Anti-ballistic protection device

Abstract

Disclosed is an anti-ballistic protection device comprising - a shield (22) comprising a shielding part (12) capable of protecting a target from a projectile fired by a firearm, and - a sensor (24) comprising two electrical conductors (28e, 28i) and a separator (22) arranged between the conductors, and - an interrogator (26) electrically connected to the conductors and configured to measure an electrical property depending on the layout of the conductors and / or on the shape of the conductors and / or on the structure of the separator and / or on the shape of the separator, or a connector capable of electrically connecting the conductors to a said interrogator, at least one portion of the shield, preferably at least one portion of the shielding part, totally or partially forming the separator.

Description

[0001] Description

[0002] Title: ANTIBALLISTIC PROTECTION DEVICE

[0003] Domain

[0004] The invention relates to an anti-ballistic protection device, in particular a bulletproof vest or a device for protecting a vehicle or any other military equipment.

[0005] Prior art

[0006] A ballistic shield is a device capable of resisting the impact of a bullet in order to protect a target, for example a person, a police or law enforcement vehicle, defense or other military equipment. It is preferably in the form of a plate, flat or not, which, in the service position, extends in front of the target in order to protect it.

[0007] The shield may in particular be a bulletproof vest conventionally comprising, as illustrated in Figure 1:

[0008] - a protective plate 10 consisting of a superposition of a shielding part 12 in the form of a plate, preferably an intermediate layer 14, and a damping plate 16, called “backing”, and

[0009] - an external envelope 18 surrounding said protective plate.

[0010] For the sake of clarity, a distinction is made between the outer portion 18e of the outer casing, which extends on the outer side and is exposed to the projectiles, and the inner portion 18i of the outer casing, which extends on the opposite side. Each of these portions has an outer face facing the environment and an opposite inner face, facing the armor piece.

[0011] The bulletproof vest is intended to protect a target C against the projection of a bullet B launched against an impact face 20.

[0012] The good condition of the shield is conventionally checked visually. However, signs of possible damage to a piece of shielding made of a fragile material are often very difficult to detect. Brittle fracture, or "catastrophic fracture," can indeed result from the multiplication of microcracks that are difficult to detect. The piece of shielding may also be coated or placed in an environment that makes visual inspection difficult, or requires the acquisition of X-ray images. WO2021 / 116349A1 discloses a device for checking the physical condition of a shield. It comprises a plastic sensor fixed to the piece of shielding and capable of detecting in a localized manner the appearance of an internal defect, for example a crack.

[0013] US20120191373A1 describes an anti-ballistic protection device comprising an armour piece and a sensor adapted in particular to electrical reflectometry. The sensor conductors are placed on the same face of the armour piece. Furthermore, the sensor does not have sufficient sensitivity to reliably detect significant damage to the armour piece.

[0014] There is a continuing need for solutions for monitoring the physical condition of a protective shield that are simpler, faster, and more reliable, and that can be achieved with a more compact and less expensive device than in the prior art.

[0015] One aim of the invention is to meet, at least partially, this need.

[0016] Statement of the invention

[0017] Summary of the invention

[0018] The invention proposes an anti-ballistic protection device, comprising:

[0019] - a shield comprising a piece of armour capable of protecting a target from a projectile fired by a firearm, and

[0020] - a sensor comprising:

[0021] - two electrical conductors,

[0022] - a separator arranged between said conductors, and

[0023] - an interrogator electrically connected to said conductors and configured to measure an electrical property depending on the arrangement of said conductors and / or the shape of said conductors and / or the structure of the separator and / or the shape of the separator, or a connector capable of electrically connecting said conductors to a said interrogator.

[0024] Remarkably, at least a portion of the shield, preferably at least a portion of the shielding piece, constitutes, totally or in part, preferably totally, said separator.

[0025] The electrical property can be modified in the event of a change in the physical state of the separator, which makes it possible to detect damage to the shield, for example resulting from the appearance of cracks, in particular in the shielding part. The electrical property can also be modified in the event of separation or disassembly of the different parts constituting the shield, and in particular of the shielding part with another part of the shield. When the shield is a bulletproof vest, the sensor can for example detect micro-cracking of the shielding part, but also a loss of cohesion between the shielding part, the damping plate, the intermediate layer and the layers of the external envelope, which a simple visual observation of the shield does not generally allow.

[0026] As will be seen in more detail in the rest of the description, the shield therefore has a dual function. It provides protection for the target and contributes to the construction of the sensor. This makes the device easier to manufacture. In addition, reducing the number of parts reduces the weight of the device, increases its compactness and improves its reliability and accuracy. In particular, the shield, preferably the shielding part, extends between the conductors, i.e. at an optimal location so that its deformation or change of state affects the measurements made with the sensor. Finally, the measurement and analysis by the interrogator are rapid and can be automated.

[0027] The shield may in particular be a bulletproof vest comprising an external envelope enveloping a protective plate consisting of a superposition of said armoring part in the form of a plate, optionally an intermediate layer, and a damping plate, a conductor being:

[0028] - integrated into the outer part of the external envelope, or

[0029] - arranged on the external face (facing the shield environment) of the outer part of the outer casing, and preferably protected by a resin-based environmental protection layer, for example a polyurethane-based layer, in particular Line-X®, or

[0030] - arranged between the outer casing and the impact face of the shielding part, the other conductor being

[0031] - arranged between the face of the armor piece opposite the impact face and the intermediate layer, or

[0032] - arranged in the intermediate layer or

[0033] - arranged between the intermediate layer and the damping plate, or

[0034] - arranged between the damping plate and the outer casing, or

[0035] - integrated into the inner part of the outer envelope, or

[0036] - arranged on the outer face of the inner part of the outer casing. In one embodiment, the device comprises several conductors, for example more than two or more than 3 conductors, arranged at different depths, for example a conductor integrated in the outer part of the outer casing, a conductor arranged on the outer face of the shielding part, a conductor arranged on the inner face of the shielding part, a conductor arranged between the shielding part and the damping plate and a conductor arranged in the damping plate. This forms several electromagnetic waveguides.

[0037] In one embodiment, the damping plate comprises a fabric, preferably a fibrous composite, and a conductor is integrated into the fabric, for example as a warp or weft yarn.

[0038] In one embodiment, the separator is constituted by the shielding part or by an assembly constituted by the shielding part and a damping plate, preferably made of a fibrous or metallic material intended to be arranged between the target and the shielding plate in the service position of the shield.

[0039] The separator is preferably in the form of a plate. It may be an armor piece in the form of a plate, and / or one or more other pieces integral with the armor piece. It may be in particular, especially for a bulletproof vest, a cushioning plate and / or an intermediate layer and / or one or more layers of the outer casing. Preferably, the separator consists exclusively of the armor piece.

[0040] A separator in the form of a plate has outer and inner faces. The electrical conductors, referred to as "outer" and "inner" conductors, preferably extend on the side of the outer and inner faces, respectively, preferably in contact with the outer and inner faces, respectively. The surfaces of said outer and inner faces are preferably greater than or equal to 100 cm 2 As will be seen in more detail in the remainder of the description, a device according to the invention advantageously makes it possible to monitor the physical state of a shield whose shielding part has a large surface area, without having to multiply the number of sensors.

