3D FREQUENCY SELECTIVE SURFACES

The focus of this paper is to develop a low cost, light weight three dimensional (3D) frequency selective surface (FSS) with reduced fabrication complexity over 2D FSSs and can be used in the communication field. Nowadays, 3D FSS is taking too much attention because it provides high degree of freedom in controlling transmission/reflection response. Therefore, in this paper, a 3D FSS has been attempted by inserting three concentric conductive cylindrical rings in to a polyurethane foam. The proposed concentric triple cylindrical ring 3D FSS aims to work as a band stop in the GSM-900, UMTS-1800 and LTE-2300 frequencies. CST software is used to simulate and optimize the dimensions of FSS. After that, measurement of developed concentric triple cylindrical ring 3D FSS is carried out in free space. Measurement results are in good agreement with simulation results. To shield the communication band in the secure places, this type of low cost structure may be quite useful.

A three‐dimensional (3D) frequency selective surface (FSS) with a response that is independent of incident angle is presented in this study. The proposed FSS is a periodic array of 3D hollow‐tapered resonators. The proposed 3D FSS has reduced sensitivity to the angle of incidence of the electromagnetic wave compared with other 2D and 3D FSSs as a result of tapered structure. The transverse electric (TE) and transverse magnetic (TM) incident angle independences are obtained by tapering the width of a cylinder with a square cross‐section from the upper opening to the lower opening. Impressive frequency stability and transmission characteristics have been achieved up to 80° for both TE and TM incidence angles. The principles of operation along with guidelines for the design of the proposed FSS structures are presented in this study. A prototype of the proposed 3D‐tapered FSS is also fabricated and tested using a free‐space measurement system to verify performance.

A novel 3D Frequency Selective Surface (FSS) with horn shaped resonators is proposed which exhibits a very wide stop band. This new horn shaped resonator is a modification from a 3D FSS consisting of square cylinder unit elements. This feature introduces frequency-selective surfaces with the added advantage of lowering the sensitivity of the FSS frequency response with respect to the incidence angle. Simulation results prove that the FSS can realize broad selectivity of waves with the bandwidth more than 57%. The wideband transmission behavior is stable under oblique TM incidence angles from 0 to 80 degrees. The influence of various key parameters on 3D Horn Shape FSS characteristics has been investigated using the CST simulation software tool. By understanding the effect of each parameter, a comprehensive study for a better design of 3D Horn Shape FSS with wideband response is presented.

Professor Yongmeng Liu from the Harbin Institute of Technology in China talks about the research behind his Letter ‘Optical-transparent Wi-Fi bandpass mesh-coated frequency selective surface’ on page 381. Professor Yongmeng Liu Our group's work is focused on designing novel frequency selective surfaces (FSSs) as security wallpaper for optical windows of electromagnetic filtering and interference shielding. A FSS is an array of periodic apertures perforated on a conducting sheet or metallic patches which exhibits bandpass or bandstop responses. A traditional FSS generally has very low optical transmittance and cannot be easily applied as a dual-mode filter to achieve simultaneous high optical transparency and Wi-Fi bandpass filtering. The solution is to create novel periodic structures that have unique and fascinating features attracting us to this field of research. We have reported a FSS periodic structure fabricated using a UV lithography technique to achieve simultaneous high optical transparency and Wi-Fi bandpass filtering. The FSS is a resonance cavity structure with a periodic array of apertures removed from an optically transparent conductive mesh coating. Simulation and experimental results show that the resonance centre frequency of the mesh-coated FSS is about 5.3 GHz with transmittance loss of −2dB, while its optical transmittance is greater than 87.5% in a waveband of 1.35 to 3.3 µm. Such a FSS has the merits of ameliorable electromagnetic shielding effectiveness and improvable optical transmittance by optimising the thickness of the mesh layer. Our FSS can be used as security wallpaper for optical windows to solve the problem of transmission security of Wi-Fi communications. Generally, transparent conductive mesh coating is widely used to provide both strong RF/microwave shielding and optical transmittance, however this seriously attenuates Wi-Fi transmittance. A bandpass FSS is used to provide spatial filtering, but suffers from low optical transmittance due to the large fraction of the area obscured by metallic films. Neither of these existing technologies can meet the dual requirement of optics/Wi-Fi filtering for security wallpaper. It is a significant advancement to develop a periodic structure to achieve simultaneous optical transparency and stable Wi-Fi bandpass. One potential application is as security wallpaper for securing confidential business data. Another application is to enhance the transmission of the specific signal of interest through optical windows. State-of-the-art FSS technology includes indium tin oxide (ITO). This kind of ITO-FSS is used for energy saving windows since the ITO layer reflects a significant portion of long and short infrared wave energy. However, the restrictive relationship between conductivity and optical transparency of ITO is the fatal flaw in this implementation. We are working on a project to design conductive metallic meshes to shield radio-frequency/microwave interference for optical windows to optimise mesh patterns and parameters to improve optical transmission and to minimise the high-order optical diffraction effect, as well as enhance electromagnetic shielding effectiveness. Challenges will be to further optimise the structure of the mesh-coated FSS to improve the performance, specifically the sheet resistance, bandwidth and the transmission stability of incidence angles and polarisations. The FSS has high sheet resistance which will impact Wi-Fi transmission, however the FSS has adjustable thickness to enhance its conductivity and improve Wi-Fi transmission performance while having no impact on optical transparency. Additional challenges include developing ways to integrate the mesh-coated FSS with optical windows of existing buildings. Fortunately we can fabricate the FSS on flexible PET films and add the composite films to each side of existing optical windows. Over the next few years novel periodic electromagnetic structures will integrate metamaterials, active circuit elements and other new techniques to develop security wallpapers to protect communications security. The trend of periodic electromagnetic structures for electromagnetic filtering and shielding will evolve from expensive, heavy and passive to low-cost, lightweight, active and self-tuning. We would like to see increasing numbers of new periodic electromagnetic structures being developed throughout numerous frequency ranges, perhaps even the entire electromagnetic spectrum. We believe all these beautiful periodic electromagnetic structures will be brought into real-world use and will make our lives better!

