Multilayer Absorber Research Articles

A multilayer solar absorber coating based on NbMoTaW refractory high entropy alloy: optical properties, thermal stability, and failure mechanism

The newly increasing development of abruptly high entropy alloy nitride (HEAN), especially the refractory HEAN, manifests excellent mechanical, corrosion resistance, and optical properties, which exhibits a wide application prospect in the field of coatings. Herein, we develop a high entropy nitride NbMoTaWN-based solar selective absorber coatings (SSACs), providing a potential to strengthen structural and optical advance through component selection and structure design. The coating exhibits a high solar absorptance (α) of 0.936 and a low thermal emittance (ε) of 0.126 at 82 °C. Investigation on structural and optical robustness demonstrates that the NbMoTaW HEAN-based SSAC could endure heat treatment at 500 °C for 10 h in vacuum environment. In addition, through the evolution of XRD and Raman spectra after annealing, the failure mechanism of coatings annealed in vacuum at 500 °C for 10 h and 400 °C in air for 5 h are obtained. Obviously, the advantages such as low-cost preparation, easily scalable production, convenient technology process, and repeatability in this work promise potentially valuable applications for photothermal conversion techniques.

Microwave absorption properties of multilayer impedance gradient absorber consisting of Ti3C2TX MXene/polymer films

Ti3C2TX MXene has been proven to be a material of high application potential in the field of electromagnetic (EM) protection. Considering the density, MXene/polymer films (MPFs) are fabricated by employing the simple tape casting process and exhibit excellent electromagnetic shielding performance with respect to the MXene content. However, the absorption properties of as-fabricated MPFs are not satisfactory due to the impedance mismatch. Herein, a multilayer impedance gradient absorber with MPFs arranged in order has been successfully designed and prepared. The developed absorber possesses excellent EM wave absorption properties owing to the well-matched impedance and adjustment of permittivity. Moreover, the effect of the thickness of MPFs on the EM wave absorbing properties has been investigated by theoretical calculations and experimental measurements. The HFSS calculation reveals that the effective absorption bandwidth is capable to cover the whole X-band (8.2–12.4 GHz) with only a micro-adjustment of the thickness, with the minimum reflection coefficient (RCmin) reaching up to −26.10 dB. In addition, the synergistic effect of the multiple loss mechanisms has been discussed in detail. This study not only proposes the effective design of a novel multilayer impedance gradient absorber, but also provides new fundamental basis for combining the simulation technology and material design.

Model and Optimization of Low-Frequency Sound Absorption Performance of Multilayer Microperforated Panel Absorber

Optimization of the low-frequency sound absorption performance of the multilayer microperforated panel (MPP) absorber is favourable to promote its practical application in the noise reduction. Theoretical model of the multilayer MPP absorber was constructed based on the Maa’s theory for the further optimization. For target frequency range of 100-500Hz, parameters of the multilayer MPP absorbers with layer number of 1 to 4 were optimized through the cuckoo search algorithm according to the certain optimization objectives and the constraint conditions. Judging from the achieved optimal structural parameters for the multilayer MPP absorber with the target frequency ranges and the corresponding average sound absorption coefficients, it could be concluded that the parameter optimization was not only effective, but also be quite necessary. Meanwhile, it could be seen that average sound absorption coefficients of the optimal multilayer MPP absorbers decreased gradually along with increase of the layer number from 1 to 4. Through the optimization of structural parameters of the multilayer MPP absorbers, not only the sound absorption performance could be improved, but also the fabrication cost could be reduced. The research results exhibited outstanding low-frequency absorption performance, and it would be favourable to promote their practical applications to reduce the industrial noise in urban area.

A multilayer graphene-based absorber for the sub-THz regime

This work presents a four-layer absorber based on graphene patterns. Periodic arrays of biased graphene nanodisks and ribbons are exploited, while a graphene sheet top layer enhances the overall absorption. The presented structure is modeled using the circuit model method and simulated to verify its validity and accuracy. A sufficient number of simulations are performed to investigate the robustness of the proposed structure versus the variation of physical parameters such as the thicknesses of the layers, the chemical potentials, and the electron relaxation time. Wideband absorption in the frequency range of 8–9.5 THz is obtained for the proposed device, which can thus be considered for use in several optical applications including optical sensing and detection.

