Electromagnetic Fields (EMFs) Explained – Easy To Understand Definitions

Here are a list of easy to understand, not too technical electromagnetic field (EMF) definitions.

If there is a definition you are looking for which you can't find on this page, let me know in the comment box at the bottom of the page and I'll add it in!

electromagnetic field definitionsAlternating current

An electrical current that changes strength and direction of flow with a certain regular cycle. For example, 60 Hertz alternating current (AC) is an electrical current that changes its polarity (from positive to negative and back to positive; a complete cycle) sixty times per second.



A unit of measure for electric current. Amperes or amps are quantity. Thought of in terms of water, amps are like gallons or buckets (volts are the pressure – see below).



Amplitude is the measurement of the maximum of peak displacement compared to the zero rest level, that's to say its the height of the wave. The unit of amplitude varies with the kind of waves we are talking about. E.g. The amplitude of an electric field is measured in V/m.



An antenna is a conductor that can send and receive EMFs such as microwave, radio or satellite signals. A high-gain antenna increases signal strength, a low-gain antenna receives or transmits over a wide angle. This metal device is also called an aerial.



Attenuation is the opposite of amplification. It means reduction in signal strength by losing gradually flux intensity. For RF shielding products the attenuation is commonly expressed in decibels (dB) at a certain frequency because the attenuation changes according to the frequency.


Attenuation Specification

The attenuation specification for a shielding material indicates how much radiation penetrates through the shield.


Bus or busbar

It is a metallic bar or a strip, with screw connections for either neutral or grounding conductors. The busbar is used for local high current power distribution.



As far as electricity goes in the US this refers to the National Electrical Code (NEC), which is revised every three years. This is a safety practice adopted by the states and not a federal law.



Any material which passes electrical current in one or more directions. Metal is generally used as a conductor – other substances such as the earth or the human body can be good conductors which partly explains the health issues with metal fillings and EMFs.



Typically metal pipes for carrying electrical wiring though they can be made of PVC or other materials. They can act as grounding conductors for electrical circuits in some circumstances.



An electric current is a flow of electric charge through a power line or an electric wire. Like water flows through a pipe an electric current flows in a wire. Where currents flow magnetic fields are produced.


Direct current (DC)

Direct current is an electric current that flows in one direction only, as opposed to alternating current or AC which flows back and forth. Most countries in the world use alternating current.


Distribution lines

Lines carrying power to neighborhoods (primary distribution) and to one or several buildings (secondary distribution). To simplify it is the final stage before electricity gets to your house.


Directional EMF Meter

A directional EMF meter can detect EMFs from a given direction as opposed to an omnidirectional (or triaxial) meter which at any time gives the reading of the EMFs coming from all directions in a given position. It may be seen as an advantage for a RF meter to be directional because it allows you to determine the direction of the RF source.


Dirty Electricity

Dirty electricity is a form of electrical pollution commonly found on house wiring. Dirty electricity exposures have been linked to cancer and a long list of serious diseases – thanks to the numerous electrical devices we love.



It is the English term for ground. That is to say, when there is a physical connection with the earth. The regulations for earthing systems are very different between countries.


Electric field

Electric fields are produced around physical items. It is a zone of potential difference between oppositely charged conductors or between conductors and ground. It's measured in volts per meter (or V/m) and is a function of voltage, not of current.


Electromagnetic Fields

An electromagnetic field, also called an EMF, is a region of space where electric and magnetic forces interact. Often used to refer to the general phenomena associated with fields spreading out from conductors or antennas, depending on the frequency.


Electromagnetic spectrum

The electromagnetic spectrum or EMF spectrum is used to show the relationship between different types of EMFs according to their frequency and wavelength.


A term used to refer to the excessive density of electromagnetic fields, from both wired and wireless sources, in the environment. It is also called the “electromagnetic pollution”.



Extremely low frequencies are in the range 1-300 Hz though sometimes defined as being up to 3kHz. Your homes' electrical wiring (60Hz in US) is in this ELF range.



EMFs are expressed in terms of their frequency and wavelength. Frequency is how many complete waves go by per second. This rate per second is expressed in Hertz (Hz).



A unit used for measuring magnetic field strength (flux density). Milligauss (mG) is more commonly used for measuring health impacts. One gauss equals 1,000 milligauss. Tesla or microTesla is used more commonly in Europe. 1 µT (microtesla) = 10 mG (milligauss)



A device used to measure magnetic field strength, calibrated in Gauss.


Ground EMF logo


Used as a verb or noun. As a verb it means to connect in some way to either earth or to a conductor which serves in place of the earth. Sometimes used when the more accurate term would be “bond.” N.B. it is not the earth connection which protects a circuit from a “ground fault,” but a solid connection back to the transformer neutral. Not be confused with grounding or earthing, the practice of going barefoot and/or connecting with the healing effect of the earth.



Harmonics and transients are a form of “noise” or “distortion” which attach to the fundamental wave, thereby producing a distorted waveform. Commonly known as dirt electricity.



