Metallic Frequency Selective Surface Research Articles

Fusedly Deposited Frequency-Selective Composites Fabricated by a Dual-Nozzle 3D Printing as Microwave Filter.

We report a fusedly deposited frequency-selective composite (FD-FSCs), fabricated with a dual-nozzle 3D printer using a conductive carbon black (CB) polylactic acid (PLA) composite filament and a pure PLA polymer filament. The square frequency-selective pattern was constructed by the conductive CB/PLA nanocomposite, and the apertures of the pattern were filled with the pure dielectric PLA material, which allows the FD-FSC to maintain one single plane, even under bending, and also affects the resonating frequency due to the characteristic impedance of PLA (εr' ≈ 2.0). The number of the deposition layer and the printing direction were observed to affect electrical conductivity, complex permittivity, and the frequency selectivity of the FD-FSCs. In addition, the FD-FSCs designed for an X-band showed partial transmission around the resonant frequency and was observed to, quite uniformly, transmit microwaves in the decibel level of -2.17~-2.83 dB in the whole X-band, unlike a metallic frequency selective surface with full transmission at the resonance frequency. FD-FSCs embedded radar absorbing structure (RAS) demonstrates an excellent microwave absorption and a wide effective bandwidth. At a thickness of 4.3 mm, the 10 dB bandwidth covered the entire X-band (8.2~12.4 GHz) range of 4.2 GHz. Therefore, the proposed FD-FSCs fabricated by dual-nozzle 3D printing can be an impedance modifier to expand the design space and the application of radar absorbing materials and structures.

Frequency selective surface filters with high-quality factors based on a Fano resonance.

In this work, we propose a design method of the narrow passband filter with a high Q-factor based on a Fano resonance. A single-layer metallic frequency selective surface (FSS) with a simple structure is first designed according to this idea, but the result is not satisfying since the filter transmittance will significantly decrease with the increase of the Q-factor due to the presence of an inherent ohmic damping. Further, to improve the design, a ceramic-based FSS filter based on the similar mechanism is proposed, and the requirements of the ultrahigh Q-factors can be met owing to the high permittivity and low loss tangent of microwave ceramics. The design strategy proposed in this paper may have a promising potential in modern wireless communication and related fields.

Fully metallic frequency selective surface (FSS) circular polarizer based on cost‐effective chemical etching manufacturing technique

AbstractThis letter presents a fully metallic circular polarizer based on a bandpass frequency selective surface (FSS) that converts linear polarization (LP) to circular polarization (CP) in the Ka‐band. The proposed FSS circular polarizer consists of three cascaded identical perforated metal screens. The Jerusalem slot is used as the element of the FSS circular polarizer to produce an entirely metallic screen with a compact footprint. The Jerusalem slot allows the all‐metallic design to be realized without mechanical issues. A 35 × 35 elements prototype has been designed and manufactured using a cost‐effective chemical metallic etching technique, and performed measurements agree well with the numerical simulations. At broadside direction (), the proposed polarizer operates from 27.5–30.1 GHz, while at the oblique angle of incidence , the operating frequency is reduced to 27.7–29.4 GHz. The manufactured prototype has a low insertion loss (IL), i.e. dB and a good axial ratio performance, i.e. AR ⩽ 2 dB at the desired operating frequency band. Thus, based on a cost‐effective manufacturing technique, the proposed circular polarizer demonstrates an excellent approach to devising all‐metallic FSS polarizers with good IL.

Linear-to-Circular Polarization Transmission Converter Exploiting Meandered Metallic Slots

A novel wideband linear-to-circular polarization transmission converter composed by a cascade of two identical fully metallic frequency selective surfaces (FSSs) separated by an air gap is presented. The adoption of meandered slots patterned on a metallic layer, along with an interwoven FSS unit cell geometry, allows achieving up to 25% of 3 dB axial ratio bandwidth for a normally impinging plane wave. Moreover, by exploiting the FSS unit cell compactness, the converter provides a prominent robustness to oblique incidence, and it is therefore suitable to be employed in radomes and dichroics. As a proof of concept, a prototype of the proposed converter is manufactured and tested for assessing the design approach.

