Multi-layer electromagnetic wave absorber

Abstract

The invention relates to an electromagnetic wave absorber having a multi-layer structure. The electromagnetic wave absorber comprises a primary surface (1) on which the electromagnetic wave is incident, a secondary surface (2) provided opposite the primary surface (1), and, arranged in sequence between the primary surface (1) and the secondary surface (2), a first dielectric layer (10), an absorber layer (20) with a thickness in the range of 75-140 nm, a second dielectric layer (30), and a substrate (40).

Description

[0001] MULTI-LAYER ELECTROMAGNETIC WAVE ABSORBER

[0002] TECHNICAL FIELD

[0003] The present invention relates to a multi-layer electromagnetic wave absorber.

[0004] STATE OF THE ART

[0005] After the discovery of microwave ranges in the electromagnetic spectrum, certain radar systems have been used to determine the size, altitude, direction, or velocity of objects. During the Second World War, the scenario changed significantly, leading to the development of Radar Absorbing Materials (RAMs). Consequently, invisibility technology and radar cross-section terminology have emerged in scientific research. To reduce the detectability of objects in radar detection systems, lowering the radar cross-section plays an important role. Dielectric and magnetic materials with radar-absorbing properties have been developed for the absorption of microwaves. To broaden the frequency range (bandwidth) of absorption, many materials have been proposed by researchers to date. Almost all of the proposed materials are optically opaque and thus cannot be applied to regions where transparency is required.

[0006] EP4202141A1 relates to a technique for making the thickness of a radio wave-absorbing layer thin. Specifically, EP4202141A1 discloses a radio wave absorber that absorbs radio waves in a certain frequency band, has a visible light transmittance of 50% or higher, and is provided with a first main surface on which radio waves are incident, and a second main surface on the opposite side of the first main surface. This layered structure includes, in order from the first main surface toward the second main surface, a first dielectric layer, a conductive layer, a second dielectric layer, a radio wave-reflecting layer, and a third dielectric layer. The conductive layer consists of a series of conductors and gaps arranged to separate these conductors, with the conductors being isolated from one another.

[0007] BRIEF SUMMARY OF THE INVENTION

[0008] The object of the invention is to provide a multi-layer transparent electromagnetic wave absorber. To achieve this objective, the invention concerns an electromagnetic wave absorber with a multi-layer structure. The electromagnetic wave absorber comprises: a primary surface on which the electromagnetic wave is incident, a secondary surface provided opposite the primary surface, and, arranged in order between the primary surface and the secondary surface, a first dielectric layer, an absorber layer, a second dielectric layer, a substrate, and a metallic reflection layer. The absorber layer applied on the first surface provides broadband absorption in the microwave region.

[0009] In a preferred embodiment of the invention, a metallic reflection layer is provided adjacent to the substrate. In this way, electromagnetic waves that pass through the absorber layer are reflected back into the absorber layer by the metallic layer on the secondary surface, thereby increasing the total amount of absorption. Additionally, the structure acquires a reflective property for electromagnetic waves in the infrared region due to the metallic layer applied to the secondary surface.

[0010] In a preferred embodiment of the invention, the absorber layer is ITO (indium tin oxide). Thus, it can be produced on a wide area of glass, polycarbonate, and acrylic surfaces.

[0011] In a preferred embodiment of the invention, the oxygen level of the ITO is in the range of 4-10 seem. By this means, the ITO layer can acquire different optical and electrical properties at different oxygen contents. While the optical transmittance can be adjusted according to the amount of oxygen in the layer, the number of free electrons it contains can also vary. The target electromagnetic absorption property in the microwave region is directly related to the free electrons of the absorber layer.

[0012] In a preferred embodiment of the invention, its visible light transmittance is 50% or higher. This creates an advantageous use in areas where optical transparency is important in addition to electromagnetic wave absorption. These materials can absorb electromagnetic waves in the microwave region to evade radar systems, while still transmitting light in the visible region. Hence, the object / environment behind the invention can be seen by the naked eye but is less detectable by radar systems. This feature is useful in military applications and other areas requiring confidentiality. For example, it reduces the radar cross-section of defense industry vehicles’ cockpit sections while providing visibility to the driver or pilot. In a preferred embodiment of the invention, the first dielectric layer contains SiOx. Thus, it protects the absorber layer from external environmental effects. The thickness of the layer is designed to maximize transmittance in the visible region.

[0013] In a preferred embodiment of the invention, the second dielectric layer contains SiOx. In this way, the adhesion of the absorber layer to the substrate material is increased, thereby enhancing the mechanical durability of the entire structure.

