WO2016062344A1 - Fast and accurate design method for broadband multi-layered radar absorbers - Google Patents
Fast and accurate design method for broadband multi-layered radar absorbers Download PDFInfo
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- WO2016062344A1 WO2016062344A1 PCT/EP2014/072746 EP2014072746W WO2016062344A1 WO 2016062344 A1 WO2016062344 A1 WO 2016062344A1 EP 2014072746 W EP2014072746 W EP 2014072746W WO 2016062344 A1 WO2016062344 A1 WO 2016062344A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
- H01Q15/0046—Theoretical analysis and design methods of such selective devices
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
- H01Q17/002—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems using short elongated elements as dissipative material, e.g. metallic threads or flake-like particles
Definitions
- This invention is related to a fast and accurate design method of broadband and multi- layered radar absorbing structures comprising of lossy frequency selective surface layers.
- Broadband multilayered circuit analog absorbers consist of lossy FSS (Frequency Selective Surface) layers backed by a conducting plane.
- FSS structures have periodic geometrical conductive (usually metallic) patterns used for frequency selectivity in electromagnetic applications such as radomes, reflectors, reflect arrays, etc. Periodic geometrical patterns provide low loss frequency dependent reactive impedances which are used for realization of frequency selective transmission and/or reflection characteristics for the waves passing through the layers.
- periodic structures are realized by lossy materials instead of conductive elements, they can be used as frequency selective absorptive layers and by using multiple of these layers broadband absorbing structures with low mass and thickness could be achieved.
- a method for the design of broadband multi-layered electromagnetic absorber comprises the steps of, computing transmission and reflection characteristics of the candidate frequency selective surface types; generating equivalent lumped circuit models for said candidate frequency selective surface types according to computed characteristics; generating a database using generated equivalent lumped circuit models; for each frequency selective surface layers, forming an initial design according to the requirements of the multi-layered radar absorbing structure by using optimization techniques with transmission line theory; according to initial design, obtaining appropriate frequency selective surface structures from said database for each layer; performing electromagnetic analysis techniques for overall structure and optimizing frequency selective surface structure of each layer according to result of the electromagnetic analysis in order to eliminate interactions between different frequency selective surface layers.
- initial model of the FSS layers are designed without using electromagnetic analysis. Therefore, said initial models are designed in a fast and reliable manner. Moreover, according to the present invention, electromagnetic analysis is performed for the final model and optimization techniques are performed according to the electromagnetic analysis. Therefore, complexity of the overall design process is reduced.
- the main object of the invention is to construct a fast and accurate design method which can be used for the design of broadband, thin and multi layered circuit analog radar absorbing structures comprising of lossy FSS layers.
- Another object of the invention is to adjust number of layers, geometric pattern types together with surface resistance values of the lossy FSS layers, overall thickness of the structure are the parameters by the designer according to the desired specifications.
- Another object of the invention is to take mutual coupling effects into consideration, in order to eliminateso unexpected inconsistencies due to unpredicted effects.
- Figures 1 a-1 e shows examples of various FSS geometries.
- FIG. 2 shows flowchart of the design method of the invention.
- FIG. 3 show the detailed flowchart of the design method of the invention.
- Multi-layered radar absorbing structures usually comprises lossy frequency selective surface (FSS) layers.
- Said FSS layers comprise conductive (usually metallic) areas with different patterns (as shown in figures 1 a-1 e).
- different patterns on different FSS layers are provided.
- different layers usually affect each other. Therefore, multi-layered structures do not operate as combination of single layers.
- designing of the multi-layer structures is a challenging process.
- a fast and accurate design method of broadband and multi-layered radar absorbing structures comprising of lossy frequency selective surface layers is provided.
