A wave absorbing grid with artificial surface plasmon, method and air inlet

Abstract

The present invention discloses an artificial surface plasmon absorbing grid, method and air intake, which belong to the field of stealth technology of air intake system; the absorbing grid is composed of a plurality of square cavity unit arrays, the square cavity unit is a square ring cavity, and its circumferential wall surface is a multi-layer dielectric structure, and the wall surface is a frequency selective surface FSS, a synthetic resin PR, and a polyester resin PET from the inside to the outside, and each layer is placed in parallel; wherein the polyester resin PET of adjacent square cavity units is bonded by an indium tin oxide ITO film to form an artificial surface plasmon absorbing grid. The purpose of the present invention is to change the electromagnetic scattering characteristics of the air intake, reduce its radar scattering cross-sectional area, and thus improve the radar stealth performance of the aircraft.

Description

Technical Field

[0001] The present invention belongs to the technical field of stealth of air intake systems, and in particular relates to an artificial surface plasmon absorbing grid, a method and an air intake duct. Background Art

[0002] As an electrically large cavity structure, the aircraft air inlet is one of the strong electromagnetic scattering sources in the aircraft's forward angle domain. How to reduce and minimize its radar cross-sectional area has always been a hot research issue in aircraft stealth design. Installing a grille at the inlet entrance is a common air inlet stealth measure. The foreign F117 stealth bomber and RQ170 flying wing drone are typical applications of grille shielding technology. On the one hand, the grille can cause some electromagnetic waves to scatter at the grille and cannot enter the interior of the air inlet cavity. On the other hand, it forces the electromagnetic waves to reflect multiple times between the grille and the air inlet, reducing the echo intensity.

[0003] The current air intake grilles are mainly made of metals such as aluminum alloy, and absorbing materials can be coated on their surfaces. They are usually heavy, have low absorption rates, and use a narrow frequency band, making it difficult to meet the expected stealth design requirements. The grille-inlet air intake disclosed in the prior art can improve the overall stealth effect of the aircraft. However, since the inlet grilles are made of metal, they are heavy. Installing an air intake with a metal grille on an aircraft will increase the weight of the aircraft itself, affect its flight capability, and result in a reduction in mission load and a shortened combat radius. In addition, metal grilles generally change their absorbing characteristics by changing the porosity and thickness of the grille. The above parameters have a small adjustable range due to the shape and space limitations of the air intake. Therefore, there is an urgent need for a lightweight absorbing grille structure with a wide adjustable working frequency band. While reducing the weight of the absorbing grille, it can also reduce the radar scattering cross section of the air intake in multiple electromagnetic wave bands and improve its radar stealth performance. Summary of the invention

[0004] Technical issues to be solved:

[0005] In order to avoid the shortcomings of the prior art, the present invention provides an artificial surface plasmon absorbing grid, method and air inlet, wherein the absorbing grid uses a multi-layer dielectric structure as the square cavity wall, and a plurality of square cavity units are arranged in an array and installed with the air inlet, the purpose is to change the electromagnetic scattering characteristics of the air inlet, reduce its radar scattering cross-sectional area, and thus improve the radar stealth performance of the aircraft. The present invention solves the problems of heavy weight, low absorption rate and narrow frequency band of metal absorbing grids in the prior art.

[0006] The technical solution of the present invention is: a wave absorbing grid with artificial surface plasmon, characterized in that: it is composed of a plurality of square cavity unit arrays, the square cavity units are square ring cavities, and their circumferential walls are all multi-layer dielectric structures, and the walls are frequency selective surfaces FSS, synthetic resin PR, and polyester resin PET from the inside to the outside, and each layer is placed in parallel; wherein the polyester resin PET of adjacent square cavity units are bonded by indium tin oxide ITO films to form a wave absorbing grid with artificial surface plasmon.

[0007] A further technical solution of the present invention is that the length, width and height of the square cavity unit are consistent.

[0008] A further technical solution of the present invention is: the material of the frequency selective surface FSS is copper, and multiple "L"-shaped copper strips are evenly distributed along the diagonal of the square cavity unit wall to form a FSS layer with a square outline, and the FSS layer is located as a whole at the center of each wall of the square cavity unit.

