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