Multilayer radar absorbing elements with adjustable microwave absorption properties

Abstract

A multi-layer radar-absorbing element (10) with adaptable properties for microwave absorption for vehicle components (20) is provided. The element (10) comprises a core layer (11) with a first layer thickness, an insulating layer (12) with a second layer thickness, and an outer absorption layer with a third layer thickness. The core layer (11) is made of a magnetically absorbent material. The insulating layer (12) is made of a material that is both electrically insulating and magnetically permeable. The outer absorption layer (13) is made of a material that is both electrically conductive and magnetically permeable. The insulating layer (12) is arranged between the core layer (11) and the outer absorption layer (13). Furthermore, a vehicle component (20) having a plurality of such radar-absorbing elements (10) and a method (40) for producing such a vehicle component (20) are provided.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to multilayer radar absorbing elements with adjustable properties for microwave absorption as well as to vehicle components comprising such elements and to vehicles (e.g. aircraft) with corresponding vehicle components. TECHNICAL BACKGROUND

[0002] The latest generation of military aircraft are increasingly highly camouflaged, especially against enemy radar. Part of the radar camouflage is achieved through the design itself. However, in some cases, this is not possible. In particular, the design of the wing leading edges, air intakes, etc., can only be designed within certain limits to avoid compromising their respective functions.

[0003] In such locations, radar-absorbing materials (RAM) and / or radar-absorbing structures (RAS) are used to increase the absorption of radar waves and thus reduce the radar cross-section. RAM and RAS can be constructed as either magnetic or electrical absorbers. Both types of absorbers have their specific advantages. To produce both types of absorbers, additives (electrically conductive for electrical absorbers, or magnetic additives for magnetic absorbers) can be incorporated into a polymer (fiber-reinforced or non-fiber-reinforced).

[0004] To date, mainly electrical or magnetic absorbers are known. Independent adjustment of the properties of combined absorbers is not possible. While both magnetic and dielectric absorbers are known, as are combinations of both. Currently, however, only mixtures of dielectric and magnetic particles are used. Furthermore, combined (electric and magnetic) absorbers are very complex to manufacture.

[0005] DE 10 2022 128 629 A1 describes a coating material for a surface of an aircraft. The coating material comprises a polymer- or rubber-based dielectric matrix material and first flakes made of a metallic or soft-magnetic, electrically conductive material embedded in the matrix material. The first flakes are geometrically flat and have a thickness-to-average diameter ratio of 1:3 or less. The first flakes are separated from one another in the matrix material and / or have an electrically non-conductive coating.

[0006] US 2003 / 0 235 709 A1 describes electromagnetic wave-absorbing materials comprising magnetic alloy particles and an insulating matrix. The magnetic alloy particles comprise a transition metal such as Fe and / or Co and further at least one refractory metal such as Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W. The magnetic alloy particles may further contain Ni and / or Al or other alloying additives that provide the desired absorption properties. In a preferred embodiment, the magnetic alloy particles consist of an Fe-Cr-Ni-Al alloy. The insulating matrix of the electromagnetic wave-absorbing material may consist of a water-miscible polysilicate or a refractory cement. The materials may be provided in the form of coatings applied to a substrate, e.g., the hot engine exhaust region of an aircraft.The electromagnetic wave absorbing materials are capable of functioning at very high temperatures for extended periods of time while maintaining satisfactory electromagnetic wave absorbing properties. DESCRIPTION

[0007] Accordingly, it is an object of the invention to provide a simple to manufacture broadband, dielectric and magnetic absorber with targeted adjustment of the absorption properties.

[0008] This object is achieved by the subject matter of the independent claims. Further embodiments emerge from the dependent claims and the following description.

[0009] According to a first aspect, a multilayer radar-absorbing element with adjustable properties for microwave absorption for vehicle components is provided. The element comprises a core layer with a first layer thickness, an insulating layer with a second layer thickness, and an outer absorption layer with a third layer thickness. The core layer is made of a magnetically absorbent material. The insulating layer is made of a material that is both electrically insulating and magnetically permeable. The outer absorption layer is made of a material that is both electrically conductive and magnetically permeable. The insulating layer is arranged between the core layer and the outer absorption layer.