[0009] A further technical solution of the present invention is: the FSS layer is attached to the surface of the PR layer and is printed on the surface of the PR layer using printed circuit board technology.

[0010] A further technical solution of the present invention is that the PR layer is attached to the surface of the PET layer and is tightly bonded by using a hot pressing technology.

[0011] A further technical solution of the present invention is: a dense ITO film is sputtered on the surface of the PET layer by magnetron sputtering, and is bonded to the PET layer on the wall of the adjacent square cavity unit to form a FSS-PR-PET-ITO-PET-PR-FSS symmetrical multilayer dielectric structure.

[0012] A further technical solution of the present invention is: the square contour side length of the FSS layer is b=8mm, the width of the "L"-shaped copper strip is w=125μm, and the thickness is c=35μm; the thickness of the PR layer is h=1mm, and the thickness of the PET layer is d=10μm.

[0013] A further technical solution of the present invention is: the dielectric constant of the PR layer is ε=4.3, the loss tangent of the material is tanδ=0.025, the dielectric constant of the PET layer is ε=4.3, the loss tangent of the material is tanδ=0.18.

[0014] A method for preparing a wave absorbing grid with artificial surface plasmons, characterized in that the specific steps are as follows:

[0015] Prepare a wave absorbing grid strip unit; the wave absorbing grid strip unit is formed by a plurality of multi-layer dielectric structures evenly distributed along the length direction, and a strip unit notch is opened between adjacent multi-layer dielectric structures;

[0016] Under high vacuum conditions, two wave-absorbing grid strip units are bonded together through ITO thin films to form a symmetrical multilayer dielectric structure.

[0017] A plurality of symmetrical multilayer dielectric structures are plugged in through strip unit notches to form an artificial surface plasmon absorbing grid.

[0018] An air inlet duct is characterized in that: an inlet plane of the air inlet duct is provided with an artificial surface plasmon absorbing grid, and the outer peripheral surface of the absorbing grid is bonded to the inner wall surface of the air inlet duct.

[0019] Beneficial Effects

[0020] The beneficial effect of the present invention is that the present invention proposes an air intake with an artificial surface plasmon absorbing grid. Compared with an air intake without an air intake grid, the air intake grid has a shielding effect on electromagnetic waves, and electromagnetic waves can be reflected multiple times between the absorbing grid and the air intake cavity, reducing the echo intensity and greatly reducing the forward RCS of the air intake. In addition, compared with an air intake equipped with a metal grid or a metal grid coated with absorbing material, the average material density of the artificial surface plasmon absorbing grid is smaller than that of general metal materials, so compared with a metal grid or a metal grid coated with an absorbing coating, its weight is lighter.

[0021] The multilayer dielectric structure of the present invention confines electromagnetic incident waves between interfaces of each layer for dissipation, especially at the interface between metal and dielectric. Compared with ordinary surface plasmons, the plasmons generated by the collective oscillation of free electrons in metal conductors in the artificial surface plasmons adopted by the multilayer dielectric structure have stronger electromagnetic wave confinement ability, so that the field strength in the normal direction of the multilayer dielectric structure decays exponentially, which is more convenient for the miniaturized design of the absorbing grid.

[0022] Therefore, the present invention has properties such as negative electromagnetic parameters that conventional metal materials do not have, has a low electromagnetic wave reflectivity, can also achieve microwave to visible light absorption by changing the FSS pattern characteristics, has a wider operating frequency band, and can reduce the radar scattering cross-section of the air inlet at a wider electromagnetic wave detection frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a three-dimensional axonometric diagram of an air intake with an artificial surface plasmon absorbing grid;

[0024] Figure 2 It is a schematic diagram of a strip unit of an absorbing grid;

[0025] Figure 3 It is a schematic diagram of a square cavity unit of an absorbing grid;

[0026] Figure 4 It is a schematic diagram of a two-dimensional array of FSS metal patches of an absorber grid;

[0027] Figure 5 is a schematic side view of a multi-layer absorbing structure;

[0028] Figure 6 It is a schematic side view of a multi-layer absorbing structure bonded by ITO;

[0029] Figure 7 This is a schematic diagram of the equivalent transmission line model of a multi-layer absorbing structure.

