IMPROVED ANTIFOULING SYSTEM FOR TRANSFER TO A MEASURING DEVICE

Description

TECHNICAL FIELD

[0001] The field of the invention is that of so-called "antifouling" systems (according to an anglicism which can be translated into French as anti-biological fouling) intended to equip measuring devices (in particular optical measuring devices) immersed in a liquid medium, in particular sensors and measuring probes. STATE OF THE PRIOR ART

[0002] Many sensors are used in liquid media to control the properties of the medium (pH probe, density, etc.) or to measure various characteristics such as turbidity, the presence of chemical species or certain strains of bacteria, etc.

[0003] These sensors can be used in an industrial environment (tanks, pipes) or natural environment (sea, oceans, rivers, etc.). Thus, millions of submerged sensors are used in liquid environments.

[0004] However, any surface immersed in a liquid, whether in fresh water or sea water, is subject to the deposit and adhesion of organisms which can be bacteria, algae, molluscs, etc. This phenomenon is known under the English term "biofouling", or biological fouling. The adhesion of microorganisms to materials and their multiplication leads to the formation of a film (called "biofilm") on the surface of the immersed materials, and this after only a few minutes of immersion.

[0005] This biofouling phenomenon is problematic in the world of sensors, because it will often impact the measurements of these sensors in liquid environments.

[0006] We can take the example of optical sensors, which use an optical beam to monitor a property of the liquid medium, for example turbidity. Biofouling on the optical window (or porthole) of the optical sensor will impact the passage of the beam and thus degrade the measurement, to the point of making it impossible.

[0007] According to another example, in the case of a biological sensor that must detect the specific adhesion of desired agents to the surface of a functionalization layer, the presence of biofouling will make it impossible for the desired target to reach the functionalization layer; the sensor will therefore no longer function at all, or worse, will give false positive alert results.

[0008] It is easy to understand that so-called "antifouling" solutions, designed to combat biofouling of sensors, are necessary to obtain consistent data quality from the sensors and to reduce the maintenance required for cleaning them.

[0009] Among the known solutions, we can cite the Applicant's anti-fouling device, which is described in patent application FR 3 106 211 and which is designed to equip a measuring system intended to be immersed.

[0010] As illustrated in the figure 1 , a measuring device 10 (for example an optical sensor), which comprises a surface sensitive to fouling (in other words, which is subject to fouling or likely to be fouled by microorganisms), is equipped with an anti-fouling system 20 (or antifouling system). This anti-fouling system 20 comprises: a plate 110 capable of vibrating; holding means 12, configured to hold the plate 110 above the sensitive surface 7 of the measuring device 10 (for example, the sensitive surface may be an optical window), a rear face of the plate facing the sensitive surface; at least one actuator 22 capable of setting the plate 110 into vibration, so as to generate an acoustic wave capable of at least limiting attachment of microorganisms to the sensitive surface.

[0011] In a known manner, a control unit CU (not shown) is configured to control said actuator to vibrate the plate.

[0012] In the figure 2 a top view of this prior art system is illustrated. Here, it can be seen that the measuring device 10 is cylindrical in shape and the plate is rectangular in shape. The holding means 12 for holding the plate above the sensitive surface 7 may be bars.

[0013] In this configuration, the liquid in which the assembly formed by the measuring device 10 and the antifouling system 20 is immersed circulates between the device 10 and the antifouling system 20. The acoustic wave generated by the vibration of the plate will propagate in the liquid and, upon reaching the sensitive surface 7, limit or even prevent biological fouling of this sensitive surface.

[0014] Thus, in this state of the art, it is the acoustic wave generated by the vibrating plate that will cause the antifouling effect. But the vibrating plate can be fragile. For greater robustness, efficiency and for greater compactness, the inventors have imagined the case where the holding means are a single element which, with the sensitive surface 7 of the measuring device 10 and the plate 110, delimits a closed space (or closed cavity).

