Thermal spatial sound modulator and method for sound modulation

Abstract

The present invention relates to a sound modulator for modifying the amplitude and / or phase of an ultrasonic wave comprising: a thermally-responsive material, wherein at least one acoustic property of the thermally-responsive material is variable in response to a change in temperature; a source of ultrasonic waves, which is suitable to emit an ultrasonic pulse or a continuous ultrasonic wave toward the thermally-responsive material; a tempering device, which is in thermal communication with the thermally-responsive material, to trigger a local change of at least one property of the thermally-responsive material; a control signal, which is suitable to control heating and / or cooling of the tempering device. Furthermore, the invention relates to a method for spatially and temporally modulate the amplitude and / or phase of an ultrasonic wave, comprising the steps of: transmitting an ultrasonic wave toward a thermally-responsive material of a sound modulator, wherein at least one acoustic property of the thermally-responsive material is variable in response to a change in temperature; transmitting a control signal to the sound modulator; and tempering one or a plurality of areas of the thermally-responsive material, in response to the control signal, causing a local change of an acoustic property of the thermally-responsive material.

Description

[0001] Thermal Spatial Sound Modulator and Method for Sound Modulation

[0002] Description

[0003] Arrays of mechanical transducers with many, small elements can be difficult to fabricate and operate. Apart from electrical power, the transducer array typically requires electrical control elements or wiring to provide accurate, high-power electrical signals at each element. Dense arrays of many elements thus require complex electrical components or wiring, making it challenging to create very large arrays (e.g. 1 ,000 elements or more). Herein we report the invention of a thermal spatial sound modulator and control methods that separates the power generation via an ultrasonic transducer from the phase or amplitude modulation via the sound modulator. Our design provides a localized, tunable phase or amplitude shift leveraging a modulation medium whose acoustic properties undergo a rapid change across a phase transition. When the modulation medium is distributed over micro-sized pockets that can be individually heated, an ultrasonic wavefront can be shaped dynamically with high fidelity. The proposed invention can be efficiently run using electronic circuits or can be wirelessly controlled using a spatially-varying optical control signal.

[0004] Spatially-structured ultrasound fields find increasing use in many fields, particularly in medicine and bioengineering. Established methods to control the spatial propagation of ultrasound include the use of phased array transducers (see A. Macovski, “Ultrasonic array for reflection imaging,” US3918024A, Nov. 04, 1975 Accessed: Jan. 23, 2024. [Online], Available: https: / / pa- tents.google.com / patent / US3918024A / en?oq=US3918024 and B. W. Drinkwater and P. D. Wilcox, “Ultrasonic arrays for non-destructive evaluation: A review,” NDT & E International, vol. 39, no. 7, pp. 525-541 , Oct. 2006, doi: 10.1016 / j.ndteint.2006.03.006.), which allow direct control over the amplitude and phase emitted by individual piezoelectric source elements across a distributed transducer. By spatially varying the amplitude and / or phase of each source element, a wavefront can be created that will diffract into a desired pressure distribution. While phased arrays can provide exact control over the source pressure field at each element, the number of active elements per transducer is technologically limited in most cases to less than 1000, meaning that complex spatial patterns cannot be produced with high fidelity (see L. Cox, K. Melde, A. Croxford, P. Fischer, and B. W. Drinkwater, “Acoustic Hologram Enhanced Phased Arrays for Ultrasonic Particle Manipulation,” Phys. Rev. Applied, vol. 12, no. 6, p. 064055, Dec. 2019, doi: 10.1103 / PhysRevApplied.12.064055.).

