Dielectric behavior of highly conducting perfluoropolyetherwater-in-oil microemulsions

The dielectric and conductive properties of a new ternary water-in-oil microemulsion consisting of perfluoropolyether (PFPE) oil, PFPE surfactant and water, were investigated by an impedance analysis technique in the frequency range of 5 Hz to 100 MHz. The trend of both the electrical conductivity and the static permittivity was analyzed as a function of the temperature in the interval from -10 to +40°C. Maxwell-Wagner relaxation phenomena in the MHz range and a percolative transition, of dynamic type against temperature, were observed     

Dielectric Properties of Ba0.5Sr0.5TiO3 Thin Films from DC to Ka Band

Much of the interest in Ba_0.5Sr_0.5TiO₃ (BST) thin films has focused on DRAM applications. For this application, the most studied characteristics have been the dielectric constant and the leakage current, both of which are usually measured either at DC or at low frequencies. A few studies have made use of impedance measurements in the 100 Hz to 100 MHz range. Unfortunately, all these measurements fall far short of current DRAM speeds, which are quickly approaching 1 GHz. Other technologies, such as digital computing and wireless communications are already well into the microwave range. The importance of microwave characterization of BST films is therefore clear. Such a characterization technique is described and results from DC to Ka band are presented.     

Dielectric and conductive spectra of the composite of barium titanate and LiClO/sub 4/-doped polyethylene oxide

Dielectric and conductive frequency spectra in a 10 mHz-10 GHz range have been measured for a composite consisting of barium titanate (BaTiO/sub 3/) inclusions dispersed in a LiClO/sub 4/-doped polyethylene oxide (Li-PEO) matrix with volume fraction /spl Phi/ = 0-40%. Pure Li-PEO behaves as a dielectric showing a segmental-mode dielectric relaxation at high frequencies (dielectric regime) and transfers to an ionic conductor below 10 MHz (conductive regime). BaTiO/sub 3/ is a ferroelectric having a very large dielectric permittivity and spontaneous polarization. The introduction of BaTiO/sub 3/ into Li-PEO caused a rapid increase in permittivity in the dielectric regime. In the conductive regime, the composite exhibited an additional relaxation at a frequency related to the ratio of DC conductivity of Li-PEO and the permittivity of BaTiO/sub 3/. This relaxation was attributed to accumulation of dissociated Li/sup +/ and ClO4/sup o/ns at the inclusion/matrix interface which resulted in an increase of effective permittivity and a decrease of effective conductivity. Quantitative analyses based on mixing laws for the two-phase spherical dispersion system have shown that the Bruggeman equation accurately predicted the /spl Phi/-dependence of the effective permittivity over the entire frequency range. Regarding the effective conductivity, it predicted values lower than the observed. We attributed this discrepancy to the spontaneous polarization of BaTiO/sub 3/, which induced ion trapping to reduce the DC conductivity of Li-PEO matrix.     

Properties of Ferroelectric Liquid Crystal/Multiwall Carbon Nanotube Doped Composite

Carbon nanotubes-ferroelectric liquid crystal composites have been prepared and studied. Doping of carbon nanotubes into ferroelectric liquid crystal in varying concentration has been investigated in thin cells in the frequency range of 50 Hz–1 MHz. Decrease in the dielectric permittivity and dielectric strength is found with the doping of carbon nanotubes, however ～32% increase in the relaxation frequency has been observed in higher concentration carbon nanotubes doped ferroelectric liquid crystal composite than pure ferroelectric liquid crystal sample. A decrease in conductivity has also been noticed after doping.     

