Ultrasonic manipulation of matter

Abstract

According to an example aspect of the present invention, there is provided a method, comprising controlling plural ultrasound transducers submerged in a first physical medium to emit a pattern of ultrasound into the first physical medium, to thereby cause a first acoustic protrusion to occur in a surface of the first physical medium, and manipulating the first acoustic protrusion by selecting parameters with which to drive the plural ultrasound transducers to move droplets of oil floating on the first physical medium, the manipulating comprising changing at least one tilt angle of one or more of the plural ultrasound transducers.

Description

ULTRASONIC MANIPULATION OF MATTERFIELD

[0001] The present disclosure relates to manipulation matter using ultrasound energy.BACKGROUND

[0002] Phased ultrasound transducer arrays may be used to create a sound field which is shaped according to the need at hand, for example to conduct weld inspection or linear scanning of components. By selecting phases of transmitted ultrasound wave fronts accordingly, beams of ultrasound may be formed much like beamforming is performed in wireless communication for electromagnetic wavefronts.SUMMARY

[0003] According to some aspects, there is provided the subject-matter of the independent claims. Some embodiments are defined in the dependent claims.

[0004] According to a first aspect of the present disclosure, there is provided a method, comprising controlling plural ultrasound transducers submerged in a first physical medium to emit a pattern of ultrasound into the first physical medium, to thereby cause a first acoustic protrusion to occur in a surface of the first physical medium, and manipulating the first acoustic protrusion by selecting parameters with which to drive the plural ultrasound transducers to move droplets of oil floating on the first physical medium, the manipulating comprising changing at least one tilt angle of one or more of the plural ultrasound transducers.

[0005] According to a second aspect of the present disclosure, there is provided an apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to control at least one phased array of ultrasound transducers submerged in a firstphysical medium to emit a pattern of ultrasound into the first physical medium, to thereby cause a controllable acoustic protrusion to occur in a surface of the first physical medium, and manipulate the controllable acoustic protrusion by selecting parameters with which to control the phased array of ultrasound transducers to move matter floating on the first physical medium, the manipulating comprising changing at least one tilt angle of one or more of the plural ultrasound transducers.

[0006] According to a third aspect of the present disclosure, there is provided a non- transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause a transmission reception point to at least control plural ultrasound transducers submerged in a first physical medium to emit a pattern of ultrasound into the first physical medium, to thereby cause a first acoustic protrusion to occur in a surface of the first physical medium, and manipulate the first acoustic protrusion by selecting parameters with which to drive the phased array of ultrasound transducers to move droplets of oil floating on the first physical medium, the manipulating comprising changing at least one tilt angle of one or more of the plural ultrasound transducers.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIGURE 1 illustrates an example system in accordance with at least some embodiments of the present invention;

[0008] FIGURE 2 illustrates an example system in accordance with at least some embodiments of the present invention;

[0009] FIGURE 3 illustrates an example apparatus capable of supporting at least some embodiments of the present invention, and

[0010] FIGURE 4 is a flow chart of a method in accordance with at least some embodiments of the present invention.EMBODIMENTS

[0011] Disclosed herein are methods and devices to employ phased ultrasound arrays to create physical protrusions in a physical medium, such as a liquid, for example. These protrusions may be used, in turn, to move or otherwise manipulate solid objects or liquid floating on the physical medium, or even a gas layer disposed on the physical medium. Thus the floating items may be manipulated touch-free in a controlled manner by using the protrusion(s). This yields advantages in that the floating items do not receive fingerprints or grease, do not begin oscillating, and in the case of e.g. disease-causing pathogens on the floating item, humans are protected from contamination from them via touch. Further, the floating item does not suffer marks or physical deformation from e.g. needles or tweezers. Yet further, when the floating item is a layer of oil pollution on water, its removal is facilitated using the protrusions occasioned by the phase-controlled ultrasound emission as limiting booms.

[0012] FIGURE 1 illustrates an example system in accordance with at least some embodiments of the present invention. This example system is usable in disclosing principles underlying embodiments of the present invention. Container 110 contains, in the example of FIGURE 1, a liquid 120 therein. The liquid is an example of a physical medium. The liquid may be water or another compound in liquid form, such as methane or ammonia, for example. Floating on liquid 120 is object 150, which is an example of matter floating on liquid 120. Density of object 150 is lower than that of liquid 120.

