Synthesis and Microwave Absorbing Properties of Porous One-Dimensional Nickel Sulfide Nanostructures

Progress in microwave absorbing materials: A critical review

Microwave-absorbing materials play a significant role in various applications that involve the attenuation of electromagnetic radiation. This critical review article provides an overview of the progress made in the development and understanding of microwave-absorbing materials. The interaction between electromagnetic radiation and absorbing materials is explained, with a focus on phenomena such as multiple reflections, scattering, and polarizations. Additionally, types of losses that affect the performance of microwave absorbers are also discussed, including dielectric loss, conduction loss, relaxation loss, magnetic loss, and morphological loss. Each of these losses has different implications for the effectiveness of microwave absorbers. Further, a detailed review is presented on various types of microwave absorbing materials, including carbonaceous materials, conducting polymers, magnetic materials, metals and their composites, 2D materials (such as MXenes and 2D-transition metal dichalcogenides), biomass-derived materials, carbides, sulphides, phosphides, high entropy (HE) materials and metamaterials. The characteristics, advantages, and limitations of each material are examined. Overall, this review article highlights the progress achieved in the field of microwave-absorbing materials. It underlines the importance of optimizing different types of losses to enhance the performance of microwave absorbers. The review also recognizes the potential of emerging materials, such as 2D materials and high entropy materials, in further advancing microwave-absorbing properties.

Dielectric and material analysis on physicochemical activity of porous hydroxyapatite/cornstarch composites

This paper provides a comprehensive analysis of the dielectric and physicochemical properties of the porous hydroxyapatite/cornstarch (HAp/Cs) composites in a new perspective. The porous composites have been characterized via SEM, FTIR, XRD and dielectric spectroscopy. The dielectric permittivity spectra were obtained in Ku-band (12.4-18.0 GHz) and it was correlated with the physicochemical properties of the porous HAp/Cs. Porous HAp/Cs composites exhibits low ε' and negative ε″, which influenced by the microstructural morphology, interaction between Hap and Cs, as well as crystalline features due to the various proportion of the HAp/Cs. The physicochemical effect of the composites results in the dielectric polarization and energy loss. This phenomenon indicates the presence of the three obvious relaxation responses in the ε' spectrum (13.2-14.0, 15.2-16.0, and 16.6-17.4 GHz) and the negative behaviours in the ε″ spectrum. The relationships between physicochemical and dielectric properties of the porous composite facilitate the development of the non-destructive microwave evaluation test for the porous composite.

Excellent microwave absorption properties based on a composite of one dimensional Mo2C@C nanorods and a PVDF matrix

MoO₃ nanowires were synthesized by a wet chemical process and then coated by glucose, and finally successfully turned into Mo₂C@C nanorods by carbonation reaction. An excellent absorption strength of −39.0 dB and absorption bandwidth of 12.2 GHz in the thickness range of 2.0–5.0 mm were achieved by the Mo₂C@C/PVDF with 10% filler content, derived from effective Debye dipolar relaxation processes. It is expected that the composite can be applied as a novel and desirable microwave absorber.

A Mo₂C@C/PVDF composite with excellent absorption performance has been synthesized. The results indicate that the maximum reflection loss can reach −39.0 dB, and the absorbing bandwidth is up to 3.1 GHz at a thickness of 2.0 mm.