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Permalloy*1 Foil with high magnetic noise suppression effect under strong magnetic fields
~ A way to prevent noise in Power Electronics ~

Daido Steel Co., Ltd. (President: Takeshi Ishiguro) has launched the new product "STARPAS®-DF42N" with excellent characteristics under strong magnetic fields and high frequency. It is started selling in January. STARPAS is effective on suppressing electromagnetic wave noise*2 (mainly magnetic noise) which is generated with communication technology, high frequency of IoT devices*3, and electrification of automobiles. In the future, we aim to expand applications to growing power electronics (systems that convert DC and AC power using semiconductors such as inverters).

STARPAS-DF42N is a foil contained 42 % Nickel with thickness between 10 μm and 30 μm, and has high saturation magnetic flux density*4 of 1.4 T equivalent to 800 A/m which is twice as high as that of the current product MEN® PC-2S with high magnetic permeability*5. By making DF42N thin foil, relative permeability more than around 100 kHz can be improved than that of conventional DF42N strip with 0.1mm thickness (fig.1). Furthermore, STARPAS-DF42N shows superior relative permeability under strong magnetic field (fig.2).

In addition, STARPAS can be provided as hoop and sheet which is easily pressed and cut into various shape. And it can easily attached to devices that generate electromagnetic noise or equipment that needs to avoid noise. We can also supply a laminated sheet using STARPAS-PC2S with high magnetic permeability onto STARPAS-DF42N.

* MEN and STARPAS are registered trademarks of Daido Steel Co., Ltd.

Fig.1  Effect of foiling at high frequencies

Fig.2  Comparison of characteristics


Power electronics, which has been developed in the field of electric power equipment, has been increasingly applied to in-vehicle and home appliances in recent years. The semiconductors used for these have high switching frequencies and tend to handle large currents. Also, in control semiconductors*6, the current tends to increase as the number of transistors increases due to process miniaturization.

For this reason, there are some issues that these devices easily generate various electromagnetic noise due to large currents at high frequencies that causes the malfunctions with other and own devices and therefore, the shield materials that can function in such an environment are required. By contrast, the current product STARPAS-PC2S has high shield effect in a small magnetic field less than about 10 A/m, but sometimes it was necessary to increase the volume of the shield material for stronger magnetic fields because it was magnetically saturated.

Alternatively, STARPAS-DF42N with high saturation magnetic flux density shows the maximum relative permeability in a magnetic field around 50 A/m, so the shielding effect can be expected in a magnetic field until about 100 A/m. (fig.3) According to the simulation, STARPAS-DF42N maintains its performance even under strong magnetic field. (fig.4)

In addition, it is possible to suppress eddy currents*7 generated by alternating current and maintain relatively high magnetic permeability even at high frequencies by foiling thicker than 30 μm, as well as conventional products. Moreover, the foil material also contributes to reducing the weight of equipment with magnetic shields.

Fig.3  Range of applicable magnetic field

Fig.4  Comparison of magnetic shield properties

2. Products Lineup (This product)

Product name Thickness Relative permeability at 100 KHz Relative permeability at 1 MHz
STARPAS-10DF42N 10μm 1,400 1,300
STARPAS-20DF42N 20μm 1,700 1,200
STARPAS-30DF42N 30μm 1,500 800
Manufacturable shape Hoop material, and sheet
Manufacturable dimensions Thickness: 10μm, 20μm, and 30μm, width: 100mm or less

3.For your additional information

This product will be exhibited at NEPCON JAPAN, which will be held at Tokyo Big Sight from January 19th to 21st in 2022.




*1 Permalloy
One of soft magnetic materials (It sticks to a magnet and loses its magnetism when the magnetic field is removed) and it is an alloy of iron-nickel having the highest permeability among them.
*2 Electromagnetic wave noise
Electromagnetic wave from the alternating current, which is not intended to be generated.
*3 IoT device
Anything connected to Internet. It has sensor and communication functions.
*4 Saturation magnetic flux density
Maximum magnetic flux density that the material can tolerate. An index of magnetic shield performance that indicates the difficulty of magnetic saturation
*5 Permeability
A numerical value representing the magnetism, which indicates the ease of magnetization of a material (ease of magnetic flux passage). Proportional constant representing the relationship between the strength of the magnetic field and the magnetic flux density. One index of magnetic shield performance. Relative permeability is a relative ratio by vacuum permeability (4π×10-7 H/m)
*6 Control semiconductor
Control semiconductor
*7 Eddy currents
Current generated in the direction of canceling the change in the magnetic field in the material due to electromagnetic induction with an AC magnetic field is applied to a metal material