Radar scattering yarn with reduced reflectivity

Abstract

A yarn structure (14) is provided for use in a camouflage net. It comprises first (3), second (4) and third (5) yarn elements comprising, respectively, polymer, metal and carbon- or graphene-based material. The yarn elements are combined to form the yarn structure. The second yarn element (4) is present in an amount sufficient to provide radar scattering capabilities. The third yarn element (5) is present in an amount sufficient to reduce radar reflectivity of the yarn structure, compared to a yarn structure without the third yarn element.

Description

[0001] Radar scattering yarn with reduced reflectivity

[0002] Field of the invention

[0003]

[0001] The invention relates to the field of camouflage nets. More specifically, it relates to yarns for use in radar-scattering camouflage nets with reduced radar reflectivity.

[0004] Background of the invention

[0005]

[0002] Camouflage nets are widely used in military and civilian applications to conceal objects, personnel, and equipment from visual and electronic detection. These nets are designed to blend in with the surrounding environment, making it difficult for observers to distinguish the camouflaged object from its background. Ultra-Light Camouflage Nets (ULCANs) are a specific type of camouflage net that offers enhanced concealment properties while being lightweight and easy to deploy.

[0006]

[0003] One of the key challenges in designing effective ULCANs is the reduction of radar reflectivity. Radar systems emit electromagnetic waves that bounce off objects and return to the receiver, allowing the detection and location of the objects. In order to minimize the chances of detection by radar, ULCANs must be designed for reducing the amount of energy that is reflected back to the receiver of the radar system.

[0007]

[0004] Traditionally, ULCANs have incorporated materials such as stainless steel fibers to enhance radar scattering and concealment. These fibers disrupt the coherent reflection of radar signals, making it more difficult for the radar receiver to detect the camouflaged object. However, the use of stainless steel fibers alone may not provide sufficient reduction in radar reflectivity: nets containing these fibers can still exhibit radar reflectivity levels that are too high in certain cases.

[0008]

[0005] The high radar reflectivity of ULCANs containing stainless steel fibers can be attributed to several factors. The size, shape, and orientation of the fibers, as well as the overall structure of the net, can influence how radar waves interact with the UCLAN. As a result, there is a need for further advancements in ULCAN technology to address the issue of high radar reflectivity while maintaining the desired radar scattering properties. Summary of the invention

[0009]

[0006] It is an object of embodiments of the present invention to provide a yarn structure for use in a camouflage net that reduces radar reflectivity while maintaining radar scattering capabilities. This objective is accomplished by a yarn structure for use in a camouflage net comprising: a first yarn element comprising polymer; a second yarn element comprising metal; and a third yarn element comprising a carbon based material, wherein the second yarn element is present in an amount sufficient to provide radar scattering capabilities and wherein the third yarn element is present in an amount sufficient to reduce radar reflectivity of the yarn structure compared to a yarn structure comprising the first and second yarn elements without the third yarn element according to the invention.

[0010]

[0007] In the first aspect, the present invention relates to a yarn structure for use in a camouflage net, comprising: a first yarn element comprising polymer; a second yarn element comprising metal; and a third yarn element comprising carbon-based material, wherein the first, second, and third yarn elements are combined to form the yarn structure, wherein the second yarn element is present in an amount sufficient to provide radar scattering capabilities, and wherein the third yarn element is present in an amount sufficient to reduce radar reflectivity of the yarn structure compared to a yarn structure comprising the first and second yarn elements without the third yarn element.

[0011]

[0008] This yarn structure provides an improved camouflage net material that reduces radar reflectivity while maintaining radar scattering capabilities by incorporating both metal materials and carbon-based materials into the yarn structure.

[0012]

[0009] In embodiments, the third yarn element may comprise at least one of carbon core conductor fibers, carbon surface conductor fibers, pure carbon fibers, a carbon core conductor filament, a carbon surface conductor filament, a pure-carbon filament, graphene yarn or a yarn element containing graphene. These radar-absorbent materials, which reduce the radar reflectivity of the camouflage net, can be easily provided.

[0013]

[0010] In embodiments, the yarn structure may comprise from 30% to 95% by weight of polymer, the remainder of the yarn structure being a combination of the second and third yarn elements. This yarn structure composition provides a good balance of radar reflectivity reduction and good radar scattering. In some embodiments, the yarn structure comprises from 5% to 60% by weight of the third yarn element. In some embodiments, the yarn structure comprises from 5% to 25% by weight of each of the second and third yarn elements. A yarn structure comprising from 5% to 25% by weight of each of the second and third yarn elements provides a balance of low weight and good reduction in radar reflection.

[0014]

[0011] In embodiments, a single yarn of the yarn structure may comprise from 1% to 100% by weight of the third yarn element.

[0015]

[0012] In embodiments, the yarn structure may be a twisted yarn comprising at least two single yarns, wherein at least one of the single yarns comprises the second yarn element and at least another of the single yarns comprises the first and / or the third yarn element.

[0016]

[0013] In embodiments, the twisted yarn may be further wrapped by at least a further single yarn comprising a first, second or third yarn element, e.g. the twisted yarn may be wrapped by two single yarns, such as double wrapping. Two single yarns can be wrapped in the same or in different directions. It is possible to wrap more than two single yarns around one twisted yarn core.

[0017]

[0014] In some embodiments, the yarn structure can also comprise a single yarn that is wrapped. The wrapping may be done with one or multiple further single yarns. Where wrapping is done with multiple single yarns, the single yarns can be wrapped in the same or in different directions.

[0018]

[0015] In embodiments, the third yarn element may comprise carbon surface or carbon core conductor fibers, or carbon-based monofilament or multifilament, wherein percentage of third yarn element in one single yarn ranges from 1% to 100% by weight. In some embodiments, the third yarn element content, e.g. the carbon surface or core conductor content, in the yarn structure may be from 5% to 60% by weight. This provides a yarn structure, e.g. including carbon core conductor, that is easy to process, while still giving the required result in terms of reducing the radar reflectivity. In some embodiments, the yarn structure comprises from 5% to 25% by weight of carbon surface or core conductor. This allows the yarn structure to be provided with relatively inexpensive materials and good reduction of radar reflection, without negatively affecting (i.e., increasing) weight.

