Cleaning apparatus and method of using an acoustic transducer

Abstract

An apparatus for cleaning a surface includes a body defining a cavity and terminating in a distal end that is adapted, in use, to be in the vicinity of a surface to be cleaned such that the surface forms an end wall of a chamber including the cavity; at least one cleaning liquid inlet for flow of a cleaning liquid into the chamber; a divider located in or at the end of the cavity that divides the chamber into first and second portions, the second portion, in use, being in fluid communication with the surface to be cleaned; and an acoustic transducer associated with the first portion to introduce acoustic energy into the chamber; wherein the divider is adapted to permit the passage of acoustic energy therethrough from the first portion to the second portion of the chamber to thereby allow pressure fluctuations to be generated at the surface.

Claims

1. An apparatus for treating a surface, the apparatus comprising: a body defining a cavity, the body terminating in a distal end that is adapted to be in a vicinity of a surface to be treated such that the surface to be treated forms an end wall of a chamber including the cavity; at least one liquid inlet for flow of a treating liquid into the chamber; a divider positioned within the cavity and spaced from 1-60 mm from the distal end of the body, the divider dividing the chamber into a first portion and a second portion, the second portion being in fluid communication with the surface to be treated; and an acoustic transducer adapted to introduce acoustic energy into the first portion of the chamber; wherein the divider is positioned between the acoustic transducer and the distal end of the body and adapted to permit passage of the acoustic energy therethrough from the first portion of the chamber to the second portion of the chamber to thereby allow pressure fluctuations to be generated at the surface to be treated.

2. An apparatus according to claim 1, wherein the divider comprises at least one hole extending through the divider for allowing the treating liquid to flow from the first portion of the chamber into the second portion of the chamber.

3. An apparatus according to claim 2, wherein the at least one hole comprises a plurality of holes provided in an array.

4. An apparatus, for treating a surface, the apparatus comprising: a body defining a cavity, the body terminating in a distal end that is adapted to be in a vicinity of a surface to be treated such that the surface to be treated forms an end wall of a chamber including the cavity; at least one liquid inlet for flow of a treating liquid into the chamber; a divider positioned within the cavity and spaced from 1-60 mm from the distal end of the body, the divider dividing the chamber into a first portion and a second portion, the second portion being in fluid communication with the surface to be treated; and an acoustic transducer adapted to introduce acoustic energy into the first portion of the chamber; wherein the divider is adapted to permit passage of the acoustic energy therethrough from the first portion of the chamber to the second portion of the chamber to thereby allow pressure fluctuations to be generated at the surface to be treated, wherein the divider comprises at least one hole extending through the divider for allowing the treating liquid to flow from the first portion of the chamber into the second portion of the chamber, and wherein the at least one hole is positioned between the acoustic transducer and the distal end of the body.

5. An apparatus according to claim 1, wherein the divider comprises a membrane.

6. An apparatus according to claim 5, wherein the membrane is formed of a material that is substantially impedance matched to the treating liquid.

7. An apparatus according to claim 5, wherein the membrane is sufficiently thin so as to not substantially attenuate sound passing therethrough from the first portion of the chamber to the second portion of the chamber.

8. An apparatus according to claim 5, wherein the membrane is formed of a material with specific acoustic properties that match an acoustic field at a location of the membrane.

9. An apparatus according to claim 1, further comprising a liquid conditioning unit adapted to remove bubbles from the treating liquid supplied to the chamber.

10. An apparatus for treating a surface, the apparatus comprising: a body defining a cavity, the body terminating in a distal end that is adapted to be in a vicinity of a surface to be treated such that the surface to be treated forms an end wall of a chamber including the cavity; at least one liquid inlet for flow of a treating liquid into the chamber; a divider positioned within the cavity and dividing the chamber into a first portion and a second portion, the second portion being in fluid communication with the surface to be treated; and an acoustic transducer adapted to introduce acoustic energy into the first portion of the chamber, wherein the divider is positioned between the acoustic transducer and the distal end of the body and is spaced from the acoustic transducer, such that the first portion of the chamber is configured to contain an acoustic energy conducting material separating the acoustic transducer from the divider; wherein the divider is adapted to permit passage of the acoustic energy therethrough from the first portion of the chamber to the second portion of the chamber to thereby allow pressure fluctuations to be generated at the surface to be treated.

