Design and optimization method of ultra-wide bandwidth oblique-incident angle absorber

Abstract

The present invention discloses a design and optimization method for an ultra-wide bandwidth oblique incident angle absorber, which significantly expands the working bandwidth of the absorber by using a multi-layer periodic structure. The absorber can simultaneously meet the conditions of normal incidence, TE polarization preset angle and TM polarization preset angle within a preset working bandwidth, that is, achieve ultra-wideband and oblique incident angle. The optimization method includes: modeling a periodic lossy square ring, using equivalent circuit theory to establish a mathematical model of the absorber, the model can calculate the reflection coefficient of the absorber under oblique incident conditions, and based on a genetic algorithm, a global optimal search is performed on the working bandwidth of the absorber to obtain the initial optimal value of the unknown parameter, and the initial value of the parameter is optimized by full-wave simulation to determine the final parameters of the absorber, and the design of the absorber is completed. This can significantly improve the design efficiency of the absorber, so that the performance of the absorber in ultra-wideband and wide incident angle can meet actual needs.

Description

Technical Field

[0001] The invention belongs to the field of microwaves, and in particular relates to a design and optimization method of an ultra-wide bandwidth oblique incident angle absorber. Background Art

[0002] An absorber is a device that can absorb electromagnetic waves in a specific frequency band. It can absorb electromagnetic waves in a specific frequency band according to needs and be used to reduce the radar cross-section RCS, and has important applications in the field of national defense. In recent decades, many types of absorbers have emerged, such as Dallenbach layer, Salisbury screen and frequency selective surface FSS. Traditional absorbers have narrow bandwidth and cannot meet application requirements. Therefore, researchers have made many meaningful attempts to broaden the bandwidth and obtained good results. Among them, using a multilayer structure to increase the bandwidth is an effective method. Some researchers have designed a multilayer absorber structure, which achieves a bandwidth of 12.88:1 frequency doubling under normal incidence conditions and a total profile of only 0.101λL. Although the above absorber has good performance in terms of bandwidth, it only considers the conditions of normal incidence and cannot meet the requirements of wide oblique incidence angles. In summary, there is still a lot of room for improvement in the performance of absorbers in ultra-wideband and wide oblique incidence angles.

[0003] In order to better understand the absorption principle of absorbers and design absorbers with better performance, researchers have proposed many meaningful research methods, such as equivalent medium theory and interference theory. However, the equivalent medium theory treats the absorber as a uniform medium and extracts S parameters for inversion to achieve impedance matching. This method can obtain accurate equivalent impedance, but it requires the extraction of S parameters through experiments or numerical simulations, which is not conducive to the optimization design of structural parameters. Interference theory uses the analysis method of geometric optics to calculate the reflection and refraction of electromagnetic waves between different media, thereby obtaining the reflection coefficient of the absorber. It can well analyze the absorption of absorbers under different oblique incident angles. However, this theory is complex to calculate when analyzing multilayer structures.

[0004] In view of the problem that the performance of existing absorbers in ultra-wide bandwidth and wide incident angle cannot meet actual needs, it is urgent to propose a design and optimization method for ultra-wide bandwidth oblique incident angle absorbers. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a design and optimization method for an ultra-wide bandwidth oblique-incident angle absorber.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] A design and optimization method for an ultra-wide bandwidth oblique incidence angle absorber, the method comprising the following steps:

[0008] S100: designing a structure of an absorber unit, wherein the absorber unit includes a ground plate, at least two different lossy square rings, and at least three different dielectric layers, wherein the ground plate is connected to the bottom dielectric layer, and a lossy square ring is disposed between the two different dielectric layers;

[0009] S200: establishing a mathematical model of the absorber based on the structure of the absorber unit and the equivalent circuit theory, and obtaining an expression of a reflection coefficient of the absorber equivalent circuit under two polarizations according to the mathematical model of the absorber;

[0010] S300: performing a global optimal search based on a genetic algorithm and taking the working bandwidth of the absorber as an objective function according to an expression of the reflection coefficient of the absorber equivalent circuit under two polarizations, and obtaining an initial optimal value of the unknown parameters; wherein the unknown parameters include the square resistance of the lossy square ring, the outer width of the lossy square ring, the ring width of the lossy square ring, the period of the lossy square ring, the thickness of the dielectric layer, and the relative dielectric constant of the dielectric layer; wherein the working bandwidth of the absorber is defined as the reflection coefficient being less than a preset value;

[0011] S400: According to the influence relationship between the preset unknown parameters and the reflection coefficient, the initial optimal values ​​of the unknown parameters are optimized based on the full-wave simulation, the final parameters of the absorber are determined, and the design and optimization of the absorber is completed based on the structure of the absorber unit and the final parameters of the absorber.

