Electromagnetics (EM) is a branch of physics or electrical engineering in
which electric and magnetic phenomena are studied.
Electromagnetic interference exist in every communication link.it
manifests itself as noise.
Electromagnetic interference (EMI) is electromagnetic energy that
adversely affects the performance of electrical/electronic equipment by
creating undesirable responses or complete operational failure.
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 intentional EMI.
The most common methods of noise reduction include proper equipment
circuit design, shielding , grounding, filtering, isolation, separation and
orientation and noise cancellation techniques.
DEFINITION OF EMI & EMC:
Electromagnetic interference is the degradation in the performance of a
device due to the fields making up the electromagnetic environment.
Electromagnetic compatibility is achieved when a device functions
satisfactorily without introducing intolerable disturbances to the
BASIC ELEMENTS OF EMI
Interference occurs if the received energy causes the receptor to
function in unwanted manner.
Whether the receiver is functioning in wanted or unwanted
manner, depends on the coupling path as well as the source and
The medium is to be made as inefficient as possible.
Narrow band interference usually arises from intentional transmissions such as radio
and TV stations, pager transmitters , cell phones etc. It is a high frequency operation .
Example: proximity effect
Broad band interference usually comes from incidental radio frequency emitters.
These includes electric power transmission lines, electric motors etc. It is a low
Example : skin effect
Conducted electromagnetic interference is caused by the physical contact of the
conductors as opposed to radiated EMI, which is caused by induction (without
physical contact of the conductors).
Electromagnetic disturbances in the EM field of a conductor will no longer be
confined to the surface of the conductor and will radiate away from it.
This persists in all conductors and mutual inductance between two radiated
electromagnetic fields will result in EMI
Differences between conducted and
Intra system EMI
Inter system EMI
Effects of EMI
Momentary disturbance in TV and radio reception due to operation of mixer-
grinder/electric shavers/a passing vehicles etc
Reset of computers and loss of data.
Change of setting of status of control equipments.
Failure of pace maker implemented in a patient due to a „walkie talkie‟
Malfunctioning of flight controlling system due to use of laptop by passenger.
Sources of EMI:
The sources of EMI can be broadly classified into two groups
Natural sources of EMI
Manmade sources of EMI
example: commercial radio and telephone communications
In specific we can classify as
Functional: EMI can originate from any source designed to generate
electromagnetic energy and which may create interference as a normal part of its
Incidental: EMI can originate from man made sources .These sources are not
designed specifically to generate electromagnetic energy but which do infact cause
Natural: EMI can be caused by natural phenomena, such as electrical storms ,
rain particles , solar and interstellar radiation.
Fig: 2 Fig1-lightning hitting
EMI CONTROL TECHNIQUES:
To control or suppress EMI, the
three common means employed
in the design process are
Grounding is the establishment of an
electrically conductive path between two points
to connect electrical and electronic elements of
a system to one another or to some reference
point, which may be designated as the ground.
.An ideal ground plane is a zero-potential
,zero-impedance body that can be used as a
reference for all signals in associated circuitry
and to which any undesired current can be
transferred for the elimination of its effects.
Bonds provide protection from electrical shock, power circuit current return paths, and antenna
ground plane connections, and also minimize the potential difference between the devices. They
have the ability to carry large fault current.
Bonding is the establishment of a low-impedance
path between two metal surfaces. Grounding is a
circuit concept, while bonding denotes the physical
implementation of that concept.
The purpose of shielding is to confine radiated energy to a specific region or to prevent radiated
energy from entering a specific region.
Shields may be in the form of partitions and boxes as well as in the form of cable and connector
Shield types include solid, nonsolid (e.g., screen), and braid, as is used on cables. In all cases, a
shield can be characterized by its shielding effectiveness.
The shielding effectiveness is defined as
SE=10 log incident power density
transmitted power density
where the incident power density is the power density at a measuring point before a shield is
installed and the transmitted power is the power density at the same point after the shield is in place.
An electrical filter is a network of lumped or
distributed constant resistors, inductors, and
capacitors that offers comparatively little
opposition to certain frequencies, while blocking
the passage of other frequencies.
Filter provides the means whereby levels of
conducted interference are substantially reduced.
The most significant characteristic of a filter is
the insertion loss it provides as a function of
Insertion loss is defined as
IL=20 log V2/V1
Where V1 is the output voltage of a signal source
with the filter in the circuit, and V2 is the output
voltage of the signal source without the use of
Electromagnetic compatibility (EMC) is the branch of electrical science which
studies the unintentional generation, propagation and reception of electromagnetic
energy with reference to the unwanted effects (Electromagnetic interference, or
EMI) that such energy may induce.
