ELECTROSTATIC CONVERTER

Abstract

This electrostatic converter comprises a rotor comprising at least one blade designed to receive an air flow; a stator comprising at least one electrode; a flexible membrane fitted on the blade, and comprising a counter-electrode, the electrode or the counter-electrode being coated with a dielectric material suitable to be polarized; the flexible membrane describing a trajectory when the rotor performs a rotation; the flexible membrane being configured to come into sliding contact with the stator on a first part of the trajectory, and configured to be at a distance from the stator on a second part of the trajectory so as to form a variable electric capacitance variable suitable to induce an electric current.

Claims

1. Electrostatic converter comprising: a rotor comprising at least one blade designed to receive an air flow; a stator comprising at least one electrode coated with a dielectric material suitable to be polarized; a flexible membrane fitted on the blade, and comprising a counter-electrode; the flexible membrane describing a trajectory when the rotor performs a rotation; the flexible membrane being configured so that the counter-electrode comes into sliding contact with the dielectric material on a first part of the trajectory, and so that the counter-electrode is situated at a distance from the dielectric material on a second part of the trajectory so as to obtain a variable electric capacitance suitable to induce an electric current.

2. Electrostatic converter according to claim 1, wherein the flexible membrane is at least partially ferromagnetic, and wherein the stator comprises magnetization means arranged to keep the flexible membrane in sliding contact with the stator on the first part of the trajectory.

3. Electrostatic converter according to claim 1, comprising ballast means arranged to keep the flexible membrane in sliding contact with the stator on the first part of the trajectory.

4. Electrostatic converter according to claim 1, wherein the flexible membrane presents a flexural stiffness comprised between 1 mN/m and 10 N/m.

5. Electrostatic converter according to claim 1, wherein the electrode presents a length, noted L.sub.0, and in that the flexible membrane presents a length, noted L, verifying L.sub.0L5L.sub.0.

6. Electrostatic converter according to claim 1, wherein the dielectric material is an electret.

7. Electrostatic converter according to claim 1, wherein the flexible membrane and the stator are suitable to exchange electrostatic charges by triboelectric effect on the first part of the trajectory via the dielectric material.

8. Electrostatic converter according to claim 1, wherein the rotor presents an axis of rotation, in that the blade presents a distal end relatively to the axis of rotation, and in that the flexible membrane is fitted on the distal end of the blade.

9. Electrostatic converter according to claim 1, wherein the stator comprises a set of electrodes arranged preferably uniformly around the trajectory.

10. Converter according to claim 9, wherein the set of electrodes comprises N.sub.e successive electrodes arranged around the trajectory, N.sub.e being a natural integer greater than or equal to 3; and in that the counter-electrode of the flexible membrane forms a network of patterns arranged so that, on the first part of the trajectory, two consecutive patterns are: in contact with a k-th electrode and a (k+2)-th electrode, and at a distance from a (k+1)-th electrode, with k1,N.sub.e.

11. Electrostatic converter according to claim 1, wherein the rotor comprises N.sub.p blades, N.sub.p being an integer greater than or equal to 1, the flexible membrane being fitted on each blade, and wherein the stator comprises a set of N.sub.e electrodes, N.sub.e being an integer verifying N.sub.e=2N.sub.p.

12. Electrostatic converter according to claim 1, wherein the flexible membrane comprises a film made from the material presenting a Young's modulus comprised between 100 MPa and 5 GPa, preferably comprised between 1 GPa and 5 GPa.

13. Electrostatic converter according to claim 13, wherein the film presents a thickness comprised between 1 m and 1 mm, preferably comprised between 1 m and 125 m, more preferentially comprised between 1 m and 50 m.

14. Electrostatic converter according to claim 1, wherein the dielectric material presents a thickness comprised between 1 m and 125 m, preferably comprised between 25 m and 100 m.

15. Electrostatic converter according to claim 1, wherein the stator comprises an electric circuit in which the induced current flows, the electric circuit being connected to said at least one electrode.

16. Electrostatic converter comprising: a rotor comprising at least one blade designed to receive an air flow; a stator comprising at least one electrode; a flexible membrane fitted on the blade, and comprising a counter-electrode coated with a dielectric material suitable to be polarized; the flexible membrane describing a trajectory when the rotor performs a rotation; the flexible membrane being configured so that the counter-electrode comes into sliding contact with the electrode on a first part of the trajectory, and so that the dielectric material is situated at a distance from the electrode on a second part of the trajectory so as to obtain a variable electric capacitance suitable to induce an electric current.

17. Electrostatic converter according to claim 16, wherein the flexible membrane is at least partially ferromagnetic, and wherein the stator comprises magnetization means arranged to keep the flexible membrane in sliding contact with the stator on the first part of the trajectory.

