EP4260123A1

EP4260123A1 - Device for cleaning an optical surface

Info

Publication number: EP4260123A1
Application number: EP21839087.0A
Authority: EP
Inventors: Michaël BAUDOIN; Ravinder CHUTANI; Frederic Bretagnol; Adrien PERET
Original assignee: Centre National de la Recherche Scientifique CNRS; Valeo Systemes dEssuyage SAS; Universite Lille 2 Droit et Sante; Universite Polytechnique Hauts de France; Ecole Centrale de Lille
Current assignee: Centre National de la Recherche Scientifique CNRS; Valeo Systemes dEssuyage SAS; Universite Lille 2 Droit et Sante; Universite Polytechnique Hauts de France; Ecole Centrale de Lille
Priority date: 2020-12-14
Filing date: 2021-12-13
Publication date: 2023-10-18
Also published as: FR3117385A1; WO2022128919A1; JP2024500374A; CN116669872A; US20240042969A1

Abstract

Disclosed is a device (5) for cleaning an optical surface, which device comprises: - a transparent optical surface (10); - a cleaning unit (15) for cleaning the optical surface, having a piezoelectric layer (20) and at least two wave transducers (45), each wave transducer having electrodes (40) of opposite polarity in contact with the piezoelectric layer and being acoustically coupled to the optical surface so as to generate at least one surface ultrasonic wave (W_s) or a Lamb wave (W_L) propagating in the optical surface, the transducers being further arranged on the periphery of the optical surface.

Description

Title: Device for cleaning an optical surface

The present invention relates to a device for cleaning a body in contact with an optical surface by means of ultrasonic waves.

In various fields, it is necessary to overcome the effects linked to the accumulation of a body, in particular drops of rain, frost or snow, on an optical surface.

It is known to rotate drops of a liquid to evacuate them from a surface. However, such a technique is not suitable for surfaces whose area is greater than a few square centimeters.

The implementation of an electric field to control the hydrophobicity of a surface is also known, for example from KR 2018 0086173 AL This technique, known by the acronym EWOD (for "Electro Wetting On Devices" in English) consists applying a potential difference between two electrodes, so as to electrically polarize the surface to change its wetting properties. By controlling the location of the polarization, the drop can then be moved. However, this technique can only be implemented with particular materials and requires a particularly precise positioning of the electrodes over the entire surface where we want to control the wetting properties.

It is also well known to apply a mechanical force to the liquid, for example by means of a windscreen wiper on a windshield of a motor vehicle. However, a windscreen wiper limits the field of vision accessible to the driver. It also spreads the greasy particles deposited on the surface of the windshield. In addition, it is necessary to renew the wiper linings regularly.

WO 2015/011064 A1 describes a device for cleaning a windscreen using surface ultrasonic waves. However, the device of WO 2015/011064 is complex to manufacture, since it requires the bonding of a substantial number of transducers to the windshield.

There is therefore a need for a device for removing a body from an optical surface, which is easy to manufacture. The invention aims to satisfy this need and proposes a device comprising:

- a transparent optical surface,

- an optical surface cleaning unit comprising a piezoelectric layer and at least two wave transducers, each wave transducer comprising electrodes of opposite polarity in contact with the piezoelectric layer and being acoustically coupled with the optical surface to generate at least one surface ultrasonic wave or a Lamb wave propagating in the optical surface, the transducers further being arranged at the periphery of the optical surface.

The device according to the invention thus makes it possible to effectively clean the optical surface, by inducing the displacement of one or more bodies, for example drops of water, coating the optical surface by means of the propagation of surface ultrasonic waves or Lamb waves.

Furthermore, the device is easy to manufacture. For example, a piezoelectric layer is first deposited, for example glued, on the optical surface, then the electrodes of the various transducers are deposited in a single deposition step, for example by printing or screen printing on the piezoelectric layer. Furthermore, the position at the periphery of the optical surface facilitates the protection of the transducers, for example by means of a structure carrying the optical surface and which can cover the transducers.

By "layer" is usually meant a uniform extent applied or deposited on a surface.

Preferably, each wave transducer extends from an edge of the optical surface over a distance of less than 10%, or even less than 5% of the length of the optical surface. By "length of the optical surface" is meant the distance separating two opposite edges of the optical surface along one face of the optical surface.

Preferably, each wave transducer extends from an edge of the optical surface over a distance of less than 30 mm, preferably less than 20 mm, preferably less than 10 mm.

