Mu metal foil is designed to shield sensitive devices. I use it to shield my phono step up transformer which picks up audible noise from nearby HVAC devices otherwise. Low level devices like step up transformers in a phono stage are most sensitive. Line level devices like preamps are less problematic.
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Mu-metal can be used for RFI (Radio Frequency Interference) shielding, but its effectiveness depends on the frequency of the interference. [[1]](https://www.eevblog.com/forum/projects/mu-metal-for-shielding-rf/) Here's a breakdown:
**1. How Mu-Metal Works for Shielding:**
* **High Permeability:** Mu-metal is a nickel-iron alloy with very high magnetic permeability. [[2]](https://eureka.patsnap.com/blog/mu-metal/)[[3]](https://www.spinquanta.com/news-detail/mu-metal-shield-in-quantum-computers-explained) This means it can easily attract and redirect magnetic field lines.
* **Shielding Mechanism:** It doesn't block magnetic fields but provides a low-reluctance path, diverting them around the shielded area. [[4]](https://en.wikipedia.org/wiki/Mu-metal)[[5]](http://www.mu-metal.com/faqs.html)
* **Low-Frequency Shielding:** Mu-metal is most effective at shielding against static or low-frequency magnetic fields. [[2]](https://eureka.patsnap.com/blog/mu-metal/)[[6]](https://resources.pcb.cadence.com/3d-electromagnetic-simulation/2022-the-impact-of-rf-shielding-effectiveness-on-interference-mitigation)
**2. Mu-Metal and Radio Frequencies:**
* **Up to 100 kHz:** Mu-metals provide interference control of H-fields (magnetic fields), DC or AC, up to approximately 100 kHz. [[5]](http://www.mu-metal.com/faqs.html)
* **Reduced Permeability at Higher Frequencies:** The permeability of mu-metal alloys decreases significantly near 1 kHz. [[5]](http://www.mu-metal.com/faqs.html)
* **Conductivity for Higher Frequencies:** Mu-metal is conductive and *can* potentially shield higher frequency (RF) fields in the 1-100 kHz range. [[5]](http://www.mu-metal.com/faqs.html) However, it's primarily designed for low-frequency magnetic fields. [[5]](http://www.mu-metal.com/faqs.html)
* **Not Ideal for High RF:** For frequencies above 100 kHz, highly conductive materials like copper, aluminum, or conductive coatings are generally more effective for RF shielding.
**3. When to Use Mu-Metal for RFI:**
* **Low-Frequency Magnetic Fields:** Use mu-metal when the dominant interference is from low-frequency magnetic fields (e.g., power lines, transformers).
* **Combination with RF Shielding:** When both high and low-frequency fields are present, mu-metal can be used in combination with other RF shielding techniques. In these cases, grounding the mu-metal and using proper RF shielding practices is important. [[5]](http://www.mu-metal.com/faqs.html)
**4. Limitations:**
* **Saturation:** Mu-metal can saturate in strong magnetic fields, reducing its shielding effectiveness. [[2]](https://eureka.patsnap.com/blog/mu-metal/)[[4]](https://en.wikipedia.org/wiki/Mu-metal)
* **Brittleness:** It's a brittle alloy and can be damaged by stress or impact. [[2]](https://eureka.patsnap.com/blog/mu-metal/)
* **Cost:** Mu-metal is relatively expensive compared to other shielding materials. [[2]](https://eureka.patsnap.com/blog/mu-metal/)
* **Skin Depth:** At higher frequencies, the skin effect becomes important. [[7]](https://www.eastcoastshielding.com/metal-rf-shielding-guide-optimize-applications.php) The skin depth is the depth to which an electromagnetic wave penetrates the material. [[7]](https://www.eastcoastshielding.com/metal-rf-shielding-guide-optimize-applications.php) Thinner layers are sufficient for higher frequencies.
**5. Alternatives for High-Frequency RFI Shielding:**
* **Copper:** Excellent conductivity, easy to manufacture. [[6]](https://resources.pcb.cadence.com/3d-electromagnetic-simulation/2022-the-impact-of-rf-shielding-effectiveness-on-interference-mitigation)
* **Aluminum:** Lighter than copper, sufficient high-frequency shielding. [[7]](https://www.eastcoastshielding.com/metal-rf-shielding-guide-optimize-applications.php)
* **Steel:** Effective for low-frequency magnetic fields due to its high magnetic permeability. [[7]](https://www.eastcoastshielding.com/metal-rf-shielding-guide-optimize-applications.php)
* **Conductive Coatings:** Can be applied to various surfaces.
* **Faraday Cages:** Enclosures made of conductive mesh or solid metal, effective at blocking electromagnetic radiation.
**In summary:** Mu-metal is a good choice for shielding low-frequency magnetic interference. [[3]](https://www.spinquanta.com/news-detail/mu-metal-shield-in-quantum-computers-explained)[[7]](https://www.eastcoastshielding.com/metal-rf-shielding-guide-optimize-applications.php) For higher frequency RFI, other materials like copper or aluminum are generally more effective. [[1]](https://www.eevblog.com/forum/projects/mu-metal-for-shielding-rf/) When dealing with a combination of both, a layered approach using mu-metal for the low frequencies and a conductive material for the high frequencies can be optimal. [[3]](https://www.spinquanta.com/news-detail/mu-metal-shield-in-quantum-computers-explained)
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Learn more:
1. [Mu-Metal for shielding RF - EEVblog](https://www.eevblog.com/forum/projects/mu-metal-for-shielding-rf/)
2. [Mu Metal: The Ultimate Protector Against Magnetic Interference - Patsnap Eureka](https://eureka.patsnap.com/blog/mu-metal/)
3. [Mu-metal Shield in Quantum Computers Explained \[2025\] - SpinQ](https://www.spinquanta.com/news-detail/mu-metal-shield-in-quantum-computers-explained)
4. [Mu-metal - Wikipedia](https://en.wikipedia.org/wiki/Mu-metal)
5. [MuMetal Relative Permeability](http://www.mu-metal.com/faqs.html)
6. [The Impact of RF Shielding Effectiveness on Interference Mitigation - PCB Design & Analysis](https://resources.pcb.cadence.com/3d-electromagnetic-simulation/2022-the-impact-of-rf-shielding-effectiveness-on-interference-mitigation)
7. [Choosing the Right Metal for RF Shielding: A Detailed Guide to Optimize Performance Across Diverse Applications](https://www.eastcoastshielding.com/metal-rf-shielding-guide-optimize-applications.php)”
