A simple method for measuring the dielectric constant of solids

This paper presents a simple method for determining the dielectric constant of a solid material. The method consists of measuring the return loss due to a slab of such material inserted into a rectangular waveguide. The dielectric slab presents a discontinuity inside the waveguide, and the electric field at each interface of the slab is described as a summation of weighted sinusoidal basis functions. The scattered magnetic field on either side of the slab is determined using the modal expansion approach. These weights are solved by using the method of moments on the boundary conditions of continuity of the tangential magnetic field at the interfaces. The component of the electric field (scattered) for the dominant TE₁₀ mode can then be determined in terms of these weights, and from this result the reflection coefficient can be theoretically evaluated. A comparison between the experimentally obtained reflection/transmission coefficient and the theoretical values provide a figure for the dielectric constant of the material     

Electric-field sensors utilizing coupling between a D-fiber and an electro-optic polymer slab

This paper provides a detailed analysis of electric field sensing using a slab-coupled optical fiber sensor (SCOS). This analysis explains that the best material for the slab waveguide is an inorganic material because of the low RF permittivity combined with the high electro-optic coefficient. The paper also describes the fabrication and testing of a SCOS using an AJL chromophore in amorphous polycarbonate. The high uniform polymer slab waveguide is fabricated using a hot embossing process to create a slab with a thickness of 50 μm. The fabricated polymer SCOS was characterized to have a resonance slope of ΔP/Δλ=6.83E5 W/m and a resonance shift of Δλ/E=1.47E-16?m(2)/V.     

基于里德堡原子的微波功率精密测量

提出一种基于里德堡原子量子相干效应的功率测量新方法。将装有铷蒸气的低电磁扰动原子气室置于特定的导波系统中,基于里德堡原子量子相干效应将对导波电场测量转化为对原子吸收光谱的探测,利用功率和导波电场的解析量化关系,实现一种全新的可溯源至普朗克常数的微波功率测量。在10.22GHz频率处与传统功率测量进行比较,-40dBm至-20dBm的功率范围内两者平均偏差为0.08dB(1.86%)。这种全新的微波功率量子测量方法具有灵敏度高、动态范围大、测量不确定度小等优势,有望形成新一代可直接溯源至国际单位制(SI)的微波功率基准。     

Open-ended rectangular waveguide for nondestructive thicknessmeasurement and variation detection of lossy dielectric slabs backed bya conducting plate

Solutions for fields inside a slab of a generally lossy dielectric medium backed by a conducting plate, placed outside a waveguide-fed rectangular aperture, are used for the microwave nondestructive thickness measurement of such dielectric slabs. Upon construction of the waveguide terminating admittance expression from its variational form, an inverse problem is solved to extract the slab thickness form the conductance and susceptance in a recursive manner. A comparison between the experimental and theoretical results showed that the significance of higher order modes is minimal; hence, the dominant mode assumption is, in general, valid for describing the aperture field distribution. The validity of this assumption has led to the construction of a simple integral solution which is fast converging for generally lossy dielectric slabs, and may easily be implemented for real-time applications. Good agreement was obtained between the theoretical and experimental results. Multiple thicknesses of two different dielectric samples were estimated in this way     

三天线法环天线校准系统建立及测量结果不确定度评定

在350kHz~30MHz频段内,为了准确得到环天线所处位置的场强,环天线的天线系数需要校准。三天线法是一种校准天线系数的绝对方法,需要3个环天线,两两组对测量,且不需要任何参考标准。介绍了三天线法校准环天线的原理,基于矢量网络分析仪建立校准系统,并评定校准系统的测量结果不确定度。基于K(i,j)的计算公式复杂,很难计算出其引入的不确定度,因此采用数字电磁学代码(NEC)建模评定K(i,j)的不确定度。评定结果表明,在350kHz~30MHz频段内4个典型频点的扩展不确定度小于0.81dB(k=2)。     

Complex microwave susceptibility of a ferrofluid with Mag-Hematiteparticles: nonreciprocal phenomena in magnetic liquids

We present susceptibility measurements on a ferrofluid in the microwave frequency range with three different measurement cells: a coaxial line, an X-band rectangular waveguide, and an X-band slab-loaded rectangular waveguide. We use the reflection/transmission method to obtain the complex susceptibility χ^*. We have subjected the cells to a constant magnetic field applied parallel or transversal to the propagation direction. We observe an increase of the gyromagnetic resonance phenomenon and some discrepancies between the consequences of a parallel or transverse applied field. Nonreciprocal phenomenon has been observed for the first time in a ferrofluid when a transversal field is applied to an X-band slab-loaded rectangular waveguide     

LabWindows/CVI电场自动控制系统研制

基于LabWindows/CVI开发平台构建了电场自动控制系统,提出了GTEM室内场强的校正方式和软件的编制流程,在开环校正的基础上,通过对开环校正数据文件的调用实现了更为精确的闭环校正。经过校正后的场强值满足规定的场强误差限,适合用于RS103电场辐射敏感度自动测试。     

