摘要:

A new method for obtaining the microwave absorption spectrum of optically transparent condensed media is described. Phase fluctuations impressed on a single‐frequency laser beam passing through a sample are detected by optical heterodyning. These phase fluctuations result from density fluctuations induced by the absorption of microwave energy. Preliminary experiments on water and ethanediol yield absorption spectra which are consistent with those obtained in previous investigations using conventional technique

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0085S

年代:1982

数据来源: WILEY

摘要:

Pupae of the insectTenebrio molitor L.were thermographically imaged during waveguide irradiation through longitudinal slots.T. molitorpupae have been subjects of microwave‐induced teratology for a number of years, but until now the smallness of the insect has prevented detailed dosimetry. High‐resolution thermographic imaging equipment was used to obtain the magnitude and spatial distribution of absorbed microwave energy at three frequencies, 1.3, 5.95, and 10 GHz. The detail of the thermal images obtained is sufficient to show the differential heating of structures as small as a single insect leg. Results show that the electrical properties of the head, thorax, and abdomen are sufficiently different to seriously impair the usefulness of any theoretical dosimetric model of homogeneous composition. Some general features of correlation with a slab model in waveguide are gi

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0095S

年代:1982

数据来源: WILEY

摘要:

An interferometric measurement system capable of accurate return loss measurements over the frequency range 65–85 GHz is described. The system exploits the sedimentation rate of a highly aqueous cell suspension. Both fixed frequency and swept frequency systems are described, and the sources of error measurement are discussed. Experimental observations are compared with values predicted from an analytical mode

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0105S

年代:1982

数据来源: WILEY

摘要:

A procedure using microwave transmission to estimate the absolute value of lung water content is described. The method involves obtaining a transverse cross‐sectional image of a human subject using a computerized axial tomographic X ray scanner, with the microwave applicators in position. The electromagnetic field problem, including the size and shape of the internal organs, is then solved numerically using the method of moments. Since the mismatch between the microwave applicators and the patient's skin is found to be highly insensitive to the changes in the underlying lung parenchyma, the transmission coefficient can then be directly related to the average amount of total water content in the lung. Results for human and animal cross sections are presente

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0111S

年代:1982

数据来源: WILEY

摘要:

A class of new direct‐contact microwave applicators has been developed for diathermy and hyperthermia applications. They consist of three concentric, circular, cylindrical tubes. The inner cylinder may serve as a port for circulating coolant to reduce surface temperature or as a port for introducing ionizing radiation in combination therapy for cancer. The coaxial waveguides formed by the inner and middle cylinders and by the middle and outer cylinders permit the propagation of TE11and TE21modes, respectively, for dual‐beam, single‐frequency use. The combinations give relatively uniform, circularly symmetric heating distributions in the tissue. Heating pattern and leakage level measurements obtained for a 10‐cm‐diameter dual‐beam 2450±50‐MHz applicator show that the maximum leakage level at a distance of 5 cm from the surface of the applicator in contact with planar fat‐muscle phantoms is less than 4 mW/cm2for a therapeutic specific absorption rate (SAR) of 235 W/kg. This value corresponds to a net forward power of 26 W. The measured VSWR is about 1.25. The width of the heating pattern is about 4 cm at a depth of 2.2 cm into the simulated muscle, where the SAR is half the maximum, and decreases slowly as the depth into the muscle increases, thus giving it a fairly unif

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0119S

年代:1982

数据来源: WILEY

摘要:

We describe the design of coaxial microwave radiators suitable for localized hyperthermia of neoplasia in the esophagus, brain, and other organs which are accessible through body orifices. These radiators can be implanted surgically and are small enough to be passed through such devices as nasogastric tubes and bronchoscopes. The radiators consist of combinations of cross‐switched half‐wavelength coaxial sections and/or needle antenna terminations. The performance of these radiators, as determined by thermogram recordings in tissue phantoms and the results of in vivo animal tests, is descri

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0125S

年代:1982

数据来源: WILEY

摘要:

