WO2019144980A1 - Composite material - Google Patents

Composite material Download PDF

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Publication number
WO2019144980A1
WO2019144980A1 PCT/CZ2019/000003 CZ2019000003W WO2019144980A1 WO 2019144980 A1 WO2019144980 A1 WO 2019144980A1 CZ 2019000003 W CZ2019000003 W CZ 2019000003W WO 2019144980 A1 WO2019144980 A1 WO 2019144980A1
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WO
WIPO (PCT)
Prior art keywords
waveform
layer
composite material
conductive
radiation
Prior art date
Application number
PCT/CZ2019/000003
Other languages
French (fr)
Inventor
Lukáš VOJTĚCH
Original Assignee
Czech Defense S.R.O.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Czech Defense S.R.O. filed Critical Czech Defense S.R.O.
Publication of WO2019144980A1 publication Critical patent/WO2019144980A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/005—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems using woven or wound filaments; impregnated nets or clothes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B33/00—Layered products characterised by particular properties or particular surface features, e.g. particular surface coatings; Layered products designed for particular purposes not covered by another single class
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/02—Physical, chemical or physicochemical properties
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41—WEAPONS
    • F41H—ARMOUR; ARMOURED TURRETS; ARMOURED OR ARMED VEHICLES; MEANS OF ATTACK OR DEFENCE, e.g. CAMOUFLAGE, IN GENERAL
    • F41H3/00—Camouflage, i.e. means or methods for concealment or disguise
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41—WEAPONS
    • F41H—ARMOUR; ARMOURED TURRETS; ARMOURED OR ARMED VEHICLES; MEANS OF ATTACK OR DEFENCE, e.g. CAMOUFLAGE, IN GENERAL
    • F41H3/00—Camouflage, i.e. means or methods for concealment or disguise
    • F41H3/02—Flexible, e.g. fabric covers, e.g. screens, nets characterised by their material or structure
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/38—Jamming means, e.g. producing false echoes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems

Definitions

  • the invention relates to a composite material, specifically a sandwiched composite material, for achieving passive virtual electromagnetic reality.
  • metal structures with corner reflectors were used to increase the scattering of reflected wave radar signals, resulting in a significant reduction in the accuracy of the radar used, including the generation of false signals.
  • Stepth technology, implemented by electromagnetic radiation-absorbing ferrite layers in combination with fractured surfaces for reflected electromagnetic wave scattering. Due to the secrecy of these technologies, it is very difficult to analyse their effectiveness.
  • the task is to ensure the highest quality construction possible of the covering material in terms of absorption and low reflection of incident electromagnetic (hereafter EM) waves.
  • EM incident electromagnetic
  • metamaterials which thanks to their construction achieve extraordinary material properties, particularly in respect to electromagnetic parameters.
  • These artificially prepared material structures for example, exhibit negative permeation or permeability.
  • the device for radio camouflage is further described in the patent document RU 2360365.
  • This device is intended for masking radio waves of computer and control systems. It uses the effects of spreading the spectrum of high frequency radiation and reducing the non-uniformity of the spectral density of the signal generated by the operation of computer equipment and control systems.
  • antennae systems As far as antennae systems are concerned, these also comprise antennae structures of various types, carrying out loads that are usually short-circuited for maximum reflection of transmitted radar signals.
  • US 4621012 is known a material that masks wavelengths from visible light to radar waves. It consists of a fabric, a soft thermoplastic layer with dipole antennae designed to absorb radar waves, metallic layers for infrared reflection and transmission of radar waves, and layers of paint.
  • radar camouflage material is known from patent document US 5014070. It describes a radar wave masking material consisting of a thin layer of dielectric material with various antennae elements, specifically circular ones, which terminate in impedances with a purely reactive component.
  • the disadvantage common to these solutions is the relatively narrowband of the solution, because the implemented antennae elements have to, for proper operation, correspond to their dimensions, usually half the wavelength otherwise their efficiency decreases. If the condition of suitable sizes is not met, such a masking of the source of undesirable parasitic reflections may occur.
  • lure systems As far as lure systems are concerned, they also implement structures enabling the location of spurious, i.e. false targets.
  • an electromagnetic camouflage blanket which is comprised of three parts, namely a flexible foil, an inner and an outer part.
  • the inner part contains a metallised layer and lies upon the masked device.
  • the outer part contains random folds, which are formed by a masking net connected to a flexible dielectric net and which, between the two nets, creates an air gap.
  • the dielectric network is carbon based with a conductivity in the conductivity range of 1-100 S/m.
  • the flexible foil is polymer based with a maximum thickness of 0.3 mm.
  • the surface camouflage material composed of three-layers is known from patent US 4953922.
  • the first layer consists of metal foil with at least one reflective surface directed against a potential observer.
  • the second layer with a thickness of less than 1 pm is placed just behind the first layer and serves as an absorbent material for visible light, infrared radiation with wavelengths up to 2 pm and thermal infrared radiation at wavelengths of 3-100 pm.
  • This layer contains nickel particles and their oxides.
  • the third layer is made of plastic with a thickness of 10-20 pm and serves to absorb radiation with wavelengths of 8-13 pm.
  • Patent file CN206420380 further describes a composite material in the form of a graphite alkene foam comprising several layers, i.e. a conductive layer, a polymerisation layer, a fibreglass net, etc., for the purpose of absorbing electromagnetic waves in the frequency range 8-60 GHz, with a shielding efficiency of 30 dB. From the claims described it follows that it is a net-like structure coated with graphene foam. However, such an arrangement cannot ensure a wide range of electromagnetic camouflage requirements, precisely because of the mesh structure used, where the size of the eyes of the mesh fundamentally affects electromagnetic parameters.
  • the patent furthermore deals only with shielding issues, but not with the issue of altering the reflection coefficient, which is the main parameter when solving electromagnetic camouflage tasks.
  • the bandwidth of the described solution beginning at 8 GHz does not cover conventional electromagnetic reconnaissance technology.
  • the electromagnetic wave absorbing material for masking an object from radar signals consisting of several layers: a metal reflective layer, a surface- absorbent surface layer, an impedance matching layer, a heat-absorbing medium and a surface layer, all of which are sequentially arranged from bottom to top, is described in patent file CN 105799260 (A). From study of the patent claims and patent description, it follows that this is a composite arrangement of polymeric material produced based on resins, hence non-flexible material - fixed formations- panels. Individual layers are defined with offset material as well as electromagnetic properties, which does not allow material with a wide range of electromagnetic camouflage applications or materials with the required efficiency for reduction or emulation of reflection coefficients. A disadvantage is also the rigid construction of the material (panels), which does not allow the general shapes of the objects to be wrapped.
  • the camouflage net including a resonance absorber for incident electromagnetic waves with a wavelength in free space between about 1 - 20 cm is described in patent document US 3315259.
  • the camouflage net consists of several layers; a cover layer, an impedance layer, four layers for phase shifting and absorption, and furthermore of a metal base.
  • the mentioned impedance matching, phase shifting and absorption layers comprise several protuberances which are in the form of truncated pyramids, equilateral triangles or squares.
  • the disadvantage of this solution is not only the insufficient considered band 30MHz to 1 5GHz, but also the design of the structure, which in principle must attain considerable thicknesses, specifically by using truncated pyramids and other formations against the working frequencies considered.
  • the proposed solution utilises different layer thicknesses and slit sizes, according to the required operating frequency. Although this solution allows one to tune the material to the desired frequencies, the solution cannot work in broadband. In addition, the solution uses metal and metallised foils, making it difficult to handle the overall material and which complicates its production.
  • a camouflage material comprising carbonaceous materials for the absorption and/or reflection of electromagnetic radiation (particularly microwave radiation).
  • the material comprises at least one layer of non-conductive non-flammable fluorinated or non-fluorinated carbonaceous material for infrared absorption.
  • the principle of the patent is the layering of carbon fibre materials for the absorption of, particularly, radar waves.
  • the disadvantage of this solution is the use of carbon- based fibres which, though they enable the effective application of damping layers which cause muffled EM radiation energy, they also only with difficulty prevent the effects of EM wave reflections.
  • This solution combines the ability to dampen infrared radiation and radar waves, however its efficiency for absorbing incident EM waves without their reflection is low.
  • the use of carbon fibres in combination with foils and foam materials complicates mass production.
  • a layered camouflage material is known from patent document US 3733606.
  • a layered material for absorbing and reflecting radar waves in which there is at least one layer of thin non-homogeneous electrically conductive foil which may be formed as a metal lattice, metallic or metallised fibres, flakes or a layer of colloidal conductive particles.
  • the blanket for the masking of radar and heat radiation is further known from patent document US 3300781.
  • the layered material is, as described, composed of at least two layers which are formed of thin plastic foil, and each layer is vacuum-sealed with metallic material.
  • the principle of the above noted solution is the use of a single metal layer in the form of a thin electrically conductive foil and one insulating layer, and does not enable reflection of incident EM waves, which is a major drawback of this solution. Additionally, the material composition used does not enable continuous changing of the electrical parameters of the assembly and thus the setting of the desired electromagnetic behaviour of the entire masking camouflage.
  • Another patent document US 7511653 B2 presents a camouflage system composed of a substrate, where the first layer on the substrate is a polymeric matrix with magnetic nanoparticles scattered on the polymer matrix and the second layer is adjacent to the first layer with a second polymer matrix and carbon black dispersed on this second polymer matrix.
  • This solution employs polymer matrices with built-in iron oxides, which serves to ensure that EM radiation energy requirements are dampened only in a narrow frequency band, as shown by the measurements in the patent application.
  • Camouflage fabric is further known from patent document KR 20130035821. Fabric is used to shield EM radiation, to protect against thermal equipment and to create a visual camouflage effect. The proposed method does not solve with sufficient efficacy the limitation of EM reflection, which, according to experiments carried out using a single layer of fabric, is essentially merely dampened and with only minimal efficiency leading to limited reflection.
