Method for producing a frequency-selective absorber, and frequency-selective absorber

Abstract

The present invention relates firstly to a method for producing flexible, frequency-selective absorbers, said method comprising the following steps: coating (I) a woven flat textile with an upper layer made of a coating material, printing (II) the coated flat textile with an absorption structure using an electrically conductive paste as an absorption structure layer, wherein the absorption structure meets specified absorption and / or reflection characteristics in order to be able to frequency-selectively absorb electromagnetic signals incident on the absorber, and drying (III), by means of thermal radiation, the flat textile printed with the absorption structure. The invention also relates to a flexible, frequency-selective absorber.

Description

[0001] METHOD FOR PRODUCING A FREQUENCY SELECTIVE

[0002] ABSORBERS AND FREQUENCY-SELECTIVE ABSORBERS

[0003] TECHNICAL AREA

[0004] The present invention relates to a method for producing a frequency-selective absorber and a frequency-selective absorber.

[0005] STATE OF THE ART

[0006] For some time now, research has been conducted on the simulation of frequency-selective structures for narrowband or multiband reflection attenuation in the GHz (gigahertz) and THz (terahertz) range. The following scientific publications are representative of some results of this research:

[0007] V. YU. SOBOLEVA et al, “Development of narrow bandpass filters based on cross cavities for the terahertz frequency range” Opticheski Zhurnal 84, 23-26;

[0008] Jin Woo Park et al , „Multi-band metamaterial absorber based on the arrangement of donut-type resonators" Optics Express , Vol . 21 , No . 8 - 9691 ; YU-JHAN LIN, „Transmission line metamaterials based on strongly coupled split ring / complementary split ring resonators", Optics Express Vol. 25, No. 24 | OPTICS 30395;

[0009] Lei Zhang, Min Zhang, and Huawei Liang, „Realization of Full Control of a Terahertz Wave Using Flexible Metasurfaces", Adv. Optical Mater. 2017, 5, 1700486;

[0010] GUANGWU DUAN et al, „Analysis of the thickness dependence of metamaterial absorbers at terahertz frequencies" Optics Express, Vol. 26, No. 3 2243;

[0011] - P.V.Tuong et al. Appl . Phys. Letter 102, 081122 (2013) .

[0012] The research results described here, which are hereby declared to be part of the disclosure content of this application, are based on so-called metamaterials. A brief description of metamaterials is provided in the second-mentioned article by Jin Woo Park et al. Essentially, periodic structures of high conductivity are deposited onto a dielectric. The aim of the known structure is to minimize both reflection and transmission, thus achieving high absorption.

[0013] The paper by Tuong et al., listed last in the above enumeration, presents an example of a possible structure for a metamaterial for narrowband absorption. The properties of this structure were measured, and the measurement results are presented. Furthermore, a simulation of absorption and reflection was performed and also presented. Using simulation software—such as the commercially available "Comsol"—the behavior of various structures described in the literature was simulated, and the influence of the dielectric thickness as well as the omission of the back side was calculated. By changing parameters such as shape (e.g., cross, split ring), ring size, and dielectric thickness, etc., the angular dependence, polarization dependence, absorption frequencies, and absorption bandwidths, etc., can be varied and thus specifically optimized for a particular requirement.

[0014] The calculations are based on Maxwell's equation using the finite element method in the frequency domain for an incident plane wave with periodic boundary conditions. Problems for a direct calculation arise from the small thickness of the metallic coating compared to the other dimensions. This can be overcome in the calculations by assuming an ideal conductor layer (PEC - perfect electric conductor), which guarantees the appropriate boundary conditions. Alternatively, a transition boundary condition can be introduced, which accounts for the discontinuity in the tangential component of the electric field. DESCRIPTION OF THE INVENTION

[0015] One object of the present invention is to provide a method for producing flexible, frequency-selective absorbers as well as flexible, frequency-selective absorbers.

[0016] This problem is solved by the manufacturing process with the features of claim 1. Further embodiments of the manufacturing process as well as flexible, frequency-selective absorbers are defined by the features of further claims.