[0019]

[0016] In embodiments, the yarn structure comprises multiple single yarns. A first single yarn may comprise the first yarn element and the second yarn element.

[0020]

[0017] In embodiments, the yarn structure comprises multiple single yarns. A first single yarn may comprise 100% by weight of the first yarn element and a second of the single yarns may comprise 1% to 50% by weight of the second yarn element, 1% to 50% by weight of the third yarn element, and a balance of the first yarn element.

[0018] In embodiments, the second single yarn may comprise a blend by weight of 50%-80% polyester or polyamide, 5% - 20% of metal fiber or filament, and 5% - 20% of carbon core conductor fiber or filament.

[0021]

[0019] In embodiments, the yarn count of each single yarn may be between NM5 / 1 and NM500 / 1 , for example between NM5 / 1 and NM455 / 1 (corresponding to 22dtex), for example between NM5 / 1 and NM80 / 1 , or for example between NM80 / 1 and NM500 / 1 , or, for example, from NM400 / 1 to NM500 / 1 . For example, the yarn count may be between NM34 / 2 and NM50 / 1 . This yarn count provides a good balance between the price, performance, weight and processability of the single yarns.

[0022]

[0020] In embodiments, the yarn structure may comprise one single yarn for use in a camouflage net.

[0023]

[0021] In embodiments, the yarn structure may comprise 30%-95% by weight of the first yarn element, and 5% - 70% by weight of the second and third yarn elements combined.

[0024]

[0022] In a further aspect, the present invention relates to a camouflage net comprising a plurality of yarns, wherein at least a portion of said yarns comprise a yarn structure according to the invention. This yarn structure provides a camouflage net with high radar scattering and low radar reflection.

[0025]

[0023] In a further aspect, the present invention relates to a method of manufacturing a radar-scattering yarn structure with reduced radar reflectivity, the method comprising: providing a first yarn element comprising polymer, a second yarn element comprising metal, and a third yarn element comprising carbon-based material; and combining the first, second, and third yarn elements, wherein the second yarn element is included in an amount sufficient to provide radar scattering capabilities, and wherein the third yarn element is included in an amount sufficient to reduce radar reflectivity of the yarn structure compared to a yarn structure comprising the first and second yarn elements without the third yarn element.

[0026]

[0024] This method provides an improved camouflage net material that reduces radar reflectivity while maintaining radar scattering capabilities by incorporating both metal fibers and carbon-based fibers in the yarn structure. In some embodiments, combining the yarn elements comprises combining the yarn elements in two single yarns, and forming a twisted structure comprising the two single yarns, thus forming the radarscattering yarn structure.

[0025] In embodiments, providing the third yarn element may comprise providing at least one yarn element comprising graphene, carbon core conductor fibers, carbon surface conductor fibers, pure carbon fibers, carbon core conductor filament, carbon surface conductor filament, pure carbon filament. These radar-absorbent materials can be easily provided.

[0027]

[0026] It is an advantage of embodiments of the present invention that an improved camouflage net material that reduces radar reflectivity while maintaining radar scattering capabilities is provided, by incorporating both metal and carbon-based materials into the yarn structure. It is an advantage of embodiments of the present invention that the radar-absorbent material, which reduces the radar reflectivity of the camouflage net, can be easily provided. It is a further advantage that the radar reflectivity can be reduced while maintaining good radar scattering. It is also an advantage that the yarn structure provides a balance of low weight and good reduction of radar reflection. In some embodiments, the yarn structure comprises from 5% to 60% by weight of the third yarn element. In some embodiments, the yarn structure comprises from 5% to 25% by weight of each of the second and third yarn elements. The third yarn element preferably comprises carbon core conductor fiber or carbon surface conductor fiber. It is an advantage of embodiments of the present invention that such a fiber, e.g. including carbon core conductor or carbon surface conductor, is easier to process and more economical than a 100% carbon yarn. It is a further advantage that such yarn elements will give the required result in terms of reducing the radar reflectivity. It is an advantage of embodiments of the present invention that the yarn structure can be provided with relatively inexpensive materials that achieve a good reduction in radar reflection, without negatively affecting the weight of the yarn structure. It is an advantage that camouflage net made from the yarn structure of the present invention achieves high radar scattering and low radar reflection.

[0028]

[0027] In some embodiments, combining the yarn elements comprises combining the yarn elements in two single yarns, and forming a twisted structure comprising the two single yarns, thus forming the radar-scattering yarn structure.

[0029]

[0028] In embodiments, providing the second and / or third yarn elements comprises providing the corresponding yarn element at 1% up to 50% by weight of the yarn structure.

[0030]

[0029] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

[0031]

[0030] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This detailed description is given for the sake of example only, without limiting the scope of the invention beyond what is defined in the accompanying claims. The reference signs quoted below refer to the accompanying drawings.

[0032] Brief description of the drawings

[0033]

[0031] FIG. 1 illustrates a yarn structure according to some embodiments of the present invention. The yarn structure of FIG. 1 is a twisted yarn including a single polymeric yarn and a single yarn including carbon-based fibers, polymeric fibers and metal fibers.

[0034]

[0032] FIG. 2 illustrates a yarn structure according to some embodiments of the present invention. The yarn structure of FIG. 2 is a twisted yarn including a single yarn including polymeric and metal fibers and a single yarn including carbon-based fibers and polymeric fibers.

[0035]

[0033] FIG. 3 and FIG. 4 illustrate a cross section of yarn elements comprising carbon-based materials, in particular carbon core conductor fibers or filaments.

[0034] FIG. 5 and FIG. 6 illustrate a cross section of yarn elements comprising carbon-based material, in particular a carbon surface conductor and pure carbon fibers or filaments, respectively.

[0036]

[0035] FIG. 7 illustrates a yarn structure according to some embodiments of the present invention. The yarn structure of FIG. 7 is a twisted yarn including a single polymeric yarn including metal fibers and a carbon-based filament yarn.