  • a roofing solution comprising a frame, a cover, and a coating that absorbs and reflects EM waves.
  • the cover is made of multi-layer, bullet resistant fabric.
  • the solution describes the standard application of a camouflage area with the aid of anchor elements and supports. The patent does not indicate how the declared absorption properties and low reflection of EM waves is achieved.
  • RU 2008144276 is known equipment for masking wavelengths from several centimetres to tens of meters with a device thickness of not more than 2 mm.
  • the device is composed of an electrically conductive base, a dielectric and an electrically conductive shielding layers with defined openings.
  • the solution is a classic approach to passive antenna elements in an embodiment of patches formed of different slots, which thus perform as the onus of incident EM waves at the given operating frequencies of the slit dimensions.
  • the solution is thus rather narrowband with a low capability of reducing the reflection of incident EM waves.
  • the camouflage cover is further known from patent document IL196752.
  • the cover comprises flexible foil with air-filled grooves and a dielectric lattice.
  • electrically conductive foil is limited in this way to a shielding cover, without the ability to stop reflections. On the contrary, maximum reflection is used here to enable EM shielding capability.
  • Such a solution still does not completely disguise the object, nor does it camouflage various types of objects with sufficient accuracy.
  • camouflage material which forms a structure of carbonaceous materials for the absorption and reflection of EM radiation, i.e. for masking or shielding principally in the range of microwaves.
  • This is a composite material with no option of programming electromagnetic properties, designed to maximise electromagnetic shielding efficiency (henceforth ESE) by aid of maximum reflection and supplemented by partial absorption.
  • This solution particularly reflects incident EM waves rather than absorbing them.
  • the camouflage cover is further known from patent document RU 2192606.
  • a covering solution with panels with a protective coating and elements connecting these panels at their edges.
  • the panels are filled with absorbent and reflective materials in the form of foam, fibres, layers, etc.
  • the solution further comprises valves for filling / emptying the interior of the panels.
  • This solution is based on the use of filled panels, thanks to which, the possibility of manipulating them is limited, and the given solution limits the possibility of programming electromagnetic properties as required for the intensity and efficiency of the camouflage as well.
  • Camouflage material according to patent document JPH 0328697 consists of a fabric coated with a resin-bonded conductive layer, an adhesive layer, a metal layer, and another layer of supporting resin.
  • the material is designed for the visible, infrared and radar spectrum.
  • electrically conductive foils allows for the attenuation of incident electromagnetic radiation, but only because most of the energy of the incident EM waves is reflected by the material. The absorption capability of the waves is thus minimal.
  • the EM-absorbing and reflective cover composed of a layer of polyvinyl fluoride, foam, and a layer of metallised polyester, polyvinyl fluoride, polyvinyl chloride, or synthetic material in a sandwich structure between two polyvinyl chloride layers is described in GB 2038712.
  • This solution utilises rigid covers, which again reduces the possibility of having flexible camouflage. Additionally, the construction does not allow for a system with sufficient capability to absorb incident waves without their being reflected back to the transmitter. This solution does not even allow the programming of electromagnetic properties.
  • EP0426141 is known a layered material for absorbing radar radiation from a reflecting substrate to reflect EM wavelengths of mm and cm wavelengths and bonding layers with high electrical resistance and 10-60% conductive particles with a conductivity of 1-100 S/m.
  • This solution employs an EM reflective material and layers with high electrical resistance, which to a certain extent allows shading and absorption of incident EM waves.
  • the stated solution fundamentally does not allow the setting of desired parameters of surface and volumetric conductivity. This does not allow the making of variously effective electromagnetically camouflaged and/or masked structures.
  • EP 0122243 is known a method which contains a woven fabric with metallic fibrils laminated with a metallised plastic layer, which, according to the description, achieves good reflective properties throughout a wide range of EM waves. This solution merely focuses on the reflection of incident EM waves, which will limit their penetration of the material, but radar technology reliably detects these reflections.
  • the metal coated masking system is further known from patent document CZ20010054. This metal coated masking system is composed of several layers of conductive and non-conductive materials.
  • the camouflage kit is further described in patent document BG 102546.
  • the masking kit contains a radio-absorbent coating, radio-absorbent heat reflecting coating, a radio-absorbent anti-accumulation coating, and a device for creating a false heat field.
  • the kit provides a masking effect in the visible, near infrared, thermal and radar regions of electromagnetic waves simultaneously.
  • patent document US 5035942 are disclosed flexible materials for reflecting EM waves which are from non-woven fibre based on carbon fibre with shielding electromagnetic efficiency greater than 50 dB in the range of 100 MHz to 1000 MHz.
  • the basis of the patent is flexible materials for EM wave shielding.
  • the disadvantage of the solution is the reality that it only solves the shielding of EM radiation induced by the reflection of EM waves, thereby compromising the shielded object using radar technology. Additionally, the considered frequency range is insufficient to address EM camouflage or masking under the conditions of modern radar systems.
  • the masking net for EM wave absorption is known from patent document US 3427619.
  • the masking net comprises a plurality of wave absorbers with different surface shapes.
  • the disadvantage of this solution is the relatively complicated installation of the panels and basically the impossibility of pre-programming or changing the electromagnetic behaviour of various installations.
  • the masking material for shielding radar waves comprising a warp spun from pieces of yarn, with metallic fibres which are set out by so-called lay-out technique in such a way that the sum of the elongation of the yarn will be substantially the same in both directions on the plane of the knitting is further known from the patent US 5532052.
  • the solution is merely aimed at attenuation using the reflection of EM radiation and therefore without the ability to absorb incident EM waves.
  • camouflage material is known from patent documents US 5225454 and EP0394207. Here is used a composite based on polyvinyl chloride (henceforth PVC) and carbon fibre with a radar wave attenuation of 1-3 dB per cm. This solution has the disadvantage that the plastic material used is not flexible and has little EM shielding efficiency, in essence without the possibility of regulating it.
  • patent document SE 446124 is described a water-based or aerated plastic foam in which metal strips are imbedded which reflect electromagnetic radiation.
  • the solution employs the above-mentioned construction for making decoy targets, which allows for little mobility of the goal achieved as well as its complex removal.
  • the occurrence of the metallic strips of electrically conductive camouflage elements is randomly distributed in the bulk of the material, which does not allow predetermined electromagnetic parameters to be predefined and adjusted in the resulting material.
  • Electromagnetic masking and camouflage are currently targeting jamming radar systems, but without the possibility of effectively programming the electromagnetic behaviour of the materials used.
  • An exception is the systems with bags filled with air or liquids, which allow changing permittivity or its dimensions. Even these systems, however, do not allow with sufficient efficiency the absorption of incident EM radiation, let alone the programming of the electromagnetic behaviour of the system within a sufficient range of electrical conductivity.
  • the object of the present invention is a masking material which will allow for a wide range of electromagnetic behaviour programming of materials intended for the creation of a protected or camouflaged object and its surroundings and to enable the development of advanced camouflage and camouflage systems of a new generation.
  • a composite material specifically a sandwich composite material comprising at least three bonded layers, according to the invention, whose essence lies in that it comprises a first conductive layer behind which is arranged the first dielectric layer behind which is arranged a second conductive layer whose specific electrical conductivity is equal to or greater than the specific electrical conductivity of the first conductive layer.
  • the advantage is that the first conductive layer reflects the minimal amount of EM radiation that is not trapped by known tracking devices, while the next layer reflects at most the amount of EM radiation the majority of which can be trapped by the first conductive layer after reflection by this conductive layer.
  • the main advantage is the progressively controlled "imprisonment" of the incident electromagnetic radiation in the assembled composite for, gradually the passing electromagnetic radiation is dampened by the layers of the composite, yet back out of the composite they can no longer be emitted by reflection.
  • the first conductive layer has to advantage a specific electrical conductivity o1 greater than 10 10 S/m.
  • the second conductive layer there are at least one additional dielectric layer and at least one additional conductive layer alternately arranged, with the specific electrical conductivity of each of the other conductive layers being always the same or greater than the specific electrical conductivity of the conductive layer preceding.
  • the advantage is that it is possible to create a composite material which with there is a gradual lessening of the complete visibility of the hidden object, and it is possible by specific layering to create a camouflage material which produces a reflection of EM radiation specific to a particular object, material or even specific natural conditions, such as a fictitious forest or lake etc.
  • the basic principle is that by increasing specific electrical conductivity of the surface of an actual object (e.g.
  • the conductive layers are made of a textile material.
  • the conductive layers are created from fabric and/or knitted and/or non-woven fabrics containing conductive material fibres.
  • the dielectric layers are created from fabric and/or knitted and/or non-woven fabric containing fibres of the desired dielectric material.
  • the advantage of using textile material is that it can simply change its properties by simply changing the content of the conductive material in the yarn, more precisely by simply changing the conductive fibre content of the yarn.
  • Desired specific electrical conductivity of the fabric is achieved in production of the fabric and/or knit fabric either by changes in the size both in warp and weft or in the conductivity of the yarn used as well.
  • the specific electrical conductivity of the yarn is influenced not only by the material used in its construction, being the conductivity of the electrically conductive and non-conducting fibres and/or cuttings but also by other technological parameters such as the length of twist, the furriness of the yarn, the method of spinning, the fineness of the yarn, and the modifications used.
  • Electromagnetic shielding efficiency is also influenced by the size of the sett. With a rise in the value of the sett, as a rule the electromagnetic shielding efficiency (henceforth ESE) increases as well.
  • the individual layers may be solidly connected, for example, they may be sewn together, but it is advantageous if the individual layers are joined together in a detachable manner. In this way, the desired reflective properties of the camouflage can be precisely adjusted at the place of implementation.
