A hydrogeophysical synthetic model generator

HGmod is a computer program that builds on stochastic realizations of porosity fields to derive electrical conductivity, dielectric permittivity and hydraulic permeability models. The presence of clay, the influence of salinity as well as temperature of the fluid of imbibition are taken into account in the underlying formulations. The saturated and unsaturated zones are also considered through the application of a saturation profile on the porosity field. A micro-geometrical model is used to relate the porosity to the clay fraction. This model also used to derive an expression for the pore specific surface of the sand–clay mixture. The specific surface is subsequently used to compute the conduction at the pore surface when building electrical conductivity models. Dielectric permittivity fields are built by successive applications of either the Hanai–Bruggeman or Maxwell–Garnett mixing models, depending on the relative proportions of sand, clay, water or air. In addition, the dielectric permittivity of water and clay follow a Cole–Cole behavior. HGmod is therefore a versatile tool useful to generate synthetic datasets needed to anticipate the geophysical response under specific conditions and to study hydrogeophysical sensitivity or resolution analysis.     

Dieletric and relaxation behaviors of (PbMg1/3Nb2/3O3)0.67(PbTiO3)0.33 single crystal

Dielectric permittivity along the [111] direction has been measured as a function of temperature for a relaxor ferroelectric single crystal (PbMg_1/3Nb_2/3O₃)_0.67(PbTiO₃)_0.33 (PMN-33%PT). A sharp ferroelectric phase transition was observed near 425 K and 429 K for cooling and heating processes, respectively. As temperature decreases, a diffuse phase transition (which begins near 330 K upon cooling) was detected. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transitions (near 330 and 425 K upon cooling) are diffuse first-order and first-order, respectively. The frequency-dependent dielectric data ε'₁₁₁ (ƒ, T) prove the existence of an electric dipolar relaxation process between 350 and 400 K. The activation energy, the Vogel-Fulcher temperature and attempt frequency corresponding to this relaxation process are also calculated.     

Evaluation of the Applicability of Different Dielectric Models for Soil Moisture Retrieval based on the Ground-based Radiometer Measurements

Based on soil moisture and freeze/thaw comprehensive experiments conducted at the north-eastern part of the Tibetan Plateau, the L-band brightness temperature, the in-situ soil moisture and temperature, vegetation leaf area index are measured simultaneously for the purpose of evaluating performances on forward brightness temperature simulation and soil moisture retrieval using four dielectric constant models, including Wang-Schmugge, Mironov, Dobson, and Four-Phase model. The forward brightness temperature simulations indicate that the difference of simulated brightness temperature between Wang schmugge model and the other three dielectric constant models is most significant at lower soil moisture content condition (soil moisture is less than 0.23 m3·m^-3) , nevertheless, the difference of Mironov model simulation is most significant in contrast with the ones of other three models at higher soil moisture condition (soil moisture is greater than 0.23 m3·m^-3). The practical retrieval of soil moisture from the ground-based radiometer measurements indicate that Wang-Schmugge model can effectively reduce the underestimation of soil moisture at the horizontal polarization, this resulted an improvement to the accuracy of retrieved soil moisture. Mironov model can reduce the underestimation of retrieved soil moisture at the vertical polarization. In accordance with a state-of-the-art parameterization scheme, the evaluation of performances of four dielectric constant models at the typical alpine meadow is potential for selecting optimum soil moisture retrieval by using soil dielectric model from space-borne L-band radiometer observation over the Tibetan Plateau     

Nano-Al2O3/PANI composites with high negative permittivity

Polyaniline (PANI) composites filled with ferroferric oxide and barium titanate were discovered to have metamaterial characteristics in recent years. In this paper, based on micron-Al₂O₃/PANI composites with negative permittivity, the dielectric properties of nano-Al₂O₃/PANI composites were studied. Nano-Al₂O₃/PANI composites had negative permittivity, which was considerably higher than that of PANI and micron-Al₂O₃/PANI composites. The higher negative permittivity was caused by the better dispersibility of nano-Al₂O₃, resulting in the enlargement of polarization voltage on a greater range of PANI molecular chain. Moreover, nano-Al₂O₃/PANI composite with 5 wt% nano-Al₂O₃ has the largest negative permittivity (−2.24 × 10⁶) that has not been reported so far in oxide/PANI composites.     

