Electromagnetic fields(EMF) are created by electric current. Wherever current flows, changing in strength or polarity, electric charges are moved and generate electromagnetic fields. These are dependent on current strength and frequency and are expressed in field strength. The electromagnetic field knows the electric and the magnetic field strength and the field characteristic impedance.
Since electromagnetic fields already occur at very low frequencies, but above all lead to increased exposure at high frequencies, a distinction is made between low-frequency and high-frequency electromagnetic fields. A measure of the strength of electromagnetic fields, in addition to the field strength used at higher frequencies, is the energy flux density.
At low frequen cies, a distinction is made between low-frequency electric and magnetic fields. Low-frequency electric fields are generated by low-frequency voltages. They are present even when no current flows in the conductors or devices. The magnitude of the electric field depends on the voltage, which in buildings is 230 V/400 V and 50 Hz. In outdoor areas, the values range from medium voltages of 20 kV to high voltages of up to 400 kV.
The low-frequency magnetic fields only occur when current flows. The higher the current, the higher the magnetic field. The magnetic field strength is given in amperes per meter and thus depends on the distance from the current-carrying conductor. The magnetic flux density is given in Tesla (T) and refers to the power per area (W/m2).
High-frequency electromagnetic fields dissipate as electromagnetic waves from conductors and antennas and are used for radio transmission. Inhigh-frequency technology, these fields have a special significance, which is expressed in exposure and electrosmog. The frequency range of high-frequency electromagnetic waves includes all frequencies between 30 kHz and 300 GHz. The most important biological effect of high-frequency electromagnetic fields is the heating effect, as used in microwaves to heat food.