材料性质对介质阻挡放电特性的影响

选取三种典型的介质材料：玻璃、环氧、聚四氟乙烯,通过试验研究它们的放电特性和介质厚度对放电特性的影响。结果表明阻挡层介质材料的选取对介质阻挡放电的特性有较大影响。试验和分析结果还显示了这样的规律,即选用介电常数较大、厚度较薄的材料容易产生强烈的放电。在理论上对这一试验结果给出了合理的解释．     

复合电介质介电性能有限元仿真

以聚合物基体添加具有非线性填料非线性复合电介质为研究对象,利用编程实现填料颗粒在基料中随机分布和基于蒙特卡洛(MC)模拟的模型随机构建,并通过三维有限元数值分析软件求得不同电压激励下的响应电流.采用时域最小二乘法对仿真得到的总电流进行分解并获得材料的宏观介电参数与电场强度的关系.结果表明:填料在空间的随机分布导致复合材...     

The dielectric properties of meat

The permittivity and conductivity of beef and chicken samples were measured in the frequency range of 1 Hz to 1 MHz. Differences were observed in these dielectric spectra for commercially purchased, as compared to freshly slaughtered samples. In particular, fresh samples display a greater directional anisotropy in their electrical properties and a smaller, frequency-dependent conductivity. Changes in the dielectric properties are also produced by freezing and cooking procedures. These results indicate that measurement of the low-frequency dielectric properties of meat products could serve as a monitor of their storage and preparation history     

Electrical and optical properties of microwave dielectric thin films prepared by pulsed laser deposition

Abstract

Bi₂(Zn_1/3Nb_2/3)₂O₇, BiZN, materials possess high dielectric constant and low loss factor in microwave frequency region. They have good potential for device application, especially in the form of thin films. However, the microwave dielectric properties of a thin film are very difficult to be accurately measured. Evaluation on the dielectric behavior of the films through the performance of the microstrip line devices made of these films involves metallic conduction and stray field losses. A novel measuring technique, which can directly evaluate the microwave dielectric properties of a thin film is thus urgently needed.

In this paper, BiZN thin films were grown on [100] MgO single crystal substrates using pulsed laser deposition process. The high-frequency dielectric properties of thus obtained thin films were determined using optical transmission spectroscopy (OTS). The [100] preferentially oriented films with pyrochlore structure can be obtained for the thin films deposited at 400–600°C substrate temperature under 0.1 mbar oxygen pressure. OTS measurements reveal that the index of refraction (n=1.95–2.35) and absorption coefficient (k=0.28x10^?4-2.25 × 10^?4 nm^?1) of the films vary insignificantly with the crystallinity of the BiZN films.     

Numerical simulations and experimental study of frequency-dependent dielectric properties of composite material with stochastic structure

Results of a computer modeling and analytical estimations of frequency-dependent dielectric properties of a composite material with stochastic structure in the frequency range from 1 mHz to 1 kHz are presented and are compared with experimentally obtained parameters. The studied composite was a mixture of materials having considerably different properties, where the inclusion phase with the volume fraction of 0.31 was distributed randomly in the host material forming a complex three-dimensional structure. For such composite dielectric, the applicability of bounds on the effective complex permittivity and different known mixing formulas for estimating of the effective parameters is examined. The numerical simulations performed using measured frequency-dependent characteristics of the constituents and the reconstructed three-dimensional stochastic structure of the composite, yielded values of the effective dielectric permittivity which were in good agreement with the measured ones. Frequency variations of the computed distributions of the microscale electric field and energy losses in the bulk of the studied composite dielectric are presented and discussed.     

Numerically established correlation in electrical responses ofpolymer film capacitors to ac and pulsed voltages

In this paper, an equivalent circuit model is used to simulate electrical responses of metalized polymer film capacitors to either ac voltage or pulsed voltage stresses, in particular electric field induced on the electrode coating surface and power dissipation within the film capacitor. Electrode segmentation patterns are taken into consideration by means of arrays of interconnected lumped surface resistors, and the film capacitance is modeled by a set of shunt capacitors distributed across the length of the capacitor film. Voltage magnitude and waveform characteristics are studied in great detail for their effects on surface electric field and power dissipation. Through numerical examples, surface electric field and dissipated power induced by one type of external stress (ac or pulsed) at one frequency are shown to correlate with those at a different frequency. Further correlation is also established to relate surface field and dissipated power induced by one type stress (e.g. ac) to those by the other (pulsed), provided the waveform. characteristics of the two different stresses are specifically related. These numerically established correlations can permit significant reduction in development time of metalized film capacitors     

Experimental measurements of very fast transient voltages based on an electro-optic effect

In this paper the Kerr electro-optic effect is considered from the aspect of its application in high-voltage engineering. Comparative analysis between measurements of electric fields established by fast transient voltages in liquid dielectrics with standard methods and with Kerr electro-optic effect is performed. Physical basiscs of the Kerr electro-optic effect are presented. Characteristics of a He–Ne laser significant for its application in the range of high voltage transient fields with Kerr electro-optic effect are pointed out.     

