Multilayer Frequency Selective Surface Research Articles

Accelerating multilayer frequency selective surface absorber design by combining equivalent circuit models with machine learning

Designing high-performance electromagnetic functional materials and artificial structures is of great significance for electromagnetic wave modulation applications. Optimizing performance in the high-dimensional parameter space of electromagnetic functional materials has posed a challenging problem. This paper proposes the use of reinforcement and transfer learning methods to facilitate the quick and accurate design of wideband circuit analog absorbers (CAA). A trained reinforcement learning network is utilized to comprehend the relationship between reflectivity performance and changes in impedance parameter. Furthermore, the transfer learning method is applied to accelerate the training process, leading in a 20-fold reduction in the number of simulations. To validate the effectiveness of this approach, a double-layer absorber aiming for reflectivity less than −20 dB at 3–10 GHz is designed, requiring only 50 simulations. This demonstrates that the proposed method provides a flexible strategy for the interactive design of equivalent circuit and electromagnetic structural parameters. Moreover, it presents a novel and efficient solution for microwave absorber design, with potential applications across various microwave design fields.

A machine learning-based method for co-design and optimization of microwave-absorbing/load-bearing multifunctional structures

Simultaneously considering the absorption performance and load-bearing capability is a trend in the design of multifunctional structures. Nevertheless, the collaborative design and optimization involved in this process present a challenging problem. Herein, guided by multifunctionality, a lightweight microwave-absorbing/load-bearing multifunctional structure is intelligently inversely designed based on machine learning. A co-design scheme is developed to address the contradiction between the absorption performance and load-bearing performance. An approach for rapid inverse design of metamaterial absorbers containing multilayered frequency-selective surfaces is proposed. The simulation results obtained using multi-objective optimization based on surrogate models indicate that the optimized multifunctional structure achieves more than 90% absorption in the frequency range of 2.5 GHz–18.0 GHz and simultaneously exhibits superior load-bearing performance with an out-of-plane Young’s modulus of 334.8 MPa and an out-of-plane compressive strength of 4.95 MPa, demonstrating the effectiveness of the co-design scheme. Finally, the experimental results are analysed. This study provides a reference for co-design and multi-objective optimization of similar multifunctional structures.

22/43 GHz low-insertion-loss dual-polarized multi-layer bandpass frequency selective surfaces for millimeter astronomy

We design a frequency selective surface (FSS) capable of transmitting K-band and reflecting Q-band radio waves. The equivalent circuit approach assists the distribution of multi-layer FSS to achieve a third-order bandpass response with an incident angle of less than 30°. The unit structure consists of three metal layers embedded with two dielectric substrates. Especially, the FSS provides a 3 dB transmission bandwidth range from 18.6 to 26.7 GHz with a maximum measured insertion loss of 0.61 dB. Hence the proposed polarization-insensitive FSS with low insertion loss can be applied in the observation system of millimeter astronomy.

Low-Profile Dual-Band Dual-Polarized Transmitarray Antenna Based on Multilayer Frequency Selective Surfaces

Low-Profile Dual-Band Dual-Polarized Transmitarray Antenna Based on Multilayer Frequency Selective Surfaces

Dual-Polarized Frequency Selective Rasorber With Two Wide Transmission Bands

This paper presents a design method for dual-polarized stacked frequency selective rasorber (FSR) with two wide transmission bands. In order to achieve three absorbing bands and two broadband transmission windows simultaneously in a wide operating frequency range, two similar lossy layers, a low-pass frequency selective surface (FSS) and a dual band-pass multilayer FSS is cascaded from the top to the bottom. The low-pass FSS acts as the ground of the lossy layers to generate a high-frequency absorption band. The interaction between the dual band-pass FSS and two lossy layers results in low- and intermediate-frequency absorption bands. Two transmission windows are achieved when two transmission bands of the lossy layer coincide with those of the low-pass and dual band-pass FSSs. The designed FSR has two wide -3-dB transmission bands with the fractional bandwidths of 45.98% and 23.31% and three absorbing bands with the fractional bandwidths of 81.11%, 13.67% and 3.36% for absorptivity greater than 80%. Prototype of the proposed FSR is fabricated and good agreement between the simulation and the measurement is obtained.