[0010] Vehicles, particularly in the military sector (e.g. military aircraft, ships, etc.) are often equipped with camouflage technology to prevent detection by the enemy using radar technology. To detect objects, a radar emits radar waves, which are reflected by the object to be detected. By measuring the reflection, the location and movement of the object can be determined. A radar beam basically comprises electromagnetic waves that have both electrical and magnetic components. Detection by radar can be achieved in particular by reducing the radar cross-section (reflection surface or effective reflection surface) of the object (e.g. an aircraft). Such a reduction in the radar cross-section results in particular from appropriate design of the surface geometry ("geometric absorbers").For example, to prevent radar energy from being reflected back to the transmitter, surfaces are tilted relative to it or presented with sharp edges. However, there are limits to such a corresponding geometric design in some places, such as the wing edges or engine inlets of an aircraft, in order not to impair their function. Furthermore, a good geometric shape can reduce the radar cross-section by a factor of 10 to 100. However, an even higher factor is difficult to achieve because, due to Huygens' principle, even an extremely tilted plate reflects radar energy back to the transmitter, but considerably less than if the signal were incident at a right angle. Radar-absorbing materials are therefore essential for further reducing the radar cross-section. However, these are generally less effective against low-frequency radars.Particularly at the aforementioned locations, such as wing edges and engine inlets, radar-absorbing materials (RAM) and / or radar-absorbing structures (RAS) can be used to further reduce the radar cross-section. Electrical and magnetic absorbers are used for such structures, typically using mixtures of magnetically absorbing particles and electrically absorbing particles, which are incorporated into the component, for example, into a polymer that may or may not be fiber-reinforced. This poses particular problems in ensuring the desired arrangement of the individual particles relative to one another. With combined absorber materials, independent adjustment of the absorption properties is also not possible.

[0011] The core idea of the invention is to combine the magnetic and electrical absorbers with one another, in particular in a common element. The radar-absorbing element is a microscopic element, for example in the range of 1 µm to 10 µm in size. Such a radar-absorbing element can be in the form of round, essentially spherical particles or elongated fibers, for example. Another possibility is flake-like designs ("flakes") in which, for example, the core layer or the material of the core layer is first ground and then coated with the corresponding additional layers. A large number of such radar-absorbing elements can then be incorporated into a vehicle component during production (for example, on the wing edges described above, but also over the entire surface), but also into any other component that is to be protected from radar detection.For example, corresponding particles can be introduced into a base material (for example a matrix material of a fiber-reinforced plastic or generally a plastic material, such as a polymer, or even a paint or paint system) before curing. Furthermore, the disclosed radar-absorbing elements can also be used in ceramic materials. The term "base material" is therefore to be understood as open and all-encompassing in this disclosure. In principle, it includes all possible base materials. If the radar-absorbing elements are present as fibers, they can also be incorporated / introduced into the already existing fiber bundles (e.g. made of glass fibers) in fiber-reinforced plastic components, for example, or can be woven with the glass fibers. The individual radar-absorbing elements combine the absorption of magnetic waves and electric waves in the same element.

[0012] The core layer serves to absorb the magnetic components of the radar energy. The outer absorption layer, on the other hand, serves to absorb the electrical components of the radar energy. In order to absorb the electrical components of the radar energy, the outer absorption layer must exhibit a certain degree of electrical conductivity. For the magnetic absorbers (i.e., the core layer), however, the individual magnetic absorbers (i.e., in particular, the individual core layers of several of the radar-absorbing elements) must be electrically insulated from one another (i.e., not electrically conductive). This insulation is provided by the insulating layer located between the core layer and the outer absorption layer.The outer absorption layer accordingly has a corresponding ohmic resistance, but is transparent to the magnetic components of the radar energy, allowing it to penetrate to the core layer and be absorbed there. For the same reason, the insulating layer is also magnetically transparent and, to ensure electrical insulation, electrically non-conductive.

[0013] Using the radar-absorbing elements described here, the electrical resistance can be tailored to the application by selecting the material and the thickness (third layer thickness) of the outer absorption layer. The magnetic moment can also be tailored to the application by selecting the material or the diameter (first layer thickness) of the inner core layer. A further advantage of the invention is that the magnetic and electrical properties can be adjusted independently of one another (whereby the adjustment of the corresponding parameters is meant before manufacture of the component (i.e. in particular before manufacture of the radar-absorbing elements) for the desired application, but not during operation). This allows the absorption properties to be adjusted optimally for the respective application with regard to bandwidth and absorption capacity, which was not previously possible in the prior art.It is also conceivable to add additional layers, such as other magnetically or electrically absorbing materials with different absorption properties, to further optimize the overall absorption properties. It is important to ensure the necessary insulation of the magnetic absorbers.

