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Forum De LElectronique 2006 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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Forum de lélectronique 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.

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Forum de lélectronique 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.

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Forum de lélectronique 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

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Forum de lélectronique 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 ( MHz clock)

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Forum de lélectronique 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

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Forum de lélectronique D 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

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Forum de lélectronique 2006 From Time to Frequency Impulse ResponseFrequency Response Fourier Transform applied to Impulse Response…

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Forum de lélectronique 2006 Emissions Cylinder Scans Vertical Polarization Horizontal Polarization Emissions vary with angle around the box SE calculation must take this into account

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Forum de lélectronique 2006 Delta Test for SE SE (dB) = E REF (dB) – E SHIELDED (dB)

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Forum de lélectronique 2006 SE of EMC Test Box

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Forum de lélectronique 2006 Surface Current 530 MHz954 MHz

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Forum de lélectronique 2006 Surface Current 1590 MHz 1908 MHz

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Forum de lélectronique 2006 Guesswork Design Try closing the 8 horizontal slots to improve the shielding… It may work!

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Forum de lélectronique 2006 SE with Apertures Taped

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Forum de lélectronique 2006 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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Forum de lélectronique 2006 Sources of EMI 1 KHz1 MHz10 MHz100 MHz1 GHz10 GHz100 GHz Lightning Nuclear EMP HIRF Radar Digital Electronics

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Forum de lélectronique 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) = I o (e -t/ – e -t/ ) I o = 218,810 A = s =1.545 s

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Forum de lélectronique 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

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Forum de lélectronique 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

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Forum de lélectronique 2006 Simulated Magnetic Field Diffusion through walls slows responseLightning waveform (source) Hz Hx Hy Current in conductor Al box

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Forum de lélectronique 2006 Simulated Magnetic Field Faster response with slot presentMagnetic field reduced with PEC side walls Hz Hx Hy Hz Hx Hy PEC side walls, Al lid PEC side walls, Al lid, slotted front panel

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Forum de lélectronique 2006 Current Distribution 100 KHz 10 MHz Diffusion dominatesSlot leakage dominates

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Forum de lélectronique 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

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Forum de lélectronique 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 E o (e -t/ – e -t/ ) E o = 50,000 V/m K = 1.3 = 25 nS = 1.67 nS

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Forum de lélectronique 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

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Forum de lélectronique 2006 H Field Simulation & Test Results TLM predictionmeasured M. DAmore et. al, IEEE trans. On EMC, Vol. 42, No. 1, February 2000

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Forum de lélectronique 2006 E Field Simulation & Test Results TLM predictionmeasured

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Forum de lélectronique 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…

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