基于TDR的多孔介质中含水/水合物饱和度测量方法仿真研究

为了优化设计时域反射技术（TDR）中的探针结构,建立基于TDR响应的含水/水合物测量模型,利用有限元数值模拟方法建立了TDR测量过程数值仿真模型。分别以空气、不同浓度氯化钠溶液以及不同水合物含量的石英砂为被测介质验证了模型的正确性、研究了被测介质电导率和介电常数对反射波形的影响规律。通过改变被测介质的介电常数来模拟含水/水合物饱和度不同的石英砂,随着石英砂中水合物含量的增加,含水量逐渐降低,表观介电常数随之减小,电磁波传播速度随之以非线性形式增加;与理论值相比较,仿真计算所得到的传播速度最大误差处于5%以内。下一步需要在数值模型中的被测区域中填充各相异性材料来更加真实地模拟含水合物沉积物被测介质。     

基于含水合物多孔介质复电导率的渗透率测试有限元仿真研究

渗透率是影响天然气水合物储层产气效率的关键参数，野外尚缺少实时监测水合物储层渗透率动态变化的技术，实验室内测试渗透率的方法存在成本高、周期长、可靠性低等问题。研究了一种基于复电导率的含水合物沉积物渗透率测试新方法。首先，针对含水合物多孔介质建立了能够计算其渗透率和复电导率的有限元数值模型，然后开展了不同水合物饱和度条件下的仿真实验，获取了0~40%水合物饱和度时多孔介质的流场和电场响应参数，分别探讨了孔隙中水合物及其饱和度变化对复电导率虚部和渗透率的影响规律和机理，最后建立并验证了基于复电导率虚部的含水合物多孔介质渗透率评价模型，为深入研究基于激发极化原理的含水合物沉积层渗透率测试新技术提供了理论和模型基础。     

基于开口谐振环结构的介电常数测量传感器研究

固态材料介电常数的测量常采用双端口传感器，但传感器尺寸较大，针对此问题，设计了一款单端口特性的射频传感器，尺寸仅为30×40 mm。射频传感器采用开口谐振环结构，选用介电常数为4.4的FR4材料作为传感器基板，厚度为1 mm。首先使用电子设计自动化软件ADS设计了传感器，并对加载不同介电常数模型的传感器进行仿真，以得到不同介电常数下的回波损耗S11；随后使用MATLAB对S11谐振频率进行处理，得到待测样品厚度为0.8 mm的拟合公式。最后，将实测数据代入拟合公式得到材料介电常数的测量值，并与样品介电常数标准值比较。实验结果表明，使用该射频传感器测量Rogers 5880得到的介电常数为2.18，误差为0.91 %；测量FR4得到的介电常数为4.32，误差为1.82 %。因此，射频传感器可以用于固态材料介电常数的精准测量。     

多孔介质中天然气水合物二维模拟实验装置

本文介绍了一种天然气水合物模拟实验装置,该装置能模拟多孔介质中天然气水合物的生成和分解过程.能够通过测量平板内探针的电容判断水合物的状态变化.实践证明,该装置工作稳定可靠,性能符合实验要求.     

基于电阻抗谱特性与集成神经网络的天然气水合物饱和度软测量模型

含天然气水合物饱和度的计算是储层优选和资源量评估的关键参数,针对目前数据解释模型计算精度低以及模型输入参数少等问题,提出了一种基于电阻抗特性参数和集成神经网络的软测量模型建立方法。在对电阻抗谱数据进行预处理、特征参数提取以及选择的基础上形成了样本集,针对四对传感器分别设计了BP神经网络,采用平均法作为集成策略将四个BP网络作为子网络进行集成得到集成网络模型。模型测试结果表明：通过集成网络模型计算得到的含水合物饱和度值平均相对误差3.33%、平均绝对误差0.0014、均方根误差为6.56%,三项误差指标均低于各个子网络的计算误差。在宽频范围内对含水合物沉积物进行电阻抗谱测试能够获得沉积物的频率响应特性以及特性描述参数,可为神经网络模型提供大量的输入参数;利用集成神经网络能够综合应用位于不同测量方位的多个传感器的测量数据,通过采用适合的集成策略能够克服水合物空间分布不均匀对饱和度计算准确度的不利影响。     

基于内部阵列电极的电容层析成像系统

为了研究电容层析成像系统在测量高介电常数流体中的应用,设计了一套具有内部阵列电极的电容层析成像传感器,改善了传统传感器的灵敏度和非线性特性,拓宽了系统的测量范围。用蒸馏水作为连续相介质进行了数据采集和图像重建,并进一步研究了介质电导率对系统成像的影响。实验表明,该系统可以实现高介电常数介质的测量,并且可用来测量具有微弱导电能力的物体。     