[0014] To achieve certain desired absorption properties, i.e., in particular, a desired bandwidth and absorption capacity, a computer simulation can be used, for example. This simulation takes into account the geometry of the respective component (e.g., an aircraft wing) and the desired absorbing properties and then outputs the corresponding values for the layer thicknesses, materials, and arrangement of the radar-absorbing elements in the component. Based on these outputs, the radar-absorbing elements can then be manufactured and embedded in the component. It is also conceivable to use artificial intelligence (AI), for example, using machine learning techniques such as neural networks, to determine the parameters.

[0015] According to one embodiment, the material of the core layer comprises a ferromagnetic material.

[0016] Ferromagnetic materials are materials with a magnetic permeability of µ r >> 1. Such ferromagnetic materials absorb the magnetic field components of the incoming radar waves. The corresponding physical mechanisms are known to those skilled in the art and are therefore not explained in detail here. The magnetic permeability µ r the core layer between 500 and 1,000,000.

[0017] According to another embodiment, the ferromagnetic material comprises an iron-, cobalt-, or nickel-based alloy. Ferrites or other materials with magnetic moments are also conceivable.

[0018] According to a further embodiment, the material of the insulating layer comprises a material that is both non-ferromagnetic and electrically insulating.

[0019] Such a material is magnetically transparent and also electrically insulates the core layers of individual radar-absorbing elements from each other. This allows the magnetic field components to penetrate to the core layer and be absorbed there.

[0020] According to a further embodiment, the material of the insulating layer comprises a glass and / or a ceramic material.

[0021] Such a glass and / or ceramic material is, on the one hand, mechanically resistant and, on the other hand, both magnetically permeable and electrically insulating and is thus well suited for the purposes of the disclosed radar-absorbing elements.

[0022] According to a further embodiment, the material of the outer absorption layer comprises a specific ohmic resistance in the range between 0.01 Ω · mm 2 / m and 50 Ω · mm 2 / m.

[0023] A good electrical absorber requires an ohmic resistance that is neither too large (i.e., weak electrical conduction) nor too small (insufficient conversion of electromagnetic energy into heat). The specified range has proven advantageous for the purposes of the present disclosure.

[0024] According to a further embodiment, the multilayer radar-absorbing element further comprises an insulating top layer. The insulating top layer is made of a material that is both electrically insulating and magnetically permeable.

[0025] According to a further embodiment, the element has a particulate shape in the form of a sphere. The core layer, the insulating layer, and the outer absorption layer form concentric spherical shells.

[0026] In this embodiment, the radar-absorbing elements can be easily incorporated into a base material, such as a base material (which may, for example, be a matrix material of a fiber-reinforced plastic and may, for example, comprise a polymer material). It is also conceivable to incorporate such particles into a component during additive manufacturing.

[0027] According to a further embodiment, the element has a fibrous shape in the form of an elongated fiber. The core layer, the insulating layer, and the outer absorption layer are arranged concentrically to one another in the cross-section of the fiber.

[0028] Such elongated fibers are particularly suitable for use in fiber-reinforced plastic components. For example, the radar-absorbing elements, if they are in the form of fibers, can be woven with reinforcing fibers (e.g., glass fibers, carbon fibers, aramid fibers, etc.) or incorporated into corresponding fiber bundles. This allows, in particular, the desired distribution of the radar-absorbing elements within the component to be controlled very precisely. However, the radar-absorbing elements in the form of fibers do not have to be woven with reinforcing fibers, but can also be incorporated into a corresponding matrix material. Furthermore, the radar-absorbing elements in fiber form can also be used in components that are not designed as fiber-reinforced plastic components.

[0029] According to a second aspect, a vehicle component is provided. The vehicle component comprises a base material and a plurality of multilayer radar-absorbing elements according to any of the embodiments described herein. The plurality of multilayer radar-absorbing elements are embedded at least partially in the base material, thus enhancing the absorption of radar waves by the vehicle component.

