FR2889514A1 - Transmission of pressure to micro-membrane e.g. for electronic Braille book uses electrical activation of liquid droplet to modify contact with hydrophobic surface - Google Patents

Abstract

A device for transmitting pressure to a micro-membrane (22), comprising a liquid droplet (30) on an electrically insulating and hydrophobic surface of a supporting substrate (10), comprises a plate (20) with an aperture (21) covered by the micro-membrane to hold the micro-membrane in contact with the droplet, and an electrical activator in the form of a disc electrode (12) and a wire (17) to modify the line of contact between the droplet and the hydrophobic surface. The droplet is positioned by a star-shaped electrode (14) within the supporting substrate and located concentrically with the wire that delivers a centering electrical potential.

Description

2889514 1

  DEVICE AND METHOD FOR TRANSMITTING PRESSURE USING THE ELECTROWET EFFECT

DESCRIPTION TECHNICAL FIELD

  The invention relates to a device and a method for transmitting pressure using the electrowetting effect.

  STATE OF THE PRIOR ART The effect of electrowetting on dielectric or EWOD (for ElectroWetting On Dielectric) provides very promising solutions in the field of micro-fluidics. This effect makes it possible to move micro-drops along well-controlled paths, to merge them or to divide them by using suitable electric fields. With respect to this technique, reference can be made to the following documents: - Electrowetting-based actuation of liquid droplets for microfluidic applications of G. POLLACK et al., Applied Physics Letters, vol. 77, No. 11, September 2000, p. 1725 and 1726; Low voltage electrowetting-ondielectric H. MOON et al., Journal of Applied Physics, vol. 92, No. 7, October 2002, p. 4080 to 4087; Creating, transporting, and merging liquid droplets by electrowetting-based actuation for digital microfluids circuits of S. K. CHO et al., Journal of Microelectromechanical Systems, vol. 12, No. 1, February 2003, p. 70 to 80; 2889514 2 - Moving droplets with microcatenaries of Y. FOUILLET et al., Proceedings of the 7th International Conference on Miniaturized Chemical and Biochemical Analysis Systems (TAS), 5-9 October 2003, Squaw Valley, CA, USA; - Electrode shapes for electrowetting arrays by J. LIENEMANN et al., Proceedings of the 2003 Nanotechnology Conference and Trade Show, Nanotech 2003, vol. 1, 2003.

  Electric activation or deactivation of a micro-drop also has another effect. This effect is the change in pressure of the micro-drop resulting from its activation or deactivation. It can be shown that a drop placed between two parallel plates exerts a different pressure on the walls of the plates according to whether there is electrical activation or not of the drop.

  PRESENTATION OF THE INVENTION The inventors of the present invention have thought to use this effect to produce devices for transmitting pressure via micromembranes. This pressure variation effect can give rise to several applications, among others: the electronic book in Braille characters, - fluid agitation, - the measurement of the pressure of a fluid.

  The subject of the invention is therefore a device for transmitting a pressure via at least one micro-membrane, comprising a drop of a liquid 28895143 positioned on an electrically insulating and hydrophobic surface of a support substrate. means for maintaining the micromembrane in contact with a part of the surface of the drop, and electrical activation means of the drop capable of modifying the line of contact between the droplet and the hydrophobic surface.

  Advantageously, the means for holding the micro-membrane comprise a blade disposed opposite the support substrate, the micromembrane closing an opening of the blade.

  Advantageously also, the electrical activation means of the drop are included in the support substrate. They may comprise a first electrode constituted by a wire disposed transversely to the support substrate, and a second electrode constituted by a disk pierced at its center and concentrically disposed in said wire.

  The drop of liquid can be positioned by means of at least one centering electrode for applying an electric centering potential of the drop. The centering electrode may especially have a star shape. It may be included in the support substrate and be arranged concentrically to said wire.

  The invention also relates to a system consisting of an association of several devices as described above, the devices being made from a common support substrate and a common blade.

  The micromembranes may be arranged in a regular arrangement, for example in a matrix. This matrix can be a matrix of points reproducing Braille characters according to whether the corresponding drops are activated or not.

  The subject of the invention is also a fluid stirrer comprising at least one device for transmitting a pressure or at least one system as described above, a voltage generator supplying voltage pulses to the transmission devices of a transmission device. pressure.

