Electromagnetic fields
Living conditions in modern societies imply exposure, in a greater or lesser degree, to electromagnetic fields generated by a wide range of sources, both artificial (created by the inventive spirit of Man) and natural, i.e. those that have always surrounded us.
Artificial sources include the systems of generation and distribution of electrical energy, electrical lighting, electrical appliances, televisions, computer monitors, radio wave emission, radars and other telecommunications systems, among many others. Natural sources, such as the sun or the Earth's core also create Electromagnetic Fields of the same nature as those generated artificially, releasing radiation of different frequencies. Truthfully radio waves, in essence, only differ from visible light regarding the frequency with which they propagate.
The electromagnetic fields radiation must be clearly divided between ionising and non-ionising. Ionising radiation correspond, as described in Image 1, to high frequencies over 1 million GHz. Radiation emitted at these frequencies contains enough quantum energy to trigger the release of electrons from atoms of matter (Ionisation), possibly breaking chemical bonds and leading to new atomic and molecular formations.
Non-ionising radiation, related with much lower frequencies, like those used in mobile communications (0.9 to 2.2 GHz), only contain enough energy to cause an increase in temperature depending on the transmitted power used, not leading to any modification in cellular formations. This variation in temperature has relatively low amplitude when compared to other temperature variations such as those caused by natural factors we are subject to every day.
Image 1 - Electromagnetic spectrum
The mobile telecomunications network
Mobile communications require a telecommunications network. This network consists of wide-ranging and scattered interconnected elements that guarantee coverage satisfying Customers and complying with the requirements defined when the licence was granted. The elements of the network that are most visible to the general public are the mobile handsets, commonly called mobile phones, and antennas that allow connection to these handsets. It is important to distinguish the antennas from the structure that supports them. The supporting structure, the mast, serves solely to position the antennas at the height that best guarantees coverage.
The presence of antennas in our surroundings is not a new thing as radio transmission over AM, FM and television broadcasting has been undertaken for decades. Firemen, policemen and other organisations use radio frequencies to communicate. These transmissions normally use high power in order to allow wide coverage zones. Table 1 outlines typical values of potential users:
| Source |
Power |
|
|
| Terminal equipment - mobile phone |
up to 2 watts |
|
|
| GSM indoor station - inside buildings |
up to 5 watts |
|
|
| GSM outdoor station |
up to 270 watts |
|
|
| VHF Police transmitter |
up to 450 watts |
|
|
| HF transmitter |
300 to 1000 watts |
|
|
| Air traffic radar |
2000 to 10000 watts |
|
|
| FM radio station |
100000 watts |
|
|
| TV broadcasting station |
100000 to 750000 watts |
|
|
Table 1 - Comparison of Transmission Powers
Analysing the values of table 1, we should ask ourselves why are concerns raised in relation almost exclusively to radiation emitted by mobile communication antennas. The answer is definitely associated with the lack of sufficient knowledge to promote adequate perception and, also, to the fact that GSM antennas are more common and are installed closer to or even within urban areas. However, their contribution to the total Electromagnetic Field is very small.
Image 2 - Relation between the electromagnetic emissions sources
The geographic distribution of these antennas is related predominantly to two factors: