骨肿瘤微波等效体模的实验研究

本文介绍了2450MHz骨肿瘤微波等效体模的配制方法,利用三态四端口反射计测试系统测量了等效体模的介电常数,并与骨肿瘤组织的介电常数进行比较,结果证明该体模与骨肿瘤组织等效。     

用多模分析方法测试介质谐振器复介电常数的频率特性

本文提出了测试微波介质谐振器复介电常数的多模分析方法。ＴＥ０ｍｍ高次模的谐一文提出了工得到，利用高次模谐振频率计算可工作模式从杂模中分辩出来测试，以考察复介电常数的频率特性。     

一种新的微波频率下混合电解质水溶液复等效介电常数的计算方法

目前,大部分电解质水溶液的等效介电常数计算模型是针对静止频率下其实部进行的.而对于实部与虚部同时计算方法的报道中,都是通过大量实验测量,利用德拜参数拟合而得到相应结果的,且局限于少数几种溶液,例如盐水和海水等.本文中,通过实验得到了不同电解质水溶液的复等效介电常数,基于此实验结果,提出了一个新的计算模型,引入了不同离子的复影响因子的概念,用来计算微波频率下电解质水溶液的复等效介电常数.在915MHz和2450MHz下,比较了实验结果和计算结果,它们比较好地符合,从而证明了公式的有效性.这将为微波化学中微波加热稀溶液化学反应中的电磁场和温度分布计算提供基础,同时也将对地球物理、遥感以及水污染监测等相关领域研究有帮助.     

微波氢气等离子体介电特性的研究

通过实验发现微波矩形波导谐振腔中氢气等离子体生成前后谐振腔的谐振频率发生了变化.根据实验测量和HFSS软件仿真计算出了等离子体的等效相对介电常数,并研究了压强对介电特性的影响.由仿真结果可知:氢气和氢气等离子体的相对介电常数明显不同,微波氢气等离子体的等效相对介电常数小于1.在一定的压强范围内,微波氢气等离子体的等效相对介电常数随着等离子体压强的变化而变化.     

测量技术与设备

0225652HFC双向系统的噪声测量(刊]/陈韬//电视技术.—2002,(7).—98～99(L)0225653微波电路基片复介电常数无损测量的简单方法[刊]/ 田步宁//西安电子科技大学学报.—2002,29(4).—543～546(K)提出了一种无损测量微波电路基片复介电常数的简单方法。该方法把被测材料及取样器等效为测量网络与误差网络的并联,得到了复介电常数无损测量的计算公式。理论分析与实验结果表明:与传统的“场”     

高温超导微波电路衬底材料复介电常数的测量

本文讨论了在液氮温度下高温超导微波电路介质衬底材料复介电常数测试技术。利用TMono模高Q圆柱形谐振腔,对高温超导常用的几种单晶介质材料进行了测试。结果表明,该测试技术在不同温度下,可对低耗单晶和各向同性介质材料进行准确的测试,且测试简便、迅速、自动化程度高,具有测试介质材料某一方向复介电常数的优点。     

液相化学反应介电常数的测量与气泡影响分析

溶液中化学反应的等效介电常数是微波化学研究中的重要内容,等效介电常数的精确测量是研究微波与化学反应系统相互作用的基础.介绍了一种对溶液中化学反应等效介电常数随时间微弱变化跟踪测量的方法并对测量中经常遇到的气泡影响进行了分析.最后制作了一批测量探头,该探头可以有效排除其中的气泡.通过测量得到的反射系数和遗传算法(GA)可以对等效介电常数的微小变化进行精确测量.对稀溶液中的皂化反应测量的结果证实了该测量方法的有效性.     

带状线法测量微波材料的复介电常数

精确测量低损耗微波材料的复介电常数十分重要。利用带状线法测量微波介质基板常温和变温的复介电常数,得到了高精度的测试结果。结果表明了用带状线法测量低损耗微波介质基板复介电常数的有效性和准确性。还分析了带状线测试方法中产生的误差和应该注意的事项。     

微带线法测量微波材料的复介电常数

电磁波传输介质的电磁参数的准确测量,对材料的实际应用十分重要。研究微波材料介电常数的微带线测量方法,通过正演和反演过程的求解分析,对不同介电常数的材料进行了实际计算,同时还对测试误差进行了简要分析。结果表明,微带线测试微波材料的复介电常数方法可行,测量过程较为简单,测量结果准确。     

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。     

A dry phantom material composed of ceramic and graphite powder

Details of an artificially synthesized dry phantom material developed for experimental studies of microwave exposure to the human body are shown. The material is solid and can simulate electrical characteristics of high water content biological tissues such as muscles and the brain. The material is composed of high-ϵ_r ceramic powder, graphite powder, and bonding resin. Any shape of phantom models can be constructed to simulate different parts of the body, as well as the head. The paper reports the synthesis technique to obtain the desired complex permittivity and the fabrication technique of the phantom models for usage of specific absorption rate (SAR) estimation at 900 MHz     

Contribution to numerical methods for calculation of complex dielectric permittivities

A numerical method is described for computing complex dielectric permittivities by the von Hippel?Roberts method, using two samples of the same material and different size. In the process, the Newton?Raphson method is applied to the complex domain     

The empirical formula for calculating the complex effective permittivity of an aqueous electrolyte solution at microwave frequency

So far, some models have been established to calculate the complex effective permittivity of an aqueous electrolyte solution. Almost all of the models based on the fitting parameters in Debye's equation were used to calculate the complex effective permittivity of a few aqueous electrolyte solutions, such as saline water and seawater. In this paper, we propose a new empirical formula to calculate the complex effective permittivity of a mixed aqueous electrolyte solution based on the measurement of complex impact factors for fundamental ions. The calculated complex effective permittivities of six mixed aqueous electrolyte solutions were compared with the measured results at 915 and 2450 MHz. The complex permittivity of saline water obtained by this model was compared with the published data as well. Good agreement can be observed.     