[0037]

[0036] FIG. 8 illustrates a yarn structure, the yarn structure being a single yarn comprising a mixture of polymeric, metal and carbon-based yarn elements.

[0038]

[0037] FIG. 9 illustrates a camouflage net comprising a yarn structure according to embodiments of the present invention.

[0039]

[0038] FIG. 10 is a flowchart of a method of manufacture of a yarn structure according to embodiments of the present invention.

[0039] FIG. 11 illustrates a yarn structure according to some embodiments of the present invention, wherein the yarn structure is a wrapped yarn.

[0040]

[0040] The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0041]

[0041] In the different drawings, the same reference signs refer to the same or analogous elements.

[0042] Detailed description of illustrative embodiments

[0043]

[0042] The present invention will now be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto. The invention is only limited by the claims. Any reference signs in the claims shall not be construed as limiting the scope of the claims.

[0044]

[0043] The following terms are provided solely to aid in the understanding of the invention.

[0045]

[0044] As used herein, and unless otherwise specified, the term "yarn" refers to a continuous strand of textile fibers, filaments, or material in a form suitable for knitting, weaving, or otherwise intertwining to form a textile fabric. The term “yarn structure” refers to a structure including yarn. A yarn structure may include, but is not limited to, a single yarn, a folded yarn, a cabled yarn, a twisted yarn, e.g. a wrapped yarn. The yarn structure can be used in combination with other components, such as coatings.

[0045] Yarn structures are used to form camouflage nets, for example by knitting. In particular, a yarn structure comprising strand component(s) or yarn element(s), for example fibers, or one or more filaments, can provide good scattering capabilities of electromagnetic signals, in particular good radar scattering capabilities. The present invention relates to such yarn structures, yarn elements and camouflage nets.

[0046]

[0046] As used herein, and unless otherwise specified, the term "yarn element" refers to a monofilament, multifilament or grouping of fibers of a particular material composition that is used in the construction of the yarn structure. A yarn element specifically made of fibers is a “fiber element”. In the same way, “filament element” will be used if the yarn element is made of monofilament or multifilament. The present invention is not limited to yarn structures made exclusively of fibers or of filament(s): other components may also be included, and the yarn structure may comprise a combination of fibers and one or more filaments.

[0047] Examples of fiber elements include, but are not limited to, polymer fibers, metal (e.g. stainless steel) fibers, carbon-based fibers, carbon core conductor fibers, carbon surface conductor fibers, and pure carbon fibers. Examples of filament elements include polymer filament, metal filament, and carbon-based filament such as carbon core conductor filament, carbon surface conductor filament, even pure-carbon filament.

[0047]

[0048] As used herein, and unless otherwise specified, the material or object with "radar scattering capabilities" is able to scatter incident radar waves in various directions, thereby making the material or object hard to detect by radar systems: fewer incident radar waves are reflected directly back to source. The presence of conductive materials, such as stainless steel fibers, can enhance the radar scattering capabilities of a yarn structure.

[0048]

[0049] As used herein, and unless otherwise specified, the term "radar reflectivity" refers to a measure of the ability of a material or object to reflect incident radar waves directly back to the source. A higher radar reflectivity indicates a stronger reflection or weaker absorption of the radar waves, while a lower radar reflectivity indicates a weaker reflection or increased absorption of the radar waves.

[0049]

[0050] In an aspect of the present invention, a yarn structure suitable to form, e.g. by knitting, a camouflage net is provided. The yarn structure includes yarn elements (for example in fiber form or filament form) including polymer material, highly conductive material (typically metal) and carbon-based material.

[0050]

[0051] The yarn structure may comprise from 30% up to 95% by weight of the first yarn element and from 2.5% to 60% by weight of the third yarn element, the second yarn element added as balance. For example, the yarn structure may comprise at least 30 wt.% up to 95 wt.% of the first yarn element, and from 5 wt.% to 70 wt.% (preferably from 5 wt. % to 60 wt. %) of the sum of the second and third yarn elements, for example: from 2.5 wt.% to 30 wt.% of each of the second and third yarn elements; more preferably from 50 wt.% to 90 wt.% of the first yarn element and from 5 wt.% to 25 wt.% of one of the second or third yarn elements, the balance being the other of the second and third yarn elements. In some embodiments, the yarn structure comprises for example 60 wt.%-90 wt.% polymer (e.g., polyester or polyamide, the present invention not being limited thereto), and from 10 wt.% to 40 wt.% combined of metal and carbon-based yarn elements, for example, from 5 wt.% - 20 wt.% of metal and 5 wt.% - 20 wt.% of carbon based yarn elements. For example, the yarn structure may comprise approximately 85 wt.% polymer yarn element, 7.5 wt.% of metal yarn element, and 7.5 wt.% of carbon-based yarn element.

[0051]

[0052] Any suitable yarn structure can be used. For example, a single yarn or a twisted yarn, including at least two single yarns wrapped around each other, or a wrapped yarn, can be used. The yarns may comprise, e.g., fibers, one or more filaments, or even a combination. For example, fibers may be spun around a filament or wire, thus forming a (single) yarn combining one or more filaments with fibers. Such yarns may be formed by, for example, core spinning. The present invention is not limited to these examples, and spun yarns or mono / multifilament yarns can be used.

[0053] A filament used in the present invention, in particular metal filament, for example a stainless steel filament, may have a diameter from 20 microns to 80 microns, in particular from 35 microns to 70 microns.

[0052]

[0054] In some embodiments, the yarn structure comprises two single yarns forming a twisted structure. The difference between ‘yarn structure’ and ‘single yarn’, as used herein, is that a yarn structure may include a single yarn, or a plurality of so-called single yarns (e.g. twisted or wrapped around each other).

[0053]

[0055] As used herein, and unless otherwise specified, the term "twisted structure" refers to an arrangement where a set of single yarns are twisted together to form a cohesive multi-stranded yarn. The twisting can be done in a single direction or in opposite directions, and the degree of twisting can vary depending on the desired properties of the resulting yarn structure.

