Lecture no.1 emi new

OMEGA SEMESTER 2013/2014
SESSION
1
V O M A T T H E W S 2 0 1 4 E I E 5 2 1 C U
ELECTROMAGNETIC
INTERFERENCE &
COMPATIBILITY
-EIE 521-

Today's electronic equipment must satisfy
a host of global regulations that limit a
given device's susceptibility to EMI, as
well as EMI emitted by the device itself
Higher electronic clock or operating
frequencies make EMI more difficult to
control. As business and consumer
electronics incorporate greater
functionality and elevated operating
frequencies, their emissions often
exceed specified limits.
COURSE OBJECTIVE
2

OBJECTIVE CONT’ED
3
At the end of this course you will be able to:
1. Outline the general principle of the
electromagnetic compatibility,
2. List the various areas of EMI influence in the
environment,
3. Differentiate between sources and victims of
EMR,
4. State the courses of EM Interferences and
various ways of eliminating or reducing it’s
influence.

ELECTROMAGNETI
C INTERFERENCE
FUNDARMENTALS
EMIF
4

Faraday’s Laws of Electromagnetic Induction
(discovered in 1831) are :
1. A changing magnetic field induces an
electromagnetic force in a conductor;
2. The electromagnetic force is proportional to
the rate of change of the field;
3. The direction of the induced electromagnetic
force depends on the orientation of the field.
5

RFI/EMI electromagnetic radiation is made of both
electric (E) and magnetic (H) fields.
High-frequency radiation tends to have a large
electricfield component; low-frequency radiation
tends to have a large magnetic field component.
High current devices produce magnetic fields that
could cause interference problems.
GENERAL THEORY
6

7

Electromagnetic radiation involves electric
(E) and magnetic (H) fields.
Any change in the flux density of a magnetic
field will produce an electric field change in
time and space (Faraday's Law).
This change in an electric field causes another
change in the magnetic field due to the
displacement current (Maxwell).
A time-varying magnetic field produces an
electric field and a time-varying electric field
results in a magnetic field.8

It is possible for electromagnetic energy from an
emitter to adversely affect electronic devices not
designed to work with the emitter?.
This is called Electromagnetic Interference
(EMI).
A common example of EMI is when a two-way
radio, such as a walkie-talkie, transmits a signal
near a television.
The radio signal can be received through the
television’s antenna, distorting the picture and
masking the sound with the radio operator’s
voice.
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EXAMPLES OF EMI
TRANSMISSION LINES - unintentional
activation or explosion of electro explosive devices
apart from presenting radiation hazards to humans.
MAINS POWER SUPPLY- impair the operation
of computers and many IT products.
SWITCHES AND RELAYS- Affects telephone
circuit and radio telescopes
TELEPHONE EQUIPMENT - picks up
transmissions from nearby television stations

EXAMPLES OF EMI CONTD…
AIRCRAFT NAVIGATION- affects
navigational equipment during takeoff and landing
BIOLOGICAL EFFECTS- induces steady
current, surging of shock current through the
body and induce electrochemical process and
voltage in human body
MILITARY EQUIPMENT- causes missile
launch failure.
INSECURE COMMUNICATIONS -
intelligence bearing signal can be analyzed by
sensors which leads to insecure communication.

EXAMPLES OF EMI CONTD…
INTEGRATED CIRCUITS- sometimes
burnout the devices. In digital circuits -
increases BER or malfunctions the circuit and
in analog circuits -increases noise levels and
degrades the operation of circuits and systems.
RADIO ASTRONOMY- Weak radio signals
from pulsars and distant galaxies are difficult to
detect.

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CELESTIAL EM NOISE:
DISCRETE SOURCES- sun, moon and
Jupiter. They emit broadband as well as
narrowband EM noise.
continuous sources like galaxy emit
broadband EM noise. cosmic noise does not
vary with time.
OTHER SOURCES: Intense point sources -
radio stars, pulsars, radiation from neutral
hydrogen clouds.

CELESTIAL EM NOISE
•Affects sensitive low noise
receivers using high gain
antennas especially at
VHF, UHF and higher
frequencies.

