Frequency Selective Surface Research Articles

Flexible Double‐Layer Adjustable Frequency Selective Surfaces Based on 3D Cross‐Shaped Kirigami Structure

AbstractFrequency‐selective surfaces (FSS) with flexible treatment can be employed in various applications. This paper develops a mechanically constructed flexible double‐layer adjustable FSS based on a 3D cross‐shaped kirigami structure design. Through mechanical stretching, the kirigami structure partly adhered to the ecoflex substrate enables this FSS to modulate the resonant frequencies of two filter bands synchronously. Meanwhile, the structural deformation triggered by mechanical stretching may function as a switch to adjust the filter band with a higher resonant frequency. According to the results of EM experiments and simulations, in the absence of stretching, the undeformed FSS with a double‐layer structure has two filter bands. Compared to the undeformed configuration, the stretching induces structural deformation, which results in apparent resonant frequency shifts of both the two filter bands and the contraction of the filter band with higher resonant frequency. A buckling model that has been theoretically, cumulatively, and experimentally proven is utilized to investigate the structural deformation of this FSS caused by stretching. It is convenient to switch flexible double‐layer adjustable FSS' deformation by mechanical method. This flexible double‐layer adjustable FSS offers a new design strategy for the application of FSS, paving the route for new developments in electromagnetic compatibility.

Electromagnetic and microwave absorption properties of flexible fabric coatings containing Ag decorated spherical graphene powders with FSS incorporation

Flexible textile microwave absorbing materials own the advantages of flexibility, foldability and cuttability, have become a research hotspot in electromagnetic stealth technology. In this study, a microwave absorbing coating was prepared on a fabric substrate using Ag decorated spherical graphene (SG) as the absorbent. XRD results demonstrated the metallic Ag ion was successfully reduced. TEM photographs showed the silver nanoparticles were stuck to the spherical graphene. The complex permittivity was enhanced after compositing with Ag particles. Along with the increase of silver content from 0 to 20 wt%, the complex permittivity rises from 3.29–0.42j to 6.93–2.22j owing to its higher electric conductivity and stronger relaxation effect. Meanwhile, the flexible coating containing Ag decorated spherical graphene (Ag@SG) also exhibited better microwave absorption performance. The minimum reflection loss (RLmin) for the coating with a thickness of 3.0 mm was −15 dB. And the effectively absorbing broadband (EAB) is located at 9.08–11.52 GHz. In addition, the microwave absorbing performance was greatly enhanced after being combined with periodic frequency selective surface (FSS). The EAB was obtained over the entire X-band frequency range, and the RLmin value achieved −41.72 dB at 10.25 GHz. What's more, the coating owned an EAB in a wide range incident angle of 60°–90°. This work was help to developing high performance flexible fabric coating containing Ag decorated spherical graphene with FSS incorporation.

Broadside Gain Enhancement of Wideband Monopole Circular Shaped Antenna Using FSS for Sub-6 GHz Applications

This paper introduces a wideband circular patch antenna designed with a frequency selective surface (FSS) for sub-6 GHz applications. The proposed antenna features a monopole circular-shaped patch with a partial ground plane, delivering an omnidirectional radiation pattern in the azimuth plane, resulting in relatively uniform gain in all directions. An FSS metamaterial enhances the antenna's gain and improves the broadside radiation pattern. The design incorporates three inner circular patches connected to the main patch. The FSS utilizes hybrid square/circle loop-based unit cells. The antenna and FSS are simulated using CST software and subsequently fabricated on an FR-4 substrate. The measured results demonstrate an impedance bandwidth of 1.6 GHz with a peak gain of 5.4 dB at 3.5 GHz. The omnidirectional radiation pattern is converted into a directional one by placing a reflector FSS as a bottom substrate layer. The overall structure size is compact, measuring (0.34λ0 × 0.27λ0 × 0.016λ0), where λ0 is the free space wavelength corresponding to the lowest resonant frequency within the operational bandwidth. This design achieves significant antenna size reduction and is well-suited for future sub-6 GHz applications.

