Double-layer Absorber Research Articles

Dielectric gene engineering on biochar for ultrawide-band microwave absorption with a rational double-layer design

Biomass char is very promising in developing microwave absorbing materials with low minimum reflection loss (RLmin) and ultrawide effective absorption bandwidth (EAB) owing to its low cost and natural availability of various pores, but however is facing a dilemma between the conduction loss and interface polarization loss where new heating technology is highly desirable. In this work, a microwave confined plasma/microwave hybrid heating technology is developed based on the unique interaction between porous carbon and microwave for simultaneous enhancement of conduction loss and interface polarization loss of cellulose char. Compared to the conventional heating product at the same temperature, the as-prepared microwave char showed almost doubled conductivity which is beneficial for conduction loss, higher content of C–O bond that has longer bond length and dielectric susceptibility than CO bond, and more condensed carbon nanoparticles embedded in the carbon matrix which is responsible for increasing the heterointerface polarization loss. As such the tangent loss of MW900-40 % ranges from 0.69 to 0.97 while that of CH900-40 % only ranges from 0.34 to 0.64 in the frequency range of 2.0–18.0 GHz. Further, based on multilayer impedance gradient principle, a double-layer absorber is constructed with products of different MW900 loading, yielding a RLmin of −59.0 dB at 15.9 GHz with an EAB of 10.0 GHz at 4.0 mm, whose working mechanism is comprehensively studied by simulations in terms of impedance matching and microwave dissipation distribution.

Accelerating multilayer frequency selective surface absorber design by combining equivalent circuit models with machine learning

Designing high-performance electromagnetic functional materials and artificial structures is of great significance for electromagnetic wave modulation applications. Optimizing performance in the high-dimensional parameter space of electromagnetic functional materials has posed a challenging problem. This paper proposes the use of reinforcement and transfer learning methods to facilitate the quick and accurate design of wideband circuit analog absorbers (CAA). A trained reinforcement learning network is utilized to comprehend the relationship between reflectivity performance and changes in impedance parameter. Furthermore, the transfer learning method is applied to accelerate the training process, leading in a 20-fold reduction in the number of simulations. To validate the effectiveness of this approach, a double-layer absorber aiming for reflectivity less than −20 dB at 3–10 GHz is designed, requiring only 50 simulations. This demonstrates that the proposed method provides a flexible strategy for the interactive design of equivalent circuit and electromagnetic structural parameters. Moreover, it presents a novel and efficient solution for microwave absorber design, with potential applications across various microwave design fields.

Optimized microwave absorption through multilayer structure of flaky Fe and graphite

In this paper, a double-layer and a three-layer absorbers of the flaky Fe/PU and the graphite/PU composites are designed for achieving a wide-frequency microwave absorption (MA) at a thin thickness. The minimum reflection loss and the maximum effective absorption bandwidth reach −80.05 dB and 9.24 GHz in the double-layer absorber with a total thickness of 2.2 mm, even up to −84.73 dB and 9.73 GHz in the three-layer absorber at a total thickness of 2.1 mm, showing that it is effective to enhance the MA intensity and widen the MA bandwidth by multilayer structure of the magnetic Fe micro-flakes and the dielectric graphite.

Facile fabrication of bilayer electromagnetic wave absorber via hierarchical Mo2C/La0.6Sr0.4MnO3 nanocomposite with multi-heterointerfaces for efficient low-frequency absorption

Bi-layer absorbers, which include porous and hierarchical materials, benefit from their slight weight, garnering increased interest in electromagnetic wave dissipation adaptability. However, developing a simple manufacturing process and utilizing such unique structures with particular compounds to achieve rational electromagnetic wave dissipation performance remains a challenge. In this case, a novel hierarchical flower-like Mo2C particle and scraps' firewood-shaped La0.6Sr0.4MnO3 were chemically synthesized and employed as the single component in each layer of a manufactured double-layer absorber. The mechanical and electromagnetic wave dissipation capability of optimized bilayer absorber samples was excellent. The best absorption was found in bilayer samples with a total thickness of just 1.2 mm, –39 dB dissipation intensity, and 3 GHz bandwidth at 5.4 GHz frequency. This performance was obtained by manipulating the order and layer thickness of the components, as well as modifying their morphology and microstructure.