  • the individual layers are joined together by lamination, sewing or fastening by velcro.
  • the advantages of such an arrangement are the possibility to operatively change the resulting electromagnetic properties of the composite, by changing its composition, more precisely by removing or adding functional layers.
  • such a solution enables on-site application in almost realtime and operatively to change the resulting electromagnetic behaviour of the composite and with this, to change the resulting electromagnetic reality.
  • each layer contains multiple layers with the same properties.
  • Such an arrangement makes it possible to minimise production costs and minimise the number of different types of layers used.
  • Theory as well as experiments conducted show that the desired properties of dielectric and electrically conductive layers can be achieved with satisfactory results by a sandwich arrangement of layers integrating the resulting parameters.
  • An advantage is the economic benefits and simplification of logistics operations.
  • the dielectric layer is made of non-conductive knitted fabric and/or fabric and/or non-woven fabric. It is to advantage to use cotton yarn and/or non- woven textile and/or yarns containing polyester (henceforth PES) and/or polyacrylonitrile (henceforth PAC) and / or polypropylene (henceforth PP) fibres and/or teflon fibres.
  • the dielectric layer may be formed by an air layer created by mechanically defining the relative position of the adjacent conductive layers, or, bubble wrap and /or 3D fabric may be used.
  • the dielectric layer is kevlar fabric. Its advantage is its high strength, shape stability and non-absorbability of moisture.
  • the main advantage of the composite material according to the invention is that it allows the achieving of passive virtual electromagnetic reality (henceforth EVR) and with this, to emulate various real objects or their surfaces and thus their electromagnetic response to excitation by incident radar signals.
  • the proposed design enables, already at their production, the programming and adjustment of the required electromagnetic parameters in a wide range of required values of surface and volumetric conductivity, electromagnetic shielding efficiency, absorption and coefficient of reflection not only of the structure of the base material of the functional layer, but also of the composition of the composite.
  • Such an object is made with a non-conductive design, for example made of wood and wire structures, a composite or inflatable core, in the form of the desired object, and the structure is covered with a fabric having the required surface specific electrical conductivity.
  • Another advantage is that unusual properties can be achieved by the composite arrangement of electrically conductive fabrics into sandwiches. Laying electrically conductive fabrics directly on top of each other results in increased electrical conductivity, electromagnetic shielding efficiency of the sandwich, and the ability to absorb electromagnetic radiation. The coefficient of reflection is then affected, in particular, by the most conductive layer in the sandwich.
  • a suitable composition of the textile composite with a gradual alignment of electrically conductive and non-conducting layers can also, in a limited frequency range, provide the desired combination of absorption and reflection of incident electromagnetic radiation.
  • the resultant fabric structure then corresponds in its absorption, attenuation and reflection capability, surface structure, or volume to the object and/or scenes forming the EVR-created pattern.
  • the generalisation of the behavioural phenomenon of the shielding partition on incident electromagnetic radiation is used. Incident electromagnetic waves on the shielding partition is generally partially reflected back from the partition, while the more the surface is electrically conductive, the more the partition can be considered a mirror, and part of the energy is damped in that partition, while the more the partition is wide and electrically conductive, the more the energy is transformed into heat influenced by the lossy environment, and the rest of the energy passes through the partition and continues to further disseminate. If, at a suitable distance behind this first partition, we place a further or further partitions, the above phenomenon is repeated.
  • the composite material according to the invention is assembled as a textile composite in such a way that electrically conductive and non-conductive layers are sequentially arranged, for example, they are laminated to each-other so that, in the direction of the incident radiation, the electrically conductive layers are sequentially arranged with increasing specific electrical conductivity.
  • This sequencing results in a gradual increase in the reflection coefficient and a gradual increase in the energy absorption of incident electromagnetic radiation of the individual layers.
  • this composite design causes trapping of incident electromagnetic waves, as a whole exhibiting a small reflection coefficient and a high absorption capacity at the same time.
  • FIG. 1 shows a schematic view of a seven-layer sandwich composite material
  • Fig. 2 shows a graph of an example of the EM masking process using this seven-layer sandwich composite material and compares it to radiation into open space and against a metallic mirror
  • Fig. 3 shows a detailed graph of EM masking using this sevenlayered sandwich composite material and its comparison to radiation into open space
  • Fig.4 shows schematically a three-layer sandwich composite material for the making of EM water camouflage of surface water
  • Fig.5 is a graph of an example of the EM water camouflage construction and its comparison to the radiation into open space and against a metallic mirror
  • Fig. 1 shows a schematic view of a seven-layer sandwich composite material
  • Fig. 2 shows a graph of an example of the EM masking process using this seven-layer sandwich composite material and compares it to radiation into open space and against a metallic mirror
  • Fig. 3 shows a detailed graph of EM masking using this sevenlayered sandwich composite material and its comparison to radiation into open space
  • FIG. 6 shows a detail of a graph of implementation of EM camouflage of surface water and its comparison to the radiation against the sample object, which is surface water
  • FIG. 7 shows a schematic representation of a three-layered sandwich composite material for the implementation of EM greenfield camouflage
  • Fig. 8 shows a graph of an example of the EM camouflage of a greenfield and its comparison to radiation into open space and against a metallic mirror
  • Fig. 9 shows a detail of a graph of the EM camouflage of a greenfield and its comparison to radiation against a sample object, which is green leaves;
  • Fig. 7 shows a schematic representation of a three-layered sandwich composite material for the implementation of EM greenfield camouflage
  • Fig. 8 shows a graph of an example of the EM camouflage of a greenfield and its comparison to radiation into open space and against a metallic mirror
  • Fig. 9 shows a detail of a graph of the EM camouflage of a greenfield and its comparison
  • Fig. 10 shows schematically a three layer sandwich composite material for the implementation of EM camouflage of a sandy area
  • Fig.1 1 shows a graph of an example of the implementation of EM camouflage of a sandy area and its comparison to radiation into open space and against a metallic mirror
  • Fig. 12 shows a detail of the graph of the EM camouflage of sand and its comparison to the radiation against the sample object, which is dry sand.
  • a sandwich composite material 2 (Fig. 1) for the implementation of EM masking structures, limiting the reflection of EM radiation 1 in the 1 - 8 GFIz band incident on the composite material 2.
  • the sandwich composite material comprises a first conductive layer 3 behind which a first dielectric layer 4 is arranged, behind which a second conductive layer 5 is arranged, while behind the second conductive layer 5 a further dielectric layer 4 is arranged, and behind this, another conductive layer 6 and a dielectric layer 4 and a final conductive layer 7, while the specific electrical conductivity of each further conductive layer 5,6,7 located behind the first conducting layer 3 being always greater than the specific electrical conductivity of the conductive layer preceding.
  • the conductive layers 3, 5, 6, 7 are made of a textile material, which is a fabric containing fibres of an electrically conductive material.
  • the conductive layers 3, 5, 6, 7 may be made of a non-woven fabric containing fibres of an electrically conductive material in a corresponding weight ratio.
  • the individual layers 3, 4, 5, 6, 7 are treated with an anti-water absorption medium and are laminated to each-other.
  • the individual layers 3, 4, 5, 6, 7 have these parameters:
  • the first dielectric layer 4 consists of two layers of 1.5 mm thick knitted fabric and 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
  • next dielectric layer 4 again consists of two layers of 1.5 mm thick knitted fabric having a composition of 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
  • the next dielectric layer 4 again consists of two layers of 1.5 mm thick knitted fabric having a composition of 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
  • the graph shows the measurement of the reflection coefficient (henceforth S11) for metering preparations made by modified clamps, based on ASTM D4935, calibrated short.
  • the waveform 8 corresponds to the metallic mirror calibration (maximum reflection), the waveform 9 into free space, and the waveform 10 of the use of the four electrically conductive layers.
  • the result shows that gradual folding of the layers resulted in elimination, to total avoidance of the reflection of the incident EM radiation on the composite structure where the use of seven layers increased the ability of the composition to absorb incident EM radiation.
  • parameter S11 fig. 3
  • the waveform H corresponds again to the ideal state of emission into free space - nothing is reflected, and at waveform 12, EM masking is achieved.
  • a sandwich composite material (Fig. 4) for implementation of EM water camouflage structures comprises a first conductive layer 3 behind which a dielectric layer 4 is arranged, behind which a second conductive layer 5 is arranged, the specific electrical conductivity of the second conductive layer 5 located behind the first conductive layer 3 is higher than the specific electrical conductivity of the first conductive layer 3.
  • the conductive layers 3,5 are made of a textile material which is a fabric containing fibres of conductive material.
  • the individual layers 3,4,5 are detachably joined together by means of velcro.
  • the individual layers 3,4,5 have the following parameters:
  • the dielectric layer 4 consists of a needle-punched non-woven fabric of 1 mm thickness and a composition of 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
  • a graph shows the measurement of the S11 parameter for the modified measuring clamps ASTM D4935, calibrated short.
  • the waveform 16 corresponds to the metal mirror calibration (maximum reflection), a waveform 17 to radiation into open space, a waveform 18 to a reflection of surface water, a waveform 19 the result of a measurement for camouflage of surface water.
  • the result proves that by gradually folding the layers, the desired reflection of EM radiation by surface water can be camouflaged, allowing the implementation of passive EVR objects or scenes, for example, for hiding ships, as detailed in the graph (Fig. 6) which shows the comparison of the S11 parameter for the sample surface water object waveform 20 and for attaining camouflage waveform 21.
  • a sandwich composite material for implementation of structures for EM greenfield camouflage EM structures comprising a first conductive layer 3 behind which a dielectric layer 4 is arranged, behind which a second conductive layer 5 is arranged, while the specific electrical conductivity of the second conductive layer 5, located behind the first conductive layer 3 is the same as the specific electrical conductivity of the first conductive layer 3.