Switchable and optically transparent ultrawide stopband frequency selective surface for electromagnetic shielding

In view of the fact that high-frequency electromagnetic waves mainly enter buildings through windows and glass doors, switchable optically-transparent shielding with broad stopband is increasingly needed. Herein, a novel design for a switchable and optically transparent frequency selective surface (FSS) with ultrawide-stopband is presented in this study. The structure consists of a polymethyl methacrylate (PMMA) layer sandwiched between polydimethylsiloxane (PDMS) layers which contain liquid metal microchannels arranged in an orthogonal Ω-shaped configuration. The mobility of the liquid metal can switch the FSS response from an all-pass to an ultrawide bandstop behavior. The proposed FSS achieves a rejection bandwidth of 18.1 GHz, covering P, L, S, C, X and Ku bands, while maintaining a transparency of 81% and high angular stability up to 80°, regardless of polarization. Furthermore, the mechanism behind the ultrawide stopband and high angular stability is explored through an analysis of reflection and absorption for both TE polarization and TM polarization. Experimental validation under both normal and oblique incidence demonstrates the ultrawide-stopband performance of the fabricated FSS.

Ultra-wideband thin frequency-selective surface absorber against sheet resistance fluctuation

The design of thin frequency selective surface (FSS) absorber based on resistive film that meets the requirements of broadband, polarization independence, incident angle stability, and strong absorption is a challenging task. Fabrication tolerance of resistive film can result in fluctuations in sheet resistance, which negatively affects the absorber performance. To tackle these problems, this work firstly investigates how sheet resistance fluctuations affect the absorbing performance of resistive film FSS absorber. The analysis of simulated surface current density distribution and impedance reveals that the diversity of current paths provides an effective way to mitigate the influence of sheet resistance fluctuation. This is achieved by enabling flexible variation of surface current in response to sheet resistance fluctuations. Consequently, the variation of input impedance of the FSS absorber due to the fluctuation of sheet resistance is suppressed within a small range. Then, a method of extending bandwidth is proposed by employing the complementary variation of FSS impedance with frequency at different layers. By combining this approach with a miniaturization design, a thin and light FSS absorber is developed that exhibits ultra-wide bandwidth, polarization independence and angle stability while mitigating the effects of sheet resistance perturbation. The proposed FSS absorber achieves a 90% absorption bandwidth from 1.50 GHz to 20.50 GHz, covering Ku, X, C, S bands and part of the L and K bands, with a relative bandwidth reaching 173%. The absorber has a thickness of 0.093<i>λ</i><sub>L</sub> for both transverse electric (TE) polarization and transverse magnetic (TM) polarization, yielding a figure of merit (FoM, the ratio of the theoretical minimum thickness to the actual thickness) of 0.95, indicating that the thickness is close to the theoretical limit. The absorber maintains over 90% absorption rate for TM polarization at an incidence angle of up to 70°, and 80% absorption for TE polarization at 45°. Furthermore, the 90% absorbance bandwidth of the absorber remains at 167.0% when the sheet resistance of any FSS layer fluctuates within a range from 12 to 30 Ω/sq. A prototype of the proposed FSS absorber is fabricated and measured, and the experimental results are in good agreement with the simulation results, thus validating the effectiveness of the proposed method.

A Monolayer Frequency‐Selective Surface for Wideband Shielding Application with Adequate Out‐of‐Band Separation and Angular Stability

In the proposed paper, a monolayer band‐stop frequency‐selective surface (FSS) is structured and analyzed for application in wideband shielding. The paper proposes an organized step‐by‐step method to design the frequency‐selective surface (FSS) to achieve enhanced shielding effectiveness (SE) over the entire band. The suggested FSS comprises of tripole‐shaped unit cells on both sides of a monolayer FR‐4 substrate to offer adequate shielding over the band of 3.2–8.82 GHz which includes both C‐ and X‐bands. The operating band of the FSS achieves ultrawideband shielding by means of 93% bandwidth with 60–100 dB shielding effectiveness. Experimental data are employed for the characteristics that are fairly well congruent to simulated results. Higher angular stability beyond 80° characterizes the proposed FSS. A wide range of potential uses for the proposed design exists, including microwave shielding, wideband filtering, as well as radar cross‐section (RCS) reduction, among others. The out‐of‐band RCS reduction capability of the FSS is also investigated and presented in this paper.

