WAVE MANIPULATION IN A PROPAGATION MEDIUM

Abstract

The present invention relates to a method and device for manipulating waves in a medium of interest intended to receive injected waves having initial wavefronts, said device (1) comprising fluctuation means (9) configured to introduce into the medium of interest (3) a fluctuation adapted to disperse the initial wavefronts into a confined dispersion zone while redirecting them to a compact recombination zone (13) in which the confined wavefronts recombine to produce superimposed wavefronts whose profiles include additional patterns enabling them to propagate in depth into said medium of interest, thus enabling them to be used for in-depth diagnosis of said medium of interest. Figure for the abstract: Fig. 1

Description

Title of the invention: MANIPULATION OF WAVES IN A PROPAGATION MEDIUM Technical field

[0001] The present invention relates to the field of wave manipulation in a propagation medium and in particular, for a diagnosis of a medium of interest. State of the prior art

[0002] The manipulation of waves in a propagation medium has numerous practical applications in the industrial and medical fields, ranging from the diagnosis of a medium of interest to non-destructive testing of a complex part.

[0003] The technique of manipulating waves in a propagation medium consists of injecting waves into this medium of interest from one or more sources and monitoring the profiles of the waves during their propagation within the medium. The source can be, for example, an acoustic transducer in the audible, ultrasound, or infrasound range.

[0004] Most wave manipulation techniques in the prior art use reflection means (mirrors, deflectors, etc.) or transmission means (lenses, slits, interfaces, etc.).

[0005] An example of wave manipulation is described in document US 11067687. The system according to this document aims to produce coherent acoustic waves and comprises reflection means to allow acoustic beams to bypass an obstacle without reversing direction compared to the initial propagation.

[0006] Other examples of wave manipulation involve acoustic transmission membranes whose properties are tuned to produce coherent acoustic waves.

[0007] These techniques are implemented on propagating regions called "far field" or plane waves. Only simple compositions propagate in the far field, which does not allow for precise analysis of the health status of the environment of interest.

[0008] It is possible to create and manipulate certain effects in non-propagating regions known as "near field", the sites of evanescent waves. However, in the near field domain the description of local particle movements by superposition is very complex and the reproduction of these movements is spatially limited to a very small propagation distance. Thus, it is not possible to know the state of health or carry out non-destructive testing of characteristics of the medium of interest au- beyond a very small distance from the place of injection of the waves.

[0009] Furthermore, it is very difficult to control the spatial spread of the energy injected by acoustic sources. There are passive acoustic lenses of the Fresnel lens type for focusing acoustic waves. But these lenses are bulky and cannot achieve a resolution lower than the wavelength. All these elements generally lack compactness because they are limited by interference effects or the formation of standing waves and are difficult to integrate into devices meeting application needs.

[0010] The object of the present invention is to remedy the aforementioned drawbacks by proposing a method and a compact device for manipulating waves in a medium of interest which makes it possible to increase the spatial extent of near-field zones without producing interference, thus allowing in-depth diagnosis of the medium of interest. Statement of the invention

[0011] The present invention is defined by a device for manipulating waves in a medium of interest intended to receive injected waves having initial wavefronts, said device comprising fluctuation means configured to introduce into the medium of interest a fluctuation adapted to disperse the initial wavefronts in a confined dispersion zone while redirecting them towards a compact recombination zone in which the confined wavefronts recombine to produce superimposed wavefronts whose profiles comprise additional patterns allowing them to propagate in depth in said medium of interest and thus being able to be used for an in-depth diagnosis of said medium of interest.

[0012] Thus, the manipulation device makes it possible to transform the propagation medium of interest into a medium behaving like a waveguide concentrating the energy of desired waves at a recombination location where the injected waves acquire additional properties after having been subtly dispersed and re-concentrated towards this location, then allowing the waves to propagate further in the medium of interest, allowing in-depth diagnosis.

[0013] Advantageously, the fluctuation means comprise at least one obstacle arranged in the medium of interest and in the path of said injected waves, said at least one obstacle being configured to diffract the initial wave fronts along a plurality of propagation paths ending in said compact recombination zone.

[0014] This makes it possible to optimize the compactness of the device while increasing the spatial extent of near-field areas without producing interference. This further allows, to modify the apparent position of the source and / or the direction of propagation and allows waves to be injected into a target medium which is not favorable to this injection.

[0015] Advantageously, the fluctuation means comprise first and second obstacles, called obstacle and counter-obstacle, arranged in the medium of interest, the obstacle being configured to transmit a portion of the initial wavefronts to the counter-obstacle and to redirect the other portion along a plurality of propagation paths to said compact recombination zone, the counter-obstacle being configured to redirect in almost the same predetermined direction the wavefronts received from the first obstacle as well as possibly initial wavefronts to said compact recombination zone.