[0054]

[0056] In embodiments of the present invention, at least one of the single yarns of the yarn structure may be a spun yarn. Spun yarns are easy to manufacture with a desired composition. For example, a twisted yarn structure may be formed by a set of single spun yarns. The present invention is not limited to single yarns being spun yarns.

[0055]

[0057] For example, a twisted yarn structure may comprise a set of single yarns wherein the set consists of two single yarns. The single yarns of the twisted structure include polymer, which enhances knittability. They also include highly conductive materials and carbon-based materials. This combination allows for both radar scattering and radar absorption by a camouflage net obtained from said yarn structure. The presence of carbon-based materials reduces overall radar reflectivity while the presence of a highly conductive material maintains the radar scattering capabilities. The specific percentages of conductive materials and carbon-based materials, and specific yarn structure allow for fine-tuning of these properties.

[0058] The first yarn element of the yarn structure is polymeric, for example polyamide (PA) fibers, polyester (PES) fibers, or a mixture of both, the present invention not being limited to these two examples. For example, the first yarn element may comprise filaments, instead of fibers or in combination with fibers. The polymeric yarn element ensures the yarn structure has the required properties to be able to process the net, e.g. ensure the knittability of the yarn structure. The present invention is not limited to PA and PES, and other polymers may be used, including e.g. nylon, polypropylene, high-performance polyethylene, etc.

[0056]

[0059] The second yarn element comprises highly conductive materials, i.e., metal. In some embodiments, these may comprise metal filaments, or fibers, for example but not limited to steel fibers, e.g. stainless steel fiber (SSF). The presence of highly conductive material allows incident radar signals to be scattered, so that the radar receiver does not receive bounced radiation, thereby improving camouflage. The second yarn element may consist of one or more filaments, e.g. one or more stainless steel filaments.

[0057]

[0060] The third yarn element comprises a carbon-based material. As used herein, and unless otherwise specified, the term "carbon-based material" refers to material that contains carbon as a primary constituent. Hence, a carbon-based material may comprise graphene-based materials. For example, the third yarn element may include carbon-spun yarn, which comprises carbon-based fibers. Additionally or alternatively, the third yarn element may include carbon or graphene filament yarn, which comprises monofilament or multifilament of carbon and / or graphene.

[0058]

[0061] For example, the yarn structure may be a single yarn formed by core spinning and comprising polymer and carbon-based materials, e.g. polymer fibers and carbon or carbon core / surface conductor fibers, spun around a metallic monofilament, e.g. a stainless steel monofilament, from 20 microns to 80 microns in diameter, e.g. from 35 microns to 70 microns in diameter.

[0059]

[0062] The percentage by weight of metal fibers or pure carbon fibers (or filament) in one single yarn of the yarn structure can range from minimum 1% to maximum 50%, typically from 5% to 25%.

[0060]

[0063] The percentage by weight of carbon surface or core conductor in one single yarn of the yarn structure can range from 1% to 100%, typically 5 to 30%. A carbon core conductor is usually easier to process than a 100% carbon yarn, as well as more economical, while providing the required results in terms of reducing the radar reflectivity.

[0064] In some embodiments, multiple single yarns as described above combine in amounts such that the yarn structure comprises from 30% up to 95% by weight of the first yarn element, and from 5% to 70% by weight of the second and third yarn elements combined, e.g.: 50% - 90% by weight of the first yarn element, 5% -25% by weight of one of the second or third yarn elements, the balance being the other of the second and third yarn elements; or 50% - 80% by weight of the first yarn element, 5% - 20% by weight of the second yarn element, and 5% - 20% by weight of the third yarn element; or 70% by weight of polymer yarn element, 15% by weight of metal yarn element, and 15% by weight of carbon-based yarn element.

[0061]

[0065] Examples of carbon-based fibers include but are not limited to: carbon core conductor fibers, which have a conductive carbon core surrounded by a non- conductive sheath; carbon surface conductor fibers, which have a conductive carbon layer on the surface of a non-conductive core; and pure carbon fibers, which are made entirely of carbon. In case of conductive carbon core, the core may be in the center or off-centered relative to the fiber cross section of the fiber. Filaments can also be carbon core or carbon surface conductor filament.

[0062]

[0066] An example of a yarn structure, for use in a camouflage net, in accordance with embodiments of the present invention is shown in FIG 1. The yarn structure 1 comprises a first yarn element 3 consisting of polymer fibers, a second yarn element 4 made of metal, e.g. SSF, and a third yarn element 5 comprising carbon-based fibers. In the present example, the third fiber element includes carbon-based fibers which may comprise graphene, or pure carbon fibers, or carbon core conductor fibers, or carbon surface conductor fibers, or a mixture of two or more of these. The present invention is not limited to these examples. Carbon allows reduction of radar signal reflection, by improving absorption of the radar signal.

[0063]

[0067] These different types of yarn elements 3, 4, 5 are combined to form two single yarns in a twisted structure 6. The second fiber element 4 is present in an amount sufficient to provide radar scattering capabilities, while the third fiber element 5 is included in an amount sufficient to reduce radar reflectivity of the yarn structure 1 compared to a yarn structure comprising the first and second fiber elements 3, 4 but lacking the third fiber element 5.

[0064]

[0068] The carbon fibers facilitate effective radar absorption. The percentage of carbon surface or carbon core conductor fibers in a single yarn of the yarn structure may range from 1% to 100%, allowing for flexibility in tailoring radar-absorbing properties. Additionally, the yarn structure 1 may comprise 1% to 50% by weight of each of the second 4 and third yarn elements 5, achieving a balance between radar scattering and absorption.

[0065]

[0069] FIG 1 shows that the twisted structure 6 of the yarn structure 1 may comprise or, e.g., consist of two single yarns 10, 11 twisted together, where at least one single yarn 10 includes the first fiber element 3 and at least another single yarn includes the third fiber element 5, optimizing the distribution of the different fiber types. In one embodiment, a single yarn 10 may consist of 100% by weight of the first yarn element 3, while the other single yarn 11 may contain 1% to 50% by weight of the second yarn element 4 and 1% to 50% by weight of the third yarn element 5. The second single yarn may further include the first yarn element 3 to advantageously reduce costs, and potentially increase strength of the yarn. In embodiments of the present invention the second single yarn may include only the second and third yarn elements (e.g. in the form of fibers). Moreover, the present invention is not limited to twisted yarns made out of two single yarns. More than two single yarns may be included, and further components, such as coating, may also be included.

