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

Abstract

Device and method for cleaning a support by converting an ultrasonic body wave into an ultrasonic surface wave. 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 fixed on a first face (3) of the support, - an electrical generator (11) connected to the electrodes to apply an electrical signal and generate an ultrasonic body wave (Sv) 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 to the first face.The conversion structure is positioned opposite the ultrasonic wave transducer and is configured to convert the ultrasonic body wave into an ultrasonic surface wave (Ss) propagating along the second face of the support in order to displace and / or induce a phase change of the impurities (P) resting on said second face. Figure for the abbreviation: Fig. 1,

Description

Title of the invention: Device and method for cleaning a support by converting an ultrasonic volume wave into an ultrasonic surface wave technical field

[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 implementing this device to clean the support and a use of this device to detect the presence of impurities on said support. Previous technique

[0003] In various fields, it is necessary to overcome the effects of the accumulation of impurities on a surface, for example, the accumulation of droplets, liquid films, ice, frost, snow, mud, or solid particles such as dust, sand grains, or soil. It is particularly preferable, or even necessary, to clean a surface to remove the impurities present on it. This is the case, for example, for the surfaces of photovoltaic panels, optical devices, and the windows of land or aircraft vehicles.

[0004] In particular, the accumulation of impurities on the surface of photovoltaic panels can induce 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 said impurities, for example by means of a windshield wiper. However, a windshield wiper limits visibility through the surface. It also spreads the greasy particles deposited on the surface. In addition, it is necessary to replace the wiper blades regularly.

[0006] Moreover, for certain surfaces, for example the surfaces of optical sensors, such as a lidar, or probes, such as a Pitot probe, a 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 known to use robots equipped with brushes that move along the outer surface of the protective glass of the photovoltaic panels. However, these robots are expensive, require regular maintenance, and have a short lifespan, much shorter than the warranty period of the photovoltaic panels. Furthermore, the use of brushes to clean photovoltaic panels can, in the long term, damage the protective glass of these panels, and in particular the anti-reflective coating of said protective glass.

[0008] Patent applications FR3100999A1, FR3100998A1, FR3101000A1, and FR3121370A1 each describe a device implementing transducers for cleaning a surface using an ultrasonic surface wave propagating through said surface. However, these devices are not very robust and are exposed to external environments, which makes them unsuitable for a large number of 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 kinds of impurities on large surfaces.

[0009] French patent applications FR3117384A1 and FR3117385A1 each describe a device implementing transducers to clean a surface using an ultrasonic surface wave propagating through said surface. These devices have the advantage of not being exposed to external environments. However, these devices remain somewhat fragile 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 that includes a surface to be cleaned is difficult because these devices require a significant portion of the surface area.

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

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

[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 one face of the support and acoustically coupled to the support, - an electrical generator connected to the transducer electrodes to apply an electrical signal to the transducer electrodes in order to generate an ultrasonic volume wave propagating through the medium, - at least one conversion structure arranged on the surface of the support, on the side of a second face of the support opposite the first face, the conversion structure being opposite the transducer and being configured to convert the ultrasonic volume wave into an ultrasonic surface wave propagating in the second face of the support in order to move and / or generate a phase change of 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 an external environment. The transducer is then protected by the support, thus greatly limiting its degradation. The transducer can be positioned 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] Contrary to 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 obtainable 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 exhibits a displacement amplitude, along a direction normal to the support, greater than -A, where K denotes a constant on the order of 5 x 10'V1, and ω denotes the angular frequency of the ultrasonic surface wave, = 2 nf, with fs the frequency of the ultrasonic surface wave. This amplitude can be measured, for example, using a laser Doppler vibrometer. The amplitude can be adapted according to the type of impurity to be cleaned, its quantity, and the surface of the support, for example, its material, its roughness, and / or its 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 fv of the ultrasonic volume wave and / or the frequency f 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 background.

[0022] The wavelength  vs of the ultrasonic volume foundation in the support is equal to hi, if the ultrasonic volume foundation is longitudinal, or equal to hx, if the JFJ foundation is y ultrasonic volume is transverse, with denoting the speed of longitudinal sound waves in the medium, L' being the speed of transverse sound waves in the medium and fv being the background frequency of ultrasonic volume.

[0023] The wavelength As of the ultrasonic surface background is equal to Js cs denoting the speed of surface sound waves, also called Rayleigh waves, in the medium and f being the ultrasonic surface frequency.

