Electroacoustic Device

Abstract

An electroacoustic device (5) comprises: an ultrasonic transducer (15), the ultrasonic transducer (15) comprising a piezoelectric substrate (25) and a first electrode (30) and a second electrode (35) in contact with the piezoelectric substrate, and a carrier (10), the transducer being fixed on the carrier and acoustically coupled to the carrier, and the first electrode and the second electrode being at least partially sandwiched between the piezoelectric substrate and the carrier, the device being configured to generate an ultrasonic surface wave (W) when current passes through the first electrode and the second electrode, the ultrasonic surface wave (W) propagating in the carrier at a certain distance from the transducer.

Description

Technical Field

[0001] The invention relates to a device for generating ultrasonic surface waves propagating in a carrier and to a method for implementing the device to melt an object located on the carrier and / or to displace an object in a liquid state on the carrier. Background Art

[0002] In various fields, there is a need to overcome the effects associated with the accumulation of liquids on surfaces, and the effects associated with the solidification of such liquids when the ambient temperature and / or the temperature of the surface is below the solidification temperature of the liquid.

[0003] In order to remove the droplets that have accumulated on a surface, it is known to apply mechanical forces to the droplets, for example by means of windscreen wipers on the windscreen of a motor vehicle. However, windscreen wipers restrict the field of vision available to the driver. Furthermore, they also spread the fat-containing particles deposited on the surface of the windscreen. Furthermore, the blades of windscreen wipers must be replaced regularly.

[0004] Furthermore, modern motor vehicles often include one or more driver assistance systems that implement multiple sensors, such as optical sensors (e.g. LiDAR for evaluating the distance between the vehicle and an object) or probes (e.g. Pitot tube probes). Nowadays, mechanical forces cannot be easily applied to the droplets to clean the surface of such sensors due to the lack of space available for suitable mechanical devices, which could also damage the surface.

[0005] For example, in the field of motor vehicles, in winter conditions, it is necessary to defrost the mirrors of the rearview mirrors of the vehicle, the windshield or the rear window to ensure safe driving. A known defrosting technique is to blow hot air onto the surface of the windshield opposite to the surface on which the frost and / or ice layer is deposited. However, the defrosting time required for this technique is particularly long. In order to defrost the rear window, it is known to arrange metal wires in the rear window by mass or by volume, which follow a path formed by evenly spaced lines. The current circulation in the wire generates heat through the Joule effect, causing the frost and / or ice layer near the wire to melt into the form of a water film, which then evaporates. However, this wire limits the rear view that can be seen by the vehicle driver. In addition, the frost and / or ice layer usually includes particles that are still in contact with the carrier after the water film evaporates. It is then necessary to clean the rear window frequently, which proves to be tedious. In addition, the formation of frost and / or ice can also interfere with the operation of sensors embedded in the driving system.

[0006] Furthermore, when in use, the surfaces of such sensors may also be impacted by external elements (e.g. insects, dust particles, dirt) at speeds similar to the speed of the vehicle they are in. Therefore, cleaning devices for such surfaces must be robust enough to withstand such an environment. Summary of the invention

[0007] Therefore, a device is needed to solve these shortcomings.

[0008] According to a first aspect, the present invention provides an electroacoustic device, comprising:

[0009] - an ultrasonic transducer comprising a piezoelectric substrate and a first electrode and a second electrode in contact with the piezoelectric substrate, and

[0010] - carrier,

[0011] The transducer is fixed on the carrier and acoustically coupled to the carrier, and the first electrode and the second electrode are at least partially sandwiched between the piezoelectric substrate and the carrier,

[0012] The device is configured to generate ultrasonic surface waves when current passes through the first electrode and the second electrode, the ultrasonic surface waves propagating in the carrier at a distance from the transducer.

[0013] The device according to the invention is robust. Since the first and second electrodes are protected by the carrier and the piezoelectric substrate, degradation thereof is limited, for example when the transducer is placed in contact with external elements as described above.

[0014] Furthermore, as will emerge more clearly hereinafter, the device according to the invention can advantageously be implemented to clean surfaces covered by objects, such as liquids.

[0015] Preferably, the transducer is configured to generate a guided wave that is converted into an ultrasonic surface wave in a carrier at a distance from the transducer. The ultrasonic "guided" wave propagates in both the carrier and the transducer to the respective surfaces of the substrate and the carrier facing each other. In a variant described below in which the device comprises an intermediate layer between the carrier and the transducer, the guided wave may also propagate in the intermediate layer. The ultrasonic guided wave may in particular be a Stoneley wave.

[0016] Preferably, the first electrode and the second electrode are arranged on the piezoelectric substrate. Preferably, the first electrode and the second electrode are in contact with the piezoelectric substrate.

