electromagnetic shielding of cables and connectors

7/28/2019 Electromagnetic Shielding of Cables and Connectors

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4/2002 IEEE-EMC 2002 Cable Zt 1

ANALYSIS OF ELECTROMAGNETIC

SHIELDING OF CABLES ANDCONNECTORS

(Keeping Currents/Voltages Where They

Belong)

ANALYSIS OF ELECTROMAGNETICANALYSIS OF ELECTROMAGNETIC

SHIELDING OF CABLES ANDSHIELDING OF CABLES ANDCONNECTORSCONNECTORS

(Keeping Currents/Voltages Where They(Keeping Currents/Voltages Where They

BelongBelong))

Lothar O. (Bud) Hoeft, PhDConsultant, Electromagnetic Effects

9013 Haines Ave., NEAlbuquerque, NM 87112-3921

Voice/Fax: (505) 298-2065E-Mail: [email protected]


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DEFINITION OF SHIELDING

EFFECTIVENESS

DEFINITION OF SHIELDING

EFFECTIVENESS

IEEE DEFINITION:"for a given external source, the ratio of electric or magnetic field

strength at a point before and after placement of the shield in

question."

RATIO OF CURRENTS:Commonly used to convert surface transfer impedance to shielding

effectiveness.

S. E. = 20 log ( Iin/Iext )

At low frequencies:S. E. = 20 log ( Zt / (R1 + R2 ))

Ratio of Powers

Preferred by some S. E. = 10 log ( Pin / P ext ) Other Definitions Have Been Used-- Some Logical, Some Illogical


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DEFINITION OF SURFACE

TRANSFER IMPEDANCE

DEFINITION OF SURFACEDEFINITION OF SURFACE

TRANSFER IMPEDANCETRANSFER IMPEDANCE

Zt = (1/Io ) dV/dz

Io = Current flowing on Shield

dV/dz = Voltage per unit length on inside of shield

For Connectors, V is a point source

Zt = Voc / Iowhere Voc is the open circuit voltage on inside of shield

Similar To Common Impedance Coupling Current On One Side Of Barrier Produces Voltage On Other

Side Of Barrier Due To Impedance Of Barrier

At Low Frequencies, Impedance Is Resistance Due ToCurrent Diffusion And Contact Resistance At High Frequencies, Impedance Is Mutual Inductance Due To

Apertures, Porpoising, Etc.


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ELECTRICAL LENGTHELECTRICAL LENGTH

If the system is smaller than a wavelength, it iselectrically small and all voltages, currents, and fields

are the same throughout the system and the system

may be analyzed using lumped parameters. This is

usually true when the length is less than a tenth

wavelength.

If the system is larger than a wavelength, it iselectrically large and the voltages, currents, and fields

will depend on location, as well as time. Exact analysis

is much more complex, but simplifying assumptions

can sometimes be made. The system should be viewed

as a collection of transmission lines.


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THE SOLID PIPE APPROXIMATIONTHE SOLID PIPE APPROXIMATION

Only Current Diffusion Is Important At Low Frequencies, Zt Equals D.C. Resistance Coupling Decreases Dramatically by a Few Tens of kHz ZT = RO (1 +j) (T/)/ Sinh ((1 +j) (T/)) where:

T = Wall Thickness

Ro = D. C. Resistance = 1/(2 a T)

a = Shield Radius

= Conductivity

= Skin Depth = 1/( f )1/2

f = Frequency

= Permeability Of Shield Material = 4 x 10-7r


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SOLID PIPE AND SURFACE/CONTACT

RESISTANCE MODEL

SOLID PIPE AND SURFACE/CONTACT

RESISTANCE MODEL

Expect Square Root of Frequency (10 dB/decade)Dependence Above Diffusion Cutoff Frequency

Many Points Of Contact

Resistance of Each Point of Contact is FrequencyDependent Because Current is Carried on OuterSurface at High Frequencies (Skin Effect)

