Ultrathin broadband electromagnetic wave absorber based on EBG structure

Abstract

The invention discloses an ultra-thin broadband electromagnetic wave absorber based on an EBG structure, and belongs to the technical field of electromagnetic compatibility design in the antenna radio frequency technology. The invention aims to solve the problems of electromagnetic wave resonance in a metal cavity package of a Ka-band microwave assembly, crosstalk caused by low isolation degree between ports and difficulty in meeting the water vapor atmosphere requirement of a traditional organic wave absorber. The electromagnetic wave absorber is formed by periodically arranging a plurality of unit structures, each unit structure of the electromagnetic wave absorber comprises an upper metal top plate, a middle ceramic medium and a bottom patch layer, and a resistive film patch and a conductor film patch are arranged on the patch layer. The resistive film patches and the conductor film patches on the patch layer are symmetrically arranged in a staggered manner, namely, the patch layer is of a symmetrical structure; meanwhile, part of the conductor film patches are connected with the metal top plate through metal through holes, and the metal through holes penetrate through the ceramic dielectric layer and are symmetrically arranged.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic compatibility design in antenna radio frequency technology and relates to an ultra-thin broadband electromagnetic absorber. Background Art

[0002] The cavity resonance problem of metal packaging of microwave components arises with the increase of the operating frequency of microwave circuits. The classic methods of suppressing resonant electromagnetic waves in cavities at lower frequencies, such as reducing the package size to less than half the wavelength and using mode strips, become difficult to implement. The solution using traditional absorbing materials will cause problems of difficult integration and water vapor atmosphere in the components. Designing a new metamaterial absorber based on the EBG (Electromagnetic Band Gap) structure is an effective way to solve this problem. The bandgap characteristics of the EBG structure can effectively prevent the radiation of electromagnetic waves.

[0003] EBG is a periodically arranged artificial electromagnetic material, a type of electromagnetic metamaterial. For a two-dimensional EBG structure, because its surface has high impedance characteristics, it is also called a high impedance surface (HIS). The surface of the EBG structure can therefore be equivalent to a perfect magnetic conductor (PMC), so it is also called an artificial magnetic conductor (AMC). The concept of EBG comes from the electronic band gap in solid-state physics. Because photons follow the same Schrödinger equation and Maxwell equation as electrons in atomic crystals, it is proven that they also have a band gap similar to that of electrons in a special periodic structure, which can prevent the propagation of electromagnetic waves within a certain range, and is called a photonic band gap (PBG). The EBG structure was first used in antenna design. Because of its characteristic of preventing the propagation of electromagnetic waves, the EBG structure is also called an electromagnetic soft surface, borrowing the concept of soft and hard surfaces in acoustics.

[0004] The bandgap characteristics of the EBG structure enable it to be used in gap waveguides to prevent the normal radiation of electromagnetic waves in the waveguide. When the packaging of microwave components encounters cavity resonance problems, the EBG structure can prevent the propagation of electromagnetic waves within a certain frequency band. Loading the EBG structure in the metal cavity package can suppress the cavity resonance mode and parallel plate mode within a certain frequency band, and optimize the reliability and stability of microwave components. Summary of the invention

[0005] The present invention aims to solve the problems of electromagnetic wave resonance in the metal cavity package of Ka-band microwave components, low isolation between ports and crosstalk, and the difficulty of traditional organic absorbers in meeting the requirements of water vapor atmosphere.

[0006] An ultra-thin broadband electromagnetic absorber based on an EBG structure, the electromagnetic absorber is composed of a plurality of unit structures arranged periodically, the unit structure of the electromagnetic absorber comprises an upper metal top plate, a middle ceramic medium and a bottom patch layer, the patch layer is provided with a resistor film patch and a conductor film patch, and the resistor film patch and the conductor film patch on the patch layer are arranged in an alternating symmetrical arrangement, that is, the patch layer has a symmetrical structure; at the same time, some of the conductor film patches are connected to the metal top plate through metal through holes, the metal through holes pass through the ceramic medium layer, and the metal through holes are symmetrically arranged.