[0005] A major advance that overcame this challenge was the advent of the acoustic hologram (see K. Melde, A. G. Mark, T. Qiu, and P. Fischer, “Holograms for acoustics,” Nature, vol. 537, no. 7621 , pp. 518-522, Sep. 2016, doi: 10.1038 / nature19755. and K. Melde, P. Fischer, and P.- K. WEBER, “Apparatus and method for creating a holographic ultrasound field in an object,” US11262699B2, Mar. 01 , 2022 Accessed: Jan. 08, 2024. [Online], Available: https: / / pa- tents.google.com / patent / US11262699B2 / en?inventor=Peer+Fischer), which utilized a patterned solid to impart a phase shift to an ultrasound field that was transmitted through or reflected from the hologram. Acoustic holograms are able to project ultrasound fields with unmatched complexity and detail, which has led to applications ranging from particle and cell assembly (see K. Melde, E. Choi, Z. Wu, S. Palagi, T. Qiu, and P. Fischer, “Acoustic Fabrication via the Assembly and Fusion of Particles,” Advanced Materials, vol. 30, no. 3, p. 1704507, 2018, doi: 10.1002 / adma.201704507.; Z. Ma et al., “Acoustic Holographic Cell Patterning in a Biocompatible Hydrogel,” Advanced Materials, vol. 32, no. 4, p. 1904181 , 2020, doi: 10.1002 / adma.201904181.; and K. Melde et al., “Compact holographic sound fields enable rapid one-step assembly of matter in 3D,” Science Advances, vol. 9, no. 6, p. eadf6182, Feb. 2023, doi: 10.1126 / sciadv.adf6182.), to compressive sensing, and ultrasound therapy (see P. Kruizinga et al., “Compressive 3D ultrasound imaging using a single sensor,” Science Advances, vol. 3, no. 12, p. e1701423, Dec. 2017, doi: 10.1126 / sciadv.1701423.; S. Jimenez- Gambin, N. Jimenez, J. M. Benlloch, and F. Camarena, “Holograms to Focus Arbitrary Ultrasonic Fields through the Skull,” Phys. Rev. Applied, vol. 12, no. 1 , p. 014016, Jul. 2019, doi: 10.1103 / PhysRevApplied.12.014016. ; S. Jimenez-Gambin, N. Jimenez, A. N. Pouliopoulos, J. M. Benlloch, E. E. Konofagou, and F. Camarena, “Acoustic Holograms for Bilateral Blood- Brain Barrier Opening in a Mouse Model,” IEEE Transactions on Biomedical Engineering, vol. 69, no. 4, pp. 1359-1368, Apr. 2022, doi: 10.1109 / TBME.2021.3115553.; and S. Jimenez- Gambin, S. Bae, R. Ji, F. Tsitsos, and E. E. Konofagou, “First In-vivo Demonstration of Holo- gram-assisted Bilateral Blood-Brain Barrier Opening in Non-Human-Primates,” in 2023 IEEE International Ultrasonics Symposium (IUS), Sep. 2023, pp. 1-4. doi: 10.1109 / I US51837.2023.10307955.).

[0006] However, one of the challenges of current acoustic holograms is that they are static: once fabricated, the shape of the projected field cannot be changed. This limitation has motivated the development of techniques to add flexibility to the projected fields, including frequency multiplexing, partial phase modulation, combined holograms and phased arrays, and multiplane diffractive acoustic networks. However, these existing methods provide limited improvements over the static holograms, and a more general, dynamic full-field modulator long remained elusive.

[0007] Only recently was a dynamic spatial sound modulator developed, which used electrochemically-generated gas bubbles to block sound (see Z. Ma et al., “Spatial ultrasound modulation by digitally controlling microbubble arrays,” Nature Communications, vol. 11 , no. 1 , Art. no. 1 , Sep. 2020, doi: 10.1038 / s41467-020-18347-2.; and Z. Ma, H. Joh, D. E. Fan, and P. Fischer, “Dynamic Ultrasound Projector Controlled by Light,” Advanced Science, vol. 9, no. 9, p. 2104401 , 2022, doi: 10.1002 / advs.202104401.). Because the gas bubbles have a much lower density and sound speed than water, they serve as near-perfect reflectors, preventing the transmission of ultrasound in regions of the device where bubbles are present. By patterning the production of bubbles using localized hydrolysis, binary amplitude holograms can be realized, which could then be reset and recreated multiple times over after mechanically removing the bubble pattern.

[0008] Despite the recent advances, the field is still in need of a more general, robust solution that is capable of continuous amplitude and / or phase modulation of ultrasound with spatial and temporal addressing across a large area. In this respect, the goal would be the realization of a spatial sound modulator that can be updated without the need for additional external actuators or that can be updated at desirable rates, and that has high resolution. For comparison compact, fast, high resolution, tunable modulators are known in optics, where these so called spatial light modulators enable a vast number of applications.

[0009] Current applications of spatially-structured ultrasound fields include medical imaging, focused ultrasound therapy, neurostimulation, material assembly and fabrication, 3D displays, com- pressive sensing, non-contact micromanipulation, acoustofluidic processing, and tissue engineering, and all of these fields would benefit from a compact, fast, high resolution device that can modulate ultrasound akin to a spatial light modulator.

[0010] Thus, there is still a need for a method and apparatus for dynamically modifying the local amplitude and / or phase of an ultrasonic wave. The method as well as the apparatus should not show the above-mentioned drawbacks of the existing devices.

