Atomic-scale gradual architecture in conductive metal-organic frameworks for microwave absorption.

Metal-organic frameworks (MOFs) manifest enormous potential in promoting electromagnetic wave (EMW) absorption thanks to the tailored components, topological structure, and high porosity. Herein, rodlike conductive MOFs (cMOFs) composed of adjustable metal ions of Zn, Cu, Co, or Ni and ligands of hexahydroxytriphenylene (HHTP) are prepared to attain tunable dielectric properties for a tailored EMW absorption. Specifically, the influences of the cMOFs' composition, charge transport characteristic, topological crystalline structure, and anisotropy microstructure on dielectric and EMW absorption performance are ascertained, advancing the understanding of EMW attenuation mechanisms of MOFs. The boosted conductive and polarization losses derived from the conjugation effects and terminal groups, as well as shape anisotropy, lead to a prominent EMW absorption of the cMOFs. The Cu-HHTP confers a minimum reflection loss (RLmin) of -63.55 dB at the thickness of 2.9 mm and a maximum effective absorption bandwidth of 5.2 GHz. Moreover, Zn-HHTP showcases the absorption superiority in the S-band (2-4 GHz) with an RLmin of -62.8 dB at a thickness of 1.9 mm. This work not only hoists the mechanistic understanding of the structure-function relationships for the cMOFs but also offers guidelines for preparing functional MOF materials.

Conductive metal-organic frameworks (cMOFs) with π-d conjugation that can effectively promote the transport and migration of free electrons and improve electrical conductivity are considered as potential high-efficiency electromagnetic wave (EMW) absorption materials. However, the microstructural regulation of cMOFs with highly efficient EMW absorption remains a challenge due to the complexity of organic ligands and the uncontrollability of self-assembly reactions. Herein, two distinctly different microstructures or morphologies of Ni-TABQ cMOFs are synthesized by assembling the 2,3,5,6-tetraaminobenzoquinone (TABQ) ligands and Ni2+ ions through the manipulation of different reaction environments. The synergistic effect between the intrinsic conductivity and bulk microstructure of the obtained Ni-TABQ-1 optimizes electromagnetic parameters, displaying outstanding EMW absorption performance, with an RLmin value of -62.68 dB at 2.94 mm and an EAB of 5.12 GHz. These results demonstrate that the microstructural and conductivity control of cMOFs could offer an accessible and positive guide to developing superior EMW absorption materials.

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.

Synthesis and electromagnetic wave absorption performances of a novel (Mo0.25Cr0.25Ti0.25V0.25)3AlC2 high-entropy MAX phase

Development of multiscale Fe/SiC–C fibrous composites for broadband electromagnetic and acoustic waves absorption

Conduction and polarization are known to profoundly impact conductive metal-organic frameworks (c-MOFs) for their applications in electromagnetic wave (EMW) absorption. Albeit a few advances along c-MOF platforms in enhancing their EMW absorption performances, reticular modulation-led inter/intra-layer conduction and polarization loss remains an unmet challenge. To address this, a ligand substitution-guided bottom-up structural control strategy is introduced to study the depth of reticular modulation-led inter/intra-layer conduction and polarization loss in c-MOFs under an electromagnetic (EM) field. A family of triphenylene-X ligands (X = -NH2, -OH, and -SH) is harnessed to afford an isoreticular family of three Cu-based c-MOFs. Thanks to the distinct Cu─X bonds, such a platform allowed to systematically study the synergistic features of conduction and polarization loss in EMW absorption enhancement. One of the trio, Cu3(HITP)2 (X = -NH2; HITP, 2,3,6,7,10,11-hexahydroxytriphenylene) is identified with an optimal EM loss capacity under the EM field, achieving a record-high reflection loss of -63.03dB in the effective absorption range of 3-18GHz band. Setting up a new benchmark for EM loss among c-MOFs, this study introduces a way to leverage control in the charge mobility characteristics of Cu─X bonds relative to the dielectric losses at both molecular and atomic scales.

Porous materials emerging as potential high‐efficiency electromagnetic (EM) wave absorbers confront a critical trade‐off between impedance matching and attenuation capability. In this study, a versatile strategy is reported to overcome this challenge by constructing gradient pores via solvent‐assisted linker exchange for the fabrication of metal‐organic framework (MOF) derived Fe/Fe 3 Co 7 /Co/C composites with high porosity. The impedance and attenuation characteristics of single‐pored and gradient‐pored derivatives are investigated through combined experimental and simulation approaches. Simulated space EM field, loss density, and Smith charts reveal significantly enhanced EM interactions and optimized impedance within the pores. Compared to individual MOF derivatives, the gradient derivative exhibits improved impedance matching from the large‐pored shell and superior attenuation capability from the small‐pored core, giving rise to a Pareto improvement in EM absorption with strong reflection loss (−64.7 dB) and wide effective adsorption bandwidth (5.8 GHz) at a thickness of 2.5 mm. This work not only advances a novel gradient pore strategy for constructing efficient absorbers with enhanced impedance matching and attenuation capability, but also sheds light on the underlying mechanisms of EM interaction with varied porosity, offering insights for extended designs in magnetic, electric and optic devices.

