Force measurement device on a complex surface

Abstract

Force measurement device on a complex surface. This description relates to a conformable force measurement device, intended to be subjected simultaneously to compressive and bending forces, the device comprising sensors (11, 12) arranged on either side of a substrate (100), the sensors comprising an organic piezoelectric layer (120) disposed between a first electrode (110) and a second electrode (130), the sensors (11, 12) being arranged opposite each other, so as to form a bimorph (10), the sensors being connected to electrically conductive tracks (200) intended to be connected to measuring devices, the organic piezoelectric layers (120) of the sensors (11, 12) being polarized and the sensors (11, 12) being intended to be electrically connected to the measuring devices so as to cancel either the compressive or the bending forces. Figure for the abridged version: Fig. 6

Description

Title of the invention: Force measurement device on a complex surface. Technical field

[0001] This description relates generally to force measurement devices, and in particular to force measurement devices on complex and / or deformable surfaces. Previous technique

[0002] Piezoelectric sensors can be used to measure forces, particularly compressive forces. Generally, the sensor is positioned on a surface such that the mechanical stress is not only uniform across the sensor surface but also unidirectional in the direction transverse to the sensor. Thus, it is possible to have a proportionality between the electrical charge Q generated by the sensor and the applied force F.

[0003] For flat surfaces, the sensors may include rigid inorganic piezoelectric materials such as ceramics.

[0004] For certain applications, surfaces are non-planar and / or deformable, and the sensors must be flexible. For these applications, flexible sensors comprising a thin piezoelectric polymer film are generally used.

[0005] For example, in the article by Hong et al. (Hong, Y. et al. “Highly anisotropic and flexible piezoceramic kirigami for preventing joint disorders”. Sci. Adv. 7, eabf0795 (2021)), a flexible sensor is presented. The sensor is made from a honeycomb-shaped nylon textile. The textile is coated with a solution of [Pb(Zr₂O₅₂TiO₄₈)₃. After evaporation of the solvent, a gel forms around the nylon. PDMS is then added to form a polymer matrix. Finally, silver nanowire electrodes are formed. Two 1.5 cm x 1.5 cm sensors thus fabricated are positioned one above the other to form the final device. This device is flexible and can be used on the skin. It serves to determine the direction of the bending applied to the sensor. For example, when positioned on a person's neck or shoulder, various deformations can be detected. There is no compression measurement.

[0006] The article by Lin et al. (Lin, W. et al. “Skin-Inspired Piezoelectric Tactile Sensor Array with Crosstalk-Free Row+Column Electrodes for Spatiotemporally Distinguishing Diverse Stimuli”. Adv. Sci. 8, 2002817 (2021)) presents a flexible device comprising several piezoelectric sensors. The sensors comprise PVDF layers arranged between PDMS films. The number of connections The electrical value corresponds to the sum of the number of rows and the number of columns. The different stresses are tested one by one. The device allows for the differentiation of amplitude, positions, and various external stimuli in real time (bending, compression, and shear). Compression causes a bending deformation of the piezoelectric film.

[0007] There is no simple theoretical model that allows the electric charge generated by the piezoelectric to be linked to bending stresses when the device is subjected to both bending and compressive forces.

[0008] Indeed, when the conformable sensor is positioned on a complex surface, the flexural deformation of the sensor generates electrical charges that interfere with the charges generated by the force to be measured. If this force is too weak (in particular, less than 100 kPa) and the flexural deformations are too large, it is then not possible to measure the force.

[0009] By way of example, [Fig. 1] shows tests of piezoelectric force sensors. The referenced graph (a) represents a compressive force applied to a non-conformable sensor mounted on a rigid surface. The referenced graph (b) shows the sensor's response. The signal is easy to interpret: a first peak appears when the force is applied, and a second peak opposite the first is visible; this peak is characteristic of the release after the force has been applied. The graph shown (c) shows the response of a conformable sensor that takes the shape of the surface on which the force is applied. The sensor is therefore subjected to bending and compression: the signal is chaotic, with numerous peaks, and uninterpretable. Summary of the invention

[0010] There is therefore a need to provide a measuring device that can measure compressive forces (even weak ones), or bending forces, when it is placed on a complex and / or deformable surface and when it is subjected to both bending and compressive forces.

[0011] This objective is achieved by a conformable force measuring device, intended to be subjected simultaneously to compressive and bending forces, the device comprising a substrate having a first face and a second face, at least one first sensor disposed on the first face of the substrate and at least one second sensor disposed on the second face of the substrate, the sensors comprising an organic piezoelectric layer disposed between a first electrode and a second electrode, the sensors being arranged opposite each other so as to form a bimorph. The sensors are connected to electrically conductive tracks. intended to be connected to measuring devices. The organic piezoelectric layers of the sensors are polarized in the same or opposite ways.

[0012] Advantageously, the sensors are covered by a stack comprising successively a first dielectric layer, a ground plane and a second dielectric layer.

[0013] Advantageously, the ground plane is made of carbon and / or the first dielectric layer and the second dielectric layer are made of ED AG or PVDF.

[0014] Advantageously, the substrate is a PEN or PI substrate.

[0015] Advantageously, the substrate comprises two support substrates, for example made of TPU, joined together by an adhesive element.

[0016] Advantageously, the first face of the substrate is covered by a first sensor matrix and the second face of the substrate is covered by a second sensor matrix, the first matrix and the second matrix being arranged opposite each other.

[0017] According to this advantageous variant, on the one hand, the first electrode of each sensor of the first matrix can be connected to an individual electrically conductive track and, on the other hand, all the second electrodes of the sensors of the first matrix can be connected to a common electrically conductive track and, on the one hand, the first electrode of each sensor of the second matrix can be connected to an individual electrically conductive track and, on the other hand, all the second electrodes of the sensors of the second matrix can be connected to another common electrically conductive track.

[0018] This objective is also achieved by a force measurement system comprising a conformable device intended to be subjected simultaneously to compressive and bending forces, the device comprising a substrate having a first face and a second face, at least one first sensor disposed on the first face of the substrate and at least one second sensor disposed on the second face of the substrate, the sensors comprising an organic piezoelectric layer disposed between a first electrode and a second electrode, the sensors being arranged opposite each other so as to form a bimorph. The system further comprises measuring devices electrically connected to the sensors for measuring the sensor signals.The organic piezoelectric layers of the sensors are polarized and the sensors are electrically connected to the measuring devices in such a way as to cancel either the compressive or bending forces, and to measure, respectively, either the bending or compressive forces applied to the device.