11. An apparatus according to claim 10, wherein the at least one liquid inlet is configured to introduce the treating liquid into the first portion of the chamber, such that the treating liquid is the acoustic energy conducting material.

12. An apparatus according to claim 11, wherein the divider comprises at least one hole extending through the divider for allowing the treating liquid to flow from the first portion of the chamber into the second portion of the chamber.

13. An apparatus according to claim 12, wherein the at least one hole comprises a plurality of holes provided in an array.

14. An apparatus according to claim 12, wherein the at least one hole is positioned between the acoustic transducer and the distal end of the body.

15. An apparatus according to claim 10, wherein the at least one liquid inlet is configured to introduce the treating liquid into the second portion of the chamber.

16. An apparatus according to claim 15, wherein the acoustic energy conducting material is a solid or gel material.

17. An apparatus according to claim 11, wherein the divider comprises a membrane.

18. An apparatus according to claim 11, further comprising a liquid conditioning unit adapted to remove bubbles from the treating liquid supplied to the chamber.

19. An apparatus for treating a surface, the apparatus comprising: a body defining a cavity, the body terminating in a distal end that is adapted to be in a vicinity of a surface to be treated such that the surface to be treated forms an end wall of a chamber including the cavity; at least one liquid inlet for flow of a treating liquid into the chamber; a divider positioned within the cavity and dividing the chamber into a first portion and a second portion, the second portion being in fluid communication with the surface to be treated; and an acoustic transducer adapted to introduce acoustic energy into the first portion of the chamber; wherein the divider is positioned between the acoustic transducer and the distal end of the body, and wherein the divider comprises at least one hole positioned between the acoustic transducer and the distal end of the body, the at least one hole extending through the divider for allowing the treating liquid to flow from the first portion of the chamber into the second portion of the chamber, and wherein the divider is adapted to permit passage of the acoustic energy therethrough from the first portion of the chamber to the second portion of the chamber to thereby allow pressure fluctuations to be generated at the surface to be treated.

20. An apparatus according to claim 19, wherein the at least one hole comprises a plurality of holes provided in an array.

21. An apparatus according to claim 19, wherein the divider comprises a membrane.

22. An apparatus according to claim 21, wherein the membrane is formed of a material that is substantially impedance matched to the treating liquid.

23. An apparatus according to claim 21, wherein the membrane is sufficiently thin so as to not substantially attenuate sound passing therethrough from the first portion of the chamber to the second portion of the chamber.

24. An apparatus according to claim 21, wherein the membrane is formed of a material with specific acoustic properties that match an acoustic field at a location of the membrane.

25. An apparatus according to claim 19, further comprising a liquid conditioning unit adapted to remove bubbles from the treating liquid supplied to the chamber.

Description

BRIEF DESCRIPTION OF FIGURES

(1) Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic view of an apparatus for cleaning a surface according to a first embodiment of the present invention;

(3) FIG. 2 is a schematic view of the interface between the apparatus of FIG. 1 and the surface in use;

(4) FIG. 3a is a schematic view of one arrangement of a cavity and a chamber that may be used in one embodiment of the present invention;

(5) FIG. 3b is a schematic view of another arrangement of a cavity and a chamber that may be used in one embodiment of the present invention;

(6) FIG. 3c is a schematic view of another arrangement of a cavity and a chamber that may be used in one embodiment of the present invention;

(7) FIG. 4 is a schematic view of an alternative apparatus for cleaning a surface according to a second embodiment of the present invention;

