摘要:

In order for meaningful comparisons to be made between experiments from different laboratories, reliable dosimetry is needed for biological systems exposed to microwave radiation. We present an improved analytical method for determining energy absorption which uses heating and cooling curves. The method is demonstrated forin vitrosamples that were exposed to microwave radiation in two different exposure systems. Advantages and disadvantages of the method, as well as practical considerations, are discussed.

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00001

年代:1977

数据来源: WILEY

摘要:

Free‐field power density has long been used as an index of energy dosing in studies of biological effects of microwave radiation. However, this method of quantifying dose can lead to considerable error if it is used as an index of the rate of energy actually being absorbed by a specimen, because the relative absorption cross sections of different specimens may vary greatly. The integral of absorbed energy is a more meaningful measure of exposure; it can be accomplished by using such sophisticated equipment as twin‐well calorimeters, or by using the cruder system of saline‐filled phantoms This paper describes a calorimetric system for the measurement of absorbed energy in laboratory animals and inin vitrosamples that can be assembled from such common laboratory equipment as Dewar flasks, magnetic stirrers, foamed polystyrene, and an accurate temperature measuring device. Measurements of absorbed energy by this system for a standard tissue‐culture flask are compared to values obtained by electrical measurements, by direct temperature measurements, and by heating and cooling curves. Also, application of the system to measurements of dose in experimental animals is demon

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00009

年代:1977

数据来源: WILEY

摘要:

A set of miniature isotropic probes has been used experimentally to map electric fields within two small spheres of simulated muscle tissue (3.3‐cm and 8‐cm radii) that were irradiated by 450‐, 915‐, and 2450‐MHz plane waves. Good agreement was obtained with the theoretically predicted spatial distribution of fields in both spheres, even in the immediate proximity of the boundaries. The absolute calibrations of the probes were found to be moderately to significantly dependent upon the dielectric constant of the medium (1 ≤ ∈r≤ 50) in which the probe was implanted, with the least dependence occurring at 2450 MHz (±2.25 dB), and the greatest dependence occurring at 450 MHz (±4.25 dB). A set of design criteria is presented that are necessary for proper performance of such a dipole/diode probe. Of particular importance are the thickness of the insulation surrounding the dipole antenna, and the dimensions of the dipole. Both must be small compared to the wavelength of the field in the biological media. The validity of the design criteria has been experimentally demonstrated, illustrating the feasibility of producing an improved probe whose response to an electric field of given strength would be relatively constant regardless of the dielectric constant of the media and independent of boundary‐proximity effects. Preliminary results ofin vivomeasurements are presented; improved, biologically compatible de

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00015

年代:1977

数据来源: WILEY

摘要:

In the first of two studies distributions of rates of EM energy absorption were observed in simulated biological bodies with embedded tumors. Part‐ and whole‐body simulacra as irradiated by EM fields that ranged in frequency from 15 to 500 MHz exhibited differentially greater heating of tumors. Reduction of tumor conductivity resulted in enhancement of tumor heating. In the second study, a model of man was observed for induction of EM fields by 1 to 500‐MHz energy. Greater rates of energy absorption occurred in regions of smaller cross sections and in tissues with lower conductiv

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00027

年代:1977

数据来源: WILEY

摘要:

Generalized curves are given for rates of whole‐body absorption of electromagnetic energy by models of human beings as a function of frequency. Exposures were made in free space, or when the model made electrical contact with the ground. The effects of the presence of reflecting surfaces also were analyzed. Peaks of absorption with and without a ground, are projected, respectively, to be (31 to 34 MHz) and (62 to 68 MHz) × (1.75/height of model in meters). Rates of energy deposition are given for models of man and for animals subjected to radiation at a power density of 10 mW/cm2for the various conditions of exposure. At resonance, values of whole‐body absorption as high as 4,077 to 8,154 watts for the adult human being are predicted. The times‐to‐convulsion of ∼100‐g rats at power densities of 3 to 20 mW/cm2confirmed predictions of extremely high rates of absorption in the presence of reflect

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00039

年代:1977

数据来源: WILEY

摘要:

Data on environmental levels of radio‐frequency energy have been obtained for Atlanta, Boston, Miami, and Philadelphia; about 5% of the population of the United States lives within these Standard Metropolitan Statistical Areas. Data are collected at 15 to 30 sample sites within each metropolitan area. Earlier investigations led to the working hypothesis that the principal sources of environmental radio‐frequency radiation are contained within the broadcast service. The frequency bands measured are the standard AM broadcast band (0.5 to 1.6 MHz), the VHF‐television bands (54 to 88 and 174 to 216 MHz), the FM‐radio band (88 to 108 MHz), two land‐mobile bands (150 and 450 MHz), and the UHF‐television band (470 to 890 MHz). Representative spectra are presented. Values of power density integrated over the frequency range from 54 to 900 MHz generally fall into the range between 0.001 and 1 μ/cm2with most values between 0.01 an

