Performance Of Frequency Selective Surface Research Articles

Frequency reconfigurable antipodal Vivaldi 2-port antenna based on graphene for terahertz communications

A graphene-based two ports antipodal Vivaldi antenna with improved gain for THz applications is introduced. The single antenna is composed of an antipodal Vivaldi antenna with a graphene radiator on the top and copper ground plane on the back with a total size equal to 108 µm × 84 µm to achieve reconfigurable performance from 3 to 4.5 THz. The reconfigurability is validated by changing the external DC Volt which in turn changes the graphene chemical potential and then changes the operating frequency. As well, to enhance the antenna gain, frequency selective surfaces (FSS) with a metallic patch are utilized to enhance the antenna gain. The FSS performance is investigated and optimized using a finite integral technique (FIT) software to achieve a reflective feature with band rejection from 2 up to 5 THz within the operating bands of the suggested antenna. The FSS is inserted below the MIMO antenna to reflect the antenna radiation and then enhance the antenna gain. The antenna gain is increased from 6 dB (single antenna without FSS) to 10.8 dB (with FSS) at 3.4 THz. The MIMO antenna is operated from 3.2 to 4.45 THz with S11 ≤ − 10 dB, isolation ˃ 20, gain from 8 to 10.8 dB, and efficiency higher than 80%. Finally, the MIMO parameters outcomes achieved good values which suggested the antenna to be employed in IoT THz applications.

Reconfigurable Terahertz Moiré Frequency Selective Surface Based on Additive Manufacturing Technology

We designed and fabricated a terahertz (THz) frequency selective surface (FSS) based on two distinct additive manufacturing technologies, namely, printable electronics (PE) and three-dimensional (3D) printing. Silver nanoparticle ink was printed on a polyethylene terephthalate (PET) substrate utilizing a large-scale roll-to-roll industrial PE technique with a flexographic printed unit, while the 3D-printed THz FSS was fabricated based on a powder bed fusion-selective laser melting system. The filtering characteristics of both types of FSS were verified through calculation, simulation, and experiments. Furthermore, the rotational tuning approach was applied to two identical FSS to form reconfigurable FSS which could be defined as Moiré FSS. Based on the numerical results obtained, our proposed technique which used a PE-based Moiré FSS achieves a 58% modulation depth at 0.25 THz, while experimental verification found a modulation depth of 41% at 0.22 THz, confirming that its adoption is simple and cost-effective. To the best of our knowledge, this is the first demonstration of a Moiré reconfigurable printed FSS operating in the THz region.

Active frequency selective surface with switchable response for satellite communications in X and Ka bands

This article proposes an active frequency selective surface (FSS) with application to satellite multi-band antennas in X and Ka bands. The FSS offers two reflective bands at 20 and 30 GHz (downlink and uplink frequencies of broadband communication satellites in Ka-band) under one biasing state, whereas the frequency characteristics are switched in X-band (between 9 and 12 GHz, frequencies used for broadcast satellite services and space exploration) under the second biasing state. The unit cell of the FSS consists of three metallization layers, including four PIN diodes on the bottom layer that provide reconfigurability in X-band. The FSS performance has been analyzed using an equivalent circuit model diagram, which provides a better understanding of the operation principle. The proposed FSS exhibits a robust transmission response for incidence angles up to 40°. Several samples of the FSS formed by a 2 × 4 cell array have been fabricated and measured in a waveguide simulator to confirm the results of the electromagnetic simulations at the lower operating frequencies.

Fabrication and characterisation of Frequency Selective Surface (FSS) for Terahertz Sensing Application

Abstract A frequency selective surface (FSS) structure based on a circular slot with 28 to 31 μm was fabricated using Electron Beam Lithography combined with wet etching technique on a 400 μm thick quartz substrate. The circular slot pattern, designed using the CST software, was transferred during the Electron Beam (EBL) exposure with 100 kV voltage acceleration, 2 nA of e-beam current, and line dosage of 1000 μC2. A 0.5 μm thick aluminium layer was deposited on a quartz substrate using the thermal evaporator technique. The aluminium thickness was confirmed by laser microscope and surface profiler measurement. The investigation shows that 20 seconds is the optimal etching time for producing the desired FSS circular slot structure compared to 40 and 60 seconds. The fabricated samples surface metrology was examined using an optical microscope, Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscope (AFM). The material compositions of the samples were confirmed by using the Energy Dispersive X-ray (EDX) measurement. Results show that, on average, there are ±1.5 μm of tolerance produced for fabricated sample size on the circular slot pattern compared to the CST simulation results. FSS performance slightly shifted in the frequency from actual 1.80 THz to 1.79 THz, whereas the transmission magnitude has increased by 0.03 from 0.91 to 0.94.

