ATI's Grounding and Shielding for EMC Technical Training Short Course Sampler

Professional Development Short Course On: Grounding and Shielding for EMC Instructor: Dr. William G. Duff (Bill)ATI Course Schedule: http://www.ATIcourses.com/schedule.htm http://www.aticourses.com/intro_to_grounding_shielding.htmATIs Grounding and Shielding for EMC:

www.ATIcourses.comBoost Your Skills 349 Berkshire Drive Riva, Maryland 21140with On-Site Courses Telephone 1-888-501-2100 / (410) 965-8805Tailored to Your Needs Fax (410) 956-5785 Email: ATI@ATIcourses.comThe Applied Technology Institute specializes in training programs for technical professionals. Our courses keep youcurrent in the state-of-the-art technology that is essential to keep your company on the cutting edge in today’s highlycompetitive marketplace. Since 1984, ATI has earned the trust of training departments nationwide, and has presentedon-site training at the major Navy, Air Force and NASA centers, and for a large number of contractors. Our trainingincreases effectiveness and productivity. Learn from the proven best.For a Free On-Site Quote Visit Us At: http://www.ATIcourses.com/free_onsite_quote.aspFor Our Current Public Course Schedule Go To: http://www.ATIcourses.com/schedule.htm

What Is Ground?• Earth Ground• Power Ground• Signal ground• Safety Ground• Return• Reference Level

Ground Means any ReferenceConductor Used for a Common Return

Grounding Misuse and Myths• Reasons for Grounding Are Not Clear• The Word "Grounding" is Often Misused when other Words are Meant, such as: Connect to Bonding Return Path Earthing• Many Myths Exist, such as: "Lower Impedance is Always Better" "Use Grounds for Digital-Circuit Reference" "Use Separate Safety, Instrument & System Gnd.• Reasons for Grounding Are Not Clear

Grounding for EMC• Ground Circuits, Equipments, Systems, Cables, Shields• Common Mode and Differential Mode Coupling• Avoid Ground Loops• More Grounds are not Better

Interconnected Equipment Having 29Questions = 229 = 500,000,000 Answers

Effects of Shared Ground Impedance• Common Source or Common Ground Impedance Coupling• EMI and signal use same impedance• Shared impedance provides path for EMI to couple from a source to a victim.• Minimizing the shared ground impedane will help mitigate the problem.• A single point ground may help.

Common Ground Impedance Common Mode EMI CMC Power Source Load CMC EMI EMI IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 10. Common Ground Impedence Common Mode EMI

Illustration of Common Mode Currents CMC 1 Power Source Load CMC 2 CMCIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 4. Illustration of Common Mode Currents

Illustration of Differential Mode Currents DCM1 Power Source Load DCM2 Figure 3. Illustration of Differential Mode Currents

Illustration of Common and Differential Mode Currents CMC 1 DMC 1 Power Source Load CMC 2 DMC 2 CMC IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 5. Illustration of Common and Differential Mode Currents Illustration of Common and Differential Mode Currents Illustration of Common and Differential Mode Currents

PRINCIPAL RADIATION SOURCES ON PRINTED CIRCUIT BOARD Radiation from IC dips Logic families clock rates • Large single-layer board • PCB card cage with back plane • Multi-layer board Radiation from ribbon cables

Common Mode Radiated EMI Radiated EMI CMC 1 Power Source Load CMC 2 CMCIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Metallic Structure Figure 11. Common Mode Radiated EMI

Ground-Loop CouplingConverts Common Mode Voltage to Differential-Mode Voltage

Using Ferrites to Absorb Common-Mode EMI

Added Feed-Thru Capacitors -Help Reduce ESD and RF Susceptibility Note: Max Cap Value Must Support Data Bandwidth C < 1/ωR

Coupling Rejection Offered by Twisting Wire Pair

SHIELDING APPLIES TO ALL LEVELS• Components • Systems• Circuits • Cables• Functional Stages • Platforms• Equipments • Buildings

CONCEPTUAL ILLUSTRATION OF FIELD INTENSITIES VS. SOURCE TYPE AND DISTANCE High Current Corresponds to Low Current Corresponds to Low Impedance High Impedance High E Low E Monopole Eθ Eθ Loop Hθ Low H I High H Hθ V Near Far Near Far Field Field V Field Field High-Impedance Source Low - Impedance, Electric-Field Source and Wave Magnetic - Field Source and Wave

FIELD IMPEDANCE AS A FUNCTION OF DISTANCE FROM SOURCE

ELECTRIC FIELD VS SOURCE DISTANCE

SUMMARY Near Field Far FieldElectric Fields Plane Waves Are Generated for allZ > 377 OhmsRadiated From High Source Impedances forImpedance Sources Distance Greater ThanMagnetic Fields Approximately 1/6 of a WavelengthZ < 377 OhmsRadiated from LowImpedance Sources

REPRESENTATION OF SHIELDING PHENOMENA FOR PLANE WAVES Ey Inside of Enclosure Hz Incident WaveA Ey Transmitted Wave Ey B H Ey Attenuated Hz Incident Hz Ey Hz Reflected Wave Wave Internal Reflecting Outside World Metal Wave Barrier

SHIELDING EFFECTIVENESS (SE) SEdB = 20 log10(Eoutside/Einside) SEdB = 20 log10(Houtside/Hinside)where: E = Electric-field Strength H = Magnetic-field Strength SEdB = RdB + AdB where: RdB = Reflection Loss in dB AdB = Absorption Loss in dB

REFLECTION LOSS ( K + 1)2 ZW RdB = 20 log10 ,K = VSWR 4K Zb  Zw  ≅ 20 log10  , K ≥ 10  4 Zb Where : E Zw = wave impedance = H jω μ jω μ Zb = barrier impedance = = σ + jω ε σfor ω ε < < σ

REFLECTION LOSS (RdB) OF PLANE WAVES VS FREQUENCY 3kHz 30kHz 300kHz 3MHz 30MHz 300MHz 200 200 150 150 Copper 100 100 Iron* 50 Hypernick* 50 0 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz 0 Radio Frequency Valid for thickness > 3 δ δ = Skin Depth * Permeability assumed constant with frequency

ABSORPTION LOSS, A Current Density 0.066 δ= mm f MHz μ r σ r δ t AdB = 8.68 t / δ = 131 t f MHz μ r σ r where t = thickness in mm f MHz = frequency in MHz μ r = permeability relative to copper σ r = conductivity relative to copper

ABSORPTION LOSS VS FREQUENCY

PRINCIPAL BOX SHIELDING COMPROMISES Holes or Slots Screw Spacing Cover Plate for Convection Cooling = Slot Radiation for Access Status Indicator Lamp Forced Air Cooling Panel Meter Potentiometer Connectors Fuse Switch

SLOT AND APERTURE LEAKAGE L t h  t << h Shield MaterialSE (dB) •  Log Frequency •λ / 2

Reducing Radiation Coupling by Shielding Cable Wires

To learn more please attend ATI course Grounding and Shielding for EMC Please post your comments and questions to our blog: http://www.aticourses.com/blog/ Sign-up for ATIs monthly Course Schedule Updates :http://www.aticourses.com/email_signup_page.html

ATI's Grounding and Shielding for EMC Technical Training Short Course Sampler

by Jim Jenkins on Mar 15, 2011

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ATI’s Grounding and Shielding for EMC Technical Training Short Course Sampler — Presentation Transcript