Absorption Characteristics of ?/4 EM Wave Absorber with Frequency-Selective Operation

Generally, a silicone rubber and a chlorinated polyethylene(CPE) have been used as a binder for the development of high-performance composite EM(Electro Magnetic) wave absorbers. In this paper, the EM wave absorption performance of natural lacquer, which is newly proposed as a binder was investigated. The prepared MnZn ferrite EM wave absorbers are mixed with natural lacquer showed excellent EM wave absorption characteristics compared with MnZn ferrite EM wave absorbers which are mixed with the conventional binders. MnZn ferrite EM wave absorbers mixed with natural lacquer were prepared and their absorption ability was also investigated The EM wave absorbers are fabricated in different proportions of MnZn, or NiZn ferrite and natural lacquer, and their reflection coefficients are measured. The permittivity and permeability are calculated by using the measured reflection coefficients. The EM wave absorption abilities are calculated according to different thicknesses of the EM wave absorbers.

Electromagnetic wave absorption properties of Ni0.5Zn0.5Fe2O4–BaTiO3–epoxy composites

Novel magnetic silicate composite for lightweight and efficient electromagnetic wave absorption

A quantitative permittivity model for designing electromagnetic wave absorption materials with conduction loss: A case study with microwave-reduced graphene oxide

In this paper, we designed and fabricated an electromagnetic(EM) wave absorber for automotive radar in cars using <TEX>$TiO_2$</TEX> as a dielectric material and chlorinated polyethylene(CPE) as a binder. First of all, we confirmed that the optimum composition ratio of <TEX>$TiO_2$</TEX> was about 70 wt.%. The complex relative permittivity of a sample containing <TEX>$TiO_2$</TEX>: CPE=70:30 wt.% was calculated from S-parameter. The EM wave absorption abilities were simulated for the EM wave absorbers of different thickness using the calculated relative permittivity, and the EM wave absorber was manufactured based on the simulated design. A comparison of simulated and measured results is in good agreement. Measurement shows that a 1.85 mm thick absorber has absorption ability higher than 20 dB in the frequency range of <TEX>$76{\sim}77$</TEX> GHz for automotive radars.

EM waves absorption properties of nitrogenous porous carbon derived from PANI fiber clusters carbonization

In recent years, researches on electromagnetics (EM) wave absorber have been intensively investigated for numerous applications. One of essential issues in the EM wave absorber is the deficiency in its performance particularly bandwidth and absorption characteristics. In this paper, a multilayer EM wave absorber composed of metasurface is studied for X-band application. The utilization of metasurface and multilayer structures is aimed to enhance the characteristics of absorber in bandwidth and absorption performances. The structure of metasurface is configured by combining split ring resonator (SRR) and narrow thin strip deployed on different layers of 0.8mm thick FR4 epoxy dielectric substrate. The proposed EM wave absorber is characterized through its unit cell with the dimension of 3.80mm × 3.80mm. Some attempts by inserting another layer with varied thickness between the SRR layer and the narrow thin strip layer is performed to investigate the absorber characteristics. The characterization result shows that the insertion of another layer could improve the characteristics of proposed EM wave absorber.

Rational heterostructure design can bring interfacial polarization relaxation to significantly enhance the electromagnetic wave (EMW) absorption performance. However, intelligently building a homogeneous heterostructure with superior EMW absorption properties remains a great challenge. Herein, a typical conductive metal–organic framework Cu3(HHTP)2 (hexahydroxytriphenylene, HHTP) is delicately packed onto a polypyrrole (PPy) conductive polymer surface via a one‐step in situ polymerization approach. Results show that Cu3(HHTP)2 is well packed on the PPy surface to form an elegant Cu3(HHTP)2@PPy hybrids interfacial microstructure with a unique superiority regarding EMW absorption compared with single components of PPy and Cu3(HHTP)2. Interestingly, the interfacial microstructure of Cu3(HHTP)2@PPy hybrids can be tuned by adjusting the composition of the PPy and Cu3(HHTP)2, resulting in the improvement of impedance matching, conductive loss, and enhancement of interfacial polarization relaxation, endowing the optimization of the EM wave absorption properties of the Cu3(HHTP)2@PPy. The broad effective absorption bandwidth covers a range as broad as 6.68 GHz (11.00–17.68 GHz), which is higher than most reported metal‐organic frameworks (MOFs) and conductive polymer‐based EM absorbing materials. Herein, new insight for developing highly efficient EMW absorption materials through hybridized interfacial microstructure engineering is provided.