  • the conductive layers 3,5 are made of a textile material, which is a fabric containing fibres of an electrically conductive material.
  • the individual layers 3,4,5 are treated with a water-absorbing medium, which are connected by being sewn together.
  • the individual layers 3,4,5 have the following parameters:
  • the dielectric layer 4 is kevlar fabric of 1 mm thickness
  • the graph (Fig. 8) shows the measurement of the reflection coefficient parameter (henceforth only S11) for the modified measuring clamps ASTM D4935, calibrated short.
  • the waveform 25 corresponds to the metal mirror calibration (maximum reflection), the waveform 26 to radiation into free space, the waveform 27 to reflection from the greenfield (a layer of green leaves), the waveform 28 the measurement result of the material for greenfield camouflage.
  • the result proves that by gradually folding the layers, the desired reflection of EM radiation can be achieved, thus enabling the implementation of passive EVR objects or scenes.
  • the solution will allow for greenfield camouflage or for hiding another type of object under the virtual reality of green vegetation, as shown for clarity on the graph (Fig. 9), waveform S11 for a sample greenfield object 29, and for the achieved EM camouflage waveform 30.
  • a sandwich composite material (Fig. 10) for implementation of structures for EM camouflage of sandy areas comprises a first conductive layer 3, behind which a first dielectric layer 4 is arranged, behind which a second conductive layer 5 is arranged, while the specific electrical conductivity of the second conductive layer 5 located behind the first conductive layer 3 is greater than the specific electrical conductivity of the first conductive layer 3.
  • the conductive layers 3,5 are made of a textile material which is a fabric containing fibres of an electrically conductive material.
  • the individual layers 3,4,5 are joined to each-other by lamination.
  • the dielectric layer 4 consists of a 1 mm thick knitted fabric and 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
  • the graph (Fig. 11) shows the measurement of the reflection coefficient parameter (S11 ) for the modified measuring clamps ASTM D4935, calibrated short.
  • the waveform 34 corresponds to the metallic mirror calibration (maximum reflection), the waveform 35 of the radiation into free space, the waveform 36 reflection from dry sand, the waveform 37 the measurement result of the material for the camouflage of dry sand layers.
  • the result proves that by gradually folding the layers, the desired reflection of EM radiation can be achieved, thus enabling the implementation of passive EVR objects or scenes.
  • the solution allows a sandy surface to be camouflaged or to hide another type of object under the virtual reality of a sandy surface, as shown by the graph (Fig. 12) for parameter S11 of the sample sand layer 38 and for the achieved EM camouflage waveform 39.
  • a composite material according to the invention can be used to achieve passive virtual electromagnetic reality in industrial applications such as electromagnetic absorbers, reflectors and attenuation materials, and in security applications for electromagnetic masking and electromagnetic camouflage.

Abstract

A composite material, specifically a sandwich composite material (2) comprising at least three bonded layers which comprises a first conductive layer (3) behind which a first dielectric layer (4) is arranged, behind which a second conductive layer (5) is arranged, whose specific electrical conductivity is equal to or greater than the specific electrical conductivity of the first conductive layer (3).

Description

Composite material
Technical field
The invention relates to a composite material, specifically a sandwiched composite material, for achieving passive virtual electromagnetic reality.
State of the Art
The rapid development of material engineering reaches into many branches of industry, with security and military applications certainly being no exception. Research and development in the field of reconnaissance systems and protection against them, represents the classic duel of protection / defence and offensive technologies since antiquity. The classic solution of disguise technologies and camouflage in the visible spectrum was followed by the discovery of radar technology as well as the search for masking and camouflage systems and technologies in the radio or infrared spectrums.
The first attempts to solve electromagnetic invisibility problems in the area of radio waves date back to World War II, especially for hiding aircraft flying night missions or other military techniques to locate radar systems. Another solution for the visible and infrared part of the electromagnetic spectrum followed.
From the very beginnings of this task a solution was developed using a parasitic antenna structure in dipole design with dimensions corresponding to half the wavelength of the radar equipment being used. Strips of thin metallic foil were implemented and large quantities of such parasitic dipoles were dropped by aircraft over the areas of interest for radar technology jamming.
For ground warfare, metal structures with corner reflectors were used to increase the scattering of reflected wave radar signals, resulting in a significant reduction in the accuracy of the radar used, including the generation of false signals.
Subsequently, electromagnetic radiation absorbing materials began to be applied, ideally so as to avoid reflection, so that radar systems became jammed. These solutions, however, in most cases still do not achieve the required efficiency, and so more often the method chosen for jamming is by using by various technologies that perform reflection or scattering of incident electromagnetic signals from reconnaissance radar or other systems.
One of the most effective solutions is "Stealth" technology, implemented by electromagnetic radiation-absorbing ferrite layers in combination with fractured surfaces for reflected electromagnetic wave scattering. Due to the secrecy of these technologies, it is very difficult to analyse their effectiveness.
In the area of theoretical considerations appears the solution using active elements of electromagnetic radiation protection, where the protected object is essentially wrapped in a thin layer of electromagnetic cloud with which the incident electromagnetic signals interact.
From the principles of physics therefore, the task is to ensure the highest quality construction possible of the covering material in terms of absorption and low reflection of incident electromagnetic (hereafter EM) waves. Among modern trends are solutions using so-called metamaterials, which thanks to their construction achieve extraordinary material properties, particularly in respect to electromagnetic parameters. These artificially prepared material structures for example, exhibit negative permeation or permeability.
Current methods to solve electromagnetic masking and camouflage use a number of basic principles, among which can be numbered so-called active systems which contain sources of radiation, whose activity can either jam surveillance technology through interference with radar signals from active reconnaissance systems, or by transmitting false characteristic types of electromagnetic signals of passive radar systems. Additionally, antennae systems are known which include antennae structures of various types, involving loads that are mainly short-circuit for reflecting the transmitted radar signals back to the transmitter, thus causing the radar technology to be jammed or scrambled. In addition are known passive lures, which are systems that allow the localisation of spurious, consequently false targets.
As far as active systems are concerned, they include solutions with sources of radiation that either jam or interrupt reconnaissance technology. All of this as a rule is thanks to interference with radar signals from active reconnaissance systems, or by transmitting false characteristic types of electromagnetic signals of passive radar systems. These solutions include, for example, the solution described in patent US 7199344 B2. Here a device is utilised with several sources of electromagnetic radiation that generate a specified EM radiation spectrum and a control unit which sets sources of electromagnetic radiation so that they generate an EM spectrum identical to the EM spectrum surrounding the desired object.
In a further patent document US 3127608 is described a method of object camouflage based on the reflection or absorption of a radar spectrum with a linear electron accelerator located in the front of the aircraft used to ionise the air under the aircraft. Such an ionised, be it only local, cloud changes the physical properties around the accelerator and thus prevents, according to the author, detection of the aircraft by radar.
The device for radio camouflage is further described in the patent document RU 2360365. This device is intended for masking radio waves of computer and control systems. It uses the effects of spreading the spectrum of high frequency radiation and reducing the non-uniformity of the spectral density of the signal generated by the operation of computer equipment and control systems.
The disadvantage of the above solutions is their very nature, this being the necessity of building an infrastructure of radiating elements which can be easily targeted and localised by passive radars.
As far as antennae systems are concerned, these also comprise antennae structures of various types, carrying out loads that are usually short-circuited for maximum reflection of transmitted radar signals.
From patent document US 4606848 is known the use of a paint for absorbing and scattering incident microwave radiation. The coating comprises dipole segments produced from electrically conductive fibres.
From another patent document US 4621012 is known a material that masks wavelengths from visible light to radar waves. It consists of a fabric, a soft thermoplastic layer with dipole antennae designed to absorb radar waves, metallic layers for infrared reflection and transmission of radar waves, and layers of paint.
Further, radar camouflage material is known from patent document US 5014070. It describes a radar wave masking material consisting of a thin layer of dielectric material with various antennae elements, specifically circular ones, which terminate in impedances with a purely reactive component. The disadvantage common to these solutions is the relatively narrowband of the solution, because the implemented antennae elements have to, for proper operation, correspond to their dimensions, usually half the wavelength otherwise their efficiency decreases. If the condition of suitable sizes is not met, such a masking of the source of undesirable parasitic reflections may occur.
As far as lure systems are concerned, they also implement structures enabling the location of spurious, i.e. false targets.
From patent document US 4882076, a device is known whose function is based on the principle of distorting radar using a lure of solidified foam, whose shape corresponds to the shape of the simulated object. Unobtrusive, electrically conductive elements for the reflection of radar waves are used. The disadvantage of the solution is not only the way of making lures as solid objects, which complicate subsequent transport, but particularly the use of unobtrusive electrically conductive elements which do not permit the correct reaction of the solution at different wavelengths. This solution may rather baffle the reconnaissance technology used than to create credible virtual objects that have to display their "correct" electromagnetic behaviour in a wider spectrum of frequencies.
From another patent document US 4659602 is known a masking pad with a backing layer and with tufted strips of filaments affixed to the backing layer, on which are then created loops of different sizes and colours. In this way, the terrain or landscape is simulated. The reflection and absorption of visible light, ultraviolet (hereafter UV) radiation and microwave radiation is, according to this document, caused by various materials contained in the tufted strips. The disadvantage of this solution is again the ability to baffle reconnaissance systems rather than effective masking or the creation of virtual objects. The reason is again to use the pad construction by sewing yarn strips to the backing layer. In principle, suitable broadband behaviour cannot be achieved up against the incident of electromagnetic waves, as the dimensions and shapes are more likely to demonstrate the trait to divide rather than to deploy purposefully on the surface of the pad.
Various types of layered materials are also known that cause the reflection and absorption of incident electromagnetic waves with varying efficiency given by the superiority of a particular technical solution.