[0016] This makes it possible to maximize the reflection of the energy of the injected waves towards the recombination zone and to obtain functions which cannot be obtained in the far field of the source.

[0017] Advantageously, the obstacle comprises at least one cavity comprising a medium of a predetermined nature which may be the same as that of the medium of interest.

[0018] The resonance of the cavity makes it possible to further enrich the initial wave fronts with new properties.

[0019] Advantageously, the obstacle comprises at least one wall configured to vibrate and / or to vibrate the volume of the obstacle upon receipt of the injected waves.

[0020] This makes the formation of interference almost impossible while further enriching the initial wavefronts with yet other new properties.

[0021] Advantageously, the obstacle has dimensions smaller than the wavelength of the injected waves.

[0022] Advantageously, the counter-obstacle is configured to vibrate upon reception of the waves.

[0023] Advantageously, the obstacle and the counter-obstacles are arranged in the medium of interest while being separated from each other by a distance smaller than the longest wavelength of the injected waves.

[0024] Advantageously, the counter-obstacle is configured to define a preferred direction in the medium of interest.

[0025] Advantageously, the obstacle and / or the counter-obstacle comprise metamaterials having elastodynamic properties.

[0026] According to another embodiment, the fluctuation means comprise thermal means configured to introduce into the medium of interest a temperature change dispersing the initial wave fronts of the injected waves while redirecting them towards the compact recombination zone.

[0027] According to yet another embodiment, the fluctuation means comprise external mechanical means configured to introduce into the medium of interest an elastic fluctuation dispersing the initial wave fronts of the injected waves while redirecting them towards the compact recombination zone.

[0028] The invention also relates to a housing comprising the manipulation device, according to any one of the preceding characteristics, the housing being made of a material compatible with the medium of interest while allowing the waves injected by the source to pass.

[0029] The invention also relates to a method for manipulating waves in a medium of interest intended to receive injected waves having initial wave fronts, said method comprising the following steps:

[0030] -introduce into the medium of interest a fluctuation adapted to disperse the initial wave fronts in a confined dispersion zone, and

[0031] -redirecting the dispersed wavefronts to a compact recombination zone in which the confined wavefronts recombine to produce superimposed wavefronts whose profiles include additional patterns allowing them to propagate in depth in said medium of interest and thus being able to be used for an in-depth diagnosis of said medium of interest. Brief description of the drawings

[0032] Other characteristics and advantages of the invention will appear on reading a preferred embodiment of the invention, described with reference to the attached figures among which:

[0033] [Fig.l] schematically represents a device 1 and a method for manipulating waves in a medium of interest 3, according to an embodiment of the invention;

[0034] [Fig.2A] schematically represents a device for manipulating waves in a medium of interest, according to a first preferred embodiment of the invention;

[0035] [Fig.2B] schematically represents the structure of an obstacle, according to a preferred embodiment of the invention;

[0036] [Fig.3] schematically represents a wave manipulation device in a medium of interest, according to a second preferred embodiment of the invention;

[0037] [Fig.4] schematically represents the handling properties and of wave interaction according to the device of [Fig.3];

[0038] [Fig.5A]

[0039] [Fig.5B]

[0040] [Fig.5C]

[0041] [Fig.5D]

[0042] [Fig.5E] schematically represent different application examples and advantages of the devices for manipulating waves in a medium of interest, according to the embodiments of Figs. 2A to 4; and

[0043] [Fig.6] schematically represents a box comprising the device of my nipulation, according to one embodiment of the invention. Description of the embodiments

[0044] The concept underlying the invention is to create specific wavefronts from waves injected into a target medium by locally modifying the coherence of the injected waves or by taking advantage of their potential lack of coherence. The present invention proposes a method and a device for manipulating waves intended to improve their propagation in a medium of interest.

[0045] [Fig.l] schematically represents a device 1 and a method for manipulating waves in a medium of interest 3, according to an embodiment of the invention.

[0046] The medium of interest 3 may be of a solid, fluidic or gaseous nature, defined by an initial reference state. The reference state of the medium of interest 3 is determined by its overall mechanical properties (Young's modulus, Poisson's ratio, density, viscosity, etc.) which depend on the microscopic properties of the particles composing the medium 3. The medium of interest 3 may optionally be incompressible and / or non-deformable and / or confined.

[0047] Propagating waves having initial wave fronts 5 can be injected into the medium of interest 3 in order, for example, to control or monitor this medium 3. These waves can be emitted from a source 7 of any design and having a wide frequency band. The wave source 7 can be natural (for example, a noise source) or artificial (for example, an acoustic transducer in the audible range, ultrasound, or infrasound). It can be single or multiple but for simplification, will be referred to hereinafter in the singular.