The wave transducers are preferably in contact with the optical surface.

Wave transducers can be attached to the optical surface in different ways. For example, the wave transducers can take the form of a foil which is transferred onto the optical surface. By "foil" is meant a flexible and thin film, in particular having a thickness of less than 100 μm.

The transducers can be glued to the optical surface, in particular by means of a polymeric adhesive which further acoustically couples the transducers to the optical surface. The adhesive may be crosslinkable by illumination with ultraviolet radiation. It is for example an epoxy resin. The transducers can be fixed by molecular adhesion, or by means of a thin metallic layer providing adhesion between the optical surface and the piezoelectric layer. The layer can be made of a metal or an alloy with a low melting temperature, i.e. having a melting temperature of less than 200° C., for example an indium alloy. As a variant, the metallic layer can be made of a metal or of an alloy having a melting temperature greater than 200° C., for example of an aluminum and/or gold alloy.

An example of bonding by molecular adhesion is described in "Glass-on-LiNbO heterostructure formed via a two-step plasma activated lo -temperature direct bonding method", J. Xu et al., Applied Surface Science 459 (2018) 621-629 , doi:10.1016/j.apsusc.2018.08.031. According to another variant, the transducers can be fixed on the optical surface by means of a method comprising a step of melting a portion of the piezoelectric layer and/or a portion of the optical surface followed by a step consisting in compressing the piezoelectric layer and the optical surface together, the respective molten portions of the optical surface and of the piezoelectric layer being in contact with each other. According to another variant, the transducers can be fixed on the optical surface by means of a process comprising the deposition of bonding layers of an alloy with a low melting temperature on a portion of the transducer and on a portion of the optical surface respectively, at least partially melting said bonding layers, then compressing the piezoelectric layer and the optical surface, the faces of the bonding layers opposite the optical surface and the piezoelectric layer being brought into contact with each other during compression. The bond layers can be deposited by sputtering, or by an evaporation technique implemented in the field of thin film deposition.

Preferably, the piezoelectric layer has the shape of a strip which extends over one face of the optical surface, for example between two opposite edges of the optical surface. Preferably, the strip extends along an edge of the optical surface, and preferably parallel to said edge.

In particular, the optical surface may comprise a region of optical interest not superimposed on the transducers and the piezoelectric layer may form a frame surrounding at least partially, in particular entirely, the region of optical interest. The outer contour and/or the inner contour of the frame can be homothetic to the contour of the face of the optical surface on which the piezoelectric layer is placed.

The thickness of the piezoelectric layer can be chosen according to the wavelength Â of the ultrasonic surface wave. Preferably, the thickness of the piezoelectric layer is less than or equal to 5*Å, preferably less than or equal to 1.5*Å, preferably less than or equal to Å, or even less than or equal to 0.5*Å, in particular for a frequency of the surface ultrasonic wave of between 0.1 MHz and 60 MHz.

The piezoelectric layer can have a thickness of between 1 μm and 300 μm. It may have a thickness less than or equal to 100 μm, less than 50 μm, or even less than 10 μm.

The ratio of the thickness of the optical surface to the thickness of the piezoelectric layer is preferably greater than 2, preferably greater than 10, or even greater than 50.

It can be deposited on the optical surface by a process chosen from physical vapor deposition, chemical vapor deposition, magnetron sputtering and electron cyclotron resonance.

The piezoelectric layer can be made of a material chosen from the group formed by lithium niobate, aluminum nitride, zinc oxide, lead titano-zircanate, and mixtures thereof.

The piezoelectric layer may be opaque to light. The frame can thus promote the concentration of the vision of an observer who looks through the optical region of interest.

Alternatively, the piezoelectric layer may be transparent. Thus, the transducers may appear invisible to the user.

By "transparent" is meant a transparency to light radiation in the visible and/or to radiation in the infrared and/or to radiation in the ultraviolet. The electrodes of each transducer are of opposite polarity, that is to say they are intended to be electrically powered by electrical voltages of opposite signs.

The opposite polarity electrodes of each transducer may each have a comb having a branch from which fingers extend. Preferably, the combs are interdigitated.

