Kind Of Absorber Research Articles

Time-domain model for spherical wave reflection in a flat surface with absorber character – Application to the SOPRA measurement method

This paper presents a developed time-domain model for the reflection of spherical waves in an absorber-like surface. The model is made to enable evaluation of measurement methods for assessing the sound absorptive properties of traffic noise barriers in direct sound field, it is thus called the Direct Field Absorption (DFA) model. In this study, the DFA model is applied to the in-situ SOPRA method for quick sound reflection index measurements on road noise barriers. The DFA model results in an impulse response (IR), based on a theoretically derived impedance of a certain absorber. The DFA IR is entered to the SOPRA formula to calculate the reflection index, RIQ, of the absorber, which is subsequently compared to the measured RIQ of a wall fitted with the absorber in question. If the results are similar, it is reasonable to assume that the SOPRA measurement results are valid. But if there are any significant differences between the DFA and SOPRA sound reflection indices, possible reasons for them should be examined.The first results are encouraging, showing that the DFA model can be a valuable tool to evaluate the results of reflection measurements. Furthermore, the DFA model could be useful for estimating the sound absorptive performance at lower frequencies of a noise barrier limited to its spatial extent in width and height, i.e., when it is physically impossible to measure. Further studies are necessary though, since the conclusions of this paper are based on only one kind of absorber.

Research progress of small molecule carbon dioxide capture agent

At present, the excessive emission of carbon dioxide has threatened people 's living environment and future development. More and more countries have begun to pay attention to carbon emission reduction. China has set the dual-carbon strategic goal of “carbon dioxide content reaches its peak” and “carbon neutrality”. According to the research on carbon dioxide capture technology by many scholars at home and abroad, it is found that the use of chemical absorbents to capture carbon dioxide is a relatively low cost, less technical difficulty, and can be widely put into industrial production. In this paper, several common chemical absorbents such as hot potassium alkali method, organic amine absorption method, amino acid salt, ionic liquid and phase change absorbent are reviewed. Through the research of various kinds of absorbents by researchers from various countries, their reaction principle, performance advantages and disadvantages, research status are introduced, and the future development direction of carbon dioxide negative emission technology is analyzed.

Polarization-insensitive ultra-wideband metamaterial absorber comprising different forms of ZrN structures at the metasurface

Ultra-wideband metamaterial absorber comprising zirconium nitride (ZrN)-based metasurface was investigated. In particular, the metasurface had three different kinds of resonating element patterns (composed of ZrN), namely the concentric annular square, circular and triangular air gaps of different samples of ZrN, as distinguished by the nitrogen content of the medium (i.e., ZrN). Spectral performance of metamaterials was evaluated in terms of absorbance, and it was found that the metasurface structure with annular circular resonating elements provides the best performance owing to high absorbance with relatively stable wideband feature. The performance of the proposed structures was investigated under varying parametric situations considering the incidence excitations with the transverse electric (TE-) and transverse magnetic (TM-) conditions, and also, the normal and oblique incidence of waves. The nearly-perfect absorption along with the ultra-wideband property of the structure were shown. Apart from this, it also exhibits the polarization-insensitive characteristic regardless of the polarization state as well as polarization angle of the incidence waves. Such a kind of absorber would be useful for antireflection coating and solar energy harvesting applications in a wide spectral range from the visible to far-red regimes of wavelength.

High-Quality Graphene-Based Tunable Absorber Based on Double-Side Coupled-Cavity Effect.

Graphene-based devices have important applications attributed to their superior performance and flexible tunability in practice. In this paper, a new kind of absorber with monolayer graphene sandwiched between two layers of dielectric rings is proposed. Two peaks with almost complete absorption are realized. The mechanism is that the double-layer dielectric rings added to both sides of the graphene layer are equivalent to resonators, whose double-side coupled-cavity effect can make the incident electromagnetic wave highly localized in the upper and lower surfaces of graphene layer simultaneously, leading to significant enhancement in the absorption of graphene. Furthermore, the influence of geometrical parameters on absorption performance is investigated in detail. Also, the device can be actively manipulated after fabrication through varying the chemical potential of graphene. As a result, the frequency shifts of the two absorption peaks can reach as large as 2.82 THz/eV and 3.83 THz/eV, respectively. Such a device could be used as tunable absorbers and other functional devices, such as multichannel filters, chemical/biochemical modulators and sensors.

