Selective Surface Research Articles

Adjusting microwave sensing frequency through aspect ratio variation and bending repetitions in Permalloy ellipses

The Ferromagnetic Resonance (FMR) phenomenon, marked by the selective absorption of microwave radiation by magnetic materials in the presence of a magnetic field, plays a pivotal role in the development of radar absorbing materials, high speed magnetic storage, and magnetic sensors. This process is integral for technologies requiring precise control over microwave absorption frequencies. We explored how variations in resonance fields can be effectively modulated by adjusting both the shape and stress anisotropies of magnetic materials on a flexible substrate. Utilizing polyethylene-naphthalate (PEN) as the substrate and Permalloy (Ni79Fe21, noted for its positive magnetostriction coefficient) as the magnetic component, we demonstrated that modifications in the aspect ratio and bending repetitions can significantly alter the resonance field. The results, consistent with Kittel’s equation and the predictions of a uniaxial magnetic anisotropy model, underscore the potential for flexible substrates in enhancing the sensitivity and versatility of RF-based magnetic devices.

Robust photopolymerized superoleophobic/superhydrophilic mesh for oil-water separation

Selective superwetting surfaces preserve the opposite superwetting properties of oil and water and have attracted considerable attention for their application in oil-water separation owing to their efficient surface energy since 2000. Among these surfaces, superoleophobic/superhydrophilic surfaces are considered remarkable because of their anti-oil properties. The coexistence of superoleophobicity and superhydrophilicity poses a challenge based on the traditional surface/interface theory. However, the fabrication of superoleophobic surfaces requires extremely low surface energy, which is achieved by introducing compounds with long fluorocarbon chains. However, these compounds are harmful to the environment. Herein, a mesh with superoleophobic/superhydrophilic properties was developed by coating a chemically etched copper mesh substrate with photopolymerized short fluorocarbon chains and water-insoluble hydrophilic monomers. This mesh can separate different types of oil-water mixtures with a separation efficiency of >99 %. The mesh demonstrated excellent underwater stability as well as chemical and mechanical durability. The water resistance and chemical durability of the mesh are stronger than those of the control copper mesh using metal ions and long fluorocarbon chains. Moreover, oil-water separation was achieved even after immersion in deionized water and salt, acid, and alkali solutions. In addition, the mesh preserves the ability of oil-water separation after being cleaned and reused for 10 times. The proposed superoleophobic/superhydrophilic mesh offers a solution for continuous oil-water separation and has prospects for developing anti-fouling/sweat-absorbing fabrics and self-cleaning surfaces.

Detection of breast tumor with a frequency selective surface loaded ultra-wide band antenna system

Breast tumors are a significant cause to the global death rate among women. However, the fatality rate can be lowered through early detection. This paper presents an ultra-wideband, modified patch antenna of a compact size that can be used for microwave-sensing biomedical applications in the detection of breast cancer. A partial ground plane and slots are implemented in a transformed patch antenna to enhance the impedance bandwidth. The antenna is backed by a uniform frequency selective surface of 5 × 5 unit cells to achieve the necessary antenna characteristics, specifically directivity and gain, for microwave detection applications. Through optimization and fabrication, the final design maintained (|S11|< −10 dB) over the entire frequency band of 11.6 GHz (3.1–14.7 GHz) and achieved an average gain of over 5 dBi. Other metrics, such as group delay and the fidelity factor in different setups, are also simulated to observe the expected performance in the required frequency range. Finally, based on simulation, a model is suggested that comprises various configurations of antenna arrays, including one Tx antenna and one to seven Rx antennas. Further, breast phantom with different tumor sizes and locations were used in the simulation. The simulation results successfully validated the detection of breast cancer cells. We believe these technologies can open possibilities in healthcare applications for identifying tumors.

Optically Transparent Frequency Selective Surfaces with Wideband Capability for IoT Applications: A Polarization-Independent Double-Layer Design.