Theory is Not as Precise as Desirable, but Effectis Real

For Connectors, the Predominant Effect Above aFew Hundred kHz


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PIPE, SURFACE/CONTACT

RESISTANCE, MUTUAL INDUCTANCE

(APERTURE/PORPOISING) MODEL

PIPE, SURFACE/CONTACTPIPE, SURFACE/CONTACT

RESISTANCE, MUTUAL INDUCTANCERESISTANCE, MUTUAL INDUCTANCE

(APERTURE/PORPOISING) MODEL(APERTURE/PORPOISING) MODEL

Includes All Mechanisms For Imperfect Shields

ZT = RO (1 +j) (T/)/ Sinh ((1 + j) (T/)) +j M

= Angular Frequency = 2 f

M = Shield Mutual Inductance

Mutual Inductance May Be Due To Aperturesor Porpoising Coupling

Porpoising Dominates in Most Braided Shields


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MEASURED SURFACE TRANSFER

IMPEDANCE OF 1-1/4 DIAMETER

Cu PIPE WITH A SINGLE HOLE

MEASURED SURFACE TRANSFERMEASURED SURFACE TRANSFER

IMPEDANCE OF 1-1/4 DIAMETERIMPEDANCE OF 1-1/4 DIAMETER

Cu PIPE WITH A SINGLE HOLECu PIPE WITH A SINGLE HOLE


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APERTURE AND PORPOISING

COUPLING

APERTURE AND PORPOISINGAPERTURE AND PORPOISING

COUPLINGCOUPLING

High Frequency Effects Modeled As Mutual Inductance (f > 1 MHz) Aperture Coupling Depends On Magnetic

Polarizability

M12

= O

m

/( D)2

m = 4 r3/3 (circular hole) m = w2 length/16 (rectangular slot)

Electric Field Contribution Can Be Included as{Effective m} = (1 + (e/ m) )m

Usually e = m/2 and

{Effective e} = 1.5 m


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PORPOISING COUPLINGPORPOISING COUPLINGPORPOISING COUPLING

No Calculations

Depends on Contact Impedance BetweenCarriers of Braid

Opposite in Phase from Aperture Coupling Balancing Aperture Against Porpoising Results

in Optimized Braid

Dominates When Optical Coverage is GreaterThan Optimum


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LONG LINE EFFECTSLONG LINE EFFECTS


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MEASUREMENT OF SURFACE

TRANSFER IMPEDANCE (2)

MEASUREMENT OF SURFACE

TRANSFER IMPEDANCE (2)

Triaxial--many Configurations Reference Plane is a Problem Many Configurations Are Not Broadband IEC 96-1

Traditional Triaxial Inside-Out (Terminated/Broadband) Line Injection (Terminated/Broadband)

Mil-C-85485 Mil-C-38999

Quadraxial All Transmission Lines Are Terminated Relatively Broadband and Good Reference Plane


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CABLE AND CONNECTOR

CALIBRATION STANDARDS

CABLE AND CONNECTOR

CALIBRATION STANDARDS

5/8 Diameter Brass Tube.

RDC = 1 m

Connector Calibration Standard

MMNH-4


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MIL-STD-1344A MODE STIRRED

METHOD FOR MEASURING

SHIELDING EFFECTIVENESS

MIL-STD-1344A MODE STIRREDMIL-STD-1344A MODE STIRRED

METHOD FOR MEASURINGMETHOD FOR MEASURING

SHIELDING EFFECTIVENESSSHIELDING EFFECTIVENESS


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SUMMARY OF SURFACE TRANSFER

IMPEDANCE MEASUREMENT

TECHNIQUES

SUMMARY OF SURFACE TRANSFER

IMPEDANCE MEASUREMENT

TECHNIQUES

All Methods Work at Low Frequencies

Terminated Methods Have an Octave MoreBandwidth

D.C. Resistance Measurements and CalibrationSamples are Important (Vital) for EstablishingCredibility

Sample Ends Usually Limit Measurement ofGood Cables


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SURFACE TRANSFER IMPEDANCE

OF CONDUITS AND PIPES

SURFACE TRANSFER IMPEDANCESURFACE TRANSFER IMPEDANCE

OF CONDUITS AND PIPESOF CONDUITS AND PIPES

Flexible ConduitCopper and Steel Pipe


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TRANSFER IMPEDANCE OF TIN-COATED