(8) FIG. 5 is a schematic view of an another alternative apparatus for cleaning a surface according to a third embodiment of the present invention;

(9) FIG. 6 is a schematic view of a cleaning assembly including multiple apparatuses according to a fourth embodiment of the present invention;

(10) FIG. 7 is a schematic view of a cleaning apparatus according to a fifth embodiment of the present invention; and

(11) FIG. 8 is a schematic view of a γ=4 mode in an apparatus for cleaning a surface according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(12) FIG. 1 shows a cleaning apparatus 1 in accordance with the present invention. The apparatus 1 comprises a metal or polymeric (for example acrylic) body 10 defining a cavity 10a in the form of a circular, square or rectangular cylinder. The body 10 terminates in a planar distal end 12 that is, in use, held in the vicinity of a planar surface to be cleaned 2 (the surface), as shown in FIG. 1. When the body 10 is held with the distal end 12 of the body 10 in the vicinity of the surface 2, the surface 2 forms an end wall of a chamber 11, the chamber 11 including both the cavity 10a formed within the body 10 and also a further region extending between the distal end 12 of the body 10 and the surface 2. (Other possible arrangements of the cavity and the chamber that may be used in different embodiments of the present invention are discussed below with reference to FIG. 5). The body 10 is provided with casters 13 for positioning the apparatus 1 relative to the surface 2.

(13) The apparatus 1 further comprises a cleaning liquid inlet 14 through which a cleaning liquid such as water can be supplied to the cavity 10a from a cleaning liquid reservoir 3, and a cleaning liquid outlet 15 through which the cleaning liquid can be removed from the cavity 10a and returned to the cleaning liquid reservoir 3.

(14) The apparatus 1 further comprises a divider 16 located at the end of the cavity 10a (and at the distal end 12 of the body 10). When the apparatus 1 is positioned with the distal end 12 of the body 10 in the vicinity of a surface to be cleaned 2 with the surface forming an end wall of a chamber 11 including the cavity 10a (as shown in FIG. 1), the divider divides the chamber 11 into a first portion 11a and a second portion 11b. The first portion 11a of the chamber 11 is bounded by a top wall 10b or end wall of the body 10 that opposes the distal end 12, by the divider 16, and by a side wall 10c of the body 10 that extends between the top wall 10b and the divider 16. The second portion 11b of the chamber 11 is bounded by the divider 16, by the surface 2, and by a flexible skirt 17, for example a rubber skirt, that extends between the body 10 and the surface 2. In the embodiment shown in FIG. 1 the divider 16 is located at the distal end 12 of the body 10 and so the second portion 11b of the chamber 11 is located wholly outside the body 10, but other possible arrangements are discussed below with reference to FIG. 3. The second portion 11b of the chamber is in fluid communication with the surface 2 when the apparatus is in position for use so that cleaning liquid in the second portion 11b of the chamber 11 can directly engage the surface 2 and effect cleaning, as described below.

(15) The divider 16 is a thin sheet or membrane formed of a material that is substantially impedance matched to the cleaning liquid. Where the cleaning liquid is water, a Rho-C rubber membrane with an acoustic impedance of approximately 1,500,000 Rayls may be used, although other materials with other acoustic impedances may also be used depending on the intended cleaning liquid. The divider 16 is sealed with respect to the body 10 around its perimeter, and is generally impervious to water, except for a 0.9 mm diameter hole 16a formed through the divider that provides fluid communication between the first portion 11a of the chamber 11 and the second portion 11b of the chamber 11.

(16) The cleaning liquid inlet 14 and the cleaning liquid outlet 15 are both located inboard of the divider 16 so that cleaning liquid is delivered to and removed from the first portion 11a of the chamber 11.