Each of the fingers of a comb can have a width equal to the fundamental wavelength of the surface ultrasonic wave of the Lamb wave, divided by 4 and the spacing between two consecutive fingers of a comb can be equal to the fundamental wavelength of the ultrasonic surface wave or of the Lamb wave, divided by 4. The spacing between the fingers determines the resonant frequency of the transducer, which a person skilled in the art can easily determine. The alternating electrical voltage of electrodes of opposite polarity induces a mechanical response of the piezoelectric material, which results in the generation of an ultrasonic surface wave or a Lamb wave which propagates in the optical surface.

The electrodes can be metallic. They can be in chrome, or aluminum or in the combination of a grip layer such as titanium and a conductive layer such as gold.

As variants, the electrodes can be made of a conductive transparent oxide, for example chosen from indium tin oxide, zinc oxide doped with aluminum and mixtures thereof. In particular, each transducer can be transparent and be formed from such electrodes and from a transparent piezoelectric layer of lithium niobate or zinc oxide.

The electrodes can be deposited on the piezoelectric layer by an evaporation or sputtering process and shaped by photolithography.

They can be printed, for example by inkjet printing, in particular on the piezoelectric layer. In particular, they can be printed on a foil, for example made of a flexible thermoplastic material, and be applied by transferring the foil onto the piezoelectric layer. Such a process for transferring electrodes is particularly simple to implement.

The transducer can be configured to emit a surface ultrasonic wave or a Lamb wave whose fundamental frequency can be between 0.1 MHz and 1000 MHz, preferably between 10 MHz and 100 MHz, for example equal to 40 MHz, and/or the amplitude can be between 1 nanometer and 500 nanometers. The amplitude of the wave corresponds to the normal displacement of the face of the optical surface on which the ultrasonic surface wave propagates. It can be measured by laser interferometry.

The ultrasonic surface wave can be a Rayleigh wave, when the optical surface has a thickness greater than the wavelength of the ultrasonic surface wave. A Rayleigh wave is favored because a maximum proportion of the wave's energy is concentrated on the face of the optical surface on which it propagates, and can be transmitted to a body, for example a raindrop, resting on the optical surface.

Preferably, the device comprises more than two transducers, for example more than five, or even more than ten transducers.

The transducers can be configured to emit surface acoustic waves propagating in parallel or secant directions. For example, the device comprises at least three transducers which are configured so that the directions of propagation of the waves that they are able to generate intersect in a common place.

The transducers can be distributed regularly over the contour of the face of the optical surface on which they are arranged.

The optical surface can be self-supporting, in the sense that it can deform, in particular elastically, without breaking under its own weight.

The face of the optical surface on which the ultrasonic surface wave or the Lamb wave emitted by each transducer propagates can be planar. It can also be curved, provided that the radius of curvature of the face is greater than the wavelength of the ultrasonic surface wave. Said face may be rough. The roughnesses will preferably be lower than the fundamental wavelength of the ultrasonic surface wave, in order to prevent them from significantly affecting their propagation.

The optical surface may be in the form of a flat plate, or having at least one curvature in one direction. The thickness of the optical surface can be between 100 µm and 5 mm. The length of the plate may be greater than 1 mm, or even greater than 1 cm, or even greater than 1 m.

By “thickness of the optical surface”, one considers the smallest dimension of the optical surface measured along a direction perpendicular to the surface on which the surface ultrasonic wave or the Lamb wave propagates. The optical surface can be laid flat relative to the horizontal. As a variant, it can be inclined with respect to the horizontal by an angle α greater than 10°, or even greater than 20°, or even greater than 45°, or even greater than 70°. It can be arranged vertically.

The optical surface is preferably transparent at least to light in the visible. Preferably, it is opaque to ultraviolet radiation or to infrared radiation.

Furthermore, the optical surface may comprise a monolayer or multilayer coating which covers one face of the acoustically conductive portion.

The coating may in particular comprise a hydrophobic layer, an antireflection layer or a stack of these layers. For example, the hydrophobic layer is made up of self-assembled monolayers of OTS or can result from the deposition of a fluorine-based plasma. The coating may include one or more anti-reflective layers depending on the intended application (Visible, IR, . . .).

Each transducer can be in contact with the acoustically conductive portion and the hydrophobic layer can entirely cover the transducer, in order to protect it from contact with water. In a variant, the coating is placed between the transducer and the acoustically conductive portion.

Preferably, the optical surface includes an acoustically conductive portion, each transducer being acoustically coupled to, and preferably in contact with, the acoustically conductive portion.

The acoustically conductive portion is preferably transparent.

