Amorphous cut cores are magnetic cores made from metallic glass ribbon rather than conventional crystalline steel. The ribbon is wound into shape, heat treated, and then precisely cut into core halves.

Their main advantage is extremely low core loss combined with high permeability—something that directly shows up as less heat and better efficiency in real power designs. That’s why they’re often chosen in applications like PFC chokes, solar inverters, and EV chargers where efficiency targets are harder to meet.

As demand for higher efficiency grows, manufacturers like HWHG (Hongwang Group) are also expanding their capabilities in amorphous materials to support these applications.

This guide covers how they are made, where they perform best, and what engineers usually consider when selecting them.

Image source: https://www.mag-inc.com/Products/Tape-Wound-Cores/Nanocrystalline/Learn-More-About-Nanocrystalline-Cores

Quick Highlights

High Efficiency: Very low core loss means less wasted energy—and in many designs, that translates into easier thermal management.
Unique Material Structure: These cores are made from metallic glass ribbon, an alloy with no conventional crystal grain structure. That’s a big reason their magnetic losses stay low.
Why the Cut Matters: The cut creates an air gap, which is essential when the core is used in inductors that need to store energy and handle DC bias current.
Best Use Cases: They are commonly used in high-frequency power electronics, including PFC stages, solar inverters, chargers, and industrial power supplies.
Cost vs Performance: While material cost is higher, the trade-off often makes sense once you factor in reduced cooling requirements and long-term energy savings.

How Amorphous Cut Cores Are Manufactured

Understanding the production process helps explain why amorphous cut cores perform so well. Material handling, heat treatment, and cutting accuracy all have a direct impact on the final magnetic properties.

Step 1: Rapid Solidification of Amorphous Ribbon

Production starts with a molten alloy that is rapidly cast onto a fast-spinning chilled wheel. Cooling happens extremely fast—around 10⁶ °C per second—which prevents normal crystal grains from forming (10^6 °C/sec). The rapid cooling essentially “freezes” the atomic structure before crystals can form, which is what gives the material its low-loss behavior.

Step 2: Creating the Wound Core

The ribbon is then wound into the required core shape, usually toroidal or rectangular depending on the final application. Thus, the basic wound core structure is formed.

Step 3: Annealing for Magnetic Properties

Next, the wound core goes through annealing under controlled conditions. This particular step is carried out in the presence of a magnetic field. This step relieves mechanical stress from winding and, more importantly, stabilizes magnetic performance across the core. It also helps optimize permeability and reduce losses. You can learn more about the manufacturing process to see how this step is crucial for performance.

Step 4: Impregnation and Cutting

After annealing, the core is typically impregnated with epoxy for mechanical strength and stability. Thus, it becomes more rigid and secure. .

Once cured, it is cut into matched halves, creating the familiar cut-core structure.

In practice, consistency at this stage depends heavily on manufacturing control. Suppliers like HWHG, with large-scale integrated production spanning high-grade electrical steel and amorphous materials (e.g. Guangxi Hongwang’s full processing lines), are better positioned to maintain stable batch performance.

Hongwang's amorphous ribbon production line

Amorphous Cut Cores vs Ferrite and Silicon Steel

In power electronics design, core material selection has a major effect on efficiency, size, temperature rise, and cost. Amorphous cut cores mainly compete with Ferrite and Silicon Steel core elements. Each material has its place—the right choice usually comes down to how you prioritize efficiency, frequency, and cost.

Here is a basic comparison of the two to facilitate your decision making.

Core Material	Core Loss	Saturation Flux Density (Bsat)	Permeability	Operating Frequency Range
Amorphous	Very Low	High	Very High	Medium to High
Ferrite	Low	Low	Medium	High to Very High
Silicon Steel	High	High	Low	Low

Core loss is one of the biggest efficiency drivers in high-frequency magnetic components. Lower loss means less heat generation, which can reduce cooling requirements and improve reliability. That’s a big reason amorphous cores keep showing up in newer high-efficiency designs.

Higher saturation flux density (Bsat) allows the core to handle stronger magnetic flux before saturating, which can support smaller or higher-power designs.

