Electromagnetic interference protection for radomes

Abstract

The present disclosure relates to a cover for at least one antenna emitting or sensing electromagnetic radiation in at least one first frequency band, the cover includes at least one first surface facing the antenna and at least one second surface averted to the antenna, where the cover includes at least one substrate being transmissible for electromagnetic radiation and at least one first coating covering the substrate in at least one first area, the first coating being transmissible for electromagnetic radiation of at least the first frequency band, whereas the first coating is reflective for electromagnetic radiation falling onto the second surface and having a frequency within at least one second frequency band.

Claims

1. A cover for at least one antenna emitting or sensing electromagnetic radiation in at least one first frequency band, being radar frequency, the cover comprising: at least one first surface facing the antenna and at least one second surface averted to the antenna; at least one substrate being transmissible for electromagnetic radiation of the first frequency band and a second frequency band comprising visual light and at least one first coating covering the substrate in at least one first area, the first coating being transmissible for electromagnetic radiation of at least the first frequency band and being reflective for electromagnetic radiation falling onto the second surface and having a frequency within the second frequency band, wherein the first coating acts as a frequency selective surface bandpass filter trimmed such that electromagnetic radiation of the first frequency band is transmitted, whereas radiation in the second frequency band is reflected, and wherein the cover further comprises: at least one covering layer located on a side of the first coating being located averted to the substrate, the covering layer being transparent, at least semitransparent, for the second frequency band, or at least one second coating, at least partly located between the first coating on the one hand and the antenna on the other hand, the second coating being at least partly non transmissible and/or opaque in the second frequency band.

2. The cover according to claim 1, wherein at least one of the antenna is a radar antenna, or the first frequency band is 10 GHz to 130 GHz, 20 GHz to 100 GHz, 20 GHz to 30 GHz, 70 GHz to 80 GHz, 90 GHz to 100 GHz, 24 GHz, 77 GHz, or 93 GHz.

3. The cover according to claim 1, wherein the substrate is transmissible for electromagnetic radiation in at least one third frequency band, wherein the second frequency band is at least partly identical to the third frequency band.

4. The cover according to claim 1, wherein the first coating is at least one of located between the substrate and the antenna or located on the side of the first surface of the substrate.

5. The cover according to claim 1, wherein the first coating is located on the side of the second surface of the substrate.

6. The cover according to claim 5, wherein at least one stress controlling layer is located between the substrate and the first coating.

7. The cover according to claim 1, wherein at least one of: the second coating is at least partly located between the substrate on the one hand and the antenna on the other hand, or the second coating is one or more of at least partly non transmissible, opaque in at least one fourth frequency band or the third frequency band, or transmissible in the first frequency band.

8. The cover according to claim 1, wherein at least one masking layer at least partly covering the first coating or the substrate, wherein the masking layer is at least partly non transmissible or opaque in at least one fifth frequency band, the second frequency band, the third frequency band or the fourth frequency band, or transmissible in the first frequency band.

9. The cover according to claim 1, wherein one or more of the second frequency band, the third frequency band or the fourth frequency band, comprises 384 THz to 789 THz or visual light.

10. The cover according to claim 1, wherein one or more of the second frequency band, the fourth frequency band or the fifth frequency band covers the area of 384 THz to 789 THz, or the third frequency band covers only partly the area of 384 THz to 789 THz.

11. The cover according to claim 1, wherein the covering layer is transparent or at least semitransparent for one or more of the third, fourth, or fifth frequency band.

12. The cover according to claim 1, wherein the substrate comprises at least partly at least one of a thermoplastic material, a polycarbonate, polymethylmethacrylate, polyethylene, polyester, polyvinyl chloride, polypropylene, polystyrene, acrylonitrile butadiene styrene, acrylonitrile ethylene styrene, polyacrylate, or a mixture thereof.

13. The cover according to claim 1, wherein the first coating comprises at least one metallic material, chrome, aluminum, zinc, copper, nickel, vandium, titanium, zirconium, niobium, gold, rhodium, cobalt, manganese, molybdenum, tantalum, silver, or a mixture thereof.

14. The cover according to claim 1, wherein the first coating comprises at least one repetitive pattern, wherein the pattern comprises a plurality of elements being formed as crosses, circles, squares, stars, rectangles, lines, hexagons, ellipsoids, polygons, annulus, semicircles, circular sectors, triquetra, lune, arbelos, spiral, lemniscates, triangles, or oval forms.

