Annealing effects on the microwave permittivity and permeability properties of Fe_(79)Si_(16)B_5 microwires and their microwave absorption performances

This paper reports that amorphous magnetic microwires （Fe79Si16Bs） have been fabricated by a melt-extraction technique and have been annealed at 600℃ and 750℃ respectively. Differential scanning calorimeter measurements show that nanocrystalline magnetic phase （α-Fe） has been formed in the amorphous matrix when it was annealed at 600℃. Hard magnetic phase （Fe2B） was formed in the microwires annealed at 750℃, which increases the magnetic coercivity. Microwave permittivity and permeability are found to be dependent on the microstruetures. The permittivity fitting results show that multi Lorentzian dispersion processes exist. For microwires annealed at 750℃, their resonance peaks due to the domain wall movements and natural resonance are found higher than those of microwires annealed at 600℃. The microwave absorption performance of microwires annealed at 600℃ is found better than microwires annealed at 750℃.

Fabrication and electromagnetic wave absorption properties of amorphous Ni-P nanotubes

Amorphous Ni-P nanotubes are fabricated through electroless chemical deposition inside an anodic aluminum oxide template. The hysteresis loops of Ni-P nanotube arrays are each found to exhibit an unusual isotropic behaviour, which is believed to be due to the competition results between the shape anisotropy and the magnetostatic interaction among nanotubes. The dynamic dependence of permittivity on the frequency spectrum is fitted to the Lorentzian-type dispersion law. The permeability dispersion behaviours have been fitted based on the Kittel equation. Electromagnetic wave absorption properties of Ni-P nanotubes/paraffin composites with different values of thickness （t） are clearly shown by a three-dimensional graph. Furthermore, the bandwidths of composites with different ＂t＂ values can be well presented by a two-dimensional contour graph, which is a novel presentation form. The results show that the composites each have a good microwave absorption performance with t larger than 5.5 mm and with the frequency around 8 gigahertz.

Enhanced Microwave Absorption for High Filler Content Composite Molded from Polymer Coated Flaky Carbonyl Irons Modified by Silane Coupling Agents

A microwave absorbing sheet with a high complex permeability and a relatively low complex permittivity is obtained by molding of the densely coated flaky carbonyl iron particles(FCIPs)by styrenebutadiene-styrene block copolymer(SBS)in the assistance of coupling agent modification.Direct molding of the core-shell FCIPs without adding extra binder results in a large permeability due to the high filling ratio(55vol%)of absorbents.Importantly,the permittivity is well suppressed by the dense insulate polymer shell on the FCIPs,avoiding the severe impedance mismatch problem of the high filler content microwave absorbing materials.Investigations show that modifying the surface of FCIPs by proper amount of silane coupling agent is critical for the coating quality of the SBS shell,which is verified by resistivity and corrosion current density measurements,and can be interpreted by improved interfacial compatibility between the modified FCIPs and SBS.The obtained microwave absorbing sheet shows a minimum reflection loss of-38.74 dB at 1.57 GHz and has an effective absorption bandwidth from 1.1 to 2.3 GHz at a relatively small thickness of 2 mm.

扁平型铁基非晶粉末的取向对吸波材料电磁性能的影响

采用水雾化法和球磨处理工艺制备了扁平形Fe74Cr2Mo2Sn2P10Si4B4C2粉末,通过涂布工艺和非涂布工艺分别制备了扁平形粉末取向分布和随机分布的吸波材料,探讨了取向对其微波电磁性能的影响。结果表明:取向分布的吸波材料具有更高的磁导率和更低的介电常数,在10 MHz下,对取向分布的吸波材料,μ'=20.1,ε'=110,对随机分布的吸波材料,μ'=14.4,ε'=194。同时建立了取向度与磁导率的关系式,并与实验结果定量一致。