Detection device having electroactive transducers and associated detection assembly

Abstract

The invention relates to a detection device comprising: a flexible substrate (20) comprising a first surface (30) and a second surface opposite the first surface; a plurality of transducers (21, 22) attached to the substrate; and a plurality of electrical tracks (23, 24) extending over the substrate. Each transducer has: an electroactive polymer film (50); and a first and a second electrode (54) that are stacked on either side of the film. Each of the first and second electrodes of the corresponding transducer (21, 22) has a conductive layer in contact respectively with a first face and a second face (66) of the film.

Description

[0001] TITLE: Detection device with electroactive transducers and associated detection assembly

[0002] The present invention relates to a detection device of the type comprising: a flexible substrate, including a first and a second opposing surface; a plurality of transducers, fixed to the substrate; and a plurality of electrical tracks, extending over the substrate; each transducer comprising: an active zone, formed of an electroactive material; and a first and a second electrode, stacked on either side of said active zone.

[0003] The invention is particularly applicable to devices for detecting mechanical waves, especially acoustic waves.

[0004] In particular, the invention is intended for the detection of mechanical waves in pressure vessels, especially in composite walled pressure vessels (COPV).

[0005] To prevent failures of pressure vessels, such as those used for hydrogen storage, it is necessary to monitor the condition of their casings in real time. One known method is to use a device capable of detecting acoustic waves generated by mechanical stresses on these casings.

[0006] Tank casings commonly have curved shapes. Therefore, to conform to such a shape, the detection device must be flexible.

[0007] A detection device such as the one described above is notably described in document WO2022214976. However, the constraints indicated above complicate the implementation of this detection device.

[0008] The present invention aims to provide a high-performance detection device, capable of conforming to curved surfaces and easy to manufacture.

[0009] To this end, the invention relates to a detection device of the aforementioned type, in which: each transducer comprises a flexible electroactive polymer film, said film comprising a first and a second opposite face; said film including the active area of ​​the corresponding transducer; and each of the first and second electrodes of the corresponding transducer comprises a conductive layer, in contact respectively with the first and second face of said film, at the level of the active area of ​​said film.

[0010] According to other advantageous aspects of the invention, the detection device comprises one or more of the following features, taken individually or in all technically possible combinations: - each transducer comprises a first and a second connection lug, each of said lugs being electrically connected to one of the plurality of electrical tracks of the detection device; each of the first and second lugs comprising a support layer and a conduction strip, the support layer of each of said lugs being included in the flexible film of the corresponding transducer, the conduction strip of each of the first and second lugs extending over the corresponding support layer, from, respectively, the first and second electrode;

[0011] - the plurality of electrical tracks comprises at least a first track and at least a second track, said first track and said second track extending respectively over the first surface and over the second surface of the substrate; and the first and second electrodes of one of the plurality of transducers are electrically connected, respectively, to the first track and to the second track;

[0012] - the first electrode of the transducer is disposed between the flexible film of said transducer and the first surface of the substrate; said substrate includes a through slot; the second connecting leg of the transducer is disposed in said slot; and the conduction strip of said second leg is electrically connected to the second track;

[0013] - the detection device further includes a conductive coating, extending over the second surface of the substrate;

[0014] - the electroactive polymer forming the flexible film is a piezoelectric polymer;

[0015] - the piezoelectric polymer comprises a fluorinated polymer derived from the polymerization of vinylidene fluoride;

[0016] - the fluorinated polymer is obtained from the co-polymerization of vinylidene fluoride (VDF) and vinylidene trifluoride (TrFE), a molar proportion of said vinylidene trifluoride being preferably between 15% and 50% in said fluorinated polymer.

[0017] The invention further relates to a detection assembly comprising: an enclosure, including an external surface; and a detection device as described above, the substrate of said detection device being fixed to the external surface of the enclosure, the first surface of said substrate being oriented towards said external surface.