15. The cover according to claim 14, wherein the elements are formed by, with each other separated, one or more of openings or gaps within the first coating.

16. The cover according to claim 14, wherein the elements are formed by, with each other separated or not interconnected, areas of the first coating.

17. The cover according to claim 1, wherein the second coating or the mask layer comprises one or more of at least one thermoplastic, Polycarbonate (PC), Acrylonitrile butadiene styrene (ABS), Acrylnitril-Ethylen-Styrol (AES), or Polycarbonate acrylonitrile butadiene styrene (PCABS).

18. The cover according to claim 1, wherein the first coating, when viewed onto the second surface of the cover presents at least one logo, character, number, graphical trademark, trademark, decorative design, or decorative pattern.

19. The cover according to claim 1, wherein the masking layer covers the first coating such that when viewed onto the second surface, only at least a first area of the first coating is visible, wherein the first area has the form of at least one logo, character, number, graphical trademark, trademark, decorative design or decorative pattern, wherein the first area is contiguous or formed by at least partly separated subareas.

20. The cover according to claim 1, wherein at least one third coating is located on the first surface, between the substrate and the first coating, wherein the third coating is electrically insulating.

21. The cover according to claim 1, wherein at least one fourth coating is at least one of located on the second surface or a side of the second surface of the substrate, between the substrate and the first coating or the covering layer, or located on the side of the first coating or the covering layer averted to the substrate, wherein the fourth coating forms a thermal hardcoat including light scattering particles.

22. The cover according to claim 1, wherein at least one of the first coating reflects more than 50%, more than 75%, more than 85%, more than 90%, or more than 95%, the first coating has at least one edge being at least partly curved, or the first coating comprises, in the area of the edge, at least one resistive loading.

23. A method of producing a cover for at least one antenna emitting and/or sensing electromagnetic radiation in at least one first frequency band being radar frequency, especially a cover according to one of the preceding claims, the method comprising: one or more of proving or producing at least one substrate being transmissible for electromagnetic radiation of the first frequency band and a second frequency band comprising visual light; covering the substrate with at least one first coating, wherein the first coating provides a frequency selective surface bandpass filter being transmissible for radiation having a frequency in the first frequency band, wherein as first coating a material being highly reflective for frequencies in the second frequency band is used, wherein the method further comprises: locating at least one covering layer on a side of the first coating being located averted to the substrate, wherein the covering layer is transparent, at least semitransparent, for the second frequency band, or at least partly locating one second coating between the first coating on the one hand and the antenna on the other hand, wherein the second coating is at least partly non transmissible and/or opaque in the second frequency band.

24. The method according to claim 23, wherein covering the substrate with at least one masking layer being non transmissible for electromagnetic radiation in the second frequency band, the substrate being covered with the masking layer before covering the substrate with the first coating, the first coating being located at least partly on the masking layer.

25. The method according to claim 23, wherein the frequency selective surface bandpass filter is produced by structuring of the first coating after its deposition onto the substrate, by laser etching.

26. The method according to claim 23, wherein the structure comprises the forming of a plurality of elements, forming a pattern, wherein the elements comprise, with each other separated, one or more of openings or gaps within the first coating or comprise, with each other separated, areas of the first coating separated by the gaps or openings.

27. The method according to claim 23, wherein the first coating is produced by sputtering or PVD magnetron sputtering deposition.

28. The method according to claim 23, further comprising providing at least one first fourth coating which is hardcoat forming, or at least one stress controlling layer being at least partly located between the substrate and the first coating.