  The invention also relates to a detector for measuring a fluid pressure comprising a device for transmitting a pressure as described above, the drop being disposed between two measuring electrodes forming capacitor plates, the face of the blade opposite the support substrate being in contact with the fluid whose pressure is to be measured, whereby the drop deforms as a function of the fluid pressure, which modifies the capacity of the capacitor, the measurement of the value of the capacitor for determining the corresponding fluid pressure.

  The invention also relates to a method for transmitting a pressure via at least one micro-membrane, comprising the following steps.

  contacting at least a portion of the micro-membrane with a drop of a liquid 30 positioned on a hydrophobic surface, 2889514 5 application of electrical activation means to the drop able to modify the line of contact between the droplet and the hydrophobic surface.

  The electrical activation means may be means causing an overpressure swelling the membrane during their application.

  The electrical activation means can also be means causing the vibration of the membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

  The invention will be better understood and other advantages and features will become apparent on reading the following description, given by way of non-limiting example, accompanied by the appended drawings in which: FIG. 1 is a diagram of a drop liquid confined between two plates; FIGS. 2A to 2C show three examples of Braille characters; FIGS. 3A to 3B are cross-sectional views illustrating the operation of a pressure transmission device according to the present invention; FIGS. 4 to 6 show several possible examples for the centering electrode; FIG. 7 represents a chip comprising 20 membrane pads that can be activated by electrowetting; Figure 8 illustrates a fluid shaker according to the present invention; FIG. 9 illustrates a detector for measuring a fluid pressure according to the present invention.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS FIG. 1 is a diagram of a droplet 1 of liquid confined between two plates 2 and 3. The plate 2 comprises an electrode for activating the droplet. To calculate the pressure exerted by the droplet on one of the plates, reference can be made to J. BERTHIER et al., Proceedings of the Nanotech 2005 Conference, An analytical model for the prediction of microdrop extraction and splitting in digital microfluidics systems. , Anaheim, CA, USA, May 8-12, 2005.

  The pressure exerted on one of the plates is given by the law of Laplace: 1 1 + Ri R2 i where y is the surface tension of the liquid and R1 and R2 are the radii of curvature. The radius of curvature in the horizontal plane R1 is a function of the volume V of the drop: R1 P = Y (1) (2) where 8 is the distance between the plates. The radius of curvature in the vertical plane R2 is given by: R2 (-cosO1 -cos02) where 01 and 02 are the angles of contact with the plates. The pressure in the drop is then: When the electrode of the plate 2 is energized, the contact angle θ changes to 0. This results in a difference As a result of taking 0 = 80 and 01 = 120, 8 = 50 ° G and 20 = 70 mN / m, a pressure difference of P = 943 Pa is found.

  The stiffness coefficient of a membrane is (see Theory of Plates and Shells of S. P. TIMOSHENKO et al., McGraw-Hill Book Co., 1959, 51). D = 12 (1- v2) (3) P = y (4) (5) E.h3 (6) where h is the thickness of the membrane, E is the Young's modulus and v is the Poisson's ratio. The maximum deflection is then (assuming a linear regime). Pa4 Wmax 64D where P is the applied pressure and has the diameter of the membrane. After substitution of (5) and 10 (6) in (7), we obtain: cosO cosO1 4 is 16 E.h3 3 (1- By introducing the characteristic numerical values of a polydimethylsiloxane (PDMS) membrane: E = 8.5 105 (Pa), v = 0.5, h = 50), a = 1 mm, a deformation of about 1 mm is obtained.

  The approach that has just been made is more an estimate than a rigorous one. Two criticisms can be formulated: - the relation (7) supposes a linear regime of small deformations which is not verified by the equation (8). Therefore, a nonlinear calculation should be done using numerical methods; - a rigorous approach requires the coupling between the pressure in the drop and the deformation of the surface. The effect of the deformation of the membrane on the radii of curvature should be taken into account (7) Wmax (8) 28895149.

  However, if we refer to the studies already done on PDMS membranes (see Development of magnetic micro-membranes for the actuation of fluids in biological and chemical microsystems of J. BERTHIER and F. RICOUL, Applied Nanoscience, vol 1, 2004 ), the deformation can be estimated at about 500 to 700 μm for a diameter of 3 to 4 mm and a membrane thickness of 50 to 100 μm.

