Taking the Guesswork out of EMCEMI Design

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Taking the Guesswork out of EMC/EMI Design!

• Flomerics
• Forum de lélectronique 2006

David P. Johns (Flomerics Inc) Yannis Braux
(Flomerics France)
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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.

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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 GHza different story!
• Design rules that worked in the past may not work
  in the future.

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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

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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 (106.25 MHz clock)
Corner seams (4 in. x 10 mil)
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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
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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
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From Time to Frequency
Fourier Transform applied to Impulse Response
Impulse Response
Frequency Response
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Emissions Cylinder Scans
Emissions vary with angle around the box
Vertical Polarization
Horizontal Polarization
SE calculation must take this into account
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Delta Test for SE
SE (dB) E REF (dB) ESHIELDED (dB)
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SE of EMC Test Box
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Surface Current
530 MHz
954 MHz
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Surface Current
1908 MHz
1590 MHz
1590 MHz
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Guesswork Design

• Try closing the 8 horizontal slots to improve the
  shielding
• It may work!

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SE with Apertures Taped
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Electromagnetic Interference - EMI

• NATO definition
• An electromagnetic disturbance which interrupts,
  obstructs, or otherwise degrades the effective
  performance of electronic or electrical equipment

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Sources of EMI
1 KHz
1 MHz
10 MHz
100 MHz
1 GHz
10 GHz
100 GHz
Lightning
Nuclear EMP
HIRF
Radar
Digital Electronics
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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 88.07
ms b 1.545 ms
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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

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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
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Simulated Magnetic Field
Al box
Current in conductor
Hz
Hx
Hy
Diffusion through walls slows response
Lightning waveform (source)
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Simulated Magnetic Field
PEC side walls, Al lid
PEC side walls, Al lid, slotted front panel
Hz
Hy
Hx
Hx
Hy
Hz
Faster response with slot present
Magnetic field reduced with PEC side walls
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Current Distribution
100 KHz
10 MHz
Diffusion dominates
Slot leakage dominates
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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

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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
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EMP Test Problem
70cm size box
Carbon fiber reinforced front panel
Incident EMP wave 50 KV/m, 5ns rise time and
200ns fall time
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H Field Simulation Test Results
TLM prediction
measured
M. DAmore et. al, IEEE trans. On EMC, Vol. 42,
No. 1, February 2000
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E Field Simulation Test Results
TLM prediction
measured
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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