Shielded Cables — Lesson 5

This lesson covers the concept of electromagnetic shielding, focusing on the factors that contribute to total shielding effectiveness. It delves into the details of shielding absorption, reflection, and multiple reflections. The lesson explains how the thickness of the shield, frequency, magnetic permeability, and conductivity affect absorption. It also discusses the use of different materials like copper, iron, and aluminum for effective shielding. The lesson further explores the concept of attenuation due to reflection and multiple reflections, and how these factors vary with frequency and material properties. It concludes with methods to increase absorptive attenuation, such as using high permeability materials or generating opposing flux.

Video Highlights

00:13 - Introduction to shielded cables and field penetration inside cable shield
05:28 - Transmission line model for shielded cables
09:40 - Transfer impedance of cylindrical shields and homogeneous tube
17:27 - Transfer impedance of different types of cable
20:14 - Experimental determination of transfer impedance
24:50 - Conclusion of the module on electromagnetic shielding

Key Takeaways

- Total shielding effectiveness is composed of reflection loss, absorption in the metal, and multiple reflection within the metal.
- Shielding effectiveness due to absorption is proportional to the thickness of the shield and the square root of frequency.
- High permeability materials like iron offer more absorption loss than copper and aluminum of the same thickness.
- Attenuation due to reflection is largest at low frequencies and high conductivity materials.
- In the near-field region, wave propagation in the shield can still be approximated as TEM.
- The effect of multiple reflections can be neglected if the thickness is much greater than the skin depth.
- Low frequency magnetic field shielding can be achieved using high permeability materials or superconducting materials.