[0007] Furthermore, the staggered symmetrical arrangement of the resistor film patches and the conductor film patches and the symmetrical setting of the metal through holes are determined based on iterative optimization calculations.

[0008] Furthermore, in the process of iterative optimization calculation, the score is increased until the score stops converging and the optimization process ends. At this time, the staggered symmetrical arrangement of the resistor film patch and the conductor film patch and the symmetrical setting of the metal through hole are the final patch layer.

[0009] The scores are as follows:

[0010]

[0011] Where f is the frequency, E(f) and D(f) are functions of the frequency f; E(f) is the ideal suppression rate curve; D(f) represents the actual S at the same frequency as E(f). 11 The corresponding S 11 The difference between the parameter curve and the ideal inhibition rate curve; ∫ 目标频带 ·df means integrating the function with respect to f over the target frequency band.

[0012] Furthermore, during the iterative optimization calculation, the ideal inhibition rate curve E(f) is determined by:

[0013] Based on the parameter curve S 11 (f) is obtained by fitting the five points, namely, the edge of the frequency band 0dB, the edge of the target frequency band -10dB, and the center of the target frequency band -25dB, through the smooth interpolation method; the parameter curve S 11 (f) refers to S at frequency f 11 The curve corresponding to the parameter.

[0014] Furthermore, the metal top plate of the electromagnetic absorber is a metal copper plate, the ceramic dielectric material is alumina, and the conductor film patch is a metal film.

[0015] Furthermore, the relative dielectric constant of the ceramic dielectric material is 9.8, and the loss tangent is 0.002.

[0016] Furthermore, the square resistance of the resistor film patch is 100Ω / sq.

[0017] Furthermore, the thickness of the metal top plate of the unit structure is 0.035 mm, the thickness of the ceramic medium is 0.508 mm, and the thickness of the patch layer provided with the resistor film patch and the conductor film patch is 0.035 mm.

[0018] Furthermore, the unit structure is a cube with a square bottom, the side length of the bottom is 1.3 mm, and the height of the cube is 0.508 mm; the resistor film patch and the conductor film patch are both squares with a side length of 0.13 mm, and the through hole diameter is 0.05 mm.

[0019] Furthermore, when a plurality of unit structures are periodically arranged to form an electromagnetic absorber, the unit structures are periodically arranged in the following manner: the unit structures are closely arranged on the same plane with the metal top plate as a reference, and the unit structures are periodically arranged in two directions within the plane.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention is based on the EBG structure and utilizes its bandgap characteristics to form a periodic arrangement structure, which can prevent the propagation of electromagnetic waves in the working frequency band in the cavity, reduce crosstalk, and improve the isolation between ports.

[0022] 2. The present invention adds a reasonable resistance film to the EBG structure to convert electromagnetic waves into heat, which can absorb electromagnetic waves in the metal cavity and reduce the impact of the reflection of electromagnetic wave energy on microwave devices.

[0023] 3. The present invention is a surface mounted structure with a small size and is easy to be integrated in a metal shell of a microwave component.

[0024] 4. Compared with traditional organic absorbers, the present invention significantly improves the water vapor atmosphere inside microwave components. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the electromagnetic absorber unit;

[0026] Figure 2 for Figure 1 A schematic diagram of a patch layer of a unit structure of an electromagnetic absorber shown;

[0027] Figure 3 is the reflection coefficient and absorptivity of the electromagnetic absorber unit structure;

[0028] Figure 4 This is the assembly effect diagram of the ultra-thin broadband electromagnetic absorber based on EBG structure in the metal cavity type microwave component;

[0029] Figure 5 for Figure 4 Schematic diagram of top view;

[0030] Figure 6 This is a comparison chart of the absorption effect of ultra-thin broadband electromagnetic absorbers based on EBG structure in metal cavity type microwave components;

[0031] Figure 7 This is the assembly diagram for the actual test;