[0015] In this particular case, the front face of the plate is intended to be in contact with the liquid and the rear face is located on the measuring device 10 side. The plate 110 therefore has, on either side, two environments which can have very different pressures: on the measuring device side, the pressure is atmospheric pressure, while on the liquid side, the pressure is the pressure of the liquid (for example, water), which increases with depth.

[0016] We then understand the limit of such an assembly: the plate must be flexible to present high vibration amplitudes and, therefore, cannot withstand the high pressures generated by immersion at depth or in a pressurized liquid medium.

[0017] The inventors therefore sought to design an antifouling system which could equip a measuring device, by isolating the sensitive surface of the device, so that the assembly thus formed could operate when immersed in depth and / or in a pressurized liquid. STATEMENT OF THE INVENTION

[0018] To this end, the invention relates to a system for combating biological fouling by microorganisms, intended to be transferred to a measuring device which is intended to be immersed in a liquid at a liquid pressure P and which comprises a surface sensitive to biological fouling, the system being configured to cover the sensitive surface, the system comprising: a plate capable of vibrating, having two opposite main faces, called front face and rear face, the front face being intended to be in contact with the liquid; and at least one actuator, located on one of the main faces of the plate, capable of setting the plate into vibration, so as to at least limit the attachment of microorganisms to the plate; the system being characterized in that it further comprises: a closed cavity, which is delimited at least in part by the rear face of the plate, and which is filled with a fluid at a pressure P cavity; and a fluid compressor, in fluid communication with the closed cavity, capable of modulating the pressure P cavity of fluid in the cavity, so that the absolute value of the difference between the pressure P liquid on the front face and the pressure P cavity on the rear face is less than 2.10 5< Pa (2 bar), preferably less than 5.10 4< Pa (0.5 bar), ideally the pressures are equal. Indeed, preferably, the compressor is able to modulate the pressure in the cavity P cavity so that it is equal to the pressure of the liquid P liquid . .

[0019] Preferably, the plate is a membrane. A "membrane" is understood to mean a structure having a small thickness compared to its planar dimensions. It should be noted that in the case of an embedded membrane, it will be considered at its periphery.

[0020] Preferably, the actuator is located on the rear face of the plate.

[0021] The fluid compressor is preferably an air compressor. For example, a compressor from the manufacturer Fluigent or Würth can be used.

[0022] Preferably, the closed cavity has a depth, in a direction perpendicular to the rear face of the plate, of between 1 and 10 mm, inclusive. Preferably, this depth is equal to 1 mm.

[0023] Advantageously, the sensitive surface may be an optical window, for example in the case where the measuring device is an optical measuring device. The term "optical window" means the area through which the optical signal will pass to go from the optical measuring device to the medium to be characterized.

[0024] According to another variant, the sensitive surface may be a functionalization layer, in the case where the measuring device is a biological sensor having to detect the specific attachment of desired agents to the surface of the functionalization layer.

[0025] The measuring device can for example be an optical sensor or an optical probe.

[0026] The actuator can be a piezoelectric, ferroelectric, electrostatic, magnetic or thermal actuator.

[0027] The invention also relates to an assembly according to a first variant, comprising a measuring device and a system for combating biological fouling as described above, in which the cavity is arranged in contact with the entire sensitive surface, the sensitive surface and the plate facing each other.

[0028] Preferably, the measuring device is disposed inside a protective housing (e.g., an enclosure), the biofouling control system being used to close and seal the housing, the cavity, and optionally the fluid compressor of the system, being disposed inside the housing.

