Device and method for cleaning a support by converting an ultrasonic body wave into an ultrasonic surface wave

Abstract

The invention relates to an electroacoustic device (1) comprising: - a support (2); - at least one transducer (5) comprising a piezoelectric substrate (6) and electrodes (7) in electrical contact with the piezoelectric substrate, the transducer being attached to a first face (3) of the support; - an electrical generator (11) connected to the electrodes in order to apply an electrical signal thereto and to generate an ultrasonic body wave (Sv) that propagates through the support; - at least one conversion structure (9) arranged at the surface of the support, on the side of a second face (4) of the support opposite the first face, the conversion structure being opposite the ultrasonic wave transducer and being configured to convert the ultrasonic body wave into an ultrasonic surface wave (Ss) that propagates over the second face of the support in order to move and / or bring about a phase change in impurities (P) resting on the second face.

Description

Device and method for cleaning a surface by converting an ultrasonic volume wave into an ultrasonic surface wave

[0001] The present invention relates to a device for cleaning a support by generating an ultrasonic surface wave propagating through the support to the impurities resting on said support in order to remove them.

[0002] The present invention also relates to a method using this device to clean the support and a use of this device to detect the presence of impurities on said support.

[0003] In various fields, it is necessary to mitigate the effects of accumulating impurities on a surface, such as the buildup of droplets, liquid films, ice, frost, snow, mud, or solid particles like dust, sand, or soil. Cleaning a surface to remove these impurities is often preferable, if not essential. This is the case, for example, with photovoltaic panels, optical devices, and the windows of land and aircraft vehicles.

[0004] In particular, the accumulation of impurities on the surface of photovoltaic panels can lead to efficiency losses of up to 30%, or even 40%. The accumulation of impurities on the surface of an optical device, such as a sensor, lidar, or camera, renders that optical device inoperative. Similarly, the accumulation of impurities on the surface of a vehicle window, such as a windshield or cockpit window, significantly reduces the driver's visibility.

[0005] To remove liquid impurities accumulated on a surface, it is well known to apply mechanical force to these impurities, for example, using a windshield wiper. However, a windshield wiper limits visibility through the surface. It also spreads the grease particles deposited on the surface. In addition, it is necessary to replace the wiper blades regularly.

[0006] Furthermore, for certain surfaces, for example the surfaces of optical sensors, such as a lidar, or probes, such as a Pitot probe, mechanical force cannot be applied to clean said surfaces, due to a lack of available space to have suitable mechanical means which could also damage the surface.

[0007] In the case of photovoltaic panels, it is common practice to use robots equipped with brushes that move along the outer surface of the protective glass. However, these robots are expensive, require regular maintenance, and have a short lifespan, far shorter than the warranty period of the photovoltaic panels themselves. Furthermore, using brushes to clean photovoltaic panels can, in the long term, damage the protective glass, and in particular the anti-reflective coating.

[0008] French patent applications FR3100999A1, FR3100998A1, FR3101000A1, and FR3121370A1 each describe a device using transducers to clean a surface with an ultrasonic surface wave propagating through that surface. However, these devices are not very robust and are exposed to the elements, making them unsuitable for many applications. Furthermore, these devices are difficult to integrate into systems that include a surface to be cleaned. In addition, these devices are not suitable for cleaning all types of dirt on large surfaces.

[0009] French patent applications FR3117384A1 and FR3117385A1 each describe a device using transducers to clean a surface with an ultrasonic surface wave propagating through that surface. These devices have the advantage of not being exposed to external environments. However, they are not very robust and have a limited lifespan. Furthermore, these devices are only suitable for small surfaces and cannot clean large areas. In addition, integrating these devices into a system with a surface to be cleaned is difficult because they require a significant portion of the surface area.

[0010] There is therefore a need for a robust cleaning device that is easily integrated and capable of removing all kinds of impurities from both large and small surfaces.

[0011] The purpose of the invention is to meet, at least in part, this need(s).

[0012] To this end, the invention relates to an electroacoustic device comprising: - a support, - at least one transducer comprising a piezoelectric substrate and electrodes in electrical contact on either side of the piezoelectric substrate, the transducer being fixed to a first face of the support and acoustically coupled to the support, - an electrical generator connected to the electrodes of the transducer to apply an electrical signal to the electrodes of the transducer so as to generate an ultrasonic volume wave propagating in the support, - at least one conversion structure arranged on the surface of the support, on the side of a second face of the support opposite to the first face,The conversion structure is positioned opposite the transducer and configured to convert the ultrasonic volume wave into an ultrasonic surface wave propagating along the second face of the support in order to displace and / or induce a phase change in the liquid and / or solid impurities resting on said second face.

[0013] The electroacoustic device according to the present invention has the advantage of allowing the transducer to be positioned on the side of the support that is not exposed to the external environment. The transducer is thus protected by the support, and its degradation is therefore greatly limited. The transducer can be placed in a protected environment that does not cause wear, for example, an environment free of elements that could strike the transducer, such as insects, dust particles, mud, sand, or liquids. The same applies to the electrical generator and its connections to the transducer.

