![LPDA-Antenna](https://upload.wikimedia.org/wikipedia/commons/a/ab/LPDA-Antenna.jpg)
Electromagnetic compatibility (EMC) is the ability of electrical equipment and systems to function acceptably in their
electromagnetic environment In telecommunication, the term electromagnetic environment (EME) has the following meanings:
#For a telecommunications system, the spatial distribution of electromagnetic fields surrounding a given site. The electromagnetic environment may be ex ...
, by limiting the unintentional generation, propagation and reception of electromagnetic energy which may cause unwanted effects such as
electromagnetic interference (EMI) or even physical damage in operational equipment.
The goal of EMC is the correct operation of different equipment in a common electromagnetic environment. It is also the name given to the associated branch of electrical engineering.
EMC pursues three main classes of issue. Emission is the generation of electromagnetic energy, whether deliberate or accidental, by some source and its release into the environment. EMC studies the unwanted emissions and the countermeasures which may be taken in order to reduce unwanted emissions. The second class, susceptibility, is the tendency of electrical equipment, referred to as the victim, to malfunction or break down in the presence of unwanted emissions, which are known as Radio frequency interference (RFI). Immunity is the opposite of susceptibility, being the ability of equipment to function correctly in the presence of RFI, with the discipline of "hardening" equipment being known equally as susceptibility or immunity. A third class studied is coupling, which is the mechanism by which emitted interference reaches the victim.
Interference mitigation and hence electromagnetic compatibility may be achieved by addressing any or all of these issues, i.e., quieting the sources of interference, inhibiting coupling paths and/or hardening the potential victims. In practice, many of the engineering techniques used, such as grounding and shielding, apply to all three issues.
Introduction
"Electromagnetic interference" (EMI) is defined as the "''degradation in the performance of equipment or transmission channel or a system caused by an electromagnetic disturbance''" ( 161-01-06) while "electromagnetic disturbance" is defined as "''an electromagnetic phenomenon that can degrade the performance of a device, equipment or system, or adversely affect living or inert matter'' (IEV 161-01-05). The terms "electromagnetic disturbance" and "electromagnetic interference" designate respectively the cause and the effect,
Electromagnetic compatibility (EMC) is an equipment ''characteristic'' or ''property'' and is defined as " ''the ability of equipment or a system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment'' " (IEV 161-01-07).
EMC ensures the correct operation, in the same electromagnetic environment, of different equipment items which use or respond to electromagnetic phenomena, and the avoidance of any interference. Another way of saying this is that EMC is the control of EMI so that unwanted effects are prevented.
Besides understanding the phenomena in themselves, EMC also addresses the countermeasures, such as control regimes, design and measurement, which should be taken in order to prevent emissions from causing any adverse effect.
Types of interference
Electromagnetic interference divides into several categories according to the source and signal characteristics.
The origin of interference, often called "noise" in this context, can be man-made (artificial) or natural.
Continuous interference
Continuous, or continuous wave (CW), interference arises where the source continuously emits at a given range of frequencies. This type is naturally divided into sub-categories according to frequency range, and as a whole is sometimes referred to as "DC to daylight".
* Audio frequency, from very low frequencies up to around 20 kHz. Frequencies up to 100 kHz may sometimes be classified as audio. Sources include:
** Mains hum from: power supply units, nearby power supply wiring, transmission lines and substations.
** Audio processing equipment, such as audio
power amplifier
An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspea ...
s and
loudspeaker
A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or " ...
s.
** Demodulation of a high-frequency carrier wave such as an
FM radio
FM broadcasting is a method of radio broadcasting using frequency modulation (FM). Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high fidelity sound over broadcast radio. FM broadcasting is cap ...
transmission.
* Radio frequency interference (RFI), from typically 20 kHz to an upper limit which constantly increases as technology pushes it higher. Sources include:
** Wireless and radio frequency transmissions
** Television and radio receivers
** Industrial, scientific and medical equipment (ISM)
** Digital processing circuitry such as
microcontroller
A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable i ...
s
**
Switched-mode power supplies
A switched-mode power supply (switching-mode power supply, switch-mode power supply, switched power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently.
Like ...
