Pseudo-Fourier modal analysis of two-dimensional arbitrarily shaped grating structures

The pseudo-Fourier modal analysis of two-dimensional arbitrarily shaped grating structures is described. It is shown that the pseudo-Fourier modal analysis has an advantage of improved structure modeling over the conventional rigorous coupled-wave analysis. In the conventional rigorous coupled-wave analysis, grating structures are modeled by the staircase approximation, which is well known to have inherent significant errors under TM polarization. However, in the pseudo-Fourier modal analysis, such a limitation of the staircase approximation can be overcome through the smooth-structure modeling based on two-dimensional Fourier representation. The validity of the claim is proved with some comparative numerical results from the proposed pseudo-Fourier modal analysis and the conventional rigorous coupled-wave analysis.     

Artificial dielectric medium possessing simultaneously negative permittivity and magnetic permeability

An artificial dielectric medium comprising two sublattices of spherical particles made of a high-dielectric-constant (high-ε) material, which are embedded into a low-ε dielectric matrix, are considered. Particles belonging to different sublattices have different diameters. It is shown that the properties of this composite structure are equivalent to those of an isotropic medium possessing a negative refractive index (n < 0) in the vicinity of frequencies at which the H ₁₁₁ and E ₁₁₁ oscillation modes exhibit simultaneous resonance in particles of different diameters, which leads to the appearance of electric and magnetic dipole moments, respectively. Averaging of these dipole moments over the volumes of cells formed by the corresponding spherical particles determines their contributions to the permittivity and magnetic permeability of the composite medium. At frequencies above the resonance, both contributions become negative and, hence, the medium exhibits simultaneously negative values of the permittivity and magnetic permeability. The proposed composite structure consists only of dielectric components. Spherical particles with ε_d > 200 can be made of a ferroelectric material.     

A composite medium with simultaneously negative permittivity and permeability

A new composite medium that possesses simultaneously negative permittivity and permeability in the microwave wavelength range is proposed. The medium is composed of evanescent waveguide structures responsible for the negative permittivity, with embedded cylindrical elements of a one-dimensional chiral medium accounting for the negative permeability. The evanescent waveguide structures exhibit blooming and antiresonances in the reflection coefficient.     

Standard-independent estimation of dielectric permittivity with microdielectric fringe-effect sensors

Microdielectric spectroscopy with planar fringe-effect (FE) interdigital sensors is a useful method for noninvasive characterization of the interfacial properties of the materials. Unfortunately, obtaining an accurate dielectric spectrum is difficult because of the complexity of the probing electrical field created by the FE sensor and the contribution of the sensor substrate and stray elements to the overall measurements. Previously, quantitative microdielectric spectroscopy required the calibration of the FE sensor with standard materials that are known to be dielectrically similar to an unknown sample of interest. This limitation complicates the application of microdielectric spectroscopy, particularly in cases where the monitored sample undergoes a transformation that changes its dielectric permittivity. A standard-independent method for quantitative FE microdielectric measurements is proposed in this paper. The developed method is based on comparison of the theoretically predicted admittance of the FE sensor with the sample of known dielectric properties and the measured sensor admittance. Comparison of the theoretical predictions with the admittance measurements reveals the contribution of the unknown stray elements. The measurements with an unknown sample are then adjusted for the strays. The contribution of the sensor substrate to the sensor measurements is removed using the theoretical model derived from the electroquasistatic approximation of Maxwell equations. The dielectric permittivity of the material being tested is calculated by successively solving the system of complex nonlinear equations for each frequency at which the sensor admittance is measured. The developed method is illustrated by applying it to the dielectric measurements of several dissimilar samples. The results are in excellent agreement with those obtained using the gold standard parallel-plate measurement method over the entire range of frequencies.     

低介电常数聚酰亚胺薄膜的制备与性能研究

用单体4,4′-二胺基二苯醚（ODA）和均苯四甲酸二酐（PMDA）添加纳米SiO2,在溶剂N,N-二甲基乙酰胺（DMAC）中,采用原位聚合法合成SiO2/聚酰亚胺（PI）复合薄膜。用氢氟酸刻蚀SiO2纳米粒子,引入纳米微孔,形成含有微孔的PI薄膜。造孔剂含量为15%时,薄膜的介电常数从纯聚酰亚胺的3.54降低至3.05（1kHz）。用透射电镜表征微孔结构,分析了微孔孔径和造孔剂（SiO2）含量对薄膜介电常数、耐热性、疏水性和机械强度等性质的影响。     

The effects of permittivity and thickness of dielectric layers on micro dielectric barrier discharges

The discharge characteristics of a plasma display panel (PDP) cell are investigated by two-dimensional fluid simulation and experiment in order to analyze the effects of permittivity and thickness of dielectric layers. Four-inch test panels having the same cell size as a 50-inch FHD (full high definition) resolution were fabricated to measure static margin, luminance, power consumption, and luminous efficacy. As the dielectric permittivity decreases and the dielectric thickness increases, firing voltage increases, but luminous efficacy increases due to the decreases of power consumption. It was observed that the luminous efficacy increases by 30% in the case of relative permittivity ε_r = 7 and dielectric thickness d = 25 µm compared with the case of ε_r = 12 and d = 35 µm.     