[0019] Advantageously, the polarization of the sensors is opposite, in that the sensors are connected to the measuring devices in opposite ways and in that the signals The forces measured by the measuring devices are added together, thereby canceling out the bending forces and measuring the compressive forces.

[0020] Advantageously: - the polarizations of the sensors are identical, the sensors are connected to the measuring devices in the same way, and the signals measured by the measuring devices are summed, or - the polarizations of the sensors are opposite, the sensors are connected to the measuring devices in the same way, and the signals measured by the measuring devices are subtracted, or - the polarizations of the sensors are identical, the sensors are connected to the measuring devices in opposite ways, and the signals measured by the measuring devices are subtracted. whereby the bending forces are canceled out and the compressive forces are measured.

[0021] This objective is also achieved by a method for measuring force in compression and bending, comprising the following steps: - to provide a force measurement system comprising a conformable device intended to be subjected simultaneously to compressive and bending forces, the device comprising a substrate having a first face and a second face, at least one first sensor disposed on the first face of the substrate and at least one second sensor disposed on the second face of the substrate, the sensors comprising an organic piezoelectric layer disposed between a first electrode and a second electrode, the sensors being arranged opposite each other so as to form a bimorph, the system further includes measuring devices electrically connected to the sensors, for measuring the sensor signals, the organic piezoelectric layers of the sensors being polarized and the sensors being electrically connected to the measuring devices in such a way as to cancel either the compressive or bending forces, - simultaneously apply compressive and bending forces to the measuring device, - to add or subtract the signals measured by the measuring devices, so as to cancel either the compressive forces or the bending forces, and thus measure, respectively, either the bending forces or the compressive forces applied to the device.

[0022] Advantageously, the device comprises a first sensor array on the first face of the substrate and a second sensor array on the second face of the substrate, the first matrix and the second matrix being arranged opposite each other.

[0023] Advantageously, the sensor(s) of the first face have a polarization opposite to the polarization of the sensor(s) of the second face, the sensor(s) of the first face are electrically connected to first charge amplifiers, the sensor(s) of the second face are electrically connected to second charge amplifiers, the electrical connections to the first charge amplifiers and the electrical connections to the second charge amplifiers being opposite, the signals from the sensors being added together to eliminate the signal of the bending forces and obtain the signal of the compressive forces.

[0024] Advantageously, on the one hand, the first electrode of each sensor of the first matrix is ​​connected to an individual electrically conductive track, itself electrically connected to a charge amplifier, and, on the other hand, all the second electrodes of the sensors of the first matrix are connected to a common electrically conductive track, electrically connected to the ground of one of the measuring devices, and, furthermore, on the one hand, the first electrode of each sensor of the second matrix is ​​connected to an individual electrically conductive track, itself electrically connected to a charge amplifier, and, on the other hand, all the second electrodes of the sensors of the second matrix are connected to a common electrically conductive track, electrically connected to the ground of one of the measuring devices. Brief description of the drawings

[0025] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0026] Fig. 1, previously described, represents graphs corresponding to tests of piezoelectric force sensors for prior art sensors;

[0027] [Fig.2] schematically represents, in top view, a measuring device comprising a substrate, each face of which is covered by a sensor according to a particular embodiment of the invention;

[0028] [Fig.3] schematically represents, in top view, a measuring device comprising a substrate, each face of which is covered by a sensor matrix according to another particular embodiment of the invention;

[0029] [Fig.4] represents, schematically and in cross-section, a measuring device according to another particular embodiment of the invention;

[0030] [Fig.5] represents, schematically and in cross-section, a measuring device according to another particular embodiment of the invention;

[0031] [Fig.6] represents, schematically and in cross-section, a measuring device according to another particular embodiment of the invention;

[0032] [Fig.7] represents, schematically and in cross-section, a measuring device according to another particular embodiment of the invention;

[0033] [Fig.8A], [Fig.8B], [Fig.8C] and [Fig.8D] represent, respectively, schematically and in cross-section, unitary devices on convex, concave or complex surfaces and a matrix device on a complex surface;

[0034] [Fig.9A], [Fig.9B] and [Fig.9C] represent, schematically and according to different sections, a measuring device positioned in a heart valve comprising an anterior leaflet (AL) and a posterior leaflet (PL), according to different particular embodiments of the invention;

[0035] [Fig. 10] schematically represents a compression test for the calibration of sensors according to another particular embodiment of the invention;

[0036] [Fig.1 1] schematically represents a conformability test in bending and compression, according to another particular embodiment of the invention;

[0037] [Fig. 12A] is a graph representing the response of two sensors (noted Cl and C2) positioned on each side of the same substrate for a compression test, for calibration as shown in [Fig. 10];

[0038] [Fig.12B] is a graph representing the response of the two sensors Cl and C2 for a test in bending alone;

[0039] [Fig. 13] is a graph representing the response of the two sensors Cl and C2 for a conformability test in bending and compression as shown in [Fig. 11]

[0040] [Fig. 14] and [Fig. 15] are photographs of different measuring devices according to different particular embodiments of the invention;

[0041] [Fig. 16] and [Fig. 17] are photographic images of the device of [Fig. 15] on complex surfaces; and

[0042] [Fig. 18] is a photographic image of several types of piezoelectric sensors printed according to different particular embodiments of the invention. Description of the implementation methods

[0043] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0044] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been represented and are detailed.

[0045] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") together, this means that these two elements can be connected or linked through one or more other elements.

[0046] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0047] Unless otherwise specified, the expressions "approximately", "roughly", and "in the order of" mean within 10%, preferably within 5%.

[0048] We will now describe the device in more detail with reference to Figures 2, 3, 4, 5, 6 and 7.

[0049] Piezoelectric force measurement devices are devices comprising at least two organic electronic sensors 11, 12 arranged on either side of a substrate 100. The first face 100a of the substrate 100 is covered by at least one first sensor 11 and the second face 100b of the substrate 100 is covered by at least one second sensor 12. The first sensor 11 is arranged opposite the second sensor 12 to form a bimorph 10.

[0050] The invention is fundamentally distinguished from the prior art by the use of a conformable device having at least two sensors 11, 12 arranged symmetrically on either side of the substrate 100, and whose sensors 11, 12 have a particular polarization and a particular connection, thereby canceling the signal of compressive forces or the signal of bending forces, and thus obtaining a measurement of the force, respectively, in bending or compression. In particular, the device makes it possible to obtain a precise measurement of a compressive force by eliminating, by means of the piezoelectric bimorph, the generated bending signal.