[0014] Unlike patent applications FR3117384A1 and FR3117385A1, the transducer of the electroacoustic device according to the present invention does not require interdigitated electrodes but is simply a transducer comprising a piezoelectric substrate sandwiched between two electrodes. Such a transducer has the advantage of being more robust, simpler to manufacture, less expensive, and easier to integrate into a system.

[0015] Furthermore, generating an ultrasonic volume wave that is subsequently converted into an ultrasonic surface wave makes it possible to obtain an ultrasonic surface wave suitable for cleaning large areas. In particular, it is possible to obtain an ultrasonic surface wave with a power greater than that of the ultrasonic surface waves achievable with the devices described in patent applications FR3117384A1 and FR3117385A1.

[0016] Thus, the advantages of the present invention are numerous. The electroacoustic device according to the present invention has a long lifespan, is easily integrated, requires no maintenance, and can clean all kinds of impurities on a wide variety of surface sizes. The electroacoustic device is suitable for cleaning both piezoelectric and non-piezoelectric media.

[0017] Liquid and / or solid impurities may include, but are not limited to, droplets, liquid films, ice, frost, snow, mud, or solid particles such as dust, grains of sand, or soil.

[0018] The device can be configured so that the ultrasonic surface wave has a displacement amplitude, in a direction normal to the support, greater than where K denotes a constant of the order of , etω sdenotes the pulsation of the ultrasonic surface wave, , with The frequency of the ultrasonic surface wave. This amplitude can be measured, for example, using a laser Doppler vibrometer. The amplitude can be adjusted according to the type of impurity to be cleaned, its quantity, and the surface of the substrate, for example, its material, roughness, and / or electrical charge.

[0019] Preferably, the conversion structure is configured to convert at least 30% of the ultrasonic volume wave power into an ultrasonic surface wave.

[0020] Preferably, the frequency of the ultrasonic volume wave and / or frequency of the ultrasonic surface wave is / are between 1 MHz and 1 GHz, preferably between 5 and 100 MHz, preferably between 8 and 45 MHz.

[0021] Preferably, the device is configured so that the frequency of the ultrasonic volume wave is equal to the frequency of the ultrasonic surface wave.

[0022] The wavelength λ v s the volumetric ultrasonic wave in the medium is equal to , if the ultrasonic volume wave is longitudinal, or equal to , if the ultrasonic volume wave is transverse, with denoting the speed of longitudinal sound waves in the medium, being the speed of transverse sound waves in the medium and being the frequency of the ultrasonic volume wave.

[0023] The wavelength λ s the ultrasonic surface wave is equal to with denoting the speed of surface sound waves, also known as Rayleigh waves, in the medium and being the frequency of the ultrasonic surface wave.

[0024] Preferably, the conversion structure comprises a network of conversion patterns on the surface of the support, the conversion patterns each having a general elongated shape and being spaced from each other transversely to their longitudinal axis in a substantially periodic manner.

[0025] By "in a substantially periodic manner," it is meant that there exists a length p, called the period p, of the conversion patterns, such that, for each conversion pattern, the distance between the longitudinal median plane of said conversion pattern and the longitudinal median plane of each adjacent conversion pattern is between 0.9 and 1.10 p, or even between 0.95 and 1.05 p. Preferably, for each conversion pattern, the distance between the longitudinal median plane of said conversion pattern and the longitudinal median plane of each adjacent conversion pattern is equal to the period p.

[0026] The period p of the conversion patterns can be between 0.8nλs and 1.2nλ s , or even between 0.95nλ s and 1.05nλ s , being a positive integer and λ s being the wavelength of the ultrasonic surface wave, preferably n being equal to 1, preferably the period p of the conversion patterns being substantially equal to a multiple of the wavelength λ s of the ultrasonic surface wave, preferably the period of the conversion patterns being substantially equal to the wavelength λ s of the ultrasonic surface wave. Advantageously, this allows increasing the conversion rate of the ultrasonic volume wave into the ultrasonic surface wave through resonance.

[0027] Preferably, conversion patterns are rectilinear or curvilinear, for example in the form of a circular arc.

[0028] Preferably, the gap between two adjacent conversion patterns is constant over their entire length.

[0029] Preferably, the conversion structure includes between 2 and 1000 conversion patterns, or even between 4 and 200 patterns, or even between 10 and 50.

[0030] According to one variant, the conversion patterns may include grooves made in the second face of the support.

[0031] Preferably, the ratio of groove depth to wavelength λ s The ultrasonic surface wave is between 0.001 and 0.3, or even between 0.05 and 0.1. This increases the efficiency of the electroacoustic device by limiting the trapping of the ultrasonic surface wave in the conversion structure while exhibiting a high conversion rate of the ultrasonic volume wave into the ultrasonic surface wave.