[0032] Figure 8 For actual test of absorption effect. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0034] In order to reduce the resonance in the microwave component and improve the isolation between ports in the microwave component, a microwave component absorber can be designed based on the EBG structure to suppress the resonance in the metal cavity of the microwave component in the metal package and improve the isolation of the port. In order to improve the absorption performance of the absorber for electromagnetic waves, a resistor film is loaded in it to lose the electromagnetic waves in the cavity. The use of the resistor film also plays a role in increasing the absorption bandwidth of the absorber. The present invention is further described in detail below in conjunction with specific embodiments. Specific implementation method one:

[0036] The present embodiment is an ultra-thin broadband electromagnetic absorber based on an EBG structure. The electromagnetic absorber is designed based on the EBG structure. The electromagnetic absorber is composed of a number of unit structures arranged periodically. The unit structure of the electromagnetic absorber includes an upper metal top plate 1, a middle ceramic medium 2, and a bottom patch layer 3. The patch layer is provided with resistor film patches and conductor film patches, and the resistor film patches and the conductor film patches on the patch layer are arranged in an alternating symmetrical arrangement, that is, the patch layer has a symmetrical structure; at the same time, some conductor film patches are connected to the metal top plate through metal through holes, and the metal through holes pass through the ceramic dielectric layer, and the metal through holes are also symmetrically arranged.

[0037] When designing an ultra-thin broadband electromagnetic absorber based on an EBG structure, the unit structure of the electromagnetic absorber to be designed is simulated and analyzed in the electromagnetic calculation software. Numerical calculation software is required for design optimization. This embodiment uses Ansys EM, and other electromagnetic simulation software can also achieve the same effect. Set periodic boundaries and Floquet ports on the unit structure (Floquet ports refer to electromagnetic wave irradiation ports with arbitrary plans and arbitrary incident angles set during simulation calculations, which are used for simulation of periodic structures) to simulate the situation when electromagnetic waves are incident on it when it is arranged periodically. Analyze the reflection coefficient S of the periodically arranged unit structure 11 ; Then calculate the unit structure absorption rate

[0038] A(f)=1-R(f)-T(f)

[0039] Where R(f)=|S 11 2 is the reflectivity, and T(f) is the transmittance. They are all functions of frequency. Since the upper layer of the unit is a metal top plate, it is considered that T(f) = 0.

[0040] The reflection coefficient and absorptivity of the unit structure of the ultra-thin broadband electromagnetic absorber are as follows: Figure 3 The reflectivity-based analysis determines the score used to optimize the cell structure.

[0041] The resistor film patches and conductor film patches of the unit structure patch layer are staggered and distributed in a mosaic pattern that is symmetrical about the x-axis and y-axis. The arrangement of the resistor film patches and the conductor film patches and the connection positions of the metallized vias are calculated by algorithm iteration. Genetic algorithms or other iterative calculation methods are used to optimize the arrangement of the resistor film and conductor film of the patch layer and the position of the metal vias. In order to quantitatively calculate the advantages and disadvantages of each unit structure, the distance integral of each unit's suppression rate curve and the ideal suppression rate curve in the target absorption frequency band can be used to obtain the score of each unit structure.

[0042]

[0043] Where f is the frequency, E(f) and D(f) are functions of the frequency f; E(f) is the ideal inhibition rate curve, which is based on the parameter curve S 11 (f) The parameter curve S is obtained by fitting the five points of the participating calculation band edge 0dB, the target band edge -10dB, and the target band center -25dB through the smooth interpolation method. 11 (f) refers to S at frequency f 11 The curve corresponding to the parameters; D(f) represents the actual S at the same frequency as E(f). 11 The corresponding S 11 The difference between the parameter curve and the ideal inhibition rate curve; ∫目标频带 ·df means integrating the function with respect to f over the target frequency band.

[0044] During the optimization process, the score will increase until the score stops converging and the optimization process ends. At this time, the unit obtained is the optimal unit of the ultra-thin broadband electromagnetic absorbing material based on the EBG structure in the target absorbing frequency band.