[0030] For example, radar-absorbing elements can be incorporated into vehicle components, such as aircraft, where the "geometric absorption" of radar waves is limited due to functional constraints. At least partial embedding is understood to mean, for example, embedding only at the wing edge (or generally at locally isolated points on the component). However, radar-absorbing elements can also be incorporated into vehicle components other than wings.

[0031] According to one embodiment, the base material comprises a fiber-reinforced plastic material.

[0032] A fiber-reinforced plastic material can, for example, be a composite component with glass, carbon, or aramid fibers (or any other type of reinforcing fibers) embedded in a matrix material, such as a polymer matrix. Such a composite component can be manufactured in the conventional manner, although the radar-absorbing elements are introduced at a suitable time before the matrix material cures. Since the process for manufacturing a composite component, apart from the embedding of the radar-absorbing elements, is known and not essential to the invention, it will not be discussed in detail here.

[0033] According to a further embodiment, the vehicle component is an aircraft wing. The aircraft wing has a wing edge. The plurality of multilayer radar-absorbing elements are embedded in the base material at least in a region of the wing edge.

[0034] According to a third aspect, a vehicle is provided. The vehicle comprises a vehicle shell and at least one vehicle component according to one of the embodiments described herein.

[0035] The vehicle may, for example, be an aircraft, a spacecraft, a ship, a land vehicle, or any other vehicle. The vehicle component may be any component of the vehicle intended to provide radar shielding, such as, in particular, hull components, such as, in a non-limiting example, the aircraft wing of an aircraft.

[0036] According to a fourth aspect, a method for manufacturing a vehicle component according to any of the embodiments described herein is provided.The method comprises the following steps: providing the base material, providing a desired geometry of the vehicle component, determining the first layer thickness, the second layer thickness, and the third layer thickness of the multilayer radar-absorbing elements based on a desired radar absorption behavior and the geometry of the vehicle component, determining a quantity and a distribution of the multilayer radar-absorbing elements within the base material based on the desired radar absorption behavior and the geometry of the vehicle component, providing the determined quantity of multilayer radar-absorbing elements according to the result of the determinations, and incorporating the provided multilayer radar-absorbing elements into the base material during the manufacture of the vehicle component.

[0037] If the vehicle component to be manufactured is, for example, a fiber-reinforced plastic component, the base material can be, for example, a matrix material of a fiber-reinforced plastic (for example, a polymer material) into which reinforcing fibers are introduced in a known manner and which is cured to form the vehicle component. The radar-absorbing elements according to the invention can be introduced into such a matrix material at a suitable location and in a suitable amount, so that a desired absorption behavior for radar energy is achieved. The radar-absorbing elements can be in any suitable form, such as, for example, as substantially spherical particles or as fibers, as described herein. However, it should be noted that the radar-absorbing elements according to the invention can also be used in any other suitable base material.

[0038] The provision of the base material may, for example, comprise the provision of a matrix material of a fiber composite component, but also any other base material in which the radar-absorbing elements are to be embedded.

[0039] The desired geometry of the vehicle component emerges during the design phase of the vehicle component and can, for example, be a CAD model of the vehicle component. The desired radar absorption behavior (e.g., with regard to bandwidth and absorption capacity) arises primarily from the application. In general, the radar absorption behavior is also based on the geometry of the respective vehicle component. For example, when designing vehicles with stealth technology, the radar cross-section is usually reduced as much as possible by choosing a suitable design geometry. However, due to functional constraints, this is not completely possible in all positions. For example, a further reduction of the radar cross-section may be necessary at the wing edges or engine inlets of an aircraft; this can be achieved by suitable incorporation of radar-absorbing elements.The radar absorption behavior of the vehicle component is influenced in particular by the properties of the radar-absorbing elements and their quantity, arrangement, and respective concentration within the vehicle component. To determine the desired radar absorption behavior, these properties of the radar-absorbing elements—in particular the layer thicknesses of the core layer, the insulating layer, and the outer absorption layer, as well as their materials—and the quantity and distribution of the individual radar-absorbing elements within the vehicle component can be determined empirically or by means of a calculation model or computer simulation, taking into account the desired radar absorption behavior and the specified geometry. In a computer simulation, it is also conceivable to use a machine learning model, for example, with neural networks.An empirical determination is understood as a trial approach by varying the parameters and the desired radar absorption behavior (for example by appropriate measurements in the laboratory).