[0032] Preferably, the grooves are filled with a filling material having an acoustic impedance such that the ratio of the absolute difference between the acoustic impedance of the filling material and the acoustic impedance of the support to the acoustic impedance of the support is greater than 0.05, or even greater than 0.10, or even greater than 0.20. Preferably, the filling material is a polymeric resin.

[0033] The grooves can have a profile, observed according to a cross-section of the support, having a rectangular, sinusoidal or triangular shape.

[0034] According to a second variant, the conversion patterns may include closed tubular cavities formed in the support.

[0035] Preferably, the tubular cavities are at a distance less than λ s of the second face of the support, λ sbeing the wavelength of the ultrasonic surface wave. This increases the efficiency of the electroacoustic device by increasing the conversion rate of the ultrasonic volume wave into the ultrasonic surface wave and by promoting resonance phenomena.

[0036] Preferably, the ratio of the diameter of the tubular cavities to the wavelength λ s The ultrasonic surface wave is between 0.001 and 0.3, or even between 0.05 and 0.1. This increases the efficiency of the electroacoustic device by limiting the attenuation of the ultrasonic surface wave while exhibiting a high conversion rate of the ultrasonic volume wave into the ultrasonic surface wave.

[0037] Tubular cavities can be filled with a filling material having an acoustic impedance such that the ratio of the absolute difference between the acoustic impedance of the filling material and the acoustic impedance of the support to the acoustic impedance of the support is greater than 0.05, or even greater than 0.10, or even greater than 0.20. Preferably, the filling material is a polymeric resin.

[0038] Tubular cavities may have a cross-section, observed from a transverse section of the support, having a polygonal shape, notably rectangular or rhomboid, ellipsoidal or circular.

[0039] According to a third variant, the conversion patterns may include ribs protruding from the second face of the substrate. The ribs may be formed from the same material as the substrate, for example, be monolithic with the substrate, or may be formed by a deposition of material onto the substrate.

[0040] The ribs can be transparent in the visible range, for example in glass, polycarbonate, quartz or sapphire, and / or transparent in the infrared range, for example in germanium, silica or metal.

[0041] Preferably, the ratio of the rib thickness to the wavelength λ s The ultrasonic surface wave is between 0.001 and 0.3, or even between 0.05 and 0.1. This increases the efficiency of the electroacoustic device by limiting the attenuation of the ultrasonic surface wave while exhibiting a high conversion rate of the ultrasonic volume wave into the ultrasonic surface wave.

[0042] The thickness of the ribs corresponds to the distance, measured along an axis orthogonal to the second face, between the second face and the point of the rib furthest from the second face.

[0043] The ribs can have a profile, observed according to a cross-section of the support, having a rectangular, sinusoidal or triangular shape.

[0044] Preferably, the thickness of the piezoelectric substrate is between 0.45mλ vp and 0.55mλ vp , being a positive integer and λ vp This is the ratio of the speed of sound in the piezoelectric substrate to the frequency of the ultrasonic body wave in the piezoelectric substrate. The speed of sound in the piezoelectric substrate is the propagation speed of longitudinal or transverse sound waves, depending on the thickness of the piezoelectric substrate. This increases the efficiency of the electroacoustic device by promoting the resonance of the ultrasonic body wave.

[0045] The transducer can be glued to the substrate. Preferably, the ratio of the thickness of the glue layer between the transducer and the substrate to the wavelength λ v s The ultrasonic volume wave is less than 0.1, or even less than 0.01. Advantageously, a thin layer of adhesive increases the transmission of the ultrasonic volume wave into the substrate.

[0046] Preferably, the glue is elastic and / or has a melting point above 100°.

[0047] Alternatively, the transducer can be deposited on the support by a thin film deposition method, preferably by chemical vapor deposition, more preferably by plasma-assisted chemical vapor deposition.

[0048] Preferably, the piezoelectric substrate is a lead zirconate titanate (PZT), for example PZT-5H or PZT-5A, a niobate, for example lithium niobate, zinc oxide or aluminium nitride.

[0049] Preferably, the thickness of the support is between 0.45pλ v s and 0.55pλ v s ,breaking a positive integer and λ vs being the wavelength of the ultrasonic body wave propagating in the medium. This increases the efficiency of the electroacoustic device by promoting the resonance phenomena of the ultrasonic body wave.

[0050] Preferably, the support is transparent in the visible range, for example glass, polycarbonate, quartz or sapphire, and / or transparent in the infrared range, for example germanium, silica or metal.

[0051] The support can vary greatly in size. In particular, the support can have a length and / or width ranging from 1 mm to 100 m.

[0052] Preferably, the device includes a reflection structure extending at least partially, preferably entirely, along one side of the conversion structure, the reflection structure being configured to reflect the ultrasonic surface wave.

[0053] Preferably, the reflective structure includes at least one groove cut into the second face of the support.

[0054] Preferably, the ratio of the groove depth to the wavelength λ s the ultrasonic surface wave is between 0.3 and 3.