Facile synthesis of MOF-derived concave cube nanocomposite by self-templated toward lightweight and wideband microwave absorption

The green and facile strategy of producing high efficiency microwave absorption materials (MAMs) has attracted wide attention, but remains a challenge. In this work, polydopamine (PDA) was used as carbon source and nitrogen source, polyvinylpyrrolidone (PVP) was used as protective layer and dispersant, and nanoparticles with concave cube morphology were prepared by self-template eco-friendly method. By adjusting the addition amount of PDA and PVP, the MOF derived materials with three morphologies of pure ZIF-67 nanoparticles, core-shell adhesion cube and concave cube can be precisely controlled. Compared with the other two kinds of absorbers, the sample with concave cube morphology shows excellent electromagnetic wave absorption (EMA) performance. Furthermore, the excellent EMA performance comes from the efficient electron transport channel with unique concave cube morphology, multi-interface polarization process and Co nanoparticles high impedance matching. The analysis demonstrates that when the filling ratio of the concave cube sample is 15%, its effective absorption bandwidth is 5.97 GHz, which can basically cover the Ku band (12.0–18.0 GHz), and the corresponding thickness is 1.88 mm. Our research provides a meritorious approach for the design and preparation of high efficiency MAMs by considering the effects of the morphology and filling ratio of the absorber comprehensively.

Low-frequency broadband lightweight magnetic composite absorber based on metamaterial structure

In recent years, the development of lightweight broadband absorbers has always been pursued by researchers. In this paper, a low-frequency, broadband and lightweight absorber is designed and prepared by combining the metamaterial structure with the magnetic composite material. First of all, the quality of the absorber was low, which was 40% lower than that of traditional absorber composite materials. Secondly, the absorber had excellent absorbing effect, and its absorbing bandwidth (bandwidth with reflectivity less than −10 dB) reached 6.72 GHz, and its RLmin (minimum reflection loss) value had dropped to − 23.94 dB. Finally, the absorber also had obvious effects at low frequencies, the absorber's RLmin value reached − 10.10 dB at 7.36GH. Simultaneously, the experimental results also verify the above results very well. Therefore, this kind of absorber gives full play to the advantages of magnetic composite material and metamaterial structure. This design concept provides a new development path for the design of absorber materials, and will also play a huge role in promoting the application of absorbing materials in military and civilian fields, such as the research and development of a new generation of stealth fighters.

ZrN fractal-graphene-based metamaterial absorber in the visible and near-IR regimes

The absorption characteristics of zirconium nitride (ZrN)-based metamaterial absorber of fractal geometry are studied. The proposed absorber is comprised of fractal metasurface at the top having subwavelength-sized periodic pattern of specially designed ZrN circular nano-discs arranged over silicon dioxide (SiO2) substrate. A tri-layer graphene, owing to its exhibiting better tunability, is introduced at the interface of metasurface and substrate. The bottom side of SiO2 is coated with silver nanolayer to block transmission. The absorptivity essentially depends on the kind of fractal design used in metasurface to configure the absorber. The obtained results exhibit the absorption characteristics to remain insensitive to the incidence polarizations. The chemical potential of graphene could be used to tune the spectral characteristics. Such a kind of absorber would be useful for filtering, antireflection coating, and solar energy harvesting applications in the visible and near-infrared regimes of electromagnetic spectrum.

