Below we provide basic information on the nature of electromagnetic fields and electromagnetic radiation, as well as on the legal exposure limits and non-official precautionary levels.
Electromagnetic waves, or electromagnetic fields, are measured and shielded in different ways depending on their frequency; in addition, the biological effects of electromagnetic waves vary according to their frequency. For this reason, we divide electromagnetic fields into two groups: low frequency and high frequency.
In general, we refer to low-frequency electromagnetic waves as low frequency electromagnetic fields or EMF, and to high-frequency electromagnetic waves as high frequency electromagnetic radiation.
The set of electromagnetic waves of all possible frequencies is called the electromagnetic spectrum, which includes emissions from very different sources: from electromagnetic fields generated by the power grid, radio waves, infrared waves, visible and ultraviolet light, through to X-rays and gamma radiation. All these emissions are electromagnetic waves that differ only in their wavelength:
The only difference between these three waves is their wavelength, which determines, for example in the case of visible light, the colour that we perceive.
The wavelength is linked to the frequency of the wave by a simple relationship: the frequency is equal to the speed of the wave (which we call the speed of light) divided by its wavelength:
Wave frequency = speed of light ÷ wavelength
The frequency of an electromagnetic wave is expressed in units of hertz (Hz). One hertz corresponds to one cycle per second, which can be understood as one wave passing per second.
However, these differences in wavelength and frequency lead to enormous differences in how the waves interact with materials and, of course, with the human body.
We divide the electromagnetic spectrum into various regions which correspond, more or less, to frequency bands that have similar properties, effects or uses:
| Region | Frequency band | Wavelength |
|---|---|---|
| Extremely low frequencies | 30 Hz - 300 Hz | > 1000 km |
| Low / medium frequencies | 300 Hz - 3 MHz | 1000 km - 100 m |
| Radio frequencies | 3 MHz - 300 MHz | 100 m - 100 cm |
| Microwaves | 300 MHz - 30 GHz | 100 cm - 1 cm |
| Very high-frequency microwaves | 30 GHz - 300 GHz | 1 cm - 1 mm |
| Infrared waves | 300 GHz - 430 THz | 1 mm - 700 nm |
| Visible light | 430 THz - 770 THz | 700 nm - 390 nm |
| Ultraviolet radiation | 770 THz - 30 PHz | 390 nm - 10 nm |
| X-rays | 30 PHz - 10 EHz | 10 nm - 10 pm |
| Gamma radiation | 10 EHz - 1022 Hz | 10 pm - 0.3 pm |
| Cosmic rays | 1022 Hz - 1025 Hz | 0.3 pm - < 10-17 m |
| Very high-energy cosmic rays | > 1025 Hz | < 10-17 m |
The shielding materials supplied by Radiansa cover the regions from extremely low frequencies up to microwaves.
Electromagnetic fields have two components, as the name suggests: the electric field and the magnetic field. In the diagram below, you can see how the electric and magnetic components form a complete electromagnetic wave:
The relationship between the magnetic field and the electric field depends on the distance to the emitting source and on the wavelength.
If we are at a distance much greater than the wavelength of the electromagnetic wave, we are in the far field; if we are closer to the source, we are in the near field.
The transition point between near field and far field can be complex to calculate, but in general we can consider that we are in the near field when we are at distances shorter than one wavelength.
In practical terms, we can consider the following:
Thus, at power grid frequencies (low frequency), we are always in the near field. In contrast, at mobile phone frequencies and other telecommunications systems (high frequency), we are almost always in the far field.
This is why we shield and measure low- and high-frequency electromagnetic fields in different ways. Installations that generate low-frequency electromagnetic fields include transformer substations and high-voltage power lines, whereas high-frequency radiation is emitted by mobile phone antennas, WiFi and telecommunications systems in general.
In practice, when we talk about low frequency electromagnetic fields, we are usually interested in emissions at the mains frequency, that is, a frequency of 50 hertz (50 Hz).
Sources of low frequency electromagnetic fields include:
As mentioned above, low frequency electromagnetic fields can be considered as two different components: the magnetic field and the electric field. The methods used to measure and shield electric fields and magnetic fields are different.
The electric component (electric field) originates from voltage differences and, the higher the voltage, the stronger the resulting field. An electric field can exist even when there is no current.
The magnetic component (or magnetic field), on the other hand, originates from electric currents. A higher current results in a stronger magnetic field; in other words, the magnitude of the magnetic field changes with the consumption of electrical power.
The controversy about a possible link between electromagnetic fields and cancer is focused on the magnetic component, that is, on magnetic fields.
Magnetic fields are strongest close to their source and their intensity decreases rapidly as the distance from the source increases. Common materials, such as building walls, do not block magnetic fields.
To characterise the value of a magnetic field, the quantity most commonly used is known as magnetic flux density, which is measured in units of tesla or gauss.
