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HighlightsA general method was developed to fabricate a series of honeycomb-like N-doped nanocarbons (3D M–NxC) doped with metal single atoms (Mn, Fe, Co, Cu, or Ni) with a high yield.The intrinsic dielectric properties of 3D M–NxC were identified for the first time at the atomic-level, revealing that the introduction of metal single atoms greatly increases both conductive loss and polarization loss.3D Mn–NC exhibited high-performance electromagnetic wave absorption at a low filler loading of 10 wt% outperforming most reported absorbers.Atomically dispersed metals on N-doped carbon supports (M–NxCs) have great potential applications in various fields. However, a precise understanding of the definitive relationship between the configuration of metal single atoms and the dielectric loss properties of M–NxCs at the atomic-level is still lacking. Herein, we report a general approach to synthesize a series of three-dimensional (3D) honeycomb-like M–NxC (M = Mn, Fe, Co, Cu, or Ni) containing metal single atoms. Experimental results indicate that 3D M–NxCs exhibit a greatly enhanced dielectric loss compared with that of the NC matrix. Theoretical calculations demonstrate that the density of states of the d orbitals near the Fermi level is significantly increased and additional electrical dipoles are induced due to the destruction of the symmetry of the local microstructure, which enhances conductive loss and dipolar polarization loss of 3D M–NxCs, respectively. Consequently, these 3D M–NxCs exhibit excellent electromagnetic wave absorption properties, outperforming the most commonly reported absorbers. This study systematically explains the mechanism of dielectric loss at the atomic level for the first time and is of significance to the rational design of high-efficiency electromagnetic wave absorbing materials containing metal single atoms.

Polymer electrolytes and composites have prevailed in the high performance and mobile marketplace during recent years. Polymer-based solid electrolytes possess the benefits of low flammability, excellent flexibility, good thermal stability, as well as higher safety. Several researchers have paid attention to the optical properties of polymer electrolytes and their composites. In the present review paper, first, the characteristics, fundamentals, advantages and principles of various types of polymer electrolytes were discussed. Afterward, the characteristics and performance of various polymer hosts on the basis of specific essential and newly published works were described. New developments in various approaches to investigate the optical properties of polymer electrolytes were emphasized. The last part of the review devoted to the optical band gap study using two methods: Tauc’s model and optical dielectric loss parameter. Based on recently published literature sufficient quantum mechanical backgrounds were provided to support the applicability of the optical dielectric loss parameter for the band gap study. In this review paper, it was demonstrated that both Tauc’s model and optical dielectric loss should be studied to specify the type of electron transition and estimate the optical band gap accurately. Other parameters such as absorption coefficient, refractive index and optical dielectric constant were also explored.

Fluorinated aromatic polyimide (FAPI) films with rigid polymer backbones have been prepared by chemical imidization approach. The polyimide films exhibited excellent mechanical properties including elastic modulus of up to 8.4 GPa and tensile strength of up to 326.7 MPa, and outstanding thermal stability including glass transition temperature (Tg) of 346.3–351.6 °C and thermal decomposition temperature in air (Td5) of 544.1–612.3 °C, as well as high colorless transmittance of >81.2% at 500 nm. Moreover, the polyimide films showed stable dielectric constant and low dielectric loss at 10–60 GHz, attributed to the close packing of rigid polymer backbones that limited the deflection of the dipole in the electric field. Molecular dynamics simulation was also established to describe the relationship of molecular structure and dielectric loss.

Copper clad laminates (CCLs) with low dissipation factor (Df) are urgently needed in the fields of high-frequency communications devices. A novel resin matrix of modified poly (2,6-dimethyl-1,4-phenylene ether) (MPPE) and styrene-ethylene/butylene-styrene (SEBS) was employed in the fabrication of high-frequency copper clad laminates (CCLs). The composites were reinforced by E-glass fabrics, which were modified with phenyltriethoxysilane (PhTES). The composite laminates obtained exhibited impressive dielectric loss of 0.0027 at 10 GHz when the weight ratio of MPPE to SEBS was 5:1. In order to modify the dielectric constant (Dk), coefficient of thermal expansion (CTE) and other performances of laminates, Li2TiO3 (LT) ceramic powders were introduced into the resin matrix. The composite laminates showed low dielectric loss of 0.0026 at 10 GHz and relatively high flexural strength of 125 MPa when the mass ratio of LT fillers to resin is 0.4. Moreover, the composite laminates all maintain low water uptake (<0.5%). The microstructure and thermal properties of composite laminates filled with LT ceramic powders were also tested. These results show that copper clad laminates prepared with modified polyphenylene ether (MPPE)/SEBS and LT ceramic fillers have strong competitiveness to fabricate printed circuit boards (PCBs) for high-frequency and high-speed applications.

