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Electromagnetic Fields > High Frequency Fields
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High Frequency Fields
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Basic Principles, Definitions
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High frequency electromagnetic fields cover the frequency range from 100 kHz to 300 GHz of the electromagnetic spectrum. The physical unit for the frequency, one Hertz, is equivalent to one oscillation per second. Frequency and wavelength of electromagnetic fields are linked by the speed of the travelling wave. The higher the frequency is, the shorter is the wavelength and vice versa. The wavelength of high frequency fields ranges from 3 km at 100 kHz to 1 mm at 300 GHz. High frequency electromagnetic fields have two components, the electric field and the magnetic field. Far away from a radiating antenna both fields are closely connected through the wave impedance of free space.
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Applications of High Frequency Fields
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Numerous technologies use high frequency (HF) electromagnetic fields: Every day life cannot be imagined without broadcasting and television, cordless phones increase comfort when phoning indoors and in the garden, babies are monitored in their rooms using baby monitors, computers are linked to each other and to peripheral devices by using Wireless LAN (WLAN) and Bluetooth and recently ultrawideband (UWB) technologies, police and fire brigades use their own radio network for communication. Moreover high frequency fields are applied for radar units, in microwave ovens and for electronic article surveillance systems. At present new applications for high frequency fields in the terahertz range are developed and tested (e.g., security scans at airports). The strongest increase in use, however, has been stated in mobile telecommunication for some years. UMTS and WiMAX technology for fast data transmission will further increase the frequency of utilisation.
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Limit Values and Precaution
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The German Electromagnetic Field Ordinance, which is based on the Federal Pollution Control Act (26th BImSchV), entered into force in 1997. It was enacted to protect the population against possible health effects from electric, magnetic, and electromagnetic fields, taking into account recommendations by the German Commission on Radiological Protection (SSK) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The basis of these recommendations is scientifically proven and takes into account health-relevant biological effects, which can be caused by exposure to such fields. Limit values specified in the ordinance apply to fixed low and high frequency installations.
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Biological and Health Effects of High Frequency Electromagnetic Fields
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High frequency electromagnetic fields are absorbed by biological systems and lead, above all, to a warming of the tissue. The physical basis of this thermal effect is well known and beyond dispute. It is questionable, however, if there are non-thermal biological effects in the region of low intensities of high frequency radiation. Their existence has not been proven up to now but intensive research in this field is going on.
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Recommendations of the Federal Office for Radiation Protection for Mobile Phone Calls
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Mobile telecommunication uses electromagnetic fields for information transmission. Mobile phones produce these fields, directly at the head while calling. At present there is no scientific proof of any health hazards below exposure limits. However, for reasons of precautionary health protection the Federal Office for Radiation Protection (BfS) recommends to keep exposures to these fields as low as reasonably achievable. This applies especially for mobile phone use where exposure is normally much higher than for mobile phone base stations in the neighbourhood.
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Risk perception in the general public
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For many years discussions about possible health risks due to high-frequency electromagnetic fields, e. g. in the vicinity of broadcasting stations and television transmitters, have taken place. The rapid extension of the mobile phone networks and the strong increase in the number of mobile communication users a few years ago aroused the intensity of the discussion in the general public about the possible risks of this technology.
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Occupational Safety
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Although the exposure to high frequency electromagnetic fields is relatively low for the general public, there are certain working environments where exposure is high, for example, applications in medicine, equipment for warming and connecting of materials in industry, as well as repair or maintenance of technical installations during operation. The Employers’ Liability Insurance Association Regulations, the pertinent EU Council Directive, and other provisions are applied to protect employees against potential damage to their health.
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