29. The method according to claim 23, further comprising providing at least one second fourth coating which is at least one hard coat forming, being at least partly located on the side of the first coating averted to the substrate and/or at least one covering layer, which is transparent, at least semitransparent, for visual light or electromagnetic radiation in a frequency band comprising at least partly 384 THz to 789 THz.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages of the invention are explained in the following description of preferred embodiments with the help of the following figures:

(2) FIG. 1 shows a schematic cross-sectional view of an inventive cover according to the first embodiments;

(3) FIG. 2 shows a schematic cross-sectional view of a second embodiment of an inventive cover;

(4) FIG. 3a shows a first set of exemplary elements of the pattern to provide a frequency selective surface band pass filter;

(5) FIG. 3b shows a further second set of exemplary elements of the pattern;

(6) FIG. 3c shows a further third set of exemplary elements of the pattern;

(7) FIG. 3d shows a fourth set of exemplary elements of the pattern;

(8) FIG. 3e shows an exemplary first pattern to provide a frequency selective surface band pass filter;

(9) FIG. 4 shows a view on a cover according to the invention;

(10) FIG. 5 shows a schematic cross-sectional view of a third embodiment of an inventive cover;

(11) FIG. 6a shows an exemplary second pattern to provide a frequency selective surface bandpass filter;

(12) FIG. 6b shows an exemplary third pattern to provide a frequency selective surface bandpass filter;

(13) FIG. 6c shows an exemplary fourth pattern to provide a frequency selective surface bandpass filter; and

(14) FIG. 7 shows a diagram showing the correlation between the size of elements within a pattern and the attenuation for electromagnetic correlation of 76 to 77 GHz.

DETAILED DESCRIPTION

(15) FIG. 1 shows a schematic cross-sectional view on a cover 1 according to the invention.

(16) Cover 1 comprises substrate 3, for example comprising molded clear polycarbonate.

(17) On the side of a first surface 5 of the substrate 3, a first coating 7 in form of a reflective patterned metallic coating, is provided. On the side of the first coating 7, being opposite to the substrate 3, a second coating 9, preferably comprising a molded dark polycarbonate material is provided. By the cover 1, an antenna in form of a radar unit 11 is covered. In the first embodiment between the first coating 7 and the substrate 3, a third coating 13 in form of an insulating coating is provided. Finally, on the side of the substrate 3 being opposite to the first coating 7 and the third coating 13, a fourth coating in form of a thermal hardcoat 15 is provided.

(18) Cover 1 may be produced by first providing the substrate 3, then depositing the third coating 13 onto the substrate 3 before depositing the first coating 7, for example by PVD magnetron sputtering. The first coating 7 includes a highly reflective metal material like chrome or aluminium. Before the second coating 9 is deposited on the first coating 7, the first coating 7 is structured, for example by a CNC femtosecond laser. The laser allows to laser etch a pattern into the first coating 7 that provides a frequency selective surface band pass filter. The structure is described in more detail with the help of FIGS. 3a to 3e later.

(19) This allows the first coating 7 to be transmissible for electromagnetic radiation in a first frequency band, especially that is emitted by the radar unit 11. However, the first coating 7 is highly reflective for electromagnetic radiation in a second frequency band, especially for visual electromagnetic radiation falling onto the first coating.

(20) With the substrate 3 being transmissible for radiation in the first frequency band as well as radiation in the second frequency band, especially visual light, as well as electromagnetic radiation produced by the radar unit 11, the cover 1 does not negatively influence the functionality of the radar unit 11 but allows to provide an aesthetic visual outer appearance of cover 1.

(21) To reach this aim, the second coating 9 is transmissible for the radiation of the first frequency band, so that radiation of the radar unit 11 can pass but is not transmissible for radiation of a third frequency band, that is preferably identical to the second frequency band, so that radiation in the visual wave lengths is blocked. Thus, a person 16 looking at the cover from a direction 17, sees an area 19 that is highly reflective and a more or less black area 21, screening the radar unit 11 from any visual light, so that a user 16 cannot see the radar unit 11 but only sees the structure or logo provided by the first coating 7. Especially the area 21 appears to be black, whereas the area 19 has a lustrous appearance.

(22) In FIG. 2, a second embodiment of a claimed cover 100 is shown. The elements of cover 100, having the same functionalities as the respective elements in cover 1, have the same reference signs, however increased by 100. In comparison to cover 1, in cover 101, the first coating 107 is not restricted to a respective area but nearly covers the complete substrate 103.

(23) To generate the outer appearance of the wanted logo or emblem, additionally masking layer 123 is used. A masking layer 123 is provided between the substrate 103 and the first coating 107. The masking layer 123 is, similar to the second coatings 9 or 109, non transmissible for a radiation in a fifth frequency band, especially the second frequency band, but transmissible for radiation in the first frequency band. Thus the masking layer 123 provides a black area for a user 16 looking at cover 101 from the direction 117.

