Method for Melting a Body by Means of an Ultrasonic Wave

Abstract

Method comprising: supplying electricity to at least one wave transducer (25) for synthesising an ultrasonic surface wave propagating in a medium (10) to a body (15) arranged on one side of the medium, at least one portion of the electrical supply energy being converted into heat by the transducer, the electrical energy supplied to the transducer being sufficient for the heat and the energy of the ultrasonic surface wave to cause: —the body to melt when the body is in the solid state, and/or—the body to be maintained in the liquid state when the temperature of the medium is below the solidification temperature of the body.

Claims

1.-16. (canceled)

17. A method of heating a body disposed on a support using a wave transducer, the method comprising: providing electrical power to the wave transducer to generate ultrasonic surface waves that propagate through the support; and heating the body using the ultrasonic surface waves, such that the body is converted from a solid state to a liquid state, and/or such that the body is maintained in the liquid state when the support is at a first temperature that is lower than a melting temperature of the body.

18. The method as claimed in claim 17, wherein when in the liquid state, the body comprises a droplet or a film.

19. The method of claim 17, further comprising displacing the body in the liquid state on the support using the ultrasonic surface waves.

20. The method of claim 17, wherein the body is aqueous.

21. The method of claim 17, wherein: in the solid state, the body comprises frost, ice, and/or snow; and in the liquid state, the body comprises liquid water and/or mud.

22. The method of claim 17, wherein the first temperature is a temperature of 0° C. of less.

23. The method of claim 17, wherein a fundamental frequency of the ultrasonic waves is between 0.1 MHz and 1000 MHz.

24. The method of claim 17, wherein a fundamental frequency of the ultrasonic waves is between 10 MHz and 100 MHz.

25. The method of claim 17, wherein the support is transparent or translucent.

26. The method of claim 17, wherein the support comprises a material chosen from piezoelectric materials, polymers, glasses, metals, or ceramics.

27. The method of claim 17, wherein the support comprises: a motor vehicle surface; a visor of a headset; a window of a building; a sensor; a lens of an optical device; or a protection element of an optical device.

28. The method of claim 17, wherein the transducer directly contacts the support or is connected to the support by an intermediate layer.

29. The method of claim 17, wherein the transducer comprises interdigitated electrodes disposed on the support.

30. The method of claim 29, wherein the transducer comprises a piezoelectric material disposed between the electrodes and the support.

31. The method of claim 30, wherein the piezoelectric material comprises lithium niobite, aluminum nitride, lead zirconate titanate, zinc oxide, a combination thereof.

32. The method of claim 17, wherein the providing electrical power to the wave transducer further comprises using the transducer to resistively heat the support and/or the body.

33. The method of claim 17, wherein the providing electrical power to the wave transducer further comprises: generating an ultrasonic guided wave that is propagated between the support and the transducer; and transforming the ultrasonic guided wave into a surface ultrasonic wave in a zone of the support disposed at a distance from the transducer.

34. A method of clearing a support using a wave transducer disposed on the support, the method comprising: providing electrical power to the wave transducer to generate ultrasonic waves that propagate through the support and to resistively heat the support; heating ice disposed on the support using the ultrasonic waves, such that the ice is converted into water droplets; and displacing the water droplets from the support using the ultrasonic waves.

35. The method of claim 35, wherein: the wave transducer comprises interdigitated electrodes disposed directly on the support; the support comprises a piezoelectric material; the providing electrical power to the wave transducer comprises providing power to the interdigitated electrodes, such that the piezoelectric material generates the ultrasonic waves; and the ultrasonic waves comprise Rayleigh waves.

36. The method of claim 35, wherein: the wave transducer comprises interdigitated electrodes disposed on a piezoelectric layer; the providing electrical power to the wave transducer comprises providing power to the interdigitated electrodes, such that the piezoelectric layer generates the ultrasonic waves; and the ultrasonic waves comprise Rayleigh waves.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The invention will be able to be better understood on reading the following detailed description, of nonlimiting exemplary implementations thereof, and on studying the attached drawing, in which:

[0076] FIG. 1 schematically represents, by a perspective view, a device for implementing the method according to a first mode of implementation,

[0077] FIG. 2 is a cross-section of the device illustrated in FIG. 1,

[0078] FIG. 3 schematically represents a device for implementing the method according to the invention according to a second mode of implementation,

[0079] FIG. 4 represents, schematically and by a cross-sectional view, a device for implementing the method according to the invention according to a third mode of implementation,

[0080] FIG. 5 represents, schematically, by a cross-section, a device for implementing the method according to the invention according to a fourth mode of implementation,

[0081] FIGS. 6 a) to c) are photographs illustrating the defrosting of a glass support covered by a frost, by means of the method according to the invention, and

[0082] FIGS. 7 a) to c) are photographs illustrating the defrosting of a glass support covered with ice, by means of the method according to the invention.