Gradually perforated porous materials backed with Helmholtz resonant cavity for broadband low-frequency sound absorption

Conventional sound absorbers can hardly own the good performance of low-frequency and broadband absorption simultaneously. In order to combine these two functions into one kind of absorbers, the gradually perforated porous materials backed with Helmholtz resonant cavity are proposed. A theoretical model and a finite element (FE) model are developed to investigate the sound absorption of the proposed sound absorber. Experimental measurements are conducted to successfully verify the developed theoretical and numerical models. In the theoretical model, the gradually perforated porous material is divided into a series of thin layers and each layer is described by the double porosity theory. The backed Helmholtz resonant cavity and the connection between these thin layers are modeled by applying the transfer matrix method, so as to achieve the surface acoustic impedance of the absorber via a bottom-up approach. The FE simulations reveal the sound absorption mechanisms of the proposed absorber from the viewpoints of particle vibration velocities, sound energy flow and energy dissipation distributions. The influences of the porous material matrix and the structural parameters on the sound absorption of the proposed absorber are analyzed. Results show that the gradually perforation hole substantially improves the impedance match between the material and air to enhance broadband sound absorption. Meanwhile, the backed Helmholtz resonant cavity brings a low-frequency sound absorption peak to augment sound absorption. This proposed absorber realizes an excellent combination of low-frequency and broadband sound absorption. In addition, its easy-to-manufacture characteristics show great application potential.

A Multi-Band Near Perfect Polarization and Angular Insensitive Metamaterial Absorber With a Simple Octagonal Resonator for Visible Wavelength

A multi-band, ultrathin, polarization-insensitive, near-perfect metamaterial absorber (PMA) has been proposed and substantiated numerically for solar thermophotovoltaic (STPV) systems which also can be used in some other applications. This kind of absorber currently drawing massive interest throughout the research of optics. Especially in solar harvesting metamaterial absorbers can give a huge boost in efficiency by intensifying the solar electromagnetic wave. Visible wavelength has been the key focus of the proposed design so that the structure can utilize solar energy proficiently. Aluminum (Al) and Gallium Arsenide (GaAs) have been chosen as materials for their higher electron mobility along with good temperature stability. The PMA is a three-layer metal-dielectric-metal called sandwiched structure. For proper characterization of the PMA absorber, extensive parametric inspections were carried out with underlying physics. The finite integration technique (FIT) in computer simulation technology microwave studio (CST MWS) is used to perform the numerical analysis and for verification finite element method (FEM) in COMSOL Multiphysics has been used along with interference theory model (ITM) for calculating the absorbance. The PMA shows 99.27%, 99.89%, 99.91%, and 99.06% perfect absorption at 454.75nm, 505.53nm, 568.72nm, and 600.85nm resonance wavelength in all three modes of waveguide propagation. The design also exhibits incident wave stability up to 60° for both transverse electric (TE), and transverse magnetic (TM) wave modes. Excellent glucose concentration sensing ability was also observed with the proposed structure. So, the proposed PMA can be implemented in solar energy harvesting devices along with solar sensors or detectors, light trappers, light modulators, or light wavelength detectors.

Polarization-insensitive multi-band metamaterial absorber operating in the 5G spectrum

A polarization-insensitive multi-band metamaterial absorber comprised of four concentric rectangular rib structures, mounted over a dielectric medium, was investigated. The performance of the absorber was studied under different polarization and oblique incidence angles. Both the transverse electric (TE) and transverse magnetic (TM) incidence radiations were exploited to investigate the absorption characteristics. It was found that the four-fold symmetry in the configuration makes the absorber to remain insensitive under the influence of such operational conditions. The proposed structure yields four independent high absorption peaks within the 5G spectral range. The absorptivity of the structure was also investigated for various values of the thickness of dielectric substrate on which the metasurface was constructed. The electric field and surface current distribution patterns were also obtained corresponding to three different resonance peaks. It is expected that this kind of absorber would be effectively used for 5G applications in the context of MIMO antennas.