All-Metal Wideband Frequency-Selective Surface Bandpass Filter for TE and TM Polarizations

A novel technique to design a low-cost frequency-selective surface (FSS) bandpass filter is presented in this article. Wideband polarization-independent FSS bandpass filters are predominantly made of multiple microwave dielectric substrates or noncommercially available composite materials with or without active components, contributing to a very high manufacturing cost. The presented FSS filter has neither microwave substrates, nor any active devices, while it has a large controllable operational frequency band, which can support all polarizations, due to its symmetrical configuration. To the best of our knowledge, such a polarization-independent wideband bandpass response has never been achieved by any low-cost fully metallic FSS filter. The proposed FSS filter is made of three thin metal sheets composed of an engineered metallic substrate (EMS) and a metallic orthogonal dipole resonator (ODR). The EMS is responsible for ensuring the mechanical integrity of the filter without imposing electromagnetic (EM) restrictions throughout the desired frequency band. The integration of EMS and ODRs realizes a fully controllable wideband bandpass verified thorough circuital and modal analyses. According to the predicted and measured results, the FSS filter has a large bandwidth of around 31%, extending from 8.76 to 11.96 GHz with sharp roll-offs for the normal incidence. Simulated and measured results show a low sensitivity of the FSS filter response to oblique angles of incidence for both TM and TE polarizations.

A Frequency-Selective Surface Rasorber Based on Four Functional Layers

In this article, a frequency-selective surface (FSS) rasorber based on four metallic FSS functional layers is proposed. The rasorber consists of two metallic FSS absorption layers, two metallic FSS transmission layers, and four corresponding dielectric isolation layers. The top absorption layer and third absorption layer are applied to generate a wide absorption band at high frequency and low frequency, respectively. The second and bottom transmission layers are adopted to generate a low-pass transmission band and bandpass transmission band, respectively. The multilayer structure of the rasorber guarantees the great span, broad bandwidth, and stable scattering characteristics. Moreover, we adopt the equivalent circuit model (ECM), surface current distribution, and loss distribution to comprehend the physical mechanism of the rasorber. The simulated results show that the transmission is -0.67 dB at 6.5 GHz, and the reflection below -10 dB ranges 1.5-4.6 and 9.2-13.7 GHz. To validate our design, we fabricated and measured the prototypes, and the measurement results show reasonable agreement with the simulated results.

An Improved Fabrication Technique for the 3-D Frequency Selective Surface based on Water Transfer Printing Technology

Manufacturing an array of high-quality metallic pattern layers on a dielectric substrate remains a major challenge in the development of flexible and 3-D frequency selective surfaces (FSS). This paper proposes an improved fabrication solution for the 3-D FSS based on water transfer printing (WTP) technology. The main advantages of the proposed solution are its ability to transform complicated 2-D planar FSS patterns into 3-D structures while improving both manufacturing quality and production costs. WTP technology makes use of water surface tension to keep the thin metallic patterns of the proposed FSS floating flat with the absence of a solid planar substrate. This feature enables these metallic FSS patterns to be transferred onto 3-D structures through a dipping process. To test the effectiveness of the proposed technique, the FSS was designed using computer simulation software Microwave Studio to obtain the numerical performance of the FSS structure. The WTP technology was then used to fabricate the proposed FSS prototype before its performance was tested experimentally. The measurement results agreed well with the numerical results, indicating the proposed manufacturing solution would support the development of complicated 3-D electronics devices, such as conformal antenna arrays and metamaterials.

Multiband FSS Analysis and Synthesis Based on Parallel Non Coupled Metallic Strips Using WCIP Method

A novel parallel coupled Metallic strips frequency selective surface (FSS) is presented. The design is based on a filter composed of horizontal and vertical metallic strips. The structure has the advantage of simplicity and gives multi resonant frequencies easily controlled by a simple variation in the strips length. The proposed FSS rejects frequencies at 7GHz, 9.4GHz with bandwidths of 0.646GHz, 0.793GHz respectively when the structure is excited with an x polarized plane wave, and two frequencies at 9.1GHz and 11.2 GHz with bandwidth of 280.3MHz, 63MHz respectively when the structure is excited with a y polarized plane wave. To suppress frequencies ideal diode on reverse bias are inserted. The simulated results obtained using WCIP (Wave Concept Iterative Method) are compared to the COMSOL Multiphysics 4.3b software results, and measurements, a good agreement is observed. Then, an FSS synthesis approach based on non coupled parallel metallic strips is presented. It allows the synthesis of FSS for resonant frequencies ranging from 4.5GHz and 12.25 GHz for strips lengths inversely varying from 5mm to 19mm. To validate the synthesis approach, measured resonant frequencies are used as desired resonant frequencies to determine the metallic strips lengths. As a result the metallic strips FSS dimensions are extracted. Then the WCIP method is used to characterize the synthesized FSS. Three FSSs are synthesized based on the fabricated FSS and good agreement between measurements and synthesized FSSs results is recorded.

