改进矩形腔微扰法测试微波电介质复介电常数

本文讨论了测试电介质微波复介电常数的矩形腔微扰法。对介质样品加载后的ＴＥ１０ｎ模矩形腔腔内场进行了理论分析。通过对腔内场的数值求解，得出了与微扰公式相似的、已修正的准确计算公式。     

Measurement of complex dielectric permittivity at microwavefrequencies using a cylindrical cavity

A technique is presented for measuring complex dielectric permittivity using a full field analysis of a coaxially driven cylindrical cavity. The analysis of the junction is based on a model which fully considers the coaxial form of the cavity excitation, and which has been shown to produce very accurate results for a wide range of cases. Values of permittivity predicted by this method for two materials of well known permittivity are presented     

On RF material characterization in the stripline cavity

We examine the accuracy of the air-filled stripline cavity in measuring the dielectric and magnetic properties of bulk materials in the frequency range of 150-2000 MHz. Measured data on complex permittivity and permeability for several different-sized specimens of dielectric and magnetic materials were compared with reference values obtained using other techniques of known uncertainties. Major differences were noted for both complex permittivity and permeability data, and we largely attribute these to less-than-optimal perturbation of the internal cavity fields by the material specimens under test. The technique is particularly unsuited to measuring the dielectric loss of the higher-permittivity low-loss materials due to energy scatter by the specimen under test. In order to improve measurement accuracy, we suggest guidelines on the range of specimen electric and magnetic volume needed for optimal cavity perturbation     

A microwave instrument for the continuous monitoring of the water content of crude oil

Since the effective permittivities of water and oil differ by an order of magnitude, it is shown that it is possible to measure their relative concentrations in crude oil by measuring the effective permittivities of the mixture at microwave frequencies. Dielectric mixture theory is used to show the relationship between the permittivity and the relative concentrations of two materials in a mixture. It is shown that equivalent results are obtained for the case of small concentrations of water in oil by using a perturbation theory analysis for a liquid cylindrical sample flowing through a resonant cavity. Results are presented for a sample enclosed in a thin-walled Pyrex tube with measurements taken for water concentrations in oil of 0-10 percent by volume. A practical instrument is described which uses a comparative technique for continuously comparing two samples of oil, one "dry" and one "Wet." Results show that this type of instrumentation can obtain sensitivities of 0.05-percent water content. The instrument is very simple, and has an output that can be readily adapted to automatic control applications.     

基于瞬态微波光电导测试仪的谐振腔传感器设计

利用微波谐振腔微扰原理建立了应用于测量半导 体和发光材料的谐振腔的传感器模型。采用HFSS 仿真软件对谐振腔参数和结构进行仿真。仿真结果表明,采用矩形孔时,微波谐振腔中具有 符合实验要求 的电场形式以及电场强度;实验结果也表明,样品在采用矩形耦合孔的谐振腔获得了较强的 信号。将不同 的样品放置于谐振腔中,并用纳秒激光脉冲照射,获得了较理想的动力学曲线,证明该谐振 腔的实用性, 为下一步测量样品的介电常数和电导率等物理参数等实验奠定了基础。     

Extended cavity perturbation technique to determine the complexpermittivity of dielectric materials

An improved measurement technique to determine the complex dielectric properties of materials has been developed that extends the validity of the conventional cavity perturbation technique for circular cylindrical rod-shaped samples in circular cylindrical cavities resonating in TM_0n0 modes. The method is particularly useful for the dielectric characterization of fragile, low-loss materials that are difficult to machine to typically required thin dimensions. The method further allows for multi-frequency measurements using higher-order radial modes and somewhat alleviates the very small cavity dimensions typically required by the conventional perturbation technique at higher microwave frequencies. A validity criterion for the extended method is given. Measurements of the complex permittivity of NaCl single crystals are presented, showing excellent agreement with theory     

Measurements of Microwave Conductivity and Dielectric Constant by the Cavity Perturbation Method and Their Errors

The theory and technique of the cavity perturbation method for measuring the conductivity and dielectric constant of materials are reviewed. An analytical formula for calculating the errors of the conductivity and dielectric constant caused by the measured error in the resonant frequency and quality factor are derived. This formula can be used for both rectangular and cylindrical cavities. The results of measurements on silicon samples are presented to illustrate this analysis.     