[0041] In one embodiment, the device comprises several said sensors, the separator being common to the plurality of sensors. The device thus comprises several pairs of conductors, each pair comprising an outer conductor and an inner conductor, extending respectively on the outer and inner faces of a plate-shaped separator, flat or not, parallel to each other, the distance between the outer conductor and the inner conductor preferably being substantially equal to the thickness of the plate. The device may in particular comprise 2, more than 2, more than 3, more than 5, more than 10 and / or less than 1000 pairs. The surfaces of said outer and inner faces are then preferably each greater than 300 cm 2 , especially above 500 cm 2 , and more particularly greater than 1000 cm 2 .

[0042] Preferably, each pair of conductors is connected to a respective connector, suitable for connecting the sensor to the interrogator. Several pairs of conductors may also be connected to the same connector. The device may also include a multiplexer to manage the incident signals injected into the different pairs of conductors, as well as the signals reflected accordingly.

[0043] The shielding part is preferably made of a material with a Vickers hardness greater than 3 GPa.

[0044] Preferably, at least one of the conductors consists of a deposit of material, preferably produced by laser engraving, screen printing or pad printing, or by application of a conductive paint, which improves the compactness and ensures good transmission, to the conductor, of the deformation and / or modification of the possible physical state(s) of the separator.

[0045] The electrical property is preferably an electric potential difference between the two conductors.

[0046] Preferably, the conductors and the separator together form an electromagnetic waveguide. Preferably, the interrogator is configured to inject into the waveguide an incident signal, preferably an electrical signal, preferably a pulse, representing a potential difference between the two conductors, receive a reflected signal accordingly, and analyze said reflected signal or a change in the reflected signal. In a preferred embodiment, the analysis comprises, preferably is a time-domain or frequency-domain reflectometry analysis. Such an embodiment advantageously makes it possible not only to detect damage, but also to measure and locate it, even with a large shielding part.

[0047] Preferably, the interrogator is programmed to perform an analysis of an electrical potential difference or an impedance difference measured between electrical conductors.

[0048] Preferably, the sensor constitutes a waveguide and the interrogator is configured to carry out a said analysis by time or frequency reflectometry from a reflected signal returned by the waveguide, preferably so as to implement the following steps: a) at a “reference” instant, in a reference situation, injection, into the waveguide, of an incident signal, preferably an electrical signal; b) reception of a signal reflected by the waveguide in response to said injection, or “reference reflected signal”; c) at an “updated” instant, injection, into the waveguide, of an incident signal identical to that injected in step a); d) reception of a signal reflected by the waveguide in response to said injection, or “updated reflected signal”;comparison of the reference and updated reflected signals so as to determine a difference between said signals, and to deduce therefrom information on the physical state of the shield, in particular of the shielding part, in the updated situation; e) optionally, preferably, transmission of a message containing said information.;

[0049] Preferably, in step d),

[0050] - a score is determined by integrating over time a function providing, as a function of time, the difference between said reference and updated reflected signals, then

[0051] - the score is compared to a threshold and based on the difference between the score and the threshold, the said information is determined.

[0052] The invention also provides a method for monitoring the physical condition of a shock protection shield, preferably anti-ballistic, in particular the physical condition of an armor part of said shield, said method comprising the following steps:

[0053] 1) implementation of said steps a) and b), and at a first updated time, implementation of said steps c) and d), or even e), so as to evaluate a first updated physical state of the shield, in particular an initial physical state of the shielding part;

[0054] 2) at a second updated time after the first updated time, for example more than 1 hour, a day, or a week, implementation of said steps c) and d), or even e), so as to evaluate a second updated physical state of the shield, in particular of the shielding part, at the second updated time;

[0055] 3) comparison of said first and second updated physical states so as to evaluate a difference between said first and second updated physical states, and deduce therefrom information on an evolution of said physical state between the first and second updated instants, and optionally, preferably, transmission of a message relating to said evolution. Step 2) can be repeated, two successive updated instants being for example separated by more than 1 minute, 1 hour, one day, or one week, and / or less than 6 months or less than 1 month.

[0056] Definitions

[0057] A piece whose width is greater than five times its thickness is called a "plate".

[0058] By "brittle" is meant a material whose plastic deformation range under load before rupture represents less than 1% of the elastic deformation range, preferably is substantially zero. In other words, the width of the stress range leading to plastic deformation without rupture represents less than 1% of the width of the stress range leading to elastic deformation.

[0059] A “Ceramic Matrix Composite,” or “CMC,” is a product composed of fibers, preferably ceramic, bonded together by a ceramic matrix.

[0060] A "ceramic material" is any non-metallic, non-organic material. Diamond, graphite, graphene, a carbide, and a cermet are considered here as ceramic materials.

[0061] An “Organic Matrix Composite”, or “OMC”, is a product composed of fibers, preferably ceramic, bound together by an organic matrix, preferably made of resins comprising more than 50% by volume of thermoplastic and / or elastomeric and / or thermosetting polymers.

[0062] The nature of the projectile is not limiting. It can be, for example, a bullet or a rocket. A firearm can be, in particular, a rifle, a handgun, or even a cannon.

[0063] A shield comprises an armor piece, typically made of a hard material, and optionally a cushioning plate that extends between the target and the armor piece in the service position. The cushioning plate is preferably made of a ductile material, typically:

[0064] - made of a fibrous material consisting mainly of polyethylene fibers, for example Tensylon™, Dyneema®, or Spectra™, aramid fibers, for example Twaron™, or Kevlar®, glass fibers, or

[0065] - made of a metal, for example steel or an aluminum alloy.

[0066] Vickers hardness H v of a material can be measured by applying a force F, in Newtons, perpendicular to the surface of a sample of said material, with a standardized pyramidal diamond point with a square base and an apex angle between faces equal to 136°. The imprint made on this surface therefore has the shape of a square. The two diagonals ch and cfe of this square are measured, in mm, using an optical device. If cf denotes the arithmetic mean of c and cfe, the hardness is calculated according to the following formula: Hv = 0.189* F / cF.

[0067] The equivalent diameter of the grains of the material is determined from the observation of the microstructure of the material, conventionally using images taken by SEM (scanning electron microscopy) on a section of a sample of the material comprising a sufficient number of grains, in particular at least 500 grains, or even at least 600 grains, preferably after a chemical attack aimed at revealing the grains and their joints. The grain diameter thus measured corresponds to the diameter of a disc of surface equivalent to said grain, as observed in two dimensions on the SEM image.

[0068] The 10th (P10), 50th (D50), and 90th (D90) percentiles for equivalent grain diameters are the equivalent diameters corresponding to the percentages, by number, of 10%, 50%, and 90%, respectively, on the cumulative distribution curve of equivalent grain diameters ranked in ascending order. In particular, the median equivalent diameter (or D50 percentile) is the diameter for which 50% by number of the grains have an equivalent diameter less than or equal to this said diameter.

[0069] The "physical condition" of the shield, particularly the armor part, can be, for example, "damaged condition" or "undamaged condition." It can also be more specific. For example, it can be "little damaged condition," "moderately damaged condition," or "heavily damaged condition." "Damage" is an irreversible consequence of the application of stress during, before, or after use of the shield. Damage can, in particular, be manifested by microcracks.

[0070] The equivalent diameter of a conductor in wire form is the diameter of a disc having the same surface area as the cross-section of a conductor.