[0051] By arranged opposite each other, it is meant that the alignment is perfect or that there is a maximum of 50 pm of misalignment between the electrodes of the two sensors 11, 12.

[0052] The substrate is a flexible substrate. By flexible, we mean that the element can deform reversibly.

[0053] Advantageously, a substrate with an elasticity of less than 8 GPa and a flexural stiffness of less than 10⁴ N / m will be chosen. Preferably, all layers of the device have an elasticity of less than 8 GPa and a flexural stiffness of less than 10⁴ N / m.

[0054] The device is conformable, meaning that it can take the form of a complex surface (i.e., deformable and / or non-planar, for example, having concave and / or convex areas) to measure the forces acting on it. The device is also lightweight and can be worn by a person.

[0055] With this force measuring device, it is possible to differentiate between compressive forces and bending forces when the device is subjected to these two forces simultaneously.

[0056] Preferably, the first face 100a of the substrate 100 is covered by a first group of sensors 11 and the second face 100b of the substrate 100 is covered by a second group of sensors 12.

[0057] The first group of sensors comprises the same number of sensors as the second group of sensors. In other words, the first face 100a and the second face 100b are covered by the same number of sensors.

[0058] Each sensor 11 of the first group of sensors is arranged opposite a sensor 12 of the second group of sensors.

[0059] The sensors 11,12 on the same face can be arranged in a line or in the form of a matrix ([Fig.3]).

[0060] For example, a line may include between X and Y sensors.

[0061] By between X and Y, it is meant here and thereafter that the bounds are included.

[0062] The matrices are matrices of nxm sensors with n and m positive integers, greater than or equal to 2, and preferably between 2 and 10. For example, as shown in [Fig.3], this is a 4 x 7 sensor matrix.

[0063] For matrices having common electrodes (n+m electrodes), larger matrices can be used (for example up to 50 rows / columns).

[0064] This matrix shape allows several sensors to be arranged side-by-side on the same face of a substrate 100. Each sensor 11, 12 has an identical sensor placed symmetrically on the other side of the substrate 100 in order to form bimorphs 10. This embodiment is particularly advantageous because it allows forces to be measured at several points in space and thus a force map to be created on a surface.

[0065] The sensors 11, 12 comprise at least one flexible piezoelectric polymer film 120 (also called a flexible organic piezoelectric layer or electroactive layer). Each piezoelectric polymer film 120 is disposed between a first electrode 110 and a second electrode 130.

[0066] The sensor 11, 12 may comprise a single electroactive layer 120 or several electroactive layers 120 (two or three electroactive layers, for example). When the sensor comprises several electroactive layers 120, the sensor is formed of a stack comprising an alternation of piezoelectric layers 120 and electrodes 110, 130. The stack begins and ends with an electrode.

[0067] Preferably, each sensor 11,12 comprises a single piezoelectric polymer film 120, disposed between a first electrode 110 (also called the lower electrode) and a second electrode 130 (also called the upper electrode).

[0068] Each piezoelectric layer 120 has a thickness, for example, between 1 and 11 pm, preferably between 2 and 5 pm, for example 3 pm. Such thicknesses make it possible to obtain layers 120 with good flexibility.

[0069] Preferably, each piezoelectric layer 120 is an organic piezoelectric layer. Each piezoelectric layer preferably comprises a polymer matrix of PVDF, a PVDF copolymer, or a PVDF terpolymer. This may be a copolymer of vinylidene fluoride and at least one other monomer copolymerizable with VDF. Advantageously, the copolymer comprises at least 50 mol%, preferably at least 70 mol%, and even more preferably at least 90 mol% of VDF.

[0070] By way of illustration, the copolymerizable monomer(s) are, for example, chosen from chlorotrifluoroethylene (CTFE), chlorofluoroethylene (CFE), hexafluoropropylene (HFP), trifluoroethylene (VF3), methyl methacrylate (MMA), tetrafluoroethylene (TFE), and perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE).

[0071] For example, the copolymer is a copolymer of poly(vinylidene fluoride-trifluoroethylene) PVDF / TrFe, also noted P(VDF-TrFe) or PVDF-CTFE.

[0072] It may also be a terpolymer. For example, a PVDF / CTFE / CFE terpolymer will be chosen.

[0073] According to another embodiment, the polymer is not a ferroelectric polymer: it may be PVDF-HFP.

[0074] According to another embodiment, the polymer is polylactic acid (also noted as PLA or PLLA).

[0075] Preferably, the piezoelectric films 120 are piezoelectric polymers selected from PVDF, P(VDF-TrFE) and PLLA.

[0076] Each organic piezoelectric layer 120 can be a composite material. For example, layer 120 can comprise, in addition to a piezoelectric or non-piezoelectric polymer matrix, piezoelectric particles and / or PEDOT:PSS particles. The particles will be small enough not to alter the roughness.

[0077] For example, ferroelectric particles are in BaTiO3 (BTO), PZT (lead zirconate titanate), AIN, ZnO, or in SBN (Sr-Ba-Nb oxide) or SBT (Sr-Ba-Ti oxide).

[0078] For example, piezoelectric films 120 are formed from composite materials comprising, for example, a polymer (piezoelectric type PVDF, or non-piezoelectric type TPU, PDMS, PVDF HFP) and piezoelectric nanoparticles or nanofibers (PVDF, PZT, BaTiO3, AIN).

[0079] The piezoelectric films 120 are polarized under an electric field such that, in the final device, the polarization direction of the piezoelectric film(s) of the sensors 11 positioned on the first face 100a of the substrate 10 is identical or opposite to the polarization direction of the sensors 12 positioned on the second face 100b of the substrate 100. By way of illustration, the arrows in figures 4 and 6 represent opposite polarization directions.

[0080] The piezoelectric films 120 are arranged between electrodes 110, 130. The electrodes 110, 130 are flexible electrodes.

[0081] The electrodes 110, 130 have, for example, a thickness between 0.1 and 3 pm, preferably between 0.5 and 1.5 pm, for example 1 pm.

[0082] Preferably, the electrodes 110, 130 are made of an electrically conductive polymer or a metal such as gold. Electrically conductive polymers provide a better interface with P(VDF-TrFE). Preferably, this is PEDOT-PSS (poly(3,4-ethylenedioxythiophene).

[0083] The sensors 11,12 can be covered by a stack comprising one or more dielectric layers 140, 160 and / or a ground plane 150 (Figures 6 and 7).

[0084] Preferably, the ground plane 150 is disposed between the two layers of a dielectric material 140, 160.

