Elektromagnetische Felder Aktualisierung 2009

6. Intermediate frequency fields like those from computer screens and anti-theft devices

• 6.1 What are the sources of intermediate frequency fields (IF fields)?
• 6.2 What possible health effects of intermediate frequency fields have been studied?

6.1 What are the sources of intermediate frequency fields (IF fields)?

In this assessment, intermediate frequency (IF) fields designate electromagnetic fields with frequencies ranging from 300 Hz to 100 kHz, roughly the frequencies that are lower than radio frequencies (RF) and higher than extremely low frequencies (ELF).

The term covers frequencies of the electromagnetic spectrum that are sometimes referred to as very low frequency (VLF) and low frequency (LF).

Applications generating intermediate frequency fields have been increasing in recent years and will likely continue to do so. Examples are some anti-theft devices operated at the exits of shops, induction hotplates, computer and television screens which use cathode ray tubes, compact fluorescent lamps, as well as some radio transmitters. Such fields are also generated by some industrial uses such as welding. In most cases exposure is limited, but for radio transmitters and welding, exposure can be above the recommended limits, so safety precautions should be taken.

Some medical applications lead to exposures in this frequency range, like electrosurgery that uses an electric current to cut or remove tissues and magnetic resonance imaging (MRI) that provides three-dimensional images of internal structures such as the brain. More...

Typical frequencies for devices generating intermediate frequency fields 

6.2 What possible health effects of intermediate frequency fields have been studied?

Well-known biological effects at the intermediate frequency range are nerve stimulation at the lower end of the range and heating at the upper end of the range. These are explained by the mechanisms known to occur in the radio frequency and extremely low frequency (ELF) ranges.

Very little useful human population data on intermediate field exposure and health risks are available, and laboratory data is still very sparse.

Exposure to intermediate frequency fields at work is in some cases considerably higher than exposure to the general public. However, very little research on intermediate frequencies and health risks in occupational settings or for the general public have been made recently, and no new epidemiological studies have appeared. The data are thus still too limited for an appropriate risk assessment.

In view of the increasing exposure to intermediate frequency fields at the work place, for instance in shops and certain industries, it is important that research in this area is given priority. More...