Magnetic shielding principle Decide whether the following statement is correct: "For effective magnetic shielding of low-frequency or static magnetic fields, a ferromagnetic material (high-permeability alloy) is required to provide a low-reluctance path and divert flux away from the protected region."

Introduction / Context:
Magnetic shielding is essential in precision instrumentation, medical imaging, and metrology. The physical mechanism depends strongly on frequency: static and low-frequency fields are best mitigated by high-permeability paths, while high-frequency fields often rely on conductive shields and eddy currents.

Given Data / Assumptions:

• We consider static or low-frequency magnetic fields (quasi-DC).
• Shielding enclosure can be made from high-μ alloys (e.g., mu-metal).
• Superconducting options (Meissner effect) are not required or practical for most applications.

Concept / Approach:
A ferromagnetic shield presents a material with very high relative permeability μr. Magnetic flux prefers low-reluctance paths, so the shield attracts and guides flux lines around the protected volume. This is analogous to providing a shunt path in magnetic circuits. For AC at higher frequencies, conductive materials create eddy currents that oppose incident fields (skin effect), but for static/slow variations, permeability dominates shield performance.

Step-by-Step Solution:
Identify the field regime: static/low-frequency.Select materials with high μr to reduce magnetic reluctance.Design geometry (thickness, continuity, multiple layers) to minimize leakage and saturation.Thus, a ferromagnetic material is appropriate and effective.

Verification / Alternative check:
Practical enclosures for magnetometers or CRTs historically use mu-metal. Superconducting shields work via flux expulsion but require cryogenics; diamagnets have μr slightly less than 1 and are far less effective than high-μ alloys.

Why Other Options Are Wrong:
False: Contradicts standard practice. True only for RF: RF shielding is often dominated by conductivity and skin depth, not high μ alone. Only superconductors: Impractical and unnecessary for most uses. Only diamagnets: Very weak effect (μr ≈ 1).

Common Pitfalls:
Confusing electric-field shielding (Faraday cages) with magnetic shielding; overlooking saturation of high-μ materials at large flux densities.

Final Answer:
True