How to Choose the Right Core Material

From the engineering angle, it comes down to the individual needs of your application. No single material is ideal for every design. Engineers usually balance efficiency, cost, switching frequency, thermal limits, and available space.

When to Choose Amorphous Cut Cores: When Efficiency Starts Driving the Design

Amorphous Core Manufacturing System of HWHG

If efficiency is one of your primary constraints—not just a nice-to-have—amorphous cut cores are usually worth considering early in the design. This is often seen in high-frequency (over 10 kHz) switch-mode power supplies (SMPS). It is also common in Power Factor Correction (PFC) chokes and solar inverters. In these applications, core loss reduction results in energy savings and lower heat. The higher upfront cost is often offset over time through lower losses and reduced cooling complexity.

When Ferrite Cores Might Be a Better Fit: High-Frequency, Lower Power

Ferrite cores can be a right option for designs with very high frequencies, usually 500 kHz and above. They are also the best choice when cost is most important for lower-power devices. Ferrite has the advantage of very low loss at these high frequencies. However, using ferrite rather than an amorphous core at the same power level may require a larger core, since ferrite has a lower saturation density.

When to Stick with Silicon Steel: Low-Frequency, High Power

For low-frequency applications like 50/60 Hz mains transformers, silicon steel is still the king. It is very affordable and has a high saturation level. In these situations, its higher core losses are more acceptable. Its low cost makes it the most economical choice for large power distribution systems.

Why the Cut Matters: Air Gap, Magnetic Path, and Tolerance

The "cut" is a key feature of amorphous cut cores. It turns a simple wound core into a more versatile component. Understanding the purpose of the cut is essential for proper design.

Why Cut a Perfectly Good Wound Core?

One practical reason is assembly—cut cores make it much easier to install pre-wound coils, especially in production environments. With a cut core, a pre-wound coil on a bobbin can be installed quickly without threading wire through a closed toroid. That saves labor time and is often more practical for volume production.

The Air Gap's Role in the Magnetic Path

When the two core halves are assembled, the cut forms a controlled air gap in the magnetic path. This gap is intentional—and in many inductor designs, it’s not optional. It allows the inductor to store energy and improves tolerance to DC bias current. In practical terms, it helps prevent premature saturation under load.

The Critical Importance of Manufacturing Tolerance

Cut-surface quality is critical. Poor machining tolerance can create uneven mating surfaces or inconsistent air gaps. That often leads to part-to-part inductance variation. It can also increase stray flux and create EMI issues in nearby circuits. High-quality cut cores are valued for tight dimensional control and repeatable magnetic performance.

Common Applications for Amorphous Cut Cores

Today, amorphous cut cores are increasingly used in applications where efficiency targets are becoming stricter.

PFC Chokes: Low loss helps improve efficiency and supports compliance with energy standards.
SMPS Output Inductors: Useful where switching frequency is high and thermal margin is limited.
Solar Inverters and UPS Systems: Lower magnetic loss helps maximize usable energy from batteries or solar input.
EV On-Board Chargers: A strong fit for compact designs where both efficiency and thermal limits are tight.
High-Frequency Transformers: Chosen when designers need better efficiency in a smaller footprint.

Frequently Asked Questions

1. Are amorphous cut cores more expensive than ferrite?

In most cases, yes—but many designs still benefit overall once system-level efficiency is considered.

2. What’s the difference between amorphous and nanocrystalline cores?

Both start from similar ribbon materials, but nanocrystalline cores go further in processing and typically achieve higher permeability.

How does the air gap in a cut core affect its performance?

The air gap lowers the core's overall permeability. But it greatly improves its ability to handle DC current without saturating. This makes the cut core perfect for energy storage inductors. An uncut wound core (toroid) is better for transformers where you want the lowest possible magnetizing current.

4.Can amorphous cores handle high temperatures?

Yes, many grades offer good thermal stability. Actual operating limits depend on insulation systems, coatings, and final component design—not only the core material itself.

5. What does the "tolerance" of a cut core refer to?

Tolerance refers to the allowed variation in both physical size (like the air gap length) and magnetic properties (like inductance). A tight tolerance is very important. It ensures that every core performs consistently, which is critical for the mass production of electronic devices.

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