TERRESTRIAL NOISE
ATMOSPHERICS
LIGHTNING DISCHARGE
cloud to ground discharge
cloud to cloud discharge
ESD

EM FIELDS PRODUCED BY LIGHTNING
Clouds capture charges from the
atmosphere.
When the field intensity in a charged cloud
exceeds the breakdown level, the result will
be an electric discharge.
discharge -cloud to ground and cloud to
cloud.

EM FIELDS PRODUCED BY LIGHTNING
Clouds capture charges from the atmosphere.
When the field intensity in a charged cloud
exceeds the breakdown level, the result will be an
electric discharge.
discharge -cloud to ground and cloud to cloud.

CLOUD TO GROUND
DISCHARGE
The total discharge between cloud and the ground- flash,
with series of high current pulses -strokes.
preliminary breakdown in the cloud sets the stage for
negative charge to be channeled toward the ground in a
series of short luminous steps called stepped leader.
A fully developed stepped leader causes a downward
movement of about 5 coulombs of negative charge cloud
with velocity of about 2x 10e8 m/s. The pulse currents are
of the order of 1 KA .

CLOUD TO GROUND DISCHARGE
CONTD…
As the leader tip with a negative potential of
10e8 volts approaches the ground, initiates an
upward moving discharge.
The contact between the upward moving and
downward moving discharges connects the leader
tip to the ground potential. This is called return
stroke and has an upward velocity of about one
third the velocity of light.

CLOUD TO CLOUD
DISCHARGE
Static charges acquired by a cloud produce a static
electric field.
The duration of electric and magnetic field
transients caused by lightning processes is of order
of a fraction of a microsecond.
excite resonances in the body of an aircraft , digital
electronics circuits are susceptible to damage.

EM FIELDS PRODUCED BY
LIGHTNING
A natural source of EMI can be considered as a
time dependant current dipole.

EM FIELDS PRODUCED BY
LIGHTNING

LIGHTNING DISCHARGE:
cloud to ground -vertical column of current
cloud to cloud -horizontal column of current and cross
section of the current column very small.
In the far field zone, D>>dl,
In the near field zone, D<<dl, where all terms except
last term are significant.

EFFECTS ON TRANSMISSION LINE
Without arrestors it produces 30kv-40kv in a std power
line.
With arrestors voltage on the line is around 300-400v.

ESD PHENOMENA AND EFFECTS
Accumulated static electric charges are
discharged and produces EMI.
Static electricity is generated when two
materials of different dielectric constants
rub against each other. e.g.; wool and glass

CHARGE ACCUMULATION & DISCHARGE
–E.G.
a person wearing shoes with soles made of an
insulating material (polyurethane foam) walks
over a carpet (wool or any synthetic material).
result in a voltage of up to 15kv and upper limit
to a voltage a person can attain is about 35kv.

OTHER EXAMPLES:
Wheel chairs, rolling furniture, conveyor
belts, cooling fans, plastic roller blades, paper
movement in copiers and printers, cleaning with
an air gun, packaging with PVC layer using hot
air blast, cleaning with solvent, thermal
blankets, rockets and exhaust nozzles.

Electromagnetic radio frequency (RF) emitters are
common in everyday life.
They work by sending invisible electromagnetic energy
into the air or down a wire.
RF emitters are used in a variety of applications,
including wireless communication, navigation (e.g.,
Global Positioning System), radar, etc. Some familiar
examples of RF emitters include broadcast radio
transmitter towers, cellular phones, two-way radios,
microwave ovens, weather radars, police radars, cable
television, and local area networks.
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RFIs can damage electronics (see next slide) and/or
cause them to malfunction, even in ways that
compromise built-in, fail-safe mechanisms.
The impact of the malfunction depends on what
equipment is affected, how it is affected, when it is
affected, and what function it is performing.
If the affected electronics control critical processes,
the impact may be significant, resulting in economic
loss, reduced defenses, and infrastructure facility
downtime.
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V O M A T T H E W S 2 0 0 7 E I E 5 2 1

Standards governing electromagnetic compatibility commonly refer
to EMI/RFI, or electromagnetic interference/radio frequency
interference.
Such interference is caused by stray voltages and/or currents
coupling between electronic systems creating undesirable effects.
These undesirable effects can vary between a brief
annoyance, such as a vacuum cleaner disturbing the family
television viewing, to more serious situations, such as a cellular
phone interfering with the controls of a machine tool, or a noisy
power supply interfering with the proper operation of an industrial
robot.
With the increased emphasis on electronic
technology, electromagnetic interference/radio frequency
interference is a growing concern.36

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38

39

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V O M A T T H E W S 2 0 0 7 E I E 5 2 1
SO EMI IS
WHAT???

