Single Absorber Research Articles

Study on a bifunctional switchable metasurface with perfect absorption and polarization conversion based on VO2 and graphene in THz region

A switchable metamaterial device with dual function (SMDDF) based on vanadium dioxide (VO2) and graphene is designed in this paper, where VO2 is a phase change material and it can transition from the insulating state to the metallic state when it is stimulated by external conditions such as heat, electricity or light. In addition, graphene is a 2D active material and its conductivity can be well controlled by adjusting its bias voltage dependent chemical potential, which makes it have the advantage of easy integration. When VO2 is in the metallic state and the chemical potential of graphene is set as 0.65 eV, the proposed SMDDF can behave as a single band absorber with the peak absorbance higher than 99.9 % at 1.8768 THz. However, when VO2 is in the insulated state, and the chemical potential of the graphene pattern layer (GPL) is set as 0 eV, the proposed SMDDF will behave as a broadband linear polarization converter. It can convert the incident linearly polarized EM waves into the cross-polarized reflected waves within the frequency range of 2.12–3.58 THz, and the polarization conversion ratio (PCR) is >90 % with the relative bandwidth (WRB) up to 51.23 %. Research results prove that the overall performances of the proposed bifunctional metamaterial device is superior to some of those reported in the literatures. Therefore, the research results of this paper may provide guidance for designing switchable multi-function terahertz devices using VO2 and graphene in variable areas of practical applications.

Dual Optimization of Back Electrode Interface and Bulk via the Synergistic Passivation Effect of Niobium Pentoxide Enables Efficient Kesterite Solar Cells

As compared to the predecessor Cu(In,Ga)Se2 device, the current efficiency of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is still much lower mainly due to the known carriers recombination issue within interface and absorber bulk. In contrast to the majority of researches concerning recombination issues that focus on either single absorber bulk or interface passivation strategy, this study is pioneering in constructing synergistic passivation effects (SPE) to address the bulk and interface recombination issue simultaneously. By introducing a novel niobium pentoxide passivation layer into the back electrode interface (BEI), it is identified that SPE can be constructed due to Nb (& O) diffusion from Nb2O5 layer to absorber bulk and BEI during high‐temperature selenization. The chemical passivation effect is fulfilled via the intrinsic high resistance characteristic of Nb2O5 layer, and also through the NbOx passivation aiming to absorber bulk benefited from Nb (& O) diffusion. Meanwhile, the occupations of Nb (& O) on the Mo (& Se) sites induce a conduction type inversion in MoSe2 interfacial layer and create a preferable interface p+‐Mo(Se,O)2:Nb/CZTSSe, achieving an interfacial field passivation effect. Ultimately, the promoted absorber quality and improved charge carrier transportation from SPE contribute to the boost of device performance beyond 10% efficiency.

Microwave absorption and electromagnetic evaluations of the single and bilayer absorbers of sphere like BFO and pompon flower-like CoGd ferrites

In the modern world, electromagnetic interference has emerged as a serious issue. It is difficult yet necessary to prepare materials effectively for excellent electromagnetic wave dissipation capabilities. Here, pompon-flower-like CoGd0.5Fe1.5O4 (CoGd) and spheres resembling BiFeO3 (BFO) were synthesized using the sol-gel technique, and their absorption capabilities were tested in single layer absorbers before being placed under bi-layer conditions to evaluate for the best results. The findings demonstrate that impedance matching may be successfully improved in a bi-layer absorber by using BiFe as the first layer and CoGd as the second layer, leading to high absorption with a broad effective absorption bandwidth. The efficacy of electromagnetic wave dissipation is enhanced by the synergistic interaction of several loss processes, such as multiple wave scattering and dispersion inside the sample, and synergistic interaction between two layers. With a CoGd layer that was 0.5 mm thick and a BiFe layer that was 1.5 mm thick, the double-layer absorber's minimum reflection loss value was -24 dB. The effective absorption bandwidth (EAB) of the double-layer absorber was 3.4 GHz, which was wider than the EAB in single-layer samples despite the identical thickness.