[0017] Preferably, the first electrode and the second electrode are in contact with the carrier or with an intermediate layer arranged on the carrier, preferably formed of glue. The generation of ultrasonic surface waves is thus promoted. The thickness of the intermediate layer is preferably less than the fundamental wavelength of the ultrasonic guided wave. In particular, the thickness of the intermediate layer can be less than one tenth of the fundamental wavelength of the guided wave to limit the transmission losses through the intermediate layer.

[0018] The device may be configured such that the fundamental frequency of the ultrasonic guided waves is between 0.1 MHz and 1000 MHz, preferably between 10 MHz and 100 MHz, for example equal to 40 MHz.

[0019] Preferably, the thickness of the piezoelectric substrate is greater than the fundamental wavelength of the ultrasonic guided wave. The ultrasonic guided wave is thus prevented from reaching the surface opposite to the surface coated with the first electrode and the second electrode. Advantageously, an additional member, such as a protective member described below, can be arranged on the opposite surface without the guided wave being able to reach the member.

[0020] A portion of each of the first electrode and the second electrode may protrude from the carrier. The portion of each of the first electrode and the second electrode protruding from the carrier may define a power connector. The power connector may be configured to be electrically connected to a generator.

[0021] Furthermore, according to a second aspect, the present invention provides an acoustic device, comprising:

[0022] - an ultrasonic transducer comprising a piezoelectric substrate and a first electrode and a second electrode in contact with the piezoelectric substrate, and

[0023] - carrier,

[0024] The transducer is fixed on the carrier and acoustically coupled to the carrier.

[0025] The transducer protrudes from the edge of the carrier, the first electrode and the second electrode are coated on the surface of the piezoelectric substrate opposite to the carrier and are arranged on a portion of the piezoelectric substrate that is not superposed on the carrier,

[0026] The apparatus is configured to generate ultrasonic surface waves propagating in the carrier at a distance from the transducer when current is passed through the first electrode and the second electrode.

[0027] The first and second electrodes can thus be protected from external elements by the piezoelectric substrate, which limits their degradation. Furthermore, since the electrodes are arranged to protrude from the edge of the substrate, the area of ​​the carrier coated by the transducer is reduced.

[0028] Furthermore, the specific arrangement of the first and second electrodes makes it possible to reduce the heating of the device during the generation of ultrasound waves. In particular, since the electrodes are not arranged on the carrier, heating of the carrier by conduction of the heat generated by the electrodes is limited.

[0029] Furthermore, in the variant in which the transducer is bonded to the carrier by means of a polymer adhesive, the risk of separation between the transducer and the carrier, which separation could result from excessive heating of the adhesive due to conversion of a portion of the ultrasonic energy absorbed by the adhesive, is reduced.

[0030] Preferably, the transducer is configured to generate an ultrasonic primary wave propagating in the substrate when current passes through the first electrode and the second electrode, and the ultrasonic primary wave is converted into an ultrasonic surface wave propagating in the carrier at a distance from the transducer.

[0031] The apparatus according to any aspect of the present invention may also have any of the following optional features.

[0032] The transducer can be fixed to the carrier in different ways. It can be bonded to the carrier, in particular by means of a polymer adhesive. The adhesive can be crosslinked by exposure to UV radiation. The adhesive is, for example, an epoxy resin. The transducer can be fixed by molecular adhesion or by means of a thin metal layer to ensure adhesion between the carrier and the substrate. This layer can also be made of a metal or an alloy with a low melting point, i.e. a melting point below 200° C., for example of an indium alloy. As a variant, the metal layer can be made of a metal or an alloy with a melting point above 200° C., for example of an aluminum alloy and / or a gold alloy.

[0033] An example of fixation by molecular adhesion is described in "Glass-on-LiNbO3 heterostructure formed via a two-step plasma activated low-temperature direct bonding method" by J. Xu et al., Applied Surface Science 459 (2018) 621–629, doi: 10.1016 / j.apsusc.2018.08.031. According to another variant, the transducer can be fixed to the carrier by a method comprising the steps of melting a portion of the substrate and / or a portion of the carrier, and then pressing the substrate and the carrier together, the corresponding melted portions of the carrier and the substrate contacting each other. According to another variant, the transducer can be fixed to the carrier by a method comprising depositing a bonding coating made of an alloy having a low melting point on a portion of the substrate and a portion of the carrier, respectively, at least partially melting the bonding coating, and then pressing the substrate and the carrier, and during pressing, the surfaces of the bonding coating opposite to the carrier and the substrate contacting each other. The bonding coating can be deposited by cathode sputtering or by an evaporation technique implemented in the field of thin film deposition. Preferably, the substrate is bonded to the carrier. The surface of the substrate opposite to the carrier is preferably bonded to the carrier via an intermediate layer formed by glue, which also couples the transducer acoustic wave to the carrier. Preferably, the thickness of the glue layer is less than the wavelength of the ultrasonic primary wave, so that the ultrasonic primary wave can be effectively transmitted from the transducer to the carrier, that is, by limiting the loss in the glue layer, the ultrasonic primary wave can be effectively transmitted from the transducer to the carrier.

