Electromagnetic Interfacing (New)

7/15/2019 Electromagnetic Interfacing (New)

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VL402 Electro Magnetic Interference & Compatibility in Design.

(common for M.Sc.(Tech.) VLSI Design and M.Sc.(Tech.) DSP & ESD)

EMI ENVIRONMENT:

Sources of EMI, conducted and radiated EMI, Transient EMI, EMI – EMC definitionsand units

parameters. EMI Coupling Principles conducted, Radiated and Transient Coupling,

Common

impedance Ground Coupling, Radiated Common Mode and Ground loop coupling ,

Radiated

Differential mode coupling, Near field cable to cable to coupling, Power mains and

power supply

coupling.

EMI SPECIFICATION/ STANDARDS / LIMITS :

Units of specification, civilian standards Military standards.

EMI MEASUREMENT:

EMI Test Instruments, Systems, EMI test, EMI shielded chamber. Open Area test site, TEMCell Antennas, Conductors Sensors / Injectors /Couplers, Military test methods and

Procedures, Calibration Producers.

EMI CONTROL TECHNIQUES :

Shielding, Filtering,Grounding , Bonding, Isolation Transformer, Transient Suppressors,

Cable

Routing , Signal control, Component selection and Mounting.

EMI DESIGN OF PCB :

PCB Traces Cross Talk, Impedance control, Power Distribution Decoupling, Zoning

Mother board

Design and Propagation delay performance models.

REFERENCE BOOKS:

1.. Bernhard Keiser “Principles of Electromagnetic Compatibility”, Artech House, #rd Ed,

1986.

2. Henry W. Ott., “Noise education Techniques in Electronic System”, John Wiley and

Sons, New

York,1988.

3. V.P.Kodali, “Engineering EMC Prnciples, Measurements and Technologies”, IEEE

Press,1996.



ELECTROMAGNETIC Interference

Department of System Design

Andhra University

Chapter-1

EMI Environment

Source of EMI,

Conducted and Radiated EMI,

Transient EMI,

EMI-EMC definitions and units of parameters,

EMI Coupling Principles,

Conducted, Radiated, and Transient Coupling,

Common Impedance Ground Coupling,

Radiated common mode and ground loop coupling,

Power mains and power supply coupling.

By

M. Hareesh Babu

[email protected]

mailto:[email protected]

mailto:[email protected]



EMI Environment

ntroduction: The electromagnetic environment is an integral part of

the world in which we live. Various apparatus such as Radio and

television broadcasting stations, communication transmitters, and

other radar and navigational aids radiates electromagnetic energy during

their normal operations. These are intentional radiations of

electromagnetic energy into the environment. Many appliances, such asIAutomobile ignition systems and industrial control equipment systems

used in everyday life also emit electromagnetic energy although these

emissions are not an essential part of normal operations. The

electromagnetic environment created by these intentional and

unintentional sources, when sufficiently strong, interferes with the

operation of the electrical and electronic equipment and systems. Theinterference from the electromagnetic environment began to gain

recognition as a subject of practical importance in the 1920s. With the

beginning of the radio broadcast transmission, the interference from

radio noise (also called electromagnetic noise) was viewed with concern

by the manufactures of electric power equipment electric utility

companies in the United States.

What is EMI: An electromagnetic disturbance is any electromagnetic

phenomenon which may degrade the performance of a device, or anequipment, or a system. The electromagnetic disturbance can be in the

nature of an electromagnetic noise, or an unwanted signal, or a change in

the propagation medium itself.

Electromagnetic interference is a disturbance that affects an electrical

circuit due to either electromagnetic conduction or electromagnetic

radiation emitted from an external source. (or EMI, also called radio

frequency interference or RFI). The disturbance may interrupt, obstruct,

or otherwise degrade or limit the effective performance of the circuit.

The words electromagnetic interference (EMI) and radio interference

(RFI) are sometimes used interchangeably, this is not correct. Radio

frequency interference is the degradation in the reception of a wanted

signal caused by radio frequency disturbance, which is an

electromagnetic disturbance having components in the radio frequency

range.



PRACTICAL EXPERIENCES AND CONCERNS

Today we use a greater variety and number of

apparatus and appliances which generate EMI, these apparatus,

appliances, and systems are also the victim of EMI. Also, the use of semiconductors and operate circuits and systems using lower power

supply levels to electromagnetic interference, being susceptible to

malfunction or burnout. The EMI is experienced in many new ways and

situation. Some examples of practical experiences in the recent past are

briefly described in the following.

1. Transmission Lines

High-voltage electric power transmission lines are asource of electric and magnetic fields in the their immediate vicinity.

Such power transmission lines usually carry voltages in excess of 100 kV

and currents of more then 100A.

Above figure shows the electric field at ground level under a 525 kV

power transmission line located about 10 m above the ground. It is seen

from the data that high electric field intensities at midspan under electric

power transmission lines carrying different voltages.

High-intensity electric and magnetic fields also exist in

the immediate vicinity of surface-to-submarine extremely low frequencycommunication stations and radio or television transmitters. Such high-



intensity fields can cause unintentional activation or explosion of electro

explosive devices, apart from presenting radiation hazards to humans.

2. Switches and Relays

The electric discharges associated with the make or brake

operation of an electrical switch or a relay in telephone circuits or control

instrumentation can cause electromagnetic interference. This is a real-life

problem in telephone circuits and in radio telescope and other high-

sensitivity control and telecommand circuits, where ultra-low-level

signals are handled.