For example, from the patent document US 3325808 is known a material which utilises an attenuator comprising a conductive layer and a layer of resistant material. These two layers are spaced apart and can be filled with a liquid of known permittivity if necessary. The thickness of the filling can be varied, including the amount of liquid, thereby changing the permittivity of the entire attenuator. The disadvantage of this solution is the ability to only change the level of attenuation of the incident EM radiation, but the solution does not allow EM radiation at broadband frequencies to be regulated or squeezed.
From US 20090317596 is further known an electromagnetic camouflage blanket which is comprised of three parts, namely a flexible foil, an inner and an outer part. The inner part contains a metallised layer and lies upon the masked device. The outer part contains random folds, which are formed by a masking net connected to a flexible dielectric net and which, between the two nets, creates an air gap. The dielectric network is carbon based with a conductivity in the conductivity range of 1-100 S/m. The flexible foil is polymer based with a maximum thickness of 0.3 mm. The disadvantage of this solution is that it provides mere shielding capability and, in particular, reflection of incident EM waves, even in wider frequency bands. This makes it possible to implement systems for jamming reconnaissance systems, but it is not possible to ensure the creation of quality virtual objects. Another disadvantage is the use of metallised foils, which can degrade from the exterior (due to oxidation and subsequent corrosion), while simultaneously limiting the flexibility of the material as produced.
The surface camouflage material, composed of three-layers is known from patent US 4953922. The first layer consists of metal foil with at least one reflective surface directed against a potential observer. The second layer with a thickness of less than 1 pm is placed just behind the first layer and serves as an absorbent material for visible light, infrared radiation with wavelengths up to 2 pm and thermal infrared radiation at wavelengths of 3-100 pm. This layer contains nickel particles and their oxides. The third layer is made of plastic with a thickness of 10-20 pm and serves to absorb radiation with wavelengths of 8-13 pm. The disadvantage of this solution for electromagnetic camouflage application is the fact that camouflage made in this way only jam reconnaissance systems, thanks to the maximum reflection of incident EM waves. This draws even more attention to its presence in the field of interest for electromagnetic reconnaissance. Additionally, the use of metallic foils reduces camouflage flexibility. Patent file CN206420380 further describes a composite material in the form of a graphite alkene foam comprising several layers, i.e. a conductive layer, a polymerisation layer, a fibreglass net, etc., for the purpose of absorbing electromagnetic waves in the frequency range 8-60 GHz, with a shielding efficiency of 30 dB. From the claims described it follows that it is a net-like structure coated with graphene foam. However, such an arrangement cannot ensure a wide range of electromagnetic camouflage requirements, precisely because of the mesh structure used, where the size of the eyes of the mesh fundamentally affects electromagnetic parameters. This also corresponds to the frequency band. The patent furthermore deals only with shielding issues, but not with the issue of altering the reflection coefficient, which is the main parameter when solving electromagnetic camouflage tasks. The bandwidth of the described solution beginning at 8 GHz does not cover conventional electromagnetic reconnaissance technology.
The electromagnetic wave absorbing material for masking an object from radar signals consisting of several layers: a metal reflective layer, a surface- absorbent surface layer, an impedance matching layer, a heat-absorbing medium and a surface layer, all of which are sequentially arranged from bottom to top, is described in patent file CN 105799260 (A). From study of the patent claims and patent description, it follows that this is a composite arrangement of polymeric material produced based on resins, hence non-flexible material - fixed formations- panels. Individual layers are defined with offset material as well as electromagnetic properties, which does not allow material with a wide range of electromagnetic camouflage applications or materials with the required efficiency for reduction or emulation of reflection coefficients. A disadvantage is also the rigid construction of the material (panels), which does not allow the general shapes of the objects to be wrapped.
The camouflage net including a resonance absorber for incident electromagnetic waves with a wavelength in free space between about 1 - 20 cm is described in patent document US 3315259. The camouflage net consists of several layers; a cover layer, an impedance layer, four layers for phase shifting and absorption, and furthermore of a metal base. The mentioned impedance matching, phase shifting and absorption layers comprise several protuberances which are in the form of truncated pyramids, equilateral triangles or squares. The disadvantage of this solution is not only the insufficient considered band 30MHz to 1 5GHz, but also the design of the structure, which in principle must attain considerable thicknesses, specifically by using truncated pyramids and other formations against the working frequencies considered. The proposed solution utilises different layer thicknesses and slit sizes, according to the required operating frequency. Although this solution allows one to tune the material to the desired frequencies, the solution cannot work in broadband. In addition, the solution uses metal and metallised foils, making it difficult to handle the overall material and which complicates its production.
From another patent document US 5312678 is known a camouflage material comprising carbonaceous materials for the absorption and/or reflection of electromagnetic radiation (particularly microwave radiation). The material comprises at least one layer of non-conductive non-flammable fluorinated or non-fluorinated carbonaceous material for infrared absorption. Furthermore, there is at least one layer of electrically conductive material for absorbing electromagnetic waves. The principle of the patent is the layering of carbon fibre materials for the absorption of, particularly, radar waves. The disadvantage of this solution is the use of carbon- based fibres which, though they enable the effective application of damping layers which cause muffled EM radiation energy, they also only with difficulty prevent the effects of EM wave reflections. This solution combines the ability to dampen infrared radiation and radar waves, however its efficiency for absorbing incident EM waves without their reflection is low. In addition, the use of carbon fibres in combination with foils and foam materials complicates mass production.
From patent document US 4495239 is known a layered camouflage surface material for masking in the realms of visible light, radar spectrum (3 - 3000 GHz) and infrared radiation (1-20 pm). The base layer consists of a sealed metal coated reflective layer with a surface conductivity of 0.1 - 10 W / square and on this a painted masking layer. The disadvantage of this solution is the fact that it covers bands from upwards of 3GHz and, furthermore, its electromagnetic radiation construction is merely for the attenuation and reflection of incident EM radiation, without the ability to absorb incident EM waves.
Another layered camouflage material is known from patent document US 3733606. Here there is used a layered material for absorbing and reflecting radar waves in which there is at least one layer of thin non-homogeneous electrically conductive foil which may be formed as a metal lattice, metallic or metallised fibres, flakes or a layer of colloidal conductive particles. The blanket for the masking of radar and heat radiation is further known from patent document US 3300781. The layered material is, as described, composed of at least two layers which are formed of thin plastic foil, and each layer is vacuum-sealed with metallic material.
From patent document US 20080220269 is known a masking material for use in a snowy environment. It contains a laminate, extruded, polyethylene foil, an aluminium layer on one side of the foil and a nylon layer on the other side. The resulting white material is reflective of radar and thermal radiation.
The principle of the above noted solution is the use of a single metal layer in the form of a thin electrically conductive foil and one insulating layer, and does not enable reflection of incident EM waves, which is a major drawback of this solution. Additionally, the material composition used does not enable continuous changing of the electrical parameters of the assembly and thus the setting of the desired electromagnetic behaviour of the entire masking camouflage.
Another patent document US 7511653 B2 presents a camouflage system composed of a substrate, where the first layer on the substrate is a polymeric matrix with magnetic nanoparticles scattered on the polymer matrix and the second layer is adjacent to the first layer with a second polymer matrix and carbon black dispersed on this second polymer matrix. This solution employs polymer matrices with built-in iron oxides, which serves to ensure that EM radiation energy requirements are dampened only in a narrow frequency band, as shown by the measurements in the patent application.
From patent document UA88989 is further known a masking covering or net, for example, for the manufacture of textile masks with a material which, according to the authors, absorbs, reflects and scatters EM radiation. Strips of this material are compressed between layers of water-resistant polymer material. The proposed solution does not allow, due to the strips used, their orientation and compression between the polymer layers and thus does not allow for sufficient absorption by and minimal reflection of EM radiation incident to the implemented net.
Camouflage fabric is further known from patent document KR 20130035821. Fabric is used to shield EM radiation, to protect against thermal equipment and to create a visual camouflage effect. The proposed method does not solve with sufficient efficacy the limitation of EM reflection, which, according to experiments carried out using a single layer of fabric, is essentially merely dampened and with only minimal efficiency leading to limited reflection.
From patent document RU 201 1146774 is further known a roofing solution comprising a frame, a cover, and a coating that absorbs and reflects EM waves. The cover is made of multi-layer, bullet resistant fabric. The solution describes the standard application of a camouflage area with the aid of anchor elements and supports. The patent does not indicate how the declared absorption properties and low reflection of EM waves is achieved.
From patent document RU 2008144276 is known equipment for masking wavelengths from several centimetres to tens of meters with a device thickness of not more than 2 mm. The device is composed of an electrically conductive base, a dielectric and an electrically conductive shielding layers with defined openings. The solution is a classic approach to passive antenna elements in an embodiment of patches formed of different slots, which thus perform as the onus of incident EM waves at the given operating frequencies of the slit dimensions. The solution is thus rather narrowband with a low capability of reducing the reflection of incident EM waves.
The camouflage cover is further known from patent document IL196752. The cover comprises flexible foil with air-filled grooves and a dielectric lattice. The use of electrically conductive foil is limited in this way to a shielding cover, without the ability to stop reflections. On the contrary, maximum reflection is used here to enable EM shielding capability. Such a solution still does not completely disguise the object, nor does it camouflage various types of objects with sufficient accuracy.
From patent document US5312678 a camouflage material is known which forms a structure of carbonaceous materials for the absorption and reflection of EM radiation, i.e. for masking or shielding principally in the range of microwaves. This is a composite material with no option of programming electromagnetic properties, designed to maximise electromagnetic shielding efficiency (henceforth ESE) by aid of maximum reflection and supplemented by partial absorption. This solution particularly reflects incident EM waves rather than absorbing them.
