US3688224A - Electric source filter - Google Patents

Abstract

This invention relates to an electric source filter for a coaxial cable. The cable has a plurality of wave absorbing members each containing a ferrite plate arranged between an inner and an outer conduit. Each ferrite plate is lined with a metallic plate and the metallic plate is arranged facing opposite to the direction of the travelling wave for absorbing the electric wave passing through the cable. The metallic plates are arranged in such a manner as not to short circuit the inner and outer conduits.

Description

United States Patent 1 1 3,688,224

Suetake et al. Aug. 29, 1972 [54] ELECTRIC SOURCE FILTER v [56] References Cited [72] Inventors: Kunihiro Suetake, No. 11, IO-ban, UNITED STATES PATENTS Minami 3-chome 'Meguro-ku 2,877,433 3/1959 Devot .333/730 Ywmyuk Nam, P- 3,460,142 8/1969 Suetake ..333/8l Suenaga, fi 2,973,492 2/1961 Mack ..333/97 Eiji Fujiwara, No. 4, 7-ban, Tsur u ma 479mm? Setagaya'ku Primary Examiner--Paul L. Gensler lkyor ofJaPan Attorney-Clario Ceccon [22] Filed. May 14, 1971 ABSTRACT [2]] Appl' 143348 This invention relates to an electric source filter for a Related US Application Data coaxial cable. The cable has a plurality of wave absorbing members each containing a ferrite plate 'ar- Continuation-impart 0f 355,272, P ranged between an inner and an outer conduit. Each 4, 1969, abandoned. ferrite plate is lined with a metallic plate and the metallic plate is arranged facing opposite to the [52] US. Cl. ..333/73 C, 333/79 direction of the travelling wave for absorbing the elec- [51] Int. Cl ..H01p l/20 e wa pas ng th oug the c e. The meta c 58 Field of Search.333/73 R, 73 c, 79, 97 R, 24 G, Pl are arranged in Such a manner as not to Short 333/81 circult the inner and outer conduits.

8 Claims, 16 Drawing Figures FERRITE f3 METAL Patented Aug. 29, 1972 6 Sheets-Sheet 1 M T E M Patented Aug. 29, 1972 3,688,224

6 She ef s-Sheet 2 @m'/ra 218 27? I I )si wkf 410/50 INVENTOR5 BY @111 t Patented Aug.29,1972 7 3,688,224

6 Sheets-Sheet 5 fFig. 7

Patented Aug. 29, 1972 6 Sheets-Sheet 4 33:, mu mm m QN m B q w cur ELECTRIC SOURCE FILTER This application is a continuation-in-part of U.S. Application Ser. No. 855,272 filed on Sept. 4, 1969 and now abandoned.

This invention relates to'electric source filters and, particularly, to a filter which absorbs electric waves travelling through or admitted into a coaxial cable.

The electric source filter of the present invention comprises absorbing members consisting of a ferrite plate with a metallic plate lining, which are located between the outer and the inner conduits of a coaxial tube the ferrite plate facing the wave as the wave travels.

, In accordance with the present invention, the absorbing member, prepared by lining a metal plate on one face of the ferrite plate is positioned so as to face the travelling wave through the electric cable. The very effective absorption of the wave thus results in the passage of low frequency power, for example, commercial frequency of 50 cycles.

When building a wave dark room or shielding chamber, often, despite the good property of the shielding chamber surroundings, there are electric wave leaks from an electric source lead, so that the shielding efficiency of the dark room or shielding chamber against the wave is deteriorated.

It is therefore important to increase the wave absorbing capacity or the shielding efficiency of the internal wall of the chamber, as well as to eliminate the wave travelling through the electric wire. This, in accordance with conventional methods, has been effected by means a filter in which a reactance is used. However, the wave travelling through the electric wire is reflected by said filter, and when it is desired to have a low frequency filter, it is necessary to increase considerably the size of the coil or capacitor element, as a result, its volume is so large that it brings about practical inconveniences.

Contrary to the known art and in accordance with the present invention, the waves travelling through the electric wire are completely absorbed and no reflecting of waves is observed.

Furthermore, in accordance with the conventional methods for absorbing waves, the thickness of the absorbent for absorbing low frequency waves is considerable and even if it were theoretically possible, the actual size of the filter would therefore be too large and impractical.

However, in accordance with this invention, when a ferrite magnetic material is used, it is possible to produce very thin wave absorbers regardless of the wave length of the wave desired to be absorbed.

