JP2884512B1 - Through EMI filter - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To provide a simple and low-cost structure for switching from the MHz band to G
Provided is a through-type EMI filter capable of favorably removing and suppressing conductive EMI down to the Hz band. SOLUTION: An inner conductor 2 is coaxially arranged so as to penetrate a center of a metal cylinder 1 as a cylindrical outer conductor, and is formed by Si-
A composite magnetic body 4 mainly composed of an Fe-based magnetic powder is disposed between the metal cylinder 1 and the internal conductor 2, and the metal cylinder 1
Are closed by insulating resin lids 3-1 and 3-2 that support the internal conductor 2 in a penetrating state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a through-type EMI filter using a composite magnetic material comprising a metallic magnetic powder and a binder as a filter element, and more particularly to an AC and DC power supply line and a signal line. EMI has a performance suitable for suppressing high-frequency (from MHz band to GHz band) conductive electromagnetic interference noise (hereinafter abbreviated as conductive EMI) for control lines and the like, and has a simple structure of through-type EMI.
It is about filters.

[0002]

2. Description of the Related Art A conventional through-type EMI filter of this type is a combination of a cylindrical through-type capacitor 31 and a ferrite bead 32 as shown in FIG. 57-40515
13) and a ferrite bead 34 combined with a disc-shaped feedthrough capacitor 33 as shown in FIG. 13 (Japanese Utility Model Publication No. 3-748).

[0003] A cylindrical or disc-shaped through capacitor has no self-resonance due to the inductance of the lead wire because it has no lead wire. In the type capacitor, the resonance frequency f ₀ is expressed by the following equation (1).

[0004]

(Equation 1) Here, L: electrode length (cm), ε: dielectric constant of ceramic. As a trial calculation example, when L = 1 cm and ε = 5700, the resonance frequency f ₀ = 198 MHz. Further, in the disk-shaped feedthrough capacitor of FIG. 15, the resonance frequency f ₀ is expressed by the following equation (2).

[0005]

(Equation 2) Here, D: diameter of electrode (cm), ε: dielectric constant of ceramic. As a trial calculation example, when D = 1 cm and ε = 5700, the resonance frequency f ₀ = 484 MHz.

In the conventional examples 1 and 2 shown in FIGS. 12 and 13, the frequency characteristic of the reactance of the feedthrough capacitor becomes as shown in FIG. 16 due to the self-resonance phenomenon on the shape surface as described above. When the frequency is in the GHz band, the function as a filter element is deteriorated. Further, the ferrite beads, that is, the ferrite of the sintered body were obtained by using the samples A,
As can be seen from the frequency characteristics of the complex relative magnetic permeability (μr′−jμr ″) of B and C, as the frequency increases, a dispersion phenomenon occurs in the complex relative magnetic permeability, and the peak of the imaginary part (μr ″) is observed. The function as a series impedance element deteriorates.

[0007]

In recent years, as in the case of electronic equipment using digital circuits, the clock frequency has increased to several hundred MHz, and the frequency component of electromagnetic interference noise due to its harmonics is in the GHz band. Up to. The high-frequency components superimposed on the power supply line, the signal line, and the control line leak through the above-described line as conductive EMI to the outside of the device, and are further radiated from the line to the space.

In order to suppress such high-frequency components, there is a method in which the housing of the device is made to have a shielding structure, and an EMI filter having a through-type structure is attached to each of the lines described above. The through filter has a problem that the effect of removing the conductive EMI in the GHz band is insufficient.

In view of the above, the present invention provides a simple and low-cost conductive EM from the MHz band to the GHz band.
An object of the present invention is to provide a through-type EMI filter capable of satisfactorily removing and suppressing I.

[0010] Other objects and novel features of the present invention will be clarified in embodiments described later.

[0011]

In order to achieve the above object, a through-type EMI filter according to the present invention has an inner conductor coaxially disposed so as to penetrate the center of a cylindrical outer conductor, and has a
-A composite magnetic body mainly composed of an Fe-based magnetic powder is disposed between the outer conductor and the inner conductor.

In the penetrating EMI filter, the openings at both ends of the cylindrical outer conductor may be closed by insulating lids that support the inner conductor in a penetrating state.

[0013] A ferrite bead may be further provided around the inner conductor.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A through-type EMI according to the present invention will be described below.
An embodiment of a filter will be described with reference to the drawings.