It is well known that in low-dimensional systems, the motion of electrons is restricted. The confinement of electron in these systems has changed the electron mobility remarkably. This has resulted in a number of new phenomena, which concern a reduction of sample dimensions. These effects differ from those in bulk semiconductors, for example, electronphonon interaction effects in two-dimensional electron gases (Mori & Ando, 1989; Rucker et al., 1992; Butscher & Knorr, 2006), electron-phonon interaction and scattering rates in one-dimensional systems (Antonyuk et al., 2004; Kim et al., 1991) and dc electrical conductivity (Vasilopoulos et al., 1987; Suzuki, 1992), the electronic structure (Gaggero-Sager et al., 2007), the wave function distribution (Samuel & Patil, 2008) and electron subband structure and mobility trends in quantum wells (Ariza-Flores & Rodriguez-Vargas, 2008). The absorption of electromagnetic wave in bulk semiconductors, as well as low dimensional systems has also been investigated (Shmelev et al., 1978; Bau & Phong, 1998; Bau et al., 2002; 2007). However, in these articles, the author was only interested in linear absorption, namely the linear absorption of a weak electromagnetic wave has been considered in normal bulk semiconductors (Shmelev et al., 1978), the absorption coefficient of a weak electromagnetic wave by free carriers for the case of electron-optical phonon scattering in quantum wells are calculated by the Kubo-Mori method in quantum wells (Bau & Phong, 1998) and in doped superlattices (Bau et al., 2002), and the quantum theory of the absorption of weak electromagnetic waves caused by confined electrons in quantumwires has been studied based on Kubo’s linear response theory andMori’s projection operator method (Bau et al., 2007); the nonlinear absorption of a strong electromagnetic wave by free electrons in the normal bulk semiconductors has been studied by using the quantum kinetic equation method (Pavlovich & Epshtein, 1977). However, the nonlinear absorption problem of an electromagnetic wave, which has strong intensity and high frequency, in low dimensional systems is still open for study. In this book chapter, we study the nonlinear absorption of a strong electromagnetic wave in low dimensional systems (quantumwells, doped superlattices, cylindrical quantumwires and rectangular quantum wires) by using the quantum kinetic equation method. Starting from the kinetic equation for electrons, we calculate to obtain the electron distribution functions in low dimensional systems. Then we find the expression for current density vector and the nonlinear absorption coefficient of a strong electromagnetic wave in low dimensional The Nonlinear Absorption of a Strong Electromagnetic Wave in Low-dimensional Systems

Precursor infiltration and pyrolysis cycle-dependent mechanical and microwave absorption performances of continuous carbon fibers-reinforced boron-containing phenolic resins for low-density carbon-carbon composites

Structural modification of mesoporous lanthanum oxide into 3D coral-like and nano needle-like structure for effective broadband microwave absorbing materials☆

16 - Defects engineering in metal oxides for gas sensing and electromagnetic wave absorption

Excellent electromagnetic wave loss and impedance matching are typical characteristics of superior‐performance electromagnetic wave (EMW) absorption materials. Changing the component ratios and multidimensional combinations of various absorbing materials is one of the best methods to improve absorption performance. This work used a convenient physical mixing approach to combine three wave‐absorbing materials with various dimensions to successfully prepare Graphene/carbon nanotubes/Fe3O4 (G/C/Fe3O4)/paraffin composites. One‐dimensional (1D) tube carbon nanotubes (CNTs) pierced two‐dimensional (2D) sheet graphene to form a strong three‐dimensional (3D) conductive network, enhancing interfacial polarization without introducing zero‐dimensional (0D) magnetic Nano‐Fe3O4. Nevertheless, because of their significant dielectric characteristics, the graphene/carbon nanotube (G/C) paraffin composites displayed low impedance matching and electromagnetic wave absorption properties. At a mass ratio of 1:1, the G/C/paraffin composites achieved an ideal reflection loss (RL) of −11.99 db and an impedance matching value of 0.59. Adding Fe3O4 improved the impedance matching and electromagnetic wave loss performance and promoted the formation of a non‐homogeneous interface, improving interfacial polarization and reflection. The G/C/Fe3O4/paraffin composite, with a mass ratio of 1:1:6 and a filler ratio of 20%, achieved an optimum reflection loss of −37.2 dB and an effective absorption bandwidth of 4.16 GHz. This work optimized and improved the performance of EMW materials practically and rapidly, providing a research method for the widespread application of superior‐performance electromagnetic wave absorption materials.Highlights The EMW absorption materials with various architectures. 1D CNTs pierced 2D sheet graphene to form a strong 3D conductive network. Adding Fe3O4 promoted the formation of a non‐homogeneous interface. Electromagnetic synergies and different structural combinations It achieved excellent impedance matching and electromagnetic loss performance.

In this paper, we use Permalloy and CPE (Permalloy: CPE=70:30 wt.%) to fabricate the electromagnetic (EM) wave absorber for W-band radars. The EM wave absorption abilities at different thicknesses were simulated using material properties of the EM wave absotber, and an EM wave absorber was manufactured based on the simulated design. The comparisons of simulated and measured results show good agreement. Measurements show that a 1.15 mm thick EM wave absorber has absorption ability higher than 18 dB at 94 GHz for missile guidance radars, and a 1.4 mm EM wave absorber has absorption ability higher than 20 dB at 76 GHz for collision-avoidance radars.

We have studied the absorption, reflection, and transmission of electromagnetic waves in an unmagnetized uniform plasma layer covering a metal surface in atmosphere conditions. Instead of the absorption of the electromagnetic wave propagating only once in previous work on the plasma layer, a general formula of total power absorption by the plasma layer with an infinite time of reflections between the atmosphere-plasma interface and the metal surface has been derived for the first time. Effects of plasma parameters, especially the dependence of the fraction of positive ions, negative ions and electrons in plasmas on the power absorption processes are discussed. The results show that the existence of negative ions significantly reduces the power absorption of the electromagnetic wave. Absorptions of electromagnetic waves are calculated.

Outstanding electromagnetic wave absorption performance of polyacrylonitrile-based ultrahigh modulus carbon fibers decorated with CoZn-bimetallic ZIFs