[0085] The ground plane 150 is flexible. It has a thickness between 3 pm and 10 pm, for example 5 pm.

[0086] The ground plane 150 makes it possible to greatly reduce measurement noise, improve measurement accuracy and therefore open up a wider range of applications.

[0087] The ground plane 150 is preferably printed. It is integrated into the device during its manufacture by printing.

[0088] To produce the ground plane 150, any flexible conductive ink can be used.

[0089] The ground plane 150 is preferably made of carbon. Carbon is highly conductive and exhibits good biocompatibility, which is advantageous when it comes into contact with the human body, as it is one of the layers closest to the external environment.

[0090] Alternatively, the ground plane 150 can be made of gold.

[0091] The lower dielectric layer 140 serves to electrically isolate the sensor 11, 12 from the ground plane 150. The upper dielectric layer 160 serves to protect the sensor 11, 12 from the outside (humidity, mechanical wear...).

[0092] The dielectric layers 160 are also flexible. They have a thickness of between 3 pm and 10 pm, for example 5 pm.

[0093] The dielectric layer 140 between the electrode and the ground plane is sufficiently thick to prevent breakdown during polarization, but not so thick as to make the sensor rigid. Thicknesses of 30 µm can be used.

[0094] The dielectric material presents few constraints. Preferably, a printable and curable material should be chosen. For example, it could be non-piezoelectric crosslinked PVDF or EDAG. Preferably, EDAG is preferred because, during printing, it does not contain a solvent that could damage the underlying layers (unlike the TEP solvent in PVDF, which damages the silver).

[0095] Despite the layering of materials, the assembly formed by the sensor 11, 12, the dielectric layers 140, 160 and the ground plane 150 remains very thin. In particular, it has a total thickness of less than 100 pm.

[0096] The shape and size of the sensor 11, 12 can be varied as long as the two double-sided sensors have the same shape. They can be adapted to the intended application.

[0097] The size of the sensors 11 and 12 will be chosen to be neither too small, to facilitate the alignment of the two sensors face-to-face, nor too large, to avoid the presence of slight defects in the sensor. Indeed, defects can cause an asymmetry between two sensors positioned opposite each other, which can lead to a different electrical response and thus hinder the proper functioning of the sensor.

[0098] For example, the largest dimension of the sensors 11,12 (length, width, side or diameter in particular) is between 2 mm and 3 cm, preferably between 0.5 and 3 cm, and even more preferably between 1.5 and 2.5 cm.

[0099] To make denser matrices, reduce the probability that a sensor has a defect that could create an asymmetry in the double-sided and / or to have a uniform compressive stress over the entire surface of the sensor, sensors with a larger dimension between 2 and 5 mm will be preferred.

[0100] The distance between two sensors 11,12 is, for example, between 0.1 and 5 mm, preferably between 0.5 and 2 mm.

[0101] The different sensors 11, 12 may have the same dimensions or different dimensions. Sensors positioned opposite each other will nevertheless have the same dimensions.

[0102] The sensors 11,12 may have the same shape or different shapes.

[0103] They can be, for example, square, rectangular or circular. Preferably, they are circular.

[0104] Simple shapes (round or rectangular) are preferred for ease of manufacturing. Preferably, they are round because the axial symmetry of this geometry also slightly facilitates the alignment of the face-to-face sensors. Furthermore, in the case of high-density sensor matrices 11, 12, the round shape leaves a little more room for electrical tracks, for example in silver, and thus facilitates manufacturing.

[0105] The materials forming the different sensors 11, 12 may be identical or different. Preferably, they are identical. Even more preferably, each sensor 11, 12 comprises electrodes 110, 130 made of PEDOT-PSS and a piezoelectric layer 120 made of P(VDF-TrFe).

[0106] Substrate 100 is a flexible substrate.

[0107] The substrate 100 serves as mechanical support for the manufacture and use of the device.

[0108] It plays an essential role in the conformability of the device.

[0109] The substrate 100 can be made of polyimide (PI), poly(ethylene naphthalate) (PEN), polyethylene terephthalate (PET), thermoplastic polyurethane (TPU) or polydimethylsiloxane (PDMS).

[0110] The thickness of the substrate 100 is, for example, between 10 and 500 pm, preferably between 20 and 250 pm.

[0111] The flexural rigidity of the substrate 100 depends on its modulus of elasticity and its thickness, each of which must have a sufficiently low value for the substrate 100 to be flexible.

[0112] Flexibility can be defined by means of the flexural stiffness of the substrate according to the following equation:

[0113] D = with Y the modulus of elasticity of the substrate, e its thickness and v its Poisson's ratio

[0114] The substrate 100 is considered flexible if D < 10⁴ Nm. Preferably, D = 10⁵ Nm is chosen.

[0115] By way of illustration, the flexibilities of different substrates 100 have been calculated and listed in the following table:

[0116] [Tables 1] Substrate Elastic Modulus (MPa) Thickness (pm) Flexural Stiffness (Nm) Conformable Glass 55,000 1,100 7 No PEN 4,000 125 7 x 10⁴ No PI 5,000 25 7 x 10⁶ Yes TPU 50,100 5 x 10⁶ Yes PDMS 1,100 1 x 10⁷ Yes

[0117] The thickness of the substrate 100 depends on the material chosen. For example, for PI, PEN, PET, a thickness of less than 50 µm can be chosen, for TPU a thickness of less than 250 µm and for PDMS a thickness of less than 500 µm.

[0118] TPU is advantageously used because under high mechanical stress TPU has the advantage of not breaking / tearing, but rather of deforming plastically, which is a considerable advantage for in vivo applications.

[0119] As shown, for example, in Figures 4 and 6, the substrate 100 can be a one-piece support substrate (i.e. the substrate is formed in one piece).

[0120] As shown for example in Figures 5 and 7, the substrate 100 can be formed of two support substrates 101, 102 joined together, for example by means of an adhesive element 103, for example an adhesive film or a layer of glue, preferably deposited by screen printing. The two support substrates 101, 102 are preferably identical.

[0121] Thus, the sensors 11, 12 can be printed on two different substrates 101, 102, which are then joined together. Indeed, it can be difficult to achieve a printing technique on two sides of the same substrate for certain thicknesses and / or certain materials such as TPU.

[0122] Preferably, an adhesive film is used. The adhesive film has little or no inhomogeneity in its thickness and does not require a solvent.

[0123] This is a double-sided adhesive. The double-sided adhesive may be a polyimide tape, for example a tape marketed under the name Kapton.