Rheological investigations on frequency selective surface carbon composite microwave absorber.

A high-performance stealth platform is one of the crucial requirements in defence technology that could practically be realized by building effective microwave frequency selective surface (FSS) absorbers. Herein, we report the design and manufacturing of an absorber by tuning the rheology of cell architecture. Initially, a fan-shaped cell (10.4 mm2) was designed for its surface and bulk rheology. The FSS overlayer composition was investigated using SEM, EDX, and XRD and tuned for 0.25% carbon: 1.5% silver to achieve the ink resistivity ∼255 Ω □-1. The bulk rheology was optimized for air (Roha) spacer (thickness ∼2.8 mm), interlayer dielectrics (0.2 mm each), carbon composition (5%), and cell dimension (10.2 mm). Analyses are presented for absorption loss (RC, dB), bandwidth (GHz), resonance dispersion, and constitutive (ε, μ) parameters, compounded with an equivalent circuit model with the settings R = 273.55 Ω, L = 2.25 nH, C = 0.057 pF and the Fabry-Perot reactance mode@10 GHz. The bi-modal response was investigated for induced polarization, electromagnetic fields, volume power distribution, and angular (Θ = 0°-50°) and rotational stability (Φ = 0°-90°) against TE/TM incidences. The FSS pattern was implemented using a screen printing technique to fabricate a prototype absorber and subjected to the free space measurements in an anechoic chamber. The prototype behaviour was found to be commensurate with the simulated performance, thereby achieving a figure of merit of RC ∼-25 dB@10 GHz, accessible bandwidth 4 GHz (in X band) by using the thickness of 0.057 λ0. Details are presented in this study.

Ultrathin and conformal frequency selective surfaces bandpass filter to eliminate the 5G bands on radio altimeters

AbstractThis work proposes a frequency‐selective surface‐based radome structure to selectively allow the radar altimeter operating band and also minimize the interference from Sub‐6GHz 5 G frequency bands. A Jerusalem cross and combinational loop (JCL) based frequency selective surfaces (FSS) unit cell of overall dimension 0.37λ was synthesized using a thin flexible substrate for use in fuselage of airborne systems. The proposed FSS unit cell exhibits transmission zero at 3.61 and 6.025 GHz and highly selective pass band at 4.3 GHz. The effect of bends and angle of incidence on the frequency response of the synthesized FSS was studied in transverse electric and transverse magnetic modes. A lumped element‐based equivalent circuit model for the proposed design was also presented. Finally, the fabricated prototype was experimentally validated in an Anechoic chamber setup and the suitability of the proposed FSS layers for aviation radar systems was confirmed.

Frequency Selective Surfaces as Reconfigurable Superstrate Applied to a Dipole Antenna for 5G NR

Frequency Selective Surfaces as Reconfigurable Superstrate Applied to a Dipole Antenna for 5G NR

Highly efficient optics/microwave beam splitter based on frequency selective surface

Highly efficient optics/microwave beam splitter based on frequency selective surface

Frequency-Selective Surfaces With Quasielliptic Bandpass Response for Filtering FRA Application

Frequency-Selective Surfaces With Quasielliptic Bandpass Response for Filtering FRA Application

Design of Terahertz FP Interference Filter Based on Frequency Selective Surfaces

Design of Terahertz FP Interference Filter Based on Frequency Selective Surfaces

Frequency Selective Surface Toward 6G Communication Systems: A Contemporary Survey

Frequency Selective Surface Toward 6G Communication Systems: A Contemporary Survey

Notice of Violation of IEEE Publication Principles: A thin broadband microwave absorber with hexagonal resistive frequency selective surface