Estimation of Complex Permittivities of Three-Dimensional Inhomogeneous Biological Bodies

Complex permittivities are estimated for a 36-cell model which represents the chest portion of the block model of man by using moment-method formulation of the electric field integral equation. The errors in the calculated complex permittivities are lower with saline/water the surrounding medium, as compared to air, presumably on account of better matching of energy to the biological body. It has been shown that the rest of the human body has little effect on the estimation of complex permittivities because of the near-field natore of the illuminating sonrces. small number of buried cells can be handled for solving the inverse problem, but the problem becomes ill-posed and unsolvable for a larger number of buried cells.     

Intercomparison of Terahertz Dielectric Measurements Using Vector Network Analyzer and Time-Domain Spectrometer

We describe a method for direct intercomparison of terahertz permittivities at 200 GHz obtained by a Vector Network Analyzer and a Time-Domain Spectrometer, whereby both instruments operate in their customary configurations, i.e., the VNA in waveguide and TDS in free-space. The method employs material that can be inserted into a waveguide for VNA measurements or contained in a cell for TDS measurements. The intercomparison experiments were performed using two materials: petroleum jelly and a mixture of petroleum jelly with carbon powder. The obtained values of complex permittivities were similar within the measurement uncertainty. An intercomparison between VNA and TDS measurements is of importance because the two modalities are customarily employed separately and require different approaches. Since material permittivities can and have been measured using either platform, it is necessary to ascertain that the obtained data is similar in both cases.     

A Microstrip Resonator With Slotted Ground Plane for Complex Permittivity Measurements of Liquids

A novel microstrip resonator is designed to measure complex permittivities of liquids with medium loss. The enclosed resonator is based on a lambda/2 open-circuit microstrip line with a slot in the ground plane. It is immersed into the liquid under test to measure the S-parameter from 2.2 to 2.6 GHz. The complex permittivities of binary liquid mixtures of methanol and ethanol are reconstructed from the resonant frequency and the unloaded quality factor. The experimental results agree with reference values. The maximum errors are 4.4% and 8.6% for the real and imaginary part of the permittivity, respectively.     

Is the SAM phantom conservative for SAR evaluation of all phone designs?

The specific anthropomorphic mannequin (SAM) phantom was designed to provide a conservative estimation of the actual peak spatial specific absorption rate (SAR) of the electromagnetic field radiated from mobile phones. However, most researches on the SAM phantom have been based on early phone models. Therefore, we numerically analyze the SAM phantom to determine whether it is sufficiently conservative for various types of mobile phone models. The peak spatial 1‐ and 10‐g averaged SAR values of the SAM phantom are numerically compared with those of four anatomical head models at different ages for 12 different mobile phone models (a total of 240 different configurations of mobile phones, head models, frequencies, positions, and sides of the head). The results demonstrate that the SAM phantom provides a conservative estimation of the SAR for only mobile phones with an antenna on top of the phone body and does not ensure such estimation for other types of phones, including those equipped with integrated antennas in the microphone position, which currently occupy the largest market share.     

Quantification of electromagnetic absorption in humans from body-mounted communication transceivers

The internal electric (E) field and energy deposition in a full-size adult male mannequin in the immediate vicinity of 1.5 W body-mounted communication transceivers have been measured. Transceivers operating at the four frequencies 50, 150, 450, and 800 MHz, and placed at various locations vis-à-vis the body were used. The mannequin was filled with two-thirds muscle-simulant biological phantom mixtures at each of the four frequencies. The complex permittivities (ε^*) of these mixtures were confirmed by measurement. The internal E-field distribution was measured by three-dimensional implantable E-field probes. Relatively superficial energy depositions were obtained at points close to the location of the transceiver antenna for the two higher frequencies with energy depositions typically less than 1-2 W/kg. Considerably reduced energy depositions were measured at the two lower frequencies on account of in-depth and wider dissemination of the absorbed energy and the relatively high ε^*of the tissues which results in an increased shielding of the body.     

Complex modes in lossless shielded microstrip lines

The possible existence of complex modes in lossless shielded microstrip lines was investigated using the singular integral equation method. The method is used for the analysis of three lossless shielded microstrip line structures with different substrate permittivities. To confirm the validity of the method, results are compared with existing data for propagating modes. Complex modes were found in the moderate and high permittivity structures.<>     

Complex-permittivity measurement on high-Q materials via combined numerical approaches

A modified indirect algorithm for extracting real permittivities from measured resonant frequencies has been developed. It is based on the perturbation theory along with the Newton iteration method, and improves the speed of the calculation with a factor of 2-4. It is superior, especially when system matrices under calculation are large. Based on the complementary advantages of the modified algorithm and a direct algorithm, a mixed algorithm of high speed and accuracy has been described. A real measurement system incorporating the linear fractional curve-fitting method and the mixed algorithm has been built to measure complex permittivities of high-Q materials.