[0011] The present invention solves this problem by the subject matter of the independent claims.

[0012] Accordingly, a solution for the above-mentioned problem is provided by a sound modulator for modifying the amplitude and / or phase of an ultrasonic wave, comprising:

[0013] - a fluid or solid medium,

[0014] - a thermally-responsive material, in acoustic communication with the fluid or solid medium, wherein at least one acoustic property of the thermally-responsive material is variable in response to a change in temperature,

[0015] - a source of ultrasonic waves, which is in acoustic communication with the medium and suitable to emit an ultrasonic pulse or a continuous ultrasonic wave into the medium, wherein the ultrasonic pulse or the continuous ultrasonic wave is directed toward the thermally-responsive material,

[0016] - a tempering device, which is in thermal communication with the thermally-responsive material, to trigger a local change of at least one property of the thermally-responsive material,

[0017] - an energy source, which is in physical communication with the tempering device, to provide power to the tempering device, and

[0018] - a control signal, which is suitable to control heating and / or cooling of the tempering device.

[0019] Preferably, the thermally-responsive material is in acoustic communication with the fluid or solid medium, whose acoustic properties vary in response to changes in temperature. Thus, sound waves traveling through the fluid or solid medium reach the thermally-responsive material and the further propagation of the sound waves through the thermally-responsive material is dependent from its respective acoustic properties. The acoustic properties of the thermally- responsive material are preferably selected from a group comprising sound speed, density and attenuation coefficient. Preferably, the sound waves are ultrasonic waves generated by a source of ultrasonic waves. This source of ultrasonic waves is preferably in acoustic communication with the medium and thus suitable to emit an ultrasonic pulse or a continuous ultrasonic wave into the medium. Preferably, the ultrasonic pulse or a continuous ultrasonic wave is directed toward the (thermally-) responsive material.

[0020] The tempering device may be or may comprise a heating and / or cooling body. This body is preferably in thermal communication with the (thermally-)responsive material, in order to trigger a local change in properties of the (thermally-)responsive material.

[0021] To allow this change of the properties of the (thermally-)responsive material preferably an energy source is provided, which is in physical communication with the (thermally-) responsive material. Thus, power can be provided to the heating and / or cooling body.

[0022] Preferably a control signal is provided by a control device. This control device is preferably in physical communication with the (thermally-) responsive material and / or the tempering device (e.g. the heating and / or cooling body), to control the activation of the heating (and / or cooling) source.

[0023] In a preferred embodiment, the thermally-responsive material comprises a pure or alloyed metal providing a thermal phase transition at a temperature between 0 - 100°C. This phase transition may be any phase transition including polymorphic transitions as well as melting and vaporization transitions. However, in a preferred embodiment, the thermal phase transition includes a melting process. Preferably the thermally-responsive material has a melting point between 0 - 100°C.

[0024] Preferably, a speed of sound and / or a density of the thermally-responsive material is changeable as a result of a thermal phase transition of the thermally-responsive material. Thus, as a result of a thermal phase transition of the (thermally-) responsive material the sound speed(s) and / or density change.

[0025] Advantageously, the sound speed(s) and / or density change as a result of a thermal phase transition of a pure or alloyed metal with a melting point between 0 - 100°C. In a preferred embodiment, the tempering device comprises at least one, preferably a plurality of tempering elements.

[0026] The at least one electrical tempering element, preferably each of the electrical tempering elements, is powered by an electric current and preferably individually controllable by a control signal. Thus, the tempering element(s) is / are preferably (an) electrical tempering element(s).

[0027] Preferably, the (electrical) tempering elements are in thermal communication with the ther- mally-responsive material. Especially in the embodiment comprising a plurality of (electrical) tempering elements, the temperature of the thermally-responsive material can be locally different due to a different temperature of the tempering elements. Thus, the acoustic properties of a defined area of the thermally-responsive material can be set depending on the location of this area.

[0028] Preferably, the at least one electrical tempering element is a heater. Since heat can be generated quickly and easily using electricity, a rapid change of the acoustic properties of the thermally-responsive material can be achieved. Thus, preferably, the tempering device and / or the tempering element(s) form a heating body, which consist of a single or many electrical heaters.

[0029] Independent of the energy source of the tempering element(s), the tempering element(s) (or heaters) are preferably in thermal communication with the (thermally-) responsive material. However, it has been found advantageous, that the heaters being powered by an electric current, and controlled by a digital control circuit.