铁电微晶粉粒的介电性能研究

用3种不同方法测量了钛酸钡微晶粉料在铁电相变过程中表观介电常数的变化．用理论模型说明了不显露出宏观的介电常数居里峰的原因．对钛酸钡的测量证实了理论结果．按理论预言,测量了钛酸锶钡粉料与水混合成两相不均匀系的相变介电峰,实验结果与理论公式符合得很好．实验还表明,用TSC方法可以很好地观察到粉料的极性相变．     

Effect of re-oxidation on dielectric properties in Ni-MLCC

The effect of re-oxidation treatment on the solubility of dopants and the dielectric properties of rare-earths (La, Ho) and V-substituted BaTiO₃ solid solutions, assuming the shell phase of X7R dielectrics, was investigated. Ho-V-substituted samples showed larger increase of the lattice parameter and T _c by re-oxidation treatment compared with La-V-substituted samples. Electron spin resonance measurements revealed that the oxidation of V³⁺ to V⁴⁺ or V⁵⁺ appeared in the range in which the increase of lattice parameter by re-oxidation treatment was observed. This suggests that the increase of T _c is due to the change of preferential occupational site of Ho ion from A-site to B-site, being accompanied with the oxidation of V³⁺. We also investigated the effect of re-oxidation treatment on the electrical properties and microstructure in Ni-MLCC samples, using rare-earths (La, Ho, Yb) and acceptors (Mn, V) doped BaTiO₃ based X7R dielectrics. The change in temperature characteristic of the dielectric constant by re-oxidation treatment was observed for the MLCC samples containing V with smaller content. In the case of Ho-V- and Yb-V-doped samples showed larger increase of the dielectric constant at around 120 °C compared with La-V-doped samples. The relationship between the microstructure and electrical properties of the MLCC sample was investigated by impedance measurement at elevated temperature.     

The effects of chemical structure on the dielectric properties of polyetherimide and nanocomposites

Low dielectric constant polyetherimides have been synthesized by incorporating a bisphenol A dianhydride, BPADA, and 2,7-bis(4-aminophenoxy) naphthalene (BAPN), a phenylene ether diamine. The flexible ether and larger planar naphthalene structure of BAPN led to more spacing between polymer molecules, resulting in less efficient chain packing and an increase in the free volume, thus decreasing the dielectric constant. New PEI/silica hybrid nanocomposites were prepared from this novel polyetherimide via sol-gel process. The dielectric constants were further decreased with the incorporation of silica. These synthesized PEI and nanocomposites have high thermal stability and good mechanical properties.     

Crystallographic and dielectric properties of highly oriented BaTiO3 films: Influence of oxygen pressure utilized during pulsed laser deposition

The crystal structure of BaTiO₃ thin films grown by pulsed laser deposition on MgO substrates was found to be strongly influenced by the oxygen pressure used during growth. Low pressures produced epitaxial films with highly strained out-of-plane lattice parameter c compared to in-plane parameter a, while increasing oxygen pressure resulted in the ratio c/a < 1 with a concomitant increase in polycrystallinity. The dielectric properties varied with changing crystal structure reaching a maximum permittivity value in films near the minimum point of tetragonal distortion and exhibiting relaxor-like behavior in c/a < 1 films close to this point. Hysteresis observed in dielectric tuning loops pointed to the presence of the ferroelectric phase in all films at room temperature. As a result of high electric field poling treatment at 300 °C, the tunability generally increased and initially symmetric tuning curves became asymmetric. The tuning curve in c/a < 1 samples became nearly linear, supporting the premise of polarization reorientation with changing deposition condition. Phase transitions to the paraelectric phase were highly suppressed and shifted upwards in temperature from the bulk transition temperature of 130 to ∼250 °C in strongly c-oriented films. Moderate shifts in oxygen working pressure were demonstrated to produce films with very different properties thereby offering convenient means for strain engineering and control of preferred crystal orientation and polarization direction of highly oriented BTO films.     

The effect of deposition temperature on the material and electrical properties of PZT thin films for ULSI DRAM applications

Abstract

The effects of deposition temperature on the properties of thin films of sputtered lead-zirconate-titanate (PZT) have been studied for ULSI DRAM storage capacitor dielectric applications. The films were deposited by reactive dc magnetron sputtering from a multi-component target. The grain size for the films deposited at 400°C was found to be less than 1000 Å, while it was ～ 10–30 μm for films deposited at 200°C. Small grain-sized material is desirable since it leads to better cell-to-cell uniformity in terms of charge storage capacity and other electrical and reliability properties. The optimum lead compensation was found to increase as the deposition temperature (T _dep) increased. Leakage current density stays fairly constant as T _dep is varied. As-deposited films, with a deposition temperature of 500°C, were rich in the perovskite phase and showed a high charge storage density of 11.2 μC/cm² and a low leakage current density of 5.1 × 10^?7 A/cm² (both at 1.5 V). This implies the possibility of eliminating the high temperature crystallization-annealing step.     