Detection of Low Sugar Concentration Solution Using Frequency Selective Surface (FSS)

Sugar is important in daily food intake since it is used as food preservative and sweetener. Therefore, is important to analyze the influence of sugar on the spectroscopic properties of the sample. Terahertz spectroscopy is proven to be useful and an efficient method for sugar detection as well as for future food quality industry. However, the lack of detection sensitivity in Terahertz Spectroscopy has prevented it from being used in a widespread spectroscopic analysis technology. In this paper, Frequency Selective Surface (FSS) using the Terahertz Spectroscopy Time Domain Spectrum (THz-TDS) which operates at terahertz frequency range has been demonstrated for application of sugar detection. The FSS is designed with a circle slot structure and has been optimized in line with the molecular resonance of glucose and fructose at different level concentration at 1.98 THz and 1.80 THz, respectively. Transmission magnitude of glucose and sucrose is inversely proportional with the level of sugar concentrations. The realization of the FSS structure is using electron beam lithography and wet etching technique. Results show that the FSS performance for glucose and sucrose reveal fair shifts in measured transmission magnitude from its original in CST by approximately 30%. The use of fabricated FSS with circle structure indicates that the concentration can be improved averagely at 25% for glucose and 13% for sucrose. Thus, it shows that the FSS circle structure combined with THz-TDS has the potential to become an alternative method for food sensing technology in the future.

Design of Miniaturized and Polarization-Insensitive Double-Layer Frequency Selective Surface Based on Meander Lines

The work presented in this paper concerns a method for the miniaturized frequency selective surface (FSS) based on the meander lines. A miniaturized dual-bandstop FSS structure based on meander lines with spiral-shape is proposed and simulated. The equivalent circuit and current distributions are introduced to explain the FSS performance. The size of the unit cell is 10 mm, which is about 0.037 wavelength at the first resonant frequency. Simulation results indicate that the proposed FSS has a frequency shift smaller than 1% for different polarizations with an oblique incident angle of 60°. A prototype of the FSS is fabricated and measured. The measurement results show that the FSS is polarization-insensitive and angle-insensitive.

Genetic-algorithm-empowered metasurface design: simultaneous realization of high microwave frequency-selection and low infrared surface-emissivity.

With the improvement of equipment integration, it is difficult to meet the increasing functional requirements with the function of a single spectrum. In this work, a multispectral functional metasurface (MFM) is designed to achieve multispectral compatibility between microwave and infrared using multi-optimization. For microwaves, a frequency selective surface (FSS) is designed to achieve frequency selectivity. And for infrared, a twice genetic algorithm (GA) is employed to further increase the metallic filling ratio, thus reducing the infrared emissivity while maintaining the performance of microwave FSS. In order to verify our design and method, the MFM is fabricated and measured, and all the results are consistent with the theoretical design. The performance of FSS can achieve 3dB bandwidth in 7.2-11.2GHz with low insertion losses and stability, and meanwhile the mean infrared emissivity has been reduced to 0.24 in 3-14μm. In summary, the designed multispectral compatible metasurface has wide application value in radome. What's more, the multi-optimization method for designing the multispectral metasurface can also be extended to other fields.