[0013] Objects floating on a liquid surface cause deformation of the liquid touching them due the wettability of the particle material particle weight and buoyancy force. For a driving force to act on a particle, a nearby surface deformation must appear, which will either attract or repel the particle depending on the direction of the bend curvature. This phenomenon is known as the “Cheerios effect” and typically leads to the clustering of floating particles. Herein is described use of ultrasound to control the interface deformation via the acoustic radiation force, ARF, acting on the interface. Employing planar underwater ultrasonic emitters leads to the formation of a conical deformation with its shape determined by factors such as frequency, acoustic power, the emitter’s geometric characteristics and its position relative to the liquid surface. By adjusting the parameters of the electrical excitation signal the surface deformation shape can be controlled in real-time. Since the capillary force depends on the meniscus slope of the liquid surface, its control allows for modification of the magnitude and direction of the force acting on nearby floating particles.

[0014] An array of ultrasound transducers 130 is coupled with container 110 such, that individual transducers 130 of the array are configured to emit ultrasound into liquid 120 in container 110. Transducers 130 of the array are controlled by a control device, not illustrated in FIGURE 1 for the sake of clarity, to emit ultrasound into liquid 120 such that ultrasound wavefronts from the transducers 130 will interfere with each other so as to move liquid 120 in a controlled manner. The control device will drive the transducers by providing to each transducer parameters, the parameters including a phase and, optionally, also an amplitude at which the transducer is to emit its ultrasound wavefront. A further example of a parameter is whether transmission is to be conducted or no. In detail, a protrusion 140 is caused to occur in liquid 120 by the interference of the ultrasound wavefronts from transducers 130, by selecting the phases of ultrasound transmission in each transducer appropriately. Protrusion 140 is an acoustic protrusion, as it is a result of constructive interference of sound waves, in this case ultrasound waves. Reflection of ultrasound from a side of container 110 may be taken into account and leveraged in manipulating liquid 120 with the ultrasound field comprised of the wavefronts, to thereby cause protrusion 140 to occur. Protrusion 140 may be fairly low in terms of extending from the surface of liquid 120, its height being exaggerated in FIGURE 1 for the purpose of clarity of the illustration. For example, protrusion 140 may be one millimetre or between 0.5 and 5 millimetres high.

[0015] The parameters may be delivered to the transducers using a radiofrequency signal with adjustable phase and amplitude parameters, for example. The transducers may be under the surface of liquid 120, for example between 10 and 3 centimetres, cm, under this surface. An example is 5 cm below the surface.

[0016] Protrusion(s) 140 have configurable shape(s), the shape(s) being configurable by selecting phase differences between transducers 130 accordingly. The shape of an individual protrusion 140 may be caused to change by changing the phase differences provided from the control device to transducers 130 during use, such that the existing protrusion 140 will change shape without vanishing before assuming the new shape. By not vanishing it is herein meant, that the height of the protrusion will not decline by more than 50% during the transition from the earlier shape to the new shape. Likewise, protrusion 140 may be caused to move along the surface of liquid 120 by changing the phase differences provided from the control device to transducers 130 during use. Another way of performing the manipulation of object 150 is by creating protrusions 140 in a linear configuration at an angle, which causes net streaming in liquid 120 on which they are created, and thus massflow, which causes object 150 to move with the mass flow. In other words, acoustic streaming may cause a mass flow in the liquid. At the liquid surface, the acoustic field partially reflects according to Snell’s law but the generated mass flow continued up from the interface and falls due to gravity, continuing to proceed along the surface. Multiple transducers can combine these mass flows to move particles which are on the surface. The same ultrasonic transducers may be used to cause the mass flow and the manipulation of object 150 using moving protrusions, as herein described.

[0017] Protrusions 140 may be used to move object 150 on the surface of liquid 120 by moving at least one protrusion next to object 150 and then moving the protrusion towards object 150, to thereby push the object along the surface of liquid 120. Further, or alternatively, plural protrusions 140 may be used to surround object 150 and then move object 150 in a controlled manner by moving these protrusions in the same direction at the same speed. This accomplishes grabbing on to particle or pushing the particle with the Cheerios effect, generated by protrusion(s) 140 and then moving the protrusion(s) 140 to move object 150. Causing the moving to occur may comprise moving and / or rotating individual transducers 130 or focusing transducers 130 which are comprises in a phased array.

