COMPARATIVE ANALYSIS OF EMBROIDERY AND SCREEN-PRINTING TECHNIQUES FOR TEXTILE-BASED FREQUENCY SELECTIVE SURFACES

A novel method of designing the frequency selective surface (FSS) based on spoof surface plasmon polariton (SSPP) modes is proposed and demonstrated. The high-efficiency transmission and a stopband with a steep falling edge can be mediated by the SSPP modes below and above the cutoff frequency, respectively. So the prolific filtering performances can be customized by integrating with the traditional FSSs. As examples, the two kinds of FSSs were designed and demonstrated by simulations and experiments. A bandstop FSS with the suppression level more than 28 dB is first realized in the frequency region of 9.0–14.7 GHz with the steep rising and falling edges. Then, a dual bandpass FSS is designed by sandwiching the SSPP structure array between the two layers of traditional FSSs. It is indicated that the designed FSS shows two passbands in the frequency ranges of 4.2–4.3 GHz and 8.7–10.3 GHz, and the insert loss is less than 0.5 dB.

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 paper, a dual-band Frequency Selective Surface (FSS) absorber is presented for Wireless Local Area Network (WLAN) security. The FSS absorber is designed for two frequencies of interest, i.e., 2.45 GHz (lower band) and 5.25 GHz (upper band), respectively. FSS design consists of two layers; first layer consists of conducting square-loop elements while second layer consists of resistive square-loop elements, placed in-front of a conducting FSS layer. The proposed FSS design provides good frequency stability for oblique incidences for perpendicular (TE) and parallel (TM) polarizations. It provides better absorption rate for 2.45 GHz and 5.25 GHz frequency bands and allow the transmission of other microwave frequencies. Also, the proposed FSS design reduces multipath fading of additional WLAN signals which occurred due to the placement of conducting FSS layer. Presented results demonstrate that the proposed FSS design has a stable frequency response for the desired frequency bands for TE and TM polarizations with good absorption rate when the incident wave angle varied from 0<SUP>0</SUP> to 45<SUP>0</SUP>.

Thicknesses of window glasses, radomes, plastic cases of wireless systems are comparable with the wavelength in the millimeter-wave band. The reflections from the dielectric plate surfaces are canceled out of phase when the thickness is identical to a half of the wavelength. However, they are not canceled at any other frequencies except integer multiple of a half wavelength. Therefore, return loss is a serious problem in the millimeter-wave band. A frequency selective surface (FSS) loaded to the dielectric plate controls reflection amplitude and phase, thus, return loss is canceled for various dielectric thickness and frequency. A complex scattering matrix (S-matrix) of FSS is represented by only reflection amplitude |S 11 | from the condition of zero thickness of FSS expressed by shunt suceptance. The total reflection is calculated by converting S-matrices of FSS and a dielectric plate to a transfer matrices (T-matrix) and synthesizing them. We propose to find the required characteristics of FSS from the desired characteristic of whole structure. Broadband characteristic was designed by inserting FSS at the center of the dielectric plate.

This thesis presents the development and the additive manufacturing of smart antennas and frequency selective surfaces (FSS) for microwave, millimetre wave, and low-Terahertz applications. Numerous fabrications techniques such as etching, low-cost inkjet-printing, Fused Filament Fabrication (FFF) and Aerosol Jet Printing are employed to fabricate the antennas and FSS. Firstly, frequency reconfigurable antennas with close-coupled biasing technique are developed using double-sided etching on a thin mylar substrate for smart current and voltage sensing applications. The frequency tunable antenna also acts as a novel current sensing antenna in a smart sensing system that can sense the alternating current passing through a wire. The design is followed by introducing a low-cost inkjet-printed industry ready solution for frequency reconfigurable antennas where a single antenna aperture solution is utilised to demonstrate frequency reconfigurability in both switching and tuning configurations. Development of Frequency Selective Surfaces using low-cost printing machine is demonstrated in which FSS structures are inkjet-printed as wallpaper posters for Radio Frequency (RF) shielding and signal enhancements for 4G and 5G applications. A novel approach for fully 3D printing an FSS structure is also demonstrated using a low-cost open-source printer, which was modified to print the filament and the conductive inks simultaneously. Widespread investigation of industry-grade Aerosol Jet printing is utilised for additive manufacturing of bandstop and bandpass FSS designs for RF shielding and signal filtering. The bandstop designs are developed for microwave and millimetre-wave applications. The bandpass slot FSS designs are developed for millimetre wave and low-Terahertz applications for futuristic Beyond 5G and 6G systems.

Fractal geometries have been extensively implemented in the design of multiband antenna and frequency selective surface (FSS). For example, convoluted and Hilbert patch elements were first proposed to reduce the unit cell size of FSS (Parker and El Sheikh, IEE Proc.-H, 138, 19–22, 1991.) A fractal FSS with self-similar Sierpinski dipole array was shown to have two stop bands (J. Romeu and Y. Rahmat-Samii, IEEE Trans., AP-48, 1097–1104, 2000). However, its resonant frequencies are rather sensitive to incident angles and polarizations. Minkowski patch FSS and Sierpinski carpet fractals have been shown to provide two or three stop bands with dual polarization capability (J.P. Gianvittorio, et. al., IEEE Trans., AP-51, 3088–3096, 2003.) Recently miniature band-pass FSS with fractal antenna-filter-antenna arrays was designed and demonstrated with good frequency selectivity (S. Zheng, et. al., IEEE AWPL, 11, 240–243, 2012.) A dual band fractal FSS with a 3:1 reflection to pass band ratio and significantly improved resonant frequency stability was proposed by the author (T.K. Wu, Microwave Optical Tech. Letters, 54, 833–835, 2012).