[0071] An electromagnetic waveguide is a waveguide preferably having the general shape of a transmission line, suitable for measurement by electrical time or frequency reflectometry. It typically comprises two electrical conductors electrically insulated from each other and extending along the length direction of the waveguide.

[0072] The incident signal is typically a variation in the electrical potential difference between the electrical conductors. The incident signal is injected at the input end of the waveguide and then propagates as an electromagnetic wave. A variation in electrical impedance causes a partial reflection of this wave.

[0073] The reflected signal is also a temporal variation of potential difference between electrical conductors.

[0074] An "echo" is the part of a reflected signal that is returned, in response to the incident signal, by a discontinuity (discontinuity echo), by the input end of the waveguide, at the connector (transmit echo), or by the output end of the waveguide (bottom echo).

[0075] A discontinuity is a local modification of a waveguide, in particular of a conductor or the separator, in particular when the conductors are in contact with the separator and preferably follow the shape of the separator, capable of partially reflecting a signal circulating in the waveguide.

[0076] A region of a waveguide "matches" a portion of a reflected signal when it originates the portion of the reflected signal, that is, it has reflected the incident signal to generate the portion of the reflected signal.

[0077] The adjectives "reference" or "updated" are used for clarity only. The adjective "outside" refers to the side of a shield likely to be exposed to bullets in the service position, that is, in the position in which the shield is used to protect the target. The adjective "inside" refers to the side opposite the outside side.

[0078] “Behave,” “present,” or “include” should be interpreted broadly and not exhaustively.

[0079] Brief description of the drawings

[0080] Other characteristics and advantages of the invention will become apparent upon reading the detailed description which follows and upon examining the attached drawing in which

[0081] - Figure 1 [Fig 1] schematically represents, in cross-section, a bullet-proof vest of the prior art;

[0082] - figure 2 [Fig 2] schematically illustrates a device according to a first embodiment of the invention;

[0083] - figure 3 [Fig 3] schematically illustrates a device according to a second embodiment of the invention;

[0084] - Figure 4 [Fig 4] schematically represents, in cross-section, a bulletproof vest according to different embodiments of the invention; - Figure 5 [Fig 5] schematically illustrates a device according to a third embodiment of the invention;

[0085] - Figure 6 [Fig 6] represents an example of reflected signals received by the interrogator in one embodiment of the invention;

[0086] - figure 7 [Fig 7] represents an enlargement of a part of figure 6;

[0087] - figure 8 [Fig 8] schematically illustrates a device according to a fourth embodiment of the invention;

[0088] - Figure 9 [Fig 9] schematically illustrates the bending test used for the second series of examples;

[0089] - Figures 10 [Fig 10] a and b and 11 [Fig 11] a and b show the recordings of the reflected signals obtained.

[0090] In the various figures, identical references are used to designate identical or similar organs.

[0091] Detailed description

[0092] A device 21 according to the invention comprises a protective shield 22, a sensor 24 and preferably an interrogator 26, as illustrated in FIG. 2.

[0093] Shield

[0094] The shield 22 is a device for protection against military projectiles, and in particular against bullets, preferably intended for the protection of a vehicle, in particular a military vehicle, or a person. It may in particular be a bulletproof vest or a helmet.

[0095] The shield preferably has the shape of a plate, preferably flat, possibly made up of a superposition of plates made of different materials.

[0096] A shield comprises a piece of shielding 12, or is even made up of a piece of shielding, as in Figure 2.

[0097] The armor piece is preferably shaped to provide NIJ-IIIA, NIJ-III or NIJ-IV protection, preferably at least NIJ-III protection. For vehicles, it is preferably shaped to provide STANAG 4569 level 1, or 2, or 3, or even 4 protection.

[0098] The shielding part 12 may have a mass greater than 200g, preferably greater than 500g, preferably greater than 1kg and / or less than 100kg, less than 50kg, less than 10kg, or even less than 5kg. The shielding part 12 may have any shape, determined according to the intended application.

[0099] The shielding part 12 preferably has the shape of a plate, preferably flat, for example the shape of a plate having:

[0100] - an overall length greater than 20 cm and / or less than 50 cm, and / or

[0101] - an overall width greater than 10 cm, or greater than 20 cm, and / or less than 30 cm and / or

[0102] - an overall thickness greater than 3 mm, preferably greater than 5 mm, preferably greater than 10 mm, and / or less than 2 cm.

[0103] The shielding part preferably has an average thickness greater than 3 mm, preferably greater than 5 mm, greater than 7 mm, preferably greater than 10 mm, preferably greater than 15 mm, preferably greater than 20 mm, and / or less than 100 mm, preferably less than 2 cm.

[0104] The length and / or width and / or thickness are preferably constant.

[0105] The armor piece preferably has a length and width greater than 5, 10, 30 or 50 times the thickness of the plate.

[0106] A plate-shaped armor piece 12 typically has an outer face 12e, or "impact face", an inner face 12i opposite the outer face, and a peripheral edge 12p defining the thickness of the plate and connecting the inner and outer faces to each other.

[0107] The thickness of the shielding part is preferably substantially constant, that is to say that said inner and outer faces are substantially parallel to each other.

[0108] The surface area of ​​the inner face and / or the outer face is preferably greater than 150 cm 2 , greater than 200 cm 2 , greater than 250 cm 2 , preferably greater than 400 cm 2 , preferably greater than 500 cm 2 , or even greater than 1000 cm2 , and / or less than 10,000 cm 2 .

[0109] The shape of the inner face and / or the outer face is not limiting. It can be smooth or rough, have through holes or be continuous, optionally have cavities or bosses, be developable or not, be flat or not. Preferably, this shape is flat.

[0110] The shielding part is preferably made of a metallic and / or ceramic material and / or a glass and / or a glass ceramic and / or an organic matrix composite (OMC) or ceramic (CMC), preferably a ceramic material, preferably alumina, SiC or B4C.

[0111] The shielding part material can be, classically, a brittle material.

[0112] The shielding part material, preferably ceramic, preferably has:

[0113] - an apparent density of less than 8 g / cm 3, preferably less than 5 g / cm 3 , preferably less than 3.2 g / cm 3 , preferably less than 3.0 g / cm 3 and / or greater than 1.0 g / cm 3 , and / or

[0114] - a Vickers hardness greater than 3 GPa, preferably greater than 10 GPa.

[0115] The shielding part material is preferably an agglomerate of grains, preferably a sintered material.

[0116] The grain material is preferably metallic and / or ceramic and / or a cermet.

[0117] Said grains are preferably made of a metal carbide or a metal boride. More preferably, the grains are grains of silicon carbide or boron carbide or grains of a mixture of these two carbides.

[0118] According to one embodiment, the grains are exclusively silicon carbide grains, with optionally a metallic phase, preferably comprising the element silicon.

[0119] The whole grain preferably presents:

[0120] - a median equivalent diameter D50, less than 500 micrometers, preferably less than 200 micrometers, preferably less than 100 micrometers, preferably less than 50 micrometers, and / or

[0121] - an equivalent diameter D 90 less than or equal to 1000 micrometers, preferably less than or equal to 700 micrometers or even less than or equal to 500 micrometers, and / or greater than 1 micrometer, preferably greater than 5 micrometers or even greater than 20 micrometers.

