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EMC and COMPLIANCE ENGINEERING
1 – INTRODUCTION -OVERVIEW
1.1 EMC DEFINITION
The acronym EMC represents Electro Magnetic Compatibility
Electromagnetic Compatibility (EMC) is the ability of electronic equipment to operate or function
without degradation or error and NOT be an interference source in its intended operating or EM
environment
1.2 ELECTROMAGNETIC SPECTRUM

FIGURE 1.1

The range of frequency and wavelength of electromagnetic waves is called the electromagnetic
spectrum. Different parts of the spectrum have different names and different uses, as shown in
Figure 1.1.
f
The frequency range for conducted emissions (150 kHz – 3 MHz) shown in Figure 1.1 is based on
current standards for compliance. The radiated emissions range (3 MHz – 1 GHz) is for the
current standard frequency range, but this may rise to 3 GHz – the frequency used by 3G mobile
phones. Note: radiated emissions exist beyond the range shown! The medical equipment standard
is more stringent and increases to 18 GHZ for radiated emissions and reduces to 9 kHz for
conducted emissions.
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1.3 ELECTROMAGNETIC WAVE
FIGURE 1.2
The term electromagnetic implies EM Field Theory as shown in the electromagnetic wave
representation of Figure 1.2.
The Electric Field (E V/m) component of the EM wave is a vector quantity that represents the
force created by uneven charge distribution and results from voltage fluctuations.
The Magnetic Field Intensity (H A/m) component of the EM wave is a vector quantity that
represents the magnetizing force created by moving charges.
The Magnetic Flux Density (  ) is the direct result of circulating current and includes the effect
of the medium (    H ) .
An Electromagnetic Field is created whenever charges (electrons) are accelerated.
All electrically charged particles are surrounded by electric fields and when the charges are in
motion magnetic fields are produced. When the velocity of the charged particle changes an EM
field is produced.
Historically electromagnetic fields were first discovered in the 19th century when physicists
noticed that electric arcs (sparks) could be reproduced at a distance with no connecting wires in
between.
All electromagnetic waves travel through the same medium at the same speed but at different
frequencies and wavelengths. In vacuum or free space it is the speed of light
v  f   2.9979 108 m / s
The velocity depends on the material permittivity (  ) that relates to the material interaction with
the electric field, and permeability () that expresses the material interaction with the magnetic
field.
1
v

In a plane wave, as shown in Figure 1.2, the electric field is perpendicular to the magnetic field
and the direction of propagation is perpendicular to both the electric and the magnetic fields.
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1.4 NEAR FIELDS and FAR FIELDS
1.4.i NEAR FIELDS
Fields in the region close to the source are called Near Fields and the E and H Fields are not
necessarily perpendicular.
The strength of the Near Fields often varies rapidly with space, and is dependent on the distance r
from the source
field strength 
1
r
1
,
r
2
,
1
r
3
r 
...

2
Objects placed close to near sources may strongly affect the nature of the Near Fields.
A measurement probe close to a source may change the nature of the Field.
1.4.ii FAR FIELDS
At larger distances from the source the Field strength is proportional to the reciprocal of the
distance ‘r’, the higher-order ‘r’ terms being negligible and the fields are termed Far Fields.
r 

2
Far Fields are approximately spherical waves and can be approximated in a limited region of
space by plane waves.
Making measurements is usually easier in Far Fields than in Near Fields.
v  f   2.9979 108 m / s
v  f   2.9979 108 m / s
E
E
H
I
H
I
~V
~
V
FIGURE 1.3
FIGURE 1.4
In the Near Field the wave impedance depends mainly on the source type (electric or magnetic).
A high voltage low current high impedance mainly electric field source is represented by the
monopole shown in Figure 1.3.
A low voltage high current low impedance mainly magnetic field is represented by the loop
shown in Figure 1.4.
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1.5 WAVE IMPEDANCE
The ratio of the electric field strength to the magnetic field strength is termed the characteristic
impedance (Z) and depends on the permittivity and permeability of the material the wave is
travelling through.
