Holographic reconstruction of source distributions from microwave height-gain curves

Using the fast Fourier transform (FFT) algorithm, computer-reconstructed images of radio sources are obtained from conventional height-gain measurements over line-of-sight propagation paths for microwave frequencies of 2 and 4 GHz. The height-gain curves are regarded as one-dimensional microwave holograms.     

A microwave heating system for improving temperature uniformity in heated tissue.

A microwave heating system, designed to improve temperature uniformity in heated tissue, is described. The system employs parallel-opposed waveguide applicators, operating in the TE10 mode at 2450 MHz with the tissue to be heated (i.e. mouse intestine) immersed in a liquid which is both biologically compatible with and dielectrically similar to the tissue. The liquid improves the microwave coupling and avoids shape and size dependent absorption characteristics of the irregularly shaped tissue. Also, by maintaining this liquid at a suitable temperature with respect to that required in the tissue, the thermal losses and hence temperature gradients in the tissue are reduced compared with heating in hot liquid alone.     

Dual-mode antenna design for microwave heating and noninvasive thermometry of superficial tissue disease

Hyperthermia therapy of superficial skin disease has proven clinically useful, but current heating equipment is somewhat clumsy and technically inadequate for many patients. The present effort describes a dual-purpose, conformal microwave applicator that is fabricated from thin, flexible, multilayer printed circuit board (PCB) material to facilitate heating of surface areas overlaying contoured anatomy. Preliminary studies document the feasibility of combining Archimedean spiral microstrip antennas, located concentrically within the central region of square dual concentric conductor (DCC) annular slot antennas. The motivation is to achieve homogeneous tissue heating simultaneously with noninvasive thermometry by radiometric sensing of blackbody radiation from the target tissue under the applicator. Results demonstrate that the two antennas have complimentary regions of influence. The DCC ring antenna structure produces a peripherally enhanced power deposition pattern with peaks in the outer corners of the aperture and a broad minimum around 50% of maximum centrally. In contrast, the Archimedean spiral radiates (or receives) energy predominantly along the boresight axis of the spiral, thus confining the region of influence to tissue located within the central broad minimum of the DCC pattern. Analysis of the temperature-dependent radiometer signal (brightness temperature) showed linear correlation of radiometer output with test load temperature using either the spiral or DCC structure as the receive antenna. The radiometric performance of the broadband Archimedean antenna was superior compared to the DCC, providing improved temperature resolution (0.1 degree C-0.2 degree C) and signal sensitivity (0.3 degree C-0.8 degree C/degree C) at all four 500 MHz integration bandwidths tested within the frequency range from 1.2 to 3.0 GHz.     

一种紧凑型宽带高功率微波驱动源

为实现对传输线开关振荡器或振荡天线进行快速充电,以提高其耐压能力和产生高频振荡信号的能量效率,本文研制了一种基于Tesla变压器的电容储能型脉冲驱动源。本文首先介绍该驱动源的工作原理和运行过程,接着利用等效电路方法分析了关键电路参数对负载充电过程的影响,然后介绍该驱动源的具体工程设计,最后介绍该驱动源初步测试结果以及将其应用于变压器油在10 ns量级脉冲下击穿特性研究的实验情况。实验表明,输出火花开关在中储电容器充电电压为-191 kV导通时,通过电感对等效电容为15 pF的传输线充电电压峰值为-224 kV,电压上升时间约10 ns。研究结果表明本文研究的驱动源能够满足对传输线开关振荡器等电容负载进行快速充电至数百kV高压的应用需求。     

Reliability of microwave heating for hemoderivative thawing

The spoiling of coagulation factors, proteic patterns and specific activity has been comparatively determined in fresh frozen plasma, cryoprecipitates and hemodiagnostic sera, thawed in a 37 degrees C water bath and in a microwave oven. Effects of conventional and microwave heating are not significantly different, while results of the latter technique are rapid and aseptic. Previously, heating performances of a commercial microwave oven have been investigated for deionized water, saline solutions, and bovine serum. Furthermore, plastic containers of hemoderivatives have been tested to assure that no toxic products are released during microwave heating.     

高精度星载微波定标源黑体温度测量控制系统的设计

微波辐射定标源作为微波辐射计的重要载荷设备,可校准微波辐射计输入亮温度与输出量值间的关系,实现微波辐射计灵敏度、线性度和稳定度等参数的标定。针对辐射源黑体及其测温传感器,设计了一种在轨温度测量与控制电路,用于温度信号的检测与调理、低通滤波、数据采集、温度数据处理以及温度的稳定控制。地面测试与在轨运行均表明,系统满足星载微波辐射计的设计要求,具有高精度、高可靠性的特点。     

Effect of surface cooling and blood flow on the microwave heating of tissue

The one-dimensional heat transport equation has been solved for a semi-infinite plane of tissue irradiated by microwave radiation, to determine the effects of thermal convection due to blood flow and transfer of heat from the tissue surface into space on the steady-state temperature distribution in the tissue. For microwaves in the 1 to 10-GHz range, the effective heating depth is 1 to 2 cm, and can be much deeper than the penetration depth of the radiation in the tissue. The position of the maximum tissue temperature can be varied by a centimeter or so by cooling the surface. The results suggest that microwave irradiation of simulated biomaterials is not likely to provide accurate estimates of the actual microwave-induced temperature distribution in tissue.     