(SMPS)
* Broadband noise may be spread across parts of either or both frequency ranges, with no particular frequency accentuated. Sources include:
**
Solar activity
Solar phenomena are natural phenomena which occur within the atmosphere of the Sun. These phenomena take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots.
These phenomena are ...
** Continuously operating
spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conduct ...
s such as arc welders
**
CDMA
Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...
(spread-spectrum) mobile telephony
Pulse or transient interference
An
electromagnetic pulse
An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial, and can occur as an electromagnetic fie ...
(EMP), sometimes called a
transient disturbance, arises where the source emits a short-duration pulse of energy. The energy is usually broadband by nature, although it often excites a relatively narrow-band ''
damped sine wave'' response in the victim.
Sources divide broadly into isolated and repetitive events.
*Sources of isolated EMP events include:
**Switching action of electrical circuitry, including inductive loads such as relays, solenoids, or electric motors.
**
Power line
An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-p ...
surges/pulses
**
Electrostatic discharge
Electrostatic discharge (ESD) is a sudden and momentary flow of electric current between two electrically charged objects caused by contact, an short circuit, electrical short or dielectric breakdown. A buildup of static electricity can be caused ...
(ESD), as a result of two charged objects coming into close proximity or contact.
**
Lightning
Lightning is a naturally occurring electrostatic discharge during which two electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...
electromagnetic pulse
An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial, and can occur as an electromagnetic fie ...
(LEMP), although typically a short series of pulses.
**
Nuclear electromagnetic pulse
A nuclear electromagnetic pulse (nuclear EMP or NEMP) is a burst of electromagnetic radiation created by a nuclear explosion. The resulting rapidly varying electric and magnetic fields may couple with electrical and electronic systems to produce ...
(NEMP), as a result of a nuclear explosion. A variant of this is the high altitude EMP (HEMP) nuclear weapon, designed to create the pulse as its primary destructive effect.
**Non-nuclear electromagnetic pulse (NNEMP) weapons.
*Sources of repetitive EMP events, sometimes as regular ''
pulse
In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the nec ...
trains'', include:
**
Electric motor
An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
s
**Electrical ignition systems, such as in gasoline engines.
**Continual switching actions of digital electronic circuitry.
Coupling mechanisms
Some of the technical terms which are employed can be used with differing meanings. Some phenomena may be referred to by various different terms. These terms are used here in a widely accepted way, which is consistent with other articles in the encyclopedia.
The basic arrangement of
noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
emitter or source,
coupling
A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end mov ...
path and victim,
receptor
Receptor may refer to:
* Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse
*Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...
or sink is shown in the figure below. Source and victim are usually
electronic hardware
Electronic hardware consists of interconnected electronic components which perform analog or logic operations on received and locally stored information to produce as output or store resulting new information or to provide control for output actu ...
devices, though the source may be a natural phenomenon such as a
lightning strike
A lightning strike or lightning bolt is an electric discharge between the atmosphere and the ground. Most originate in a cumulonimbus cloud and terminate on the ground, called cloud-to-ground (CG) lightning. A less common type of strike, ground- ...
,
electrostatic discharge
Electrostatic discharge (ESD) is a sudden and momentary flow of electric current between two electrically charged objects caused by contact, an short circuit, electrical short or dielectric breakdown. A buildup of static electricity can be caused ...
(ESD) or, in
one famous case, the
Big Bang
The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
at the origin of the Universe.
![EMI coupling modes](https://upload.wikimedia.org/wikipedia/commons/0/00/EMI_coupling_modes.svg)
There are four basic coupling mechanisms:
conductive
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gener ...
,
capacitive
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of a c ...
,
magnetic
Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...
or inductive, and
radiative. Any coupling path can be broken down into one or more of these coupling mechanisms working together. For example the lower path in the diagram involves inductive, conductive and capacitive modes.
Conductive coupling
Conductive coupling
In electronics, direct coupling or DC coupling (also called conductive coupling and galvanic coupling) is the transfer of electrical energy by means of physical contact via a conductive medium, in contrast to inductive coupling and capacitive coup ...
occurs when the coupling path between the source and victim is formed by direct electrical contact with a conducting body, for example a transmission line, wire, cable,
PCB
PCB may refer to:
Science and technology
* Polychlorinated biphenyl, an organic chlorine compound, now recognized as an environmental toxin and classified as a persistent organic pollutant
* Printed circuit board, a board used in electronics
* ...
trace or metal enclosure.