Z
0
4  10  7

 377 
0
8.85  10 12
Z0 
E
H
In free space the characteristic impedance Zo is 377 
H
Z
1
H
r2
1
E
r3
1
r
E
1
r
Zo = 377 
1
H
r
1
H
r
3
E
1
E
r
boundary
1
r2
r 

2
FIGURE 1.5
In basic terms the difference between Near Fields and Far Fields is the variation in field strength
with distance from the source, as shown in Figure 1.5.
The transition at the boundary between the near-field and far-field regions is not sharp because the
near fields gradually become less important as the distance from the source increases.
1.6 ENGINEER TYPE CONSIDERATIONS
Electrical and Electronic Engineers develop circuits and systems that involve both currents and
voltages and are therefore EM systems.
The objective is to function in the time and frequency domain with the signal confined to the
conductor. Signals will be confined to the conductor if the signal wavelengths are significantly
less than the physical length of the conductor, or twisted pairs or co-axial type cables are
involved. If not confined to the conductor then we need to use other means to confine it, as that
conductor has become an antenna and this leads to Electromagnetic Interference (EMI)
Communication Engineers however tend to function in space and are more concerned with the
conductors acting as antennae.
EMC Engineers are primarily interested in organising / managing the electromagnetic fields in
space.
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1.6 MAXWELL’s EQUATIONS
EM Field Theory brings to mind the Scottish physicist / mathematician James Clerk Maxwell
(1831-1879), Figure 1.6, and the 4 equations that unified magnetic and electrical forces.
FIGURE 1.6
Maxwell’s Theory tends to suggest that the EET422 course will be highly mathematical. EET422
is introductory (applied) EMC, hence the mathematical approach for specialist EMC Engineers is
NOT involved.
Lack of Mathematical rigour should not diminish the importance of the subject as Maxwell’s
work was based on Michael Faraday’s ‘lines of force’ experimental observations.
Maxwell discovered that electric and magnetic fields were intrinsically related with or without a
conductive path for electrons. In simple terms and as shown in Figure 1
‘a changing electric field produces a perpendicular magnetic field'
'a changing magnetic field produces a perpendicular electric field'
Maxwell also predicted that electromagnetism would be propagated through space at a finite rate,
an idea that subsequently led to the discovery of radio waves.
1.7 ELECTROMAGNETIC INTERFERENCE
EMI is often referred to as RFI (radio frequency interference), but the latter is generally only
related to interference created by radio transmitters or disturbances that effect radio receivers.
Electromagnetic Interference (EMI) involves any unwanted emission (signal) from a device or
system that adversely affects (interferes with) the normal operation of another device or system.
EMI is therefore not restricted to only electromagnetic radiation; it also includes surges, line
harmonic currents (power factor), supply voltage variations and electrostatic discharge (ESD)
EMI SOURCES
INTRINSIC
NATURAL
components
atmospheric
solar
cosmic
ESD
MAN MADE
WANTED
transmitters
radio & TV
mobiles
UNWANTED
SMPS
light dimmers
fluorescents
FIGURE 1.7
Examples of EMI sources are shown in Figure 1.7.
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1.8 EMI EFFECTS
Numerous EMI effects are observed including
• RF Reception
• annoying noise
• loss of sensitivity
• data upset
• data link disruption
• control signal errors
• sense line feedback errors
• analogue signal errors
• signal-to-noise degradation
• jamming
• circuit malfunction
• measurement errors
• power variations
• power levels outside range
• equipment damage
• physical damage
1.9 EMI ‘SITUATION’
FIGURE 3
FIGURE 1.8
3 coincident elements are required to create an EMI ‘situation’, as shown in Figure 1.8
 a disturbance source (equipment that generates noise) normally referred to as the culprit
 a sensitive receptor (equipment susceptible to noise) normally referred to as the victim
 a coupling mechanism normally referred to as the propagation medium
The source must be emitting at a time when the receptor is operating, on a frequency at which the
receptor will be affected and the interference level needs to be noticeable.
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1.10 DISTURBANCE ‘TYPE’ and PATH
B
C
CULPRIT
OURCE
VICTIM
A
D
FIGURE 1.9
The coupling path defines 2 types of disturbance or EMI.