Mechanical and electromagnetic behavior of fabricated hybrid composite sandwich radome with a new optimized frequency-selective surface

A multidisciplinary design procedure was presented to fabricate hybrid composite sandwich (HCS) panels used in radomes based on conducting several mechanical and electromagnetic experiments. Accordingly, six specimens made of E-glass/aramid/polyester face sheets with different stacking sequences and polyvinyl chloride foam core were prepared using the vacuum-assisted resin transfer molding process. Afterward, three-point bending and low-velocity impact tests were performed and several mechanical characteristics were reported for specimens. Besides, electromagnetic wave transmission performance of the HCSs was experimentally and numerically determined. The accuracy of the simulated results was confirmed by free-space measurement method.The most efficient design of the hybrid stacking sequence was subsequently found by implementing the complex proportional assessment method and considering the mechanical and electromagnetic characteristics together with the moisture resistance of the specimens. Eventually, a new embedded frequency-selective surface (FSS) was designed for the radome using a genetic algorithm to maintain the transmission rate in the desired band at the order of higher than 90 percent. The comparison of the new FSS performance with conventional FSSs in the literature exhibited that the present optimization procedure not only achieves the maximum transmission at the resonance frequency but also enhances the transmission loss outside of the desired frequency band.

Single-layer angularly-stable bandpass frequency-selective surface with interdigital resonator

A miniaturized periodic element for constructing bandpass frequency selective surface (FSS) independent of incident angles and polarizations is presented. An interdigital resonator (IR) with one extending finger to connect the two separate parts of the interdigital capacitor is explored to achieve parallel resonance. The equivalent circuit model (ECM) and electric field distributions are introduced to explain frequency performance of FSS. The whole structure has only one layer and possesses a low profile (a thickness of 0.001 5λ, where λ represents the resonant wavelength in free space) as well as a small size (0.03λ×0.03λ). This FSS performs as a spatial bandpass filter which exhibits a great angular stability with incident angles ranging from 0° to 80° for both transverse electric (TE) and transverse magnetic (TM) polarizations. As an example, a prototype of one proposed FSS is fabricated and tested. The measured results show a good angular stability.

Synthesis analysis of frequency selective surface using the generalized sheet transition conditions

Based on the generalized sheet transition conditions (GSTCs), the surface electric/magnetic susceptibilities of frequency selective surface (FSS) are extracted and analyzed. Key factors that affect the FSS performance, including frequency variations, structure shapes, angular dependent, and bandwidth are studied through the susceptibility parameters. Based on the analysis of four typical FSS structures, potential automatic structure designs are suggested and several illustrative examples are given. Finally, the method is compared with the equivalent circuit method.

A frequency selective surface with 3-D unit cells

This paper conceptualizes the development of a frequency selective surface (FSS) with 3-D unit cells. The FSS unit cells individually present a three-dimensional structure, whereas collectively these are more like planar FSS. The unit cell substrate has been printed using 3-D printing technique and metallized using copper paint. The 3-D printing offers a degree of freedom to fabricate substrate material in three dimensions. Various designs of unit cell have been studied by fabricating a dual-band FSS which highlights the significance of the dimensional change of the 3-D unit cell over FSS performance. The designed FSS has been fabricated and tested using VNA where test results are found as per desire. The main objective of the paper is to develop a comprehensive method for rapid prototyping of FSS in applications in the area of radar, satellite and navigation.

Design and Analysis of an Ultraminiaturized Frequency Selective Surface With Two Arbitrary Stopbands

The paper proposes a new design and its analysis of a 2.5-D ultraminiaturized frequency selective surface (FSS) with two arbitrarily and independently adjustable stopbands. These two stopbands can be adjusted very far away or combined to a single wideband. This new FSS consists of only one dielectric layer printed on both sides with refined meandering-lines connecting vertical via arrays. By applying the proposed approach with an exactly equivalent circuit and closed-form equations, four representative prototypes are demonstrated. The first one has two distant stopbands, which high-to-low resonant frequency ratio can be as large as 6.2. The second one shows that its unit-cell size can be highly reduced to only 2.8% of the free space wavelength at the lower resonant frequency. The third one has a wide stopband, having a fractional bandwidth up to 75.7%. The final one meets the specification of 2.4-GHz and 5-GHz wireless local area network application. The simulated and measured results both validate the FSS performance and demonstrate its excellent versatility never found in literatures before.