Broadband Linear to Circular Polarizer Based on Multilayer Frequency-Selective Surface

In this work, a transmission polarizer is described by using a frequency-selective surface to transform linearly polarized waves into circularly polarized waves. The linear to circular (LTC) polarizer consists of four layers. Two types of unit cells are designed in the LTC polarizer to improve design freedom. As a result, two orthogonal polarized components of transmission waves display nearly 90° phase differences while maintaining nearly high transparency for the generation of CPWs. The less than 3 dB axial ratio with a fractional width of over 76.8% from 9.20 to 20.67 GHz for this LTC polarizer is obtained. Even when the incident angle reaches 20°, its operating frequency band covers 9.69 to 20.21 GHz. Compared with the converters proposed before, the one proposed in this paper has a wider bandwidth. In order to evaluate the design strategy, a prototype is manufactured and tested. The results of the simulation and the experiment are in good accord.

A novel dual‐band miniaturized frequency selective surface with high selectivity

AbstractIn this paper, a novel dual‐band multilayer frequency selective surface (FSS) with high selectivity and miniaturization characteristics is proposed. The FSS consists of a top and bottom resonant layer and an intermediate coupling layer. The top and bottom resonant layers provide dual‐band passbands, and the cross‐coupling between the three layers makes the structure produce four transmission zeros (TZs) distributed two‐by‐two on both sides of the passband to improve the sharp roll‐off characteristics of the structure. Use bent structures in the top and bottom layers of the cell design to achieve miniaturization of the elements. FSS provides stable performance in incident angles from 0° to 45° with different polarizations of incident waves (TE and TM wave). The lower band of FSS works at 9.1 GHz and the higher band works at 10.26 GHz, the cell size of FSS is , FSS samples were made and tested, and the test results fit well with the simulation results.

Broadband absorber based on multilayer frequency selective surface

This study proposes a unitized arc-shaped frequency selective surface for achieving broadband absorption. The design is three-layered with the unit cell of each layer being a combination of four identical arcs. The structure possesses a broad absorbing bandwidth along with high absorption. Its absorbing capability is more than 90% in the range of 3.87–10.49 GHz and exceeds 95% in the range of 5.65–10.35 GHz, thus covering the whole C-band and most of the X-band. In addition, the structure is insensitive to polarization and retains reasonable properties at an oblique incidence angle of 45°. A sample absorber is processed and tested, which according to the results operates from 3.68 to 10.25 GHz with an absorption capacity of over 80% and a working bandwidth of up to 94.3%.

Equivalent Circuit-Assisted Multi-Objective Particle Swarm Optimization for Accelerated Reverse Design of Multi-Layer Frequency Selective Surface.

In this paper, a fast reverse design method of multi-layer frequency selective surface (FSS) based on the equivalent circuit (EC)-assisted multi-objective particle swarm optimization (MOPSO) algorithm is proposed. Converting the desired frequency response requirements into an EC and then determining structural parameters via building blocks' EC and MOPSO simplifies the inverse design process of the FSS. The layer-by-layer building blocks of EC are used instead when dealing with the problem of complicated EC computation associated with multi-layer FSS. By converting factors that are difficult to calculate, such as interlayer coupling, into an MOPSO seeking process, the computational complexity is reduced while the design accuracy can be improved. To begin with, it is necessary to determine the distribution of zeros and poles according to the design goals in order to calculate the appropriate EC. Then, the preliminary design of the FSS has been completed in accordance with the EC and the associated building block structure. Finally, the objective function of the optimization algorithm is determined according to the desired frequency response, and the FSS structure parameters are optimized. Taking dual band-stop FSS and triple band-pass FSS structures as examples, the transmission coefficient results obtained by the proposed reverse design method are consistent with the transmission coefficient results based on the ECs, which verifies the effectiveness of the proposed method. The optimized triple band-pass FSS demonstrates strong stability even at oblique incident angles of up to 45° in both TE and TM polarizations.