- Said design method comprises the steps of, computing transmission and reflection characteristics of the candidate FSS types (101 ); generating equivalent lumped circuit models for said candidate FSS types according to computed characteristics (102); generating a database using generated equivalent lumped circuit models (103); for each FSS layers, forming an initial design according to the requirements of the multi-layered radar absorbing structure by using optimization techniques with transmission line theory (without using electromagnetic analysis), (104); according to initial design, obtaining appropriate FSS structures from said database for each layer (105); performing electromagnetic analysis techniques for overall structure (106) and optimizing FSS structure of each layer according to result of the electromagnetic analysis (107).
- any FSS geometry can be a candidate for the lossy layers
- the inputs (requirements) (1 ) of the invention proposed for the design of broadband multilayer radar absorbing structures are:
- characterization of the candidate FSS types (2) either by using full wave electromagnetic analysis (2.2a) or existing analytical formulations of specific geometries (2.2b) is realized.
- FSS layers are modeled as perfectly conducting sheets in order to decrease the number of cases to be simulated and computation time of characterization.
- equivalent lumped circuit model and lumped components are extracted by using equivalent capacitors and inductors.
- This characterization step is based on the generation of a database (3) relating the LC model parameters of each FSS type to the altering geometrical dimensions of the pattern (for example edge length of a square patch type FSS, arm width and length of a crossed dipole, inner and outer edge lengths of a square ring type FSS, etc.)-
- the aim is to extract upper and lower limits for the L (inductance) and C (capacitance) parameters of their lumped models. These limits will be used in the synthesis part (4) of the invention as boundaries of the search space for the associated layers' optimum reactance values. If the separating slabs for the absorber to be designed are not air lines, there are two alternative methods for candidate FSS types' characterizations.
- the first one is to model the surrounding medium in the full wave EM analysis with the corresponding material characteristics.
- the other method is to use analytical formulas existing for some specific FSS types and used to convert LC parameters obtained for free standing case in air to the case where FSS is embedded into the corresponding dielectric medium.
- the suitable FSS types among the candidate ones and proper lumped resistance values are determined for each layer of the absorber (4).
- the corresponding decisions are realized by using optimization techniques (4.2) together with transmission line theory (4.3) in which the FSS layers are modeled as lumped components and loss is introduced by using series resistors to these lumped models.
- the thickness values of the separating slabs with the predefined electrical characteristics; optimum inductance, capacitance and resistance values for each layer of the structure are searched within the specified reactance limits of candidate FSS types (3).
- optimum lumped reactance and resistance values of the solution set for the synthesis parameters (5) are realized by altering the geometrical dimensions of the selected FSS patterns among the candidate ones with the aid of database (3) generated in the first step (2) and optimum surface resistance values are searched to achieve desired lumped resistance values (6).
- This optimization process (6.3, 6.4 and 6.5) is carried out in an iterative manner.
- As an initial guess for each selected FSS geometry, by using the database 3 geometrical dimensions of the pattern are selected (6.1 ) to realize optimum L and C values for the solution set (5).
- the ratio between the area of one period and the physical area of the FSS being simulated is used (6.2): effective area
- the lossy FSS with the defined geometric dimensions and initial surface resistance is analyzed (6.3) with one of full wave computational electromagnetic methods (FEM, MoM, FDTD, etc.).
- FEM full wave computational electromagnetic methods
- the surface resistance value together with the geometric dimensions of the pattern is modified in an iterative manner until desired optimum lumped model parameters are realized within a predefined error.
- This iterative lossy layer realization step is conducted by focusing on the center of the desired frequency band for all of the lossy FSS layers to be used in the design. Since the effective area of the FSS pattern changes with respect to frequency, it is not possible to achieve a constant lumped resistance value throughout the whole frequency range with a constant surface resistance value. Due to this fact, the target resistance value is realized at the center of the specified frequency range.
- the outputs of this step are:
- the absorption characteristics of the designed broadband multilayer absorber are obtained by using one of electromagnetic analysis techniques (FEM, FDTD, MoM, etc.) (8.1 ). If the final characteristics do not satisfy the aimed absorption criteria due to unconsidered coupling effects between the layers, a further optimization is conducted over the whole structure by using an optimization technique (8.3) (algorithms, iterative methods, heuristic approaches, etc.) in corporation with a full wave electromagnetic simulation technique (8.4).