[0030] Furthermore, it could be advantageous, that the heating body consist of a single or many electrical heaters. Preferably, the heaters being in thermal communication with the (thermally-) responsive material, and the heaters being powered by an electric current, which is gated by light incident upon a photoresponsive material (e.g. photoresistor, photoconductor).

[0031] In a preferred embodiment, the heating body consist of a single or many electrical heaters, the heaters being in thermal communication with the responsive material, and the heaters being powered by an electric current, which is controlled by an electrical circuit incorporating one or many discrete photosensitive circuit elements. In a preferred embodiment the tempering device comprises at least one, preferably a plurality of optical tempering elements. These one or more optical tempering element / s can be present alternatively or in addition to the above-mentioned (electrical) tempering element / s. Preferably, the optical tempering element / s is / are in thermal communication with the thermally-responsive material, wherein the at least one optical tempering element is suitable for converting incident light emitted by a corresponding light source into heat. Thus, it is possible to amend the (acoustic) properties of the thermally-responsive material even without (or in addition to) electrical energy.

[0032] In this embodiment, the heating body may comprise a single or multiple optical absorbers. Accordingly, the energy source can be a structured light beam incident on the absorbers.

[0033] In combination thereto or alternatively, the at least one electrical tempering element, preferably each of the electrical tempering elements, is controllable, preferably individually, by light. More preferably, the at least one electrical tempering element is controllable by light directed onto a photoresponsive element of the respective electrical tempering element or by light directed onto a photoresponsive element of the tempering device which is clearly assigned to a respective electrical tempering element.

[0034] In a preferred embodiment, the tempering device comprises at least one, preferably a plurality of Peltier elements. Preferably, at least one, more preferably a plurality of Peltier elements form a cooling body of the tempering device. Peltier elements have been found to be especially suitable for rapidly cooling the thermally-responsive material (preferably locally), accordingly, the cooling body consists of a single or multiple Peltier elements.

[0035] In combination thereto or alternatively the sound modulator comprises a temperature control device to set a base temperature of the thermally-responsive material. The (above-mentioned) tempering device is suitable to for changing the base temperature locally. Preferably a predefined baseline temperature is maintained across the entire (thermally-) responsive material using active cooling (or heating), preferably as long as no temperature change is initiated by the at least one tempering element.

[0036] Preferably the sound modulator is a thermal spatial sound modulator for modifying the amplitude and / or phase of an ultrasonic wave using the temperature-dependent acoustic property changes of the (thermally-) responsive material. Advantageously, the sound modulator comprises > 4, preferably > 9, more preferably > 16, more preferably > 25, even more preferably > 256, more preferably > 512, most preferably > 1024 tempering elements. Each of these tempering elements is preferably controllable individually. Thus, a pattern of different acoustic properties can be applied to the (thermally-) responsive material. Accordingly, the ultrasonic wave will propagate differently when passaging areas with different acoustic properties and will take on a pattern analogous to the pattern of different acoustic properties of the (thermally-) responsive material. It should be noted that the number of tempering elements can be increased further to provide pattern of higher resolution. However, the numbers mentioned above, especially with more than several hundred or thousand elements, already provide significant improvements with respect to the prior art and are already sufficient for most applications.

[0037] Advantageously, the thermally-responsive material is divided into > 4, preferably > 9, more preferably > 16, more preferably > 25, even more preferably > 256, more preferably > 512, most preferably > 1024 areas. Preferably, the temperature of each of these areas is controllable individually. Thus, a pattern of different acoustic properties can be applied to the (thermally- ) responsive material. Accordingly, the ultrasonic wave will propagate differently when passaging areas with different acoustic properties and will take on a pattern analogous to the pattern of different acoustic properties of the (thermally-) responsive material as already described above for the embodiment with the plurality of tempering elements. Similar, it should be noted that the number of areas in which the thermally-responsive material is divided can be increased further to provide pattern of higher resolution. However, the numbers mentioned above, especially with more than several hundred or thousand elements, already provide significant improvements with respect to the prior art and are already sufficient for most applications.

[0038] A further solution for the above-mentioned problem is provided by a method for spatially and temporally modulate the amplitude and / or phase of an ultrasonic wave, the method comprising the following steps:

[0039] - transmitting an ultrasonic wave via a fluid or solid medium toward a thermally-responsive material of a sound modulator, wherein the thermally-responsive material is in acoustic communication with the fluid or solid medium, wherein at least one acoustic property of the thermally-responsive material is variable in response to a change in temperature;

[0040] - transmitting a control signal to the sound modulator; and - tempering one or a plurality of areas of the thermally-responsive material, in response to the control signal, causing a local change of an acoustic property of the thermally-responsive material.