V-Band Dual-Polarized Filtering Transmitarray Antenna Enabled by a Planar Filtering Illumination Source

This article introduces a transmitarray antenna presenting excellent filtering and dual-polarization properties. Conventional transmitarrays resort to multilayered frequency-selective surfaces (FSSs) for filtering responses. In contrast, we propose a planar dual-polarized filtering antenna as an illumination source to enable a filtering transmitarray. The V-band dual-polarized filtering antenna is excited by a substrate integrated waveguide (SIW) feeding structure. By a novel trisection feed and a well-design radiating element, up to four radiation nulls are produced, leading to an excellent filtering response validated with experimental results. Subsequently, the antenna is employed to illuminate a phase-shifting surface (PSS), achieving outstanding filtering response, stable dual-polarization characteristics, low profile, and ease of integration. The proposed antenna and transmitarray demonstrate significant potential in V-band millimeter-wave (mmW) applications.

Electromagnetic Characteristics Calculation of FSS by the Mixed Method FDTD/Extrapolation/Cascade Method

In this paper, a mixed method (MM) combining the advantages of finite difference time domain (FDTD), extrapolation, and matrix cascade methods is proposed. First, the hybrid algorithm combining the FDTD and extrapolation method is used to compute the electromagnetic characteristics of the single-layer frequency selective surface (FSS). Subsequently, matrix cascade method is used to calculate the electromagnetic characteristics of the multi-layer FSS. By introducing the Floquet theorem and considering the periodic boundary condition (PBC), absorbing boundary conditions (ABC) of the FSS, a three-dimensional model, is established. The computational results show that, while maintaining the same level of accuracy, the hybrid method greatly improves the computation speed and reduces the computer memory compared with the simulation software. It can provide an important reference for the subsequent study of the electromagnetic characteristics ofthe FSS.

High gain wideband and multi-band on-demand reconfigurable antenna for modern wireless application

AbstractThis paper proposes a wide band and multiband frequency reconfigurable antenna that can operate in the UWB, GSM, GPS, 4G LTE, WLAN, and WiMAX bands. The antenna is made up of a trapezoidal-shaped monopole radiator, which was inspired by a rectangular monopole antenna. The ground plane is modified by embedding T and L-shaped slots to notch the desired operating frequency. The proposed antenna can switch to six different frequencies using RF PIN diodes, making it suitable for modern wireless applications. A multilayer frequency selective surface (FSS) reflector is presented to improve the gain of the proposed reconfigurable antenna. The low-profile design achieved a significant increase in gain while retaining the UWB antenna's excellent impedance bandwidth. Because of the use of the FSS reflector, the antenna's average peak gain has increased from 6 to 10.4 dBi. The proposed antenna has a wide switching capability, which validates its unique feasibility for high-speed multiple Internet of Things applications via a common embedded platform under various applications.

Frequency-Selective-Surface-Based Mechanically Reconfigurable Terahertz Bandpass Filter

Frequency-tunablefilters are in demand for applications requiring high spectral selectivity. To this end, frequency-selective surfaces (FSSs) have been widely applied for spatial filtering, where varactors well serve the purpose for electronic reconfiguration at microwave frequencies. For terahertz applications, however, varactors are unavoidably lossy owing to their relatively small cross section required to yield small values of capacitance. In this work, we propose a terahertz bandpass multilayer FSS with a finesse around 20, with 80% power transmission. Its operation frequency is mechanically tunable in a 40% frequency range by varying an interlayer spacer thickness. The experimentally validated bandwidth is 31% due to the limitation in measurement apparatus, and the power transmission is above 75%. The filter is insensitive to misalignment and can maintain tunability under oblique angles of incidence. This proposed filter outperforms a series of notable reconfigurable filters available in the literature in terms of tunable range and insertion loss. The proposed design is among the first few reconfigurable terahertz filters, and the design methodology can be readily applied to other FSS-based structures.