[0012] Preferably, in S200, a mathematical model of the absorber is established based on the structure of the absorber unit and the equivalent circuit theory, specifically:

[0013]

[0014] in,

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022] Where R is the equivalent lumped resistance, Rs is the square resistance of the lossy square ring, p is the absorber period, d is the outer width of the lossy square ring, s is the ring width of the lossy square ring, h is the thickness of the dielectric layer, g is the difference between the absorber period and the outer width of the lossy square ring, Z0 is the free space equivalent impedance, θ is the oblique incident angle, ω is the angular frequency, and X L is the inductive reactance, B C To accommodate, F(p,2s,λ,θ) is the lossy square ring geometry parameters (p,s,g) and the equivalent inductive reactance X L and accommodate B C The function of the relationship between them, w represents the parameter 2s or g, λ is the absorber working wavelength, G(p,w,λ,θ) is the correction term of the function F(p,w,λ,θ), A ± is the first type of correction factor related to the absorber period p, oblique incident angle θ and working wavelength λ, β is the second type of correction factor related to the absorber period p and parameter w, ε eff is the equivalent dielectric constant of the whole composed of the lossy square ring and the dielectric substrate, and m is the unit of length.

[0023] Preferably, it is characterized in that in S200, an expression of a reflection coefficient of an absorber equivalent circuit under two polarizations is obtained according to a mathematical model of the absorber, specifically:

[0024] According to Fresnel's law, the relationship between the refraction angle in the medium and the oblique incidence angle is:

[0025]

[0026] The propagation constants in different media are:

[0027]

[0028] Under oblique incidence conditions, the equivalent impedance of TE polarization and TM polarization dielectrics is:

[0029] For TE polarization:

[0030]

[0031] For TM polarization:

[0032]

[0033] Where i=1,2...n(n≧3)

[0034] The input impedance of the equivalent circuit diagram corresponds to the following:

[0035] Z in1 =jZ1 tan(β1h1)

[0036]

[0037]

[0038]

[0039] In summary, the reflection coefficient of the absorber equivalent circuit under two polarizations can be obtained:

[0040] For TE polarization:

[0041]

[0042] For TM polarization:

[0043]

[0044] Among them, θ i is the refraction angle of the i-th dielectric, ε ri is the relative dielectric constant of the i-th dielectric, β i is the propagation constant of the ith dielectric, Z i is the equivalent impedance of the i-th dielectric, Z in(2k) is the even-numbered input impedance marked in the equivalent circuit, Z in(2k-1) are the odd-numbered input impedances marked in the equivalent circuit, For the is the equivalent impedance of the frequency selective surface, and Γ is the reflection coefficient of the absorber equivalent circuit.

[0045] Preferably, the influence relationship between the preset unknown parameters and the reflection coefficient includes: the influence relationship between the square resistance of the lossy square ring and the reflection coefficient, the influence relationship between the outer width of the lossy square ring and the reflection coefficient, the influence relationship between the ring width of the lossy square ring and the reflection coefficient, and the influence relationship between the thickness of the dielectric layer connected to the ground plate and the reflection coefficient.

[0046] Preferably, in S400, according to the influence relationship between the preset unknown parameters and the reflection coefficient, the initial optimal value of the unknown parameter is optimized based on the full-wave simulation, including:

[0047] According to the influence relationship between the square resistance and the reflection coefficient of the lossy square ring, the square resistance of the lossy square ring is adjusted according to a preset first adjustment amplitude based on full-wave simulation to reduce the square resistance of the lossy square ring;

[0048] According to the influence relationship between the outer width of the lossy square ring and the reflection coefficient, the outer width of the lossy square ring is adjusted according to a preset second adjustment amplitude based on full-wave simulation to reduce the outer width of the lossy square ring;

[0049] According to the influence relationship between the ring width of the lossy square ring and the reflection coefficient, the ring width of the lossy square ring is adjusted according to a preset third adjustment amplitude based on full-wave simulation to increase the ring width of the lossy square ring;

[0050] According to the influence relationship between the thickness of the dielectric layer connected to the ground plate and the reflection coefficient, the thickness of the dielectric layer connected to the ground plate is adjusted according to a preset fourth adjustment amplitude based on full-wave simulation.

