Altair Feko: What are the supported braided shield models for cable harnesses?

Esti
Esti
Altair Employee
edited April 15 in Altair HyperWorks

This article describes the braided shield models for cable harnesses supported by Feko.

Many cables used today in the industry and at home, has a flexible woven braid to shield the cable from EMI as well as to provide mechanical strength. The braid consists of conducting filaments or wires, with the weave providing a series of periodic apertures along the cable length and around its circumference.

At high frequencies, the shielding properties are dominated by the braid coverage and at lower frequencies, it is the number of wires, weave angle and the shield material conductivity.

 

image

The weave parameters of a braided cable where d is the filament diameter and  image the weave angle.

 

Single-layered braided shield models

 

Common to all the models are the diffusion impedance (image)  due to the current induced in the shield:

image

where:

  • image is the resistance per unit length of the shield
  • image where image is the skin depth in the wire
  • image is the filament diameter

 

The following braided shielded models are included in CADFEKO and EDITFEKO:

 

Vance

This model takes into account hole inductance caused by fields penetrating the apertures in the braided cable.

The transfer impedance expression consists of two terms:

image

where:

image represents penetration of magnetic fields through diamond shaped holes

 

Tyni

This model takes into account braid inductance caused by magnetic coupling between the inner and outer braid layers.

The transfer impedance expression consists of three terms:

image

where:

image represents a porpoising term given by the mutual inductance between inner and outer carrier layers at the crossovers 

 

Demoulin

This model takes into account that image is not linearly increasing with frequency and that the phase variance is not between ±π/2 as theory predicts for the diffraction model.

The transfer impedance expression is given by:
 
image

 

Kley

This model relies on ‘tuning’ models using measurement data.
 
The transfer impedance expression is given by:

image

where:

  • image is the penetration inductance 
  • image  is a hole inductance, also correcting for shield curvature 
  • image  is a mutual braid inductance between the carriers in the braid
  • image  is due to the magnetic field inducing two types of eddy currents 

 

 

References:

  • E.F. Vance, “Shielding Effectiveness of Braided-Wire Shields,” IEEE Transactions on Electromagnetic Compatibility, vol. EMC-17, no. 2, pp. 71-77, May 1975.
  • F.M. Tesche, M.V. Ianoz, and T. Karlsson, “EMC Analysis Methods and Computational Models,” Wiley Interscience, Chapter 9, 1997.
  • T. Kley, “Optimized Single-Braided Cable Shields,” IEEE Transactions on Electromagnetic Compatibility, vol. EMC-35, no. 1, Feb. 1993.
  • M. Schoeman, E.A.Attardo, J.S Castany, "Recent Advances to the Feko Integrated Cable Harness Modeling Tool", 2019 International Symposium on Electromagnetic Compatibility - EMC EUROPE, September 2019.
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