FIG. 1 is a front sectional view of a first embodiment showing a basic structure of a through-type EMI filter according to the present invention, and FIG. 2 is a side view of the same. As shown in these figures, a metal cylinder 1 made of brass or the like is used as a cylindrical outer conductor, and an inner conductor (center conductor) 2 is arranged coaxially at the center thereof to form a coaxial tube. One end is provided with a lid 3-1 made of an insulating resin such as PBT (polybutadiene terephthalate). After inserting the composite magnetic body (heat-molded product) 4 from the other end, it is sealed with an insulating resin lid 3-2 similar to the lid 3-1. The insulating resin lids 3-1 and 3-2 close and hold the openings at both ends of the metal cylinder 1 so that the composite magnetic body 4 does not fall off, and support the internal conductor 2 coaxially in a penetrating state. At both ends of the outer peripheral surface of the metal cylinder 1, screw portions 5 used for mounting on a housing of an electronic device or for connecting a coaxial connector are formed.

In this case, instead of using the preformed composite magnetic material 4, a composite magnetic material obtained by mixing and kneading a magnetic powder and a resin powder is pressurized and filled into the coaxial tube, and then heated and cured. May be.

The complex magnetic material 4 has a complex relative magnetic permeability (μr'-jμ) at a high frequency (MHz to GHz band).
r ″) and complex relative permittivity (εr′−jεr ″), which are large and have a length of about 40 to 50 μm, a width of about 10 μm, and a thickness of about 10 μm.
A composite magnetic material having thermal stability and using an inexpensive polyester-based resin as a binder is heated and cured into a predetermined shape (a cylindrical shape in the present embodiment) for use. However, when the composite magnetic material 4 is preformed by heating, the upper limit of the weight mixing ratio of the magnetic material powder and the resin powder is about 80:20 from the viewpoint of moldability. Further, in a configuration in which the magnetic substance powder and the resin powder are pressurized, filled, and then heated and cured in the coaxial tube, the weight mixing ratio of the magnetic substance powder and the resin powder can be increased to about 95: 5. The lower limit of the mixing ratio of the magnetic powder must be 50% by weight or more in order to secure a sufficient attenuation.
If the amount is less than 50% by weight, the properties as a magnetic material are greatly reduced.

The frequency characteristics of the complex relative magnetic permeability and the complex relative permittivity of the composite magnetic material 4 (magnetic material powder 80% by weight, binder material powder 20% by weight) are as shown in FIGS. Complex relative magnetic permeability (μr′−jμr ″) shown in FIG.
Is required to exhibit as large a value as possible up to a high frequency region in terms of attenuation in a GHz band, and 1 GHz
In z, the real part μr ′ of the complex relative magnetic permeability is 3 or more, and the imaginary part μr ″
Is preferably 2 or more.

FIG. 1 in which the composite magnetic material is inserted into a coaxial tube.
FIG. 6 shows the results of measuring the frequency characteristics of the insertion attenuation of the through-type EMI filter having the structure according to the second embodiment by the two-port method using the network analyzer of FIG. However, the insertion attenuation was measured while changing the length of the composite magnetic body 4 in the axial direction of the coaxial tube to 5 mm, 10 mm, 20 mm, and 40 mm.

This through-type EMI filter can be regarded as a distributed constant circuit, and an equivalent circuit per unit length (although a fine length may be better) is as shown in FIG.

The insertion attenuation amount α of this through-type EMI filter
[DB] is represented by the following equation.

[0022]

(Equation 3)

As described in the first basic embodiment, the following effects can be obtained with this through-type EMI filter.

(1) It has a large insertion attenuation characteristic at a high frequency (especially in the GHz band) with respect to the conductive EMI that conducts AC and DC power supply lines, signal lines, control lines, and the like.

In a through-type EMI filter combining a conventional ferrite bead and a cylindrical or disk-shaped ceramic feedthrough capacitor, the frequency at which dispersion of the complex relative magnetic permeability occurs is low (about 40 MHz in the case of an initial magnetic permeability of 100). The peak of the imaginary part of the complex relative magnetic permeability (μr ″ has an effect on the absorption loss) generated in the process also appears at a low frequency (about 60 MHz in the case of the initial magnetic permeability of 100), and in the GHz band, the presence of ferrite beads. Loses value.

Also, a cylindrical or disc-shaped ceramic feedthrough capacitor causes a resonance phenomenon from the shape surface in the GHz band, the reactance changes from capacitive to inductive, and the insertion attenuation characteristic has a relation with the suppression characteristic of conductive EMI. It causes deterioration.