Application of pulsed HV discharges to material fragmentation andrecycling

The physical basis of electric impulse fragmentation and its applications to the recycling of composite materials are reviewed. The method is based on the initiation of a pulsed electric discharge inside the solid dielectric material. With pulse amplitudes of ~300 kV, material layers of ~2 cm can be punctured. Specific energy deposition, of ≲100 J/cm at a GW power level, leads to pressure buildup of ≲10¹⁰ Pa in the discharge channel. Pressure waves and radially propagating cracks are launched into the solid body, which can lead to the separation of inclusions from the matrix or to detachment at material boundaries. To induce the discharge in the solid dielectric it must be immersed in a dielectric liquid with higher breakdown strength. Most applications use water, which has excellent breakdown strength at fast ramp rates and, due to its high permittivity, leads to field concentration in the solid dielectric. Electric impulse fragmentation is a clean physical method without any environmental burden and therefore well suited for recycling applications. In this paper we consider applications in the fields of demolition debris, incineration ashes, contaminated surface layers, electric appliances, glass, and elastoplastic materials. Finally, the economy and the scaling of the technique to large material throughput are discussed     

基于脉冲漏磁理论的铁磁性材料斜裂纹检测

在广泛应用于各行各业的铁磁性材料中,由于应力和环境等因素的作用,裂纹是其最常见的缺陷之一,且多以不规则的形状(如斜裂纹)存在.为了分析斜裂纹的脉冲漏磁信号特点,建立了脉冲漏磁检测斜裂纹的有限元仿真模型,对比分析了斜裂纹与垂直裂纹的脉冲漏磁信号的差异,提取并研究了相关特征量与斜裂纹尺寸的关系.同时,利用脉冲漏磁检测系统对几种斜裂纹进行了实验,检测结果与仿真分析结果一致,验证了利用脉冲漏磁检测斜裂纹的可行性,为下一步对斜裂纹的定量检测提供了理论指导.     

计算机陶瓷元件的介电性能研究

采用传统的固相法合成了(1-x)MgTiO_3~-xCaTiO_3复合陶瓷,通过改变CaTiO_3的加入量和烧结温度的方法,采用X射线衍射光谱法(XRD)、扫描电子显微镜法(SEM)、能量散射光谱(EDS)等多种分析测试手段,研究了陶瓷的相组成和微观结构等对材料介电性能的影响,并探索介电性能的演变规律。结果表明,0.97MgTiO_3-0.03CaTiO_3复合陶瓷在1 300℃下具有较好的微波介电性能:介电常数ε_r=18.21,品质因数Q×f=76 640 GHz,谐振频率温度系数τ_f=-34.79×10~(-6)/℃。     

混凝土仿真材料特性及其应用的试验研究

大型混凝土结构模型试验材料的选择对于试验结果有重要意义。本文作者对低强度仿真混凝土材料的材料配比、力学性能以及实际应用进行了分析研究 ,分析结果表明 ,仿真材料对于大体积混凝土结构的物模试验是比较理想的材料。     

Substrate effect on in-plane ferroelectric and dielectric properties of Ba0.7Sr0.3TiO3 thin films

Heteroepitaxial Ba_0.7Sr_0.3TiO₃ thin films were grown on (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.35 (001) (LSAT) and SrTiO₃ (001) (STO) single crystal substrates using pulsed laser deposition (PLD). X-ray diffraction characterization revealed a good crystallinity and a pure perovskite structure for films grown on both LSAT and STO substrates. The in-plane ferroelectric and dielectric properties of the films were studied using interdigital electrodes (IDE). The film grown on LSAT substrate exhibited an enhanced in-plane ferroelectricity, including a well-defined P-E hysteresis loop with the remnant polarization P _r = 10.5 μC/cm² and a butterfly-shaped C-V curve. Nevertheless, only a slim hysteresis loop was observed in the film grown on STO substrate. Curie temperature T _c of the film grown on LSAT substrate was found to be ∼105^∘C, which is nearly 70^∘C higher than that of the bulk Ba_0.7Sr_0.3TiO₃ ceramics. T _c of the film grown on STO substrate has almost no change compared to the bulk Ba_0.7Sr_0.3TiO₃ ceramics. The dielectric tunabilities were found to be 64% and 52% at 1 MHz for the films grown on LSAT and STO substrates, respectively.     

Mg2+-Zr4+复合取代对CoFe2O4磁致伸缩材料性能的影响

为了实现钴铁氧体在低磁场下有较高的应变灵敏度,采用Mg2+-Zr4+协同取代的方式,通过固相合成法制备了CoFe2O4磁致伸缩材料,并研究了Mg2+-Zr4+复合取代对材料的微观结构、饱和磁化强度、磁致伸缩性能及应变灵敏度的影响.结果表明,在1300℃烧结的样品均为纯净的尖晶石相,并且随着Zr4+离子取代量的增加,材料的饱和磁化强度与磁晶各向异性常数呈现增大趋势,磁致伸缩系数减小,应变灵敏度先增大后减小.在Mg2+取代量为0.05、Zr4+取代量为0.02时,低磁场域下CoFe2O4磁致伸缩材料的应变灵敏度达到最高值,为4.3×10–9 A/m,可应用于磁传感器等领域.