[0017] An inventive method for producing flexible, frequency-selective absorbers comprises the following process steps:

[0018] - Coating a woven fabric with a top layer of a coating material ,

[0019] - Printing the coated surface textile with an absorption structure using an electrically conductive paste as an absorption structure layer, wherein the absorption structure fulfills predetermined absorption and / or reflection characteristics in order to be able to frequency-selectively absorb electromagnetic signals incident on the absorber, and

[0020] - Drying the fabric printed with the absorption structure by means of heat radiation. One embodiment of the inventive method consists in the woven fabric being made of at least one of the following materials:

[0021] - Polyester;

[0022] - Polyamide;

[0023] - Glass fibers;

[0024] - Aramid fibers.

[0025] Further embodiments of the inventive method consist in the fact that, for the coating step, the woven fabric is stretched in a tensioning frame and that the coating is carried out using a squeegee or a foulard method.

[0026] Further embodiments of the inventive method consist of coating with at least one of the following coating materials:

[0027] - Polyurethane;

[0028] - Polyacrylate .

[0029] Further embodiments of the inventive method consist of adding a flame-retardant substance, such as antimony trioxide, to the coating material. Further embodiments of the inventive method consist of using a silver paste as the electrically conductive paste.

[0030] Further embodiments of the inventive method consist in the fact that, after printing the surface textile with the electrically conductive paste, the printed surface textile is coated again, preferably using a polyurethane or a silicone for the recoating.

[0031] Further embodiments of the inventive method consist of laminating the surface textile with an aluminum foil on a reverse side opposite a printed side.

[0032] Further embodiments of the inventive method consist of carrying out the coating step and the printing step multiple times, using, for example, an acrylic adhesive as an intermediate layer, or stacking printed and coated textile surfaces in multiple layers on top of each other.

[0033] Furthermore, the invention relates to a flexible, frequency-selective absorber comprising:

[0034] - woven flat textile with a top layer on one side and

[0035] - an absorption structure layer comprising an absorption structure formed by means of electrically conductive paste printed onto the top layer, wherein the absorption structure fulfills predetermined absorption and / or reflection characteristics in order to be able to frequency-selectively absorb electromagnetic signals incident on the absorber.

[0036] One embodiment of the flexible, frequency-selective absorber consists of a woven fabric made of at least one of the following materials:

[0037] - Polyester;

[0038] - Polyamide;

[0039] - Glass fibers;

[0040] - Aramid fibers.

[0041] Further variations of the flexible, frequency-selective absorber consist of the top layer being coated with at least one of the following coating materials:

[0042] - Polyurethane;

[0043] - Polyacrylate .

[0044] Further variations of the flexible, frequency-selective absorber include a flame-retardant substance, such as antimony trioxide, in the top layer. Another variation involves the electrically conductive paste containing silver.

[0045] Further embodiments of the flexible, frequency-selective absorber consist of a cover layer to cover the electrically conductive paste printed on the surface textile, wherein the cover layer preferably consists of polyurethane or silicone.

[0046] Other variations of the flexible, frequency-selective absorber consist of having an aluminum foil on a back side opposite a printed side of the surface textile.

[0047] Other variations of the flexible, frequency-selective absorber consist of having several absorption structure layers with different absorption properties, with, for example, an acrylic adhesive being used as an intermediate layer.

[0048] The aforementioned implementations of the method can be used in any combination, provided the combinations do not contradict each other. The same applies to the implementation variants of the flexible, frequency-selective absorber. BRIEF DESCRIPTION OF THE FIGURES

[0049] Exemplary representations of the present invention are explained in more detail below with reference to the figures. These serve only for illustration and are not to be interpreted restrictively. They show

[0050] Fig. 1 shows a block diagram with the process steps of an embodiment of the manufacturing process according to the invention and

[0051] Fig. 2 shows a cross-section through a flexible, frequency-selective absorber according to the invention.

[0052] DETAILED DESCRIPTION OF THE INVENTION

[0053] Fig. 1 shows a block diagram of the manufacturing process according to the invention with the main process steps I to III for the production of a flexible, frequency-selective absorber.

[0054] In general, the production of the flexible, frequency-selective absorber 1 (Fig. 4) requires a dielectric medium and a conductive layer with a suitable structure. In a first process step I (Fig. 1) according to the invention, a woven fabric 2 (Fig. 2) – for example, made of polyester, polyamide, or glass fiber in a plain weave, or optionally a combination of these materials – is coated with a top layer 3 (Fig. 2) of a coating material. To achieve a smooth top layer 3, the fabric 2 is coated with polyurethane or polyacrylate as the coating material using a doctor blade or foulard process in a stenter frame. Preferably, the coating material also contains flame-retardant substances such as antimony trioxide or similar substances.