The tesla is the unit defined by the International System of Units (SI), whereas the gauss (or milligauss, mG) appears more frequently in older texts.
More precisely, the intensity of a magnetic field is expressed in amperes per metre (A/m); however, in practice, magnetic flux density, expressed in teslas, is usually used to indicate the field strength.
Because one tesla is a very large value, it is common to use millitesla (mT), microtesla (µT) or even nanotesla (nT) to express the strength of low frequency magnetic fields. One millitesla is equal to 0.001 tesla; one microtesla is equal to 0.001 millitesla; and one nanotesla is equal to 0.001 microtesla.
It is easy to convert between tesla, gauss and A/m:
| microtesla (µT) | nanotesla (nT) | milligauss (mG) | amperes/metre (A/m) |
|---|---|---|---|
| 1 | 1000 | 10 | 0.67 |
| 0.001 | 1 | 0.01 | 0.0067 |
| 0.1 | 100 | 1 | 0.067 |
Magnetic field strength is measured using instruments called magnetometers, also known as teslameters or gaussmeters.
The electric field strength is expressed in volts per metre (V/m). Electric field strength is measured using a voltmeter. Many low frequency field meters include both electric-field and magnetic-field sensors.
Spanish regulations set out in RD 1066/2001 a maximum exposure limit for the general public of 100 microtesla (100,000 nanotesla) for electromagnetic fields at 50 Hz. The equivalent figure for workers is specified in RD 299/2016 as 1000 microtesla (lower action level).
These values are based on the recommendations of the International Commission on Non-Ionizing Radiation Protection (ICNIRP). This non-governmental organisation, formally recognised by the World Health Organization (WHO), evaluates the results of scientific studies carried out worldwide and issues guidelines which set recommended exposure limits.
In 2010, ICNIRP published new recommendations in which the exposure limit for the general public was raised to 200 µT, but no change to national legislation is currently planned.
These exposure limits have been adopted by most European countries. However, in some countries reference levels have been set below the ICNIRP limits; for example, in Italy there is a “quality objective” of 3 microtesla for new installations, including buildings and electrical infrastructure.
In the frequency range from 1 Hz to 1 MHz, which includes 50 Hz mains frequency, the recommendations specify exposure limits solely to prevent harmful effects on the functioning of the nervous system (the only effect that has been demonstrated unequivocally with scientific evidence). In this way, Spanish regulations consider that exposure to electromagnetic fields below 100 microtesla (100,000 nanotesla) does not cause any harmful effect on human health.
However, today the controversy focuses on other possible harmful effects that are suspected but not unequivocally proven, above all a possible association between exposure to magnetic fields and cancer. Several scientists have raised the need to review exposure limits. ICNIRP has stated that “... some epidemiological studies indicate a possible small increase in the risk of childhood leukaemia associated with time-averaged power-frequency (50/60 Hz) magnetic fields in the range 0.3–0.4 µT (300–400 nT).”
This has led the International Agency for Research on Cancer (IARC), a WHO body, to classify ELF magnetic fields as possibly carcinogenic.
In its latest guidelines, ICNIRP, despite the increase in the reference level mentioned above, acknowledges that “epidemiological studies have consistently shown an association between chronic low-intensity (0.3–0.4 µT) power-frequency magnetic-field exposure and an increased risk of childhood leukaemia. However, the lack of a well-established causal relationship means that this effect cannot be addressed in the basic restrictions.”
Research into possible mechanisms of action is ongoing. In a recent publication, researchers reviewed 34 studies on the genotoxicity of low frequency magnetic fields and concluded that “There is abundant scientific evidence pointing to a genotoxic potential of magnetic fields, as determined by micronucleus (MN) assays under different experimental conditions intended to mimic human exposure. A pathway involving chromosomal damage is possible, although no clear mechanism has yet been identified to explain these lesions. Likewise, the biological consequences that this increase in chromosomal damage could have for health remain to be determined.” (M. Alcarez et al., Radioprotección 71, 28–36).
In view of this uncertainty, it is advisable to apply the principle of “prudent avoidance”, which recommends reducing exposure to magnetic fields that can be avoided easily with minimal investment of cost and effort, especially in the case of children and pregnant women. As a practical measure, we recommend an action level of 0.3 microtesla (300 nanotesla).
In everyday life, we are almost continuously exposed to electromagnetic waves emitted by telecommunications systems, such as mobile phone network antennas. In this context, the electromagnetic wave represents the transfer of energy from one point to another, and is more properly referred to as electromagnetic radiation.
In the following section we provide an overview of the factors that influence exposure to emissions from mobile phone antennas.
A typical mobile phone base station antenna consists of one or more (usually three) “sector” antennas; each sector antenna concentrates its emissions forwards and horizontally, in the form of a relatively flat beam covering a sector of between 60 and 120 degrees.