In this study, the electromagnetic (EM) wave absorption properties of a two-layered structure composed of La0.7Sr0.3MnO3-epoxy (10 wt.%) (LSMO) and SrFe9.5Co1.25Ti1.25O19-epoxy (10 wt.%) (SFCTO), both exhibiting distinct high-frequency magnetic and dielectric properties, were investigated using a High Frequency Simulation Software (HFSS) simulation tool. LSMO had a high dielectric constant (ε' &gt;30) within the measurement range (0.1-18 GHz), indicating that dielectric loss mechanisms primarily contribute to EM wave absorption. In contrast, SFCTO is a material capable of significantly absorbing EM waves near 10 GHz due to ferromagnetic resonance (FMR). The simulations were validated by comparing the measured and simulated reflection losses (RL) of an unpatterned LSMO/SFCTO bilayer. The RL spectra were examined by varying the layer thickness and pattern size in three configurations: a continuous LSMO/SFCTO structure, a cross-patterned LSMO on SFCTO, and a square-patterned LSMO on SFCTO. In the continuous LSMO/SFCTO structure, tunable absorption frequency bands were achieved by adjusting the layer thickness. However, it was difficult to achieve broadband absorption due to the reflective characteristics of the high dielectric LSMO layer. The cross-patterned LSMO structure on SFCTO demonstrated broader bandwidth absorption, with layer thickness being more influential than pattern width. The square-patterned LSMO on SFCTO exhibited the best broadband EM wave absorption (max Δf = 7.39 GHz). These results suggest that broader absorption is achievable by partially covering the high-dielectric layer with patterns on a hexaferrite sheet.

For wider‐band and stronger electromagnetic (EM) wave absorption, macroporous short carbon fibers/mullite matrix (C f /Mu) composites were prepared via introducing short carbon fibers (0, 0.7, and 1.3 vol%) with length of 2‐3 mm into macroporous mullite ceramic by gel‐casting. The density of as‐prepared C f /Mu composites decreases from 2.93 g/cm 3 to 2.74 g/cm 3 , while the porosity increases from 3.32% to 10.76% with the rise in carbon fibers content. The diameter of macropores in C f /Mu composites is ranging from several microns to tens of microns. Complex permittivity and dielectric loss of the prepared composites in X‐band (8.2‐12.4 GHz) are significantly enhanced with increased carbon fibers content. The best EM wave absorption performance is obtained in the macroporous C f /Mu composites containing only 0.7 vol% carbon fibers (C f /Mu‐0.7). The maximum absorption loss of C f /Mu‐0.7 is −38.3 dB at 12.08 GHz at the thickness of 2.1 mm, and effective absorption bandwidth below −10 dB (over 90% of EM wave absorption) covers the whole X band with the thickness of 2.35 mm. The results suggest that the C f /Mu composites can be promising high‐performance EM wave absorbing materials.

Electromagnetic (EM) wave absorption materials have drawn a lot of attention because they can effectively reduce EM wave pollution from electronic equipment. In this work, we combined ZrO2 nanoparticles with multi-walled carbon nanotubes (MWCNTs) and explored applications of MWCNT/ZrO2 composites in EM wave absorbing field. ZrO2 nanoparticles with a high crystalline were synthesized by one-step hydrothermal method. Adding MWCNTs in this hydrothermal process, ZrO2 nanoparticles aggregated together to form uneven lumps and wraps on MWCNTs surfaces. MWCNTs improved the conductivity loss and electron polarization capability of composites. The minimum reflection loss (RL) of MWCNT/ZrO2 composites reached [Formula: see text]39.73 dB at a thickness of 2[Formula: see text]mm. Such excellent EM wave absorption properties are attributed to the dielectric loss, dipole polarizations and interfacial polarizations. This composite can be a promising candidate as high efficiency EM wave absorption material and used for commercial production because of the simple synthesis methods.