[0124] For medical applications, an adhesive will be chosen which does not lose its adhesion properties in the target medium, and in particular which does not lose its adhesion properties with moisture.

[0125] The two support substrates 101, 102 can also be assembled with a three-layer structure comprising a thin substrate (typically less than 50 µm thick) sandwiched between two adhesive transfer tapes. The substrate is, for example, a PI substrate. It preferably has a thickness between 10 µm and 50 µm, for example, 25 µm. The adhesive tapes are preferably resistant to temperature and immersion in water. For example, the adhesive tape marketed by 3M under the reference VHB may be chosen.

[0126] The device includes electrical connection means 200 arranged to carry the electrical signal from the sensors, preferably to amplifiers 301, 302, and then to measuring devices, preferably electronic measuring devices. Voltage measuring devices may also be used. Preferably, the two measuring devices are identical for each sensor.

[0127] Electrically connected measuring devices to the sensors allow the sensors signals to be measured (11, 12).

[0128] The connection is preferably made by means of electrical tracks 200 (i.e., electrically conductive tracks). The tracks 200 can be printed on the substrate.

[0129] Any highly conductive ink that can be printed with a fairly fine resolution (typically the track width is less than 100 pm for high-density matrices) can be used.

[0130] The tracks 200 may be made of a metal (gold, for example), or of an electrically conductive polymer material. For example, the electrically conductive polymer material is PEDOT:PSS. It may also be a polymer in which electrically conductive particles are dispersed, for example, carbon particles. Silver may also be used in the form of ink, preferably formulated with a solvent-resistant polymer matrix (for example, with a silicone, TPU, or acrylate base).

[0131] Preferably, a silver-type ink (in particular a silicone matrix with silver particles) is used for the electrical connections between the sensor and the measuring electronics.

[0132] In the case of 200 gold electrical connections, highly conductive tracks are obtained. These tracks are also biocompatible. The thickness of such tracks is preferably less than 200 nm to obtain flexible tracks. The thickness is preferably between 10 nm and 200 nm, for example 100 nm.

[0133] Gold can be deposited by photolithography, which makes it possible to achieve very high resolution and thus obtain high density sensor matrices.

[0134] Preferably, gold is used with a PI substrate, which is resistant to the solvent used during photolithography (typically acetone).

[0135] Preferably, each sensor 11, 12 on the same face has an individual electrode, and all sensors 11, 12 on the same face share a common electrode connected to ground. For example, for an n row xm column matrix, there are anxm + 1 electrodes. Thus, each sensor 11, 12 can be connected to a charge amplifier 301, 302. The charge amplifiers convert the electrical charges generated by the sensor into a proportional voltage signal.

[0136] For example, the first electrode 110 of each sensor 11 of the first matrix is ​​connected to an individual electrically conductive track 200 and, on the other hand, all the second electrodes 120 of the sensors 11 of the first matrix are connected to a common electrically conductive track 200. This reduces noise. According to another example, on the one hand, the second electrode 120 of each sensor 11 of the first matrix is ​​connected to an individual electrically conductive track 200 and, on the other hand, all the first electrodes 110 of the sensors 11 of the first matrix are connected to a common electrically conductive track 200.

[0137] The same applies to the second matrix.

[0138] Alternatively, it is possible to have n + m connections 200, that is, on one side all the sensors on the same row share a common electrode, and on the other side all the sensors on the same column share a common electrode. However, this configuration does not allow the signal from each sensor to be decoupled individually.

[0139] According to one embodiment, instead of connecting each sensor (or each row or each column) to a different charge amplifier, it is possible to short-circuit the lower electrodes of both sensors and thus connect them to a single charge amplifier. The electrical charges naturally sum. By dividing the signal by 2, the average of the signals is obtained. The signal corresponds to the sum of the signals from the sensors because the signal from each sensor can no longer be isolated.

[0140] Depending on the polarization direction and how the sensors are electrically connected to the measuring devices, several configurations are possible. The signals from the sensors 11 on the first face 100a of the substrate 100 and the signals from the sensors 12 on the second face 100b of the substrate 100 can be either added or subtracted.

[0141] For example, to preserve a compressed signal, the different possible configurations are listed in the following Table 2:

[0142] [Tables2] Sensor polarizations. Connecting sensors to measuring devices. Operation to eliminate bending. Opposite opposites sum identical identical sum opposites identical subtraction identical opposites subtraction

[0143] By opposite polarization, it is understood that the sensor(s) on one side of the substrate have a polarization opposite to the polarization of the sensor(s) on the other side of the substrate. Such polarization is represented by the arrows in [Fig. 4].

[0144] By opposite connection of the sensors to the measuring devices (and charge amplifiers), it is understood that the sensor(s) on one side of the substrate are connected to the measuring devices in the opposite way to the way the sensor(s) on the other side of the substrate are connected to the measuring devices. For example, [Fig. 6] shows two charge amplifiers connected in opposite ways.

[0145] The first configuration is the most optimal. This is the configuration shown in [Fig. 6] (the arrows represent the direction of polarization of the piezoelectric layers 120). In particular, it reduces noise by connecting the upper electrodes (closer to the external environment) to ground.

[0146] For certain applications, it may be advantageous to eliminate compression and retain bending. In this case, referring to Table 2, it suffices to reverse the operation performed on the two signals (i.e., subtract instead of adding, add instead of subtracting).

[0147] We will now describe in more detail the manufacturing process of such a device.

[0148] The device can be implemented in the following manner:

[0149] a) depositing several electrically conductive areas on a first face 100a of a substrate 100, the electrically conductive areas forming first electrodes 110,

[0150] b) form piezoelectric layers 120 on the electrically conductive areas,

[0151] c) form second electrodes 130 on the piezoelectric layers 120,

[0152] d) optionally, form successively a first dielectric layer 140, a ground plane 150 and a second dielectric layer 160,

[0153] e) repeat steps a), b), c) and where appropriate d) on the second face 100b of substrate 100.

[0154] It is also possible to carry out step a) on the first face 100a and on the second face 100b, then step b) on the first face 100a and on the second face 100b, then step c) on the first face 100a and on the second face 100b, then, if necessary, step d) on the first face 100a and on the second face 100b.

[0155] According to one embodiment, steps a), b), c) and possibly d) are carried out on a first support substrate 101, step e) is carried out on a second support substrate 103 and then the support substrates 101 and 103 are assembled by means of an adhesive element 102.

