Question

Explain the process for assessing the variable field strength exposure of a person in an RF/microwave field.

Answer 1

electromagnetic field or radiofrequency (RF) field these are terms used to indicate the presence of electromagnetic or RF energy. An RF field has both an electric ("volts per meter" (V/m)) and a magnetic( "amperes per meter" (A/m) component .

RF waves can be assessed by a wavelength and a frequency. The wavelength can be is the defined as the distance covered by one complete cycle of the electromagnetic wave and the frequency can be defined as the number of electromagnetic waves passing through a given point in one second.

The frequency of an RF signal is usually expressed in terms of a unit called the hertz (Hz). One Hz equals one cycle per second. One megahertz (MHz) equals one million cycles per second. The RF part of the electromagnetic spectrum is generally defined as that part of the spectrum where electromagnetic waves have frequencies in the range of about 3 kilohertz (3 kHz) to 300 gigahertz (300 GHz).

The FCC guidelines for human exposure to RF fields were derived from the two expert organizations, NCRP (National Council on Radiation Protection and Measurements and the second one is IEEE (Institute of Electrical and Electronics Engineers). the scientists and engineers developed both the NCRP exposure criteria and the IEEE standard after studying the reviews of the scientific literature related to RF biological effects.

These guidelines of exposure are based on thresholds for known adverse effects, and they incorporate appropriate margins of safety. Many countries in Europe and elsewhere use exposure guidelines developed by the International Commission on Nonionizing Radiation Protection (ICNIRP).

The NCRP, IEEE, and ICNIRP exposure guidelines state the threshold level at which harmful biological effects may occur, and the values for maximum permissible exposure (MPE) recommended for electric and magnetic field strength and power density in both documents are based on this threshold level.

The threshold level is a SAR value for the whole body of 4 watts per kilogram (4 W/kg). The most restrictive limits on whole-body exposure are in the frequency range of 30-300 MHz where the RF energy is absorbed most efficiently when the whole body is exposed. For devices that only expose part of the body, such as mobile phones, different exposure limits are specified.