[0014] In a preferred embodiment of the invention, the substrate contains polycarbonate. Polycarbonate is a material that is easy to shape and exhibits high mechanical strength. Furthermore, it has 90% light transmittance in the visible region and a 40% absorption performance at radar frequencies.

[0015] In a preferred embodiment of the invention, the reflection layer comprises a third dielectric layer, a metallic layer, and a fourth dielectric layer. Thus, a layer structure can be designed that has high microwave and infrared reflectivity and is transparent in the visible region.

[0016] In a preferred embodiment of the invention, the metallic layer contains silver. Hence, a layer structure can be designed with high microwave and infrared reflectivity and transparency in the visible region by using a silver layer.

[0017] In a preferred embodiment of the invention, the reflection layer has a thickness in the range of 8- 12 nm. This ensures that the reflection layer has maximum visible transmittance.

[0018] In a preferred embodiment of the invention, the ratio of the distance from the absorber layer to the surface of the substrate facing the absorber layer, to the distance from the substrate to the metallic layer-facing side is in the range of 1 :3 to 1 :4. Thus, by reflecting back the electromagnetic wave that has passed through the absorber layer once again via the metallic layer into the absorber layer for absorption, a super absorber structure is achieved. We believe this may be added as a future claim. Therefore, we suggest removing it from the claims and keeping it in the short description.

[0019] In a preferred embodiment of the invention, the thickness of the third dielectric layer is in the range of 35-40 nm. This ensures that the reflection layer has maximum visible transmittance. In a preferred embodiment of the invention, the thickness of the fourth dielectric layer is in the range of 40-45 nm. Thus, at these specified total thicknesses of the fourth dielectric layer, maximum visible transmittance of the reflection layer is achieved.

[0020] In a preferred embodiment of the invention, the frequency of the electromagnetic wave that is incident from the first surface is in the range of 12-18 GHz. This provides an electromagnetic wave absorber for a high-frequency range.

[0021] BRIEF DESCRIPTION OFTHE FIGURES

[0022] Figure 1 is a schematic representation of the electromagnetic wave absorber according to the invention.

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] In this detailed description, the inventive development is described with references to examples, without imposing any limitation, and solely to better explain the subject matter.

[0025] Figure 1 schematically shows the layer sequence of the electromagnetic wave absorber according to the invention. The electromagnetic wave absorber comprises a primary surface (1 ), on which the electromagnetic wave is incident, and a secondary surface (2) provided opposite the primary surface (1). The electromagnetic wave incident from the primary surface (1) passes through a first dielectric layer (10) in sequence. The first dielectric layer (10) contains SiOx and has a thickness in the range of 75-85 nm. The electromagnetic wave passing through the first dielectric layer (10) then reaches an absorber layer (20), where a portion of it is absorbed by the absorber layer (20). The absorber layer (20) contains ITO and has a thickness ranging from 75 to 300 nm. The oxygen percentage in the ITO is in the range of 4-10 seem. Apart from the amount absorbed within the absorber layer (20), the remaining portion of the electromagnetic wave is transmitted to a third dielectric layer (30). The third dielectric layer (30) contains SiOx and has a thickness of 9.5-10.5 nm. Behind the third dielectric layer (30), a substrate (40) made of polycarbonate is provided. The substrate (40) has a thickness in the range of 2.5 mm to 3 mm. A metallic layer (50) is provided on the rear side of the substrate (40). The reflection layer (50) exhibits optical transparency. The reflection layer (50) comprises multiple layers. Within the reflection layer (50), there is a third dielectric layer (52) containing TiOx, SixNy, ZnAlOx with a thickness of 37 nm. The electromagnetic wave passing through the third dielectric layer (52) reaches a metallic layer (54), from which it is reflected back to the absorber layer (20). The metallic layer (54) contains silver and has a thickness of 10 nm. Behind the metallic layer (54) is a fourth dielectric layer (56) containing TiOx, SixNy, ZnAlOx with a thickness of 41 nm. The outward-facing surface of the fourth dielectric layer (56) forms the secondary surface (2).

[0026] In an example multi-layer electromagnetic wave absorber, the first dielectric layer (10) contains SiOx and has a thickness of 78 nm. Behind the first dielectric layer (10), there is an absorber layer (20) containing ITO with an oxygen value of 4 seem and a thickness of TSTl .7 nm. Behind the absorber layer (20), there is a second dielectric layer (30) containing SiOx with a thickness of 10 nm. Behind the second dielectric layer (30), there is a substrate (40) containing polycarbonate with a thickness of 2.9 mm. On the rear face of the substrate (40), the reflection layer (50) is arranged in the order of a third dielectric layer (52), a metallic layer (54), and a fourth dielectric layer (56). The third dielectric layer consists of 3 nm TiOx, 23 nm SixNy, and 11 nm ZnAlOx layers. The metallic layer (54) is 10 nm thick and contains silver. The fourth dielectric layer (56) consists of 11 nm ZnAlOx, 26 nm SixNy, and 4 nm TiOx layers, in sequence. Tests conducted with this example electromagnetic wave absorber achieved a surface resistance value of 60 ohms / sq and a transparent material that exhibits 88% absorption capability in the Ku band (12-18 GHz) frequency range. The visible region transmittance of the material was determined to be 52.9%.

