Presentation on theme: "Taking the Guesswork out of EMC/EMI Design!"— Presentation transcript:
1Taking the Guesswork out of EMC/EMI Design! FlomericsForum de l’électronique 2006David P. Johns (Flomerics Inc)Yannis Braux (Flomerics France)
2EMC DesignEMC/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”.?????????????
3EMC Design EMC/EMI Design is a moving target! The EM environment is flooding:proliferation of wireless communications devicesproducts emitting higher frequencies (faster switching)Below GHz, Radiated Emissions launch mechanisms are relatively well understoodAbove 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.
4EMC DesignEM Design tools have matured considerably over the last 5 yearsTremendous opportunity for EMC/EMI Engineers to:work more effectively with greater confidenceidentify problems earlier in DesignBe more definite and accurate in their recommendationsminimize the test, fix, re-test cyclepass compliance and enter the market quickerThere 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.
5SE: 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)
6FLO/EMC Simulation Model Seams drawn on enclosureEquivalent model for air-vent (perforated plate)Shapes assigned electrical properties of air to model large aperturesWire loops combined with monopole for noise source
73D TLM Analysis E and H fields calculated in each cell Seams are sub-cellFine cells are recombined away from geometry – reduces cell count from 412k to 60kGrid uses graded density meshLarge apertures are meshedWires and circuits are sub-cell
8From Time to Frequency Fourier Transform applied to Impulse Response… Frequency Response
9Emissions Cylinder Scans Emissions vary with angle around the boxVertical PolarizationHorizontal PolarizationSE calculation must take this into account
10Delta Test for SESE (dB) = E REF (dB) – ESHIELDED (dB)
16Electromagnetic 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
18Lightning AnalysisMIL-STD-464 defines a current component A that represents a severe lightning strokeThe component can be modeled by a double exponential waveformTLM is a time-domain technique and the lightning waveform can be applied as a transient sourcei(t) = Io(e-t/a – e-t/b)Io = 218,810 Aa = msb =1.545 ms
19Current DiffusionLightning 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 1.2mmCurrent will diffuse through the metal according to the skin depth
20Lightning Test Problem Lightning conductor13.2m sized metal box with interchangeable lid and front panel;Side walls are perfect electrical conductors (PEC)Top can be PEC or 1.2mm thick AluminumFront panel can be closed or contain a slotLightning current driven into conductorMagnetic field calculated inside the boxPMLSlot aperture (12 x 0.01)M. Sarto, IEEE trans. On EMC, Vol. 43, No. 3, August 2001
21Simulated Magnetic Field Current in conductorAl boxHzHxHyLightning waveform (source)Diffusion through walls slows response
22Simulated Magnetic Field PEC side walls, Al lidPEC side walls, Al lid, slotted front panelHzHxHyHxHyHzMagnetic field reduced withPEC side wallsFaster response with slot present
24Electromagnetic Pulse (EMP) Gamma rays from a nuclear burst collide with air molecules producing Compton electronsThe Compton electrons interact with the earth's magnetic field, producing an intense electromagnetic pulse (EMP) that propagates downward to the earth's surfaceIf a weapon were to be detonated 250 miles above the US, nearly the entire nation would be affectedPeak electric fields can reach tens of thousands of volts per meter
25EMP AnalysisMIL-STD-464 defines an Electric field transient that represents a high altitude EMP (HEMP)Transient is modeled by a double exponential waveformEMP spectrum ranges from 1 MHz to 1 GHzE(t) = k Eo(e-t/a – e-t/b)Eo = 50,000 V/mK = 1.3a = 25 nSb = 1.67 nS
26EMP Test Problem 70cm size box Carbon fiber reinforced front panel Incident EMP wave 50 KV/m, 5ns rise time and 200ns fall time
27H Field Simulation & Test Results TLM predictionmeasuredM. D’Amore et. al, IEEE trans. On EMC, Vol. 42, No. 1, February 2000
28E Field Simulation & Test Results TLM predictionmeasured
29Summary 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 DesignAnalysis helps Engineers justify Design changesEngineers can Design with greater confidence and certaintyMany thanks to Boris Shusterman and EMC Corp for contributing applications and test results to the presentation…