Active boundary and interior absorbers for one-dimensional wave propagation: Application to transmission-line metamaterials

We address the problem of generating active absorbers for wave propagation in a class of one-dimensional continuous media. In particular, we consider the emerging application of metamaterials, which are engineered structures supporting unconventional wave propagation phenomena. We design two kinds of absorbers. The first absorber achieves a complete elimination of wave reflections from the metamaterial boundaries independently of the working frequency regime. The associated controller is implemented in a feedback loop and is given in general terms of the metamaterial effective constitutive parameters. The second absorber blocks wave propagation beyond a prescribed location at the metamaterial interior with minimized back-scattering, thus generating a sink without any physical boundary present. It is implemented in a feed-forward loop via a unique near unidirectional control wave method, using two concentrated actuators. Both the interior and boundary absorbers are based on an exact fractional order transfer function model that we derive for the metamaterial. The model explicitly exhibits essential wave characteristics, including delays, dispersion, impedance, boundary reflections etc. The resulting controllers are of fractional order as well and are realized via a dedicated approximation technique. We verify the results by numerical simulations of a representative mechanical metamaterial.

UV–Visible silicon detectors with zinc oxide nanoparticles acting as wavelength shifters

Broad spectral response of photon detectors without cryogenic cooling is of great interest in many fields of application like spectroscopy and high-energy particle physics. In order to achieve broad spectral range, different approaches can be found in literature. One approach is the multijunction detector incorporating different kind of absorbers. The drawback here is the fabrication cost as well as complicated fabrication technique [1]. Another approach is the application of wavelength shifters which absorb the UV light and re-emit it in the lower energy range which preferably matches the peak sensitivity of the detector. The application of chemical wavelength shifters like e.g. Tetraphenyl Butadiene (TPB) has been reported, but they posses some drawbacks like instability in contact with some substances and photo-degradation behavior [2]. There is also a concept of the application of luminescent nanoparticles on top of the detector, which act as wavelength shifters [3]. This approach has several advantages such as little interference in the detector structure (even the UV-blocking window of the detector does not pose a problem), straightforward deposition technique and large possibility of adjustment of the spectral regions depending on the kind of the nanoparticles. Thanks to the quantum confinement related to small size of the particles, the bandgap of the material can be engineered, therefore the absorption and emission properties of the material can be tuned. Other feature which has an impact on the emission and excitation properties are the defects, which can act as luminescent centers. The wavelength shifters considered for this application are two kinds of commercially available zinc oxide (ZnO) nanoparticles. The differences between them lay in the size and the structural quality, which influence their optical properties like emission and excitation spectra as well as photoluminescence quantum yield. For the application they are distributed in the poly (methyl methacrylate) – PMMA - matrix and spin-coated on the detector window. The work consists of the analysis of the parameters of the zinc oxide nanopowders only as well as the nanopowders dispersed in the PMMA matrix. The problem has been investigated both theoretically and experimentally. The experimental part involved examination of the samples deposited on the laboratory glass and finally on the photodetector. Apart from the kind of zinc oxide nanoparticles, the technological parameters which were optimised was the concentration of ZnO in PMMA as well as thickness of the layer. Two types of photodetectors have been considered for modification: silicon photodiodes with broad spectral response from 190 nm to 1000 nm and Multi Pixel Photon Counters (MPPC) sensitive in the range 270 – 900 nm. These latter ones are used for sophisticated applications as well as single-photon detection. The comparison of parameters of the detectors before and after modification is shown. 1.Gessert, T.A., Colegrove, E., Stafford, B., Kodama, R., Gao, W., Moutinho, H.R., Kuciauskas, D., Reedy, R.C., Barnes, T.M., Sivananthan, S. MRS Advances, 1 (50), pp. 3391-3402 (2016) 2.Alvarez, V. et al., Journal of Instrumentation 7, P02010 (2012) 3.Sahi, S., Magill, S., & Ma, L., Xie, J., Chen, W., Jones, B., Nygren, D., Scientific Reports. 8:10515, (2018)

Nonlinear Torsional Vibration Absorber for Flexible Structures

A new kind of nonlinear energy sink (NES) is proposed to control the vibration of a flexible structure with simply supported boundaries in the present work. The new kind of absorber is assembled at the end of structures and absorbs energy through the rotation angle at the end of the structure. It is easy to design and attached to the support of flexible structures. The structure and the absorber are coupled just with a nonlinear restoring moment and the damper in the absorber acts on the structure indirectly. In this way, all the linear characters of the flexible structure will not be changed. The system is investigated by a special perturbation method and verified by simulation. Parameters of the absorber are fully discussed to optimize the efficiency of it. For the resonance, the maximum motion is restrained up to 90% by the optimized absorber. For the impulse, the vibration of the structure could attenuate rapidly. In addition to the high efficiency, energy transmits to the absorber uniaxially. For the high efficiency, convenience of installation and the immutability of linear characters, the new kind of rotating absorber provides a very good strategy for the vibration control.

