Microwave ferromagnetic properties of as-deposited Co_2FeSi Heusler alloy films prepared by oblique sputtering

The Co2FeSi films are deposited on Si （100） substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe-330 Oe （1 Oe = 79.5775 A.m ^-1）, and low coercivities in a range of 5 Oe-28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.

Microwave absorption performance of porous carbon particles modified by nickel with different morphologies

In this work,porous carbon particles were prepared from wheat flour by pyrolysis and activation.Through the subsequent coprecipitation and electroless plating,the surface and pores of carbon particles were modified by nickel-rich particles with different morphologies.Several loss mechanisms,including dielectric loss,magnetic loss,multiple reflection and scattering loss,were used to assess the attenuation ability to incident electromagnetic waves of these composite particles.The result shows that the chain-shaped morphology of nickel can provide the highest dielectric loss.Under the filler loading of 20 wt.%,the minimum reflection loss(RL min)reached-38.42 dB at 13.2 GHz,and the_(max)imum effective absorption bandwidth(EAB_(max))was 5.2 GHz with a matching thickness of 2 mm.The excellent performance of the composite particles is attributed to the synergistic effect of outstanding impedance matching and supe-rior electromagnetic loss ability caused by the chain structure.The result shows that the morphology of modifiers in carbon-based composites is important to improve microwave absorption performance,and this work provides inspiration for the design of high-performance porous carbon-based composites.

The optimization of hydrothermal process of MoS2 nanosheets and their good microwave absorption performances

In this study,flower-like MoS2 constructed by nanosheets was synthesized by a simple hydrothermal method.The hydrothermal process was optimized and the effects of hydrothermal condition,including reaction temperature,reaction time and the ratio of Mo source to S source(Mo:S)in precursor,on microwave absorption performances and dielectric properties were investigated.Our results showed that when the reaction temperature was 180℃,the reaction time was 18 h,and the Mo:S was 1:3.5,the synthesized MoS2 had the best performance:Its minimum reflection loss could reach-55.78 dB,and the corresponding matching thickness was 2.30 mm with a wide effective bandwidth of 5.17 GHz.Further researches on the microwave absorption mechanism revealed that in addition to the destructive interference of electromagnetic waves,various polarization phenomena such as defect dipole polarization were the main reasons for microwave loss.We believe that MoS2 is a candidate for a practical microwave absorbent.

Single-shot incoherent optical processing of microwave signals： opening the path to low cost high performance analog photonics

Incoherent optical processing of microwave signals,where low-coherence broadband light sources are employed instead of costly mode locked lasers,has attracted great interest thanks to its wide applications in microwave photonics filtering[1–3],arbitrary generation[4–6]and analog to digital conversion[7]。

Fabrication of Z-type barium ferrite/silica composites with enhanced microwave absorption

The Z-type barium ferrite/silica composites(Z-BCF/SiO2)were fabricated by in situ chemical synthesis method.The composition,structure,morphology and magnetic behavior of the composites were characterized by chemical analysis,IR,XRD,SEM,TEM and VSM.The results indicated that there were some interactions between two components in the Z-BCF/SiO2 composites due to the coating of SiO2 on the Z-BCF particles.The magnetic properties of the Z-BCF/SiO2 composites were evidently less than that of the Z-BCF,owing to the small volume fraction of magnetic components in the samples.Due to the good transmission and loss properties on electromagnetic waves,the composites were better at microwave absorption than the parent component.Therefore,this research laid a foundation for the fabrication of highly efficient microwave absorbing material with enhanced wave impedance matching.

Use of Hi-resolution data for evaluating accuracy of traffic volume counts collected by microwave sensors

Over the past few years, the Utah Department of Transportation has developed the signal performance metrics （SPMs） system to evaluate the performance of signalized in- tersections dynamically. This system currently provides data summaries for several per- formance measures, one of them being turning movement counts collected by microwave sensors. As this system became public, there was a need to evaluate the accuracy of the data placed on the SPMs. A large-scale data collection was carried out to meet this need. Vehicles in the Hi-resolution data from microwave sensors were matched with the vehicles by ground-truth volume count data. Matching vehicles from the microwave sensor data and the ground-truth data manually collected required significant effort, A spreadsheet- based data analysis procedure was developed to carry out the task. A mixed model analysis of variance was used to analyze the effects of the factors considered on turning volume count accuracy. The analysis found that approach volume level and number of approach lanes would have significant effect on the accuracy of turning volume counts but the location of the sensors did not significantly affect the accuracy of turning volume counts. In addition, it was found that the location of lanes in relation to the sensor did not significantly affect the accuracy of lane-by-lane volume counts. This indicated that accu- racy analysis could be performed by using total approach volumes without comparing specific turning counts, that is, left-turn, through and right-turn movements. In general, the accuracy of approach volume counts collected by microwave sensors were within the margin of error that traffic engineers could accept. The procedure taken to perform the analysis and a summary of accuracy of volume counts for the factor combinations considered are presented in this paper.