[0018] While a single linear array of ultrasound transducers is illustrated in FIGURE 1, more generally the system may comprise more than one array of ultrasound transducers 130. When present, the plural arrays may be e.g. linear and set at an angle to each other to facilitate generation of a desired type of ultrasound field additively from the wavefronts produced by individual transducers. When three linear arrays are used, they may be set at angles with respect to each other. Further, the transducers 130 may be arranged in other ways than linear arrays, for example, one or more of the at least one array used may have transducers 130 arranged along the shape of a curve.

[0019] In particular where plural arrays of ultrasound transducers are used, the arrays of ultrasound transducers may be immersed in the liquid which is not bounded nearby the arrays by any container 110. In particular, the liquid may be water of a lake, sea or ocean. In the absence of walls of a container, the ultrasound wavefronts do not reflect back, except from the surface of the liquid back downward. However, the arrays may nonetheless be used to generate one or more protrusion 140, of configurable shape through interference.

[0020] In addition to, or alternatively to, moving object 150 along the surface of liquid 120, object 150 may be caused to be ejected from the surface of liquid 120 by causing a protrusion 140 to emerge underneath object 150 floating on water 120, such that this protrusion occurs with sufficient speed to dislodge object 150 from the surface of liquid 120. This may be caused to happen by emitting a brief ultrasound signal from the transducers 130 with sufficient power. For example, object 150 may first be manipulated, using at least one protrusion 140, along the surface of liquid 120 to a selected location, and then object 150 may be ejected in this manner from the surface of liquid 120, all without touching object 150 except by the liquid.

[0021] Protrusion 140 may have a circular shape with a single central peak 142 at a single point, when viewed from above, or it may have an elliptical or linear shape, when viewed from above. A linear protrusion, by which it is meant a protrusion extending vertically upward from liquid 120 such that a central peak of the protrusion extends along a shape of a straight geometric line, is usable in amassing small objects on the surface of liquid 120. A linear protrusion may be produced by purposive selection of the phase differences between the ultrasound transducers 130 of the array(s), as described herein above.

[0022] Yet further, plural linear protrusions may be used at the same time to amass items from the surface of liquid 120, or prepare the surface for measurements or other actions, for example.

[0023] Yet further, instead of a linear shape, a protrusion may be generated, again by purposive selection of the phase differences between the ultrasound wavefronts emitted by ultrasound transducers 130 of the array(s), such that the central peak of the protrusion has a curved shape, enabling easy collection of items from the surface of liquid 120.

[0024] Further, the surface upon which objects, or more generally matter, float need not be a surface of a liquid, although a liquid is referred to above to facilitate disclosure of the principles of the system. More generally the protrusions generated as herein described may be used with phase separated matter, where solids float on a liquid, a liquid layer floats on another liquid, a gas layer lies on a liquid surface, and in some cases a liquid floats on a solid. Thus the protrusions may be used, for example, to amass oil from the surface of a lake or sea, making collection of the oil faster than by using movable solid oil control booms. Likewise, microplastics may be amassed from a water surface, for example, and samples may be handled in laboratories, in particular liquids floating on liquids, which are difficultto otherwise manipulate. Some gel-type solids may be used to generate prominent acoustic protrusions 140. A boom-based method may first be used to remove most of oil on a water surface, and the herein disclosed ultrasound-based method may be used to collect droplets of oil remaining on the water surface after the use of the booms to collect most of the oil.

[0025] In an experimental test it was noticed that as oil is hydrophobic as it curves a water surface downwards and thus attracts non-wetting particles with acoustic streaming forces. When placed near an ultrasound generated protrusion the oil droplet did not show significant repulsion or attraction. However, when the oil droplet radius intersected with protrusion, the oil was attracted to the middle of the protrusion due to the acoustic streaming forces. Thus it is possible to amass oil droplets using protrusions generated using ultrasound, for example to move the oil droplets to a location from where they may be removed from the water surface. On the other hand, an ultrasound protrusion in water will attract a Styrofoam sphere toward itself, enabling manipulation of floating Styrofoam pieces using the ultrasound protrusions.

