Here, we present a unique method to enhance the low-frequency absorption performance of a honeycomb absorber by integrating a metasurface. The geometrical dimensions of the proposed metasurface have been numerically optimized. The introduction of the metasurface allows exploitation of its robust resonance and superior impedance matching in low-frequency bands, thereby improving microwave absorption properties. The incorporation of the metasurface does not impact the wave transmission performance of the honeycomb core absorber at high-frequency band, thus preserving its high-frequency performance. This broadens the absorption range, leading to an expanded bandwidth. Simulation results reveal that the composite absorber (CA) exhibits strong absorption performance with an incident angle stability up to 45° for both transverse electric (TE) and transverse magnetic (TM) modes. The absorption mechanism of the CA has been investigated by using an equivalent circuit model and electromagnetic field analysis. A prototype was designed, fabricated, and tested to validate the proposed method. Both simulation and measurement results demonstrate that the prototype can achieve an average absorption rate exceeding 90% across a 1-18.0 GHz range. This study introduces an innovative technique for creating microwave absorbers for low-frequency wideband applications.

With the rapid development of wireless communication technology and electronic devices, the issue of electromagnetic interference (EMI) is becoming increasingly severe. Developing a new and flexible electromagnetic interference shielding material has become a challenging task. Here, a sandwich-structured EMI shielding composite film was prepared using electrospinning and vacuum filtration methods. In this process, a porous MXene was synthesized through a reaction with cobalt acetate and served as the intermediate layer in the composite film to shield electromagnetic waves. The electrospun polyimide (PI) fibers were used as the top and bottom layers of the composite film, which can protect the porous MXene from oxidation. This lightweight and flexible composite film integrates electromagnetic interference shielding and thermal insulation capabilities, showing excellent comprehensive performance. The composite film achieves an EMI shielding effectiveness of 48.8 dB in X-band (8.2–12.4 GHz), and absolute shielding effectiveness of the composite film reached a satisfying 4142.43 (dB·cm²)/g. Owing to the design of a multi-layer porous structure, the density of the composite film is 0.65 g/cm³. Furthermore, the thermal conductivity of the film is 0.042 W/(m·K) due to the clamping of electrospun PI fibers, showing excellent thermal insulation performance. Additionally, the composite film exhibits excellent high and low-temperature resistance. In summary, this work provides a feasible strategy for preparing a lightweight polymer-based EMI shielding film.

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 (RL_min) 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.

Arm symmetrical PbS dendrite (ASD-PbS) nanostructures can be prepared on a large scale by a solvothermal process. The ASD-PbSs exhibit a three-dimensional symmetrical structure, and each dendrite grows multiple branches on the main trunk. Such unique ASD-PbSs can be combined with polyvinylidene fluoride (PVDF) to prepare a composite material with enhanced dielectric and microwave-absorption properties. A detailed investigation of the dependence of the dielectric properties on the frequency and temperature shows that the ASD-PbS/PVDF composite has an ultrahigh dielectric constant and a low percolation threshold. The dielectric permittivity is as high as 1, 548 when the concentration of the ASD-PbS filler reaches 13.79 vol.% at 102 Hz, which is 150 times larger than that of pure PVDF, while the composite is as flexible as pure PVDF. Furthermore, the maximum reflection loss can reach -36.69 dB at 16.16 GHz with a filler content of only 2 wt.%, which indicates excellent microwave absorption. The loss mechanism is also elucidated. The present work demonstrates that the addition of metal sulfide microcrystals to polymer matrix composites provides a useful method for improving the dielectric and microwave-absorption properties.