[0030] Figure 8 This is the RCS distribution curve of different types of inlet forward detection angle range of -40° to 40° under vertical polarization mode of 10GHz incident frequency obtained by experimental test;

[0031] Explanation of the reference numerals: 1. absorbing grid, 2. air inlet, 11. strip unit notch, 12. FSS layer, 13. PR layer, 14. PET layer, 15. ITO layer. DETAILED DESCRIPTION

[0032] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0034] The air intake grille based on the prior art uses metals such as aluminum alloy, which has the problems of heavy weight, low absorption rate, narrow frequency band, and difficulty in meeting the expected stealth design requirements. The present invention proposes an artificial surface plasmon absorbing grille, method and air intake, wherein the absorbing grille is located on the inlet plane of the air intake. The absorbing grille as a whole presents a periodic square cavity cross array structure, and the length, width and height of each square cavity unit formed are consistent.

[0035] The walls of the square cavity units are all made of a multi-layer dielectric structure. The multi-layer dielectric structure includes a frequency selective surface (FSS), a synthetic resin (PolyResin, PR), and a polyester resin (Polyethylene terephthalate, PET). The layers are placed in parallel. The square cavity units are bonded by an indium tin oxide (ITO) film. Among them, the frequency selective surface (FSS) is a metamaterial that has been widely used in electromagnetic compatibility and electromagnetic shielding in recent years. It exhibits bandpass and bandstop filtering characteristics for electromagnetic waves of different frequencies, and has the advantages of lightness, small volume structure, and broadband absorption. Among them, artificial surface plasmon (spoof surface plasmon polariton, SSPP) can couple the incident wave to the surface of the structure for propagation, has a good application prospect, and can meet the lightweight and broadband requirements of the air intake grille.

[0036] The present invention uses the multilayer dielectric structure to confine electromagnetic incident waves between the interfaces of each layer for dissipation, especially at the interface between metal and dielectric. Compared with ordinary surface plasmons, the plasmons generated by the collective oscillation of free electrons in the metal conductor in the artificial surface plasmons used in the multilayer dielectric structure have stronger electromagnetic wave confinement ability, so that the field strength in the normal direction of the multilayer dielectric structure decays exponentially, which is more convenient for the miniaturized design of the wave-absorbing grid.

[0037] The above technical solution is further described below with reference to the accompanying drawings.

[0038] Example:

[0039] The present embodiment is an air inlet with an artificial surface plasmon absorbing grid, which mainly includes an inlet absorbing grid and an air inlet. Figure 1-8 The air intake is described in detail.

[0040] Reference Figure 1 As shown, the connection method between the absorbing grille 1 and the air inlet 2 is that the outermost sides of the absorbing grille 1 are connected to the inner wall surface of the inlet duct 2, and the front end surface of the absorbing grille is flush with the inlet end surface of the air inlet. Optionally, the air inlet duct 2 is a rectangular square cavity structure, and its length, width and height are L=600mm, W=240mm, and H=240mm respectively. Optionally, the material of the air inlet duct 2 is stainless steel.

[0041] Reference Figure 2As shown, the strip-shaped unit of the absorbing grid constituting the absorbing grid 1. The strip-shaped unit of the absorbing grid is formed by a plurality of multi-layer dielectric structures evenly distributed along the length direction, and a strip-shaped unit notch is opened between adjacent multi-layer dielectric structures; the multi-layer dielectric structure includes a top FSS layer 12, an intermediate PR layer 13 and a bottom PET layer 14, a total of three-layer structure. The specific processing method of the absorbing grid 2 is: under high vacuum conditions, a dense ITO film is formed on the surface of the bottom PET layer of any two of the strip-shaped units by magnetron sputtering, and then the ITO films of the two strip-shaped units are tightly bonded together by hot pressing technology, and the two strip-shaped units form a symmetrical multi-layer dielectric structure with the ITO film as the middle layer. After adding the ITO film layer, its conductive properties promote the coupling of the FSS layers on both sides of the symmetrical multi-layer dielectric structure, promote the electric field to penetrate the PR layer, increase the resonance strength of the FSS layer, and finally improve the absorbing efficiency of the absorbing structure. Multiple symmetrical multi-layer dielectric structures are spliced ​​along the notch 11 to finally form the absorbing grid 2.