[0026] When a transducer is placed under the liquid’s surface and pointed directly upward, at a right angle (90 degrees) to the surface, a symmetrical protrusion is generated. On the other hand, when the transducer is pointed toward the liquid surface at an angle, an asymmetrical protrusion is generated which exhibits a surface flow along the surface of the protrusion, away from the transducer. As such, tilted submerged transducers may be used to manipulate objects or e.g. oil on a surface of a liquid, such as water. The angle at which the transducer points to the surface may be between 40 and 60 degrees, for example, or more generally between zero and ninety degrees. Using plural submerged transducers at an angle between 0 and 90 degrees, such as between 40 and 60 degrees, a configurable flow field of the liquid may be generated, enabling versatile manipulation of objects on the surface. Generating a mass flow, wetting and non-wetting particles act in a similar manner. Wetting and non-wetting surfaces are both moved along with the acoustic mass flow, and sometimes depending on the acoustic mass flow velocity, a particle can be attracted by the Cheerios effect and repelled by mass flow. This results in precise, configurable control.

[0027] The ultrasound transducers may be e.g. 1.75 MHz transducers, or more generally transducers of between 1 and 10 MHz, for example between 1.25 and 2 MHz. The transducers may have a radius of between 0.5 to 5 cm, for example between 0.8 to 1.2 cm.In some embodiments, the ultrasound transducers may produce ultrasound at 50 kHz to 1 MHz, resulting in larger protrusions due to the longer associated wavelength.

[0028] An oil control method is thus enabled, using plural ultrasound transducers under a surface of water, places at an angle different from 90 degrees with respect to the surface, that is, the wavefronts emitted by the transducers do not encounter the surface at a right angle. Droplets of oil are, in the method, attracted to tips of protrusions to which they are attracted and the protrusions may then be moved to move the respective attached oil droplet to a collection area, from where the oil droplet may be collected, or ejected using a sudden ultrasound ejection as described herein above. Also, plural protrusions may be used concurrently or alternatively to the fixing of the oil droplets to the tips of protrusions to generate a surface flow field of the water, enabling moving the oil droplets to the collection area. The angles at which the transducers are placed may be configurable to facilitate control of oil droplets on the surface, thus, a support on which the transducers are fixed may have a controllable motor arrangement configured to tilt the transducers. When collecting oil, the ultrasound transducers need not necessarily be in a phased array configuration, although they may be, to facilitate control of more complex simultaneous patterns of the acoustic protrusions.

[0029] In some embodiments, a transducer is placed in the liquid such that its wavefront encounters the reflecting surface and causes a standing wave to occur in the overlapping area of the wavefront proceeding from the transducer and the reflected wavefront proceeding from the surface. The size of this area of standing wave may be controlled by changing the tilt angle of the transducer, to thereby trap particles smaller than half the wavelength in diameter which are immersed in the liquid, that is, these may be e.g. microplastic particles beneath the surface of the liquid. The microplastic particles may thus be controlled to move to a specific place with mass flow from acoustic streaming in, or on, the liquid for ejection from the liquid

[0030] FIGURE 2 illustrates an example system in accordance with at least some embodiments of the present invention. Like numbering denotes like structure as in FIGURE 1. In the case of FIGURE 2, the protrusion 140 has a linear shape in that its peak 242 is a straight line. As described above, such linear protrusions are usable in amassing plural items from a surface of a liquid, or, for example, amassing a layer of liquid or gas on the physical medium which is used to form the protrusion.

[0031] FIGURE 3 illustrates an example apparatus capable of supporting at least some embodiments of the present invention. Illustrated is apparatus 300, which comprises the control device which selects the relative phases that the ultrasound transducers will employ when emitting their wavefronts, to obtain a desired protrusion in the physical medium, such as, for example, a liquid. Comprised in device 300 is processor 310, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. Processor 310 may comprise, in general, a controller. Processor 310 may comprise more than one processor. When processor 310 comprises more than one processor, device 300 may be a distributed device wherein processing of tasks takes place in more than one physical unit. A processing core may comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Zen processing core designed by Advanced Micro Devices Corporation. Processor 310 may comprise at least one Qualcomm Snapdragon and / or Intel Atom processor. Processor 310 may comprise at least one application-specific integrated circuit, ASIC. Processor 310 may comprise at least one field-programmable gate array, FPGA. Processor 310 may be configured, at least in part by computer instructions, to perform actions.