[0040] Once the properties of the radar-absorbing elements, as well as their quantity and distribution within the vehicle component, have been determined, the corresponding radar-absorbing elements are provided or manufactured. For example, using an appropriate chemical / physical process, the core layers of the radar-absorbing elements are coated / functionalized with the insulating layer and the outer absorption layer. Such processes can include, for example, silicon coating or physical vapor deposition (PVD). However, in principle, all other suitable coating processes are also conceivable. In particular, different coating processes can be used for the individual layers.In the case of fibrous designs as described herein, the core layer, for example, when drawn from the melt, can also be drawn through further corresponding baths, for example through metallic baths in the case of the outer absorption layer, in order to apply the corresponding layer.

[0041] In a final step, the radar-absorbing elements are then incorporated into the base material during the production of the vehicle component. This can be achieved, for example, by incorporating them into a matrix material of a fiber composite component.

[0042] According to one embodiment, the introduction of the multilayer radar-absorbing elements comprises at least one of the following: direct introduction of the multilayer radar-absorbing elements into the base material, or introduction of the multilayer radar-absorbing elements as part of a fiber bundle of a fiber-reinforced vehicle component, wherein in the latter case (introduction as part of a fiber bundle) the multilayer radar-absorbing elements have a fibrous shape in the form of elongated fibers, and wherein the base material is a matrix material of the fiber-reinforced vehicle component.

[0043] Direct introduction includes, for example, appropriate sprinkling / mixing into a matrix material of a fiber composite component (if one is provided) prior to its curing, into a plastic material without reinforcing fibers prior to its curing, introduction into a base material during additive manufacturing (e.g., during 3D printing), and the like. In particular, if the vehicle component is a fiber composite component and the radar-absorbing elements are in the form of elongated fibers, these can alternatively be woven with the reinforcing fibers (such as glass fibers, aramid fibers, carbon fibers) or otherwise incorporated into corresponding fiber bundles (e.g., the fibrous radar-absorbing elements can be incorporated into a corresponding preform).This allows for particularly good localization and control of the concentration of the individual radar-absorbing elements within the vehicle component. Furthermore, the radar-absorbing elements can then also contribute to mechanical stabilization. In principle, however, any other suitable method of installation is also conceivable. BRIEF DESCRIPTION OF THE CHARACTERS

[0044] The following examples are described in more detail with reference to the accompanying drawings. The illustrations are schematic and not to scale. Like reference numerals refer to like or similar elements. They show: Fig. 1 A schematic view of spherical multilayer particles as radar absorbing elements, comprising both magnetically absorbing and electrically absorbing concentric spherical shells. Fig. 2 A schematic cross-sectional view of the spherical multilayer particles from Fig. 1 along the section line AA of the Fig. 1, or a vertical sectional view through the fibrous radar absorbing elements of the Fig. 3 along the section line CC. Fig. 3 A schematic perspective view of radar absorbing elements in the form of fibers comprising both magnetically absorbing and electrically absorbing concentric layers. Fig. 4 A schematic longitudinal cross-sectional view of the radar absorbing elements in the form of fibers from Fig. 3 along the section line BB. Fig. 5 A schematic view of an aircraft having two aircraft wings with radar absorbing elements incorporated into their wing edges. Fig. 6 A flow diagram of a process for manufacturing a component with increased radar absorption. DETAILED DESCRIPTION

[0045] The Fig. 1 shows a highly schematic view of a multilayer radar absorbing element 10 in the form of spherical particles in an external view. Fig. 2 shows the radar absorbing element 10 of the Fig. 1 in a cross-sectional view along the section line AA. Furthermore, Fig. 2 the identical vertical cross-section through a further below with reference to the Fig. 3 and Fig. 4 described multilayer radar absorbing element 10 in the form of a fiber.

[0046] The radar absorbing element 10 of the Fig. 1 comprises a core layer 11, an insulating layer 12 and an outer absorption layer 13. The core layer 11, the insulating layer 12 and the outer absorption layer 13 are in the configuration of the Fig. 1 in the form of concentric spherical shells, with the core layer 11 corresponding to the inner core of the particle (i.e., the radar-absorbing element 10) and the outer absorption layer 13 corresponding to the outermost layer of the particle. The insulating layer 12 is arranged between the core layer 11 and the outer absorption layer 13 and connects them together.