[0122] Preferably, the grains are bound by a matrix. Preferably, the matrix comprises or consists of a silicon nitride phase and / or a silicon oxynitride phase. It preferably represents between 5 and 40% by mass, preferably between 15 and 35% by mass, of the mass of the shielding part.

[0123] Besides the armor piece, the shield may have other parts.

[0124] A bulletproof vest as described in the preamble is an example of an anti-ballistic protection shield. Preferably, the armor piece is glued to the intermediate layer, which is itself glued to the shock absorber plate. The outer casing may also be glued to the protective plate. The glue may be based, for example, on polyurethane, epoxy polymers or thermoplastic polymers or elastomers.

[0125] The armor part of a bulletproof vest is preferably made of metal or a ceramic material, typically alumina, SiC and / or B4C.

[0126] Preferably, the damping plate is made of a material of lower hardness than that of the material constituting the shielding part. Preferably, the damping plate is made of a material chosen from polyethylenes PE, in particular ultra-high-density polyethylenes (UHMPE), glass or carbon fibers, aramids, metals such as aluminum, titanium or their alloys or steel.

[0127] The intermediate layer is optional. It is preferably a textile, preferably made of a material chosen from polyethylenes PE, in particular ultra high density polyethylenes (UHMWPE), glass or carbon fibers, aramids, and metals such as aluminum, titanium or their alloys and steel.

[0128] The outer shell is preferably made of a fabric, for example glass or carbon fibers. It may be made of a material chosen from polyethylenes PE, in particular ultra high density polyethylenes (UHMPE), aramids, in particular Kevlar®, metals such as aluminum or even steel, in particular in the case of non-personal protection.

[0129] In the service position, i.e. when the bulletproof vest is worn, the shock absorber plate extends towards the wearer of the bulletproof vest. The shock caused by a projectile therefore first reaches the armor part, then the shock absorber plate.

[0130] Sensor 24 includes

[0131] - 28e and 28i electrical conductors,

[0132] - a separator arranged between said conductors and which, according to the invention, is constituted by the shield or by a part of the shield, and

[0133] - the interrogator 26 electrically connected to said conductors so as to measure said electrical property, and / or a connector 30 capable of electrically connecting the conductors to the interrogator, for example by means of a connection cord 32, preferably a coaxial cable. The structure of the two electrical conductors may or may not be the same.

[0134] At least one, preferably each conductor may be in the form of a plate or a strip or a wire or a cable, preferably in the form of a strip or a wire or a cable formed of one or more wires.

[0135] Preferably, at least one, preferably each driver has:

[0136] - a length less than 1000 mm, preferably less than 500 millimeters, and / or greater than 10 mm, preferably greater than 100 mm; and / or

[0137] - a width or, when the conductor is in the form of a wire or cable, an equivalent diameter of less than 10 millimeters, less than 5 mm, and / or preferably greater than 1 mm;

[0138] - when the conductor is in the form of a plate or a ribbon in particular, a thickness preferably less than 10 millimeters, less than 5 mm, and / or preferably greater than 10 micrometers, preferably greater than 50 micrometers, or even greater than 1 mm.

[0139] In a particularly advantageous embodiment, the conductor is deposited on the shielding part 12, preferably in the form of a ribbon having a width of between 3 mm and 10 mm and a thickness preferably of between 10 μm and 100 μm, preferably less than 50 μm.

[0140] The conductor may be produced by a local modification of the microstructure of the shielding part 12, in particular when the shielding part comprises more than 50% by mass of ceramic, preferably made of ceramic. The local modification may for example result from local doping or from a decomposition or a local phase transformation, preferably by means of a beam of high surface power, preferably greater than 50 W / mm 2. For example, for products comprising more than 50%, more than 80%, more than 90% or 100% silicon carbide (SiC), it is possible, for example using a laser (in particular YAG or CO2), to locally decompose the SiC into Silicon and Carbon and thus create one or more lines in a material having an electrical resistivity at least 100 times, preferably at least 1000 times lower than that of the material which surrounds it and which preferably constitutes the rest of the shielding part.

[0141] In a preferred embodiment, the two conductors have the same shape and preferably extend facing each other, ignoring the separator, and more preferably parallel to each other, as in Figures 2 and 3. For example, as illustrated in Figure 3, each conductor may have the same shape of a spiral ribbon fixed to a respective face of a plate-shaped separator, preferably the shielding piece, the two ribbons being superimposed in register, that is to say in such a way that when they are observed perpendicular to said faces, they overlap substantially exactly.

[0142] The predetermined distance between the two electrical conductors is preferably substantially constant. The two conductors are preferably parallel except, possibly, in the areas of discontinuities. Local defects of parallelism may be provided to create discontinuities, as described below.

[0143] The material of a conductor, preferably of each conductor, is preferably an electrically conductive metal, such as aluminum, copper, steel or a metal alloy. It may also be a ceramic or a cermet. In particular, in applications in which the shield is subjected to temperatures above 500°C, said material of the conductors is preferably chosen from:

[0144] - Inconel, for example alloys 625 and 690, usable up to 1100°C;

[0145] - platinum,

[0146] - a Kanthal of the FeCr type, for example KANTHAL APM, usable up to 1425°C;

[0147] - tungsten,

[0148] - rhodium,

[0149] - ruthenium, and

[0150] - palladium.

[0151] At least one, preferably each conductor may be made of a metal coated with an electrically conductive refractory oxide, preferably SnO2 or C^Os-MgO spinel or perovskite or metalloid or metal carbide.

[0152] Preferably, the difference between the coefficient of thermal expansion of at least one, preferably each conductor and the coefficient of thermal expansion of the shielding piece is, in absolute value, less than 20%, preferably less than 10% of the coefficient of thermal expansion of the shielding piece.

[0153] At least one, preferably each conductor is preferably a material having an electrical resistivity:

[0154] - at least 100 times, preferably at least 1,000 times, preferably at least 100,000 times, or even at least 1,000,000 times lower than the electrical resistivity of the material constituting the separator, preferably the material of the shielding part; and / or

[0155] - less than 1000 micro-ohm. cm in the temperature range of the shield environment, preferably between 20°C and 1000°C. If the electrical resistivity of the material constituting the separator, preferably of the material of the shielding part, is insufficient, an electrically insulating layer, for example made of a polymer (for example PET or PE), or of a ceramic can be deposited on the separator, preferably the shielding part.

[0156] The complex dielectric constant of a dielectric is classically written E* = E'-iE". The loss angle 5 of a dielectric with zero electrical conductivity is defined by tan(5) = E" / E'. The loss angle is a quantity usually referenced in tables concerning dielectric materials for microwaves. For a good dielectric, 5 is low and tan(5) « 5.

[0157] The separator preferably has a dielectric loss angle tangent at 1 Ghz less than 10 2 , preferably less than 5.10 -3 , preferably less than 1.10 -3 .

[0158] In one embodiment, a conductor, preferably each conductor, may be inserted into a protective sheath in order to protect the conductor from heat and / or corrosion and / or chemical attacks. The protective sheath may be made in particular of a polymer (for example PET or PE), or of ceramic, in particular alumina, in particular for an environment at a temperature above 400°C. The protective sheath is preferably made of a material having a coefficient of thermal expansion substantially identical to that of the material of the conductor.

[0159] Sheathing with a sheath made of an electrically insulating material is particularly advantageous if the separator, in particular the shielding piece and / or the damping plate and / or the outer casing, has a resistivity of less than 1000 microohm.cm, or even less than 100 microohm.cm.