Comparative performance analysis of Cs2TiX6 (X = Br-, Cl-, I-) lead-free perovskite solar cells incorporating single, double and triple layer halides by SCAPS −1D

Halide perovskites have risen in popularity as appealing light absorber materials, owing primarily to their wide range of applications in solar cells, lasers, photodetectors. However, lead-containing perovskites have the potential to cause substantial environmental damage. As a result, there is a significant need to produce environmentally acceptable lead-free perovskites. In this work, we studied the single, double and triple halides perovskite by numerical simulator SCAPS-1D for maximum performance. We have optimized the absorber layer thickness, NA/ND/Nt and interface defect density, back contact electrodes, and temperature effects in a single absorber layer structure. Further, we have optimized the double and triple-layer absorbers for perovskite solar cell structures. The maximum efficiency achieved in the double halide perovskite solar cell is VOC = 1.54 V, JSC = 24.04 mA/cm2, FF = 82.72%, and PCE = 30.06%. Such performance is due to the absorption coefficient spectrum with a wide range of energy band gaps. This has proved its suitability for photovoltaic devices. Overall, our findings reveal that Cs2TiX6 (X = Br, Cl, I) Pb-free perovskites have promising and potential features for device performance.

Evaluation of anti-nucleocapsid level variation to assess SARS-CoV-2 seroprevalence in a vaccinated population

Background Serosurveys have been key to public health decision-making since the beginning of the SARS-CoV-2 pandemic. However, several studies have uncovered that vaccination blunts the anti-nucleocapsid (N) response to a subsequent infection, which hinders the ability of serologic assays (including commercial ones) to detect recent infections. We therefore developed a new analytical approach to increase the sensitivity of detection of infection in vaccinated individuals. Methods Two samples were obtained from 248 SARS-CoV-2-positive (PCR-confirmed), vaccinated donors: one before the infection (reference sample) and one after (test sample). All samples were tested using an in-house, anti-N enzyme-linked immunosorbent assay (ELISA) which had a sensitivity of 98.1% before the mass vaccination campaign. Instead of applying a seropositivity threshold based on a single absorbance value (i.e. conventional approach), seropositivity was determined based on the ratio between the anti-N absorbance of the test and reference samples. Results The sensitivity of the new approach to detect infection in vaccinated individuals was 95.2% using a cut-off of 1.5 for the anti-N ratio, whereas that of the conventional approach was 63.3%. Conclusion The new analytical approach described herein captured a significantly greater proportion of vaccinated individuals with a known history of SARS-CoV-2 infection than the conventional approach used in most serosurveys.

Nonlinear Absorption and Refraction Properties of V4C3 MXene and its Use for an Ultra‐Broadband Saturable Absorber

AbstractLarge optical nonlinearity at short‐wavelength‐infrared (SWIR) has enabled 2D MXene to be used explosively in ultrafast nonlinear photonics and optoelectronics. Despite the high technological interest in V4C3 MXene in electrochemistry, investigations from a nonlinear photonics perspective have yet to be conducted. Here, the nonlinear optical characteristics of V4C3 MXene at SWIR wavelengths are systemically investigated. First, Z‐scan measurements are performed and the saturated absorption and self‐defocusing properties of V4C3 MXene at both wavelengths of 1560 and 1910 nm are observed. Density functional theory calculation shows metallic characteristics of V4C3 MXene. Based on the saturable absorption properties of V4C3 MXene, a single saturable absorber (SA) operating at both wavelengths of 1560 and 1910 nm is experimentally implemented. Stable mode‐locked pulses of 638 fs pulse duration at 1559.9 nm are produced instantaneously from an erbium‐doped fiber ring cavity using SA. The same SA generates 1.08 ps mode‐locked pulses at 1911.9 nm from the thulium holmium co‐doped fiber ring cavity. This indicates that the operating bandwidth of this realized V4C3 MXene‐based SA could be at least 350 nm. This work strongly suggests that V4C3 MXene can serve as an ultra‐broadband and high‐performance nonlinear optical material platform in the SWIR regions.