[0156] In step b), the layer of piezoelectric material 120 can be deposited by spin coating. Other types of localized deposition can be used, such as screen printing, spraying, or even inkjet deposition. Preferably, the piezoelectric layer 120 is deposited by screen printing. In a single pass, the deposited thickness is between 1 and 20 µm. It is possible to superimpose several layers by screen printing until the desired final thickness is achieved.

[0157] Steps a), b) and c) can be repeated to form several electroactive layers 120 intercalated between two electrodes 110, 130, according to the following sequence: N x (electrode / composite / electrode).

[0158] The process also includes a step of crystallizing (or aligning the dipoles) the layer of piezoelectric material to improve its piezoelectric performance. This irradiation is carried out, for example, with a UV flash light, with a flash duration, or pulse, of between approximately 500 ps and 2 ms, a fluence (energy delivered per unit area) of between approximately 15 J / cm² and 25 J / cm², and with a light wavelength of between approximately 200 nm and 380 nm. The number of UV flashes, or pulses, produced during this irradiation varies depending on the thickness over which the piezoelectric material is to be crystallized. For example, for a P(VDF-TrFe) thickness of approximately 2 pm, irradiation can be implemented with a fluence of approximately 17 J / cm2, a pulse duration of approximately 2 ms and a number of pulses of 5.

[0159] The piezoelectric material, possibly having undergone previous crystallization, is then subjected to annealing, for example, carried out at about 130°C for about 60 min, to finalize the total crystallization of the piezoelectric material.

[0160] The crystallization of the piezoelectric material can therefore be carried out in two stages: firstly, irradiation by UV light pulse to properly crystallize the second face of the layer in piezoelectric material in order to increase its thermal conductivity, then a thermal annealing completing the crystallization for the rest of the piezoelectric material not crystallized by the previous irradiation.

[0161] When the piezoelectric material is a P(VDF-TrFe)-based copolymer, a biasing step is performed before use. This step can be carried out, for example, by applying a direct current voltage across its terminals via the electrodes to improve the piezoelectric coefficient of the material. This biasing is performed only once for the entire lifetime of the piezoelectric material. This electric field biasing can be done at room temperature or at high temperatures (up to approximately 100°C). When the biasing is performed at room temperature, it is possible to apply a direct current voltage of up to approximately 150 V / m of piezoelectric layer thickness for a duration, for example, of a few seconds to a few minutes. For example, a voltage of 120 V / m could be applied for 20 seconds.When polarization is performed hot, for example at a temperature of approximately 90°C, a DC voltage of, for example, between approximately 50 V and 120 V per micron of piezoelectric layer thickness can be applied for a duration of, for example, between approximately 1 and 5 minutes. The temperature is then lowered to ambient temperature, and the electric field applied to the piezoelectric material via the applied DC voltage is then switched off. Such polarizations allow PVDF to achieve piezoelectric coefficients of approximately 10 to 40 pC / N.

[0162] The molecules within the piezoelectric layer remain oriented in this way, even when the material is no longer subjected to this electric field. The material can thus be polarized by applying an initial polarization voltage across the electrodes. Preferably, a piezoelectric material thickness of approximately 3 pm or less is chosen to promote the polarization of the piezoelectric material by this capacitance, and the level of the electric voltage applied between the electrodes to achieve the initial polarization of the piezoelectric material (when the piezoelectric material is to be initially polarized) is also chosen.

[0163] For example, we will aim for an ideal remanent polarization of 8 pC / cm2.

[0164] Annealing is advantageously carried out at the end of the process, or between the different steps. Annealing is, for example, at a temperature between 100°C and 150°C, preferably around 100°C to remove residual traces of solvent and / or finalize the crystallization of the piezoelectric material.

[0165] Each sensor 11, 12 of the device is preferably screen-printed on a substrate 100. The printing manufacturing method simplifies and reduces the cost of the manufacturing process.

[0166] All sensors on the same side of the substrate can be printed at the same time.

[0167] As mentioned previously, the sensors can be printed on each side of the same substrate 100 or printed on two different support substrates 101, 102 which are then assembled with an adhesive element 103 (e.g., glue or double-sided adhesive).

[0168] During the assembly of the support substrates 101, 102, care must be taken to align them so that they are superimposed and the bimorph principle functions correctly. For example, to achieve this, the two sensors 11, 12 can be printed on the same face of a substrate so that they are perfectly symmetrical along an axis. Then, a double-sided adhesive 103 is placed on the other side of the substrate 100. The substrate 100 is then folded along this axis of symmetry: the sensors 11, 12 are glued and superimposed.

[0169] The electrically conductive tracks 200 are preferably obtained by screen printing for silver after the sensor formation. If the tracks are made of gold, they can be deposited by evaporation or spraying and then etched by photolithography before the sensor formation to avoid damaging them. Advantageously, the tracks are formed before double-sided assembly.

[0170] The device is used to measure forces in compression or bending.

[0171] To perform a measurement, the lower electrodes 110 of each sensor are each connected to a measuring device, and preferably to a charge amplifier 301, while the upper electrodes 130 and the ground planes 150 are connected to the ground of the measuring electronics (the connections of the sensor(s) The connections on the first face are therefore opposite to those of the sensor(s) on the second face of the substrate. In this specific configuration, when the device is subjected to compressive stress, the two sensors 11 and 12 will produce an identical signal; when the device is subjected to bending stress, the two sensors 11 and 12 will produce opposing signals. It is then possible to numerically calculate the average of the two signals to measure only the compression signal and eliminate the bending signal.

[0172] The method for measuring force in compression and bending comprises the following steps: - provide a conformable device comprising a substrate 100, having a first face 100a and a second face 100b, at least one first sensor 11 disposed on the first face 100a of the substrate 10 and at least one second sensor 12 disposed on the second face 100b of the substrate 10, the sensors 11, 12 being disposed opposite each other, the two sensors 11, 12 being polarized and electrically connected so as to cancel either the compressive forces or the bending forces, - apply compressive and bending forces on the device, - add or subtract the signals from the piezoelectric sensors 11, 12 so as to obtain either a compressive signal or a bending signal, and thus determine the compressive force or the bending force applied to the device.