[0041] Accordingly, an ultrasonic wave is directed toward a thermal spatial sound modulator. The ultrasonic wave can be generated by any suitable source for ultrasonic waves or be naturally occurring ultrasonic wave.

[0042] To steer propagation of the ultrasonic wave preferably a control signal is transmitted to the thermal spatial sound modulator.

[0043] Based on the information of this control signal, one or a plurality of areas of the thermally- responsive material are tempered. This could be realized by heating and / or cooling one or multiple localized regions (also “areas” or “pixels”) of the spatial sound modulator. In response to the control signal, preferably a local change in the acoustic properties of the modulator is caused.

[0044] Preferably the method comprises a step of actively cooling or heating of areas of the thermally- responsive material to return the temperature and / or the acoustic properties of the thermally- responsive material to a base temperature. By such a cooling or heating of the spatial sound modulator to return the temperature and therefore the acoustic properties to a basis value (e.g. the acoustic properties present at the baseline temperature), further amendments and variations of the acoustic properties are possible.

[0045] Regardless of whether the temperature is returned to a base temperature or not, it is preferred, that the method comprises a step of modulating the control signal in time, in order to produce a temporally- and spatially-varying ultrasonic field.

[0046] In a preferred variant of the method, the control signal comprises a light pattern, preferably a 2D-image, which is applied onto a photoresponsive element of at least one tempering element, preferably the light pattern is applied onto plurality of photoresponsive elements, wherein each of the photoresponsive elements is individually associated to a defined tempering element for tempering one or a plurality of areas of the thermally-responsive material. In a preferred variant of the method, the control signal is an electrical control signal, which is provided by a digital control circuit, preferably directly provided by a digital control circuit.

[0047] Preferably, the spatially-addressable light field is transmitted to the modulator as the control signal.

[0048] In a preferred embodiment, the spatially-addressable light field is transmitted to the modulator and heats the modulator locally.

[0049] Advantageously, the digital control circuit directly provides an electrical control signal.

[0050] In a preferred embodiment of the invention, the ultrasonic wave is modulated by transmission through the thermal spatial sound modulator.

[0051] In combination thereto or alternatively the ultrasonic wave is modulated by reflection from the thermal spatial sound modulator.

[0052] Further advantages and embodiments are described in the following paragraphs and are illustrated in the drawings. It should be noted that it is not necessary that all features described or illustrated in combination with each other have to be realized in this combination. It might be possible that the above-mentioned problem could also be solved by an apparatus or a method featuring only some of the described or illustrated features. Furthermore, it might be advantageous that some features a combined with each other, which are not described in combination with each other but described in separate paragraphs or with respect to different embodiments of the invention. Also, features illustrated in different figures might be combined in an advantageous manner to solve the above-mentioned problem.

[0053] Preferably, the apparatus (the thermal spatial sound modulator) is set up, suitable and / or intended to carry out the method as described herein as well as all method steps described in connection with the method individually or in combination with each other or individual method steps using the same. Conversely, the method can be carried out using all the features described in the context of the apparatus, either individually or in combination with each other. The method of operation and the components of the described invention together with further objects and advantages thereof, may best be understood by reference to the following description in conjunction with the accompanying drawings in which numerical characters represent the parts throughout the drawings, and in which:

[0054] Fig. 1 is a block diagram of an exemplary thermal spatial sound modulator;

[0055] Fig. 2 is an illustration of an exemplary thermal spatial sound modulator operating in transmission;

[0056] Fig. 3 is an illustration of an exemplary thermal spatial sound modulator operating in reflection;

[0057] Fig. 4 is a detailed cross-section of a thermal spatial sound modulator, illustrating the individual pockets of the active modulation medium, each independently driven by an electric heater, wherein the entire assembly is in thermal contact with a fluid, whose temperature is maintained using an active cooling system;

[0058] Fig. 5 is a detailed cross-section of a thermal spatial sound modulator using light projected onto an optical absorbing layer to heat the active modulation medium, wherein the modulator is mounted onto a backing plate that is actively cooled to maintain a fixed temperature;

[0059] Fig. 6 is a detailed cross-section of an integrated, monolithic thermal spatial sound modulator, where a sound source is directly coupled to the modulator using a solid that transmits ultrasonic waves, wherein the modulator is driven in this figure by an electrical control system; and

[0060] Fig. 7 is a detailed cross-section of a thermal spatial sound modulator, where the active modulation medium is heated using an electrical heater, and the current flow to the heater is controlled by light incident upon a photoswitchable conductor.