Conducted noise is also characterised by the way it appears on different conductors:
* Common-mode coupling: noise appears in phase (in the same direction) on two conductors.
* Differential-mode coupling: noise appears out of phase (in opposite directions) on two conductors.
Inductive coupling
Inductive coupling occurs where the source and victim are separated by a short distance (typically less than a
wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
). Strictly, "Inductive coupling" can be of two kinds, electrical induction and magnetic induction. It is common to refer to electrical induction as ''capacitive coupling'', and to magnetic induction as ''inductive coupling''.
Capacitive coupling
Capacitive coupling
Capacitive coupling is the transfer of energy within an electrical network or between distant networks by means of displacement current between circuit(s) nodes, induced by the electric field. This coupling can have an intentional or accidental ...
occurs when a varying
electrical field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
exists between two adjacent conductors typically less than a wavelength apart, inducing a change in
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
on the receiving conductor.
Magnetic coupling
Inductive coupling or magnetic coupling occurs when a varying
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
exists between two parallel conductors typically less than a wavelength apart, inducing a change in
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
along the receiving conductor.
Radiative coupling
Radiative coupling or electromagnetic coupling occurs when source and victim are separated by a large distance, typically more than a wavelength. Source and victim act as radio antennas: the source emits or radiates an
electromagnetic wave
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
which propagates across the space in between and is picked up or received by the victim.
EMC control
The damaging effects of electromagnetic interference pose unacceptable risks in many areas of technology, and it is necessary to control such interference and reduce the risks to acceptable levels.
The control of electromagnetic interference (EMI) and assurance of EMC comprises a series of related disciplines:
* Characterising the threat.
* Setting standards for emission and susceptibility levels.
* Design for standards compliance.
* Testing for standards compliance.
The risk posed by the threat is usually statistical in nature, so much of the work in threat characterisation and standards setting is based on reducing the probability of disruptive EMI to an acceptable level, rather than its assured elimination.
For a complex or novel piece of equipment, this may require the production of a dedicated ''EMC control plan'' summarizing the application of the above and specifying additional documents required.
Characterising the threat
Characterisation of the problem requires understanding of:
* The interference source and signal.
* The coupling path to the victim.
* The nature of the victim both electrically and in terms of the significance of malfunction.
Laws and regulators
Regulatory and standards bodies
Several organizations, both national and international, work to promote international co-operation on standardization (
harmonization
In music, harmonization is the chordal accompaniment to a line or melody: "Using chords and melodies together, making harmony by stacking scale tones as triads".
A harmonized scale can be created by using each note of a musical scale as a root ...
), including publishing various EMC standards. Where possible, a standard developed by one organization may be adopted with little or no change by others. This helps for example to harmonize national standards across Europe.
International standards organizations include:
*
International Electrotechnical Commission
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
(IEC), which has several committees working full-time on EMC issues. These are:
** Technical Committee 77 (TC77), working on electromagnetic compatibility between equipment including networks.
**
(CISPR), or International Special Committee on Radio Interference.
** The Advisory Committee on Electromagnetic Compatibility (ACEC) co-ordinates the IEC's work on EMC between these committees.
*
International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
(ISO), which publishes standards for the automotive industry.
Among the main national organizations are:
* Europe:
**
Comité Européen de Normalisation
The European Committee for Standardization (CEN, french: Comité Européen de Normalisation) is a public standards organization whose mission is to foster the economy of the European Single Market and the wider European continent in global tr ...
(CEN) or European Committee for Standardization).
**
Comité Européen de Normalisation Electrotechniques (CENELEC) or European Committee for Electrotechnical Standardisation.
**
European Telecommunications Standards Institute
The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of Information and communications technology, information and communications. ETSI supports the developmen ...
(ETSI).
* United States:
** The
Federal Communications Commission
The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...
(FCC).
** The
Society of Automotive Engineers
SAE International, formerly named the Society of Automotive Engineers, is a United States-based, globally active professional association and standards developing organization for engineering professionals in various industries. SAE Internatio ...
