JP2003174279A - Electromagnetic wave suppressor for high frequency range - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave suppressor formed by dispersing a soft magnetic metal powder in a rubber or plastic matrix and forming the same into a sheet shape, which has an electromagnetic wave suppressing ability even in a high frequency region of 1 GHz or more. Provide something that can be used effectively without lowering. SOLUTION: As a soft magnetic metal powder, Hc × δs × d
≧ 20,000 [where Hc is the coercive force (unit Oe), δs
Is the saturation magnetization (unit emu / g), d is the true density of the metal (unit g / c
m ³ )], and using flat powders having a thickness of 5 μm or less in which 90% or more of the number of powders in the microscope field of view of 60 μm square are dispersed in a matrix and formed into a sheet. I do.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to high frequencies, in particular 1.
The present invention relates to an electromagnetic wave suppressor used in a high frequency region near GHz or higher.

[0002]

2. Description of the Related Art In order to prevent leakage of noise electric waves from various electronic devices and mutual interference between parts in the devices, a soft magnetic metal powder is dispersed in a rubber or plastic matrix, and usually a sheet. An electromagnetic wave suppressor formed into a shape is widely used. It is often used by attaching a sheet to an IC or a circuit board or adding it to a cable coating layer.

The mechanism by which such an electromagnetic wave suppressor works effectively has not been fully clarified yet, but the magnetic permeability of the electromagnetic wave suppressor has the effect of confining magnetic flux, and the magnetic permeability has an inductance component L (permeability of It is argued that the real part μ ′) and the reactance component R (imaginary part μ ″ of the magnetic permeability) may suppressively act on the mechanism of noise electromagnetic wave generation.

Regarding an electromagnetic wave suppressor in which a powder of soft magnetic metal is dispersed in a matrix of rubber or plastic,
When the frequency characteristics of magnetic permeability are examined, generally, the real part (μ ′) maintains a substantially constant value up to a certain frequency, and it tends to gradually decrease on the high frequency side beyond that frequency.
On the other hand, the imaginary part (μ ″) tends to gradually increase from around the frequency where the value of the real part decreases, has a peak value, and then gradually decreases. Sometimes there are two peaks.

As presumed from the above-mentioned electromagnetic wave suppression mechanism, in an electromagnetic wave suppressor in which the real part (μ ′) of magnetic permeability already begins to decrease from a low frequency, the imaginary part (μ ″) also has a relatively large value. Since it reaches a peak at a low frequency, the electromagnetic wave suppression effect is naturally low in the high frequency region. As the electromagnetic wave suppressor, there have been ferrite type ones for a long time, but since ferrite has a low magnetic permeability at high frequencies, the suppressing effect is low and it can be used only up to about 300 MHz.

In practice, the conventional electromagnetic wave suppressor in which a soft magnetic metal powder is dispersed in a matrix can be effectively used at a limit of about 1 GHz. Until now, it was in time, but the frequencies used in electronic devices are spreading to the higher side, and next-generation mobile phones (1.95 GHz), Bluetooth (2.4 GHz) and wireless LAN (2.55 GHz).
GHz, 5 GHz) and the like, frequency regions exceeding 1 GHz are becoming practical. Therefore, the emergence of an electromagnetic wave suppressor effective in such a high frequency region is desired.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electromagnetic wave suppressor which can be effectively used in a frequency range of 1 GHz and higher in response to such a demand.

[0008]

An electromagnetic wave suppressor for a high frequency region according to the present invention which achieves the above object is an electromagnetic wave suppressor in which a powder of a soft magnetic metal is dispersed in rubber or plastic. As powder, Hc × δs × d ≧ 20000 [where Hc is coercive force (unit Oe), δs is saturation magnetization
(Unit: emu / g), d is a true density of metal (unit: g / cm ³ )], and 90% or more of the number of powders in a 60 μm square microscope field has a thickness of 5 μm or less. It is characterized by using powder.

[0009]

As the soft magnetic metal powder, any powder can be used as long as it can satisfy the above-mentioned characteristic requirements of the electromagnetic wave suppressor, but it may be slightly different depending on the type of metal or alloy. Since it is different, it is necessary to select the appropriate one. According to the experience of the inventors, it is preferable that Fe or Fe-Cr alloy is sprayed, particularly water is sprayed to obtain a powder, and the powder is flattened by an attritor treatment as seen in Examples described later. .

It is said that the cause of the decrease in the value of the real part (μ ') of the magnetic permeability at high frequencies is that eddy currents flow and that resonance occurs. Therefore, in order to suppress the eddy current, the soft magnetic metal powder is made flat. In the electromagnetic wave suppressor, the soft magnetic metal powder is present in a form oriented in a certain direction, although the degree varies depending on the manufacturing method. For the best manufactured sheets, the powders are oriented parallel to the plane of the sheet. The eddy current induced by the magnetic field due to the current along the surface of the sheet flows so as to draw an eddy in the plane perpendicular to the sheet surface, so the powder thickness has the greatest effect on the eddy current. Is. “90 of the number of powders in a 60 μm square microscope field
The condition that “% or more is 5 μm or less in thickness” is a limit derived from the electromagnetic wave suppression performance, and the thinner the powder, the more preferable. In order to increase the value of the real part (μ ′) of the magnetic permeability of the sheet, the soft magnetic metal powder is preferably flat rather than spherical.

