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EMF stands for Electromagnetic Field. In basic terms, EMF is present where ever electricity occurs.
EMF occurs both naturally and from man-made objects. For example, the Earth's magnetic field is produced by electric currents circulating in our planet's core. Man-made EMFs are created by things as diverse as electrical power systems and kitchen appliances, e.g. toasters.
EMF can be viewed as the combination of an electric field and a magnetic field. It is produced by moving electrical charges, and it affects the behavior of charged objects in the vicinity of the field. The electric field is produced by stationary charges, and the magnetic field by moving charges (currents). Therefore two are often described as the sources of the field.
Electromagnetic Radiation has been around since the birth of the universe; sunlight is its most familiar form. Electric and magnetic fields are part of the spectrum of electromagnetic radiation which extends from static electric and magnetic fields, through radio frequency and infrared radiation, to X-rays.
Electromagnetic Spectrum: wavelength and frequency
What are Electromagnetic Fields?
Definitions and Sources
Electric and Magnetic Field
Natural Sources
Electromagnetic fields are present everywhere in our environment but are invisible to the human eye. They have always existed. In fact, we are completely surrounded by natural EMF.
Sunlight is the most obvious example of an EMF. This field (in the form of light and heat) provides the energy for most life on our planet.
The earth itself produces an EMF from deep within its core. This field gives rise to the north and south poles, which allow for navigation by compass.
Our body also creates an EMF. This is generated by the electrical signals that constantly flash through our nervous system.
Man-made Sources
Besides natural sources, EMFs are also generated by artificial objects. Anything with an electrical current will produce an EMF. This includes hair dryers, televisions, car batteries and electricity power lines. X-rays are employed to diagnose a broken limb after a sport accident. The electricity that comes out of every power socket has associated low frequency electromagnetic fields. And various kinds of higher frequency radio waves are used to transmit information – whether via TV antennas, radio stations or mobile phone base stations.
Mobile phone is one of the man-made EMF sources
Differences between Electric and Magnetic Fields
There are some important difference between electric and magnetic fields.
For example, electric fields can be blocked very easily by buildings, hedges, fences, trees, etc. As a result, very little energy from any electric fields outside a house (e.g. from a power line) can penetrate inside it.
By contrast, magnetic fields are much harder to screen and not generally screened by buildings.
Another difference is that electric fields are created whenever an appliance (such as a radio or TV) is plugged in. The appliance does not have to be turned 'on' in order to produce the electric field. The field is created because a voltage is present.
However, magnetic fields are only produced when an appliance is turned on and electric current is flowing.
Electromagnetism, your bicycle and EMFs
Electric and magnetic fields are very tightly linked. In fact, they are just 2 aspects of a single force called electromagnetism.
Electromagnetism is what allows us to create electricity from a magnet, or to create a magnet from electricity.
When you pedal a bicycle, it causes a magnet to spin very quickly inside a coil of tightly wrapped wire. The spinning magnetic field causes the electrons in the wire to move. This creates electricity, which in turn lights the lamp. The same electrical current also causes an electric field to be generated.
The opposite is also true.
Spin a coil of tightly wrapped wire carrying an electrical current around a piece of iron, and it will be magnetised. It also causes a magnetic field to be created.
In both instances, an EMF has been generated by the dynamo. This EMF surrounds and penetrates your body.
The Basics of Wavelength and Frequency
What makes the various forms of electromagnetic fields so different?
One can imagine electromagnetic waves as series of very regular waves that travel at an enormous speed, the speed of light. The frequency simply describes the number of oscillations or cycles per second, while the term wavelength describes the distance between one wave and the next. Hence wavelength and frequency are inseparably intertwined: the higher the frequency the shorter the wavelength.
A simple analogy should help to illustrate the concept: Tie a long rope to a door handle and keep hold of the free end. Moving it up and then down slowly will generate a single big wave; more rapid motion will generate a whole series of small waves. The length of the rope remains constant, therefore, the more waves you generate (higher frequency) the smaller will be the distance between them (shorter wavelength).
Non-Ionizing EMF vs. Ionizing Radiation
Some electromagnetic waves carry so much energy per quantum that they have the ability to break bonds between molecules. In the electromagnetic spectrum, Gamma Rays given off by radioactive materials, Cosmic Rays and X-Rays carry this property and are called 'Ionizing Radiation'.
Fields whose quanta are insufficient to break molecular bonds are called 'Non-Ionizing Radiation'. Man-made sources of EMFs that form a major part of industrialized life - electricity, microwaves and radio frequency fields – are found at the relatively long wavelength and low frequency end of the electromagnetic spectrum and their quanta are unable to break chemical bonds.
EMFs at Low Frequencies
Electric fields exist whenever a positive or negative electrical charge is present. They exert forces on other charges within the field. The strength of the electric field is measured in Volts per Meter (V/m). Any electrical wire that is charged will produce an associated electric field. This field exists even when there is no current flowing. The higher the voltage, the stronger the electric field at a given distance from the wire.
Electric fields are strongest close to a charge or charged conductor, and their strength rapidly diminishes with distance from it.
