1. Professional Development Short Course On:
Practical EMI Fixes
Instructor:
Dr. William G. Duff
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3. ELEMENTS OF EMI
SOURCES VICTIM OF
OF EMI COUPLING
EMI

4. EMI CULPRIT AND VICTIM
EMI
CULPRIT
Source
VICTIM
Signal Signal
Source Receiver
COUPLING PATH

5. CONDUCTED OR RADIATED COUPLING
 SOURCE COUPLING VICTIM

6. Historical EMI/E3-Related Incidents
Operation Restore Democracy (Haiti-1995)
• Air wings of USS America & USS Eisenhower
replaced with men & helicopters of 10th Pershing II Nuclear Missile (Germany)
Infantry Div. and 75th Ranger Regiment. • Missile motor exploded during routine
• Army aircraft not designed or tested for carrier maintenance
operation, carriers required to turn off almost all • Electrostatic discharge identified as the
communications and radar surveillance systems. cause
• 3 dead
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
Blackhawk Helicopter (Germany and USA - 1987)
• Several potentially fatal incidents and a fatal crash HMS Sheffield (Falkland Islands -1982)
• Suspected cause was interference from high Courtesy of Jose Reza
• Hit by undetected EXOCET missile
power radio transmitters • EMI caused degradation of surveillance
• Entire fleet grounded for 3 months during radar
investigation • 21 dead,
• Extensive test and retrofit program necessary • Ship sank 4 days later

7. Shielding May Have Avoided
Some of These Problems

8. Proper Grounding May Have
Avoided Some of These Problems

9. CONCEPTUAL ILLUSTRATION OF
CONDUCTED AND RADIATED
EMISSIONS AND SUSCEPTIBILITY

10. NARROWBAND AND BROADBAND
EMISSIONS

11. Filter Affects on a Pulse
Vin
V1
Tin
Vin T1
F1
Tin
V1 = F1TinVin
T1 = 1/F1

12. UWB PRF > IFBW
Ai Ao
Time Domain
t t
RF Input Output
Receiver
A’i passband A’o
f f f
Frequency Domain

13. UWB PRF< IFBW
Ai Ao
Time Domain
t t
RF Input Output
Receiver
A’i passband A’o
f f f
Frequency Domain

14. THREE-DIMENSIONAL GEOMETRY
ILLUSTRATING GAIN OF ANTENNA

16. RECEIVER SUSCEPTIBILITY
CHARACTERISTICS

17. RECEIVER SPURIOUS RESPONSES
50 MHz
60 MHz RF I.F.
10 MHz
Mixer
100 MHz
120 MHz
L.O.
210 MHz 110 MHz
230 MHz
220 MHz fSR = pfLO  fIF
320 MHz
340 MHz 330 MHz q

18. RECEIVER INTERMODULATION
100 MHz
101 MHz RF AMP
R.F. Amplifier 100 MHz
102 MHz
fIM = mf1  nf2
m = 2; n = 1 (-)
m = 3; n = 2 (-)
m = 4; n = 3 (-)

19. INTERSYSTEM EMC DESIGN AND EMI
CONTROL
Communication-System
Interference
Design
and Control
Frequency Time Location Direction
Management Management Management Management

20. Illustration of Common Mode Currents
CMC 1
Power Source Load
CMC 2
CMC
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
Metallic Structure
Figure 4. Illustration of Common Mode Currents

21. Illustration of Differential Mode Currents
DCM1
Power Source Load
DCM2
Figure 3. Illustration of Differential Mode Currents

22. Illustration of Common and Differential Mode Currents
CMC 1 DMC 1
Power Source Load
CMC 2 DMC 2
CMC
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
Metallic Structure
Figure 5. Illustration of Common and Differential Mode Currents
Illustration of Common and Differential Mode Currents
Illustration of Common and Differential Mode Currents

23. Common Mode Currents Resulting From
Distributed Capacitance to Ground
CMC 21
Power Source Load
CMC 21
CMC1
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
Metallic Structure
Figure 6. Common Mode Currents Resulting From
Distributed Capacitance to Ground

24. Common Ground Impedance Common Mode EMI
CMC
Power Source Load
CMC
EMI EMI'
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
Metallic Structure
Figure 10. Common Ground Impedence Common Mode EMI

25. Controlling Conducted EMI
Source Victim
Power Supplies Analog Equipment
Motors Conducted Digital Equipment
Inductive Loads EMI Video Display
High Level Analog Recorders
Digital Signals Instruments
Transmitters Sensors
EM Environment Control Systems
Receivers
Applicable EMI Control Techniques
Differential Mode Common Mode (Ground Loop)
Power Signal Power Signal
Filter Filters Filters Filter
Ferrites Ferrites Ferrites Ferrite
Isolation Transformers Isolation Transformers Isolation Transformers Isolation Transformers
Translent Suppressors Translent Suppressors Balanced Systems Balanced Circuit
Float Float
Inductor in Ground Inductor in Ground
Optical Isolator

26. WHAT IS GROUND ?
 SIGNAL RETURN?
 CHASSIS REFERENCE?
 SAFETY WIRE REFERENCE?
 EARTH REFERENCE?

27. ELECTROMAGNETIC
SHIELDING

28. SHIELDING APPLIES TO ALL LEVELS
 Components  Systems
 Circuits  Cables
 Functional Stages  Platforms
 Equipments  Buildings

29. CABLES, CIRCUITS AND COMPONENTS ACT
AS ANTENNAS

30. REPRESENTATION OF SHIELDING PHENOMENA
FOR PLANE WAVES
Ey Inside of Enclosure
Hz
Incident WaveA Ey Transmitted Wave
Ey
B
H
Ey Attenuated
Hz Incident
Hz
Ey Hz
Reflected Wave
Wave Internal Reflecting
Outside World Metal Wave
Barrier

31. REFLECTION LOSS
( K  1) 2 ZW
R dB  20 log 10 ,K  VSWR
4K Zb
 Zw 
 20 log 10   , K  10
 4 Zb 
Where :
E
Z w  wave impedance 
H
jω μ jω μ
Z b  barrier impedance  
σ  jω ε σ
for ω ε   σ

32. REFLECTION LOSS (RdB) OF PLANE WAVES VS FREQUENCY
3kHz 30kHz 300kHz 3MHz 30MHz 300MHz
200
200
150 150
Copper
100 100
Iron*
50 Hypernick* 50
0
1kHz 10kHz 100kHz 1MHz 10MHz 100MHz 0
Radio Frequency
Valid for thickness > 3 
 = Skin Depth * Permeability assumed constant with frequency

33. ABSORPTION LOSS, A
Current Density
0.066
δ mm
f MHz μ r σ r

t
AdB  8.68 t / δ  131 t f MHz μ r σ r
where t  thickness in mm
f MHz  frequency in MHz
μ r  permeabili ty relative to copper
σ r  conductivi ty relative to copper

34. ABSORPTION LOSS VS FREQUENCY

35. TOTAL SHIELDING EFFECTIVENESS

36. PRINCIPAL BOX SHIELDING COMPROMISES
Holes or Slots Screw Spacing
Cover Plate for Convection Cooling = Slot Radiation
for Access
Status
Indicator
Lamp
Forced Air
Cooling
Panel Meter
Potentiometer
Connectors
Fuse
Switch

37. SLOT AND APERTURE LEAKAGE
L
t
h

t << h Shield Material
SE (dB)
20 V. P
dB .
/d
ec
.
•

Log Frequency • / 2

38. Shielded 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

39. PP
EMI-Fix Matrix - Fixes vs. Coupling Paths, Part 1
PP

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