[0034] The device according to any aspect of the present invention may have one of the following features.

[0035] The device may be configured such that the fundamental frequency of the ultrasonic surface waves is between 0.1 MHz and 1000 MHz, preferably between 10 MHz and 100 MHz, for example equal to 40 MHz.

[0036] The ultrasonic surface wave may be a Rayleigh wave or a Lamb wave. In particular, when the thickness of the carrier is greater than the wavelength of the ultrasonic surface wave, the ultrasonic surface wave may be a Rayleigh wave. Rayleigh waves are preferred because the largest proportion of the energy of the Rayleigh wave is concentrated on the surface of the carrier in which it propagates and can be transmitted to an object in contact with the carrier.

[0037] The device may be configured to provide an ultrasonic surface wave with an amplitude between 1 picometer and 500 nanometers. The amplitude may depend on the frequency of the fundamental wave. In particular, the higher the frequency, the lower the amplitude may be. The amplitude of the ultrasonic surface wave corresponds to the normal displacement of the surface of the carrier on which the ultrasonic surface wave propagates and may be measured by laser interferometry.

[0038] The carrier may be made of any material capable of propagating ultrasonic surface waves. The carrier may be selected so that the decay length of the surface waves in the carrier is greater than the area to be insonified.

[0039] The carrier may be self-supporting in that it can deform, in particular elastically, without breaking under its own weight.

[0040] The surface of the carrier on which the longitudinal surface wave propagates can be flat. The surface can also be curved, provided that the radius of curvature of the surface is greater than the wavelength of the ultrasonic surface wave.

[0041] The surface may be rough. Preferably, the roughness is smaller than the fundamental wavelength of the ultrasonic surface wave to prevent the roughness from significantly affecting the propagation of the ultrasonic surface wave.

[0042] The carrier may in particular be in the form of a flat plate or a curved plate. The thickness of the carrier may be less than 0.01 m. The length of the carrier may be greater than 1 mm, even greater than 1 cm, even greater than 1 m.

[0043] The surface area of ​​the plate can be between 0.01m 2 and 10m 2 between.

[0044] The "thickness of the carrier" is considered to be the smallest dimension of the carrier measured at right angles to the surface on which the ultrasound waves propagate.

[0045] The carrier may be optically transparent, in particular optically transparent to visible light, or ultraviolet or infrared radiation.The method is therefore particularly suitable for applications seeking to improve the visual comfort of a user viewing his or her surroundings through the carrier.

[0046] The carrier may be made of a material selected from the group consisting of piezoelectric materials, polymers (in particular thermoplastics, especially polycarbonate), glass, metals and ceramics.

[0047] Preferably, the carrier is made of a material other than a piezoelectric material.

[0048] Preferably, the carrier is selected from the group consisting of:

[0049] a motor vehicle surface, for example selected from the windshield of the vehicle, the glass of the rearview mirror, or

[0050] - the visor of the helmet,

[0051] - Windows of buildings,

[0052] a sensor, such as an optical sensor, a thermal sensor, an acoustic sensor, or a pressure sensor or a velocity sensor, in particular a probe, such as a Pitot tube probe,

[0053] - surfaces of optical devices, for example selected from camera lenses, eyeglass lenses, and

[0054] - Protective element for this sensor.

[0055] Other types of carriers are conceivable. In particular, the carrier may be a lab-on-a-chip substrate, in particular a substrate for microfluidic applications.

[0056] The carrier may be a structural element of the aircraft, such as a wing, a fuselage or a tail.

[0057] The carrier is preferably thin. The ratio of the carrier length to the carrier thickness may be greater than 10, even greater than 100, even greater than 1000.

[0058] The carrier may also be selected from elements of heat exchangers, plumbing, and elements of ventilation systems.Such media generally have surfaces that are difficult to access in order to remove droplets that have deposited thereon, for example by condensation, and which may solidify.

[0059] The carrier can be a food storage element, such as the inner wall of a refrigerator, or a wall exposed to condensation of a solidifiable liquid. For example, in a refrigerator, condensation and solidification of water droplets on the wall increases the heat exchange between the wall and the refrigerator cold air volume, thereby reducing its efficiency.

[0060] The ratio of the area of ​​the carrier covered by the transducer to the area of ​​the surface of the carrier to which the transducer is fixed may be less than 15%.

[0061] The transducer is preferably thin. The ratio of the transducer length to the transducer thickness may be greater than 10, even greater than 100, even greater than 1000.