Because a base station consists of several sector antennas which emit a highly asymmetrical beam, a significant variation in signal strength can be expected depending on the position relative to the base station, even when the distance is the same. The following diagram shows a typical variation in the horizontal radiation pattern emitted by a sector antenna transmitter.
The service range of each base station is limited and depends on the number of users and on obstacles encountered by the waves along their path. In open areas, the signal from a base station can reach several kilometres. However, in cities the presence of buildings drastically reduces the range of emissions due to absorption of radiation and to the so-called “umbrella effect”. To maintain network coverage, in addition to installing more base stations, a large number of smaller antennas called “microcell” antennas are often installed, typically mounted on walls in the street and also inside buildings.
Where an antenna only has to serve a small number of users (for example in rural areas), an omnidirectional antenna is often installed, consisting of a central rod-type transmitting antenna and two receiving antennas on either side. This type of antenna emits radiation with almost the same intensity in all horizontal directions.
In theory, high frequency radiation would decrease according to an inverse-square law, which means that the radiation intensity varies inversely with the square of the distance from the source; in other words, if we double the distance from the source, the radiation intensity falls by a factor of 4. In practice, however, high frequency radiation almost never decreases as a simple function of distance, due to reflections, scattering and diffractions caused by interactions with buildings, trees, construction materials, etc. These effects can give rise to large variability in radiation intensity within the measurement area, even when the distance to the antenna is the same.
To characterise the intensity of electromagnetic radiation, we generally use one (or both) of the following units:
A value in volts per metre is a measure of the electric field strength; a value in watts per square metre is a measure of the power density of the waves.
As an approximation, the two quantities are related by the following mathematical expression:
Power density W/m2 = (Electric field V/m)2 × 377
This relationship applies strictly only to plane waves, that is, waves that do not carry any kind of modulation conveying information such as voice or data.
Spanish regulations on exposure to mobile phone radiation are set out in the Royal Decrees mentioned previously, namely: RD 1066/2001 for public exposure, and RD 299/2016 for occupational exposure, and follow the recommendations of ICNIRP and the directives of the European Union.
The criteria applied by ICNIRP in its review were chosen to assess the reliability of the various conclusions reached; however, only “proven” effects were used as a basis for the recommendations, i.e. only the thermal effects resulting from heating of the human body by microwaves emitted by mobile phone antennas.
As a reference level, we highlight the most restrictive public exposure limit within the mobile phone frequency range (which corresponds to the 700 MHz band):
However, several scientists have argued that maximum exposure levels should be reviewed, pointing out that there is extensive biomedical literature on non-thermal effects, such as their influence on certain types of cell proliferation, hormonal changes, circadian rhythms, radiofrequency syndrome, etc. Nonetheless, the exposure levels at which these effects appear are generally quite high.
It must also be borne in mind that the massive proliferation of new telecommunications technologies involves the introduction of electromagnetic energy into our living environment at levels that did not exist a few years ago, and there are not yet enough studies on long-term exposure to this radiation, due to the relative novelty of this phenomenon.
To provide guidance for our clients in this confusing situation, Radiansa Consulting recommends 1000 µW/m2, equivalent to 0.1 µW/cm2, as a non-official precautionary limit. This level corresponds to 1.5% of the legal limit at a frequency of 900 MHz in Spain (GSM900 mobile phone systems). An exposure of 1000 µW/m2 is equivalent (for continuous signals) to an electric field strength of 0.6 V/m, and corresponds to the action level recommended by several non-official organisations (Salzburg 2000, Bioinitiative, for example).
From 1000 µW/m2 upwards, the levels are far above the average level we usually find in an urban environment.
It should be emphasised that this does not mean that radiation above 1000 µW/m2 is necessarily harmful to human health — our knowledge is still incomplete, especially for long-term exposure — but it does mean that, if harmful effects were to exist, exposure above this level would represent a risk higher than normal.
Therefore, 1000 µW/m2 serves as an “action level” for clients who are concerned about the possibility that emissions may be harmful to their health.
It is easy to convert microwatts per square metre (µW/m2) into other commonly used power density units, such as microwatts per square centimetre (µW/cm2), milliwatts per square metre (mW/m2), watts per square metre (W/m2) and also volts per metre (V/m), although the latter is strictly valid only for continuous signals, such as radio broadcasts:
| µW/m2 | µW/cm2 | mW/m2 | W/m2 | V/m |
|---|---|---|---|---|
| 10 | 0.001 | 0.01 | 0.00001 | 0.06 |
| 100 | 0.01 | 0.1 | 0.0001 | 0.19 |
| 1000 | 0.1 | 1 | 0.001 | 0.61 |
| 10000 | 1 | 10 | 0.01 | 1.94 |
Electromagnetic fields:
This website uses third-party cookies (Google Analytics) to obtain anonymous statistics on how users navigate the site; by browsing our website, you accept our cookie policy.