- FEM electromagnetic analysis techniques
- the cost functions of the optimization processes are determined by using full wave simulations (8.5), hence reasonable values are chosen for the limits of the optimization variables (geometrical dimensions of FSS patterns and surface resistance values) in order not to increase the time elapsed for this final optimization stage and to sustain the efficiency of the invention. These limits are specified to be in proximity of the values determined in the previous step (7) in order not to disturb the final design significantly. Also, since the search space for the final optimization of absorbing structure's parameters is narrow, the time consumed by full wave electromagnetic solutions is minimized in an effective way.
- the outputs of the final step of the invention are:
- initial model of the FSS layers are designed without using electromagnetic analysis. Therefore, said initial models are designed in a fast and reliable manner. Moreover, according to the present invention, electromagnetic analysis is performed for the final model and optimization techniques are performed according to the electromagnetic analysis. Therefore, complexity of the overall design process is reduced.
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Abstract
The invention is related to a fast and accurate method for the design of broadband multi layered radar absorbing structures comprising of lossy FSS layers. The method comprises of four main steps, namely; candidate FSS types characterization by altering the geometrical dimensions of the FSS patterns, optimization by using circuit equivalent lumped models together with transmission line theory, optimum sheet conductivity (surface resistance) and geometrical dimensions determination within the predefined reactance limits extracted with the aid of full wave computational methods in an iterative manner, and optimization of the final structure within predefined limits concerning FSS dimensions and sheet conductivities to eliminate the effects of undesired and unpredicted couplings between lossy layers.
Description
DESCRIPTION
FAST AND ACCURATE DESIGN METHOD FOR BROADBAND MULTI-LAYERED
RADAR ABSORBERS
Technical Field
This invention is related to a fast and accurate design method of broadband and multi- layered radar absorbing structures comprising of lossy frequency selective surface layers.
Prior Art
Broadband multilayered circuit analog absorbers consist of lossy FSS (Frequency Selective Surface) layers backed by a conducting plane. FSS structures have periodic geometrical conductive (usually metallic) patterns used for frequency selectivity in electromagnetic applications such as radomes, reflectors, reflect arrays, etc. Periodic geometrical patterns provide low loss frequency dependent reactive impedances which are used for realization of frequency selective transmission and/or reflection characteristics for the waves passing through the layers. When these periodic structures are realized by lossy materials instead of conductive elements, they can be used as frequency selective absorptive layers and by using multiple of these layers broadband absorbing structures with low mass and thickness could be achieved.
In the literature, for the design of single layered circuit analog radar absorbing structures, some optimization techniques (algorithms, iterative methods, heuristic approaches, etc.) are used together with a full wave computational electromagnetic method. With this technique, without investigating the impedance characteristics of the FSS layers, the geometrical parameters of the single layer FSS pattern are searched in a very wide space to obtain the desired absorption performance in the specified frequency band. When iteration cycles in the optimization process are taken into consideration, numerous full wave electromagnetic solutions seem to be time consuming processes, and if one does not have an initial guess in the neighborhood of the optimal geometrical parameters of the single FSS layer, this technique incorporating associated full wave electromagnetic solutions for every parameter set becomes very inefficient in terms of computation time.