[0029] The invention also relates to an assembly according to a second variant, comprising a measuring device and a system for combating biological fouling as described above, in which the cavity is arranged at a distance from the sensitive surface, the sensitive surface and the plate facing each other, the system for combating biological fouling being used to close and seal the housing, the cavity, and possibly the fluid compressor of the system, being arranged inside the housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other characteristics and advantages of the invention will emerge from the description which follows, taken as a non-limiting example, with reference to the appended figures in which: there figure 1, already described above, is a schematic representation, in a side view, of a prior art assembly comprising a measuring device having a surface sensitive to biological fouling, which is equipped with an antifouling system; the figure 2 is a top view of the entire prior art illustrated in the figure 1 ; there figure 3 is a schematic sectional view according to a side view of an example of an anti-fouling system according to the invention; figure 4 is a schematic sectional view of an example of an anti-fouling system according to the invention, integrated on the sensitive surface of a measuring device; the Figure 5 is a schematic sectional view of another example of an anti-fouling system according to the invention, integrated on the sensitive surface of a measuring device, the whole being inserted into a housing; the Figure 6ais a schematic cross-sectional representation of a first step of an exemplary embodiment of an anti-fouling system according to the invention; Figure 6b is a schematic sectional representation of a second step of an exemplary embodiment of an anti-fouling system according to the invention; Figure 6c is a schematic sectional representation of a third step of an exemplary embodiment of an anti-fouling system according to the invention; Figure 6d is a schematic cross-sectional representation of a fourth step of an exemplary embodiment of an anti-fouling system according to the invention; Figure 6e is a schematic cross-sectional representation of a fifth step of an exemplary embodiment of an anti-fouling system according to the invention; Figure 6f is a schematic sectional representation of a sixth step of an exemplary embodiment of an anti-fouling system according to the invention; figure 6gis a schematic cross-sectional representation of a seventh step of an exemplary embodiment of an anti-fouling system according to the invention; figure 6h is a schematic cross-sectional representation of an eighth step of an exemplary embodiment of an anti-fouling system according to the invention; Figure 6i is a schematic cross-sectional representation of a ninth step of an exemplary embodiment of an anti-fouling system according to the invention; figure 6j is a schematic sectional representation of a tenth step of an exemplary embodiment of an anti-fouling system according to the invention. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0031] An exemplary embodiment of an anti-fouling system 1 according to the invention is illustrated in the figure 3The system 1 comprises a plate 110 capable of vibrating, having a front face and a rear face, the front face being intended to be in contact with the liquid; an actuator 22, which is here located on the rear face of the plate; the plate 110 and actuator 22 assembly is designated by the reference 11; a closed cavity 2, which is delimited at least in part by the rear face of the plate 110, and which is filled with a fluid at a pressure P cavity; and a fluid compressor 3, which is in fluid communication with the closed cavity 2.

[0032] The fluid compressor is capable of modulating the fluid cavity pressure P in the cavity, so that the absolute value of the difference between the liquid pressure P on the front face and the cavity pressure P on the rear face is less than 2 bar, preferably 0.5 bar, ideally the pressures are equal.

[0033] The cavity 2 of the anti-fouling system 1 can be arranged at a distance from the sensitive surface 7, and in this case the cavity and the measuring device with the sensitive surface must be placed in a protective housing 4 so that the sensitive surface, despite this distance, is protected.

[0034] Preferably, the cavity 2 of the anti-fouling system 1 is intended to be arranged in contact with at least a portion of the sensitive surface 7 (preferably, the entire sensitive surface) of a measuring device 10, the sensitive surface 7 and the plate (membrane) 110 being intended to face each other, the assembly of the measuring device 10 and the biological fouling control system 1 forming an assembly 30. For example, the sensitive surface 7 may be the optical window of an optical measuring device (for example of the optical sensor type).

[0035] An exemplary embodiment of an assembly 30 according to the invention is illustrated in the figure 4 . It should be noted that, for the sake of simplification, we have not included the level of detail present in the figure 3 to represent the plate 110 and the actuator 22, and we have only used the reference 11 to designate all of these elements.