(17) An acoustic transducer 18 is mounted on the top wall 10b of the body 10 and arranged to introduce acoustic energy into the chamber 11. The acoustic transducer 18 is controlled by a controller 19 and can be driven at a frequency of 20 kHz to 20 MHz. A modulator allows amplitude or frequency modulation of pulses of acoustic energy. Acoustic isolation devices (not shown) in the cleaning liquid inlet 14 and the cleaning liquid outlet 15 prevent sound propagation out from the chamber 11.

(18) The acoustic transducer 18 is operable to, in use, generate acoustic resonance within the chamber 11 when the apparatus 1 is positioned on or adjacent to a surface to be cleaned 2 (as shown in FIG. 1) and the chamber 11 is filled with cleaning liquid, with an acoustic pressure antinode being formed at or adjacent to the surface 2.

(19) A liquid conditioning unit 20 is located upstream of the cleaning liquid inlet 14, and is adapted to remove bubbles from the cleaning liquid supplied to the chamber 11, for example with a physical mesh to substantially reduce the number of bubbles present in the cleaning liquid entering the chamber 11, which would otherwise attenuate the acoustic field.

(20) A bubble generator 21 comprising electrodes in the form of wires is built into the divider 16 for generating bubbles in the cleaning liquid. The bubble generator is controlled by a controller 22, and generates bubbles with radii in the range 0.1 to 100 microns. The bubble generator controller 22 may be operated to generate bubbles in timed pulses.

(21) An aggressive or chaotropic agent introduction system 23 can be used to introduce one or more aggressive or chaotropic agents into the first portion 11a of the chamber 11b, for example ozone, chlorine and/or hydrogen peroxide. A chemically active agent introduction system 24 can be used to introducing one or more chemically active agents into the cleaning liquid, for example a detergent, a surfactant and/or a biocide.

(22) Operation of the apparatus will now be described.

(23) In use, the apparatus is positioned on the surface to be cleaned 2 with the casters 13 holding the body 10 such that the distal end 12 and the divider 16 are spaced apart from the surface by approximately 5 mm to 8 mm and the surface 2 forms an end wall of the chamber 11 including the cavity 10a. Water (or another cleaning liquid) is treated by the liquid conditioning unit 20 to remove bubbles and supplied to the first portion 11a of the chamber 11 via the cleaning liquid inlet 14. The water fills the first portion 11a of the chamber 11, and is also allowed to bleed through the hole 16a in the divider 16 into the second portion 11b of the chamber 11. The skirt 17 retains the water in the second portion 11b of the chamber 11 and in contact with the surface 2. In one mode of operation water may be supplied through the inlet 14 at a rate of 1 to 2 dm.sup.3/min while water bleeds through the hole 16a at a rate of 1 to 5 cm.sup.3/s.

(24) When the chamber 11 is filled with water, the ultrasonic transducer 18 is used to introduce acoustic energy into the chamber 11. The divider 16, which is formed of a material that is substantially impedance matched to the cleaning liquid, allows acoustic energy to pass therethrough from the first portion 11a of the chamber 11 into the second portion 11b of the chamber 11, as shown in FIG. 2, and a strong acoustic field is generated in the lower portion 11a of the chamber 11. The surface 2 forms an acoustically rigid end wall of the chamber 11, and acoustic resonance is generated within the chamber 11, with an acoustic pressure antinode being formed at or adjacent to the surface 2. In this way pressure fluctuations are generated at the surface 2. (The same apparatus can also be used to clean a surface that is not acoustically rigid because the walls of the body 10 enable a mode to be generated even when the surface to be cleaned is not acoustically rigid. However, cleaning is less efficient for non-rigid surfaces.)

(25) The bubble generator 21 is operated to generate bubbles 50 in the second portion 11b of the chamber 11, as shown in FIG. 2. The bubbles are driven towards the surface by the acoustic field in the chamber 11.

(26) The acoustic transducer 18 may be operated to control the acoustic energy in the chamber 11 to cause non-inertial bubble motion at the surface 2. The acoustic transducer may, for example, be operated at a frequency of 20 kHz with a zero-to-peak pressure amplitude of well below 120 kPA, for example 90 kPa.