This study proposes wide-band frequency selective surfaces (FSS) with polarization-independent characteristics that are tailored for IoT applications. The design consists of two different layers with band-stop characteristics that target key frequency bands in sub-6 GHz: 3.7 GHz (n77) and 4.5 GHz (n79), offering a 1.39 GHz bandwidth spanning from 3.61 GHz to 5.0 GHz. This study also presents a double-layer structure with a WB property with a fractional bandwidth of 32%. Simulations have been conducted to observe variations in insertion loss across incident and polarization angles ranging from 0 to 60 degrees for both TE and TM modes in the suggested FSS structures. These simulations demonstrate the design's polarization independence. Transparent polyvinyl chloride with a dielectric constant of 2.77 and a thickness of 1.48 mm has been utilized as the substrate material. The optical transmittance is calculated to be 96.7% for Layer 1, 95.7% for Layer 2, and 92.4% for the double-layer structure, and these calculated optical transmittance values were found to be higher compared to the studies in the literature. The proposed design is well-suited for sub-6 GHz IoT applications due to their high transparency, cost-effectiveness, robust high-performance capabilities in suppression, and polarization-independent features. The results of 3D full-wave simulations were compared with measurement and the equivalent circuit model outcomes, and a good agreement between the results was observed.

Flexible Mesopores in Nanoscrolls: Extraordinarily Large Alteration of Pore Sizes and Their Reversibility.

Flexible porous materials have gained considerable interest for their potential applications in selective absorption and controlled release/storage of specific molecules or compounds. Here, nanoscrolls are proposed as a type of inorganic solids with reversibly flexible mesopores. Nanoscrolls exhibit a rolled-up structure composed of nanosheets with a 1D rod-like morphology, possessing two distinct nanospaces. The first space comprises 1D tubular mesopores located at the center of the rod, while the second space exists in the interlayer regions on the wall of the mesopore, resulting from the layer stacking caused by the scrolling of nanosheets. By replacing the interlayer cations on the nanoscroll walls with other cations, a drastic alteration in the size of the 1D mesopores is observed. For instance, exchanging bulky dodecylammonium cations with small NH4 + cations leads to a substantial change in pore size, with differences ranging from 10 to 20nm-a notably larger variation compared to previous reports on flexible porous materials. Importantly, the alteration of pore size induced by the exchange reaction is found to be reversible. This reversible alteration in pore size holds promise for applications in host-guest chemistry involving large moieties such as nanoparticles and enzymes.

A low profile high gain concave conformal ring cylindrical dielectric resonator antenna loaded with split ring resonator for ISM and C band applications

SummaryA low profile, concave conformal ring cylindrical dielectric resonator antenna (CDRA) employing frequency selective surface (FSS) using split ring resonator (SRR) for wideband and high gain applications is presented. The ring CDRA loaded with the monopole is designed to excite the TM01δ mode to increase the antenna's bandwidth. The effect of a curved ground plane (GP) on the radiation performance of CDRA is studied. A 5 × 5 array of the SRR is placed above the conformal GP at a far‐field distance optimized to (2n ± 1) λ/4 from the radiating element to enhance the gain of the proposed structure. The planar CDRA with FSS is compared with the conformal CDRA with FSS and a 4.3 GHz improvement in bandwidth is observed due to the multiple reflection and surface reflection leading to a 3.2 dBi improvement in gain. An impedance bandwidth of 51.8% (5 to 8.5 GHz) with a maximum gain of 8.7 dBi at 7.3 GHz resonant frequency and 99% radiation efficiency at 5.9 GHz is offered by the proposed antenna with FSS. Additionally, the proposed CDRA has a low profile of 0.12 λ0 where λ0 is the lower cut‐off frequency's wavelength. A good agreement is observed between the simulated and measured results.

Metasurface loaded dual band antenna for high gain on- and off- body communication

Metasurfaces are specially made materials designed to have unique properties not found in nature. They are categorized into different types, such as artificial magnetic conductor (AMC), partial reflecting surfaces (PRS), and frequency selective surfaces (FSS). Among these, FSS is commonly used in today’s technology to improve antenna performance, especially in boosting signal strength by blocking unwanted radiation. Recent research is focused on creating FSS-based antennas for Ultra-wideband (UWB) or single band applications, with a significant emphasis on enhancing signal strength. Unlike traditional methods, this study concentrates on designing antennas that are both simple in shape and offers broader frequency coverage, specifically for 2.45 GHz and 5.8 GHz applications. To enhance antenna performance, a dual-band FSS is employed, optimizing the system for improved operation at both resonating frequencies. This results in a high-gain antenna system, which is further investigated for body area network (BAN) systems, considering the crucial performance metric of specific absorption rate (SAR). The findings are compared with recently reported FSS-based antennas to underscore their scientific contribution and potential for high gain, low SAR applications within the 2.45 GHz and 5.8 GHz frequency bands.