[0051] Preferably, the absorber unit in S100 includes a ground plate, at least two different lossy square rings and at least three different dielectric layers, the ground plate is connected to the bottom dielectric layer, and a lossy square ring is arranged between two different dielectric layers, specifically:

[0052] The absorber unit includes a ground plate, three different lossy square rings and four different dielectric layers, the ground plate is connected to the bottom dielectric layer, and a lossy square ring is arranged between two different dielectric layers;

[0053] The working bandwidth of the absorber in S300 is defined as the reflection coefficient is less than the preset value, specifically:

[0054] The operating bandwidth of the absorber is defined as the reflection coefficient less than -10dB.

[0055] The above-mentioned ultra-wide bandwidth oblique incidence angle absorber design and optimization method proposes a new absorber unit structure, and uses a multi-layer periodic structure to significantly expand the working bandwidth of the absorber. The absorber can meet the conditions of normal incidence, TE polarization preset angle and TM polarization preset angle (greater than or equal to 45°) within the preset working bandwidth, that is, it realizes ultra-wide bandwidth and oblique incidence angle. A fast optimization method for ultra-wide bandwidth oblique incidence angle absorber is also proposed. First, the periodic lossy square ring is modeled. Secondly, the mathematical model of the absorber is established using the equivalent circuit theory. The model can calculate the reflection coefficient of the absorber under oblique incidence conditions. Then, the working bandwidth of the absorber is globally optimally searched based on the genetic algorithm to obtain the initial optimal values ​​of the unknown parameters. Finally, the initial values ​​of the parameters are optimized through full-wave simulation to determine the final parameters of the absorber and complete the design of the absorber. When many parameters are unknown, this method uses genetic algorithms to quickly obtain reference optimal values ​​of the parameters, which can significantly improve the design efficiency of the absorber and ensure that the performance of the absorber in ultra-wide band and wide incident angle can meet actual needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a flow chart of a design and optimization method for an ultra-wide bandwidth oblique-incident angle absorber in one embodiment of the present invention;

[0057] Figure 2 A schematic diagram of the structure of a lossy square ring in one embodiment of the present invention;

[0058] Figure 3 This is a schematic diagram of the structure of an absorber unit in one embodiment of the present invention;

[0059] Figure 4 Schematic diagram of an equivalent circuit model of an absorber in one embodiment of the present invention;

[0060] Figure 5 It is a curve diagram showing the change of the reflection coefficient of the absorber under normal incidence, TE polarization 45° and TM polarization 45° with frequency in the equivalent circuit model in one embodiment of the present invention;

[0061] Figure 6 It is a curve diagram of the change of reflection coefficient with frequency under three conditions of the equivalent circuit model and full-wave simulation in one embodiment of the present invention;

[0062] Figure 7 Schematic diagram of the relationship between the reflection coefficient of the absorber and the square resistance of the lossy square ring in one embodiment of the present invention;

[0063] Figure 8 Schematic diagram of the relationship between the reflection coefficient of the absorber and the outer width of the lossy square ring in one embodiment of the present invention;

[0064] Fig. 9 Schematic diagram of the relationship between the reflection coefficient of the absorber and the width of the lossy square ring in one embodiment of the present invention;

[0065] Fig.10 Schematic diagram of the relationship between the reflection coefficient of the FSS absorber and h1 under the conditions of TE 45° and TM 45° in one embodiment of the present invention;

[0066] Fig.11 This is a curve diagram showing the variation of the reflection coefficient of the optimized absorber under normal incidence, TE polarization 45° and TM polarization 45° with frequency in one embodiment of the present invention. DETAILED DESCRIPTION

[0067] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0068] In one embodiment, Figure 1 As shown, a design and optimization method for an ultra-wide bandwidth oblique incident angle absorber comprises the following steps:

[0069] S100: Designing a structure of an absorber unit, the absorber unit comprising a ground plate, at least two different lossy square rings and at least three different dielectric layers, the ground plate is connected to the bottom dielectric layer, and each lossy square ring is arranged between two different dielectric layers.