Used to measure the rate at which charge changes polarity of an AC electric current. One Hertz is one cycle per second.



As a noun it refers to the ungrounded circuit conductor carrying the voltage.


Ionizing Radiation

According to the World health Organization (WHO), ionizing radiation is “radiation with enough energy so that(…)it can remove tightly bound electrons from the orbit of an atom, causing the atom to become charged or ionized”. These unpaired electrons are otherwise termed ‘free radicals'. Therefore non-ionizing radiation is just the opposite, it's radiation that doesn't have enough energy to remove electrons from atoms. Nevertheless non-ionizing radiation is dangerous.



A material which is a poor conductor of electric current and has a higher resistivity.


Magnetic field

A zone of energy which accompanies every electric current. Can be an AC or DC magnetic field (MF) – measured in milligauss. A typical source of magnetic fields is faulty electrical wiring and power lines.



In the US the FCC (Federal Communications Commission) defines “microwaves” as a subcategory of RF radiation operating at frequencies ranging from about 1 GHz upward.



One-thousandth of a gauss (mG). It's the unit of measurement for magnetic fields most commonly used in North America.


National Electrical Code

The National Electrical Code (NEC) is a set of electrical code requirements that govern electrical installations for the safe installation of electrical wiring and equipment.



Or neutral conductor. The common term for a grounded conductor (GC), white in the US.


Non-ionizing radiation

Devices like cell phones, cordless phones, WiFi emit non-ionizing radiation. Ionizing radiation has the ability to break molecular bonds, non-ionizing radiation was once considered safe because it can't do this.



Usually refers to one of the voltage carrying conductors in a power line or in an entrance cable to a building.



The positioning of each phase of the circuit on a utility line with respect to the other phases so as to minimize EMFs through cancellation.


Power Line Frequency EMFs

Otherwise known as ‘extremely low frequency' (ELF) electromagnetic fields (see above). The frequencies used are typically in the 50 – 60 Hz range. These frequencies are what typically should be found on household wiring.



A term for energy which leaves its source and travels. Power frequencies as found in electrical wiring generate negligible radiation. Radio frequencies and above are true radiating sources.


Radio Frequency Radiation (RF)

Radio frequency radiation are high frequency EMFs in the range 10 MHz-300 GHz. This category of EMFs is transferred through the air; the term “wireless” is often used. They relate essentially to telecommunication devices like cell phones, WiFi etc. Click here for a more detailed explanation of radio frequency radiation.



The property of a material to resist the flow of electrical current. Current flowing through resistance always results in dissipation of energy usually in the form of heat.


Service Drop

The overhead which brings power to a residence or business from the distribution line. It usually attaches to the eave of the building if overhead.



Shielding is the word used to describe all the various means which are used to protect from electromagnetic field exposures. Typically this will involve placing a barrier between yourself and the source of an EMF. The effectiveness of shielding is called ‘shielding performance'.


Short circuit

An unintentional connection between hot and neutral conductors in a circuit or between two hots.


Switched Mode Power Supply (SMPS)

A device used to convert electrical power and commonly found in many modern electrical devices that work at low voltage including smart meters, DECT phone chargers, computers etc. SMPS converts voltage and current (AC to DC) by constantly switching the source on and off to supply the needed voltage at the output. This switching can create dirty electricity. The alternative, linear mode power supply avoids this problem by offering a constant voltage but is less energy efficient and more expensive.


Stray Voltage

A misnomer, neutral current does not stray, it follows all available paths to complete the circuit back to the transformer or substation.


Tri-axial EMF Meter

A tri-axial EMF meter is a meter which gives a reading based on the 3 axes (X,Y and Z). To obtain the equivalent with a single axis meter, in any given location typically means you would have to take measurements on the x, y and z axes, square these numbers then add them together and take the square root. One of the best known Tri-axial EMF meters is the Trifield meter.



A large unit of measure for magnetic fields. One tesla (T) equals 10,000 gauss. One microtesla equals 10 milligauss.


Three-Phase Service

A service that brings in all three phases from the power line plus the neutral. Common in commercial buildings.


Two-Phase Service

Service that brings in two of the three phases from the power line plus a neutral. This type of service always produces significant neutral current since the two phases never balance.


Very Low Frequency (VLF)

EMFs in the frequency range of 3 kHz to 30 kHz.



Used to measure electrical potential. Its the electrical force which propels current in a conductor. The usual comparison is with water. A volt is the pressure, like psi in water, but applied to electrons.


Volts per meter

Electric fields are usually measured in volts per meter (V/M).



The distance between waves. As frequency increases, wavelength decreases, and vice versa. At 60 Hz the wavelength is approximately 3,100 miles. At radio frequency ranges the wavelength is closer to thirty or forty feet.


If you're looking for more developed definitions I recommend you read Tracing EMFs in Building Wiring and Grounding by Karl Riley, which served as my reference guide in preparing the above.





