By National Council on Radiation Protection and Measurements
This record examines the literature on organic results of publicity to modulated radiofrequency (RF) strength to figure out no matter if current publicity criteria and directions have to be changed extra to take modulation into consideration. Modulation happens in a wide selection of varieties really expert for radar, instant communications, broadcast communications, and commercial techniques with the outcome that many waveforms, pulse widths, spectral homes, and temporal styles desire attention. In pulse modulation the RF strength is speedily switched off and on, while amplitude modulation produces a constantly altering point of RF strength. Frequency-modulated RF power has sign amplitudes that stay basically consistent, yet range in frequency inside a few narrowly prescribed diversity and extra heavily resembles nonmodulated RF power than pulsed or amplitude modulated RF fields. For radar, pulses usually have periods measured in fractions of a microsecond to a couple microseconds. periods among pulses (or pulse teams) are significantly longer leading to low responsibility cycle, that's, RF power is on for a small fraction of time in the course of each one interval. yet pulsed signs used for communications platforms may have periods within the diversity of milliseconds, greater accountability cycles, and extra modulation beneficial properties. really expert army structures represent a subcategory with very excessive, short pulses.
desk of Contents
2. In vitro reports
three. In vivo experiences
four. Human experiences
five. Epidemiological stories
6. Biophysical concerns
7. dialogue and Conclusions
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These studies do not suggest a hazard that might be present under exposure conditions allowed by the current limits. There is some evidence, both theoretical and experimental, that very intense RF pulses, which increase the temperature of tissue by several degrees within a second, can lead to adverse effects through a mechanism that relates to the rate of heating. Exposures to such pulses are, in principle, permissible under some contemporary exposure guidelines. However, such exposures are associated with specialized military weapon systems.
Histological, morphological and chemical studies were performed at the end of the exposure sequence with no deleterious effects found for either PW or CW exposures. 6 W kg–1) pulsed microwaves on central cholinergic neurotransmitters have been extensively studied by Lai et al. (1989; 1991; 1992a; 1992b) and shown to behave like environmental stressors in alteration of brain concentrations. , 1994). 2). 5 µs pulse width, peak power densities of 20 to 750 W m–2 Merritt et al. 3 W kg –1 Salford et al.
4 W kg –1 will produce a rate of temperature rise of 10–4 °C s–1 in soft tissue such as muscle or brain, ignoring the cooling effects of heat conduction away from the heated region by thermal conduction or blood flow. 4 W kg –1 corresponds to somewhat less than one-half the basal metabolic rate of an adult human. 1 PHYSICAL INTERACTION MECHANISMS / 39 significant temperature increases in the body, while SARs much higher than this value are likely to produce measurable heating if the exposure persists for a sufficient time.
Biological Effects of Modulated Radiofrequency Fields by National Council on Radiation Protection and Measurements