[0062] The transducer can be in the form of a flat plate or a curved plate.

[0063] The thickness of the transducer may be between 10 picometers and 1 micrometer.The transducer may have a length and / or width preferably between 1 millimeter and 20 centimeters.

[0064] Preferably, the first electrode and the second electrode form a first comb-shaped member and a second comb-shaped member of an interdigitated type.

[0065] The first comb and the second comb may preferably include a base from which a row of fingers extend, the fingers preferably being parallel to each other. The width of the fingers may be between the fundamental wavelength of the ultrasound divided by 8 and the fundamental wavelength of the ultrasound divided by 2. The width of the fingers partially determines the fundamental frequency of the ultrasonic surface wave. In addition, a smaller finger width increases the resistance of the transducer, which can be reflected by heating that helps to melt an object in contact with the carrier or keep the object in a liquid state.

[0066] Furthermore, a spacing between two consecutive adjacent fingers of each of a row of the first comb-shaped element and the second comb-shaped element may be between the fundamental wavelength of the ultrasonic wave divided by 8 and the fundamental wavelength of the ultrasonic wave divided by 2.

[0067] The number of interdigitated fingers can be increased to improve the quality factor of the transducer.

[0068] Each comb preferably comprises 2 to 50 fingers.

[0069] The substrate may be a thin layer deposited on a carrier, for example by chemical vapor deposition or by physical vapor deposition. As a variant, the substrate may be self-supporting, that is to say rigid enough not to bend under its own weight. A self-supporting substrate may be fixed (for example bonded) to a carrier.

[0070] The piezoelectric material may be selected from the group consisting of lithium niobate, aluminum nitride, lead zirconate titanate, zinc oxide, and mixtures thereof. The piezoelectric material may be opaque to visible light.

[0071] In a variant, the carrier is formed of a piezoelectric material and the transducer comprises the carrier.The first comb element and the second comb element are preferably arranged in contact with the carrier.

[0072] In another variant, the carrier is made of a material other than a piezoelectric material and the electrodes are arranged on an intermediate substrate.

[0073] The first electrode and the second electrode may be deposited on the carrier and / or the substrate by photolithography.

[0074] The object may be located on the surface of the carrier at a distance from the transducer.

[0075] The maximum distance for the part of the object farthest from the transducer may be 1 meter.

[0076] The temperature of the carrier may be below 0°C, even below -10°C, and the object may be aqueous.

[0077] The object may be in contact with the surface of the carrier to which the transducer is fixed, or on a surface opposite to the surface of the carrier to which the transducer is fixed.An object may be in contact with the surface of the carrier to which the transducer is fixed, and another object may be in contact with the surface where the above objects are located.

[0078] The object may include a portion in a solid state and a portion in a liquid state. For example, the object may be water, and may be formed of a frost, ice or snow portion, and a liquid portion in contact with the frost, ice or snow portion, respectively.

[0079] The object in the liquid state can take the form of at least one droplet or at least one film. "Film" is understood to mean a thin film formed on a support. The film can be continuous or discontinuous.

[0080] The object may be water-containing. In particular, the object may be rain or dew. Rain and / or dew may contain particles. Dew forms sludge on the carrier surface. It is produced by condensation of water in the form of water vapor contained in the air on the carrier under certain pressure and temperature conditions. The object may be deposited by condensation before solidification on the carrier.

[0081] The object in the solid state may be selected from frost, ice and snow. The object in the liquid state may be a flake or at least one droplet, such as mist. "Frost" is formed by water droplets which have solidified before being deposited on the carrier. "Ice" is formed by water droplets condensing on the carrier and then solidifying on the carrier.

[0082] Furthermore, in order to protect the transducer, in particular to protect the transducer from external elements as described above, the device preferably comprises a protective member superposed on the piezoelectric substrate.

[0083] Preferably, the transducer is housed in a chamber defined by the protective member and the carrier.

[0084] In particular, in the device according to the first aspect of the present invention, at least one, or even all, of the surfaces of the substrate that are not coated by the first electrode and the second electrode may be in contact with the protective member.

[0085] The protection member is preferably at a distance from the carrier so as not to interfere with the propagation of the ultrasonic surface waves.

[0086] The protective member may be in contact with a surface of the transducer that is not coated by the first and second electrodes. The protective member then does not interact with the guided wave or the primary wave. Preferably, the protective member is in contact with a surface of the transducer that is opposite to the surface on which the first and second electrodes are deposited. In particular, the protective member may be fixed (e.g. bonded) to the transducer. The manufacture of the device is thus simplified.

[0087] Furthermore, the device may be electrically connected to a generator to power the transducer.The generator may be configured to deliver a power supply preferably between 1 milliwatt and 500 watts.

