JPH11203954A - Low noise cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low noise cable that can prevent external noise from intruding and has a high shielding effect particularly against noise in a high frequency range when it is used as a communication cable. SOLUTION: Conductors 1, 1' are covered by using a material, as a cover 2 material, made by dispersing a soft magnetic metal like permalloy into a matrix formed from rubber or soft synthetic resin. This cover 2 should contain 30 vol.% or more, preferably, 50 vol.% or more of the powder of the soft magnetic metal, and in addition, 10<11> Ω.cm or more of specific resistance should be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-noise cable mainly used as a signal cable for a personal computer to prevent intrusion of common-mode noise.

[0002]

2. Description of the Related Art For example, when a LAN is formed by two or more personal computers, noise enters from outside through a signal cable connecting the personal computers. This noise comes from unspecified electrical and electronic devices around the signal cable, especially from the components and peripherals of each personal computer. The waveform is not constant and the frequency range is wide, so it is called "common mode" noise. ing.

In order to remove this kind of noise, a ring-shaped core having a structure as shown in FIG. 1 is used. In this noise filter, since a noise signal generally flows in the same direction on a twisted pair cable, it disappears as a result of the magnetic flux being caught by the core and converted into heat, while the communication signal flowing in the normal mode on the twisted pair cable is: It is based on the principle that signal attenuation does not occur because magnetic fluxes cancel each other. As the core, a ferrite sintered body that is easy to mold and is inexpensive has been favorably used.

On the other hand, with the use of signals in a high-frequency region such as a recent tendency to increase the clock speed of a personal computer CPU, the frequency of generated noise increases.
Along with that, it is necessary to remove high frequency noise,
It is also growing. However, a conventional noise filter using a ferrite core is effective only in a frequency region up to about 250 MHz, and in a high frequency region near 500 MHz and further close to 1 GHz, the filter function deteriorates and is not useful.

As one solution to this problem, the inventor has proposed a soft magnetic metal foil having a magnetic permeability μ in a specific range in a frequency range of 100 MHz to 1 GHz as a core material of a coil of a twisted pair cable. It has been proposed to use a material laminated with an insulator (Japanese Patent Application No. 9-167726).

As a result of further study, it has been found that if a cable is manufactured by kneading soft magnetic metal foil in the form of flakes into a coating material, the cable can exhibit the function of preventing noise contamination. Knew. As soft magnetic metal, suitable for the above core material, 100 MHz to 20 G
It was also confirmed that the use of a cable having a magnetic permeability μ in Hz within a specific range in relation to the frequency enables the noise prevention effect of this cable to be obtained even in the high frequency range described above. Furthermore, it was also confirmed that the soft magnetic metal powder is not limited to the flake-like powder obtained by crushing the foil, but may be the one produced by crushing an alloy.

[0007]

SUMMARY OF THE INVENTION The basic object of the present invention is to make use of the above-mentioned knowledge obtained by the inventor and to use a soft magnetic metal powder in an ordinary parallel conductor cable which does not take the form of a twisted pair cable. By adding to the coating,
It is to provide a low-noise one.

A specific object of the present invention is to provide
By using a powder of a soft magnetic material whose permeability μ at 0 GHz is in a specific range in relation to frequency,
It is to exhibit the performance of the low-noise cable even in a high-frequency region.

[0009]

A low-noise cable according to the present invention is, for example, as shown in FIG. 2, in which two conductor wires (1, 1 ') arranged in parallel are covered with an insulator (2). The insulator is a soft magnetic metal powder (21).
With a matrix (2) made of rubber or a soft synthetic resin.
2) is a material dispersed and mixed therein, and has soft magnetism because the soft magnetic metal powder occupies 30% by volume or more of the mixed material, while having a specific resistance of 10 ¹¹ Ω · cm or more and insulating performance. This is a low-noise cable that is coated with a material that ensures the above.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As the soft magnetic metal, any material can be selected and used, and electromagnetic waves such as PC permalloy, sendust, permendur alloy, and Fe-Al-Cr alloy and Fe-Al-Si alloy can be used. An amorphous alloy such as stainless steel or an Fe-Si-B alloy is useful. Most of these alloys satisfy the condition of the magnetic permeability described above, that is, the condition that the magnetic permeability μ at 100 MHz to 20 GHz is within a specific range in relation to the frequency. If used, the low noise cable of the present invention will exhibit its performance even in the high frequency range.

As the rubber or soft synthetic resin constituting the matrix of the insulator, various synthetic rubbers, polyvinyl chloride, polyester, polyamide, chlorinated polyethylene and the like can be used. Polyvinyl chloride and chlorinated polyethylene are preferred with some flame retardancy.

The soft magnetic metal powder is preferably dispersed in the matrix at a concentration as high as possible, and has a practically significant noise attenuating ability, for example, -10 dB over the entire operating frequency range when measured by the method described later. To secure, 30% by volume or more, preferably 50% by volume
The above mixing is required.

