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ELEMENTS OF EMIELEMENTS OF EMI

SOURCESOF EMI COUPLING VICTIM OF

EMI

EMI CULPRIT AND VICTIMEMI CULPRIT AND VICTIM

EMISource

SignalSource

SignalReceiver

CULPRIT

VICTIM

COUPLING PATH

CONDUCTED OR RADIATEDCONDUCTED OR RADIATED COUPLING COUPLING

SOURCE COUPLING VICTIM

Historical EMI/EHistorical EMI/E33--Related IncidentsRelated Incidents

Operation Restore Democracy (Haiti-1995)• Air wings of USS America & USS Eisenhower

replaced with men & helicopters of 10th Infantry Div. and 75th Ranger Regiment.

• Army aircraft not designed or tested for carrier operation, carriers required to turn off almost all communications and radar surveillance systems.

Pershing II Nuclear Missile (Germany)• Missile motor exploded during routine

maintenance• Electrostatic discharge identified as the

cause• 3 dead

Blackhawk Helicopter (Germany and USA - 1987)• Several potentially fatal incidents and a fatal crash• Suspected cause was interference from high

power radio transmitters• Entire fleet grounded for 3 months during

investigation• Extensive test and retrofit program necessary

USS Forrestal (Vietnam -1969)• ZUNI rocket inadvertently launched by a ship radar • 134 dead• 27 aircraft destroyed• $72M damage to ship ($335M in 2000 dollars)• Largest Naval loss of life since WW II

HMS Sheffield (Falkland Islands -1982)• Hit by undetected EXOCET missile• EMI caused degradation of surveillance

radar• 21 dead, • Ship sank 4 days later

Courtesy of Jose Reza

Shielding May Have Avoided Shielding May Have Avoided Some of These ProblemsSome of These Problems

Proper Grounding May Have May Have Avoided Some of These ProblemsAvoided Some of These Problems

CONCEPTUAL ILLUSTRATION OF CONCEPTUAL ILLUSTRATION OF CONDUCTED AND RADIATED CONDUCTED AND RADIATED

EMISSIONS AND SUSCEPTIBILITY EMISSIONS AND SUSCEPTIBILITY

NARROWBAND AND BROADBAND NARROWBAND AND BROADBAND EMISSIONSEMISSIONS

F1

Vin

TinT1

V1

V1 = F1TinVin

T1 = 1/F1

Vin

Tin

Filter Affects on a PulseFilter Affects on a Pulse

RF Input Output

Time Domain

Frequency Domain

t t

Ai Ao

Receiver

passbandA’i A’o

f f f

UWB PRF > IFBW UWB PRF > IFBW

RF Input Output

Time Domain

Frequency Domain

t t

Ai Ao

Receiver

passbandA’i A’o

f f f

UWB PRF< IFBWUWB PRF< IFBW

THREETHREE--DIMENSIONAL GEOMETRY DIMENSIONAL GEOMETRY ILLUSTRATING GAIN OF ANTENNAILLUSTRATING GAIN OF ANTENNA

RECEIVER SUSCEPTIBILITY RECEIVER SUSCEPTIBILITY CHARACTERISTICSCHARACTERISTICS

RECEIVER SPURIOUS RESPONSESRECEIVER SPURIOUS RESPONSES

MixerI.F.RF

10 MHz

50 MHz60 MHz

100 MHz120 MHz

L.O.110 MHz

220 MHz

330 MHz

210 MHz230 MHz

320 MHz340 MHz

fSR = pfLO fIF

q

RECEIVER INTERMODULATIONRECEIVER INTERMODULATION

R.F. AmplifierRF AMP 100 MHz

100 MHz

101 MHz

102 MHz

fIM = mf1 nf2

m = 2; n = 1 (-)m = 3; n = 2 (-)m = 4; n = 3 (-)

INTERSYSTEM EMC DESIGN AND EMI INTERSYSTEM EMC DESIGN AND EMI CONTROLCONTROL

Communication-SystemInterference

Designand Control

FrequencyManagement

Location Management

TimeManagement

DirectionManagement

Power Source Load

Figure 4. Illustration of Common Mode Currents

CMC 1

CMC 2

CMC

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

Metallic Structure

Illustration of Common Mode Currents

Power Source Load

DCM1

DCM2

Figure 3. Illustration of Differential Mode Currents

Illustration of Differential Mode Currents

Power Source LoadCMC 1

CMC 2

CMC

Metallic Structure

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

Figure 5. Illustration of Common and Differential Mode Currents

DMC 1

DMC 2

Illustration of Common and Differential Mode CurrentsIllustration of Common and Differential Mode Currents