[0061] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and / or structurally similar elements). Fig. 1 is a block diagram of an exemplary thermal spatial sound modulator 1. The thermal spatial sound modulator 1 is a device comprising a single or multiplicity of sealed pockets 10, each pocket 10 containing a modulation fluid 20 or solid (below referred to as the modulation fluid without loss of generality), whose acoustic properties such as speed of sound or density vary with temperature. Each pocket 10 is in thermal contact with at least one heat source 30 that, when provided with energy, can locally heat the modulation fluid 20, thereby changing the local acoustic properties of the modulator 1. In the case that the modulator 1 comprises multiple pockets 10 of modulation fluid 20, each pocket 10 may be considered a ‘pixel’ for the sound modulation. In the case that the modulator 1 comprises a single pocket 10, but multiple heat sources 30, the locations of the heat sources 30 may define a local pixel for sound modulation. Here a ‘pixel’ refers to the smallest region of the modulator 1 that can be independently controlled.

[0062] The modulator 1 is in mechanical contact with an ambient fluid 40 (which may be liquid or gas), where said fluid 40 is external to the modulator device 1 , and in which incident and radiated (modulated) acoustic waves 50 may propagate. The modulator 1 controls the local amplitude and / or phase of an incident acoustic wave 50. In some realizations, this incident acoustic wave 50 may be transmitted toward the modulator 1 through the ambient fluid 40. In others, it may be generated by an acoustic source (such as a piezoelectric element) that is mechanically coupled to the modulator.

[0063] As a result of interactions between the incident acoustic wave 50 and the modulation fluid 20, a modulated acoustic wave 60 is produced that propagates (radiates) away from the device 1 . In one possible realization (exemplarily illustrated in Fig. 2), the device 1 may operate in transmission mode, so that the incident acoustic wave 50 is modulated when passing through the device 1. In an alternate realization (exemplarily illustrated in Fig. 3), the device 1 may operate in reflection mode, so that the incident acoustic wave 50 is modulated by reflection off of the fluid-device interface 42. In a third realization, the sound source may be built directly into the device 1 , such that the modulation medium 20 plays a role in the emission of acoustic waves 60 into the medium. Depending on the operating mode and modulation fluid 20, the modulator 1 may provide spatial control over the amplitude, the phase, or both amplitude and phase of the outgoing (modulated) acoustic wave 60. Phase modulation may be achieved in transmission (see Fig. 2, illustrating an exemplary thermal spatial sound modulator operating in transmission) mode by differences in accumulated phase in the heated vs unheated modulation fluid 20. Amplitude modulation may be achieved in transmission mode because of differences in acoustic impedance in the heated vs unheated modulation fluid 20. In reflection mode (see Fig. 3 illustrating an exemplary thermal spatial sound modulator operating in reflection), amplitude and phase modulation may occur because of differences in acoustic impedance in the heated vs unheated modulation fluid 20. Modulation in reflection can also occur because of critical angle reflection effects that are shifted as the modulation fluid 20 heats and cools. Such effects may be enhanced by a phase transition between liquid and solid state in the modulation fluid 20 or near the resonances of inclusions or structures in the modulation fluid 20.

[0064] Fig. 4 is a detailed cross-section of a thermal spatial sound modulator 1 , illustrating the individual pockets 10a - 10n of the active modulation medium 20a - 20n, each independently driven by an electric heater 32a - 32n, wherein the entire assembly 1 is in thermal contact with a fluid 72, whose temperature is maintained using an active cooling system 70. The local state of the modulator 1 is controlled by a signal 32a - 32n that may be electrical or optical in nature, and which controls the delivery of energy to the local heaters 34a - 34n. In some realizations, the control signal 32a - 32n itself may directly provide energy for the local heating. In other realizations, the control signal 32a - 32n may serve as a gate signal that allows or inhibits the flow of electrical power to the heaters 34a - 34n from an appropriate energy source 30.

[0065] In one preferred embodiment of the modulator 1 , the modulation fluid 20 is locally heated by an array of independent electrical heaters 34a - 34n driven by an electrical control signal 32a - 32n. The electrical heaters 34a - 34n may be driven independently, in parallel, or may be driven sequentially using electrical addressing / demultiplexing techniques. The electrical heaters 34a - 34n may be resistive or inductive.