The permittivity and dielectric loss of reaction-bonded silicon nitride

Using recently developed coaxial line methods values of permittivity and dielectric loss have been determined over the frequency range 0.5 to 7 GHz for a series of reaction-bonded silicon nitride specimens in which the degree of nitridation has been varied. For fully nitrided material (having a weight gain of 62% and a volume porosity of 19%) the measured permittivity was 4.60 and was almost independent of frequency; fitting both the permittivity and loss data to the Universal Law of dielectric response confirmed that the limiting condition of lattice loss applied withn=0.98±0.02. Reduction of the degree of nitridation caused progressive increases in permittivity and loss, both of which closely approached the quoted values for pure silicon at weight gains below about 40%.     

Coaxial line methods for measuring permittivity and dielectric loss

Two coaxial line techniques for the determination of complex permittivities of solid and liquids are described. The first, the matched termination method, is essentially a comparison technique using air as the reference dielectric, producing accurate values of . In the second, the resonant line method, the characteristic impedance termination is replaced by an adjustable short circuit. This method was developed primarily for the purpose of determining the values of tan in low loss materials. Both methods can be used for frequencies in the 200 MHz to 9 GHz range and normally require only conventional apparatus. The results obtained for the materials under test agreed well with the published data, thus underlining the suitability of the two techniques for dielectric measurements.     

Use of conjugate dielectric and metamaterial slabs as radomes

An interesting application of left-handed metamaterials is proposed and numerically verified. Specifically, a structure consisting of a conventional dielectric slab adjacent to a metamaterial slab of the same width but of opposite material characteristics, is used as a radome. The behaviour of the structure for normal as well as for oblique incidence is considered. The results are satisfactory in both cases. It is shown that cylindrical structures similar to the aforementioned straight structures could also be used as radomes. However, the behaviour of the structure is non-reciprocal for incoming and outgoing waves. The dispersive finite-difference time-domain method is applied to study all the structures and the numerical results verify that the straight conjugate slabs are transparent in normal incidence and reduce the reflections for oblique incidence, which are the desirable characteristics for a radome     

Methoxypolyethylene glycol functionalized carbon nanotube composites with high permittivity and low dielectric loss

High relative permittivity and low dielectric loss were simultaneously achieved in the percolative nanocomposites with methoxypolyethylene glycol (mPEG) modified multi-walled carbon nanotubes (MWCNTs). The dense mPEG layer with a thickness of approximately 1.7 nm was continuously coated on the surface of MWCNTs. MWCNTs exhibited excellent dispersibility after being functionalized by mPEG (mPEG@MWCNTs), the mPEG@MWCNTs/ethanol suspension was still turbid even when the suspension was deposited for two months. A high permittivity of 69.7 and a low dielectric loss of 0.042 were simultaneously achieved in the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposite with 4.02 vol% mPEG@MWCNTs at 1 kHz. The improved dielectric properties in the nanocomposite is mainly ascribed to the following reasons: (i) the increased microcapacitors formed by MWCNTs and insulated dielectric composite; (ii) the enhanced interfacial polarization due to the homogeneous dispersion of mPEG@MWCNTs in the nanocomposites and tight adhesion between mPEG@MWCNTs and P(VDF-HFP) matrix.     

High dielectric permittivity of Li and Sc co-doped NiO ceramics

Microstructures, phase structures, and dielectric properties of Li and Sc co-doped NiO ceramics were systematically investigated. A high ε′ (~10⁴) is observed in a wide temperature (200–420 K) and frequency (100–10 kHz) range. The increase of ε′ with Li concentration is related to the increase of grain size. With increasing temperature, ε′ enhances and the ε″ peak shifts to higher frequency, indicating a thermally activated relaxation process. The activation energy for relaxation is nearly comparable to that for grain conduction, implying the polarization process depends on the conducting of the charge in the grain interior. Complex impedance spectroscopy analysis shows the dielectric behavior is attributed to the boundary-layer capacitor mechanism and existing huge polarization.     

Giant dielectric permittivity of Ca and Sb-co-doped TiO2 ceramics

The continuous development of microelectronic devices with integrated functions has led to an increasing interest in the development of dielectric ceramics with high dielectric constant, low dielectric loss, good frequency, and temperature stability. In this work, (Ca, Sb)-co-doped TiO₂ (CSTO) ceramics were prepared by solid-phase reaction sintering method and their phase structure, microstructure, giant dielectric properties, and mechanism were systematically investigated. The results show that the secondary phase of CSTO ceramic samples appeared when x?≥?4%. The average grain size of CSTO ceramics decreased as the amount of doping increases, and all CSTO ceramics had giant dielectric constants. When the doping amount was x?=?4%, the CSTO ceramics obtained optimum dielectric properties, where ε′ = 2.6?×?10⁵ and tan δ?=?0.10. X-ray photoelectron spectroscopy (XPS) results showed that the giant dielectric origin was mainly due to the Sb⁵⁺ doping that generated electrons inside the material, Ca²⁺ doping that enhanced the generation of vacancies inside the material, and the defective dipole clusters produced that improved the dielectric properties of the CSTO ceramics. This work is critical for the development and deployment of new TiO₂-based giant dielectric ceramics.

     

高导热率及低介电常数的AlN/PI纳米复合薄膜研究

通过将纳米氮化铝加入到原位聚合而成的聚酰亚胺中以提高纳米复合薄膜的导热系数.采用KH550偶联剂对氮化铝粒子表面进行物化处理,以提高有机-无机两相界面的结合力.采用SEM、TGA等对材料的微观结构、热性能等进行了研究.结果显示无机粒子在纳米复合薄膜中分散均匀,并在保持较低的介电性能同时提高了复合材料的热稳定性和导热性能.这样的材料在电子封装材料和印刷线路板中具有很大的应用前景.