41
• The widespread use of small, high speed
electronic devices which are often
operated near other electrical systems,
as well as the explosion in the number
and variety of wireless communication
devices available, has resulted in
concern about interference effects.
• Faster and more complex circuits are
being crowded into ever smaller spaces,
increasing the likelihood that devices
containing such systems will adversely
affect one another.

42
Modern electronic devices must
therefore be able function properly
in an increasingly cluttered
electromagnetic environment.
Thus, the minimization of
electromagnetic interference and
susceptibility has become a major
design objective.

43
• Often the effects of electromagnetic interference are not
discovered until product testing occurs.
• The resolution of interference problems in the late
phases of product development often involves the
addition of extraneous components which add to system
complexity and reduce reliability.
• Additionally, it is illegal to sell products which do not
meet government regulations regarding electromagnetic
emissions.
• It is therefore desirable that electromagnetic
interference issues, and compliance with federal
regulations regarding emissions and susceptibility, be
addressed in the initial stages of product design.

44

45
PLEASE NOTE
It should be remembered that effects described
by fundamental electromagnetic principles are
always present, and are simply more pronounced
under certain conditions. "Non-ideal behaviour"
is, in fact, a
misnomer, because it implies that devices are
functioning in an abnormal way, when they are
really behaving in a perfectly natural way. It is
only through the application of fundamental
principles that the behaviour of devices under all
operating conditions is predictable.

46
WHERE IS THE CHALLENGE?
What makes the task of producing
electromagnetically compatible systems
particularly difficult is that, in addition
to understanding the broader principles
which govern device behaviour, the
designer often cannot anticipate what
types of interference devices will
encounter, and must prepare for all
contingencies.

47
For these reasons, systems must
be designed not only to minimize
emissions, but also to be immune
from external interference.
Unfortunately, as the
electromagnetic environment
becomes more complex, this goal
becomes more difficult to achieve.

48
INTENTIONAL RADIATORS
• Intentional radiators are devices which emit
electromagnetic energy as part of their desired
function. These include such devices as radio
and radar transmitters, cellular phones, remote
controls for car alarms, etc.
• Because intentional radiators emit signals by
design, their operation may interfere with other
electronic devices.
• Example, digital computers may interpret radio
or television signals as data, resulting in
spurious commands being executed.

49
UNINTENTIONAL RADIATORS
• Unintentional radiators are devices which
are not designed to radiate but still emit
electromagnetic energy. These include
digital devices, motors, relays and
switches, etc.
• An intentional radiator such as a cellular
phone may also be an unintentional
radiator at frequencies other than those
at which it normally transmits.

50
A BRIEF HISTORY OF EMC/EMI
• Until the early part of the twentieth
century, few man-made sources of
electromagnetic radiation existed.
• While the first crude radio receivers tended
to be susceptible to interference from natural
noise sources, the correction of this problem
was usually a relatively simple task.
• Conflicts between early radio transmitters
were easily resolved by changing frequencies
or by simply moving the transmitter or
receiver.

51
• In the years that followed, more and more
man-made sources of electromagnetic
radiation began to appear.
• At nearly the same time that it became
possible to transmit and receive complex,
information-carrying signals via radio,
television, and telephones, the increased
generation and use of electricity caused a
proliferation of noise sources such as dc
motors, ac power lines, relays, and fluorescent
light bulbs .

52
• World War II saw the introduction of radar
and other remote sensing systems, along
with the use of radio communication in
combat. Instrumental in the development of
radar was the introduction of small
microwave sources, such as the cavity
magnetron.
• This and other relatively small electronic
devices, were incorporated into vehicles such
as ships, airplanes, and automobiles.