[0048] The source 7 may include several discrete elements which may be organized in a network and / or in matrices. It may be provided with acoustic impedance matching and / or focusing means. The source 7 may be a second source distant from a primary source or be an interface (in the sense of wave propagation). The waves may thus be primary waves or secondary waves re-emitted from existing waves. Furthermore, the wave fronts 5 of the injected energies may be flat, spherical, or other.

[0049] The source 7 may be located in the medium of interest 3 or in another medium. This other medium may be of a different nature from that of the medium of interest or even tually, of the same nature but with inhomogeneity or discontinuous delimitation or with a continuous separation between the two media. For example, the waves can be injected by the source 7 into the medium of interest 3 through a delimited surface, materially defined (for example through a solid interface, a wall, a membrane, etc.) or undefined (for example, in a fluid). In this case, the waves propagate to the medium of interest 3 by taking advantage of the properties of the source 7.

[0050] According to the invention, the device 1 comprises directional fluctuation means 9 configured to introduce into the medium of interest 3 a fluctuation which modifies its initial reference state. This fluctuation is adapted to disperse initial wavefronts 5 injected into the medium of interest 3 over a restricted zone 11 while redirecting them towards a compact recombination zone 13. The directions of the wavefronts in the medium of interest 3 are represented by arrows.

[0051] For example, in the case where the source 7 is coherent and injects plane waves into the medium of interest 3, the fluctuation means 9 introduce a modification of the initial coherence of the phases and therefore a modification of the shape of the wave fronts. The modification of the coherence can be defined in connection with the notions of statistical dispersion of the particles within a wave.

[0052] Furthermore, the wavefronts concentrated in the compact recombination zone 13 recombine to produce superimposed wavefronts whose profiles include additional effects or patterns. This makes it possible to increase the spatial extent of near-field zones without producing interference.

[0053] In particular, the fluctuation means 9 are adapted to locally and temporarily modify the statistical dispersion of the particles within a wave by generating a result capable of persisting by propagating in depth.

[0054] Furthermore, the richness of the patterns induced by the fluctuation of the medium of interest 3 and by the recombination of the wave fronts gives the latter very good resolution properties allowing precise analysis and / or monitoring of the medium of interest.

[0055] It will be noted that the fluctuations of the reference state of the medium of interest 3 can be obtained by different means depending on the applications and the media considered.

[0056] According to a first example, the fluctuation can be obtained by a diffraction phenomenon, for example, by an obstacle placed in the path of the injected waves (see Figs. 2A-5E).

[0057] According to a second example, the fluctuation can be obtained by a change in temperature in particular, when it is possible to manage rapid dynamics. In this case, the fluctuation means 9 comprise thermal means configured to introduce into the medium of interest 3 a change in temperature dispersing the initial wave fronts 5 while redirecting them towards the compact recombination zone 13.

[0058] According to a third example, the fluctuation can be obtained by vibrations produced in the medium of interest 3.

[0059] According to a fourth example, the fluctuation can be obtained by an external mechanical force adapted to generate elastic fluctuations in the medium of interest 3. In this case, the fluctuation means 9 comprise external mechanical means configured to generate in the medium of interest 3 an elastic fluctuation dispersing the initial wave fronts of the injected waves while redirecting them towards the compact recombination zone 13.

[0060] Furthermore, the combination of the wave fronts concentrated in the compact recombination zone 13 may result from several factors. For example, it may result from the combination of the statistical dispersions of the particles set in local motion at the place and time when the waves are passing. According to another example, the combination may be due to the meeting in the recombination zone 13 at a given time of the waves which have been caused to propagate along multiple paths. According to yet another example, the combination may be due to the superposition of local and temporal fluctuations of the reference state of the medium linked to the average value of the particles present and / or to the variation of the average pressure.

[0061] Figs. 2A, 2B and 3 schematically represent devices for manipulating waves in a medium of interest, according to preferred embodiments of the invention.

[0062] According to these embodiments, the fluctuation means 9 of the manipulation device 1 comprises at least one obstacle 91 arranged in the medium of interest 3.

[0063] More particularly, the fluctuation means 9 of the device 1 according to [Fig.2A] comprise an obstacle 91 arranged in the medium of interest 3 and in the propagation path of the injected waves. It will be noted that the obstacle 91 is preferably anchored so that it does not move. Advantageously, the obstacle 91 has dimensions smaller than the wavelength of the injected waves and more particularly, smaller than the smallest wavelength of the injected waves. The geometric shape of the obstacle 91 can be arbitrary with or without symmetries, with or without edges.

[0064] The arrangement of the obstacle 91 in the medium of interest 3 can be chosen so as to modify the apparent position of the source 7 and / or the direction of propagation of the waves. Preferably, waves having initial wave fronts are injected into the medium of interest 3 in a direction d1 different from a predetermined direction of interest d2 so that no energy radiates directly towards the medium of interest 3.

