EP0816793B1 - Personal protection liner for infantry - Google Patents

Description

The invention relates to a coating for personal protection of an infantryman, compatible with protection against splinters and allowing a reduction of the radar and infrared signature of the infantryman.

The field of application of the present invention relates to coverings for the personal protection of infantrymen in operation on a battlefield.

Document DE-A-3 507 889 describes the protection of objects such as devices and vehicles by shielding, a coating absorbing the waves radars and an infrared camouflage paint. This protection can also be effected by means of camouflage against recognition by radars and infrared radiation of objects as described by the document FR-A-2 543 286. The preamble of claim 1 is based on DE-A-3 507 889.

As for personal protection, it is only based today on either protection against projectile shards (cf. documents US-A-5,472,769 and US-A-4,442,162), i.e. discretion in the visible domain, either BNC protection (Nuclear Biological Chemical), or discretion in the radar wave domain (cf. document US-A-3,349,396).

It is known, to provide protection against splinters, to use metallic structures, solution increasingly replaced by structures composites based on aramid fibers, or polyamides.

The two protected areas of the human body are the head by the helmet, and the trunk by a vest. Regarding the reduction of the signature in the visible frequency domain, it is mainly based on a multicolored traditional type. This variegation can have a two-dimensional appearance on a fabric, or three-dimensional on a camouflage net.

During a penetration mission inside enemy lines, the infantryman may face a threat of radar detection and / or infrared. The type of radar threat considered in the present invention is a double threat: a first threat emanating from a surveillance radar battlefield typically operating around 10 GHz, and a second threat from a working target designation radar typically in the band 36 to 37 GHz. These two types of speed cameras have a range of the order of 10 to 20 km. The range of the first is about 7 km for one person, and about 15 km for one vehicle. As for the second type of speed camera, it is more specifically used for vehicle designation, but nevertheless poses a real threat to the infantrymen.

Personal protection for infantrymen known today do not protect infantrymen from such threats.

The invention aims to overcome the aforementioned drawback.

For this purpose, it relates to a coating for protection personal of an infantryman as defined in claim 1.

The coating according to the invention is in particular optimized for radar frequency bands X and Ka, as well as in bands II and III of infrared.

• une première partie de revêtement protégeant la tête et le tronc du fantassin ; la couche diélectrique du revêtement étant en matériau diélectrique sensiblement rigide pour assurer une protection contre les éclats ;
• une deuxième partie du revêtement recouvrant les membres inférieurs et supérieurs du fantassin ; la couche diélectrique du revêtement étant en matériau diélectrique souple, de propriétés diélectriques proches de celles du matériau diélectrique sensiblement rigide, permettant d'assurer la mobilité des membres inférieurs et supérieurs du fantassin.

The invention also relates to an infantryman's combat uniform made from a coating comprising:

• a first part of covering protecting the head and the trunk of the infantryman; the dielectric layer of the coating being of substantially rigid dielectric material to provide protection against splinters;
• a second part of the covering covering the lower and upper limbs of the infantryman; the dielectric layer of the coating being of flexible dielectric material, with dielectric properties close to those of the substantially rigid dielectric material, making it possible to ensure the mobility of the lower and upper limbs of the infantryman.

The present invention has the advantage of providing a structure for infantryman coating compatible with military use, i.e. waterproof, flexible, resistant, allowing a reduction of the radar signature and infrared, while remaining compatible with splinter protection shells, mines, etc.

This structure can also be used to cover a helmet than for a garment, the only difference between the two applications being the overall flexibility of the two structures; flexible structure for clothing and rigid structure for the helmet.

• la figure 1, une coupe transversale d'un revêtement selon l'invention,
• les figures 2 et 3, des courbes illustrant l'évolution du coefficient de réflexion spéculaire en puissance pour trois angles d'incidence 0, 30 et 60°, respectivement pour les polarisations HH et VV des ondes électromagnétiques incidentes, et
• la figure 4, une tenue de combat pour fantassin réalisée à partir d'un revêtement selon l'invention.

Other advantages and characteristics of the present invention will appear more clearly on reading the description which follows and the appended figures which represent:

• FIG. 1, a cross section of a coating according to the invention,
• FIGS. 2 and 3, curves illustrating the evolution of the specular power reflection coefficient for three angles of incidence 0, 30 and 60 °, respectively for the HH and VV polarizations of the incident electromagnetic waves, and
• Figure 4, an infantryman combat outfit made from a coating according to the invention.

The radar threat considered is a surveillance radar type battlefield surveillance coupled to a target designation radar. The infrared threat considered concerns the infrared bands II and III corresponding respectively to wavelengths 3 to 5 µm and 8 to 12 µm.