Conductors such as metal shield them very effectively. Other materials, such as building materials and trees, provide some shielding capability. Therefore, the electric fields from power lines outside the house are reduced by walls, buildings, and trees. When power lines are buried in the ground, the electric fields at the surface are hardly detectable.
Magnetic fields arise from the motion of electrical charges. The strength of the magnetic field is measured in Amperes per Meter (A/m); more commonly in EMF research, scientists specify a related quantity, the Flux Density (in microtesla, µT) instead. In contrast to electric fields, a magnetic field is only produced once a device is switched on and current flows. The higher the current, the greater the strength of the magnetic field.
Like electric fields, magnetic fields are strongest close to their origin and rapidly decrease at greater distances from the source. Magnetic fields are not blocked by common materials such as the walls of buildings.
|
Electric Fields |
Magnetic Fields |
|
Arise from voltage. |
Arise from current flows. |
| Volts per Meter (V/m) |
Amperes per Meter (A/m). Microtesta (µT) / millitesla (mT) as flux density. |
| An electric field is present even when a device is switched off. | Magnetic field exists only when a device is switched on and current flows. |
|
Field strength decreases with distance from source. |
Field strength decreases with distance from source. |
|
Most building materials shield electric fields to some extent. |
Magnetic fields are not attenuated by most materials. |
What are the Main Sources of Low, Intermediate and High Frequency fields?
The effects of EMFs on the human body depend not only on their field level but on their frequency and energy.
ELF: Electricity power supply and all appliances using electricity.
IF: Computer screens, anti-theft devices and security systems.
RF: Radio, television, radar, cellular telephone antennas and microwave ovens.
These fields induce currents within the human body, which if sufficient can produce a range of effects such as heating and electrical shock, depending on their amplitude and frequency range. However, to produce such effects, the fields outside the body would have to be very strong, far stronger than present in normal environments.
EMFs at High Frequencies
Mobile telephones, television and radio transmitters and radar produce RF fields. These fields are used to transmit information over long distances and form the basis of telecommunications as well as radio and television broadcasting all over the world. Microwaves are RF fields at high frequencies in the GHz range. In microwaves ovens, we use them to quickly heat food.
At radio frequencies, electric and magnetic fields are closely interrelated and we typically measure their levels as Power Densities in Watts per Square Meter (W/m2).
Mobile phone is one type of EMF at High Frequencies
Measuring EMFs
Even though a bicycle dynamo may be very close to us, the risk posed by its EMF is insignificant. This is because the strength of the fields is tiny.To measure the intensity of an EMF, 2 factors are needed to be evaluated:
1. How far are you from the object that creates it?
2. How strong is the field that surrounds you?
The Importance of Distance
Measuring EMF Strength
1. Electric Field Strength
This field is measured using "Volts per Meter" or V/m.
2. Magnetic Field Strength
This field is measured using a scientific quantity called "Magnetic Flux Density", expressed in the unit "Tesla" or T.
3. Frequency
The force of electromagnetism is carried in "waves" at the speed of light. These waves have "peaks" and "troughs" - just like a water wave.
In a "high frequency" wave all the peaks and troughs are packed closely together. As a result, they carry lots of energy.
In the "low frequency" wave, the peaks and troughs are spaced out. As a result, they are low in energy.
Basically, the higher the frequency of an electromagnetic wave, the more powerful the resulting electric or magnetic field becomes.
Frequency is measured in a unit called Hertz (Hz).
EMF Risks, Strength and Distance
The frequency of the Electric and Magnetic Fields (EMFs) created by the electricity system in Malaysia is 50 Hz, i.e. 50 waves per second.
In comparison with other types of electromagnetic waves, this is extremely low. Since the frequency of the electromagnetic waves is low, the strength of the resulting EMF is also low.
The frequency of the EMFs created by the cellular base stations in Malaysia is in 900 MHz, 1800 MHz and 2100 MHz band, i.e. 900 million, 1.8 billion and 2.1 billion waves per second.
This is illustrated in the diagram below.
Research into EMFs
Millions have now been spent on research into EMFs and human health. A debate about the possible harmful effects of EMF on humans and animals has continued since the 1970s. Despite extensive worldwide authoritative research, no conclusive evidence has been found that such fields are harmful, at levels to which we can expect to be exposed caused by power systems, electric / wireless appliances, cellular phones and base stations.
This view is shared by many respected international organizations, including the World Health Organization. The Department of Communications, Marine and Natural Resources and the EU also agree that - based on the balance of evidence - EMFs do not have any adverse effect.
Both of these bodies recommend compliance to the International Guideline Exposure Limits set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). These guidelines are designed to limit human exposure to electromagnetic fields.
The guidelines have become the international standard for EMF safety. The ICNIRP guidelines are reviewed on a regular basis and were endorsed by the World Health Organization's most recent EMF report in 2007.
We do not want to tell you what to think about EMFs. We invite you to reach your own conclusions. You can explore these details and decide for yourself if EMFs are a problem.
The WHO International EMF Project has compiled many fact sheets regarding electromagnetic fields and public health.
Refer to the following link for a few of their more recent sheets on various topics:
WHO EMF Publications and Information Resources