Superlong Metal-Organic Framework Micro-/Nanofibers for Selective Vitamin Absorption.

Superlong MOF-74-type micro/nanofibers, which have aspect ratios much higher than 200, are synthesized via nanoparticulate MOF-mediated recrystallization. Co-MOF-74 microfibers have high crystallinity, whereas Co-MOF-74-II nanofibers are composed of nanocrystals and amorphous phases, even though they have nanofibrous morphology. Both MOFs consist of plenty of micropores with diameters in the range of 1.0 to 2.0 nm, and they exhibit high thermal stability with a decomposition temperature higher than 260.0 °C. The MOFs are demonstrated for selective absorption of some vitamins including riboflavin, folic acid, and 5-methyltetrahydrofolate. Co-MOF-74-II nanofibers can efficiently absorb riboflavin and folic acid from their aqueous solution with absorption percentages approaching 90.0%, and they have enhanced capability for absorbing tocopherol in methanol. The micro/nanofibrous morphology, together with the capability for selective vitamin absorption, makes the novel MOFs highly promising for applications in micro-solid-phase extraction.

In Situ Exsolution-Prepared Solid-Solution-Type Sulfides with Intracrystal Polarization for Efficient and Selective Absorption of Low-Frequency Electromagnetic Wave.

The excellent dielectric properties and tunable structural design of metal sulfides have attracted considerable interest in realizing electromagnetic wave (EMW) absorption. However, compared with traditional monometallic and bimetallic sulfides that are extensively studied, the unique physical characteristics of solid-solution-type sulfides in response to EMW have not been revealed yet. Herein, a unique method for preparing high-purity solid-solution-type sulfides is proposed based on solid-phase in situ exsolution of different metal ions from hybrid precursors. Utilizing CoAl-LDH/MIL-88A composite as a precursor, Fe0.8Co0.2S single-phase nanoparticles are uniformly in situ formed on an amorphous substrate (denoted as CoAl), forming CoAl/Fe0.8Co0.2S heterostructure. Combing with density functional theory (DFT) calculations and wave absorption simulations, it is revealed that Fe0.8Co0.2S solid solution has stronger intracrystal polarization and electronic conductivity than traditional monometallic and bimetallic sulfides, which lead to higher dielectric properties in EM field. Therefore, CoAl/Fe0.8Co0.2S heterostructure exhibits significantly enhanced EMW absorption ability in the low-frequency region (2-6GHz) and can achieve frequency screening by selectively absorbing EMW of specific frequency. This work not only provides a unique method for preparing high-purity solid-solution-type sulfides but also fundamentally reveals the physical essence of their excellent EMW absorption performance.

Second order frequency selective surface design multi-functional at two bands

This paper proposes an active frequency selective surface which furnishes three bands of higher order filtering characteristics. It controls multi-functional features, at two bands (centered at 2 GHz and 4 GHz), namely electromagnetic response and polarization of plane wave. Nine discrete filtering outputs are independently controlled through switching in bias supply to four PIN diodes embedded in two layers of AFSS unit cell. Two multifunctional bands hold stability upto 45° angles under all polarizations of wave. Passive band at around 5.9 GHz contributed by all the independent binary combinations exhibits stability upto 45° angles of TE wave only. The equivalent circuit method is used to explain and verify the designed structure. Finally, the AFSS structure is fabricated and reliability of the simulation results is verified through experiments.