[0055] Preferably, the groove width is greater than 500 nm.

[0056] Preferably, the groove is filled with a filling material having an acoustic impedance such that the ratio of the absolute difference between the acoustic impedance of the filling material and the acoustic impedance of the support to the acoustic impedance of the support is greater than 0.05, or even greater than 0.10, or even greater than 0.20. Preferably, the filling material is a polymeric resin.

[0057] Preferably, the device includes a temperature sensor configured to measure the temperature of the substrate and / or the transducer, and a control unit configured to control the frequency of the electrical signal applied by the power generator according to the measured temperature. Advantageously, this allows the frequency of the electrical signal to be adapted to the expansion phenomena of the substrate and / or the transducer and to the changes in the speed of sound induced by temperature variations. The frequency of the electrical signal can thus be chosen to promote the resonance phenomena of the ultrasonic body wave and / or the ultrasonic surface wave.

[0058] The support can be inclined relative to the horizontal. Thus, gravity also acts as an external force to move impurities so as to remove them from the second side of the support.

[0059] The device may include at least two transducers and at least two conversion structures, each opposite one of the corresponding transducers. One transducer is located near a first lateral edge of the support, and the other transducer is located near a second lateral edge of the support, in particular opposite the first lateral edge. Preferably, the support is inclined relative to the horizontal, and the first lateral edge is arranged higher than the second lateral edge.

[0060] The device may include at least one first transducer with a first conversion structure opposite the first transducer, and at least one second transducer with a second conversion structure opposite the second transducer, the first transducer being configured to emit a detection signal in the form of an ultrasonic volume wave propagating through the support to the first conversion structure which converts the detection signal into an ultrasonic surface wave propagating through the second face to the second conversion structure which converts the detection signal into an ultrasonic volume wave propagating through the support to the second transducer, the device including a detection unit for measuring the detection signal received by the second transducer and determining, from this measurement, the presence of liquid and / or solid impurities resting on the second face of the support.

[0061] The device may include a plurality of transducers and a plurality of conversion structures, each opposite one of the corresponding transducers, the transducers being arranged so as to form at least one row of transducers.

[0062] Preferably, the device includes a heat sink arranged on the side of the first face of the support and being in thermal contact with the transducer and / or with the support.

[0063] Preferably, the device includes an acoustically insulating layer covering the face of the transducer opposite the support, the acoustically insulating layer having a thickness greater than 100 nm, or even 500 nm.

[0064] Acoustically insulating means an acoustic impedance ratio of the insulating layer to the acoustic impedance of the piezoelectric substrate of less than 0.001 or even 0.0001.

[0065] The acoustically insulating layer can be a gas, a porous structure, or an aerogel.

[0066] Preferably, the support is chosen from the group formed by: - ​​a protective glass of a photovoltaic panel, - an automotive surface, for example chosen from a vehicle windscreen, a rearview mirror glass, a bodywork element - a helmet visor, - a building window, - a surface of an optical device, for example chosen from a camera, a camera lens, a lidar, a periscope, a lens of a spectacle or viewfinder, a sensor, in particular a probe, and a medical imaging device, for example an endoscope, - a protective element of such an optical device, - a surface of an aeronautical vehicle, for example an aircraft wing, a Pitot tube, a cockpit window, an aircraft canopy.

[0067] The present invention also relates to a photovoltaic panel comprising an electroacoustic device according to the present invention, the support forming the protective glass of the photovoltaic panel, the second face of the support being an external face of the photovoltaic panel.

[0068] Preferably, the photovoltaic panel includes a layer of resin arranged between the protective glass and the photovoltaic cells of the photovoltaic panel.

[0069] Preferably, the transducer(s) of the electroacoustic device are located more than 100 nm, or even more than 500 nm, away from the resin layer.

[0070] The invention also relates to a method, implementing the device according to the present invention or the photovoltaic panel according to the present invention, for cleaning the second side of the substrate, the method comprising the following successive steps: a) generation by the transducer of an ultrasonic body wave propagating through the substrate to the second side of the substrate, b) conversion by the conversion structure of the ultrasonic body wave into an ultrasonic surface wave propagating through the second side, c) displacement and / or phase change induced by the ultrasonic surface wave of the liquid and / or solid impurities resting on the second side

[0071] Preferably, the support is inclined relative to the horizontal. Even more preferably, the support comprises a first lateral edge and a second lateral edge, the first lateral edge being arranged higher than the second lateral edge, the device comprising at least two transducers and at least two conversion structures each opposite one of the corresponding transducers, one of the transducers being disposed near the first lateral edge of the support and being used to move and / or change the phase of the liquid impurities, another of the transducers being disposed near the second lateral edge of the support and being used to move and / or change the phase of the solid impurities.

