1. Taking the Guesswork out of EMC/EMI Design!
Flomerics
Forum de l’électronique 2006
David P. Johns (Flomerics Inc)
Yannis Braux (Flomerics France)

2. EMC Design
EMC/EMI Design has been far from an exact science.
Engineers have not been able to say:
“Do it like this and it will work…”.
Instead, Engineers have said:
“Do it like this and it may work”,
or,
“This is more likely to work, but at a higher cost!”
Considerable guesswork is involved.
In the past, EMC/EMI design has been far from an exact science. EMC/EMI Engineers have not been able to say, “Do it like this and it will work”. Instead, by drawing on past experience and applying general design guidelines, Engineers have said “Do it like this and it may work”, or, “This is more likely to work, but at a higher cost”.
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3. EMC Design EMC/EMI Design is a moving target!
The EM environment is flooding:
proliferation of wireless communications devices
products emitting higher frequencies (faster switching)
Below GHz, Radiated Emissions launch mechanisms are relatively well understood
Above GHz…a different story!
Design rules that worked in the past may not work in the future.
To make matters worse, EMC/EMI design is a constantly moving target. The electromagnetic environment is flooding, due to the proliferation of wireless communications devices. Electronics products are emitting higher frequencies due to faster switching and circuits are becoming more sensitive to interference. Design techniques that worked in the past may not work in the future. Considerable guesswork is involved.

4. EMC Design
EM Design tools have matured considerably over the last 5 years
Tremendous opportunity for EMC/EMI Engineers to:
work more effectively with greater confidence
identify problems earlier in Design
Be more definite and accurate in their recommendations
minimize the test, fix, re-test cycle
pass compliance and enter the market quicker
There is a growing desire for EMC/EMI Engineers to identify problems earlier in design, to more definite and accurate in their recommendations and to minimize the test, fix, re-test cycle, enabling products to pass compliance and enter the market quicker. Electromagnetic simulation tools have matured considerably over the last 5 years and offer tremendous opportunity for EMC/EMI Engineers to work more effectively and with greater confidence.

5. SE: EMC Corp Test Box Aluminum Box (6 x 6 x 4 in.) Overlapping Lid
(1cm overlap)
Horizontal slots
(1.5 x 0.25 in.)
Vertical slots
(1.5 x 0.25 in.)
Noise Source
( MHz clock)
Corner seams
(4 in. x 10 mil)

6. FLO/EMC Simulation Model
Seams drawn on enclosure
Equivalent model for air-vent (perforated plate)
Shapes assigned electrical properties of air to model large apertures
Wire loops combined with monopole for noise source

7. 3D TLM Analysis E and H fields calculated in each cell
Seams are sub-cell
Fine cells are recombined away from geometry – reduces cell count from 412k to 60k
Grid uses graded density mesh
Large apertures are meshed
Wires and circuits are sub-cell

8. From Time to Frequency Fourier Transform applied to Impulse Response…
Frequency Response

9. Emissions Cylinder Scans
Emissions vary with angle around the box
Vertical Polarization
Horizontal Polarization
SE calculation must take this into account

10. Delta Test for SE
SE (dB) = E REF (dB) – ESHIELDED (dB)

11. SE of EMC Test Box

12. Surface Current
530 MHz
954 MHz

13. Surface Current
1590 MHz
1908 MHz
1590 MHz

14. Guesswork Design
Try closing the 8 horizontal slots to improve the shielding…
It may work!

15. SE with Apertures Taped

16. Electromagnetic Interference - EMI
NATO definition;
“An electromagnetic disturbance which interrupts, obstructs, or otherwise degrades the effective performance of electronic or electrical equipment”
Flight critical and mission critical systems

17. Sources of EMI 1 KHz 1 MHz 10 MHz 100 MHz 1 GHz 10 GHz 100 GHz
Lightning
Nuclear EMP
HIRF
Radar
Digital Electronics

18. Lightning Analysis
MIL-STD-464 defines a current component A that represents a severe lightning stroke
The component can be modeled by a double exponential waveform
TLM is a time-domain technique and the lightning waveform can be applied as a transient source
i(t) = Io(e-t/a – e-t/b)
Io = 218,810 A
a = ms
b =1.545 ms

19. Current Diffusion
Lightning is a low-frequency phenomenon (1 Hz to 10 MHz)
At low frequencies, metals are not good magnetic shields;
Consider an Aluminum panel of thickness 1.2mm
Current will diffuse through the metal according to the skin depth

20. Lightning Test Problem
Lightning conductor
13.2m sized metal box with interchangeable lid and front panel;
Side walls are perfect electrical conductors (PEC)
Top can be PEC or 1.2mm thick Aluminum
Front panel can be closed or contain a slot
Lightning current driven into conductor
Magnetic field calculated inside the box
PML
Slot aperture (12 x 0.01)
M. Sarto, IEEE trans. On EMC, Vol. 43, No. 3, August 2001

21. Simulated Magnetic Field
Current in conductor
Al box Hz Hx Hy
Lightning waveform (source)
Diffusion through walls slows response

22. Simulated Magnetic Field
PEC side walls, Al lid
PEC side walls, Al lid, slotted front panel Hz Hx Hy Hx Hy Hz
Magnetic field reduced with
PEC side walls
Faster response with slot present

23. Current Distribution 100 KHz 10 MHz Diffusion dominates
Slot leakage dominates

24. Electromagnetic Pulse (EMP)
Gamma rays from a nuclear burst collide with air molecules producing Compton electrons
The Compton electrons interact with the earth's magnetic field, producing an intense electromagnetic pulse (EMP) that propagates downward to the earth's surface
If a weapon were to be detonated 250 miles above the US, nearly the entire nation would be affected
Peak electric fields can reach tens of thousands of volts per meter

25. EMP Analysis
MIL-STD-464 defines an Electric field transient that represents a high altitude EMP (HEMP)
Transient is modeled by a double exponential waveform
EMP spectrum ranges from 1 MHz to 1 GHz
E(t) = k Eo(e-t/a – e-t/b)
Eo = 50,000 V/m
K = 1.3
a = 25 nS
b = 1.67 nS

26. EMP Test Problem 70cm size box Carbon fiber reinforced front panel
Incident EMP wave 50 KV/m, 5ns rise time and 200ns fall time

27. H Field Simulation & Test Results
TLM prediction
measured
M. D’Amore et. al, IEEE trans. On EMC, Vol. 42, No. 1, February 2000

28. E Field Simulation & Test Results
TLM prediction
measured

29. Summary EM Simulation has come a long way over the last 5 years
Simulation enables EMC/EMI Engineers to be more scientific in their approach to Design
Analysis helps Engineers justify Design changes
Engineers can Design with greater confidence and certainty
Many thanks to Boris Shusterman and EMC Corp for contributing applications and test results to the presentation…