[0055] The surface textile l 2 coated with the top layer 3 is

[0056] In a second process step II (Fig. 1), an absorption structure is printed, for example, using a rotary printing process with a conductive paste—such as a silver paste—to create the absorption structure layer 4 (Fig. 2). An example of such a paste is known under the trademark Micromax™ Intexar™ PE874 from DuPont. A polyester screen with a thread count of 120–77 threads / cm is used for the rotary printing process.

[0057] Finally, in a third procedural step III,

[0058] - The surface textile l 2, coated with surface 3 and provided with the absorption structure layer 4, was dried in a stent at approximately 130 °C. This temperature is suitable for both conventional surface textiles and polyurethane pre-coatings. The thickness of the absorption structure layer 4 is approximately 1 micrometer, so that a two-dimensional structure can be assumed in the simulation.

[0059] In a further embodiment of the manufacturing process according to the invention, the flexible fabric 2 is laminated with an aluminum foil 6 on a reverse side 8 of the fabric 2 opposite the printed side.

[0060] Another embodiment of the manufacturing process according to the invention consists in providing the absorption structure layer 4 with a cover layer 5 (Fig. 2). This makes the

[0061] Absorption structure layer 4 protected against corrosion, wherein the cover layer 5 consists, for example, of polyurethane or silicone.

[0062] The surface textile 2 coated with a cover layer 3 forms a dielectric that has a significant influence on absorption. In particular, the absorption layer can be optimized by selecting the thickness of the cover layer 3, i.e., by selecting the surface textile 2 (substrate) as well as the thickness of the cover layer 3. The dielectric constant of the material also influences the absorption layer. The corresponding constant can be determined by measuring the raw material. In Fig. 1, a decision block E is provided between process steps II and III. If several layers with different absorption structures are to be realized on the surface textile 2, process steps I and II must be repeated as many times as absorption structure layers 4 are to be produced.

[0063] This allows multilayer structures to be created by stacking several absorption structure layers 4 in order to obtain a broader absorption spectrum. The corresponding effects (absorption spectrum, etc.) can be calculated numerically in the same way as described above.

[0064] The multi-layered sheets can be industrially produced by laminating using acrylic adhesives or by lamination using the hot melt process.

[0065] The metamaterials specified in the introductory description are used for the absorption structure layers. These are manufactured as periodic, conductive structures and applied to a dielectric with or without backing, allowing for the design of predetermined frequency responses for absorption. Reflection attenuations of approximately 20 dB (peak) can be verified through measurements. For low frequencies in the GHz range, the absorption structure is in the size range of a few millimeters ("sub-wavelength"), thus enabling simple production. Figure 2 shows a cross-section through a flexible, frequency-selective absorber 1, which is preferably manufactured according to the manufacturing process described above.

[0066] The absorber 1 consists of a woven fabric 2 which is coated with a top layer 3 on one side of the fabric 2.

[0067] An absorption structure layer 4 is printed onto the upper layer 3, which has an absorption structure that is realized by means of electrically conductive paste printed onto the upper layer 3, wherein the absorption structure fulfills predetermined absorption and / or reflection characteristics in order to be able to absorb electromagnetic signals incident on the absorber in a frequency-selective manner.

[0068] The woven fabric 2, for example, consists of at least one of the following materials:

[0069] - Polyester;

[0070] - Polyamide;

[0071] - Glass fibers;

[0072] - Aramid fibers.

[0073] Furthermore, the top layer 3 consists, for example, of at least one of the following coating materials:

[0074] - Polyurethane; Polyacrylate .

[0075] Another embodiment of the flexible, frequency-selective absorber 1 consists in the upper layer 3 comprising a flame-retardant substance, such as antimony trioxide.

[0076] The electrically conductive paste contains, for example, silver.

[0077] Finally, a cover layer 5 is provided to cover the electrically conductive paste printed on the surface textile 2, wherein the cover layer 5 preferably consists of polyurethane or silicone.

