ICES Database ElectroMagnetic Field Literature Search Engine |
 |
| |
| Home |
| View EMF Studies (Static,ELF) 0-300 Hz |
| View EMF Studies (Intermediate) 300 Hz-300 KHz |
| View EMF Studies (RF/mmW/THz) 300 kHz-300 GHz |
| Advanced Search |
| Citation List (Author Search) |
(Database last updated on Mar 27, 2024)
| ID Number | 195 | |
| Study Type | Human / Provocation | |
| Model | 100, 220, 450, 2450 MHz, 94 GHz (CW) exposure to humans and analysis of thermophysiology, thermo-regulation, and pain thresholds | |
| Details | Human subjects were exposed to 2450 MHz (CW) MW or IR light to determine threshold levels for perception (noticeable warming). Threshold levels for MW were 28.2 mW/cm2 for women and 25.3 mW/cm2 for men. Threshold levels for detection of IR were 2.0 and 1.5 mW/cm2, respectively. This 15-fold difference between MW and IR thresholds corresponds to a 5-fold difference in the quantities of absorbed energy. The authors conclude that thermoreceptors are stimulated less efficiently by the more deeply penetrating and diffusely absorbed MWs. In similar studies, human volunteers were exposed to 94 GHz mm waves for 3 seconds at increasing field strength levels (to a maximal 1800 mW/cm2) and examined for pain threshold. Non-MW heating was used as a positive control, with a threshold skin temperature increase required for pain sensation of 9.9 degrees. Mm wave exposure necessary to cause pain corresponded well to that required by non-MW heating and support a simple model for predicting thresholds of thermal pain at other mm wave frequencies based upon heat conduction and penetration depth. In similar studies using localized 2450 MHz exposure for ~45 minutes to the backs of humans at peak local SARs of 15.4 W/kg (whole body estimated SAR of ~1W/kg, ~2x greater than IEEE C95.1 [1999] partial body exposure guidelines), no consistent change in core temperature or heart rate was observed (vigorous sweating and increased blood flow maintained homeostasis in the most extreme cases). The authors conclude that upon significant MW insult the ability to dump significant heat through normal physiological mechanisms as well as the motivation to make a timely retreat to avoid prolonged MW exposure before heat compensation mechanisms are exhausted appears to be sufficient to protect against thermal overload from exposure levels of up to 2x the IEEE C95.1 limits. Subsequent studies at 100 MHz (resonant frequency of the human body) showed similar results and the authors report "physiological heat loss responses are mobilized just as quickly during deep tissue heating at resonance as they are during superficial heating by higher RF frequencies". IN early studies, human subjects were exposed to 2450 MHz (CW) MW or IR light to determine threshold levels for perception (noticable warming). Threshold levels for MW were 28.2 mW/cm2 for women and 25.3 mW/cm2 for men. Threshold levels for detection of IR were 2.0 and 1.5 mW/cm2, respectively. This 15-fold difference between MW and IR thresholds corresponds to a 5-fold difference in the quantities of absorbed energy. The authors conclude that thermoreceptors are stimulated less efficiently by the more deeply penetrating and diffusely absorbed MWs. AUTHORS' ABSTRACT: Nelson et al. 2013 (IEEE #5220): Human exposure to radio frequency (RF) electromagnetic energy is known to result in tissue heating and can raise temperatures substantially in some situations. Standards for safe exposure to RF do not reflect bio-heat transfer considerations however. Thermoregulatory function (vasodilation, sweating) may mitigate RF heating effects in some environments and exposure scenarios. Conversely, a combination of an extreme environment (high temperature, high humidity), high activity levels and thermally insulating garments may exacerbate RF exposure and pose a risk of unsafe temperature elevation, even for power densities which might be acceptable in a normothermic environment. A high-resolution thermophysiological model, incorporating a heterogeneous tissue model of a seated adult has been developed and used to replicate a series of whole-body exposures at a frequency (100 MHz) which approximates that of human whole-body resonance. Exposures were simulated at three power densities (4, 6 and 8 mW cm(-2)) plus a sham exposure and at three different ambient temperatures (24, 28 and 31 °C). The maximum hypothalamic temperature increase over the course of a 45 min exposure was 0.28 °C and occurred in the most extreme conditions (T(AMB) = 31 °C, PD = 8 mW cm(-2)). Skin temperature increases attributable to RF exposure were modest, with the exception of a 'hot spot' in the vicinity of the ankle where skin temperatures exceeded 39 °C. Temperature increases in internal organs and tissues were small, except for connective tissue and bone in the lower leg and foot. Temperature elevation also was noted in the spinal cord, consistent with a hot spot previously identified in the literature. |
|
| Findings | Not Applicable to Bioeffects | |
| Status | Completed With Publication | |
| Principal Investigator | USAF Research Lab, Brooks AF Base, USA - Eleanoradair@aol.com | |
| Funding Agency | AF, USA | |
| Country | UNITED STATES | |
| References |
|
|
| Comments |