WCIP Method Applied To Modeling an L-Notched Rectangular Metallic Ring FSS for Multiband Applications and its Equivalent Structure

A frequency selective surface (FSS) with a unit cell containing of an L-notched rectangular metallic ring pattern that can be adopted for dual polarization applications is proposed and analyzed using the wave concept iterative procedure (WCIP). The presented FSS is fed with a normal incident plane wave and it shows three resonant frequencies at 6.5GHz, 9 GHz and 11.5 GHz when the FSS is x -polarized and two resonant frequencies at 6GHz and 8GHzwhen the FSS is y -polarized. The parametric study of the FSS provides three FSS dimensions where their variation independently or simultaneously results in resonant frequencies tuning. They are the two dimensions of the L part of the FSS and its notch penetration and changing their values in the FSS allowed intervals gives rise to charts and equations based on polynomials determined by the use of least mean square method. Thus no need to softwares to determine the FSS resonant frequencies once the application is restricted to a specific FSS such as the L-notched rectangular metallic ring FSS for low cost FSS use. The presented synthesis approach is extended to the determination of the equivalent FSS structures based on non-coupled parallel metallic strips for the complex FSS structures of difficult comprehensive resonance sources. One FSS is manufactured and characterized. A good agreement is recorded when the WCIP results for the transmission coefficient are compared with the results of COMSOL Multiphysics software and measurement.

Characterization of Switchable Rectangular Ring FSS with Non Coupled Parallel Metallic Strips for Multi Band and Dual Polarized Applications Using WCIP Method

In this paper, a rectangular metallic ring FSS (Frequency Selective Surfaces) with parallel metallic strips for multi band applications are characterized by the WCIP (Wave Concept Iterative Procedure) method. The resonant characteristics of the proposed FSS are determined. The structure shows three resonant frequencies when the incident wave is x-polarized and three resonant frequencies when the source is polarized in the orthogonal direction. A variation in the length of the strips and the rectangular ring allows a fine tuning in the FSS resonant frequencies to give raise to tuned bandwidths. The suppression of a resonant frequency can be insured either by the elimination of the responsible metallic strip or by the insertion of a PIN diode switch. Three FSS structures are manufactured and characterized. The FSS bandwidth can be enhanced in both perpendicular FSS exciting source directions by only varying the strips lengths and the ring dimensions to the corresponding resonant frequencies. A good agreement is obtained when the WCIP results are compared with the simulations of COMSOL Multiphysics software and experiment.

Wearable Fabry–Pérot Antenna

A wearable version of Fabry–Perot antenna is presented. This is a simple way of designing a medium- to high-gain antenna with low back radiation. The study of the effect of antenna bending in the performances is presented. Besides, the replacement of a superstrate layer by a metallic frequency selective surface is proposed. In this way, there is no need of finding a specific material and thickness for a targeted gain and frequency. Experimental validation confirms the viability of this design.

Design of Absorptive/Transmissive Frequency-Selective Surface Based on Parallel Resonance

This communication presents a novel frequency-selective surface (FSS) with high in-band transmission at high frequency and wideband absorption at low frequency. It consists of a resistive sheet and a metallic bandpass FSS separated by a foam spacer. The resistive element is realized by inserting a strip-type parallel $LC$ (PLC) structure into the center of a lumped-resistor-loaded metallic dipole. The PLC resonates at the passband of the bandpass FSS and exhibits an infinite impedance, which splits the resistive dipole into two short sections per the surface current; this setup allows for high in-band transmission at high frequency. Below the resonance frequency, the PLC becomes finite inductive and the entire FSS performs as an absorber with the metallic FSS as a ground plane. The surface current distribution on the resistive element can be controlled at various frequencies via the PLC structure. The wideband absorption and high in-band transmission of the proposed design are verified by both numerical simulation and experimental measurements. The potential extension to polarization-insensitive designs is also discussed.