(SAE).
** The
Radio Technical Commission for Aeronautics
RTCA, Inc. (formerly known as Radio Technical Commission for Aeronautics) is a United States non-profit organization that develops technical guidance for use by government regulatory authorities and by industry. It was founded in 1935 and was re-in ...
(RTCA); see
DO-160
DO-160, Environmental Conditions and Test Procedures for Airborne Equipment is a standard for the environmental testing of avionics hardware. It is published by the Radio Technical Commission for Aeronautics (RTCA) and supersedes DO-138.
Outline ...
* Britain: The
British Standards Institution
The British Standards Institution (BSI) is the national standards body of the United Kingdom. BSI produces technical standards on a wide range of products and services and also supplies certification and standards-related services to business ...
(BSI).
* Germany: The
(VDE) or Association for Electrical, Electronic and Information Technologies.
Laws
Compliance with national or international standards is usually laid down by laws passed by individual nations. Different nations can require compliance with different standards.
In
European law
European Union law is a system of rules operating within the member states of the European Union (EU). Since the founding of the European Coal and Steel Community following World War II, the EU has developed the aim to "promote peace, its valu ...
, EU directive 2014/30/EU (previously 2004/108/EC) on EMC defines the rules for the placing on the market/putting into service of electric/electronic equipment within the
European Union
The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
. The Directive applies to a vast range of equipment including electrical and electronic appliances, systems and installations. Manufacturers of
electric and electronic devices are advised to run EMC tests in order to comply with compulsory
CE-labeling. More are given in the
list of EMC directives
The following list outlines a number of electromagnetic compatibility (EMC) standards which are known at the time of writing to be either available or have been made available for public comment. These standards attempt to standardize product E ...
. Compliance with the applicable harmonised standards whose reference is listed in the OJEU under the EMC Directive gives presumption of conformity with the corresponding essential requirements of the EMC Directive.
In 2019, the USA adopted a program for the protection of critical infrastructure against an electromagnetic pulse, whether caused by a
geomagnetic storm
A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field.
The disturbance that d ...
or a high-altitude nuclear weapon.
EMC design
Electromagnetic noise is produced in the source due to rapid
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
and
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
changes, and spread via the coupling mechanisms described earlier.
Breaking a coupling path is equally effective at either the start or the end of the path, therefore many aspects of good EMC design practice apply equally to potential sources and to potential victims.
A design which easily couples energy to the outside world will equally easily couple energy in and will be susceptible. A single improvement will often reduce both emissions and susceptibility.
Grounding and shielding
Grounding and shielding aim to reduce emissions or divert EMI away from the victim by providing an alternative, low-impedance path. Techniques include:
* Grounding or earthing schemes such as ''star earthing'' for audio equipment or ''ground planes'' for RF. The scheme must also satisfy safety regulations.
*
Shielded cables, where the signal wires are surrounded by an outer conductive layer that is grounded at one or both ends.
* Shielded housings. A conductive metal housing will act as an interference shield. In order to access the interior, such a housing is typically made in sections (such as a box and lid); an RF gasket may be used at the joints to reduce the amount of interference that leaks through. RF gaskets come in various types. A plain metal gasket may be either braided wire or a flat strip slotted to create many springy "fingers". Where a waterproof seal is required, a flexible
elastomer
An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...
ic base may be impregnated with chopped metal fibers dispersed into the interior or long metal fibers covering the surface or both.
Other general measures
*
Decoupling or filtering at critical points such as cable entries and high-speed switches, using
RF chokes and/or
RC elements. A
line filter
A line filter is the kind of electronic filter that is placed between electronic equipment and a line external to it, to attenuate conducted radio frequencies -- RFI, also known as electromagnetic interference (EMI) -- between the line and the ...
implements these measures between a device and a line.
*
Transmission line
In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmis ...
techniques for cables and wiring, such as balanced differential signal and return paths, and impedance matching.
* Avoidance of antenna structures such as loops of circulating current, resonant mechanical structures, unbalanced cable impedances or poorly grounded shielding.
* Eliminating spurious rectifying junctions that can form between metal structures around and near transmitter installations. Such junctions in combination with unintentional antenna structures can radiate harmonics of the transmitter frequency.