[0072] The invention also relates to the use of the device according to the present invention for detecting liquid and / or solid impurities resting on the second face, the device comprising at least a first transducer with a first conversion structure opposite the first transducer, and at least a second transducer with a second conversion structure opposite the second transducer, the use comprising the following successive steps: a) generation by the first transducer of a detection signal in the form of an ultrasonic body wave propagating through the support to the second face of the support, b) conversion by the first conversion structure of the shape of the detection signal into an ultrasonic surface wave propagating through the second face, c) conversion by the second conversion structure of the shape of the detection signal into an ultrasonic body wave propagating through the support.d) reception of the detection signal by the second transducer, e) determination of the presence of liquid and / or solid impurities resting on the second face of the support and / or the presence of tactile contact on the second face of the support and / or the presence of a surface defect on the second face of the support.

[0073] When liquid and / or solid impurities are present on the second surface of the substrate, they disrupt the detection signal. The presence of these impurities can then be determined by analyzing the resulting disruptions to the detection signal.

[0074] Similarly, the presence of tactile contact on the second side of the substrate or a surface defect on the second side of the substrate disrupts the detection signal. It is therefore possible to determine this by analyzing the disturbances in the detection signal.

[0075] The surface defect can be an impact, a crack, or a fissure.

[0076] Preferably, the use subsequently includes the process according to the present invention, when liquid and / or solid impurities are detected.

[0077] If a touch contact or surface defect is detected, it is preferable not to carry out the cleaning process according to the present invention.

[0078] Other advantages and features will become apparent upon reading the detailed description, which is provided for illustrative purposes only and is not exhaustive, with reference to the following figures:

[0079] lare represents schematically, according to a cross-sectional view, an electroacoustic device according to the present invention, the conversion patterns of said device being grooves engraved in the support;

[0080] lare represents schematically, in cross-section, an electroacoustic device according to the present invention, the conversion motifs of the device being grooves engraved in the support and filled with a filling material;

[0081] lare represents schematically, according to a cross-sectional view, an electroacoustic device according to the present invention, the conversion motifs of said device being closed tubular cavities formed in the support;

[0082] lare represents schematically, according to a cross-sectional view, an electroacoustic device according to the present invention, the conversion motifs of said device being ribs protruding from the second face of the support;

[0083] lare represents schematically, according to a cross-sectional view, an electroacoustic device according to the present invention, comprising a reflection structure;

[0084] lare represents schematically, according to a cross-sectional view, a photovoltaic panel comprising an electroacoustic device according to the present invention;

[0085] Figures 7A and 7B are photographs illustrating the cleaning of a support covered with droplets by an electroacoustic device according to the present invention;

[0086] Figures 8A and 8B are photographs illustrating the cleaning of a support covered with a film of water resulting from a fog by an electroacoustic device according to the present invention;

[0087] Figures 9A and 9B are photographs illustrating the cleaning of a support covered with grains of sand by an electroacoustic device according to the present invention. Detailed description

[0088] For clarity, the different elements of the figures are represented to a free scale, the actual dimensions of the different parts not necessarily being respected.

[0089] An electroacoustic device 1 according to the present invention is illustrated. The device 1 comprises a support 2 having a first face 3 and a second face 4 opposite the first face 3. The support 2 is capable of propagating an ultrasonic body wave and an ultrasonic surface wave.

[0090] Device 1 also includes a transducer 5 fixed to the first face 3. The transducer 5 comprises a piezoelectric substrate 6 and electrodes 7 sandwiching the piezoelectric substrate 6 by being in electrical contact with it. One of the electrodes 7 is arranged between the first face 3 and the piezoelectric substrate 6. The other of the electrodes 7 is arranged on the piezoelectric substrate 6 on the side opposite the support 2.

[0091] In the embodiment illustrated in Figure 1, the device 1 includes an adhesive layer 8 for bonding the transducer 5 directly to the first face 3. The adhesive layer 8 is in contact on one side with the support 2 and on the other side with one of the electrodes 7. Alternatively, the transducer 5 can be fixed to the first face 3 by a thin-film deposition method, comprising a step of depositing one of the electrodes 7 onto the support 2, followed by a step of depositing the piezoelectric substrate 6 onto said electrode 7, and then a step of depositing the other electrode 7 onto the piezoelectric substrate 6. The deposition of the electrodes 7 and / or the piezoelectric substrate 6 can be carried out by plasma-assisted chemical vapor deposition.

[0092] The device 1 also includes a conversion structure 9 arranged on the second face 4 of the support 2 opposite the transducer 5. In the embodiment illustrated in Figure 1, the conversion structure 9 is etched into the support 2, for example by laser etching, in particular by femtosecond laser, or by chemical etching, in particular by HF vapor etching. In particular, the conversion structure 9 comprises a periodic array of grooves 10 formed in the second face 4 of the support 2, the grooves 10 forming conversion patterns of said periodic array.

[0093] The grooves 10 are parallel to each other and are periodically spaced from each other. The grooves 10 can be straight or curved.