[0027] In an alternative example multi-layer electromagnetic wave absorber, the first dielectric layer (10) contains SiOx and has a thickness of 85 nm. Behind the first dielectric layer (10), there is an absorber layer (20) containing ITO with an oxygen value of 4 seem and a thickness of 157 nm. Behind the absorber layer (20), there is a second dielectric layer (30) containing SiOx with a thickness of 10 nm. Behind the second dielectric layer (30), there is a substrate (40) containing polycarbonate with a thickness of 2.9 mm. On the rear face of the substrate (40), the reflection layer (50) is arranged in the order of a third dielectric layer (52), a metallic layer (54), and a fourth dielectric layer (56). The third dielectric layer consists of 3 nm TiOx, 23 nm SixNy, and 11 nm ZnAlOx. The metallic layer (54) is 10 nm thick and contains silver. The fourth dielectric layer (56) consists of 11 nm ZnAlOx, 26 nm SixNy, and 4 nm TiOx, in sequence. Tests conducted with this example electromagnetic wave absorber achieved a surface resistance value of 90 ohms / sq and a transparent material that exhibits 85% absorption capability in the Ku band (12-18 GHz) frequency range. The visible region transmittance of the material was determined to be 80.5%.

[0028] In another alternative example multi-layer electromagnetic wave absorber, the first dielectric layer (10) contains SiOx and has a thickness of 78 nm. Behind the first dielectric layer (10), there is an absorber layer (20) containing ITO with an oxygen value of 4 seem and a thickness of 78.6 nm. Behind the absorber layer (20), there is a second dielectric layer (30) containing SiOx with a thickness of 10 nm. Behind the second dielectric layer (30), there is a substrate (40) containing polycarbonate with a thickness of 2.9 mm. On the rear face of the substrate (40), the reflection layer (50) is arranged in the order of a third dielectric layer (52), a metallic layer (54), and a fourth dielectric layer (56). The third dielectric layer consists of 3 nm TiOx, 23 nm SixNy, and 11 nm ZnAlOx. The metallic layer (54) is 10 nm thick and contains silver. The fourth dielectric layer (56) consists of 11 nm ZnAlOx, 26 nm SixNy, and 4 nm TiOx, in sequence. Tests with this example electromagnetic wave absorber revealed that the surface resistance exceeded 200 ohms / sq, and a transparent material demonstrating 98% absorption capability in the Ku band (12-18 GHz) frequency range was obtained. The visible region transmittance of the material was determined to be 76.7%.

[0029] In an alternative example multi-layer electromagnetic wave absorber, the first dielectric layer (10) contains SiOx and has a thickness of 80 nm. Behind the first dielectric layer (10), there is an absorber layer (20) containing ITO with an oxygen value of 6 seem and a thickness of 137 nm. Behind the absorber layer (20), there is a second dielectric layer (30) containing SiOx with a thickness of 10 nm. Behind the second dielectric layer (30), there is a substrate (40) containing polycarbonate with a thickness of 2.9 mm. On the rear face of the substrate (40), the reflection layer (50) is arranged in the order of a third dielectric layer (52), a metallic layer (54), and a fourth dielectric layer (56). The third dielectric layer consists of 3 nm TiOx, 23 nm SixNy, and 11 nm ZnAlOx. The metallic layer (54) is 10 nm thick and contains silver. The fourth dielectric layer (56) consists of 11 nm ZnAlOx, 26 nm SixNy, and 4 nm TiOx, in sequence. Tests with this example electromagnetic wave absorber achieved a surface resistance of 65 ohms / sq and resulted in a transparent material with 85% absorption capability in the Ku band (12-18 GHz) frequency range. The visible region transmittance of the material was determined to be 86%.

