基于材料微扰的多模谐振器谐振特性研究北大核心CSCD

提出了利用介质材料进行微扰实现多模谐振的微带谐振器设计方案。首先分析了材料微扰多模谐振器的谐振机理,然后在谐振器两端介质材料不变情况下,通过改变谐振器中间部分的介质材料,分别设计了两端开路和两端短路的半波长微带多模谐振器。仿真结果表明,上述不同设计得到的微带谐振器均可实现简并模分裂,具有多模谐振的特点。     

基于材料微扰的多模谐振器谐振特性研究

提出了利用介质材料进行微扰实现多模谐振的微带谐振器设计方案。首先分析了材料微扰多模谐振器的谐振机理,然后在谐振器两端介质材料不变情况下,通过改变谐振器中间部分的介质材料,分别设计了两端开路和两端短路的半波长微带多模谐振器。仿真结果表明,上述不同设计得到的微带谐振器均可实现简并模分裂,具有多模谐振的特点。     

谐振腔微扰法测量原油含水率仿真研究

与传统在线测量原油含水率的方法相比,高频微波谐振腔微扰法具有受外界环境影响小,不受矿化度影响,测量精度高的特点。由于原油和水的介电常数相差较大,微小的含水率变化会引起介电常数较大变化,使得不同含水率原油对微波场的损耗不同。通过软件仿真的方法可以测量出含微扰源(样品原油)的微波谐振腔的谐振频率和品质因数变化情况,根据矩形谐振腔微扰公式可得出样品原油的介电常数,然后将所得结果代入原油含水率和介电常数关系公式求得原油含水率。并且将铝制边界条件和铜制边界条件下所测得的原油介电常数数据与理论值进行分析,求出其相对百分比误差,得出一种较为简单、实用、快速准确的测量中低含水率原油的方法。     

微波复合介质基板性能研究

采用微扰法、螺旋圆柱谐振法和带状线谐振法分别对聚四氟树脂复合精细电子陶瓷微波复合介质的复介电常数进行了测量与误差分析。基于扫描电子显微镜 (SEM )观察 ,从微观上解释了辊压工艺对介质介电性能一致性改善的原因。研究了不同的表面处理方法对基板金属化剥离强度的影响规律。     

微扰用介质薄片介电常数的精确测量

本文介绍作为平面结构慢波系统耦合阻抗测量用的介质薄片(云母片,陶瓷片等)介电常数ε_r的测量方法——谐振微扰法;并考虑到测试腔耦合元件电纳对测量结果的影响,提出了修正公式。在三厘米波段,对几种介质薄片进行了实际测量,并与传输线驻波比法进行了比较。这种测量方法还适用于各种半导体材料薄膜介电特性的测量。     

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。     

太赫兹平板材料介电常数测试技术

讨论了太赫兹波段平板材料的介电常数测试技术,在传统自由空间法原理的基础上,改进相位-群时延法解决了高频材料测试出现的多值性问题,利用介电常数及磁导率之间的震荡关系解决了厚度谐振问题,采用多项式曲线拟合的方式抑制校准误差,最后搭建了实物测试系统,对典型的空气层、聚四氟乙烯平板材料进行实验测量,实现了0.17～0.22 THz 频段范围内的2%误差测试精度。     

测量低损耗薄膜材料介电常数的标量法

依据被测介质性质,在现有实验设备条件下,提出了一种标量法测量低损耗薄膜介质介电常数的新方法.该方法利用传输线法测量原理,先测量待测介质损耗,间接得到反射系数,由反射系数与介电常数关系式,推导得出待测介质的介电常数.该方法有样品容易制作,测量简单准确等特点.通过测量实例的误差分析,指出标量法测量薄膜材料介电常数的不足,提出相应的改进措施.     