基于HFSS的Hilbert分形天线分导线段设计

对采集变压器局部放电超高频信号的四阶Hilbert分形天线进行重新建模和设计,以达到更好的效果。首先分析天线的三种导线段在采集信号过程中的作用,并以导线段为单元,基于HFSS对天线重新建立模型,将三种导线段长度、介质厚度、介电常数和导线宽度六个变量应用SNLP算法优化。优化结果显示,0.3 GHz~3 GHz超高频范围内,谐振频率点达到四个,并将0.3 GHz~1 GHz范围内的通频带拓宽整合为超过500 MHz宽带,1 GHz以上的三个通频带也均超过450 MHz,且方向性良好,增益参数也有了很大程度的改善。所述特性经过试验验证。天线尺寸较小,可以置于变压器箱体内,能很好地应用于油浸式变压器局部放电超高频信号的采集。     

Dielectric relaxation phenomenon of rare earth Nd3+ modified bismuth layer ferroelectric ceramics fabricated by plasma active sintering method

Abstract

The crystalline structure, dielectric relaxation and ferroelectric properties of the solid solution, Nd _x Bi_4-x Ti₃O₁₂ (NBIT) compound were measured. The Curie temperature of the NBIT ceramics was determined to be 490°C from dielectric measurements. The dielectric constant of the NBIT ceramics shows a small anisotropic property. Polarization switching was observed using a Sawyer-Tower circuit at 50 Hz. Remnant polarizations and coercive fields could not be confirmed since the hysteresis loops were not saturated. The large dielectric relaxation is observed in the frequency range between 100 kHz and 1 MHz.     

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     

高损耗介电材料的介电参数测量方法研究

介绍一种高损耗介电材料的介电参数(介电常数、介质损耗角正切、交流电导率)测量的新方法及其原理。这种测量方法只需使用数字式示波器,或者高频电压表等常用仪器就可以在10 Hz至10 MHz范围内的比较宽的频率下测量高损耗电介质的介电性能。     

Microwave Characterization of BST Thin Films on LAO Interdigital Capacitor

The dielectric properties of (Ba_0.5Sr_0.5)TiO₃ (BST) thin films on LaAlO₃ (LAO) single crystals were studied over a wide frequency range. The samples with interdigital electrodes were prepared by microelectronic processing. The dielectric characterizations were carried out in the following steps: 1) the standard calibration of the instrument, 2) the removal of parasitic capacitance and the extraction of the capacitance of the interdigital capacitor (IDC) and 3) the extraction of the dielectric permittivity (?) of BST. It was found that ? of BST has a constant value (about 400) from 50 MHz to 2 GHz; at higher frequencies, ? gradually decreases. The BST interdigital capacitors exhibited good dielectric tunability.     

Structural and Dielectric Properties of Ca Doped Barium Iron Niobate

Ceramic materials with high dielectric constant are being used in many electric and electro-optics applications. Ca substituted barium iron niobate with general formula (Ba_1-xCa_x) (Fe_0.5Nb_0.5)O₃ with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by conventional solid state reaction method. Structural properties were investigated using X-ray diffraction and scanning electron microscope. Two types of phases were observed for 0.4 ≤ x ≤ 08. Dielectric constant and loss tangent were measured using impedance analyzer in the frequency range of 20 Hz–1 MHz at room temperature. Dielectric constant and loss tangent were found to decrease with increasing the frequency. A relatively good combination of dielectric constant and loss tangent was obtained for x = 0.2 (?_r = 1441 and tan δ = 0.19) at 10 KHz.     

Dielectric characteristics of spin-coated dielectric films using on-wafer parallel-plate capacitors at microwave frequencies

Dielectric properties of spin-coated dielectric insulators suitable for high-speed device fabrication are investigated. Complex dielectric permittivities and tangential losses of two polyimides, bisbenzocyclobutene (BCB), and a spin-on-glass (SOG) were extracted from the measured microwave reflection coefficient, S/sub 11/, of parallel-plate capacitors over a frequency range of 50 MHz to 40 GHz. A model for the dielectric permittivity as a function of frequency is developed based on measured data with a minimum square error of less than 10/sup -4/ between measured and modeled microwave reflection coefficients. A circuit model for the pad capacitance is obtained based on geometrical and physical considerations. The relationship between the dielectric loss and its thickness is considered. Experimental results are fitted to Debye and Cole-Cole models.     

