Precise intensity measurements of electric and magnetic fields are necessary to avoid or limit occupational risks where there are high levels of NIR ( electromagnetic fields ) as well as in applications requiring Electro-Magnetic Compliance ( EMC ) such as: maintenance of telecommunications or radar equipments, welding systems, diathermy equipment and other medical devices generating microwaves , Magnetic Resonance scanners , drying equipment in tanning industry and timber production.
These measures are also necessary for public health reasons to assess electromagnetic pollution caused by the increased use of telecommunications technologies or power lines. The diagram shows some typical applications related to NIR production/use.
The frequency spectrum is normally divided in two bands: the low frequencies up to 30 kHz and high frequencies above 30 kHz. The first band includes, for example, the general power of the 16.6 Hz railway network power, the distribution of domestic electric power at 50 Hz (home networks and power lines) and extends up to 30 kHz of VDU workstations. The second band includes, for example, the FM broadcasting (88 to 108 MHz) TV signals (40 to 900 MHz), the mobile radio communications, the so-called mobile phones (400 to 1800 MHz) and satellite communications ( up to 18 GHz).
Electromagnetic fields are characterized by two components: the electric field E (measured in V / m) and the magnetic field H (measured in A / m). In the far field (beyond a certain distance from the source) E and H are strongly coupled and one of them can be deduced from measurement of the other. Conversely in the head near (within a certain distance from the source) E and H need to be measured independently.
The thresholds of maximum exposure, for e.m. fields are different among national legislations but they will soon comply with the international standards . In Europe (CENELEC) these thresholds are expressed (as a function of frequency) in V / m for electric fields ( E) , in A / m for the magnetic fields ( H ) and in W / m2 for the power density.
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