[0047] The core layer 11 is made of a magnetically absorbent material, i.e., in particular, a material with high magnetic permeability, especially a ferromagnetic material. The insulating layer 12 is made of a material that is both electrically insulating and magnetically permeable, i.e., a material that allows magnetic waves to pass through essentially unhindered. The outer absorption layer 13, in turn, is made of a material that is both electrically conductive and magnetically permeable.

[0048] The core layer 11 serves to absorb the magnetic component of the radar energy. For this purpose, the outer layers (i.e. the insulating layer 12 and the outer absorption layer 13) must be magnetically transparent so that the magnetic waves can penetrate to the core layer 11. The outer absorption layer, on the other hand, serves to absorb the electrical components of the radar energy. In order to absorb the electrical components of the radar energy, the outer absorption layer 13 must have a certain electrical conductivity. For the magnetic absorbers (i.e. the core layer 11), however, the individual magnetic absorbers (i.e. in particular the individual core layers 11 of several of the radar-absorbing elements) must be electrically insulated from one another (i.e. not electrically conductive). This insulation is provided by the insulating layer 12, which lies between the core layer 11 and the outer absorption layer 13.The outer absorption layer 13 accordingly has, on the one hand, a corresponding ohmic resistance, but on the other hand, is transparent to the magnetic components of the radar energy, so that these can penetrate to the core layer 11 and be absorbed there. For the same reason, the insulating layer 12 is also magnetically transparent and, to ensure electrical insulation, electrically non-conductive. This arrangement enables combined absorption of the electrical and magnetic components of the radar energy by a common, multi-layer, radar-absorbing element 10. This, in particular, avoids an undesirable, incorrect relative concentration of the individual particles to one another, as can occur, for example, with separate electrically and magnetically absorbing particles.In particular, this prevents the formation of agglomerations of the individual magnetic and electrical particles from the outset, which enables a simpler process technology.

[0049] To improve the radar absorption of a component or part, such as a vehicle component 20 (e.g. Fig. 5 (aircraft wing 20)), a plurality of such radar absorbing elements 10 can be incorporated into a base material 22 (in the Fig. 1 to 4 not shown, see Fig. 5). The introduction of such radar-absorbing elements 10 can be carried out in any suitable manner, in particular uniformly over the entire component, locally limited in the component, with varying concentrations across the component, or in any other suitable manner, depending on the desired radar absorption behavior. Furthermore, the overall radar absorption behavior can be adjusted by selecting appropriately matched materials (i.e. materials with corresponding properties (e.g. ohmic resistance, magnetic permeability, etc.)) as well as layer thicknesses of the layers 11, 12, 13. A further parameter for adjusting the desired radar absorption behavior is the arrangement, distribution and / or concentration of the radar-absorbing elements 10 in the vehicle component.

[0050] The Fig. 3 and Fig. 4 show an alternative embodiment of the radar-absorbing element 10, in which the radar-absorbing element 10 is designed as an elongated fiber. Fig. 3 shows the radar absorbing element 10 in a perspective view from the outside. Fig. Figure 4 shows the radar-absorbing element 10 in a longitudinal cross-section along the section line BB. Since the fiber is round / cylindrical, the above-described with reference to the radar-absorbing element 10 in the form of spherical particles Fig. 2 also as a vertical cross-section along the section line CC of the fibrous radar absorbing element 10 of the Fig. 4 should be considered.

[0051] The fibrous radar absorbing element 10 of the Fig. 3 and Fig. 4 also has a core layer 11, an insulating layer 12, and an outer absorption layer 13. The above statements regarding these individual layers 11, 12, 13 of the spherical radar-absorbing element / particle 10 are also fully valid for the fibrous design and are therefore not repeated here for the sake of brevity. Fig. 3 and Fig. 4 differs, however, from the design of the Fig. 1 in that the layers 11, 12, 13 are not present as concentric spherical shells, but as concentric cylindrical layers.

[0052] The design of the radar absorbing elements 10 as fibers according to the Fig. 3 and Fig. 4 is particularly advantageous for fiber-reinforced composite components, since the radar-absorbing elements 10 can, for example, be woven with the already present reinforcing fibers or otherwise incorporated into the fiber bundles of the reinforcing fibers, as already described hereinabove.

