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
This paper reports that single-phase γ-Y2Si2O7 is prepared via a sufficient blending and cold-pressed sintering technique from Y2O3 powder and SiO2 nanopowder. It studies the dielectric properties of γ-Y2Si2O7 as a ...This paper reports that single-phase γ-Y2Si2O7 is prepared via a sufficient blending and cold-pressed sintering technique from Y2O3 powder and SiO2 nanopowder. It studies the dielectric properties of γ-Y2Si2O7 as a function of the temperature and frequency. The γ-Y2Si2O7 exhibits low dielectric loss and non-Debye relaxation behaviour from 25 to 1400℃ in the range of 7.3 18 GHz. The mechanism for polarization relaxation of the as-prepared γ-Y2Si2O7 differing from that of SiO2 is explained. Such particular dielectric properties could potentially make specific attraction for extensive practical applications.展开更多
The effects of Cd^(2+) ions on the microstructure,magnetic properties,and dielectric properties of Bi_(2)O_(3)-added MgFe_(2)O_(4) ferrites(Cd_(x)Mg_(1-x)Fe_(2)O_(4),x=0.00,0.15,0.30 and 0.45)are obtained by adopting ...The effects of Cd^(2+) ions on the microstructure,magnetic properties,and dielectric properties of Bi_(2)O_(3)-added MgFe_(2)O_(4) ferrites(Cd_(x)Mg_(1-x)Fe_(2)O_(4),x=0.00,0.15,0.30 and 0.45)are obtained by adopting the solid-state reaction method at a low temperature(910℃).The objective is to achieve matching impedances,low magnetic and dielectric losses(tanδμand tanδε,respectively),and a relatively large miniaturization factor to reduce antenna size.Experimental results indicate that the cations occupying the tetrahedral(A)and octahedral(B)ion sites are redistributed,resulting in an enhanced super-exchange interaction between the two sublattices.As a result,improved magnetization,including the increase in saturation magnetization(41.74 emu/g)and decrease in coercivity(63.75 Oe),is realized.The real part of permeability(μ')also increases with increasing concentration of Cd^(2+) ions.When x is 0.15,matching impedances with equivalent μ'and ε'values are obtained over a long frequency range(1–150MHz).Moreover,the formation of a dense microstructure guarantees that losses occur at low orders of magnitude(tanδμ≈10−2 and tanδε≈10−3).Accordingly,these properties afford wide application perspectives for the proposed compounds in the high-frequency region,i.e.,from high-frequency to very-high-frequency bands.展开更多
为准确地评估交联聚乙烯(cross linked polyethylene,XLPE)电缆的水树老化程度,该文提出一种基于超低频介损和U-I滞回曲线的评估方法。对3组XLPE样本分别进行0、96和168h的加速水树老化,老化结束后采用快速超低频介损设备(very-low freq...为准确地评估交联聚乙烯(cross linked polyethylene,XLPE)电缆的水树老化程度,该文提出一种基于超低频介损和U-I滞回曲线的评估方法。对3组XLPE样本分别进行0、96和168h的加速水树老化,老化结束后采用快速超低频介损设备(very-low frequency dielectric loss detector,iFDS)在1mHz~1kHz范围内测试不同水树老化状态的XLPE电缆的介电频谱和不同频率下U-I滞回曲线。结果发现:水树老化后的电缆段在超低频段(1mHz~0.1Hz)的介损值显著增大,并在0.002和0.1Hz附近出现两个明显的松弛损耗峰。老化越严重的试样,U-I滞回曲线形变越严重。水树老化后电缆绝缘中产生了新的松弛极化过程,相较于单一频率0.1Hz下的介损值,超低频介电谱能够提供更丰富的绝缘状态信息。在1mHz下,U-I滞回曲线特性的偏转角变化率与曲线形变率均随超低频介损值的上升而增大,能够更加准确地评估电缆绝缘的水树老化程度。将超低频介损结合U-I滞回曲线可以有效地评估电缆绝缘的水树老化程度。展开更多
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.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50872159)the National Defense Pre-research Foundation of China (Grant Nos. 513180303 and A2220061080)
文摘This paper reports that single-phase γ-Y2Si2O7 is prepared via a sufficient blending and cold-pressed sintering technique from Y2O3 powder and SiO2 nanopowder. It studies the dielectric properties of γ-Y2Si2O7 as a function of the temperature and frequency. The γ-Y2Si2O7 exhibits low dielectric loss and non-Debye relaxation behaviour from 25 to 1400℃ in the range of 7.3 18 GHz. The mechanism for polarization relaxation of the as-prepared γ-Y2Si2O7 differing from that of SiO2 is explained. Such particular dielectric properties could potentially make specific attraction for extensive practical applications.
基金This work was supported by National Key Scientific Instrument and Equipment Development Project No.51827802by Major Science and Technology projects in Sichuan Province Nos.2019ZDZX0026 and 20ZDYF2818+1 种基金by the National Natural Science Foundation of China No.51872041by Foundation for University Teacher of Education of China No.ZYGX2019J011.
文摘The effects of Cd^(2+) ions on the microstructure,magnetic properties,and dielectric properties of Bi_(2)O_(3)-added MgFe_(2)O_(4) ferrites(Cd_(x)Mg_(1-x)Fe_(2)O_(4),x=0.00,0.15,0.30 and 0.45)are obtained by adopting the solid-state reaction method at a low temperature(910℃).The objective is to achieve matching impedances,low magnetic and dielectric losses(tanδμand tanδε,respectively),and a relatively large miniaturization factor to reduce antenna size.Experimental results indicate that the cations occupying the tetrahedral(A)and octahedral(B)ion sites are redistributed,resulting in an enhanced super-exchange interaction between the two sublattices.As a result,improved magnetization,including the increase in saturation magnetization(41.74 emu/g)and decrease in coercivity(63.75 Oe),is realized.The real part of permeability(μ')also increases with increasing concentration of Cd^(2+) ions.When x is 0.15,matching impedances with equivalent μ'and ε'values are obtained over a long frequency range(1–150MHz).Moreover,the formation of a dense microstructure guarantees that losses occur at low orders of magnitude(tanδμ≈10−2 and tanδε≈10−3).Accordingly,these properties afford wide application perspectives for the proposed compounds in the high-frequency region,i.e.,from high-frequency to very-high-frequency bands.
文摘为准确地评估交联聚乙烯(cross linked polyethylene,XLPE)电缆的水树老化程度,该文提出一种基于超低频介损和U-I滞回曲线的评估方法。对3组XLPE样本分别进行0、96和168h的加速水树老化,老化结束后采用快速超低频介损设备(very-low frequency dielectric loss detector,iFDS)在1mHz~1kHz范围内测试不同水树老化状态的XLPE电缆的介电频谱和不同频率下U-I滞回曲线。结果发现:水树老化后的电缆段在超低频段(1mHz~0.1Hz)的介损值显著增大,并在0.002和0.1Hz附近出现两个明显的松弛损耗峰。老化越严重的试样,U-I滞回曲线形变越严重。水树老化后电缆绝缘中产生了新的松弛极化过程,相较于单一频率0.1Hz下的介损值,超低频介电谱能够提供更丰富的绝缘状态信息。在1mHz下,U-I滞回曲线特性的偏转角变化率与曲线形变率均随超低频介损值的上升而增大,能够更加准确地评估电缆绝缘的水树老化程度。将超低频介损结合U-I滞回曲线可以有效地评估电缆绝缘的水树老化程度。