[0066]

[0070] FIG 2 shows an embodiment wherein the second yarn element 4 (SSF) may be spun with the first yarn element 3 (polymer fibers) to form a first single yarn 12, and the third yarn element 5 (carbon fibers) may be spun into a separate (second) single yarn 13, both yarns being twisted together to form the final yarn structure 14.

[0067]

[0071] In some embodiments, the yarn structure comprises: a first single yarn with steel fibers further combined with polymer fibers; and a second single yarn comprising only the carbon-based yarn element. As the single yarn containing the conductive materials also includes polymer, the single yarn achieves improved mechanical properties and is more readily processed. In some embodiments, as shown in FIG 2, the second single yarn 13 comprising the second yarn element 5 (carbon-based fibers) may also include the first yarn element 3, to improve workability.

[0068]

[0072] In general, a first single yarn may comprise at least polymer, while a second single yarn may comprise carbon-based fibers, for example pure carbon fibers, including e.g. graphene, carbon core conductor fibers, etc. One of the first and second single yarns, or both, may include metal fibers. This way, the metal fibers (e.g. SSF) are mixed with polymer or carbon, thus reducing the contribution of single yarns comprising metal fibers to the radar reflection. This way, each single yarn includes one fiber element, or two fiber elements. The elements of each single yarn must be combined so that the twisted yarn structure as a whole includes the three elements of the yarn structure, i.e. the polymer fibers, the highly conductive fibers for radar scattering, and the carbon-based fibers to reduce radar signal reflection.

[0069]

[0073] Preferably, the metal yarn element and the polymer yarn element form part of the same single yarn. Embodiments with such single yarns present better workability than embodiments comprising a single yarn with metal and without polymer yarn element.

[0070]

[0074] FIG 3 shows the cross section of carbon core conductor fibers, which are one type of carbon-based fiber 50 that can be utilized as a third yarn element in the yarn structure of the present invention. The carbon-based fiber 50 features a conductive carbon core 20, for absorbing radar signals, surrounded by a non-conductive or less conductive outer layer 21 . In some embodiments, the third yarn element comprises one or more carbon core and carbon surface conductor filaments.

[0071]

[0075] FIG 4, FIG 5 and FIG 6 illustrate cross sections of alternative carbon-based fibers.

[0072]

[0076] Referring to FIG 4, another embodiment of carbon core conductor fibers 71 is shown, wherein the carbon core 22 is off-center in the cross section of the less conductive, e.g., polymeric, outer layer 23. Referring to FIG 5, carbon surface conductor fibers 8 are depicted as another type of carbon-based fiber that can serve as the third yarn element 5 in the yarn structure. These fibers 8 possess a conductive carbon layer 81 on their surface, which enhances radar signal absorption and reduces radar reflectivity. The layer 81 may be provided around a dielectric material 82. Referring to FIG 6, pure carbon fibers 9 are shown. These are entirely composed of carbon and exhibit inherent radar-absorbing properties, contributing to reduced radar reflectivity when incorporated into the yarn structure and camouflage net.

[0073]

[0077] In some embodiments, the third yarn element may comprise graphene fibers, which can act as radar absorbent materials to reduce the radar reflectivity of the yarn structure and camouflage net.

[0074]

[0078] It is noted that instead of fibers, in some embodiments, carbon-based multi- or monofilaments may be used of the same type as described above, e.g. having the same cross section shown in FIG 3 to FIG 6.

[0075]

[0079] FIG 7 shows a yarn structure 15 comprising a twisted structure 6, wherein the first single yarn 16 comprises polymer fibers 30 and metal fibers 40 (e.g. SSF), and the second single yarn 17 comprises a carbon-based material, comprising or consisting of a carbon-based filament 14, for example monofilament or multifilament, e.g. comprising or consisting of graphene.

[0080] Thus, in some embodiments a twisted yarn comprises two single yarns where one of the single yarns comprises metallic and polymer fibers and that the other single yarn is a pure carbon yarn or carbon core or surface conductor yarn. The pure carbon yarn or carbon core or surface conductor yarn can be made out of 1 or more filaments, as in FIG 7, or it can be made out of spun fibers, or a combination thereof.

[0081] Thus, embodiments of the present invention may comprise a twisted structure wherein a single yarn comprises a mixture of polymer and metal, such as a mixture of polymer and metal fibers. The other single yarn comprises the carbon-based material, which may comprise fibers, or may comprise or consist of one or more filaments, for example as a monofilament or multifilament. The filament may comprise graphene, but in other embodiments the filament may be carbon core conductor, e.g. a dielectric filament having a carbon core, a surface carbon conductor, e.g. a dielectric filament covered by a carbon surface.

[0076]

[0082] In particular embodiments, the yarn structure is a wrapped structure. Wrapping can be considered a special type of twisting which provides a high covering of a core yarn (single or twisted) with one or more further single yarns.

[0077]

[0083] In some embodiments, a single yarn comprising the first and second yarn elements (e.g. fibers) can be twisted around, or can wrap, a single yarn comprising the third yarn element (e.g. a pure carbon, carbon core, carbon surface) filament. In some embodiments of a yarn structure 24, as shown in FIG 11 , a single yarn comprises the first and second yarn elements. This single yarn is wrapped by a single yarn comprising the third yarn element, which is a carbon-based monofilament or multifilament yarn, or a carbon-based fiber yarn.

