Metamaterial wave absorber for stealth of radar and microwave radiometer

Abstract

The invention relates to a radar and microwave radiometer stealth-oriented metamaterial wave absorber, which comprises a plurality of basic units in periodic array distribution, and is characterized in that each basic unit comprises four substrates and five conductive layers, the four substrates are sequentially stacked and arranged from bottom to top, and the five conductive layers are arranged among the substrates and at the two ends of the substrates; the five conducting layers are a conducting layer I, a conducting layer II, a conducting layer III, a conducting layer IV and a conducting layer V in sequence from bottom to top; the conductive layer I comprises an outer closed-loop wire and a plurality of inner closed-loop wires arranged in the outer closed-loop wire, and the peripheries of the plurality of inner closed-loop wires are connected through a connecting wire; the conductive layer II and the conductive layer V have the same structure and comprise a conductive thin film, a cross etching region arranged in the conductive thin film and a cross conductive wire located in the cross etching region, and the end part of the cross conductive wire is connected with the conductive thin film; the conductive layer III and the conductive layer IV have the same structure and are conductive films; according to the invention, the stealth facing the radar and the microwave radiometer is realized at the same time, and the absorptivity and the absorption bandwidth are high.

Description

Technical Field

[0001] The present invention belongs to the technical field of absorbers, and particularly relates to a metamaterial absorber for radar and microwave radiometer stealth. Background Art

[0002] With the rapid development of target detection technologies, the technologies in the fields of radar detection and microwave remote sensing in various countries are becoming increasingly advanced, which poses a serious threat to high-value ground targets and also puts forward more stringent stealth requirements for them. Therefore, how to effectively improve the stealth ability of targets has become an important research topic at present. In order to cope with the challenges of the coordinated detection of high-value ground targets by radars and microwave radiometers, electromagnetic stealth technology has emerged and become the key research direction of many research teams.

[0003] As a unique research direction in the field of electromagnetic metamaterials, metamaterial absorbers have promoted a major breakthrough in electromagnetic stealth technology. A metamaterial absorber is a new type of artificial composite material formed by arranging periodically or aperiodically artificial-designed sub-wavelength-scale unit structures, and has advantages such as high-efficiency wave absorption, low profile, strong designability, easy processing and integration, etc., showing broad application prospects in popular fields such as electromagnetic stealth, electromagnetic shielding, and electronic countermeasures, which is of great significance for improving the survival ability of high-value ground targets.

[0004] In recent years, the realization of electromagnetic stealth of targets based on metamaterial absorbers has mainly been oriented towards radar detection, with the goal of reducing the radar cross section of targets. Microwave radiometer stealth refers to a technical system that utilizes the passive detection characteristics of microwave radiometers, combined with their anti-interference and anti-stealth capabilities, to achieve the covert monitoring of targets or break through traditional detection means. Microwave radiometer stealth is an important supplement to radar stealth. However, there is currently no metamaterial absorber that is simultaneously oriented towards radar and microwave radiometer stealth. Therefore, designing a metamaterial absorber for radar and microwave radiometer stealth is of great significance for improving the survival ability of high-value ground targets. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a metamaterial absorber for radar and microwave radiometer stealth, which simultaneously realizes stealth for both radar and microwave radiometers, realizes the reduction of the scattering of electromagnetic waves incident on the target surface and the absorption of the spontaneous microwave radiation of the target, and has high absorption rate and absorption bandwidth.

[0006] An embodiment of the present invention provides a metamaterial absorber for radar and microwave radiometer stealth, including a plurality of basic units distributed in a periodic array, and the basic unit includes 4 substrates stacked in sequence from bottom to top and 5 conductive layers provided between and at both ends of the substrates; The 5 conductive layers are, from bottom to top, conductive layer I, conductive layer II, conductive layer III, conductive layer IV, and conductive layer V; The first conductive layer includes an outer closed-loop wire and a plurality of inner closed-loop wires disposed within the outer closed-loop wire. The outer peripheries of the plurality of inner closed-loop wires are connected by connecting wires. The second conductive layer and the fifth conductive layer have the same structure, including a conductive thin film, a cross etching region disposed within the conductive thin film, and a cross conductive wire located within the cross etching region. The ends of the cross conductive wire are connected to the conductive thin film. The third conductive layer and the fourth conductive layer have the same structure, which is a conductive thin film.