Double layered radar absorbing structures of Silicon Carbide fibers/polyimide composites

High performance radar absorbing structures were fabricated using polyimide as matrix, Silicon Carbide fibers (SiCf) as reinforcement, and the effect of carbon-based absorbent (carbon nanotubes (CNTs) and graphene nanoplatelets (GNP)) content on the mechanical and electromagnetic absorbing properties was studied and analyzed. The results indicated that the complex permittivity increased with increasing the filler content due to the high polarization ability, while the flexural strength of the composites decreased owing to the poor dispersion properties. The absorbing properties of carbon filler-SiCf/polyimide composites can be adjusted by the kinds of absorbent, the content and the thickness. In order to enhance the absorbing bandwidths, double layered structures were designed and simulated, and the minimum reflection value can reach to −29.8dB. This material can be using as a kind of high performance radar absorbing structures.

Preparation of Polyaniline@MoS2@Fe3O4 Nanowires with a Wide Band and Small Thickness toward Enhancement in Microwave Absorption

It is well-known that the absorbing property of materials is related to the microstructure and can be enhanced by magnetic nanoparticles coating. However, the mechanism is still unclear that the magnetic coating structure plays an important role in the microwave absorption behavior. Hence, a novel kind of absorber with efficient performance and relatively clear enhancement mechanism is very necessary. To solve these problems, polyaniline@MoS2 nanowires (PANI@MoS2 NWS) and a series of polyaniline@MoS2@Fe3O4 nanowires (PANI@MoS2@Fe3O4 NWS) with hierarchical structure were successfully prepared by in situ polymerization and versatile hydrothermal reactions and investigated in microwave absorption. The results reveal that compared with the articles related to MoS2-based composites, the as-prepared PANI@MoS2@Fe3O4 NWS (e2) displays the widest absorption frequency range (6.48 GHz) and strong absorption (−49.7 dB at a thickness of 1.3 mm), and the excellent MAP can be interpreted by optimizing impedance matching...

Influence of the imaginary part of the dielectric layer on the bandwidth of metamaterial absorber and the design of broadband absorption

It is well known that dielectric layer imaginary part (or loss tangent of tan(δ)) plays a crucial role in modulating the absorption rate of metamaterial absorber (MA). However, there is not any systematic investigation into whether tan(δ) impacts resonance bandwidth of the MA. Herein, we investigated the dependence of resonance bandwidth of the MA on the change of tan(δ). Three kinds of absorbers with top layers of frequently used metallic patterns of square patch, cross, and strip were demonstrated. To facilitate comparison of the bandwidth, each case of tan(δ) was optimized for perfect absorption. Results proved that the bandwidths of the three absorbers were broadened greatly with tan(δ) increase. Their bandwidth enhancement factors are all at least 10. Based on this, this paper further makes some discussions on the design of broadband MA, which consists of three alternating stack of square patches and dielectric layers with large value of tan(δ) on top of a metallic board. >80% absorption of the resonance bandwidth of the triple-layer absorber can cover a frequency range of 3.689 THz. The relative resonance bandwidth of absorber can reach 138.893%, which is far higher than that of previous broadband absorbers using small value of tan(δ).