3. Biological Effects

The effects of electric and magnetic fields on biological

systems and human beings are a subject of considerable concern and

investigation. There are two types of concerns about the exposure of

humans to high-intensity electromagnetic fields. One of these relates to

the steady-state current induced in the human body as a result of its

exposure to electric/magnetic fields for a long period of time. A second

concern is about the surging of shock current through the body when a

person located in a high-intensity field touches an insulated metallic

object such as a motor vehicle which is also located in the same electric

field.

4. Aircraft Navigation

Most recently, gross navigational errors were observed in

omega navigation instruments of a passenger airplane which was on a

flight from Newark to Saint Marten. The reading of the instruments

disagreed with each other and was inconsistent in time and heading with

the last known position of the plane. Subsequent investigation pointed to

the source of error-causing EMI as a portable television set beingwatched by a passenger. In yet another incident, the operation of a laptop

computer by a passenger was found to interfere seriously with the

navigation equipment of the aircraft during takeoff and landing.

5. Integrated Circuits

Integrated circuits, which are today extensively used in many

instruments or apparatus, including information technology products,

suffer the most from EMI. In extreme cases, EMI may cause burnout of such devices. In circuits involving digital signal, the effect of EMI could



be one of increasing the bit error rate or malfunctioning of the circuits. In

case of analog signals, EMI increases the noise level and leads to a

degrade operation of circuits and systems.

SOURCES OF EMI

The electromagnetic interference source may be any object,

artificial or natural, that carries rapidly changing electrical currents, such

as an electrical circuit, the Sun or the Northern Lights.

(or)

The source of electromagnetic interference is both natural

and human-made. Natural sources include sun and stars, as well as

phenomena such as atmospherics, lightning, thunderstorms, and

electrostatic discharge. This electromagnetic interference is alsogenerated during the practical use of a verity of electrical, electronic, and

electromechanical apparatus. The below table gives a list of several

source of electromagnetic interference.

Electromagnetic Noise|

---------------------------------------------------------| |

Equipment noise Natural noise( EMI in circuits & systems) _______|_______

| | | |

Systems Circuits & components Terrestrial Celestial

Communication Local oscillators Atmospherics

cosmic/galactic

Radar/navigation Switches Lightning noise

Equipment Motors Electrostatic discharge solar noise

Automobile ignition FiltersIndustrial equipment Relays

Fluorescent tubes Non-linear ckt elements

Home appliances- Magnetic armatures

-Such as Logic & Digital gates

Mixers,

Electric shavers



Depending on mode of interference, EMI or RFI may be broadlycategorized into two types.

Source

Radiated Conducted

N.band Broadband Physical

Radiated EMI

Radiated EMI or RFI may be broadly categorized into two types;

1. Narrowband and

2. Broadband.

Narrowband interference usually arises from intentional transmissions

such as radio and TV stations, pager transmitters, cell phones, etc.

Broadband interference usually comes from incidental radio frequency

emitters. These include electric power transmission lines, electric motors,

thermostats, bug zappers, etc

Anywhere electrical power is being turned off and on rapidly is a

potential source. The spectra of these sources generally resemble that of

synchrotron sources, stronger at low frequencies and diminishing at

higher frequencies, though this noise is often modulated, or varied, by

the creating device in some way. Included in this category are computers

and other digital equipment as well as televisions. The rich harmonic

content of these devices means that they can interfere over a very broad

spectrum. Characteristic of broadband RFI is an inability to filter it

effectively once it has entered the receiver chain.



Conducted EMI

Conducted Electromagnetic Interference is caused by the

physical contact of the conductors as opposed to radiated EMI which iscaused 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.

Celestial Electromagnetic Noise

It is well know that celestial bodies like the sun, stars, andgalaxy are at a very high temperature. The electromagnetic radiation

from these bodies can be attributed to the random motion of charged ions

resulting from thermal ionization at very high temperatures. These heated

parts of the celestial bodies emit thermal noise. The characteristics of

such emissions depend upon the temperature attained by these bodies.

The sources of extraterrestrial emission have an approximately

continuous as well as discrete distribution. Potential sources of discrete

emission are the sun, moon, and Jupiter. They emit broadband as well as

narrowband electromagnetic noise. Radiation from the sun changes

drastically during solar flares and sunspot activity. Continuous sources

like the galaxy normally emit broadband electromagnetic noise. A

spectral distribution of celestial electromagnetic noise is shown in the

below figure.

The level of electromagnetic noise emitted by a cosmic source does not

vary appreciably with time, unless the source itself undergoes a change

which results in a corresponding variation in the emitted electromagnetic

noise. However, the cosmic noise received at a given point on the earth

varies with the time of the day because earth rotates around the sun andalso revolves around its own axis.



Electromagnetic Compatibility

Electromagnetic Compatibility is a the branch of electrical

sciences which studies the unintentional generation, propagationand reception of electromagnetic energy with reference to the

unwanted effects (Electromagnetic interference, or EMI).

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.

How to achieve this EMC

To achieve this, EMC pursues two different kinds of issues

Emission:



related to the unwanted generation of electromagnetic energy by

some source, and to the countermeasures which should be taken in

order to reduce such generation and to avoid the escape of any

remaining energies into the external environment .

Susceptibility of Immunity:

refer to the correct operation of electrical equipment, referred to

as the victim, in the presence of unplanned electromagnetic

disturbances.

Principles and Types of Coupling Paths:

These are Basically 4 types.

1. Transmitter-to-Transmitter EMI (via Antenna) Coupling.

2. Common mode or Common Impedance Ground Coupling.

3. Differential Mode Coupling.

4. Power Line Coupling.



Chapter 2







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Electromagnetic Interfacing (New)