[0018] According to other advantageous aspects of the invention, the detection assembly comprises one or more of the following features, taken individually or in all technically possible combinations:

[0019] - the detection device further includes a layer of coupling material, arranged between the first surface of the substrate and the external surface of the enclosure, so as to transmit acoustic waves from the enclosure between the active areas of the plurality of transducers of said device;

[0020] - the external surface of the enclosure has a curved shape; and the substrate and the plurality of transducers of the detection device conform to said curved shape;

[0021] - the enclosure is made of a composite material.

[0022] The invention further relates to a method for manufacturing a detection device as described above, comprising the following steps: supplying a flexible sheet of electroactive polymer, comprising a first and a second opposite face; then producing a plurality of first patterns, substantially identical, by depositing a first electrically conductive material on the first face of the flexible sheet; then producing a plurality of second patterns, substantially identical, by depositing a second electrically conductive material on the second face of the flexible sheet; each second pattern being opposite one of the first patterns; then cutting the flexible sheet into a plurality of flexible films, each of said films bearing a first pattern and a second pattern opposite each other;the plurality of transducers of the detection device being thus obtained, each of the first and second motifs of one of said films forming respectively the first and second electrode of the corresponding transducer.

[0023] According to other advantageous aspects of the invention, the method comprises one or more of the following features, taken individually or in all technically possible combinations:

[0024] - the first and second motifs of the film comprise the conduction strip, respectively of the first and second connecting lugs; said conduction strips being separated from each other by a space in the flexible film; and the method then comprises forming a notch in said space in the film;

[0025] - the process then includes the following steps: fixing a transducer on the first surface of the substrate, near a through slot; inserting the second connecting leg of the transducer into said slot, up to the second surface of the substrate; and connecting the conduction strip of said second leg to the second track.

[0026] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the drawings in which:

[0027] [Fig 1] Figure 1 is a schematic view of a detection assembly according to one embodiment of the invention;

[0028] [Fig 2] Figure 2 is a detailed, cross-sectional view of the detection assembly in Figure 1; [Fig 3] [Fig 4] Figures 3 and 4 are detailed views of a detection device that is part of the detection assembly in Figures 1 and 2; and

[0029] [Fig 5] [Fig 6] Figures 5 and 6 are views of an element of the detection device of Figures 3 and 4.

[0030] Figure 1 shows a detection assembly 10 according to one embodiment of the invention.

[0031] The detection assembly 10 includes an enclosure 12 and a detection device 14.

[0032] The enclosure 12 comprises an external surface 16 and a filling element 17. In one embodiment, the external surface 16 has a curved shape. In the embodiment shown, the external surface 16 of the enclosure 12 has a cylindrical shape of revolution, extending along a principal direction X.

[0033] According to one embodiment, the enclosure 12 is formed of a composite material 18 (Figure 2). In particular, the enclosure 12 is formed of a material comprising a thermoplastic or thermoset matrix and at least one reinforcing filler.

[0034] In the case of a thermoplastic matrix, the matrix is ​​preferably chosen from polypropylenes, polyamides, polyaryletherketones, PMMA and their mixtures.

[0035] In the case of a thermoset matrix, the matrix is ​​preferably chosen from among epoxies, polyesters and vinyl esters.

[0036] The reinforcing material is preferably a fibrous material, more preferably a material comprising long fibers, in particular glass and / or carbon fibers.

[0037] According to one embodiment, the enclosure 12 is part of a pressurized fluid reservoir, for example a pressurized hydrogen reservoir.

[0038] The detection device 14 comprises: a substrate 20; a plurality of transducers 21, 22; and a plurality of electrical tracks 23, 24, 25 (Figures 3-4). In one embodiment, the device 14 further comprises an electrical connector 26 (Figure 1). In another embodiment, the device 14 further comprises a shielding coating 27 and / or a coupling element 28 (Figure 2).

[0039] The substrate 20 comprises a first 30 and a second 32 opposing surfaces. The device 14 is assembled to the enclosure 12 such that the first surface 30 of the substrate 20 is opposite the external surface 16 of said enclosure, as described below.

[0040] The substrate 20 is made of a flexible material, particularly suited to conforming to the curved shape of the external surface 16 of the enclosure 12. The flexible material of the substrate 20 is, for example, a polyimide. In the embodiment shown, the substrate 20 comprises a main strip 34 and a plurality of lateral strips 36, 38 (Figure 1).