[0007] Preferably, the four substrates stacked in sequence from bottom to top are a first substrate, a second substrate, a third substrate, and a fourth substrate. The second conductive layer is disposed on the lower surface of the second substrate, the third conductive layer is disposed on the lower surface of the third substrate, and the fourth conductive layer is disposed on the upper surface of the third substrate.

[0008] Preferably, the outer closed-loop wire is rectangular, and the inner closed-loop wire is rectangular.

[0009] Preferably, the outer closed-loop wire is square, and the inner closed-loop wire is square.

[0010] Preferably, the number of the inner closed-loop wires is 4. The 4 inner closed-loop wires are distributed in an array, and the connecting wires connect the outermost sides of adjacent inner closed-loop wires.

[0011] Preferably, the substrate is a PET substrate, the relative dielectric constant of the substrate is 3.2, the loss tangent is 0.003, and the thickness h1 is 0.125 mm.

[0012] Preferably, the sheet resistance Rs of the first conductive layer, the second conductive layer, and the fifth conductive layer is 120 Ω / sq, and the sheet resistance Rs of the third conductive layer and the fourth conductive layer is 6 Ω / sq.

[0013] Preferably, the material of the conductive layer is an ITO conductive thin film.

[0014] Preferably, the space between the four substrates is air, and the thickness is 5 mm.

[0015] Preferably, the basic unit is square, the side length is 9 mm, the outer closed-loop wire is square, and the side length is 8.5 mm; The conductive thin films of the second conductive layer and the fifth conductive layer are square, and the side length is 8.5 mm; The conductive thin films of the third conductive layer and the fourth conductive layer are square, and the side length is 9 mm.

[0016] The beneficial effects of the present invention are as follows. The present invention can achieve effective absorption of the target's spontaneous microwave radiation within a wide frequency band. The simulation results show that the present invention can achieve an absorption performance with an absorption rate greater than 90% in the frequency range of 3.74 - 21.6 GHz, and the relative absorption bandwidth can reach 140.99%. By using the metamaterial absorber, the absorption of the target's spontaneous microwave radiation can be realized, making the brightness temperature of the target basically the same as the ambient brightness temperature.

[0017] The present invention can achieve scattering reduction of the electromagnetic waves incident on the target within a wide frequency band. The simulation results show that the present invention can achieve an absorption performance with an absorption rate greater than 90% in the frequency range of 5.93 - 15.19 GHz, and the relative absorption bandwidth can reach 87.69%. Compared with a metal plate of the same size, the metamaterial absorber can achieve a continuous reduction in the radar cross section of 10 dB in the frequency range of 6.12 - 15.39 GHz.

[0018] The metamaterial absorber of the present invention has high absorption rate and broadband absorption characteristics, and can simultaneously achieve scattering reduction of the electromagnetic waves incident on the target surface and absorption of the target's spontaneous microwave radiation.

[0019] The metamaterial absorber of the present invention has good optical transparency and easy conformal characteristics, and also has the advantages of low profile, compact structure, easy processing, etc., providing a new idea for realizing the electromagnetic stealth technology for radar and microwave radiometers. Description of the Drawings

[0020] Figure 1 is a schematic diagram of the overall structure of the metamaterial absorber of the present invention.

[0021] Figure 2 is a side view of the overall structure of the metamaterial absorber of the present invention.

[0022] Figure 3 is a schematic diagram of the patterned conductive film on the first dielectric layer of the metamaterial absorber of the present invention.

[0023] Figure 4 is a schematic diagram of the patterned conductive films on the second and fourth dielectric layers of the metamaterial absorber of the present invention.

[0024] Figure 5 is a schematic diagram of the third dielectric layer and the fully covered conductive film of the metamaterial absorber of the present invention.