[0078]

[0084] In the embodiment of FIG 11 , the single yarn 26 includes polymer and metal fibers, for example polyester and steel fibers. Such single yarn 26 may be similar to the single yarn 16 with the first and second components as shown in FIG 7, however the single yarn 26 in FIG 11 acts as a core around which at least another single yarn wraps, rather than being one of the twisted single yarn as in FIG 7. For example, the single yarn element may be a spun yarn comprising 85 wt.% polyester and 15 wt.% of steel fiber in yarn count Nm34 / 1. In some examples, a carbon surface conductor monofilament wraps the single yarn of polymer and metal fibers. For example, the monofilament may have a count up to NM500 / 1 , e.g. between NM80 / 1 and NM500 / 1 , e.g. between NM400 / 1 and NM500 / 1 , e.g. NM455 / 1 , and it may be a pure carbon, carbon core conductor, or carbon surface conductor monofilament, e.g. it may be a 22 denier carbon surface conductor monofilament. Since the wrapping filament is carbon- based, radar reflectivity is reduced. Alternatively, as shown in the particular example of FIG 11 , the core single yarn 26 can be wrapped by at least two other yarns 25, 27. The two other yarns 25, 27 can be monofilaments (carbon surface or carbon core conductor monofilaments) or spun yarns made of carbon / graphene- based material. In some embodiments, the yarns wrap the core yarn in different directions (i.e., in the S and in Z directions), although in other embodiments both yarns may wrap the core yarn in the same (S or Z) direction. The number of wrapping pitch per meter can vary. The wrapping pitch is dependent on the wraps per unit length and is the measured distance between two nearby wraps of the wrapping component. A large wrapping pitch results in a very open wrap. A small wrapping pitch can completely cover the core yarn.

[0079]

[0085] In some embodiments, the yarn structure may comprise up to 60 wt.% of the third yarn element, and at least 30 wt.% of the first yarn element. For example, in embodiments wherein a single yarn is wrapped by a 100 wt.% carbon-based yarn, such as a carbon core, carbon surface mono or multifilament (e.g. as shown in FIG 11), the carbon content can go up to 60 wt.% of the yarn structure.

[0080]

[0086] As used herein, and unless otherwise specified, the term “yarn count” refers to a numerical designation indicating the fineness or coarseness of a yarn, typically expressed as a number followed by a unit of measure. The yarn count can be based on various systems, such as the Number Metric (NM) system, where the number represents the length of the yarn in (kilo)meters per (kilo)gram. Analogously, the denier is the yarn count as mass in grams per 9000 meters (of e.g. filament).

[0081]

[0087] A monofilament wrapped around the single spun yarn improves stability of the single spun yarn. Additionally, compared to a non-wrapped twisted structure, a thinner yarn structure is possible, since the first single yarn can be wrapped with a very thin monofilament. This allows providing lighter camouflage nets, compared to the prior art.

[0082]

[0088] An advantage of wrapping a spun fiber with filament is the reduction of fiber detachment, e.g. the wrapping prevents steel fibers from the spun fiber detaching from the yarn structure during knitting.

[0083]

[0089] The present example is not limited to a carbon-surface conductor filament. For example, it could also be a carbon-core conductor filament.

[0084]

[0090] In some embodiments of the present invention, the count of both single yarns is from 5 kilometers per kilogram to 500 kilometers per kilogram, in other words between NM5 / 1 and NM500 / 1 , or e.g. between NM5 / 1 and NM80 / 1. In some embodiments, the count of both single yarns is between NM5 / 1 and NM80 / 1 so that the combined single yarns are between NM5 / 2 and NM500 / 2. These values are suitable for camouflage net applications. For example, the range between NM34 / 2 and NM50 / 1 can be used, providing good scattering and low radar reflection, and saving on costly materials.

[0085]

[0091] Thus, yarn structures are not limited to twisted yarn of two single yarns, and it may include wrapped yarns or the like, or even a twisted yarn or in particular a wrapped yarn with more than two single yarns. In some embodiments, the twisted structure is further wrapped by one or more further single yarns comprising a first, second or third yarn element.

[0086]

[0092] In some embodiments, the yarn structure is a double wrapping structure. For example, a single yarn or a twisted yarn may be wrapped by a single yarn, or by two yarns with different wrapping direction, or in the same wrapping direction. In some embodiments, a filament wraps a single or twisted yarn in S direction and another in Z direction, or twice in the same (S or Z) direction. It is also possible to wrap more than two times. A particular, non limiting example may comprise a, for example, twisted yarn including a polyester / Bekinox® metal fiber yarns at 85 / 15 and Nm34 / 1. The structure can be wrapped in S direction with a 22dtex carbon-plated polyamide filament. During the same operation during manufacture, a second single yarn can be wrapped in Z the direction. The second single yarn may comprise for example a 22dtex carbon-plated polyamide filament.

[0087]

[0093] In an aspect, the present invention provides a yarn structure comprising or consisting of a single yarn as a blend of the three yarn elements comprising each polymer, metal and a carbon-based material, such as carbon-based filaments or fibers.

[0088]

[0094] An exemplary embodiment of such yarn structure is shown in FIG 8. The yarn structure 18 includes polymer fibers 30. They may be any polymer that improves knittability of the yarn structure, for example it may be PA, PES, or a combination thereof, the present invention not being limited thereto. The second yarn element may comprise metal fibers 40 such as for example SSF, and it is present in an amount sufficient to provide radar scattering capabilities. The third yarn element may comprise carbon-based fibers 50, such as pure carbon fibers, or preferably carbon surface conductor fibers or carbon core conductor fibers, in an amount sufficient to reduce radar reflectivity of the yarn structure 18 compared to a yarn structure comprising the first and second yarn elements without the third yarn element.

[0095] In some embodiments, the single yarn comprises 50-80 wt.% PES or PA, 5-20 wt.% SSF, and 5-20 wt.% carbon fibers (e.g. carbon core conductor fiber), providing a balanced composition.

[0089]

[0096] In some embodiments of the present invention, the count of the single yarn is between NM5 / 1 and NM80 / 1 , e.g. between NM17 / 1 and NM50 / 1.

[0090]

[0097] Such a single yarn can be used to provide a camouflage net, for example in weft direction. On the other hand, it is generally easier to work with twisted yarns (e.g. in weft or warp direction) than with single yarns, since they are usually more wear resistant. In some embodiments, a twisted yarn as specified in the previous aspect can be provided, wherein one of the single yarns corresponds to the single yarn of the present aspect. This is shown in FIG 1.