The camouflage cover is further known from patent document RU 2192606. There is described a covering solution with panels with a protective coating and elements connecting these panels at their edges. The panels are filled with absorbent and reflective materials in the form of foam, fibres, layers, etc. The solution further comprises valves for filling / emptying the interior of the panels. This solution is based on the use of filled panels, thanks to which, the possibility of manipulating them is limited, and the given solution limits the possibility of programming electromagnetic properties as required for the intensity and efficiency of the camouflage as well.
Camouflage material according to patent document JPH 0328697 consists of a fabric coated with a resin-bonded conductive layer, an adhesive layer, a metal layer, and another layer of supporting resin. The material is designed for the visible, infrared and radar spectrum. The use of electrically conductive foils allows for the attenuation of incident electromagnetic radiation, but only because most of the energy of the incident EM waves is reflected by the material. The absorption capability of the waves is thus minimal.
The EM-absorbing and reflective cover composed of a layer of polyvinyl fluoride, foam, and a layer of metallised polyester, polyvinyl fluoride, polyvinyl chloride, or synthetic material in a sandwich structure between two polyvinyl chloride layers is described in GB 2038712. This solution utilises rigid covers, which again reduces the possibility of having flexible camouflage. Additionally, the construction does not allow for a system with sufficient capability to absorb incident waves without their being reflected back to the transmitter. This solution does not even allow the programming of electromagnetic properties.
From another patent document EP0426141 is known a layered material for absorbing radar radiation from a reflecting substrate to reflect EM wavelengths of mm and cm wavelengths and bonding layers with high electrical resistance and 10-60% conductive particles with a conductivity of 1-100 S/m. This solution employs an EM reflective material and layers with high electrical resistance, which to a certain extent allows shading and absorption of incident EM waves. The stated solution fundamentally does not allow the setting of desired parameters of surface and volumetric conductivity. This does not allow the making of variously effective electromagnetically camouflaged and/or masked structures.
From patent document EP 0122243 is known a method which contains a woven fabric with metallic fibrils laminated with a metallised plastic layer, which, according to the description, achieves good reflective properties throughout a wide range of EM waves. This solution merely focuses on the reflection of incident EM waves, which will limit their penetration of the material, but radar technology reliably detects these reflections.
The metal coated masking system is further known from patent document CZ20010054. This metal coated masking system is composed of several layers of conductive and non-conductive materials.
The camouflage kit is further described in patent document BG 102546. The masking kit contains a radio-absorbent coating, radio-absorbent heat reflecting coating, a radio-absorbent anti-accumulation coating, and a device for creating a false heat field. The kit provides a masking effect in the visible, near infrared, thermal and radar regions of electromagnetic waves simultaneously.
In both cases, it is a solution utilising a coating system with fillers capable of partially damping incident EM radiation, however more or less only as a complement to masking in the range of visible and infrared radiation. Coating systems cannot from the main view achieve the desired reflection coefficient parameters or sufficiently high EM shielding efficiency levels due to the thickness, concentration, and distribution of the fillers.
In patent document US 5035942 are disclosed flexible materials for reflecting EM waves which are from non-woven fibre based on carbon fibre with shielding electromagnetic efficiency greater than 50 dB in the range of 100 MHz to 1000 MHz. The basis of the patent is flexible materials for EM wave shielding. The disadvantage of the solution is the reality that it only solves the shielding of EM radiation induced by the reflection of EM waves, thereby compromising the shielded object using radar technology. Additionally, the considered frequency range is insufficient to address EM camouflage or masking under the conditions of modern radar systems.
From patent document US 4479994 is known a design solution of flexible blankets for the absorption and suppression of radar, thermal and acoustic energy. The absorbent material is in the form of polygonally shaped panels, which, according to the authors, leads to suppression of the types of energy mentioned. The panels are either removably arranged or otherwise suitably tied into complementary blanket pockets and are oriented into a grid. This panel solution is intended for fixed installations, it exhibits little mobility and is virtually impossible to program desired electromagnetic behaviour.
The masking net for EM wave absorption, particularly in the infrared and centimetre wavelength range, is known from patent document US 3427619. The masking net comprises a plurality of wave absorbers with different surface shapes. The disadvantage of this solution is the relatively complicated installation of the panels and basically the impossibility of pre-programming or changing the electromagnetic behaviour of various installations.
The masking material for shielding radar waves, comprising a warp spun from pieces of yarn, with metallic fibres which are set out by so-called lay-out technique in such a way that the sum of the elongation of the yarn will be substantially the same in both directions on the plane of the knitting is further known from the patent US 5532052. The solution is merely aimed at attenuation using the reflection of EM radiation and therefore without the ability to absorb incident EM waves.
Another camouflage material is known from patent documents US 5225454 and EP0394207. Here is used a composite based on polyvinyl chloride (henceforth PVC) and carbon fibre with a radar wave attenuation of 1-3 dB per cm. This solution has the disadvantage that the plastic material used is not flexible and has little EM shielding efficiency, in essence without the possibility of regulating it.
Another patent document US 5656794 describes the use of masking smoke for visible, infrared and radar (mm) spectra. This method of masking is, by its very nature, only temporary and easily detectable.
In patent document SE 446124 is described a water-based or aerated plastic foam in which metal strips are imbedded which reflect electromagnetic radiation. The solution employs the above-mentioned construction for making decoy targets, which allows for little mobility of the goal achieved as well as its complex removal. Moreover, the occurrence of the metallic strips of electrically conductive camouflage elements is randomly distributed in the bulk of the material, which does not allow predetermined electromagnetic parameters to be predefined and adjusted in the resulting material.
From patent document FR 2344143 is known the use of weather-resistant panels to camouflage stationary objects. The panel consists of an insulating pad coated with several layers of paint which absorb EM radiation. The angle of inclination of the panel is selected so that the incident waves reflect vertically upwards. The disadvantage of this solution is, on the one hand, the low efficiency, given the use of a painting system, and a rigid construction that prevents the mobile installation of this solution, especially for the camouflage or masking of mobile 3D objects. The main disadvantage of the current state of technology is that current designs of electromagnetic camouflage focus either on the making of structures allowing merely the shielding of electromagnetic radiation using its attenuation and reflection, or attempt to limit the reflection of incident radiation back to its transmitter. The above mentioned solutions however, do not show the desirably low values of reflection coefficient so that the proposed measures would hide protected objects from radar surveillance and eventually replace them with camouflaged objects. Electromagnetic masking and camouflage are currently targeting jamming radar systems, but without the possibility of effectively programming the electromagnetic behaviour of the materials used. An exception is the systems with bags filled with air or liquids, which allow changing permittivity or its dimensions. Even these systems, however, do not allow with sufficient efficiency the absorption of incident EM radiation, let alone the programming of the electromagnetic behaviour of the system within a sufficient range of electrical conductivity.
The object of the present invention is a masking material which will allow for a wide range of electromagnetic behaviour programming of materials intended for the creation of a protected or camouflaged object and its surroundings and to enable the development of advanced camouflage and camouflage systems of a new generation.
Principle of the Invention
The above-mentioned drawbacks are largely eliminated and the object of the invention is fulfilled by a composite material, specifically a sandwich composite material comprising at least three bonded layers, according to the invention, whose essence lies in that it comprises a first conductive layer behind which is arranged the first dielectric layer behind which is arranged a second conductive layer whose specific electrical conductivity is equal to or greater than the specific electrical conductivity of the first conductive layer. The advantage is that the first conductive layer reflects the minimal amount of EM radiation that is not trapped by known tracking devices, while the next layer reflects at most the amount of EM radiation the majority of which can be trapped by the first conductive layer after reflection by this conductive layer. The main advantage is the progressively controlled "imprisonment" of the incident electromagnetic radiation in the assembled composite for, gradually the passing electromagnetic radiation is dampened by the layers of the composite, yet back out of the composite they can no longer be emitted by reflection.
The first conductive layer has to advantage a specific electrical conductivity o1 greater than 10 10 S/m.
It is to advantage if behind the second conductive layer, there are at least one additional dielectric layer and at least one additional conductive layer alternately arranged, with the specific electrical conductivity of each of the other conductive layers being always the same or greater than the specific electrical conductivity of the conductive layer preceding. The advantage is that it is possible to create a composite material which with there is a gradual lessening of the complete visibility of the hidden object, and it is possible by specific layering to create a camouflage material which produces a reflection of EM radiation specific to a particular object, material or even specific natural conditions, such as a fictitious forest or lake etc. The basic principle is that by increasing specific electrical conductivity of the surface of an actual object (e.g. sand, dry brush, brick / concrete / reinforced structures, greenfield, snow, water, and iron structures) with the requirement for the specific electrical conductivity of the material to create virtual objects by electromagnetic camouflage. The more electrically conductive the surface of the original, the more electromagnetic energy of the incident radiation will, as a rule, be reflected. The advantage of such an arrangement is the possibility to achieve beforehand the desired electromagnetic behaviour of the camouflage or masking. At the same time, this arrangement allows, by gradually folding or removing the correctly selected layers, the type of virtualised electromagnetic object to be changed.
It is very advantageous when the conductive layers are made of a textile material. In a preferred embodiment, the conductive layers are created from fabric and/or knitted and/or non-woven fabrics containing conductive material fibres.
It is also to advantage that the dielectric layers are created from fabric and/or knitted and/or non-woven fabric containing fibres of the desired dielectric material.