[0053] Fig. 5 shows an exemplary vehicle 10 in the form of an aircraft 10. It should be noted that the invention can also be used in other vehicles, such as ships, spacecraft, and the like. The aircraft 10 comprises a vehicle shell 31 and two aircraft wings 20 (or generally vehicle components 20). Each of the aircraft wings 20 is generally made of a base material 22, such as a fiber-reinforced plastic as a composite component, and each includes a wing edge 21 (or generally component edge 21). In each of the wing edges 21, a plurality of the previously described radar-absorbing elements 10 are accommodated, which thus absorb radar energy and reduce the radar cross section.However, it should be noted that the wing edges 21 serve only as an example for the inclusion of the radar-absorbing elements 10 and that the radar-absorbing elements 10 can in principle also be locally limited at any other desired location or can also be included over the entire vehicle component 20 or over the entire vehicle shell 31.

[0054] Fig. 6 shows a flowchart of a method 40 for producing a vehicle component 20 ( Fig. 4). The method 40 begins with the provision 41 of a base material 22 (e.g., a matrix material of a fiber composite component, a preform of such a composite component, a plastic material, a paint system, etc.). Furthermore, in step 42, a desired geometry (e.g., the design shape of the vehicle component 20) is provided, for example, in the form of a CAD model.

[0055] Subsequently, in steps 43 and 44, which can take place either sequentially / iteratively or simultaneously, the necessary properties for the radar-absorbing elements 10 (step 43) as well as their required quantity and distribution within the vehicle component 20 (step 44) are determined. To determine the distribution, locations within the base material 22 are determined, in particular, at which the radar-absorbing elements 10 are to be introduced in order to achieve the desired radar absorption behavior. The properties of the radar-absorbing elements 10 relate in particular to their layer thicknesses and materials, which are also selected to achieve the desired radar absorption behavior.Both the properties of the radar-absorbing elements (step 43) and their quantity and distribution (step 44) are determined based on the desired radar absorption behavior and the desired geometry, for example, empirically or using a computer simulation (but also in any other suitable manner). A computer simulation, for example, considers the desired radar absorption behavior and the geometry of the vehicle component 20 as input parameters and then determines the respective output parameters. Optionally, a computer simulation can also use a machine learning model with neural networks previously trained using training data. However, other determination methods are also possible.

[0056] After determining the properties and the quantity and distribution of the radar-absorbing elements 10, a certain quantity of the radar-absorbing elements 10 having the determined properties is provided in step 45. The provision can comprise manufacturing the corresponding radar-absorbing elements 10, as described further above. In step 46, these multilayer radar-absorbing elements 10 are then introduced into the base material 22, for example by appropriate sprinkling or other incorporation into a matrix material of a fiber composite component or into another material (e.g., generally a plastic material or a paint) before the latter cures. For example, the radar-absorbing elements 10 can also be applied to reinforcing fibers of a fiber composite component, which are then infiltrated with a matrix material / resin in the usual way.If the vehicle component to be manufactured is a fiber composite component with reinforcing fibers and the radar-absorbing elements 10 are in the form of fibers, these can also be woven with the reinforcing fibers or otherwise incorporated into strands of the reinforcing fibers before they are incorporated into the matrix material and the matrix material is cured. The base material 22 can also be, for example, a paint or paint system into which the radar-absorbing elements 10 are incorporated. In principle, the application of the present disclosure is not limited to specific base materials 22, but can be used with all conceivable base materials 22. In this sense, the term base material 22 is to be understood as open and all-encompassing.

[0057] Additionally, it should be noted that "comprising" or "having" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be considered as limitations. LIST OF REFERENCE SYMBOLS 10 multilayer radar absorbing element 11 Core layer 12 Insulating layer 13 outer absorption layer 14 insulating final layer AA Cross section through particles BB Longitudinal section through fiber CC Vertical cut through grain 20 Vehicle component (e.g. aircraft wing) 21 Component edge (e.g. wing edge) 22 Base material 30 Vehicle (e.g. aircraft) 31 Vehicle shell 40 Method for manufacturing a vehicle component 41 Providing the basic material 42 Providing a geometry 43 Determining layer thicknesses 44 Determining the quantity and distribution of radar absorbing elements 45 Provision of radar-absorbing elements 46 Insertion of radar absorbing elements