[0160] In the case where the sensor is intended for reflectometry analysis, the sheath can be segmented to create discontinuities, as described below.

[0161] The separator establishes a minimum separation distance, or "gap", between the two conductors. The minimum and / or maximum and / or average gap between said conductors is preferably less than 100 mm, preferably less than 80 mm, or even less than 60 mm or even 50 mm, and / or greater than 3 mm, preferably greater than 5 mm, or greater than 10 mm.

[0162] The conductors are not necessarily in contact with the separator, but such contact is preferred because it facilitates the measurement of deformation and / or a change in the state of the separator. Y1

[0163] One, preferably each conductor is preferably attached to the separator, preferably on or in the shielding piece, or, for a bulletproof vest, on or in the damping plate 16, the intermediate layer 14 arranged between the shielding piece 12 and the damping plate 16, or the outer casing 18. In one embodiment, the conductor is attached between two shield pieces, preferably in the form of a plate or layer, for example between the shielding piece 12 and the outer casing 18 or between the damping plate 16 and the outer casing 18.

[0164] In the particular embodiment where the shield is a bulletproof vest, the 28th conductor may be arranged:

[0165] - within the material of the outer part of the outer shell, preferably between two layers of fabric, as shown in Figure 4A, or

[0166] - between the outer part of the outer casing and the outer face (i.e. exposed on the side opposite the target in the service position) of the shielding part 12, as shown in Figure 4B, or

[0167] - on the external face of the outer part of the outer envelope, as shown in Figure 4F.

[0168] The 28e conductor may be embedded in the glue securing the outer jacket 18 to the shielding piece 12.

[0169] The 28i driver can be arranged

[0170] - between the shielding part 12 and the intermediate layer 14, as shown in Figure 4A, or

[0171] - preferably in the intermediate layer 14 as shown in Figure 4B,

[0172] - between the intermediate layer 14 and the damping plate 16, as shown in Figure 4C, or

[0173] - between the damping plate and the inner part of the outer casing, as shown in Figure 4D, or

[0174] - within the material of the inner part of the outer casing, preferably between two layers of fabric, as shown in Figure 4E, or

[0175] - on the outer face of the inner part of the outer casing, as shown in Figure 4F. The conductor 28i may be integrated into the glue fixing the intermediate layer 14 to the shielding piece 12 or into the glue fixing the intermediate layer 14 to the damping plate 16 or into the glue fixing the outer casing 18 to the damping plate 16.

[0176] In one embodiment, the damping plate is glued directly to the shielding piece and the conductor 28i is embedded in the glue securing the damping plate to the shielding piece 12.

[0177] In one embodiment, at least one, or even each conductor extends at least partially, preferably completely inside the shielding part. This embodiment is well suited when the shielding part is a sintered part from a mixture of grains which is shaped and then subjected to a consolidation heat treatment compatible with the mechanical and thermal resistance of the conductor. For example, at least one conductor can be produced by infiltrating a metal into the open porosity of the material constituting the shielding part. In particular, in the case of a shielding part comprising more than 80%, more than 90% or 100% by mass of silicon carbide and / or boron carbide, the infiltrated metal can advantageously be silicon or a silicon alloy. In particular for an alumina shielding part, a metal comprising more than 80%, more than 90% or 100% by mass of aluminum may be suitable.

[0178] Preferably, the outer envelope is made up of several superimposed layers and, preferably, a conductor, or even each conductor, is inserted between two said layers. Thus, advantageously, at least one said layer of the outer envelope protects it.

[0179] The fixing of a conductor can be obtained in particular:

[0180] - by gluing and / or

[0181] - by insertion into a recess, preferably a groove, in particular into a groove, previously provided, preferably on the surface of the shielding part, and / or

[0182] - by deposition, preferably by screen printing or pad printing or by application of a conductive paint, in particular on the shielding part, and / or

[0183] - by incorporation, or “integration”, within a constituent part of the shield or between two constituent parts of the shield, in particular between two superimposed layers of the external envelope.

[0184] The conductor may in particular be fixed, in particular glued at several separate fixing points, each fixing point having a length, along the conductor, preferably less than 5 cm, 3 cm, 2 cm, 1 cm, or 0.5 cm. In one embodiment, the conductor is not rectilinear between two fixing points, at room temperature. Preferably, the length of the conductor between two successive fixing points is greater than 1.05 times, preferably greater than 1.1 times and / or preferably less than 1.5 times, preferably less than 1.4 times, preferably less than 1.3 times the distance between said fixing points. Advantageously, the conductor can thus adapt to dimensional variations of the substrate on which it is fixed.

[0185] A conductor, preferably each conductor, is preferably non-intrusive, i.e. does not penetrate the shielding part. Preferably, the conductor results from a deposition of material, preferably on the shielding part. Screen printing or pad printing advantageously makes it possible to reduce the excess thickness resulting from the fixing of the conductors, without machining the substrate.

[0186] The different arrangements described above for the two drivers can be combined.

[0187] The conductor may also be fixed to a support, for example a plate, itself fixed to the separator, the support preferably being arranged in contact with the shielding part, preferably so as to match the shape of the separator, preferably the shape of the shielding part. An advantage of this embodiment is a separate preparation of the conductor, which allows better organization of the production of the device according to the invention. In addition, the conductor can be deposited quickly and reliably on the separator.

[0188] The support is preferably at least partly, preferably completely, made of a composite material consisting of fibers bonded together by a matrix, or "ceramic matrix composite" (CMC).

[0189] The fibers and the matrix are preferably chosen according to the environment of the shield in the service position, in particular according to the temperature and / or corrosion and / or thermal cycling and / or expansion conditions, and / or according to the nature of the shielding part. The arrangement of the fibers is chosen according to the desired shape for the CMC, and the ease of fixing or inserting the conductor therein. For example, a stack of woven fabrics or fiber sheets is well suited for simple plates, a filament winding is well suited for plates having a geometry of revolution, a filament placement is well suited for large complex shapes. When the shielding part is plate-shaped, one of the conductors is on the outer side of the shielding plate and the other is on the inner side of the shielding plate, the conductors being in contact or not with the shielding part.

[0190] The total surface area of ​​said conductors projected onto the total surface area of ​​said outer and inner faces of the shielding part preferably represents less than 50%, less than 30%, less than 20%, less than 10%, preferably less than 5% of the total surface area of ​​said outer and inner faces, in particular when the conductors are in the form of wires, ribbons or cables.

[0191] In one embodiment, the conductors are arranged so as not to be exposed to the impact of a projectile, in particular a bullet, in the service position, and in particular so as not to be opposite the outer face of the shielding part. They may in particular be arranged at the periphery of the shielding part, preferably along parallel edges of the shielding part, preferably in contact with the 12p edge of the shielding part which defines said edges, as illustrated in Figure 8. Advantageously, this configuration reduces the risk of destruction during use of the shield. It may be in particular advantageous for acquiring information on the state of the shield after the impact of a low-energy projectile on the exposed outer face of the shielding part.

[0192] The conductors are preferably arranged on the most vulnerable parts of the shielding piece, for example corners and edges.

