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Designing highly reliable and practical microwave absorbers is one of the most important research directions in the microwave absorbing field. Many absorbents suffer from concentration-sensitivity and environmental-sensitivity dilemmas in practical applications. Here, sea urchin-like aggregates of MnO2 nanotubes were synthesized by a simple hydrothermal method, which exhibit an outstanding impedance matching characteristic. The composites based on sea urchin-like aggregates of MnO2 nanotubes show excellent microwave absorption performance in a wide concentration domain from 20 wt.% to 70 wt.%, corresponding to electrical conductivities from 1.86 × 10−7 to 1.85 × 10−5 S/m. Such a wide concentration range of absorbent for excellent microwave absorption is mainly attributed to the beneficial impedance matching properties of sea urchin-like aggregates of hollow nanotubes. A competitive absorption bandwidth of 3.36 GHz is achieved at 1 mm thickness, which can be broadened to 13.4 GHz by structural design. This work shows a new scheme for designing reliable and practical microwave absorbers benefit from the wide absorbent concentration domain. [ABSTRACT FROM AUTHOR]

The impedance mismatch of carbon materials is a key factor limiting their widespread use in electromagnetic (EM) wave absorption. In this work, the novel CeO2/nitrogen-doped carbon (CeO2/N-C) nanofiber was prepared to solve the problem by electrospinning and sintering. X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) analyses demonstrated CeO2 was successfully loaded onto the surface of partially graphitized carbon fibers. Different sintering temperatures change the graphitization degree of material, and the oxygen vacancy structure of CeO2 and defects from N doping optimize the impedance matching of the material. When the sintering temperature reaches 950 °C, CeO2/N-C fiber possesses the minimum reflection loss (RLmin) value of −42.59 dB at 2.5 mm with a filler loading of only 3 wt.% in polyvinylidene difluoride (PVDF). Meanwhile, the CeO2/N-C fiber achieves a surprising wideband (8.48 GHz) at a thickness of 2.5 mm, covering the whole Ku-band as well as 63% of the X-band at the sintering temperature of 650 °C. This work provides the research basis for widely commercial applications of carbon-based nanofiber absorbers. [ABSTRACT FROM AUTHOR]

Pb0.99Nb0.02(Zr0.85Sn0.13Ti0.02)O3 (PNZST) antiferroelectric (AFE) thick films are successfully deposited on silicon‐based Pt and LaNiO3 electrodes by a sol‐gel method. The coexistence of ferroelectric (FE) and AFE phases are revealed in PNZST films by XRD, electric‐induced hysteresis loops, dielectric, and leakage current properties. Comparing with PNZST/Pt film, larger recoverable energy density and efficiency are obtained in PNZST/LaNiO3 film due to the lower FE phase proportion. It is analyzed and demonstrated by a thermodynamic model of AFE and FE coexistence system. In addition, the fatigue behaviors of both AFE films are also affected by the proportion of the coexisting FE phase. PNZST/LaNiO3 film exhibits good fatigue resistance on energy storage even after 1010 switching cycles, which is attractive to pulsed power applications. [ABSTRACT FROM AUTHOR]

Based on the unique geometrical structure of nanotetra-ZnO needle (T-ZnON), we investigate the microwave responses of T-ZnON, including interface scattering, microcurrent attenuation, microantenna radiation, and dielectric relaxation, and build an energy attenuation model. The associated quantitative formula is deduced for calculating the microwave absorption properties of T-ZnON/SiO2 nanocomposite (T-ZnON/SiO2) in the range 8–14 GHz according to the present energy attenuation model. Very good agreement between the calculated and experimental results is obtained in a wide frequency range. The maximum deviation less than 0.5 dB in the range 8–14 GHz is obtained. Using the aforementioned model, we analyze the contribution of microwave responses to the energy attenuation in the frequency range 2–18 GHz, and the results reveal that interface scattering and microcurrent attenuation make the contribution most important. In addition, we calculate the effects of the volume fraction, conductivity, permittivity, needle length of T-ZnON, and thickness of T-ZnON/SiO2 on the reflectivity. The results show that the microwave absorption is evidently dependent on these effect factors, and the optimal microwave absorption band and the strongest microwave absorption peak of T-ZnON/SiO2 would appear when these physical parameters are changed. [ABSTRACT FROM AUTHOR]