[0025] Figure 6 is the absorption rate curve achieved by the metamaterial absorber of the present invention.

[0026] Figure 7 is the absorption rate curve of the first and second dielectric layers of the metamaterial absorber of the present invention and the position of their patterned conductive films swapped (i.e., Comparative Example 1).

[0027] Figure 8It is the comparison absorption rate curve between the structure of the lower surface of the second dielectric layer of the metamaterial absorber of the present invention and a similar structure (i.e., Comparative Example 2).

[0028] Figure 9 It is the curve of reducing the radar cross section realized by the metamaterial absorber of the present invention.

[0029] Figure 10 It is the curve of realizing the regulation of the spontaneous microwave radiation of the target by the metamaterial absorber of the present invention.

[0030] In the figure, 1 is the first dielectric layer, 2 is the second dielectric layer, 3 is the third dielectric layer, 4 is the fourth dielectric layer, 5 is the substrate, 6 is the conductive layer I, 7 is the conductive layer II, 8 is the conductive layer III, 9 is the conductive layer IV, 10 is the conductive layer V, 11 is the outer closed-loop wire, 12 is the inner closed-loop wire, 13 is the connecting wire, 14 is the conductive thin film, 15 is the cross etching area, and 16 is the cross conductive wire. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners, but it is not a limitation of the present invention.

[0033] Embodiment 1 A metamaterial absorber for radar and microwave radiometer stealth, including a plurality of periodically arrayed basic units, and the basic unit includes 4 substrates 5 stacked in sequence from bottom to top and 5 conductive layers arranged between and at both ends of the substrates 5; The 5 conductive layers are, from bottom to top, conductive layer I 6, conductive layer II 7, conductive layer III 8, conductive layer IV 9, and conductive layer V 10 in sequence; The conductive layer I 6 includes an outer closed-loop wire 11 and a plurality of inner closed-loop wires 12 arranged inside the outer closed-loop wire 11, and the outer peripheries of the plurality of inner closed-loop wires 12 are connected through connecting wires 13; The conductive layer II 7 and the conductive layer V 10 have the same structure, including a conductive thin film 14, a cross etching area 15 arranged inside the conductive thin film 14, and a cross conductive wire 16 located inside the cross etching area 15, and the end of the cross conductive wire 16 is connected to the conductive thin film 14; The conductive layer III 8 and the conductive layer IV 9 have the same structure, which is a conductive thin film.

[0034] As shown in Figure 1 and Figure 2 shown, the basic unit includes a first dielectric layer 1, a second dielectric layer 2, a third dielectric layer 3, and a fourth dielectric layer 4 that are stacked in sequence from bottom to top. Each dielectric layer includes a substrate and a conductive layer provided on the surface of the substrate. The first dielectric layer 1 includes a first substrate and a conductive layer I 6 provided on the lower surface of the first substrate. The second dielectric layer 2 includes a second substrate and a conductive layer II 7 provided on the lower surface of the second substrate. The third dielectric layer 3 includes a third substrate, a conductive layer III 8 provided on the lower surface of the third substrate, and a conductive layer IV 9 provided on the upper surface of the third substrate. The fourth dielectric layer 4 includes a fourth substrate and a conductive layer V 10 provided on the upper surface of the fourth substrate.

[0035] Air is used as the spacer between adjacent dielectric layers, and the height h2 = 5 mm.

[0036] The substrates 5 of all dielectric layers are made of PET as the substrate material. The relative dielectric constant of the substrate is 3.2, the loss tangent is 0.003, and the thickness h1 = 0.125 mm.

[0037] The materials of the conductive layer I 6, the conductive layer II 7, the conductive layer III 8, the conductive layer IV 9, and the conductive layer V 10 are ITO conductive films.

[0038] The basic unit is square, with a side length a = 9 mm, that is, the substrate is square with a side length a = 9 mm.

[0039] As shown in Figure 3 shown, the lower surface of the first dielectric layer 1 is the conductive layer I 6. The conductive layer I 6 is a patterned conductive film, including an outer closed-loop wire 11 and a plurality of inner closed-loop wires 12 provided inside the outer closed-loop wire 11. The outer peripheries of the plurality of inner closed-loop wires 12 are connected by connecting wires 13.