Study of 5.8 GHz Band-Stop Frequency Selective Surface (FSS)

This paper presents the study of 5.8 GHz frequency selective surface (FSS) acts as a band stop to eliminate unwanted radiation signal at 5.8GHz. The FSS was designed using computer simulation technology (CST) Microwave Studio software. The paper shows the comparison of square loop, octagon loop and hexagon loop of Band stop FSS (BSFSS) performance at 5.8 GHz. Besides, the BSFSS design using four different type of dielectric substrate such as FR-4, TLY-5, Roger RT5870 and Roger RT5880 were compared. The results obviously show that the Rogers RY5880 has the attenuation -44.72 dB. The fabricated FSS were measured by using free space technique with two horn antennas connected to performance network analyzer (PNA). The measured and simulated results were compared. The results show that the square loop FSS structure have the better attenuation -26.76 dB (simulated) and -38.34 dB (measured) at 5.8 GHz.

Design of SIW cavity models to control the bandwidth of frequency selective surface

This study describes substrate integrated waveguide (SIW) cavity models to control the bandwidth of frequency selective surfaces (FSSs). Two different SIW cavities were presented: one model to reduce (cavity-I) and another model to improve (cavity-II) bandwidth of FSS, respectively. The periodic structures were made of SIW cavies and an FSS slot on either side of the dielectric substrate at the centre of the cavity. To prove the concept, a well-known cross-slot FSS element has been studied in two different cases and compared their performance. The conformal behaviour of the unit cells has been estimated by considering the practical requirements. The addressed SIW cavities will improve the electromagnetic (EM) performance of conventional FSS without altering its basic shape. The high Q-factor of SIW cavity greatly improves the performance of FSS. A full-wave simulation is used to analyse the response of FSS. The cavity-I shows 12.61% lesser bandwidth and cavity-II shows 25.0% higher bandwidth compared to its conventional shape in planar form and 9.1, 26.17% in the conformal form at a bent radius of 50 mm. Besides, performance parameters were studied to evaluate the structural dependency on EM performance. Finally, two designed cavity models are fabricated and proved their performance experimentally.

Flexible Serpentinelike Frequency Selective Surface for Conformal Applications With Stable Frequency Response

In this letter, a flexible stopband frequency selective surface (FSS) with serpentine stripe unit cell is presented. Compared with the FSS with straight stripe and zigzag stripe unit cell, the proposed FSS on planar thin polyimide (PI) substrate shows very small offset of resonant frequency with electromagnetic waves having incident angles from 0 $^\circ$ to 60 $^\circ$ , according to the simulation results. The stable transmission performance of flexible FSS with serpentine stripe unit cell on PI substrate is further demonstrated by the computational and experimental results. When the FSS with serpentine stripe unit cell is bent with bending angles from $ \pi /3$ to $ \pi$ , the offset of resonant frequency is negligible, whereas the resonant frequency of FSS with straight stripe and zigzag stripe unit cell shifts about 15.4% and 5.8% when bending angle is $ \pi$ , respectively.

Polarization Insensitive Dual Band Frequency Selective Surface for RF Shielding Through Glass Windows

This paper reports on a dual-band, polarization-insensitive frequency-selective surface (FSS) directly realized on window glass for Wi-Fi and WLAN shielding applications. The design incorporates an annular ring and modified flower-shaped geometry to suppress 2.45 and 5.5 GHz bands, respectively, while acting ineffective to the rest of the frequency spectrum. The proposed design is completely insensitive to incoming wave polarization owing to its symmetry. The FSS also offers excellent incident wave angular stability up to 45°. Additionally, a wide rejection bandwidth (−10 dB) of more than 630 and 1430 MHz for lower and higher bands, respectively, is obtained suffice to cover the WLAN spectrum. Unlike conventional screen-printed FSS for glass applications, the conducting patterns of the proposed FSS are realized with copper foil directly laminated and etched on the glass substrate while maintaining 86% transparency for sufficient light passage. The detailed analysis of all parameters has been carried out, and their effect on the performance of FSS is reported. An equivalent lumped circuit model is also generated for the proposed design to better understand the physical phenomena of electromagnetic (EM) wave suppression. A finite prototype containing 13 × 10 elements is fabricated and tested. The measured results are in good agreement with the simulated ones. The FSS offers measured suppression of 43 and 40 dB at 2.45 and 5.5 GHz bands, respectively. The design has excellent potential for EM field suppression, WLAN isolation, and security applications in indoor environments.