Design Optimization of Ultra-Wideband Vivaldi Antenna using Artificial Intelligence

In this work, computationally efficient design optimization of frequency selective surface (FSS)-loaded ultra-wideband Vivaldi antenna via the use of data-driven surrogate model is studied. The proposed design methodology consists of a multi-layer FSS structure aimed for performance improvement of the Vivaldi design, which makes the design a multi-objective multi-dimensional optimization problem. For having a fast and accurate optimization process, a data-driven surrogate model alongside the metaheuristic optimizer honeybee mating optimization (HBMO) had been used. The optimally designed antenna had been prototyped and its performance characteristics had been measured. The obtained experimental results are compared with the simulated results of the proposed method. Results show that the obtained FSS-loaded structure has enhanced directivity compared with the design without FSS structure, without any performance losses in the return loss characteristics. The FSS-loaded Vivaldi antenna operates at 2–12 GHz band with a maximum gain of 10 dBi at 10 GHz which makes the design a good solution for RADAR applications.

A High-Temperature and Frequency-Reconfigurable Multilayer Frequency Selective Surface Using Liquid Metal

A high-temperature and frequency-reconfigurable multilayer frequency selective surface (FSS) based on liquid metal is proposed in this work. After construction of a multilayer dielectric cavity with specific dielectric-shaped pillars and the injection of liquid metal (EGaIn) into each layer of the cavity, the liquid metal and dielectric pillars form a slot-type bandpass FSS, and frequency reconfiguration is realized by switching the injection layer. A prototype of the proposed FSS was designed, fabricated and measured. The measured results validated the design well. The good conductivity and fluidity of the liquid metal are utilized to realize the reconfigurable electromagnetic performance of the proposed FSS. This works in the C-band (5 GHz) and Ku band (13 GHz) and has a frequency switching time between 13.1 to 14.2 s. Moreover, due to the good thermal conductivity of liquid metal, the flowing liquid metal can take away heat, and the multilayer FSS can work as cooling plate. The heat transfer performance was investigated by numerical simulations. A 1000 ° plane heat source was set on the bottom surface of the double-layer FSS. The average temperature on the top surface was 62.2 °, when the liquid metal fluid in the FSS had a speed of 1 m/s. The proposed multilayer FSS has strong potential for applications in some special application fields involving stealth and hypersonic aircraft.

Analysis of Radome Cross Section of an Aircraft Equipped With a FSS Radome

We study the radar cross section (RCS) property of an aircraft considering the electromagnetic (EM) characteristics of a frequency selective surface (FSS) radome, mounted on the aircraft. Instead of full-wave methods, we utilize high-frequency methods, such as the shooting and bouncing rays (SBR), physical theory of diffraction (PTD), and flat model, taking a significant computational efficiency. Based on the developed algorithm, we analyze monostatic and bistatic RCSs of the aircraft equipped with either single- and multi-layer dielectric, FSS, or PEC radomes in terms of frequency and polarization. Our calculations are validated by comparing with those of the commercial EM simulator with significant computational efficiency. The present numerical study indicates that including the radome EM characteristics into the overall aircraft RCS study is crucial for the accurate RCS estimate

Design Optimization of Ultra Wide Band Vivaldi Antenna Using Artificial Intelligence

In this work, computationally efficient design optimization of Frequency Selective Surface (FSS) loaded Ultra-wide band Vivaldi antenna is studied. The proposed design consists of a multi-layer FSS structure aimed for performance improvement of the Vivaldi design, which makes the design a multi-objective multi dimension optimization problem. For having a fast and accurate optimization process, a data driven surrogate model alongside of meta-heurists optimizer Honey Bee Mating Optimization had been used. The obtained results are compared with 3D EM full wave simulator. Results show, the obtained FSS loaded structure have enhanced directivity compared with the design without FSS structure, without any performance losses in the return loss characteristics. The FSS loaded Vivaldi antenna operates at 2–12 GHZ band with a maximum gain of 10 dBi at 10 GHz which makes the design a good solution for RADAR applications.

