EMC Fundamentals Presented By: Mike Violette Washington Laboratories, Ltd. September 15, 2006

1. EMC FundamentalsPresented By:Mike VioletteWashington Laboratories, Ltd.September 15, 2006

2. IntroductionElements of an EMI Situation • Source "Culprit" • Coupling method "Path" • Sensitive device "Victim" VICTIM SOURCE PATH

3. Let’s see how this all got startedDead Smart Guys • First Transmitters: Spark Devices • Heinrich Hertz (1857-1894) clarified and expanded on • James Clerk Maxwell’s Electromagnetic Theory • Marconi: first use & patent Maxwell Hertz Marconi

4. How Does EMI Affect Electronics? • Radiated and conducted interference • Conducted Interference Enters and Exits Equipment through Wiring and Cabling • Radiated Interference Enters and Exits Equipment through Wiring and Enclosure Penetration Radiated Susceptibility Radiated Emissions Conducted Susceptibility Conducted Emissions

5. Interference to TV Reception No Interference Two Interfering Signals Injected into TV

6. Common “Coupling Modes” Common and Differential Mode • Crosstalk (cabling and conductors) • Field to cable (“Antenna”) • Conducted (direct) • Field to enclosure

7. SOURCE VICTIM Crosstalk(cable-to-cable coupling)

8. Induced Current Radiated Coupling: Field to Cable Electromagnetic Wave Loop Area Coupling proportional to: E/H Field, Loop Area, Frequency

9. VDM VCM INoise COMMON and DIFFERENTIAL MODE • COMMON-MODE: “Line to Ground” • DIFFERENTIAL MODE: “Line-to-Line” (Normal Mode)

10. Loop Area Induced Current Radiated Coupling: Field to Cable Radio Electromagnetic Wave Patient Monitor VCM

11. NOISE Frequency (MHz) Frequency (Hz) Real Response Ideal Response Instrumentation Interference EKG Signal Interference Current, If

12. AMPLITUDE MODULATION AMPLITUDE MODULATION AMPLITUDE MODULATION Interference Current, If Effect of Modulation

13. How Does EMI Affect Electronics? • Electrostatic Discharge & Transient Pulses • ESD can induce “glitches” in circuits, leading to false triggering, errors in address & data lines and latch-up of devices • Upset • Damage • Degradation leading to future failure(s) Gee, the humidity is low in here. What’s this for?

14. C EKG Signal Interference Current C EKG Signal Interference Current Filtering Please, I’m very ticklish

15. Direct Indirect Surge Coupling • Lightning and pulse sources cause high-energy transients into power and data cables

16. T A F(t) Log F f = 1/T 2f 3f Spectrum of a Trapezoidal Wave (Characteristic of Digital Devices) T f =1/ptr A t F(t) tr Log F f = 1/pt Digital Equipment SourcesFourier Analysis Spectrum of a Square Wave

17. Equipment Emissions Limits

18. The decibel (dB) Named after me! • The dB is used in Regulatory Limits (FCC, CISPR, etc.) • The dB is a convenient way to express very big and very small numbers • The “Bel” was named after Alexander Graham Bell Bel = LOG10(P2/P1) • deciBel provides a more realistic scale: dB = 10LOG10(P2/P1) • Voltage & Current are expressed as follows: dB (V or I) = 20LOG10(V2/V1) “20LOG” derives from the conversion from Power to Voltage (ohm’s Law: P = E2/R)

19. dB • Can have several reference units: • Watt: dB above one Watt (dBW) • Milliwatt: dB above one milliwatt (dBm) • Volt: dBV • Microvolt: dBuV • Microamp: dBuA • picotesla: dBpT • Electric Field: dBuV/m • Radio Receiver Sensitivity ~ 10 dBuV • E-Field Limit for FCC: ~40-60 dBuV/m • Distance to moon: 107dBmile (20LOG2.5E+5miles) • National debt: 128dB$ (10LOG6E+12)

20. Broadband Sources • Man-made noise dominates • Intended transmissions, switching transients, motors, arcing • Intermittent operation of CW causes transient effects • Digital Switching • Inductive kick • Switch bounce • Digital Signaling • Broad spectrum based on pulse width & transition time • HDTV • CDMA • UWB Technologies

21. Pulsed SourcesFourier Analysis Fourier-> Do you like my new shirt? A f =1/ptr t F(t) Log F f = 1/pt tr Spectrum of a Pulse

22. Urban Ambient Profile Cell phone FM Radio Switching noise

23. Cables - Overview • Major coupling factor in radiating emissions from an equipment and coupling of emissions from other sources into an equipment • Acts as radiating “antenna”, receiving “antenna”, and cable-to-cable coupling mechanism • External cables are not typically part of the equipment design but the installation requirements must be considered during the design • Problem is a function of cable length, impedance, geometry, frequency of the signal and harmonics, current in the line, distance from cable to observation point • Frequency Effects: Tied into Cable Wavelength • For example, wavelength at FM Radio Band (100 MHz) is 1 meter • Human Body Resonance • = c/f = 3X108/frequency • = 300/fMHz

24. Cables - Length/Impedance • Efficiency as an antenna - function of length compared to wavelength • At typical data transfer rates - length is short • At harmonics or spurs the length may become long • Impedance mismatch creates a high SWR

25. How very important • Frequencies of testing from 26 MHz to 1 GHz • Corresponding cable lengths: • L ~ 11 meters @ 26 MHz to 30 cm @ 1 GHz • “Short” cables can be large contributors to Interference Problems • Power cables • Grounding wires • Patient cables • Data cables • Control harnesses • Structures!

