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The core–shell Ni@C submicrospheres were fabricated by sintering method and combined with PVDF to prepare Ni@C/PVDF composite, which possessed optimal wave absorption property with RL min of −71.32 dB and EAB of 5.62 GHz at 1.95 mm.

The perfect control over the constituent and architecture of porous nanomaterials is still a significant challenge in developing high performance electromagnetic wave absorption materials. In this work, we have designed and prepared a novel lightweight electromagnetic wave absorption material with the combination of hollow structure and bimetallic constituents by the thermal decomposition of metal−organic framework (MOF) ZIF-67. We found that by introducing additional metal Nickle into the porous Co/C composites, the CoNi/C-800-PVDF nanocomposite could yield an excellent reflection loss of −61.02 dB at 13.68 GHz and simultaneously possess effective absorbing bandwidth of 5.2 GHz with lower filler loading as 10 wt%, which corresponding to a less absorber thickness of 2 mm. These results demonstrate that the synergistic effects between the bimetallic components and hollow structure of novel CoNi/C composite optimize impedance matching, and thus improve the absorption performance greatly. The properties of specific surface area, interface polarization, dipole polarization, ferromagnetic resonance, eddy current loss and multiple scattering are investigated to further explain the high performance of materials.

A two-dimensional carbon-based composite material loaded with magnetic nanoparticles Fe3C (CN–Fe3C) was successfully designed and prepared to ensure the dielectric loss and magnetic loss effect occur simultaneously. The impedance matching of the material is better realized, and the absorbing performance is improved. The loading of ferromagnetic Fe3C effectively improves the magnetic properties of the composites. When the filling amount is only 10 wt%, the composite can achieve a reflection loss value of −46.78 dB at 13.53 GHz, and the effective absorption bandwidth is as high as 5.01 GHz. The excellent absorbing performance is mainly due to the enhancement of interfacial polarization and the synergistic effect between the dielectric properties of carbon materials and the magnetic properties of Fe3C. CN–Fe3C/PVDF also shows good electromagnetic shielding effectiveness. This work has developed new ideas for designing and preparing “thin”, “light”, “wide”, and “strong” two-dimensional carbon-based composite absorbing materials.

Highlights Ultralight 3D NiCo compound@MXene nanocomposites that inherited hollow polyhedral skeleton and excellent conductive network were fabricated.Excellent electromagnetic absorption performance was achieved with optimal RLmin value of − 67.22 dB and ultra-wide EAB of 6.72 GHz under the low filler loading.Electromagnetic parameters and microwave absorption property can be distinctly or slightly regulated by adjusting the filler loading and decoration of Ti3C2Tx nanoflakes. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00727-y., The 3D hollow hierarchical architectures tend to be designed for inhibiting stack of MXene flakes to obtain satisfactory lightweight, high-efficient and broadband absorbers. Herein, the hollow NiCo compound@MXene networks were prepared by etching the ZIF 67 template and subsequently anchoring the Ti3C2Tx nanosheets through electrostatic self-assembly. The electromagnetic parameters and microwave absorption property can be distinctly or slightly regulated by adjusting the filler loading and decoration of Ti3C2Tx nanoflakes. Based on the synergistic effects of multi-components and special well-constructed structure, NiCo layered double hydroxides@Ti3C2Tx (LDHT-9) absorber remarkably achieves unexpected effective absorption bandwidth (EAB) of 6.72 GHz with a thickness of 2.10 mm, covering the entire Ku-band. After calcination, transition metal oxide@Ti3C2Tx (TMOT-21) absorber near the percolation threshold possesses minimum reflection loss (RLmin) value of − 67.22 dB at 1.70 mm within a filler loading of only 5 wt%. This work enlightens a simple strategy for constructing MXene-based composites to achieve high-efficient microwave absorbents with lightweight and tunable EAB. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-021-00727-y.

Bi2Fe4O9(BFO) nanocubes have been prepared in proportion by a simple and easy hydrothermal method, and then the BFO nanocubes were assembled on the reduced graphene oxide (rGO) multilayered sheets. The excellent microwave absorption properties of Bi2Fe4O9/rGO nanohybrids were achieved by properly adjusting impedance matching and getting high attenuation capability contributed from different ratios of the BFO and rGO. A minimum reflection loss value of -61.5 dB at 12.8 GHz was obtained with Bi2Fe4O9/rGO ratio of 2:1, and the broadest bandwidth below -10 dB is up to 5.0 GHz (from 10.8 to 15.8 GHz) with a thickness of 2.4 mm. Additionally, elementary mechanism of wave absorption performance is also investigated.

Dual dielectric relaxation and multiple magnetic resonances contribute to form dielectric-magnetic matching effect, which tends to become a strategy to explore the optimization of magnetic components for improved the microwave absorption (MA) performance. Herein, CoNi alloy with tunable magnetism embedded in N-doped carbon (NC) nanosheets has been successfully fabricated by facile pyrolysis process. It is worth noting that the saturation magnetization of these nanocomposites will be regulated effectively via changing the Co2+/Ni2+ ratio. The results confirm that the wave attenuation ability is relevant with the ratio of Co to Ni. The optimized Co0·80Ni0.20-NC/PVDF composites exhibit extraordinary wave attenuation capacity with a minimum reflection loss value of up to −61.26 dB at a low filler amount of 10 wt% (2.4 mm). Moreover, the effective absorption bandwidth can reach 4.55 GHz (12.95–17.50 GHz) when the thickness is only 1.7 mm. The composites well achieve wide and strong absorption at low filler amount and thin thickness. The superior MA performance is attributed to dielectric loss and better impedance matching characteristic caused by CoNi alloy. This work guided a promising direction for synthesizing dielectric-magnetic composites with excellent MA property by varying their magnetism.

In the control signal process theory, the state equation is an important approach for modelling, analyzing and designing a wide range of systems. Furthermore, the state equation is often the most efficient form from the standpoint of computer simulation for highly complex systems. The existing researches exploit the fact that for networks containing dependent sources, bridging elements and coupling elements, the derivation of the closed-form state equation becomes rather complicated. On the other hand, a simple and valuable unifying approach of finding the state equations for complicated physical systems is successfully presented in the paper. The new unifying approach needs only the substitution theorem and the author’s invented simple matrix operations. The main fascinating peculiarity of this approach is exposed in its systematic, graphic and human structure that improves the shortcomings of those traditional approaches. One comparative example is proposed to show the distinguished advantages our method offers over existing methods. In order to demonstrate the practical applicability, the paper has investigated an electronic operational-amplifier circuit that can be easily stabilized by our approach.

The device-to-device (D2D) communications can improve the spectrum efficiency with low power and effectively offload the traffic from the macro-eNB. However, the macro/femto/D2D heterogeneous networks face a complicated three-tier interference issue. The completely centralized resource management is not applicable in such three-tier heterogeneous networks. Therefore, we propose a network-assisted device-decided (NADD) scheme to jointly select the channels and adjust the transmission power for D2D devices. In the NADD method, the macro-eNB broadcasts resource allocation instruction to D2D devices. According to the resource allocation instruction and the device's communication quality, D2D devices autonomously and dynamically select the suitable channels and adjust the transmission power. Simulation results show that NADD scheme can significantly improve the total throughput and ensure the link reliability of macrocell users, comparing to both the fixed power scheme and the network-decided (ND) power control scheme.