The advantage of using textile material is that it can simply change its properties by simply changing the content of the conductive material in the yarn, more precisely by simply changing the conductive fibre content of the yarn. Desired specific electrical conductivity of the fabric is achieved in production of the fabric and/or knit fabric either by changes in the size both in warp and weft or in the conductivity of the yarn used as well. The specific electrical conductivity of the yarn is influenced not only by the material used in its construction, being the conductivity of the electrically conductive and non-conducting fibres and/or cuttings but also by other technological parameters such as the length of twist, the furriness of the yarn, the method of spinning, the fineness of the yarn, and the modifications used. It is true that with an increase in the thickness of the fabric used, the absorption capacity of the incident electromagnetic radiation gradually increases, whose high frequency energy in this layer can change by the heat produced due to the occurrence of eddy currents. Likewise it is true that the higher the specific electrical conductivity of the yarn, the greater the specific electrical conductivity of the resulting material. The typical values of specific electrical conductivity of the textile materials suitable for the above solution range from 10 10 S/m for materials emulating rather less conductive than insulating objects. Values in the order of S/m units for layers approach the conductivity of water. The upper limit then includes materials with a specific electrical conductivity of 107 S/m, which correspond to metallic materials. The amount of furriness of the yarn used (the amount of fibres "bunching" from the yarn) and the surface treatment applied, for example by raising it, it is possible to increase the furriness and thus to reduce the reflection from the surface of electrically conductive fabric prepared this way. Electromagnetic shielding efficiency is also influenced by the size of the sett. With a rise in the value of the sett, as a rule the electromagnetic shielding efficiency (henceforth ESE) increases as well.
In this way, it is possible to model and subsequently produce the desired types of materials within a wide range of specific electrical conductivity, electromagnetic shielding efficiency and reflectivity. Thanks to the method described above, materials with unusual properties, referred to as metamaterials, can also be made.
The individual layers may be solidly connected, for example, they may be sewn together, but it is advantageous if the individual layers are joined together in a detachable manner. In this way, the desired reflective properties of the camouflage can be precisely adjusted at the place of implementation.
To advantage, the individual layers are joined together by lamination, sewing or fastening by velcro. The advantages of such an arrangement are the possibility to operatively change the resulting electromagnetic properties of the composite, by changing its composition, more precisely by removing or adding functional layers. In practice, such a solution enables on-site application in almost realtime and operatively to change the resulting electromagnetic behaviour of the composite and with this, to change the resulting electromagnetic reality.
It is also to advantage if each layer contains multiple layers with the same properties. Such an arrangement makes it possible to minimise production costs and minimise the number of different types of layers used. Theory as well as experiments conducted show that the desired properties of dielectric and electrically conductive layers can be achieved with satisfactory results by a sandwich arrangement of layers integrating the resulting parameters. An advantage is the economic benefits and simplification of logistics operations.
For reasons of simplicity of construction and manufacture, it is further to advantage that the dielectric layer is made of non-conductive knitted fabric and/or fabric and/or non-woven fabric. It is to advantage to use cotton yarn and/or non- woven textile and/or yarns containing polyester (henceforth PES) and/or polyacrylonitrile (henceforth PAC) and / or polypropylene (henceforth PP) fibres and/or teflon fibres. Alternatively, the dielectric layer may be formed by an air layer created by mechanically defining the relative position of the adjacent conductive layers, or, bubble wrap and /or 3D fabric may be used.
In an advantageous embodiment, the dielectric layer is kevlar fabric. Its advantage is its high strength, shape stability and non-absorbability of moisture.
It is also to great advantage if the individual layers are treated with an anti water-absorbing medium. This advantage is especially for absorbent materials which require the same conductive properties under all conditions.
The main advantage of the composite material according to the invention is that it allows the achieving of passive virtual electromagnetic reality (henceforth EVR) and with this, to emulate various real objects or their surfaces and thus their electromagnetic response to excitation by incident radar signals. The proposed design enables, already at their production, the programming and adjustment of the required electromagnetic parameters in a wide range of required values of surface and volumetric conductivity, electromagnetic shielding efficiency, absorption and coefficient of reflection not only of the structure of the base material of the functional layer, but also of the composition of the composite.
The advantage is the ability to create an object that can reflect, damp and/or absorb on its surface incident electromagnetic radiation with a given efficiency and, of course, combinations of these properties. Without the ability to properly combine these properties, passive virtual electromagnetic reality cannot be effectively carried out. In a preferred embodiment, such an object is made with a non-conductive design, for example made of wood and wire structures, a composite or inflatable core, in the form of the desired object, and the structure is covered with a fabric having the required surface specific electrical conductivity.
Another advantage is that unusual properties can be achieved by the composite arrangement of electrically conductive fabrics into sandwiches. Laying electrically conductive fabrics directly on top of each other results in increased electrical conductivity, electromagnetic shielding efficiency of the sandwich, and the ability to absorb electromagnetic radiation. The coefficient of reflection is then affected, in particular, by the most conductive layer in the sandwich. A suitable composition of the textile composite with a gradual alignment of electrically conductive and non-conducting layers can also, in a limited frequency range, provide the desired combination of absorption and reflection of incident electromagnetic radiation. The resultant fabric structure then corresponds in its absorption, attenuation and reflection capability, surface structure, or volume to the object and/or scenes forming the EVR-created pattern.
In creating structures with maximum absorption, the generalisation of the behavioural phenomenon of the shielding partition on incident electromagnetic radiation is used. Incident electromagnetic waves on the shielding partition is generally partially reflected back from the partition, while the more the surface is electrically conductive, the more the partition can be considered a mirror, and part of the energy is damped in that partition, while the more the partition is wide and electrically conductive, the more the energy is transformed into heat influenced by the lossy environment, and the rest of the energy passes through the partition and continues to further disseminate. If, at a suitable distance behind this first partition, we place a further or further partitions, the above phenomenon is repeated. However, the fundamental change is that the reflected wave from the second partition back to the first partition not only interferes with the wave’s progression, but at the same time it is, in the already described manner, influenced by the first partition. The partition is thus electrically acting symmetrically double-sided, and so it dampens this returning wave. In a preferred embodiment, the composite material according to the invention is assembled as a textile composite in such a way that electrically conductive and non-conductive layers are sequentially arranged, for example, they are laminated to each-other so that, in the direction of the incident radiation, the electrically conductive layers are sequentially arranged with increasing specific electrical conductivity. This sequencing results in a gradual increase in the reflection coefficient and a gradual increase in the energy absorption of incident electromagnetic radiation of the individual layers. In consequence, this composite design causes trapping of incident electromagnetic waves, as a whole exhibiting a small reflection coefficient and a high absorption capacity at the same time.
Overview of the Figures
The invention will be further elucidated using drawings, in which Fig. 1 shows a schematic view of a seven-layer sandwich composite material; Fig. 2 shows a graph of an example of the EM masking process using this seven-layer sandwich composite material and compares it to radiation into open space and against a metallic mirror, and Fig. 3 shows a detailed graph of EM masking using this sevenlayered sandwich composite material and its comparison to radiation into open space, Fig.4 shows schematically a three-layer sandwich composite material for the making of EM water camouflage of surface water, Fig.5 is a graph of an example of the EM water camouflage construction and its comparison to the radiation into open space and against a metallic mirror, and Fig. 6 shows a detail of a graph of implementation of EM camouflage of surface water and its comparison to the radiation against the sample object, which is surface water, Fig. 7 shows a schematic representation of a three-layered sandwich composite material for the implementation of EM greenfield camouflage; Fig. 8 shows a graph of an example of the EM camouflage of a greenfield and its comparison to radiation into open space and against a metallic mirror, Fig. 9 shows a detail of a graph of the EM camouflage of a greenfield and its comparison to radiation against a sample object, which is green leaves; Fig. 10 shows schematically a three layer sandwich composite material for the implementation of EM camouflage of a sandy area; Fig.1 1 shows a graph of an example of the implementation of EM camouflage of a sandy area and its comparison to radiation into open space and against a metallic mirror, and Fig. 12 shows a detail of the graph of the EM camouflage of sand and its comparison to the radiation against the sample object, which is dry sand.
Examples of the Performance of the Invention
Example 1
A sandwich composite material 2 (Fig. 1) for the implementation of EM masking structures, limiting the reflection of EM radiation 1 in the 1 - 8 GFIz band incident on the composite material 2.
The sandwich composite material comprises a first conductive layer 3 behind which a first dielectric layer 4 is arranged, behind which a second conductive layer 5 is arranged, while behind the second conductive layer 5 a further dielectric layer 4 is arranged, and behind this, another conductive layer 6 and a dielectric layer 4 and a final conductive layer 7, while the specific electrical conductivity of each further conductive layer 5,6,7 located behind the first conducting layer 3 being always greater than the specific electrical conductivity of the conductive layer preceding.
The conductive layers 3, 5, 6, 7 are made of a textile material, which is a fabric containing fibres of an electrically conductive material. Alternatively, the conductive layers 3, 5, 6, 7 may be made of a non-woven fabric containing fibres of an electrically conductive material in a corresponding weight ratio.
The individual layers 3, 4, 5, 6, 7 are treated with an anti-water absorption medium and are laminated to each-other.
The individual layers 3, 4, 5, 6, 7 have these parameters:
- the first conductive layer 3 has ESE1 5 GHZ = 0,1 dB, and a specific electrical conductivity of s = 10~10 S/m,
- the first dielectric layer 4 consists of two layers of 1.5 mm thick knitted fabric and 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
- the second conductive layer 5 has an ESEI 5 GHZ = 5dB and a specific electrical conductivity of s = 5 S/m,
- the next dielectric layer 4 again consists of two layers of 1.5 mm thick knitted fabric having a composition of 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
- the third conductive layer 6 has an ESE-i ,5 GHZ = 10dB and a specific electrical conductivity of s = 10 S/m, - the next dielectric layer 4 again consists of two layers of 1.5 mm thick knitted fabric having a composition of 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
- and the last conductive layer 7 consists of two layers of electrically conductive fabric with ESEI S GHZ = 70 dB and a specific electrical conductivity of s = 15000 S/m.
A comparison of the properties of the above-mentioned sandwich composite material was made with respect to the metal panel (metallic mirror) and radiation into free space.