  The pressure increase effect can be used to create an electronic book in Braille characters. The problem is that of electronic reading for blind people. The goal is to allow reading much faster than the usual manual reading. Braille characters are very suitable for electronic display.

  Figures 2A to 2C show three examples of Braille characters.

  Each character is represented by the combination of 1 to 6 points in relief, arranged on a matrix of two points of width on three points of height. Figure 2A shows an e. Figure 2B shows a v. Figure 3C shows a z.

  Six points are enough to define the entire alphabet.

  Figures 3A and 3B are cross-sectional views illustrating the operation of a pressure transmission device according to the invention.

  The device comprises a support substrate 10 constituted by a stacked structure successively comprising a glass plate 11, an electrode 12, an insulating layer 13 of silicon nitride, another electrode 14, another insulating layer 15 made of silicon nitride and a hydrophobic layer 16, for example Teflon. The support substrate 10 is pierced with a hole 18 allowing the passage of a conductive wire 17 along the axis of the hole 18. The electrodes 12 and 14, pierced at their center, are centered on the conductive wire 17. A solid blade 20, for example based on glass or silicon, is arranged parallel to the support substrate 10. It comprises an opening 21 in which is fixed a membrane 22, for example polydimethylsiloxane (PDMS), disk-shaped centered on the axis of the hole 18.

  The distance separating the blade 20 from the support substrate 10 is, for example, 100 μm. A drop of an electrically conductive liquid, for example water, is disposed between the blade 20 and the support substrate 10 and is centered on the axis of the hole 18.

  The hole 18 is closed by an insulating material 19.

  The electrode 12 called the main electrode has the shape of a disc. It allows, in cooperation with the lead 17, to apply an electric field to the drop 30 by their connection to a voltage generator.

  The electrode 14 allows the centering of the drop 30 under the membrane 22. This centering is obtained by applying an electrical voltage between the electrode 14 and the lead wire 17. The electrode 14 has a star shape.

  FIGS. 4 to 6 show several possible forms for the centering electrode 14. In these figures, which are views from above, there is shown the electrode 12, the hole 18 and the centering electrode 14. The insulating layer which separates the electrodes 12 and 14 has not been shown.

  FIG. 3A shows the state of the device when the main electrode 12 is activated and / or a non-zero activation voltage is applied between the electrode 12 and the wire 17. FIG. 3B shows the state of the device when the main electrode is not activated and / or when the activation voltage between the electrode 12 and the wire 17 is zero. The transition from an activated state to a non-activated state of the electrode 12 causes a contraction of the droplet. This contraction generates an overpressure in the drop, which causes deformation of the membrane 22 in the form of swelling.

  This pressure transmission device allows the production of an electronic book Braille characters by combining several devices on the same chip, arranged according to a matrix of points. The dot matrix reproduces the Braille characters according to whether or not the corresponding drops are overpressurized.

  FIG. 7 shows a chip comprising electrically actuatable membrane pads. The chip consists of a support substrate 41 of the type shown in FIGS. 3A and 3B, a blade 42 facing the support substrate 41 and parallel to the support substrate, and a peripheral spacer 43. The blade 42 comprises twenty openings each provided with a deformable membrane. Under each membrane is disposed and centered a drop as shown in Figures 3A and 3B. In the example shown in FIG. 7, seven pads, corresponding to the membranes 44, are activated. The other thirteen pads, corresponding to the membranes 45, are not activated.

  The chip thus created may be the size of the tip of a finger. Activation or deactivation of the main electrode produces almost instantaneously a deformation of the membrane or its return to the state of rest. According to the information from a recording system (micro-memory), scrolling characters can be obtained on the chip without having to modify the location of the finger.

  Another application of the present invention is the production of a fluid stirrer under the effect of stirring a membrane. Such a fluid stirrer is represented, in principle, in FIG. 8. In this figure, an insulating support substrate 51, having a hydrophobic surface 52, comprises a buried electrode 53. A blade 54 is arranged facing each other. of the support substrate 51. It comprises an opening 55 covered with a membrane 56. A drop of liquid is disposed between the support substrate 51 and the blade 54, between the membrane 56 and the portion of the surface of the support substrate 51 located 2889514 13 just above the electrode 53. The volume of the drop 57 is advantageously sufficient to obtain a swelling of the membrane 56 when the agitator is at rest. Thus, the drop 57 is centered relative to the electrode 53 of circular shape. The blade 54 is provided with a not shown electrode in contact with the drop 57. An electric voltage can then be applied to the drop. By applying an electrical voltage in the form of pulses, it is possible to obtain pressure waves propagating in a fluid 58 situated on the other side of the blade 54. The pressure waves allow the fluid 58 to be mixed by stirring.