[0091]

[0098] In a further aspect, the invention relates to a camouflage net 2 as shown in FIG 9, comprising a plurality of yarn structures, where at least a portion 19 of these yarn structures includes a yarn structure as described herein, e.g. a single yarn or twisted yarn as described above. This camouflage net 2 benefits from the balanced radar scattering and absorption properties provided by the yarn structures. The incorporation of these yarn structures helps to reduce radar reflectivity while maintaining radar scattering capabilities.

[0092]

[0099] In a further aspect, the invention involves a method for manufacturing a radarscattering yarn structure with reduced radar reflectivity. This method, as shown schematically in FIG 10, includes providing S01 the first yarn element comprising polymer, the second yarn element comprising high-conductive material (e.g. metal), and the third yarn element being carbon-based material, followed by combining S02 these yarn elements to form a yarn structure. The second yarn element is included in an amount sufficient for radar scattering, while the third yarn element is present in an amount sufficient to reduce radar reflectivity compared to a yarn structure comprising the first and second yarn elements without the third yarn element. The amounts of the yarn elements to be used can be as described above.

[0093]

[0100] Finally, the method comprises S03 knitting a net using the yarn structure.

[0094]

[0101] The step of combining S02 can be done by combining S12 the elements into one single yarn, which can be directly used to knit S03 the net.

[0095]

[0102] The method may comprise a step of twisting two single yarns, thus combining S22 the three yarn elements in two single yarns and forming a twisted structure.

[0096]

[0103] In some embodiments, the method comprises providing a first single yarn S42 and combining it with the previously obtained S12 second single yarn structure. For example, the first single yarn is a polymeric yarn, e.g. formed by 100 wt.% polymer fibers, the second single yarn is obtained by combining S12 the three elements. The resulting yarn structure is shown in for example FIG 1 . The first single yarn may comprise two or more yarn elements. For example, both of the two single yarns may comprise the three yarn elements.

[0097]

[0104] Alternatively, combining S22 the yarn elements in a twisted structure comprises providing S32 a single yarn and providing S42 at least a further single yarn wherein each single yarn comprises one or two yarn elements. The multiple yarns are combined so that the yarn structure comprises all three yarn elements, as discussed above.

[0098]

[0105] In some embodiments, providing S32, S42 two single yarns comprises providing the first and second yarn elements as a first single yarn, and the third yarn element (carbon-based material) as a second single yarn. The combination can be done in the amounts disclosed in the previous aspects of the present invention.

[0099]

[0106] Other combinations are possible. The metal yarn element is preferably combined with the first or third yarn elements, to reduce the radar reflection. In advantageous embodiments, the metal yarn element are combined with polymer yarn elements, to further improve formability of the resulting net.

[0100]

[0107] Some exemplary combinations are laid out as follows. A yarn structure comprising: a single yarn with polymer (PL) and metal (M); and a single yarn with carbon base material (C), is given the following notation: a) PL+M / C

[0101]

[0108] The following combinations can be provided, using the same notation, the present invention not being limited to these: b) PL+C+M I PL c) PL+C / PL + M d) PL+C+M / PL+C+M e) PL+C+M / PL+C f) PL+C+M / PL+M g) PL / C + M

[0102]

[0109] The first combination a) corresponds to the embodiment of FIG 7. The second combination b) corresponds to the embodiment of FIG 1 . The third combination c) corresponds to the embodiment of FIG 2. The following three combinations d)-f) are also possible. The last combination g) is also possible, however the second yarn element is preferably combined with the first yarn element to improve workability.

[0110] The yarn elements in these examples may comprise or consist of fibers. For example, both single yarns may be spun yarns comprising or consisting of fibers, e.g. all three elements may be provided as fibers (polymer fibers, metal fibers, e.g. SSF, and carbon fibers, e.g. carbon core conductor, carbon surface conductor, pure carbon fibers). In some embodiments, at least one of the single yarns may comprise or consist of a filament. For example, both single yarns may comprise or consist of a filament, or one of them may be a spun yarn and the other may be provided as a filament. For example, the particular embodiment a) (i.e., PL+M / C) may comprise a single spun yarn with polymer and metal (e.g. steel) fibers, and a second single yarn comprising a mono- or multi-filament of carbon, such as e.g. graphene or carbon core / carbon surface conductor filament.

[0103]

[0111] In some embodiments, combining S22 the yarn elements comprises wrapping the single yarn elements, thus providing a wrapped structure, wherein at least one single yarn is wrapped around another yarn, i.e., a core yarn, that is usually kept straight.

[0104]

[0112] In some embodiments, combining the yarn elements S02 may comprise twisting at least two single yarns and further wrapping the twisted structure with at least one further single yarn comprising at least one of the first, second, or third yarn elements.

[0105]

[0113] In a further aspect, the invention presents a method for reducing radar reflectivity of a camouflage net, while maintaining radar scattering capabilities. This method involves incorporating a plurality of yarns into the camouflage net, where at least a portion of these yarns have the yarn structure of the present invention.

[0106]

[0114] The method comprises providing a combination of polymer yarn element, highly-conductive (metal) yarn element, and carbon-based yarn element, and forming a yarn structure from these yarn elements. The amounts of each yarn element can be as specified above. The yarn elements may be combined into a single yarn. The single yarn may be processed into a material for the camouflage net as a weft. Alternatively, the single yarn may be processed by, e.g., sizing the single yarn, as weft and warp of a net. In other embodiments, the yarn structure may be provided as a twisted yarn comprising at least two single yarns. The twisted yarn can easily be processed as warp and / or weft of a net.

[0107]

[0115] The yarn structure ultimately provides radar scattering capabilities due to the second yarn element, while reducing radar reflectivity due to the third yarn element.

[0116] The present invention enhances the performance of Ultra-Light Camouflage Nets (ULCANs), by reducing the radar reflectivity of nets containing SSF while maintaining their radar scattering effect. The approach involves incorporating radar absorbent materials, such as carbon or graphene, into the yarn structure. An exemplary prior art yarn structure may consist of PES and / or PA fibers combined with SSF. In the present invention, a portion of the PES / PA fibers is replaced with carbonbased yarn elements, such as carbon core conductor fibers. These carbon-based materials act as radar absorbent materials, reducing the overall radar reflectivity of the camouflage net.