The goal of EMC is the correct operation, in the same electromagnetic
environment, of different equipment which use electromagnetic phenomena, and
the avoidance of any interference effects.
A system is said to be electro magnetically compatible if :-
• It doesn't cause interference with other system .
• It is not susceptible to emissions from other systems.
• It doesn‟t cause interference with itself.
EMI is a phenomenon while EMC is an equipment characteristic or a property not
to generate EMI above a certain limit and not to be affected or disturbed by EMI.
The statement "Live and let live" is the best way to describe EMC.
used to prevent
Suppress the emissions at source
point , best method to control EMI.
Make the coupling path as inefficient
Make the receiver less susceptible to
The basic arrangement of noise source, coupling path and victim, receptor or sink is
shown in the figure below. Source and victim are usually electronic hardware devices,
though the source may be a natural phenomenon such as a lightning strike, electrostatic
discharge(ESD) or, in one famous case, the Big Bang at the origin of the Universe.
There are four basic coupling mechanism :
Conductive coupling occurs when the coupling path between the source and the
receptor is formed by direct contact with a conducting body, for example a
transmission line, wire, cable, PCB trace or metal enclosure.
Conducted noise is also characterized by the way it appears on different conductors:
Common mode or common impedance coupling:
Noise appears in phase(in the same direction) on two conductors.
Differential mode coupling:
Noise appears out of phase(in the opposite direction)on two conductors.
Capacitive coupling occurs when a varying electrical field exists between
two adjacent conductors typically less than a wavelength apart, inducing a
change in voltage across the gap.
Inductive coupling occurs where the source and receiver are separated by
a short distance (typically less than a wavelength).
Strictly, "Inductive coupling" can be of two kinds, electrical induction and
It is common to refer to electrical induction as capacitive coupling, and to
magnetic induction as inductive coupling.
Magnetic coupling (MC) occurs when a varying magnetic field exists
between two parallel conductors typically less than a wavelength apart,
inducing a change in voltage along the receiving conductor.
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 which propagates across the open space in
between and is picked up or received by the victim.
NEED FOR EMC STANDARDS:
The EMC standards are required for trouble free co-existence
and to ensure satisfactory operation.
They are also required to provide compatibility between
electrical, electronic, computer, control and other systems.
Standards are required as manufacturer-user interaction and
user‟s knowledge on EMI are limited.
They are also required for establishing harmonized standards
to reduce international trade barriers and to improve product
reliability and life of the product.
These are of two types
Military Standards :
Military EMC standards are made in order to ensure system-to-system
compatibility in the real time military environment. Military standards
are more stringent than civilian standards. Most of the military standards
are broadly based on MIL-STD 461 and 462.
The civilian EMC standards are applicable for equipments used for
commercial, industrial and domestic applications. The emission
standards are specified to protect the broadcast services from
ADVANTAGES OF EMC
The advantages are:
Compatibility, reliability and maintainability
Design safety margin is provided.
The equipment operates in EMI scenario
Product life and profits are increased.
EMC STANDARDS IN DIFFERENT
1 CISPR(IEC) Committee International
2 FCC Federal Communications
3 SAE Society of Automobile
4 VG Military standard Germany
5 VDE Verband Deutscher
6 ISI EMI measurements &
The fact that EMI was recognized as a problem of significant practical
concern three-quarters of a century ago generally suggests that by now this
must be a well-understood field, and solutions to problems are
consequently a routine technology.
The position is that a great deal of theoretical, analytical and practical
information is today available to understand EMI, have graduated from the
traditional EMC fixes based on trail and error approach.
EMC has developed into a very interdisciplinary subject.
Many problems and topics in this field are how ever still open for further
There is aerial need for further research on several aspects of EMC .These
include characterization of interferences, measurements techniques etc...
“Emi protection for communication systems” a textbook by kresimir
“Elements of electromagnetics” a textbook by Sadiku,3rd edition.
“Applied electromagnetics and Electromagnetic compatibility” a
textbook by Dipak L.Sengupta, Valdis V.liepa
Interference/ElectroMagnetic Interference, ARRL
EMC Testing and Standards in Transient Immunity Testing, RF Immunity.
Electronics-project-design.com. Retrieved on 2011-07-19.