[0041] The main band 34 is substantially straight and extends along an axis 40. In an assembled configuration of the set 10, as seen in Figure 1, the axis 40 is parallel to the main direction X of the enclosure 12. The main band 34 includes in particular an end 42 along the axis 40, called the connection end 42.

[0042] The lateral bands 36, 38 are arranged on either side of the main band 34. Each lateral band 36, 38 extends substantially perpendicularly to the axis 40, from said main band 34.

[0043] In the embodiment shown, the substrate 20 has pairs of lateral strips 36, 38 opposite each other along the axis 40. In an alternative not shown, the lateral strips are offset from each other along the axis 40.

[0044] The transducers 21, 22 of the detection device 14 are fixed to the substrate 20, as described in more detail below. Preferably, the device 14 comprises a plurality of transducers 21, 22, distributed over the main band 34 and over the side bands 36, 38 of the substrate 20.

[0045] In particular, Figures 3 and 4 show a first 36 and a second 38 sidebands of the substrate 20, arranged near the connection end 42 of the main band 34. Figures 3 and 4 also show a first 21 and a second 22 transducers of the device 14, attached respectively to the first 36 and the second 38 sideband.

[0046] Preferably, the transducers 21 and 22 of the device 14 are substantially identical to each other. The first 21 and second 22 transducers will be described in more detail below.

[0047] The electrical traces 23, 24, 25 extend onto the substrate 20, as described in more detail below. The assembly formed by the substrate 20 and the electrical traces 23, 24, 25 is specifically of the Printed Circuit Board Flexible (PCB flex) type.

[0048] In the embodiment shown, the electrical tracks 23, 24, 25 extend to the connection end 42 of the main strip 34 of the substrate 20.

[0049] In particular, Figures 3 and 4 show electrical tracks 23, 24, 25 connected to the first 21 and / or the second 22 transducers. Preferably, the device 14 also includes other electrical tracks, not shown in Figures 3 and 4, connected to other transducers of the device 14. The first 21 and second 22 transducers of the device 14 will now be described together, under the designation "the transducer 21, 22". By way of illustration, the first transducer 21 is shown alone in Figures 5 and 6, the corresponding description also being valid for the second transducer 22.

[0050] The transducer 21, 22 is in the form of a stack of flexible layers. By "flexible," we mean that the stack forming the transducer 21, 22 is particularly capable of conforming to the curved shape of the external surface 16 of the enclosure 12, as will be described later.

[0051] More specifically, the transducer 21, 22 comprises: a flexible film 50; a first 52 and a second 54 electrode; and a first 56 and a second 58 connecting pins.

[0052] In the embodiment shown, the transducer 21, 22 further comprises a first 60 and a second 62 motifs, stacked on either side of the film 50. As will be described below, the first 52 and the second 54 electrodes are included, respectively, in the first 60 and in the second 62 motif.

[0053] The film 50 comprises: a first 64 and a second 66 opposite faces; and a peripheral edge 68. In the embodiment shown, the peripheral edge 68 is substantially rectangular.

[0054] Preferably, a thickness of 70 of the 50 film between its first 64 and second 66 faces is between 1 pm and 200 pm, more preferably between 5 pm and 100 pm, even more preferably between 10 pm and 50 pm.

[0055] The flexible 50 film is made of an electroactive material.

[0056] The term "electroactive material" refers, in particular, to piezoelectric or piezoresistive materials. A piezoelectric material becomes electrically polarized when subjected to mechanical stress. A piezoresistive material exhibits electrical resistance that varies according to the mechanical stress applied to it.

[0057] More specifically, the film material 50 comprises at least one electroactive polymer, said electroactive polymer being selected from among a piezoelectric polymer and a piezoresistive polymer. A "piezoresistive polymer" is defined as an insulating polymer matrix in which conductive particles are embedded. Such a matrix is, for example, silicone, polyurethane, or epoxy; the conductive particles are, for example, graphite fibers, carbon nanotubes, or carbon black.