(27) By controlling the acoustic energy to cause non-inertial bubble motion at the surface 2, the apparatus 1 provides enhanced cleaning of the surface without subjecting the surface to the stresses and possible damage that may result from inertial cavitation.

(28) Alternatively, or in addition, the acoustic transducer 18 may be operated to control the acoustic energy in the chamber 11 to cause inertial cavitation of the bubbles at the surface 2 and/or at a distance from the surface 2. By controlling the acoustic energy to cause inertial cavitation of the bubbles at the surface 2 and/or at a distance from the surface 2, the apparatus 1 may provide enhanced cleaning for tougher surfaces. The acoustic transducer may, for example, be operated at a frequency of 20 kHz with a zero-to-peak pressure amplitude of well above 120 kPA, for example 250 kPa.

(29) As the zero-to-peak pressure amplitude is increased, the range of bubble sizes that undergo inertial cavitation is increased and so the number of bubbles undergoing inertial cavitation is increased. In this way non-inertial bubble motion and/or inertial cavitation can be generated by the apparatus, depending on the ultrasound frequency and the range of bubble sizes.

(30) Alternatively, or in addition, the acoustic transducer 18 may be operated to control the acoustic energy in the chamber 11 to generate surface waves in the bubbles and/or microstreaming.

(31) Surface waves may be controlled by varying the zero-to-peak pressure amplitude and/or the ultrasound frequency and/or bubble size. In general, the closer a bubble is to its pulsation resonance size, the lower the threshold acoustic pressure required to excite the Faraday wave (and other related waves).

(32) The sound field may be continuous or alternatively amplitude or frequency modulated, and the cleaning operation may comprise employing modulated acoustic energy to cause the non-inertial bubble motion and/or inertial cavitation and/or to generate the surface waves and/or microstreaming.

(33) Where the surface 2 comprises cavities, the cleaning operation may include causing the bubbles to enter cavities, recesses or pores formed in the surface 2 and using the acoustic energy to excite the surfaces of the bubbles while the bubbles are in the cavities, recesses or pores.

(34) In one mode of operation, the bubble generator controller 22 may be used to control the bubble generator 21 to generate pulses of bubbles, instead of generating bubbles continuously. The acoustic transducer controller 19 may be used to control the acoustic transducer 18 to generate pulses of acoustic energy. The pulses of bubbles and the pulses of acoustic energy may be generated with a mutually controlled time relationship, for example to impact the surface substantially simultaneously. In this way it is possible to operate the transducer more efficiently by only generating acoustic energy in pulses and by reducing attenuation caused by the bubbles.

(35) A wet/dry vacuum device 25 is operated to remove excess water, as well as any displaced contamination. The skirt 17 generally retains the water within the second portion 11b of the chamber 11 and prevents the water from leaking out from the apparatus in large quantities. The apparatus 1 therefore leaves behind only as much liquid as might be expected from a domestic mop. As water leaks out from the second portion 11b of the chamber 11 under the skirt 17 and is removed by the wet/dry vacuum device 23, it is replenished as water continues to bleed through the hole 16a from the first portion 11a of the chamber 11 into the second portion 11b of the chamber 11.

(36) The apparatus 1 can be moved across the surface 2 to clean a larger area, or alternatively held stationary at a single location to provide localised cleaning.

(37) In the embodiment described with reference to FIG. 1, the divider 16 is located at the distal end of the cavity 10a and so the first portion 11a of the chamber 11 is located wholly within the cavity 10a and the second portion 11b of the chamber 11 is located wholly outside the cavity 10a, as illustrated in FIG. 3a. However, in an alternative embodiment, the divider 16 may be stepped back from the distal end of the cavity 10a, such that a part of the second portion 11b of the chamber 11 is located within the cavity 10a, as illustrated in FIG. 3b. In another alternative embodiment, the skirt may be omitted and the distal end 12 of the body 10 may lie substantially directly on the surface, such that substantially all of the second portion 11b of the chamber 11 is located within the cavity 10a, as illustrated in FIG. 3c.