The enhancement of CZTSSe solar cell performance through active construction of the double-layer absorber

The absorbers of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) that have undergone rapid thermal process (RTP) selenization typically exhibit a double-layer structure, with a fine crystal layer at the bottom, which degrades the performance of devices. We propose an efficient strategy for actively constructing the double-layer absorber to improve the quality of the small grains in the bottom layer. Compared to traditional methods, this method ensures uniform element distribution, particularly for Se element, and enables a more desirable Cu-poor and Zn-rich composition with a Zn/Sn ratio closer to the standard stoichiometric ratio, resulting in a reduction in harmful internal defects. This strategy eliminates small grains at the bottom and decreases grain boundary formation, resulting in a dense double-layer structure. The high-quality CZTSSe absorber not only reduces carrier recombination during back transmission, further reducing reverse saturation current (J0) and increasing optical current density (JL), but also enhances shunt resistance (Rsh) and decreases series resistance (RS). The estimated contribution percent for PCE improvement due to changes in JL, J0, Rsh, RS, and A are 17.20 %, 120.01 %, 1.15 %, 6.50 %, and -44.86 %, respectively. Ultimately, the highest photoelectric conversion efficiency (PCE) increased from 8.73 % to 10.49 %, and device uniformity improved considerably. This study highlights the significance of optimizing the microstructure of CZTSSe absorber layer in enhancing the performance of CZTSSe solar cells, and will provide guidance for producing high-quality CZTSSe absorber layers.

Design of a Broadband Double-layer Absorber Using a Resistive Ink Based on Frequency-selective Surfaces Arrangement

The traditional way to enhance the absorption performance of absorbers is to optimize the structural parameters of the unit cell, taking no consideration of the coupling between units. Here, based on the first presented double-layer metamaterial absorber unit cell using resistive ink patterns printed on an FR-4 sheet, the impact of arranging the frequency selective surfaces within constrained units on the absorption performance is studied, providing a method to improve the absorption performance through absorption and phase cancellation of the unit cell by arranging frequency selective surfaces. The optimized double-layer absorber structure achieves over 90% absorption within 3.3~15.6 GHz with a small thickness of 10.05 mm, and exhibits a preferred absorption performance than the original one within the operating frequency band.

Single and double-layered Tri-band Microwave absorbing materials

Absorbers at microwave frequencies with multiple frequency-band response are particularly important for use in military for stealth technology. Specially, ferrite based absorbing materials are significant for electromagnetic shielding and signal attenuation. The enhancement of reflection loss of ferrites along with carbonaceous materials are even more beneficial. Recently double-layer absorbers have extensively studied to meet the requirements of advanced absorbing materials in multiple frequency-band response. It still remains a challenge how to determine the type and thickness to couple the impedance-matching-layer to the absorption-layers for a double-layer absorber. We applied hydrothermal method to prepare Fe3O4 nanoparticle and combine them with either graphene oxide (GO) or reduced graphene oxide (rGO) to prepare a composite of specific quality to obtain Fe3O4@GO and Fe3O4@rGO nanocomposite. We studied microwave attenuation capabilities of single and double-layer absorbers containing these two materials. We have demonstrated that with a thin impedance matching layer as a first layer and an absorbing layer behind this layer for the double-layered absorber has much higher reflection loss (RL) than a single-layer. The Fe3O4@rGO composite as a single-layer absorber shows the best microwave absorption performance with RL close to −30 dB in all three microwave bands (X, Ku and K bands). The use of a double-layer structure as Fe3O4@GO as impedance matching layer and Fe3O4@rGO as absorbing layer exhibits the best absorption of −50 dB. This is much larger than the single-layered absorbers at all three frequency-bands. Such a performance is superior to many reported ferrite-based carbonaceous composites. Therefore, a double-layer absorber is best suited to coat the whole body of the aircraft or missiles to evade satellite detection, a preparation towards new-generation weapons for future warfare. Before performing the absorption studies we have characterized the ferrites, GO and rGO materials with various microstructural and magnetic characterizations.

