Human exposure at two radio frequencies (450 and 2450 MHz): Similarities and differences in physiological response

United States Air Force Research Laboratory, HEDR, Brooks Air Force Base, Texas 78235-5324, USA.
Bioelectromagnetics (Impact Factor: 1.71). 02/1999; Suppl 4(S4):12-20. DOI: 10.1002/(SICI)1521-186X(1999)20:4+3.0.CO;2-N
Source: PubMed


Thermoregulatory responses of heat production and heat loss were measured in two different groups of seven adult volunteers (males and females) during 45-min dorsal exposures of the whole body to 450 or 2450 MHz continuous-wave radio frequency (RF) fields. At each frequency, two power densities (PD) were tested at each of three ambient temperatures (T(a) = 24, 28, and 31 degrees C) plus T(a) controls (no RF). The normalized peak surface specific absorption rate (SAR), measured at the location of the subject's center back, was the same for comparable PD at both frequencies, i.e., peak surface SAR = 6.0 and 7.7 W/kg. No change in metabolic heat production occurred under any exposure conditions at either frequency. The magnitude of increase in those skin temperatures under direct irradiation was directly related to frequency, but local sweating rates on back and chest were related more to T(a) and SAR. Both efficient sweating and increased local skin blood flow contributed to the regulation of the deep body (esophageal) temperature to within 0.1 degrees C of the baseline level. At both frequencies, normalized peak SARs in excess of ANSI/IEEE C95.1 guidelines were easily counteracted by normal thermophysiological mechanisms. The observed frequency-related response differences agree with classical data concerning the control of heat loss mechanisms in human beings. However, more practical dosimetry than is currently available will be necessary to evaluate realistic human exposures to RF energy in the natural environment.

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    • "In view of this slow response, the equilibrium temperature arising from the oscillating fields of mobile telecommunications will essentially be determined by the average power absorbed, [17]. It has not yet proved possible to measure the small changes in temperature directly, except those at the outer skin, [18] and, although temperature is a more direct determinant of thermally induced tissue damage, the majority of theoretical studies up to the present time have restricted themselves to the computation of SAR alone. "
    M. Ouda ·

    the second International Engineering Conference on Construction and Development; 06/2007
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    • "Nevertheless , even under ambient conditions that were often judged uncomfortable and very warm, T esoph was regulated with precision because appropriate autonomic heat loss responses, principally sweating, were mobilized. A second study [Adair et al., 1999b] compared the results described above with those collected on a second group of volunteers, exposed to 2450 MHz CW energy. The basic protocol was identical, as were the three T a and response measures, with the addition of local skin blood flow (SkBF) at three sites on the body. "
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    ABSTRACT: This white paper combines a tutorial on the fundamentals of thermoregulation with a review of the current literature concerned with physiological thermoregulatory responses of humans and laboratory animals in the presence of radio frequency (RF) and microwave fields. The ultimate goal of research involving whole body RF exposure of intact organisms is the prediction of effects of such exposure on human beings. Most of the published research on physiological thermoregulation has been conducted on laboratory animals, with a heavy emphasis on laboratory rodents. Because their physiological heat loss mechanisms are limited, these small animals are very poor models for human beings. Basic information about the thermoregulatory capabilities of animal models relative to human capability is essential for the appropriate evaluation and extrapolation of animal data to humans. In general, reliance on data collected on humans and nonhuman primates, however fragmentary, yields a more accurate understanding of how RF fields interact with humans. Such data are featured in this review, including data from both clinic and laboratory. Featured topics include thermal sensation, human RF overexposures, exposures attending magnetic resonance imaging (MRI), predictions based on simulation models, and laboratory studies of human volunteers. Supporting data from animal studies include the thermoregulatory profile, response thresholds, physiological responses of heat production and heat loss, intense or prolonged exposure, RF effects on early development, circadian variation, and additive drug-microwave interactions. The conclusion is inescapable that humans demonstrate far superior thermoregulatory ability over other tested organisms during RF exposure at, or even above current human exposure guidelines.
    Bioelectromagnetics 01/2003; Suppl 6(S6):S17-38. DOI:10.1002/bem.10133 · 1.71 Impact Factor
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    • "The power densities over the rectenna sites would be around 25 000 W/cm or 25 mW/cm and a potential problem for some birds, but not serious since they could easily escape from the site. Furthermore, recent studies of human exposure [54] have shown that man can tolerate easily such exposure at least for periods of an hour or so at moderate environmental tem- peratures. Over the last two decades, there has been an enormous amount of work around the world, particularly in Japan, Russia, France, Canada, and Germany on various derivatives of the SPS concept—at lower powers, different satellite orbits, different frequencies, as well as some earthbound projects for microwave power transmission (MPT). "
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    ABSTRACT: The field of microwave power applications is little recognized within the publications of the IEEE, yet it represents the most universal connection of microwave technology to the everyday life of people worldwide through the microwave oven. The technology of efficient low-cost microwave power sources has progressed not only to permit the economic feasibility of the microwave oven, but also a growing myriad of other commercial and industrial applications. The most successful of these is in the food industry for meat tempering and cooking-mostly of bacon. Other successful applications include plasma discharge devices for UV curing and lighting. In the future, applications to comfort heating of man and animals and various microwave power transmissions are foreseen. Problems of hazard perception and interference are now recognized as potential impediments to accelerated progress. The resolution of these problems requires cooperation between various parties, including the power application industries and the wireless communication industries. Another prerequisite for the realization of the vision by Kapitsa of primacy of power applications is the extension of efficient and economical power sources to a variety of operating frequencies and power levels. At the moment, only the magnetron qualifies as a candidate device for this task, despite its excess noise characteristics. It is in the device area, as well as new applications that surprises are sure to come, repeating the feature of surprise so evident in the history of this field to this point.
    IEEE Transactions on Microwave Theory and Techniques 04/2002; 50(3):975-985. DOI:10.1109/TMTT.2002.989981 · 2.24 Impact Factor
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