Properties Of Frequency Selective Surfaces Research Articles

Influence of Flexible and Textile Substrates on Frequency-Selective Surfaces (FSS).

Frequency-selective surfaces (FSS) are two-dimensional geometric structures made of conductive materials that selectively transmit or reflect electromagnetic waves. In this paper, flexible FSS made on textile and film substrates is presented and compared to show the effect of the texture associated with the type of substrate on the shielding properties. Three geometries of patterns of squares in the border, inversion of squares in the border, and circles with a border were used, and the patterns were made by the silver paste screen printing technique. Microscopic analysis (SEM and optical) was performed to determine the degree of substrate coverage and the actual geometry of the pattern. The resistance per square of the obtained patterns was about 50 mΩ/□. The shielding properties of FSS were simulated in Comsol Multiphysics 6.2 software and then measured by the antenna method. Selective textile filters were obtained, depending on the pattern used, with one or two modals with a transmission attenuation of about 15 dB. The paper analyzes the effect of the substrate and the screen printing technique used on the shielding properties of the flexible FSS.

Intelligent electromagnetic mapping via physics driven and neural networks on frequency selective surfaces

The high mapping efficiency between various structures and electromagnetic (EM) properties of frequency selective surfaces (FSSs) is the state-of-the-art in the EM community. The most straightforward approaches for beam analysis depend on measurements and conventional EM calculation methods, which are inefficient and time-consuming. Equivalent circuit models (ECMs) with excellent intuitiveness and simplicity have been put forward extensively. Despite several applications, bottlenecks in ECM still exist, i.e. the application scope is restricted to narrow bands and specific structures, which is triggered by the ignorance of EM nonlinear coupling. In this study, for the first time, a lightweight physical model based on neural network (ECM-NN) is proposed , which exhibits great physical interpretability and spatial generalization abilities. The nonlinear mapping relationship between structure and beam behavior is interpreted by corresponding simulations. Specifically, two deep parametric factors obtained by multi-layer perceptron networks are introduced to serve as the core of lightweight strategies and compensate for the absence of nonlinearity. Experimental results of single square loop (SL) and double SL indicate that compared with related works, better agreements of the frequency responses and resonant frequencies are achieved with ECM-NN in broadband (0–30 GHz) as well as oblique incident angles (0°–60°). The average accuracy of the mapping is higher than 98.6%. The findings of this study provide a novel strategy for further studies of complex FSSs.

Modeling of Frequency Selective Surfaces Using Impedance Type Boundary Condition

The electromagnetic properties of frequency selective surfaces (FSS) are often calculated using integral equations. The metal strips of an FSS are usually modeled as an infinitesimally thin perfect conductor. This assumption is valid as long as the thickness of the metal strip is significantly smaller than the skin depth. If this condition is not applicable, the discretization of the volume of the metal strip is necessary. In this paper, we propose a method based on the same assumption from which the impedance type boundary condition is also derived to avoid the volumetric discretization when the thickness of the metal strip is comparable to the skin depth. We will show that in this case the accuracy of the modeling is significantly increased, while the number of unknowns remains very low as compared to the full volumetric discretization.

Polarization Properties of Frequency-Selective Surfaces Comprised of Spiral Resonators

Arrays of spiral resonators are used in the design of frequency-selective surfaces operating in the frequency range 2-18 GHz. The transmission spectrum of linearly polarized radiation incident on each array exhibits a multiplicity of resonance features, the number and frequency of which is a function of the design of the spiral geometry. The transmission spectra are also functions of the slant angle, the array rotation angle, and the polarization of the receiving antenna. From an analysis of the acquired data it is concluded that the spiral resonator arrays act primarily as rotators of the incident radiation and that the angle of rotation and the axial ratio is shown to be a function of the frequency of the resonance feature. These general conclusions have been confirmed by numerical simulations performed by Ansoft's finite-element software package HFSS.

Applications of Split-Ring Resonances on Multi-Band Frequency Selective Surfaces

Multi-band frequency selective surfaces (FSSs) are proposed by utilizing the split-ring resonators (SRRs) as the basic unit cells. The magnetic resonance of SRRs, which makes an additional dip in the reflection and transmission spectrums of FSSs, is discussed based on the equivalent circuit method and the simulation models. Because of the electric and the magnetic resonances of the single SRR as well as the coupling between periodically arrayed SRRs, the multi-band properties of FSSs are realized. Finally, the dependence of the geometrical parameters of SRRs on the resonance frequencies of FSSs is investigated.

Finite-difference time-domain analysis of frequency-selective surfaces in the mid-infrared

We use the finite-difference time-domain (FDTD) method to model the spectral properties of frequency-selective surfaces (FSSs) at normal incidence in the 1-10 microm wavelength. At these wavelengths the usual assumption that the metallic portions of a FSS are infinitesimally thin perfect conductors are no longer valid. We include the effects of dispersive complex conductivity for real metals and dispersive permittivity for dielectric materials by developing a unified approach that is especially suited for use in FDTD simulations. We concentrate on the finite nature of the metallic conductivity and its variation with wavelength in FSS structures. Our simulation results indicate that the resonant spectrum of a FSS in this wavelength range depends not only on the geometry of the structure and the dielectric substrate present, but also critically on the dispersive properties of the metal species used for the conductors.

Frequency selective surface as a polarisation transformer

The polarisation transformation properties of frequency selective surfaces are reported. Examples of microstrip structures which transform polarisation from linear to circular are described. A relatively broadband polarisation transformer can be designed for a limited range of angles of incidence. Alternatively, a polariser for a wide range of angles of incidence can be designed to operate over a narrow frequency band. A polariser that can be electronically switched is also characterised. The finite-difference time-domain (FDTD) method and the waveguide simulator technique are used to analyse the reflection of a plane wave from these periodic structures.

Resonant enhancement of emission and absorption using frequency selective surfaces in the infrared

We investigate the infrared properties of frequency selective surfaces consisting of aluminum patches on silicon substrates. Resonant behavior is found not only in the transmission and reflection, but also in the absorption and emission of these surfaces. The resonance location is a controllable function of the surface pattern. Simple model calculations reproduce well the qualitative behavior of our samples.

Influence of supporting dielectric layers on the transmission properties of frequency selective surfaces

Single layer arrays of linear dipole slots and patches symmetrically embedded in a dielectric layer or bonded to its surface illustrate dielectric tuning effects in this mainly computer aided but partly experimental study. After its initial rapid decline as the layer thickness increases, the resonant frequency of the slots varies cyclically about the limiting value for the patches. Contours of transmission level on a frequency/thickness plot illustrate this frequency pulling effect and lead to a discussion of passband shaping and the sensitivity to angle of incidence. Equivalent circuit concepts account for the observed bandwidth and resonant frequency variations. The performance of two experimental surfaces is described, including the influence of trapped waves in the dielectric.