[0088] Furthermore, the present invention relates to a method for producing a device according to the invention comprising the following consecutive steps:

[0089] a) forming a first electrode and a second electrode on a surface of a piezoelectric substrate to obtain a wave transducer,

[0090] b) Fixing the wave transducer on a carrier to obtain the device.

[0091] Preferably, the carrier and / or the wave transducer are coated with a layer of glue and the appropriately coated carrier and / or wave transducer are then assembled.

[0092] The present invention also relates to a first method, comprising synthesizing ultrasonic surface waves by means of an electroacoustic device according to the present invention, wherein the ultrasonic surface waves propagate in a carrier to a liquid object, the liquid object being located on the surface of the carrier and at a certain distance from a transducer, the energy of the ultrasonic waves being sufficient to cause displacement of the object on the carrier.

[0093] Objects can be displaced in the direction of propagation of the ultrasonic surface waves.

[0094] The present invention also relates to a second method comprising:

[0095] - providing an electroacoustic device according to the invention, and

[0096] - supplying power to a wave transducer to synthesize an ultrasonic surface wave, which propagates in the carrier to an object located on the surface of the carrier and at a distance from the transducer, at least part of the supply power being converted by the transducer into the form of heat,

[0097] The electrical energy supplied to the transducer is sufficient to generate the energy of the heat or ultrasonic surface waves to cause:

[0098] - melt the object while it is in a solid state, and / or

[0099] -Keep an object in liquid state when the temperature of the carrier is below the solidification temperature of the object.

[0100] Additionally, the energy of the ultrasonic waves may be sufficient to cause melting of objects or displacement of objects that remain liquid on the surface.

[0101] The present invention also relates to a third method, comprising:

[0102] - Provided is a device comprising:

[0103] An ultrasonic transducer and a carrier, the ultrasonic transducer comprising a piezoelectric substrate, a first electrode and a second electrode in contact with the piezoelectric substrate, the transducer being fixed on the carrier and acoustically coupled to the carrier, the first electrode and the second electrode being at least partially sandwiched between the piezoelectric substrate and the carrier, the device being configured to generate an ultrasonic surface wave when current passes through the first electrode and the second electrode, the ultrasonic surface wave propagating in the carrier at a certain distance from the transducer, the transducer being configured to generate a guided wave, the guided wave being converted into an ultrasonic surface wave in the carrier at a certain distance from the transducer,

[0104] - synthesizing an ultrasonic surface wave by means of the device, which propagates in the carrier to a liquid object, which is located on the surface of the carrier and at a certain distance from the transducer, the energy of the ultrasonic wave being sufficient to cause displacement of the object on the carrier,

[0105] The object is a sheet or droplet with a diameter less than or equal to 5 mm.

[0106] The "diameter" of an object is understood to mean the diameter of the smallest circumscribed sphere of the object. The diameter of the object is determined before the ultrasound waves are synthesized.

[0107] The first method and / or the second method and / or the third method may include the following features.

[0108] An object may have any of the above characteristics.

[0109] The object may be a sheet. The sheet may be on the carrier at a height greater than or equal to 2 cm. 2 , or even greater than or equal to 5cm 2 , even greater than or equal to 10cm 2 , even greater than or equal to 100cm 2 , even greater than or equal to 500cm 2 The thickness of the flakes may be between 10 μm and 10 mm, or even between 50 μm and 5 mm.

[0110] The object may be a droplet having a diameter less than or equal to 5 mm. The droplet may have a diameter less than or equal to 1 mm, or even less than or equal to 0.1 mm. The droplet may have a diameter between 2 mm and 5 mm. The droplet may have a diameter between 0.1 mm and 2 mm.

[0111] Objects can be displaced in the direction of propagation of the ultrasonic surface waves.

[0112] The object can be displaced along the surface of the carrier on which it is located.

[0113] Furthermore, the temperature of the carrier may be below 0°C, and the object is preferably aqueous.

[0114] Finally, the invention relates to the use of the device according to the invention for cleaning and / or demisting and / or defrosting surfaces of carrier bodies, in particular motor vehicle surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0115] The invention will be better understood by reading the following detailed description, its non-limiting exemplary embodiments, and by studying the accompanying drawings, in which:

[0116] [ Figure 1 ] Figure 1 A cross-sectional view schematically showing an example of an electroacoustic device according to the present invention,

[0117] [ Figure 2 ] Figure 2 Represented in perspective Figure 1 The wave transducer of the electroacoustic device shown,

[0118] [ Figure 3 ] Figure 3 represents another example of the electroacoustic device according to the present invention, and

[0119] [ Figure 4 ] Figure 4 Still another example of the electroacoustic device according to the present invention is shown.

[0120] For the sake of clarity, the constituent elements of the drawings are not shown to scale. DETAILED DESCRIPTION

[0121] Figure 1 A first example of an electro-acoustic device 5 according to the first aspect of the present invention is shown.