Experimental Study of a Prototype Solar Water Heater Used in Sahelian Homes

Environmentally-friendly, low-cost energy supplies are the backbone of sustainable development. Development must not only meet current needs, but must also look to the future and consider environmental issues as a challenge. Solar power as an environmentally-friendly energy source is a promising way of reducing greenhouse gas emissions. One of the most important applications of solar energy is the production of hot water using solar water heaters. These solar water heaters, which can provide between 100 and 200 l/d of hot water over a temperature range of 40-70°C., are of the separate-element and integrated-storage types. In the Saharan environment, hot water requirements are concentrated in winter. It is therefore necessary to develop efficient systems adapted to this reality. It is then necessary to develop effective systems adapted to this reality. There is a need to propose a new design to boost the solar irradiation absorbed by the collector-storage while reducing nighttime thermal losses. For greater user-friendliness and with the aim of adapting them to the Saharan environment, it is also necessary to offer solar water heaters integrated into the building and operating mainly in the winter period. The present work represents an experimental study of a solar water heater with separate elements and a simple design, in a Burkinabe climate. This is a separate element solar water heater with a capacity of 200 liters with an aluminum collector as absorber designed at the Research Institute of Applied Sciences and Technologies (IRSAT). The water in the tank forms a loop with the sensor. In the tank, donut a copper coil of a length equal to 15m with a diameter of 16mm. They use the principle of thermosyphon (cold water pressure) to circulate and store heat and are simpler and less expensive, but can only be installed in sunny countries and have limited efficiency. During the measurement period from 11:25 a.m. to 4:05 p.m., the maximum temperature of the hot water was around 57°C at 11:45 a.m., and that of the cold water was around 27°C at 12:15 p.m.. The experimental results showed acceptable thermal performance despite the simplicity of the sensor. Finally, an improvement can easily be made whether by perfecting the thermal insulation or using selective collection surfaces.

Sign reversal of visible to UV photocurrent in core–shell n-InGaN/p-GaN nanowire photodetectors

We demonstrate the change of the sign from negative to positive of the self-powered photovoltaic photocurrent in core–shell n-InGaN/p-GaN nanowire heterojunctions within the visible to UV wavelength range. Such dual-polarity photodetectors are of broad interest to provide extended functionalities for optoelectronic devices, starting with dual-wavelength photodetectors. The physics of the photocurrent sign reversal is understood by a well-balanced selective absorption and photocarrier generation, photocarrier transfer, and thermal excitation paths in the core–shell n-InGaN/p-GaN nanowire functional absorber with different bandgap energies and opposite inner- and surface energy band bendings. The basic dual-wavelength photodetector operation parameters are given.

Dynamic selective emitter for low infrared signal over wide temperature range based on VO2

The infrared signal intensity of objects contains the thermal radiation from objects themselves and the reflected signal from their surface. Here, we theoretically propose the rule of regulating the infrared signal intensity in mid-wave infrared band, which is influenced by both the reflected solar irradiation and the self-emitted radiation. Then we propose a dynamic selective emitter (DSE) operating in the mid-infrared (MIR) band based on vanadium dioxide (VO2) for lowest infrared signal intensity within the low and high temperature ranges. In the dielectric state of VO2, the selective emitter exhibits the broadband selective absorption attributed to the excitation of magnetic polariton resonance, which can effectively reduce the solar irradiation reflection in 3–4.5 μm band (R‾3–4.5 μm = 0.18) and suppress the thermal radiation in 4.5–5 μm and 8–14 μm band (ε‾4.5–5 μm = 0.28, ε‾8–14 μm = 0.02). In the metallic state of VO2, the resonance absorption disappears and the structure exhibits broadband low emissivity in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) bands (ε‾3–5 μm = 0.28, ε‾8–14 μm = 0.21) for suppression of the thermal radiation. This work highlights the impact of solar irradiation on MWIR camouflage and offers new possibilities for solar and infrared spectral regulation.

Switchable Terahertz Metasurfaces for Spin-Selective Absorption and Anomalous Reflection Based on Vanadium Dioxide.