[0070] Specifically, absorbers mostly use periodic structures, which have a strong ability to manipulate the amplitude, phase, and polarization characteristics of electromagnetic waves. The absorber unit usually consists of a dielectric layer, a ground plate, and a lossy square ring layer, where the lossy square ring is located on the dielectric. Among them, the lossy square ring is a square ring resistor with a specific square resistance. The specific structure is as follows Figure 2 Because the lossy square ring has central symmetry, that is, the absorber unit is centrally symmetric, the designed absorber is insensitive to polarization.

[0071] The absorber unit designed in the present invention is composed of a ground plate, at least two layers of different lossy square rings and at least three layers of different dielectric layers. In this embodiment, the ground plate, three layers of different lossy square rings and four layers of different dielectric layers are used as an example for explanation. Figure 3 As shown. In order to significantly increase the bandwidth of the absorber, a multilayer structure is used, and a dielectric layer is placed on the top lossy square ring to achieve better impedance matching. By properly designing the parameters, the structure can achieve an 8:1 frequency-multiplied working bandwidth, that is, it simultaneously meets the conditions of normal incidence, TE polarization 45° and TM polarization 45°. The absorber achieves better performance in ultra-wideband and wide oblique incidence angles.

[0072] S200: establishing a mathematical model of the absorber based on the structure of the absorber unit and the equivalent circuit theory, and obtaining an expression of a reflection coefficient of the absorber equivalent circuit under two polarizations according to the mathematical model of the absorber.

[0073] In one embodiment, in S200, a mathematical model of the absorber is established based on the structure of the absorber unit and the equivalent circuit theory, specifically:

[0074]

[0075] in,

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] Where R is the equivalent lumped resistance, Rs is the square resistance of the lossy square ring, p is the absorber period, d is the outer width of the lossy square ring, s is the ring width of the lossy square ring, h is the thickness of the dielectric layer, g is the difference between the absorber period and the outer width of the lossy square ring, Z0 is the free space equivalent impedance, θ is the oblique incident angle, ω is the angular frequency, and X L is the inductive reactance, B C To accommodate, F(p,2s,λ,θ) is the lossy square ring geometry parameters (p,s,g) and the equivalent inductive reactance X L and accommodate B C The function of the relationship between them, w represents the parameter 2s or g, λ is the absorber working wavelength, G(p,w,λ,θ) is the correction term of the function F(p,w,λ,θ), A ± is the first type of correction factor related to the absorber period p, oblique incident angle θ and working wavelength λ, β is the second type of correction factor related to the absorber period p and parameter w, ε eff is the equivalent dielectric constant of the whole composed of the lossy square ring and the dielectric substrate, and m is the unit of length.

[0084] In one embodiment, in S200, an expression of a reflection coefficient of an absorber equivalent circuit under two polarizations is obtained according to a mathematical model of the absorber, specifically:

[0085] According to Fresnel's law, the relationship between the refraction angle in the medium and the oblique incidence angle is:

[0086]

[0087] The propagation constants in different media are:

[0088]

[0089] Under oblique incidence conditions, the equivalent impedance of TE polarization and TM polarization dielectrics is:

[0090] For TE polarization:

[0091]

[0092] For TM polarization:

[0093]

[0094] Where i=1,2...n(n≧3)

[0095] The input impedance of the equivalent circuit diagram corresponds to the following:

[0096] Z in1 =jZ1 tan(β1h1)

[0097]

[0098]

[0099]

[0100] In summary, the reflection coefficient of the absorber equivalent circuit under two polarizations can be obtained:

[0101] For TE polarization:

[0102]

[0103] For TM polarization:

[0104]

[0105] Among them, θ i is the refraction angle of the i-th dielectric, ε ri is the relative dielectric constant of the i-th dielectric, β i is the propagation constant of the ith dielectric, Z i is the equivalent impedance of the i-th dielectric, Z in(2k) is the even-numbered input impedance marked in the equivalent circuit, Z in(2k-1) are the odd-numbered input impedances marked in the equivalent circuit, For the is the equivalent impedance of the frequency selective surface, and Γ is the reflection coefficient of the absorber equivalent circuit.

