Use of microwave radiation in surgery and cancer therapy.

In considering the therapy of cancer, the author has been interested in the internal dielectric heating property of microwaves and applied their capacity of rapid protein coagulation to medical treatment. With the purpose of utilizing this phenomenon for the resection of fragile parenchymatous organs, the experiment was conducted on rabbit livers, which were irradiated with microwaves for about 3 min. The effect of this phenomenon on cancer cells was also observed. Malignant tumors induced in rats were exposed to microwave radiation for 2 min.     

Antenna radiation modeling for microwave landing system

Geometric optics and diffraction techniques are used to develop radiation models of antennas mounted on an aircraft structure. Measurements at 35 GHz on a 1/35 scale model space shuttle and 1/11 scale Boeing 737 are used for comparison with computed patterns and are in very good agreement. Radiation coverage in the elevation plane on full scale Boeing 737 and Boeing 747 at 5.1 GHz, as applied to the microwave landing system (MLS), is examined for vertically- and horizontally-polarized antennas mounted at different locations on the aircraft.     

The spectrum of microwave radiation from InSb

The frequency spectrum of the microwave radiation emitted from InSb in the presence of applied electric and magnetic fields at 77°K was observed using a spectrum analyzer. In the frequency region from 7 to 26 Gc/s the spectrum showed oscillatory behavior with a period of 2.2 Gc/s, with the average value decreasing with increasing frequency. Such a structure could be due to a series of harmonics of a fundamental mode with frequency of 2.2 Gc/s. The frequencies of the peaks did not shift on changing the magnetic field and current. The spectrum near the frequency of 2.2 Gc/s was measured in detail in a coaxial-type cavity. The intensity of the radiation in this frequency region was much higher than that in the higher frequency region. The spectrum did not show clearly the expected peak at 2.2 Gc/s, but showed a further oscillatory behavior with a period of about 150 Mc/s. The physical mechanism which gives such a structure to the spectrum is not yet understood. It was also observed that the threshold conditions for the observation of radiation depended on the sample geometry, the thresholds being lower for thin samples, with the magnetic field perpendicular to both the current and the thin direction.     

Inverse black body radiation at microwave frequencies

The inverse black body radiation, which is the problem of determining the area-temperature distribution of a black body from its measured radiated power spectrum, was recently solved by Bojarski. His solution employs the inverse Laplace transform to reconstruct the area-coldness distribution from an integral equation based on Planck's law. Our solution is similar but restricted to microwave frequencies and employs the Rayleigh-Jeans approximation to yield the corresponding portion of the area-coldness distribution using the inverse Laplace transform but avoiding the iterative procedure of Bojarski.     

Effects of 2.6-4.0 GHz microwave radiation on E-coli B.

The effects of 2.6-4.0 GHz microwave radiation on living E. coli B bacteria were studied using measurement of the colony forming ability (CFA) of the cells and alterations in the molecular structure determined by comparing the infrared spectrum of irradiated and unirradiated cell cultures. At absorbed power levels of 20 mW in 1 ml of cellular suspensions (i.e., a specific absorption rate of 20 W/kg) for 10-12 hour exposures, no effects were observed on either the molecular structure or the CFA for this particular strain of E. coli.     

A notch filter for 140 GHz microwave radiation

The construction of a notch-filter for 140 GHz with very low passband insertion loss is described. It is based on a single-mode rectangular waveguide and cylindrical cavities matched to it. The typical transmission characteristic is also presented.     

Broad-band microwave measurement of water using transient radiation

Previous workers have demonstrated the utility of optoelectronically pulsed antennas to make broadband microwave measurements of the dielectric properties of relatively low loss materials. Here the authors present an extension of the analysis technique that allows measurements to be made on highly absorptive samples. Experimental results for water in the 10-70 GHz frequency range are presented, error sources analyzed, and results compared with measurements made with a different technique     

Effects of low level microwave radiation on the digestive transit of the rat.

The effects of low level microwave radiation (3-4 mW/cm2--2450 MHz) during 4 and 8 h on the WISTAR Rat digestive transit has been studied. The results showed no effect after 4 h radiation and an acceleration of the digestive transit after 8 h of radiation (p less than .001). The acceleration of the digestive transit was still observed after 24 h (p less than .001). 60-90 s after radiation time the rectal temperature of radiated animals did not differ from the controls.     

Bremsstrahlung radiation as a source of coherent microwave power

Coherent microwave power in the 100-mw level is produced by the bremsstrahlung radiation of a prebunched 0.8 Mev beam. Two different schemes are analyzed and tested. The first consists of a prebunched beam impinging on a flat conducting surface; the second consists of a beam striking a flat dielectric surface. The power and radiation resistance in the frequency range between 30 and 40 kMc are measured and compared with theory. It is shown that the radiation resistance is independent of frequency as long as the bunch size is small compared to a wavelength and the structure is nondispersive. The power is in the form of periodic large bursts of energy; the duration of each burst is about 2 × 10^-12sec. The condition of coherence of electromagnetic radiation requires that the beam be pointwise tight in space. Hence a magnetic lens is used to focus the megavolt beam on the point of impact and thereby obtain power at the 42nd harmonic of the fundamental bunching frequency, i.e., at a wavelength equal to 2.56 mm. Based on the results obtained, the utility of bremsstrahlung radiation is discussed as a means of generating coherent power in the submillimeter region.     