Study on electromagnetic wave absorbing properties of nanocrystalline Fe81.5Si3B9P3C1Cu1Ti1.5/Graphene oxide composite

To prevent and control electromagnetic pollution problems, there is an urgent need to develop better wave-absorbing materials. In this study, nanocrystalline alloy/graphene oxide(GO) composite modified powder was obtained on the basis of Fe81.5Si3B9P3C1Cu1Ti1.5 nanocrystalline alloy powder with different weight percentages of GO, which was mechanically mixed by high-energy ball milling treatment, and the microstructure and morphology of the materials and the electromagnetic wave absorption properties were characterized. The results show that the Fe81.5Si3B9P3C1Cu1Ti1.5/GO composite powder has excellent wave absorption performance, and the loss mechanism is magnetic loss including eddy current loss and natural resonance. Defects and groups in GO not only improve the impedance matching characteristics, but also introduce defect polarization relaxation and electron dipole polarization relaxation of the groups, which are beneficial to the penetration and absorption of electromagnetic waves. The minimum reflection loss (RLmin) of the nanocrystalline alloy powder can reach −37.55 dB and the maximum effective absorption bandwidth (ΔfRL<-10dB) can reach 5.95 GHz; the RLmin of the composite powder is as high as −52.55 dB when the GO content is 1.5 wt%, and the widest bandwidth can reach 6.12 GHz at 2.00 mm when the GO content is 0.5 wt%. With the addition of GO, its RLmin increased by 40%. This indicates that the composite material have superior absorption performance compared to a single absorber.

Triple band single layer microwave absorber based on closed loop resonator structures with high stability under oblique incidence

A novel triple-band microwave absorber design which is independent of polarization with extremely high stability under oblique incidence is described in this paper. The proposed absorber structure's unit cell architecture contains three closed loop microstrip resonator components with rotational symmetry. The suggested design engenders three reflection nulls at 2.4 GHz (WiMAX), 5.5 GHz (WLAN) and 7.51 GHz (downlink satellite communication frequencies in the X-band). These gives rise to triple absorption peaks with near-unity (almost 100 %) absorptivity at the mentioned frequencies. The absorber design is fully immune to polarization for both TE and TM modes of propagation. Furthermore, the structure offers very high stability under oblique incidence for both TE and TM modes where beyond 90 % absorptivity is obtained up to 520 incident angles and beyond 80 % absorptivity is achieved up to 750 incident angles. The unit cell size is 0.12λ0 × 0.12λ0, where λ0 is the wavelength corresponding to the lowest absorption frequency. The advantage of the proposed structure over other reported absorbers is assessed by its superiority in terms of multiband functionality, full polarization insensitivity, stability under oblique incidence and compactness. A prototype of the proposed absorber was fabricated and the measured results agree closely with the simulation results.

Simulation study of CsPbIxBr1-x and MAPbI3 heterojunction solar cell using SCAPS-1D

The perovskite solar cells are attaining maximum efficiency but lagging in stability as compared with other solar cells. The consistent use of hybrid organic–inorganic materials in PSC poses greatest hurdle in the path of stability. To overcome this problem the attention of research community, is diverted from methyl ammonium based perovskite solar cells to cesium (Cs) based perovskite solar cell. To enhance the efficiency of PSCs further, effective absorption of solar-spectrum by the multi-layer will allow the maximum utilization of spectrum and in turn it will increase the efficiency of the resulting Perovskite Solar Cell (PSC). Here, we have analyzed the efficiencies of single, double and triple absorber layers PSCs. Initially we have simulated and studied the performance of two CsPbI2Br and CsPbIBr2 based single-junction perovskite solar cell. Then we have simulated a PSC with CsPbI2Br and CsPbIBr2 as the two absorber layers and have optimized the performance of bilayer solar cell. Finally, we simulated a triple layer PSC have used the combination of CsPbI2Br, CsPbIBr2 and MAPbI3 as absorber layers. The bilayer and triple layer PSCs are optimized with respect to different variables i.e., absorber layer thickness, defect density and interface defect density in all three PSCs. In this study we achieved a remarkable efficiency of 29.92%, 20.62% and 7% efficiency in case of triple layer solar cell, in case of bilayer solar cell and in case of single-junction PSC respectively. Thus, well aligned multiple absorber layers in PSC will provide the future pathways for highly efficient PSCs.