Infrared discretion, given the passive nature of the coating, is mainly based on a very efficient heat shield minimizing any heat transfer in one direction as in the other, and on an adjustment of the emissivity of the coating relative to that of the environment.

The thermal screen thus produced makes it possible to avoid heat transfer on the outside, a key factor for infrared detection, but it allows also to avoid heat transfer to the interior, which in the case of a infantryman, reduces internal heating which is a factor of comfort important for an infantryman.

Visible discretion is based on the surface pattern exterior of the covering or on the use of a variegated net giving the whole a three-dimensional effect. These known solutions are quite standard.

Radar discretion is mainly obtained by absorption of the energy of electromagnetic waves received by the coating. The diffusion phenomenon created by the net used for visible discretion can possibly be used to further improve the performance level.

Figure 1 illustrates a cross-sectional diagram of a coating according to the invention.

The coating according to the invention is formed by a stack of four successive layers 1 to 4. The definition of each of these layers given below by way of nonlimiting example, represents an optimal solution for the reduction of the radar signature in the frequency bands considered.

The definition of each of these layers 1 to 4 is given below starting from the outermost layer 1 of the coating.

The first layer 1 has several functions: it constitutes a screen against the weather and is formed for example of an impermeable film and resistant, thin, about 150 µm. This layer 1 can be by example a PVC film, English abbreviation for "PolyVinyle Chlorid". This screen also allows the reduction of the infrared and visible signature, because this first layer 1, which is the outermost layer, is covered a bidimensional or three-dimensional variation in emissivity close to 1 for the infrared frequency bands considered.

In addition, thermally, the non-negligible thickness of the coating according to the invention, approximately 4 mm, ensures excellent properties ensuring thermal insulation between the body and the outside of the coating. This condition is mandatory for any reduction structure of passive infrared signature.

Layer 2 is a resistive layer. Its role is to create the best compromise between reflections and multiple transmissions created at the interfaces of each of the layers 1 to 4 of the coating to ensure the best possible destructive interaction when the coating receives a wave electromagnetic.

The thickness and resistivity of this layer 2 are suitable for optimize destructive interactions so that the coating according to the invention generally appears as an absorbent material for the strips of frequencies considered.

The thickness of layer 2 is approximately 200 μm. Its conductivity and its thickness are adapted so that the reverse of their product, which represents a surface resistance, ie close to 330Ω.

Typically, this resistive layer is made of textile fiber loaded with carbon.

Layer 3 is a layer of substantially dielectric material rigid, having a thickness and mechanical properties allowing also to ensure the protection of the infantryman against shrapnel and bullets, like for example an aramid, a polycarbonate, etc ...

It also allows to set the radar frequency bands absorbed by destructive interference. The energies brought into play in this cases are low, therefore no temperature rise that could impair infrared discretion is observed.

Layer 4 is a reflective layer of electrical conductivity tending towards infinity, generally greater than or equal to 10 ⁴ Ω ^-1 .m ^-1 , which corresponds to a surface resistance of between approximately a few ohms and ten ohms as a function of the thickness of layer 4. It defines the reference reflective plane of the coating according to the invention. It consists for example of an aluminum film with a thickness of approximately 50 μm.

The distance between this reference plane and the rest of the coating, that is to say the stacking of the different layers 1 to 4 described above, is determined and fixed in order to achieve the desired optimization.

The materials mentioned above must be isotropic and homogeneous at the frequencies considered. These conditions are necessary due to theories used for optimization. Characteristics not specified are supposed to be any.

The coating according to the invention is compatible with protection against splinters. Either the structure providing protection against splinters fits into the definition of the radar absorbing screen at layer 3 formed by the dielectric material, or it does not fit into the definition of the radar screen and in this case, it is placed behind the reflective plane formed by layer 4 which is the innermost layer of the coating.

The different layers 1 to 4 and their characteristics which have just been defined are reported below in the form of a synthetic table below called table 1. Layers Layer characteristics 1 2.85 permittivity waterproof dielectric material for the real part, thickness 150 μm (for example a PVC film) 2 Material with a surface resistance of approximately 330Ω equal to the inverse of the product of electrical conductivity and thickness (for example 200 µm in thickness and 15Ω ^-1 .m ^-1 ) (for example carbon-laden polyamide fabric) 3 Dielectric permittivity of 3.2 and thickness 3.4 mm (e.g. aramid fabric) 4 Electrical conductivity which can be considered as infinite about 10 ⁴ Ω ^-1 .m ^-1 , and of thickness at least equal to a few microns (for example aluminum film)

Figures 2 and 3 illustrate the evolution of the reflection coefficient specular in power in dB, for the coating according to the invention such as defined above, for three angles of incidence, 0 °, 30 ° and 60 °, respectively, for the HH and VV polarizations; HH and VV meaning horizontal-horizontal polarization and polarization respectively vertical-vertical of the electromagnetic wave. The first term corresponds to the polarization of the incident wave, and the second term to that of the wave reflected. The calculation is based on the conditions of passage through a diopter.

