The document discusses characterizing an unknown shielded cable for electromagnetic interference (EMI) analysis in EMI Analyst software. It provides the known properties of a coaxial cable and shows how to determine the necessary conductor and transfer impedance properties to model the cable in EMI Analyst. Key properties of the coaxial cable are extracted from its data sheet and input into the software to simulate radiated susceptibility and evaluate the shielding effectiveness of the cable.

1. EMI Analyst™
EMI ANALYST™ Software Suite
I n t u i t i v e  A c c u r a t e  E f f e c t i v e
How to extract shielded cable
properties from data sheets
A radiated susceptibility example.
Applicable to all four types of electromagnetic interference analysis.

2. EMI Analyst™
The task is to characterize cables for EMC
• Often we have to determine
if a certain cable is adequate
for the environment
• How to input cable
characteristics into EMI
Analyst to perform RE/RS
type tests?
• Published cable spec is
shown at right.
• It incompletely defines cable
characteristics

3. EMI Analyst™
What do we need to know?
Conductor properties Transfer Impedance properties
Several physical properties are needed before cable electrical characteristics can be calculated.

4. EMI Analyst™
Known cable properties
What we know
• Coaxial cable
• 50 ± 2  characteristic impedance
• 90 pF/m
• #29 AWG center conductor
• Nickel-plated copper covered
steel
• Extruded TFE dielectric
• 90% optical coverage shield
• Nickel-plated wire shield

5. EMI Analyst™
Conductor form properties
 Cable configuration- Shielded
wire over ground plane
 Wire material - Nickel
 Wire gauge - #29 AWG
 Ctr-Ctr Offset - 0.0 mm, (coax)
 Insulation - Extruded TFE
(Teflon)
 Height - 5 cm
 Length - 2 m
 Shield Diameter - Derived
 Shield Thickness - Estimated
 Shield Material - Nickel
Click links to see rationale for each property selection

6. EMI Analyst™
Transfer Impedance form properties
 Braided (woven wire)
 Strand material - Nickel
 1 mm shield diameter - Derived
 #38 AWG - Assumed
 32 strands max. - Derived
 90% optical coverage
4th option on Transfer Z form is
best fit for known properties
• Carriers x Ends < Optical
Coverage x Shield Dia. / Strand
Dia.
Click links to see rationale for each property selection

7. EMI Analyst™
1 mΩ
50 Ω
1 mΩ1 mΩ1 mΩ
50 Ω
5 cm
2 m
50 Ω 50 Ω
Analysis model for evaluating shield
Strategy
• Expose cable to 1
V/m, 2 MHz to 18 GHz
• See how much current
flows on center
conductor
• For perfect shield, no
current flows on
center conductor

8. EMI Analyst™
EMI Analyst Model

9. EMI Analyst™
Frequency Range
2 MHz – 10 GHz

10. EMI Analyst™
Limit
1 V/m from 2 MHz to 10 GHz

11. EMI Analyst™
Field Direction
Broadside, Vertical Polarization

12. EMI Analyst™
Left-Hand End Circuit
50  Termination, Chassis Referenced

13. EMI Analyst™
Cable Conductors
As Defined in Previous Slides

14. EMI Analyst™
Shield Transfer Impedance
As Defined in Previous Slides

15. EMI Analyst™
Shield Terminations
360-Degree (Coax), 1 m

16. EMI Analyst™
Right-Hand End Circuit
50  Termination, Chassis Referenced

17. EMI Analyst™
Nickel Braid Shield, Induced Current

18. EMI Analyst™
Copper Braid Shield, Induced Current

19. EMI Analyst™
Nickel Solid Shield, Current on Wire 1

20. EMI Analyst™
Property Slides
The slides below are linked to slides 5 and 6.

21. EMI Analyst™
Conductor material
• Center conductor is nickel-plated copper-covered steel, shield is nickel-
plated wire
• RS frequency range is 2 MHz to 18 GHz
• At 2 MHz, skin depth is 3.8 m
• Minimum plating thickness is 1.25 m for nickel
• Over most of the RS frequency range, current flows primarily in nickel
plating, so use nickel for conductor material
http://chemandy.com/calculators/skin-effect-calculator.htm
http://www.fiskalloy.com/products/electroplating/
Return to Conductor Properties
Standard nickel plated conductors have a minimum plating thickness of 50
micro-inches (1.25 microns) as specified in ASTM B 355.

22. EMI Analyst™
Dielectric properties
• Extruded TFE
• DuPont TFE (Teflon)
• r = 2.1
• 1 mm dia. shield -> 50  char. Z
• Very small coax
• Halocarbon TFE
• data sheet at right
• r = 26.14
• 21 mm dia. shield -> 50  char. Z
• Seems too large for #29 center
• Assuming DuPont Teflon
Return to Conductor Properties

23. EMI Analyst™
Test setup – MIL-STD-461F (assumed)
• Cable configuration
Shielded wire over ground
plane
• Height
• 5 cm per MIL-STD-461
• Length
•  2 m per MIL-STD-461
Return to Conductor Properties

24. EMI Analyst™
Shield diameter
• Derived from known properties
• #29 AWG center conductor
• Teflon dielectric
• 50  characteristic impedance
• 90 pF/m
• Shield Diameter = 1mm
• Found using TAEM*
• Higher characteristic
impedance at low frequencies
is due to resistance of nickel
conductors, 𝑍0 =
𝑅+𝑗𝜔𝐿
𝐺+𝑗𝜔𝐶
*TAEM = trial-and-error-method. Try shield diameter,
then calculate Z0. Repeat until correct shield
diameter found.
Return to Conductor Properties

25. EMI Analyst™
Shield thickness
• For braided wire shield, shield
thickness = strand diameter
• Shield diameter is 1 mm
• Estimate shield is #38 AWG strands
• 100.72 m dia. strands
• 32 woven strands, max.
Return to Conductor Properties