Emissions suppression
![Aaronia Spectrum Analyzer Software](https://upload.wikimedia.org/wikipedia/commons/6/6e/Aaronia_Spectrum_Analyzer_Software.jpg)
Additional measures to reduce emissions include:
* Avoid unnecessary
switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
ing operations. Necessary switching should be done as slowly as is technically possible.
* Noisy circuits (e. g. with a lot of switching activity) should be physically separated from the rest of the design.
* High peaks at single frequencies can be avoided by using the
spread spectrum
In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal (e.g., an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency dom ...
method, in which different parts of the circuit emit at different frequencies.
*
Harmonic
A harmonic is a wave with a frequency that is a positive integer multiple of the ''fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', the ...
wave filters.
* Design for operation at lower signal levels, reducing the energy available for emission.
Susceptibility hardening
Additional measures to reduce susceptibility include:
* Fuses, trip switches and circuit breakers.
* Transient absorbers.
* Design for operation at higher signal levels, reducing the relative noise level in comparison.
* Error-correction techniques in digital circuitry. These may be implemented in hardware, software or a combination of both.
* Differential signaling or other common-mode noise techniques for signal routing
EMC testing
Testing is required to confirm that a particular device meets the required standards. It divides broadly into emissions testing and susceptibility testing.
Open-area test sites, or OATS, are the reference sites in most standards. They are especially useful for emissions testing of large equipment systems.
However RF testing of a physical prototype is most often carried out indoors, in a specialised EMC test chamber. Types of chamber include
anechoic
An anechoic chamber (''an-echoic'' meaning "non-reflective") is a room designed to stop reflections of either sound or electromagnetic waves. They are also often isolated from energy entering from their surroundings. This combination means t ...
,
reverberation
Reverberation (also known as reverb), in acoustics, is a persistence of sound, after a sound is produced. Reverberation is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is abso ...
and the
gigahertz transverse electromagnetic cell (GTEM cell).
Sometimes
computational electromagnetics
Computational electromagnetics (CEM), computational electrodynamics or electromagnetic modeling is the process of modeling the interaction of electromagnetic fields with physical objects and the environment.
It typically involves using computer ...
simulations are used to test virtual models.
Like all compliance testing, it is important that the test equipment, including the test chamber or site and any software used, be properly calibrated and maintained.
Typically, a given run of tests for a particular piece of equipment will require an ''EMC test plan'' and follow-up ''test report''. The full test program may require the production of several such documents.
Emissions testing
Emissions are typically measured for radiated field strength and where appropriate for conducted emissions along cables and wiring. Inductive (magnetic) and capacitive (electric) field strengths are near-field effects, and are only important if the device under test (DUT) is designed for location close to other electrical equipment.
For conducted emissions, typical transducers include the
LISN
A line impedance stabilization network (LISN) is a device used in conducted and radiated radio-frequency emission and susceptibility tests, as specified in various electromagnetic compatibility (EMC)/EMI test standards (e.g., by CISPR, Internat ...
(line impedance stabilisation network) or AMN (artificial mains network) and the RF
current clamp
In electrical and electronic engineering, a current clamp, also known as current probe, is an electrical device with jaws which open to allow clamping around an electrical conductor. This allows measurement of the current in a conductor without t ...
.
For radiated emission measurement, antennas are used as transducers. Typical antennas specified include
dipole
In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways:
*An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system i ...
,
biconical,
log-periodic, double ridged guide and conical log-spiral designs. Radiated emissions must be measured in all directions around the DUT.
Specialized EMI test receivers or EMI analysers are used for EMC compliance testing. These incorporate bandwidths and detectors as specified by international EMC standards. An EMI receiver may be based on a
spectrum analyser
A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal that most co ...
to measure the emission levels of the DUT across a wide band of frequencies (frequency domain), or on a tunable narrower-band device which is swept through the desired frequency range. EMI receivers along with specified transducers can often be used for both conducted and radiated emissions. Pre-selector filters may also be used to reduce the effect of strong out-of-band signals on the front-end of the receiver.