COPPER TUBULAR-BRAIDED SHIELDS

TRANSFER IMPEDANCE OF TIN-COATEDTRANSFER IMPEDANCE OF TIN-COATED

COPPER TUBULAR-BRAIDED SHIELDSCOPPER TUBULAR-BRAIDED SHIELDS


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WORST CASE LARGE BRAIDED

CABLE MODEL

WORST CASE LARGE BRAIDEDWORST CASE LARGE BRAIDED

CABLE MODELCABLE MODEL

Mutual Inductance,

Single Braid Cables

R M

/m H/m

SINGLE BRAID 4 X 10-3 3 X 10-9

DOUBLE BRAID 2 X 10-3 3 X 10-10

TRIPLE BRAID 1.5 X 10-3 3 X 10-11


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TRANSFER IMPEDANCE OF

BLENDED METAL CLAD ARAMID

FIBER AND WIRE BRAIDED CABLE

TRANSFER IMPEDANCE OFTRANSFER IMPEDANCE OF

BLENDED METAL CLAD ARAMIDBLENDED METAL CLAD ARAMID

FIBER AND WIRE BRAIDED CABLEFIBER AND WIRE BRAIDED CABLE

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09

Frequency [Hz]

100% Aracon(R) Brand Yarn

Aracon(R) Brand Yarn

Blended with Wire

Nickel Pl ated Coppe


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TRANSFER IMPEDANCE OF SINGLE AND

DOUBLE WRAPPED CABLE SHIELDS:

TRANSFER IMPEDANCE OF SINGLE ANDTRANSFER IMPEDANCE OF SINGLE AND

DOUBLE WRAPPED CABLE SHIELDS:DOUBLE WRAPPED CABLE SHIELDS:

Knitted Wire Mesh

(60% Overlap)

Copper Foil/knitted Wire

Mesh


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TRANSFER IMPEDANCE OF COMBINATION

BRAID AND FOIL CABLES

TRANSFER IMPEDANCE OF COMBINATIONTRANSFER IMPEDANCE OF COMBINATION

BRAID AND FOIL CABLESBRAID AND FOIL CABLES

Figure 1. Surface Transfer Impedance Measurements of Cables that used

Braid/Foil Shields

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09

Frequency (Hz)

SurfaceTransferImpedance(Ohms/meter)

Cable A

Cable B

Cable C

Cable D

Cable E

Cable F


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MIL-C-38999 SERIES IV CIRCULAR

CONNECTOR WITH BACKSHELL AND

BRAID TERMINATION

MIL-C-38999 SERIES IV CIRCULARMIL-C-38999 SERIES IV CIRCULAR

CONNECTOR WITH BACKSHELL ANDCONNECTOR WITH BACKSHELL AND

BRAID TERMINATIONBRAID TERMINATION

Mil-C-38999 Requirements

Converted Into Transfer

Impedance

Effect of Spring Fingers on

Transfer Impedance


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SEVERAL MEASUREMENTS OF THE

TRANSFER IMPEDANCE OF A DUAL CONE

RFI/EMI BACKSHELL TERMINATION

SEVERAL MEASUREMENTS OF THESEVERAL MEASUREMENTS OF THE

TRANSFER IMPEDANCE OF A DUAL CONETRANSFER IMPEDANCE OF A DUAL CONE

RFI/EMI BACKSHELL TERMINATIONRFI/EMI BACKSHELL TERMINATION


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TRANSFER IMPEDANCE OF SAMPLES

USING THE MIL-C-38999

CONNECTOR/BACKSHELL INTERFACE

TRANSFER IMPEDANCE OF SAMPLESTRANSFER IMPEDANCE OF SAMPLES

USING THE MIL-C-38999USING THE MIL-C-38999

CONNECTOR/BACKSHELL INTERFACECONNECTOR/BACKSHELL INTERFACE

Effect of TorqueInitial Measurements


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TRANSFER IMPEDANCE OF A

COMPOSITE CONNECTOR/BACKSHELL

PAIR

TRANSFER IMPEDANCE OF ATRANSFER IMPEDANCE OF A

COMPOSITE CONNECTOR/BACKSHELLCOMPOSITE CONNECTOR/BACKSHELL

PAIRPAIR


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TRANSFER IMPEDANCE OF DB-25

SUBMINIATURE CONNECTOR/BACKSHELL

COMBINATIONS

TRANSFER IMPEDANCE OF DB-25TRANSFER IMPEDANCE OF DB-25

SUBMINIATURE CONNECTOR/BACKSHELLSUBMINIATURE CONNECTOR/BACKSHELL

COMBINATIONSCOMBINATIONS

Diecast Backshell and a

Compression Insert Braid

Termination

Plastic Backshell and a

Pigtail Braid Termination


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SURFACE TRANFER IMPEDANCE OF