[0193] Preferably, the sensor comprises a connector 30 to which the conductors are connected and which allows an electrical connection of the conductors to the interrogator 26. Alternatively, the interrogator, preferably miniaturized, can be integrated into the shield, as in Figure 5, so as to be permanently connected to the conductors. The connector 30 is then optional.

[0194] In a preferred embodiment, the sensor is a waveguide for reflectometry measurement.

[0195] In one embodiment, the two conductors of the sensor form a capacitor, the electrical property measured being the capacitance between the two conductors. The two conductors preferably have the shape of two parallel plates.

[0196] In one embodiment, the sensor is an impedance sensor, preferably an acoustic and / or electrical impedance, preferably at least an electrical resistance, variable depending on the shape of the separator. When the separator deforms, elastically or plastically, the impedance variation resulting from this deformation, for example resulting from the appearance of cracks, can be measured by the interrogator.

[0197] Preferably, electrically conductive particles, preferably carbon particles, preferably carbon nanotubes, are distributed in the separator, preferably in the shielding part. Together, they form a conductive network whose impedance, preferably the electrical resistance, preferably exclusively the electrical resistance, is a function of an arrangement of the conductive particles constituting the conductive network. The arrangement of the conductive particles of the conductive network is modified when the separator is deformed, so that this results in a modification of the impedance of the conductive network.

[0198] A sensor operating in a similar manner is described in PCT / EP2020 / 085638.

[0199] Details of this embodiment are described in PCT / EP2020 / 085638, the sensor matrix described in PCT / EP2020 / 085638 being, according to the present invention, constituted by the separator, preferably by the shielding part.

[0200] EP2129991 B1 and US2012144934A1 describe variable impedance sensors intended to be attached to a bulletproof vest. However, they do not suggest that a part of the bulletproof vest can be used as a separator.

[0201] To perform an electrical property measurement, the input ends of the conductors are electrically connected to the interrogator 26. The interrogator may be integrated into the shield (Figure 5) or be selectively connected to a connector 30 itself connected to the conductors (Figure 3).

[0202] The interrogator is chosen according to the electrical property to be measured. It typically comprises a processor, computer memory and software configured to evaluate, from one or more measurements made by the sensor, the physical state of the shield, preferably of the shielding part.

[0203] Preferably, the value of the property depends on the spacing between the two conductors and / or the middle of the separator. The spacing between the two conductors may in particular change when different elements of the shield become separated. The middle of the separator may in particular change in the event of deformation of the shielding part and / or the appearance of cracks. Preferably, communication between the interrogator and the waveguide is wireless, preferably over the air, via Wi-Fi or Bluetooth®.

[0204] Preferred special case of a measurement by reflectometry

[0205] Electrical time domain reflectometry (E-TDR) or electrical frequency domain reflectometry (E-FDR) is a technique for measuring changes in the state of a medium using a sensor forming a waveguide.

[0206] When the device is intended for measurement by reflectometry, as illustrated in FIG. 3, the sensor is adapted so as to form a waveguide 34 which extends between an input end 34i and an output end 342.

[0207] The free ends of the conductors are not electrically connected to each other and define the output end of the waveguide. The conductors therefore do not form a closed electrical circuit, as in a resistive measuring sensor in which direct or alternating current flows.

[0208] When the waveguide is damaged, it can advantageously continue to operate. The damage can lead to the appearance of a specific echo, which makes it possible to detect and locate the damage. If the waveguide is cut, the part of the waveguide still connected to the interrogator can continue to serve as a waveguide. The use of a waveguide thus provides robustness to the device.

[0209] To improve the interpretation of the reflected signal, the waveguide preferably has discontinuities preferably distributed, preferably randomly, along the waveguide. The discontinuities in fact make it possible to generate specific identifiable echoes in the signal reflected by the waveguide. To facilitate this identification, the waveguide preferably satisfies the Rayleigh scattering condition.

[0210] In one embodiment, discontinuities are surface irregularities on the separator, preferably the shielding part, preferably arranged opposite the conductors, preferably in at least one area of ​​the separator in contact with the conductors. Texturing said area advantageously makes it possible to generate random discontinuities. Preferably, the texturing comprises the creation of micro-reliefs with a height greater than 0.05 mm, preferably greater than 0.1 mm, preferably greater than 0.2 mm, preferably greater than 0.2 mm, preferably greater than 0.5 mm, or even greater than 0.8 mm, and / or less than 3 mm, less than 2 mm or less than 1 mm.

[0211] It is also possible to create random discontinuities by modifying the surface condition on the separator or on a sheath surrounding a conductor, for example by creating roughness by abrasion.

[0212] In one embodiment, one or more dielectric cleats 36 are disposed on said area or around at least one conductor of the waveguide so as to create discontinuities.

[0213] Dielectric cleats can have the same or different shapes and / or dimensions and / or be made of the same or different materials. Even if the dielectric cleats appear identical, no two cleats are completely identical. This makes it possible to create discontinuities randomly.

[0214] Dielectric cleats, and in particular beads threaded onto a conductor, may have a length, measured along the length of the conductor, greater than 10 mm, 15 mm or 20 mm and / or less than 100 mm or 50 mm.

[0215] Preferably, the discontinuities are spaced apart from each other by a distance, measured along the waveguide, at least 20 times, preferably at least 15 times, preferably at least 10 times less than the wavelength equal to the inverse of the frequency of the highest peak in the frequency spectrum of the reflected signal. For example, for a wavelength of about fifteen centimeters, beads with a length of less than 2 cm or 1 cm are well suited.

[0216] This distance may in particular be defined by the length of dielectric cleats, in particular beads threaded onto the conductors. The dielectric cleats, and in particular the beads, preferably have a width, i.e. a largest dimension in a plane transverse to the direction of their length, greater than 1 mm, 2 mm or 3 mm and / or less than 10 mm or 5 mm.

[0217] Variations in the shape and composition of the beads and variations in the positioning of the beads relative to the conductors make it possible to randomize the discontinuities they generate.

[0218] The beads also facilitate the identification of regions containing discontinuities.

[0219] The separator, preferably the shielding part, preferably has an electrical resistivity greater than 10, 50, 100 or 1000 times that of the conductors. To electrically insulate the conductors from each other, the separator may comprise a dielectric material interposed between the conductors, preferably in the form of a layer, for example of an organic nature, for example made of an uncharged polymer, for example polyethylene or polyamide, or of a mineral nature, for example mica or a mica derivative, or comprising more than 50% by mass of titanium, or barium, mullite, cordierite or alumina.

[0220] The dielectric insulator may be a single piece. It may consist of an assembly of several dielectric cleats. Preferably, the dielectric cleats are in the form of beads threaded onto at least one of the conductors, or onto each of the conductors.

[0221] A protective sheath surrounding a conductor can also contribute to the electrical insulation between the conductors, or even constitute said dielectric insulator.

[0222] Typically, the interrogator, called a “reflectometer”, is configured to:

[0223] - inject incident signals into the waveguide; and

[0224] - analyze reflected signals in response to incident signals.

[0225] Each incident signal, preferably in the form of a pulse or "Dirac", is generated by establishing a variation in the potential difference between the two conductors of the waveguide. The latter returns a reflected signal, which is then analyzed in order to deduce information on the medium crossed by the pulse. In the presence of an impedance discontinuity, for example a significant physicochemical variation of the medium leading to a local variation in impedance, part of the incident signal is reflected towards the interrogator, which makes it possible to identify and analyze this variation.