The evolution of sixth-generation wireless communications demands advanced metasurfaces capable of precise beam steering and adaptive electromagnetic (EM) wave absorption to enhance signal quality and mitigate interference. In this work, we present a programmable and reconfigurable digital THz-metasurface, engineered through the integration of metal patch, graphene wire grid, and a vanadium dioxide (VO2)-based square ring to switch between dynamic beam steering (ON-state) and EM wave absorption (OFF-state). In the former state, without physically altering the patch dimensions to create a required phase gradient in the metasurface, here the idea of digitally increasing the patch dimensions only by changing the crystallization level of the VO2 ring is proposed. Consequently, a programmable and reconfigurable coding metasurface by digitally changing the arrangement of coding sequence is achieved that can shift the mainlobe of the reflected EM wave from 0° to 40°. Remarkably, in the OFF-state, a dual-band EM wave absorption is observed based on a dual mechanism including tunable crystallinity level of the VO2 ring, and the Fermi energy of the patterned graphene. In addition, in the OFF-state, the performance of the absorber is investigated by increasing the angle of incidence. The results of detailed full-wave simulations are compared and verified by analytical modeling based on an array antenna theory and an equivalent electric circuit model. The presented structure is a strong candidate for integration into future Reconfigurable Intelligent Surfaces platforms, sensing and imaging systems in the THz band.

A glass-like carbon-wrapped Y2Si2O7 core-shell structure for improving electromagnetic wave absorption

Developing intelligent electromagnetic wave (EMW) absorption materials with real‐time response‐ability is of great significance in complex application environments. Herein, highly compressible Fe@CNFs@Co/C elastic aerogels were assembled through the electrospinning method, achieving EMW absorption through pressure changes. By varying the pressure, the effective absorption bandwidth (EAB) of Fe@CNFs@Co/C elastic aerogels shows continuous changes from low frequency to high frequency. The EAB of Fe@CNFs@Co/C elastic aerogels is 14.4 GHz (3.36–17.76 GHz), which covers 90% of the range of S/C/X/Ku bands. The theoretical simulation indicates that the external pressure prompts a reduction in the spacing between the fiber layers in the aerogels and facilitates the formation of a 3D conductive network with enhanced attenuation ability of EMW. The uniform distribution of metal particles and appropriate layer spacing can effectively optimize the impedance matching to achieve the best EMW absorption performance. This work state clearly that the hierarchically assembled elastic aerogels composed of metal–organic frameworks (MOFs) derivatives and carbon fibers are ideal dynamic EMW absorption materials for intelligent EMW response.image

Although microstructure optimization is an effective strategy to improve and regulate electromagnetic wave (EMW) absorption properties, preparing microwave absorbents with enhanced EMW absorbing performance and tuned absorption band by a simple method remains challenging. Herein, ZnIn2S4/reduced graphene oxide (rGO) composites with flower-like and cloud-like morphologies were fabricated by a convenient hydrothermal method. The ZnIn2S4/rGO composites with different morphologies realize efficient EMW absorption and tunable absorption bands, covering a wide frequency range. The flower-like structure has an optimal reflection loss (RL) of up to -49.2 dB with a maximum effective absorption bandwidth (EAB) of 5.7 GHz, and its main absorption peaks are concentrated in the C and Ku bands. The minimal RL of the cloud-like structure can reach -36.3 dB, and the absorption peak shifts to the junction of X and Ku bands. The distinguished EMW absorption capacity originates from the uniquely optimized microstructure, complementary effect of ZnIn2S4 and rGO in dielectric constant, and synergy of various loss mechanisms, such as interfacial polarization, dipole polarization, conductive loss, and multiple reflections. This study proposes a guide for the structural optimization of an ideal EMW absorber to achieve efficient and tunable EMW absorption performance.