[0065] The obstacle 91 is configured to diffract the initial wavefronts 5 by directing them along a plurality of different propagation paths cl,... .converging or quasi-converging. These paths are limited to a pro restricted pagation 11 and end up in a compact recombination zone 13. The meeting in the recombination zone 13 of the wave fronts which have been caused to propagate along the different paths cl,... in fact that these wave fronts recombine to produce superimposed wave fronts whose profiles include additional effects or patterns.

[0066] [Fig.2B] schematically represents the structure of an obstacle, according to a preferred embodiment of the invention.

[0067] The obstacle 91 has a soft shape (without edges) possibly with several radii of curvature. Preferably, the obstacle 91 is a hollow ellipsoid comprising at least one compressible cavity 911 comprising a medium or a fluid of a predetermined nature (air, water, or other). This medium may be of the same nature or of a different nature than that of the medium of interest 3. The resonance of the cavity 911 further enriches the initial wavefronts with new properties.

[0068] Advantageously, the walls of the obstacle 91 are locally thin and may comprise stretched elastic means or parts 913 arranged and designed to promote the spatial spreading of the injected energies as a function of their spectral content. The temporal dynamics of the thin parts 913 also contribute to the spreading by producing different delays.

[0069] The obstacle 91 comprises at least one wall (planar or other) configured to vibrate and / or to vibrate the entire volume of the obstacle 91 upon receipt of the injected waves. Indeed, the obstacle may comprise vibrating elements 915 arranged on the walls or forming the walls. Other deformable or vibrating elements 917 under the effect of injected pressure may also occupy the interior volume of the obstacle 91. These elements 913, 915, 917 may be metamaterials having elastic properties, 913 or elastodynamic properties, 915, 917. It will be noted that a simple metamaterial is passive and generally derives its properties from local breaks in regularity at the heart of a particular repeated pattern.

[0070] Furthermore, the obstacle 91 may also be a defect already existing in the medium of interest 3. The obstacle 91 may for example be an inclusion in the propagation medium of interest 3 which does not move but which is arranged so that the injected energy sets it into vibration, for example, elastically so that it self-modulates. The vibrations of the obstacle 91 prevent the formation of interference while further enriching the wavefronts.

[0071] [Fig. 3] schematically represents a device for manipulating waves in a medium of interest, according to a second preferred embodiment of the invention.

[0072] According to this embodiment, the fluctuation means 9 comprise several obstacles. In particular, the example of [Fig. 3] illustrates first 91 and second 93 obstacles, called obstacle 91 and counter-obstacle 93, arranged in the medium of interest 3.

[0073] The obstacle 91 is configured to transmit a portion of the initial wavefronts towards the counter-obstacle 93 and to redirect the other portion along a plurality of limited propagation paths over a restricted propagation zone 11 towards a compact recombination zone 13.

[0074] The counter-obstacle 93 is configured to redirect in almost the same predetermined direction d3 the wavefronts received from the first obstacle 91 as well as possibly initial wavefronts 5 towards the compact recombination zone 13. The predetermined direction d3 is a preferred direction defined by the arrangement and the geometry of the counter-obstacle 93 which is further configured to reflect the maximum of the injected energy.

[0075] The obstacle 91 and the counter obstacle 93 are arranged in the medium of interest 3, being separated from each other by a distance smaller than the longest wavelength of the injected waves. This distance may, for example, be equal to 1 / 10 of the longest wavelength.

[0076] Advantageously, the elastic contribution of the obstacle 91 and the counter obstacle 93 is coupled locally with the medium of interest 3 to introduce waves whose contributions will interact with the injected waves.

[0077] The meeting in the recombination zone 13 of the wavefronts propagating along multiple paths from the obstacle and the counter-obstacle recombine to produce superimposed wavefronts whose profiles include additional effects or patterns.

[0078] The counter-obstacle 93 may be a simple, fixed, solid wall, shaped (in a spheroidal, ellipsoidal, or other manner) to concentrate the waves, thus acting as an acoustic mirror. For example, it may be the non-useful end of the propagation medium of interest 3. The counter-obstacle 93 may also consist of a set of inclusions.

[0079] Optionally, the counter-obstacle 93 may be designed in the same way as the obstacle 91 according to [Fig.2B]. Thus, the obstacle and the counter-obstacle may each comprise at least one cavity comprising a medium of the same nature or of a different nature than that of the medium of interest. In addition, the obstacle and the counter-obstacle may each be configured to vibrate upon receipt of the injected waves. The vibrations prevent the formation of standing waves. In addition, the obstacle and the counter-obstacle may accommodate elastic means 913 of the metamaterials and / or metasurfaces 915 in the walls or inside the volumes with localized anchoring to the walls (see [Fig.2B]). The metasurfaces and the metamaterials which “dress” the obstacle 91 and / or the counter-obstacle 93 may be passive or active (autonomous or powered wirelessly for example by RFID or NFC).