Conventional chiral metasurfaces are constrained by predetermined functionalities and have limited versatility. To address these constraints, we propose a novel chirality-switchable terahertz (THz) metasurface with integrated heating control circuits tailored for spin-selective anomalous reflection, leveraging the phase-change material vanadium dioxide (VO2). The reversible and abrupt insulator-to-metal phase transition feature of VO2 is exploited to facilitate a chiral meta-atom with spin-selectivity capabilities. By employing the Pancharatnam-Berry phase principle, complete 2π reflection phase coverage is achieved by adjusting the orientation of the chiral structure. At the resonant frequency of 0.137 THz, the designed metasurface achieves selective absorption of a circularly polarized wave corresponding to the state of the VO2 patches. Concurrently, it reflects the circularly polarized wave of the opposite chirality anomalously at an angle of 28.4° while maintaining its handedness. This chirality-switchable THz metasurface exhibits promising potential across various applications, including wireless communication data capacity enlargement, polarization modulation, and chirality detection.

Solar to Thermal Energy Conversion Potential of Carbon Nanotubes Modified Copper Oxide Nanocomposite Thin Film Solar Selective Absorbers

AbstractCarbon nanotubes modified copper oxide nanocomposite (CNTs–CuO NC) selective absorbers were prepared through a sol‐gel method by varying weight percentage of CNTs and coated on aluminum (Al) substrates using a dip coating technique to form thin films (TFs). The surface morphology of CNTs–CuO NC TF examined by scanning electron microscopy disclosed linear arrangement of CNTs–CuO NC TF with average particle diameter of 200±30 nm. The X‐ray diffractometer analysis of the CNTs–CuO NC TF revealed the presence of CuO in monoclinic crystal structure. Moreover, the X‐ray diffractometer analysis disclosed good crystalline quality of the CNTs–CuO NC TF and average crystallite size of the CuO and CNTs–CuO NC TF was found to be 69.38 and 85.94 nm, respectively. The energy dispersive X‐ray spectrum of CNTs–CuO NC TF ascertained the presence of Cu, O and C elements with atomic weight proportion of 71.07, 21.61 and 7.32 %, respectively. The functional groups investigation by FTIR spectroscopy exhibited distinct spectral features of CNTs and the peaks observed at 516.78 and 588.70 cm−1 correspond to the characteristic vibrations of metal‐oxygen (M−O) bond that indicates the presence of CuO in the hybrid CNTs‐CuO NC TF. The optical property of the CNTs–CuO NC TF with CNTs weight proportion of 0.5 % inspected through UV‐Vis‐NIR spectroscopy exhibited high solar absorptance and thermal emittance values of 85.9 and 4.3 %, respectively. The observed highest solar selectivity value of 19.98 suggests that the CNTs–CuO NC TF coating can be apparently used as solar selective absorber.

Mixed-Matrix Organo-Silica-Hydrotalcite Membrane for CO2 Separation Part 2: Permeation and Selectivity Study.

This study introduces an innovative approach to designing membranes capable of separating CO2 from industrial gas streams at higher temperatures. The novel membrane design seeks to leverage a well-researched, high-temperature CO2 adsorbent, hydrotalcite, by transforming it into a membrane. This was achieved by combining it with an amorphous organo-silica-based matrix, extending the polymer-based mixed-matrix membrane concept to inorganic compounds. Following the membrane material preparation and investigation of the individual membrane in Part 1 of this study, we examine its permeation and selectivity here. The pure 200 nm thick hydrotalcite membrane exhibits Knudsen behavior due to large intercrystalline pores. In contrast, the organo-silica membrane demonstrates an ideal selectivity of 13.5 and permeance for CO2 of 1.3 × 10-7 mol m-2 s-1 Pa-1 at 25 °C, and at 150 °C, the selectivity is reduced to 4.3. Combining both components results in a hybrid microstructure, featuring selective surface diffusion in the microporous regions and unselective Knudsen diffusion in the mesoporous regions. Further attempts to bridge both components to form a purely microporous microstructure are outlined.