[0173] In practice, even with a rigorous and controlled manufacturing method, it can be difficult to obtain two or more perfectly identical sensors assembled on both sides. The sensors may then have slightly different responses under bending stress. It is then possible that calculating the average of their signals will not be sufficient to completely eliminate the bending signal. The greater the bending, the more inaccurate the compression measurement will become, eventually rendering it uninterpretable. This asymmetry can be corrected by adding a digital gain in the software that complements the measurement electronics. Indeed, when a bimorphic device is subjected to stress in a bending direction, regardless of the radius of curvature, the difference in response between sensors remains the same.For example, in a bending direction, a first sensor may generate 30% less load than a second sensor. Therefore, simply adding a gain of x0.7 to the second sensor is enough for both sensors to have an identical response, thus completely eliminating the bending signal. However, this signal difference between sensors can vary depending on the bending direction. So, for example, for a single conformable device (a single bimorphic sensor 10), if the measurement is performed on a convex surface ([Fig. 8A]), it may be necessary to apply a gain of x0.7 to the second sensor 12, whereas on a concave surface, a gain of x0.9 should be applied to the first sensor 11. For more complex surfaces ([Fig. 8C]), it may be... Finding a simple correction factor is difficult because the surface has both convex and concave areas. In this configuration, a device with a matrix composed of several bimorphic sensors 10 is particularly interesting because it allows the complex surface to be virtually divided into several concave or convex subsurfaces ([Fig. 8D]). Thus, each sensor is deformed locally only in one direction of bending, and the numerical gain correction method can be applied to each bimorphic sensor 10.

[0174] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0175] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

[0176] In general, the invention makes it possible to measure compressive forces with a flexible sensor even when the surface of the sensor is deformed (i.e. the surface is not flat during the measurement) or when it deforms during the measurement (for example when the sensor is placed on a flexible surface which will deform during the application of the force).

[0177] The invention is of particular interest for the medical field. The device can be used to measure the force on a biological tissue, generally flexible and with a complex surface.

[0178] This invention is particularly aimed at medical applications, especially that of the mitral valve.

[0179] In particular, it can be used to measure coaptation forces in a heart valve to verify proper closure of the heart valve, especially during surgery. The device described above is particularly advantageous for such applications because it can conform to the curved shape of flexible valves and ignore bending.

[0180] For example, Figures 9A, 9B and 9C represent conformable measuring devices in a closed heart valve (mitral valve) consisting of an anterior leaflet (AL) and a posterior leaflet (PL) according to different views.

[0181] The use of a device having sensor arrays is advantageous for having a map of forces over the entire coaptation surface.

[0182] The device can also be placed directly on the skin, which is flexible and deforms considerably when flexed. It can be used as pulse sensors, swallowing sensors, respiration sensors, or touch sensors on the body (tactile sensors measuring the force between the skin and an external object).

[0183] The sensors are conformable and the elimination of the bending signal allows for a quantitative analysis of the measured signal.

[0184] The device is also of interest for applications outside the medical field.

[0185] For example, the device can measure the pressure in a tire. The two-sided device makes it possible to measure the pressure variation in the tire without being influenced by rolling. Indeed, the surface of a tire deforms in bending during rolling, and a pressure variation corresponds to a compressive stress.

[0186] The device can also be used to measure a force on a textile material. The device can be integrated directly onto a textile without altering its flexibility and allow the measurement of compressive forces.

[0187] Illustrative and non-limiting example of a particular embodiment

[0188] The device described here is designed to measure, for example, coaptation forces in the mitral valve. The device is a unit device (two sensors facing each other), but it could be a matrix device or a linear device. All the sensors on the same side of the substrate could be printed simultaneously.

[0189] The sensors are screen-printed onto a 100 µm thick TPU substrate (for example, commercially available under the name Intexar TE-1 IC from DuPont). A layer of PEDOT:PSS (commercially available from Heraeus) is printed first to form the first electrode. This is then annealed at 135°C for 30 minutes to evaporate the solvent (final thickness approximately 1 µm). The piezoelectric material, P(VDF-TrFE) 80 / 20 commercially available from Arkema Piezotech, is printed and then annealed for 3 minutes at 135°C under vacuum (thickness 3 µm). The upper PEDOT:PSS electrode is then deposited in the same way as the lower electrode. Silver traces (Taiyo) are also printed. The traces are approximately 10 µm thick. Then, a 10-minute annealing process at 135°C is carried out. These traces allow the sensor to be connected to the measurement electronics.Then the first layer of dielectric (commercially available under the reference Loctite ED AG PF 455B) is printed. Exposure under a mercury (UV) lamp allows the layer to crosslink (layer thickness approximately 10 µm).

[0190] For example, for a speed of 10 m / min, three passes and 35% of the power (for a conventional mercury lamp for exposure), the following fluences (energies delivered per unit area) were used:

[0191] [Tables3] mJ / cm2 W / cm2 UVA 430 248 UVB 257 155 UVA2 98 61 uvv 340 195

[0192] Depending on the Young's modulus of the substrate, it is possible to modify this fluence range between 100 and 500 mJ / cm2. UVA and UVB account for the majority of the crosslinking energy.

[0193] If the substrate has a Young's modulus of less than 0.5GPa, as is the case for a TPU substrate, a fluence of about 150 mJ / cm2 is sufficient and avoids creating too much stress in the piezoelectric layer (which could affect the ferroelectric performance).

[0194] The ground plane is then printed. This consists of a 1 Opm layer of carbon, commercially available from DuPont under the reference PE 671, and is then annealed for 10 minutes at 135°C. The thickness can be between 1 and 20 µm and preferably around 5 µm.

[0195] Finally, the second dielectric layer is deposited in the same way as the first.

[0196] Once two identical sensors are printed in the same way on two separate substrates, they are laser-cut with the same geometry. Then, the substrates are bonded, using the precision of the cutting for alignment. The bonding is achieved using a three-layer adhesive made from a 25 µm thick polyimide film onto which, on each side, an adhesive marketed by 3M under the reference VHB has been transferred.

[0197] The sensors are then polarized. The first sensor is connected to a voltage source via its electrodes. A low DC voltage (electric field in the piezoelectric material ~ 30 V / pm) is applied for 3 minutes to discharge as much electrical charge as possible from the sensor. A first AC voltage ramp-up at 10 Hz (from approximately 30 V / pm to 120 V / pm) can then be performed to eliminate certain sensor defects. The same voltage ramp-up is then repeated at 1 Hz to finalize the alignment of the dipoles. The same polarization procedure is repeated for the second sensor, ensuring that the lower and upper electrodes are connected to the outputs of the voltage source in the same configuration as for the first sensor.

[0198] For the measurements, each lower electrode of each sensor is connected to a charge amplifier (DDC118 with 2 kHz sampling). The upper electrodes and ground planes are connected to the ground of the measurement electronics.

[0199] A program, for example a Python program, allows visualization of the response of the two load amplifiers, application of a 20 Hz low-pass filter to eliminate noise, and calculation of the average of the two signals.