On the other hand, the feed-through EMI filter shown in the embodiment of the present invention is basically a distributed constant circuit, and a resonance phenomenon like a conventional feed-through EMI filter having a lumped constant circuit configuration appears. Absent. Since the Si—Fe-based magnetic material is also a composite magnetic material, μr ′ can be held at a high frequency, and accordingly, the peak-like phenomenon of μr ″ can be increased in frequency. As a result, in the MHz band to the GHz band, Good insertion attenuation characteristics can be obtained.

(2) Variations in characteristics can be reduced because of the simple structure.

In a conventional through-type EMI filter in which a ferrite bead is combined with a cylindrical or disk-shaped ceramic through-type capacitor, the number of elements is increased, and characteristics vary.

(3) The cost can be reduced because of a simple structure and easy assembly.

The conventional one using a ferrite bead and a cylindrical or disk-shaped ceramic feedthrough capacitor complicates the assembly structure and, at the same time, electrically connects the ceramic feedthrough capacitor to the outer conductor and the inner conductor by soldering or the like. Must be done, resulting in high costs.

FIG. 8 shows the through-hole type E shown in the first embodiment.
This is for describing EMI measures by separating zones using an MI filter. The housing of the electronic device has a shielding structure, that is, a shield 1, shields the indoor zone 1 and the zone 2 in the electronic device, and supplies a through-type EMI filter 10 to AC and DC power supply lines, signal lines, control lines, and the like. Attach. Further, a method is adopted in which the zone 3 of a specific unit in the zone 2 is shielded by the shield 2 and the through-type EMI filter 10 is attached to each line described above.

FIG. 9 shows the through-hole type E shown in the first embodiment.
4 illustrates a structure for attaching the MI filter 10 to a conductive shielding partition. In FIG. 9A, a metal flange 11 for screwing is provided on a metal cylinder 1 as an external conductor, and is fixed to a shielding partition wall 20 with screws 21. In FIG. 3B, the metal cylinder 1 as an external conductor is pushed into the through hole of the shielding partition 22, and the metal cylinder 1 is pressed against the through hole of the shielding partition 22. In FIG. 2C, a female screw portion 12 is provided at an intermediate portion of the outer peripheral surface of the metal cylinder 1, and is fixed to a shielding partition 23 with a nut 24. Although not shown, a structure in which a metal flange for soldering is integrated with the metal cylinder may be adopted.

In the first embodiment, a flaky magnetic powder of a Si—Fe alloy is used as a component of the composite magnetic material 4. However, the attenuation in the GHz band can be ensured. In this case, the shape of the Si—Fe-based alloy magnetic material powder does not necessarily have to be scale-like.

FIG. 10 shows a second embodiment of the present invention. In this case, the inner conductor 2 is coaxial with the center of the metal cylinder 1.
Are arranged to form a coaxial tube, and a PBT is provided at one end of the coaxial tube.
The lid 3-1 made of an insulating resin is disposed. After the composite magnetic material (heat molded product) 4 and ferrite beads 8 made of cylindrical sintered ferrite were sequentially inserted from the other end, the lid 3-1 was inserted.
And sealed with an insulating resin lid 3-2 similar to that described above. The insulating resin lids 3-1 and 3-2 are composed of the composite magnetic body 4 and the ferrite beads 8
The openings at both ends of the metal cylinder 1 are closed and held so as not to fall off. In this case, instead of using the preformed composite magnetic material 4, the composite magnetic material obtained by mixing and kneading the magnetic material powder and the resin powder is pressurized and filled into a coaxial tube in which ferrite beads are arranged, and then heated. It may be cured. Ferrite beads are suitable for high frequency band.
It is desirable to use a Zn type or the like.

The other structure is the same as that of the first embodiment.

In this second embodiment, scaly Si
-By arranging both the composite magnetic body 4 containing the magnetic powder of the Fe-based alloy and the ferrite beads 8 in a coaxial tube in a multiple form, the composite magnetic body 4 ensures a sufficient attenuation in the GHz band. The ferrite beads 8 can sufficiently secure the attenuation in the MHz band.