[0045] Figure 1 is an embodiment of a unit structure of an electromagnetic absorber, Figure 2 for Figure 1 The patch layer of the unit structure of the electromagnetic absorber shown in the figure has a symmetrical structure as shown in the figure. Figure 2 The discrete mosaic pattern shown in this example has an absorbing frequency band of Ka band. In this example, the period p of the unit structure is 1.3 mm, the height h is 0.508 mm, the through hole diameter is 0.05 mm, l1-l4 are 0.52 mm, 0.26 mm, 0.39 mm and 0.52 mm respectively, and w1-w3 are 0.26 mm, 0.13 mm and 0.13 mm respectively. In this embodiment, there are 4 through holes connecting the conductor film patch of the patch layer and the metal top plate.

[0046] In fact, in order to ensure the symmetric arrangement of metal through holes, the number of metal through holes is an even number. The specific number is actually determined through the optimization process. Figure 2 The unit structure shown in the figure is optimized to obtain 4 through holes, located at Figure 2 Position shown.

[0047] In this embodiment, the metal top plate of the electromagnetic absorber is a metal copper plate with conductive properties, the ceramic dielectric material is aluminum oxide (Al2O3), the relative dielectric constant is 9.8, and the loss tangent is 0.002; the square resistance of the resistor film patch is 100Ω / sq, and the conductor film patch is a metal film with conductive properties.

[0048] Preferably, the electromagnetic absorber unit structure is a cube with a square bottom surface and a height of 0.578 mm, and the height includes a 0.035 mm metal top plate, a 0.508 mm alumina ceramic medium and a 0.035 mm bottom patch layer.

[0049] The electromagnetic absorber is composed of a plurality of unit structures arranged periodically. The unit structures are arranged periodically in the following manner: the unit structures are closely arranged on the same plane with the metal top plate as a reference, and the unit structures are arranged periodically in two directions within the plane.

[0050] The electromagnetic absorber is assembled on the top cover of the metal cavity type microwave component. The size of the electromagnetic absorber in the combined use state is consistent with the internal size and size of the metal cavity, and the metal top plate of the electromagnetic absorber material is connected to the metal cavity.

[0051] In some implementations, when used in a metal cavity type microwave assembly with an inner cavity size of 6 mm×6 mm, an electromagnetic absorber is loaded on the upper top cover of the inner cavity of the metal cavity type microwave assembly, that is, a 4×4 unit structure, and the assembly effect is as follows: Figure 4 and Figure 5 shown.

[0052] Add two ports to the component and simulate and analyze the transmission parameter S from port 1 to port 2 with and without the absorber. 21 The results are as follows Figure 6 The absorption rate of the absorber is

[0053]

[0054] Among them, |S 21 | with_absorber (f),|S 21 | withour_absorber (f) represents the corresponding transmission parameter S with and without the absorber loaded 21 ;

[0055] In the absence of an electromagnetic absorber, resonant transmission occurs inside the metal cavity, with a transmission parameter of about -30dB, and a large transmission mainly between 32GHz and 36GHz. After loading the designed electromagnetic absorber, the transmission between the two ports is significantly suppressed. Between 32GHz and 36GHz, the suppression of electromagnetic wave radiation is more than 13dB. In the target frequency band, the designed absorber can absorb more than 90% of the electromagnetic wave radiation in the cavity-type microwave component.

[0056] In order to verify the simulation results, actual tests were carried out. A 4 mm x 4 mm tube shell was used. Figure 7 The connection relationship of the two ports is used to test the isolation of the two ports. The electromagnetic wave transmission inside the metal cavity is compared with the non-absorber, the traditional absorber and the proposed electromagnetic absorber. The results are shown in Figure 8 As shown, from the target frequency band, transmission occurs between the two ports of the cavity without the electromagnetic absorber loaded, and the transmission is suppressed after the electromagnetic absorber is loaded, and its suppression effect is similar to that of the traditional electromagnetic absorber.

