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。     

How Wind Affects Passive Microwave Measurements of Sea Surface Temperature

Uncertainty in the wind speed is a major source of error in passive microwave measurements from satellites of sea surface temperature (SST) because of the non-linear relationship between sea surface emissivity and wind speed. The accuracy of the SST measurement that can be achieved with only passive microwave measurements was assessed by computer modeling. Our investigation showed that the second-order terms must be included in the equation of radiative transfer in an analysis of the errors in the retrieved SST. In addition, we found that the effects of wind roughening and foam production should be treated separately. We have concluded that the accuracy of SST measurements would be improved by including data from an active remote-sensing instrument such as a scatterometer.     

微波辐照猪肉透热深度影响因素和表面变化

生物组织吸收微波辐照的影响因素及微波辐照效率是临床上进行体外辐照治疗时需要考虑的重要问题之一。以猪肉样本块为研究对象,用频率为2450 MHz 的微波,通过控制辐照的3 个变量(时间、功率、距离),分别探测了表层、透热最深层的温度和微观组织形貌变化。实验结果表明:增大辐照功率提升上表面温度效果最明显;根据不同深度位置的温度变化曲线,当上表面达到一定温度后才产生透热深度;从理论上解释了由于极化和弛豫现象而使上表面温度影响透热深度的原因,并由热传导方程的推导公式,验证了控制辐照影响上表面温度能够间接影响透热深度的实验结果,为微波辐照热疗中温度控制的进一步研究提供基础。     

Analysis of Frequency-Conversion Techniques in Measurements of Microwave Transistor Noise Temperatures

Frequency-conversion effects on microwave effective noise temperature measurements are analyzed and conditions under which they are noticeable are given. When necessary, the experimental data can be corrected using the analytical relationships derived here.     

The Performance of a New Direct Contact Applicator for Microwave Diathermy

A direct contact applicator, specifically designed for microwave diathermy at the Industrial, Scientific Medical (ISM) frequency of 2.45 GHz was evaluated by studying near-field patterns in free space, thermographic heating patterns in phantoms of simulated fat and muscle tissue, and associated leakage radiation. The main features are a circular waveguide with a short conical flare horn output section surrounded by an annular choke and two sets of dual posts to generate far-field circular polarization. The significant near field components of the therapeutic beam are in a transverse plane, parallel to the aperture. Heating patterns on the exposed surface of muscle phantoms and inside fat-muscle phantoms are spatially similar and relatively uniform. The leakage level is 0.8 mW/cm/sup 2/ per 100 W of forward power for direct contact and 4 mW/cm/sup 2/ per 100 W of forward power for a 1-cm air gap between aperture and planar phantoms. The uncertainty of these leakage measurements is /spl plusmn/2 dB. This investigation demonstrates the technical feasibility of a safe and effective direct contact microwave diathermy applicator operating at 2.45 GHz. The applicator is a viable candidate for hyperthermia appllications.     

光热偏转技术测量蓝宝石激光手术刀头温度分布

利用光热偏转技术测量了连续YAG激光的蓝宝石手术刀头的横向温度分布和纵向温度衰减长度。其分布曲线与用CCD器件测量的光强分布具有很好的一致性。     

微波晶体管参数的测量方法

本文用信号流国和矩阵方法分析了测量激彼晶体管S参数的三种方法，分别给出了10个和8个误差参数信号流图新的显式解。为各种型号的矢量网络分析仪测量做液晶体管S参数，提供了精确测试方法。     

Aperture Synthesis Thermography -- A New Approach to Passive Microwave Temperature Measurements in the Body

The radio astronomical technique of aperture synthesis is proposed for use in medical applications to give, noninvasively, a thermal image of a large fraction of the human body to a depth of several centimeters with no microwave irradiation. The principles of operation are illustrated by a practical design which could give a sensitivity of a few milli-Kelvin over a 50-cm field in a 10-s exposure. Applications of the proposed system include detection of cancers and other infections, and also rest-time monitoring of the effects of hyperthermia on the surrounding tissue.     