基于宽频电阻抗特性与阿尔奇公式的含水合物饱和度计算模型

以自主设计开发的水合物电学参数测量装置为基础，在频率范围5Hz~400kHz内测试了不同饱和度条件下的含四氢呋喃水合物海沙体系的宽频阻抗。分析了水合物生成分解过程中模拟沉积物的宽频阻抗特性，讨论了不同含水合物饱和度条件下的阻抗幅值频散特性及其与饱和度之间的定量关系，建立了基于宽频阻抗幅值和阿尔奇公式的含水合物饱和度计算模型。研究结果表明:（1）含水合物天然海沙体系的阻抗幅值呈现出频散特性，频散特性受到孔隙壁与孔隙流体之间界面极化效应的影响，阻抗幅值频散度与含水合物饱和度之间呈现近似线性关系；（2）在测试频率200~200kHz时，阿尔奇公式中的胶接指数较为稳定，饱和度指数与测试频率的对数之间呈现出近似线性的关系，测试频率应作为含水合物饱和度计算模型的参数。本研究为沉积物中含水合物饱和度的评价提供了新方法，通过测量宽频阻抗幅值并应用所提出的模型，综合多个频率的模型计算结果有望得到更加准确可靠的饱和度评价值。     

电容传感器对介质厚度的检测

本文论述用电容传感器检测介质材料厚度，对测量灵敏度和检测厚度精度进行分析，指出减小介质介电常数变化影响的方法。本文提出的频率变换型测厚方法，所需设备结构简单，处理方法先进，精度高，还具有自校和自补偿功能。     

用电容探针测量铁磁介质 气固流化床的空隙率

通过分析介质极化的微观机制,提出了消除外界电磁场对铁磁介质介电常数影响的方法,使电容法能应用于铁磁介质气固流化床空隙率的测量.介绍了提高电容探针测量灵敏度、稳定度的措施,并列举了测量实例.     

基于鲁棒估计的动态数据校正方法

针对目前动态数据校正方法存在的缺陷，本文在以前的工作基础上把基于鲁棒估计原理构造的鲁棒估计函数用于含异常点类型的过失误差的数据校正，Monte Carlo模拟结果及对TE问题的校正计算结果表明，这种基于鲁棒估计的过换误差侦破和数据协调同步方法可以在得到协调数据的同时很准确的侦破和识别出测量数据中所含的过失误差，具有较强的优越性。     

Calibration of a TDR probe for low soil water content measurements

Time domain reflectometry (TDR) probes are increasingly used for field and laboratory estimation of soil water content. Usual calibration of TDR probes for the determination of soil water content uses two media: air for low and water for high values of dielectric permittivity, although the measured range of dielectric permittivity in soil is much smaller as compared to the range implied by the calibration media. The use of air for calibration of short TDR probes gives calibration errors due to overlapping incident and reflected pulses in the reflectogram, which result in their relative shift in time. This phenomenon, named the convolution effect, can be avoided by the application of selected calibration media. The presented approach minimizes of dielectric permittivity measurement errors by choosing the calibration media with dielectric permittivity values close to the limits of the measurement range and the possibility to use TDR probes of various lengths. The comparison of errors of TDR apparent dielectric permittivity measurement in three sandy soils, based on the probe calibrations in various media, is also presented.     

Dielectric Properties of Saline Soil and an Improved Dielectric Model

The measurement and analysis of the dielectric constant of soil samples with different moisture and salinity are achieved based control experiment. The saturation is introduced to the dielectric model of salinity soil to improve simulation accuracy by taking the Stogryn model and the influence of soil solution ion concentration, conductivity, moisture content, and salt content for dielectric constant imaginary part into consideration. The results indicate that the soil salt content has little influence on both real part and imaginary part of dielectric constant when soil volumetric moisture content is low, while soil volumetric moisture content is high, the real part of the dielectric constant decreases with the increase of soil salt content, and the imaginary part of the dielectric constant increases. The improved dielectric model of salinity soil can well reveal the changes of dielectric constant, and it is also having a great effect in Baiyin soil samples. That is to say, the improved dielectric model can apply to different soil types.     