[0078] For example, an aluminum foil 6 is present on a reverse side 7 opposite a printed side of the surface textile 2.

[0079] Finally, it is conceivable that several absorption structure layers 4 with different absorption properties are present for broadband absorption or reflection of signal components, with, for example, an acrylic adhesive being used as an intermediate layer 8. 17 REFERENCE MARK

[0080] 1 flexible, frequency-selective absorber

[0081] 2. Surface textile

[0082] 3 upper class

[0083] 4 Absorption structure layer

[0084] 5 Top layer

[0085] 6 aluminum foil

[0086] 7 Back

[0087] 8 Intermediate shift

[0088] I, II, III (Main) -Procedure steps

[0089] E Decision block

Claims

PATENT CLAIMS 1. Method for the production of flexible, frequency-selective absorbers (1) , comprising the following steps: - Coating a woven flat textile (2) with a top layer (3) made of a coating material, - Printing the coated surface textile (2) with an absorption structure using an electrically conductive paste as the absorption structure layer (4) , wherein the absorption structure fulfills predetermined absorption and / or reflection characteristics in order to be able to absorb electromagnetic signals incident on the absorber in a frequency-selective manner, and - Drying of the surface textile printed with the absorption structure (2) by means of heat radiation.

2. Method according to claim 1, characterized in that the woven fabric (2) consists of at least one of the following materials: - Polyester; - Polyamide; - Fiber optics; - Aramid fibers.

3. Method according to claim 1 or 2, characterized in that for the coating step the woven fabric (2) is stretched in a tensioning frame and that the coating is carried out using a squeegee or a foulard method.

4. Method according to one of the preceding claims, characterized in that the coating is carried out with at least one of the following coating materials: - Polyurethane; - Polyacrylate.

5. Method according to claim 4, characterized in that a flame-retardant substance, such as antimony trioxide, is added to the coating material.

6. Method according to one of the preceding claims, characterized in that the electrically conductive paste is a silver paste.

7. Method according to one of the preceding claims, characterized in that after printing the surface textile (2) with the electrically conductive paste, the printed surface textile (2) is coated again, preferably using a polyurethane or a silicone for the recoating.

8. Method according to one of the preceding claims, characterized in that the surface textile (2) is laminated with an aluminum foil (6) on a reverse side (8) opposite a printed side.

9. Method according to one of the preceding claims, characterized in that the coating step and the printing step are carried out multiple times, wherein, for example, an acrylic adhesive is used as an intermediate layer (8).

10. Flexible, frequency-selective absorber (1) , comprising: - woven flat textile (2) with a top layer (3) on one side and - an absorption structure layer (4) comprising an absorption structure formed by means of electrically conductive paste printed onto the top layer (3), wherein the absorption structure fulfills predetermined absorption and / or reflection characteristics in order to be able to frequency-selectively absorb electromagnetic signals incident on the absorber.

11. Flexible, frequency-selective absorber (1) according to claim 10, characterized in that the woven surface textile (2) consists of at least one of the following materials: - Polyester; - Polyamide; - Fiber optics; - Aramid fibers.

12. Flexible, frequency-selective absorber (1) according to Claim 10 or 11, characterized in that the upper layer (3) with at least one of the following Coating materials are coated: - Polyurethane; - Polyacrylate.

13. Flexible, frequency-selective absorber (1) according to one of claims 10 to 12, characterized in that the top layer (3) comprises a flame-retardant substance, such as antimony trioxide.

14. Flexible, frequency-selective absorber (1) according to one of claims 10 to 13, characterized in that the electrically conductive paste contains silver.

15. Flexible, frequency-selective absorber (1) according to one of claims 10 to 14, characterized in that a cover layer (5) is provided for covering the electrically conductive paste printed on the surface textile (2), wherein the cover layer (5) preferably consists of polyurethane or silicone.

16. Flexible, frequency-selective absorber (1) according to one of claims 10 to 15, characterized in that an aluminum foil (6) is present on a back side (7) opposite a printed side of the surface textile (2).

17. Flexible, frequency-selective absorber (2) according to one of claims 10 to 16, characterized in that several absorption structure layers (4) with different absorption properties are present, with an intermediate layer ( 8 ) being, for example, a Acrylic glue is used.

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