How to shield against magnetic interference—from low-frequency magnetic fields to high-frequency EMI, and choosing the right shielding material
Introduction
Magnetic interference is one of the most common—and most frustrating—EMI problems. Unlike electric fields, magnetic fields penetrate most materials easily. A piece of aluminum or copper does almost nothing to block low-frequency magnetic fields.
Shaanxi SiRui Technology Co., Ltd. supplies high-permeability magnetic shielding materials for EMI applications worldwide. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Two Types of Magnetic Shielding
- Shunt Shielding (Low Frequency): High-permeability material provides low-reluctance path. Best for DC – 10 kHz. Materials: mu-metal, nanocrystalline, amorphous.
- Eddy Current Shielding (High Frequency): Conductive material (copper, aluminum). Best for 100 kHz+. Materials: copper, aluminum.
2. Materials Comparison
| Material | Permeability | Best Frequency | Best Application |
|---|---|---|---|
| Mu-Metal | 50k–300k+ | Low (DC–10k Hz) | Precision instruments, audio |
| Nanocrystalline | 30k–100k+ | Wide (10Hz–100k Hz) | Transformer shielding, CMC |
| Amorphous | 1k–5k | Medium-high | High-Bsat, power frequency |
| Copper/Aluminum | Non-magnetic | High (100k Hz+) | RF, high-frequency EMI |
3. Common Design Mistakes
- Using copper for low-frequency magnetic fields (does nothing!)
- Forgetting about seams and holes (magnetic fields leak through gaps)
- Underestimating thickness (more material = better shielding)
- Saturating the shield (high-permeability materials saturate!)
4. Custom Shielding Materials from SiRui-Tech
At Shaanxi SiRui Technology Co., Ltd., we supply nanocrystalline toroidal cores for transformer shielding, amorphous cores for high-Bsat applications, ferrite cores for high-frequency EMI, and finished CMC chokes for conducted EMI shielding.
Web: www.sirui-tech.com | Email: sales@sirui-tech.com
Conclusion
Magnetic shielding is harder than electric shielding—but its solvable. Low frequency needs high-permeability material. High frequency needs conductive material. Wide range needs both layers combined.