[0030] In an alternative example multi-layer electromagnetic wave absorber, the first dielectric layer (10) contains SiOx and has a thickness of 80 nm. Behind the first dielectric layer (10), there is an absorber layer (20) containing ITO with an oxygen value of 6 seem and a thickness of 130 nm. Behind the absorber layer (20), there is a second dielectric layer (30) containing SiOx with a thickness of 10 nm. Behind the second dielectric layer (30), there is a substrate (40) containing polycarbonate with a thickness of 2.9 mm. On the rear face of the substrate (40), the reflection layer (50) is arranged in the order of a third dielectric layer (52), a metallic layer (54), and a fourth dielectric layer (56). The third dielectric layer consists of 3 nm TiOx, 23 nm SixNy, and 11 nm ZnAlOx. The metallic layer (54) is 10 nm thick and contains silver. The fourth dielectric layer (56) consists of 11 nm ZnAlOx, 26 nm SixNy, and 4 nm TiOx, in sequence. Tests with this example electromagnetic wave absorber revealed that the surface resistance exceeded 100 ohms / sq, and a transparent material with 92% absorption capability in the Ku band (12-18 GHz) frequency range was obtained. The visible region transmittance of the material was determined to be 87%.

[0031] In an alternative example multi-layer electromagnetic wave absorber, the first dielectric layer (10) contains SiOx and has a thickness of 80 nm. Behind the first dielectric layer (10), there is an absorber layer (20) containing ITO with an oxygen value of 6 seem and a thickness of 142 nm. Behind the absorber layer (20), there is a second dielectric layer (30) containing SiOx with a thickness of 10 nm. Behind the second dielectric layer (30), there is a substrate (40) containing polycarbonate with a thickness of 2.9 mm. On the rear face of the substrate (40), the reflection layer (50) is arranged in the order of a third dielectric layer (52), a metallic layer (54), and a fourth dielectric layer (56). The third dielectric layer consists of 3 nm TiOx, 23 nm SixNy, and 11 nm ZnAlOx. The metallic layer (54) is 10 nm thick and contains silver. The fourth dielectric layer (56) consists of 11 nm ZnAlOx, 26 nm SixNy, and 4 nm TiOx, in sequence. Tests with this example electromagnetic wave absorber revealed that the surface resistance exceeded 200 ohms / sq, and a transparent material with 95% absorption capability in the Ku band (12-18 GHz) frequency range was obtained. The visible region transmittance of the material was determined to be 68%.

[0032] REFERENCE NUMERALS

[0033] 1 Primary Surface

[0034] 2 Secondary Surface

[0035] 10 First Dielectric Layer

[0036] 20 Absorber Layer

[0037] 30 Second Dielectric Layer

[0038] 40 Substrate

[0039] 50 Reflection Layer

[0040] 52 Third Dielectric Layer

[0041] 54 Metallic Layer

[0042] 56 Fourth Dielectric Layer

Claims

CLAIMS1 . A multi-layer electromagnetic wave absorber, characterized by a primary surface (1 ) on which the electromagnetic wave is incident, a secondary surface (2) provided opposite the primary surface (1), a first dielectric layer (10) provided in sequence between the primary surface (1) and the secondary surface (2), an absorber layer (20) with a thickness in the range of 75-140 nm, a second dielectric layer (30), and a substrate (40).

2. The electromagnetic wave absorber according to Claim 1 , wherein a metallic reflection layer (50) provided adjacent to the substrate (40).

3. The electromagnetic wave absorber according to any of the preceding claims, wherein the absorber layer (20) contains ITO.

4. The electromagnetic wave absorber according to Claim 3, wherein the oxygen level of the absorber layer (20) is in the range of 4-10 seem.

5. The electromagnetic wave absorber according to Claims 3-4, wherein the thickness of the absorber layer (20) is in the range of 75-300 nm.

6. The electromagnetic wave absorber according to any of the preceding claims, wherein its visible region transmittance is 50% or higher.

7. The electromagnetic wave absorber according to any of the preceding claims, wherein the first dielectric layer (10) contains SiOx.

8. The electromagnetic wave absorber according to any of the preceding claims, wherein the second dielectric layer (30) contains SiOx.

9. The electromagnetic wave absorber according to any of the preceding claims, wherein the substrate (40) contains polycarbonate.

10. The electromagnetic wave absorber according to any of the preceding claims, wherein the reflection layer (50) comprises a third dielectric layer (52), a metallic layer (54), and a fourth dielectric layer (56).11 . The electromagnetic wave absorber according to Claim 10, wherein the metallic layer (54) contains silver.

12. The electromagnetic wave absorber according to Claim 11 , wherein the thickness of the metallic layer (54) is in the range of 8-12 nm.

13. The electromagnetic wave absorber according to any of the preceding claims, wherein the thickness of the third dielectric layer (52) is in the range of 35-40 nm.

14. The electromagnetic wave absorber according to any of the preceding claims, wherein the thickness of the fourth dielectric layer (56) is in the range of 40-45 nm.

15. The electromagnetic wave absorber according to any of the preceding claims, wherein the frequency of the electromagnetic wave incident from the first surface (1 ) is in the range of 12-18 GHz.

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