[0200] To calibrate the compression device, it is attached to a rigid glass plate with double-sided adhesive (for example, double-sided adhesive sold under the reference "Sticky double face 9030 W" by Teraoka). Then, a flat indenter perfectly parallel to the surface of the sensor is pressed with different forces ([Fig. 10]).

[0201] To test the proper functioning of the device (elimination of bending), the device is placed between two curved parts having complementary shapes to fit together, and pressure is applied with different forces ([Fig. 11]). To conform to the curved shape, the sensors are thus subjected to bending as well as compression when the parts are pressed against each other.

[0202] The response of the sensors in compression on the one hand and in bending on the other hand was studied (figures 12A and 12B).

[0203] The signal under compression is very clear ([Fig. 12A]). Under compression, the two sensors have a similar response.

[0204] The signal in bending can be cancelled ([Fig.l2B]).

[0205] The combination of the two stresses (bending and compression) results in a distorted signal for the two sensors taken individually ([Fig. 13]). However, averaging the two signals eliminates the bending signal, leaving only a compression signal, as in the compression calibration test. It is thus possible to determine the value of the force applied between the two parts.

[0206] Various devices have been implemented. Figure 14 shows a 4x7 sensor array on a convex surface. Figure 15 shows a 4x7 sensor array covered by an encapsulation layer with long connections. Figures 16 and 17 show the device of Figure 15 on complex surfaces.

[0207] Fig. 18 represents several types of piezoelectric sensors printed on a 38 cm x 32 cm substrate.

Claims

1. Demands A force measurement system comprising a conformable device intended to be subjected simultaneously to compressive and bending forces, the device comprising a substrate (100) having a first face (100a) and a second face (100b), at least one first sensor (11) disposed on the first face (100a) of the substrate (100) and at least one second sensor (12) disposed on the second face (100b) of the substrate (100), the sensors (11, 12) comprising an organic piezoelectric layer (120) disposed between a first electrode (110) and a second electrode (130), the sensors (11, 12) being arranged opposite each other so as to form a bimorph (10), the system further comprising measuring devices electrically connected to the sensors (11, 12) for measuring the signals from the sensors (11, 12), the organic piezoelectric layers (120) of the sensors (11, 12) being polarized and the sensors (11,12) being electrically connected to the measuring devices so as to cancel either the compressive forces or the bending forces, and to measure, respectively, either the bending forces or the compressive forces applied to the device, system in which:, - the polarization of the sensors (11, 12) is opposite, in that the sensors are connected to the measuring devices in opposite ways and in that the signals measured by the measuring devices are added together, whereby the bending forces are canceled out and the compressive forces are measured, or - the polarizations of the sensors (11, 12) are identical, the sensors are connected to the measuring devices in the same way and the signals measured by the measuring devices are added together, thereby canceling out the bending forces and measuring the compressive forces, or - the polarizations of the sensors (11, 12) are opposite, the sensors are connected to the measuring devices in the same way and the signals measured by the measuring devices are subtracted, thereby canceling the bending forces and measuring the compressive forces, or - the polarizations of the sensors (11, 12) are identical, the sensors are connected to the measuring devices in opposite ways and the signals measured by the measuring devices are subtracted, thereby canceling the bending forces and measuring the compressive forces.

2. System according to claim 1, characterized in that the sensors (11, 12) are covered by a stack comprising successively a first dielectric layer (140), a ground plane (150) and a second dielectric layer (160).

3. System according to any one of claims 1 and 2, characterized in that the ground plane is made of carbon and / or in that the first dielectric layer (140) and the second dielectric layer (160) are made of ED AG or PVDF.

4. System according to any one of claims 1 to 3, characterized in that the substrate (100) is a PEN or PI substrate.

5. System according to any one of claims 1 to 3, characterized in that the substrate (100) comprises two support substrates (101, 102), for example made of TPU, joined together by an adhesive element (103).

6. System according to any one of the preceding claims, characterized in that the first face (100a) of the substrate (100) is covered by a first sensor matrix and the second face (100b) of the substrate (100) is covered by a second sensor matrix, the first matrix and the second matrix being arranged opposite each other.

7. System according to the preceding claim, characterized in that, on the one hand, the first electrode (110) of each sensor (11) of the first matrix is ​​connected to an individual electrically conductive track (200) and, on the other hand, in that all the second electrodes (120) of the sensors (11) of the first matrix are connected to a common electrically conductive track (200) and in that, on the one hand, the first electrode (110) of each sensor (12) of the second matrix is ​​connected to an individual electrically conductive track (200) and, on the other hand, in that all the second electrodes (120) of the sensors (12) of the second matrix are connected to another common electrically conductive track (200).

8. A method for measuring force in compression and bending, comprising the following steps: - providing a force measurement system as defined in any one of the preceding claims, - simultaneously applying forces in compression and bending on the measuring device, - adding or subtracting the signals measured by the measuring devices, so as to cancel either the forces in compression or the forces in bending, and thus measuring, respectively, either the forces in bending or the forces in compression applied to the device.

9. Method according to claim 8, characterized in that the device comprises a first sensor array on the first face (100a) of the substrate (100) and a second sensor array on the second face (100b) of the substrate (100), the first array and the second array being arranged opposite each other.

10. A method according to any one of claims 8 to 9, characterized in that the sensor(s) (11) of the first face (100a) have a polarization opposite to the polarization of the sensor(s) (12) of the second face (100b), in that the sensor(s) (11) of the first face (100a) are electrically connected to first charge amplifiers (301), the sensor(s) (12) of the second face (100b) are electrically connected to second charge amplifiers (302), the electrical connections to the first charge amplifiers (301) and the electrical connections to the second charge amplifiers (302) being opposite, the signals from the sensors being summed to eliminate the signal of the bending forces and obtain the signal of the compressive forces.

11. A method according to claims 8 to 10, characterized in that, on the one hand, the first electrode (110) of each sensor (11) of the first matrix is ​​connected to an individual electrically conductive track (200), itself electrically connected to a charge amplifier, and, on the other hand, in that all the second electrodes (120) of the sensors (11) of the first matrix are connected to a common electrically conductive track (200), electrically connected to the ground of one of the measuring devices, and in that, on the one hand, the first electrode (110) of Each sensor (12) of the second matrix is ​​connected to an individual electrically conductive track (200), itself electrically connected to a charge amplifier, and, on the other hand, in that all the second electrodes (120) of the sensors (12) of the second matrix are connected to a common electrically conductive track (200), electrically connected to the ground of one of the measuring devices.

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