In order to prevent resonance, it is effective to increase the crystal magnetic anisotropy of the soft magnetic metal powder, specifically, to set the crystal magnetic anisotropy constant Ku to a certain value or more. . However, since Ku cannot be easily measured, the inventors have used Ku as a substitute parameter.
Attention was paid to the value of Hc (coercive force) × Is (magnetization strength). Originally, HA (anisotropic magnetic field) × Is (magnetization strength) directly relates to the anisotropic torque and represents the magnitude of Ku, so it is desirable to use this value, but HA is also related to soft magnetic materials. Since it is difficult to measure accurately, coercive force Hc was used instead of HA. As a result, the value of Hc × Is showed that the magnetic permeability of the electromagnetic wave suppressor in which the soft magnetic metal powder was dispersed started to decrease. Found to be related to.

The coercive force Hc can be used instead of the anisotropic magnetic field HA because HA and Hc in a soft magnetic material.
The inventors envision that the value of H is close to each other, and the magnitude of HA and the magnitude of Hc are in a parallel relationship.
The intensity of magnetization Is (unit: emu / cm ³ ) is actually the saturation magnetization δs (unit: emu / g) if a vibrating magnetometer (VMS) is used.
Can be directly measured, and Is can be obtained by multiplying the measured value by the true density d (unit: g / cm ³ ) of the metal. The above equation was thus derived.

The soft magnetic metal powder is often subjected to a heat treatment in order to eliminate the strain caused by the attritor treatment and to exhibit better characteristics. Even in the practice of the present invention, such heat treatment is the preferred step. When the heat treatment is performed, the value of the coercive force Hc used is of course measured for the flat powder after the heat treatment.

As the matrix material for dispersing the powder, a commonly used chlorinated polyethylene rubber is easy to use, but when heat resistance is required, an appropriate material such as acrylic rubber is selected. In addition, the molding method of electromagnetic wave suppression body,
It may be performed according to a technique known in the art.

[0015]

Examples 1 to 4 and Comparative Examples 1 and 2 Molten metals or alloys shown in Table 1 were sprayed with water, and the obtained powder was treated with a wet attritor for 6 hours to obtain a flat powder. Each powder was hardened with an epoxy resin and cut, the cross section was polished, and a photograph was taken. The thickness of each of the 50 pieces was measured and averaged.
The results are shown in Table 1 together with the true density d of the metal or alloy.
Listed. The coercive force Hc and the saturation magnetization δs of each powder were further measured using VMS. The value of Is calculated by multiplying δs by d and the value of Hc × δs × d are
The results are also shown in Table 1.

Table 1

Each powder was blended with chlorinated polyethylene rubber so that the powder occupies 55% by volume of the mixture, a small amount of a processing aid was added, and the mixture was kneaded with a mixing roll and rolled with a calendar roll. , And formed into a sheet having a thickness of 1 mm. With respect to these electromagnetic wave suppression sheets, frequency characteristics of magnetic permeability (real part μ ′) were measured by the short circuit coaxial method and the S parameter method. The results are shown in Figure 1.

As is clear from this graph, Hc · δs
The soft magnetic metal powder having a d (Oe · emu / cm ³ ) value of more than 20,000 is used, and the electromagnetic wave suppression sheets of Examples 1 to 4 have a magnetic permeability of 2000. Compared with this, the frequency at which the magnetic permeability begins to decrease is high, and 1G
It can be confirmed that a practically sufficient electromagnetic wave suppressing effect is exhibited at a frequency exceeding Hz.

[0019]

The electromagnetic wave suppressor of the present invention is an electromagnetic wave suppressor obtained by dispersing a soft magnetic metal powder in a rubber or plastic matrix and having a specific magnetic property as the soft magnetic metal powder. By using
The conventional electromagnetic wave suppressor can exhibit a sufficient electromagnetic wave suppressing effect even in a high frequency range where the performance deteriorates and is not suitable for practical use, specifically, in a high frequency range of 1 GHz or higher. Therefore, this electromagnetic wave suppressor
We will provide useful products for the high-frequency electronic technologies that are being developed.

[Brief description of drawings]

FIG. 1 is a graph showing data of the present invention, showing frequency characteristics of magnetic permeability of an electromagnetic wave suppression sheet obtained by dispersing soft magnetic powders of Examples 1 to 4 and Comparative Examples 1 and 2 in rubber.

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Claims (2)

[Claims] 1. An electromagnetic wave suppressor comprising a soft magnetic metal powder dispersed in rubber or plastic, wherein Hc × δs × d ≧ 20000 [where Hc is a coercive force (unit Oe), δs is the saturation magnetization
(Unit: emu / g), d is a true density of metal (unit: g / cm ³ )], and 90% or more of the number of powders in a 60 μm square microscope field has a thickness of 5 μm or less. An electromagnetic wave suppressor for a high frequency region characterized by using powder. 2. Fe or F as the soft magnetic metal powder
The electromagnetic wave suppressor according to claim 1, wherein the spray powder of the e-Cr alloy is flattened by an attritor treatment.