Another technique is the utilization of Smith Chart for obtaining the desired impedance characteristics of the associated FSS layer together with the thickness as a design tool (Document: ΊΕΕΕ TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 55, NO. 1, JANUARY 2007). Although this technique is easy to use for single layered structures, it becomes very complicated for the design of multi layered FSS structures. Yet, there exists no example for multi layered FSS design methodology incorporating Smith Chart solely. Indeed in this technique since none of the mathematical optimization methods is used, it is very hard to find the global optimum parameters regarding the characteristics of the layers. Still another point is that with the design methods in the literature given above mutual coupling effects between the layers could not be taken into consideration during the design process. This shortage may result significant inconsistencies between the desired absorption characteristics and realized performance by these design methodologies. Brief Description of the Invention
With the present invention, a method for the design of broadband multi-layered electromagnetic absorber is provided. Said method comprises the steps of, computing transmission and reflection characteristics of the candidate frequency selective surface types; generating equivalent lumped circuit models for said candidate frequency selective surface types according to computed characteristics; generating a database using generated equivalent lumped circuit models; for each frequency selective surface layers, forming an initial design according to the requirements of the multi-layered radar absorbing structure by using optimization techniques with transmission line theory; according to initial design, obtaining appropriate frequency selective surface structures from said database for each layer; performing electromagnetic analysis techniques for overall structure and optimizing frequency selective surface structure of each layer according to result of the electromagnetic analysis in order to eliminate interactions between different frequency selective surface layers.
According to the present invention, initial model of the FSS layers are designed without using electromagnetic analysis. Therefore, said initial models are designed in a fast and reliable manner. Moreover, according to the present invention, electromagnetic analysis is
performed for the final model and optimization techniques are performed according to the electromagnetic analysis. Therefore, complexity of the overall design process is reduced.
Object of the Invention
The main object of the invention is to construct a fast and accurate design method which can be used for the design of broadband, thin and multi layered circuit analog radar absorbing structures comprising of lossy FSS layers. Another object of the invention is to adjust number of layers, geometric pattern types together with surface resistance values of the lossy FSS layers, overall thickness of the structure are the parameters by the designer according to the desired specifications.
Another object of the invention is to take mutual coupling effects into consideration, in order to eliminateso unexpected inconsistencies due to unpredicted effects.
Description of Drawings
Figures 1 a-1 e shows examples of various FSS geometries.
Figure 2 shows flowchart of the design method of the invention.
Figure 3 show the detailed flowchart of the design method of the invention.
Characterization of candidate FSS types (101 )
Generating equivalent lumped circuit models (102)
Generating database (103)
Forming an initial design (104)
Obtaining appropriate FSS structures from database (105)
Electromagnetic analysis (106)
Optimization (107)
Detailed Description of the Invention
Multi-layered radar absorbing structures usually comprises lossy frequency selective surface (FSS) layers. Said FSS layers comprise conductive (usually metallic) areas with
different patterns (as shown in figures 1 a-1 e). According to the requirements (such as frequency ranges) of the multi-layered radar absorbing structures, different patterns on different FSS layers are provided. In a multi-layer structure, different layers usually affect each other. Therefore, multi-layered structures do not operate as combination of single layers. As a result, designing of the multi-layer structures is a challenging process. In order to simplify said challenging process, according to the present application a fast and accurate design method of broadband and multi-layered radar absorbing structures comprising of lossy frequency selective surface layers is provided.
Flowchart of the design method of the present application is given in figure 2. Said design method comprises the steps of, computing transmission and reflection characteristics of the candidate FSS types (101 ); generating equivalent lumped circuit models for said candidate FSS types according to computed characteristics (102); generating a database using generated equivalent lumped circuit models (103); for each FSS layers, forming an initial design according to the requirements of the multi-layered radar absorbing structure by using optimization techniques with transmission line theory (without using electromagnetic analysis), (104); according to initial design, obtaining appropriate FSS structures from said database for each layer (105); performing electromagnetic analysis techniques for overall structure (106) and optimizing FSS structure of each layer according to result of the electromagnetic analysis (107).
With the invention, it is possible to design a broadband multilayer absorber with the following properties:
• Backed by a highly conducting plane used to eliminate the dependence of absorption characteristics on environmental effects, as in almost all the absorber types
• Multilayered structure, without any constraint on the number of layers,
• Periodic structure, a common period for all the layers,
• Freedom of FSS type choice, any FSS geometry can be a candidate for the lossy layers,
• Degree of freedom for selection of overall thickness together with the thickness values of the separating slabs,
• Degree of freedom for selection of electrical characteristics of the slabs,
• Limitations regarding practical considerations in terms of allowable surface resistance values, in house slab characteristics and thickness values can be imposed to the design method. An exemplary embodiment of the present application, which is shown in figure 3, is given below.
