Radiofrequency (RF) energy is a type of electromagnetic radiation.  Electromagnetic radiation consists of waves of electrical and magnetic energy which 'radiate' (that is, travel) through space.  The number of waves occurring per second is known as the frequency of the electromagnetic radiation and is measured in Hertz (Hz).  Radiofrequency electric and magnetic waves occur at a rate of 3 kilohertz (kHz) - 300 Megahertz (MHz) (that is, 3 thousand to 300 million waves per second).

Typical sources of radiowaves include television and radio transmitters, and mobile phone signals, mobile phone towers, magnetic resonance imaging (MRI), and microwave ovens.  The sun also emits radiowaves.

Radiowaves are only one portion of the electromagnetic spectrum.  Other forms of electromagnetic radiation includes ultraviolet light, visible light, and x-rays.  Each of these types of radiation are defined by their frequency.

The frequency of an electromagnetic wave has very important consequences for the way in which it interacts with the human body.  Very high frequency electromagnetic waves, such as x-rays, gamma rays, and radiation emitted from radioactive substances are classified as ionising forms of radiation.  This means that they carry sufficient quantum energy to strip electrons away from atoms creating free radicals which can be damaging to cells in the human body, subsequently high doses of ionising radiation is damaging to the human body and human DNA and can cause cancer.

Radiowaves, visible light and microwaves are all considered non-ionising forms of radiation.  This is because, no matter how intense, non-ionising radiation is incapable of breaking electrical bonds within atoms.  However, non-ionising radiation does cause a heating effect which is proportional to its intensity and if present in sufficient quantity may be harmful.

There has been numerous studies of the relationship between radiowave exposure and cancer, ranging from animal and biological tissue sample studies to human studies in which the health of human volunteers is monitored in relation to their exposure to radiowaves (e.g. through mobile phone use).  This literature has been reviewed by numerous national and international committees, expert working groups and agencies.  Recently, National Radiological Protection Board (UK) reviewed 26 such reports regarding the health effects of mobile phones that were published between 2000 and 2004.  These reports were similar in their conclusions and recommendations.  Overall, these reports suggested that mobile phone emissions may have subtle biological effects, but that there is no strong evidence to suggest that mobile phone emissions have adverse health effects such as cancer.

It is widely accepted that emissions from mobile phones cause minute heating of the brain.  This is due to two factors.  First, the electric field generated by mobile phone causes electrically charged particles in brain tissue to move.  The electrical properties of the brain tissue provide some resistance to this movement, and this produces heat.  Second, the electric field causes water molecules, which are positively charged at one end and negatively charged at the other, to rotate such that they are electrically aligned with the electrical field.  Due to the cohesive properties of water, there is again some resistance to this process, thus producing heat.

The power output of mobile phones are limited by international standards to protect users from excessive heating.  These standards dictate that the average specific energy absorption rate (SAR) in any 10g region of biological tissue produced by radiofrequency emission must be less than 2 W/kg for the public and 10 W/kg for those who are occupationally exposed.  At these levels, the degree of heating within the brain at the point closest to a mobile phone antenna is thought to be less than 1°C.  This heat is thought to dissipate quickly to surrounding tissue and is thought to pose no health risk.  Based on current evidence, RF-induced heating of brain tissue is the only widely accepted explanation for possible RF-induced changes in cognition (memory and attention).

Nevertheless, there have been several theories about how mobile phone emissions may interact with biological tissue through mechanisms which do not involve heat (non-thermal mechanisms).  For example, it has been suggested mobile phone emission could also exert magnetic forces on the ferrimagnetic compound magnetite (Fe₃O₄) which occurs naturally within the body.  Because this compound is often mechanically linked to cellular ion channels (the gates to the inside of cells) within the brain, these forces may open ion channels leading to altered nerve cell activity.  However, this and many other non-thermal theories are doubtful, as almost all supporting evidence has been obtained using electromagnetic radiation outside of the radiofrequency range or of far greater intensity than is emitted by mobile phones.  Based on present evidence and currently accepted laws of biophysics, it has been argued in several recent scientific reviews that it is very unlikely that mobile phones are able to interact with biological matter through non-thermal mechanisms.  Nevertheless, a select number of proposed non-thermal interaction mechanisms have some experimental support which requires further research. 

The antennas used by base stations are placed up high and emit radiowaves in a horizontal direction.  Radiowaves spread out as they travel and hit the ground at some distance from the antenna, like water from a water sprinkler.  This means that the point of maximum radiowave exposure is located at some distance from the antenna.  Typically peak exposure may occur at 100 metres from the antenna, but even here the amount of radiowave exposure received is considered very low and is considerably less than one would receive when using a mobile telephone. However distances to peak radiowave strength vary considerably based on the antenna height, tilt and orientation (e.g. distance of 14 to 480 metres from the antenna have recently been reported in Australia). The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) conducted a study in which radiowaves were measured in the vicinity of 60 mobile phone base stations in five Australian state capitals. In all cases the measured levels were found to be far below the applicable exposure limits (follow this link for the report).