Frequency selective surfaces (FSS) have been widely used for many years in antennas applications, like beams multiplexer, or filtering for microwave and optical signals. We present a new application for FSS. For the former applications, FSS are free standing or backed by a perfect dielectric. It can be also embedded into a dielectric medium or sandwiched between different dielectric media. In the new application, FSS are used as components of radar absorbing materials (RAM). Classical RAM are composed of several layers of dielectric or magnetic media. For example, the two most famous absorbing screens are the Dallenbach and the Salisbury screens. The first is a short circuited lossy dielectric (or magnetic) layer, while the second is composed of two layers. The Salisbury screen consists of a thin resistive film deposited on a perfect metal-backed dielectric layer. We show how a FSS can modify and improve the absorption performance of Dallenbach screens. The FSS is deposited on the outer surface of the Dallenbach screen in this new application. We show numerically that the absorption band can be either shifted or broadened by the presence of an FSS. We illustrate the numerical results with measurements. The theoretical aspects of the computation of the interaction between the electromagnetic field and the structure are discussed, and the properties of the new absorbing screen are examined.

The requirements of frequency-selective surface (FSS) between high transparency in pass band and high reflectance in stop band are contradictory, when they have loaded medium on one side and receive a large range of illumination. In order to solve the contradiction, this paper employs a discrete particle swarm optimization approach (hereafter referred to as a DPSO). In order to seek a balanced FSS with high transparency in pass band and high reflectance in stop band, the periodic intervals and geometrical dimensions of FSS-structures are optimized and designed by using the DPSO method. Simulation and test results indicate that the FSS of super dense Y loop elements in a half-loaded medium structure is presented in this paper: the transparency in pass band and stop band are 80% and 30% respectively. The DPSO method will offer an excellent FSS for the radome which receives a large range of illumination, and on the other hand, it provides a theoretical guidance for the requirements of FSS between high transparency in pass band and high reflectance in stop band.

A new permittivity measurement method for low loss dielectric materials using frequency selective surface (FSS) resonator and rectangular waveguide are researched in this paper. FSS resonator is designed by analyzing the influences of outer radius, ring width, length and width of substrate integrated waveguide (SIW). The developed FSS resonator is placed in the flanged ridge waveguide, while the dielectric material is placed closely to the FSS resonator. Then it analyzed the relationship between the resonant frequency point shifting value before and after putting sample in tester. This technique is based on the frequency only, with enough measurement accuracy for the dielectric permittivity.

In this paper, we propose methods for designing all‐dielectric frequency selective surface (FSS) by using microwave dielectric materials. Dielectric materials with relative permittivity of 3.75–960 are employed for designs. The design methods work efficient in framework of dielectric resonator theory. By adjusting the permittivity and thickness of the dielectric materials, band‐stop response can be designed at frequencies from 3 to 80 GHz. To design FSSs using different dielectric materials, there clearly shows a rule to keep the x‐o‐y cross sectional size of the unit cell still, simultaneously to keep the magnetic and electric resonant modes stable inside the dielectrics. The variation relationship of the fractional bandwidth with the ratio of the wavelength and the periodic size is concluded. The rule is workable for dielectric materials with the most relative permittivities. This paper provides significant methods of using nearly all possible dielectric materials to design all‐dielectric FSS with a quite simple structure in the desired frequencies.

This work reveals the Design and development of Dual wide band frequency selective surfaces (FSS). Dual-band FSS based on single and multi layers with or without or extra discrete components has been discussed and analyzed. Dual wide band-pass FSSs has been designed and developed by using two metallic layers for the wide targeted pass band frequency bands range of 3.53-5.3 GHz and 3.53-4.21 GHz. In the initial step of Development ultra thin double layer slotted FSS has been used. These generate resonance at 4.0 GHz and 4.8 GHz. Furthermore Hilbert shaped slotted resonator increase pass band width enhancement. Lastly the opposite alignment of similar FSS metallic plate to form the proposed dual layer FSS which exhibit the bandwidth enhancement of the frequency bands.