[0042] Reference Figure 3 As shown, the partial schematic diagram of the absorbing grid 2 is enlarged to be a structural schematic diagram of the square cavity unit. The square cavity unit is a square ring cavity, and its circumferential wall is a multi-layer dielectric structure. The wall from the inside to the outside is a frequency selective surface FSS, a synthetic resin PR, and a polyester resin PET, and each layer is placed in parallel; wherein the polyester resin PET of adjacent square cavity units are bonded by an indium tin oxide ITO film to form an absorbing grid with an artificial surface plasmon.

[0043] Reference Figure 4 and Figure 5As shown, according to the design theory of FSS, the basic "L"-shaped FSS layer metal patch is first designed, and the spacing between each "L"-shaped metal patch is equal and evenly distributed along the diagonal of the face of the square cavity unit. The multilayer dielectric structure specifically includes a top FSS layer 12, a PR layer 13, and a bottom PET layer 14. In order to increase the resonance effect of the plasmon as much as possible, the cutoff frequency is changed by changing the size and structure of the FSS layer metal patch. The full-wave electromagnetic simulation optimization calculation of the air intake structure with the absorbing grid is performed to obtain the final geometric parameters of the multilayer dielectric structure. The metal patch is located in the center of the PR layer as a whole. Preferably, specifically, the square contour side length of the FSS layer is b=8mm, the width of the "L"-shaped copper strip is w=125μm, and the thickness is c=35μm. The width a=10mm and the thickness h=1mm of the PR layer 13, and the thickness d=10μm of the PET layer 14. Among them, the dielectric constant of the PR layer is ε=4.3, and the loss tangent of the material is tanδ=0.025; the dielectric constant of the PET layer is ε=4.3, and the loss tangent of the material is tanδ=0.18. When the electromagnetic wave is incident on the interface between the FSS metal patch and the medium, the free electrons in the metal conductor will oscillate collectively, and the electromagnetic field strength at the interface reaches a peak value. The designed periodic metal patch structure has a stronger binding ability for electromagnetic waves, reduces interference with adjacent structures, and facilitates the miniaturization design of the absorber. It should be noted that due to the large difference in thickness between the dielectric layers, in order to more clearly describe the multi-layer dielectric structure, the attached Figure 5 It is only a schematic diagram of the multi-layer dielectric structure and does not represent the actual thickness ratio.

[0044] Reference Figure 6 As shown, the symmetrical multi-layer dielectric structure is formed by hot pressing and bonding the multi-layer dielectric structure through the ITO film 15. Through further simulation calculation, preferably, the square resistance R of the ITO film is 200Ω / m 2 .

[0045] Reference Figure 7 As shown, an equivalent transmission line model of the symmetrical multilayer dielectric structure is established. 0 =377Ω, which represents the air impedance on both sides of the symmetrical multilayer dielectric structure. The PR layer 13 can be equivalent to a transmission line, and its impedance can be expressed by Z 1 Indicates that Z 1 =Z 0 / ε r The PET layer 14 is also equivalent to a transmission line, but due to its small thickness, its transmission line impedance can be ignored. The ITO layer 15 is equivalent to a parallel resistor, and its resistance is R. The FSS layers on the upper and lower surfaces can be equivalent to two LC series branches.