[0040] The conductive layer I 6 is composed of two concentrically nested squares and four L-shaped structures provided in the innermost square. The number of inner closed-loop wires 12 is 4, and the inner closed-loop wires 12 are distributed in blocks inside the outer closed-loop wire 11. The outer closed-loop wire 11 is square, with a side length b = 8.5 mm. The inner closed-loop wires 12 are square, and the sum of the side lengths of the two inner closed-loop wires 12 plus the length of the connecting wire 13, that is, c = 6 mm. Figure 3 As shown in, the length of d = 2.3 mm and the width e = 0.3 mm. That is, the ratio of the sum of the side lengths of the two inner closed-loop wires 12 to c is greater than 80%.

[0041] The conductive layer I 6 is obtained by etching an ITO conductive film with a sheet resistance Rs of 120 Ω / sq on a PET substrate.

[0042] The lower surface of the second dielectric layer 2 is the conductive layer II 7, and the upper surface of the fourth dielectric layer 4 is the conductive layer V 10. The conductive layer II 7 and the conductive layer V 10 have the same structure. As Figure 4 shown, it includes a conductive thin film 14, a cross-etching area 15 provided in the conductive thin film 14, and a cross-conductive wire 16 located within the cross-etching area 15. The ends of the cross-conductive wire 16 are connected to the conductive thin film 14.

[0043] The basic unit is square, with a side length a = 9 mm. The conductive thin film 14 is square, with a side length b = 8.5 mm. The lengths at both ends of the cross-etching area 15 are the same, with a length f = 6 mm and a width k = 2 mm. The length of the cross-conductive wire 16 is f = 6 mm and the width g = 0.6 mm. The material of the cross-conductive wire 16 is the same as that of the conductive thin film 14.

[0044] The overall structure of the conductive layer II 7 and the conductive layer V 10 is a square nested with two intersecting crosses. The cross-conductive wire 16 and the conductive thin film 14 are obtained by etching an ITO conductive thin film with a sheet resistance of 120 Ω / sq on a PET substrate.

[0045] As Figure 5 shown, both sides (i.e., the upper surface and the lower surface) of the third dielectric layer 3 are covered with a conductive thin film, and it is completely covered, that is, the side length a of the conductive thin film is the same as the side length a of the basic unit, which is 9 mm, and is obtained by completely covering a PET substrate with an ITO conductive thin film with a sheet resistance of 6 Ω / sq.

[0046] Example 2 The absorption rate of the structure of Example 1 in the range of 0 - 25 GHz is obtained through simulation by the commercial electromagnetic simulation software CST Studio Suite. The abscissa represents the frequency, and the ordinate represents the magnitude of the absorbed electromagnetic wave energy, obtaining an absorption rate curve as Figure 6 shown.

[0047] The metamaterial absorber of the present invention is used to achieve the absorption of the spontaneous microwave radiation of the target, and at the same time, it can achieve the reduction of the scattering of the electromagnetic wave incident on the target surface. It can be seen that in the frequency range of 3.74 - 21.61 GHz, an absorption performance with an absorption rate greater than 90% is achieved, and the relative absorption bandwidth can reach 140.99%; in the frequency range of 5.93 - 15.19 GHz, an absorption performance with an absorption rate greater than 90% is achieved, and the relative absorption bandwidth can reach 87.69%.

[0048] Example 3 Comparative Example 1: On the basis of Example 1, the positions of the first dielectric layer 1 and its patterned conductive thin film and the second dielectric layer 2 and its conductive thin film are interchanged, that is, the basic unit includes the second dielectric layer 2, the first dielectric layer 1, the third dielectric layer 3, and the fourth dielectric layer 4 stacked in sequence from bottom to top. The second dielectric layer 2 includes a second substrate and a conductive layer II 7 provided on the lower surface of the second substrate, and the first dielectric layer 1 includes a first substrate and a conductive layer I 6 provided on the lower surface of the first substrate. Others are the same as in Example 1.

