Toroidal cores



Fe … iron based amorphous alloys*

Fe … iron-based nanocrystalline alloys*

NiFe 49 – 68%

NiFe 80%

CoFe 50%

In general, toroidal cores, which practically form an air gap-free magnetic circuit with a constant cross-section, allow the most advantageous use of the magnetic material properties.

Viewed very precisely, however, the tape core also has an air gap, since it consists of a wound “endless” tape and the magnetic flux must pass from one tape layer to the other.


  • EMC filters for frequency converters and all types of switching power supplies
  • network-independent residual current circuit breaker
  • electronic energy meters
  • solar inverter
  • inductive heating
  • battery chargers
  • automotive industry – fully electric steering aids, DC / DC converters in the on-board network
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Delivery condition: On request. Customized design and manufacture.

* Explanations


A disordered atomic structure without crystalline areas and grain boundaries is characteristic of amorphous alloys. A basic requirement that promotes soft magnetic behavior.

From Spektrum der Wissenschaft 7/1994, page 108:

“It is not that easy to manufacture a metallic solid that is disordered down to the smallest detail. While a melt solidifies as it cools, the metal atoms generally have sufficient time to form crystal nuclei that grow locally into microcrystals. An amorphous solid is only created if the melt is cooled extremely quickly – for example at a million degrees per second. As with glass, the atoms then remain in a largely disordered state.

Solidifying in a split second

.. In order to achieve cooling speeds of one million degrees per second, however, its thickness must be well below 0.1 millimeters. This is essentially controlled by the roller speed: at 20 to 50 meters per second, 0.02 to 0.04 millimeters can be achieved. The dimensions of the casting nozzle and the cooling roller determine the film width.

Soft against changing magnetic fields

… This is most noticeable when the direction of the magnetic field changes again. In a metal with a lattice structure, it is often more energy-intensive to restore the original state. There remains initially a residual magnetization known as remanence. An additional field force – the coercive field strength – is required to bring the magnetic moments back to their original state. For applications in alternating fields, therefore, soft magnetic materials are preferred, which already change their magnetism in weak fields. These include amorphous metals and nickel-iron alloys.


Soft magnetic iron-amorphous ribbons, produced using fast solidification technology, are used for the production of amorphous tape wound cores and toroidal cores.

See also -> Tape wound cores.


The primary material is iron-amorphous ribbon, which was produced using fast solidification technology. The amorphous ribbons are subjected to an additional heat treatment at 500 to 600 ° C in order to enable the formation of a fine-grained microstructure. The term nanocrystalline refers to a achieved grain size in the range of 10 nm.

See also -> Tape wound cores.