薄板型介质材料复介电常数的无损测量

采用带法兰结构的TE01n圆柱谐振腔,用无损检测的方法测量薄板型微波介质材料的复介电常数。利用轴向模式匹配法对谐振腔内的电磁场进行了求解,给出了相对介电常数和损耗角正切的计算公式,并利用矢量网络分析仪对几种常用微波介质材料进行了测量,其结果表明：该测量方法对相对介电常数的测量误差不超过1%,而对损耗角正切的测量误差不超过10%。该方法还具备一腔多模的测试能力,测量频率可调,可用于介质材料频率特性的测量。     

薄板型介质材料复介电常数的无损测量

采用带法兰结构的TE01n圆柱谐振腔,用无损检测的方法测量薄板型微波介质材料的复介电常数。利用轴向模式匹配法对谐振腔内的电磁场进行了求解,给出了相对介电常数和损耗角正切的计算公式,并利用矢量网络分析仪对几种常用微波介质材料进行了测量,其结果表明:该测量方法对相对介电常数的测量误差不超过1%,而对损耗角正切的测量误差不超过10%。该方法还具备一腔多模的测试能力,测量频率可调,可用于介质材料频率特性的测量。     

Enhanced dielectric permittivity of fluorine polyimide matrix with embedded graphene

A polymer nanohybrid material with enhanced dielectric permittivity was prepared using the fluorine‐containing polyimide (PI) 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride/4,4′‐oxydianiline (6FDA/ODA) as matrix and graphene as conductive filler in our present work. Studies on the dielectric properties of the 6FDA/ODA–graphene nanohybrid films show that the dielectric permittivity (ε) can be significantly enhanced by the layer‐by‐layer structure of graphene and the presence of fluorine also has an important influence on the improvement of ε. The percolation theory and microcapacitor model are used to explain the change of dielectric properties and a percolation threshold f_c = 0.0152 (2.45 wt%) was obtained by a linear‐fit calculation.

     

Temperature compensated, high permittivity dielectric resonators for millimeter wave systems

The properties of selected low loss, temperature compensated high permittivity microwave and millimetre wave dielectrics are summarised and experimental convenience suggests that planar hybrid microstrip is the preferred circuit technology for the initial studies of dielectric resonators at the millimetre wavelengths. Data are presented for temperature stabilised oscillators and some simple band pass filters are discussed.This paper is based on a talk given by G. B. Morgan, Dielectric resonators for millimetre wave circuits, Digest No. 1983/8, Inst. of Elect. Eng. Colloquium on Millimetre Waves, pp. 6.1–6.5, Jan. 1983.     

Automatic measurement of the complex permittivity at millimeter wavelengths

A measuring system including an oversized cavity resonator operating in the TE₀₁ mode for the determination of the complex permittivity - j of low-loss liquids at frequencies of about 36 GHz is described. While is obtained by wavelength measurements in the filled and the empty resonator, is determined from the variation of the Q factor of the filled resonator with the length of the dielectric sample. The Q factors of values of about 2·10⁴ to 10⁵ can be measured automatically by means of a desk calculator which controls the frequency and collects the digitized values of the detector output voltage. By means of the calculator, the Q factors of the resonator are determined by fitting analytical (Lorentzian) resonance curves to the measurement data. and the Q factor for zero sample length are calculated according to Göttmann's methods.     

Electric permittivity and dielectric loss of castor oil during its transformation to the high pressure phase

Abstract

The changes of permittivity and dielectric loss of commercially pure castor oil observed during its transition to the high pressure phase are described. Discussion about physical properties of this phase is shortly presented too.     

