Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
1999-03-15
2001-05-01
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S012000, C333S185000, C439S620040
Reexamination Certificate
active
06225876
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a feed-through EMI filter in which composite magnetic material comprising metallic magnetic powder and a binding material is made into an element for a filter, and more particularly to a feed-through EMI filter which is used in a power supply line of alternating and direct current, a signal line, a control line, etc., and which has a characteristic suitable for suppressing conductive electromagnetic interference (hereinafter, referred to as conductive EMI) of high frequencies (ranging from MHz to GHz) and has a simple structure.
2. Description of the Prior Art
Heretofore, a feed-through type EMI filter has been available having combined a cylindrical feed-through type capacitor
101
with ferrite bead
102
as shown in the conventional example 1 of
FIG. 39
(Japanese Utility Model Publication No. 40512/1982, Japanese Utility Model Publication No. 40515/1982, etc.) or having combined a feed-through type capacitor
103
with ferrite bead
104
as shown in the conventional example 2 of
FIG. 40
(Japanese Utility Model Publication No. 748/1991).
The cylindrical or disc-shaped feed-through type capacitor has no lead wire to cause a self-resonance owing to the inductance of lead wires. It has, however, a self-resonance based on the configuration, and the self-resonance frequency fo of the cylindrical feed-through type capacitor as shown in
FIG. 41
is expressed by the following formula (1):
f
0
≈
3
×
10
10
2
×
L
×
ϵ
(
Hz
)
(
1
)
where L is a length (cm) of electrode and &egr; is a dielectric constant of ceramics. As a calculation example, let L be 1 cm and &egr; be 5700, then the self-resonance frequency is expressed by 198 MHz. Further, the self-resonance frequency fo of the disc-shaped feed-through type capacitor as shown in
FIG. 42
is expressed by the following formula (
59
2):
f
0
≈
3
×
10
10
0.82
×
D
×
ϵ
(
Hz
)
(
2
)
where D is an outer diameter (cm) of electrode and &egr; is a dielectric constant of ceramics. As a calculation example, let D be 1 cm and &egr; be 5700, then the self-resonance frequency is expressed by 484 MHz.
In the conventional examples 1 and 2 of
FIGS. 39 and 40
, as described above, the frequency characteristic of the reactance of the feed-through type capacitor is defined as shown in
FIG. 43
owing to the self-resonance based on the configuration. When the frequency of the conductive EMI reaches the GHz band, the function of the feed-through type capacitor as the element for the filter is deteriorated. As it is evident from the frequency characteristic of the complex relative permeability (&mgr;r′, &mgr;r″) of samples A, B, C as shown in
FIG. 44
, the ferrite bead, i.e. the ferrite of a sintered compact causes dispersion phenomenon in the complex relative permeability when the frequency becomes higher, and its function as a series impedance element is deteriorated, though the mountain-shaped characteristic curve of an imaginary part (&mgr;r″) is observed.
By the way, recently as it is evident from the case of electronic equipment using digital circuitry, a clock frequency is made higher to the level of hundreds of MHz, and the frequency component of the electromagnetic interference owing to the higher harmonies even reaches the GHz band. The high frequency components superimposed by a power supply line, a signal line and a control line are conducted to the lines and leak outside the equipment as conductive EMI and are further radiated into the atmosphere from the lines.
To suppress such high frequency components as these, a method is available wherein the housing portion of the equipment is made from a shielded structure and each of said lines is equipped with the feed-through type EMI filter. There is a problem, however, in that the feed-through type EMI filters as shown in the conventional examples of 1, 2, are not effective to eliminate the conductive EMI in the GHz band.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a feed-through type EMI filter operative from MHz to GHz with a simple and low cost structure.
A second object of the present invention is to provide the feed-through type EMI filter for a magnetron tube which is able to satisfactorily eliminate and suppress conductive EMI generated from the magnetron tube by a simple and low cost structure.
According to the present invention, the feed-through type EMI filter can be realized wherein an inner conductor is arranged so that it penetrates into a hollow (pipe-shaped) outer conductor and the composite magnetic material comprising magnetic metal flakes as a main component is disposed between said outer conductor and said inner conductor. It is able to have an insertion attenuation characteristic large enough to reach a high frequency including GHz for the conductive EMI. The magnetic powder of Fe—Si, Fe—Ni, Fe—Al—Si families, or the like can be used as the magnetic metal flakes.
REFERENCES:
patent: 2782381 (1957-02-01), Dyke
patent: 3289118 (1966-11-01), Garstang
patent: 4197146 (1980-04-01), Frischmann
patent: 4583810 (1986-04-01), Gliha, Jr.
patent: 4887185 (1989-12-01), Okumura
patent: 5614063 (1997-03-01), Graf et al.
Akachi Yoshiaki
Akino Tadaharu
Konno Tadashige
Sasaki Hisanori
Tanaka Takashi
Bettendorf Justin P.
Electromagnetic Compatibility Research Laboratories Co., Ltd.
Leydig , Voit & Mayer, Ltd.
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