Sustainable and low-cost cellulose aerogel-based absorber for solar steam generation

Solar steam generation is a promising technology for sustainable seawater desalination. However, its practical application is hindered by the low water evaporation rate and the high cost of materials. Carbon aerogels have demonstrated superior properties for clean water production through solar steam generation, but the complex and time-consuming preparation process inhibits their development and applications. In this study, high-performance solar steam absorbers based on cellulose-derived carbon aerogels were prepared from paper and waste paper using a simple green method. The fabricated carbon aerogels have a typical microporous structure (pore diameter: 20–250 µm), super-hydrophilic properties, good mechanical properties and efficient solar light absorption (∼96 %), which make them ideal for application in solar steam generation. Three different configurations based on cellulose and carbon aerogels were fabricated (bulk absorber, double-layer absorbers and ink-based absorber) to achieve the best design with high efficiency for steam generation. The surface temperature of the bulk absorber and dry double-layer absorbercan achieve 100 °C under 1 kWm−2irradiation. Among all configurations, the double-layer absorbers represented the highest efficiencies, 90.4 % for paper and 84.3 % for waste paper, under 1 kWm−2 irradiation, which are higher than most reported results. According to the results, the sustainable cellulose-based double-layer absorbers were promising materials for efficient solar steam generation due to their high hydrophilicity, high sunlight absorption, open porous structure, non-toxicity, biodegradability, availability and low cost.

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.

Design of double-layer absorbers based on Co2Y@C core-shell nanofibers and carbon nanofibers for high-efficient and tunable microwave absorption

A novel double-layer microwave absorber based on Ba2Co2Fe12O22@C core-shell nanofibers (Co2Y@C NFs) and carbon nanofibers (CNFs) was designed, and their microwave absorption properties were systematically investigated in the frequency range of 2–18 GHz. Benefiting from the better impedance matching characteristic of the matching layer (50 wt% Co2Y@C NFs/paraffin composite) and the stronger dielectric loss ability of the absorbing layer (5 wt% CNFs/paraffin composite), the optimized double-layer absorbers exhibit stronger absorption and wider effective absorption bandwidth compared to the corresponding single-layer absorbers. When the thicknesses of the absorbing and matching layer are respectively 0.62 mm and 1.38 mm (total thickness of 2 mm), the optimal reflection loss (RL) reaches −46.9 dB at 16.8 GHz, and the effective absorption bandwidth (EAB) is 4.1 GHz (from 13.9 to 18 GHz). Meanwhile, when the thicknesses of the absorbing and matching layer are 1.03 and 1.98 mm (total thickness of 3.01 mm), respectively, the optimal RL is up to −63.7 dB at 10.0 GHz with an EAB of 9.5 GHz ranging from 8.5 to 18 GHz. The absorption intensity and range of the double-layer absorber can be easily adjusted by regulating the thickness of the absorber, which shows good potential for practical applications.

Electromagnetic wave absorption properties of the FeSiAl/PLA and FeSiAl-MoS2-Graphene/PLA double-layer absorber formed by fused deposition modeling