Illustration of Common and Differential Mode Currents

Power Source LoadCMC 21

CMC 21

CMC1

Metallic Structure

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

Figure 6. Common Mode Currents Resulting From Distributed Capacitance to Ground

Common Mode Currents Resulting FromDistributed Capacitance to Ground

Power Source LoadCMC

CMC

EMI'

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

Metallic Structure

Figure 10. Common Ground Impedence Common Mode EMI

EMI

Common Ground Impedance Common Mode EMI

Controlling Conducted EMIControlling Conducted EMI

Source

Power SuppliesMotors

Inductive LoadsHigh Level Analog

Digital SignalsTransmitters

EM Environment

Victim

Analog EquipmentDigital Equipment

Video DisplayRecorders

InstrumentsSensors

Control SystemsReceivers

Conducted EMI

Applicable EMI Control Techniques

PowerFilterFerritesIsolation TransformersTranslent Suppressors

SignalFiltersFerritesIsolation TransformersTranslent Suppressors

PowerFiltersFerritesIsolation TransformersBalanced SystemsFloatInductor in Ground

SignalFilterFerriteIsolation TransformersBalanced CircuitFloatInductor in GroundOptical Isolator

Differential Mode Common Mode (Ground Loop)

WHAT IS GROUND ?WHAT IS GROUND ?

SIGNAL RETURN?SIGNAL RETURN?

CHASSIS REFERENCE?CHASSIS REFERENCE?

SAFETY WIRE REFERENCE?SAFETY WIRE REFERENCE?

EARTH REFERENCE?EARTH REFERENCE?

ELECTROMAGNETIC ELECTROMAGNETIC

SHIELDINGSHIELDING

SHIELDING APPLIES TO ALL LEVELSSHIELDING APPLIES TO ALL LEVELS

ComponentsComponents

CircuitsCircuits

Functional StagesFunctional Stages

EquipmentsEquipments

SystemsSystems

CablesCables

PlatformsPlatforms

BuildingsBuildings

CABLES, CIRCUITS AND COMPONENTS ACTAS ANTENNAS

REPRESENTATION OF SHIELDING PHENOMENAREPRESENTATION OF SHIELDING PHENOMENAFOR PLANE WAVESFOR PLANE WAVES

Outside World

Inside of Enclosure

Incident Wave

AttenuatedIncident

WaveInternal Reflecting

WaveMetalBarrier

ReflectedWave

Transmitted WaveA

B

Ey

Ey

HzEy

Ey

EyHz Hz

Hz

H

REFLECTION LOSSREFLECTION LOSS

σ ε ωfor σ

μ ω j ε ω j σ

μ ω j impedancebarrier Z

HE impedance wave Z

:Where

10 K ,Z 4

Z log 20

VSWR ZZ K,

4K1) K ( log 20 R

b

w

b

w10

b

W2

10dB

REFLECTION LOSS (REFLECTION LOSS (RRdBdB) OF PLANE WAVES VS FREQUENCY) OF PLANE WAVES VS FREQUENCY

Copper

Iron*

Hypernick*

0

50

100

150

200

0

50

100

150

200

1kHz 10kHz 100kHz 1MHz 10MHz 100MHz

3kHz 30kHz 300kHz 3MHz 30MHz 300MHz

Radio Frequency

Valid for thickness > 3 = Skin Depth * Permeability assumed constant with frequency

ABSORPTION LOSS, AABSORPTION LOSS, A

Current Density

t

mm σμ f

0.066 δrr MHz

copper to relative tyconductivi σcopper to relative typermeabili μ

MHz in frequencyfmm in thickness t where

σμft 131 δ t / 8.68 AdB

r

r

MHz

rr MHz

ABSORPTION LOSS VS FREQUENCY

TOTAL SHIELDING EFFECTIVENESSTOTAL SHIELDING EFFECTIVENESS

PRINCIPAL BOX SHIELDING COMPROMISESPRINCIPAL BOX SHIELDING COMPROMISES

Connectors

Fuse

Switch

PotentiometerPanel Meter

StatusIndicator

Lamp

Cover Platefor Access

Holes or Slotsfor Convection Cooling

Screw Spacing= Slot Radiation

Forced AirCooling

SLOT AND APERTURE LEAKAGESLOT AND APERTURE LEAKAGE

L

ht

t << h Shield Material

Log Frequency

•

• / 2

V. P. 20dB/dec.SE

(dB

)

Shielded EnclosuresShielded Enclosures

Provide metal-to-metal contact at seams

Use RF gasketing on access panels

Use screws with lockwashers

Use perforated grids or slots for opening

EMIEMI--Fix Matrix Fix Matrix -- Fixes vs. Coupling Paths, Part 1Fixes vs. Coupling Paths, Part 1

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PP

EMIEMI--Fix Matrix Fix Matrix -- Fixes vs. Coupling Paths, Part 2Fixes vs. Coupling Paths, Part 2

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