Improved Temperature Stability of Microwave Properties in Tunable Devices Using Substituted Ba 1− x Sr x TiO 3

An improvement in ferroelectric device technology has become possible through optimization of the properties of the ferroelectric materials used to make the devices. The improvements discussed herein impact true time delay line and phase shifter performance by enhancing control over dielectric constant and extending the temperature range of tunability and device operation. Figures of merit were obtained for substituted-Ba 1 m x Sr x TiO 3 materials which have lower, less varying dielectric constant and adequate, less varying tunability at 1 MHz over the mil spec ( m 50 °C to 100 °C) range. For the sample whose figure of merit varies the least, dielectric constant and losses at 20 GHz and room temperature are reported. Dielectric constant and losses at 1 kHz are discussed.     

High quality BaxSr1-xTiO3 films grown by mocld and novel ferroelectric/ferrite structures for dual-tuning microwave devices

Abstract

Excellent single crystal Ba_xSr_1-xTiO₃ (BST) films were grown on LaAlO₃ substrates using the metal-organic chemical liquid deposition (MOCLD) method. Very low losses (tanδ ∽0.002-0.008) were measured from these films at 400 KHz. Biaxially oriented BST films were successfully grown on polycrystalline YIG substrates using both MOCLD and pulsed laser deposition methods with biaxially oriented MgO and YSZ buffer layers. The dielectric losses of the films range from 0.005 to 0.015 while 25% of dielectric constant change was observed with 40V bias voltage up to 10 MHz. Both the dissipation and dielectric constant of the films remained nearly constants over a wide temperature range (77 K to 380 K). A dual-tuning microwave coplanar phase shifter using a BST film grown on a MgO buffered polycrystalline YIG substrate was fabricated. A significant phase shift was observed in GHz frequency range when an electric bias or a magnetic field was applied to the device.     

Effect of water inclusions on charge transport and polarization inporous media

Wideband dielectric spectroscopy measurements (100 Hz to 10 GHz) were carried out on different microporous systems (including sintered glass filters, sandstone and carbonate rocks) saturated with brine (electrolytic water solution) and a hydrocarbon oil at different relative fractions. Three main contributions were singled out in the dielectric spectra: low frequency dispersion (LFD) effects (<100 kHz) related to long range ionic transport and dependent on the connectivity of the water phase; Maxwell-Wagner-Sillars (MWS) polarization effects (100 kHz to 1 GHz), essentially controlled by the shape of the water inclusions; and high-frequency effects (>1 GHz) due to short-range ion transport and related to specific pore surface. For each analyzed system, oil-wet (o-W) and water-wet (w-w) samples were obtained by chemical treatment of the pore surfaces. Systematic differences were observed in the electrical response on varying wettability (and so the respective distribution of the fluids in the pore space). Parameters such as the loss tangent value, the strength and the exponent of the LFD power law, as well as the characteristic time and strength of the MWS relaxation were good indicators of wettability. Results were discussed by using some standard models that account for the pore wettability effects on dielectric spectra. A new method for wettability determination of reservoir rocks from both laboratory and borehole electric measurements was presented     

A wideband low‐spur 0.18‐µm CMOS phase‐locked loop with bandwidth calibration

This paper presents a 0.18‐µm complementary metal‐oxide‐semiconductor wideband phase‐locked loop with low reference spurs. The dual‐level charge‐pump current calibration technique is proposed to maintain a constant loop bandwidth for wide operation frequency range and achieve low reference spurs. The first level charge‐pump current calibration is seamlessly incorporated in the automatic frequency band hopping control and the mechanism also ensures enough negative transconductance for the voltage‐controlled oscillator to function throughout the whole frequency range. The charge‐pump current mismatch is calibrated by the second level charge‐pump current calibration combined with the pulse‐width scaling technique. The operation frequency range of the phase‐locked loop covers from 4.7 GHz to 6.1 GHz. The measured phase noise is?116 dBc/Hz at 1‐MHz offset and the reference spurs are below?66.8 dBc. Copyright © 2015 John Wiley & Sons, Ltd.     