Design of a frequency selective rasorber with fast roll‐off and wide absorption/transmission band

A frequency selective rasorber (FSR) with fast roll-off and wide absorption/transmission band is introduced in this article, working as a band-pass filter from 1.7 to 3.1 GHz, while working as an absorber from 5.72 to 17 GHz. The proposed FSR is designed by the lossy layer at the top and the band-pass frequency selective surface (FSS) at the bottom. The lossy layer is constructed by two parts including a square loop and a series RLC structures to provide a wide absorption band. The band-pass FSS is a three-tier structure including two patch layers and one meander line layer in the middle. This multilayer FSS is used to generate a transmission window in S band and a wide reflection band in the high frequency. The working mechanism of the FSR is explained by the equivalent circuit model. Finally, the fabricated prototype and the measurement results are presented to verify the design of the FSR.

РЕЗУЛЬТАТЫ ЧИСЛЕННОГО ИССЛЕДОВАНИЯ ХАРАКТЕРИСТИК РАССЕЯНИЯ АНТЕННЫХ ОБТЕКАТЕЛЕЙ НА ОСНОВЕ МЕТАЛЛОДИЭЛЕКТРИЧЕСКИХ ДИФРАКЦИОННЫХ РЕШЕТОК

Mathematical model of multilayered printed frequency selective surfaces with dielectric coversis presented in this paper. The model is built on the suggestion of array infinity and perfectconductivity of microstrip elements. Such printed structures can be used as frequency selectivesurface and as covers with controllable characteristics (for example tunable filters, adaptive radarcover, electronically switched polarizers). Full-wave analysis is executed by the integral equationmethod of electromagnetics. The numerical solution of an integral equation has been obtained byGalerkin’s method. Unknown distribution of surface magnetic currents has been approximated byroof-top basic functions. The generalized scattering matrix method was used for simulation ofmultilayered printed frequency selective surface. The paper presents the compound algorithmwhich combines the integral equation method with the method of generalized scattering matrix. Alot of numerical examples are presented proving the algorithm effectiveness. By means of thismodel there were synthesized multilayer frequency selective surface as periodic arrays of theprinted elements, which have arbitrary shape of reradiators. It is known, that the printed elementsof special shape ensure, as rejecting and as transacting of electromagnetic waves in the givenfrequencies, and have neglected angular sensitivity. The results of constructive synthesis of printedfrequency selective surfaces as rejecting or transmitting filters, which have neglected angularsensitivity, are represented in paper. Such an algorithm is rather flexible and multiple repeats thebasic problem solution. It makes the procedure of computer code preparing much more effectiveand do not require to change the problem decision itself.

Ultra-wideband and low-loss linear-to-circular polarizer based on multilayer frequency selective surface

Linear-to-circular (LTC) polarizers based on frequency selective surfaces (FSSs) are evolving and upgrading; however, designing polarizers with low loss and broad band is still a challenging task. To upgrade the polarizer, this paper proposes an ultra-wideband and low-loss LTC polarizer composed of FSSs. In each layer of the polarizer, two sides of the substrate are covered by inductive and capacitive patterns, respectively. For this reason, the constant transmission phase differences are acquired within wide band. And stacking four layers of FSSs is effective to improve performances of the proposed polarizer. What’s more, the extra sheets are added in the middle of adjacent FSSs to reduce the distance between layers. Finally, the thickness is reduced by 29.1% and the performances of polarizer are almost unaffected. Under normal incident wave, the simulated results show that the 3-dB axis ratio (AR) bandwidth is 93%. The total transmittance is better than − 0.5 dB when the linear polarized waves pass through the polarizer within 6–13 GHz. In addition, the proposed LTC polarizer exhibits a stable response with wide incident angle variation. The experimental data closed to the simulated results have been obtained.