 9, comprising repeatedly providing a pocket of gas within the non-gaseous medium. 12. A method as claimed in claim 11, wherein the frequency at which the pocket of gas is repeatedly provided within the non-gaseous medium is greater than 10 Hz. 13. A method as claimed in claim 9, comprising nucleating the pocket of gas within the non-gaseous medium. 14. A method as claimed in claim 13, comprising using a laser to nucleate the pocket of gas. 15. A method as claimed in claim 13, comprising using a spark to nucleate the pocket of gas. 16. A method as claimed in claim 13, comprising applying a standing wave or pressure variation to the non-gaseous medium to nucleate the pocket of gas and/or to expand an already nucleated pocket of gas. 17. A method as claimed in claim 13, comprising applying a negative pressure shockwave to the non-gaseous medium to nucleate the pocket of gas, and/or to expand an already nucleated pocket of gas. 18. A method as claimed in claim 17, wherein the negative pressure shockwave is created by inverting a positive pressure wave using a low acoustic impedance reflector. 19. A method as claimed in claim 1, wherein the gas pocket is formed with the use of a pre-manufactured membrane that defines the boundary between the gas pocket and the non-gaseous medium. 20. A method as claimed in claim 1, comprising providing a non-gaseous medium having therein a plurality of pockets of gas. 21. A method as claimed in claim 20, wherein the surface comprises a plurality of depressions each shaped so as to at least partially receive a pocket of gas. 22. A method as claimed in claim 1, comprising heating the non-gaseous medium and/or the pocket of gas.