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DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

ACE Engineering College Ankushapur(V), Ghatkesar(M), R.R.Dist - 501 301

2013-14

Under the esteemed guidance of Mr.P.SUBRAHMANYAMAssistant Professor

Submitted by

B.Venkateswara (11AG5A0401)

ELECTROMAGNETIC INTERFERENCE AND ELECTROMAGNETIC COMPATIBILITY

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• Introduction about EMI and EMI

• Examples of EMI

• Sources of EMI

• EMI problems

• EMI controlling technics

• EMC testing methods

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EMI: Electromagnetic interference is the degradation in the performance of a

device or equipment or a system

RFI: Radio frequency interference is the degradation in the reception of a wanted

signal caused by radio frequency disturbance

EMC: An electronic system that is able to function compatibly with other

electronic systems and not produce or be susceptible to interference

Every electronic device is a source of radiated electromagnetic fields

called radiated emissions. These are often an accidental by product of the

design.

An electromagnetic disturbance can be electromagnetic noise, an

unwanted signal or a change in the Propagation medium itself.

INTRODUCTION

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Conducted noise

AC power circuitElectric Motors

Power Line

Lightning

Radio & TV Broadcast

IgnitionMobile Radio

Ship

Radar

Handy Talkie

Telecommunications

Electronic equipment is subjected to a variety of electromagnetic interference sources. Careful design is required to guarantee compatibility with environment- Intersystem EMI

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TRANSMISSION LINES

MAINS POWER SUPPLY

SWITCHES AND RELAYS

TELEPHONE EQUIPMENT

AIRCRAFT NAVIGATION

BIOLOGICAL EFFECTS

MILITARY EQUIPMENT

INSECURE COMMUNICATIONS

INTEGRATED CIRCUITS

RADIO ASTRONOMY

EXAMPLES OF EMI

6SOURCES OF EMI

7CELESTRIAL 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.• Affects sensitive low noise receivers using high gain antennas especially at VHF, UHF and

higher frequencies.

ATMOSPHERIC EM NOISE

lightning discharge cloud to ground discharge cloud to cloud discharge

• 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. • Discharging path may be cloud to ground and cloud to cloud.

8Cloud to ground discharge

9Cloud to cloud discharge

10• As mentioned earlier, any electronic device may be the source of EMI, although this is not

the intension of the designer.• Intrasystem problem:

The cause of EMI either within the system, in which case it is termed as intrasystem problem.• Intersystem problem:

problem from the outside, in which case it is called an intersystem problem.• The term emitter is commonly denoting the source of EMI, while the term susceptor is

used to designate the victim device.

Emitters Susceptors

Power supplies relays

Radar transmitters

Radar receivers

Mobile radio transmitters

Mobile radio receivers

Car ignition system

Car radio receivers

Emitters Susceptors

Lightining strokes Radio receivers

Computers TV sets

Radar transmitter Aircraft navigational sysstem

Police radio transmitters taxicab receivers

11EMI CONTROLING TECHNICS

• The source of EMI can be classified as natural or artificial (man-made).• The origin of EMI basically undesired conducted emissions (voltage and/or

currents) or radiated emissions (electrical and/or magnetic fields).• Conducted emissions are currents that are carried by metallic paths (the unit’s

power cord) and place on the common power network, where they may cause interference with other devices that are connected to the network.

• Both intrasystem and intersystem EMI can be controlled by following some design guidelines and techniques.

1. coupling2. Grounding or wiring3. Shielding 4. Filtering.

12Coupling mechanisms:Some of the technical words employed can be used with differing meanings.Source and victim are usually electronic hardware devices.The four electromagnetic interference (EMI) coupling modes.There are four basic coupling mechanisms: 

1. conductive2. capacitive3.  magnetic or inductive4. radiative

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1.Conductive coupling: It 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 characterised 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 opposite directions) on two conductors.

2.Capacitive coupling: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.Magnetic coupling. h propagates across the open space in between and is picked up or received by the victim.

3.Inductive coupling: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.

4.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.

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• Grounding is the establishment of an electrically conductive path between two points to connect electric and electronic elements of a system to one another or to some reference point which is designated as ground.

• An ideal ground plane have a zero impedance and zero potential that can be used as reference point for all signals in associated circuitry.

• The purpose of the floating ground is to isolate elements or circuits from a common ground plane

• Bonding is the the establishment of a low impedance path between two metal surfaces

• The purpose of a bond to make a structure homogeneously with respect to the flow of electrical currents thus avoiding the development of potentials between the metallic parts, since such potentials may results in EMI.

Grounding:

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• Electromagnetic shielding is the practice of reducing the electromagnetic fields in a space by blocking the field with barriers made of conductive or magnetic materials.

• Shielding is typically applied to enclosures to isolate electrical devices from the 'outside world', and to cables to isolate wires from the environment through which the cable runs. Electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as RF shielding.

• The shielding can reduce the coupling of radio waves , electromagnetic fields and electrostatic fields.

• A conductive enclosure used to block electrostatic fields is also known as a Faraday cage. • The amount of reduction depends very much upon the material used, its thickness, the size of

the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic field.

Shielding

16• The EMC filter design is critical to the electromagnetic compatibility, EMC performance.• The EMC filter must be capable of providing the required level of attenuation of the unwanted

signals while allowing through the wanted signals. • In addition to this the EMC filter design must match both the source and load impedances.• Typically for a high impedance circuit, a capacitor connected between the line and ground provides

better results, while for low impedance circuits a series inductor placed within the line provides the best results.

• Often a single component like this designed to have a reactance with little effect at frequencies appropriate to the wanted signals, but a much higher effect at the higher frequencies of the unwanted signal can provide levels of attenuation of up to 30 dB or 40dB in some cases.

• To improve the performance of one of these basic filters, further components can be added to make multi-component EMC filters. However to give the required performance they must be configured correctly.

• One precaution to ensure that inductors face a low impedance sink or source and capacitors face a high impedance.

Filtering:

17EMC testing:Testing is required to confirm that a particular device meets the required standards. It divides broadly into emissions testing and susceptibility testingSusceptibility testing:• Radiated field susceptibility testing typically involves a high-powered source of RF or EM

pulse 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 or pulse generator, and a current clamp or other type of transformer to inject the test signal.

• Transient immunity is used to test the immunity of the DUT against power line disturbances including surges, lightning strikes and switching noise. In motor vehicles, similar tests are performed on battery and signal lines.

• Electrostatic discharge testing is typically performed with a piezo spark generator called an "ESD pistol”.

• Higher energy pulses, such as lightning or nuclear EMP simulations, can require a large current clamp 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.

18Emissions 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.

• Typically a spectrum analyzer is used to measure the emission levels of the DUT across a wide band of frequencies (frequency domain). Specialized spectrum analyzers for EMC testing are available, called EMI Test Receivers or EMI Analyzers. These incorporate bandwidths and detectors as specified by international EMC standards. 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.

• For conducted emissions, typical transducers include the LISN (Line Impedance Stabilisation Network) or AMN (Artificial Mains Network) and the RF current clamp.

• For radiated emission measurement, antennas are used as transducers. Typical antennas specified include dipole, biconical, log-periodic, double ridged guide and conical log-spiral designs. Radiated emissions must be measured in all directions around the DUT.

• Some pulse emissions are more usefully characterized using an oscilloscope to capture the pulse waveform in the time domain.

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?Queries

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THANKYOU