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00049

年代:1977

数据来源: WILEY

摘要:

Considerable effort has been expended recently in biological experimentation and theoretical analyses of the effects of radio‐frequency electromagnetic radiation on experimental animals and human beings. An important part of this work is dosimetry, the determination of the quantities and time rates of energy absorbed by a biological body. To provide the link between biological effects that are observed in irradiated animals and corresponding effects that might occur in man, theoretical methods are needed to relate measures of absorbed energy in man and animals to the power density of incident radiation. A handbook of data has been compiled to fill this need and is described herei

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00057

年代:1977

数据来源: WILEY

摘要:

Whole‐body absorption of 2450‐MHz radiation was measured in rats that ranged from 6 to 440 grams and in mice that ranged from 30 to 50 grams. Simultaneous exposure of groups of animals in varying numbers and in various configurations were made under free‐field conditions in an electrically anechoic chamber. Measurements of whole‐body absorption were made with twin‐well calorimeters. The results indicate that, for animals within a given narrow range of body mass, individual rates of absorption may, at the extreme, vary by a factor of seven. One implication of this variability is that studies of dose‐response relations may be confounded unless power densities of incident radiation are sufficiently different to provide nonoverlapping dose rates. Comparisons of measured doses to predicted values as derived from a spherical shell model show considerable variations of observed from predicted values. Specific relationships of the SAR to the position and mass of the animals ar

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00061

年代:1977

数据来源: WILEY

摘要:

Perturbation theory has been used to find the first‐order internal electric field, the SAR (specific absorption rate), the spatial variations of the SAR, and the maximum SAR in prolate spheroidal and ellipsoidal models of man and experimental animals during irradiation by an electromagnetic plane wave when the wavelength is long as compared to the dimensions of the exposed body. In our “conductor” model of man, conductivity is written explicitly in the curlHequation as: ∇ ×H= σE+jω∈E. In what we call the “dielectric” model, the conductivity is contained implicitly in the complex permittivity, so that the curlHequation is ∇ ×H=jω∈E. The two models give different results for first‐order fields because the equations are expanded in a power series ink(k= ω√μ∈); in the conductor model σ enters into the zero‐order equations but in the dielectric model it does not. Because of the nature of the zero‐order equations, the expressions obtained from the conductor model are not valid as σ→0. We have found that the conductor model is valid only if ∈2»ϵ1where ϵ1and ∈2, respectively, are the real and imaginary parts of the complex dielectric constant of the models. Consequently, some caution must be exercised in applying the results of perturbation theory as based on the conductor model. In this paper, the results of perturbation theory as applied to a lossy dielectric ellipsoidal model are described. The SAR in a dielectric ellipsoidal model of a rhesus monkey is calculated and compared with that of the conductor model. The SAR in the two models is found to be the same if the conduction current in the body is much larger than the displacement current. Although the conductor model is inaccurate for low values of conductivity, the equations are simpler than the ones for the dielectric model, and hence t

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00065

年代:1977

数据来源: WILEY

摘要:

In a passive state, the pelted mammal is well insulated against loss of thermal energy. Further, the rapidity with which the circulatory system equilibrates thermal energy would render the living animal a useful whole‐body calorimeter but for the complicating factors of physiological and behavioral thermoregulation. Moderate thermal loading of the intact mammal by, say, microwave radiation, will bring a host of responses into play by which an excess of energy is actively dissipated. If, however, a reversible chemical lesion could be introduced that rendered the mammal ectothermic–cold blooded–then one could use pre‐ and post‐radiation temperatures of the living animal to make fairly accurate estimates of quantities of absorbed energy. An ectothermic preparation would be useful in dosimetric studies in the free field where an empirical fit between measures of incident and absorbed energy is the objective with the freely behaving animal. We report studies of two compounds, sodium salicylate and cortisone acetate, and their effects upon body temperatures of rats, guinea pigs, and rabbits of both sexes and of pigmented and albino strains. While the salicylate produced a reliable hypothermal response in the albino rat, it was less effective in the pigmented rat, and was virtually ineffective in the guinea pig and rabbit. Cortisone appeared to produce a more uniform hypothermal response; studies of rats revealed that increments of colonic temperature after short periods of highly thermalizing microwave radiation yield estimates of energy dosing that are accurate w

ISSN:0048-6604    

DOI:10.1029/RS012i06Sp00073

年代:1977

数据来源: WILEY