Todd H. Hubing. Michelin Professor of Vehicle Electronics Clemson University

Transcription

1 Todd H. Hubing Michelin Professor of Vehicle Electronics Clemson University

2 August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 2

3 August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 3

4 August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 4

5 Tapes, Foils and Gaskets August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 5

6 Coating, Plating, Glue August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 6

7 Circuit Board Shields August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 7

8 Absorbing Materials August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 8

9 Shielded Air Vents August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 9

10 There are 4 possible EM coupling mechanisms! Conducted Coupling Electric Field Coupling Magnetic Field Coupling Radiation Coupling Shielding strategies depend on the type of coupling. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 10

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12 Electric field lines start on positive charge and end on negative charge. Electric field lines start on conductors with one voltage and terminate on conductors with a lower voltage. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 12

13 - V + August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 13

14 - V + August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 14

15 - V + August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 15

16 - V + August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 16

17 (a.) Electric Field Shielding (b.) + V - - V+ (c.) Field lines are intercepted and redirected August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 17

18 Any two conductors at different potentials (voltages) have electric field lines between them. It is important to be able to visualize the electric field in order to mitigate coupling effectively. Shielding involves capturing and redirecting the electric field. Materials to use: Good conductors such as copper, aluminum, steel, etc. Electric field shields are usually connected to something labeled ground. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 18

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20 Magnetic field lines circulate around flowing electric charge (current). Lines of magnetic field do not start or stop. They always close on themselves. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 20

21 Magnetic Field Shielding (at low frequencies) August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 21

22 Material Relative Permeability Gold, copper, aluminum 1 Concrete, water, air, vacuum 1 Ferrite U60 (UHF Chokes) 8 Common Steel Pure Nickel 600 Ferrite M33 (inductors) 750 Pure Iron 5,000 Permalloy (20% iron, 80% nickel) 8,000 Ferrite T38 (RF Transformers) 10,000 Mu-metal 20,000 50,000 Supermalloy (recording heads) 100,000 August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 22

23 You can t stop a magnetic flux line; you can only redirect it. It is important to be able to visualize the magnetic field in order to mitigate coupling effectively. Shielding involves capturing and redirecting the magnetic field. Materials to use: high permeability materials such as steel or iron-nickel alloys. Grounding does not affect the shielding effectiveness of LF magnetic field shields. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 23

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25 Magnetic Field Shielding (at high frequencies) August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 25

26 You can t stop a magnetic flux line; you can only redirect it. At frequencies above a few khz, magnetic flux lines will not pass through good conductors due to eddy currents induced in these conductors. Shielding involves redirecting the magnetic field. Materials to use: thick aluminum, copper or steel plates. Grounding does not affect the shielding effectiveness of HF magnetic field shields. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 26

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28 E ref E inc E E s s 0 0 E slab E inc T E 1 T E 2 1 s s 0 August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 28

29 E trans E inc 2 s 0 s s t e For good conductors: j j j e j 4 S. E. 20 log E E inc trans S. E. 20 log 0 4 s 20 log e t R db A db Note: These are NOT accurate representations of the relative amounts of power reflected and absorbed. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 29

30 Copper (10 m thick) Schelkunoff decomposition: SE (db) = R(dB) + A(dB) + B(dB) Mismatch decomposition: SE (db) = L M (db) + L D (db) Nanofiber Composite (100 m thick) August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 30

31 ZW E H E 1 2 f r 0 Z H H E 2 f r W 0 August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 31

32 Shielding Effectiveness Measurements power received at the termination S. E. 10log forward power from thesource August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 32

33 A shield made of a material with a shielding effectiveness of 100 db will reduce the radiation from an enclosed source by, a.) 100 db b.) at least 100 db c.) between 0 db and 100 db d.) possibly less than 0 db August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 33

34 What makes an efficient antenna? l/2 Half-Wave Dipole Electrically Small Loop l/4 Quarter-Wave Monopole Size Two Halves August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 34

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36 Shielded Enclosure August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 36

37 screw overlapping Seam finger stock conductive gasket August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 37

38 V V metal connector shell plastic connector shell 360-degree connection to shield pigtail connection to shield August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 38

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40 Drain Wire 4 Twisted Wire Pairs Foil Shield Foil provides highfrequency shielding. Drain wire carries most of the lowfrequency current. PVC Jacket CAT5e Cable August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 40

41 Foil provides highfrequency shielding. Braid carries highcurrents. PVC Jacket August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 41

42 Serves different purposes in different applications. Sometimes carries intentional signal currents. This is an example of self-shielding. May prevent coupling of external electric or magnetic fields to signals carried by wires in the cable. Beware of transfer impedance data. It should only be used to compare similar cables for a similar application measured with the same test set-up. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 42

43 Electric field shielding, magnetic field shielding, cable shielding and shielded enclosures are very different concepts requiring different materials and approaches. It is important to be understand the coupling mechanism you are attempting to attenuated before coming up with a shielding strategy. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 43

44 Electric field shields terminate or redirect electric fields. Where they are grounded is often critical. Magnetic fields cannot be terminated. Magnetic field shields redirect the magnetic field. Low frequency (<khz) magnetic fields must be redirected with high permeability materials. High frequency magnetic fields can be redirected with good conductors of sufficient thickness. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 44

45 Shields and imperfect shielded enclosures can significantly increase radiated emissions. Shields reduce radiated emissions by disrupting the coupling from near-field sources and the antennas in a system. In the near field, shields are either electric or magnetic field shields that redirect high-frequency current flow. August 4, 2014 IEEE EMC Symposium Fundamentals Workshop 45