Checkerboard Plasma Electromagnetic Surface for Wideband and Wide-Angle Bistatic Radar Cross Section Reduction

Bistatic radar cross section (RCS) of a metal plate is reduced by an improved checkerboard surface cover. Plasma and metallic frequency selective surfaces are studied analytically to achieve a proper reflection phase interval. More than 140° phase of the reflected wave is obtained as a promising method to reduce the returned wave in the way of incident wave or any other directions. Hence, a checkerboard surface is designed using the concrete numerical and analytical solutions for backscattering cancellation. Monostatic and bistatic cross sections of metal screens are reduced with the designed plasma electromagnetic surface coat. The amount of bistatic (RCS) is analyzed with a valuable equation. Wide frequency band, vast incident wave angles, and different wave polarizations are achieved for the bistatic analysis. Incorporation of plasma dielectric with metal surface, reconfigurable design, and analysis of the bistatic backscattering of the structure are the promising achievements.

Tunable Terahertz Metamaterials Employing Layered 2-D Materials Beyond Graphene

In this study, we extend recent investigations on graphene/metal hybrid tunable terahertz metamaterials to other two-dimensional (2-D) materials beyond graphene. For the first time, use of a nongraphitic 2-D material, molybdenum disulfide (MoS2), is reported as the active medium on a terahertz metamaterial device. For this purpose, high-quality few atomic layer MoS2 films with controlled numbers of layers were deposited on host substrates by means of pulsed laser deposition methods. The terahertz conductivity swing in those films is studied under optical excitation. Although no-appreciable conductivity modulation is observed in single-layer MoS2 samples, a substantial conductivity swing, i.e., 0 to ∼0.6 mS, is seen in samples with ∼60 atomic layers. Therefore, although exhibiting much smaller maximum terahertz conductivity than that in graphene, which is a consequence of much smaller carrier mobility, MoS2 can still be employed for terahertz applications by means of utilizing multilayer films. With this in mind, we design and demonstrate optically actuated terahertz metamaterials that simultaneously exhibit a large modulation depth (i.e., >2× larger than the intrinsic modulation depth by a bare MoS2 film) and low insertion loss (i.e., <3 dB). The advantages of using a 2-D material with a bandgap, such as MoS2, rather than a gapless material, such as graphene, are: 1) a reduced insertion loss, which is owed to the possibility of achieving zero minimum conductivity, and 2) an enhanced modulation depth for a given maximum conductivity level, which is due to the possibility of placing the active material in a much closer proximity to the metallic frequency selective surface, thus allowing us to take full advantage of the near-field enhancement. These results indicate the promise of layered 2D materials beyond graphene for terahertz applications.

Characterization of novel open notched quasi‐square metallic ring FSS using WCIP method for multiband applications

ABSTRACTA novel notched quasi‐square open metallic ring frequency selective surfaces (FSS) with single layer for triband applications is proposed. By the use of the wave concept iterative process (WCIP), the resonant characteristics of the proposed FSS are determined. The presented FSS shows three resonant frequencies when the incident wave is x‐polarized and one resonant frequency when the source is polarized in the orthogonal direction. A variation in the notched quasi‐square metallic ring dimensions allows a fine tuning in the FSS resonant frequencies to give raise to a tuned and enhanced bandwidth. Four FSS structures are manufactured and characterized. A good agreement is obtained when the WCIP results are compared with the simulations of COMSOL Multiphysics software and experiment. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2071–2075, 2016

Exceptional Terahertz Wave Modulation in Graphene Enhanced by Frequency Selective Surfaces

In this paper we theoretically and experimentally analyze the design trade-offs in terahertz metamaterial modulators consisting of hybrid graphene/metal stacked structures. In these devices graphene is used as the active medium, whereas a passive metallic frequency selective surface is employed to enhance the light–matter interaction in graphene. When altering the key geometrical structural parameters, we observe a close match between our experiments and theory, showing that it is possible to achieve an optimal trade-off between modulation depth, insertion loss, and speed in these devices. Moreover, a transmission line based compact mathematical model is introduced in order to explain our experimental observations and predict the performance limits in these structures.