The inputs (requirements) (1 ) of the invention proposed for the design of broadband multilayer radar absorbing structures are:
> Operational frequency band
> Target absorption characteristics throughout the operational frequency band
o Absorption levels for sub frequency bands
o Spot frequency values (notches in the band) together with desired heavy absorption values regarding these notches
> Candidate FSS patterns to be used for the lossy layers
> Thickness specifications
o Total thickness of the structure,
o Number of separating slabs,
o Maximum (or exact) thickness values of the seperating slabs
> Electrical characteristics of the seperating slabs
o Complex permittivity values,
o Complex permeability values,
> Allowable discrete (or maximum and minimum) surface resistance values for lossy FSS layers
> Electrical characteristics for the cover layer if exists
In the first step of the embodiment, characterization of the candidate FSS types (2) either by using full wave electromagnetic analysis (2.2a) or existing analytical formulations of specific geometries (2.2b) is realized. FSS layers are modeled as perfectly conducting sheets in order to decrease the number of cases to be simulated and computation time of characterization. According to computed transmission and reflection characteristics of the associated lossless FSS geometry, equivalent lumped circuit model and lumped components (2.3) are extracted by using equivalent capacitors and inductors. This
characterization step is based on the generation of a database (3) relating the LC model parameters of each FSS type to the altering geometrical dimensions of the pattern (for example edge length of a square patch type FSS, arm width and length of a crossed dipole, inner and outer edge lengths of a square ring type FSS, etc.)- The aim is to extract upper and lower limits for the L (inductance) and C (capacitance) parameters of their lumped models. These limits will be used in the synthesis part (4) of the invention as boundaries of the search space for the associated layers' optimum reactance values. If the separating slabs for the absorber to be designed are not air lines, there are two alternative methods for candidate FSS types' characterizations. The first one is to model the surrounding medium in the full wave EM analysis with the corresponding material characteristics. The other method is to use analytical formulas existing for some specific FSS types and used to convert LC parameters obtained for free standing case in air to the case where FSS is embedded into the corresponding dielectric medium. By using the S- parameters of the analyzed FSS geometries, the optimum series LC representation of the frequency selective surfaces is realized with the equations:
-2S 11
"shunt.r
Z0(l + S )
2(1 - S21)
shunt.t
S21Z0
(Yshunt.t Yshunt.r)
shunt.avg
shunt.avg.
In the next step of the invention, by using the extracted LC limits in the previous step 2 and according to the design constraints specified 1 , the suitable FSS types among the candidate ones and proper lumped resistance values are determined for each layer of the absorber (4). The corresponding decisions are realized by using optimization techniques (4.2) together with transmission line theory (4.3) in which the FSS layers are modeled as lumped components and loss is introduced by using series resistors to these lumped
models. In this step, the thickness values of the separating slabs with the predefined electrical characteristics; optimum inductance, capacitance and resistance values for each layer of the structure are searched within the specified reactance limits of candidate FSS types (3). By considering the practical limitations regarding the production of lossy FSS layers, allowable resistance values can be used as input to the synthesis as the search space for determination of optimum lumped resistance values. During this optimization process, every layer is modeled with a lumped impedance value which is connected as shunt to the transmission lines representing the layer separator slabs (4.3). By using transmission line theory, the input impedance of the structure is optimized to free space intrinsic impedance, which is approximately 377 ohms. The fastness of the invention is obtained by synthesis part (4) namely, calculating the desired absorption characteristics with numerous iterations in circuit equivalent lumped model by transmission line theory approach with very short computation times to synthesize the main absorber configuration. The output of this step is the solution set for the synthesis parameters (5) which are:
> Number of layers,
> Thickness values of each separating slab,
> Optimum FSS patterns among the candidate ones for each