[0058] Preferably, the film material 50 comprises at least one piezoelectric polymer. More preferably, said piezoelectric polymer comprises a fluorinated polymer resulting from the polymerization of vinylidene fluoride. Even more preferably, said fluorinated polymer is of the P(VDF-TrFE) type, that is to say, said fluorinated polymer is resulting from the co-polymerization of vinylidene fluoride (VDF) and vinylidene trifluoride (TrFE). In other words, said fluorinated polymer is essentially composed of, or made up of, repeating units resulting from the polymerization of vinylidene fluoride (VDF) and vinylidene trifluoride (TrFE).

[0059] Even more preferably, the molar proportion of vinylidene trifluoride is between 15% and 50% in the fluorinated polymer. In other words, the molar proportion of the repeating unit derived from TrFE in the fluorinated polymer is between 15% and 50% relative to the total number of moles of repeating units derived from VDF and TrFE.

[0060] A piezoelectric polymer suitable for the formation of the 50 film is notably marketed under the name Piezotech®.

[0061] The first 52 and the second 54 electrodes are arranged respectively on the first 64 and the second 66 faces of the film 50.

[0062] The first 52 and second 54 electrodes are arranged opposite each other with respect to the film 50 and are preferably superimposed on each other. An area of ​​said film 50, called the active area 72, is defined between said first 52 and second 54 electrodes.

[0063] In the embodiment shown, the first 52 and second 54 electrodes and the active area 72 have a circular outline. Other shapes can be considered for said outline, for example an oval or polygonal shape.

[0064] Each of the first 52 and second 54 electrodes is formed of an electrically conductive layer. Preferably, each electrode 52, 54 is formed of a conductive polymer composition or a composition based on conductive metals. Said composition is more preferably chosen from: a composition of poly(3,4-ethylenedioxythiophene and poly(styrene sulfonate) (PEDOT:PSS); a composition based on a metal oxide, for example indium tin oxide; a composition based on silver, for example silver flakes or silver nanowires; a composition based on copper or carbon, for example graphene.

[0065] Preferably, the first 52 and second 54 electrodes and the active zone 72 are elastically stretchable. More preferably, electrodes 52 and 54 can withstand deformations of 1% to 4% elongation without loss of conductivity.

[0066] Each of the first 56 and second 58 connecting pins has a conduction strip 74, 76 and a support layer 78.

[0067] The conduction band 74, 76 of each of the first 56 and second 58 connecting pins extends over the film 50, from, respectively, the first 52 and second 54 electrodes. The conduction band 74, 76 is formed of an electrically conductive layer, preferably continuous with the corresponding electrode 52, 54.

[0068] The conduction band 74 of the first leg 56 extends over the first face 64 of the film 50 and is included in the first motif 60. The conduction band 76 of the second leg 58 extends over the second face 66 of said film 50 and is included in the second motif 62.

[0069] The support layer 78 is included in the film 50 and defined by the conduction band 74, 76 in contact with said support layer 78.

[0070] A non-zero spacing 80 is provided between the conduction bands 74 and 76 of the first 56 and second 58 pins, in the plane of the film 50.

[0071] In the embodiment shown, the conduction bands 74 and 76 are substantially straight and parallel to each other. Other configurations can be considered, such as a non-zero angle formed between said conduction bands.

[0072] In the embodiment shown, the first motif 60 is formed solely by the first electrode 52 and the conduction band 74 of the first leg 56; and the second motif 62 is formed solely by the second electrode 54 and the conduction band 76 of the second leg 58. Each of the first 60 and second 62 motifs thus has a shape substantially in p or q. Preferably, the first 60 and second 62 motifs are identical.

[0073] Preferably, the film 50 has a substantially straight notch 82 extending from the peripheral edge 68. This notch 82 is located between the two connecting tabs 56 and 58, so that the tabs can move apart. The notch 82 is formed in the gap 80 between the conduction strips 74 and 76.

[0074] The electrical tracks 23, 24, 25 of device 14 will now be described.

[0075] Each of the electrical tracks 23, 24, 25 of the device 14 extends on the substrate 20, between at least one input 84, 85, 86 and one output 88, 90. At least one input 84, 85, 86 of each of said tracks 23, 24, 25 is connected to one of the transducers 21, 22 of the device 14. In the embodiment shown, the output 88, 90 of each of said tracks 23, 24, 25 terminates opposite the connection end 42 of the main strip 34.

