Time-Domain Analysis of Underground Station-Layered Soil Interaction Based on High-Order Doubly Asymptotic Transmitting Boundary

Based on the modified scale boundary finite element method and continued fraction solution,a high-order doubly asymptotic transmitting boundary(DATB)is derived and extended to the simulation of vector wave propagation in complex layered soils.The high-order DATB converges rapidly to the exact solution throughout the entire frequency range and its formulation is local in the time domain,possessing high accuracy and good efficiency.Combining with finite element method,a coupled model is constructed for time-domain analysis of underground station-layered soil interaction.The coupled model is divided into the near and far field by the truncated boundary,of which the near field is modelled by FEM while the far field is modelled by the high-order DATB.The coupled model is implemented in an open source finite element software,OpenSees,in which the DATB is employed as a super element.Numerical examples demonstrate that results of the coupled model are stable,accurate and efficient compared with those of the extended mesh model and the viscous-spring boundary model.Besides,it has also shown the fitness for long-time seismic response analysis of underground station-layered soil interaction.Therefore,it is believed that the coupled model could provide a new approach for seismic analysis of underground station-layered soil interaction and could be further developed for engineering.

Hierarchical graphene@MXene composite foam modified with flower-shaped FeS for efficient and broadband electromagnetic absorption

Developing high-performance broadband microwave absorption material becomes an urgent concern in the field of electromagnetic protection.In this work,an ultralight magnetic composite foam was con-structed by electrostatic self-assembly of MXene on the surface of graphene skeletons,and subsequent hydrothermal anchoring of flower-shaped FeS clusters.Under the synergistic effect of MXene coating in-creasing conductive loss and FeS clusters improving magnetic loss,the rational construction of hierarchi-cal impedance structure in foam can effectively promote the entrance and consumption of more incident electromagnetic waves.The minimum reflection loss(RL min)reaches-47.17 dB at a thickness of 4.78 mm,and the corresponding effective absorption bandwidth(EAB)is up to 6.15 GHz.More importantly,the microwave absorption performance of composite foam can be further optimized by controlling the load-ing of MXene and thermal treatment at a low temperature.The maximum of EAB for GMF-300 can be extended to an unprecedented value of 11.20 GHz(covering 6.10-17.30 GHz).

Ultrathin,flexible,and oxidation-resistant MXene/graphene porous films for efficient electromagnetic interference shielding

Designing and fabricating efficient electromagnetic interference(EMI)shielding materials becomes a significant and urgent concern.Hence,a novel ultrathin,flexible,and oxidation-resistant MXene-based graphene(M-rGX)porous film is successfully fabricated by electrostatic self-assembly between MXene and graphene oxide(GO)nanosheets,and subsequently thermal annealing under hydrogen-argon atmosphere.The rapid breakaway of functional groups on GO and MXene sheets induces formation of porous conductive network in film,thereby facilitating efficient shielding for incident electromagnetic waves.The optimal absolute shielding effectiveness(SSE/t)value of 76,422 dB·cm2·g−1 can be achieved at a thinner thickness of 15μm.More importantly,the effective removal of functional groups on MXene conspicuously improves the oxidation resistance of the film,endowing it with an excellent durability(12 months)in EMI shielding performance.

Ultralight and ordered lamellar polyimide-based graphene foams with efficient broadband electromagnetic absorption

The development of high-performance microwave absorption materials with strong absorption capacity and broad bandwidth is highly desirable in the field of electromagnetic pollution protection.Herein,ultralight polyimide-based graphene foam with ordered lamellar structure is precisely designed and controllably constructed by bidirectional freezing process.More lamellar interfaces formed inside the foam per unit volume effectively facilitate the layer-by-layer dissipation for the vertical incident electromagnetic waves,thereby endowing the foam with efficient broadband electromagnetic absorption performance.More importantly,electromagnetic absorption performance can be controllably adjusted by optimizing impedance distribution and microstructure of skeletons.As a result,the optimized foam with an ultralow density of 9.10 mg/cm^(3)presents a minimum reflection loss value of-61.29 dB at 9.25 GHz and an effective absorption bandwidth of 5.51 GHz(7.06-12.57 GHz,covering the whole X band) when the thickness is 4.75 mm.