Notice of Violation of IEEE Publication Principles A Thin Broadband Microwave Absorber with Hexagonal Resistive Frequency Selective Surface by Feifei Li, Chao Meng, Fan-guang Meng, Digang Fan, Ping Chen, and Rui-xin Wu in the IEEE Antennas and Wireless Propagation Letters (Early Access) April 2018 After careful and considered review of the content and authorship of this paper by a duly constituted expert committee, this paper has been found to be in violation of IEEE’s Publication Principles. This paper contains significant portions of work presented in the paper cited below. The original work was translated and copied without attribution (including appropriate references to the original author(s) and/or paper title) and without permission. Design of a Wide‐band Metamaterial Absorber Based on Resistance Films by Gu Chao, Qu Shao‐Bo, Pei Zhi‐Bin, Xu Zhuo, Lin Bao‐Qin, Zhou Hang, Bai Pen, Gu Wei, Peng Wei‐Dong, and Ma Hua in Acta Physica Sinica, Vol 60, No. 8, August 2011 We realized a thin, broadband absorber based on resistive frequency selective surface (FSS). By introducing a design parameter, p-factor, we successfully designed a microwave absorber, whose reflectivity below -10dB covers 6.4-24.9 GHz. The thickness of the absorber is only 0.087-L at the lowest operating frequency. We show that broadband absorption can be achieved by carefully balancing susceptances of resistive FSS and other parts of the absorber. Furthermore, we find that lossless dielectric slabs with lower dielectric constant are the best choices for broadband absorber. Experimentally, the samples were fabricated by using silk-screen printing technique and their absorbing performance was measured. Experimental results are in good agreement with simulated ones. Our work provides a method to realize broadband absorber in a simple way, which may be used for the absorbers working in THz, infrared or even optical band.

ФРАКТАЛЬНА РАДІОФІЗИКА Частина 4. ПРАКТИЧНЕ ЗАСТОСУВАННЯ

Subject and Purpose. At the beginning of the 21st century, a fundamentally new scientific direction was formed in radiophysics — fractal radiophysics. The subject of this review is the main practical ideas of "fractalization" in radio physics. The purpose of the work is a systematic presentation of the main results of the practical application of fractal theory in radiophysics, as well as a detailed analysis of the originality, novelty, and practical value of the obtained results. Methods and Methodology. The results of using the fractal approach in various fields of modern radiophysics are presented. The results of the application of fractal and multifractal analysis methods for various radiophysical objects, phenomena and processes are considered. The main features, advantages and disadvantages of this approach, as well as existing problems, are highlighted. Results. The main practical results of applying the fractal approach in radio physics are considered. The main features of solving the problem of radio wave propagation in fractal media are also discussed. The usage of fractals in applied electrodynamics is demonstrated by the example of fractal antennas, resonators, filters, capacitors, transistors, diplexers, frequency-selective surfaces and metamaterials, etc. Fractals in semiconductor and vacuum electronics are described by the example of the fractal structures of the cathode spot and the cathodes themselves, fractal electrodes and diffusers, as well as the avalanche breakdown of the p-n junction. The features of the application of fractal ideas in statistical and nonlinear radiophysics are considered. To illustrate the "fractalization" of physics and radiophysics of the geospace, the fractal processes that occur during earthquakes, in the atmosphere, ionosphere and magnetosphere, etc., are used. Conclusions. The main directions of practical application of the theory of fractals in modern radiophysics are analyzed, as well as the features of the new results obtained, which reflect one of the main properties of the surrounding world — its fractality, are discussed.

Angle-Selective Surface based on Frequency-Selective Surface using Compact Double-Layer Patch-Coupled Resonance

Angle-Selective Surface based on Frequency-Selective Surface using Compact Double-Layer Patch-Coupled Resonance

Nature-Inspired Frequency Selective Surface in Fibonacci Spiral with Closely Resonant Bands

Nature-Inspired Frequency Selective Surface in Fibonacci Spiral with Closely Resonant Bands

Triple Bandstop 2.5D Frequency Selective Surface for Sub-6 GHz 5G Communication

Triple Bandstop 2.5D Frequency Selective Surface for Sub-6 GHz 5G Communication

Transparent and Angular Stably Miniaturized Frequency Selective Surface for Tri-band GSM Shielding

Transparent and Angular Stably Miniaturized Frequency Selective Surface for Tri-band GSM Shielding

A Dual-Band Dual-Polarization Frequency Selective Surface With Wide-Range Flexible Band Ratio and Wide Angular Stability

A Dual-Band Dual-Polarization Frequency Selective Surface With Wide-Range Flexible Band Ratio and Wide Angular Stability