[0076] In the embodiment shown, the tracks 23, 24, 25 of the device 14 include at least a first track 23, 24 (figure 3) and at least a second track 25 (figure 4).

[0077] The first track 23, 24 comprises a single input 84, connected to the first electrode 52 of one of the transducers 21, 22. Preferably, the device 14 comprises a plurality of first tracks 23, 24 and the input 84 of each of said first tracks 23, 24 is connected to the first electrode 52 of one of the transducers 21, 22.

[0078] Each input 85, 86 of at least one second track 25 is connected to the second electrode 54 of one of the transducers 21, 22. In the embodiment shown, the device 14 comprises a single second track 25, said second track comprising several inputs 85, 86. Each of said inputs 85, 86 of the second track 25 is connected to the second electrode 54 of one of the transducers 21, 22.

[0079] In the embodiment shown, the first 21 and second 22 transducers of the device 10 are fixed on the first surface 30 of the substrate 20; and the first tracks 23, 24 extend over said first surface 30 of the substrate 20, as seen in Figure 3.

[0080] More specifically, each transducer 21, 22 is fixed to the first surface 30 of the substrate 20 such that the first face 64 of the corresponding film 50 is opposite said first surface 30; and the conduction strip 74 of the first connecting pin 56 is in electrical contact with the input 84 of the corresponding first track 23, 24. The first electrode 52 of each transducer 21, 22 is thus connected to the input 84 of one of the first tracks 23, 24.

[0081] Furthermore, in the embodiment shown, the second track 25 extends over the second face 32 of the substrate 20, as can be seen in Figure 4.

[0082] In order to connect the second electrode 54 to said second track 25, the substrate 20 has a plurality of through slots 92, 93, connecting the first surface 30 to the second surface 32. Preferably, each of said slots 92, 93 is substantially straight and extends between two closed ends.

[0083] Each of said through slots 92, 93 is associated with one of the transducers 21, 22. More precisely, each slot 92, 93 is provided opposite the second connecting pin 58 of the corresponding transducer 21, 22; and said second pin 58 is disposed in said slot 92, 93.

[0084] Thus, a free end 94 (figure 6) of the conduction strip 76, opposite the second electrode 54, emerges at the level of the second surface 32 of the substrate 20. Said free end 94 of the conduction strip 76 is in electrical contact with the corresponding input 85, 86 of the second track 25. The second electrode 54 of each transducer 21, 22 is thus connected to one of the inputs 85, 86 of the second track 25.

[0085] In the embodiment shown, each slot 92, 93 also extends opposite the first connecting pin 56 of the corresponding transducer 21, 22, but said first pin 56 is not disposed in said slot. Preferably, a sealing tab 96 is placed on each slot 92, 93 on the side of the second surface 32 of the substrate 20, so as to cover said slot at the level of the first connecting pin 56 of the corresponding transducer 21, 22.

[0086] According to an unrepresented variant, the second track 25 is made on the first surface 30 of the substrate 20, as are the first tracks 23, 24. In this case, another configuration of each transducer 21, 22 is required to connect the second pin 58 corresponding to said second track 25.

[0087] The electrical connector 26 of the device 14 is fixed to the connection end 42 of the main strip 34 of the substrate 20. More specifically, the electrical connector 26 is connected to the outputs 88, 90 of the tracks 23, 24, 25 of the device 14. In the embodiment shown, the electrical connector 26 is able to connect the first tracks 23, 24 to one or more measuring devices and to connect the second track 25 to ground.

[0088] Preferably, the electrical connector 26 is arranged opposite the filling element 17 of the enclosure 12, along the main direction X.

[0089] Figure 2 shows a cross-sectional view of assembly 10, along axis 40 of main strip 34 of device 14. In particular, the cross-sectional plane of Figure 2 is at a distance from transducers 21, 22 and tracks 23, 24, 25.

[0090] In the embodiment shown, the device 14 includes a shielding coating 27 and a coupling 28, visible in Figure 2.