[0036] According to another example of embodiment illustrated in the Figure 5 , the measuring device 10 can be arranged inside a protective housing 4, the anti-biofouling system 1 being used to close and seal the housing, the cavity 2 and the fluid compressor 3 of the system 1 can be arranged inside the housing 4. In the Figure 5, the housing comprises, at its opening, a recess 13 delimiting an internal shoulder on which the anti-fouling system 1 rests. Fastening elements, for example of the nut 5 and tightening screw 6 type, are then used to fix the system 1 to the housing 4 and thus close it and make it watertight. This type of housing makes it possible to integrate the antifouling system into the measuring device, but any other integration making it possible to bring together the antifouling system, the cavity capable of equalizing the pressures and the measuring device can also be used.

[0037] In the assembly 30 according to the invention, the anti-fouling system 1 is adaptable to the pressure of the liquid in which it is immersed. The anti-fouling system can thus withstand high liquid pressures, for example water, in particular for immersions in very deep water.

[0038] Thanks to the presence, on the one hand, of the cavity on the rear face of the plate, and, on the other hand, of the compressor, which is connected to the cavity, the pressure on the rear face of the plate can be adjusted, so as to equalize the pressures on either side of the plate. The pressure of the fluid inside the cavity, for example air, P air and the pressure of the liquid in which the assembly is immersed, for example water, P water , are balanced, and the vibrating plate can operate without being hindered by a potential strong pressure difference. Note that we are giving the example of using air in the cavity, but that we could consider any gaseous or liquid fluid that would not cause biological fouling in the cavity.

[0039] In the anti-fouling system 1 according to the invention, the cavity 2 on the rear face of the plate 110 extends, at a minimum, over the entire surface of the rear face of the plate capable of vibrating. This therefore gives an indication for the width and length or for the diameter of the cavity. The depth d of this cavity, for its part, must be small enough to make it possible to easily obtain potentially high pressures (for example 5.10 7< Pa (500 bar) at a depth of 5000 m), but large enough so that the plate does not strike the bottom of the cavity during its resonance.

[0040] For example, in the case where the plate is a membrane with a diameter of 2 centimeters and which can have deformation amplitudes of several micrometers, of the order of 15 µm to 50 µm, a cavity depth d = 100 µm at least is required. Due to integration constraints, a value for d of the order of 1 to 10 mm, inclusive, will be chosen, but it is quite possible to have a deeper cavity; for example, it is possible to have a cavity whose depth corresponds to the depth of the body of the measuring device 10.

[0041] By construction, the internal pressure P int in the cavity (and therefore at the level of the rear face of the plate) is equal to atmospheric pressure (P atm).

[0042] When the assembly formed by the measuring device 10 and the anti-fouling system 1 is immersed in a liquid, the pressure P ext at the front face of the plate, as a function of the immersion depth h (in meters) of the plate, is known and follows the following law: P ext = P int + 0 , 1 × h ≈ 1 + 0 , 1 × h

[0043] In the anti-fouling system according to the invention, a compressor will be used to adjust P int to the immersion depth, and therefore to P ext. The adjustment is made so that the absolute value of the difference between P int and P ext is less than or equal to 2.10 5< Pa (2 bar), or better still, less than 5.10 4< Pa (0.5 bar). Preferably, P int and P ext are equal.

[0044] The plate can then be actuated to produce an antifouling effect, without being hindered by a potential pressure difference between the front and rear faces of the plate. It should be noted that the plate can be actuated continuously or punctually (for example before measurements are taken by the measuring device 10).

[0045] It is specified that the pressure in the cavity 2 can be adjusted according to the immersion depth, but it can also be adjusted by measuring the pressure of the immersion liquid. Indeed, the anti-fouling system 1 can quite easily integrate a pressure sensor capable of measuring the pressure of the immersion liquid.

[0046] Alternatively, the plate deformation can be used to infer the pressure, with prior calibration being required.

[0047] The plate may be rectangular, square or circular; advantageously, it may be a membrane. For example, the plate may be a glass plate whose sides may measure, for example, between a few millimeters and a few centimeters.