[0080] The obstacle 91 and / or the counter-obstacle 93 may be opaque to the injected waves. (i.e. the waves do not penetrate) or semi-transparent (i.e. the waves penetrate to be able to interact with metamaterials arranged inside either acoustically or mechanically under the effect of the pressure waves). Preferably, the obstacle 91 is semi-transparent while the counter-obstacle 93 is opaque and reflective and of geometry (shape and dimensions) capable of refocusing all the energies coming directly from the source 7 or from the obstacle 91.

[0081] A non-limiting example of geometry for the obstacle or counter-obstacle is described by this reference: Application offlügge thin shell theory to the solution offree vibration behaviors for spherical-cylindrical-spherical shell: A unified formulation, Pang, F., Li, H., Cui, J., Du, Y., Gao, C., 2019, European Journal of Mechanics, AJ Solids 74, pp. 381-393.

[0082] Generally, the obstacle 91 and the counter-obstacle 93 are designed or selected so that, on the one hand, their properties adapt to each other and, on the other hand, to those of the medium of interest, knowing that one or the other of the obstacle and counter-obstacle may be available in the environment of the medium of interest.

[0083] More particularly, in the field of audible acoustics applied to a fluidic medium of interest (for example, a volume of water or air), the obstacle 91 may consist of a balloon or a bladder (non-axisymmetric shape) filled with fluid and floating (preferably immersed) in the medium of interest 3. The fluid may be identical to the medium of interest 3. The obstacle 91 in this case comprises an anchor preventing it from moving while allowing at least one of its faces to vibrate under the effect of the injected waves with its own elastic responses. It will be noted that the embodiments according to the invention do not seek to deform or set the medium of interest in motion but simply to interact or even add propagating waves. For better vibration efficiency, it is preferable for the face that vibrates to be a thin and taut wall.In an interesting configuration, the high frequencies can vibrate one or more membranes and the low part of the frequency band vibrates the entire volume of the obstacle 91.

[0084] In the infrasound domain, the obstacle 91 may, for example, consist of strata of heated air. This obstacle 91 is natural and has no material boundaries. In this case, the fluctuation functions are transferred to the counter-obstacle 93, which can accommodate all the functions in a degraded mode that may be sufficient in certain applications (for example, carrying simple information such as an alert or an overall state of good operation as far as possible). The obstacle 91 may even be the source that injects the energies. In this case, according to the invention, the reversal of the waves injected by the counter-obstacle 93 creates a retrograde path such that it passes through the source.

[0085] In the infrasound domain, the obstacle 91 can, for example, be made of layers of fluids presenting a density gradient due for example to a gradient of salt concentrations and / or a temperature gradient.

[0086] In the living, the obstacle 91 and / or the counter-obstacle 93 can be manufactured from biocompatible and biodegradable materials and can be put in place by any medical or surgical technique for short or long periods or even permanently.

[0087] [Fig.4] schematically represents the handling properties and of wave interaction according to the device of [Fig.3].

[0088] According to this example, the source injects into the medium of interest 3 propagating plane waves whose wave fronts 5 are schematized by parallel compression lines (dense lines) and rarefaction lines (sparse lines).

[0089] The obstacle 91 comprises a cavity 911 comprising a medium of predetermined nature. The walls of the obstacle 91 are locally thin and comprise elastic parts 913. For this role, the obstacle 91 may be opaque, transparent or semi-transparent. It may also be provided with metamaterials or metasurfaces and / or contain metafluids.

[0090] Furthermore, the counter-obstacle 93 is a solid wall shaped to act as an acoustic mirror and which may include a metasurface 935.

[0091] The first function of the device 1 is to spatially spread or diffract the injected waves in order to locally modify the shapes of the wavefronts without introducing parasitic effects which can be sources of distortion and / or weakening of the injected energies. The obstacle 91 being preferably small compared to the wavelengths, can play a partial role in the sense that a part of the waves emitted by the source can reach the counter-obstacle 93 without having been affected by the obstacle 91.

[0092] In the context of this first function, the obstacle 91 is configured to create in the most compact way possible several propagation paths so that the path differences are tiny fractions of the wavelength (for example, less than 1% or according to the rules of use in time reversal).

[0093] Also within the framework of the first function, the counter-obstacle 93 is configured to return the received wavefronts, towards the recombination location 13 without modifying the frequencies of the manipulated waves. Optionally, the fluctuation means 9 (obstacle 91 and counter-obstacle 93) exploit the property of time reversal applied to complex or heterogeneous media to compensate for any unwanted distortion of the waves. It will be noted that the phase differences that one wishes to create passively are not compensated.