A novel multilayer high temperature solar absorber coating based on high-entropy alloy NbMoTaW: Optical properties, thermal stability and corrosion properties

With the development of new materials and technology, high entropy alloy (HEA) nitride films have attracted much attention of researchers due to their excellent optical properties and mechanical properties. Herein, a novel SS/NbMoTaWN (HEAN)/NbMoTaWON (HEAON)/SiO2 coatings are prepared, which shows a high spectral selectivity of α/ε = 0.944/0.12. The preparation and optimization of the coating are studied by combining experiments with ellipsometric program and CODE software. High temperature thermal stability test is performed in depth, which proves that the coating could bear 400 °C in air for 2 h, and 600 °C for 2 h in vacuum. Long-term thermal stability researches indicate that the SSACs still keep good optical properties (α = 0.902, ε = 0.106) even after annealing at 600 °C for 100 h. The failure mechanism is analyzed by XRD and Raman spectra. In addition, neutral salt spray test is performed to investigate the anti-corrosion ability, which indicates the coating has a good optical performance after soaking in 3.5 wt% NaCl solution for 30 days. Obviously, this work provides a new strategy to construct solar absorber coatings based on NbMoTaW high entropy alloy.

Multilayer Huygens’ metasurface absorber toward snapshot multispectral imaging

Multispectral or hyperspectral imaging requires the collection of a three-dimensional (3D) data cube that is composed of 2D spatial information and 1D spectral information of the scene. However, conventional cameras can only record 2D information, such that to obtain the 3D data cube, one needs to sacrifice either spatial or spectral resolution, or spatial or spectral scanning is required. Here, we introduce a multilayer metasurface absorber platform that may potentially allow the collection of a multispectral data cube in a single shot, without sacrificing the resolution. We design each absorber layer composed of silicon nano-resonators to support a Huygens’ mode in the visible spectrum, such that each layer may detect an impinging scene only within a narrow spectral band. We envision that the multilayer metasurface absorber, if integrated with proper electronics, may be used for snapshot multispectral imaging, with potential applications in target identification with high spatial and spectral resolution.

Improving the Sound Absorption of Natural Waste Material-based Sound Absorbers Using Micro-perforated Plates

ABSTRACT Both natural and synthetic fibers do not perform well at low frequencies and are also subjected to erosion, moisture, fire, etc., when used as an interior finish of room walls. To overcome these problems, micro-perforated plate with different thickness is used in a multilayer sound absorber configuration to improve its sound absorption. Firstly, the acoustic properties of five natural wastes including sheep wool, goat wool, camel wool as well as pith and fiber bundles of sugarcane bagasse were determined by using an impedance tube following ISO 10534–2. Secondly, the effect of Panel thickness was investigated. The maximum sound absorption coefficient (SAC) of natural waste materials is at middle to high-frequency range and this shifted to lower frequency as the porous layer thickness increases. The sound absorption performance depends on the thickness of perforated plate and porous layer in a compound sound absorber. It is observed that the using perforated plate in the front of low thickness porous materials significantly improve the SAC and absorption bandwidth. However, it should be noted that this reduces the SAC at high frequencies. Accordingly, the thick micro-perforated panels backed by porous layer are not recommended to control sounds with frequency higher than 3000 Hz.