一种适用于现场原位校准的双输入激励方法

针对现场校准中各种非电物理量激励源实现困难的问题,提出一种双输入激励法,以电信号标准源激励校准传感器后面的数据采集系统。借助于现场物理量值提供单值激励,以现场测量标准校准包含传感器的被校测量系统,并判定传感器的工作正常性。在其工作正常情况下,以传感器稳定的传递特性模型的平移,表述其现实特性,模型参数来源于以往实验室校准结果,从而以双输入激励法完成全测量系统的现场校准。从铂电阻温度计长达6年的校准结果漂移特性,可以看出该方法具有正确性和可行性。     

Automated Characterization of Bolometric and Electrothermic Mounts

The greatest inaccuracy in making a microwave power measurement is usually the uncertainty of the calibration factor or the effective efficiency. These terms account for the RF losses and substitution errors in the bolometric or electrothermic mount. A new method for transferring calibration from a standard mount to a mount to be calibrated has production line speed and simplicity; yet its accuracy rivals standards laboratory techniques. This method uses an automatic network analyzer to measure the quantities required and to solve the mismatch equation in transferring calibration from the standard mount to the one to be calibrated. A technique is also described to evaluate the errors of the transfer measurement. An accurate method of measuring the complex reflection coefficient of a stabilized source is another result of this work. The present implementation measures effective efficiency, calibration factor, and the magnitude and phase of the reflection coefficient of a mount at six calibration frequencies in 60 seconds. The uncertainty in transferring calibration factor and effective efficiency is about 0.5 percent.     

Growth and characterization of diamond films deposited at high-pressure using a low-power microwave plasma reactor

Diamond films were deposited on molybdenum substrates from mixtures of methane diluted in hydrogen using a high-pressure microwave plasma reactor. In this reactor, a compressed waveguide structure was used to increase the electric field strength, and accordingly the reactor was able to operate stably with low gas flow rate and microwave power. The films deposited on 12 mm diameter substrates were characterized by film morphology, Raman spectra, growth rate and crystalline quality. The morphology of diamond films deposited in this reactor depends mainly on the substrate temperature. When the deposition pressure was 48 kPa and microwave power was only 800 W, high quality diamond films could be uniformly deposited with a growth rate around 20 μm/h.     

异辛烷热值标准物质

采用国家固体燃烧热基准,即电能标定的等温式氧弹热量计,为异辛烷热值标准物质定值。通过电能标定热量计的热容量,使热值结果溯源到温度、电流、时间和质量等国际单位上。采用自制的聚乙烯胶囊盛装异辛烷,避免了样品挥发引入的质量测量和不完全燃烧的系统误差。异辛烷热值标准物质在标准状态下的高位发热量为47777 J/g,扩展不确定度为52 J/g（扩展因子k=2）。     

基于高温黑体炉的钨铼热电偶校准方法研究

基于中国计量科学研究院的高温黑体炉设计了一种适用于钨铼偶等高温热电偶的校准方法。优化设计的均温块测温孔轴向均匀性20mm范围内小于0.5℃,优选的测温孔与中心孔的辐射温度差异可达到小于0.5℃。经铂铑10-铂热电偶验证了基于高温黑体炉的校准方法,在800~1300℃与S型热电偶标准热电势间差异小于0.5℃,不确定度评估为0.8~1.5℃,k=2。在800~1900℃范围内,测试了多只不同来源的C型钨铼偶热电势并考核了偶丝校准前后的均匀性,实验结果表明,钨铼偶丝与国际标准钨铼偶热电势的差异基本保持在1%以内,校准不确定度为3.7~13.0℃,相对不确定度为0.7%t (t为温度),k=2。     

X射线剂量当量仪校准因子不确定度评估

为了准确评估X射线剂量监测用防护仪表的校准因子的不确定度,依据有关技术规范,用标准电离室对参考点位置处的剂量当量率参考值进行测量;采用替代法获得待校仪表的显示值,从而确定校准因子结果的相关影响因素,并分别对影响量的不确定度进行评定;得出仪表校准因子的相对扩展不确定度为5.0％(k=2)。影响校准因子不确定度的主要来源包括校准用辐射场的均匀性、标准电离室本身的刻度因子及能量响应、剂量当量转换因子、待检仪表显示值的统计标准偏差等。在对该类仪表的校准过程中,通过提高标准参考值的不确定度水平可以改善校准因子的不确定度。     

Impact of Waveguide Filling Material on Near-Field Microwave Inspection of Carbon-Loaded Composites

The advent of carbon loaded composite materials gave a boost to many industries. This is because of their light weight, durability and strength. As new structures utilizing carbon loaded composites are built, the need for a reliable nondestructive testing technique increases. A carbon-loaded composite testing poses a challenge to most nondestructive testing and evaluation (NDT&E) techniques. Microwave NDT&I techniques main challenge is the lossy nature of carbon, especially at high microwave frequencies. Lower frequencies penetrate deeper in carbon-loaded composites, however, to operate at lower frequencies the size of the waveguide probe increases significantly which degrades the resolution rapidly. Open-ended rectangular waveguide sensors filled with a dielectric material will be used to inspect carbon-loaded composites. The filling of the waveguide reduces the frequency of operation and keeps the small size of the waveguide (i.e. increases the penetration depth and maintains the resolution). However, varying the waveguide filling material dielectric properties will have an impact on the measurement parameters optimization process and consequently on the detection sensitivity. In this paper, the use of the waveguide filling material as an optimization parameter will be investigated. Carbon-loaded composites with disbonds will be inspected and the variation of the dielectric properties of the loading material of rectangular waveguide probes for carbon loaded composites inspection will be assessed.     