[0106] Specifically, in the designed absorber, periodically arranged lossy square rings constitute a frequency selective surface FSS. The FSS unit can be equivalent to an RLC lumped element, and its impedance expression is:

[0107]

[0108] Among them, the relationship between the equivalent lumped resistance R and the lossy square ring geometric parameters p, d, s and the square resistance Rs of the square ring is as follows:

[0109]

[0110] The equivalent inductance L and equivalent capacitance C can be approximated by the equivalent circuit model, and their specific relationship with the geometric parameters p, d, s, and g of the lossy square ring is as follows:

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] According to the transmission line theory, a uniform medium can be equivalent to a section of transmission line. Therefore, the equivalent circuit model of the absorber is shown in Figure 4.

[0119] The calculation process is described below:

[0120] According to Fresnel's law, the relationship between the refraction angle in the medium and the oblique incidence angle is:

[0121]

[0122] The propagation constants in different media are:

[0123]

[0124] Under oblique incidence conditions, the dielectric equivalent impedances of TE polarization and TM polarization are different.

[0125] For TE polarization:

[0126]

[0127] For TM polarization:

[0128]

[0129] Where i = 1, 2, 3, 4

[0130] The input impedances at the marked positions in the figure correspond to the following:

[0131] Z in1 =jZ1 tan(β1h1)

[0132]

[0133]

[0134]

[0135] In summary, the reflection coefficient of the absorber equivalent circuit under two polarizations can be obtained:

[0136] For TE polarization:

[0137]

[0138] For TM polarization:

[0139]

[0140] S300: According to the expression of the reflection coefficient of the absorber equivalent circuit under two polarizations, a global optimal search is performed based on a genetic algorithm with the working bandwidth of the absorber as the objective function to obtain the initial optimal values ​​of the unknown parameters; wherein the unknown parameters include the square resistance of the lossy square ring, the outer width of the lossy square ring, the ring width of the lossy square ring, the period of the lossy square ring, the thickness of the dielectric layer and the relative dielectric constant of the dielectric layer; wherein the working bandwidth of the absorber is defined as the reflection coefficient being less than a preset value.

[0141] In one embodiment, the absorber unit in S100 includes a ground plate, at least two different lossy square rings and at least three different dielectric layers, the ground plate is connected to the bottom dielectric layer, and each lossy square ring is arranged between two different dielectric layers, specifically:

[0142] The absorber unit includes a ground plate, three different lossy square rings and four different dielectric layers, the ground plate is connected to the bottom dielectric layer, and each lossy square ring is arranged between two different dielectric layers;

[0143] The working bandwidth of the absorber in S300 is defined as the reflection coefficient is less than the preset value, specifically:

[0144] The operating bandwidth of the absorber is defined as the reflection coefficient less than -10dB.

[0145] Specifically, by building the above equivalent circuit model, we established an effective mathematical relationship between the geometric parameters and impedance bandwidth of the absorber, which is the basis for achieving rapid optimization design. Then, we used a genetic algorithm with good global search performance to optimize the parameters, thereby achieving the maximum bandwidth that simultaneously satisfies the conditions of normal incidence, TE polarization 45°, and TM polarization 45°.

[0146] For simplicity, the present invention uses the sum of the bandwidths under normal incidence, TE polarization 45°, and TM polarization 45° as the objective function to perform maximum value search to achieve parameter optimization. However, it should be emphasized that for normal incidence, the present invention uses -20dB as the bandwidth limit, while TE polarization 45° and TM polarization 45° use -10dB as the bandwidth limit. This is because, Figure 5As shown in the figure, compared with normal incidence, the low-frequency performance of TE polarization 45° and TM polarization 45° will deteriorate, among which TE polarization 45° is more obvious. And under both conditions, the resonant frequency will move to the high-frequency end, among which TM polarization 45° moves more. Therefore, in order to L -f H The range satisfies normal incidence, TE polarization 45° and TM polarization 45° at the same time. During the algorithm optimization process, the value of the low-frequency end should be appropriately smaller than f L .