Investigation on Terminal Correction in Theoretical Model of the Microperforated Panel Absorber

Microperforated panel (MPP) absorber is promising sound absorbing structure for the noise reduction. It is extremely especially to construct accurate theoretical sound absorbing model of the MPP structure for design and development of an excellent sound absorber. Thus, modification and validation of the terminal correction in theoretical sound absorption model of the MPP absorber is investigated in this research, which aimed to improve its accuracy and reasonability. Firstly, based on the Maa’s theory, classic sound absorption model of the MPP absorber was presented and treated as basic reference of the whole research. Secondly, through a set of verification experiments, necessity and importance of the research on reasonability of terminal correction was revealed. For the superposition of several monolayer MPP absorbers, when its sound absorption coefficient was derived as the multilayer MPP absorber through the transfer matrix method, the terminal corrections for the former n-1 monolayer MPPs should be removed, because length of these MPPs was 0. Thus, it was essential to take length of the rear cavity into account for the terminal corrections in the theoretical sound absorption model of the MPP absorber.

Scalable and Ultrathin High‐Temperature Solar Selective Absorbing Coatings Based on the High‐Entropy Nanoceramic AlCrWTaNbTiN with High Photothermal Conversion Efficiency

High‐entropy ceramics, especially high‐entropy alloy nitrides (HEANs), have attracted increasing attention in recent years due to their unique structural characteristics that result in their potential use in correlated high‐temperature structural materials. However, research on their optical properties, especially the spectral selectivity, is still in its infancy. According to Carnot efficiency, which demands an extremely high working temperature to elevate the performance of a concentrating solar power (CSP) system, excellent thermal stability is valuable to meet the requirements of solar selective absorbing coatings (SSACs). Herein, the high‐entropy ceramic AlCrWTaNbTiN is introduced as effective absorption layers by adjusting the nitrogen content to design and fabricate an ultrathin multilayer solar absorbing coating, which exhibits a high solar absorptance of 93% and a low emittance of 6.8% at 82 °C. Coating design (CODE) software is used to design and optimize the multilayer solar absorbing coating. Moreover, the optical properties, microstructure, thermal stability, and failure mechanism are investigated. Finite‐difference time‐domain (FDTD) calculations are used to understand the nature of the optical absorption consisting of intrinsic absorption and extinction absorption.

Experimental Determination of Water, Water/Ethylene Glycol and TiO2-SiO2 Nanofluids mixture with Water/Ethylene Glycol to Three Square Multilayer Absorber Collector on Solar Water Heating System: A Comparative Investigation

This paper investigates three square multilayer absorber solar collector in Solar Water Heating System (SWHS) experimentally. The main aim was to study the output temperature of the solar absorber collector based on distilled water (DW), water/ethylene glycol (W/EG) and TiO2-SiO2 nanofluids. An experimental apparatus for testing absorber solar collector was designed and built at Universiti Malaysia Kelantan (Jeli Campus). By using the two-step method, TiO2-SiO2 nanofluids with ratio 30:70 and volume concentration at 1.0%. For W/EG the ratio is 60:40. The effect working fluid was studied experimentally on the output temperature of three square multilayer absorber solar collector in SWHS with Angle of Sunlight (AoS) at 45°, volume flow rate at 3 litres per minute (LPM) and varies Intensity of Light (IoL) at 300, 500 and 700 W/m2. The output temperature is determined through the experimental results by using this apparatus. The result reveals that the output temperature of the solar absorber collector is TiO2- SiO2 nanofluids with 1.0% of volume concentration as a best working fluid at each intensity of light.

A terahertz dual-band metamaterial perfect absorber based on metal-dielectric-metal multi-layer columns

In this paper, a new model of multi-layer metamaterial perfect absorber (MPA) in the terahertz region has been introduced. This model is similar to the classic absorber model, ie the three traditional layers of metal-dielectric-metal. The difference is that the middle layer has changed in height and consists of 3 separate layers with the same material. Therefore, the middle layer of the proposed structure is metamaterial. Numerical results of the simulation show that the absorption rate of the perfect absorber at 6.86 THz is 99.99%. Also, by changing the width of the two middle layer columns w, a dual-band perfect absorber with an average absorption rate of 97.18% is obtained at frequencies of 4.24 THz and 6.86 THz. A significant advantage of this paper over other works is that this absorber is adjustable, in addition to obtaining a nearly perfect dual-band absorber with a narrow-band peak by adjusting the parameters and also a nearly broad-band absorber can also be obtained by changing the parameters without re-manufacturing the structure. We believe that the proposed absorber has potential in filtering, detection and imaging.