微波腔体在工业检测中的应用

本文阐明微波腔体用于工业检测湿度、温度、厚度、速度、材料电磁参数等的基本原理.综述近年来在测量湿度、速度、材料电磁特性及半导体材料电阻率、非平衡载流子寿命等的应用.o     

微波和高温器件的一种空气桥互连方法

空气桥是单片微波集成电路MMICs的一种高速互连技术,其目的是减少微波大功率器件单位而积的寄生电容,提高器件的频率特性.文中提出了一种灵活性很强,应用于微波和高温器件的空气桥定型方法.该方法利用不同性质的光刻进行多层甩胶、低温烘烤牺牲层,制出弧度很好的桥区拱形牺牲层,经低温烘烤的牺牲层的高度比烘烤前的高出60%.利用该方法可以制出高性能和高可靠性的窄气桥互连结构.     

微波和高温器件的一种空气桥互连方法

空气桥是单片微波集成电路MMICs的一种高速互连技术,其目的是减少微波大功率器件单位而积的寄生电容,提高器件的频率特性.文中提出了一种灵活性很强,应用于微波和高温器件的空气桥定型方法.该方法利用不同性质的光刻进行多层甩胶、低温烘烤牺牲层,制出弧度很好的桥区拱形牺牲层,经低温烘烤的牺牲层的高度比烘烤前的高出60%.利用该方法可以制出高性能和高可靠性的窄气桥互连结构.     

高温超导微波器件在雷达接收机中的应用

高温超导微波器件具有极低损耗和极低噪声的优良特性。文中将低温前端与常规接收机前端进行了性能指标的对比，对超导微波器件主要是低温前端的应用进行分析。得出结论：超导器件的应用使得接收机的灵敏度与抗干扰性能等关键指标得到大幅度提高。     

Mismatch Errors in Microwave Phase Shift Measurements

The phase difference between the incident and transmitted waves at the input and output ports, respectively, of a two-arm waveguide junction in a reflection free system is a characteristic of the waveguide junction and is defined as the "phase shift." The difference between the phase shift in a reflection free system and the "change of phase" observed in a system which is not reflection free will be termed mismatch error. The mismatch error depends not only on the reflections present in the system but also on the choice of the wave used as the reference wave in a phase measurement. Similar considerations hold for the measurements of variation of phase shift and the observed change of phase in adjustable components. A formal scattering matrix analysis is used to derive expressions for phase relationships of the wave amplitudes for a two-arm waveguide junction in a system with reflections. The results of this analysis are used to evaluate mismatch error for different choices of reference waves. Two techniques of variation of phase shift measurements are analyzed. Graphs of the limits of mismatch error in a commonly used method of measurement are presented.     

Raman Anisotropy Measurements: An Effective Probe of Molecular Orientation in Conjugated Polymer Thin Films

Understanding the molecular alignment of conjugated polymers within thin‐film samples is essential for a complete picture of their optical and transport properties, and hence for the continued development of optoelectronic device applications. We report here on the efficacy of Raman anisotropy measurements as a probe of molecular orientation, presenting results for aligned polyfluorene nematic glass films. Comparison is made with the results of optical dichroism measurements performed on the same samples. We show that in many cases molecular orientation can be more directly characterized by Raman anisotropy, and that it can have a greater sensitivity to the degree of molecular orientation than conventional optical dichroism. The fact that the Raman measurements can be readily performed on the same thin films (～ 100 nm thickness) that are required for optical dichroism means that there is no ambiguity in a direct comparison of results. This situation differs from that for standard X‐ray diffraction measurements (these require film thicknesses of several μm) and electron diffraction or electron energy loss spectroscopy measurements (these require film thicknesses of 10 nm or less). The Raman data allow the angle (relative to the chain axis) for the optical dipole transition moment to be deduced from the dichroic ratio, and confirm the role that its off‐axis component plays in limiting this ratio. The added fact that Raman anisotropy data can be collected in situ, in reflection geometry for standard device structures, and with microscopic resolution and chemical specificity makes the technique even more attractive as a non‐invasive device probe.     

Multifrequency Microwave Radiometer Measurements of Soil Moisture

Ground-based microwave radiometer experiments were performed to investigate the effects of moisture, temperature, and roughness on microwave emission from bare soils. Measurements were made at frequencies of 0.6-0.9, 1.4, and 10.7 GHz using van-mounted radiometers to observe prepared soil sites in Kern County, CA. The sites were instrumented for monitoring soil characteristics and surface meteorological conditions. Brightness temperature variations of approximately 15 K at 1.4 GHz and 25 K at 10.7 GHz were observed as a result of diurnal changes in the soil temperature. Increasing the soil moisture content from 2 to 15 percent by volume resulted in brightness temperature decreases of approximately 70 K at 0.775 and 1.4 GHz, and 40 K at 10.7 GHz, depending, to a lesser extent, on polarization and viewing angle. The results show the significance of soil temperature in deriving soil moisture from microwave radiometer measurements. Comparisons of the microwave measurements with theoretical predictions using a smooth surface model show reasonable agreement and support previous results of this nature obtained with other soil types. Approximately equal sensitivity to soil moisture was observed at 0.775 and 1.4 GHz, although the sampling depth is greater at the lower frequency.     