[0032] Device 300 may comprise memory 320. Memory 320 may comprise randomaccess memory and / or permanent memory. Memory 320 may comprise at least one RAM chip. Memory 320 may be a computer readable medium. Memory 320 may comprise solid- state, magnetic, optical and / or holographic memory, for example. Memory 320 may be at least in part accessible to processor 310. Memory 320 may be at least in part comprised in processor 310. Memory 320 may be means for storing information. Memory 320 may comprise computer instructions that processor 310 is configured to execute. When computer instructions configured to cause processor 310 to perform certain actions are stored in memory 320, and device 300 overall is configured to run under the direction of processor 310 using computer instructions from memory 320, processor 310, the control device and / or its at least one processing core may be considered to be configured to perform said certain actions. The control device is an apparatus. Memory 320 may be at least in part external to device 300 but accessible to device 300. Memory 320 may be transitory or non-transitory.

[0033] Device 300 may comprise a transmitter 330. Device 300 may comprise a receiver 340. Transmitter 330 and receiver 340 may be configured to transmit and receive, respectively, information in accordance with at least one suitable communication protocol,such as serial or parallel communication, for example. Transmitter 330 may comprise more than one transmitter. Receiver 340 may comprise more than one receiver. For example, transmitter 330 may be used by the control device to transmit indications of the selected relative phases to the ultrasound transducers 130, to thereby configure the transducers to emit their wavefronts with the selected relative phases.

[0034] Device 300 may comprise user interface, UI, 360. UI 360 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 300 to vibrate, a speaker or a microphone. A user may be able to operate device 300 via UI 360, for example to configure characteristics of protrusions 140 that the user desires to create in the physical medium into which the ultrasound transducers emit their ultrasound wavefronts. Device 300 may be configured to determine the relative phases to be used by the ultrasound transducers from characteristics of the protrusion the user inputs into device 300. Alternatively, device 300 may configure the transducers with relative phases that device 300 obtains from the user directly, or from a further apparatus that device 300 is coupled with. For example, device 300 may be configured to receive input from a video camera or video cameras, and to determine the relative phases to provide to the ultrasound transducers such that objects device 300 can see in the video input are amassed into a preconfigured part of the visual feed represented by the video input.

[0035] Processor 310 may be furnished with a transmitter arranged to output information from processor 310, via electrical leads internal to device 300, to other devices comprised in device 300. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to memory 320 for storage therein. Alternatively to a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise processor 310 may comprise a receiver arranged to receive information in processor 310, via electrical leads internal to device 300, from other devices comprised in device 300. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver 340 for processing in processor 310. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver. Device 300 may comprise further devices not illustrated in FIGURE 3.

[0036] Processor 310, memory 320, transmitter 330, receiver 340 and / or UI 360 may be interconnected by electrical leads internal to device 300 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a masterbus internal to device 300, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the embodiment various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the present invention.

[0037] FIGURE 4 is a flow graph of a method in accordance with at least some embodiments of the present invention. The phases of the illustrated method may be performed in device 300 of FIGURE 3, or example, or in a controller configured to control the functioning thereof, when installed therein

[0038] Phase 410 comprises controlling plural ultrasound transducers submerged in a first physical medium to emit a pattern of ultrasound into a first physical medium, to thereby cause a first acoustic protrusion to occur in a surface of the first physical medium. Phase 420 comprises manipulating the first acoustic protrusion by selecting parameters with which to drive the plural ultrasound transducers to move droplets of oil floating on the first physical medium, the manipulating comprising changing at least one tilt angle of one or more of the plural ultrasound transducers.

[0039] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0040] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0041] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on theirpresentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0042] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0043] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0044] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

[0045] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.INDUSTRIAL APPLICABILITY

[0046] At least some embodiments of the present invention find industrial application in management of matter floating on a denser physical medium.ACRONYMS LISTFPGA field-programmable gate arrayUI user interfaceREFERENCE SIGNS LIST

Claims

CLAIMS:

1. A method, comprising:- controlling plural ultrasound transducers submerged in a first physical medium to emit a pattern of ultrasound into the first physical medium, to thereby cause a first acoustic protrusion to occur in a surface of the first physical medium, and- manipulating the first acoustic protrusion by selecting parameters with which to drive the plural ultrasound transducers to move droplets of oil floating on the first physical medium, the manipulating comprising changing at least one tilt angle of one or more of the plural ultrasound transducers.