Ultra‐Broadband, Tunable, and Transparent Microwave Meta‐Absorber Using ITO and Water Substrate

AbstractIntegrating broadband absorption, dynamic tunability, and high optical transparency into a single microwave absorber remains a crucial challenge. Here, an ultra‐broadband, tunable, and transparent microwave meta‐absorber comprising double‐layer indium tin oxide resonant patterns and a water‐based substrate is theoretically presented and experimentally demonstrated. Experimental measurements indicate that the designed meta‐absorber can achieve over 90% absorption in an ultra‐broadband frequency range of 12.49–98.21 GHz with a relative bandwidth of 154.9%, while the average optical transmittance is 60.49%. In addition, a multiple reflections interference model is employed to elucidate the physical mechanisms of the ultra‐broadband absorber. Furthermore, its absorption performance can be reversibly switched between ultra‐broadband and dual‐broadband by altering the water substrate thickness. These peculiar properties make the proposed meta‐absorber more favorable for practical applications in modern stealth materials and optical windows.

Intelligent modeling of hydrogen sulfide solubility in various types of single and multicomponent solvents

This study aims to study the solubility of acid gas, i.e., hydrogen sulfide (H2S) in different solvents. Three intelligent approaches, including Multilayer Perceptron (MLP), Gaussian Process Regression (GPR) and Radial Basis Function (RBF) were used to construct reliable models based on an extensive databank comprising 5148 measured samples from 54 published sources. The analyzed data cover 95 single and multicomponent solvents such as amines, ionic liquids, electrolytes, organics, etc., in broad pressure and temperature ranges. The proposed models require just three simple input variables, i.e., pressure, temperature and the equivalent molecular weight of solvent to determine the solubility. A competitive examination of the novel models implied that the GPR-based one gives the most appropriate estimations with excellent AARE, R2 and RRMSE values of 4.73%, 99.75% and 4.83%, respectively for the tested data. The mentioned intelligent model also performed well in describing the physical behaviors of H2S solubility at various operating conditions. Furthermore, analyzing the William's plot for the GPR-based model affirmed the high reliability of the analyzed databank, as the outlying data points comprise just 2.04% of entire data. In contrast to the literature models, the newly presented approaches proved to be applicable for different types of single and multicomponent H2S absorbers with AAREs less than 7%. Eventually, a sensitivity analysis based on the GPR model reflected the fact that the solvent equivalent molecular weight is the most influential factor in controlling H2S solubility.

Performance augmentation of a solar thermal desalination system using different floating absorber plates

Interfacial evaporation is known to boost the evaporation rate compared to conventional bulk evaporation, as energy conversion and vapor generation simultaneously occur at the air–liquid interface. This work presents the investigation details on the design, fabrication, and testing to determine the performance of a floating absorber structure with the sole interest of maximizing the evaporation rate. Polyvinyl alcohol cloth is the wicking cum absorber material, while extruded polystyrene sheet is the floating structure cum thermal insulator. Phase I of the study involves the comparative study between bulk and interfacial heating and the effect of different types of patterns with the same area on interfacial heating with a single absorber. Phase II involves the effect of multiple absorbers on interfacial evaporation. To identify a better design, different absorber configurations (single, patterned, multiple, and multiple blocks with full coating and patterns) were compared to bulk heating. The study highlighted the improvement in evaporation rate achieved using floating absorbers by 43% and 56% for single and multiple absorbers under one sun illumination compared to bulk heating. Also, a multiple absorber design yields a 10% higher evaporation rate than a single absorber. An extended analysis with and without black coating on multiple absorbers design indicates an improvement of 17% evaporation efficiency compared to bare multiple absorbers. In selecting a suitable pattern embedded on the single absorber, the stripe-type pattern resulted in a 21% improvement in evaporation rate than the bare absorber among the four patterns tested. The multiple absorbers with stripe patterns obtained an evaporation rate of 1.17 kg m−2 h−1 under one sun (1 kWm−2) irradiation. Further, the multiple absorbers with stripe-type patterns obtained an evaporation rate of 1.69 kg m−2 h−1 under 1.5 sun irradiation (1.5 kWm−2).