Experimental Demonstration of Microwave Absorber Using Large-Area Multilayer Graphene-Based Frequency Selective Surface

Radar-absorbing materials are used in stealth technologies for concealment of an object from radar detection. Resistive and/or magnetic composite materials are used to reduce the backscattered microwave signals. However, nontunable characteristics or the required complex structure hampered the application of these materials. Here, multilayer graphene-based frequency selective surfaces (MLGFSS), which reach a size of 150 mm $\times $ 150 mm, are designed and fabricated. By properly changing the growth temperature of MLG using the chemical vapor deposition approach and designing the pattern of graphene layer, the impedance matching condition can be satisfied at different frequencies. As a result, two kinds of absorbers with different working bandwidths are realized. The performances of the proposed absorbers are analyzed using full-wave simulation and are also tested with experimental results. Our method of fabricating large-area MLGFSS avoids the direct contact between the stencil mask and graphene, and guarantees the integrity and quality of patterned graphene structure. A good agreement between simulation and measurement results demonstrates that such ultrathin MLGFSS is very useful in the design of graphene-based functional devices at microwave frequencies.

Wet oxidation and absorption procedure for NOx removal

Abstract The removal of NO x with low oxidation degree, low temperature, and high vapor content from small coal-fired boiler emission through selective catalytic reduction is difficult. This study investigated liquid oxidation and absorption to remove NO x systematically. Thermodynamic calculation showed that the equilibrium constants of the NO oxidation and NO x absorption reaction are high; thus, NO x treatment by liquid oxidation and absorption is feasible. Four oxidants (NaClO2, NaClO, H 2 O2, and KMnO4) and four absorbents (Ca(OH)2, CaCO3, NaOH, and Na2CO3) were used to study the reaction mechanism of the oxidation and absorption processes. Results show that NaClO2 solution is the best oxidant, and the optimum pH value of the oxidation reaction is 5–6. The oxidation degree reaches 100% when the concentration of the NaClO2 solution is 1.0%, and the oxidation degree can still reach approximately 50% when the concentration is 0.1%. Ca(OH)2 slurry has the best absorption performance among the four kinds of absorbents. The NO x removal efficiency of Ca(OH)2 slurry can reach approximately 70% when the oxidation degree is 50%. The removal efficiency is up to 80% when the oxidation degree is 100%.

Experimental study on heat and mass transfer performance of falling film absorption over a vertical tube using LiCl solution

To discover the falling film absorption performance over a vertical tube using LiCl solution in a high-pressure absorber involved in a two-stage absorption refrigeration system, an experimental study on heat and mass transfer performance of the absorption process was conducted. Effects of operating parameters such as solution mass flow rate, absorber pressure, concentration and cooling water temperature on absorber performance are analyzed. Besides, a coupled heat and mass transfer model is applied and solved with a finite difference method in order to determine the heat and mass transfer coefficients. Mass absorption rates of absorption processes respectively using LiBr solution and LiCl solution are compared under the conditions of the same temperature and saturated vapor pressure of the solution. Results show that the mass absorption rate using LiCl solution is up to 19.7% higher than LiBr solution. In addition, dimensionless formulations of heat and mass transfer coefficients are correlated with the average absolute error below 15%. The study is also helpful to design and optimize such kind of absorbers using LiCl solution as working fluid.

Novel aluminum plasmonic absorber enhanced by extraordinary optical transmission.

We report a theoretical and experimental study on a novel type of aluminum super absorber which exhibits a near perfect absorption based on the surface plasmon resonance in the visible and near-infrared spectrum. The absorber consists of Ag/SiO2/Al triple layers in which the top Al layer is patterned by a periodic nano hole array. The absorption spectrum can be easily controlled by adjusting the structure parameters including the radius of the nano hole and the maximal absorption can reach 99.0% in theory. We completely analyze the SPP and LSP modes supported by the metal-dielectric-metal structure and their contribution to the ultrahigh absorption. On this basis, we find a novel method to enhance the absorption via the simultaneous excitation of SPP at different interfaces theoretically and experimentally. Moreover, for the first time we clarify the EOT caused by the nano hole array can enhance the absorption by experiment, which is not reported in previous works. This kind of absorber can be fabricated by low-cost colloidal sphere lithography and the use of stable Al overcomes the disadvantages brought by the noble metal, which make it a more appropriate candidate for photovoltaics, spectroscopy, photodetectors, sensing, and surface enhanced Raman scattering.