[0094] The second function of the device 1 is to concentrate the energies within the waves outside of transient effects. The obstacle 91 and / or the counter-obstacle 93 is (are) also configured to perform this second function. Indeed, the obstacle 91 and / or the counter-obstacle 93 is (are) configured to concentrate the energies by amplifying the rarefaction and compression of the wave fronts. Rarefaction is defined by a maximum negative pressure deviation from the average pressure, while compression is defined by a maximum positive pressure deviation from the average pressure. This increases the intermediate space where a pressure close to the average pressure prevails. The transformation of the energy distribution of a sinusoidal wave into another distribution is quantified by the distortion rate and the duty cycle parameter. It will be noted that a zero distortion rate characterizes a perfect sinusoid and that the duty cycle parameter translates a concentration in "squares". At a given energy, a small duty cycle indicates a concentration on a narrower basis for a larger amplitude.If we take a time snapshot, the cumulative effect of distortion and duty cycle appears as a "spatial" separation between the positive and negative maximum pressure regions. This simple analysis illustrates the ability to produce patterns according to an optimized definition by numerical calculation of the positions and properties of the elements of the device 1. .

[0095] Thus, the fluctuation means make it possible to transform the medium of interest into a medium behaving like a waveguide concentrating the energy of the waves so that they propagate further in the medium of interest, allowing an in-depth diagnosis.

[0096] The obstacle 91 and the counter-obstacle 93 can introduce non-linear effects on the wavefronts. The non-linear effect of the obstacle 91 is schematized by patterns ml which are different from the reference patterns mO. This effect is due, for example, to the properties provided by the metamaterials and / or metasurfaces and / or metafluids or others. Furthermore, the effect of the counter-obstacle 93 is schematized by patterns m2 different from the mO and ml.

[0097] The statistical summation of the multiple paths in the recombination zone 13 produces a concentration of the energy in the main re-emission lobe and a minimization of the secondary lobes. This effect is well known in the state of the art described for example, in the paper by Fink entitled Time-reversal acoustics in complex environments, 2006, Geophysics 71(4).

[0098] The manipulation device 1 thus plays the role of a relay arranged in the propagation medium of interest making it possible to spread out in a compact manner (by means of an obstacle 91) and to recombine with themselves (by means of the obstacle and / or a counter-obstacle 93) the injected energies by implementing very compact arrangements.

[0099] To gain in compactness, the manipulation device 1 produces a near field using at least one of these elements (obstacle 91 and / or counter-obstacle 93) which may be objects (e.g. inclusions) already present in the medium of interest 3 whose presence can be determined by any imaging or other means.

[0100] Figs. 5A-5E schematically represent different application examples and advantages of the devices for manipulating waves in a medium of interest, according to the embodiments of Figs. 2A to 4.

[0101] [Fig.5A] schematically represents the control of the direction of propagation of waves in the medium of interest.

[0102] Indeed, the injection site may not be well located, the injected beam may be too wide or the injection direction may be poorly oriented.

[0103] For example, in order to bypass an inaccessible zone 21, the obstacle 91 can be arranged so as to modify the apparent position of the primary source 7 which is offset relative to the desired direction d2 of propagation of the waves in the medium of interest 3. Thus, the waves can be injected into the propagation medium of interest 3 by controlling their direction of propagation and / or the position of the source 7.

[0104] An advantage is to be able to propagate the waves in the medium of interest 3 far from the walls or interfaces, for example liquid / solid interface, so as to minimize the contributions of surface waves during the analysis of these waves.

[0105] [Fig.5B] schematically represents the effect of concentration of wave energy by the obstacle.

[0106] It will be noted that various propagation modes can exist in the waves emitted by the source 7. Advantageously, the fluctuation means and in particular, the obstacle 91, produce a focal locus capable of fluctuating in time and space. The fluctuation of the focal locus occurs at the level of the recombination zone 13. The end of the focal locus can resemble a truncated conic.

[0107] The obstacle 91 makes it possible to avoid combinations with undesired propagation modes such as surface modes, to favor volume propagation modes, and to confine the propagation and therefore limit the dispersion in a restricted zone. Thus, the obstacle 91 makes it possible to transform the propagation medium of interest 3 into a medium behaving like a waveguide without having the physical characteristics thereof.

[0108] Furthermore, the fluctuation means can move and / or manipulate the waves in the propagation medium of interest without producing interference and / or standing waves. Indeed, the obstacle 91 eliminates the construction of interference by sufficiently disorganizing the wavefronts. This approach is counterintuitive because the focusing and coherence properties of the waves propagating in the medium of interest are lost. However, as indicated previously, the waveguide effect induced by the obstacle 91 makes it possible to compensate for the lost properties.

[0109] [Fig.5C] schematically represents the injection of waves into a medium of interest which is not favorable to this injection.

[0110] Indeed, the waves emitted by the source 7 may be poorly adapted to the propagation medium of interest which may, for example, be poorly compressible, non-deformable and confined. Advantageously, the obstacle 91 may be configured to have compressibility properties such that the waves emitted by the source 7 produce intermediate vibrations VI which can propagate in the medium of interest 3.