(38) In the embodiment described with reference to FIG. 1, the divider 16 is formed of a material that is substantially impedance matched to the cleaning liquid to allow acoustic energy to pass efficiently therethrough from the first portion 11a of the chamber 11 into the second portion 11b of the chamber 11 to generate a strong acoustic field in the second portion 11b of the chamber 11. However, in an alternative embodiment the divider 16 may alternatively (or additionally) be sufficiently thin that it does not, in use, substantially attenuate sound passing therethrough from the first portion 11a of the chamber 11 to the second portion 11b of the chamber 11. In this way the divider 16 may be substantially non-invasive with respect to the acoustic field, and may facilitate the generation of an acoustic field in the second portion 11b of the chamber 11, and thus the generation of higher pressure fluctuations at the surface 2. In another alternative embodiment, the divider 16 may be formed of a material with specific acoustic properties that match the acoustic field at its location in use (for example, the divider may comprise a thin metal wall that substantially coincides with an acoustic pressure antinode in the chamber when the apparatus is in use), and therefore be substantially non-invasive with respect to the acoustic field. In each case, the divider 16 is adapted to allow efficient energy transfer from the acoustic transducer 18 to the surface 2 with minimal transducer heating.

(39) In the embodiment described with reference to FIG. 1, the cleaning liquid is supplied into the first portion 11a of the chamber 11 and allowed to bleed through a hole 16a formed in the divider 16 to reach the second portion 11b of the chamber 11. However, in an alternative embodiment the water (or other cleaning liquid) may instead be supplied directly to the second portion 11b of the chamber 11, as shown in FIG. 4. In such an embodiment the first portion 11a of the chamber 11 may instead be filled with a different acoustic energy conducting material 100, for example a gel, as shown in FIG. 4. In such an embodiment the divider may simply take the form of an interface between the acoustic energy conducting material 100 and the second portion 11b of the chamber 11. The acoustic energy transmitting material should have a similar acoustic impedance to that of the cleaning liquid to enable efficient operation of the apparatus as described above in relation to the apparatus of FIG. 1. It will be appreciated by the person skilled in the art that the features described above in relation to the embodiment of FIG. 1 may also be applied to the embodiment shown in FIG. 4.

(40) In another alternative embodiment, the divider may take the form of an acoustic lens that, in use, focuses acoustic energy introduced into the chamber 11 by the acoustic transducer 18 on the surface 2, as shown in FIG. 5. Focusing acoustic energy on the surface to be cleaned allows efficient energy transfer from the acoustic transducer 18 to the surface to be cleaned 2 with minimal transducer heating. A cleaning apparatus including a lens instead of (or in addition to) the membrane or interface described above may be particularly useful for cleaning a surface that does not provide a rigid boundary or approximately rigid boundary, for example a carpet, because such cleaning apparatus does not require resonance to be generated within the chamber in order to provide efficient cleaning, as described above. It will be appreciated by the person skilled in the art that the features described above in relation to the embodiments of FIGS. 1 and 4 may also be applied to the embodiment shown in FIG. 5. For example, the cleaning liquid may be introduced either into a first portion 11a of the chamber 11 formed between a top wall of the body and the lens, or into a second portion 11b of the chamber 11 formed between the lens and a surface on which the apparatus is placed. In addition, the first portion 11a of the chamber 11 may be filled with the cleaning liquid (as in the embodiment of FIG. 1), or alternatively filled with a different acoustic energy conducting material, for example a gel (as in the embodiment of FIG. 4).

