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.     

Method for measuring properties of high relative dielectricconstant materials in a cutoff waveguide cavity

In this paper, a method for measuring properties of ceramic materials with relative dielectric constant value of 20-150 is proposed. It permits us to eliminate the operating TM_01δ-mode degeneration due to its frequency coincidence with other modes, including ones of higher order. Both that fact and the possibility of precise calculation of an unloaded quality factor for a cavity permit one to execute the accurate measurements of loss tangent values as low as (1÷0, 5)×10^-4, the error of dielectric constant measurement being equal to or less than 1%. The feasibility of precise measurement of the loaded Q-factor of a cavity by the readings of micrometric probe makes the use of frequency meters unnecessary     

Analysis of modes in a free-standing nanowire cavity by FDTD simulation

The mode frequency and the quality factor of nanowire cavities are calculated for the intensity spectrum obtained by the finite-difference time-domain （FDTD） technique and the Pade approximation. In the free-standing nanowire cavity with the dielectric constant ε=6.0 and the length of 5μm, the quality factors of 130,159,and 151 are obtained for modes with frequency around 798 THz,at the cavity radius of 60 nm, 75 nm, and 90 nm, respectively. The obtained field distribution of the fundamental transverse mode shows that the mode field is confined very well by the nanowire cavity even when the radius of nanowire is much smaller than the mode wavelength.     

Dielectric property measurements of materials using the cavitytechnique

A cavity technique based on frequency shift was used to measure dielectric properties (dielectric constant and loss factor) of some particulate materials as a function of temperature. The materials studied were alumina, cobalt/alumina, dolomite, and sand. The properties were measured at various points between room temperature and 600°C in the frequency range of 925-995 MHz. The dielectric constant and loss factor of all samples, except the cobalt/alumina catalyst sample, were approximately constant with temperature. The dielectric constant and loss factor of the cobalt/alumina sample exhibited a noticeable increase with temperature     

Analysis of mode quality factors and mode reflectivities for nanowire cavity by FDTD technique

The mode frequency and the quality factor of nanowire cavities are calculated from the intensity spectrum obtained by the finite-difference time-domain (FDTD) technique and the Pade/spl acute/ approximation. In a free-standing nanowire cavity with dielectric constant /spl epsiv/=6.0 and a length of 5 /spl mu/m, quality factors of 130, 159, and 151 are obtained for the HE/sub 11/ modes with a wavelength around 375 nm, at cavity radius of 60, 75, and 90 nm, respectively. The corresponding quality factors reduce to 78, 94, and 86 for a nanowire cavity standing on a sapphire substrate with a refractive index of 1.8. The mode quality factors are also calculated for the TE/sub 01/ and TM/sub 01/ modes, and the mode reflectivities are calculated from the mode quality factors.     

微波介质陶瓷材料介电性能间的制约关系

微波介质陶瓷材料的三个主要参数相对介电常数εr、品质因数Q和谐振频率温度系数之间存在一定的关系。采用一维双原子线性振动模型,分析了微波介质陶瓷材料的εr、Q影响因素和它们之间的相互制约关系;采用Clausius-Mosotti方程,分析了谐振频率温度系数的影响因素以及它和εr之间的相互制约关系。讨论了提高高介微波介质陶瓷材料性能的途径,发现采用同电价质量较轻的离子取代,在基本不影响介电常数的情况下具有提高材料的Q·f值的可能性。     

有限元方法计算介质腔谐振频率和品质因子

采用有限元方法计算了二维方形介质腔和二维微盘的谐振频率和品质因子,并给出了两种腔中磁场、电场振幅分布图,介质腔中的谐振问题对应亥姆霍兹波动方程的本征值问题,本征值的实部和虚部与谐振腔Q值关联;比较了近似解析解、FDTD解、FEM解的结果,对于谐振频率比较,FEM和解析解更接近,对于品质因子比较,低Q值结果FDTD和FEM结果相近,高Q值结果两者相差较大。通过比较知道,FEM方法比时域有限差分方法计算更准确,求解速度更快。     

Measurement of Dielectric Materials Using a Cutoff Circuiar-Waveguide Cavity (Short Papers)

A technique is presented for accurately determinhg the dielectric constant of microwave materials. The concept is to resonate a cutoff circular-waveguide cavity by inserting the dielectric-disk sample. Unlike most dielectric measurement techniques which rely on perturbation methods, this one determines the dielectric constant from the absolute measurement of the resonant frequency. Also, the use of a cutoff cavity prevents false dielectric constant readings by eliminating spurious resonances.     

An investigation on the effect of varying the load, mesh and simulation parameters in microwave heating applications.

The paper attempts to provide a generic proposal on the influence of various microwave load parameters based on results accumulated during an investigation using a specific microwave multimode heating cavity configuration. The results have been obtained by numerical analysis using the Finite Element Method within a 3-D environment. The load parameters considered were dielectric constant, loss factor, load thickness and load position. Load material properties are typical of those used in industrial relevant applications. Of the four load parameters investigated, the configuration with a high loss factor was seen to dominate the load impact regardless of load thickness, load position or dielectric constant. With decreasing loss factor or increasing load thickness, the influence of the dielectric constant increases. Minor adjustments in the load position (10%) is generally seen to have minimal impact for all load properties considered. The paper also investigates the numerical impact of varying load properties. As the dielectric constant increases, which requires a higher number of mesh elements, so does the average iterations per numerical cycle. The number of numerical cycles and time to reach a convergence is also seen to be inversely proportional to the load loss factor.     

平板介质的微波分裂腔法介电常数测试技术

为实现微波频段平板类介质材料的介电常数的无损测试，研究了分裂式圆柱形谐振腔测试方法。介绍了分裂式圆柱形谐振腔的电磁场分析理论，采用模式匹配技术实现了介质加载条件下腔内电磁场分布的精确求解，得到了腔体谐振频率与材料介电常数之间的准确关系。在理论分析的基础上，制作了空腔谐振频率为10 GHz的分裂式谐振腔，并与前期研制的闭式谐振腔进行对比测试，介电常数实部测量结果相对误差小于1%。与国外同类产品进行对比测试，介电常数实部结果基本一致，损耗角正切测量结果更接近于文献参考值。因此，微波分裂腔法能够实现平板介质板材的无损测量，具有准确度高，使用方便等突出优势，可在微波频段内实现介电常数为 1~20，损耗角正切为1×10^-3~1×10^-5，板材厚度为0.1~2.0 mm的各类平板介质材料介电常数的准确测试。