The acoustically conductive portion preferably has an attenuation length greater than the length of the optical surface, or even greater than 10 times the length of the optical surface, or even greater than 100 times the length of the optical surface.

The acoustically conductive portion can be made of any material capable of propagating an ultrasonic surface wave or a Lamb wave. Preferably, it is made of a material having a modulus of elasticity greater than 1 MPa, for example greater than 10 MPa, or even greater than 100 MPa, or even greater than 1000 MPa, or even greater than 10,000 MPa. A material with such a modulus of elasticity has a stiffness particularly suitable for the propagation of an ultrasonic surface wave or a Lamb wave.

Preferably, the acoustically conductive portion is made of glass or of poly(methyl methacrylate), also known under the commercial reference Plexiglas®.

The optical surface may consist of the acoustically conductive portion.

Alternatively, the optical surface may include an acoustically insulating portion, that is to say absorbing the surface ultrasonic wave or the Lamb wave over a distance less than the length of the optical surface, or even less than 0 , 1 times the length of the optical surface. The acoustically insulating portion is preferably superposed on the acoustically conducting portion. The acoustically insulating portion may entirely cover the acoustically conducting portion. Preferably, the acoustically insulating portion is made of polycarbonate. Other rubber or plastic materials can be considered.

The acoustically insulating portion is preferably transparent.

In particular, the acoustically insulating portion and the acoustically conducting portion can be stacked on top of each other, and preferably in contact with each other. In particular, the acoustically conductive portion may have a thickness at least five times less than the thickness of the acoustically insulating portion. Thus, the acoustically insulating portion can confer mechanical resistance to the optical surface while the acoustically conducting portion ensures the cleaning function by transporting the ultrasonic wave.

The acoustically conductive portion can be removably mounted on the acoustically insulating portion. Thus, it is possible to easily replace one of said portions when it is damaged, for example as a result of contact with a solid body, for example a pebble during movement of the device.

In particular, the acoustically conductive portion can be bonded to the acoustically insulating portion by means of a reversible adhesive.

The device may be a motorcyclist's helmet comprising a cap intended to protect a user's skull and the optical surface may be a visor mounted on the cap so as to protect all or part of the motorcyclist's face. The wave transducer can be completely or partially hidden from view by the user who has introduced his head into the cap. The optical surface can be arranged between the wave transducers and the inside of the cap.

Alternatively, the device may be a glazed element of a building and the optical surface is a glazing. In particular, the glazed element, for example a sash of a window, comprises a structure for framing the optical surface. The optical surface can be arranged between the transducer and the interior of the building on which the glazed element is intended to be mounted.

According to another variant, the device is a motor vehicle, in particular a car or a truck, and the optical surface is a windshield of the vehicle. The wave transducers can be hidden from view by an occupant of the vehicle installed on a seat of the vehicle. The optical surface may be disposed between the transducers and a vehicle seat.

According to another variant, the device is an automated vehicle, in particular a car or a truck, the optical surface covering an optical sensor and/or an optical transmitter, for example a lidar, a camera, a camera, a radar, an infrared sensor or an ultrasonic range finder.

According to yet another variant, the device is a component of a motor vehicle, in particular automated, for example chosen from a lighting headlight module, a system containing a set of different sensors also called "pod", at least one window side window, a front window or a rear window and a driver assistance unit.

In particular, the device may include a cover superimposed in whole or in part on the transducers. In particular, the transducers can be protected by the cover. In particular, they can be entirely covered by the cover and by the optical medium.

For example, the shell of the helmet or the bodywork or the frame structure may include such a cover.

Furthermore, the cleaning unit may comprise an electric generator for electrically supplying each transducer, such that each transducer converts the electric power signal into a surface ultrasonic wave or into a Lamb wave. The invention also relates to the use of a device according to the invention, for removing a body in contact with the optical surface from the optical region of interest.

Use may include powering the cleaning unit to melt the body when the body is in a solid state, and/or maintain the body in a liquid state when the optical surface temperature is below the solidification temperature of the body. The body is for example a frost or snow.

The body in the liquid state can be in the form of at least one drop or at least one film. The energy of the surface ultrasonic wave may be sufficient to induce the liquid state body to move across the face of the optical surface. The body can be aqueous, especially is rainwater or dewwater. The optical surface temperature may be below 0°C.