2. The method according to claim 1, comprising selecting the parameters with which to control the plural ultrasound transducers to cause a second acoustic protrusion, in addition to the first protrusion, to occur in the surface of the first physical medium, and using the first and the second protrusion to move the droplets of oil floating on the first physical medium.

3. The method according to claim 1, comprising selecting the parameters with which to control the plural ultrasound transducers such that plural protrusions are generated in the surface of the first physical medium, the plural protrusions forming two geometric lines which are at an angle to each other, whereby a net streaming of the first physical medium is generated.

4. The method according to any one of claims 1 - 3, comprising controlling the at least one plural ultrasound transducers to emit an ultrasound signal into the first physical medium which causes a protrusion to emerge underneath the matter floating on the first physical medium, such that the matter is ejected from the surface of the first physical medium.

5. The method according to any one of claims 1 - 4, wherein each of the at least one tilt angle is varied within a range of zero to ninety degrees, for example within a range of 40 to 60 degrees.

6. The method according to any of one claims 1 - 5, comprising attracting a first oil droplet to a tip of the first acoustic protrusion and subsequently moving the first acoustic protrusion to thereby move the first oil droplet.

7. The method according to any one of claims 1 - 6, further comprising first using oil collection booms to remove more than 80% of an initial quantity of oil on the first physical medium surface, and then, after the using of the oil collection booms, performing the manipulating of the first acoustic protrusion to remove the droplets of oil remaining on the first physical medium after using the oil collection booms.

8. The method according to any one of claims 1 - 7, comprising generating a standing wave to occur in an area overlapping a wavefront proceeding from the plural ultrasound transducers and a reflected wavefront proceeding from the surface of the first physical medium, wherein a size of the standing wave is controlled by changing the at least one tilt angle, to thereby trap particles smaller than half a wavelength of the ultrasound in diameter which are immersed in the first physical medium.

9. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to:- control at least one phased array of ultrasound transducers submerged in a first physical medium to emit a pattern of ultrasound into the first physical medium, to thereby cause a controllable acoustic protrusion to occur in a surface of the first physical medium, and- manipulate the controllable acoustic protrusion by selecting parameters with which to control the phased array of ultrasound transducers to move matter floating on the first physical medium, the manipulating comprising changing at least one tilt angle of one or more of the plural ultrasound transducers.

10. The apparatus according to claim 9, wherein the apparatus is configured to select the parameters with which to control the phased array of ultrasound transducers to cause a second controllable acoustic protrusion, in addition to the first controllable protrusion, to occur in the surface of the first physical medium, and to use the first and second controllable protrusion to move a solid object or patch of liquid floating on the first physical medium.

11. The apparatus according to claim 9, wherein the apparatus is configured to select the parameters with which to control the phased array of ultrasound transducers such that plural protrusions are generated in the surface of the first physical medium, the plural protrusions forming two geometric lines which are at an angle to each other, whereby a net streaming of the first physical medium is generated.

12. The apparatus according to any of one claims 9 - 11, configured to control the at least one phased array of ultrasound transducers to emit an ultrasound signal into the first physical medium which causes a protrusion to emerge underneath the matter floating on the first physical medium, such that the matter is ejected from the surface of the first physical medium.

13. The apparatus according to any one of claims 9 - 12, wherein the apparatus is configured to be used with water as the first physical medium.

14. The apparatus according to claim 13, wherein the apparatus is configured to be used with water as with oil as the matter floating on the first physical medium.

15. A non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause a transmission reception point to at least:- control plural ultrasound transducers submerged in a first physical medium to emit a pattern of ultrasound into the first physical medium, to thereby cause a first acoustic protrusion to occur in a surface of the first physical medium, and- manipulate the first acoustic protrusion by selecting parameters with which to drive the phased array of ultrasound transducers to move droplets of oil floating on the first physical medium, the manipulating comprising changing at least one tilt angle of one or more of the plural ultrasound transducers.

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