[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 0.9p and 1.10p, or even between 0.95p and 1.05p. 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 0.8n s and 1.2n s, or even between 0.95n s and 1.05n s, where n is a positive integer and As is the wavelength of the ultrasonic surface wave, preferably n being equal to 1, and preferably the period p of the conversion patterns being substantially equal to a multiple of the wavelength As of the ultrasonic surface wave. Advantageously, this makes it possible to increase the conversion rate of the ultrasonic body wave to the ultrasonic surface wave by resonance.

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

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

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

[0030] According to a first variant, the conversion patterns may include grooves formed in the second face of the support.

[0031] Preferably, the ratio of the groove depth to the wavelength A s of ultrasonic surface background is between 0.001 and 0.3, or even between 0.05 and 0.1. This makes it possible to increase the efficiency of the electroacoustic device by limiting the trapping of ultrasonic surface background in the conversion structure while presenting a high conversion rate of ultrasonic volume background to ultrasonic surface background.

[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 may 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 As from the second face of the support, As being the ultrasonic surface wavelength. This increases the efficiency of the electroacoustic device by increasing the conversion rate of the ultrasonic volume wave into the ultrasonic surface wave and promoting resonance phenomena.

[0036] Preferably, the ratio of the diameter of the tubular cavities to the wavelength A s of the ultrasonic surface wave is between 0.001 and 0.3, or even between 0.05 and 0.1. This makes it possible to increase the efficiency of the electroacoustic device by limiting the attenuation of the ultrasonic surface wave while presenting a high rate of conversion of the ultrasonic volume wave into an ultrasonic surface wave.

[0037] The 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 according to a transverse section of the support, having a polygonal shape, in particular rectangular or rhomboid, ellipsoidal or circular.

[0039] According to a third embodiment, the conversion patterns may include ribs projecting 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 on the substrate.

[0040] The ribs can be 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.

[0041] Preferably, the ratio of the thickness of the ribs to the wavelength A s of the ultrasonic surface background is between 0.001 and 0.3, or even between 0.05 and 0.1. This makes it possible to increase the efficiency of the electroacoustic device by limiting the attenuation of the ultrasonic surface background while presenting a high conversion rate of ultrasonic volume background to ultrasonic surface background.

[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 may 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 0.45 mA vp and 0.55 mA vp, where m is a positive integer and A vp is the ratio of the speed of sound in the piezoelectric substrate to the ultrasonic volume background frequency 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 phenomena of the ultrasonic body wave.

[0045] The transducer can be glued to the support. Preferably, the ratio of the thickness of the glue layer between the transducer and the support to the wavelength A vs of the ultrasonic volume wave is less than 0.1, or even less than 0.01. Advantageously, a thin layer of glue allows for increased 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 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.

[0049] Preferably, the thickness of the support is between 0.45pAvs and 0.55pAv, where p is a positive integer and Avs is the wavelength of the ultrasonic body wave propagating in the support. 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 made of glass, polycarbonate, quartz or sapphire, and / or transparent in the infrared range, for example made of germanium, silica or metal.

[0051] The support can be of very varied 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 ultrasonic surface background.

[0053] Preferably, the reflection structure includes at least one groove formed in the second face of the support.

[0054] Preferably, the ratio of the groove depth to the wavelength A s of 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 electrical generator as a function of 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 participates as an external force to move the impurities so as to remove them from the second face of the support.

[0059] The device may comprise at least two transducers and at least two conversion structures, each opposite one of the corresponding transducers, one of the transducers being disposed near a first lateral edge of the support and another of the transducers being disposed near a second lateral edge of the support, in particular opposite to the first lateral edge. Preferably, the support is inclined with respect to the horizontal and the first lateral edge is arranged higher than the second lateral edge.

[0060] The device may include 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 first transducer being configured to emit a detection signal in the form of an ultrasonic volume wave propagating in the support to the first conversion structure which converts the detection signal into an ultrasonic surface wave propagating in the second face to the second conversion structure which converts the detection signal into an ultrasonic volume wave propagating in 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] By acoustically insulating we mean a ratio of acoustic impedance of the insulating layer to the acoustic impedance of the piezoelectric substrate 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 cover for a photovoltaic panel, - an automotive surface, for example chosen from a vehicle's windshield, a rearview mirror glass, a bodywork element - a helmet visor, - a window in a building, - a surface of an optical device, for example selected 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 for such an optical device, - a surface of an aeronautical vehicle, for example an airplane 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 separated from the resin layer by a length greater than 100 nm, or even greater than 500 nm.