Conducted Interference is when the disturbance propagates via low impedance electrically
conductive paths such as conductors (wires and PCB traces) as shown by ‘A’ in Figure 1.9.
Radiated Interference is when the disturbance is airborne and coupled through electric fields,
magnetic fields, and/or electro-magnetic wave propagation as shown by ‘B, C and D’ in Figure
1.9.
As a rule of thumb higher frequency disturbances are radiated interference, whereas the lower
frequency disturbances are conducted interference.
Conducted and Radiated Interference each has 2 sub categories (to be discussed later)
Differential (Normal) Mode noise
Common Mode noise
Interference may merely be an inconvenience - TV signal reception, but in some cases it can have
serious and life threatening effects.
1.11 EMISSIONS, SUSCEPTIBILITY and IMMUNITY
radiated
emissions
radiated
susceptibility
SUSCEPTIBLE
RECEPTOR
(VICTIM)
NOISE SOURCE
(CULPRIT)
conducted
emissions
conducted
susceptibility
FIGURE 1.10
Susceptibility is an indicator of the level to which a device or system will be affected by
interference, whereas Immunity reflects the ability to be unaffected by interference. Radiated
Susceptibility and Immunity together with radiated and conducted susceptibility needs to be
considered.
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1.12 EMI COUPLING
Electric and magnetic fields are relatively short-ranged at low frequencies and are concentrated in
the vicinity of the source which could be current carrying conductor wires or pcb traces.
1.12.i ELECTRIC FIELD COUPLING
E
FIGURE 1.11
FIGURE 1.12
Electric fields are proportional to voltage hence unless large voltages are involved low frequency
capacitive coupling over short distances is the EMI problem.
An electric field interference between a power cable and signal circuit is shown in Figure 1.11
with the resulting displacement currents modelled by stray capacitances, as shown in Figure 1.12.
The effect of the capacitive coupled interference increases when
 the distance between the circuits reduces
 the voltage difference between the two circuits increases
 the low frequency power circuit current contains high frequency components due to
supplying non-linear loads
 fast switching currents are present in the power cable
Example:
Power supply circuit cables and a nearby parallel local area network parallel over 10 m in a cable
tray. Sinusoidal current in the power cable from a 230 V, 50 Hz supply may produce a 10V
disturbing signal in the data cable. If the power cable current has high frequency components
generated by non-linear loads the disturbing signal in the data cable could rise to more than 90 V
which may lead to poor performance or malfunctions of LANs.
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1.12.ii MAGNETIC FIELD COUPLING
H
M
FIGURE 1.13
FIGURE 1.14
Magnetic fields are proportional to current and low frequency inductive coupling over short
distances is the EMI problem.
A time varying current in the power cable generates a magnetic field, as shown in Figure 1.13,
that induces a ‘disturbance’ voltage in the nearby signal circuit that is modelled by the mutual
inductance of the coupled circuits, as shown in Figure 1.12.
The effect of the inductive coupled interference increases when
 the distance between the circuits reduces and cover a large area
 the current creating the disturbance increases
 the frequency of the disturbing signal increases
 fast switching currents are present in the power cable
Example:
A 10 A 50 Hz power line current can generate magnetic fields of the order of 1.5 µT that will
‘disturb’ cathode ray tube-type computer terminals at a distance of 1.3 m by inducing screen
flicker. The effect is more pronounced when high frequency current components exist.
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1.12.iii IMPEDANCE COUPLING
VC
ZC
FIGURE 1.15
FIGURE 1.16
Impedance coupling occurs when circuits use common lines and /or coupling impedances, as
shown in Figure 1.15, and modeled by the impedance element Zc shown in Figure 1.16.
The common impedance in conjunction with the power circuit current introduces a voltage level
shift in the signal circuit that may be sufficient such that the signal circuit malfunctions.
The effect of the impedance coupled interference increases when
 the common impedance, resistance and self inductance, increases
 the current creating the disturbance increases
 the frequency increases
1.12.iv RADIATIVE COUPLING
High frequency long distance radiated coupling is the result of the electromagnetic fields,
previously discussed.