Accurate Phase-Length Measurements of Large Microwave Networks

The stanford two-mile linear accelerator uses 240, single-input-port, four output-port, S-band, rectangular-waveguide networks to feed RF energy sixty to seventy feet from the klystrons above ground to ten-foot-long, disk-leaded, circular-waveguide, accelerator sections below ground. During installation it is necessary to permanently adjust the phase lengths of the four network branches to be within /spl plusmn/4.5 electrical degrees of the design lengths for RF wave and electron beam synchronization. A modulated reflection phase-length comparison method is used, whereby a small signal is sent into each branch and reflected, in turn, by a diode switch, which is turned on and off at a 1 kHz rate. A null occurs in the amplitude modulation of the sum of a large reference signal and the small reflected signal, when the two signals are nearly in-phase quadrature. The reflectors are placed so that the network branches are properly adjusted when the nulls from all branches occur for the same setting of a variable phase shifter in the measurement line. Small mismatches and multiple power divisions do not affect the accuracy of this method. Frequency, temperature, and air pressure are the main environmental conditions affecting the measurement and are discussed along with the design of the reflecting diode switch, which is mounted in a vacuum-sealed waveguide flange.     

缺陷表面温度分布及空腔自然对流对红外检测的影响

对存在内部缺陷的板状结构的传热建立了二维物理和教学模型。通过有限差分法求 解得到了检测表面的温度分布。得到了缺陷尺寸、深度以及缺陷的当量导热系数对检测表面温度分布的影响规律;通过建立一维模型,分析了缺陷空腔内自然对流换热对检测表面温度分布的影响。研究认为,随着缺陷厚度的增加,缺陷的导热系数与被检材料的导热系数差异扩大,表面的最大温差增大;表面最大温差随缺陷的长度和缺陷深度的增大先增加后减小;缺陷厚度大概在10mm范围内自然对流开始起作用,高于此值后,自然对流换热对表面的温度分布具有显著的影响,并且此缺陷的厚度值受试件材料、表面对流换热系数的影响可以忽略。     

微波功率测量的误差分析

根据实际工作中对微波功率测量过程和结果的研究与分析,文章阐述了在微波功率测量中常见的各类误差及产生原因,详细介绍了失配误差的形成原因并给出了相应的解决办法,最后指出了在实际微波功率测量过程中应注意的其他问题。     

高温高压微波化学反应器耦合窗的应力分析

一些高温高压微波化学反应器使用圆形陶瓷片作为介质耦合窗口。本文基于有限元的方法,对窗口在不同腔体内压和微波输入功率下的热应力和机械应力分布进行了计算,并且进行了分析比较。结果表明:介质耦合窗上的热应力和机械应力及其形变随着腔体内压和输入功率的变化而发生很大改变,并且在不同条件下介质耦合窗上主要作用应力也不同。主要作用应力对高温高压微波化学反应器窗口的结构设计具有很高的参考价值。     

Microwave Q Measurements in the Presence of Coupling Losses

In the use of the impedance (Q-circle) method of measuring the cavity Q values, the presence of losses in the coupling network (between the cavity and the available external terminals) is usually neglected. If appreciable losses are present this simplification is not justitied, and its use can lead to significant errors. The losses in any coupling network can be described by means of an equivalent canonical circuit containing a series and a shunt resistor. The losses due to the series element are immediately apparent from the character of the impedance locus when plotted on a Smith Chart and can be corrected for an "apparent" Q value. However, unless the shunt loss can be determined by a separate calibration of the coupling network, the apparent Q value will be ambiguous because the shunt losses occurring in the coupling network are not distinguishable from those in the cavity proper. Methods for using the impedance data for determining the Q values are given on the assumption that the coupling network parameters cm be found. It is also pointed out that due to the presence of coupling losses the loaded and external Q values are no longer uniquely defined, but their meaning depends upon the application of interest. Formulas relating these to the coupling network parameters are given.