[0111] Figs. 5D and 5E schematically represent the spatial extension effect of a near field.

[0112] The introduction of an obstacle 91 in the medium of interest makes it possible to benefit from functions that cannot be obtained in the far field of a source (primary or secondary). Indeed, the obstacle 91 makes it possible to extend the spatial extension of a near field, the extent of which can be adjusted by optimizing the vibration parameters.

[0113] [Fig.5D] represents the example of the propagation and backpropagation of a wave by an obstacle.

[0114] According to this example, the obstacle 91 produces vibrations V1 while not masking or disturbing the back-propagation (property of the near field) in the medium of interest in which the propagations monitored by the obstacle and the counter obstacle are combined.

[0115] [Fig.5E] schematically represents a chopping effect of the waves in the medium of interest 3. According to this example, the obstacle 91 produces intermediate vibrations VI and V2 making it possible to subdivide the propagation of the waves by generating “packets” of waves without producing interference. Thus, the injected energy propagates in the medium of interest in a chopped manner into small packets.

[0116] [Fig.6] schematically represents a housing comprising the handling device, according to one embodiment of the invention.

[0117] According to this embodiment, a housing 25 is used to integrate the manipulation device 1 according to the preceding figures.

[0118] The housing 25 is a capsule made of a material compatible with the medium of interest and which allows the waves injected by the source 7 to pass through. The housing 25 has good elasto-dynamic coupling making it possible to transfer these waves to the medium of interest, with improved transmission efficiency. Advantageously, the recombination zone 13 of the waves modified and returned by the fluctuation means (obstacle 91 and / or counter-obstacle 93) is located in the housing 25.

[0119] For example, for a liquid medium of interest 3, the housing 25 can be formed of a soft fluid or solid medium or very viscous fluid (fat) confined by a membrane that the acoustic and elastic waves pass through without loss. For a solid medium of interest 3, the housing 25 can be formed of granular materials and in particular so-called “unconsolidated” variants, a good example of which is wet sand.

[0120] It will be noted that the dimensioning and implementation of the elements of the present invention can be carried out using methods known in the state of the art. The obstacles and counter-obstacles can be produced using additive manufacturing methods (3D printer, etc.) and numerous technologies developed on plastic, on silicon, on Graphene, DLC (Diamond Like Carbon), so-called “2-D” materials (conductive monolayers eg MoS2, TiO2, etc. or dielectrics).

[0121] For example, the dimensioning of the obstacles set into vibration by the injected waves can be carried out by numerical simulations (finite elements or others).

[0122] The introduction of metamaterials and metasurfaces into obstacles and / or counter-obstacles can be achieved by combining several techniques such as 3D printing and / or collective manufacturing and / or transfer of very thin, light and very resistant layers, for example in DLC or graphene.

[0123] Furthermore, the metasurfaces can be stretched over one or more cavities made up of or containing acoustic or elastic metamaterials in order to produce deformations normal to the surfaces or bending waves (in the surfaces). Preferably, the vibrations are chosen in a frequency range independent of the useful frequency band of the injected waves. Preferably, these vibrations are lower than the frequency band of interest.

[0124] The medium of interest, within which the obstacles according to the invention are introduced, may be a fluid medium (for example, the ocean, the human body, etc.), a solid monobloc medium (for example, beams), or an assembled solid medium (for example, assemblies of parts made of wood, metal, concrete). The obstacles may be placed before the assembly of several parts, in recesses provided for this purpose. The placement may also be carried out during the additive manufacturing of the part for polymers, metals, ceramics and composites. For concretes or parts manufactured by injection, the obstacles may be incorporated during casting / molding / injection. For metal and composite components, the elements of the handling device may be integrated during the manufacturing of a coating, for example, a protective layer on top of the element.For medical applications, obstacles can be integrated in the form of implants (for example under the skin) or for impact absorption within an external element (gloves, shoe heels, etc.).

[0125] The present invention has applications in several industrial fields. A first example is acoustic manipulation for structural health monitoring (SHM) or for non-destructive testing (NDT). SHM can be used to monitor concrete or the structure of reactors using, for example, sensors integrated into the concrete (highly attenuating medium), in particular by increasing the propagation distances at identical injected energy without amplifying it but by concentrating it in a narrower beam.

[0126] According to another example, the device according to the invention can be integrated into metal components comprising complex parts designed at least partially by additive manufacturing. In complex metal parts, the device according to the invention makes it possible to control areas (locally of low thickness, intersection of cylinders in particular with acute angles, elbows, etc.) which are inaccessible by sensors positioned outside or accessible in a degraded manner after several rebounds.

[0127] According to another example, the device according to the invention can be used for masking unwanted echoes. Indeed, by directing the injected waves towards an identified area, echoes will be avoided, which could deteriorate the non-destructive testing (NDT) of the area and come from other entities (for example attachments of parts giving a contribution during a non-linear ultrasound NDT).