Near the beginning of the second trimester of pregnancy, 33 squirrel monkeys were exposed to 2450‐MHz irradiation in a multimode cavity at whole‐body average specific absorption rates equivalent to those resulting from exposure to plane wave irradiation at 0.034, 0.34, and 3.4 W/kg; exposed monkeys were compared with eight pregnant sham‐exposed monkeys. Eighteen of the irradiated mothers and their offspring were exposed for an additional 6 months after parturition, and then their offspring were exposed for another 6 months. No differences were found between irradiated and control adults with respect to the number of live births produced or to measures of locomotor activity, maternal care, urinary catecholamines, plasma cortisol,3H‐thymidine and14C‐uridine uptake by phytohemagglutininstimulated blood lymphocytes, or electroencephalographic (EEG) activity. Similarly, no differences were found between exposed and nonexposed offspring on the same blood, urine, and EEG parameters. Growth rate and most aspects of behavioral development were not altered by exposure. The major difference between irradiated and control offspring was the high mortality rate (4/5) before 6 months of age in those exposed at 3.4 W/kg both before and after birth. These results indicate that microwaves at power densities to 3.4 W/kg might have little direct effect on the monkey fetus when exposures occur in utero during the latter half to two‐thirds of pregnancy, but that continued exposure after birth might

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0135S

年代:1982

数据来源: WILEY

摘要:

Pupae of the yellow mealwormTenebrio molitor L.were subjected to microwave irradiation for 1.5–24 hours at power density levels adjusted to produce a total dosage of approximately 1123 J/g in each insect for every experiment. Insects without visible blemishes were exposed in a standing wave irradiation system such that half of them were exposed in the plane of maximum electric field (Efield) and the other half were exposed in the plane of maximum magnetic field (Hfield). BothEfield andHfield insects exhibited nearly the same specific absorption rate (SAR) for pupal orientation parallel to the magnetic field vector at 5.95 GHz. Irradiations were conducted both with and without the use of a ventilating fan to control the temperature rise in the irradiation chamber. Abnormal development as a result of the microwave exposure was seen only in the high‐power, short‐duration experiment without chamber ventilation. This result suggests a thermal interaction mechanism for explanation of observed microwave‐induced abnormalities. A study of the time course of the average temperature rise in the irradiated insects indicates that teratological effects for this configuration have a temperature threshold of approximate

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0145S

年代:1982

数据来源: WILEY

摘要:

Evidence has accumulated that sensitivity of brain tissue to specific weak oscillating electromagnetic fields occurs in the absence of significant tissue heating (less than 0.1°C). This review focuses on the ‘windowed’ character of sensitivities of calcium binding and electrical activity in brain tissue to low‐frequency modulation and intensity characteristics of impressed RF fields. ELF fields decrease calcium efflux from isolated chick and cat cerebral tissue by about 15% only in narrow amplitude and frequency ‘windows,’ between 6 and 20 Hz and between 10 and 100 V/m (approximate tissue gradient, 10−7V/cm). VHF (147 MHz) and UHF (450 MHz) fields increase calcium efflux from isolated chick brain by about 15% when amplitude modulated between 6 and 20 Hz, but only for incident fields in the vicinity of 1.0 mW/cm2. We have now shown that this increased efflux in response to 16‐Hz amplitude‐modulated 450‐MHz, 0.75‐mW/cm2field exposure is insensitive to variations in calcium concentration from 0 to 4.16 mM in the testing solution but is enhanced by addition of hydrogen ions (0.108 mM 0.1NHCl) and inhibited in the absence of normal bicarbonate ion levels (2.4 mM). In the presence of lanthanum ions (2.0 mM), which block transmembrane movement of calcium, exposure to these EM fields decreases the45Ca2 +efflux. Low‐frequency gradients may be transduced in a specific class of extracellular binding sites, normally occupied by calcium ions and susceptible to competitive hydrogen ion binding. Transductive coupling may involve coherent charge states between anionic sites on membrane surface glycoproteins, with longrange cooperative interactions triggered by weak extracellular electric fields. Proton ‘tunneling’ may occur at boundaries between coherent an

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0149S

年代:1982

数据来源: WILEY

摘要:

Microwave pulse‐evoked potentials at the vertex show a series of waves occurring in the first 10 ms following delivery of the pulse. The sources of these waves, as in the case of acoustic click‐evoked responses, are action potentials generated in the cochlea and auditory brain stem nuclei. We shall show, using microwave‐induced auditory brain stem responses, that the experimentally observed characteristics agree with previously derived theoretical predictions in regard to pulse width and frequency of impinging microwaves, pattern of absorbed microwave energy, frequency of vibration, and threshold of sens

ISSN:0048-6604    

DOI:10.1029/RS017i05Sp0159S

年代:1982

数据来源: WILEY