Measurement of material properties with a tunable resonant cavity

A tunable resonant cavity is used to measure the complex permittivity of dielectrics and the surface conductivity of metals with high precision. The analytical approximations, traditionally used in the cavity perturbation techniques, have been replaced with a rigorous numerical solution of the electromagnetic field distribution inside the rotationally symmetric cavity filled with inhomogeneous dielectrics. The measured values of the unloaded Q factor are compared with the numerically computed values over the tuning range. The least-squares data fitting procedure yields simultaneously the values of the loss tangent and the surface conductivity, and their standard deviations.<>     

Automatic Digital Method for Measuring the Permittivity of Thin Dielectric Films

One of the most promising techniques for measuring the electric permittivity at microwave frequencies of thin dielectric materials of the order of 0.1 to 10 /spl mu/m, is the cavity perturbation method. For thin films of this type, it is necessary to determine accurately and display small changes in the resonant frequency and Q factor of the cavity in the presence of the material sample. A circuit for the simultaneous measurement and digital readout of the resonant frequency and Q factor of microwave cavity is described. For the resonant frequency measurement, a very efficient automatic frequency circuit, with a homodyne modulation-detection bridge and frequency stabilization loop, is applied. Theoretical analysis and experiments results with this circuit show that an accuracy of 5x10/sup -7/can be achieved in the resonant frequency measurement. For measuring the Q factor, two similar circuits are described. The technique is based on measuring the phase shift of the envelope of an amplitude modulated microwave signal when this signal is transmitted through a resonant cavity at resonance. Although an accuracy of 0.5 percent in the Q factor can be achieved, it is shown that the main limiting factor in both circuits is the accuracy of phase shift determination at RF frequencies.     

High-Accuracy Wide-Range Measurement Method for Determination of Complex Permittivity in Reentrant Cavity: Part A --- Theoretical Analysis of the Method

New mathematical method for calculation of complex electric permittivity (epsilon) of a wide range of materials from the direct measured parameters of a reentrant cavity containing a sample of material is presented. Condition of resonance is drawn based on analysis of electromagnetic field distribution in the cavity with a sample. Accuracy of the obtained algorithm (convergences of series) and method of shortening iterative solution is discussed in detail.     

基于矩形谐振腔的介电系数测量装置

物质介电系数的测量对微波能的应用十分重要。文中基于谐振腔微扰法设计了一种结构简单的矩形谐振腔测量装置。通过测温孔的设计,该测量装置在测量物质介电系数的同时还能测量待测物的温度,可以得到不同温度条件下物质的介电系数。频率为2.45 GHz时,采用该装置对几种有机溶剂进行测量,得到了与相关文献一致的结果。     

Determination of electrodynamical parameters of dielectric pipe-shaped materials using millimeter wave cavity

Employment ofE _0np modes of cylindrical cavity resonator for measurement of electrodynamical parameters of dielectric pipe-shaped materials in millimeter wavelength band is suggested. Dielectric permittivity ? and conductivity σ of a sample can be found by measuring the frequency shift and theQ-factor change of the resonator. Method of “mode basis” is used for the calculation of sample permittivity ? and conductivity σ. Measurements were carried out at 8mm wavelength and related calculations have demonstrated use and possibilities of the method in studying the dielectric properties of samples of cylindrical and other forms.     

Microwave Measurement of Conductivity and Permittivity of Semiconductor Spheres by Cavity Perturbation Technique

Simple analytical relations for evaluating the components of complex relative permittivity of semiconductors using a cavity perturbation technique for spherical samples are presented. The relations although derived under a simplifying approximation yield remits of almost the same accuracy obtained by computer solutions of a transcendental equation for samples with resistivity up to about 1Omega-cm.     