A Compact Tunable Broadband Acoustic Metastructure with Continuous Gradient Spiral Channels

Sound‐absorbing structures, an effective measure to reduce vibration and noise, have always been the desirable research hotspot in scientific and engineering communities. However, the mutual restriction between ultrathin thickness and broadband sound absorption is the key issue that hinders its development. Herein, a compact tunable broadband acoustic metastructure with continuous gradient spiral channels is presented, which has the ultrathin thickness and can efficiently realize low‐frequency broadband sound absorption. Coiled‐up individual absorbers are introduced to constitute the acoustic metastructure. The continuous gradient spiral channels are formed by successively decreasing the effective spiral length of labyrinthine cavity to achieve efficient broadband sound absorption. It is showed in the results that the sound‐absorption metastructure coupled with eight individual absorbers maintains the excellent broadband sound‐absorption effect over 0.8 in the frequency range of 487–930 Hz and a deep subwavelength thickness of 37 mm. In addition, the highly efficient low‐frequency broadband sound absorption can be implemented in the target range of 480–990 Hz through optimizing the adjustable parameters such as the effective spiral length, cross‐section height, orifice radius, and the coupling number of single absorbers. Herein, inspirations and threads are provided for the compact tunable broadband sound‐absorption design of acoustic metastructures.

Polarization-Insensitive, Broadband, and Tunable Terahertz Absorber Using Slotted-Square Graphene Meta-Rings

Graphene-based metamaterials are gaining popularity for developing various reconfigurable and electrically tunable optical devices – especially in terahertz (THz) and infrared (IR) bands. Therefore, in this paper, we aim to investigate the broadband metamaterial-based absorber that efficiently absorbs the THz radiation ranging from 2.2 to 4.6 THz. The proposed absorber comprises a simple meta-square ring of graphene, which possesses different slots in its structure to induce multiple plasmonic resonances. It is observed that the proposed absorber manifests above 95% absorption for the normally incident THz waves, and it also maintains its absorption value over 80% for different obliquely incident operating conditions. Furthermore, the proposed absorber shows polarization-insensitive features. In addition, the absorption characteristics regulate from 95% to 15% by adjusting the chemical potential of graphene from 1 eV to 0.1 eV. Some of the salient features of the proposed absorber is largest reported bandwidth for single layer absorber with smallest footprint without sacrificing polarization insensitivity or amplitude tunability. From the application point of view, it could provide the pathway for implementing switching, cloaking, smart absorbers, and detection phenomena in the THz range.

Implied Open‐circuit Voltage Imaging via a Single Bandpass Filter Method—Its First Application in Perovskite Solar Cells

AbstractA novel, camera‐based method for direct implied open‐circuit voltage (iVOC) imaging via the use of a single bandpass filter (s‐BPF) is developed for large‐area photovoltaic solar cells and precursors. The photoluminescence (PL) emission is imaged using a narrow BPF with centre energy inside the high‐energy tail of the PL emission, utilising the close‐to‐unity and nearly constant absorptivity of typical photovoltaic devices in this energy range. As a result, the exact value of the sample's absorptivity within the BPF transmission band is not required. The use of an s‐BPF enables a fully contactless approach to calibrate the absolute PL photon flux for spectrally integrated detectors, including cameras. The method eliminates the need for knowledge of the imaging system spectral response. Through an appropriate choice of the BPF centre energy, a range of absorber compositions or a single absorber with different surface morphologies, such as planar and textured, can be imaged, all without the need for additional detection optics. The feasibility of this s‐BPF method is first validated. The relative error in iVOC is determined to be ≤1.5%. The method is then demonstrated on device stacks with two different perovskite compositions commonly used in single‐junction and monolithic tandem solar cells.

Solar Panel Technologies for Light-to-Chemical Conversion.