Resonant applicator design for industrial microwave heating

The use of transmission-line modelling (TLM) as a general tool for designing cavity applicators for microwave heating purposes is discussed. This method is used to validate a recent procedure for designing rectangular cavities loaded with an inhomogenous dielectric layer. The influence of dielectric losses on the cavity resonances is studied.<>     

Robust temperature control for microwave heating of ceramics

This paper presents results on the development of an automatic feedback control system for controlling the temperature of ceramic samples being heated by microwave energy. Design of the temperature controller is presented, and experimental results from heating experiments are given. The temperature control system is evaluated in terms of its robustness to parameter variations in the linearized model and in terms of its performance in actual experiments     

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.     

Arsenosilica film source for microwave transistor

Arsenosilica films have been used to investigate arsenic diffusions into silicon with the object of using the dopant for emitter of a microwave transistor. A detailed study of the effect of film spin speed and different drive-in ambient on the formation of surface defects was carried out. Cross-sections of arsenic (emitter) and boron (base)_diffused junctions with oxide as the mask showed that pull of the base under the emitter (retardation) was a function of total base doping Q. For Q > 10¹⁵ atoms/cm², some push (enhancement) of the base was observed. These results are contrary to those observed previously. Microwave power transistors fabricated with arsenic emitters showed superior performance over that of phosphorus emitter.     

Remote sensing of atmospheric water content from satellites using microwave radiometry

Analysis is presented which substantiates the high correlation achieved in relating integrated water vapor and liquid water to brightness temperatures at frequencies near the 22.235 GHz water vapor line. The influence of atmospheric and surface variability is shown to be minimal over low emissivity sea surfaces. Determination of atmospheric water content using regression techniques is shown to follow directly from radiation transfer theory. Satellite data from the Nimbus-E Microwave Spectrometer (NEMS) aboard Nimbus-5 are compared with radiosonde water vapor measurements and cloud images recorded by the Temperature Humidity Infrared Radiometer aboard Nimbus 5.     

New resonant scatterer for measuring microwave magnetic-field distributions

A new resonant scatterer for measuring magnetic fields at microwave frequencies has been developed. This scatterer has the shape of a small slot antenna and is responsive only to the magnetic field.     

Wide-angle microwave lens for line source applications

A new "time-delay" scanner consists of a constrained wide-angle two-dimensional microwave lens with a straight front face in which lens elements connect arbitrary points on the inner and outer contours. The lens can operate at very short pulse lengths and can scan more beamwidths than any previously known device of its type. A phase analysis shows that this design has very small coma aberrations and that the lens can generate fractional degree beams. Criteria developed for selecting optimum lens parameters are given. The radiation patterns of an experimental model in which the lens elements consist of coaxial cables show the expected wide-angle characteristics. In further tests incremental scanning was obtained through the use of phase shifters in the coaxial lens elements. The design of symmetrical three-dimensional lenses is briefly discussed. A table of lens contour parameters is given for an optimum lens design with scan anglealphaof30deg.     

Plant water content and temperature of the Amazon forest fromsatellite microwave radiometry

An attempt is made to derive the evolution of the temperature and the water status of the Amazon forest canopy from satellite microwave radiometry. The Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) temperature-corrected tapes data are analyzed for the 6.6, 10.7, 18, and 37 GHz frequencies, at daytime and nighttime, over a zone near Manaus (3°S, 60°W), Brazil. Two periods are investigated: the wet (April-May) and dry (July-August) seasons of 1985. After separating forest- from river-contaminated pixels, atmospheric corrections are performed for water vapor, clouds, and rain, using surface and satellite data. Algorithms are developed to model the microwave thermal emission of vegetation following a continuous approach and a discrete approach. A sensitivity study is performed in order to determine which frequencies are relevant to retrieve land surface parameters. The models are then used along with an optimization procedure so as to carry out the inversion of the canopy structure parameters. The vegetation temperature and water content are retrieved through the continuous model     

微波消解技术在红外高纯材料杂质测试中的应用

微波消解是近年来迅速发展起来的样品处理技术,其具有高效、快速、易于控制、防止易挥发组分损失、对环境无污染、节能降耗等优点,目前已广泛应用在多个领域。本文以高纯Cd杂质测试为例说明微波消解技术在红外高纯材料杂质含量分析中的应用。     

Optimal spectral windows for microwave diversity imaging

Tomographic microwave diversity imaging is analyzed using linear system theory concepts, and optimal spectral windows for data acquisition are obtained either by considering window position in the spectral domain or by using simulated annealing to find an optimal phase weighting of the object frequency response samples collected over the specified spectral window. This study provides a means of microwave image formation that is applicable under general assumptions. Results of numerical simulations and representative images reconstructed from realistic experimental microwave scattering data are given, demonstrating that the proposed approach is superior to previous image reconstruction methods     

A system for controlled microwave heating of small samples.

A system for the controlled thawing and heating of small samples in a waveguide is described. A means of maintaining constant absorbed power within the sample over a wide range of sample parameters is a major feature of the system. Provision for sensing the melting point of immersed samples is include. Samples are continuously rotated to improve heating uniformity.     

Stable broadband variable noise source for microwave radiometry

A stable broadband microwave reference noise source has been designed using, as radiating elements, carbon-filament indicator lamps mounted in a waveguide. When used as a reference in an accurate radiometer, in place of a gas tube and attenuator, this source has a number of advantages. It is electronically controllable, insensitive to ambient temperature changes and the output may be set to match exactly any hot-load absolute standard of noise.