[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 Clean the second side of the support, the process comprising the following successive steps: a) generation by the transducer of an ultrasonic volume wave propagating through the medium to the second face of the medium, b) conversion by the ultrasonic volume wave conversion structure into an ultrasonic surface wave propagating in the second face, c) displacement and / or phase change induced by the ultrasonic surface wave of liquid and / or solid impurities resting on the second face

[0071] Preferably, the support is inclined with respect 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 on the second side of the support and / or the presence of tactile contact on the second side of the support and / or the presence of a surface defect on the second side of the support.

[0073] When liquid and / or solid impurities are present on the second surface of the support, they interfere with the detection signal. The presence of these liquid and / or solid impurities can then be determined by analyzing the interference in the detection signal.

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

[0075] The surface defect may 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 a surface defect is detected, it is preferable not to carry out the cleaning process according to the present invention. Brief description of the drawings

[0078] Other advantages and features will become apparent from the detailed description, given by way of illustration and not limitation, with reference to the following figures:

[0079] [Fig-1] [Fig.1] schematically represents, according to a cross-sectional view transverse, an electroacoustic device according to the present invention, the conversion patterns of said device being grooves engraved in the support;

[0080] [Fig.2] [Fig.2] schematically represents, in cross-section, a electroacoustic device according to the present invention, the conversion patterns of the device being grooves engraved in the support and filled with a filling material;

[0081] [Fig.3] [Fig.3] schematically represents, according to a cross-sectional view transverse, an electroacoustic device according to the present invention, the conversion motifs of said device being closed tubular cavities formed in the support;

[0082] [Fig.4] [Fig.4] schematically represents, according to a cross-sectional view transverse, 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] [Fig.5] [Fig.5] schematically represents, according to a cross-sectional view transverse, an electroacoustic device according to the present invention, comprising a reflection structure;

[0084] [Fig.6] [Fig.6] schematically represents, according to a cross-sectional view transverse, a photovoltaic panel comprising an electroacoustic device according to the present invention;

[0085] [Fig.7A] and [Fig.7B] 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] [Fig.8A] and [Fig.8B] Figures 8A and 8B are photographs illustrating the cleaning of a surface covered with a film of water resulting from a mist by an electroacoustic device according to the present invention;

[0087] [Fig.9A] and [Fig.9B] 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 reasons of 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] Figure 1 illustrates an electroacoustic device 1 according to the present invention. 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] The 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 [Fig. 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 of the electrodes 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 [Fig. 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 Sv which propagates in the support 2. In particular, the alternating electrical energizing of the electrodes 7 induces a mechanical response of the piezoelectric substrate 6, which results in the generation of the ultrasonic volume wave Sv.

[0095] The ultrasonic body wave Sv propagates in the support 2 until it reaches the conversion structure 9. The conversion structure 9 then converts the ultrasonic body wave Sv into an ultrasonic surface wave Ss propagating in the second face 4 of the support 2. The ultrasonic surface wave Ss is in particular a Rayleigh wave.

[0096] When liquid and / or solid impurities P are arranged on the second face 4 of the support 2, the ultrasonic surface wave Ss 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 Ss can be adjusted by modifying the electrical signal applied by the electric 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 Ss according to the impurities P to be cleaned.

[0098] The displacement of the impurities P can occur along one or more axes contained in the second face 4. In particular, the ultrasonic surface wave Ss can induce the displacement of the impurities P along the direction of propagation of said ultrasonic surface wave Ss in the absence of an external force. The direction of displacement of the impurities P can be different depending on the nature of said impurities P. In particular, solid impurities P can move towards the conversion structure 9 and liquid impurities P can move away from the conversion structure 9. In an embodiment where at least one external force is applied to the impurities P, said impurities P can 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 Ss.By "external force" is meant any force other than the acoustic force induced by the ultrasonic surface wave Ss. 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 induced radiation pressure by the ultrasonic surface wave Ss. The displacement of a solid impurity P can notably result from nonlinear acoustic contact effects of Hertz induced by the ultrasonic surface wave Ss.

[0100] The ultrasonic surface wave Ss can induce a phase change in the impurities P. In particular, some of the energy of the ultrasonic surface wave Ss is transferred to the impurities P, causing them to heat up. The energy transferred by the ultrasonic surface wave Ss can be such that it heats the impurities P above their melting or boiling point, thus 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 for measuring 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] Figure 2 illustrates another embodiment of an electroacoustic device 1 according to the present invention. The electroacoustic device 1 of Figure 2 differs from that of Figure 1 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 Ss.