[0066] Fig. 5 is a detailed cross-section of a thermal spatial sound modulator 1 using light 86 projected onto an optical absorbing layer 82 to heat the active modulation medium 20, wherein the modulator 1 is mounted onto a backing plate 74 that is actively cooled to maintain a fixed temperature.

[0067] In such an alternate embodiment, the modulation fluid 20 is locally heated by light 86 incident upon an optical absorber 82 that serves as the heat source 34. The light may be projected toward the optical absorber 82 in parallel using a projector 80 (such as a spatial light modulator), or a single light beam 86 may be sequentially directed at different regions of the modulator 1 using a scanning mirror device.

[0068] In yet another possible embodiment of the modulator 1 , the modulation fluid 20 is locally heated by an array of independent electrical heaters 34 driven by a common electrical power source 30. Electrical current is provided to each heater 34a - 34n through a photoswitchable conductor, which allows an external light source 80 (projector or scanning beam as above) to locally control the flow of power to each heater 34a - 34n at any given time.

[0069] The temperature of the inactive modulator 1 may be maintained at a baseline by a thermal energy sink 70 and / or active cooling methods, such as a Peltier element 70 or a heat-controlled fluid bath 72 in thermal contact with the modulator 1. When the local heaters 34 are on, they will heat the modulation fluid 20 and locally alter the acoustic state of the modulator 1. When the heaters 34 are turned off again, the thermal energy sink 70, 72 will draw the heat from the modulator 1 so that the local temperature and therefore the local acoustic state to return to a baseline.

[0070] Fig. 6 is a detailed cross-section of an integrated, monolithic thermal spatial sound modulator 1 , where a sound source 52 is directly coupled to the modulator 1 using a solid 40 that transmits ultrasonic waves 50, wherein the modulator 1 is driven in this figure by an electrical control system 32.

[0071] Fig. 7 is a detailed cross-section of a thermal spatial sound modulator 1 , where the active modulation medium 20 is heated using an electrical heater 34a - 34n, and the current flow 32 to the heater 34 is controlled by light 86 incident upon a photoswitchable conductor 84.

[0072] Embodiments having different combinations of one or more features or steps described in the context of the presented embodiments having all or some of the features as described in the context of the presented embodiments should also be considered in the document, the possibilities are intended to be considered included in the document. Modification and substitutions to specific process conditions and structures can be made and accordingly, the invention is not to be considered limited by the foregoing description and drawings, but is only limited by the scope of the appended claims of the document. List of reference signs

[0073] 1 (thermal spatial) sound modulator

[0074] 10 pocket / s, pixel for sound modulation

[0075] 20 thermally-responsive material, modulation fluid, modulation solid

[0076] 30 energy source heat source / s

[0077] 32 electrical control system, digital control circuit, current flow, control signal

[0078] 34, 34a - 34n heater, photoswitchable conductor, (optical) tempering element, photorespon- sive element

[0079] 40 (ambient) fluid, liquid, gas), fluid or solid medium

[0080] 42 fluid-device interface

[0081] 50 incident I radiated (modulated) acoustic wave / s

[0082] 52 sound source

[0083] 60 modulated acoustic wave / s

[0084] 70 thermal energy sink, active cooling, Peltier element

[0085] 72 heat-controlled fluid bath, thermal energy sink

[0086] 80 (external) light source, projector, scanning beam

[0087] 84 photoswitchable conductor

[0088] 86 light, light pattern

Claims

Claims1 . A sound modulator (1) for modifying the amplitude and / or phase of an ultrasonic wave (50) comprising: a fluid or solid medium (40), a thermally-responsive material (20), in acoustic communication with the fluid or solid medium (40), wherein at least one acoustic property of the thermally-responsive material (20) is variable in response to a change in temperature, a source of ultrasonic waves (52), which is in acoustic communication with the medium (40) and suitable to emit an ultrasonic pulse or a continuous ultrasonic wave (50) into the medium (40), wherein the ultrasonic pulse or the continuous ultrasonic wave (50) is directed toward the thermally-responsive material (20), a tempering device (34), which is in thermal communication with the thermally-responsive material (20), to trigger a local change of at least one property of the thermally-responsive material (20), an energy source (30), which is in physical communication with the tempering device (34), to provide power to the tempering device (34), and a control signal (32), which is suitable to control heating and / or cooling of the tempering device (30).