[0147] In addition, in order to avoid the influence of grating lobes, the period p of the absorber unit should satisfy:

[0148]

[0149] Among them, λ H The maximum frequency f H The corresponding wavelength. The value ranges of other optimized parameters are shown in Table 1:

[0150] Table 1 Value range of absorber parameters

[0151]

[0152] After the genetic algorithm performs global optimal search, the initial values ​​of the parameters are shown in Table 2:

[0153] Table 2 Initial optimal values ​​of absorber parameters

[0154]

[0155] S400: According to the influence relationship between the preset unknown parameters and the reflection coefficient, the initial optimal values ​​of the unknown parameters are optimized based on the full-wave simulation, the final parameters of the absorber are determined, and the design and optimization of the absorber is completed based on the structure of the absorber unit and the final parameters of the absorber.

[0156] In one embodiment, the influence relationship between the preset unknown parameters and the reflection coefficient includes: the influence relationship between the square resistance of the lossy square ring and the reflection coefficient, the influence relationship between the outer width of the lossy square ring and the reflection coefficient, the influence relationship between the ring width of the lossy square ring and the reflection coefficient, and the influence relationship between the thickness of the dielectric layer connected to the ground plate and the reflection coefficient.

[0157] In one embodiment, in S400, according to the influence relationship between the preset unknown parameter and the reflection coefficient, the initial optimal value of the unknown parameter is optimized based on the full-wave simulation, including:

[0158] According to the influence relationship between the square resistance and the reflection coefficient of the lossy square ring, the square resistance of the lossy square ring is adjusted according to a preset first adjustment amplitude based on full-wave simulation to reduce the square resistance of the lossy square ring;

[0159] According to the influence relationship between the outer width of the lossy square ring and the reflection coefficient, the outer width of the lossy square ring is adjusted according to a preset second adjustment amplitude based on full-wave simulation to reduce the outer width of the lossy square ring;

[0160] According to the influence relationship between the ring width of the lossy square ring and the reflection coefficient, the ring width of the lossy square ring is adjusted according to a preset third adjustment amplitude based on full-wave simulation to increase the ring width of the lossy square ring;

[0161] According to the influence relationship between the thickness of the dielectric layer connected to the ground plate and the reflection coefficient, the thickness of the dielectric layer connected to the ground plate is adjusted according to a preset fourth adjustment amplitude based on full-wave simulation.

[0162] Specifically, under normal incidence, TE polarization 45° and TM polarization 45° conditions, the reflection coefficient calculated using the equivalent circuit model is similar to the reflection coefficient of the full-wave simulation. Figure 6 As shown. The full-wave simulation results are calculated using CST's frequency domain solver. As can be seen from the figure, compared with the full-wave simulation, the equivalent circuit model can better calculate the four absorption peaks of the absorber, and its results are well consistent with the results of the full-wave simulation. Although the results of the equivalent circuit model are not very accurate, it can provide effective initial values ​​for the full-wave simulation, which will greatly improve the efficiency of the full-wave simulation optimization. In order to obtain a design that meets the requirements more quickly, the present invention performs full-wave simulation optimization in the following order:

[0163] (1) Adjust the square ring resistance Rs: The square ring resistance Rs can significantly affect the reflection coefficient of the absorber, and its relationship with the reflection coefficient is as follows: Figure 7 As shown in the figure, as Rs increases, the performance of the absorber in the low-frequency part continues to decrease, which will lead to a reduction in the absorber's working bandwidth; (2) Adjust the outer width d of the lossy square ring and the ring width s of the lossy square ring: Parameters d and s are closely related to the resonant frequency of the absorber. The relationship between parameter d and the reflection coefficient is shown in Figure 8 As shown in the figure, it can be seen that as d increases, the lowest resonance frequency of the absorber moves to the left, but the reflection coefficient of the low-frequency part gradually increases, and the performance of the low-frequency part deteriorates. Fig. 9It can be seen that as s increases, the lowest resonant frequency of the absorber moves to the left, the middle and highest resonant frequencies move to the right, the reflection coefficient of the low-frequency part gradually decreases, and the performance of the low-frequency part is improved. In summary, this shows that: in order to meet the target requirements of the low-frequency end, the parameter d can be appropriately reduced and the parameter s can be increased; (3) adjust the thickness h1 of the dielectric layer connected to the ground plane: when other parameters remain unchanged, the relationship between the parameter h1 and the reflection coefficient is as follows Fig.10 As shown in the figure. It can be seen from the figure that as h1 increases, the reflection coefficient of the absorber moves to the left as a whole. Compared with parameters s and d, h1 has less impact on the overall performance. This is because parameters s and d are closely related to the size of the equivalent RLC of the lossy square ring FSS, and their changes will have a significant impact on each resonant frequency. The parameter h1 corresponds to the distance between the lossy square ring FSS and the ground plane, and its change has the same impact on all resonant frequencies. Therefore, in the optimization process, h1 can be adjusted last to make the working bandwidth meet the target requirements.