[0122] The electroacoustic device 5 comprises a carrier 10, on which a transducer 15 is fixed by means of an adhesive layer 20. The adhesive layer couples the carrier acoustic waves to the transducer.

[0123] The transducer comprises a substrate 25 and first and second electrodes 30, 35 which are coated on a surface 40 of the substrate.

[0124] The substrate is made of a piezoelectric material, for example of lithium niobate with a 128° Y-cut. The substrate is in the form of a plate whose thickness e is greater than the wavelength of the waves generated by the transducer. The waves generated by the transducer are therefore transmitted directly in the carrier and do not reach the surface 45 of the substrate opposite to the surface on which the carrier is mounted.

[0125] The first electrode and the second electrode are sandwiched between the carrier and the substrate and are connected to a voltage generator 50 for supplying them with electricity. The first electrode and the second electrode are thus arranged facing the carrier and are protected by the carrier, the substrate and the glue layer.

[0126] The carrier in the example shown is in the form of a plate and has a top surface 55 in contact with the external environment 60. In the example shown, the top surface 55 is covered by an object 65 in the form of a water film. The object 65 can be a droplet or a flake. For example, the flake is formed by the accumulation of droplets, such as rainwater, on the carrier.

[0127] To manufacture the device, the first electrode and the second electrode can be formed by evaporation or sputtering and shaped by photolithography. It can then be made of a combination of chromium, aluminum, or a bonding coating (e.g., titanium) and a conductive layer (e.g., gold). The appropriately covered substrate can then be bonded to the carrier. In order to facilitate the bonding operation, a self-supporting carrier is preferred.

[0128] like Figure 2 As shown, the first electrode 30 and the second electrode 35 form a first comb 70 and a second comb 75, respectively. Each comb comprises a base 80, 85 and a row of fingers 90, 95 extending parallel to each other from the base. The first comb and the second comb are interdigitated.

[0129] The width l of each finger of the first comb element and the second comb element is equal to the fundamental wavelength of the ultrasonic surface wave divided by 4, and the spacing S between two consecutive fingers of one comb element is equal to the fundamental wavelength of the ultrasonic surface wave divided by 4.

[0130] The spacing between the fingers determines the resonant frequency of the transducer which can be readily determined by one skilled in the art. An alternating voltage is applied by a generator 50 and may be amplified so that the transducer generates ultrasonic surface waves.

[0131] The alternating current supply of the first electrode and the second electrode induces a mechanical response of the piezoelectric material, which results in the generation of a surface guided wave G which propagates in a propagation direction P in the carrier, in particular towards an object located on the carrier.

[0132] For a transducer configured to generate waves of a predetermined fundamental frequency, it is easy for a person skilled in the art to determine the energy generated by the transducer sufficient to displace or melt an object and / or maintain it in a liquid state. In particular, a person skilled in the art can relate the fundamental frequency of the ultrasonic guided wave to the frequency of the electrical signal used to generate the wave. He or she can then vary the amplitude of the electrical signal in order to determine sufficient electrical energy to be provided to the transducer.

[0133] When the transducer is powered by a voltage generator, the transducer generates ultrasonic waves. Since the first electrode and the second electrode are sandwiched between the carrier and the substrate, the wave G generated by the transducer is guided and propagated at the interface between the carrier and the substrate, which is defined by the surface of the substrate coated by the electrode and the surface of the carrier facing the electrode. When the guided wave reaches the lateral end 98 of the substrate along its propagation direction, the guided wave propagates in the carrier in the form of an ultrasonic surface wave W propagating on the surface of the carrier. The conversion of the guided wave to the surface wave is caused by the absence of an interface between the two solids in the part of the carrier not covered by the transducer. Then, the surface wave interacts with the object covering the carrier. For liquid objects, a transducer with a surface wave having a synthetic fundamental frequency between 0.1 MHz and 1000 MHz, preferably between 10 MHz and 100 MHz, for example equal to 40 MHz, is very suitable for ensuring the displacement of the water film. In the variant in which the water film is in the form of ice or frost, the transducer is also very suitable for causing the melting of the water film by inputting the energy of the ultrasonic surface wave and by transferring the heat generated by it, especially by the resistance heating of the electrode.

[0134] Figure 3 The device shown is Figure 1 The device shown is different in that it also includes a protective member 100 superimposed on the carrier and the transducer. The protective member 100 defines a chamber 105 for accommodating the transducer together with the carrier. The transducer, more specifically the substrate, is therefore protected from external factors (such as precipitation and dust). The protective member is fixed on the surface 45 of the substrate that is not coated by the first electrode and the second electrode. Since the thickness of the substrate is greater than the wavelength of the guided wave, the protective member does not interact with the guided wave. The protective member can be made of an impact-resistant material (such as metal or thermoplastic). In the example shown, the protective member is at a distance from the carrier. Therefore, the protective member does not hinder the propagation of ultrasonic surface waves in the carrier.