The values of the specular reflection coefficient in dB for the three angles of incidence 0, 30 and 60 °, for the two polarizations HH and VV, and for the frequencies 10 GHz and 36.5 GHz which corresponds to the average value of the bandwidth of the target designation radar, are shown in the following table 2: HH polarization VV polarization Angle of incidence 10 GHz 36.5 GHz 10 GHz 36.5 GHz 0 ° -13 -20 -13 -20 30 ° -11 -20 -13 -20 60 ° -6 -6 -8 -7

The incidence values are only given as an indication because, in such an application where the shape of the target is simple, only the value in normal incidence is actually representative of signature reduction target radar.

The following table 3 illustrates the range of values in which the given characteristics can vary while allowing a value of the specular reflection coefficient in normal incidence of -10dB for the two radar bands considered, 10 and 36-37 Ghz, for a surface resistance of around 330Ω for layer 2. Layer Permittivity (real) Electrical conductivity (Ω ^-1 .m ^-1) Thickness 1 1-8 - <650 µm 2 - 9-10 ⁸ <320 µm 3 2.4-3.6 0-1 3.1-3.6mm

A typical average thickness of a coating according to the invention is less than or equal to about 4 mm. The increase in mass of the coating linked to the properties of the reduction of SER, abbreviation for Surface Radar equivalent, is negligible compared to the mass of the base coating because a minimum initial mass is required for protection against splinters.

By retaining the RES reduction performance of the coating according to the invention, a gain in mass can be obtained, for example replacing the aramid constituting the material of layer 3 with a textile less dense, for example PVC; however, in this case, protection against splinters are no longer insured.

The performance of a coating according to the invention is given below by way of nonlimiting example. Given the simple shape of a body human, we can assume that it behaves like a plane structure, even convex (no dihedral, trihedral effect ...) with respect to waves electromagnetic.

Starting from this approximation, we can deduce from the only value of the specular reflection coefficient in normal incidence at 10 GHz, the reduction in the range of a radar of the radar type field surveillance radar battle. The range of this radar, for a human target, goes from 7 km to 3.3 km.

Assuming that only the infantryman's trunk and head are at protect against splinters or more generally the vital parts of the infantryman, a coating according to the invention can be applied to the production of a combat protecting the infantryman against the fragments and other projectiles.

Figure 4 illustrates an infantryman 5 wearing combat gear produced from a coating according to the invention.

According to this principle, the third dielectric layer 3 of the coating according to the invention covering the helmet 6 and forming the vest 7 of the holding of combat, is carried out in a material of the aramid type, polycarbonate, etc ... This dielectric layer can either be attached to the helmet or be part integral with the helmet.

The protection zones provided by the vest can extend spilling over the limbs without hampering the movements of the infantryman in operation.

The third dielectric layer 3 of the coating covering the lower limbs 8 and upper limbs 9, is made of a material softer dielectric, such as a fabric, whose dielectric properties are close to those of aramid.

Combat clothing as described above must be designed not to hinder the movements of infantryman 5 in operation.

The combat suit can also be equipped with a ventilation by natural or forced convection.

The helmet 6 covered with a coating according to the invention can be further provided with a transparent visor 10 for the frequencies of the domain visible, wearing anti-laser filters, reflective for wavelengths in the infrared and treated to minimize the radar equivalent surface. The helmet 6 is also shaped to present facets prohibiting specular reflections in radar incidence directions.

Finally, the entire combat suit can be returned impermeable to toxic products used on the battlefield. It's at first external layer 1 which is assigned this role.

Claims (18)

1. Coating for the personal protective clothing of a infantryman, compatible with protection against sharp objects, and enabling the radar and infrared signature of the infantryman to be reduced, comprising a stack of layers (1 to 4) of materials which are isotropic and homogeneous at the frequencies in question, absorbing electromagnetic radar waves received by the coating in order to simultaneously optimize the radar signature of the infantryman in the given frequency bands; the stack comprising, starting from its outermost layer:

   a layer (1), which is discreet at infrared frequencies, of emissivity close to 1 for the infrared frequency bands in question;

   a layer (3);

   a conducting layer (4);

   characterized in that:

   the layer (1) is discreet at visible frequencies, for a given thickness and for a given dielectric permittivity;

   the stack comprises a resistive layer (2), of dielectric resistivity and thickness which are determined such that the inverse of their product has a given surface resistance;

   the layer (3) consists of a dielectric of given thickness and of given dielectric permittivity; and in that

   the layer (4) is of a conductivity determined in order to be considered as a reflecting plane at given radar frequencies;