Claims

[1] Multilayer radar absorbing element (10) with adjustable microwave absorption properties for vehicle components (20), comprising: a core layer (11) having a first layer thickness; an insulating layer (12) having a second layer thickness; and an outer absorption layer (13) having a third layer thickness; wherein the core layer (11) is made of a magnetically absorbing material; wherein the insulating layer (12) is made of a material that is both electrically insulating and magnetically permeable; wherein the outer absorption layer (13) is made of a material that is both electrically conductive and magnetically permeable; and wherein the insulating layer (12) is arranged between the core layer (11) and the outer absorption layer (13). [2] A multilayer radar absorbing element (10) according to claim 1, wherein the material of the core layer (11) comprises a ferromagnetic material. [3] A multilayer radar absorbing element (10) according to claim 2, wherein the ferromagnetic material comprises an iron-, cobalt- or nickel-based alloy. [4] A multilayer radar absorbing element (10) according to any one of the preceding claims, wherein the material of the insulating layer (12) comprises a material that is both non-ferromagnetic and electrically insulating. [5] Multilayer radar absorbing element (10) according to claim 4, wherein the material of the insulating layer (12) comprises a glass and / or a ceramic material. [6] Multilayer radar absorbing element (10) according to one of the preceding claims, wherein the material of the outer absorption layer (13) has a specific resistance in a range between 0.01 Ω · mm 2 / m and 50 Ω · mm2 / m includes. [7] A multilayer radar absorbing element (10) according to any one of the preceding claims, further comprising an insulating finishing layer (14); wherein the insulating finishing layer (14) is made of a material that is both electrically insulating and magnetically permeable; [8] A multilayer radar absorbing element (10) according to any one of the preceding claims, wherein the element (10) has a particulate shape in the form of a sphere; and wherein the core layer (11), the insulating layer (12), and the outer absorption layer (13) form concentric spherical shells. [9] A multilayer radar absorbing element (10) according to any one of claims 1 to 7, wherein the element (10) has a fibrous shape in the form of an elongated fiber; and wherein the core layer (11), the insulating layer (12), and the outer absorption layer (13) are arranged concentrically to one another in the cross section of the fiber. [10] Vehicle component (20) comprising: a base material (22); and a plurality of multilayer radar absorbing elements (10) according to any one of the preceding claims; wherein the plurality of multi-layer radar-absorbing elements (10) are embedded at least in sections in the base material (22) and thus enhance absorption of radar waves by the vehicle component (20). [11] Vehicle component (20) according to claim 10, wherein the base material (22) comprises a fiber-reinforced plastic material. [12] Vehicle component (20) according to one of claims 10 or 11, wherein the vehicle component (20) is an aircraft wing (20); wherein the aircraft wing (20) has a wing edge (21); and wherein the plurality of multi-layer radar-absorbing elements (10) are embedded in the base material (22) at least in a region of the wing edge (21). [13] Vehicle (30) comprising: a vehicle shell (31); and at least one vehicle component (20) according to one of claims 10 or 11. [14] Method (40) for producing a vehicle component (20) according to one of claims 10 to 12, the method (40) comprising: Providing (41) the base material (22); Providing (42) a desired geometry of the vehicle component (20); Determining (43) the first layer thickness, the second layer thickness, and the third layer thickness of the multi-layer radar-absorbing elements (10) based on a desired radar absorption behavior and the geometry of the vehicle component (20); Determining (44) a quantity and a distribution of the multi-layer radar-absorbing elements (10) within the base material (22) based on the desired radar absorption behavior and the geometry of the vehicle component (20); Providing (45) the determined quantity of multilayer radar-absorbing elements (10) according to the result of the determinations (43, 44); and Introducing (46) the provided multi-layer radar-absorbing elements (10) into the base material (22) during the manufacture of the vehicle component (20). [15] Method (40) according to claim 14, wherein the introduction (46) of the multilayer radar absorbing elements (10) comprises at least one of the following: direct introduction (46) of the multilayer radar-absorbing elements (10) into the base material (22); or Introducing (46) the multilayer radar-absorbing elements (20) as part of a fiber bundle of a fiber-reinforced vehicle component (20), wherein the multilayer radar-absorbing elements (10) have a fiber-like shape in the form of elongated fibers, and wherein the base material (22) is a matrix material of the fiber-reinforced vehicle component (20).

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