Purpose: studies of electrodynamics properties of Fabry–Perot resonator formed by two parallel perfectly conducting screens of finite thickness with rectangular holes while its exciting by a plane wave. Design: operator method of diffraction problems solving based on the method of partial areas and the method of generalized scattering matrixes. Findings: The numerical modeling showed that module of the coefficient of plane wave reflection from the resonator is equal to zero at a fixed wavelength being prohibitive for segments of rectangular waveguides made in both screens. Here, a strong localization of electromagnetic field in the resonator volume is observed. Studying the frequencyselective properties of each screen individually it has been determined that there are no resonances of electromagnetic wave total transmission below the cut-off frequency of rectangular waveguides. It is found that with replacing one of the Fabry–Perot resonator mirrors by a solid metal plane, the amplitude of a plane wave in the resonator can increase by almost an order of magnitude as against the exciting field amplitude. Conclusions: Unique electrodynamic properties of the considered structure can find application in devices for amplifying or generating electromagnetic waves in millimeter and submillimeter bands, as well as in measuring electrical properties of composite materials with large losses.

Recently, 3D Frequency Selective Surface (FSS) designs have become popular due to their enhanced performance at oblique incidence angles as compared to planar designs. While planar FSS design has been successfully performed using discrete nature-inspired evolutionary optimization algorithms such as the Genetic Algorithm (GA) and Particle Swarm Optimization (PSO), these algorithms are not suited for the problem of 3D FSS design, due to the generation of non-contiguous structures, making manufacturing difficult. One alternative to these algorithms is the Ant Colony Optimization (ACO) technique, which guarantees contiguous segments are generated. However, traditional ACO methods require meanders to continue until they are trapped, potentially generating a PEC unit cell. In this paper, a Multi-Objective Lazy Ant Colony Optimization (MOLACO) algorithm will be applied to the problem of FSS design. The introduction of lazy ants allows exploration of solutions previously inaccessible by traditional implementations of ACO. Simulated results will show that it is well suited to the problem of 3D FSS design.

Sandwich structures with frequency selective surfaces have been widely used to fabricate low-observable radomes. Traditional frequency selective surfaces were made of metals, such as copper and aluminum. There were problems when used the frequency selective surfaces with the sandwich structures, such as a bonding layer and thermal mismatch. Because of the thermal mismatch between the sandwich structures and the metals, mechanical properties of the sandwich structures usually decreased. To avoid these disadvantages, a new type of composite frequency selective surface was put forward in this study. A four-legged slot-array frequency selective surface and a square-aperture array frequency selective surface were fabricated by cutting carbon fiber/epoxy composites. Free-space method and finite-element method were carried out to evaluate the electromagnetic transmission characteristics of the frequency selective surface specimens, respectively. Results show that the composite frequency selective surface with four-legged slot array can realize the function of frequency selection, and its minimum transmission loss can be decreased by increasing the electrical conductivities of the composite material, adjusting the thickness, and increasing the aperture-to-cell ratio of it. For the composite frequency selective surface with square-aperture array, grating lobes come closely after its resonant frequency, although its minimum transmission loss is very close to zero.

In this article, a via‐based 2.5‐dimensional (2.5D) frequency selective surface (FSS) is proposed to realize a quasi‐elliptical bandpass response with high frequency selectivity. Each FSS element is composed of two parts. Part A is a double‐layer metallic circular patches, which are etched on both sides of a thick substrate and connected by a central big metallic via and several small vias. Part B is a single layer metallic circular patch etched on a thin substrate. The proposed FSS features several transmission/reflection zeros, exhibiting a flat transmission in the passband and fast roll‐off out of band. By investigating the electric field distributions, two paths of electromagnetic wave (EMW) propagation are observed, and the physical mechanism of the transmission/reflection zeros of the FSS is obtained. A prototype of the FSS is fabricated to verify the design, and the measured transmission responses agree with the simulated ones.

Isotropic frequency selective surface (FSS) made of cubic arrangements of split ring resonators (SRRs) is proposed and analyzed. For this purpose, a suitable isotropic modification of the SRR was used in the design of a cubic unit element invariant under the tetrahedral point symmetry group. It was experimentally demonstrated that the transmission through such a FSS is angle and polarization independent. For comparison, another FSS, whose unit elements do not satisfy necessary symmetries, was measured, showing clearly anisotropic behavior. We feel then that symmetries play an important role. Potential device applications are envisioned for antenna technology at microwave and terahertz frequencies.

A patch-slot-patch frequency selective surface (FSS) exhibiting bandpass response is proposed in this paper. The FSS unit cell is composed of two cross-dipole shaped patches and a cross-dipole shaped slot in between. The proposed FSS exhibits bandpass response with two closely spaced transmission poles around 3 GHz and 3.5 GHz. A 3-dB transmission bandwidth of upto 20% is achieved for the FSS. The proposed design has a thickness on the order of 0.032 λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> . The paper presents with parametric studies how the poles can be tuned individually. The transmission phase of the FSS varies linearly towards zero with frequency that makes the FSS useful in designing Filter-Antenna when placed as a superstrate above a broadside radiator.