[0135] at last, Figure 4 The device shown is Figure 1 The device shown differs in that it comprises a portion protruding from the edge of the carrier and the first and second electrodes are arranged on a portion 108 of the piezoelectric substrate not superposed on the carrier. Since the first and second electrodes are at a distance from the carrier, it is easy to electrically connect them to the voltage generator.

[0136] When the substrate is powered, the device generates a primary wave Q, which propagates on the surface of the substrate and then propagates at the interface 110 between the substrate and the carrier. When the primary wave reaches the lateral end 98 of the substrate along its propagation direction, it propagates in the carrier in the form of an ultrasonic surface wave propagating on the surface of the carrier. Figure 1 In the example of , ultrasonic surface waves can cause displacement of liquid on the carrier.

[0137] Of course, the invention is not limited to the embodiments of the method described and in particular not to the examples presented in this description.

Claims

1. An electroacoustic device (5), comprising: - an ultrasonic transducer (15), the ultrasonic transducer (15) comprising a piezoelectric substrate (25) and a first electrode (30) and a second electrode (35) in contact with the piezoelectric substrate, and - a carrier (10), The transducer is fixed on the carrier and acoustically coupled to the carrier, and the first electrode and the second electrode are at least partially sandwiched between the piezoelectric substrate and the carrier, The electroacoustic device is configured to generate an ultrasonic surface wave (W) when an electric current passes through the first electrode and the second electrode, the ultrasonic surface wave (W) propagating in the carrier at a distance from the transducer, The transducer is configured to generate guided waves, the piezoelectric substrate includes a portion in contact with the first electrode and the second electrode and a segment located between the portion and an end of the piezoelectric substrate, in which the guided waves propagate in both the carrier and the transducer to corresponding surfaces of the piezoelectric substrate and the carrier facing each other, and when the guided waves reach the end of the piezoelectric substrate along their propagation direction, the guided waves are converted into the ultrasonic surface waves in the carrier at a certain distance from the transducer, and the electroacoustic device is configured so that the fundamental frequency of the ultrasonic guided waves is between 10 MHz and 1000 MHz. 2 . The electroacoustic device according to claim 1 , wherein the first electrode and the second electrode are in contact with the carrier or with an intermediate layer disposed on the carrier.

3. The electroacoustic device as claimed in claim 1, wherein the guided waves generated by the transducer are directly transmitted in the carrier (10) and do not reach the surface (45) of the piezoelectric substrate (25) opposite to the surface on which the carrier (10) is mounted, and the thickness (e) of the piezoelectric substrate is greater than the fundamental wavelength of the ultrasonic guided waves. 4 . The electroacoustic device according to claim 1 , wherein a portion of each of the first electrode and the second electrode protrudes from the carrier.

5. An electroacoustic device (5), comprising: - an ultrasonic transducer (15), the ultrasonic transducer (15) comprising a piezoelectric substrate (25) and a first electrode (30) and a second electrode (35) in contact with the piezoelectric substrate, and - a carrier (10), The transducer is fixed on the carrier and acoustically coupled to the carrier. The transducer protrudes from the edge of the carrier, the first electrode and the second electrode are coated on the surface of the piezoelectric substrate opposite to the carrier and are arranged on a portion of the piezoelectric substrate that protrudes from the edge of the carrier and does not overlap the carrier, The electroacoustic device is configured to generate an ultrasonic surface wave propagating in the carrier at a certain distance from the transducer when current passes through the first electrode and the second electrode, wherein the transducer is configured to generate a guided wave, the piezoelectric substrate includes a portion in contact with the first electrode and the second electrode and a section located between the portion and an end of the piezoelectric substrate, in which the guided wave propagates in both the carrier and the transducer to respective surfaces of the piezoelectric substrate and the carrier facing each other, and when the guided wave reaches the end of the piezoelectric substrate along its propagation direction, the guided wave is converted into the ultrasonic surface wave in the carrier at a certain distance from the transducer.

6. The electroacoustic device according to any one of claims 1 to 5, wherein the substrate is bonded to the carrier.

7. The electroacoustic device according to any one of claims 1 to 5, comprising a protection member (100) stacked on the piezoelectric substrate.

8. The electroacoustic device according to claim 7, the transducer being accommodated in a chamber (105) defined by the protective member and the carrier.

9. The electroacoustic device according to any one of claims 1 to 5, wherein the carrier is selected from the group consisting of: - surfaces of motor vehicles, - the visor of the helmet, - Windows of buildings, -sensor, - the surface of the optical device, -Protective element for the sensor.

