Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation

Two-dimensional transition metal carbides and nitrides(MXene)have emerged as promising candidates for microwave absorption(MA)materials.However,they also have some drawbacks,such as poor impedance matching,high self-stacking tendency,and high density.To tackle these challenges,MXene nanosheets were incorporated into polyacrylonitrile(PAN)nanofibers and subsequently assembled into a three-dimensional(3D)network structure through PAN carbonization,yielding MXene/C aerogels.The 3D network effectively extends the path of microcurrent transmission,leading to enhanced conductive loss of electromagnetic(EM)waves.Moreover,the aerogel’s rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXenebased absorbers.EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss(RL_(min))value of−53.02 dB(f=4.44 GHz,t=3.8 mm),and an effective absorption bandwidth(EAB)of 5.3 GHz(t=2.4 mm,7.44–12.72 GHz).Radar cross-sectional(RCS)simulations were employed to assess the radar stealth effect of the aerogels,revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m^(2).In addition to the MA performance,the MXene/C aerogel also demonstrates good thermal insulation performance,and a 5-mm-thick aerogel can generate a temperature gradient of over 30℃ at 82℃.This study provides a feasible design approach for creating lightweight,efficient,and multifunctional MXene-based MA materials.

Design of 35 GHz 1 Watt GaAs pHEMT Power Amplifier MMIC

By using 0.15 μm GaAs pHEMT （pseudomorphic high electron mobility transistor） technology,a design of millimeter wave power amplifier microwave monolithic integrated circuit （MMIC） is presented.With careful optimization on circuit structure,this two-stage power amplifier achieves a simulated gain of 15.5 dB with fluctuation of 1 dB from 33 GHz to 37 GHz.A simulated output power of more than 30 dBm in saturation can be drawn from 3 W DC supply with maximum power added efficiency （PAE） of 26%.Rigorous electromagnetic simulation is performed to make sure the simulation results are credible.The whole chip area is 3.99 mm2 including all bond pads.

Super energy flows in a waveguide filled with air and left-handed materials

The phenomena of super energy flows are studied theoretically and numerically in a parallel-plate waveguide which is filled with two layered equally-thick different media, i.e. air and specific left-handed materials （LHM） with εr1 = -1/（1 ＋δ） ＋iγ and μr1 = -（1 ＋ δ） ＋ iγ. In this special waveguide, two-directional super-energy flows are excited by a three-dimensional horizontal electric dipole at the same time, which has transmission patterns different from those of two-dimensional source and three-dimensional vertical electric dipole. We also show that the retardation and loss in LHM are sensitive to the amplitude of super power densities, and the dimensions of waveguide determine the propagating modes, which makes super energy flows more practical.

Multichannel direct transmissions of nearfield information

A digital-coding programmable metasurface(DCPM)is a type of functional system that is composed of subwavelength-scale digital coding elements with opposite phase responses.By configuring the digital coding elements,a DCPM can construct dynamic near-field image patterns in which the intensity of each pixel of the image can be dynamically and independently modulated.Thus,a DCPM can perform both spatial and temporal modulations.Here,this advantage is used to realize multichannel direct transmissions of near-field information.Three points are selected in the near-field region to form three independent channels.By applying various digital phase codes on the DCPM,independent binary digital symbols defined by amplitude codes(namely,weak and strong amplitudes)are transmitted through the three channels.The measured near-field distributions and temporal transmissions of the system agree with numerical calculations.Compared with the conventional multichannel transmission,the proposed mechanism achieves simultaneous spatial and temporal modulations by treating DCPM as an energy radiator and information modulator,thereby enduing DCPM with high potential in near-field information processing and communications.