The FeSiAl/PLA and FeSiAl-MoS2-Graphene (GR)/PLA composite filaments were prepared through mechanical mixing and melt extrusion process, and the double-layer absorbers while the material of layer 1 is FeSiAl/PLA and the material of layer 2 is FeSiAl-MoS2-GR/PLA were prepared by fused deposition modeling (FDM) 3D printing technology. The results show that the FeSiAl/PLA and FeSiAl-MoS2-GR/PLA double-layer absorber can effectively improve impedance matching. The electromagnetic wave absorption performance is improved under the synergistic effect of multi-loss mechanisms. The minimum reflection loss (RLmin) value of the double-layer absorber is −52.50 dB at 17.76 GHz with the thickness of FeSiAl/PLA layer is 0.6 mm and the total thickness of 1.7 mm. The effective absorption bandwidth (EAB) of the double-layer absorber reaches 5.92 GHz (12.08 ∼ 18 GHz) with the thickness of the two layers is 0.8 mm and 1.2 mm, respectively. It is 29.8 % wider than the EAB (4.56 GHz) of the single-layer FeSiAl-MoS2-GR/PLA composite with the same thickness.

Ultra-Broadband Absorber with Large Angular Stability Based on Frequency Selective Surface.

In this paper, a low-profile, double-layer absorber with ultra-broadband absorption and large-angle stability is proposed. In order to improve the angular stability, the square ring with concave–convex deformation is designed. It can expand the current path to realize the miniaturization of the absorber, which decreases the influence of oblique incident on absorption. The equivalent circuit model provides detailed resonance and admittance analysis, showing the existence of three resonances working together to achieve broadband absorption. The simulated results illustrate that the designed unit can achieve above 80% absorption within 2.09–18.1 GHz. The angular stability is up to 50° under TE/TM polarization with a period of 0.07 λL (the wavelength of the lowest operating frequency). The 300 mm × 300 mm prototype absorbers were fabricated for demonstration, with a total thickness of 0.096 λL. The measurement results are consistent with the simulated results, which shows that the designed absorber unit can achieve ultra-broadband and large-angle absorption. The performance of devices can be widely applied in infrared detection, radiation refrigeration, and stealth technology.

Construction of string-bead-like spatial conductive network derived from CoFe Prussian blue analogue and carbon nanotube composite for excellent electromagnetic wave absorption

A research hotspot material, Prussian blue analogue (PBA), with low cost, easy synthesis, and MOFs structure, has attracted extensive attention in various fields recently. Especially, with the unique unit of metal nanoparticles embedded into the N-doped carbon shell, its derivative is regarded as a candidate in the electromagnetic (EM) absorption field. In this work, CoFe-CNT-PBA, synthesized by the coprecipitation method, was used as precursor to prepare string-bead-like spatial conductive network which is composited by carbon nanotubes (CNT) concatenating units of magnetic CoFe nanoparticles embedded into N-doped carbon shell. To a great extent, the environmental suitability of metal nanoparticles is improved. The result shows, SB-CoFe@C-CNT0.02-800 with microporous and mesoporous has a minimum reflection loss (RLmin) of −67.82 dB at 13.74 GHz with 2.20 mm, and the effective absorption bandwidth (EAB, RL ≤ −10 dB) is 7.23 GHz (10.77–18 GHz) at 2.07 mm. At last, MATLAB was used to simulate by building a double-layer absorber, and EAB dramatically reaches 8.35 GHz, which covers mostly the X band and the whole Ku band. The strategy, CNT concatenating porous micro-spheres derived from PBA, induces conduction loss and interface polarization loss, and provides novel and meaningful thinking for the construction of an excellent electromagnetic wave absorption composite.

Development of high-efficient double-layer microwave absorbers based on 3D cabbage-like CoFe2O4 and cauliflower-like polypyrrole