26. E (& H) I V ~ Area Cables - Loops • Emissions are a function of 1) Current; 2) Loop Geometry; 3) Return Path of the Current • Current flow creates a magnetic field H=I/2R for a single wire model • Single wire case is not realistic • Loop geometry formed by the current carrying conductor and the return line contribute to the field strength • Electric field strength:

27. Filters - Overview • Passband • High pass • Low pass • Single component, L, Pi, T • Common mode; differential mode • Placement • Components • Lead length • Leakage Limitations

28. C EKG Signal C Noise Current Rejection Noise EKG Signal Attenuation of Noise EKG Signal Frequency (Hz) Noise Current Low Pass Filter

29. Filters - Types

30. Filters - Components • Discrete Component Filters • Component selection • Lead length considerations • Power Filter Modules • Filtered Connectors • Construction • Selective loading • Termination (bonding and grounding)

31. Circuit Design – Real Performance

32. Power Line Filter Typical Schematic Signal Line Filter Signal Line Filter (Screw-in Type) Filters

33. Filter - Placement • Isolate Input & Output • Establish boundaries with filters between • Input or Output interfaces and active circuitry • Digital and Analog • Compartments and Modules • Prevent bypass coupling • Control line exposure on line side of filter • Use dog-house compartment • Shielded cables to control exposed cable runs • Terminate - Terminate - Terminate • Low impedance to ground termination • Minimize lead length

34. Filter Filter IN Filter OUT Filter PerformancePoor Installation =Poor Performance

35. Filter Placement

36. Electric Field Coupling + - E-Field V+ Field Terminations on Inside Metal Sphere “Faraday Cage” - + V+ V=0 “Ground” 0V Potential Shield Concepts

37. I V Low residual field Ferrous Shield m >>1 I V Shield Concepts Magnetic Field Coupling Magnetic Field Shielding Common at powerline and low frequencies; High-current conditions

38. V=? + Effects of Openings Cable Leakage + - V+ Metal Sphere “Faraday Cage” V=0

39. ~ Radio Frequency Effects Shielded Enclosure VRF RF Source

40. RF Leakage Metal Box L VRF ~ RF Source L ~ l/2 Perfect Transmission

41. Shielding The Business Card Test Good to about 1 GHz

42. Shielding - Overview • Shields - conductive barriers • Reflection • Absorption • Materials • Electric field - conductivity • Magnetic field - permeability • Discontinuities • Windows • Vents • Seams • Panel components • Cable connections

43. Shielding Effectiveness Incident Field E1 Resultant Field E2 SHIELD Reflected ER SE = E2/E1 (dB)

44. Shielding -Reflection/Absorption Plane wave occurs when E to H wave impedance ratio = 1 k = 3.4 for t in inches and k = 134 for t in meters

45. Shielding - Material All are good electric field shields Need high u for Mag Field Shield

46. Shielding - Seams/Gaskets • Required openings offer no shielding in many applications • Apertures associated with covers tend to be long or require many contact points (close screw spacing) • Large opening treatment • Screens, ventilation covers, optic window treatments • WBCO formed to effectively close opening • Seam opening treatments • Overlapping flanges • Closely spaces screws or weld • Gasket to provide opening contact • Gasketed SE

47. Shielding - Penetration • Conductors penetrating an opening negates the shielding provided by absorption and reflection • Cables penetrations require continuation of the shield or • Conductors require filtering at the boundary • Cable shields require termination • Metal control shafts serve as a conductor • Use non-metallic • Terminate shaft (full circle)

48. Grounding - Overview • Purpose • Safety protection from power faults • Lightning protection • Dissipation of electrostatic charge • Reference point for signals • Reference point is prime importance for EMC • Potential problems • Common return path coupling • High common impedance • High frequency performance

49. Grounding - Impedance • Establish a low impedance return • Ground planes • Ground straps for high frequency performance • Establish single point or multipoint ground • Single point for low frequency or short distance • Distance(meters) < 15/f(MHz) • Multipoint for high frequency or long distance • Distance(meters) > 15/f(MHz)

50. Bonding • Bonds should have two basic characteristics • Low impedance < 2.5 milliohms • Mechanical & electro-chemical stability • Low impedance • Avoid contamination • Provide for flush junction to maximize surface contact • Use gaskets or fingerstock for seam bonds • Provide a connecting mechanism • Mechanical and electro-chemical stability • Torque to seat for the mechanical connection • Lock washers to retain bond • Allow for galvanic activity for dissimilar metals