Frequency independent‐dependent conductivity and dielectric properties of some ionomers

The preparation and physical properties of some ionomers have been investigated. The addition of CH₃I significantly improved the conductivity of the ionomers. At room temperature, the highest ionic conductivity value was found to be 4.93 10⁻⁸ S cm⁻¹ in the I4 ionomer. The conductivity data do not obey the Arrhenius law and the non‐linearity indicates ionic transport. The alternating current conductivity parameters and dielectric constants of the ionomers were determined. Copyright © 2005 Society of Chemical Industry     

东胜褐煤与Yallourn褐煤热解过程中微波吸收特性

利用微波网络分析仪测量S11和ψ S11参数,结合人工神经网络模型的计算方法,获取了2 450 MHz微波频率下,内蒙东胜褐煤与澳大利亚Yallourn褐煤在室温至800 ℃热解过程中的相对介电系数,并用其来表征2种褐煤热解过程中的微波吸收特性。结合热失重实验数据分析发现：热解开始温度之前,DS与YL褐煤的吸波特性参数ε′,ε″及tan δ数值接近,均处于较低水平,且随温度的上升仅有极小幅度增长。热解开始温度至热解结束温度阶段,2种褐煤的吸波特性参数ε′,ε″及tan δ数值随温度的升高均迅速上升,并在热解结束温度附近时达到峰值;DS褐煤的相关数值增长速率和幅度均比YL褐煤大。热解结束温度之后,各项吸波特性参数出现小幅度下降。实验表明,2 450 MHz微波频率下东胜褐煤比Yallourn褐煤具有更好的吸波能力,高温热解后,褐煤的微波吸收能力得到有效增强。     

On the modeling of phase and chemical equilibria by equations of state for systems containing supercritical components and ionic species

A technique of modeling of phase and chemical equilibria by equations of state for systems containing supercritical components and ionic species is considered. Attention is focused on the structure of equation of states with inclusion of non-electrolyte and electrostatic contributions. A hole quasichemical model was applied to illustrate the technique and to show how an EOS can be modified for systems with chemical reactions and electrostatic interactions in the liquid phase. The concentration dependency of the density and dielectric permittivity was taken into account in describing the electrostatic contribution that is required for thermodynamic consistency of the results of modeling. A method of assessing the appropriate relationships for mixtures containing supercritical components is suggested, alongside with the way to estimate the “true” composition of mixtures where ionic species are formed due to chemical reactions. The raised questions are discussed with respect to the following systems: solutions of acid gases in water-alkanolamine mixtures and water-ammonia-carbon dioxide system in a broad interval of temperatures and pressures.     

Enhanced Dielectric Constant for Efficient Electromagnetic Shielding Based on Carbon-Nanotube-Added Styrene Acrylic Emulsion Based Composite

An efficient electromagnetic shielding composite based on multiwalled carbon nanotubes (MWCNTs)-filled styrene acrylic emulsion-based polymer has been prepared in a water-based system. The MWCNTs were demonstrated to have an effect on the dielectric constants, which effectively enhance electromagnetic shielding efficiency (SE) of the composites. A low conductivity threshold of 0.23 wt% can be obtained. An EMI SE of ~28 dB was achieved for 20 wt% MWCNTs. The AC conductivity (σ _ac) of the composites, deduced from imaginary permittivity, was used to estimate the SE of the composites in X band (8.2–12.4 GHz), showing a good agreement with the measured results.     

Effect of B4C content and annealing on complex permittivity and microwave-absorption properties of B4C/Al2O3 coatings

The B₄C/Al₂O₃ coatings were fabricated by air plasma spraying technology, and their complex permittivity and microwave absorption properties in the X-band were investigated before and after annealing (500 °C/2 h). Both the real and imaginary parts of the complex permittivity of the coatings decreased after annealing, which can be attributed to the weakening of polarization relaxation intensity and the reduction of electrical conductivity caused by the escape of carbon atoms. In addition, the density of B₄C/Al₂O₃ coatings decreased from 3.01 to 2.16 g/cm³ with increasing B₄C content. The B₄C/Al₂O₃ coatings exhibit a minimum reflection loss (RL) value of ?39.58 dB and the effective absorption bandwidth (RL＜?10 dB, EAB) covers 1.9 GHz at a thickness of 1.6 mm. After annealing, the above coatings still had an EAB of 1 GHz. Therefore, the B₄C/Al₂O₃ coatings can be considered as a promising microwave-absorption candidate with good high-temperature microwave-absorbing performance and low density.     

Electromagnetic Metrology on Concrete and Corrosion

To augment current methods for the evaluation of reinforcing bar (rebar) corrosion within concrete, we are exploring unique features in the dielectric and magnetic spectra of pure iron oxides and corrosion samples. Any signature needs to be both prominent and consistent in order to identify corrosion within concrete bridge deck or other structures. In order to measure the permittivity and propagation loss through concrete as a function of temperature and humidity, we cut and carefully fitted samples from residential concrete into three different waveguides. We also poured and cured a mortar sample within a waveguide that was later measured after curing 30 days. These measurements were performed from 45 MHz to 12 GHz. Our concrete measurements showed that the coarse granite aggregate that occupied about half the sample volume reduced the electromagnetic propagation loss in comparison to mortar. We also packed ground corrosion samples and commercially available iron-oxide powders into a transmission-line waveguide and found that magnetite and corrosion sample spectra are similar, with a feature between 0.5 GHz and 2 GHz that may prove useful for quantifying corrosion. We also performed reflection (S₁₁) measurements at various corrosion surfaces and in loose powders from 45 MHz to 50 GHz. These results are a first step towards quantifying rebar corrosion in concrete.