Because of the widespread use of wireless communication and electronic devices, electromagnetic radiation has become a global environmental pollutant. Therefore, finding excellent microwave absorbers (MAs) with appropriate magnetic loss and dielectric loss matching is an urgent assignment. In this work, we successfully fabricated 3D architectures of cabbage-like CoFe2O4 (CFO) and cauliflower-like polypyrrole (PPy) as MAs. Firstly, the microwave dissipation features of bare CFO and PPy single-layer absorbers were evaluated, which showed no value for effective absorption bandwidth (EAB) and poor values for reflection loss (RL). Then, the microwave dissipation features of double-layer CFO and PPy absorbers were simulated, which showed good values of RL and EAB in the case of CFO as the lower (absorption) layer and PPy as the upper (matching) layer, named as CFO/PPy. Among the CFO/PPy double-layer absorbers, the CFO-1 mm/PPy-1.3 mm showed the best RL of −19 dB and EAB of 3.8 GHz. The real CFO-1 mm/PPy-1.3 mm double-layer absorber was prepared and evaluated for its microwave dissipation features, which showed the RL and EAB values of −17.5 dB and 4.2 GHz, respectively. The real and simulation RL and EAB values were close to each other. In particular, the EAB of the real CFO-1 mm/PPy-1.3 mm could be covered across the whole X band frequency range. The better microwave dissipation features of CFO/PPy double-layer absorbers than the bare CFO and PPy single-layer absorbers could be attributed to better impedance matching capability and coupling interaction between the distinctive layers. Overall, this work provided a new method to manufacture excellent (MAs) for the X band frequency range.

Optical, electromagnetic and physiochemical properties of flower-like MoS2 (D) and Ni microsphere (M) based absorbers for X and Ku band applications

Currently, absorbing materials with thin thickness, lightweight, and strong absorption are required to reduce electromagnetic pollution. Flower-like MoS2 (D) and Ni microsphere (M) with MoS2 (D/M) absorbers were successfully fabricated via hydrothermal and solvothermal methods. Structural, physiochemical, elemental, and magneto-optical studies of the D and D/M samples were evaluated. The bandgap for M, D, and D/M composite is 2.56 eV, 3.1 eV, and 3.7 eV respectively. Morphological studies confirm the shape of the Ni microsphere and flower-like structure of the MoS2 composite. D and D/M composite show synergistic performance in terms of effective bandwidth, absorption, and reflection loss. The RL from D is −24.5 dB for 1.5 mm thickness whereas the D/M sample shows −9 dB at 2.5 mm thickness. Double layer absorbers of D and D/M were simulated using CST software. The lower/upper layer of D and D/M with 1.5 mm lower and 0.5 mm upper layers’ arrangement depicted minimum reflection loss and depicted their use for Ku band application. Therefore, D and D/M composites with thin thickness and minimum reflection loss might be suggested for application in microwave absorption.

Design of Double-Layer Absorbers Based on Co2y@C Core-Shell Nanofibers and Carbon Nanofibers for High-Efficient and Tunable Microwave Absorption

Design of Double-Layer Absorbers Based on Co2y@C Core-Shell Nanofibers and Carbon Nanofibers for High-Efficient and Tunable Microwave Absorption

Boosted microwave dissipation performance via integration of magneto/dielectric particles with hierarchical 3D morphology in bilayer absorber

In this study, X-band bilayer absorber was designed based on integration of magneto/dielectric phases particles with hierarchical 3D morphology. Pure CoFe2O4, SrFe12O19 and NiO as magnetic and dielectric components with unique 3D morphology were developed via facile chemical method. Morphological evaluations confirmed the formation of hierarchical structure of CoFe2O4 (Co), SrFe12O19 (Sr) and NiO (NiO) with crochet ball, brain-coral and rose-flower-like particles morphology, respectively. In the first step, the synthesized Co and Sr particles were physically blended with 1:1 wt ratio (SC). In a second step, the as-prepared SC composite mixed with NiO powder with 1:1 wt ratio (SCN). The reflection loss simulations of bilayer absorbers with total thickness of 2 mm were performed via CST Studio software based on the electromagnetic characteristics of as-prepared resin base SC and SCN composite monolayer absorbers. The optimized bilayer absorber in which SCN composite placed as matching layer with 1.5 mm thickness and SC composite placed as absorbing layer with 0.5 mm thickness exhibited a minimum reflection loss value of −21.43 dB at 10.8 GHz matching frequency, with 3.2 effective absorption bandwidth and a loading percentage as low as 20 w%. The aforementioned results indicated that tailoring the configuration of particle morphology along with tuning optimal layers thickness could be a rational way to reach considerable absorption bandwidth in double layer absorber. The improvement in microwave dissipation performance is linked to various parameters such as defect induced dipole polarization, multiple scatterings and reflections between particles and pores, coupling interactions between layers, promotion of interfacial polarization, etc.

