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。     

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.     

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.

     

Onsager model for a variable dielectric permittivity near an interface

Using a generalization of an Onsager type approach, we are able to predict a dielectric permittivity profile of an inhomogeneous dipolar fluid in the presence of a dielectric interface. The reaction and cavity fields are calculated semi-analytically using bispherical coordinates. An asymptotic expression for the local permittivity is derived as a function of distance from the interface.     

Calculation of the dielectric permittivity tensor for the surface layer of a cubic crystal

The dielectric permittivity tensor has been calculated by the effective-field method with inclusion of spatial inhomogeneities in the crystal surface layer. Cubic crystals have been shown to have natural optical activity within a layer a few lattice constants thick. Fiz. Tverd. Tela (St. Petersburg) 40, 645–647 (April 1998)     

基于TM0mn模式微波介质材料复介电常数的测量

 提出了一种基于闭式谐振腔TM_0mn模式测量微波介质材料复介电常数的方法。利用模式匹配技术、Ritz-Galerkin方法以及传输模品质因数测量法导出了介质材料相对介电常数和损耗角正切的测量公式。最后,利用矢量网络分析仪对常用天线罩材料进行了扫频测量,结果表明：高分子量聚乙烯在3~6 GHz范围内的相对介电常数为2.30±0.05,损耗角正切为(1.8~2.0)×10^-4。     

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.     

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.     

Dependence of dielectric permittivity of moist disperse materials on the temperature

The behavior of the dielectric permittivity of a mixture of disperse materials with change in volume content of the component with high dielectric permittivity (water) and temperature is investigated. An analysis of the results is presented. A formula is given for the calculation of the dielectric permittivity of moist disperse materials as a function of the temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 65–68, January, 1982.     

Effective permittivity of periodic composite materials: Numerical modeling by the finite element method

The effective properties of composite materials are closely related to the composition and arrangement of its constituents. Many studies and articles are actively studying the dielectric properties of heterogeneous structures with random and periodic arrangement. In the quasistatic limit, we use the finite element method as a numerical tool to evaluate the effective permittivity of two and three component composites. Two heterostructures are investigated; the first is formed by crossed dielectric cylinders in permanent contact and arranged in three layers. The cylinders are immersed in a dielectric host medium. The second structure is similar to the first except that the tubes are covered by an interphase layer. The numerical tool used to extract the exact value of the effective permittivity takes into account all internal multipolar interactions which contribute to the polarization of the material medium. The impacts of the relative permittivity and volume fraction of cylinders, the thickness of interphase and its dielectric constant are reported. The Maxwell–Garnett theory fails to predict the effective permittivity of the studied structures for high volume fraction and permittivity contrast. To overcome this problem, an amendment was made to the McLachlan equation McQ also termed the Two Exponent Single Percolation Equation TESPE. The first exponent t is held equal to 1 and the other exponent s is depending on the volume fraction. s is calculated so that the whole values of the effective permittivity obtained by the McQ rule are exactly the same values obtained by the simulations. Finally, we obtained a chart and a model to find the values of s, a fast way that is very useful for practitioners and design engineers of composite materials.     

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.     

Two-step numerical procedure for complex permittivity retrieval of dielectric materials from reflection measurements

A two-step measurement procedure has been proposed for measurement of complex permittivity of dielectric materials using one-port reflection measurements. In the procedure, as a first step, a graphical method is applied to analyze on the complex reflection-coefficient plane the general pattern of dielectric behavior of the sample. Then, as a second step, optimization algorithms are utilized for retrieving electrical properties of samples. The procedure requires measurement of complex reflection scattering parameters of at least two samples with different lengths. It has been validated by X-band measurements of three polyvinyl chloride samples with lengths 5, 10, and 20 mm.     

Electrical characteristics of three-component dielectric media

We study the effective parameters of a three-component plane dielectric medium with a doubly periodic arrangement of circular inclusions. The problem is solved in the one-dipole approximation. The computational results are compared with a two-component Rayleigh model. The general structure of the formulas for the effective parameters is discussed and the reciprocity relations for a three-component matrix system are determined. Explicit expressions are given for the dielectric permittivity when the concentration of circular inclusions is low, and their domain of applicability is determined. Under certain polarization conditions, the effective conductivity in a three-component medium is exactly equal to the dielectric permittivity of the matrix. Zh. éksp. Teor. Fiz. 114, 1121–1136 (September 1998)     

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.     