[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] Figure 3 illustrates another embodiment of an electroacoustic device 1 according to the present invention. The electroacoustic device 1 of Figure 3 differs from that of Figure 1 in that the conversion patterns of the conversion structure 9 are no longer grooves 10 but closed tubular cavities 16. formed in 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 each other. The tubular cavities 16 can be straight or curved.

[0106] Figure 4 illustrates another embodiment of an electroacoustic device 1 according to the present invention. The electroacoustic device 1 of Figure 4 differs from that of Figure 1 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 may be straight or curved.

[0107] Figure 5 illustrates another embodiment of an electroacoustic device 1 according to the present invention. The electroacoustic device 1 of Figure 5 differs from that of Figure 1 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] The groove 19 can extend parallel to the conversion patterns of the conversion structure 9. The groove 19 has a width greater than the acoustic displacement of the ultrasonic surface wave Ss.

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

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

[0111] Alternatively, it is conceivable that the conversion structure 9 is configured to convert the ultrasonic volume wave Sv into a unidirectional ultrasonic surface wave Ss.

[0112] Figure 6 illustrates a photovoltaic panel 20 comprising an electroacoustic device 1 according to the present invention. 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 includes 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 transmitting heat to the resin layer 26. This gap 27 also forms an acoustically insulating layer covering the transducers 5, which prevents an ultrasonic wave 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 retaining structure 28. The retaining structure 28 also ensures that the transducers 5, the resin layer 26, and the photovoltaic cells 25 are not exposed to the external environment. Examples

[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 π equal to the wavelength Δs of the ultrasonic surface wave Ss, here equal to 158 pm, a width equal to half the wavelength Δs of the ultrasonic surface wave Ss, i.e., 79 pm, and a depth equal to 22 pm. 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 Ss 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 [Fig. 7B], the movement of the droplets P of salt water can be observed, moving away from the conversion structures 9 and eventually being evacuated from the support 2. Furthermore, the cleaning of the droplets P did not leave any 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 this is visible on [Fig.8B], we observe the evacuation of water from film P in part 29 opposite the conversion structures 9, that is to say part 29 of the second face 4 in which the ultrasonic surface wave Ss propagates.

[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 in [Fig.9B], the movement of the sand grains P can be observed as they 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 following claims.

Claims

Demands

1. 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 being 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 (Sv) 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 to the first face,the conversion structure being opposite the transducer and being configured to convert the ultrasonic volume wave into an ultrasonic surface wave (Ss) 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.

2. Device according to claim 1, the ultrasonic volume wave frequency and / or the ultrasonic surface background frequency being between 1 MHz and 1 GHz, preferably between 5 and 100 MHz, preferably between 8 and 45 MHz.

3. 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.

4. Device according to claim 3, the period p of the conversion patterns being between 0.8n and l.2n or even between 0.95n and l.05n, n being a positive integer and As being the wavelength of the ultrasonic surface wave, preferably n being equal to 1, preferably the period of the conversion patterns being substantially equal to a multiple of the wavelength As of the ultrasonic surface wave, preferably the period of the conversion patterns being substantially equal to the wavelength As of the ultrasonic surface wave.

5. Device according to claim 3 or 4, the conversion motifs comprising grooves (10) formed in the second face of the support.

6. Device according to claim 3 or 4, the conversion motifs comprising closed tubular cavities (16) formed in the support.

7. Device according to claim 3 or 4, the conversion patterns having ribs (17) projecting from the second face of the support.

8. Device according to any one of the preceding claims, the piezoelectric substrate being a lead zirconate titanoate (PZT), for example PZT-5H or PZT-5A, a niobate, for example lithium niobate, zinc oxide or aluminium nitride.

9. 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.

10. 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.

11. Device according to claim 10, the reflection structure comprising at least one groove (19) formed in the second face of the support.

12. 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.

13. 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.

14. A 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.

15. Device according to any one of the preceding claims, the support being selected from the group consisting of: - a protective glass for a photovoltaic panel, - an automotive surface, for example selected 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 selected from a camera, a camera lens, a lidar, a periscope, a lens for eyeglasses or a 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.

16. 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.

17. A method implementing 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 (Sv) propagating in the support to the second face of the support, b) conversion by the conversion structure (9) of the ultrasonic volume wave into an ultrasonic surface wave (Ss) 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.

18. 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 face (4), the device comprising at least one first transducer (5) with a first conversion structure (9) opposite the first transducer, and at least one 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 (Sv) 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 (Ss) propagating through 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 medium, 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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