3D Ultralight Hollow NiCo Compound@MXene Composites for Tunable and High-E cient Microwave Absorption

The 3D hollow hierarchi-cal architectures tend to be designed for inhibiting stack of MXene flakes to obtain satisfactory lightweight,high-e cient and broadband absorbers.Herein,the hollow NiCo compound@MXene networks were prepared by etching the ZIF 67 template and subsequently anchoring the Ti_(3)C_(2)Tx 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 Ti_(3)C_(2)Tx nanoflakes.Based on the synergistic e ectsof multi-components and special well-constructed structure,NiCo layered double hydroxides@Ti_(3)C_(2)Tx(LDHT-9)absorber remarkably achieves unexpected e ective absorption bandwidth(EAB)of 6.72 GHz with a thickness of 2.10 mm,covering the entire Ku-band.After calcination,transition metal oxide@Ti_(3)C_(2)Tx(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-e cient microwave absorbents with lightweight and tunable EAB.

MRI Finding in Delayed Extensive Brain Lesions after Radiation Therapy :Cortical Laminar Necrosis and White Matter Myelinolysis

The focal and diffuse cerebral white matter injury can be caused by treatment with radiation therapy for cranial tumors. However, the literature rarely describes a MRI finding in radiation-induced delayed extensive cerebral injury. Our objective was to report a rare case who had a delayed extensive hyperintensity injury in brain on MRI after radiation therapy due to nasopharyngeal cancer. A MRI was performed on a 40-year-old patient with extensive brain damage who had the radiation therapy two years ago.MRI finding was evaluated. On MRI, T2-weighted MRI showed an extensive hyperintensity after treated by irradiation. The radiographic pattern of extensive cerebral injury is relatively distinct. It involves the white matter and gray matter in cerebral, cerebellum, medulla oblongata, pons, internal capsule and thalamus bilaterally. Our observations demonstrate that the extensive hyperintensity lesions in brain on MRI after radiation therapy is a cortical laminar necrosis and white matter myelinolysis.

Porous Ti_(3)C_(2)T_(x) MXene nanosheets sandwiched between polyimide fiber mats for electromagnetic interference shielding

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·cm^(2))/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.

Metasurface-assisted low-frequency performance enhancement of ultra-broadband honeycomb absorber based on carbon nanotubes

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 1.0-18.0 GHz range.This study introduces an innovative technique for creating microwave absorbers for low-frequency wideband applications.

Ultrathin self-assembly MXene/Co-based bimetallic oxide heterostructures as superior and modulated microwave absorber

Lightweight and high-efficiency absorbing materials equipped with tunable electromagnetic properties are the foremost important factors for driving applications of 5 G smart era and military stealth.Stim-ulated by the remarkable merits of heterogeneous interface engineering,a series of unique flower-like Co-based multiphases nanostructures were successfully synthesized through identical hydrothermal method,and subsequently anchored on the Ti_(3)C_(2)T_(x)nanosheets.The suitable metal ion modulation is feasible to regulate the components,heterogeneous interfaces and defects for tailoring the electromag-netic parameters and microwave absorption(MA)property.Notably,the permittivity decreases of CMOT(CoO/MCo_(2)O_(4)/Ti_(3)C_(2)T_(x),M=Fe,Cu,Zn)composites proceed gradually in the order of Fe^(2+),Cu^(2+),Zn^(2+),while the MA performance with tunable absorption peak could be modulated subtly.The asobtained CFOT-12(10 wt%),CCOT-15(10 wt%)and CZOT-15(15 wt%)exhibit excellent MA capacity with a minimum reflection loss(RL_(min))of-41.06,-52.67,-52.52 dB and corresponding effective absorption bandwidth(EAB)of 3.68,4.48,3.92 GHz at 2.10,1.90,1.80 mm,respectively.This work expands a novel approach to construct multicomponent heterostructure for tuning the EM parameters and absorbing property,as well as realize the high efficient and light weight.

Binary synergistic enhancement of dielectric and microwave absorption properties： A composite of arm symmetrical PbS dendrites and polyvinylidene fluoride

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.

Porous carbon polyhedrons coupled with bimetallic CoNi alloys for frequency selective wave absorption at ultralow filler loading

Combining suitable microstructure and dielectric-magnetic synergy effect is conducive to achieve lightweight,broadband,and high-efficiency microwave absorbing materials within low filler loading.Herein,porous carbon polyhedrons coupled with bimetallic CoNi alloys were synthesized by using metalorganic frameworks(MOFs)as a template and subsequent pyrolysis treatment.Electromagnetic analysis indicated that the existence of metal Ni element could influence the wave attenuation capacity effectively,resulting in frequency selective wave absorption performance.Additionally,the pyrolysis temperature was also closely related to wave absorption intensity.The Co_(2)Ni_(1)/C/PVDF composites calcined at 800℃ possessed outstanding wave absorption performance at an ultra-low filler loading of 5 wt%.The minimum reflection loss value achieved-52 dB(10.8 GHz)under the matched thickness of 3 mm.Moreover,the broadest effective absorption bandwidth(RL<-10 dB)reached 6.2 dB(11.8-18 GHz)for Co/C-800/PVDF composites when the thickness turned into 2 mm.The remarkable wave attenuation ability was mainly ascribed to magnetic and dielectric loss,impedance matching as well as porous structure effect.

Electrospinning fabrication and ultra-wideband electromagnetic wave absorption properties of CeO_(2)/N-doped carbon nanofibers

The impedance mismatch of carbon materials is a key factor limiting their widespread use in electromagnetic(EM)wave absorption.In this work,the novel CeO_(2)/nitrogen-doped carbon(CeO_(2)/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 CeO_(2)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 CeO_(2)and defects from N doping optimize the impedance matching of the material.When the sintering temperature reaches 950℃,CeO_(2)/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 CeO_(2)/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℃.This work provides the research basis for widely commercial applications of carbon-based nanofiber absorbers.