Depending on their frequency, electromagnetic fields (EMF) may comprise electric, magnetic and electromagnetic fields or radiation. EMF travel in space in the form of waves and are characterised by their energy, frequency and wavelength. Frequency is the number of complete wave cycles that pass a given point per second. Its unit is the Hertz (Hz), which is defined as one cycle per second. Wavelength (λ) is the distance between two points of a wave that define a complete cycle. These three characteristics are related, so the higher the frequency of the wave, the higher the energy transported and the shorter its wavelength.
The table below summarises the units and quantities used when describing EMF.
|Electric field strength||E||Volt per meter||V/m||Static, ELF & RF (MW)|
|Magnetic Field strength||H||Ampere per meter||A/m||RF (MW)|
|Power Density||S||Watt per square meter||W/m2||RF (MW)|
|Magnetic flux density||B||Tesla||T||Static & ELF|
Note: ELF=extremely low frequency; RF=radiofrequency; MW=microwaves.