[0091] The shielding coating 27 of the device 14 is an electrically conductive layer, which covers the first 30 or the second 32 surface of the substrate 20, not oriented towards the enclosure 12. In the embodiment shown, the shielding coating 27 covers the second face 32 of the substrate and is in electrical contact with the second track 25.

[0092] Preferably, if the enclosure 12 is made of a sufficiently conductive material, the coating 27 and the enclosure 12 form a Faraday cage, which protects the device 14 from electromagnetic interference. In the case of an insulating enclosure 12, two shielding layers are, for example, arranged on either side of the substrate 20.

[0093] The coupling 28 is an adhesive layer, which covers the first surface 30 of the substrate 20, as well as the transducers 21, 22 at the level of the first 52 and second 54 electrodes.

[0094] The coupling 28 is positioned between the substrate 20 and the external surface 16 of the enclosure 12, so as to fix the detection device 14 to said enclosure 12. This coupling 28 is particularly suitable for efficiently transmitting waves between the transducers 21, 22 of the assembly 10 and / or between the enclosure 12 and said transducers. Preferably, the coupling 28 is chosen for its acoustic wave transmission. Preferably, the coupling 28 also exhibits: high flexibility, on the order of 1% to 4%; and stability under temperature variations, for example between -50°C and +100°C.

[0095] Coupling agent 28, for example, is made of a polymer resin, such as an epoxy resin. Suitable materials for coupling agent 28 are marketed under the names EPO-TEK® 301, Loctite® Hysol, and Araldite® 2019.

[0096] A manufacturing process for the detection device 14 will now be described.

[0097] Preferably, all transducers 21, 22 of the detection device 14 are manufactured simultaneously, so as to be as identical as possible to each other. This optimizes the detection quality, as identical transducers provide the same piezoelectric or piezoresistive response.

[0098] The transducers 21, 22 of device 14 are, for example, made in the manner described below:

[0099] A flexible sheet of electroactive polymer, comprising a first 64 and a second 66 opposing faces, is first formed. The thickness 70 of said flexible sheet is chosen to be sufficient to ensure efficient transducer performance.

[0100] Optionally, the flexible ribbon is subjected to a polarization step, for example by corona.

[0101] Next, a plurality of first motifs 60, substantially identical, are produced on the first face 64 of the tablecloth. The first motifs 60 are formed in particular by depositing a first electrically conductive material on said first face 64.

[0102] Next, a plurality of second motifs 62, substantially identical, are produced on the second side 66 of the tablecloth, each second motif 62 being opposite one of the first motifs 60. The second motifs 62 are formed, in particular, by depositing a second electrically conductive material onto the tablecloth. Preferably, the first and second electrically conductive materials are identical. The first 60 and second 62 motifs are produced, in particular, by screen printing.

[0103] Next, the flexible sheet is cut around the patterns 60, 62, so as to form the peripheral edges 68 of the films 50 of the transducers 21, 22 thus obtained. A notch 82 is also formed between the tabs 56 and 58 of each of said transducers.

[0104] The resulting plurality of transducers 21, 22 exhibits optimal homogeneity. In particular, said transducers 21, 22 have the same sensitivity to detection, therefore calibrating a single transducer allows the entire device to be calibrated.

[0105] Furthermore, the manufacturing process of the device 14 includes: cutting the substrate 20 according to the chosen shape, for example with the strips 34, 36, 38 described previously; making the tracks 23, 24, 25 on said substrate; and forming the slots 92, 93 at the locations of the transducers 21, 22.

[0106] Each of the transducers 21, 22 is then fixed to the first surface 30 of the substrate 20, in the designated location. The first pin 56 of said transducer is electrically connected to the input 84 of the corresponding first track 23, 24, for example, using a conductive adhesive, particularly a silver-based one. Suitable conductive adhesives include, for example, Super Glue MG Chemicals Silver Conductive, LOCTITE® ABLESTIK 3888, or Circuitworks Conductive Epoxy.

[0107] Furthermore, the second leg 58 of said transducer is inserted into the corresponding slot 92, 93, to be fixed to the corresponding input 85, 88 of the second track 25.