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  • Lucy said,

    Hi Lloyd,

    First of all, thank you for all the information that you freely supply on this site. There is so much useful information on here and I have recommended it to a number of friends concerned with EMF exposure.

    My question is related to the new iMAC computer. I’m a professional graphic designer which unfortunately means I’m on the computer a lot. I’m about to purchase a new desktop computer (iMAC) but I’m wondering if there are certain brands that have better EMF ratings than others.. Is this something you’re aware of? Also, would you say that the bigger the computer the higher exposure to EMFs?

    Many thanks

  • Lloyd said,

    Hi Lucy
    At the moment suppliers are not required to disclose EMF information on computers so the only way you can obtain this information is to measure with an EMF meter. Distance is important…its an effective way of reducing EMF exposures….so whatever enables you to put more distance between the computer components and where you sit is a good thing….the particularity of the iMac is that all the electronic components of the computer are in the screen housing….which means you have to have it at 3/4 feet maximum to be able to see it….for this reason a computer which enables you to set the CPU further away is safer. Bigger does not necessarily mean more EMFs…there’s no rule of thumb here.

  • Lloyd Burrell said,

    Hi Lucy
    Thanks a lot for your donation! Appreciated. Thanks.

  • Marina said,

    Dear Lloyd,

    Also, thank you so much for this and all the information you give us so willingly.

    I am living in a house with electric heat and a digital meter and I was getting surges up to and over 500 on a Stetzerizr Microsurge Meter. I used absorbers to keep the counts down but I don’t have enough absorbers.

    Right now the outlets that have no absorbers are measuring over 1900. In the past week I have gotten extremely ill, I can hardly see, and my gut and head feels like it will explode and I am extremely hot inside. I tested the outlets and I cringed to see readings over 1900 when it should probably not be over 15 for me with 15 heavy metals in me, including mercury.

    A Power employee came and poo pood my meter and the absorbers and had never heard of Graham Stetzer so he will be back on Monday with his meter which is the only meter he trusts. I told him that surges this high go on for hours but at 5:00 am this morning they were all low.

    I need a safe place to live but I am so sick and my adrenals are so low, I’m having a hard time getting my head to think straight.

    Thank you again. I have to get another meter that does not have to be plugged in and more absorbers.

    Life is just too, too complicated!

    Again, thank you!


  • Lloyd said,

    Hi Marina
    GS filters are only feasible up to a point. Given your readings you might want to consider installing a line conditioner, which is a more heavy duty solution. See http://www.solahevidutysales.com/mcr_hardwired_power_line_conditioner.htm Send them an email, see what they suggest.

  • Lloyd said,

    Hi Betsy
    The options are either you move house or you continue trying to clean up your electrical supply. If you take the second option, make sure you have eliminated everything in your own home that could be causing this problem, see https://www.electricsense.com/1825/dirty-electricity-gs-filter/….then try installing more filters, the manufacturers recommend up to 20. You should get at least a 20% reduction in GS units with each new filter so this will tell whats achievable with the filters. I know the power company employee was ignorant on the issue but you need to send the head office a registered letter. If the power coming into your home already has these high levels of DE they must deal with this – despite what the power company employee said, they are well aware of the issue and have been using industrial filters for decades.

  • Betsy said,

    I just spoke with the distributor for the sola/hd company that you referenced for the hardwired power line conditioners. They referred me to the manufacturer for information. I spoke with a person at the company that makes these products. Basically, he explained to me that the hardwired power conditioners can not be used for general home use if they are going to be connected to anything that has inductive loads like a refrigerator or where there is an initial larger current draw. He said it would cut off the power. He did suggest using the portable power conditioners for things like electronics in a home office or a home theater/tv. I may have not used the correct terms but I think this is the basic information. Do you have any additional comments on this.
    Started my journey after getting sick from a Chicago water smart meter. Since then the gas company has added another one, and now ComEd is on the move to install the electric meters in Chicago. Never in my life did I think something like this would be happening to the worlds population!

  • Linda said,

    Hi Lloyd,
    we just purchased a Trifield 100XE meter. Wow! the scariest was the electrical. We have ceiling cable heat. What are the dangers of this type? The heat is not even on and it went off the meter for electrical,but no magnetic. Short of selling our paid for home (we are 65 and 70)is there a solution? My husband laughed and said maybe we should be wearing tinfoil hats!

  • Lloyd said,

    Hi Linda
    Electric fields are present in a cable when a device is plugged in, even if the device is not switched on and in use – this is why you are getting high readings from your ceiling cable – these EMFs are dangerous. There are 2 solutions 1. shield, most materials shield electric fields or 2. switch off the circuit breaker, so go to your electrical box and cut the power to ceiling cable. If you do decide to shield you need an EMF meter to test before and after shielding.

  • Bill said,

    Is it dangerous to have an antenna for digital TV on the roof of my home. I wondered if it is just another way to pick up harmful EMF radiation. Thanks Bill

  • View All Comments

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