9 PIN MICRO-D CONNECTORS

SURFACE TRANFER IMPEDANCE OFSURFACE TRANFER IMPEDANCE OF

9 PIN MICRO-D CONNECTORS9 PIN MICRO-D CONNECTORS

Statistical Analysis9 Pin Micro-D Connectors

1.000E-04

1.000E-03

1.000E-02

1.000E-01

1.000E+00

1.000E+0

3

1.000E+0

4

1.000E+0

5

1.000E+0

6

1.000E+0

7

1.000E+0

8

1.000E+0

9

Frequency [Hz]

LFH Type X Micro-D Type Y Micro-D All Micro-D

Average Transfer Impedance 4.28E-03 1.99E-02 2.13E-02 2.06E-02

at 100 MHz, Ohms

Standard Deviation of Transfer 3.62E-03 3.51E-03 3.94E-03 3.64E-03

Impedance at 100 MHz, Ohms

Standard Deviation of Transfer 84.6 17.7 18.5 17.7

Impedance as % of Average

Maximum Transfer Impedance 0.01768 2.50E-02 2.76E-02 2.757E-02

at 100 MHz, Ohms

Maximum/Average at 100 MHz 4.13 1.26 1.29 1.34

Average Transfer Impedance 6.17E-03 3.53E-02 3.54E-02 3.54E-02at 200 MHz, Ohms

Standard Deviation of Transfer 5.99E-03 7.25E-03 9.49E-03 8.05E-03

Impedance at 200 MHz, Ohms

Standard Deviation of Transfer 9.71E+01 17.7 26.8 22.8

Impedance as % of Average

Maximum Transfer Impedance 0.01768 4.51E-02 5.22E-02 5.216E-02

at 200 MHz, Ohms

Maximum/Average at 200 MHz 2.87 1.28 1.47 1.47


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SUMMARYSUMMARY

Surface Transfer Impedance is the Intrinsic Property for

Describing Electromagnetic Shields

Transfer Impedance Measurement Techniques are WellEstablished

Resistance Measurements Provide Much of the DesiredInformation

Calibration Samples and Resistance MeasurementsEstablish the Credibility of the Measurement Systems

Transfer Impedance Measurements are Available for aVariety of Shields

Transfer Impedance Can Be Used for Analysis,Specification and Design


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SELECTED REFERENCESSELECTED REFERENCES

1. Edward F. Vance, "Coupling to Shielded Cables," Wiley-Interscience, New York, 1978.

2. Lothar O. Hoeft and Joseph S. Hofstra, "Measured Electromagnetic Shielding Performance of

Commonly used Cables and Connectors," IEEE Transactions on EMC, Vol. 30, No. 3, Part 1,August 1988.

3. Lothar O. Hoeft, "Comparison of the Electromagnetic Shielding Provided by Circular and

Rectangular Connectors and their Accessories," Proceedings of the IICIT 26th AnnualConnectors and Interconnection Technology Symposium, Sept 1993.

4. L. O. Hoeft, and J. S. Hofstra, "Electromagnetic Shielding Provided by Selected DB-25Subminiature Connectors," Record of the 1991 IEEE International Symposium onElectromagnetic Compatibility, Cherry Hill, NJ, August 1991, pp 50-53.

5. B. T. Szentkuti, "Shielding Quality of Cables and Connectors: Some Basics," Record of the 1992International IEEE Symposium on Electromagnetic Compatibility,Anaheim, CA, August 1992,pp 294-301.

6. B. Eicher and L Boillot, "Very Low Frequency to 40 GHz Screening Measurements on Cablesand Connectors; Line Injection Method and Mode Stirred Chamber," Record of the 1992International IEEE Symposium on Electromagnetic Compatibility,Anaheim, CA, August 1992,pp 302-307.

7. Lothar O. Hoeft and James L. Knighten, Measured Surface Transfer Impedance of CableShields that use Combinations of Braid and Foil and are used for 1 Gb/s Data Transfer, Recordof the 1998 IEEE International Symposium on Electromagnetic Compatibility, Denver, CO,

August 1998, pp 527-531.

electromagnetic shielding of cables and connectors

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