[0048] In known manner, a control unit may be used to control the actuator to vibrate the plate. This control unit may be configured to control the actuator so that the plate vibrates in its first mechanical vibration mode.

[0049] Several actuators can be distributed on the front face and / or on the rear face of the plate.

[0050] In a known manner, the actuator(s) may be chosen from piezoelectric, ferroelectric, electrostatic, magnetic or thermal actuators.

[0051] Preferably, the actuator(s) are produced on the rear face of the plate, i.e. on the face opposite the face (front face) of the plate intended to be in contact with the immersion liquid.

[0052] It is specified that in the case where the measuring device is an optical measuring device, for example an optical sensor, the plate and the cavity are made of materials which are transparent to the wavelength considered (i.e. they allow at least 90% of the optical beam to pass through). Similarly, the actuator is positioned so as to allow the passage of the optical beam, so that the optical beam can reach the sensitive surface.

[0053] The anti-fouling system according to the invention can be produced by different production methods; for example, to produce the actuator(s), it is possible to use a piezoelectric ceramic or even thin layers of piezoelectric materials (AlN, PZT, LNO, etc.) formed by microelectronic technologies.

[0054] To illustrate the invention, we will describe an example of a method for producing an anti-fouling system according to the invention comprising a single actuator produced using a piezoelectric ceramic (and intended to be located on the rear face of the plate). The steps are shown schematically on the Figures 6A to 6J .

[0055] On one of the main faces (which we will call the front face) of a substrate 100, for example a silicon substrate with a thickness of approximately 725 µm and a diameter of 200 mm, thermal oxidation is carried out so as to form an oxide layer 101 (SiO 2 ), for example with a thickness of 500 nm ( Figure 6A ).

[0056] On this oxide layer 101, a layer 102 of platinum, a layer 103 of TEOS (tetraethyl orthosilicate (Si(OCH 2 CH 3 ) 4 ) are successively deposited, for example by PECVD (for “Plasma Enhanced Chemical Vapor Deposition”). A layer 104 of photosensitive resin, for example of a SINR polymer from the manufacturer Shin-Etsu, is then laminated thereon ( Figure 6B ). For example, Pt / TEOS / SINR layers have a thickness of approximately 100 nm, 500 nm, 80 µm respectively.

[0057] According to another variant not shown, a titanium layer could also have been deposited before the platinum layer. For example, a Ti / Pt / TEOS / SINR multilayer could have been obtained, the layers having a thickness of approximately 10 nm, 100 nm, 500 nm, 80 µm respectively.

[0058] A piezoelectric actuator is then produced. To do this, a gold (Au) layer of approximately 500 nm ( Figure 6C ).

[0059] As a variant not shown, it would also have been possible to deposit, instead of layer 105, a multilayer comprising a first layer of tungsten W of approximately 50 nm thickness, then a second layer of tungsten nitride alloy (WN) of approximately 50 nm and finally, a third layer of gold (Au) of approximately 200 nm. The tungsten and tungsten nitride layers make it possible to improve the adhesion of the gold layer.

[0060] Then a layer 106 of conductive glue is deposited, for example a layer of silver paste, for example by screen printing ( Figure 6D ).

[0061] A piezoelectric ceramic block 107, approximately 250 µm thick, is then deposited on this layer 106 ( Figure 6E ). This block 107 will form the body of the piezoelectric actuator and the layers 105 and 109 the lower and upper electrodes, respectively, of the actuator.

[0062] Then, this block 107 and a part of the layer 105 are encapsulated by covering them using an encapsulation resin (for example with “glob top”) to subsequently electrically isolate the electrodes 105 and 109 ( Figure 6F ).

[0063] Then, this encapsulated block is leveled until a portion of the piezoelectric ceramic block is retained ( Figure 6G ). The leveled portion of the block has, for example, a thickness of 90 µm.