(24) Thus, similar to the cover 1, the area 119 provides a lustrous appearance whereas the area 121 provides an appearance as black for a user 116. Again, the masking layer 123 is chosen such that it is transmissible for the electro-magnetic radiation provided by the radar unit 111, whereas it is non-transmissible for any electromagnetic radiation in the visual spectrum.

(25) As all light falling onto the substrate 103 is either reflected or blocked by coating 107 and masking layer 123, respectively, other second coatings 109 may be used. The second coating 109 might be completely omitted or might provide a protection for the coating 107 without the necessity of being non transmissible for radiation in the visual range as long as being transmissible for radiation in the first frequency band used by radar unit 11.

(26) As described before, the first coating 7, 107 provide a frequency selective surface band pass filter. Such a filter is a thin, repetitive surface designed to reflect, transmit or absorb electromagnetic fields based on the different frequencies of the fields. In the inventive cover 1, 101 the frequency selective surface is trimmed such that electromagnetic radiation of the first frequency band (used by unit 11, 111) is transmitted, whereas radiation in the second frequency band, especially visual light, is reflected. This aim is reached by providing a highly reflective coating being made of a highly reflective material like chrome or aluminium. Into this coating, a structure or pattern is formed, especially etched, to provide the transmissibility for the first frequency band.

(27) Such a pattern consists of elements having dimensions in the size smaller than 50 μm to not be seen too easily. Preferably elements having dimensions being greater than 50 μm and having distances of a few μm.

(28) The elements might have the form of crosses 201a, 201b, either completely filled like element 201b or having a center being left open like elements 201a. Also star form elements 203a, 203b or 203c might be used. Again these elements 203a, 203b, 203c, 203d might have left open centers like elements 203a, 203d or might be solid like elements 203b, 203c. Further examples of elements being formed iteratively in the pattern might comprise solid or left open circle form elements 205a, 205b, rectangular or quadratic form elements 207a, 207b and or hexagonally formed elements 209a, 209b as well as line elements 211.

(29) In FIG. 3a, a schematic detail of a pattern 213 formed in coatings 7, 107 to provide a band pass filter, is shown. The pattern 213 comprises a repetitive structure in which the elements 215, here cross elements, are formed in a repetitive form.

(30) In FIG. 4, a perspective view onto a cover 301 of the invention is shown. As can be seen in FIG. 3, the area 321 appears to be black whereas areas 319 allow a view onto the first coating 307, providing a lustrous appearance. In this way the visual appearance is increased as the star logo is provided and simultaneously the in FIG. 4 not shown radar unit is covered and not visible for the viewer.

(31) In FIG. 5, a schematic cross-sectional view onto a third embodiment of an inventive cover 401 is shown. In contrast to the embodiments shown in FIGS. 1 and 2 as described before, a substrate 403 in form of a moulded part made for example of a dark, i.e. for visual light opaque ABS, AES, PCABS, or polycarbonate is located on the side of the cover 401 facing the radar unit 411.

(32) This means in turn that the first coating 407 is located on the side of the substrate 403 being averted to the radar unit 411.

(33) Between the substrate 403 and the first coating 407, an optional first fourth coating in form of a hardcoat 415 is located. Furthermore, a stress controlling layer 423 may be also located between the substrate 403 and the first coating 407. By the stress controlling layer 423 respective different mechanical characteristics of the substrate 403 and the first coating 407 and/or the hardcoat 415 are compensated. For example, the substrate 403 and/or the hardcoat 415 might have different thermal expansions. By the layer 423, these are compensated such that the forming of cracks or a separation of the first coating 407 from the substrate and/or the hardcoat 415 is avoided.

(34) The first coating 407 is covered by a covering layer 425 being transparent or semitransparent for electromagnetic radiation in the visual range. The covering layer 427 might be covered by a second fourth coating in form of a hardcoat 427, optionally including light scattering particles. With the light scattering particles, the overall visual impression of the cover 401 is increased as the three-dimensional impression for a viewer is increased and the emblem formed by the pattern within the first coating 407 is visible over a broader angle of view.

(35) In FIGS. 6a to 6c, alternative patterns 513a, 513b, 513c, formed in the first coating 7, 107 or 407 as described above are shown. The pattern 513a shown in FIG. 6a is formed by a plurality of elements 515a, forming metallic “islands” that are separated from each other by openings or gaps 517a.

