Mobile telephone radio wave effects

Like all other radio communication applications, mobile telephony uses radio waves to carry the information, like voice, text and images, through the air. Radio waves are a kind of electromagnetic fields (EMF) that are also called radio frequency fields or radio frequency energy. Electromagnetic fields are present in our every day life, both naturally and from man-made sources. Radio waves travel with the speed of light. They consist of an electric and a magnetic component, which vary periodically in time. The number of oscillations per second is called the frequency. The intensity of the radio waves is normally expressed as power density, and sometimes also as electric and magnetic field strength. The radio wave intensity is dependent on the distance to the transmitter, for example a mobile phone or a base station antenna, and to the output power of the transmitter. The lower the power and the longer the distance, then the lower the intensity will be.

Different types of electromagnetic fields have different frequencies. Visible light, for instance, has higher frequencies than radio waves, but lower than ultraviolet light. Electromagnetic waves with frequencies higher than ultraviolet light are called ionizing radiation, which has sufficient energy to break molecular bonds and thereby the potential to cause damage to biological tissue. X-rays and gamma rays are examples of ionizing radiation. Radio waves belong to the lower frequency part of the electromagnetic spectrum, which is called non-ionizing radiation. Here the electromagnetic energy is too low to break molecular bonds.

When a person is exposed to the radio waves from mobile phones or base stations, most of the energy will be reflected by the body or travel around it (called diffraction). Some of the energy will however be absorbed in the tissues at the surface of the body. Inside the body certain molecules, like water, will start to move or rotate due to the presence of the electromagnetic fields. By “friction” the energy is converted into heat. If the radio wave intensity is very high, the heating may be significant and potentially detrimental. The power used by mobile phones is very low and the tissue heating due to radio wave absorption is too small to be noticeable. The specific absorption rate, SAR, is used to specify the amount of radio frequency energy absorbed in the body. SAR is expressed in the unit watts per kilogram (W/kg).

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