Estimation of Microwave Absorption Properties of RGO-SiC-LLDPE Composites

The present work investigate the microwave absorption properties of reduced graphene oxide (RGO)-Silicon carbide (SiC)-Linear low-density polyethylene (LLDPE) composites prepared in different concentration of fillers(10, 20, 30, 40 wt. %) with LLDPE matrix. Synthesis of RGO is confirmed from XRD analysis and SiC is used as received from supplier. Complex permittivity of the composites is measured using Nicolson Ross method showing an increasing trend with increasing filler concentrations with maximum and for 40 wt. % composite sample. Based on transmission line theory and using measured value of complex permittivity, conductor backed single and double layer absorber is designed by thickness optimization. The calculated reflection loss (RLc) value of ~-71 dB at 11.23 GHz is observed for 40 wt. % composite sample of 7 mm thickness with -10 dB absorption bandwidth of 1.48 GHz and -20 dB bandwidth of 0.64 GHz.

Thickness optimization of a double-layered microwave absorber combining magnetic and dielectric particles

The purpose of this study is to optimize the thickness of the double-layered microwave absorber for obtaining the highest absorption. The graphenic-based carbon compounds and Fe3O4 magnetic particles were combined to fabricate the double-layered absorber. The thickness was optimized by employing a genetic algorithm (GA) to obtain high reflection loss values. These samples at a thickness of 2 mm were measured for reflection loss (RL) with a Vector Network Analyzer (VNA). Input variables, such as relatively complex permeability and relatively complex permittivity, were obtained using a conversion program that uses Nicolson-Ross-Weir (NRW) method from VNA S-parameter values (S11 and S21) data. By entering the permeability and permittivity of the complex relative to GA, the thickness can be optimized to produce high value. Optimization of the double-layer thickness of 12 absorbers produces the optimum thickness of = 5.99 mm and = 0.87 mm among the materials combination, which results in a high (−44.69 dB). This optimization is very important for designing double-layer radar absorbing material (RAM) which results in high values.

Effect of filler loading and thickness parameters on the microwave absorption characteristic of double-layered absorber based on MWCNT/BaTiO3/pitted carbonyl iron composite

In this work, single- and double-layer electromagnetic wave absorbers were prepared by as-prepared MWCNTs/BaTiO3/pitted carbonyl iron composites. MWCNT/BaTiO3 (MW/BTO) was prepared via sol-gel method whereas the carbonyl iron particles (CI) were corroded via pitting corrosion method. The structural, microstructural, magnetic and microwave absorption properties of the composites were evaluated via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA) methods. CST studio software was employed to simulate the microwave absorption characteristics of double-layer absorbers. Moreover, the effects of changing matching and absorbing layer thickness (3 mm in total) and filler loading (10, 20 and 30 wt%) of the as-prepared composite on the microwave absorption properties were investigated. According to the results, maximum RL value for single layer absorber with 20 wt% filler loading can reach −11.5 dB at 9.7 GHz with 3 mm thickness and 0.4 GHz bandwidth. In contrast, double-layered absorber using 10 wt% of the composite in the upper layer (as matching layer) and 30 wt% of the composite in lower layer (as absorbing layer) can increase the reflection loss and absorption bandwidth values to −15.5 dB and 1 GHz respectively. Improving in absorption characteristics can be attributed to coupling interactions, impedance matching and multiple scattering. The main advantages of the prepared double layer absorber than single layer absorber are tuning the intensity and effective absorption bandwidth by adjusting the layer order, thickness and filler loading of each layer which shown good potential for practical application.