Cobalt iron-oxide nanoparticle modified poly(methyl methacrylate) nanodielectrics

In this paper, we report the dielectric properties of composite systems (nanodielectrics) made of small amounts of mono dispersed magnetic nanoparticles embedded in a polymer matrix. It is observed from the transmission electron microscope images that the matrix polymeric material is confined in approximately 100 nm size cages between particle clusters. The particle clusters are composed of separated spherical particles which comprise unconnected networks in the matrix. The dielectric relaxation and breakdown characteristics of the matrix polymeric material are altered with the addition of nanometer size cobalt iron-oxide particles. The dielectric breakdown measurements performed at 77 K showed that these nanodielectrics are potentially useful as an electrical insulation material for cryogenic high voltage applications. Finally, structural and dielectric properties of nanocomposite dielectrics are discussed to present plausible reasons for the observed low effective dielectric permittivity values in the present and similar nanodielectric systems. It is concluded that polymeric nanoparticle composites would have low dielectric permittivity regardless of the permittivity of nanoparticles are when the particles are coordinated with a low dielectric permittivity surfactant.     

A comparison of the results of a numerical simulation and an approximate calculation of the statistical characteristics of radio waves in a layer with random inhomogeneities of dielectric permittivity

We consider the formation algorithm for a random inhomogeneity field of dielectric permittivity of a medium that is used in simulations of the statistical characteristics of a wave that has propagated through a randomly inhomogeneous layer. We carry out a comparison of the statistical characteristics of a geometrical-optics wave, obtained via a numerical simulation, with the results of calculations of these characteristics by approximate formulae obtained using perturbation theory. It is pointed out that the applicability limits of the perturbation method, when solving geometrical-optics equations in a randomly inhomogeneous medium, depend on the formulation (one- or two-point) of the trajectory problem. It is shown that a calculation of the spatial correlation function of the field can be carried out using the perturbation method, even in the case of relatively strong fluctuations of dielectric permittivity. This is due to the fact that, in the region where this function differs markedly from zero, the correlation function of the eikonal obtained by the perturbation method is sufficiently accurate, and amplitude fluctuations are small.     

Giant dielectric permittivity observed in pb-based perovskite ferroelectrics

Giant dielectric permittivity was observed in La-modified PbTiO (3) (PLT) with A-site vacancy. The observed values of PLT with A-site vacancy are 1 order of magnitude larger than those of relaxor ferroelectrics. The giant relative dielectric permittivity, coupled with a low dielectric loss (tandelta approximately 0.03) of the PLT, potentially makes it one of the most promising materials for numerous modern technological applications.     

Compact group method in the theory of permittivity of heterogeneous systems

The static permittivity of macroscopically homogeneous and isotropic heterogeneous systems is analyzed using the concepts of compact groups of inhomogeneities. The method makes it possible to avoid excessive specification of mutual polarization processes in the system, which ensures effective application of this method for concentrated systems with arbitrary relations between the permittivities of system components. By way of example, the Maxwell-Garnett and Bruggeman formulas for the effective permittivity of heterogeneous matrix systems are reconstructed and their interrelation is analyzed. It is shown that the Bruggeman formula is more limited in the sense that it is based on additional model assumptions concerning the properties of the system and the type of averaging of fields over the volume of the system. Generalizations of these formulas are obtained for multicomponent heterogeneous systems consisting of inhomogeneous nonspherical particles or parts.     

A study of the microwave dielectric permittivity of liquid crystals in electric and magnetic fields

A microwave detector based on a self-sustained oscillator circuit is proposed as a means to investigate the real and imaginary components of the dielectric permittivity of liquid crystals in external electric and magnetic fields. Results are given for measurements of a 500 MHz oscillator frequency for two types of nematic crystals, 5CBP and MBBA. Fundamental regularities are identified in the behavior of the microwave dielectric permittivity of samples in electric and magnetic fields. It is shown that the minimum of the high-frequency dielectric loss in liquid crystals correspond to a situation in which the long axes of the molecules are oriented parallel to the direction of the microwave electric field. Zh. Tekh. Fiz. 68, 117–121 (January 1998)     

Analysis on effect of low dielectric permittivity on indium-doped tin oxide based optically transparent terahertz patch antenna

Indium-doped tin oxide based optically transparent rectangular patch antennas are designed to resonate at 750 GHz; one on the glass substrate and the other on the polyimide substrate. Characteristics of both the transparent antennas such as impedance bandwidth, radiation efficiency, directivity and gain are analyzed and compared. Polyimide substrate has a lower dielectric permittivity than the glass substrate. The effect of low dielectric permittivity substrate on the radiation characteristics of the terahertz transparent patch antenna is analyzed. The transparent antenna on polyimide substrate is shown to have gain greater than 3.97dB in 714–795 GHz. The proposed transparent antennas are designed and simulated by using finite element method based electromagnetic solver, Ansys–HFSS.