18. Electrostatic converter according to claim 16, comprising ballast means arranged to keep the flexible membrane in sliding contact with the stator on the first part of the trajectory.

19. Electrostatic converter according to claim 16, wherein the flexible membrane presents a flexural stiffness comprised between 1 mN/m and 10 N/m.

20. Electrostatic converter according to claim 16, wherein the electrode presents a length, noted L.sub.0, and in that the flexible membrane presents a length, noted L, verifying L.sub.0L5L.sub.0.

21. Electrostatic converter according to claim 16, wherein the dielectric material is an electret.

22. Electrostatic converter according to claim 16, wherein the flexible membrane and the stator are suitable to exchange electrostatic charges by triboelectric effect on the first part of the trajectory via the dielectric material.

23. Electrostatic converter according to claim 16, wherein the rotor presents an axis of rotation, in that the blade presents a distal end relatively to the axis of rotation, and wherein the flexible membrane is fitted on the distal end of the blade.

24. Electrostatic converter according to claim 16, wherein the stator comprises a set of electrodes arranged preferably uniformly around the trajectory.

25. Converter according to claim 24, wherein the set of electrodes comprises N.sub.e successive electrodes arranged around the trajectory, N.sub.e being a natural integer greater than or equal to 3; and in that the counter-electrode of the flexible membrane forms a network of patterns arranged so that, on the first part of the trajectory, two consecutive patterns are: in contact with a k-th electrode and a (k+2)-th electrode, and at a distance from a (k+1)-th electrode (E), with k1,N.sub.e.

26. Electrostatic converter according to claim 16, wherein the rotor comprises N.sub.p blades, N.sub.p being an integer greater than or equal to 1, the flexible membrane being fitted on each blade, and in that the stator comprises a set of N.sub.e electrodes, N.sub.e being an integer verifying N.sub.e=2N.sub.p.

27. Electrostatic converter according to claim 16, wherein the flexible membrane comprises a film made from the material presenting a Young's modulus comprised between 100 MPa and 5 GPa, preferably comprised between 1 GPa and 5 GPa.

28. Electrostatic converter according to claim 16, wherein the film presents a thickness comprised between 1 m and 1 mm, preferably comprised between 1 m and 125 m, more preferentially comprised between 1 m and 50 m.

29. Electrostatic converter according to claim 16, wherein the dielectric material presents a thickness comprised between 1 m and 125 m, preferably comprised between 25 m and 100 m.

30. Electrostatic converter according to claim 16, wherein the stator comprises an electric circuit in which the induced current flows, the electric circuit being connected to said at least one electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Other features and advantages will become clearly apparent from the following description of different embodiments of the invention, given for non-restrictive example purposes only, with reference to the appended drawings in which:

[0052] FIG. 1 is a schematic perspective view of an electrostatic converter according to an embodiment of the invention,

[0053] FIGS. 2a to 2e are partial schematic side views illustrating different positions of the flexible membrane,

[0054] FIG. 3 is a partial schematic view, in cross-section, of an electrostatic converter according to an embodiment of the invention,

[0055] FIG. 4 is a partial schematic view, in cross-section, of an electrostatic converter according to an embodiment of the invention,

[0056] FIGS. 5 to 7 are schematic perspective views of an electrostatic converter according to different embodiments of the invention,

[0057] FIG. 8 is a partial schematic side view of an electrostatic converter according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0058] For the different embodiments, the same reference numerals will be used for parts that are identical or which perform the same function, for the sake of simplification of the description. The technical characteristics described in the following for different embodiments are to be considered either alone or in any technically possible combination.

[0059] The electrostatic converter illustrated in FIG. 1 is an electrostatic converter comprising: [0060] a rotor comprising at least one blade 1 designed to receive an air flow; [0061] a stator 2 comprising at least one electrode E; [0062] a flexible membrane 3 fitted on the blade 1 and comprising a counter-electrode; the flexible membrane 3 describing a trajectory when the rotor performs a rotation.

[0063] According to a first embodiment, the electrode E is coated with a dielectric material 20 suitable to be polarized. The flexible membrane 3 is configured so that the counter-electrode comes into sliding contact with the dielectric material 20 on a first part of the trajectory, and so that the counter-electrode is located at a distance from the dielectric material 20 on a second part of the trajectory so as to obtain a variable electric capacitance suitable to induce an electric current.

[0064] According to a second embodiment, the counter-electrode is coated with a dielectric material 20 suitable to be polarized. The flexible membrane 3 is configured so that the dielectric material 20 comes into sliding contact with the electrode E on a first part of the trajectory, and so that the dielectric material 20 is located at a distance from the electrode E on a second part of the trajectory so as to obtain a variable electric capacitance suitable to induce an electric current.