Variable toroidal ferrite phase shifter

Careful design of the magnetic bias circuit used in ferrite phase shifters can help to reduce space, weight and energy consumption. Low reluctance circuits must avoid air-gaps and this can be achieved using toroidal-shaped ferrite inserts positioned inside a rectangular waveguide. Here, these ferrite inserts are fabricated using a viscous plastic processing method that avoids machining and produces a continuous magnetic circuit. Finite-element methods are used to initially model the magnetostatic solution for the bias circuit before being used to analyse the microwave performance of a double toroid phase shifter. A closedform technique is introduced to model the dielectric slab waveguide impedance transformer. The final insertion loss was ,1 dB over the 9.5?10.3 GHz band and return loss of 20 dB was achievable. The phase shift calculation agrees to within 10% of the measured values.     

Optimized CdTe sensors for measurement of electric and magneticfields in the near-field region

We present novel electric and magnetic field measurement systems utilizing optical technologies, which have been developed, tested, and calibrated in the frequency region up to 2 GHz. They show an advantage over currently available measurement systems in that they are passive, all-dielectric, and EM immune. A detailed analysis of field perturbation by the measuring probes in the near-field region was performed using finite-difference time-domain (FDTD) algorithm for solving Maxwell's equations. Both probes were calibrated using a gigahertz transversal electric and magnetic cell, and the results show a linear response     

Reflectivity of buried slab waveguides

The scattering properties of an abruptly ended buried slab waveguide for both TE and TM modes are examined by an improved iteration technique that is based on the integral equation method with "accelerating" parameters. The waveguide is considered a symmetrical slab, for which the weakly guiding conditions are invalid, and it is embedded in a different dielectric material. The tangential electric field distribution on the terminal plane, the reflection coefficient of the first TE and TM guided modes, and the far-field radiation pattern are computed. Numerical results are presented for several ended waveguides, while special attention is given to the far-field radiation pattern rotation and the terminal field distributions.     

Radiometric Evaluation of Antenna-Feed Component Losses

Low-noise antenna systems are frequently used in conjunction with measurements of atmospheric and cosmic background noise at microwave frequencies. The input transmission line losses of these receiving systems must be precisely calibrated to insure proper identification of the portion of operating noise temperature attributable to the external environment. Although most components in an antenna line can be calibrated by conventional insertion-loss measurements, many feed component losses must be evaluated by means of nonstandard techniques. This paper describes a radiometric method for calibrating the loss of multimode antenna-feed components in which the field is linearly or circularly polarized. The method consists of measuring operating noise temperature, first with the components under evaluation installed and again after substitution by a waveguide section of known loss. Calibration and error analysis equations are derived and discussed. Application of the radiometric method, for the calibration of a mode-generator and quarter-wave plate polarizing section, resulted in a loss measurement of (0.0069 ±0.0016 pe)/dB.     

微波无损检测热障涂层下金属表面裂缝的参数优化

基于微波在介电材料中的传播理论及其对金属界面特性的敏感性, 利用CST-微波工作室(computer simulation technology-microwave studio)对微波检测热障涂层下金属的裂缝进行了仿真计算, 研究了热障涂层的厚度、 裂缝方向对检测结果的影响, 仿真计算了热障涂层厚度为400 μm、 裂缝长边方向平行于矩形波导探头长边的不同宽度的裂缝。结果表明: 热障涂层厚度不同时, 微波检测金属表面裂缝的敏感工作频率不同; 裂缝方向与波导口长边的夹角为50°～55°时检测敏感度低。裂缝宽度小于8 μm时用本研究中的频率范围无法检测, 裂缝宽度在10～30 μm时检测效果不明显, 裂缝宽度在30 μm～1 mm范围内, 裂缝越宽微波的反射系数相位差越大。因此, 在合适的工作频率下能利用微波无损检测技术对热障涂层下金属表面的裂缝进行无损检测。     

New calibration method for the determination of the absolute density of CH radicals through laser-induced fluorescence

Laser-induced fluorescence (LIF) was applied at the B-X transition of the CH radical to measure the absolute densities of CH radicals in an electron-cyclotron resonance methane plasma. The absolute experimental uncertainty is only approximately 30% as a result of a new calibration procedure. The experimental setup was calibrated through the comparison of the LIF signal of N(2)(+) with that of CH. The absolute N(2)(+) density was derived from the spatially resolved N(2)(+) LIF signal and the line-averaged electron density as measured with microwave interferometry.