This paper deals with a novel Frequency Selective Surface (FSS) Electromagnetic shield that operates in the low 5G vertical applications. This FSS is designed for the purpose of serving as an electromagnetic shield to eliminate EMI. The FSS designed operates at a frequency of 5GHz with a bandwidth of 1.45GHz providing a shielding of more than 40dB. The proposed FSS uses a polyester sheet as substrate and uses silver for the metallization of the FSS. Since the proposed FSS is symmetric, it behaves similarly when a Transverse Electric (TE) or a Transverse Magnetic (TM) wave is incident. The structure was designed and simulated using CST software. The results show that this FSS blocks electromagnetic radiation at lower frequencies as intended.

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.

In this paper, the Minkowski fractal is used to design the geometry of a frequency selective surface (FSS) unit cell, which resembles the shapes found in nature. The proposed FSS unit cell has both angular and polarization stabilities of incident wave. For the miniaturization of FSS and decrease of resonance frequency, interdigital capacitances (IDCs) are devised in the FSS structure, which do not eliminate angular and polarization stabilities. The dimensions of the unit cell are 5 mm × 5 mm and miniaturized 0.095λ0×0.095λ0. The resonance frequency is specified as 5.75 GHz with 155 MHz bandwidth. An equivalent circuit is derived for the unit cell to evaluate its frequency responses. The effects of variations of the geometrical dimensions of the FSS unit cell on its performance are studied. A prototype model of proposed FSS is fabricated and measured. The performance of its full-wave computer simulation results and measured data are compared and are shown to be in good agreement.

Electromagnetic transmission characteristics of composite frequency selective surfaces coated with conductive polymer–silver paste

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.

This letter presents the design and testing of a novel triple-layer frequency selective surface (FSS) with ultraminiaturization for electromagnetic shielding applications. The proposed unit cell is constructed using meandered lines running along the three layers and they are interconnected using metalized vias to increase the electrical length of FSS. The FSS is designed to offer band stop resonance at L-band frequency with a foot-print of 0.022 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> × 0.022 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> with a thickness of 0.006 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> and it provides at least 38% of miniaturization in comparison with similar literature. To validate the transmission performance, a prototype FSS with a periodicity of 6 mm is fabricated. The FSS consists of 2500 elements arranged in a 50 × 50 square lattice. The transmission performance of the proposed FSS is verified using simulation and experiment. The proposed FSS has rotational symmetry and hence it is polarization insensitive. Furthermore, the FSS offers excellent angular stability up to the maximum incidence angle of 60° under both transverse electric and transverse magnetic modes of operation. The proposed FSS can be used for shielding applications in global positioning systems tracking and aircraft surveillance systems.

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.

This paper describes an antenna design for wideband high directivity operation using an aperture coupled patch antenna as the feeding source and an FSS (frequency selective surface) based structure as the superstrate for high directivity. The new antenna device combines the wideband characteristic of the aperture coupled antenna and the desirable characteristics of the FSS structure as a superstrate for high performance operation. A coplanar waveguide (CPW) feed design is used to obtain wideband performance for the feeding antenna. Both single layer and double layer based FSS designs are studied for improvement of directivity. The performance is further enhanced by using an air gap between the patch on a thin film substrate and the CPW and aperture structures on an FR4 substrate and also between the layers of a double layer FSS design. The air gaps can be produced using micromachined PMMA rims for low cost construction. An impedance bandwidth in excess of 50% has been obtained for a centre frequency of 10 GHz. The antenna device exhibits a directivity of about 13.6 dBi. A 1-dBi ripple radiation bandwidth as high as ∼42% has been achieved.

Purpose The purpose of this paper is to present the results of a particle swarm optimization (PSO) method applied in the design of a square-loop frequency selective surface (FSS) via the equivalent circuit model (ECM), considering the dielectric effective permittivity as a variable in the optimization problem. Design/methodology/approach In the optimization process considered, besides the FSS square loop geometric parameters, the thickness and relative permittivity of dielectric material used as support are included as variables in the search space, using for this a model of dielectric effective permittivity introduced by the authors in a previous work. Findings Square loops were designed and the obtained results were compared with designs reported in literature for applications in wireless local area network and long-term evolution 4G systems. The low computational cost is remarkable as well as the acceptable accuracy obtained with the proposed approach. The PSO method results were implemented with the ECM and compared with those obtained via Ansys – high frequency structure simulator commercial software simulations. Originality/value The lack of a model of dielectric effective permittivity for the ECM causes a restricted search space in the stochastic FSS design process limited to only geometric parameters, as it is reported in the available literature. The proposed approach simplifies and makes more flexible the design process, and allows guiding the FSS design to unit cell surface and/or dielectric thickness of small dimensions.