Multiband Metallic Frequency Selective Surface With Wide Range of Band Ratio

A novel metallic multiband frequency selective surface (FSS) is presented. The proposed FSS structure has operation bands from closely spaced to far from each other (wide range of band ratio) and has high selectivity at each operation band. The unit cell comprises four small square slots, each loaded with multiple stub resonators. The stubs are placed in each slot in such a way that the unit cell response to both TE and TM polarizations are the same. To miniaturize the unit cell and cover the lower frequency range, each stub resonator is terminated with a U-shaped section. The length of each stubs within the slot determine the resonant frequency of each passbands. The band ratio can be set from 1.09 (close to each other) up to 2.35 (far from each other). Single, dual, triple, and quad band FSS structures are designed and simulated through HFSS software package. The fabricated dual-band unit cell shows that the proposed FSS structure can provide two close to each other bands, 9.8 and 10.9 GHz. Also, the measured results of a fabricated dual-band ${\bf 17} \times {\bf 17}$ FSS array show a relatively stable response to variations of incidence angle and polarization state.

A COMPACT DIPLEXER BASED ON LOW PROFILE MULTILAYER FSS FILTERS FOR ULTRA-HIGH DATA RATE POINT TO POINT WIRELESS COMMUNICATION SYSTEM

In this paper, we propose the design of multilayer frequency selective surfaces (FSS) waveguide band-pass fllters (WBPF). The WBPFs are designed to operate at two difierent frequency channels, respectively 71{76GHz (Rx) and 81{86GHz (Tx). The cross section surface of the FSS is imposed by the WR12 waveguide rectangular section's dimensions. The WBPFs are inserted symmetrically in a T-junction waveguide to design a compact diplexer. This is a basic component developed for an e-cient integration in the future E-band millimeter-wave transceiver. The multilayer FSS structure uses only non-resonant sub-wavelength unit cell elements; metallic patch and slot. To reach high channel isolation (… 70dB) a seven order fllter was required. Hence, each fllter is composed of 13 capacitive and inductive metallic FSS spaced by 12 ultra-thin dielectric substrate layers. The dielectric material is Rogers Ultralam 3850 (Liquid Crystalline Polymer; LCP circuit material). The fllter's overall thickness is < ‚=4. The numerical studies have been performed using flnite element method simulator (HFSS) and CST Studio Suites Tools. The experimental validation has been also done in the X band frequency by developing a flfth order FSS WBPF. Good agreements between simulated and measured results are obtained.

A thin radar-infrared stealth-compatible structure: Design, fabrication, and characterization

A thin radar-infrared stealth-compatible structure with reflectivity below −10 dB in the whole radar X wave band and infrared emissivity less than 0.3 in the infrared region of 8 μm–14 μm is reported. The designed stealth-compatible structure consists of metallic frequency selective surface (MFSS), resistive frequency selective surface (RFSS), and metal backing from the top down, and it is only 2.1-mm thick. The MFSS is made up of some divided low infrared emissivity metal copper films, and the RFSS consists of a capacitive array of square resistive patches. They are placed close together, working as an admittance sheet because of a mutual influence between them, and the equivalent admittance sheet greatly reduces the thickness of the whole structure. The proposed stealth-compatible structure is verified both by simulations and by experimental results. These results indicate that our proposed stealth-compatible structure has potential applications in stealth fields.

An Algebraic Multigrid Method for the Finite Element Analysis of Large Scattering Problems

An efficient iterative solver is proposed for the linear matrix equation that arises in the analysis of large scattering problems by the frequency-domain finite-element method. A Krylov method is preconditioned by a technique that approximately solves equivalent problems in two auxiliary spaces: a space of scalar functions and a space of piecewise linear, “nodal,” vector functions. On each space the traditional algebraic multigrid method is employed. Further, the “shifted Laplace” idea is used to improve the performance of the solver as the frequency increases. Results are reported for a waveguide cavity filter and three free-space scatterers: a conducting sphere, a metallic frequency selective surface, and a metamaterial lens made of split-ring resonators containing dielectric and metal.