The graph (Fig. 2) shows the measurement of the reflection coefficient (henceforth S11) for metering preparations made by modified clamps, based on ASTM D4935, calibrated short. The waveform 8 corresponds to the metallic mirror calibration (maximum reflection), the waveform 9 into free space, and the waveform 10 of the use of the four electrically conductive layers. The result shows that gradual folding of the layers resulted in elimination, to total avoidance of the reflection of the incident EM radiation on the composite structure where the use of seven layers increased the ability of the composition to absorb incident EM radiation. With the use of seven layers, a high match of parameter S11 with the waveform 10 for the emission of radiation into open space is evident, as shown on the simplified graph by parameter S11 (fig. 3), where the waveform H corresponds again to the ideal state of emission into free space - nothing is reflected, and at waveform 12, EM masking is achieved.
Example 2
A sandwich composite material (Fig. 4) for implementation of EM water camouflage structures comprises a first conductive layer 3 behind which a dielectric layer 4 is arranged, behind which a second conductive layer 5 is arranged, the specific electrical conductivity of the second conductive layer 5 located behind the first conductive layer 3 is higher than the specific electrical conductivity of the first conductive layer 3.
The conductive layers 3,5 are made of a textile material which is a fabric containing fibres of conductive material.
The individual layers 3,4,5 are detachably joined together by means of velcro. The individual layers 3,4,5 have the following parameters:
- the first conductive layer 3 has ESE1 5 GHZ = 10 dB, and a specific electrical conductivity of s = 10 S/m,
- the dielectric layer 4 consists of a needle-punched non-woven fabric of 1 mm thickness and a composition of 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
- the second conductive layer 5 has an ESEI,5 GHZ = 40 dB and a specific electrical conductivity of s = 100 S/m.
A comparison of the properties of the aforementioned sandwich composite material, which is the camouflage of surface water, was made with respect to the metal panel (metallic mirror) and radiation into free space.
A graph (Fig. 5) shows the measurement of the S11 parameter for the modified measuring clamps ASTM D4935, calibrated short. The waveform 16 corresponds to the metal mirror calibration (maximum reflection), a waveform 17 to radiation into open space, a waveform 18 to a reflection of surface water, a waveform 19 the result of a measurement for camouflage of surface water. The result proves that by gradually folding the layers, the desired reflection of EM radiation by surface water can be camouflaged, allowing the implementation of passive EVR objects or scenes, for example, for hiding ships, as detailed in the graph (Fig. 6) which shows the comparison of the S11 parameter for the sample surface water object waveform 20 and for attaining camouflage waveform 21.
Example 3
A sandwich composite material (Fig. 7) for implementation of structures for EM greenfield camouflage EM structures comprising a first conductive layer 3 behind which a dielectric layer 4 is arranged, behind which a second conductive layer 5 is arranged, while the specific electrical conductivity of the second conductive layer 5, located behind the first conductive layer 3 is the same as the specific electrical conductivity of the first conductive layer 3.
The conductive layers 3,5 are made of a textile material, which is a fabric containing fibres of an electrically conductive material.
The individual layers 3,4,5 are treated with a water-absorbing medium, which are connected by being sewn together. The individual layers 3,4,5 have the following parameters:
- the first conductive layer 3 has an ESEI 5 GHZ = 5 dB, and a specific electrical conductivity of s = 5 S/m,
- the dielectric layer 4 is kevlar fabric of 1 mm thickness,
- the second conductive layer 5 has an
Figure imgf000023_0001
= 5 dB and a specific electrical conductivity of s = 5 S/m.
A comparison of the properties of the above-mentioned sandwich composite material was made with respect to the metal panel (metallic mirror) and radiation into free space.
The graph (Fig. 8) shows the measurement of the reflection coefficient parameter (henceforth only S11) for the modified measuring clamps ASTM D4935, calibrated short. The waveform 25 corresponds to the metal mirror calibration (maximum reflection), the waveform 26 to radiation into free space, the waveform 27 to reflection from the greenfield (a layer of green leaves), the waveform 28 the measurement result of the material for greenfield camouflage. The result proves that by gradually folding the layers, the desired reflection of EM radiation can be achieved, thus enabling the implementation of passive EVR objects or scenes. The solution will allow for greenfield camouflage or for hiding another type of object under the virtual reality of green vegetation, as shown for clarity on the graph (Fig. 9), waveform S11 for a sample greenfield object 29, and for the achieved EM camouflage waveform 30.
Example 4
A sandwich composite material (Fig. 10) for implementation of structures for EM camouflage of sandy areas comprises a first conductive layer 3, behind which a first dielectric layer 4 is arranged, behind which a second conductive layer 5 is arranged, while the specific electrical conductivity of the second conductive layer 5 located behind the first conductive layer 3 is greater than the specific electrical conductivity of the first conductive layer 3.
The conductive layers 3,5 are made of a textile material which is a fabric containing fibres of an electrically conductive material.
The individual layers 3,4,5 are joined to each-other by lamination.
The individual layers 3,4,5 have these parameters: - the first conductive layer 3 has an ESEI S GHZ = 2 dB and a specific electrical conductivity of s = 7 S/m,
- the dielectric layer 4 consists of a 1 mm thick knitted fabric and 70% PES (Polyester) and 30% PAC (Polyacrylonitrile),
- the second conductive layer 5 has an ESEi.s GHZ = 5 dB and a specific electrical conductivity of s = 7 S/m.
A comparison of the properties of the above-mentioned sandwich composite material was made with respect to the metal panel (metallic mirror) and radiation into free space.
The graph (Fig. 11) shows the measurement of the reflection coefficient parameter (S11 ) for the modified measuring clamps ASTM D4935, calibrated short. The waveform 34 corresponds to the metallic mirror calibration (maximum reflection), the waveform 35 of the radiation into free space, the waveform 36 reflection from dry sand, the waveform 37 the measurement result of the material for the camouflage of dry sand layers. The result proves that by gradually folding the layers, the desired reflection of EM radiation can be achieved, thus enabling the implementation of passive EVR objects or scenes. The solution allows a sandy surface to be camouflaged or to hide another type of object under the virtual reality of a sandy surface, as shown by the graph (Fig. 12) for parameter S11 of the sample sand layer 38 and for the achieved EM camouflage waveform 39.
Industrial Application
A composite material according to the invention can be used to achieve passive virtual electromagnetic reality in industrial applications such as electromagnetic absorbers, reflectors and attenuation materials, and in security applications for electromagnetic masking and electromagnetic camouflage.

Claims

Patent Claims
1. A composite material, specifically a sandwich composite material (2) for implementation of passive electromagnetic virtual reality comprising at least three bonded layers, characterised by that it comprises a first conductive layer (3) behind which is arranged a first dielectric layer (4), behind which is arranged a second conductive layer (5), the specific electrical conductivity of which is equal to or greater than the specific electrical conductivity of the first conductive layer (3).
2. The composite material according to claim 1 , characterised by that behind the second conductive layer (5) are alternately arranged at least one additional dielectric layer (4) and at least one additional conductive layer (6), while the specific electrical conductivity of each of the additional conductive layers (6) is always equal to or greater than the specific electrical conductivity of the conductive layer (5) preceding.
3. The composite material according to any of the preceding claims, characterised by that the conductive layers (3, 5, 6) are made of a textile material.
4. The composite material according to any of the preceding claims, characterised by that the individual layers (3, 4, 5, 6) are detachably joined together.
5. The composite material according to any of the preceding claims, characterised by that the individual layers (3, 4, 5, 6) are bonded to each- other by lamination.
6. The composite material according to any of the preceding claims, characterised by that each of the layers (3, 4, 5, 6) comprises multiple layers with the same properties.
7. The composite material according to any of the preceding claims, characterised by that the first conductive layer (3) has a specific electrical conductivity s greater than 10 10 S/m.
8. The composite material according to any of the preceding claims, characterised by that the dielectric layer (4) is created of non-conductive knitted fabric.
9. The composite material according to any one of claims 1 to 7, characterised by that the dielectric layer (4) is created of non-conductive fabric.
10. The composite material according to any one of claims 1 to 7, characterised by that the dielectric layer (4) is created of non-woven non- conductive textile.
11. The composite material according to any of the preceding claims, characterised by that the conductive layers (3,5,6) is created of fabric and/or knitted fabric and/or a non-woven textile comprising fibres of conductive material.
12. The composite material according to any of the preceding claims, characterised by that the individual layers (3, 4, 5, 6) are treated with an anti water absorption medium.
List of referential marks
1 EM radiation
2 composite material
3 first conductive layer
4 first dielectric layer
5 second conductive layer
6 conductive layer
7 final conductive layer
8 waveform I - calibration on a metallic mirror
9 waveform II - radiation into free space
10 waveform III - achieved EM masking
11 waveform IV - radiation into free space
12 waveform V - achieved EM masking
16 waveform VI - calibration on a metallic mirror
17 waveform VII - radiation into free space
18 waveform VIII - reflection from surface water
19 waveform IX - achieved EM camouflage of surface water
20 waveform X - reflection from the sample object surface water
21 waveform XI - achieved EM camouflage of the sample surface water object
25 waveform XII - calibration on a metallic mirror
26 waveform XIII - radiation into free space
27 waveform XIV - reflection from greenfield (layer of green leaves)
28 waveform XV - achieved EM camouflage of greenfield (layer of green leaves)
29 waveform XVI - reflection from the greenfield sample object (layer of green leaves)
30 waveform XVII - achieved EM camouflage of the sample greenfield object (layer of green leaves)
34 waveform XVIII - calibration on a metallic mirror
35 waveform XIV - radiation into free space
36 waveform XIX - reflection from dry sand
37 waveform XX - achieved EM camouflage of dry sand layer
38 waveform XXI - Reflection from the dry sand layer sample object
39 waveform XXII - achieved EM camouflage of dry sand layer sample object
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