Multilayer electromagnetic wave absorber by a dielectric material in direct to home system

The satellite is the one which plays a vital role in the medium of satellite dishes for television, communication, internet and most important role in military application. The solution for this problem occur in the satellite dish used for television is discussed here. Whenever the development is done by taking the technology as medium and smart innovative work are done, at last it has some disadvantage which finally occurs as a problem that is changes in meteorological conditions leads to disconnection of the signal. Although a renowned parabolic reflector is there, it gets shattered before reaching the receiver due to the cold rain weather condition. The method and material proposed here will be able to overcome the problem occurred.

Fe2O3-decoration and multilayer structure design of Ti3C2 MXene materials toward strong and broadband absorption of electromagnetic waves in the X-band region

Although strong and effective absorption of electromagnetic waves in the X-band region is of utmost importance for practical applications, it still faces many challenges. In this work, we prepared Fe2O3-decorated Ti3C2 composites via a facile one-step solvothermal route. Scanning electron microscopy micrographs showed that Fe2O3 particles effectively cover the Ti3C2 surface and insert into the Ti3C2 layers. X-ray diffraction patterns demonstrated that the Fe2O3 particles are beneficial for the Ti3C2 delamination. A high attenuation constant and suitable impedance matching enabled wide-range microwave absorption properties; however, the minimum reflection loss was relatively high. To achieve both wide bandwidth and strong absorption, we designed a multi-layered structural absorber. When the thickness was 1.9 mm, the fourfold-layered structural absorber exhibited the optimal absorption properties with the minimum RL value of − 49.68 dB at 9.922 GHz and RL less than − 10.82 dB in the entire X-band region. Therefore, the synthesized multi-layered structural Ti3C2/Fe2O3 composites can be used for practical applications as a high-performance microwave absorber in the X-band region.

Design, synthesis and thermal stability study on graded TiNxOy solar selective absorbing coating fabricated by pulsed DC reactive magnetron sputtering

Design, synthesis and characterization of a solar selective absorbing coating based on titanium oxynitride are reported in this contribution. All the layers were deposited by reactive magnetron sputtering in a horizontal in-line sputtering system. The optical constants of individual layers were obtained by spectroscopic ellipsometry measurement and fitting. Multilayer solar selective absorbing coating including, from substrate to air interface, Al infrared reflective layer/ (TiNx/TiNx1Oy1/TiNx2Oy2) composite absorbing layer/SiO2:Al antireflective layer were then designed and and fabricated based on their optical properties and thickness optimization. A solar absorptance (α) of 94.6% and thermal emittance (ε) of 3.8% for operation temperature of 100 °C were obtained by analyzing the measured spectra data. Combined with X-ray diffraction and scanning electron microscopy, the relevance between the thermal stability and crystal structure and morphology of the film after annealed at 250 °C and 400 °C in air was explored

Design of an optimized multilayer absorber into the MWIR and LWIR bands

AbstractIn this article, we propose a new approach for effective detection of infrared (IR) radiation, using an absorber consisting of two successive metal‐dielectric layers. To this end, a low cost, high‐efficiency composite IR absorber structure consisting of a set of two double‐layered element of thin metal layers paired with dielectric materials is presented. The proposed composite absorber can be tuned based on the metal layer sheet resistance and the thickness of various poly‐Si media; by appropriate choice of physical, electrical, and optical parameters, so that maximal absorption over both mid‐wave IR band regions (MWIR) and long wavelength IR band regions (LWIR) (3–12 μm), is achieved. The outcome of study indicates that the presented absorber configuration may be a promising candidate for integration into microbolometric detectors; while offering improved efficiency and functionality, for not critical timing applications, synchronously in both the MWIR and LWIR atmospheric thermal windows.

Ultrathin arrayed camera for high-contrast near-infrared imaging.

