I know reading about EMFs can be heavy going.
It took me a long long time scouring articles, books and websites to get clear on a lot of this.
To demystify things I’ve drawn up a list of definitions.
These aren’t textbook definitions.
The idea is to explain using terms you can easily understand.
Because the more you understand the more effectively you can deal with EMFs.
If there any definitions missing from this list let me know in the comment box at the bottom of the page and I’ll add them in!
An electrical current that changes strength and direction of flow with a certain regular cycle. For example, 60 Hertz 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. Also called an aerial.
Attenuation is the opposite of amplification. It means reduction in signal strength. For RF shielding products the attenuation is commonly expressed in decibels (dB) at a certain frequency because the attenuation changes according to the frequency.
The attenuation specification for a shielding material indicates how much radiation penetrates through the shield.
Bus or busbar
A bar with screw connections for either neutral or grounding conductors.
As far as electricity goes in the US this refers to the National Electrical Code (NEC), which is revised every three years.
Any material which passes electrical current. 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 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)
An electric current that flows in one direction only, as opposed to AC which flows back and forth.
Lines carrying power to neighborhoods (primary distribution) and to one or several buildings (secondary distribution).
Directional EMF Meter
A directional EMF meter can detect EMFs from a given direction as opposed to an omni-directional (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.
English term for ground.
A zone of potential difference between oppositely charged conductors or between conductors and ground. It’s measured in volts per meter or V/m. Electric field is a function of voltage and not of current.
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.
The electromagnetic spectrum or EMF spectrum is used to show the relationship between different types of EMFs according to their frequency and wavelength.
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.
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.
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.
A material which is a poor conductor of electric current.
A zone of energy which accompanies every electric current. Can be an AC or DC magnetic field (MF) – measured in milligauss.
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).
Or neutral conductor. The common term for a grounded conductor (GC), white in the US.
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.
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)
These 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.
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.
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.
Methods used for reducing EMF exposures.
An unintentional connection between hot and neutral conductors in a circuit or between two hots.
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 take measurements on the x, y and z axes, square these numbers then add them together and take the square root.
A large unit of measure for magnetic fields. One tesla (T) equals 10,000 gauss. One microtesla equals 10 milligauss.
A service that brings in all three phases from the power line plus the neutral. Common in commercial buildings.
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.