Radiofrequency Fields

EMF having a frequency between 3 kHz up to 300 GHz are commonly called radiofrequency (RF) fields or radiation. They are usually emitted from an antenna to a receiver and are used to transfer information quickly over great distances. RF EMF are therefore used for radio and TV broadcasting, mobile communication, cordless phones, WiFi and bluetooth connections, and other telecommunication purposes. RF fields may be used within appliances (e.g. microwave ovens) to heat things such as food, but also in industrial settings to heat or seal plastics and other low-conductivity materials.

The most important source of public exposure to RF fields is the mobile phone. Exposure levels of the public to RF fields from mobile phone antennae (also known as base stations) are low. Assessments of the EMF levels around antennae are routinely carried out by ComReg, and are published on their website www.siteviewer.ie

The quantities and units commonly used to describe RF radiation exposure and dose are:

  • Electric field strength (E), measured in volts per meter (V/m);
  • Magnetic field strength (H), measured in amperes per meter (A/m); 
  • Power density (S), measured in watts per square meter (W/m2);
  • Specific absorption rate (SAR), measured in watts per kilogram (W/kg).

At a certain distance from the antenna (known as far-field), only the electric fields (E) need be measured, since, under these conditions, the magnetic fields (H) can be easily extrapolated from the measured electric fields. Thus, RF surveys for public exposure usually include measurements of E-fields only. The table below summarises the levels of E-fields associated with typical RF sources in everyday environments.

 
 E-field magnitude (volt per meter, V/m)
Source Distance 1 (near) Distance 2 (far)
Mobile phone (hand-held device)1 ≈100 V/m at ear ≈10 V/m at 5 cm
Mobile phone (base station) ≈2 V/m at 30 m ≈0.01 V/m at 100 m
TV (UHF) broadcasting antenna ≈5 V/m at 500 m ≈1 V/m at 1 km
TV (VHF) broadcasting antenna ≈2 V/m at 500 m ≈0.1 V/m at 1 km
Radio (AM) broadcasting antenna ≈10 V/m at 100 m ≈0.1 V/m at 1 km
Radio (FM) broadcasting antenna ≈2 V/m at 500 m ≈0.1 V/m at 1 km
Radar (police road traffic) ≈1 V/m at 30 m ≈0.1 V/m at 300 m
Radar (air traffic) ≈2.5 V/m at 200 m ≈0.01 V/m at 600 m
Microwave oven (domestic)2 ≈40 V/m at 5 cm ≈2 V/m at 1 m

Note: Electric field estimates from Mantiply et al 1997 and Valberg et al 2007. The most restrictive reference level for RF public (whole body) exposure is 28 V/m (EU 1999). 1Maximum exposure assuming a typical phone with an average SAR=1 W/kg (the current limit for head exposure is 2 W/kg). 2The reference level for (whole body) exposure to sources such as domestic microwave ovens (2.45 GHz) is 61 V/m.