[0064] On a portion of this leveled block, a layer 109 is deposited which will form the upper electrode of the actuator; for this, for example, a gold (Au) layer of approximately 500 nm is deposited ( Figure 6H ).

[0065] As a variant not shown, a bilayer could have been deposited to form the upper electrode, for example by depositing a titanium (Ti) layer of approximately 20 nm and a gold (Au) layer of approximately 500 nm. The titanium layer is a bonding layer so that the gold layer adheres well.

[0066] Then, this assembly is separated into two subassemblies by peeling, the separation taking place at the interface between the TEOS layer 103 and the platinum layer 102 ( Figure 6I ).

[0067] The subassembly comprising the leveled block forms an actuator 10 and it is bonded at its TEOS layer 103, for example using a layer of UV glue not shown, on a plate 8, which is preferably a membrane, for example a polymer sheet, for example polycarbonate ( Figure 6J ).

[0068] To form the cavity 2, the plate equipped with its piezoelectric actuator(s) can be integrated into a housing 4, as described in the Figure 5 , ensuring sealing and maintenance using screws and gaskets. For the sake of readability, the representation of the walls has been simplified in the Figure 5 compared to the figure 4 .

[0069] The cavity 2 may be a sub-part of the housing 4, obtained in particular by fixing a transparent wall, for example made of PVC, PC or any other suitable material, in the housing. An orifice will allow the passage of the fluid coming from the compressor 3.

[0070] The fluid compressor 3, which is in fluid communication with the cavity 2, may be located inside or outside the housing 4. It is connected to the cavity 2 by a channel or a pipe. The compressor may be, for example, a commercially available compressor, such as, for example, a compressor from the manufacturer Würth.

Claims

1. A system (1) for combating biological fouling by micro-organisms, intended to be transferred to a measuring device which is intended to be immersed in a liquid at a pressure Pliquid and which comprises a sensitive surface (7) sensitive to biological fouling, the system (1) being configured to cover the sensitive surface, the system comprising: - a plate (110) capable of vibrating, having two opposite main faces, referred to as front face and rear face, the front face being intended to be in contact with the liquid; and - at least one actuator, located on one of the main faces of the plate, capable of vibrating the plate, so as to at least limit binding of micro-organisms on the plate; the system being characterised in that it further comprises: - a closed cavity (2), which is delimited at least partially by the rear face of the plate 110, and which is filled with a fluid at a pressure Pcavity; and - a fluid compressor (3), in fluid communication with the closed cavity 2, capable of modulating the fluid pressure Pcavity in the cavity, such that the absolute value of the difference between the pressure Pliquid on the front face and the pressure Pcavity on the rear face is less than 2.105 Pa (2 bar), preferably 5.104 Pa (0.5 bar), ideally so that the pressures are equal.

2. The system according to claim 1, wherein the closed cavity (2) has a depth, in a direction perpendicular to the rear face of the plate (110), between 1 and 10 mm inclusive.

3. The system according to claim 1 or claim 2, wherein the sensitive surface is an optical window.

4. An assembly (30) comprising a measuring device (10) and a system (1) for combating biological fouling according to any one of claims 1 to 3, wherein the cavity (2) is disposed in contact with the entire sensitive surface (7), the sensitive surface and the plate facing each other.

5. The assembly according to claim 4, wherein the measuring device is disposed inside a protective housing (4), the system for combating biological fouling being used to close and seal the housing, the cavity, and optionally the fluid compressor of the system, being disposed inside the housing.

6. An assembly (30) comprising a measuring device (10) and a biological fouling control system (1) according to any one of claims 1 to 3, wherein the cavity (2) is disposed at a distance from the sensitive surface (7), the sensitive surface and the plate facing each other, the system for combating biological fouling being used to close and seal the housing, the cavity, and optionally the fluid compressor of the system, being disposed inside the housing.