[0049] The above Comparative Example 1 structure was tested by the simulation method as in Example 2, and the Figure 7 shown absorption rate curve was obtained. The absorber of the Comparative Example 2 structure only achieved an absorption performance with an absorption rate greater than 90% in the frequency range of 2.99–7.11 GHz, and the relative absorption bandwidth was only 81.58%. It can be seen from this that the positions of the dielectric layers and conductive thin films in the metamaterial absorber of the present invention are the structures with the optimal performance in the configuration of Example 1.

[0050] Example 4 Comparative Example 2: On the basis of Example 1, the conductive layer II 7 on the lower surface of the second dielectric layer 2 is replaced with a structure of a cross nested in a ring, including a ring-shaped conductive wire and a cross-shaped conductive wire provided inside the ring-shaped conductive wire. The inner diameter of the ring-shaped conductive wire is 3.5 mm, the outer diameter is 4 mm, the wire width is 0.5 mm, the length of the cross-shaped conductive wire is 6 mm, the wire width is 0.6 mm, and the ring-shaped conductive wire and the cross-shaped conductive wire are not connected.

[0051] The above Comparative Example 2 structure was tested by the simulation method as in Example 2, and the Figure 8 shown absorption rate curve was obtained. As Figure 8 shown, when a structure of a cross nested in a ring is adopted, the absorption bandwidth will be divided into two parts, and a 90% absorption bandwidth is achieved in the frequency ranges of 4.89–8.29 GHz and 16.84–22.83 GHz respectively. The results show that this structure cannot achieve broadband absorption characteristics, is difficult to meet the actual application requirements, and limits its application range.

[0052] The structure of Example 1 of the present invention achieves broadband absorption characteristics while achieving a high absorption rate. When the effective absorption rate ≥ 90%, the relative absorption bandwidth reaches 140.99%. The conductive layers of the present invention resonate together to achieve the effect of broadband absorption. It can be seen from this that the structural design of the patterned conductive thin film of the present invention is preferred and can achieve the effect of broadband absorption bandwidth.

[0053] Example 5 As Figure 9As shown, by using the structure of Embodiment 1 to achieve scattering reduction of incident electromagnetic waves, it can be seen that scattering reduction of more than 10 dB is achieved in the frequency range of 6.12 - 15.39 GHz, and the RCS reduction value reaches the maximum of 29.66 dB at 9.5 GHz.

[0054] Embodiment 6 As Figure 10 shown, after using the structure of Embodiment 1 to absorb the spontaneous microwave radiation of the ground metal target, the result of target brightness temperature regulation is achieved. Assuming that the brightness temperatures of the sky and the environment are 50K and 300K respectively, since the metal target only reflects the radiation from the sky, the brightness temperature of the metal target is also 50K; the operating frequency of the microwave radiometer is set to 6.9 GHz, so the absorption rate of 0.99 at 6.9 GHz is taken as the emissivity of the metamaterial absorber. At this time, the brightness temperature of the metamaterial absorber is 297.5K. It can be seen that by loading the metamaterial absorber of Embodiment 1 on the surface of the metal target, the absorption of the target's spontaneous microwave radiation can be achieved, making the target brightness temperature basically consistent with the ambient brightness temperature.

[0055] The present invention selects PET as the dielectric substrate and ITO conductive film as the reflective bottom plate and resonant layer. By patterning the ITO conductive film of the resonant layer, absorption performance with an absorption rate greater than 90% is achieved in the ranges of 3.74 - 21.61 GHz and 5.93 - 15.19 GHz respectively. Using the metamaterial absorber, scattering reduction of more than 10 dB of the electromagnetic waves incident on the target surface is achieved in the frequency range of 6.12 - 15.39 GHz; and the regulation of the target's spontaneous microwave radiation characteristics is realized, making the brightness temperature of the metal target basically consistent with the ambient brightness temperature. Through the metamaterial absorber, scattering reduction of the electromagnetic waves incident on the target surface and absorption of the target's spontaneous microwave radiation are achieved, realizing the electromagnetic stealth effect for radar and microwave radiometers. In addition, the metamaterial absorber designed in the present invention has the characteristics of high-efficiency absorption, broadband absorption, low profile, compact structure, and optical transparency, providing a new solution and technical development approach for the electromagnetic stealth technology of high-value ground targets, and having important practical application value for promoting the innovative development of electromagnetic stealth technology.