[0065] More precisely, the rotor illustrated in FIG. 1 comprises four blades 1. The rotor presents an axis of rotation that is preferably horizontal and parallel to the air flow. Each blade 1 presents a distal end 10 relatively to the axis of rotation, and the flexible membrane 3 is fitted on the distal end of each blade 1. The distal end 10 is situated at a distance R.sub.p from the centre of rotation of the rotor (visible in FIG. 2). The air flow advantageously presents a speed greater than or equal to 2 m/s.

[0066] More precisely, the stator 2 illustrated in FIG. 1 comprises a set of N.sub.e electrodes E, N.sub.e being an integer verifying N.sub.e=2N.sub.p, where N.sub.p, is the number of blades, i.e. N.sub.e=8. Such a distribution is optimized in order to have a maximum ratio N.sub.e(C.sub.maxC.sub.min) where C.sub.max and C.sub.min are respectively the maximum and minimum electric capacitance obtained when the rotor performs a rotation, as illustrated in FIG. 2b. The set of N.sub.e electrodes E is distributed uniformly around the trajectory of the flexible membrane 3 the trajectory being circular and determined by the rotor. In the first embodiment, the N.sub.e electrodes E are coated with the dielectric material 20. Each electrode E advantageously presents the same length, noted L.sub.0 in the sense of arc length and of curvilinear abscissa. The first part of the trajectory of the flexible membrane, forming an arc of a circle, 3 corresponds to the curved contact surface between the flexible membrane 3 and the corresponding electrode E. The stator 2 forms a cylindrical sump 21 designed to protect the blades 1 of the rotor. The electrodes E of the stator are located at a distance R.sub.s from the centre of rotation of the rotor (visible in FIG. 2). The distance separating an electrode E of the stator 2 and a counter-electrode of the rotor corresponds to the difference between R.sub.s and R.sub.p, i.e. R.sub.sR.sub.p. The stator 2 advantageously comprises an electric circuit (not shown) in which the induced current flows, the electric circuit being connected to each electrode E.

[0067] According to an embodiment illustrated in FIG. 8, the set of electrodes E comprises N.sub.e successive electrodes E arranged around the trajectory of the flexible membrane 3, N.sub.e being a natural integer greater than or equal to 3. The counter-electrode of the flexible membrane 3 forms a network of patterns 31 arranged so that, on the first part of the trajectory of the flexible membrane 3 two consecutive patterns 31 are:

[0068] in contact with a k-th electrode E and a (k+2)-th electrode E, and

[0069] at a distance from a (k+1)-th electrode E, with k1,N.sub.e.

[0070] In the first embodiment, the N.sub.e electrodes E are coated with the dielectric material 20, as illustrated in FIG. 8. In the second embodiment, the patterns 31 of the network are coated with the dielectric material 20. If the N.sub.e successive electrodes E are arranged around the trajectory of the flexible membrane 3 with a period p, the network of patterns 31 then advantageously presents a period 31 p/2. The network of patterns 31 is advantageously made from a metallic material forming a metallic texturing of the counter-electrode.

[0071] The dielectric material 20 is advantageously an electret. The electret is advantageously selected from the group comprising a polytetrafluoroethylene (PTFE) such as Teflon, a tetrafluoroethylene and hexafluoropropylene copolymer (FEP), a SiO.sub.2Si.sub.3N.sub.4 stack, and an amorphous perfluorinated polymer such Cytop. The polarization voltage at the terminal of the electret is such that the power of the electrostatic converter is about one W/cm.sup.2. For example purposes, the electric breakdown field of a PTFE is about 60 kV/cm and the electric polarization field is about 20 V/m.

[0072] The flexible membrane 3 and stator 2 are advantageously suitable to exchange electrostatic charges by triboelectric effect on the first part of the trajectory via the dielectric material 20. When the dielectric material 20 is not an electret, the polarization voltage at the terminals of the dielectric material 20 is such that the power of the electrostatic converter is about one nW/cm.sup.2. The dielectric material 20 is then advantageously selected from the group comprising polyvinylidene fluoride (PVDF), a polyimide such as Kapton, polymethyl methacrylate (PMMA) and nylon. The dielectric material 20 advantageously presents a thickness comprised between 1m and 125 m, preferably comprised between 25 m and 100 m.