ConspectusThe sustainable synthesis of fuels and chemicals is key to attaining a carbon-neutral economy. This can be achieved by mimicking the light-harvesting and catalytic processes occurring in plants. Solar fuel production is commonly performed via established approaches, including photovoltaic-electrochemical (PV-EC), photoelectrochemical (PEC), and photocatalytic (PC) systems. A recent shift saw these systems evolve into integrated, compact panels, which suit practical applications through their simplicity, scalability, and ease of operation. This advance has resulted in a suite of apparently similar technologies, including the so-called artificial leaves and PC sheets. In this Account, we compare these different thin film technologies based on their micro- and nanostructure (i.e., layered vs particulate), operation principle (products occurring on the same or different sides of the panel), and product/reaction scope (overall water splitting and CO2 reduction, or organics, biomass, and waste conversion).For this purpose, we give an overview of developments established over the past few years in our laboratory. Two light absorbers are generally required to overcome the thermodynamic challenges of coupling water oxidation to proton or CO2 reduction with good efficiency. Hence, tandem artificial leaves combine a lead halide perovskite photocathode with a BiVO4 photoanode to generate syngas (a mixture of H2 and CO), whereas PC sheets involve metal-ion-doped SrTiO3 and BiVO4 particles for selective formate synthesis from CO2 and water. On the other hand, only a single light absorber is needed for coupling H2 evolution to organics oxidation in the thermodynamically less demanding photoreforming process. This can be performed by immobilized carbon nitride (CNx) in the case of PC sheets or by a single perovskite light absorber in the case of PEC reforming leaves. Such systems can be integrated with a range of inorganic, molecular, and biological catalysts, including metal alloys, molecular cobalt complexes, enzymes, and bacteria, with low overpotentials and high catalytic activities toward selective product formation.This wide reaction scope introduces new challenges toward quantifying and comparing the performance of different systems. To this end, we propose new metrics to evaluate the performance of solar fuel panels based on the areal product rates and commercial product value. We further explore the key opportunities and challenges facing the commercialization of thin film technologies for solar fuels research, including performance losses over larger areas and catalyst/device recyclability. Finally, we identify emerging applications beyond fuels, where such light-driven panels can make a difference, including the waste management, chemical synthesis, and pharmaceutical industries. In the long term, these aspects may facilitate a transition toward a light-driven circular economy.

Metal organic framework-derived hierarchical 0D/1D CoPC/CNTs architecture interlaminated in 2D MXene layers for superior absorption of electromagnetic waves

Nowadays, exploring effective electromagnetic wave (EMW) absorbing materials with ultrathin thickness, lightweight, broad absorption bandwidth, and robust absorption capability is crucial to solve EMW pollution issues. Ti3C2Tx is a potential candidate for effective EMW absorbing materials by virtue of its low density, excellent electrical conductivity, high specific surface area, and tunable terminal groups. However, the intrinsic attenuation mechanisms of single dielectric absorbers are limited for practical requirements. Herein, 0D/1D/2D architecture of CoPC/CNTs@MXene hybrids with 0D cobalt nanoparticles supported on porous carbon, 1D carbon nanotubes and 2D Ti3C2Tx nanosheets have been conceptualized and fabricated successfully. By pyrolyzing bimetallic ZnCo-MOF at 800 °C, a 0D/1D hierarchical CoPC/CNTs sample was initially produced, subsequently interlaminated between the Ti3C2Tx matrix via electrostatic self-assembly to fabricate CoPC/CNTs@MXene (CCM) absorbers. The impedance matching properties was optimized by modifying the CoPC/CNTs content. Remarkably, CCM-20 hybrids achieved strong EMW absorption capability (reflection loss of −54.2 dB) at 5.56 GHz, and CCM-30 hybrids achieved ultrathin (1.8 mm) and a broad effective bandwidth (EAB) below − 10 dB (5.6 GHz), which is superior to the magnetic-dielectric hybrids with comparable components reported previously. The exceptional absorption capability can be attributed to the synergistic effects of interface polarizations and magnetic loss. The intricate construction of the 0D/1D/2D architecture facilitates the multiple reflections and scattering of EMW. This work provides an idea for fabricating MXene-based composites with remarkable electromagnetic properties and a broad absorption bandwidth for potential applications.