(36) The patterns 513a, 513b and 513c differ from each other that in FIG. 6a, the elements 515a have a square form whereas the elements 515b of the pattern 513b have the form of triangles whereas the elements 515c of pattern 513c have the form of pentagons. The openings 517b, 515c, that have been formed in the metallic coating by laser etching, have respective different forms compared to the openings 517a. It has been found by the inventors that the effectiveness of the frequency bandpass filter formed by the patterns 513a, 513b and 513c is increased, due to the separation of the metallic elements 515a, 515b and 515c, shown in white colours in FIGS. 6a to 6c. The respective gaps separating the elements 515a, 515b and 515c from each other are shown in black colours in FIGS. 6a to 6c.

(37) As shown in FIG. 7, the inventors have compared the respective dimensions of the elements with respect to the attenuation for electromagnetic radiation in the frequency area of 76 to 77 GHz. The result is shown in FIG. 7. As can be taken from FIG. 7, the size of the elements 515a, 515b and 515c should be <400 μm, even better <100 μm. Test data suggest that an attenuation is depending on the size of the longest line segment and/or the longest geometrical dimension of the respective element. This seems to be especially the case for irregularly formed elements. The inventors assume that by these dimensions, the electrical disconnection of the metallic film elements is more efficient.

(38) The attenuation seems to depend, especially for regularly formed elements, secondarily on the area covered by the respective elements. Based on the before described sizes the elements should have an area of less than 1600 μm.sup.2, even better less than 1000 μm.sup.2.

(39) Furthermore, it has been found that the openings 517a, 517b and 517c should have dimensions, especially with less than 8 μm, even better less than 5 μm. In this way the openings 517a, 517b and 517c, preferably formed by ablation, cannot be easily seen by a user and thus the overall visual impression is not negatively influenced.

(40) As shown in FIG. 7, the attenuation for the size of the elements of 500 μm, having an attenuation of about 3 db, can be reduced to 0.3 db when reducing the size of the elements to less than 100 μm. Thus, when comparing this attenuation to the attenuation of a polycarbonate hardcoat and/or hardcoated polycarbonate, it can be seen that the attenuation comes close to this attenuation without a metal coating.

(41) The patterns 513a, 513b and 513c might be formed by applying an electrically conductive chrome coating, using PVD magnetron sputtering deposition to the hardcoated polycarbonate substrate. The respective openings 517a, 517b and 517c can be formed by placing the coated substrate on a CNC femtosecond laser system. By the laser system, the patterns are laser edged into the coating allowing it to act as a radome.

(42) Examples might be bidirectional lines forming 10 μm gaps with 500 μm metal squares in between, as shown in FIG. 6a. Optionally, the gaps might have a width of 8 μm, preferably 6 μm, most preferably 3 μm, whereas the element 515a might have a side length of 200 μm, preferably 100 μm, most preferably less than 30 μm. Especially to reach the structure shown in FIG. 5, the coated substrate is then placed in a moulding machine and a rear section of the badge is formed, encapsulating the first coating and completing the radome in form of the cover 401.

(43) The features disclosed in the specification, the claims as well as the figures, can be essential for the claimed invention both taken separately or in combination with its different embodiments.

REFERENCE SIGN LIST

(44) 1 cover 3 substrate 5 surface 7 1st coating 9 2nd coating 11 radar unit 13 3rd coating 15 thermal hardcoat 16 person 17 direction 19 area 21 area 101 cover 103 substrate 105 surface 107 1st coating 109 2nd coating 111 radar unit 113 3rd coating 115 thermal hardcoat 116 person 117 direction 119 area 121 area 123 masking layer 201a, 201b, 201c, 201d cross element 203a, 203b, 203c, 203d star element 205a, 205b circle element 207a, 207b rectangle element 209a, 209b hexagonal element 211 line element 213 pattern 301 cover 303 substrate 308 coating 319 area 321 area 401 cover 403 substrate 407 first coating 411 radar unit 415 hardcoat 423 stress controlling layer 425 covering layer 427 hardcoat 513a, 513b, 513c pattern 515a, 515b, 515c elements 517a, 517b, 517c opening