[0083] The constituent elements of the drawing are not represented to scale in the interests of clarity.

DETAILED DESCRIPTION

[0084] FIGS. 1 and 2 illustrate a device 5 for implementing the method according to the invention.

[0085] The device comprises a support 10 capable of propagating an ultrasonic surface wave, a body 15 disposed on a face 20 of the support and a wave transducer 25 for generating the surface wave, disposed on the face of the support on which the body rests.

[0086] The support is, for example, transparent to visible light. It can be made of glass.

[0087] The transducer comprises a substrate 30 on which the first 35 and second 40 electrodes are disposed. The substrate is, for example, made of 128° Y cut lithium niobate.

[0088] The substrate is formed by a thin layer deposited on the support, the thickness of which is less than the fundamental wavelength of the wave generated by the transducer. Thus, the wave generated by the transducer is transmitted directly in the support.

[0089] The electrodes are formed by an evaporation or sputtering method and formed by photolithography. They can be made of chromium, or aluminum or of a combination of an adhesion layer such as titanium and a conductive layer such as gold.

[0090] The first and second electrodes form first 45 and second 50 combs. Each comb comprises a base 55, 60 and a row of fingers 65, 70, extending parallel to one another from the base. The first and second combs are interdigital.

[0091] Each of the fingers of the first comb, respectively of the second comb, has a width 1 equal to the fundamental wavelength of the ultrasonic surface wave divided by 4 and the spacing S between two consecutive fingers of a comb is equal to the fundamental wavelength of the ultrasonic surface wave divided by 4.

[0092] The spacing between the fingers determines the resonance frequency of the transducer that the person skilled in the art can easily determine. An alternating voltage is applied by a generator 80 and can be amplified, such that the transducer generates an ultrasonic surface wave.

[0093] The alternating electrical powering of the first and second electrodes induces a mechanical response from the piezoelectric material, which results in the generation of an ultrasonic surface wave W which is propagated in the support according to a direction of propagation P, notably toward the body disposed on the support.

[0094] For a transducer configured to generate a wave of predetermined fundamental frequency, the determination of the energy generated by the transducer that is sufficient to melt the body and/or maintain it in the liquid state is easy for the person skilled in the art. Notably, the person skilled in the art knows how to link the fundamental frequency of the ultrasonic surface wave to the frequency of the electrical signal to generate the wave. He or she then knows how to vary the amplitude of the electrical signal so as to determine the adequate electrical energy to be supplied to the transducer.

[0095] The method according to the invention implements several physical phenomena which induce the melting of the body or the maintaining of the body in the liquid state when the temperature of the support is lower than the temperature of solidification of the body. The ultrasonic wave which is propagated in the support is absorbed and dissipated by the body, which is accompanied by an increase in the temperature of the body by dissipation of a portion of the energy of the ultrasonic wave transmitted to the body. Furthermore, the wave transducer can heat up by Joule's effect under the effect of the passage of the electrical current to generate the ultrasonic wave, and contributes to the increase in temperature of the body. Finally, the ultrasonic surface wave can displace the body in the liquid state, notably in the direction of propagation of the wave. Thus, the body in the liquid state can enter into contact with another portion of the body which is in the solid state and contribute to the heating up, even drive the melting, of this other portion.

[0096] The body can be in the solid state or in the liquid state. In particular, a part of the body can be in the solid state and a part of the body can be in the liquid state. For example, when the body is rainwater and the temperature of the support is lower than the temperature of solidification of the water, the drops of rain that have reached the support can be in the solid state or in the liquid state, depending on the time that has elapsed since they came into contact with the support.

[0097] The device 5 of FIG. 3 differs from that of FIG. 1 in that the support 10 is a piezoelectric material and in that the device does not include an intermediate substrate. The first 45 and second 50 combs are directly in contact with the support.