The fundamental principle of. forming a wave absorber using magnetic material with a conductive backing was first presented in U.S. Pat. No. 3,460,142. It was there shown the required permeability characteristics of the magnetic material for absorbing microwaves. The wave absorber therein formed, constituted a layer of closely arrayed ferrite plates having the required characteristics and applied to a backing plate of conductive material.

In accordance with the present invention ferrite magnetic material having the permeability requirements as set forth in U.S. Pat. No. 3,460,142 is used as an electric source filter in a coaxial tube which is sufficiently small in size.

Moreover, the wave-absorbing members prepared by using various kinds of ferrites for each member can have its absorption wave length specific to an arriving electric wave, and therefore when they are connected in cascade fashion, it is possible to obtain a filter of excellent shielding efficiency over a wider frequency band. Since each type of ferrite material has a different permeability characteristic, each type of ferrite used will absorb over a given band of. frequencies. This frequency bandwidth can be altered by varying the thickness of the ferrite material used. It is therefore possible, by using the plurality of wave absorbing members cascaded, to provide the desired electric source filter which passes only the desired frequency and absorb other frequencies.

The invention will be more fully understood by the following detailed description thereof in connection with the accompanying drawings, in which:

FIGS. 1 and 1a are respectively a perspective view, partially cut-away, and a section view showing an embodiment of the electric source filter of the invention;

FIG. 2 is a diagram showing the absorption characteristics of the filter of the invention;

FIGS. '3 through 6 are the perspective views partially cut-away with the associated section views showing other embodiments of the present invention;

FIG. 7 is a perspective view, partially cut-away of a filter with a single absorbing member of the type shown in FIG. 6;

FIGS. 8 and 9 are curves describing the characteristics of'the filter of FIG. 7;

FIG. 10 is a perspective view, partially cut away a filter of two cascaded members of the type shown in FIG. 6; and

FIG. 11 is a curve describing a characteristic of the filter of FIG. 10.

In FIGS. 1 and la reference numeral 1 denotes the outer conduit of the conductor tube or coaxial cable, while the inner conduits thereof is shown at numeral 2. F F F,, are'the wave absorbing members,'each of these members being in the shape of a ring and having a ferrite plate 3 in the wave travelling direction and a metal plate 4 on the reverse side thereof.

The distance D between adjacent absorbing members is optional, but the members should not be positioned so close to each other so as to be contacting one another.

On the other hand, the height I of the absorbing members is optional but, as the height of the absorbing members is increased and as the distance between the member and the outer conduit 1 is made smaller, the amount of wave absorption is increased.

When the conducting metal plate of the absorbing member is in contact against both the inner and outer conduits of the coaxial cable, the voltage of the source to be used, for example 50 cycles, is short-circuited and this is not desirable.

On the other hand, the thickness d of the absorbing member differs in accordance with the amountof attenuation desired but it does not too strongly affect the results. Generally, a suitable thickness of the absorbing member is 8 mm.

Each ferrite composition is known to have a specific permeability. Therefore, each ferrite composition will filter out a different frequency band of electric waves. Specific examples of materials and their absorption bandwidths will be hereinafter described.

ment of the invention wherein the alternate absorbing members F,, F F are attached to the inner conduit 2, while the members F and F, are attached to the outer conduit 1. The same effect as in the embodiment shown in FIG. 1 is obtained.

In FIGS. 4 and 4a, a further embodiment is shown wherein the absorbing members F,, F, and F are attached to the outer conduit 1 through a thin insulating layer 5 provided between the outer conduit 1 and the members.

FIG. 5 and 5a show a further embodiment in which the absorbing members are all connected to the outer conduit but not to the inner conduit.

FIGS. 6 and 6a show a further embodiment in which the radius of the short-circuiting metal plates 4 is slightly smaller than the radius of the outer conduit 1 and the ferrite plates 3 are connected to both the inner and outer conduits. This uses the fact that ferrite is an excellent insulator against low frequency waves.