[0057] The above calculation examples of the present invention are only used to explain the calculation model and calculation process of the present invention in detail, and are not intended to limit the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. An ultra-thin broadband electromagnetic absorber based on an EBG structure, characterized in that: The electromagnetic absorber is composed of a plurality of unit structures arranged periodically. The unit structure of the electromagnetic absorber includes an upper metal top plate, a middle ceramic medium and a bottom patch layer. The patch layer is provided with a resistor film patch and a conductor film patch. The resistor film patches and the conductor film patches on the patch layer are arranged in an alternating symmetrical arrangement, that is, the patch layer has a symmetrical structure. At the same time, some of the conductor film patches are connected to the metal top plate through metal through holes, and the metal through holes pass through the ceramic medium layer. The metal through holes are symmetrically arranged.

2. The ultra-thin broadband electromagnetic absorber based on the EBG structure according to claim 1, characterized in that: The staggered symmetrical arrangement of the resistor film patches and the conductor film patches and the symmetrical setting of the metal through holes are determined based on an iterative optimization calculation method.

3. The ultra-thin broadband electromagnetic absorber based on EBG structure according to claim 2, characterized in that: In the process of iterative optimization calculation, the score is increased until the score stops converging and the optimization process ends. At this time, the staggered symmetrical arrangement of the resistor film patch and the conductor film patch and the symmetrical setting of the metal through hole are the final patch layer; The scores are as follows: Where f is the frequency, E(f) and D(f) are functions of the frequency f; E(f) is the ideal suppression rate curve; D(f) represents the actual S at the same frequency as E(f). 11 The corresponding S 11 The difference between the parameter curve and the ideal inhibition rate curve; ∫ 目标频带 ·df means integrating the function with respect to f over the target frequency band.

4. The ultra-thin broadband electromagnetic absorber based on EBG structure according to claim 3, characterized in that: During the iterative optimization calculation process, the ideal inhibition rate curve E(f) is determined by the following method: Based on the parameter curve S 11 (f) is obtained by fitting the five points, namely, the edge of the frequency band 0dB, the edge of the target frequency band -10dB, and the center of the target frequency band -25dB, through the smooth interpolation method; the parameter curve S 11 (f) refers to S at frequency f 11 The curve corresponding to the parameter.

5. The ultra-thin broadband electromagnetic absorber based on EBG structure according to claim 1, characterized in that: The metal top plate of the electromagnetic absorber is a metal copper plate, the ceramic dielectric material is alumina, and the conductor film patch is a metal film.

6. The ultra-thin broadband electromagnetic absorber based on EBG structure according to claim 5, characterized in that: The relative dielectric constant of the ceramic dielectric material is 9.8 and the loss tangent is 0.

002.

7. The ultra-thin broadband electromagnetic absorber based on EBG structure according to claim 6, characterized in that: The square resistance of the resistor film patch is 100Ω / sq.

8. The ultra-thin broadband electromagnetic absorber based on EBG structure according to claim 7, characterized in that: The thickness of the metal top plate of the unit structure is 0.035 mm, the thickness of the ceramic medium is 0.508 mm, and the thickness of the patch layer provided with the resistor film patch and the conductor film patch is 0.035 mm.

9. The ultra-thin broadband electromagnetic absorber based on EBG structure according to claim 8, characterized in that: The unit structure is a cube with a square bottom, the side length of the bottom is 1.3 mm, and the height of the cube is 0.508 mm; the resistor film patch and the conductor film patch are both squares with a side length of 0.13 mm, and the through hole diameter is 0.05 mm.

10. The ultra-thin broadband electromagnetic absorber based on EBG structure according to any one of claims 1 to 9, characterized in that: When a plurality of unit structures are arranged periodically to form an electromagnetic absorber, the unit structures are arranged periodically in the following manner: the unit structures are closely arranged on the same plane with the metal top plate as a reference, and the unit structures are arranged periodically in two directions within the plane.

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