  Yet another application of the present invention is the production of a detector for measuring a fluid pressure. The principle used is the opposite of the principle of the stirrer described above. The detector illustrated in FIG. 9 is identical to the agitator of FIG. 8. The detector elements are therefore referenced by adding the number 100 to the corresponding elements of the stirrer.

  The drop 157 is first activated electrically. The pressure of a fluid 100 flowing on the other side of the blade 154 deforms the membrane 156, which results in a lateral expansion of the droplet 157 and a change in the electrical capacitance existing between the electrode 153 and the blade electrode 154. The pressure variation transformed into capacitance variation is then detected by the electrodes.

Claims (2)

  A device for transmitting a pressure through at least one micro-membrane (22, 56, 156), comprising a drop (30, 57, 157) of a liquid positioned on an electrically insulating surface and hydrophobic substrate of a support substrate (10, 51, 151), means for maintaining the micromembrane in contact with a portion of the surface of the drop, and electrical activation means of the drop adapted to modify the line contact between the droplet and the hydrophobic surface.   2. Device according to claim 1, characterized in that the means for maintaining the micromembrane comprise a blade (20, 54, 154) arranged facing the support substrate (10, 51, 151), the micromembrane (22, 56, 156) closing an opening (21, 55, 155) of the blade.   3. Device according to one of claims 1 or 2, characterized in that the electrical activation means (12, 17) of the drop are included in the support substrate (10).   4. Device according to claim 3, characterized in that the electrical activation means of the drop comprises a first electrode constituted by a wire (17) disposed transversely relative to the support substrate (10), and a second electrode (12). constituted by a disk 2889514 15 pierced at its center and concentrically disposed in said wire.   5. Device according to any one of claims 1 to 4, characterized in that the drop of liquid (30) is positioned by means of a centering electrode (14) for applying an electric centering potential of the droplet .   6. Device according to claim 5, characterized in that the centering electrode (14) has a star shape.   7. Device according to one of claims 5 or 6, characterized in that the centering electrode (14) is included in the support substrate (10).   8. Device according to any one of claims 5 to 7, characterized in that the centering electrode (14) is arranged concentrically to said wire (17).   9. System consisting of a combination of several devices according to any one of claims 2 to 8, the devices being made from a common support substrate (41) and a common blade (42).   10. System according to claim 9, characterized in that the micromembranes (44, 45) are arranged in a regular arrangement.   11. System according to claim 10, characterized in that the regular arrangement is a matrix.   12. System according to claim 11, characterized in that the matrix is a matrix of points reproducing Braille characters according to whether the corresponding drops are activated or not.   13. A fluid shaker comprising at least one pressure transmission device according to any one of claims 1 to 8 or at least one system according to any one of claims 9 to 11, a voltage generator providing pulses of voltage to the devices for transmitting a pressure.   14. A detector for measuring a fluid pressure comprising a device for transmitting a pressure according to any one of claims 2 to 8, the drop (157) being disposed between two measuring electrodes forming capacitor plates, the face of the blade (154) opposite the support substrate being in contact with the fluid (100) whose pressure is to be measured, whereby the drop deforms as a function of the fluid pressure, which modifies the capacity of the capacitor , the 2889514 17 measurement of the value of the capacitor for determining the corresponding fluid pressure.   15. A method of transmitting a pressure via at least one micro-membrane, comprising the following steps: contacting at least a portion of the micro-membrane (22, 56, 156) with a drop of a liquid (30, 57, 157) positioned on a hydrophobic surface, - application of electrical activation means to the drop capable of modifying the line of contact between the droplet and the hydrophobic surface.   16. The method of claim 15, characterized in that the electrical activation means are means causing an overpressure swelling the membrane (22) during their application.   17. The method of claim 15, characterized in that the electrical activation means are means causing the vibration of the membrane (56).