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Forum De L’Electronique 2006
Taking the Guesswork out of EMC/EMI Design!
Flomerics
Forum de l’électronique 2006
David P. Johns (Flomerics Inc)
Yannis Braux (Flomerics France)
Forum de l’électronique 2006
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.
Forum de l’électronique 2006
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.
Forum de l’électronique 2006
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
Forum de l’électronique 2006
SE: EMC Corp Test Box
Vertical slots
(1.5 x 0.25 in.)
Horizontal slots
(1.5 x 0.25 in.)
Overlapping Lid
(1cm overlap)
Corner seams
(4 in. x 10 mil)
Aluminum Box
(6 x 6 x 4 in.)
Noise Source
(106.25 MHz clock)
Forum de l’électronique 2006
FLO/EMC Simulation Model
Wire loops combined with monopole for noise source
Shapes assigned electrical properties of air to model large apertures
Equivalent model for air-vent (perforated plate)
Seams drawn on enclosure
Forum de l’électronique 2006
3D TLM Analysis
Large apertures are meshed
Seams are sub-cell
Wires and circuits are sub-cell
Fine cells are recombined away from geometry – reduces cell count from 412k to 60k
Grid uses graded density mesh
E and H fields calculated in each cell
Forum de l’électronique 2006
From Time to Frequency
Impulse Response Frequency Response
Fourier Transform applied to Impulse Response…
Forum de l’électronique 2006
Emissions Cylinder Scans
Vertical Polarization
Horizontal Polarization
Emissions vary with angle around the box
SE calculation must take this into account
Forum de l’électronique 2006
Delta Test for SE
SE (dB) = E REF (dB) – ESHIELDED (dB)
Forum de l’électronique 2006
SE of EMC Test Box
Forum de l’électronique 2006
Surface Current
530 MHz 954 MHz
Forum de l’électronique 2006
Surface Current
1590 MHz 1590 MHz1908 MHz
Forum de l’électronique 2006
Guesswork Design
• Try closing the 8 horizontal slots to improve the shielding…
• It may work!
Forum de l’électronique 2006
SE with Apertures Taped
Forum de l’électronique 2006
Electromagnetic Interference - EMI
• NATO definition;– “An electromagnetic
disturbance which interrupts, obstructs, or otherwise degrades the effective performance of electronic or electrical equipment”
Forum de l’électronique 2006
Sources of EMI
1 KHz 1 MHz 10 MHz
100 MHz
1 GHz 10 GHz 100 GHz
Lightning
Nuclear EMP
HIRF
Radar
Digital Electronics
Forum de l’électronique 2006
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/ – e-t/)
Io = 218,810 A = 88.07 s =1.545 s
Forum de l’électronique 2006
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
Forum de l’électronique 2006
Lightning Test Problem
• 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
Lightning conductor
Slot aperture (12 x 0.01)
PML
M. Sarto, IEEE trans. On EMC, Vol. 43, No. 3, August 2001
Forum de l’électronique 2006
Simulated Magnetic Field
Diffusion through walls slows responseLightning waveform (source)
Hz
Hx
Hy
Current in conductor Al box
Forum de l’électronique 2006
Simulated Magnetic Field
Faster response with slot presentMagnetic field reduced with PEC side walls
Hz
Hx
HyHz
Hx
Hy
PEC side walls, Al lid PEC side walls, Al lid, slotted front panel
Forum de l’électronique 2006
Current Distribution
100 KHz
10 MHz
Diffusion dominates Slot leakage dominates
Forum de l’électronique 2006
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
Forum de l’électronique 2006
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/ – e-t/)Eo = 50,000 V/mK = 1.3 = 25 nS = 1.67 nS
Forum de l’électronique 2006
EMP Test Problem
Carbon fiber reinforced front panel
Incident EMP wave 50 KV/m, 5ns rise time and 200ns fall time
70cm size box
Forum de l’électronique 2006
H Field Simulation & Test Results
TLM prediction measured
M. D’Amore et. al, IEEE trans. On EMC, Vol. 42, No. 1, February 2000
Forum de l’électronique 2006
E Field Simulation & Test Results
TLM prediction measured
Forum de l’électronique 2006
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…