Some pulse emissions are more usefully characterized using an
oscilloscope
An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetiti ...
to capture the pulse waveform in the time domain.
Susceptibility testing
Radiated field susceptibility testing typically involves a high-powered source of RF or EM energy and a radiating antenna to direct the energy at the potential victim or device under test (DUT).
Conducted voltage and current susceptibility testing typically involves a high-powered signal generator, and a
current clamp
In electrical and electronic engineering, a current clamp, also known as current probe, is an electrical device with jaws which open to allow clamping around an electrical conductor. This allows measurement of the current in a conductor without t ...
or other type of
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
to inject the test signal.
Transient or EMP signals are used to test the immunity of the DUT against powerline disturbances including surges, lightning strikes and switching noise. In motor vehicles, similar tests are performed on battery and signal lines.
ISO 7637-3:2007 – Road vehicles – Electrical disturbances from conduction and coupling – Part 3: Electrical transient transmission by capacitive and inductive coupling via lines other than supply lines
Iso.org (2010-09-06). Retrieved on 2011-07-19. The transient pulse may be generated digitally and passed through a broadband pulse amplifier, or applied directly to the transducer from a specialised pulse generator.
Electrostatic discharge
Electrostatic discharge (ESD) is a sudden and momentary flow of electric current between two electrically charged objects caused by contact, an short circuit, electrical short or dielectric breakdown. A buildup of static electricity can be caused ...
testing is typically performed with a piezo spark generator called an "ESD pistol
An ESD simulator, also known as an ESD gun, is a handheld unit used to test the immunity of devices to electrostatic discharge (ESD). These simulators are used in special electromagnetic compatibility (EMC) laboratories. ESD pulses are fast, hig ...
". Higher energy pulses, such as lightning or nuclear EMP simulations, can require a large current clamp
In electrical and electronic engineering, a current clamp, also known as current probe, is an electrical device with jaws which open to allow clamping around an electrical conductor. This allows measurement of the current in a conductor without t ...
or a large antenna which completely surrounds the DUT. Some antennas are so large that they are located outdoors, and care must be taken not to cause an EMP hazard to the surrounding environment.
History
Origins
The earliest EMC issue was lightning
Lightning is a naturally occurring electrostatic discharge during which two electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...
strike (lightning electromagnetic pulse
An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial, and can occur as an electromagnetic fie ...
, or LEMP) on ships and buildings. Lightning rod
A lightning rod or lightning conductor (British English) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it will preferentially strike the rod and be conducte ...
s or lightning conductors began to appear in the mid-18th century. With the advent of widespread electricity generation
Electricity generation is the process of generating electric power from sources of primary energy. For electric utility, utilities in the electric power industry, it is the stage prior to its Electricity delivery, delivery (Electric power transmi ...
and power supply lines from the late 19th century on, problems also arose with equipment short-circuit
A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. ...
failure affecting the power supply, and with local fire and shock hazard when the power line was struck by lightning. Power stations were provided with output circuit breaker
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...
s. Buildings and appliances would soon be provided with input fuses
Fuse or FUSE may refer to:
Devices
* Fuse (electrical), a device used in electrical systems to protect against excessive current
** Fuse (automotive), a class of fuses for vehicles
* Fuse (hydraulic), a device used in hydraulic systems to protec ...
, and later in the 20th century miniature circuit breakers (MCB) would come into use.
Early twentieth century
It may be said that radio interference and its correction arose with the first spark-gap experiment of Marconi in the late 1800s. As radio communications developed in the first half of the 20th century, interference between broadcast
Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum ( radio waves), in a one-to-many model. Broadcasting began ...
radio signals began to occur and an international regulatory framework was set up to ensure interference-free communications.
Switching devices became commonplace through the middle of the 20th century, typically in petrol powered cars and motorcycles but also in domestic appliances such as thermostats and refrigerators. This caused transient interference with domestic radio and (after World War II) TV reception, and in due course laws were passed requiring the suppression of such interference sources.
ESD problems first arose with accidental electric spark
An electric spark is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures. Michael F ...
discharges in hazardous environments such as coal mines and when refuelling aircraft or motor cars. Safe working practices had to be developed.