53
In the early 1960's, MIL-STD-461 was
imposed, regulating not only
electromagnetic emissions, but
susceptibility as well.
Also in the years following World War II,
CISPR produced various publications
dealing with recommended emissions
limits, which were adopted by some
European countries

• Have already been used to defeat security systems,
• Commit robberies,
• Disable police communications,
• Induce fires,
• Disrupt banking computers.
• Improvised RFWs have been demonstrated to jam satellites,
• Cause a catastrophic failure in a locomotive and damage automobiles.
• Devices that can be used as RFWs have unintentionally caused aircraft
crashes and near-crashes,
• Pipeline explosions, large gas spills, computer damage, medical equipment
malfunctions,
• Vehicle malfunctions such as severe braking problems, weapons pre-
ignition and explosions,
• Public water system malfunctions that nearly caused flooding.
EMI EVIL
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For example, utilities and manufacturing facilities have
become increasingly reliant upon automated control
systems such as supervisory control and data
acquisition (SCADA) systems and distributed control
systems (DCS) to monitor, control, and regulate their
processes.
These automated control systems are basically
composed of various electronic subsystems including a
master computer called a Master Terminal Unit
(MTU), a remote processor/controller called a Remote
Terminal Unit (RTU).
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Communications using wireless radio or telephone lines,
electronic sensors (pressure sensors, current meters, etc.),
and electronically controlled actuators (e.g. valves, circuit
breakers, etc.) and relays, as shown in in the next slide.
RFIs can potentially be used to affect any of these
electronic devices and produce effects such as
unintentional valve closures, disabled communications,
false data transmissions, and damage to the electronic
device itself.
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Further complicating matters, the data displayed on
a control monitor ( Next Figure) may not reflect the
actual state of the system, which may hamper the
operator’s ability to correct the problems.
Impacts from such effects can range from nuisance
(e.g. having to send a technician to a remote site to
reset equipment) to catastrophic (e.g. gas pipeline
ruptures/explosions and mass electric power
outages).
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60
EMI DEFINATIONS
The International
Eletrotechnical
Vocabulary (IEV)
definition's on
EMI/EMC

61
According to the International
Electro technical Vocabulary IEV
161-01-07, EMC is the ability of a
device or system to function
satisfactorily in its electromagnetic
environment without introducing
intolerable electromagnetic
disturbances to anything in that
environment.

62
In recent years, several trends have
together made EMC more important than
ever:
• Disturbances are becoming stronger
with increasing voltage and current
values.
• Electronic circuits are becoming
increasingly sensitive.
• Distances between sensitive circuits
(often electronic) and disturbing circuits
(power circuits) are becoming smaller.

• Electromagnetic Compatibility (EMC) is the ability of
electrical or electronic equipment/systems to function in
the intended operating environment without causing or
experiencing performance degradation due to
unintentional EMI.
• It is recommended that the performance be tested or
qualified to insure operation within a defined margin of
safety for the required design levels of performance.
• The EMI source minus the coupling mechanism path
losses should result in an emission level that is less than
the victim's susceptibility threshold minus a
predetermined safety margin.
The goal of EMC is to minimize the influence of
electrical noise.
EMC DEFINITION
63

Electronic equipment can malfunction or become totally
inoperable if not designed to properly minimize the effects of
interference from the internal and external electromagnetic
environments.
Proper equipment and system designs are also necessary for
minimizing potential electromagnetic emissions into the
operating environment.
It is important that electronic equipment designs ensure
proper performance in the expected electromagnetic
environment, thus maintaining an acceptable degree of
Electromagnetic Compatibility (EMC).
EMC CONT….
64

SOME (EMI) DEFINITIONS CONT.
65
Attenuation in terms of EMC ,this is
the reduction of an electromagnetic
field across a shield (usually
expressed in decibels (dB) at a given
frequency).
Cutoff Frequency is the maximum
possible frequency beyond which the
waveguide will no longer shield EMI

• Electromagnetic Emission is the
energy radiated to the environment
from an electronic product.
• Electromagnetic Immunity is the
ability of an electronic product to
function in its environment in the
presence of electromagnetic
radiation.
66

Electromagnetic interference: Interference to the
operation of communications products or other electrical
and electronic devices generated by all electrical and
electronic products or natural causes.
Electromagnetic interference: The interference by
electromagnetic signals that can cause reduced data
integrity and increased error rates on transmission
channels.
Electromagnetic Frequency Interference: - Unwanted
"noise" created by current-producing devices such as
electric motors and fluorescent lights. EMI effects the
quality of the signal passing through data transmission
medium.
67