The High Frequency Properties and Crystallization of PbTiO3 Glass-Ceramics by Sol-Gel Process

PbTiO₃ glass-ceramics were produced by a sol-gel process. DTA and X-ray diffraction analysis provided information about the structural transformations and crystallization temperature. The range of crystallization temperature of PbTiO₃ is larger than that of PbTiO₃ glass-ceramics. By increasing the glass composition, the crystallization temperature was increased. The phase transformation of PbTiO₃ from the cubic to the tetragonal phase depends on the crystal size caused by the different heat treatment temperatures. The dielectric measurements in high frequency range (> 10⁷Hz) exhibited evidence of a relaxation phenomena near 850 MHz. With increasing glass composition, the position of the relaxation frequency was increased. The temperature dependence of the dielectric constant of PbTiO₃ and PbTiO₃ glass-ceramics has an obvious discrepancy. The dielectric constant of PbTiO₃ glass-ceramics shows the characteristic dispersion at the Curie point. It indicated that the glass ceramic sample has a stronger tendency for a diffuse phase transition.     

Electric properties of monophase polycrystalline sinters SiC, B4C, TiC and their composites as non-inductive volume resistors

Monophase polycrystalline SiC, B₄C, TiC and their SiC-TiC, SiC-B₄C composite sinters with a theoretical density of 97% are characterized by good mechanical and thermal durability as well as a wide range of electrical conductivity values. SiC, which has semiconductor conductivity and negative TCR, was combined with TiC, which has metallic conductivity and positive TCR. Produced in this way resistive elements, within a temperature range from 293 K to 348 K, exhibit a TCR close to zero, and an impedance independent of frequency within a range from 100 Hz to 1 MHz. The combination SiC with 40 wt% of B₄C has been produced resistive elements, which are resistive to oxidation. This combination has also completly resistive character, within a range of 100 Hz to 1 MHz. Most of the investigated materials are suitable for high temperature, noninductive volume resistors.     

Low-temperature dielectric properties of double-perovskite Ca2CoNbO6

Double-perovskite Ca₂CoNbO₆ (CCNO) ceramics were prepared via the solid-state reaction route. Their dielectric properties were investigated as a function of temperature (between 100 and 330?K) in the frequency range from 40?Hz to 10?MHz. Two thermally activated dielectric relaxations were observed with the activation energy around 0.13?eV for the low-temperature relaxation and 0.37?eV for the high-temperature relaxation. Annealing in O₂ and N₂ can remarkably change the dielectric constant, background, relaxation peak intensity and position, etc. These results can be well explained based on the fact that both oxygen and cobalt vacancies coexist in the sample. The low-temperature relaxation was found to be related to the dipolar effect due to the hopping holes, and the high-temperature relaxation was associated with the defect relaxation caused by oxygen and cobalt vacancies.     

EO polymer-based integrated-optical acoustic spectrum analyzer

An acoustic spectrum analyzer based on electrooptic (EO) polymer integrated optics is presented. The device is used in a scanning heterodyne geometry by zero biasing a Michelson interferometer. It is capable of detecting vibrations from DC to GHz range. The novelty of the work is applying EO polymers to high frequency acoustic sensing applications. EO polymers have been extensively used for communication devices. However, their use in high frequency sensing applications remains unexplored. The sensor presented is designed to analyze thin film structure by utilizing high frequency capabilities of EO polymers. The advantage of this approach over existing methods is in its potential to detect vibrations over 100 GHz with low drive voltages (V_π less than 1 V), using a device that is completely electrically controlled with no mechanical moving parts. Low frequency tests indicate good agreement between experimental results and theoretical predictions. Acoustic vibrations excited by pulsed Nd-YAG laser are detected to frequencies up to 200 MHz using the device presented