A broadband microwave composite metamaterial absorber based on the Debye model, consisting of triple dielectric loss layers and different-ordered metallic fractal pattern vertical layers, has been proposed. The research results show that when all the three dielectric layers are silicon carbide fiber (SiC f ), the composite absorber presents two intense absorption bands with a bandwidth of 5.44 GHz. The length ( l ) of the metallic pattern and thickness ( t ) of the top dielectric layer can effectively regulate the reflection loss performance. Additionally, the effective absorption bandwidth increases to 13.44 GHz when the relative absorption bandwidth reaches about 119.15% by replacing SiC f at the top dielectric layer with the dielectric loss materials which satisfy the Debye model. The research results show that the absorption bandwidth obviously increases with dielectric loss materials of distinct Imε. Furthermore, the proposed fractal pattern shows robustness to the variation of complex permittivity spectrum, expanding the range of suitable dielectric materials for composite broadband metamaterial absorbers.

Flexible microwave absorber (MAR), vital in advanced applications such as wearable electronics and precision devices, are highly valued for their lightweight, exceptional electromagnetic waves (EWs), and ease of fabrication. However, optimizing the electromagnetic parameters of microwave absorption materials (MAMs) to enhance absorption ability and expand effective absorption broadband (EAB, reflection loss (RL) <−10 dB) is a considerable challenge. Herein, a permittivity‐attenuation evaluation diagram (PAED) is constructed using parameter scanning based on the Materials Genome Initiative to determine the ideal electromagnetic parameters and thickness, optimize absorption efficiency, and obtain highly efficient absorbers. Guided by the PAED, a multilayer MAR consisting of a “matching‐absorption‐reflection layer” and a dielectric loss gradient aligned with the direction of EWs propagation is developed. This design significantly enhances the EWs penetration and ensures effective absorption, attributed to the well‐matched impedance and attenuation characteristics. As anticipated, the microwave absorption of the absorber (density = 0.063 g cm−3) is optimized, with an RL of −34 dB at d = 4 mm and an EAB covering the entire X‐band (8.2–12.4 GHz). This study presents a novel approach for establishing a material database for MAMs and developing high‐performance absorbers characterized by thinness, lightness, broad operational frequency range, and robust absorption capacity. The ideal microwave absorption curve obtained by parametric simulation can guide the rapidly screening of suitable materials for the preparation of efficient microwave absorption materials. It provides a new method for rapidly developing high‐performance microwave absorbers with thin thickness, lightweight, wide operating frequency range, and strong microwave absorption capabilities.

In this paper, an Improved Pelican Optimization Algorithm (IPOA) was proposed to optimize a BP neural network model to predict the dielectric loss factor of wood in the RF heating and drying process. The neural network model was trained and optimized using MATLAB 2022b software, and the prediction results of the BP neural network with POA-BP and IPOA-BP models were compared. The results show that the IPOA-optimized BP neural network model is more accurate than the traditional BP neural network model. After the BP neural network model with IPOA optimization was used to predict the dielectric loss factor of wood, the value increased by 4.3%, the MAE decreased by 68%, and the RMSE decreased by 67%. The results provided by the study using the IPOA-BP model show that the prediction of the dielectric loss factor of wood under different macroscopic conditions in radio frequency heating and drying of wood can be realized without the need for highly costly and prolonged experimental studies.

CdS is one of the most important II–VI semiconductors with applications in solar cells, optoelectronics and electronic devices. CdS nanoparticles were synthesized by the wet chemical method. The crystal structure and grain size of the particles were determined by X-ray diffraction. The optical properties were studied by the ultraviolet–visible absorption spectrum. The dielectric properties of CdS nanoparticles were studied in the frequency range of 50 Hz–5 MHz at different temperatures. The frequency dependence of the dielectric constant and dielectric loss is found to decrease with an increase in the frequency at different temperatures. The dielectric properties of CdS nanoparticles are found to be significantly enhanced specially in the low frequency range due to confinement. Further, electronic properties, such as valence electron plasma energy, average energy gap or Penn gap, Fermi energy and electronic polarizability of the CdS nanoparticles were calculated. The AC electrical conductivity measurements reveal that the conduction depends on both the frequency and the temperatures.

Polymer composites with high dielectric permittivity (>10) and low dielectric loss are critical for energy storage and microelectronic applications. This study reports on a semi-transparent composite of a PVDF copolymer filled with Cu7S4 nanoparticles synthesized via a wet chemical route. Only a small content (6%) of copper sulfide increases the dielectric permittivity of the material from 10.4 to 15.9 (1 kHz), maintaining a low dielectric loss coefficient (less than 0.1). The incorporated nanoparticles affect the morphology of the composite film surface and crystalline phases in the whole volume, which was studied with FTIR spectroscopy, differential scanning calorimetry and scanning probe microscopy.

With increasing demands for data transfer, the production of components with low dielectric loss is crucial for the development of advanced antennas, which are needed to meet the requirements of next-generation communication technologies. This study investigates the impact of a variation in energy density on the part properties of a low-loss cyclic olefin copolymer (COC) in the SLS process as a way to manufacture complex low-dielectric-loss structures. Through a systematic variation in the laser energy, its impact on the part density, geometric accuracy, surface quality, and dielectric properties of the fabricated parts is assessed. This study demonstrates notable improvements in material handling and the quality of the manufactured parts while also identifying areas for further enhancement, particularly in mitigating thermo-oxidative aging. This research not only underscores the potential of COC in the realm of additive manufacturing but also sets the stage for future studies aimed at optimizing process parameters and enhancing material formulations to overcome current limitations.