The invention may be better understood on reading the detailed description which follows, non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

[Fig. 1]

[Fig. 2] Figures 1 and 2 show schematically, in a front view, examples of device according to the invention,

[Fig. 3]

[Fig. 4]

[Fig. 5] Figures 3 to 5 show schematically, in a cross-sectional view, examples of device according to the invention, and

[Fig. 6]

[Fig. 7]

[Fig. 8]

[Fig. 9] Figures 6 to 9 schematically represent still other examples of device according to the invention.

The constituent elements of the drawing have not always been represented to scale for the sake of clarity.

There is illustrated in Figure 1 a first example of device 5 according to the invention seen from the front.

The device comprises an optical surface 10 and a unit 15 for cleaning the transparent optical surface. The optical surface has the shape of a plate which can be of various shapes, for example rectangular as illustrated.

The cleaning unit 15 of the optical surface comprises a piezoelectric layer 20 which extends in a strip parallel between two opposite edges 25, 26 of the optical surface. The piezoelectric layer also extends around the periphery of the optical surface, along a third edge 27 connecting the opposite edges 25, 26.

The device comprises three pairs of electrodes 40 of opposite polarity and interdigitated which are in contact with the piezoelectric layer, thus forming three wave transducers 45. Obviously, this number of transducers is not limiting, since it is greater than or equal to two. It can be adapted according to the size of the device to ensure optimal cleaning of the optical surface.

The transducers are acoustically coupled with the optical surface, so that the waves they generate can propagate in the optical surface. The cleaning unit may further comprise a current generator 50 to electrically supply the transducers by means of an electrical circuit not shown in the figure.

The transducers can each generate a surface ultrasonic wave Ws or a Lamb wave WL which propagates in the optical surface in order to move a body 55, for example a drop of rain, which can be in contact with the face of the optical surface. on which the piezoelectric layer is disposed.

The device can be configured so that the transducers emit an ultrasonic wave in the direction of the edge 28 opposite the edge 27 along which the piezoelectric layer 20 extends in a band. The body can thus be moved in the direction S of propagation of the wave and be evacuated from the optical surface by the edge 28.

The manufacture of the device illustrated in FIG. 1 is easy. The piezoelectric layer is for example deposited by a cathodic sputtering technique, then the electrodes are printed, for example in a single pass on the optical surface. It is thus possible to quickly position a large number of electrodes on the piezoelectric layer to form transducers, unlike the devices of the prior art known to the inventors which require the bonding of transducers one by one. As a variant, the electrodes can be pre-printed on a foil which is then applied to the piezoelectric layer, so as to transfer the electrodes to the piezoelectric layer, for example in the manner of a decal. The device represented in FIG. 2 differs from that illustrated in FIG. 1 in that the piezoelectric layer delimits a frame 60 which surrounds a region of optical interest 65. The frame is for example rectangular. The piezoelectric layer can be opaque, which allows an observer looking through the optical region of interest 65 to easily determine the extent of said region. The frame has an outer contour 70 which coincides with the contour 75 of the face of the optical surface on which the piezoelectric layer is deposited. Also, the transducers can be arranged evenly around the frame. It is thus possible to control only some of the transducers in order to move a body as a function of an external force applied to the body, as described for example in application FR 1910589, incorporated by reference.

Figures 3 to 5 are schematic cross-sectional views of portions of example devices as shown in Figures 1 and 2.

In the example illustrated in FIG. 3, the optical surface is monolithic and made of an acoustically conductive material, for example glass, and the piezoelectric layer is in contact with the optical surface and arranged at the periphery of the optical surface, against a edge 27. The piezoelectric layer 20 is also arranged between the electrodes 40 of the various transducers and the optical surface 10. When electrically powered, the transducers generate a surface ultrasonic wave Ws or a Lamb wave propagating in the optical surface up to to a body in contact with it. A person skilled in the art knows how to determine the frequencies and amplitude of the wave to induce the displacement of the body on the optical surface.

The example illustrated in FIG. 4 differs from the example illustrated in FIG. 3 in that the optical surface 10 comprises an acoustically insulating portion 75 entirely covering an acoustically conducting portion 80, for example made of glass. The acoustically conductive layer can be removably mounted, for example by means of a reversible adhesive, on the acoustically insulating layer. In addition, although this is optional, the optical surface includes a coating 90 completely covering one face 95 of the acoustically conductive portion, and formed by stacking an antireflection layer 100 and a hydrophobic layer 105, in order to to prevent, for example, raindrops 40 from spreading over the optical surface 10 and to facilitate their evacuation. The piezoelectric layer is arranged in contact with the coating opposite the portion acoustically conductive. The coating preferably has a sufficiently small thickness with respect to the wavelength of the surface wave generated by the transducer. Thus, the acoustically conductive portion and the transducer are acoustically coupled.