(41) A surface cleaning arrangement 1000 may include multiple cleaning apparatuses 1 as described above, for example as shown in FIG. 6. The multiple cleaning apparatuses need not be identical. In some embodiments, a surface cleaning arrangement 1000 may include an array of apparatuses of the first embodiment, the second embodiment and/or the third embodiment together in a single array. In the embodiment shown in FIG. 6, the two cleaning apparatuses located furthest to the right share a common side wall. In other embodiments the cleaning apparatuses may each be formed with at least one side wall that is shared with at least one adjacent cleaning apparatus.

(42) FIG. 7 illustrates another alternative embodiment, in which a cleaning apparatus comprises a hemispherical or dome-shaped body 10 and chamber 11a, 11b, and a plurality of acoustic transducers 18 forming an array arranged across a domed roof of the chamber such that acoustic energy generated by the acoustic transducers is, in use, focused on the surface to be cleaned 2. In this embodiment, a membrane 16 similar to that described for the embodiment of FIG. 1 is provided in the dome-shaped chamber.

(43) In one embodiment, the lateral width of the body 10 and chamber 11 (in a direction parallel to the surface to be cleaned) may be significantly greater than the length (in a direction perpendicular to the surface 2 to be cleaned) of the chamber 11. With such a width/length aspect ratio, the top wall 10b of the body 10 on which the acoustic transducer 18 is mounted (i.e. the top wall 10b of the body 10 facing and remote from the surface 2 to be cleaned) may function as an acoustic baffle that is substantially acoustically rigid for the transducer 18. The transducer 18 may be mounted on an outer face of the top wall 10b, remote from the chamber 11, or located within a closely-fitting hole provided in the top wall 10b so that the top wall 10b surrounds the transducer 18, thereby forming an acoustic baffle. When the distance between the transducer 18 and the surface 2 to be cleaned is small, additional cleaning may be induced by the contribution of the direct acoustic field from the transducer 18, which increases in amplitude close to the transducer 18 and superimposes upon the resonance mode in the chamber 11.

(44) In various embodiments of the method of the present invention, the surface 2 to be cleaned is exposed to the atmosphere. The apparatus may be translationally slid over the surface 2 to be cleaned during at least the step in which the acoustic transducer 18 is used to introduce acoustic energy into the chamber 11 and the step in which the acoustic energy is passed through the divider 16 from the first portion 11a of the chamber 11 to the second portion 11b of the chamber 11, thereby generating pressure fluctuations at the surface 2 to be cleaned, to provide a continuous cleaning action over a surface area of the surface 2 which is larger than an area of the distal end 12 of the apparatus 1. The cleaning liquid engaging the surface 2 to be cleaned can act to lubricate a translationally sliding action of the distal end 12 over the surface 2 to be cleaned during at least these steps.

(45) Alternatively, in other embodiments of the method of the present invention, the surface 2 to be cleaned is submerged in an underwater environment, optionally a ship hull, for example to clean biofouling from the exterior hull surface. Again, the apparatus may be translationally slid over the surface 2 to be cleaned during at least the step in which the acoustic transducer 18 is used to introduce acoustic energy into the chamber 11 and the step in which the acoustic energy is passed through the divider 16 from the first portion 11a of the chamber 11 to the second portion 11b of the chamber 11, thereby generating pressure fluctuations at the surface 2 to be cleaned, to provide a continuous cleaning action over a surface area of the surface 2 which is larger than an area of the distal end 12 of the apparatus 1. In these embodiments, water in the underwater environment and/or the cleaning liquid engaging the surface to be cleaned can act to lubricate a translationally sliding action of the distal end 12 over the surface 2 to be cleaned during at least these steps. Yet further, when the surface 2 to be cleaned is submerged in an underwater environment, the divider 16 can be omitted, and the chamber 11 is a single undivided chamber containing a cleaning liquid.

(46) Various other modifications of the invention will be readily apparent to those skilled in the art, and are included within the scope of the invention as defined by the appended claims.