MuMetal® Toroidal Cores
Supplied by Magnetic Shields USA, our toroidal cores are wound from high-permeability MuMetal® strip, making them well suited to current transformers, precision sensing, and high-accuracy measurement applications. Each production batch is permeability-tested to verify consistent magnetic performance.
Whether the application is a current transformer, precision metering assembly, clamp meter or other sensing device, we can support a wide range of core sizes and build formats.
Features
- Wide size range to suit compact sensing assemblies through to large current transformer builds
- Strip thicknesses from 0.1 mm to 0.35 mm for material and frequency optimization
- Custom sizes and configurations available on request
- Available cased or fixed to suit integration requirements
- Permeability-tested for consistent, batch-to-batch performance
- Optimized for low-frequency AC current-transformer and precision magnetic sensing applications.
- Hydrogen annealed to maximize magnetic permeability and ensure consistent magnetic performance
Custom Sizes & Configurations
| Specification | Inches | Millimeters |
|---|---|---|
| Internal diameter (ID) — min | 1.97 in | 50 mm |
| External diameter (OD) — max | 39.37 in | 1,000 mm |
| Strip thickness — min | 0.0039 in | 0.1 mm |
| Strip thickness — max | 0.0138 in | 0.35 mm |
Common Toroidal Core Applications
- Current Transformers: High-accuracy current measurement for protection relays, energy meters, and monitoring systems.
- Metering & Protection Equipment: Electricity metering, grid monitoring, and switchgear protection where precise magnetic performance is critical.
- Clamp Meters & Current Probes: High-permeability cores for clip-on current measurement tools and portable sensing assemblies.
- Instrumentation & Precision Measurement: Sensitive magnetic measurement systems where low core loss and stable permeability are essential.
- Motor & Position Controls: Accurate current sensing and feedback for industrial motor drives, servo systems, and precision position control equipment.
- Power Transmission Systems: High-accuracy power measurement across distribution networks, including three-phase industrial installations.
- Rail Networks: Current sensing and phase balancing in rail traction and signaling infrastructure.
- Specialist OEM Components: Custom high-permeability toroidal cores for custom magnetic assemblies.
Is MuMetal® the Right Core Material for Your Application?
Unlike ferrite cores (ceramic-based) or powdered iron cores (compressed metal powder), Magnetic Shields USA toroidal cores are manufactured from high-permeability MuMetal® strip conforming to ASTM A753 Alloy 4. This nickel-iron alloy contains approximately 80% nickel with iron and small additions of molybdenum. Its exceptionally high permeability and low coercivity make it ideally suited to precision low-frequency magnetic applications where measurement accuracy and magnetic sensitivity are critical.
MuMetal® toroidal cores are produced by winding thin nickel-iron alloy strip around a mandrel to create a continuous magnetic path. After winding, the cores are hydrogen annealed to develop their high-permeability magnetic properties.
Frequency Performance
MuMetal® toroidal cores offer high permeability for low-frequency current-transformer and precision sensing applications. The appropriate operating range depends on the complete assembly and application.
Current Handling
Core dimensions should be selected according to the required current range, operating frequency, winding arrangement and accuracy requirements. Magnetic Shields USA can advise on suitable core geometry for the application.
MuMetal® vs. Ferrite — a quick comparison
| Property | MuMetal® Toroidal Core | Ferrite Toroidal Core |
|---|---|---|
| Material | High-permeability nickel-iron alloy strip, tape-wound into a toroidal core | Ceramic material composed primarily of iron oxides |
| Permeability | Exceptionally high permeability, optimized through magnetic annealing | Typically lower than MuMetal® varies considerably by ferrite grade and frequency |
| Frequency range | Best suited to low-frequency current-transformer and precision sensing applications | Best suited to medium- and high-frequency AC applications |
| Typical applications | Precision current sensing, current transformers, metering and instrumentation | Switch-mode power supplies, inductors, EMI suppression, and RF circuits |
| DC Bias and Saturation | High permeability makes correct core sizing important where DC bias is present | Generally has a lower saturation flux density, and permeability can reduce significantly under DC bias |
How to know if MuMetal® is the right specification
Application type: MuMetal® is optimized for current transformers, precision sensing, and instrumentation. For magnetic shielding enclosures, a different form factor is likely more appropriate.
Operating frequency: MuMetal® toroidal cores offer high permeability for low-frequency current-transformer and precision sensing applications. The appropriate operating range depends on the complete assembly and application.
Field strength: Correct core sizing is essential to ensure the magnetic flux remains within the material’s optimal operating range. Magnetic Shields USA can advise on selecting the most suitable core dimensions for your application.
Manufactured by Magnetic Shields Ltd. Supplied by Magnetic Shields USA.
Magnetic Shields Limited manufactures each toroidal core using precision tape-winding equipment, followed by controlled-atmosphere hydrogen annealing to develop the required magnetic properties. Magnetic Shields USA provides North American technical, commercial and application support, backed by more than 65 years of specialist UK manufacturing experience.
Magnetic Shields USA provides local technical support and application engineering across North America, backed by world-class UK manufacturing.
Frequently Asked Questions
What are toroidal cores?
How do toroidal cores work?
Toroidal cores provide a continuous magnetic path that concentrates magnetic flux. In current-transformer applications, this allows current in a conductor passing through the core to be measured through a secondary winding.
What's the difference between ferrite and MuMetal® toroidal cores?
Ferrite cores are ceramic-based and are generally preferred for medium- and high-frequency applications such as power supplies, EMI filters, and RF circuits. MuMetal® Toroidal Cores are precision tape-wound from high-permeability nickel-iron alloy strip conforming to ASTM A753 Alloy 4, making them ideally suited to current transformers, precision metering, and sensing systems where measurement accuracy and magnetic sensitivity are critical.
What sizes are available?
Can cores be supplied cased or fixed?
Why does permeability testing matter?
For current transformers and precision sensing applications, consistent magnetic performance is essential. Permeability testing verifies that each production batch meets the required magnetic characteristics before shipment, providing confidence in repeatable performance from one batch to the next.
Can Magnetic Shields USA help specify the right core?
Yes. If you have a current transformer, sensing, or instrumentation application, Magnetic Shields USA can review your requirements and advise on the most appropriate core size, strip thickness, and supplied format for your application.
Talk to Us About Your Application
If you need MuMetal® toroidal cores for a current transformer, sensing, or instrumentation application, get in touch with your application details and any target dimensions or performance requirements.