[0094] An electrical generator 11 is connected to the electrodes 7 of the transducer 5. The electrical generator 11 is configured to apply an electrical signal to the electrodes 7 so that the transducer 5 generates an ultrasonic volume wave S v which propagates in the support 2. In particular, the alternating electrical voltage applied to the electrodes 7 induces a mechanical response in the piezoelectric substrate 6, which results in the generation of the ultrasonic volume wave S v .

[0095] The ultrasonic volume wave S v propagates through support 2 until it reaches conversion structure 9. Conversion structure 9 then converts the ultrasonic volume wave S v in an ultrasonic surface wave S s propagating in the second face 4 of the support 2. The ultrasonic surface wave S s is notably a Rayleigh wave.

[0096] When liquid and / or solid impurities P are placed on the second face 4 of the support 2, the ultrasonic surface wave S s is transmitted to said impurities P and induces a displacement and / or a phase change of said impurities P.

[0097] The power of the ultrasonic surface wave S s can be adapted by modifying the electrical signal applied by the electrical generator 11 to the electrodes 7, in particular by modifying the amplitude and / or frequency of the electrical signal. It is thus possible to adapt the power of the ultrasonic surface wave S s depending on the impurities P to be cleaned.

[0098] The displacement of impurities P can occur along one or more axes contained in the second face 4. In particular, the ultrasonic surface wave S s can induce the displacement of impurities P along the direction of propagation of said ultrasonic surface wave S sin the absence of an external force. The direction of movement of the impurities P may differ depending on their nature. In particular, solid impurities P may move towards the conversion structure 9, and liquid impurities P may move away from the conversion structure 9. In a variant where at least one external force is applied to the impurities P, said impurities P may move in a direction equal to the sum of the force vectors acting on said impurities P, including the acoustic force induced by the ultrasonic surface wave S s By "external force" is meant any force other than the acoustic force induced by the ultrasonic surface wave S s The weight of each impurity P or an aerodynamic force induced by the flow of a fluid over each impurity P are examples of external forces.

[0099] The displacement of a liquid impurity P can notably result from nonlinear acoustic effects of acoustic streaming and / or radiation pressure induced by the ultrasonic surface wave S s The displacement of a solid impurity P can notably result from nonlinear Hertz contact acoustic effects induced by the ultrasonic surface wave S s .

[0100] The ultrasonic surface wave S s can induce a phase change of the impurities P. In particular, part of the energy of the ultrasonic surface wave S s is transferred to the impurities P, causing them to heat up. The energy transferred by the ultrasonic surface wave S s may be such that it heats the impurities P beyond their melting or boiling point, thereby inducing the melting of solid impurities P and / or the vaporization of liquid impurities P.

[0101] The electroacoustic device 1 also includes a thermal sensor 12 connected to the support 2 to measure its temperature. The thermal sensor 12 is connected to a control unit 13 which controls the properties of the electrical signal applied by the electrical generator 11 to the electrodes 7. The control unit 13 can, in particular, adapt the frequency of the electrical signal according to the temperature measured by the thermal sensor 12 so as to take into account the expansion phenomena that affect the overall resonance of the electroacoustic device 1.

[0102] Furthermore, the electroacoustic device 1 includes a heat sink 14 arranged in thermal contact with the transducer 5. The heat sink 14 helps to limit the heating of the transducer 5.

[0103] Another embodiment of an electroacoustic device 1 according to the present invention has been illustrated. The electroacoustic device 1 of this differs from that of this in that the grooves 10 are filled with a filling material 15 having an acoustic impedance such that the ratio of the absolute difference between the acoustic impedance of the filling material 15 and the acoustic impedance of the support 2 to the acoustic impedance of the support 2 is at least greater than 0.05. Advantageously, filling the grooves 10 with the filling material 15 prevents impurities from becoming lodged in the grooves 10, thus improving their removal from the second face 4. Furthermore, the absorption coefficient of the filling material 15 is such that it absorbs little or no ultrasonic surface wave S s .

[0104] Preferably, the grooves 10 are completely filled with the filling material 15. Advantageously, the conversion structure 9 thus presents a smooth surface with the support 2.

[0105] Another embodiment of an electroacoustic device 1 according to the present invention has been illustrated. The electroacoustic device 1 of this one differs from that of this one in that the conversion patterns of the conversion structure 9 are no longer grooves 10 but closed tubular cavities 16 formed in the support 2. The tubular cavities 16 can be filled with the filling material 15. The tubular cavities 16 are parallel to each other and are periodically spaced from one another. The tubular cavities 16 can be straight or curved.

[0106] Another embodiment of an electroacoustic device 1 according to the present invention has been illustrated. The electroacoustic device 1 of this one differs from that of the other in that the conversion patterns of the conversion structure 9 are no longer grooves 10 but ribs 17 projecting from the second face 4 of the support 2. The ribs 17 are parallel to each other and are periodically spaced from one another. The ribs 17 can be straight or curved.