[0046] Reference Figure 8 As shown, for a plane electromagnetic wave with a detection frequency of 10GHz, the electromagnetic scattering characteristics of the air inlet square cavity and the air inlet with an artificial surface plasmon absorbing grid within the incident angle range of -40° to 40° are obtained by experimental testing. It can be seen that under the vertical polarization mode, compared with the air inlet without an absorbing grid, the RCS value of the air inlet with an artificial surface plasmon absorbing grid within the detection angle range is significantly reduced, especially in the small angle focus range of -10° to 10°, the RCS value is reduced to a greater extent. By calculating the angular mean RCS of the two air inlets in the range of -40° to 40°, the RCS mean of the air inlet with an artificial surface plasmon absorbing grid is reduced by 99.9% compared with the air inlet without an absorbing grid, and the effect is very impressive. Secondly, installing the absorbing grid at the inlet inlet changes the electromagnetic scattering law of the air inlet forward. For the air inlet, its RCS value reaches a peak value near the 0° detection angle, and then its RCS value fluctuates and decreases as the detection angle increases. However, for the air inlet with an artificial surface plasmon absorbing grid, the RCS value near the 0° detection angle directly in front is smaller than the RCS value at a large detection angle, which greatly reduces the probability of the aircraft being detected from the key angle area directly in front. It can be seen that the RCS of the air inlet with an artificial surface plasmon absorbing grid after optimization design has been significantly reduced in the key detection angle area, and has good incident angle stability.

[0047] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A wave absorbing grid with artificial surface plasmons, Features: It is composed of an array of several square cavity units, each of which is a square ring cavity, and its circumferential wall is a multi-layer dielectric structure. The wall is a frequency selective surface FSS, a synthetic resin PR, and a polyester resin PET from the inside to the outside, and each layer is placed in parallel; the polyester resin PET of adjacent square cavity units are bonded by indium tin oxide ITO film to form an artificial surface plasmon absorbing grid.

2. According to claim 1, a wave absorbing grid with artificial surface plasmons, Features: The length, width and height of the square cavity unit are all consistent.

3. According to claim 1, a wave absorbing grid with artificial surface plasmons, Features: The material of the frequency selective surface FSS is copper, and multiple "L"-shaped copper strips are evenly distributed along the diagonal of the square cavity unit wall to form a FSS layer with a square outline. The FSS layer is located at the center of each wall of the square cavity unit.

4. According to claim 3, a wave absorbing grid with artificial surface plasmons, Features: The FSS layer is attached to the surface of the PR layer and is printed on the surface of the PR layer using printed circuit board technology.

5. According to claim 4, a wave absorbing grid with artificial surface plasmons, Features: The PR layer is attached to the surface of the PET layer and is tightly bonded by using a hot pressing technique.

6. The grating with artificial surface plasmon absorption according to claim 5, Features: A dense ITO film is sputtered on the surface of the PET layer by magnetron sputtering, and is bonded to the PET layer on the wall of the adjacent square cavity unit to form a FSS-PR-PET-ITO-PET-PR-FSS symmetrical multilayer dielectric structure.

7. The grating with artificial surface plasmon absorption according to claim 6, Features: The square outline side length of the FSS layer is b=8 mm, the width of the "L"-shaped copper strip is w=125 μm, and the thickness is c=35 μm; the thickness of the PR layer is h=1 mm, and the thickness of the PET layer is d=10 μm.

8. The grating with artificial surface plasmon absorption according to claim 7, Features: The dielectric constant of the PR layer is ε=4.3, and the loss tangent of the material is tanδ=0.

025. The dielectric constant of the PET layer is ε=4.3, and the loss tangent of the material is tanδ=0.

18.

9. A method for preparing the grating with artificial surface plasmon absorption as claimed in any one of claims 1 to 8, Features The specific steps are as follows: Prepare a wave absorbing grid strip unit; the wave absorbing grid strip unit is formed by a plurality of multi-layer dielectric structures evenly distributed along the length direction, and a strip unit notch is opened between adjacent multi-layer dielectric structures; Under high vacuum conditions, two wave-absorbing grid strip units are bonded together through ITO thin films to form a symmetrical multilayer dielectric structure. A plurality of symmetrical multilayer dielectric structures are plugged in through strip unit notches to form an artificial surface plasmon absorbing grid.

10. An air intake duct, Features: The inlet plane of the air inlet is provided with an artificial surface plasmon absorbing grid as claimed in any one of claims 1 to 8, and the outer peripheral surface of the absorbing grid is bonded to the inner wall surface of the air inlet.

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