[0164] After the above optimization design, the working bandwidth of the absorber is 2.2-17.6 GHz. The final parameter values ​​of the absorber are shown in Table 3. The reflection coefficient of the absorber is shown in Fig.11 shown.

[0165] Table 3 Parameter optimization results

[0166]

[0167] In view of the problem that the performance of the absorber in ultra-wideband and wide incident angle cannot meet the actual needs, the present invention proposes a design and optimization method for an ultra-wide bandwidth oblique-incidence angle absorber with 8 times the frequency (2.2-17.6GHz). The innovations include: proposing a design for an ultra-wide bandwidth oblique-incidence angle absorber, and further proposing a design for an ultra-wide bandwidth oblique-incidence angle absorber with 8 times the frequency, and using a multi-layer periodic structure to significantly expand the working bandwidth of the absorber. The absorber can simultaneously meet the conditions of normal incidence, TE polarization 45° and TM polarization 45° within the working bandwidth of 2.2-17.6GHz, that is, to achieve ultra-wideband and oblique incident angle; a fast optimization method for an ultra-wide bandwidth oblique-incidence angle absorber is proposed. First, a periodic lossy square ring is modeled. Secondly, the mathematical model of the absorber is established using equivalent circuit theory. The model can calculate the reflection coefficient of the absorber under oblique incidence conditions. Then, a global optimal search is performed on the working bandwidth of the absorber based on a genetic algorithm to obtain the initial optimal value of the parameter. Finally, the initial parameter values ​​are optimized through full-wave simulation, the final parameters of the absorber are determined, and the design of the absorber is completed. In the case of many unknown parameters, this method uses genetic algorithms to quickly obtain the reference optimal values ​​of the parameters, which can significantly improve the design efficiency of the absorber.

[0168] The above is a detailed introduction to the design and optimization method of an ultra-wide bandwidth oblique-incident angle absorber provided by the present invention. This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A design and optimization method for an ultra-wide bandwidth oblique incidence angle absorber, characterized in that: The method comprises the following steps: S100: designing a structure of an absorber unit, wherein the absorber unit comprises a ground plate, at least two different lossy square rings and at least three different dielectric layers, wherein the ground plate is connected to the bottom dielectric layer, and a lossy square ring is disposed between the two different dielectric layers; S200: establishing a mathematical model of the absorber based on the structure of the absorber unit and the equivalent circuit theory, and obtaining an expression of a reflection coefficient of the absorber equivalent circuit under two polarizations according to the mathematical model of the absorber; S300: According to the expression of the reflection coefficient of the absorber equivalent circuit under two polarizations, a global optimal search is performed based on a genetic algorithm with the working bandwidth of the absorber as the objective function to obtain the initial optimal value of the unknown parameters; wherein the unknown parameters include the square resistance of the lossy square ring, the outer width of the lossy square ring, the ring width of the lossy square ring, the period of the lossy square ring, the thickness of the dielectric layer and the relative dielectric constant of the dielectric layer; wherein the working bandwidth of the absorber is defined as the reflection coefficient being less than a preset value; S400: optimizing the initial optimal value of the unknown parameter based on the full-wave simulation according to the influence relationship between the preset unknown parameter and the reflection coefficient, determining the final parameter of the absorber, and completing the design and optimization of the absorber based on the structure of the absorber unit and the final parameter of the absorber; In S200, a mathematical model of the absorber is established based on the structure of the absorber unit and the equivalent circuit theory, specifically: in, Where R is the equivalent lumped resistance, Rs is the square resistance of the lossy square ring, p is the absorber period, d is the outer width of the lossy square ring, s is the ring width of the lossy square ring, h is the thickness of the dielectric layer, g is the difference between the absorber period and the outer width of the lossy square ring, Z0 is the free space equivalent impedance, θ is the oblique incident angle, ω is the angular frequency, and X L is the inductive reactance, B C To accommodate, F(p,2s,λ,θ) is the lossy square ring geometry parameters (p,s,g) and the equivalent inductive reactance X L and accommodate B C The function of the relationship between them, w represents the parameter 2s or g, λ is the absorber working wavelength, G(p,w,λ,θ) is the correction term of the function F(p,w,λ,θ), A ± is the first type of correction factor related to the absorber period p, oblique incident angle θ and working wavelength λ, β is the second type of correction factor related to the absorber period p and parameter w, ε r is the relative dielectric constant of the dielectric substrate, ε eff is the equivalent dielectric constant of the whole composed of the lossy square ring and the dielectric substrate, and m is the unit of length.

