Electromagnetic waves differ in terms of their wave length and thus in their frequency and energy content. The oscillation level (amplitude) may vary, too. In technology, a differentiation is made between low-frequency and high-frequency fields.
Low- and high-frequency electromagnetic fields
The low frequency band ranges from 0 to 30,000 Hz (1,000 Hz = 1 kilohertz). Low frequency electric and magnetic fields are produced, for instance, by all electric household appliances, such as coffee machines. They are not suitable for transmitting information over long distances. The magnetic field component can penetrate comparatively deeply into the human body where it produces electric currents.
This is why public safety digital radio (also known as BOS digital radio) uses the frequency band around 400 MHz. It therefore belongs to the high-frequency band ranging from 100 KHz to 300 GHz. Commercial mobile radio communication uses this high-frequency band, too. GSM usually uses the frequency band around 900 MHZ and 1,800 MHz, while UMTS uses the one around 2,000 MHz.
High-frequency fields are absorbed by the human body. Body tissue may warm up as a result of the absorption process (thermal effect). The heat absorbed by the body is measured in watts per kilogramme of body weight by the so-called specific energy absorption rate (SAR). The absorption rate depends on the strength and frequency of the electromagnetic waves, but also on the nature and structure of the absorbing tissue.
Effects and perception of electromagnetic fields
Human beings are usually unaware of electromagnetic fields. Only if it is warm or if we suffer from skin irritations, is our body able to perceive electromagnetic radio waves. The legislation therefore contains a series of rules to protect the public from electromagnetic fields. These rules are, of course, respected by all stakeholders involved in creating and operating of the public safety digital radio network.
High-frequency fields differ from low-frequency fields in that the electromagnetic waves cannot penetrate deeply into the human body and do not stimulate neurons or muscle cells.
The human body absorbs the energy of high-frequency fields and transforms it into heat. Scientists describe this process as the thermal effect of electromagnetic fields. The greater the distance between the human body and the source of exposure, the less energy is absorbed.
A series of scientific studies has revealed the thermal effects of high-frequency fields. So far no evidence has been found that the human body experiences other effects (athermal effects) in addition to a high-frequency field. In this context, one of the questions that researchers tried to answer was whether high-frequency fields affect the central nervous system by changing cognitive skills, brain wave activity or sleeping parameters. Independent expert bodies evaluated the results of the studies, both at national and international level. The outcome: There is so far no scientific evidence that electromagnetic fields generated by mobile radio communication have adverse health effects.