What’s the difference between EMF and EMR?

Electromagnetism is usually described in a number of ways using terms such as electromagnetic field (EMF), electromagnetic radiation (EMR), or magnetic and electric fields.  These terms tend to get bandied around a bit with the result that their meanings become synonymous.  Certainly, EMF and EMR are used as though they were the same thing which is fine for most discussions although strictly speaking they are different.

To help explain this difference we need to also recognise that there are static and oscillating fields.  In simple terms, whenever there is a oscillating electrical field a magnetic field of similar frequency is induced, and where there is a vibrating magnetic field an associated electric field is induced. (This does not happen with static magnetic or electrical fields – although an object moving through such fields will have a similar effect).  Electromagnetic fields (EMFs) can be static (e.g., permanent magnetic) or they can be oscillating, sometimes at extremely high frequencies (e.g., x-rays, gamma rays).  Electromagnetic radiation (EMR) is essentially the result of an oscillating electromagnetic field (EMF).  When EMFs vibrate above a certain frequency, the energy contained in them can not return and is thrown off as radiation.  This is the reason why EMR is used to describe the effects of high-frequency radio (RF) and microwave sources.

EMFs can penetrate objects and living organisms to different extents depending on the frequency and power level as well as the  dielectric properties and the magnetic permeability of the subject.  These fields can then induce secondary fields and electric currents which can be disruptive. Magnetic fields are particularly penetrating and much more difficult to shield against than electrical fields.

EMRs can be subdivided into ionising and non-ionising radiation; where the distinction depends on the frequency, and hence energy, to be able to strip an electron off the host atom or molecule.  The distinction between ionising and non-ionising splits the electromagnetic spectrum in two, with ionising radiation occupying the high frequency end and the less energetic non-ionising radiation occupying the lower frequency end of the spectrum  Historically, EMR of the non-ionising type has generally been considered harmless because of its inability to ionise and therefore deemed incapable of doing any damage.  Extending this logic, the only caveat remaining or possibility that biologic damage might occur is only after an excessive amount of non-ionising radiation has been delivered such that the subject begins to heat up.  Determination of what constitutes a safe level based on tissue heating has been the focus of the current ICNIRP standard which was originally introduced to protect Navy radar operators from microwave radiation.  It is a standard that is in denial of the informational and electromagnetic component of living organisms and its importance to health and well-being.



   ELF         Mid-Range         RF&Microwave


The EM spectrum is described in terms of frequency and wavelength (frequency is in fact related to wavelength by the speed of light – see diagram above). Frequency is expressed as the number of times the wave cycles per second and given the variable name, Hertz (Hz), such that 1 cycle per second is equal to 1 Hz.

In general, for the current technologies in use today, the lowest frequencies (or longest wavelength) are referred to as Extremely Low Frequency (ELF). At the other end of the spectrum the higher frequencies (shorter wavelength) are referred to as Radio Frequency (RF) or Microwaves. They may also be classed as ionising radiation.  (Extremely high frequency (energy) electromagnetic events such as X-rays, gamma rays, high energy particles, nuclear radiation are not dealt here as this website’s focus is on non-ionising electromagnetic radiation).


Natural and Artificial Electromagnetic Fields

Electromagnetic radiation (EMR) occurs naturally on this planet, from the global Schumann cavity resonance and the geomagnetic field to the nerve impulses and guiding cellular communications within its living organisms.  All these EM fields and their oscillations produce a highly interconnected and balanced system for everything in the biosphere to exist in relative harmony with everything else.  This natural intricacy extends to a model of health and well-being. Over the last century or so, and particularly over the last decade, man-made EM sources and our technological advances have significantly altered this natural electromagnetic environment.The electromagnetic spectrum ranges from the earth’s natural magnetic field to the ionising radiation of gamma rays from cosmic sources, from static and low-frequency fields to high-frequency radiation. Man has swamped the natural EM background with all kinds of sources, some generating frequencies that were little or ever used throughout the planet’s long history to those that are so powerful they drown out the natural signals.The man-made contribution to the EM spectrum includes all kinds of electric motors and appliances, wireless systems for computer, radio and TV transmission, cellular phones and wireless networks and to those involving light such as infrared, visible and ultraviolet light. Even such things as streets lights in cities now prevent us from seeing the beauty of the stars in the night sky.



The term EMF is used for low frequency, alternating (AC) or direct current (DC), magnetic or electric fields. Most of the Earth’s frequency usage has been in the ELF range up to about 30 – 35 Hz.  This would include the Schumann cavity resonance which cycles at roughly 7.83 Hz and seems to influence all mammal life with its global low-level pulsing magnetic field.

These fields are usually associated with machinery, equipment and applications that require power and substantial amounts of current to run.  They do not oscillate at high frequencies and not particularly suitable for transmitting information long distances as in wireless telecommunications.

Alternating Fields

AC Magnetic Fields

Magnetic fields are created by alternating electrical current flowing in conductors. They are associated with electrical transmission, mains wiring in buildings, transformers, motors, appliances, and power supplies. They are low frequency typically running at 50Hz here in Europe.

High magnetic fields can pose significant EMF health risks. Elevated magnetic fields are often caused by incorrect wiring and improper gorunding, power lines, stray currents that can travel on water and gas lines. Magnetic fields are typically measured in milliGauss (mG) or microTelsa (uT) .

AC Electric Fields

AC electric fields are created by the alternating voltage present in the electrical system. Current flow is not necessary to create an electric field which means a device does not have to be on to create an electric field, that is, it can generate an electrical field when it is still plugged in but not turned on. Electric fields can usually easily be eliminated or shielded but measurement is generally more complicated because the body of the tester (being an electromagnetic entity) interacts with the field and ultimately influencing the resulting measurement. Electric fields are measured in Volts per meter (V/m).

Static Fields

Static fields can be created by direct current, permanent magnets, batteries and electrical build up (static electricity), etc..  Direct current power transmission systems have a constant flow of electric charge that does not change its polarity and the frequency component is absent.

DC Magnetic Fields

The earth’s magnetic field is a static (although it does change very slowly over time, i.e., days, months, years. Static DC magnetic fields are present in regular magnets. Concerns develop when steel components in buildings become magnetized leading to the creation of magnetic fields in structures. DC magnetic fields can induce electrical currents when moving within their fields.

DC Electric Fields

Electrostatic charge, which is by definition a ‘static’ or DC electric field, can be generated by rubbing two poorly conducting materials against each other, such as when the sole of a shoe rubs over an synthetic carpet and generates a charge build-up that subsequently discharges as a high-voltage low-current shock.


RF and Microwave Radiation

High frequencies allow for the effective propagation and transmission of power and information through the air, and are the basis for our wireless telecommunications and information systems. On top of this, a multitude of wave types and wave modulation techniques have been adopted, such as amplitude or frequency modulation, modulated and pulsed signals, time and code division multiplexing with new technologies constantly coming on line.

These high frequencies are used for AM and FM satellite radio, television, radar, cell towers, cell phones, cordless phones, Bluetooth, wireless computer and data transmission (WLAN, Wi-Fi, WiMAX) networks. The use of wireless technologies has exponentially increased over the last decade and has become a significant source of microwave radiation in buildings. Careless placement of wireless network installations in homes or offices can become a significant source of microwave radiation for occupants in the buildings.

The strength of the field is often expressed as Power density in microWatts per square meter (uW/m2).