[0108] Preferably, the slot 92, 93 extends over the entire width of the transducer 21, 22; and after the insertion of the second leg 58 of said transducer into said slot, the sealing tab 96 is placed on the side of the second surface 32, opposite the first leg 56. The insertion of the second leg 58 into the corresponding slot 92, 93 is thus facilitated.

[0109] After the transducers 21, 22 are fixed to the substrate 20, the shielding coating 27 is applied to the second face 32 of said substrate. Furthermore, the electrical connector 26 is assembled to the connection end 42 of said substrate.

[0110] Next, the coupling 28 is applied to the first face 30 of said substrate. The device 14 can thus be assembled to the external surface 16 of the enclosure 12 to form the detection assembly 10.

[0111] In particular, during the assembly of the enclosure 12 and the device 14, the axis 40 of the main band 34 of the substrate 20 is arranged parallel to the main direction X of the enclosure 12; and the side bands 36, 38 are wrapped around said enclosure. The transducers 21, 22 of the device 14 are therefore distributed over the highest possible proportion of the external surface 16 of the enclosure 12.

[0112] During the assembly of the enclosure 12 and the device 14, the substrate 20 and the flexible transducers 21, 22 conform to the curved shape of the external surface 16 of said enclosure, so as to fit snugly against said external surface. The device 14 is thus assembled to the enclosure 12 in such a way as to efficiently receive mechanical waves, in particular acoustic waves, propagating within said enclosure 12.

[0113] Similarly, the detection device 14 is capable of elastic deformation in the event of slight changes in the volume of the enclosure 12, eliminating the risk of mechanical rupture. In particular, if the enclosure 12 is part of a pressurized hydrogen tank, said enclosure is likely to undergo volume deformations on the order of 1% to 2%.

[0114] In the case of piezoelectric transducers 21, 22, the thickness 70 of the active zone 72 of the transducers 21, 22 gives said transducers a resonant frequency on the order of MHz. Such a resonant frequency is very far from the frequency band of interest in acoustic emission, on the order of 100 to 800 kHz.

[0115] Moreover, the thickness 70 is sufficient to provide satisfactory sensitivity to the transducers 21, 22. In particular, a screen printing of the active area 72 on the substrate 20 would not allow such thicknesses to be achieved.

[0116] The detection device 14 is easy to manufacture, particularly by the method described above. In the event of a failure of said device, it is easy to replace by detaching it from the external surface 16 of the enclosure 12. The detection assembly 10 described above therefore has a longer lifespan than a similar assembly in which the transducers would be integrated into the composite wall of the enclosure.

[0117] Similarly, the detection device 14 described above is easy to associate with the enclosure 12 of an existing tank to form a detection assembly 10.

[0118] In one embodiment, the device 14 comprises: a first series of transducers 21, 22 and associated tracks 23, 24, 25, arranged on the substrate 20; and one or more similar second series of transducers and associated tracks, arranged on the same substrate 20. For example, the first series comprises piezoelectric transducers and the second series comprises piezoresistive transducers. It is thus possible to provide a versatile device 14, detecting both acoustic waves and deformations of the enclosure 12.