盐渍土介电特性及模型改进研究

基于控制试验对配制的具有不同含水量和含盐量的土壤样本进行介电特征量测和分析,同时结合Stogryn盐水介电模型和土壤溶液离子浓度、电导率、含水量和含盐量等参数对介电常数虚部的影响,将饱和度这个关键参量引入盐渍土介电模型中,提高盐渍土介电模型模拟精度。结果表明：①当土壤体积含水量较低时,土壤含盐量对介电常数的实部和虚部均未产生明显的作用。当土壤体积含水量较高时,介电常数实部则随着土壤含盐量的增加呈逐渐下降趋势,介电常数虚部以增加态势为主;②修正后的盐渍土介电模型可以较好地刻画介电常数变化特征。此外,将修正后的模型在白银采样点进行验证,同样取得较好的模拟结果,表明修正后的盐渍土介电模型对不同土壤类型具有一定的适用性。     

Fabrication of AFM probe with CuO nanowire formed by stress-induced method

A novel method has been proposed to fabricate an atomic force microscope (AFM) probe using CuO nanowire and a stress-induced method that can form the nanowire easily. By heating a commercial AFM probe with a film coating of Ta and Cu, a Cu hillock with CuO nanowires on its surface could be formed at the end of the probe. The thickness of the coating films, the heating temperature, and the heating time were investigated to obtain CuO nanowires with a high aspect ratio for use as an AFM probe tip. It was found that a suitable probe tip can be fabricated using the a Cu film thickness of 700 nm, a heating temperature of 380 °C and a heating time of 6 h. Probe tips (~5 μm high) and nanowires of ~25 nm diameter were obtained successfully. In the range evaluated, the measurement resolution of the CuO nanowire probe was slightly worse than that of a commercial AFM probe. However, both probes had almost the same dimensional measurement precision.     

A novel wideband Minkowski fractal antenna with assistance of triangular dielectric resonator elements

This article concentrates on the design and analysis of a novel Minkowski fractal‐based antenna design with the aid of triangular dielectric resonator (TDR) elements for wideband wireless applications. mode is excited inside equilateral TDR antenna with the help of coaxial probe feed. Wide impedance bandwidth has been achieved by reducing the quality factor with the help of increasing surface area‐to‐volume ratio of radiating structure. Another important feature of this article is that recurrence formulas are derived to calculate the fraction of surface area to volume of proposed fractal antenna up to nth iteration. The proposed antenna design is fabricated and measured up to third iteration to verify its simulated outcomes. Practically measured outcome confirms that the proposed antenna design operates over the frequency range, that is, 2.23‐3.1 GHz with the maximum gain of 3.62 dBi. These features make it appropriate for wireless LAN (2.4 GHz) and WiMAX (2.5 GHz) applications.     

折叠偶极子阵列无芯标签极点特性分析

标签极点提取的准确性受多种因素影响,以折叠偶极子阵列无芯标签为研究对象,开展无耗电介质材料(厚度、相对介电常数)对其极点分布的特性分析。仿真结果表明,随着介质厚度及其相对介电常数的增大,谐振极点的衰减因子及谐振频率将呈现变小的趋势,极点分布以类S型曲线向坐标原点靠近。     

基于介电常数温变特性的食用油品质机理研究

食用油在高温煎炸过程中会生成有害物质,对身体健康及食品安全产生影响.根据食用油温度变化对其介电常数的影响,设计基于介电常数温变特性的食用油品质分析系统.在电容传感器探头设计中,采用等位环和驱动电缆技术来避免边缘电场的影响和寄生电容的产生.文中对3种食用油在32 ℃~150 ℃下进行加热检测,并对测量数据进行拟合分析,结果表明:3种被测食用油在不同温度下呈现不同介电特性,可用于分析和评价食用油的质量.     

A novel study of head motion hysteresis issues in contact probe recording systems

Contact-based recording on ferroelectric media and polymer media have been proposed and investigated for high-density probe storage. To achieve fast data rate, it is necessary to perform reading or writing with multiple probe heads simultaneously. However, localized variations in tribological behavior at the contact interface between the probes and recording media and variation in normal contact force would result in variation in friction and stiction over the interface and therefore amongst individual heads in the probe head array. This causes variation in the hysteretic motion of the heads over the array, which in turn results in off-track motion during track-positioning and timing errors during scanning. In this paper a novel method of modeling these effects is developed to study the effect of relative head-motion hysteresis (RHMH) on timing-error during data read–write and off-track errors during seek-settle. A mathematical model of RHMH during scanning along the bit-wise direction is developed based on the idea of stochastic averaging. A transient response model is similarly developed for estimating hysteresis effects during seek-settle. These models help to understand parametric dependencies of RHMH and can be used in designing the probe heads, the probe–media interface (PMI) and the probe system in general. Further several schemes involving modulation of the normal force at the PMI are proposed to mitigate RHMH and their benefits are analyzed using the models described in this paper.