> Optimum lumped L, C and R values for each lossy layer. In the next step of the method, optimum lumped reactance and resistance values of the solution set for the synthesis parameters (5) are realized by altering the geometrical dimensions of the selected FSS patterns among the candidate ones with the aid of database (3) generated in the first step (2) and optimum surface resistance values are searched to achieve desired lumped resistance values (6). This optimization process (6.3, 6.4 and 6.5) is carried out in an iterative manner. As an initial guess, for each selected FSS geometry, by using the database 3 geometrical dimensions of the pattern are selected (6.1 ) to realize optimum L and C values for the solution set (5). To relate the optimum lumped resistance to the initial values regarding surface resistance the ratio between the area of one period and the physical area of the FSS being simulated is used (6.2):
effective area
^surface ¾ ^lumped,desired
period
Then the lossy FSS with the defined geometric dimensions and initial surface resistance is analyzed (6.3) with one of full wave computational electromagnetic methods (FEM, MoM, FDTD, etc.). According to the analysis results regarding the circuit equivalent lumped model parameters (5) of the FSS model obtained in synthesis part, the surface resistance value together with the geometric dimensions of the pattern is modified in an iterative manner until desired optimum lumped model parameters are realized within a predefined error. This iterative lossy layer realization step is conducted by focusing on the center of the desired frequency band for all of the lossy FSS layers to be used in the design. Since the effective area of the FSS pattern changes with respect to frequency, it is not possible to achieve a constant lumped resistance value throughout the whole frequency range with a constant surface resistance value. Due to this fact, the target resistance value is realized at the center of the specified frequency range. The outputs of this step are:
> Optimum dimensions for selected FSS geometries,
> Optimum surface resistance values for selected FSS geometries. Together with solution set (5) of synthesis part, these outputs form the overall structural parameters of the broadband multilayer radar absorbing structure (7).
In the final step of the proposed method (8), the absorption characteristics of the designed broadband multilayer absorber are obtained by using one of electromagnetic analysis techniques (FEM, FDTD, MoM, etc.) (8.1 ). If the final characteristics do not satisfy the aimed absorption criteria due to unconsidered coupling effects between the layers, a further optimization is conducted over the whole structure by using an optimization technique (8.3) (algorithms, iterative methods, heuristic approaches, etc.) in corporation with a full wave electromagnetic simulation technique (8.4). The cost functions of the optimization processes are determined by using full wave simulations (8.5), hence reasonable values are chosen for the limits of the optimization variables (geometrical dimensions of FSS patterns and surface resistance values) in order not to increase the time elapsed for this final optimization stage and to sustain the efficiency of the invention. These limits are specified to be in proximity of the values determined in the previous step (7) in order not to disturb the final design significantly. Also, since the search space for the
final optimization of absorbing structure's parameters is narrow, the time consumed by full wave electromagnetic solutions is minimized in an effective way. The outputs of the final step of the invention are:
> Number of layers (if not specified as an input),
> Thickness values of separating slabs (if not specified as an input)
> Optimum FSS geometries for each layer,
> FSS geometrical dimensions and surface resistance values,
> Absorption characteristics of designed multilayer CA RAS.
According to the present invention, initial model of the FSS layers are designed without using electromagnetic analysis. Therefore, said initial models are designed in a fast and reliable manner. Moreover, according to the present invention, electromagnetic analysis is performed for the final model and optimization techniques are performed according to the electromagnetic analysis. Therefore, complexity of the overall design process is reduced.
Claims
A method for the design of broadband multi-layered electromagnetic absorber characterized by comprising the steps of;
- computing transmission and reflection characteristics of the candidate frequency selective surface types (101 );
- generating equivalent lumped circuit models for said candidate frequency selective surface types according to computed characteristics (102);
- generating a database using generated equivalent lumped circuit models (103);
- for each FSS layers, forming an initial design according to the requirements of the multi-layered radar absorbing structure by using optimization techniques with transmission line theory (104);
- according to initial design, obtaining appropriate frequency selective surface structures from said database for each layer (105);
- performing electromagnetic analysis techniques for overall structure (106) and
- optimizing frequency selective surface structure of each layer according to result of the electromagnetic analysis in order to eliminate interactions between different frequency selective surface layers (107).