Referring now to FIG. 7, there is shown a particular filter of the type shown in FIG. 6 having a single wave absorbing member including a ferrite plate extending through the entire radius between the inner and outer conduits and a metal plate connected to it being of a shorter radius and attached only to the inner conduit. The dimensions of the filter shown are as follows:

Diameter of the outer conductor, D, 7.65 in. (19.44 cm) Diameter of the inner conductor, D, 3.49 in. (8.66 cm) Thickness of ferrite plate, t, 0.275 in. (7.00 mm) Thickness of metal plate, t .39 in. (10.00 mm) Gap, t .02 in. (0.5 mm) In the first example (sample A) the ferrite comprised Mn-Zn ferrite composed of 53.30% Fe 0 33.0% Mn0 and 13.7% ZnO in molar ratio and rubber mixed in a proportion of 1:5. In a second example (sample B) the ferrite was composed of 48.30% Fe O 16.16% NiO, 3.518% CuO, 30.74% ZnO, and 1.277% MnCO3 in molar ratio.

The Voltage Standing Wave Ratio (VSWR) of the resulting filter using the samples A and B are shown in FIG. 8 wherein there is plotted the VSWR vs. the frequency. The frequency attenuation characteristics of the filter of F IG. 7 using each of the samples A and B are shown in FIG. 9 wherein there is plotted the attenuation in db vs. the frequency. It can be seen from these curves that the electric wave absorption characteristic of the filter is wide-band attenuation.

Referring now to FIG. 10 there is shown a filter having two wave absorbing members of the type of FIG. 6 cascaded in the coaxial tube. F, and F, are the absorbing members with ferrite plates having thickness of il' a in2ial lit' fiiiiilsiri a s' 91il1ffii$ifil plates and having a thickness of 0.39 in. (10 mm). The two wave absorbing members are spaced apart by a distance D 0.08 in. (2 mm). All other dimensions are identical to that of FIG. 7.

FIG. 11 shows the attenuation characteristics of the filter as shown in FIG. 10 wherein there is plotted the attenuation in db vs. frequency. Curve 1 represents the results obtained when the sample A was used for F, and

the sample B was used as F Curve 2 represents the results obtained when the sample B was used as F, and

ous other modifications will be apparent to the person skilled in the art, and are understood to be within the scope and spirit of this invention as claimed in the following claims.

What is claimed is:

I. An electric source filter for use with a coaxial cable having inner and outer conduits concentric with each other comprising a plurality of electric wave absorbing members spaced from each other and disposed between said inner and outer conduits, each of said members including a ferrite plate facing in the direction of travel of the electric wave through the cable and a metallic plate connected to said ferrite plate on the other side thereto.

2. A filter as in claim 1 wherein each of said ferrite plates is of a different ferrite composition.

3. A filter as in claim 1 wherein each of said members are of circular shape and are concentric with said conduits.

4. A filter as in claim 3 wherein each of said members are coupled to said inner conduit and are spaced from said outer conduit.

5. A filter as in claim 3 wherein each of said members are coupled to said outer conduit and are spaced from said inner conduit.

6. A filter as in claim 3 and further including an ins ulating layer on one of said conduits, each of said. members coupled between said insulating layer and the other of said conduits.

7. A filter as in claim 3 where the radius of each of said ferrite plates is larger than the radius of each of said metallic plates, said ferrite plates being coupled to both said conduits, said metallic plates being coupled to one of said conduits and spaced from said other conduit.

8. A filter as in claim 3 wherein alternate ones of said members are coupled to said outer conduit and spaced from said inner conduit and the remaining members are coupled to said inner conduit and spaced from said outer conduit.

Claims (8)

1. An electric source filter for use with a coaxial cable having inner and outer conduits concentric with each other comprising a plurality of electric wave absorbing members spaced from each other and disposed between said inner and outer conduits, each of said members including a ferrite plate facing in the direction of travel of the electric wave through the cable and a metallic plate connected to said ferrite plate on the other side thereto.

2. A filter as in claim 1 wherein each of said ferrite plates is of a different ferrite composition.

3. A filter as in claim 1 wherein each of said members are of circular shape and are concentric with said conduits.

4. A filter as in claim 3 wherein each of said members are coupled to said inner conduit and are spaced from said outer conduit.

5. A filter as in claim 3 wherein each of said members are coupled to said outer conduit and are spaced from said inner conduit.

6. A filter as in claim 3 and further including an insulating layer on one of said conduits, each of said members coupled between said insulating layer and the other of said conduits.

7. A filter as in claim 3 where the radius of each of said ferrite plates is larger than the radius of each of said metallic plates, said ferrite plates being coupled to both said conduits, said metallic plates being coupled to one of said conduits and spaced from said other conduit.

8. A filter as in claim 3 wherein alternate ones of said members are coupled to said outer conduit and spaced from said inner conduit and the remaining members are coupled to said inner conduit and spaced from said outer conduit.

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