(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing thetf value and improving the thermal stability.The phase composition and t...(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing thetf value and improving the thermal stability.The phase composition and the microstructure were investigated using X-ray diffraction,Raman spectra,and scanning electron microscopy.A set of phase transitions which were induced by composition had been confirmed via the sequence:rutile structure→coexistence of rutile and columbite phase→columbite phase.For(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics,the addition of ZnNb2O6 content(x=0–1)led to the decrease ofer from 62.98 to 23.94.As a result of the high Q×?of ZnNb2O6 ceramics,the increase of ZnNb2O6 content also led to the lower sintering temperatures and the higher Q×?values.Thetf value was reduced from+108.04(x=0)to–49.31 ppm/℃(x=1).Among them,high density 0.5CoTiNb2O8-0.5ZnNb2O6 ceramics were obtained at 1175℃with excellent microwave dielectric properties of εr 39.2,Q×? 40013 GHz,and tf+3.57 ppm/℃.展开更多
针对高效、快速、连续、无损的路面雷达应用技术存在的问题,研究了路面雷达电磁波在多层介质中的传播规律.基于电磁波理论的基本原理,从M axw e ll方程着手,建立了雷达电磁波在路面结构体系中的传播模型.该模型考虑了介质介电常数虚部...针对高效、快速、连续、无损的路面雷达应用技术存在的问题,研究了路面雷达电磁波在多层介质中的传播规律.基于电磁波理论的基本原理,从M axw e ll方程着手,建立了雷达电磁波在路面结构体系中的传播模型.该模型考虑了介质介电常数虚部的贡献,理论上更加严谨,并更接近于道路工程实际.应用该模型,模拟合成了多层路面结构体系中雷达电磁波的反射信号,将其与实测信号对比,验证了所建立模拟方法的正确性和适用性.展开更多
Ultra-low dielectric loss(Df)and low dielectric constant(Dk)materials are urgently required in highspeed and large-capacity transmission,in which the wholly aromatic liquid crystal polymer(LCP)has gained attention due...Ultra-low dielectric loss(Df)and low dielectric constant(Dk)materials are urgently required in highspeed and large-capacity transmission,in which the wholly aromatic liquid crystal polymer(LCP)has gained attention due to its excellent dielectric properties.However,the relationship between molecular structure and dielectric properties is still not clear.In this study,two copolyesters containing phenyl or naphthyl structures are synthesized,as well as the effects of benzene and naphthalene mesogens on dielectric properties are investigated.The synthesized copolyesters containing naphthalene structure have good comprehensive properties with high thermal stability(T_(5%)=479℃ and T_g=195-216℃),inherent flame retardance(LOI=33.0-35.0 and UL-94 V-0 level at 0.8 mm),low Dk(2.9-3.0@10 GHz)and low Df(0.0027-0.0047@10 GHz).Naphthalene mesogen can reduce the dielectric loss more significantly than benzene at high frequency by reducing the density and mobility of polarizable groups,which leads to the effectively limited dipole polarization in copolyesters.Consequently,we proposed a new strategy for designing low Dk and low Df materials.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51772022)
文摘(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing thetf value and improving the thermal stability.The phase composition and the microstructure were investigated using X-ray diffraction,Raman spectra,and scanning electron microscopy.A set of phase transitions which were induced by composition had been confirmed via the sequence:rutile structure→coexistence of rutile and columbite phase→columbite phase.For(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics,the addition of ZnNb2O6 content(x=0–1)led to the decrease ofer from 62.98 to 23.94.As a result of the high Q×?of ZnNb2O6 ceramics,the increase of ZnNb2O6 content also led to the lower sintering temperatures and the higher Q×?values.Thetf value was reduced from+108.04(x=0)to–49.31 ppm/℃(x=1).Among them,high density 0.5CoTiNb2O8-0.5ZnNb2O6 ceramics were obtained at 1175℃with excellent microwave dielectric properties of εr 39.2,Q×? 40013 GHz,and tf+3.57 ppm/℃.
文摘针对高效、快速、连续、无损的路面雷达应用技术存在的问题,研究了路面雷达电磁波在多层介质中的传播规律.基于电磁波理论的基本原理,从M axw e ll方程着手,建立了雷达电磁波在路面结构体系中的传播模型.该模型考虑了介质介电常数虚部的贡献,理论上更加严谨,并更接近于道路工程实际.应用该模型,模拟合成了多层路面结构体系中雷达电磁波的反射信号,将其与实测信号对比,验证了所建立模拟方法的正确性和适用性.
基金financially supported by the National Natural Science Foundation of China(Nos.51991351 and 51991350)the Fundamental Research Funds for the Central Universities+1 种基金the 111 Project(No.B20001)the Sichuan Science and Technology Program(No.2020YFH0016)。
文摘Ultra-low dielectric loss(Df)and low dielectric constant(Dk)materials are urgently required in highspeed and large-capacity transmission,in which the wholly aromatic liquid crystal polymer(LCP)has gained attention due to its excellent dielectric properties.However,the relationship between molecular structure and dielectric properties is still not clear.In this study,two copolyesters containing phenyl or naphthyl structures are synthesized,as well as the effects of benzene and naphthalene mesogens on dielectric properties are investigated.The synthesized copolyesters containing naphthalene structure have good comprehensive properties with high thermal stability(T_(5%)=479℃ and T_g=195-216℃),inherent flame retardance(LOI=33.0-35.0 and UL-94 V-0 level at 0.8 mm),low Dk(2.9-3.0@10 GHz)and low Df(0.0027-0.0047@10 GHz).Naphthalene mesogen can reduce the dielectric loss more significantly than benzene at high frequency by reducing the density and mobility of polarizable groups,which leads to the effectively limited dipole polarization in copolyesters.Consequently,we proposed a new strategy for designing low Dk and low Df materials.