О применении высокопористых алюминиевых сплавов и сотовых конструкций в посадочных устройствах космических аппаратов

The paper presents results of studying mechanical properties and shock-absorbing characteristics of the highly porous aluminum alloys and aluminum alloy cellular structures with the initial average density from 190 to 2250 kg/m3. The study is based on data from foreign publications and experimental results obtained by the authors. Diagrams of deformation are provided illustrating characteristic stages of the deformation process and compaction of the highly porous alloys and cellular structures made of the aluminum alloys. Highly porous alloys are identified, which deformation is close to the idealized. Based on the analysis of experimental data, presence of two groups of materials is shown: the first with deformation diagram without hardening at the compaction stage and the second with hardening. Basics for calculating specific and effective impact absorption energy are provided. Analogue shock absorbers are shown for characteristic stages of the deformation diagrams. Introduction of the effective impact absorption energy is proposed as a criterion to compare the shock absorbers with each other. The results obtained could be used in the development of the single shock absorbers.

Shape optimization for the strong routing of light in periodic diffraction gratings

In the quest for the development of faster and more reliable technologies, the ability to control the propagation, confinement, and emission of light has become crucial. The design of guide mode resonators and perfect absorbers has proven to be of fundamental importance. In this project, we consider the shape optimization of a periodic dielectric slab aiming at efficient directional routing of light to reproduce similar features of a guide mode resonator. For this, the design objective is to maximize the routing efficiency of an incoming wave. That is, the goal is to promote wave propagation along the periodic slab. A Helmholtz problem with a piecewise constant and periodic refractive index medium models the wave propagation, and an accurate Robin-to-Robin map models an exterior domain. We propose an optimal design strategy that consists of representing the dielectric interface by a finite Fourier formula and using its coefficients as the design variables. Moreover, we use a high order finite element (FE) discretization combined with a bilinear Transfinite Interpolation formula. This setting admits explicit differentiation with respect to the design variables, from where an exact discrete adjoint method computes the sensitivities. We show in detail how the sensitivities are obtained in the quasi-periodic discrete setting. The design strategy employs gradient-based numerical optimization, which consists of a BFGS quasi-Newton method with backtracking line search. As a test case example, we present results for the optimization of a so-called single port perfect absorber. We test our strategy for a variety of incoming wave angles and different polarizations. In all cases, we efficiently reach designs featuring high routing efficiencies that satisfy the required criteria.

SiO2-modified Y2Co8Fe9 multifunctional alloys with efficient microwave absorption, oxidation resistance and corrosion resistance

The application of a single metallic magnetic absorbing materials in harsh environments such as high temperature and corrosion reduces its absorption capacity significantly. Therefore, it is urgent to develop multifunctional composite materials with good absorption properties, oxidation resistance and corrosion resistance. In this work, SiO2-modified Y2Co8Fe9 (YCF) alloys with tunable tetraethyl orthosilicate content are prepared by the Stӧber method. The SiO2 coating efficiently enhances the microwave absorption properties due to the improved impedance matching characteristics. The SiO2 coating also provides effective physicochemical protection to prevent the alloys from oxidation and corrosion. Importantly, the YCF@SiO2-6 composite possesses enhanced microwave absorption properties with a minimum reflection loss (RLmin) of − 58.5 dB at 12.46 GHz with a thickness of 1.5 mm. The starting oxidation temperature of the YCF@SiO2-6 composite was 280 ℃ and 50 ℃ higher than that of the YCF and YCF@SiO2-2 samples, respectively. In addition, the corrosion resistance of the YCF@SiO2-6 composite in 3.5 wt% NaCl solution and hot and humid environment was tested by two different methods. The results indicate that the SiO2-modified sample shows good corrosion resistance. Therefore, this research provides a simple and practical method for the preparation of multifunctional composites in the field of electromagnetic wave absorption.