      the thickness and the resistivity of the resistive layer (2) and also the thickness and the electromagnetic properties of the dielectric layer (3) being matched in order to optimize the destructive interaction between the multiple transmissions and reflections created at the interfaces of each of the layers (1 to 4) of the coating, so that the latter appears overall from the outside as an absorbing material at the frequency bands in question.
2. Coating according to Claim 1, characterized in that the layer (1), which is discreet at visible and infrared frequencies, comprises a two-dimensional or three-dimensional camouflage pattern of emissivity close to 1 for the infrared frequency bands.
3. Coating according to Claim 1, characterized in that the radar signature of the infantryman is simultaneously optimized in the X and Ka radar frequency bands, respectively.
4. Coating according to Claim 3, characterized in that the layer (1), which is discreet at visible and infrared frequencies, has a thickness between a thickness close to 0 and about 650 µm, and a complex dielectric permittivity in the two bands, the real part of which permittivity is between about 1 and 8.
5. Coating according to Claim 3, characterized in that the resistive layer (2) has a thickness and an electrical conductivity which are determined such that the surface resistance of the layer (2) is about equal to 330 Ω.
6. Coating according to Claim 3, characterized in that the dielectric layer (3) has a thickness between about 3.1 and 3.6 mm, an electrical conductivity between about 0 and 1 Ω^-1.m^-1, and a complex permittivity, the real part of which is between about 2.4 and 3.6.
7. Coating according to any one of Claims 3 to 6,
   characterized in that the layer (1), which is discreet at visible and infrared frequencies, comprises a two-dimensional or three-dimensional camouflage pattern of emissivity close to 1 for infrared bands II and III.
8. Coating according to Claim 1, characterized in that it comprises a stack of layers (1 to 4) comprising, starting from its outermost layer:

   a layer (1) of waterproof dielectric with a complex permittivity, the real part of which is about 2.85 and with a thickness of about 150 µm;

   a resistive layer (2) with a resistance of about 330 Ω and which is the inverse of the product of the electrical conductivity, about 15 Ω^-1.m^-1, and of the thickness, about 200 µm;

   a layer (3) of dielectric with a complex dielectric permittivity, the real part of which is about 3.2 and with a thickness of about 3.4 mm; and

   a conducting layer (4) of thickness at least equal to a few µm, and of electrical conductivity which can be considered as infinite.
9. Coating according to Claim 8, characterized in that:

   the layer (1), which is discreet at visible and infrared frequencies, is a PVC film;

   the resistive layer (2) is a polyamide fabric filled with carbon;

   the dielectric layer (3) is an aramid fabric; and

   the conducting layer (4) is an aluminium film.
10. Coating according to Claim 9, characterized in that the PVC layer (1) comprises a two-dimensional or three-dimensional camouflage pattern, of emissivity close to 1 for the infrared frequency bands.
11. Coating according to Claim 9, characterized in that the PVC layer (1) is coated with a PVC mesh, the camouflage pattern of which is painted with polyurethane paint.
12. Battle drew for infantryman (5) made from a coating according to any one of Claims 1 to 11,
    characterized in that it comprises:

    a first coating part protecting the head (6) and the trunk (7) of the infantryman (5) comprising protection against sharp objects;

       and in that it comprises:

    a second coating part covering the lower (8) and upper (9) limbs of the infantryman (5); the dielectric layer (3) of the coating being made from a flexible dielectric with dielectric properties close to those of the dielectric of the layer (3) of the coating covering the head (6) and the trunk (7), ensuring the mobility of the lower (8) and upper (9) limbs of the infantryman (5).
13. Battle dress according to Claim 12, characterized in that the protection against sharp objects of the first part of the coating protecting the head (6) and the trunk (7) of the infantryman (5) is placed behind the internal layer (4).
14. Battle dress according to Claim 12, characterized in that the dielectric layer (3) of the coating of the first part protecting the head (6) and the trunk (7) of the infantryman (5) is made of a substantially rigid dielectric having a thickness and mechanical properties which are determined so as to provide protection against sharp objects.
15. Battle dress according to Claim 14, characterized in that the substantially rigid dielectric is aramid, and in that the flexible dielectric is PVC.
16. Battle dress according to one of Claims 12 to 15, characterized in that it is equipped with a system of ventilation by natural or forced convection.
17. Battle dress according to one of Claims 12 to 16, characterized in that the helmet (6) comprises facets preventing specular reflections in the directions of incident radar, and in that it comprises a visor (10) which is transparent at visible frequencies, bearing laser filters, and which is reflective at infrared frequencies and treated in order to minimize the laser cross section.
18. Battle dress according to one of Claims 12 to 17, characterized in that the external surface of the battle dress, which is the first layer (1) of the coating, is made impermeable to the toxic substances generally used on a battlefield.

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