2. The method according to claim 1, characterized in that In S200, an expression of the reflection coefficient of the absorber equivalent circuit under two polarizations is obtained according to the mathematical model of the absorber, which is specifically: According to Fresnel's law, the relationship between the refraction angle in the medium and the oblique incidence angle is: The propagation constants in different media are: Under oblique incidence conditions, the equivalent impedance of TE polarization and TM polarization dielectrics is: For TE polarization: For TM polarization: Where, i=1,2...n(n≧3); The input impedances marked in the equivalent circuit diagram correspond to the following: From in1 =jZ1 tan(β1h1) In summary, the reflection coefficient of the absorber equivalent circuit under two polarizations can be obtained: For TE polarization: For TM polarization: Among them, θ i is the refraction angle of the i-th dielectric, ε ri is the relative dielectric constant of the i-th dielectric, β i is the propagation constant of the ith dielectric, Z i is the equivalent impedance of the i-th dielectric, Z in1 is the first input impedance marked in the equivalent circuit, Z in(2k) is the even-numbered input impedance marked in the equivalent circuit, Z in(2k-1) are the odd-numbered input impedances marked in the equivalent circuit, For the is the equivalent impedance of the frequency selective surface, and Γ is the reflection coefficient of the absorber equivalent circuit.

3. The method according to claim 2, characterized in that The influence relationship between the preset unknown parameters and the reflection coefficient includes: the influence relationship between the square resistance of the lossy square ring and the reflection coefficient, the influence relationship between the outer width of the lossy square ring and the reflection coefficient, the influence relationship between the ring width of the lossy square ring and the reflection coefficient, and the influence relationship between the thickness of the dielectric layer connected to the ground plate and the reflection coefficient.

4. The method according to claim 3, characterized in that In S400, according to the influence relationship between the preset unknown parameters and the reflection coefficient, the initial optimal value of the unknown parameters is optimized based on full-wave simulation, including: According to the influence relationship between the square resistance and the reflection coefficient of the lossy square ring, the square resistance of the lossy square ring is adjusted according to a preset first adjustment amplitude based on full-wave simulation to reduce the square resistance of the lossy square ring; According to the influence relationship between the outer width of the lossy square ring and the reflection coefficient, the outer width of the lossy square ring is adjusted according to a preset second adjustment amplitude based on full-wave simulation to reduce the outer width of the lossy square ring; According to the influence relationship between the ring width of the lossy square ring and the reflection coefficient, the ring width of the lossy square ring is increased according to a preset third adjustment amplitude based on full-wave simulation; According to the influence relationship between the thickness of the dielectric layer connected to the ground plate and the reflection coefficient, the thickness of the dielectric layer connected to the ground plate is adjusted according to a preset fourth adjustment amplitude based on full-wave simulation.

5. The method according to claim 4, characterized in that The absorber unit in S100 includes a ground plate, at least two different lossy square rings and at least three different dielectric layers, wherein the ground plate is connected to the bottom dielectric layer, and a lossy square ring is disposed between two different dielectric layers, specifically: The absorber unit comprises a ground plate, three different lossy square rings and four different dielectric layers, wherein the ground plate is connected to the bottom dielectric layer, and a lossy square ring is arranged between two different dielectric layers; The working bandwidth of the absorber in S300 is defined as a reflection coefficient less than a preset value, specifically: The operating bandwidth of the absorber is defined as a reflection coefficient less than -10 dB.

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