Claims

DEMANDS 1. A detection device (14) comprising: a flexible substrate (20) comprising a first (30) and a second (32) opposing surfaces; a plurality of transducers (21, 22) fixed to the substrate; and a plurality of electrical tracks (23, 24, 25) extending over the substrate; each transducer (21, 22) comprising: an active zone (72) formed of an electroactive material; and a first (52) and a second (54) electrode stacked on either side of said active zone; each transducer (21, 22) comprising a flexible film (50) of electroactive polymer, said film comprising a first (64) and a second (66) opposing faces; said film (50) including the active zone (72) of the corresponding transducer (21, 22);and each of the first (52) and second (54) electrodes of the corresponding transducer (21, 22) having a conductive layer, in contact respectively with the first (64) and second (66) face of said film (50), at the level of the active area (72) of said film; each transducer (21, 22) comprising a first (56) and a second (58) connection lugs, each of said lugs (56, 58) being electrically connected to one of the plurality of electrical tracks (23, 24, 25) of the detection device; each of the first (56) and second (58) legs comprising a support layer (78) and a conduction band (74, 76), the support layer of each of said legs being included in the flexible film (50) of the corresponding transducer (21, 22), the conduction band (74, 76) of each of the first (56) and second (58) legs extending over the corresponding support layer (78), from, respectively, the first (52) and the second (54) electrode;the plurality of electrical tracks comprising at least a first track (23, 24) and at least a second track (25), said first track and said second track extending respectively over the first surface (30) and over the second surface (32) of the substrate (20); the first (52) and second (54) electrodes of one of the plurality of transducers (21, 22) being electrically connected, respectively, to the first track (23, 24) and to the second track (25); the sensing device being characterized in that: the first electrode (52) of the transducer (21, 22) is disposed between the flexible film (50) of said transducer and the first surface (30) of the substrate (20); said substrate comprises a through slot (92, 93); the second connecting pin (58) of the transducer is disposed in said slot; and the; conduction strip (76) of said second leg (58) is electrically connected to the second track (25).

2. Detection device according to claim 1, further comprising a conductive coating (27), extending over the second surface (32) of the substrate (20).

3. Detection device according to claim 1 or 2, wherein the electroactive polymer forming the flexible film (50) is a piezoelectric polymer.

4. Detection device according to claim 3, wherein the piezoelectric polymer comprises a fluorinated polymer obtained from the polymerization of vinylidene fluoride.

5. Detection device according to claim 4, wherein the fluorinated polymer is obtained from the co-polymerization of vinylidene fluoride (VDF) and vinylidene trifluoride (TrFE), a molar proportion of said vinylidene trifluoride being preferably between 15% and 50% in said fluorinated polymer.

6. Detection assembly (10), comprising: an enclosure (12), including an external surface (16); and a detection device (14) according to any one of the preceding claims, the substrate (20) of said detection device being fixed to the external surface of the enclosure, the first surface (30) of said substrate being oriented towards said external surface.

7. Detection assembly according to claim 6, wherein the detection device (14) further comprises a layer (28) of coupling material, disposed between the first surface (30) of the substrate (20) and the external surface (16) of the enclosure (12), so as to transmit acoustic waves from the enclosure between the active areas (72) of the plurality of transducers (21, 22) of said device (14).

8. Detection assembly according to claim 6 or 7, wherein: the external surface (16) of the enclosure (12) has a curved shape; and the substrate (20) and the plurality of transducers (21, 22) of the detection device (14) conform to said curved shape.

9. Detection assembly according to any one of claims 6 to 8, wherein the enclosure (12) is formed of a composite material.

10. A method for manufacturing a detection device according to any one of claims 1 to 5, comprising the following steps: 16 - supply of a flexible sheet of electroactive polymer, comprising a first (64) and a second (66) opposite faces; then - production of a plurality of first motifs (60), substantially identical, by depositing a first electrically conductive material on the first face (64) of the flexible sheet; then - production of a plurality of second motifs (62), substantially identical, by depositing a second electrically conductive material on the second face (66) of the flexible sheet; each second motif being opposite one of the first motifs; then - cutting the flexible sheet into a plurality of flexible films (50), each of said films bearing a first pattern (60) and a second pattern (62) opposite each other; the plurality of transducers (21, 22) of the detection device being thus obtained, each of the first and second patterns of one of said films (50) forming respectively the first (52) and the second (54) electrode of the corresponding transducer.

11. A manufacturing method according to claim 10, wherein: - the first (60) and second (62) motifs of the film (50) comprise the conduction strip (74, 76), respectively, of the first (56) and second (58) connecting tabs; said conduction strips being separated from each other by a gap (80) in the flexible film (50); and - the process then includes the formation of a notch (82) in said space (80) of the film (50).

12. A manufacturing method according to claim 10 or 11, further comprising the following steps: fixing a transducer (21, 22) on the first surface (30) of the substrate (20), near a through slot (92, 93); inserting the second connecting leg (58) of the transducer into said slot, up to the second surface (32) of the substrate; and connecting the conduction strip (76) of said second leg (58) to the second track (25).

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