Luo Fa

Graphene nanosheets/BaTiO3 ceramics as highly efficient electromagnetic interference shielding materials in the X-band

Graphene nanosheet (GN) filled BaTiO3 ceramics with high-performance electromagnetic interference (EMI) shielding were prepared via pressureless sintering. Both the real and imaginary parts of the complex permittivity increased with increasing GN content. The EMI shielding results showed that the absorption mechanism is the main contributor to the total EMI shielding effectiveness (SE). The total EMI SE is greater than 40 dB in the X-band at 1.5 mm thickness, which suggests the GN-BaTiO3 ceramics could be good candidates for highly efficient EMI shielding materials in the whole X-band.

Temperature dependence of the electromagnetic properties of graphene nanosheet reinforced alumina ceramics in the X-band

Graphene nanosheet (GN)/Al2O3 ceramics were prepared by hot press sintering with a significant improvement in both mechanical and electromagnetic properties. The excellent mechanical properties and electrical conductivity of the GN/Al2O3 ceramics contributed to the outstanding advantage of GNs as the reinforcing phase. The effects of GN content and temperature on complex permittivity, microwave absorption and electromagnetic interference (EMI) shielding performance of such ceramics have been studied in the frequency range of 8.2–12.4 GHz (X-band) and temperature range from 25 to 400 °C. Negative permittivity of the GN/Al2O3 ceramics with 2.0 vol% GNs appears throughout the whole X-band at 400 °C, and the mechanism was also investigated. The GN/Al2O3 ceramics show high mechanical properties, tunable electromagnetic properties, good microwave absorption and EMI shielding performance demonstrating their great potential to be applied in microwave applications.

Graphene nanosheets/E-glass/epoxy composites with enhanced mechanical and electromagnetic performance

Microwave absorbing composites with superior mechanical properties and electromagnetic absorption characteristics were fabricated using E-glass/epoxy composites containing graphene nanosheets (GNs). Compared with the composites without GNs, the incorporation of 2.0 wt% GNs enhanced the mechanical properties; the flexural strength and elastic modulus were improved by about 58.4 and 78.8%, respectively. Both the real and imaginary parts of the complex permittivity in the Ku-band increased with increasing GN content. Based on the complex permittivity of the composites, single and double layer absorbing composites were designed to obtain a wide reflection loss (RL) bandwidth below −10 dB. RL values less than −13 dB (larger than 95% absorption) can be obtained in the whole Ku-band for a double layer composite with a sample thickness of 3.4 mm.

Microstructure and Dielectric Properties of Chopping SiCf/LAS Composites

Abstract The chopping SiC f /LAS composites were prepared by the hot-pressing method. The effects of hot-pressing time and pressures on the microstructures and the dielectric properties of the composites were researched. Compared with the LAS matrix and the SiC fibre, the results of dielectric constant testing in the range of 8-12 GHz indicate that the dielectric constant real part, imaginary part and dielectric dissipation of all samples increase by 1-3 orders of magnitude, and show obvious frequency dispersion effect. Their real parts increase while their imaginary parts and dielectric dissipations decline with the increase of the hot-pressing time or pressures. The SEM fractographs show that the composite interfacial films between the fibre and the matrix are thickened with the increase of the hot-pressing time or pressures.

Na/K RATIOS DEPENDENCE OF PIEZOELECTRIC AND FERROELECTRIC PROPERTIES IN (K1-xNax)NbO3 LEAD-FREE CERAMICS

In order to clarify the Na/K ratios dependence of piezoelectric properties, (K1-xNax)NbO3 ceramics were prepared by conventional solid-state sintering at x = 0.4–0.6 with a smaller compositional interval (0.02 mol). The results demonstrate that the Na/K ratios have obvious effect on piezoelectric and ferroelectric properties of (K1-xNax)NbO3 ceramics. Piezoelectric and ferroelectric properties show the maximum (d33 = 147 pC/N, kp = 0.40, and Pr = 24 μC/cm2) at x = 0.54, which is not consistent with conventional viewpoint. The reasons should be attributed to the existence of a phase boundary at x = 0.54 mol, which is similar to the morphotropic phase boundary in Pb(Zr,Ti)O3 ceramics.

碳/氧化铝/二氧化硅涂层的介电和吸波性能研究

研究了炭黑或碳纤维填充氧化铝/二氧化硅吸波涂层在X波段范围的介电和吸波性能. 结果表明: 吸波涂层的复介电常数随着炭黑或碳纤维含量的增加而增大. 当吸收剂含量相同时, 填充碳纤维的吸波涂层比填充炭黑的吸波涂层具有更大的复介电常数. 当吸收剂含量大于5wt%时, 吸波涂层的介电常数在低频急剧增加, 且随频率增大而减少, 出现频散效应. 反射率测试结果表明: 吸波涂层的最大吸收峰随涂层厚度的增大向低频移动, 当涂层中炭黑含量为2wt%、厚度为1.8 mm时, 吸波涂层在9.2~12.4 GHz范围内反射率小于-10 dB, 具有较好的吸波效果.研究了炭黑或碳纤维填充氧化铝/二氧化硅吸波涂层在X波段范围的介电和吸波性能. 结果表明: 吸波涂层的复介电常数随着炭黑或碳纤维含量的增加而增大. 当吸收剂含量相同时, 填充碳纤维的吸波涂层比填充炭黑的吸波涂层具有更大的复介电常数. 当吸收剂含量大于5wt%时, 吸波涂层的介电常数在低频急剧增加, 且随频率增大而减少, 出现频散效应. 反射率测试结果表明: 吸波涂层的最大吸收峰随涂层厚度的增大向低频移动, 当涂层中炭黑含量为2wt%、厚度为1.8 mm时, 吸波涂层在9.2~12.4 GHz范围内反射率小于-10 dB, 具有较好的吸波效果.