液体介电体电容率的测量方法

介绍了用电磁波谐振法测量液体相对电容率的方法,解决了可变电容器的准确取值问题,液体相对电容率的实验测量结果与实际标准值符合较好。     

Bulk-phase thermodynamic properties and dielectric constant of ethanol: an ab initio quantum mechanical approach combined with a statistical model

Ab initio theory at the HF/6-311G(d,p) level has been used to compute the hydrogen bonding thermodynamics in bulk liquid ethanol. Inter-cluster hydrogen bonding is assumed to mimic the H-bonding in bulk ethanol. Rotation of the clusters has been neglected, but translational and vibrational motions are taken into account for calculating bulk thermodynamic parameters. Results are well in agreement with an earlier report [J. Chem. Phys. 116, 4212 (2002)]. For a more accurate dipole moment of monomer, MP2/6-311++G(d,p) calculation was done. Use of the computed thermodynamic data in a statistical model yields the Kirkwood-Frohlich correlation factor and the dielectric constant of ethanol (21.0) close to the experimental value, 24.3 at 298 K.     

碳纳米管/聚苯胺纳米复合管的制备及其微波介电特性研究

用原位乳液聚合法在碳纳米管表面包覆聚苯胺，制备出了碳纳米管/聚苯胺一维纳米复合管.复合管的直径为50—80 nm，聚苯胺包覆层的厚度为20—30 nm，聚苯胺在碳纳米管表面以层状和枝晶状两种形态生长.研究了碳纳米管/聚苯胺复合管在2—18 GHz的微波介电特性.与纯碳纳米管相比，碳纳米管/聚苯胺复合管的介电常数的实部ε′和虚部ε″在2—18 GHz随频率变化较小，在低频波段介电常数值较小，作为微波吸收剂容易实现与自由空间的阻抗匹配，而且它的介电损耗角正切(tanδ=ε″/ε′)较高，是一种很好的微波吸收剂. 关键词： 碳纳米管 聚苯胺 微波介电特性 微波吸收剂     

On the size-effect in the dielectric permittivity of solids

Reducing the grain size in a powder should enhance its dielectric permittivity, as unpaired electrons on the grain surface create a double electric layer, the effect of which increases together with the specific surface area of the powder.     

Temperature studies of dielectric permittivity and mass density pretransitional anomalies in binary mixtures

Results of temperature studies of dielectric permittivity and mass density in binary mixtures are presented. The anomaly of dielectric permittivity as a function of temperature in nitrobenzene-n-alkanes binary mixtures has been studied. Molar dielectric permittivity which takes into account the anomaly of dielectric permittivity and the mass density anomaly has been introduced.     

含有偏心球形微粒介质球的有效介电常量

对于处在均匀外电场中含有偏心球形微粒的介质球,利用分离变量法求出球内外的电场,给出了球外电偶极矩和电四极矩的近似表达式.首次引入含有偏心球形微粒介质球的有效介电常量,它不同于同心多层介质球的等效介电常量,不仅与介质球内的介质有关,而且与球外介质有关.数值结果显示了有效介电量数随偏心距和球外介质介电常量的变化情况.     

Dielectric permittivity of aqueous solutions of electrolytes probed by THz time-domain and FTIR spectroscopy

We have measured the dielectric permittivity of pure water and aqueous chlorides solutions in the range 0.2-1.5 THz. We considered the relaxation spectral function as the weighted sum of two independent single-parameter Debye functions. Such an approach allowed to drastically reduce the number of the parameters used in the fit which we set only by physical considerations. The resulting functions allow to fit the experimental data for pure water and solutions of LiCl, KCl, NaCl, and CsCl and to predict the excess response on the high frequency side of the relaxation without “ad hoc” corrective terms.     

Effective permittivity and permeability of one-dimensional dielectric photonic crystal within a band gap

We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal is negative within a band gap region. This means that the band gap might act as ε-negative materials （ENMs） with ε 〈 0 and μ 〉 0, or μ-negative materials （MNMs） with ε 〉 0 and μ 〈 0. Moreover the effective parameters sensitively rely on size, surface termination, symmetry, etc. The effective parameters can be used to design full transmission tunnelling modes and amplify evanescent wave. Several cases are studied and the results show that dielectric photonic band gap can indeed mimic a single negative material （ENM or MNM） under some restrictions.     