We report an ultrathin arrayed camera (UAC) for high-contrast near infrared (NIR) imaging by using microlens arrays with a multilayered light absorber. The UAC consists of a multilayered composite light absorber, inverted microlenses, gap-alumina spacers and a planar CMOS image sensor. The multilayered light absorber was fabricated through lift-off and repeated photolithography processes. The experimental results demonstrate that the image contrast is increased by 4.48 times and the MTF 50 is increased by 2.03 times by eliminating optical noise between microlenses through the light absorber. The NIR imaging of UAC successfully allows distinguishing the security strip of authentic bill and the blood vessel of finger. The ultrathin camera offers a new route for diverse applications in biometric, surveillance, and biomedical imaging.

Wideband low-frequency sound absorption by inhomogeneous multi-layer resonators with extended necks

This study develops a structure with thin thickness targeting for wideband low-frequency sound absorption, which consists of multi-layer Helmholtz resonators with extended necks (HRENs). An analytical prediction model is established based on the classic transfer matrix method to study the acoustic characteristics of the multi-layer HREN absorber. Results show that the added layer shifts the first absorption peak of the original single-layer HREN absorber to a lower frequency and induces additional absorption peak. Then, a particle swarm optimization (PSO) algorithm is coupled with the prediction model to design optimal sound absorbing structure for effective sound absorption in a prescribed wideband frequency range. For illustration, a single-layer, a double-layer and a triple-layer optimal structures composed of 9 inhomogeneous units at each layer are designed and they yield about 90% absorption in the frequency ranges of [550,700] Hz, [400,650] Hz and [300,550] Hz. The mechanism of the continuous absorption band is due to the overlapping of the absorption peaks induced by different units. The proposed structure offers an effective acoustic absorption in the target wideband frequency range while its size is in a compact scale, and thus holds great potential for noise attenuation in various realistic applications.

On the Design of Wideband Absorber Based on Multilayer and Multiresonant FSS Array

In this letter, a novel and effective design method for multilayer and multiresonant absorbers is proposed. The two-layer absorber is composed of two resistor-loaded square loop frequency selective surface (FSS) arrays printed on the Rogers 4003 dielectric substrate and a backed metal plane. Equivalent circuits for two-layer absorbers with resistive sheets and resonant FSSs are proposed, analyzed, and further improved to provide great insight into the existence of the four resonances and ultrawide bandwidth. In the equivalent circuit model, the substrate is transformed to a parallel admittance and a positive susceptance is introduced in the whole operation band, which contributes to an extra resonance. After the measurement of a fabricated sample, a fractional bandwidth of 171.2% is obtained for at least 10 dB reflection reduction, with a total thickness of only 0.087λL (wavelength at the lowest absorption frequency). The good agreement between the calculated, simulated, and measured results validates the designed absorber.

Design and simulation of multilayer hybrid foam material for acoustic application

New acoustic multilayer absorber fabricated by coupling closed-cell metallic foam and open-cell polymeric foam, which aimed to develop a practical use of metallic foam in the noise control application. In prior, the individual sound absorption coefficient of both foam materials with different thicknesses measured by the impedance tube method as per ASTM E-1050. Using inverse characterization technique, the intrinsic properties needed for five parameter models in a numerical study are predicted. The measured characteristic impedance, complex wave propagation, and sound absorption coefficient of the individual foams are in close agreement with the prediction. Subsequently, a different configuration of multilayer absorber is modeled using obtained properties, and their acoustic performance is evaluated. The result indicates that the coupling of polymeric foam with metallic one exhibits enhanced sound absorption and usage of closed-cell metallic foam in noise control material. Furthermore, the result demonstrates that absorption capability entirely relies on the placement of polymeric foam in the configuration. The proposed hybrid multilayer absorber coupled with test bench car for interior acoustic study, where 5–30 dB is reduction is noticed in 1/3rd octave plot.

Design of Multi-Layer Gear-Shaped Metamaterial Absorber with Broadband and High Absorption

Design of Multi-Layer Gear-Shaped Metamaterial Absorber with Broadband and High Absorption