2. The sound modulator (1) according to claim 1 , characterized in that the thermally-responsive material (20) comprises a pure or alloyed metal providing a thermal phase transition at a temperature between 0 - 100°C, preferably having a melting point between 0 - 100°C.

3. The sound modulator (1) according to claim 1 , characterized in that a speed of sound and / or a density of the thermally-responsive material (20) ischangeable as a result of a thermal phase transition of the thermally-responsive material (20).

4. The sound modulator (1) according to one of the previous claims, characterized in that the tempering device (34) comprises at least one, preferably a plurality of electrical tempering elements (34a - 34n), wherein the electrical tempering element / s (34a - 34n) is / are in thermal communication with the thermally-responsive material (20), wherein the at least one electrical tempering element (34a - 34n) is preferably a heater.

5. The sound modulator (1) according to the previous claim, characterized in that the at least one electrical tempering element (34a - 34n), preferably each of the electrical tempering elements (34a - 34n), is powered by an electric current (32) and preferably individually controllable by a control signal (32a - 32n); and / or the at least one electrical tempering element (34a - 34n), preferably each of the electrical tempering elements (34a - 34n), is controllable, preferably individually, by light (86) directed onto a photoresponsive element of the respective electrical tempering element (34a - 34n) or by light directed onto a photoresponsive element (34a - 34n, 84) of the tempering device which is clearly assigned to a respective electrical tempering element (34a - 34n).

6. The sound modulator (1) according to one of the previous claims, characterized in that the tempering device comprises at least one, preferably a plurality of optical tempering elements (34a - 34n), wherein the optical tempering element / s (34a - 34n) is / are in thermal communication with the thermally-responsive material (20), wherein the at least one optical tempering element (34a - 34n) is suitable for converting incident light (86) emitted by a corresponding light source (80) into heat..

7. The sound modulator (1) according to one of the previous claims, characterized in that the tempering device comprises at least one, preferably a plurality of Peltier elements (34a - 34n, 70), wherein at least one, preferably a plurality of Peltier elements form acooling body of the tempering device.

8. The sound modulator (1) according to one of the previous claims, characterized in that the sound modulator (1) comprises a temperature control device (70) to set a base temperature of the thermally-responsive material (34a - 34n), wherein the tempering device is suitable to for changing the base temperature locally.

9. The sound modulator (1) according to one of the previous claims, characterized in that it comprises > 4, preferably > 9, more preferably > 16, more preferably > 25, even more preferably > 256, more preferably > 512, most preferably > 1024 tempering elements (34a - 34n), wherein preferably each of these tempering elements (34a - 34n) is controllable individually.

10. The sound modulator (1) according to one of the previous claims, characterized in that the thermally-responsive material (20) is divided into > 4, preferably > 9, more preferably > 16, more preferably > 25, even more preferably > 256, more preferably > 512, most preferably > 1024 areas, wherein preferably a temperature of each of these areas is controllable individually.

11. A method for spatially and temporally modulate the amplitude and / or phase of an ultrasonic wave (50), comprising the steps of: transmitting an ultrasonic wave (50) via a fluid or solid medium (40) toward a thermally-responsive material (20) of a sound modulator (1), wherein the thermally- responsive material (20) is in acoustic communication with the fluid or solid medium (40), wherein at least one acoustic property of the thermally-responsive material (20) is variable in response to a change in temperature; transmitting a control signal (32) to the sound modulator (1); and tempering one or a plurality of areas of the thermally-responsive material (20), in response to the control signal (32), causing a local change of an acoustic property of the thermally-responsive material (20).

12. The method according to claim 11 , characterized by actively cooling or heating of areas of the thermally-responsive material (20) to return the temperature and / or the acoustic properties of the thermally-responsive material (20) to a base temperature.

13. The method according to claim 11 or 12, characterized by modulating the control signal (32) in time, in order to produce a temporally- and spatially-varying ultrasonic field (60).

14. The method according to one of claims 11-13, characterized in that the control signal (32) comprises a light pattern (86), preferably a 2D-image, which is applied onto a photoresponsive element (34a - 34n) of at least one tempering element, preferably onto a plurality of photoresponsive elements (34a - 34n), wherein each of the photoresponsive elements (34a - 34n) is individually associated to a defined tempering element for tempering one or a plurality of areas of the thermally-responsive material (20).

15. The method according to one of claims 11-14, characterized in that the control signal (32) is an electrical control signal, which is provided by a digital control circuit (30), preferably directly provided by a digital control circuit (30).

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