The device illustrated in Figure 5 differs from the device illustrated in Figure 6 in that the transducers 45 are sandwiched between the hydrophobic layer 100 and the acoustically conductive portion 80. Thus the hydrophobic layer protects the transducers.

FIG. 6 schematically represents a motorcycle helmet 120. The helmet comprises a cap 125, to protect the head of a motorcyclist, provided with an opening 130 and an optical surface 135 in the form of a transparent and curved visor to protect the motorcyclist's head from precipitation, spray and insects.

The visor is rotatably mounted on the cap and can be arranged between a closed position where the visor closes off the opening and an open position allowing the passage of air through the opening in the direction of the motorcyclist's head.

The visor may be made of an acoustically conductive material or may comprise, as illustrated in FIG. 4, an acoustically insulating portion and an acoustically conductive portion.

A piezoelectric layer 20 is placed on the periphery of the visor 135. In FIG. 6, it is placed on the upper edge 140 of the visor. However, other arrangements are possible. For example, it can be placed against the lower edge 141 and/or against the side edges 142,143, or even form a frame as shown in Figure 2.

Preferably, the transducers are arranged between the visor 135 and the cap 125 in order to be protected from precipitation. At least in the closed configuration, the piezoelectric layer can be completely superimposed on the cap 125, for example on the outer side 150 of the cap. Thus, the transducers are hidden from the view of the motorcyclist.

Another variant is illustrated in FIG. 7. The device 5 which is represented there is a motor vehicle 160 comprising a windshield 165. Strip piezoelectric layers 20 are arranged on the windshield and extend at the periphery along lower 170 and upper 171 edges of the windshield and between the side edges 172, 173 of the latter. The piezoelectric layer can be arranged on the face of the windshield opposite the passenger compartment of the vehicle. Groups of electrodes 40 of opposite polarity are deposited on each piezoelectric layer. Thus, the transducers can each generate an ultrasonic surface wave or a Lamb wave to clean the precipitation in contact with the windshield. Such a vehicle can advantageously be devoid of a windshield wiper.

Another variant is illustrated in Figure 8. The device 5 shown there is a window of a building 180.

The window comprises for example a frame 185 and one or more openings 190, for example two as shown, pivotally mounted on the frame.

Each opening has a framing structure 195 in which a glazing 200 is inserted. A piezoelectric layer 20 is arranged on the periphery of the glazing, preferably on the upper part of the glazing, and at least two groups of electrodes are arranged so as to generate acoustic waves W oriented from top to bottom, in order to facilitate the displacement of drops under the effect of gravity G. In the example illustrated, the piezoelectric layer has a part that is not superimposed on the framing structure. In a variant not shown, the piezoelectric layer can be sandwiched, for example entirely, between the framing structure 195 and the glazing 200, so as to be hidden from view by an observer looking through the glazing. Any other glazed element of a building can of course be considered.

Finally, Figure 9 shows yet another variant of device 5 according to the invention which is part of an automated vehicle.

The device comprises an optical surface 10, an optical surface cleaning unit 15 and an apparatus 210.

The device comprises a sensor 215 to capture radiation R and a lens to direct the radiation R towards the sensor. Alternatively or additionally, it may include a transmitter for emitting radiation. For example, the device includes a lidar that is configured to emit laser radiation and in return pick up the object-reflected portion of that laser radiation.

Furthermore, the lens 220 is optional. In an example not shown, the device is exempt.

The device defines an optical field Co which corresponds to the portion of space from which it is capable of acquiring radiation. Outside this optical field, even if the radiation can reach the sensor, the latter is not able to acquire it. Furthermore, the optical surface completely covers the sensor.

In the example illustrated, the optical surface is in the form of a disk whose thickness e _p is for example between 0.5 mm and 5 mm. In a variant, the optical surface can be curved, and for example have the shape of a lens.

The device may comprise, as illustrated, a box 225 which defines a chamber 230 housing the sensor. The chamber can in particular be delimited by a solid wall 235 of the case and by the optical surface 10, so as to be airtight and watertight. The sensor is thus protected from the weather.

In particular, the optical surface can block the box 225. For example, the optical surface is mounted on a ring 240 screwed onto the box.