[0107] Another embodiment of an electroacoustic device 1 according to the present invention has been illustrated. The electroacoustic device 1 of this differs from that of this in that it also comprises a reflection structure 18 extending along the conversion structure 9. In particular, the reflection structure 18 comprises a groove 19 formed in the second face 4 of the support 2.

[0108] Groove 19 can extend parallel to the conversion patterns of conversion structure 9. Groove 19 has a width greater than the acoustic displacement of the ultrasonic surface wave S s .

[0109] Just like the grooves 10, the groove 19 can be filled with the filler material 15 to prevent impurities from getting lodged in the groove 19.

[0110] The reflection structure 18 prevents the ultrasonic surface wave S s propagates in two directions. In particular, the reflection structure 18 acts as a mirror and reflects the ultrasonic surface wave S s so that it propagates in the second face 4 of the support 2 in only one direction. Thus, the reflection structure 18 concentrates all the power of the ultrasonic surface wave S s in one direction only.

[0111] Alternatively, it is conceivable that the conversion structure 9 could be configured to convert the ultrasonic volume wave S v in an ultrasonic surface wave S s unidirectional.

[0112] A photovoltaic panel 20 comprising an electroacoustic device 1 according to the present invention is illustrated. The support 2 of the electroacoustic device 1 forms the protective glass of the photovoltaic panel 20.

[0113] The electroacoustic device 1 comprises a first row 21 of transducers 5 arranged on the first face 3 near a first lateral edge 22 of the support 2, and a second row 23 of transducers 5 arranged on the first face 3 near a second lateral edge 24 of the support 2, opposite the first lateral edge 22. The electroacoustic device 1 also comprises conversion structures 9 arranged on the second face 4 of the support opposite each of the transducers 5. The electroacoustic device 1 allows the protective glass 2 to be cleaned as explained previously.

[0114] The photovoltaic panel 20 also includes photovoltaic cells 25 and a resin layer 26 arranged between the protective glass 2 and the photovoltaic cells 25. The photovoltaic panel 20 has a gap 27 between the transducers 5 of the electroacoustic device 1 and the resin layer 26. This gap 27 prevents the transducers 5 from transferring heat to the resin layer 26. This gap 27 also forms an acoustically insulating layer covering the transducers 5, thus preventing ultrasonic waves from being transmitted to the resin layer 26.

[0115] The electroacoustic device 1, the resin layer 26 and the photovoltaic cells 25 are held together by a support structure 28. The support structure 28 also ensures that the transducers 5, the resin layer 26 and the photovoltaic cells 25 are not exposed to the external environment.

[0116] The inventors carried out tests on their electroacoustic device 1. To this end, they fabricated an electroacoustic device 1 according to the present invention. The conversion structure comprised grooves 10 with a rectangular profile, a period equal to the wavelength λ s of the ultrasonic surface wave S s , here equal to 158 µm, a width equal to half the wavelength λ s of the ultrasonic surface wave S s , i.e., 79 µm, and a depth of 22 µm. Two transducers 5 were bonded to the first face 3 of the support 2 opposite the grooves 10. The piezoelectric substrates 6 of the transducers 5 were made of PZT-5H. The frequency of the ultrasonic surface wave S s was between 9 MHz and 11 MHz.

[0117] The inventors implemented the electroacoustic device 1 in processes according to the present invention, to clean various kinds of impurities resting on the second face 4 of the support 2.

[0118] Figures 7A and 7B illustrate the cleaning performed by the process according to the present invention for droplets P of salt water. As can be seen in Figure 7A, the movement of the salt water droplets P away from the conversion structures 9 and ultimately being evacuated from the support 2 can be observed. Furthermore, the cleaning of the droplets P left no trace of salt on the second face 4 of the support 2.

[0119] Figures 8A and 8B illustrate the cleaning performed by the process according to the present invention for a water film P resulting from a mist. As can be seen in the figure, the water is evacuated from the film P in the portion 29 opposite the conversion structures 9, that is, the portion 29 of the second face 4 in which the ultrasonic surface wave S propagates. s .

[0120] Figures 9A and 9B illustrate the cleaning carried out by the process according to the present invention for sand grains P. As can be seen on the figure, we observe the movement of the sand grains P which approach the conversion structures 9.

[0121] Other variants and improvements may be envisaged without departing from the scope of the invention as defined by the claims below.