Design and calibration of a large broadband dielectric measurementcell

A large dielectric measurement cell was designed and calibrated to operate over a 1-MHz to 3-GHz frequency range. The cell is much larger than commercially available cells and is useful for measuring samples with large-grain heterogeneities like concrete or rock. The cell works on a coaxial transmission line principle. Once the S parameters of the two end sections are calibrated, the S parameters of the sample region can be found. Then the complex permittivity of the sample can be deembedded. Because of the broad frequency range, three calibration methods are used for the low-, intermediate-, and high-frequency ranges. The accuracy of the cell is tested by measuring materials of a known dielectric constant. Error analysis is also performed to determine the uncertainty of the measurements     

Electromagnetic Field Due to a Magnetic Dipole in a Medium Containing Both Planar and Cylindrical Boundaries

An approximate method based on perturbation theory is used to calculate electromagnetic fields due to a vertical magnetic dipole in an Earth formation having both horizontal and cylindrical boundaries. The medium is first assumed to have a constant background permittivity. Any deviation from the background permittivity is treated as a perturbation. Correction terms are then found and expressed in multiple integrals. The first and the second correction terms involve threefold and sixfold integrations, respectively. An efficient integration technique is used to compute these multiple integrals. As an example, this method is used to calculate the field due to a vertical magnetic dipole over a layered Earth containing a cylindrical cavity. In another example, the response of a two-coil induction tool is calculated when it is located in a rugose borehole.     

同轴探头法测量片状介质材料的微波介电常数

提出了一种可用于测量片状介质材料微波复介电常数的同轴探头技术,该技术将同轴探头紧贴有导电衬底的片状介质,通过测量探头终端的矢量反射系数来确定介质的微波复介电常数。详细介绍了所采用的理论模型和测量系统。测量了一些常见介质材料的介电常数,测量值与理论值基本吻合。文章的同轴探头技术不仅可用于测量厚度较小的片状介质,而且可用测量样品量有限的液体。     

Microwave cavity perturbation technique: Part I: Principles

This report reviews the analysis used to extract the complex conductivity of a compound from a microwave cavity perturbation measurement. We intend to present a generalized treatment valid for any spheroidally shaped sample of arbitrary conductivity which is placed at either the electric or magnetic field antinode of the cavity. To begin with, we establish the relationship between the measured parameters and the conductivity for a spherical sample. Next, we extend these results to the case of spheroids; and for the first time, we cover all different configurations that one can possibly use to study an arbitrary conducting sample inside a cavity: in particular, all possible orientations of the sample with respect to the applied field are solved.     

Correction to open-resonator permittivity and loss measurements

A correction to the length of a dielectric sample placed in an open resonator is derived using perturbation theory. The correction takes account of the additional volume of sample extending beyond the curved phase front normally assumed in the beam wave theory. Results are presented for a range of sample lengths of a high-density polyethylene, which illustrate the improvement obtained in both permittivity and loss measurements when this correction is used.     

理想导体金属谐振腔电磁场微扰理论研究

根据电磁场Helmholtz方程与定态薛定谔方程的相似性，给出了金属谐振腔电磁场的微扰理论：在金属腔中放入一介质体时，原来空腔中电磁场的分布和谐振频率会发生改变。发生改变后的电磁场可以用原来所有模式电磁场展开。若引入的介质体很小或相对介电常数和磁导率接近于1，就可把它看成微扰。导出了谐振频率和电磁场分布的一级、二级近似解析表达式。指出了此理沦的适用范围，并对结果进行了讨论。     

Comments on “Propagation of EM pulses excited by an electricdipole in a conducting medium” [with reply]

Comments that the authors of the original paper (see Song and Chen, ibid., vol.41, no.10, p.1414-1421, 1993) wish to determine the transient electromagnetic field generated in a conducting medium by an impulsive current in a short electric dipole. Their approach and their results, however, seem to be questionable. To start with, their choice of a delta-function excitation causes serious mathematical difficulties which have been overlooked. Because the spectrum of the delta-function pulse extends over all frequencies with equal Fourier amplitudes, the assumption that the conducting medium, specifically sea water, is characterized by frequency independent permittivity and conductivity is incorrect. The authors reply that they are aware that the conductivity and permittivity of sea water is frequency dependent. They made the approximation of constant conductivity and permittivity for two reasons. First, the exciting impulse current contains all the frequency components from zero to ∞. The second reason for the assumption of constant conductivity and permittivity is that with this assumption we are able to obtain an exact solution for the EM field excited by an impulse current