A method according to claim 1 , characterized in that; step of computing transmission and reflection characteristics of the candidate frequency selective surface types (101 ) comprises using full wave electromagnetic analysis (2.2a).
A method according to claim 1 , characterized in that; step of computing transmission and reflection characteristics of the candidate frequency selective surface types (101 ) comprises using existing analytical formulations of specific geometries (2.2b).
1
4. A method according to claim 1 , characterized in that; step of forming an initial design (104) comprises determining R, L and C parameters of the frequency selective surface layers according to said requirements.
5. A method according to claim 1 , characterized in that; step of forming an initial design (104) comprises using optimization techniques (4.2) together with transmission line theory (4.3).
6. A method according to claim 1 , characterized in that; step of obtaining appropriate FSS structures (105) comprises determining initial geometrical parameters of frequency selective surface layers (6.1 ).
7. A method according to claim 6, characterized in that; step of obtaining appropriate frequency selective surface structures (105) further comprises estimating initial surface resistance values of determined FSS structures (6.2); performing electromagnetic analysis (6.3) and adjusting the dimensions of the geometry and surface resistances of the frequency selective surface structures (6.4).
8. A method according to claim 1 , characterized in that; said step of optimizing frequency selective surface structure of each layer (107) comprises performing optimization algorithms (8.3); performing electromagnetic analysis techniques for overall structure (8.4); and determining cost functions of the optimization processes by using full wave simulations (8.5).
9. A broadband multi-layered electromagnetic absorber produced according to any of the preceding claims.
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| CN106202656A (en) * | 2016-06-30 | 2016-12-07 | 西安理工大学 | A kind of method for designing of honeycomb absorbent structure aperture space |
| CN108664746A (en) * | 2018-05-17 | 2018-10-16 | 中国人民解放军陆军工程大学 | A kind of frequency-selective surfaces approximate analytical method based on Double wire transmission line model |
| CN110247194A (en) * | 2019-06-14 | 2019-09-17 | 北京航空航天大学 | The upper transmittance prediction technique and system of the double-deck bandpass-type frequency selecting structures |
| CN111783379A (en) * | 2020-07-26 | 2020-10-16 | 中国人民解放军国防科技大学 | Method for improving transmittance of reconfigurable FSS |
| CN112784464A (en) * | 2021-01-30 | 2021-05-11 | 中国人民解放军空军工程大学 | Wave absorber with arbitrary absorption frequency spectrum based on intelligent algorithm and design method thereof |
| US20210408693A1 (en) * | 2018-10-30 | 2021-12-30 | Nippon Telegraph And Telephone Corporation | Frequency selective surface designing device |
| CN114628915A (en) * | 2022-04-07 | 2022-06-14 | 四川九洲电器集团有限责任公司 | Design method, device and structure of graphene terahertz broadband wave absorber |
| CN115411531A (en) * | 2022-08-18 | 2022-11-29 | 广东威神装备科技有限公司 | High-absorption broadband wave-absorbing structure based on embedded square ring pattern |
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| CN106202656A (en) * | 2016-06-30 | 2016-12-07 | 西安理工大学 | A kind of method for designing of honeycomb absorbent structure aperture space |
| CN108664746A (en) * | 2018-05-17 | 2018-10-16 | 中国人民解放军陆军工程大学 | A kind of frequency-selective surfaces approximate analytical method based on Double wire transmission line model |
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| CN112784464B (en) * | 2021-01-30 | 2023-02-21 | 中国人民解放军空军工程大学 | Wave absorber with arbitrary absorption frequency spectrum based on intelligent algorithm and design method thereof |
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