What is EMF?
An electromagnetic field (also EMF or EM field) is a physical field produced by the movement of electrically charged objects.


Illustration of electric and magnetic field. The electric field is present when the lamp is plugged in, due to the voltage difference between the connectors. The magnetic field is only present when the lamp is switched on, because  that's when current flows in the cable. Source: Hydro-Québec

All around the world, people are constantly exposed to electromagnetic waves.
 
Examples of man-made sources:

  • cellular telephones
  • radio-, and television transmissions
  • WiFi networks
  • satellite communications
  • unintended emissions and stray fields arising from electronic circuits
  • electric motors
  • cables and power transmission networks   

Examples of natural sources:

  • local build-up of electric charges in the atmosphere associated with thunderstorms
  • light from the sun carries infrared and ultraviolet radiation
  • ionizing radiation from the Earth and space
  • the Earth's magnetic field

Electric and magnetic fields are also present in electromagnetic radiation. Electromagnetic radiation has a magnitude (size) and a frequency (time-dependent periodic variation). The frequencies of electromagnetic radiation ranges from static electric and magnetic fields, through radiofrequency and infrared radiation, to x-rays. The European power frequency is 50 Hz.


 

Published June 28, 2011

Quantities and units

B and H both describe the magnetic field. The quantities B and H are related to each other by the magnetic permeability (µ) of the medium that they exist in.

B=µH,

where µ is the magnetic permeability. For air and human tissues µ is approximately 4π x 10-7 H/m.
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 Coordinator: Andreas Vogl, SINTEF FP7
Duration: 1st May 2011 - 1st February 2014
EU contract FP7-SST-265772 in the Sustainable Surface Transport call in Framework Program 7.