[0108]

[0117] In an embodiment, the yarn structure is a twisted yarn composed of two single yarns. One single is a 100 wt.% polyester or PA spun yarn, while the other single yarn contains a blend of 70 wt.% polyester, 15 wt.% Bekinox® (SSF), and 15 wt.% carbon core conductor fibers. The count of both single yarns can range between NM5 / 1 and NM80 / 1 , with the yarn count for the combined yarns ranging between NM5 / 2 and NM80 / 2.

[0109]

[0118] In an embodiment, the steel and carbon fibers are either spun together in one single yarn or separated into two single yarns. The percentage of steel fibers or pure carbon fibers in a single yarn may range from a minimum of 1 wt.% to a maximum of 50 wt.%, typically from 5 wt.% to 25 wt.%. The percentage of carbon surface or core conductor fibers in a single yarn may range from 1 wt.% to 100 wt.%, typically from 5 wt.% to 30 wt.%. In some embodiments comprising a single yarn being a pure carbon, carbon core conductor or carbon surface conductor filament, the yarn count can be up to NM500 / 1 , for example NM455 / 1 or 22 dtex.

[0110]

[0119] The radar absorbent properties of these fibers help to counteract the high radar reflectivity associated with the SSF. The optimal composition for reduced radar reflection may be a blend of 50-80 wt.% polymer (e.g. PES or PA), 5-20 wt.% metal fiber (e.g. SSF) and 5-20 wt.% carbon core conductor fiber in one single yarn of the yarn structure. By incorporating carbon-based material into the yarn composition, it is possible to reduce the radar reflectivity of ULCANs while maintaining their radar scattering capabilities. The resulting improvement in camouflage performance can enhance the concealment and protection of military assets in various operational environments.

Claims

Claims1. A yarn structure (1 , 14, 15, 18, 24) for use in a camouflage net (2), comprising:- a first yarn element (3) comprising polymer;- a second yarn element (4) comprising metal; and- a third yarn element (5) comprising carbon-based or graphene-based material, wherein the first, second, and third yarn elements (3, 4, 5) are combined to form the yarn structure, wherein the second yarn element (4) is present in an amount sufficient to provide radar scattering capabilities, and wherein the third yarn element (5) is present in an amount sufficient to reduce radar reflectivity of the yarn structure (1) compared to a yarn structure comprising the first and second yarn elements without the third yarn element (5).

2. The yarn structure according to claim 1 , wherein the third yarn element comprises at least one of: carbon core conductor fibers (7); carbon surface conductor fibers (8); pure carbon fibers (9); a carbon core conductor filament; a carbon surface conductor filament; a pure-carbon filament; graphene yarn; and a yarn element containing graphene.

3. The yarn structure according to any one of the previous claims, wherein the yarn structure (1) comprises from 30% to 95% by weight of polymer, the remainder of the yarn structure being a combination of the second and third yarn elements.

4. The yarn structure according to any one of the preceding claims, wherein the yarn structure (1) comprises a single yarn (10, 11) comprising 1% to 100% by weight of the third yarn element (5).

5. The yarn structure according to any one of the preceding claims, wherein the yarn structure (1) is a twisted yarn comprising at least two single yarns (10, 11), wherein at least one of the single yarns (10) comprises the second yarn element (4) and at least one of the single yarns (11) comprises the first and / or the third yarn element (5).

6. The yarn structure according to any one of claims 1 to 4, wherein the yarn structure (1) is a wrapped yarn comprising a single yarn or a twisted yarn as a core yarn, wherein the core yarn comprises at least a first, second or third yarn element, and wherein the core yarn is further wrapped by another single yarn comprising at least a first, second or third yarn element.

7. The yarn structure according to claim 5 or 6, wherein the twisted yarn or wrapped yarn is further wrapped by at least another single yarn comprising at least a first, second or third yarn element.

8. The yarn structure according to any one of claims 5 to 7, wherein the third yarn element comprises carbon surface or carbon core conductor fibers, graphene yarn or a yarn element containing monofilament or multifilament of graphene, wherein the weight percentage of the third yarn element in one of the single yarns ranges from 1% to 100%.

9. The yarn structure according to any one of claims 5 to 8, wherein: a first of the single yarns comprises 100% by weight of the first yarn element; and a second of the single yarns comprises 1% to 50% by weight of the second yarn element, 1% to 50% by weight of the third yarn element, and a balance of the first yarn element.

10. The yarn structure according to claim 9, wherein the second single yarn comprises a blend by weight of 50% - 80% polyester or polyamide, 5% - 20% of metal fiber or filament, and 5% - 20% of carbon core conductor fiber or filament.

11. The yarn structure according to any one of the previous claims, wherein the yarn count of each single yarn is between NM5 / 1 and NM500 / 1.

12. The yarn structure according to any one of the claims 1 to 4, wherein the yarn structure is a single yarn.

13. The yarn structure according to the previous claim, comprising by weight: 30% - 95% of the first yarn element (3); and 5% - 70% of the second and third yarn elements (4, 5) combined.

14. A camouflage net (2) comprising a plurality of yarns, wherein at least a portion of said yarns comprises a yarn structure according to any one of the previous claims.

15. A method of manufacturing a radar-scattering yarn structure (1 , 14, 15, 18, 24) with reduced radar reflectivity, the method comprising: providing (S01): a first yarn element (3) comprising polymer; a second yarn element (4) comprising metal; and a third yarn element (5) comprising carbon-based or graphene-based material; and combining (S02) the first, second, and third yarn elements (3, 4, 5), wherein the second yarn element (4) is included in an amount sufficient to provide radar scattering capabilities, and wherein the third yarn element (5) is included in an amount sufficient to reduce radar reflectivity of the yarn structure (1) compared to a yarn structure comprising the first and second yarn elements without the third yarn element (5).

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