Fields of different frequency ranges of the electromagnetic spectrum differ considerably in their perceptibility and in their effects on humans and biological systems. Humans can indirectly perceive the effect of electric fields, for example, by small sparks and noticeable electrical discharges when taking off a pullover or touching a door knob. Magnetic fields become perceptible with the help of a permanent magnet or electromagnet. In the range of the electromagnetic fields, we know e.g. the heat effect of microwaves, which heat meals and liquids in the microwave oven.
The penetration behavior of fields into biological tissues and the effects are essentially determined by the frequency and strength of the fields as well as by reflection and absorption characteristics of the tissue, the resonance behavior and, if applicable, the grounding system.
The mechanisms accountable for the effects of fields on humans and biological systems are different depending on the frequency range of the field. Additionally, direct effects (e.g. nerve stimulation or tissue heating) and indirect effects (e.g. interference with electronic implants or spark discharge when touching charged objects) can be distinguished. According to the classification in the EMF-Portal, four frequency bands with different direct and indirect main effects can be differentiated.
Static electric fields exert actions of force on biological structures. The focus here lies on the movement of electric charges, which leads to charging actions. These cause effects like perceptible movement of hairs, minor spark discharges and major lightning discharges.
Static magnetic fields can interact with moving charges in the body, like e.g. ions in the blood. Moreover, the magnetic force can influence electronic and passive metallic implants. This is relevant for static magnetic fields with 0.5 mT or more, which can actually be found in our everyday life (e.g. near strong permanent magnets). During medical examinations in a magnetic resonance imager, much stronger magnetic fields of about 10 T occur (ICNIRP, p. 505; BAG; LUBW, p. 57).
The prevailing possible effect of extremely low frequency fields is the stimulating effect of the alternating magnetic field on excitable cells, like sensory, nerve and muscle cells. In living tissue, the effect is caused by induced electric fields and currents which activate the cells. The possible influence on electronic implants is also based on induced electric fields and currents.
The effects of intermediate frequency fields consist of a combination of effects of extremely low frequency and radio frequency fields, i.e. a stimulating effect caused by induced electric fields and currents in the lower frequency range that turns more and more into heat effects in the upper frequency range.
In the radio frequency range, the electromagnetic field has an electric and a magnetic field component. Thermal effects, which are caused by the stimulation of molecules and other electrically charged particles (frictional heat), play the dominant role as a possible effect on humans and biological systems.
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