The optical surface is thus removable, which allows it to be easily replaced when damaged.

The optical surface cleaning unit comprises transducers 45 which are arranged in contact with and acoustically coupled with the optical surface 10. The transducers share the same piezoelectric layer. The cleaning unit further comprises a current generator 50 to electrically supply the transducers.

In the example illustrated in FIG. 9, the transducers are arranged on the face 250 of the optical surface 10 opposite the face to be cleaned 255. They are preferably configured to generate a Lamb wave which reaches the face to be cleaned.

Furthermore, the transducers delimit a region of optical interest 65 which is not superimposed with the transducers.

Preferably, part of the optical region of interest 65 is contained in the optical field Co of the device. In other words, the transducers are arranged outside the optical field of the device, so that they do not substantially interfere with the radiation passing through the optical region of interest and which is picked up by the sensor.

In order to reduce the size, as illustrated in figure 9, the transducers are arranged on the periphery of the optical surface. Thus, the area of the optical region of interest is maximized.

Of course, the invention is not limited to the embodiments of the invention presented by way of non-limiting illustration.

Claims

1. Device (5) comprising:

- a transparent optical surface (10),

- a unit (15) for cleaning the optical surface comprising a piezoelectric layer (20) and at least two wave transducers (45), each wave transducer comprising electrodes (40) of opposite polarity in contact with the layer piezoelectric and being acoustically coupled with the optical surface to generate at least one surface ultrasonic wave (Ws) or a Lamb wave (WL) propagating in the optical surface, the transducers also being arranged at the periphery of the optical surface.

2. Device according to claim 1, in which the wave transducer extends from an edge of the optical surface over a distance of less than 10%, or even less than 5% of the length of the optical surface.

3. Device according to any one of claims 1 and 2, the transducer extending from an edge (27) of the optical surface over a distance less than 30 mm, preferably less than 20 mm, preferably less at 10mm.

4. Device according to any one of the preceding claims, the piezoelectric layer forming at least one strip extending over one face of the optical surface.

5. Device according to any one of the preceding claims, the optical surface comprising a region of optical interest (65) not superimposed on the transducers and the piezoelectric layer forming a frame at least partially surrounding the region of optical interest.

6. Device according to any one of the preceding claims, the wave transducers being in contact with, for example glued to, the optical surface.

7. Device according to any one of the preceding claims, the optical surface comprising an acoustically conductive portion (80), preferably made of glass, the wave transducers being acoustically coupled to the acoustically conductive portion.

8. Device according to the preceding claim, the piezoelectric layer being arranged in contact with the acoustically conductive portion.

9. Device according to any one of claims 7 and 8, the optical surface comprising a stack comprising an acoustically insulating portion (75) and the acoustically conducting portion (80) stacked on top of each other.

10. Device according to the preceding claim, the acoustically conductive portion being removably mounted on the acoustically insulating portion.

11. Device according to any one of the preceding claims, the electrodes of each transducer being obtained by sputtering or printed, for example by inkjet printing.

12. Device according to the preceding claim, the electrodes of each transducer being printed on a foil, for example of a flexible thermoplastic material, and being applied by transfer of the foil onto the piezoelectric layer.

13. Device according to any one of the preceding claims, the thickness of the piezoelectric layer being less than or equal to 5*A, preferably less than or equal to 1.5*A, preferably less than or equal to A, or even less or equal to 0.5*Å, in particular for a frequency of the surface ultrasonic wave of between 0.1 MHz and 60 MHz.

14. Device according to any one of the preceding claims, the piezoelectric layer having a thickness of between 1 μm and 300 μm.

15. Device according to any one of the preceding claims, chosen from:

- a motorcyclist's helmet (120) comprising a cap (125) intended to protect the skull of a motorcyclist and the optical surface being a visor mounted on the cap so as to protect all or part of the face of the motorcyclist,

- a glazed element (180) of a building and the optical surface being a glazing (200), and

- a motor vehicle (160) and the optical surface is a windshield (165) of the vehicle,

- an automated motor vehicle and the optical surface covering an optical sensor (215) and/or an optical transmitter, for example a lidar, a camera, a camera, a radar, an infrared sensor or an ultrasonic rangefinder, and

- a component of a motor vehicle, in particular automated, for example chosen from a lighting headlight module, a system containing a set of different sensors also called "pod", at least one side window, a front window or a window rear and a driver assistance unit.