1.12.v SUMMARY
E FIELD RECEPTORS
CAPACITANCE
(PARASITIC)
SOURCES
Electric Fields (E)
E
Magnetic Fields (H)
H
RECEPTORS
E & H FIELD
H FIELD RECEPTORS
INDUCTANCE
(PARASITIC & MUTUAL)
FAR FIELD
NEAR FIELD
FIGURE 1.17
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1.13 THE ENVIRONMENT and EMI
EMI is basically a form of environmental pollution and must be controlled and managed.
Legislation is now in place to insist on minimum standards (to be discussed later). Risk
management strategies should perhaps integrate EMC and environmental testing rather than
treating them as separate issues.
1.13.i SOURCE RECEPTOR DUAL ROLE
SOURCE
.
RECEPTOR
SOURCE
RECEPTOR
FIGURE 1.18
The evolution of electronics into every day products means that the probability of EMI generated
problems is ever increasing, of which an example of the problem is shown in Figure 1.18. It
should also be noted that circuits and systems are not exclusive and play a dual role by being both
source of and receptor of interference, as shown in Figure 1.18 and Figure 1.19.
FIGURE 1.19
Electrical and Electronic System Designers can do a lot to mitigate the occurrence of interference.
Products can be designed to minimise the generation of disturbing signal emissions and to have
good immunity to EM fields.
Noise sources cannot be completely eliminated – they always exists and have the potential of
causing interference to or degrading the performance of both the source and other ‘victim’
equipment since noise coupling pathways can never be completely broken and noise receptors
can never be completely isolated.
1.13.ii SYSTEM INTERIOR and EMI
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In addition to the dual role of source and receptor via the external environment parts of a system
can also act in the same dual roles.
FIGURE 1.20
Active electronic systems comprising interconnected modules and passive and active components
including integrated circuits involve voltage and current variations that result in the generation of
electromagnetic fields all around the equipment. The close proximity of components requires EMI
design considerations to ensure the circuit does not interfere with itself as well as other circuits
and equipment.
Technology advances have, in particular, increased noise related issues on PCB’s, Figure 1.20,
due to
 more electrical and electronic devices in operation
 increasing density of systems operating in close proximity
 increasing levels of integration
 lower voltage level signals
 higher frequency and faster switching systems
1.14 COMPATIBILITY
Compatibility, meaning ‘living in harmony’, when applied to the electro magnetic environment
means that an electronic or electrical product shall work as intended in its (EM) environment
without affecting or being affected by other equipment.
The term Electromagnetic Compatibility (EMC) was used at the beginning of the twentieth
century to point out the interference and disturbance caused by electric or electronic equipment on
broadcasting. Nowadays, the acronym EMC indicates the compatibility of electronic equipment
with the electromagnetic environment in which they are working.
The 3 criteria for compatibility are
 systems should not cause interference to other systems
 systems should not be susceptible to other system’s emissions
 systems should not cause internal interference
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FIGURE 1.21
EMC as shown in Figure 1.21 is the combination electromagnetic interference (EMI) and
electromagnetic susceptibility (EMS).
EMI involves the management of radiated and conducted emissions whereas EMS involves
immunity to radiated and conducted interference.
Emissions from and immunity of equipment have to be compliant with limits defined in national
and international regulations (to be discussed later).
1.15
MINIMISING EMI
There are three aspects to minimising EMI (to be considered later)
 suppress the emissions at source
 make the coupling path as inefficient as possible
 make the receptor less susceptible to the emission
Methods to be discussed later include
 isolation (physical separation)
 limiting circuit bandwidth
 filtering
 grounding
 shielding
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1.16
MINIMISINIG EMC DESIGN CYCLE
FIGURE 1.22
EMC should be considered as an integral part of circuit and system design, and not as an add-on
when the system fails compliance testing, as indicated in Figure 1.22
1.17 MICHAEL FARADAY and SHIELDING
FIGURE 1.23
In 1836 Michael Faraday (1791-1867), shown in Figure 1.23, (an experimenter and not a
mathematician!) observed that the charge on a charged conductor resided and travelled only on its
exterior, and had no influence on anything enclosed within it. Physicists later provided the
reasoning that the exterior charges redistribute such that the interior fields due to them cancel.