Electromagnetic Effects (EME)
includes many electromagnetic
environmental disciplines such as
Electromagnetic Compatibility (EMC),
Electromagnetic Interference
(EMI), and
Electromagnetic Pulse (EMP)68

Shielding Effectiveness (SE)
is the measure of protection provided by an
enclosure against electromagnetic
interference at a specific frequency. It is generally
expressed in decibels (dB), where.
SE = 20 Log (EO/EI)
EO (V/m) is the measure of field strength
without the shield; EI (V/m) is the field
strength with the shield in place
SHIELDING EFFECTIVENESS
69

Decibel (dB) in terms of EMC is a
dimensionless logarithmic ratio used as a
manageable value of measurement for the
reduction or attenuation of
electromagnetic
interference.
70

Most high frequency wave energy is reflected off a
conductive wall.
In the low frequency range, however, the magnetic
waves can penetrate the shield.
For low frequency magnetic-dominant noise,
therefore, the absorption characteristics of the
shield become much more important.
The absorption characteristics are related to the
magnetic permeability and wall thickness of the
shielding material.
71

When two sinusoidal electromagnetic waves of the same
wavelength reach the same location at the same time, the
superposition principle says the net electric field at that
location is the vector sum of the electric fields in each
wave.
(The same is of course true for the magnetic fields; we will
talk only about electric fields here, because they are
responsible for most of the interaction of electromagnetic
radiation and matter.)
THE SUPERPOSITION PRINCIPLE AS APPLIED
TO ELECTROMAGNETIC RADIATION
72

73

74

EMI, or electromagnetic interference can
be a problem to designers of many
products.
Personal Computer manufacturers must
design to meet the FCC Part 15 regulations
to prevent PC's from interfering with other
office equipment.
(In Nigeria there is no standard for EMI !!!)
WHY DO ELECTROMAGNETIC FIELDS
NEED MAGNETIC SHIELDING?
75

76
• Cell phone designers have to incorporate
RFI shielding to stop unwanted RF
emissions as well as to prevent other
electrical equipment from interfering with
the cellular telephone's operation.
• Designers may find that densely packed
electronic assemblies may have internal
components that interfere with each other,
requiring electro magnetic shielding.
• When the electromagnetic interference
includes low frequency radiation, magnetic
shielding is essential to assure proper
operation of the electronic equipment.

For an Electromagnetic
Interference or EMI
condition to exist, the
following conditions must
be present:
NOTE
77

There must be a source. An interference source is called
an "emitter" of electromagnetic energy.
The emitter may propagate electromagnetic energy either
intentionally, like a hand held radio, or unintentionally, like
a power transformer.
There must be a device sometimes referred to as the
"victim", that is susceptible to the electromagnetic energy
being emitted by the emitter source.
If the susceptible device does not have sufficient
immunity to reject the energy it is being exposed to,
electromagnetic interference may occur.78

79

A physical relationship must exist between the two
devices wherein they share a common propagated
electromagnetic field. The physical distance between
devices and their spatial orientation with respect to each
other may have a significant role in determining
whether the devices will react with each other.
The sensitivity of a device to EMI is described by either
susceptibility or immunity. Since susceptibility to EMI
varies with many factors, devices can be placed into an
active electromagnetic field without user awareness that
a potential EMI problem may exist.
Adjacent devices may also unintentionally radiate
electromagnetic fields that can, in turn, affect other
devices.
CONDITIONS
80

A FEW CONCEPTS
81
Everyone knows the fire triangle; well
here we have a variation on it, the EMI
triangle.
As with its predecessor, remove any of
the 3 sides and the EMI problem goes
away.

