Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
1998-07-27
2002-01-01
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C333S012000, C336S092000
Reexamination Certificate
active
06335483
ABSTRACT:
This application corresponds to Japanese Patent Application No. 9-202753, filed on Jul. 29, 1997, which is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to noise-suppressing components, and more particularly, to a noise-suppressing component mounted to a signal line for removing high-frequency noise transmitted through the signal line.
2. Description of the Related Art
A ring-shaped core made from ceramic ferrite has been known as a conventional noise-suppressing component for removing high-frequency noise traveling through a signal line. Ceramic ferrite can have a high magnetic permeability and achieves a great noise-suppressing effect on noise having a frequency of 100 MHz or less. As the initial magnetic permeability of the ceramic ferrite becomes higher, a frequency where the magnetic permeability starts decreasing becomes lower. The magnetic loss of ceramic ferrite also starts attenuating at a relatively low frequency and a required resistance cannot be obtained in some cases at a high frequency exceeding 100 MHz. If the ring-shaped core is made larger in size in order to obtain a required resistance at a high frequency, the resistance at a low frequency also increases and a normal signal waveform is distorted.
As a countermeasure to these problems, a ceramic core having a low magnetic permeability is combined with a ceramic core having a high magnetic permeability to improve the characteristics of the combined device. In a ceramic core having a low magnetic permeability, the magnetic permeability starts decreasing at a high frequency and the magnetic loss also starts increasing at a high frequency. As such, a frequency range in which the magnetic loss increases can be extended by an appropriate combination of a ceramic core having a low magnetic permeability and a ceramic core having a high magnetic permeability.
Since the ring-shaped core in the conventional noise-suppressing component is made from ceramic ferrite only, its characteristics are limited in relation to the Snoek's critical line when a ceramic core having a low magnetic permeability is combined with a ceramic core having a high magnetic permeability. Therefore, a fully satisfactory noise-suppressing effect cannot be expected in the desired frequency band. In addition, since ceramic ferrite has a weak resistance to mechanical stress, a combined ceramic core made from ceramic ferrite only may break.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a noise-suppressing component which can suppress noise in a wide frequency band ranging from the MHz band to the GHz band and which is resistant to mechanical stress.
The foregoing object is achieved according to the present invention through the provision of a noise-suppressing component including: (a) a ring-shaped ceramic core having an initial magnetic permeability of approximately 50 to 1500 and (b) an insulating member integrally formed with the ring-shaped ceramic core (e.g., to form one unit), which is made from either resin or rubber and which includes magnetic powder having an initial magnetic permeability of approximately 2 to 50. The insulating member having the magnetic powder may be configured such that the magnetic powder has an average particle diameter of approximately 1 to 100 &mgr;m and the insulating member having the magnetic powder has a magnetic-powder content of approximately 20 to 70 percent by volume. The phrase “insulating member having magnetic powder” means that the insulating member is made from either resin or rubber or like material, and includes magnetic powder added thereto. Because of the presence of the powder, which may be conductive, the insulating member as a whole may not necessarily have an insulating effect.
With the above structure, in the insulating member having the magnetic powder, the magnetic loss starts increasing in the high-frequency region. Therefore, the insulating member having the magnetic powder has a resistance increasing only in the high-frequency region due to the magnetic loss.
As will be more readily understood from the following description, according to the present invention, the ring-shaped ceramic core has an initial magnetic permeability of approximately 50 to 1500 and is integrally formed with the insulating member which includes magnetic powder having an initial magnetic permeability of approximately 2 to 50, and accordingly, a reduction in resistance due to a reduction of the magnetic loss of the ring-shaped ceramic core in a high-frequency range is compensated for by the insulating member having the magnetic powder. Further, noise in a wide frequency region ranging from the MHz band to the GHz band which is traveling through a signal line is suppressed. In addition, when the ring-shaped ceramic core is coated with an insulating member which includes magnetic powder formed of flexible resin or flexible rubber, external mechanical stress is unlikely to be applied to the ring-shaped ceramic core, and a noise-suppressing component which is resistant to external mechanical stress is thereby obtained.
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Patent Abstracts of Japan, vol. 009, No. 332 (E-370), Dec. 26, 1985, Japanese Application No. 60-163411 A.
Sugitani Masami
Uchida Katsuyuki
Burns Doane , Swecker, Mathis LLP
Murata Manufacturing Co. Ltd.
Nguyen Chau N.
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