[0073] The flexible membrane 3 advantageously presents a flexural stiffness comprised between 1 mN/m and 10 N/m. The flexible membrane 3 can be simulated as a fixed-free beam. The flexural stiffness is then expressed by the formula

[00001]$\begin{array}{cc}k=\frac{3.Math.\mathrm{EI}}{L^3}=\frac{{\mathrm{EHe}}_f^3}{4.Math.L^3},& \end{array}$

l being the quadratic moment, L being the length of the beam comprised between 1 mm and 10 cm, E being the modulus of elasticity of the beam comprised between 100 MPa and 5 GPa, e.sub.f being the thickness of the beam comprised between 1 m and 1 mm, and H being the width of the beam comprised between 1 mm and 10 cm. The flexible membrane 3 is advantageously a flexible blade. What is meant by blade is a thin strip of elongate shape. The flexible membrane 3 advantageously presents a length, noted L, verifying L.sub.0L5L.sub.0. The flexible membrane 3 advantageously presents a film made from a material presenting a Young's modulus comprised between 100 MPa and 5 GPa, preferably comprised between 1 GPa and 5 GPa. The film advantageously presents a thickness comprised between 1 m and 1 mm, preferably comprised between 1 m and 125 m, more preferentially comprised between 1 m and 50 m. The flexible membrane 3 advantageously presents an electrically conducting part, preferably metallic, forming the counter-electrode. In the first embodiment, the counter-electrode comes into sliding contact with the dielectric material 20 on the first part of the trajectory. The electrically conducting part is made from a material preferentially selected from the group comprising copper, gold, silver, aluminium, iron, platinum, and graphite. The flexible membrane 3 presents a first surface which comes into sliding contact with the dielectric material 20 on the first part of the trajectory for the first embodiment, and a second surface opposite the first surface.

[0074] The flexible membrane 3 is subjected to the following forces which determine its position:

[0075] the electrostatic force, fixed by the polarization voltage at the terminals of the dielectric material 20, which tends to attract the flexible membrane 3 to the stator 2;

[0076] the centrifugal force, proportional to the speed of rotation of the rotor, which also tends to attract the flexible membrane 3 to the stator 2;

[0077] the aerodynamic forces (lift and drag), which oppose the movement of the flexible membrane 3 in air, and which tend to move the flexible membrane 3 away from the stator 2;

[0078] the elastic return force of the flexible membrane 3.

[0079] In addition, the assembly area of the flexible membrane 3 at the distal end 10 of each blade 1. the flexural stiffness of the flexible membrane 3 and the separating distance (R.sub.sR.sub.p) are chosen such as:

[0080] to cover an electrode E while preventing simultaneous overlapping of two adjacent electrodes E by the flexible membrane 3 as illustrated in FIG. 2e,

[0081] to maximize the difference between C.sub.max and C.sub.min, as illustrated in FIGS. 2a (theoretical case) and 2b (practical case), and prevent the case illustrated in FIG. 2c where C.sub.max is too low,

[0082] prevent oscillations of the flexible membrane 3 at a distance from the dielectric material 20 on the first part of the trajectory, as illustrated in FIG. 2d for the first embodiment.

[0083] In particular, the oscillations of the flexible membrane 3 are amplified with the speed of rotation of the rotor and a too low stiffness of the membrane. The oscillations are thus amplified with the length of the membrane, a small thickness of the membrane, and the flexibility of the membrane, in accordance with the simulation of a fixed-free beam. The oscillations of the flexible membrane 3 can therefore be reduced by reducing its length, by increasing its thickness or by using a more rigid material.

[0084] According to an embodiment illustrated in FIG. 3, the flexible membrane 3 is at least partially ferromagnetic, and the stator 2 comprises magnetization means arranged to keep the flexible membrane 3 in sliding contact with the dielectric material 20 of the stator 2 on the first part of the trajectory for the first embodiment. To do this, the counter-electrode of the flexible membrane 3 is advantageously ferromagnetic. As a non-restrictive example, the magnetization means comprise permanent magnets 4 the North and South magnetic poles of which are respectively noted N and S. In the second embodiment, the magnetization means are arranged to keep the dielectric material 20 of the counter-electrode in sliding contact with each electrode E of the stator 2.

[0085] According to an alternative embodiment, the electrostatic converter comprises ballast means arranged on the second surface of the flexible membrane 3 to keep the flexible membrane 3 in sliding contact with the dielectric material 20 on the first part of the trajectory for the first embodiment. As a non-restrictive example, the ballast means comprise a plurality of weights 30 fixed to the flexible membrane 3. In the second embodiment, the ballast means arranged on the second surface of the flexible membrane 3 to keep the dielectric material 20 of the counter-electrode in sliding contact with each electrode E of the stator 2.

[0086] The electrostatic converter illustrated in FIG. 5 differs from the electrostatic converter illustrated in FIG. 1 in particular in that each blade 1 comprises three parallel supports on each of which a flexible membrane 3 is fitted. The sump 21 of the stator 2 comprises three parallel cylindrical elements, each facing a support.

[0087] The electrostatic converter illustrated in FIG. 6 differs from the electrostatic converter illustrated in FIG. 1 in particular in that the stator 2 presents the form of a disc.

[0088] The electrostatic converter illustrated in FIG. 7 differs from the electrostatic converter illustrated in FIG. 1 in particular in that:

[0089] the axis of rotation is vertical,

[0090] the sump 21 of the stator 2 comprises two walls facing one another and joined to one another by at least one disc.