10. A method for displacing an object on a carrier using an ultrasonic transducer, comprising: - Provided is a device, the device comprising: An ultrasonic transducer (15) and a carrier (10), the ultrasonic transducer (15) comprising a piezoelectric substrate (25) and a first electrode (30) and a second electrode (35) in contact with the piezoelectric substrate, the transducer being fixed on the carrier and acoustically coupled to the carrier, the first electrode and the second electrode being at least partially sandwiched between the piezoelectric substrate and the carrier, the device being configured to generate an ultrasonic surface wave (W) when a current passes through the first electrode and the second electrode, the ultrasonic surface wave (W) propagating in the carrier at a certain distance from the transducer, the transducer being configured to generate a guided wave, the piezoelectric substrate comprising a portion in contact with the first electrode and the second electrode and a section between the portion and an end of the piezoelectric substrate, in which the guided wave propagates in both the carrier and the transducer to respective surfaces of the piezoelectric substrate and the carrier facing each other, and when the guided wave reaches the end of the piezoelectric substrate along its propagation direction, the guided wave is converted into the ultrasonic surface wave in the carrier at a certain distance from the transducer, - synthesizing the ultrasonic surface wave (W) by means of the device, the ultrasonic surface wave (W) propagating in the carrier (10) to a liquid object (65), the liquid object (65) being located on the surface of the carrier and at a certain distance from the transducer, the energy of the ultrasonic surface wave being sufficient to cause displacement of the object on the carrier, The object is a sheet or droplet with a diameter less than or equal to 5 mm. The method according to claim 10 , wherein the diameter of the droplets is less than or equal to 1 mm.

12. The method of claim 11, wherein the diameter of the droplets is less than or equal to 0.1 mm.

13. A method of using an electroacoustic device, comprising: An ultrasonic surface wave (W) is synthesized by an electroacoustic device as described in any one of claims 1 to 5, and the ultrasonic surface wave (W) propagates in the carrier (10) to a liquid object (65), wherein the liquid object (65) is located on the surface of the carrier and is at a certain distance from the transducer, and the energy of the ultrasonic surface wave is sufficient to cause displacement of the object on the carrier.

14. The method according to claim 13, wherein the object is a sheet or a droplet with a diameter less than or equal to 5 mm. The method of claim 14 , wherein the diameter of the droplets is less than or equal to 1 mm. The method of claim 15 , wherein the diameter of the droplets is less than or equal to 0.1 mm.

17. A method of using an electroacoustic device, comprising: - providing an electroacoustic device (5) as claimed in any one of claims 1 to 5, and - supplying power to the ultrasonic transducer to synthesize an ultrasonic surface wave (W), the ultrasonic surface wave (W) propagating in the carrier (10) to an object (65), the object (65) being located on the surface of the carrier and at a distance from the transducer, at least part of the supply power being converted by the transducer into the form of heat, The electrical energy powering the transducer is sufficient to generate the heat and the energy of the ultrasonic surface waves to cause: - melting the object while it is in a solid state, and / or - Maintaining the object in liquid state when the temperature of the carrier is below the solidification temperature of the object.

18. The method of claim 17, wherein the energy of the ultrasonic surface waves is sufficient to cause a melted object or a displacement of the object held in a liquid state on the surface of the carrier.

19. The method of claim 10, wherein the object comprises water.

20. The method of claim 10, wherein the fundamental frequency of the guided wave and / or the fundamental frequency of the surface wave is between 0.1 MHz and 1000 MHz.

21. Use of the electroacoustic device according to any one of claims 1 to 5 for cleaning the surface of a carrier and / or for demisting the surface of a carrier and / or for deicing the surface of a carrier.

22. An electroacoustic device (5), comprising: - an ultrasonic transducer (15), the ultrasonic transducer (15) comprising a piezoelectric substrate (25) and a first electrode (30) and a second electrode (35) in contact with the piezoelectric substrate, and - a carrier (10), The transducer is fixed on the carrier and acoustically coupled to the carrier, and the first electrode and the second electrode are at least partially sandwiched between the piezoelectric substrate and the carrier, The electroacoustic device is configured to generate an ultrasonic surface wave (W) when an electric current passes through the first electrode and the second electrode, the ultrasonic surface wave (W) propagating in the carrier at a distance from the transducer, The transducer is configured to generate a guided wave which is converted into the ultrasonic surface wave in the carrier at a distance from the transducer, the electroacoustic device is configured such that the fundamental frequency of the ultrasonic guided wave is between 10 MHz and 1000 MHz, The wave generated by the transducer is directly transmitted in the carrier (10) and does not reach the surface (45) of the piezoelectric substrate (25) opposite to the surface on which the carrier (10) is mounted, and the thickness (e) of the piezoelectric substrate is greater than the fundamental wavelength of the ultrasonic guided wave.

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