[0226] The incident signal may take the form of a periodic wave of any shape. The incident signal may be repeated. Preferably, the maximum amplitude of the incident signal is between 0.1 and 100 V, preferably less than 10 V, preferably less than 1 V. The frequency of the highest peak in a frequency spectrum of the incident signal is preferably greater than 10 KHz, preferably greater than 100 KHz, preferably greater than 1 MHz, preferably greater than 100 MHz, preferably greater than 200 MHz, preferably greater than 500 MHz, preferably greater than 1 GHz, and / or less than 50 GHz, preferably less than 30 GHz, preferably less than 20 GHz, preferably less than 10 GHz, preferably less than 6 GHz, preferably less than 4 GHz. The incident signals may be sent in the form of signal trains preferably comprising a series of periodic signals of variable frequencies depending on the periodic signal in question.Each incident signal propagates in the waveguide to the free end of the conductors. At each discontinuity, part of the incident signal, or "echo," is reflected back to the interrogator. All the returned echoes together constitute the reflected signal associated with the incident signal and which the interrogator analyzes.

[0227] Figure 6 illustrates an example of a reflected signal, the y-axis giving the amplitude in Volts (V) and the x-axis giving the time elapsed since the instant to of reception of the reflected signal, in tens of nanoseconds (10 -7 s). In particular, we distinguish the emission echo E oreturned by the input end of the waveguide, the back-end echo Ef returned by the output end of the waveguide, and a set of discontinuity echoes Ei returned by discontinuities. The discontinuity echoes are of low amplitude, and are of various amplitudes and shapes. Figure 6 is described in more detail below, in the description of the examples.

[0228] The interrogator is programmed to analyze the reflected signals, and possibly compare them, in order to determine the said electrical property and / or a change in the said property.

[0229] Preferably, the interrogator implements steps a) to e) described above.

[0230] In a preferred embodiment of the invention, reflectometry is used to monitor the physical condition of the shield, and in particular of a shield comprising an assembly of several parts creating a heterogeneous medium. Reflectometry is not conventionally used for heterogeneous media and, surprisingly, has proven effective for monitoring the physical condition of a shield.

[0231] Preferably, the interrogator is programmed to generate an information message on the result of said analysis.

[0232] Preferably, the message specifies:

[0233] - a value for the physical condition of the shield, and in particular of the shielding part; and / or

[0234] - a value for an evolution of said value compared to a previous situation; and / or

[0235] - a location of defects or damage affecting said physical condition.

[0236] The message may be sent to a central computer and / or presented to an operator, for example on a screen and / or by activating a light and / or by emitting an audible signal.

[0237] The manufacture of the device follows directly from the above. The following examples are given for purely illustrative purposes and do not limit the scope of the present invention in any of the aspects described.

[0238] Two electrical conductors, each in the form of a copper-coated tape, reference 3M 2245, composed of a 35 μm thick and 6 mm wide copper foil and an acrylic adhesive undercoat, were glued to the inner and outer faces of a Forceram Premium® silicon carbide shielding piece, respectively, thus forming an electromagnetic waveguide. Observed perpendicular to the said large faces, the copper ribbons appeared superimposed, and drew a spiral with a length of 30 cm following the irregularities of the surface of the inner and outer faces of the shielding piece, the shielding piece comprising SiC grains with a median equivalent diameter of 50 micrometers bound by a silicon nitride matrix, as in Figure 3.

[0239] The shielding piece thus provided with the conductors was then bonded to a Dyneema HB26 organic matrix composite acting as a damping plate. The assembly was wrapped in Kevlar fabric. An intermediate layer of Kevlar was inserted between the shielding piece and the damping plate. A coaxial connector 30 was connected to the two conductors so that the waveguide formed by the two conductors and the shielding piece could be connected, by a coaxial patch cord 32, to a Copper Mountain S5085 interrogator 26.

[0240] The device thus constituted was installed horizontally at the bottom of a drop shaft, the upper face of the shielding piece being oriented upwards.

[0241] An incident signal, in the form of a 1 GHz (Dirac) pulse, was injected into the waveguide by the interrogator. The reference reflected signal received back by the interrogator is shown in Figure 6, in solid black line. Analysis of this reflected signal makes it possible to locate a set of 38 echoes of the incident signal returned by the connecting cable, the echo E o returned by the connector, a set 40 of echoes Ei returned by the waveguide and the backbone echo Ef returned by the end of the waveguide. The portion of the set 40 of echoes Ei , also shown in Figure 7, corresponds to the length L of the waveguide (from the connector to the free ends of the conductors) and it is possible to establish a correspondence between a peak on the reflected signal and a position along the waveguide. A 40 kg hemispherical impactor was then dropped above the shield, 20 cm above the shield.

[0242] The same incident signal was injected again. The updated reflected signal received back by the interrogator is shown in Figure 6, in dotted black line.

[0243] The reference and updated reflected signals were plotted on the same graph, with time 0 corresponding to the time of reception of the reflected signals (synchronization). The graph shows a slight time shift of the background echo.

[0244] A differential signal representing the difference between the reference and updated reflected signals is also shown in a broken black line. For clarity, the differential signal has been shown on a larger scale in Figure 7.

[0245] An analysis of the differential signal allows two peaks to be identified corresponding to positions xi at 0.1 *L (i.e. approximately 3 cm from the connector) and x2 at 0.8 *L (i.e. approximately 24 cm from the connector) along the waveguide.

[0246] Post-mortem X-rays of the armor piece were used to locate cracks at positions 0.1*L and 0.8*L. A reflectometry measurement is therefore suitable for detecting and even locating cracks.

[0247] The amplitude of the peaks also allows the amplitude of the cracks to be estimated.

[0248] The inventors also discovered that, when only detection of shield damage is sought, it is particularly advantageous to use a score calculated by integrating the differential signal. The score resulting from this integration can be compared to a threshold, so that it can be deduced that if the score exceeds the threshold, there is damage or that if the score is below the threshold, there is no damage. The threshold can be conventionally determined by a statistical analysis of a set of tests.

[0249] As is now clearly apparent, a device according to the invention makes it possible to reliably detect damage to the shield, and even to locate it and assess its extent. It is simpler to manufacture, more compact and less expensive to manufacture than the devices of the prior art. Finally, since the conductors are on either side of the shielding part, the sensor is very sensitive and makes it possible to detect deformations of low amplitudes. The device thus makes it possible to detect weak signals, and therefore to anticipate catastrophic degradation of the shielding part even though the pseudo-plastic deformation zone (resulting from microcracks) of the shielding part is extremely limited.

[0250] Two pieces of armor made of the same material as for the first example series, in Forceram Premium® silicon carbide with a thickness equal to 18 mm, were machined to obtain a length L pequal to 152 mm and a width l p equal to 30 mm. Each armor piece (reference 12 in Figure 9) was glued to a damping plate 16 of the same length and width as the armor piece. The damping plate was a 10 mm thick UHMWPE Dyneema HB26 organic matrix composite. The thermoplastic adhesive was a Pentacol adhesive forming a layer 14a.

[0251] For the test piece of the first comparative example, the two conductors, each in the form of a copper-coated tape, reference 3M 2245, composed of a 35 μm thick and 6 mm wide copper foil and an acrylic adhesive undercoat, were glued to the outer face 12e (impact face). The conductors 28 formed two straight lines extending parallel to the sides defining the length L p of the armor part.

