Achieving full effective microwave absorption in X band by double-layered design of glass fiber epoxy composites containing MWCNTs and Fe3O4 NPs

The glass fiber epoxy composites containing MWCNTs and Fe₃O₄ NPs were manufactured by composites liquid molding process. The microwave absorbing properties of single-layered and double-layered glass fiber/MWCNTs/epoxy and glass fiber/Fe₃O₄ NPs/epoxy composites were evaluated. The reflection loss(RL) were calculated by the measured complex permittivity and permeability using waveguide method by vector network analyzer. Based on the mechanism analysis and deficiency of single-layer absorber, the double-layered composites were fabricated by using matching layer and absorbing layer to enhance the microwave absorption performance, which can be modulated by tailoring the electromagnetic parameters and thicknesses of each layer. The optimized microwave absorbing properties of double-layered composites with minimum RL of −45.7 dB and full X-band effective absorption can be achieved when the total thickness of the matching layer and absorbing layer is 1.8 mm, which can be attributed to synergistic effect of improved impedance matching characteristic and superior microwave attenuation characteristic of the absorbing layer. The combined utilization of dielectric loss and magnetic loss absorbent and their double-layered structure design shows great design flexibility and diversity and can be a promising candidate for designing high performance microwave absorbing materials.     

PS-RF双层空心微球的制备

 采用聚苯乙烯(PS)空心微球为模板,间苯二酚-甲醛(RF)为前驱体溶液,邻苯二甲酸二丁酯为分散剂,以界面聚合反应为基础初步总结出一条PS-RF双层聚合物空心微球的制备工艺,并就制备过程中RF溶液与分散剂油相的选择、预聚时间、搅拌速率、固化温度等影响因素进行了讨论。当RF溶液质量分数为25%,间苯二酚与碳酸钠的物质的量之比为100,预聚24 h,搅拌速率120～200 r/min,固化温度35 ℃时,制得了球形度和同心度达到95%以上,表面粗糙度小于10 nm的PS-RF双层空心微球。     

A simple electromagnetic method of cyclic loss measurement for superconducting wires in a combined alternating transverse magnetic field and transport current

We measured cyclic losses in a superconducting wire, carrying alternating transport current, simultaneously exposed to an alternating transverse magnetic field. Samples of Bi-2223 Ag-sheathed tapes have configuration of a double-layer non-inductive coil, which itself is a pickup coil to measure the AC losses. Potential taps were attached to both terminals of the sample coil. The external field was applied along the axis of the sample coil. In this procedure, we can estimate an averaged Poynting's vector on a cylindrical surface between the two layers by means of signals from a pair of the potential taps and from pickup coils for the external magnetic field and the transport current. We can also measure a magnetization and an extended transport-current components of AC losses in addition to a total cyclic loss for a combined alternating external field and transport current. Obtained results are compared with numerical predictions of the critical state model taking into account the magnetic field dependence of critical current density.     

Influence of cement flow and aggregate type on the mechanical and acoustic characteristics of porous concrete

The influence of cement flow and aggregate type on the mechanical and acoustic characteristics of porous concrete is systematically investigated in the present study. Three levels of cement flow (80%, 110%, and 140%) and five types of aggregates (normal aggregates of 8-13 mm and 13-19 mm and lightweight aggregates of 4-8 mm, 8-12 mm, and 12-19 mm) are used, and effects of the application of AE admixtures in paste were also studied. Single-layered and double-layered porous concrete specimens are fabricated to examine the effect of different layer configuration on the acoustic characteristics. For the purpose of comparison, the void ratio, compressive strength, and sound absorption coefficient of the specimens are used as evaluation parameters. Based on the findings of the study, a sound absorbing porous concrete with a maximum absorption coefficient of approximately 1.00 is developed, and the minimum absorption coefficient of the ‘double-layered porous concrete’ structure is shown to be more than 0.60 with a frequency of 400 Hz or above, considering the tolerant error.     

磁场中耦合量子线的三阶非线性光学吸收率

本文研究了磁场中耦合量子线的三阶非线性光学吸收率,并且利用密度矩阵算符理论导出了三阶非线性光学吸收率的解析表达式.最后,以GaAs/Al_xGa_1-xAs耦合量子线为例作了数值计算,并绘出了三阶非线性光学吸收率与磁场B,光子能量h-ω以及间隔D之间的依赖关系.     

Thickness effect of the TiO2 nanofiber scattering layer on the performance of the TiO2 nanoparticle/TiO2 nanofiber-structured dye-sensitized solar cells

TiO₂ nanofibers (NFs) were fabricated by an electrospinning process and were used as scattering layers in dye-sensitized solar cells (DSSCs). The NF-coated photoanodes of the DSSCs were prepared with a variety of scattering layer thicknesses. The thickness effect of the scattering layer on the double-layered TiO₂ nanoparticle (NP)/TiO₂ NF structure was investigated through structural, morphological, and optical measurements. In the double-layered photoanode, the TiO₂ NP layer plays a major role in dye adsorption and light transmission, and the TiO₂ NF scattering layer improves the absorption of visible light due to the light scattering effects. The scattering effect of TiO₂ NFs layer was examined by the incident monochromatic photon-to-electron conversion efficiency (IPCE) and UV–Vis spectrometry. The conversion efficiency for the 12 μm-thick photoanode composed of a 2 μm-thick TiO₂ NF layer and 10 μm-thick TiO₂ NP layer was higher than that of DSSCs with only TiO₂ NPs photoanode by approximately 33%.