介质阻挡放电中电介质参量对放电时间特性的影响

采用介质参量不对称的装置,在大气压氩气介质阻挡放电中,研究了不同电介质温度及不同电介质材料对放电时间特性的影响.实验发现,外加电压较低时,正负半周的放电时间波形没有明显的差别;外加电压较高时,正负半周的放电脉冲个数不同.分析表明,电介质温度以及材料均影响壁电荷的积累,进而使放电特性发生改变. 关键词： 介质阻挡放电 时间特性 壁电荷 介电常数     

基于双负介质与负介电常数介质交叠结构的谐振腔研究

通过探讨双负介质与负介电常数介质交叠结构的谐振特性,实现了一种能够同时缩小长度和宽度的改进的小型化谐振腔(IMCR). 对IMCR谐振特性进行了数值仿真,结果表明,IMCR能够在10.3GHz上稳定谐振,但其长度和宽度却分别只有4.58和5.08mm,相比于普通金属谐振腔的长度和宽度均缩短了一半. 这些结果对基于双负介质的小型化谐振腔的发展具有理论意义. 关键词： 双负介质 负介电常数介质 改进的小型化谐振腔 各向异性     

Zero permittivity band characteristics in one-dimensional plasma dielectric photonic crystal

We consider the oblique propagation of electromagnetic waves in one-dimensional plasma dielectric photonic crystals, the superlattice structure consisting of alternating plasma and dielectric materials using transfer matrix method. Our results show that photonic band gaps for all polarizations can be obtained in one-dimensional plasma dielectric photonic crystals. These structures can exhibit a new type of band or gap, for the incidence angles other than normal incidence, near frequencies where the electric permittivity of the plasma layer changes sign. This new band or gap arises, from the dispersive properties of the plasma layer, only for TM polarized waves and its width increases with the increasing angle of incidence. This differential behaviour under polarization can be utilized in the design of an efficient polarization splitter. The band characteristic is affected by the plasma width, the plasma density, dielectric width, the dielectric constant of the dielectric medium and angle of incidence.     

Dielectric measurements of new antiferroelectric liquid crystals

Three new pure antiferroelectric materials, synthesized at the Military University of Technology (MUT), were investigated by dielectric means. Clear relaxation modes were detected, i.e., Soft, Goldstone, low frequency in-phase (P_L) as well high frequency anti-phase (P_H) modes for paraelectric Sm A*phase, ferroelectric Sm C* phase and antiferroelectric Sm C_A* phase, respectively. Additionally, a high relaxation mode in Sm C_A* was found. The relaxation frequencies f_R of the observed modes were calculated from Cole-Cole diagrams.     

Experimental study of composite medium with simultaneously negative permeability and permittivity

Inclassicalelectrodynamics,theresponse(typicallyfrequencydependent)ofamaterialtoelectricandmagneticfieldsischaracterizedbytwofundamentalquantities,thepermittivityeandthepermeabilitym.Bothmandearepositiveinmostmaterials.In1968,Veselago[1]predictedthattheelectromagneticwavepropagationinamediumhavingsimultaneouslynegativepermittivityandpermeabilityshouldgiverisetoseveralpeculiarcharacteristics.Butnoneofhispredictionsweretestedduringthelastcentury,becausenonaturalmaterialswithsimultaneouslynegativ…     

Strain and temperature-dependent dielectric permittivity of cubic SrTiO3: Self-consistent phonon theory calculations

We examine the strain effect on the dielectric permittivity of cubic SrTiO₃ (STO) with Self-Consistent Phonon (SCP) theory calculations. Despite the soft mode frequency overestimation with this theory scheme and workflow, our calculations predict the correct tendency of TO1 with respect to temperature and strain. We found that a uniform tensile strain leads to softer TO1 modes. In addition, the TO1 frequency drops suddenly to zero at a specific temperature in the presence of a ferroelectric transition. The square linear relation between TO1 and temperature is used to estimate the Curie Temperature (T_C), and the STO dielectric permittivity calculated with the Lyddane-Sachs-Teller relation follows the Curie-Weiss (CW) law; which can also be used to determine another T_C value. Results from both approaches are in good agreement with each other and show that T_C increases significantly even when the applied tensile strain is only a few percent.