Electromagnetic interference occurs when three
elements come together:
A source of interference
A receiver of the interference
A path of transfer.
According to this simple scheme, minimizing the
electromagnetic interference can be attained by
eliminating one of the three elements:
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CONCEPT CONT’ED

83
The so called source-path-receptor model
is illustrated in the slide before, suggests
that electromagnetic interference can be
prevented in one of three ways:
- suppress emissions at the source
- interrupt or reduce the efficiency of the
coupling path
- make the receptor immune to emissions

(For the purpose of this explanation I have used the
radiated propagation method)
SO HOW DO YOU DO THAT?
84

85
Coupling paths are typically
classified as belonging to one of
four general classes:
•CONDUCTIVE
•RADIATIVE
•INDUCTIVE
•CAPACITIVE

Causes of EMI can be intentional or inadvertent, hostile
or friendly, military or civil, and either foreign or
domestic.
They can come from a jamming device, malfunctioning
equipment, or improper system operation.
Regardless of the cause or intent, the effect is always the
same—interference of our electromagnetic emissions.
Electronic jamming, while not common in our everyday
operations, is nonetheless a potential threat against
which we need to be ever ready to guard and overcome.
What occurs much more frequently than is generally
realized is interference from extraneous navigation and
telecommunications systems, and other sources .
OTHER SOURCES
86

INCREASE THE DISTANCE
87

EMF causes electromagnetic interference or "EMI" with
a large variety of sensitive equipment: DC magnetic
fields from subway rail lines can disrupt computer
monitor displays.
ELF or AC magnetic fields from a building's electrical
system can interfere with computer systems.
RF from nearby broadcast antennas can interfere with
wireless LAN systems, IT equipment and highly
sensitive equipment.
With the pervasive increase in EMF sources throughout
the world, there is a corresponding increase in concern
that human exposure to EMF may cause adverse health
effects.
OTHERS
88

OTHER METHODS
89

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91

Microwave tower
The majority of EMI concerns are centered on
radio frequency (RF) emission sources due to the
massive global increase in personal computers,
digital pagers, hand-held radios, cellular phones,
wireless devices, etc.
Although most RF transmissions are achieved
under controlled conditions, it is this transmitted
energy that may create an interference producing
phenomenon, a phenomenon that may affect the
performance of many electronic devices.
INTERFERENCE FROM RADIO FREQUENCY
FIELDS
92

93

Transient Electromagnetic Fields are produced by the switching
of inductive loads such as circuit breakers or motors.
Lightning will also cause this type of disturbance.
A transient signal in a cable produces a radiated emission with a
spectral content dependent on the amplitude, rise time and pulse
width.
The reception of broadband fields at the lower frequencies is
mainly via cables, which are electrically long with respect to the
wavelength.
A cable longer than one quarter of a wavelength will be an
efficient receptor.
Broadband radiation from transient sources is rarely found to have
significant energy at frequencies exceeding 500 MHz.
94

Conducted interference may originate from the coupling of
ambient radiated interference or may be capacitive,
inductively or galvanically induced in the cable by an emitting
source.
At audio and lower radio frequencies, EMI is primarily
caused by conduction.
The impedance presented by power cables, cable screens, etc.
is generally low and this type of EMI will be readily
propagated.
95

Unfortunately, the potential of an EMI threat from
elevated AC magnetic fields to computer and
telecommunications equipment is not well
understood.
While there are numerous antidotal reports of EMI
problems with routers and distribution systems from
external AC magnetic fields, very few manufacturers
of such equipment or systems provide meaningful
sensitivity or immunity specifications or guidelines.
Moreover EMI guidelines for AC magnetic field
immunity thresholds are internationally inconsistent.96

As a precautionary measure, several major
industrial and financial services companies
have established internal guidelines which
recommend that computer equipment
including cabling, data-hubs, network
controllers, servers, etc. should not be
operated in environments where AC
magnetic field levels exceed 20 to 30 mG.
97

In patient-connected medical electronics, immunity to
external radio-frequency interference (RFI) is one of
the toughest electromagnetic interference (EMI)
problems to handle.
Patient-connected devices are often placed in high-
noise environments and often perform life-critical
functions.
And one of the most difficult EMI issues to address
is protecting analog signals from RFI generated by a
nearby handheld radio or cellular phone.
98

Three main elements contribute to the problem.
First, physiological processes emit very weak signal
levels, which makes the signals vulnerable to RFI.
Second, the input signals are impossible to shield
adequately because the end of the cable connected to
the patient cannot be terminated.
Third, leakage current limitations restrict capacitive
filtering to the ground, thereby prohibiting the most
effective method of RFI filtering.
99

THANK
YOU
100

Lecture no.1 emi new

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