Tunable liquid crystal double-layer frequency selective surface with wide transmission band and small insertion loss

ABSTRACT In this paper, a tunable Frequency Selective Surface (FSS) based on liquid crystal (LC) with a wide transmission band, large tuning range, high tuning rate, and miniaturization is designed. First, a single-layer FSS is developed with two frequency selective layers and one LC tunable layer. The simulation and experiment results show that the single-layer FSS has a transmission bandwidth greater than 4.25 GHz, and the LC change can make the center frequency of the transmitted band shift to the lower frequency by 576 MHz, with a tuning rate of 4.2%. Subsequently, a double-layer FSS is designed by adding a coupling layer to the single-layer FSS, achieving a flat-top passband and enhancing the tuning rate. Simulation and experimental validation show that altering the LC state enables continuous tuning of the center frequency of the double-layer FSS from 14.95 GHz to 13.86 GHz, with a tuning rate of 7.2%. This structure exhibits a flat-top passband wider than 5.7 GHz, a relative bandwidth of 41%, and a rectangular coefficient below 1.877. Moreover, the double-layer FSS demonstrates favorable polarization stabilization and wide incidence angle stabilisation properties in various states.

The role of cGAS in epithelial dysregulation in inflammatory bowel disease and gastrointestinal malignancies.

The gastrointestinal tract is lined by an epithelial monolayer responsible for selective permeability and absorption, as well as protection against harmful luminal contents. Recognition of foreign or aberrant DNA within these epithelial cells is, in part, regulated by pattern recognition receptors such as cyclic GMP-AMP synthase (cGAS). cGAS binds double-stranded DNA from exogenous and endogenous sources, resulting in the activation of stimulator of interferon genes (STING) and a type 1 interferon response. cGAS is also implicated in non-canonical pathways involving the suppression of DNA repair and the upregulation of autophagy via interactions with PARP1 and Beclin-1, respectively. The importance of cGAS activation in the development and progression of inflammatory bowel disease and gastrointestinal cancers has been and continues to be explored. This review delves into the intricacies of the complex role of cGAS in intestinal epithelial inflammation and gastrointestinal malignancies, as well as recent therapeutic advances targeting cGAS pathways.

Does Nesting Material Affect Wood Duck (Aix sponsa) Nest Box Selection, Reproduction, and Eggshell Bacteria?

Wood Ducks (Aix sponsa) are secondary cavity nesters that use natural cavities and artificial nest boxes, the latter of which has been attributed to the recovery of populations across the southeastern US. Continual use of these boxes results in a buildup of bacteria, parasites, and other pathogens. To avoid the accumulation of these deleterious organisms, best management practices include the occasional removal of old nesting material (i.e., wood shavings) and replacement with fresh wood shavings. No studies have been performed on the effects of shaving material on nest box selection, nest success, and bacterial growth. We monitored 142 and 111 nest boxes in Florida and Georgia, USA, respectively, and filled a random sample with aspen or cedar shavings. We then swabbed the surface of 144 and 150 eggs during 2020 and 2021, respectively, to screen for culturable bacteria. We detected no effect of shaving type on nest box selection, nest success, or egg surface bacterial growth. We found 3-8 bacterial colony types (1-123 colony-forming units [CFU]/box) and 1-8 bacterial colony types (3-382 CFU/box) among the Georgia and Florida samples, respectively. We detected no effect from shaving type on Wood Duck reproduction or bacterial growth in the sampled nest boxes. We concluded that both shaving types are suitable nesting materials for box-nesting Wood Duck populations and the continued use of either would be a reasonable decision for managers.

Reducing out-of-band radar cross-section of metasurface-based radome composites via beam-scattering mechanism

In this work, a metasurface-based radome composite (MRC) with customized electromagnetic (EM) functions is proposed. By employing a beam-scattering mechanism, high transmission at 2–4 GHz and significant radar cross-section (RCS) reduction at 8–18 GHz are achieved. The MRC prototype features a sandwiched construction and is fabricated using quartz fiber-reinforced composite (QFRC) skins, polymethacrylimide (PMI) foam cores, and silver-based frequency selective surface (FSS) screens. The calculation, simulation, and measured results demonstrated that the transmission of the planar specimen is larger than −1 dB at 2–4 GHz and the RCS reduction is less than −10 dB at 8–18 GHz. The measured results also verified that in the HH and VV polarizations, the mono-static RCS of a square pyramid (SP) specimen at specific directions from 8 GHz to 12 GHz is significantly reduced. It is believed that our finding has great application potential in stealth radome technology.