On the other hand, in order not to lose the function as an insulating coating, a mixture in which a soft magnetic metal powder is dispersed in rubber or a soft synthetic resin has a specific resistance of 10 ¹¹ Ω ·
need to be at least cm. It is preferably at least 10 ¹² Ω · cm. When extruding rubber or synthetic resin during cable production, metal powder 95
It is relatively easy to extrude a mixture of 5 parts by weight of the matrix material and 5 parts by weight of the matrix material. At this time, the soft magnetic metal powder occupies almost 60% in volume%, but the specific resistance is 10 ¹¹ Ω ·
It turned out that cm could be secured. The kind and amount ratio of the soft magnetic metal and the matrix material, the molding means, and the like can be appropriately determined according to the desired noise attenuation performance, insulation properties, and the like.

If the insulation between the conductors of the cable is less sophisticated, ie if it is desired that the coating has a higher specific resistance, as shown in FIG. The intermediate insulating layer (3) may be provided between the high-performance coating (2) and an insulating material containing no metal.

[0015]

[Function] As a simpler version of the noise filter, a ring-shaped core (4) called "ferrite bead", usually composed of two parts each having a shape obtained by dividing a cylinder into two, is shown in FIG. As shown, some are formed by winding the cable (5) at least once. The impedance R of the coil is proportional to the square root of t × L, where t is the thickness of the ring-shaped core and L is the length.

In the cable of the present invention containing a soft magnetic metal in the cable coating, the thickness t of the core is small assuming that the thickness of each metal powder is integrated in the radial direction. However, on the other hand, the length L is a large value because it extends over the entire length of the cable. therefore,
The impedance R for the noise signal has a large value as a whole, and is useful for attenuating noise.

[0017]

[Example] PC permalloy was used as a soft magnetic metal,
A flake powder was prepared by pulverizing with an attritor.
The powder has a minimum particle size of 0.01 μm to a maximum of 10 μm and an average of 1 μm, and an aspect ratio (ratio of major axis / thickness) of about 10. On the other hand, chlorinated polyethylene resin was used as the matrix material, and 95 parts by weight of metal powder and resin 5 were used.
Parts by weight were melt-kneaded in an extruder. Although the volume occupied by the metal powder in the sheet reached 60%, the specific resistance on the surface of the sheet was 10 ¹² Ω · cm. This mixture was supplied as a coating material to an electric wire manufacturing machine, and a cable having a structure shown in FIG. 2 in which two conductor wires made of a single copper wire having a diameter of 0.25 mm were arranged at an interval of 2 mm was manufactured. The thickness of the coating around the conductor averages 0.5 mm.

Using a "network analyzer" (manufactured by HP), the noise attenuation performance of this low-noise cable was measured in the range of 50 MHz to 20 GHz. The results are shown in FIG. From the graph of FIG. 5, it can be seen that attenuation of more than 15 dB is realized below 300 MHz,
The attenuation is slightly smaller during 00 MHz, but
It can be seen that 0 dB can be secured, and between 3000 MHz and 20,000 MHz, attenuation of 15 dB or more is secured again.

[0019]

The low-noise cable of the present invention has a frequency of 20 GHz.
In the following regions, high performance of securing an attenuation of more than 10 dB is shown. In this way, it is possible to prevent noise signals from being mixed without using a special noise filter. Since the performance in the high frequency range is excellent, the low-noise cable of the present invention can cope with the tendency that the operating frequency of the electronic device is increased. The low-noise cable of the present invention can be applied to cables for various uses including a cable connecting between computers and between a computer and peripheral devices.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a conventional noise filter.

FIG. 2 is a perspective view showing the structure of a basic aspect of the low noise cable of the present invention.

FIG. 3 is a perspective view showing the structure of another embodiment of the low-noise cable of the present invention.

FIG. 4 is a cross-sectional view showing one using ferrite beads used as a noise filter.

FIG. 5 shows data of an embodiment of the present invention, which is a prototype of a low-noise cable having the structure of FIG.
9 is a graph illustrating frequency characteristics of noise attenuation at 0 GHz.

[Explanation of symbols]

 1, 1 'conductor wire 2 coating having soft magnetic performance 3 intermediate insulating layer 4 ferrite bead t thickness L length 5 cable

Claims (4)

[Claims] 1. A cable in which two conductor wires arranged in parallel are covered with an insulator, the insulator dispersing and mixing soft magnetic metal powder in a matrix made of rubber or soft synthetic resin. A soft magnetic metal powder occupying 30% by volume or more of the mixed material and having soft magnetism, while using a material having a specific resistance of 10 ¹¹ Ω · cm or more and ensuring insulation performance. And a low-noise cable coated. 2. As the soft magnetic metal, permalloy, sendust, permendur alloy, Fe—Si—B alloy, F
2. The low noise cable according to claim 1, wherein said cable is selected from an e-Al-Cr alloy and an Fe-Al-Si alloy. 3. The low-noise cable according to claim 1, wherein an intermediate coating material having a specific resistance of 10 ¹² Ω · cm or more is present between the conductor wire and the coating material having soft magnetic performance. 4. The low-noise cable according to claim 1, which is used as a signal cable for connecting between computers or between a computer and peripheral devices.