电磁开腔测量各向异性媒质复介电常数

本文利用微扰原理和复数源点法,对电磁开腔测量单轴各向异性媒质复介电常数进行了理论研究,并且定量地分析了在测量中由于媒质的各向异性引起的双折射现象。最后利用一套八毫米电磁开腔自动测量系统对几种石英晶体样品进行了实际测量。     

传输/反射法测量复介电常数的若干问题

研究了传输／反射法测量线性材料复介电常数εr的厚度谐振、多值性等问题，得到了解决这些问题的有效方法。通过改进NRW传输／反射法，由散射参数直接得到了归一化特性阻抗与传播常数，从而可以把已有的三个确定复介电常数的方程用到NRW传输／反射法中。联合应用这三个方程解决了上述问题，这使得人们可以用传输／反射法对任意厚度的样品在任意频率上进行复介电常数的稳定测量。用波导取样器与同轴线取样器分别得到的实验结果证明了此方法的有效性与可实现性。     

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     

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.     

Nonreciprocal cell for the broadband measurement of tensorialpermeability of magnetized ferrites: direct problem

In this paper, a broad-band characterization method for measuring the complex permeability tensor components and complex scalar permittivity of magnetized ferrites is described. The technique is based on the reflection/transmission measurement of a rectangular waveguide partly filled with the ferrite that is to be characterized. The fundamental principle of the measurement consists in using the anisotropy of the material to lead to the nonreciprocity of the device in order to have the same number of measurable parameters (the S-parameters of the cell) for the characteristics we want to determine. Here, we will recall the principle of the mode-matching method used for the electromagnetic analysis of the cell (direct problem). We will bring to the fore the difficulties linked to the determination of the complex propagation constants of the different modes and will present a calculation procedure that makes this determination in a wide-frequency range easier. We will then compare at X-band frequencies (8-12 GHz) the theoretical S-parameters with those measured for ferrites of well-known properties in order to validate the direct problem. The determination of the permittivity and permeability values from the measured parameters (inverse problem) is not addressed here     

固体电介质微波介电参数的耦合器测量技术

论述了微带分支线耦合器非破坏性测量固体电介质复介电常数的方法,阐明了3dB分支线耦合器用于介电常数测量的原理,提出的分支线耦合器的输出与耦合端口各连接一段终端开路的微带线,待测物放在其中的一条线上。待测物的介电常数可通过测量两端口的散射参数的幅度进行计算。运用提出的方法,在2.45GHz下测量了特氟龙、聚丙烯等固体电介质的复介电常数,其结果与文献相吻合。     

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     

Effects of waveguide wall grooves used to hold samples formeasurement of permittivity and permeability

The complex permittivity and permeability of a material may be measured at microwave frequencies by placing a sample of the material in a waveguide and measuring the complex reflection and transmission coefficients. Whereas there are various approaches to holding the sample in place, for a thin rigid sample shallow grooves may be cut in the waveguide walls for this purpose. However, such grooves will be a source of error since higher order modes can be excited. In this paper the modal analysis method is used to illustrate the potential for error in measuring constitutive parameters of the sample introduced by the grooves     

A Generalized Formulation for Permittivity Extraction of Low-to-High-Loss Materials From Transmission Measurement

We have derived a one-variable metric function for fast computations of the relative complex permittivity of low-to-high-loss materials from $ S_{21} $ measurement at one frequency. We present how this function can be applied for different applications (e.g., relative complex permittivity measurement of a thin low-loss material). In addition, it can be applied as a measurement tool in broadband applications for samples with substantiate lengths, which demonstrate low-loss property at lower frequency bands and high-loss property at higher frequency bands. The derived expressions can work very well in limited frequency-band applications or for dispersive materials since it is based on point-by-point (or frequency-by-frequency) extraction. We measured the relative complex permittivity of two test samples (a low- and high-loss sample) for validation of the derived expressions.      

The improved resonator method for measuring the complex permittivity of materials

An improved resonator method for determination of the complex permittivity of materials in a reflective resonator is presented. The method is specific in the following. In the obtained relationship, imaginary part ε₂ of the permittivity of an investigated material is determined using the variation of the resonance frequency and coupling coefficient of the resonator observed when a specimen is introduced, which increases the measurement accuracy. The method is approbated in the investigations of high-resistance silicon specimens.