[0056] Those of ordinary skill in the art should understand that: the discussion of any above embodiment is only exemplary, and is not intended to imply that the protection scope of this application is limited to these examples; under the idea of this application, the technical features between the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of one or more embodiments in the present application as described above, and they are not provided in detail for the sake of brevity.

[0057] One or more embodiments of the present application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application shall be included within the protection scope of the present application.

Claims

1. A metamaterial absorber for stealth of radar and microwave radiometer, characterized in that: Comprising a plurality of basic units distributed in a periodic array, the basic unit comprising four substrates (5) stacked in sequence from bottom to top and five conductive layers arranged between and at both ends of the substrates (5); The five conductive layers are, from bottom to top, conductive layer I (6), conductive layer II (7), conductive layer III (8), conductive layer IV (9), and conductive layer V (10); The conductive layer I (6) comprises an outer closed-loop conductive wire (11), and a plurality of inner closed-loop conductive wires (12) arranged inside the outer closed-loop conductive wire (11), wherein the outer peripheries of the plurality of inner closed-loop conductive wires (12) are connected via a connecting conductive wire (13); The conductive layer II (7) and the conductive layer V (10) have the same structure, comprising a conductive film (14), a cross-etched area (15) arranged in the conductive film (14), and a cross conductive line (16) located in the cross-etched area (15), wherein the end of the cross conductive line (16) is connected to the conductive film (14); The conductive layer III (8) and the conductive layer IV (9) have the same structure and are conductive films.

2. The metamaterial absorber according to claim 1, characterized in that: The four substrates (5) stacked in sequence from bottom to top are respectively a first substrate, a second substrate, a third substrate and a fourth substrate, the conductive layer II (7) is arranged on the lower surface of the second substrate, the conductive layer III (8) is arranged on the lower surface of the third substrate, and the conductive layer IV (9) is arranged on the upper surface of the third substrate.

3. The metamaterial absorber according to claim 1, characterized in that: The outer closed-loop conductor (11) is rectangular, and the inner closed-loop conductor (12) is rectangular.

4. The metamaterial absorber according to claim 3, characterized in that: The outer closed-loop conductive wire (11) is a square, and the inner closed-loop conductive wire (12) is a square.

5. The metamaterial absorber according to claim 4, characterized in that: The number of the inner closed-loop conductors (12) is four, and the four inner closed-loop conductors (12) are arranged in an array, and the connecting conductor (13) connects the outermost sides of adjacent inner closed-loop conductors (12).

6. The metamaterial absorber according to any one of claims 1 to 5, characterized in that: The substrate is a PET substrate, the relative dielectric constant of the substrate is 3.2, the loss tangent is 0.003, and the thickness h1 is 0.125 mm.

7. The metamaterial absorber according to any one of claims 1 to 5, characterized in that: The square resistance Rs of the conductive layer I (6), the conductive layer II (7), and the conductive layer V (10) is 120Ω / sq, and the square resistance Rs of the conductive layer III (8) and the conductive layer IV (9) is 6Ω / sq.

8. The metamaterial absorber according to any one of claims 1 to 5, characterized in that: The material of the conductive layer is ITO conductive film.

9. The metamaterial absorber according to any one of claims 1 to 5, characterized in that: There is air between the four substrates (5) with a thickness of 5 mm.

10. The metamaterial absorber according to any one of claims 1 to 5, characterized in that: The basic unit is a square with a side length of 9 mm, and the outer closed-loop wire (11) is a square with a side length of 8.5 mm; The conductive film (14) of the conductive layer II (7) and the conductive layer V (10) is a square with a side length of 8.5 mm; The conductive films of the conductive layer III (8) and the conductive layer IV (9) are square in shape with a side length of 9 mm.

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