A Miniaturized Low-Profile Multilayer Frequency-Selective Surface Insensitive to Surrounding Dielectric Materials

In most applications, a frequency-selective surface (FSS) needs to be attached to a wide variety of dielectric materials. The performance of a traditional FSS is greatly influenced by the dielectric material to which it is attached. In this paper, a novel multilayer structure is proposed to construct an FSS. The performance of the proposed structure is shown to be very stable when it is attached directly to a wide variety of dielectric materials of arbitrary thickness. Both single- and dual-polarized structures are designed. The shape of the FSS element is designed by using stepped-impedance transmission lines. A new methodology is proposed to design the FSS by maximizing the value of the capacitance between adjacent layers. The proposed structure offers three distinctive advantages. First, the strong cross-layer capacitance makes the FSS element very compact. The dimensions of the miniaturized element are as small as $0.012 \lambda \times 0.012 \lambda $ . Second, for the proposed structure, the lower the profile, the stronger the cross-layer capacitance, and the lower the resonant frequency. This is unique to the proposed structure since the resonant frequency is usually higher for a lower profile for traditional structures. Third and most importantly, any external dielectric material attached to the FSS will not significantly affect the performance of the FSS due to this strong cross-layer capacitance. Through examples of a single-polarized bandpass FSS at 1 GHz and a dual-polarized bandpass FSS at 1.96 GHz, it is demonstrated that a stable resonant frequency under various incident angles up to 75° can be achieved.

Hybrid FSS and Rectenna Design for Wireless Power Harvesting

This communication presents a hybrid frequency selective surface (FSS) and rectenna design for wireless power harvesting. To this extent, the center of the original FSS structure acts as a probe-fed patch antenna and an additional layer was added to the rear of FSS structure to mimic the required antenna ground plane, while minimizing its impact on FSS performance. The proposed hybrid solution yields a bandpass frequency response at GSM 900-MHz frequency band, with band reject behavior at 2.4 GHz and, on the other hand, act as a energy harvesting system through the antenna element at the 2.4-GHz ISM band, e.g., for recycling ambient Wi-Fi energy. The developed prototype, consisting of an array of 12 unit cells, was able to power a 56-mW LED at a 2-Hz rate from an incident power level of $-10\;\text{dBm}$ , resulting in an average output power of $300\;\upmu\text{W}$ and an unit cell RF–DC conversion efficiency of 50%.

Fast Performance Prediction of Cascaded Bandpass Frequency Selective Surfaces Operating in Circular Polarization Including Oblique Incidence

In this letter, a second order bandpass frequency selective surface (FSS) operating in circular polarization (CP) is analyzed and designed. The transmission line method (TLM) combined with an interpolation scheme is proposed to analyze the FSS. Based on some sampled full wave results of the corresponding single layered FSS, the double layered second order FSS is analyzed efficiently. GFRP with relatively high permittivity and high strength is used as skin to protect the whole FSS. Foam with low permittivity is used as an interlayer to achieve low weight. This kind of dielectric configuration leads to different phase characteristics for TE and TM polarizations at oblique incidence. This difference influences the performance of the FSS operating in circular polarization, such as increasing the axial ratio (AR) of the circularly polarized wave. Optimization for AR in passband is done with the proposed method by varying dielectric thicknesses. Finally, a prototype of the optimized FSS is fabricated and measured. The measured results agree well with the simulated ones.

Design of Frequency Selective Band Stop Shield Using Analytical Method

In this article, a high-order frequency selective band-stop EMC (electromagnetic compatibility) shield is designed using multilayer square loop while each loop resonates at the specific desired frequency. The glass material is picked out as the preferred substrate for the designing process. In contrast to the computationally intensive numerical approaches (software), the equivalent circuit model offers a simple alternative method in FSS (frequency selective surface) analyses which is useful for quickly predicting the performance of FSS. The proposed FSS can be synthesized based on microwave filter theory and the synthesized FSS can control transmission-zero frequencies. A three zero-transmission transparent window is designed using the proposed method, in which 30dB insertion loss is achieved for 6 to 10 GHz bandwidth and optical opacity of the structure is 85%. The response of the analytical model is compared with the results of full-wave simulation. As a result, it predicts quite well the resonant frequencies of the designed FSS.