Essentially it is an application of "Gauss's Law": since like charges repel each other (opposites
attract), electrical charge will "migrate" to the surface of a conducting form, such as a sphere.
INTERNAL FIELD
TERMINATIONS
E FIELD
METAL SPHERE
FIGURE 1.24
FIGURE 1.25
Faraday’s concept of Electric Field coupling is shown in Figure 1.24 and Figure 1.25.
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1.18 FARADAY CAGE
To demonstrate his theory Faraday built a room coated with metal foil and allowed high-voltage
discharges from an electrostatic generator to strike the outside of the room. An electroscope was
used to show that there was no electric charge present on the inside of the room's walls.
In principle Faraday’s demonstration was equivalent to placing modern electronic circuits in an
enclosed box to eliminate external emissions and provide immunity from external EM fields!
Michael Faraday was therefore the first EMC engineer!
Faraday Cage is the general name given to metallic enclosures that prevent entry or escape of
electromagnetic fields and ideally consists of an unbroken perfectly conducting shell, and is the
forerunner to modern screened rooms and derivatives that are used in modern EMC measurement
laboratories.
1.18.i EMI IMMUNITY SHIELDING
FIGURE 1.26a
FIGURE 1.26b
Ideal immunity shielding would be total enclosure that absorbs and reflects radiated noise as
shown in Figure 1.26a. In practice however this will not be achieved for reasons that include
apertures required to input and output signals and power.
1.18.ii EMI EMISSIONS SHIELDING
FIGURE 1.27
The concept of EMI emissions screening is shown in Figure 1.27
NOTE: The concept of the Faraday Cage is not to eliminate EMI at the source hence even if
perfect screening to the ‘outside world’ existed the internal circuits still need EMI attention.
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1.19 ‘EVERY DAY’ FARADAY CAGES
Numerous examples of the Faraday Cage concept are to be found in every day situations without
realising it!
1.19.i Aircrcaft
Aircraft act as Faraday Cages protecting passengers from lightning strikes.
As long as there are no gaps in the highly conductive aluminum surface of the aircraft the
electrical current from the lightning will travel along it and all passengers may experience is the
occasional temporary flickering of lights. The pilot however may observe some short-lived radio
interference on the instrument panel!
1.19.ii Automobiles
If you are in a car when lightning strikes it you'll probably be okay as long as you don't stick your
hand out the window to check and see if it's "still raining.“ The current will simply travel along
the metallic exterior of the vehicle.
1.19.iii Microwave Ovens
The cooking chamber of the microwave often is a Faraday cage enclosure that prevents the
microwaves escaping into the environment.
1.19.iv Credit Cards and RFID Passports
Credit card and RFID passport shielding sleeves are small portable Faraday cages.
1.19.v Mobile Phones
Mobile Phones and radios may have no reception inside elevators or similar structures. Some
traditional architectural materials also act as Faraday shields.
1.19.vi Exam Rooms
A teacher in the UK has suggested a method to eliminate the cheating epidemic via text message
using cell phones. - lining every exam room with a Faraday-like cage!
1.19.vii Crazy Stuff!
Some people wear tin-foil (aluminium foil) hats in the belief that they act to shield the brain from
such influences as electromagnetic fields, or against mind control and /or mind reading.
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1.19. viii Aluminium Canoe
You find yourself out on a lake in an aluminum canoe during a thunderstorm.
Do you
stay in the canoe ?
swim to shore?
turn the canoe over and dive under it for protection
 stay in the canoe ? if you take a direct hit you are dead
in the same way that a 15 kV ESD strike kills an ic
 swim to shore? = body in water
strike hitting water = mega joules of energy of which some of the energy will pass through you.
it only takes a little bit of that energy to kill you!
 turn the canoe over and dive under it for protection
although the upturned boat acts as a Faraday Shield you are in the water!
 stay in boat; the hull of the boat will hopefully divert the current around you (Faraday Shield).
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