[0128] Finally, it should be noted that the present invention is counter-intuitive because there is always a simpler arrangement but which does not preserve or create a preliminary shaping of the information capable of producing patterns from which FIA and machine learning methods in general can take advantage. In particular, and obviously, it is always simpler to direct the waves directly towards the propagation medium of interest rather than losing energy by shooting in another direction. The loss is compensated by the invention which makes it possible to concentrate the injected energies into a finer beam without introducing distortion.

Claims

Claims

1. Device for manipulating acoustic waves in a medium of interest intended to receive injected waves having initial wave fronts, said device (1) comprising fluctuation means (9) having the function of introducing into the medium of interest (3) a fluctuation which modifies its initial reference state by modifying the initial coherence of the phases, the fluctuation means transforming the medium of interest into a medium behaving like a waveguide concentrating the energy of the waves so that they propagate further in the medium of interest,the fluctuation being adapted to disperse the initial wavefronts in a confined dispersion zone while redirecting them towards a recombination zone (13) in which the confined wavefronts recombine to produce superimposed wavefronts whose profiles comprise additional patterns increasing the spatial extent of near-field zones without producing interference, allowing them to propagate in depth in said medium of interest and thus being able to be used for an in-depth diagnosis of said medium of interest.,

2. Device according to claim 1, characterized in that the fluctuation means (9) comprise at least one obstacle (91) arranged in the medium of interest (3) and in the path of said injected waves, said at least one obstacle (91) being configured to diffract the initial wave fronts by directing them along a plurality of converging or quasi-converging propagation paths ending in said recombination zone (13).

3. Device according to claim 1 or 2, characterized in that the fluctuation means (9) comprise first and second obstacles, called obstacle (91) and counter-obstacle (93), arranged in the medium of interest (3), the obstacle (91) being configured to transmit a part of the initial wavefronts towards the counter-obstacle (93) and to redirect the other part along a plurality of propagation paths towards said recombination zone (13), the counter-obstacle (93) being configured to redirect in almost the same predetermined direction the wavefronts received from the first obstacle as well as possibly initial wavefronts towards said recombination zone (13), the predetermined direction being a direction defined by the arrangement and the geometry of the counter-obstacle.

4. Device according to claim 2 or 3, characterized in that the obstacle (91) comprises at least one cavity (911) comprising a medium of a predetermined nature which may be the same as that of the medium of interest.

5. Device according to any one of claims 2 to 4, characterized in that the obstacle (91) comprises at least one wall configured to vibrate and / or to vibrate the volume of the obstacle upon receipt of the injected waves.

6. Device according to any one of claims 2 to 5, characterized in that the obstacle (91) has dimensions smaller than the wavelength of the injected waves.

7. Device according to claim 3, characterized in that the counter-obstacle (93) is configured to vibrate upon reception of the waves.

8. Device according to claim 7, characterized in that the obstacle (91) and the counter obstacle (93) are arranged in the medium of interest (3) being separated from each other by a distance smaller than the longest wavelength of the injected waves.

9. Device according to claim 7 or 8, characterized in that the counter-obstacle (93) is configured to define a preferred direction in the medium of interest.

10. Device according to any one of claims 3 and 7 to 9, characterized in that the obstacle (91) and / or the counter-obstacle (93) comprise metamaterials having elastodynamic properties.

11. Device according to claim 1, characterized in that the fluctuation means (9) comprise thermal means configured to introduce into the medium of interest a temperature change dispersing the initial wave fronts of the injected waves while redirecting them towards the recombination zone.

12. Device according to claim 1, characterized in that the fluctuation means (9) comprise external mechanical means configured to introduce into the medium of interest an elastic fluctuation dispersing the initial wave fronts of the injected waves while redirecting them towards the recombination zone.

13. Housing comprising the manipulation device, according to any one of the preceding claims, characterized in that the housing (25) is made of a material compatible with the medium of interest and which allows the waves injected by the source to pass.

14. A method of manipulating acoustic waves in a medium of interest intended to receive injected waves having initial wave fronts, said method comprising the following steps: -introducing into the medium of interest (3) a fluctuation which modifies its initial reference state by modifying the initial coherence of the phases, the fluctuation transforming the medium of interest into a medium behaving like a waveguide concentrating the energy of the waves so that they propagate further in the medium of interest, the fluctuation being adapted to disperse the initial wavefronts in a confined dispersion zone, and -redirecting the dispersed wavefronts to a recombination zone (13) in which the confined wavefronts recombine to produce superimposed wavefronts whose profiles include additional patterns increasing the spatial extent of near-field zones without producing interference, allowing them to propagate deep into said medium of interest and thus being able to be used for deep diagnosis of said medium of interest.

Images