[0252] For the test piece of the second example, according to the invention, the two electrical conductors 28e and 28i, of the same nature and the same length as for the first example, were glued, facing each other, respectively on the outer face 12e and on the inner face 12i of the shielding part.

[0253] The inner face 12i of each specimen was then bonded to a damping plate of the same length and width as the armor piece. The damping plate was a 10 mm thick UHMWPE Dyneema HB26 organic matrix composite. The thermoplastic adhesive was a Pentacol adhesive forming a layer 14a.

[0254] A 2*2 twill aramid fabric at 170 g / m 2 was then glued to form an envelope around each armor piece-damping plate assembly. Each specimen thus obtained had a final thickness of approximately 20 mm.

[0255] For each specimen, a coaxial 30 connector was also connected to both conductors. Each 30 connector was connected, by a coaxial 32 patch cord, to a Copper Mountain S5085 26 interrogator.

[0256] Each specimen was subjected to a 3-point bending test illustrated by figures 9a (specimen of the first example) and 9b (specimen of the second example). The outer face 12e of the shielding piece rested on two supports spaced apart by a distance l e of 100 mm, via the aramid fabric envelope, not shown for clarity. A crack was then created in the shielding piece, between the two conductors. For this purpose, a punch was lowered at a speed of 0.6 mm per minute. The force F exerted on the inner face 16i of the damping plate is noted F. Each time, a crack appeared in the width direction without breaking the waveguide which remained functional.

[0257] Figures 10 (a and b) and 11 (a and b) represent the reflected signals received by the interrogator during the tests of the first and second examples, respectively. Each time, the following are represented in amplitude (Volts):

[0258] - the reference reflected signal “R” before bending stress,

[0259] - the difference between the reference signal and the reflected signal in an intermediate state “I” when the force F was 1000 N, before rupture, and

[0260] - the difference between the reference signal and the reflected signal in a state after break “C”.

[0261] The reference reflected signal for each of these examples has a classical emission echo E o between 2.4 and 2.7.10 -8 seconds produced by the 34i input end of the waveguide. For example, for the second example, this allows the 34i input end to be positioned at 2.55.10 -8seconds. The output end 342 of the waveguide can also be identified by the bottom echo Ef at 3.3.10 -8 seconds on the enlarged diagram in Figure 11.

[0262] Comparison of these signals shows the presence of a very clear time shift of the "end peak" pf reflected by the end of the waveguide, of 3.4.10 8 at 3.2.10 8 seconds at the intermediate stage during the initiation of the crack for the specimen of the second example (figure 11 a) which does not appear for the specimen of the first example (figure 10a).

[0263] The magnification in Figure 11b shows the presence of a particular and sharp peak p c at about 2.7. 10 -8 seconds. This particular peak corresponds to the position of the crack that appeared on the armor piece.

[0264] It is notable that even after detecting the occurrence of damage, the device according to the invention remains operational, which also demonstrates its high reliability and the possibility of being able to reuse or re-implant the sensor from a used device on a new device if necessary.

[0265] This test shows that the device of the first comparative example, representative of the prior art in which the connected conductors are arranged on the same layer or the same surface and in which the shielding plate is not part of the separator, has a much lower reliability than for the device of the second example according to the invention. Of course, the invention is not limited to the embodiments described and shown, provided for illustrative purposes only.

[0266] In particular, the position of the conductors, especially on the shielding part, and the number of deformation sensors are not limiting. The number of deformation sensors can in particular be adapted to the extent of the surface of the shielding part to be monitored.

Claims

CLAIMS Anti-ballistic protection device comprising - a shield (22) comprising a piece of armor (12) capable of protecting a target (C) from a projectile (B) fired by a firearm, and - a sensor (24) comprising two electrical conductors (28e, 28i) and a separator (22) arranged between said conductors, and - an interrogator (26) electrically connected to said conductors and configured to measure an electrical property depending on the arrangement of said conductors and / or the shape of said conductors and / or the structure of the separator and / or the shape of the separator, or a connector (30) capable of electrically connecting said conductors to a said interrogator, at least a part of the shield constituting said separator, device in which the sensor constitutes a waveguide, and the interrogator is programmed to carry out an analysis of an electrical potential difference or an impedance difference measured between the electrical conductors, by time or frequency reflectometry from a reflected signal returned by the waveguide. Device according to the preceding claim, in which - the shielding part (12) or - an assembly consisting of the shielding part (12) and a damping plate (16) made of a fibrous or metallic material intended to be arranged between the target and the shielding plate in the service position of the shield, constitutes, totally or in part, said separator. Device according to any one of the preceding claims, in which the shielding part (12) is shaped to provide at least NIJ-III protection. Device according to any one of the preceding claims, in which the interrogator is programmed so as to implement the following steps: a) at a “reference” instant, in a reference situation, injection, into the waveguide, of an incident signal; b) reception of a signal reflected by the waveguide in response to said injection, or “reference reflected signal”; c) at an “updated” instant, injection, into the waveguide, of an incident signal identical to that injected in step a); reception of a signal reflected by the waveguide in response to said injection, or “updated reflected signal”; d) comparison of the reference and updated reflected signals so as to determine a difference between said signals, and deduce therefrom information on the physical state of the shield in the updated situation; e) optionally, transmission of a message containing said information. Device according to the immediately preceding claim, in which in step d), - a score is determined by integrating over time a function providing the difference between said reference reflected signals and updated as a function of time, then - the score is compared to a threshold and, depending on the difference between the score and the threshold, said information is determined. Device according to any one of the preceding claims, in which at least one of the conductors consists of a deposit of material. Device according to any one of the preceding claims, in which the shield is a bulletproof vest comprising an outer casing (18) enveloping a protective plate (10) consisting of a superposition of said armor piece (12) in the form of a plate, optionally an intermediate layer (14), and a damping plate (16), a conductor (28e) being - integrated into the outer part (18th) of the external envelope, or - arranged on the external face of the outer part of the external envelope, or - arranged between the external envelope and the impact face, called the “external face” (12e), of the shielding part (12), the other conductor being - arranged between the inner face opposite the outer face of the shielding part and the intermediate layer, or - arranged in the intermediate layer or - arranged between the intermediate layer and the damping plate, or - arranged between the damping plate and the outer casing, or - integrated into the inner part (18i) of the outer envelope, or - arranged on the external face of the inner part (18i) of the outer casing. Device according to any one of the preceding claims, in which the shielding part is made of a metallic and / or ceramic material and / or a glass and / or a glass-ceramic and / or an organic or ceramic matrix composite. Device according to the immediately preceding claim, in which the shielding part is made of alumina, SiC or B4C. . Method for monitoring the physical state of a shield of a device according to any one of claims 4 to 9, said method comprising the following steps: 1) implementation of said steps a) and b), and, at a first updated time, implementation of said steps c) and d), or even e), so as to evaluate a first updated physical state of the shield; 2) at a second updated time subsequent to the first updated time, by more than one day, implementation of said steps c) and d), or even e), so as to evaluate a second updated physical state of the shield; 3) comparison of said first and second updated physical states so as to evaluate a difference between said first and second updated physical states, and deduce therefrom information on an evolution of said physical state between the first and second updated instants, and optionally, preferably, transmission of a message relating to said evolution.

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