Claims

An electroacoustic device (1) comprising: - a support (2), - at least one transducer (5) comprising a piezoelectric substrate (6) and electrodes (7) in electrical contact on either side of the piezoelectric substrate, the transducer being fixed to a first face (3) of the support and acoustically coupled to the support, - an electrical generator (11) connected to the electrodes of the transducer to apply an electrical signal to the electrodes of the transducer so as to generate an ultrasonic volume wave (S v ) propagating in the support, - at least one conversion structure (9) arranged on the surface of the support, on the side of a second face (4) of the support opposite the first face, the conversion structure being opposite the transducer and being configured to convert the ultrasonic body wave into an ultrasonic surface wave (S s) propagating in the second face of the support in order to displace and / or generate a phase change of the liquid and / or solid impurities (P) resting on said second face. Device according to claim 1, the frequency of the ultrasonic volume wave and / or the frequency of the ultrasonic surface wave being between 1 MHz and 1 GHz, preferably between 5 and 100 MHz, preferably between 8 and 45 MHz. Device according to claim 1 or 2, the conversion structure comprising a network of conversion patterns (10, 16, 17) on the surface of the support, the conversion patterns having a generally elongated shape and being spaced from each other transversely to their longitudinal axis in a substantially periodic manner. Device according to claim 3, the period p of the conversion patterns being between 0.8nλ s and 1.2nλ s, voire entre 0,95nλset 1,05nλs,nétant un nombre entier positif etλsétant la longueur d’onde de l’onde de surface ultrasonore, de préférencenétant égal à 1, de préférence la période des motifs de conversion étant sensiblement égale à un multiple de la longueur d’ondeλsde l’onde de surface ultrasonore, de préférence la période des motifs de conversion étant sensiblement égale à la longueur d’ondeλsde l’onde de surface ultrasonore. Device according to claim 3 or 4, the conversion patterns comprising grooves (10) formed in the second face of the support. Device according to claim 3 or 4, the conversion motifs comprising closed tubular cavities (16) formed in the support. Device according to claim 3 or 4, the conversion patterns comprising ribs (17) projecting from the second face of the support. Device according to any one of the preceding claims, the piezoelectric substrate being in a lead zirconate titanoate (PZT), for example in PZT-5H or PZT-5A, in a niobate, for example in lithium niobate, in zinc oxide or in aluminium nitride. Device according to any one of the preceding claims, the support being transparent in the visible range, for example made of glass, polycarbonate, quartz or sapphire, and / or transparent in the infrared range, for example made of germanium, silica or metal. Device according to any one of the preceding claims, comprising a reflection structure (18) extending at least partially, preferably entirely, along one side of the conversion structure, the reflection structure being configured to reflect the ultrasonic surface wave. Device according to claim 10, the reflection structure comprising at least one groove (19) formed in the second face of the support. Device according to any one of the preceding claims, comprising a temperature sensor (12) configured to measure the temperature of the support and / or the transducer and a control unit (13) configured to control the frequency of the electrical signal applied by the electrical generator as a function of the measured temperature. Device according to any one of the preceding claims, comprising a heat sink (14) arranged on the side of the first face of the support and being in thermal contact with the transducer and / or the support. Device according to any one of the preceding claims, comprising an acoustically insulating layer (27) covering the face of the transducer opposite the support, the acoustically insulating layer having a thickness greater than 100 nm, or even 500 nm. Device according to any one of the preceding claims, the support being chosen from the group formed by: - ​​a protective glass of a photovoltaic panel, - an automotive surface, for example chosen from a windscreen of a vehicle, a rearview mirror glass, a bodywork element - a helmet visor, - a building window, - a surface of an optical device, for example chosen from a camera, a camera lens, a lidar, a periscope, a lens of a spectacle or viewfinder, a sensor, in particular a probe, and a medical imaging device, for example an endoscope, - a surface of an aeronautical vehicle, for example an aircraft wing, a Pitot tube, a cockpit window, an aircraft canopy. Photovoltaic panel (20) comprising an electroacoustic device according to the preceding claim, the support forming the protective glass of the photovoltaic panel, the second face of the support being an external face of the photovoltaic panel. A method employing the device (1) according to any one of claims 1 to 15 or the photovoltaic panel (20) according to the preceding claim, for cleaning the second face (4) of the support (2), the method comprising the following successive steps: a) generation by the transducer (5) of an ultrasonic volume wave (S v ) propagating through the support to the second face of the support, b) conversion by the conversion structure (9) of the ultrasonic body wave into an ultrasonic surface wave (S s) propagating in the second face, c) displacement and / or phase change induced by the ultrasonic surface wave of the liquid and / or solid impurities (P) resting on the second face. Use of the device (1) according to any one of claims 1 to 15 for detecting liquid and / or solid impurities (P) resting on the second surface (4), the device comprising at least a first transducer (5) with a first conversion structure (9) opposite the first transducer, and at least a second transducer (5) with a second conversion structure (9) opposite the second transducer, the use comprising the following successive steps: a) generation by the first transducer of a detection signal in the form of an ultrasonic volume wave (S v) propagating through the support to the second face of the support (2),b) conversion by the first conversion structure of the shape of the detection signal into an ultrasonic surface wave (S s ) propagating in the second face, c) conversion by the second conversion structure of the shape of the detection signal into an ultrasonic volume wave propagating in the support, d) reception of the detection signal by the second transducer, e) determination of the presence of liquid and / or solid impurities resting on the second face of the support and / or the presence of a touch contact on the second face of the support and / or the presence of a surface defect on the second face of the support.

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