Postwar period
After World War II the military became increasingly concerned with the effects of nuclear electromagnetic pulse (NEMP), lightning strike, and even high-powered radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
beams, on vehicle and mobile equipment of all kinds, and especially aircraft electrical systems.
When high RF emission levels from other sources became a potential problem (such as with the advent of microwave oven
A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce t ...
s), certain frequency bands were designated for Industrial, Scientific and Medical (ISM) use, allowing emission levels limited only by thermal safety standards. Later, the International Telecommunication Union adopted a Recommendation providing limits of radiation from ISM devices in order to protect radiocommunications. A variety of issues such as sideband and harmonic emissions, broadband sources, and the ever-increasing popularity of electrical switching devices and their victims, resulted in a steady development of standards and laws.
From the late 1970s, the popularity of modern digital circuitry rapidly grew. As the technology developed, with ever-faster switching speeds (increasing emissions) and lower circuit voltages (increasing susceptibility), EMC increasingly became a source of concern. Many more nations became aware of EMC as a growing problem and issued directives to the manufacturers of digital electronic equipment, which set out the essential manufacturer requirements before their equipment could be marketed or sold. Organizations in individual nations, across Europe and worldwide, were set up to maintain these directives and associated standards. In 1979, the American FCC
The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdictio ...
published a regulation that required the electromagnetic emissions of all "digital devices" to be below certain limits. This regulatory environment led to a sharp growth in the EMC industry supplying specialist devices and equipment, analysis and design software, and testing and certification services. Low-voltage digital circuits, especially CMOS transistors, became more susceptible to ESD damage as they were miniaturised and, despite the development of on-chip hardening techniques, a new ESD regulatory regime had to be developed.
Modern era
From the 1980s on the explosive growth in mobile communication
Mobile telephony is the provision of telephone services to phones which may move around freely rather than stay fixed in one location. Telephony is supposed to specifically point to a voice-only service or connection, though sometimes the li ...
s and broadcast media channels put huge pressure on the available airspace. Regulatory authorities began squeezing band allocations closer and closer together, relying on increasingly sophisticated EMC control methods, especially in the digital communications domain, to keep cross-channel interference to acceptable levels. Digital systems are inherently less susceptible than analogue systems, and also offer far easier ways (such as software) to implement highly sophisticated protection and error-correction
In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communica ...
measures.
In 1985, the USA released the ISM bands for low-power mobile digital communications, leading to the development of Wi-Fi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wave ...
and remotely-operated car door keys. This approach relies on the intermittent nature of ISM interference and use of sophisticated error-correction methods to ensure lossless reception during the quiet gaps between any bursts of interference.
See also
* Conducted electromagnetic interference
Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrost ...
* Crosstalk
In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, induc ...
* IEEE Electromagnetic Compatibility Society
The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...
* International Commission on Non-Ionizing Radiation Protection
The International Commission on Non-Ionizing Radiation Protection (ICNIRP) is an international commission specialized in non-ionizing radiation protection. The organization's activities include determining exposure limits for electromagnetic fiel ...
(ICNIRP)
* List of common EMC test standards
The following list outlines a number of electromagnetic compatibility (EMC) standards which are known at the time of writing to be either available or have been made available for public comment. These standards attempt to standardize product E ...
* Television interference
Television interference (TVI) is a particular case of electromagnetic interference which affects television reception. Many natural and man-made phenomena can disrupt the reception of television signals. These include naturally occurring and art ...
References
External links
Web sites
EMC-Directive
European Commission – Harmonised standards for EMC
Federal Communications Commission
IEEE/EMC Society
News and information on Electromagnetic Compatibility regulations
Radio Technical Commission for Aeronautics
Summary of EU standards
by equipment type
General introductions
What is EMC?
YouTube video.
Introduction to EMC
Basics in EMC/EMI and Powerquality
Specific topics
Analog, RF and EMC Considerations in Printed Wiring Board (PWB) Design
Application Note: Design for EMC Compliance
Design for EMC - Effects of Via Slots, Split Planes,Gaps and Return Paths on Clock Signal
EMC Design Fundamentals
EMC Design Guidelines
EMC engineering practices for panel builders
EMC Resources
(Clemson University)
Fundamentals of the Plane Electromagnetic Shield
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