Broad-band microwave measurements with transient radiation fromoptoelectronically pulsed antennas

A broadband microwave measurement technique based on picosecond transient radiation from optoelectronically pulsed antennas is described. It is performed with exponentially tapered coplanar stripline antennas which are integrated with the photoconductive devices used for ultrafast pulse generation and sampling. The signal analysis required for deriving the desired physical properties from the measured time-domain waveforms is discussed. This is a coherent technique that independently determines both the real and the imaginary parts of the dielectric constants of materials, from 10 to 130 GHz, in a single experiment. Some representative results are presented     

A review of ferrites for microwave applications

Ferrimagnetic materials for microwave applications are reviewed with emphasis on the more recent advances. Specific areas of discussion include temperature sensitivity of the magnetization, microwave loss phenomena and the concept of effective linewidth, and the hysteresis loop in terms of the factors which influence its coercive force, remanence ratio, and stress sensitivity. The relations between specific chemical substitutions and the attendant magnetic properties are then summarized for the various spinel and garnet ferrite families of interest to the microwave device engineer. Finally, the ceramic preparation of ferrite materials is outlined with special focus on some of the newer techniques.     

Slow and rapid responses to CW and pulsed microwave radiation by individual Aplysia pacemakers.

Specific absorption rates (SARs) of microwave energy that altered firing rates were determined for individual pacemaker neurons in the abdominal ganglion of Aplysia californica. A stripline apparatus provided both for artifact-free recording of transmembrane potentials and for precise determination of the rate of absorption of microwave energy. Exposure for two to three minutes at an SAR of only a few mW/g was capable of changing the firing rate of some pacemakers. Two types of responses were observed. The response that was seen in all neurons developed slowly, reaching a steady state in one to three minutes. The other response was seen in a few neurons and occurred within five seconds from the onset of irradiation. Similar responses were obtained for two microwave frequencies, 1.5 and 2.45 GHz. Pulsed radiation induced rapid changes of firing rate more readily than did CW radiation at the same SAR. A convective heating scheme was used to study the effects of temperature changes on the pacemakers' firing rates. Since all of the responses are not readily explained by general heating of the preparation, alternate mechanisms are suggested for the observed effects.     

A new radiation balance microwave thermograph for simultaneous and independent temperature and emissivity measurements.

In the past, biomedical temperature measurements by microwave radiometry suffered from variable mismatch (emissivity less than 1) between the specimen under test and the receiving antenna. We have developed an improved radiometer, which simultaneously measures temperature and emissivity, independent by of a possible mismatch. Comparative measurements demonstrate the superiority of the new system as compared to conventional ones.     

Rat lymphocytes in cell culture exposed to 2450 MHz (CW) microwave radiation.

Rat lymphocytes were exposed to continuous wave microwave radiation at a frequency of 2450 MHz at intensities of 5, 10 and 20 mW/cm2. The corresponding rates of absorption of energy were determined to be 0.7, 1.4 and 2.8 mW/g. The lymphocytes were exposed for 4, 24 or 44 h either with or without the addition of a mitogen (phytohemagglutinin). The transformation of lymphocytes into lyphoblasts was monitored by the addition of tritiated thymidine. No significant differences (P less than .05) were found in the uptake of tritiated thymidine between exposed and control cultures.     

高功率微波辐射场功率密度测量不确定度分析方法

辐射场测量是检验高功率微波系统输出指标的重要手段.随着高功率微波测量技术的发展,辐射场测量系统的稳定性和可靠性不断提高,作为完整测量结果重要组成部分的测量不确定度越来越受到关注.文章介绍了高功率微波辐射场功率密度测量方法及系统组成,建立了功率密度测量的数学模型,给出了高功率微波辐射场功率密度测量的主要不确定度来源.对检波器输入功率计算、接收天线有效面积校准、衰减环节校准及测量系统各环节连接失配等测量不确定度分量进行了分析,并给出了高功率微波辐射场功率密度测量不确定度的合成方法.本文给出的测量不确定度分析方法较为科学、操作性强,对完善高功率微波辐射场功率密度测量结果具有一定的指导意义.     

Amplitude and phase measurements of forward-scattered microwave radiation from waterdrops

An experiment to determine the forward-scattering complex amplitude functions of waterdrops supported in a vertical wind tunnel is described. The measuring system is calibrated using a metal sphere of accurately known diameter. Measurements at 11 GHz on waterdrops in the range 1.6?3.1 mm radius are compared with theoretical values obtained by Oguchi using the point-matching technique.     

ZnO film concave transducer for focusing radiation of microwave ultrasound

A ZnO piezoelectric film has been satisfactorily deposited on a concave substrate of a gold hemispherical shell to produce a concave transducer for microwave ultrasound. The fabrication process of the concave transducer, with a focal distance of 5?9 mm, and also experiments on focusing radiation in water at 100 MHz. are described.     

A review of bulk semiconductor microwave control components

The use of semiconductor bulk phenomena in implementing microwave control components is reviewed. The principal phenomena explored to date have been the dielectric and conductive properties of the plasma state. A brief discussion of these properties is presented to identify their potentially useful characteristics for microwave control. It is noted that to date only the conductive plasma properties have proved practical for application. More specifically, electron-hole plasmas, generated by impact ionization or by contact injection, existing in silicon have been successfully incorporated in microwave circuitry to yield control components with substantially improved performance over junction devices. Examples of the design, fabrication, and results obtained for bulk semiconductor control components are presented illustrating the application of impact ionization to limiter and duplexer operation and contact injection utilizing a window configuration to switching and phase shifting operation. The principal improvements are gained through achieving at least an order of magnitude increase in power handling and full guide bandwidth in utilizing the window. In addition, it is noted that the bulk approach is virtually the only practical semiconductor approach for millimeter wave control components.