In order to reduce the inconvenience and trip hazards of running multiple connecting cables between PCs, printers, modems and other internet connections, many homes, schools and offices have installed Wireless Local Area Network (WLAN) systems. These systems have the added bonus of allowing, for example, laptops to be operated in the garden or other convenient locations rather than being restricted by cable length. Wireless communication is typically achieved by using a ‘router’ (which is a two-way transmitter and receiver) sited close to the main wired or cable internet connection and a card or plug-in device in the computer, which also acts as a transmitter and receiver of data. In office environments, numerous ‘access points’ (which are similar in function to a router) are placed at convenient points within buildings, usually on ceilings or walls. Each of these routers or access points has to comply with rigid RF emission standards with antennas designed for home or in-building use rated at less than 100 mW (which is similar to a mobile phone handset in normal operation). They typically operate at frequencies similar to the new 3G (UMTS) network or higher. In order to prevent interference the range of most domestic routers is around 30 m and the range for office locations is about the same, although multiple access points will ensure adequate coverage for a large building complex.

Laptops and PCs also have a transmitting antenna, which often is an integral part of the internal circuitry or plug-in device. The antenna is similar to a mobile phone handset antenna, but in general, operates at a lower signal strength, since the router or access point is much closer than the mobile phone base station, which could be kilometres away.

In terms of RF exposure, the worst-case scenario is probably the use of a laptop computer actually on the lap, where parts of the body may only be centimetres away. There is also the possibility of children playing near to the antennas of the computer or the router. However, this is likely to be less than the exposure to the brain from a mobile phone handset, where the antenna is probably much closer. In terms of duration of exposure, the transmission of RF energy is greatest during data uploads from and downloads to the internet. This will usually only occupy a small fraction of time spent at the computer.

The UK Health Protection Agency has conducted measurements from WLANS and have found RF emissions to be well within international health and safety guidelines.

See also: note on use of personal data assistants (PDAs); Cordless Phones

For further information see:

In most hospitals there are local rules on visitor use of mobile phones. Recently, there has been some relaxation of the earlier ‘blanket bans’ to permit visitor use in certain designated areas. Mobile phones are increasing being used by medical staff to inform relative of the outcome of medical procedures, so it is incongruous to prohibit visitor use, particularly where arrangements concerning patient wellbeing are concerned.

Blanket bans were originally introduced not because of concerns for possible effects of RF emissions on health, but because in a number of isolated instances sensitive hospital equipment, especially life support systems, were found to be affected by the RF emissions from the phone handsets. However, if the phone or other wireless device is more than 2 m from the equipment, the incidence of clinically relevant interference is very low, but not zero. There is thus some justification in designating some ‘phone and GPRS switch-off’ areas of the hospitals where sensitive life-support equipment is expected to be. Nevertheless, because of the difficulty of knowing, especially when replying to a mobile phone call, how far away particular equipment is, these areas may need to include corridors and other public space. More modern devices may be less capable of causing interference because of the higher frequencies, lower transmit powers and different modulation schemes involved.

See also: Using mobile phones at motor service stations; Use of mobile phone on aircraft

For further information:

Lawrentschuk N, Bolton DM. 2004. Mobile phone interference with medical equipment and its clinical relevance: a systematic review. Med J Aust; 181:145-9

Most motor service stations have warning signs at fuel bowsers to request that mobile phones be turned off. These signs have no legal status but have been in place for many years because of a concern not of possible health effects from RF emissions but of fuel vapour ignition from electrical sparks. Whilst it is true that sparks can ignite flammable vapour, modern mobile phone handsets are highly unlikely to produce sparks, because the switches and keys operate on different principles to those used in the early prototypes in the 1980s and which may have been the reason for initial caution. There has not been a single incident in which mobile phone use has been unambiguously implicated in the ignition of fuel vapour at filling stations, although there have been unsubstantiated media stories. Curiously, nylon clothing (which can cause significant sparks due to static electricity), is not banned at service stations.

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On air flights the announcement is routinely made at the commencement of preparation for take-off that all mobile communications equipment and hand-held games be turned off. This is because the RF emissions from mobile phones can interfere with aircraft navigation and other electronic equipment. At cruising altitude, the base stations are so far away that the handsets have to transmit at full power to try to establish contact.

Qantas introduced a 3-month trial, commencing in April 2007, in which mobile phones and personal data assistants (PDAs) can be used during domestic flights, because aircraft been installed with a ‘microcell’ to monitor and relay calls. The handsets are thus contacting a base-station a matter of metres away and thus power down to a minimum level.

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An innovated solution to providing fast internet in homes is to deliver the data as an additional RF current to the mains current provided by the power socket to the computer or computer peripheral. The RF current represents a tiny fraction of the total current and electronic circuitry can easily separate the two forms of current. What this means is that in addition to the electric and magnetic fields (EMF) associated with the electric power (so called Extremely Low Frequency of ELF fields) there are also RF EMFs. Since the values of EMF allowed in safety standards are much lower at RF compared with ELF, there is some concern that the fields could affect health. However, the currents are so small and the fields fall off very rapidly with distance, so appear to be well within the limits for human exposure. The UK Health Protection Agency has undertaken some measurements, which confirm this.

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