[0098] The device of FIG. 4 differs from the device of FIG. 1 by several aspects. The transducer comprises a substrate 30 and the first 35 and second 40 electrodes are sandwiched between the support 10 and the substrate 30. Moreover, the transducer is glued onto the substrate. When an electric current passes through the first and second electrodes, the transducer generates an ultrasonic guided wave G, which is propagated between the support and the substrate. When the guided wave reaches the end 90 of the substrate along its direction of propagation, it is transformed into an ultrasonic surface wave W which is propagated in the portion 100 of the support separated from the substrate, substantially according to the same direction of propagation P as the guided wave. The transformation of the guided wave into surface wave results from the absence of interface between two solids in the portion 100 of the support.

[0099] The mode of implementation of the method by means of the device illustrated in FIG. 4 offers the advantage of protecting the first and second electrodes. For example, the body, when it is in the liquid state, cannot flow over the electrodes and oxidize them. Moreover, optionally, the device illustrated in FIG. 4 can comprise a protection member 105 which defines, with the support, a housing 110 for the transducer. For example, when the device 5 is mobile, damage to the transducer by objects striking the device is avoided.

[0100] The transducer illustrated in FIG. 5 comprises a support made of non-piezoelectric material and a contact ultrasonic transducer 112 disposed in contact with the support. To optimize the propagation of the wave from the transducer to the support, a coupling material, for example a gel or a glue, can be disposed between the acoustic transducer and the support. In a first variant that is not illustrated, notably when the support has a thickness less than the ultrasonic surface wavelength and/or the latter is a Lamb wave, the contact ultrasonic transducer is preferably disposed at right angles with the surface on which the ultrasonic wave is propagated. A second transducer of the same type can be disposed on the face of the support opposite that on which the ultrasonic wave is propagated. In a second variant, as is illustrated in FIG. 5, notably when the support has a thickness greater than the ultrasonic surface wavelength and/or the latter is a Rayleigh wave, the contact ultrasonic transducer is disposed, for example by means of a boot 114, such that the axis of the transducer forms an angle θ with the normal to the surface on which the ultrasonic surface wave is propagated, less than 90° and the value of which can be determined by using the Snell-Descartes law.

Example 1

[0101] To prepare the implementation of the method according to the example 1, a piezoelectric support 115 having a thickness of 1 mm and a diameter of 76 mm were made available.

[0102] Two interdigital electrodes as illustrated in FIG. 1 were deposited by evaporation and formed by photolithography on the support to form a transducer 25. The electrodes have comb forms as illustrated in FIG. 1. They each comprise 20 fingers having a length of 7.9 mm and a width of 25 μm and spaced apart from one another by 25 μm. The electrodes are linked to an IFR2023A generator and an Empower brand amplifier, model BBM0D3FE, to generate a Rayleigh wave propagated in the support. The energy of the ultrasonic surface wave generated is calculated on the basis of the measurement of the normal displacement of the surface by laser interferometry and the frequency of the wave.

[0103] A layer of frost 120 is formed on the surface of the support disk and is cooled in a refrigerating truck maintained at a temperature of −20° C. via the vaporization of liquid water at a temperature of 3° C. in the truck.

[0104] An electric current with a frequency of 38.4 MHz is generated and passes through the electrodes, such that the transducer generates an ultrasonic surface wave.

[0105] FIGS. 6a) to 6c) illustrate the progress of the defrosting 1, 3 and 14 seconds respectively after the application of an electric current to the terminals of the transducer.

[0106] As can be seen in FIG. 6a), in the first instants, the melting of the frost with the transducer is observed, and primarily in the direction of propagation P of the wave which is vertical in the image. Subsequently, as observed in FIGS. 6b) and 6c), the defrosting is facilitated by the displacement of the drops of liquid resulting from the melting of the frost in the direction of propagation of the wave. The drops come into contact with the frost and transmit, by conduction, the heat that they have accumulated by dissipation of the energy of the ultrasonic surface wave. Furthermore, the defrosting takes place in the direction of propagation of the wave and according to a transverse direction.

Example 2

[0107] To prepare the implementation of the method according to the example 2, the method was as for the test 1, except that the support disk was previously covered with a film of ice.

[0108] FIGS. 7a) to 7c) illustrate the progress of the melting of the ice 1, 6 and 30 seconds respectively after the application of an electric current to the terminals of the transducer. Substantially the same effects are observed as for the example 1.

[0109] Obviously, the invention is not limited to the modes of implementation of the method, and notably to the examples, presented in the present description.