FIG. 11 shows a third embodiment of the present invention. In this case, the inner conductor 2 is coaxial with the center of the metal cylinder 1.
Are arranged to form a coaxial tube, and a PBT is provided at one end of the coaxial tube.
The lid 3-1 made of an insulating resin is disposed. From the other end, a ferrite bead 8 made of a small-diameter cylindrical sintered ferrite and a large-diameter cylindrical composite magnetic material (heat molded product) 4 are inserted in a coaxial arrangement, and then made of the same insulating resin as the lid 3-1. Lid 3-2
Seal with. The insulating resin lids 3-1 and 3-2 close and hold the openings at both ends of the metal cylinder 1 so that the composite magnetic body 4 and the ferrite beads 8 do not fall off. In this case, instead of using the pre-molded composite magnetic material 4, the composite magnetic material obtained by mixing and kneading the magnetic material powder and the resin powder is pressurized and filled into a coaxial tube in which ferrite beads are arranged,
It may be cured by heating.

The other structure is the same as that of the first embodiment.

In the third embodiment, a small-diameter ferrite bead 8 is arranged around the inner conductor 2, and a large-diameter cylindrical composite magnetic material in which a scaly Si—Fe alloy magnetic powder is blended. By arranging the body 4 in the metal cylinder 1 coaxially on the outer peripheral side of the ferrite beads 8, the composite magnetic body 4
The attenuation in the Hz band can be sufficiently ensured, and the ferrite beads 8 can sufficiently ensure the attenuation in the MHz band.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to the embodiments and various modifications and changes can be made within the scope of the claims. There will be.

[0042]

As described above, according to the through-type EMI filter of the present invention, the inner conductor is arranged coaxially so as to pass through the center of the cylindrical outer conductor, and the Si-Fe-based magnetic material is mainly used. Since the composite magnetic material as a component is disposed between the outer conductor and the inner conductor, AC and DC power lines,
Conductivity E that conducts signal lines, control lines, etc.
With respect to the MI, it is possible to have a large insertion attenuation characteristic up to a high frequency (in particular, up to the GHz band).

Also, with a simple structure, the number of parts is small,
Easy to assemble, less variation in characteristics,
It can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a first embodiment showing a basic configuration of a through-type EMI filter according to the present invention.

FIG. 2 is a side view of the same.

FIG. 3 is a graph showing a frequency characteristic of a complex relative magnetic permeability of the composite magnetic material used in the first embodiment.

FIG. 4 is a graph showing a frequency characteristic of a complex relative permittivity of the composite magnetic material used in the first embodiment.

FIG. 5 is an explanatory diagram showing a method of measuring the insertion attenuation characteristics of the through-type EMI filter shown in the first embodiment.

FIG. 6 is a graph showing the frequency characteristics of the insertion attenuation characteristics of the through-type EMI filter shown in the first embodiment, and shows that the composite magnetic body length is 5 m;
It is a graph measured about m, 10 mm, 20 mm, and 40 mm.

FIG. 7 is an equivalent circuit diagram of the feed-through EMI filter shown in the first embodiment.

FIG. 8 is an explanatory diagram showing EMI measures by zone separation.

FIG. 9 is an explanatory diagram showing a mounting structure of the through-type EMI filter shown in the first embodiment.

FIG. 10 is a front sectional view showing a second embodiment of the present invention.

FIG. 11 is a front sectional view showing a third embodiment of the present invention.

FIG. 12 is a front sectional view showing Conventional Example 1 of a through-type EMI filter.

FIG. 13 is a front sectional view showing a conventional example 2 of a through-type EMI filter.

FIG. 14 is an explanatory diagram showing that a cylindrical through ceramic capacitor has a resonance frequency depending on a shape.

FIG. 15 is an explanatory view showing that a through-the-disk ceramic capacitor has a resonance frequency depending on a shape.

FIG. 16 is a graph showing the frequency characteristics of the reactance of the feedthrough capacitor.

FIG. 17 is a graph showing a frequency characteristic of a complex relative magnetic permeability of ferrite.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal cylinder 2 Inner conductor 3-1 and 3-2 Insulating resin lid 4 Composite magnetic material 5 Screw part 8,32,34 Ferrite bead 10 Penetrating EMI filter 11 Flange 20,22,23 Shielding partition 21 Screw 24 Nut 31, 33 Through capacitor

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiki Sasaki 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Yoshiaki Akachi 1-13-1 Nihonbashi, Chuo-ku, Tokyo (56) References JP-A-9-82528 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01F 1/20 H01F 17/04

Claims (3)

(57) [Claims] 1. An inner conductor is coaxially arranged so as to penetrate a center of a cylindrical outer conductor, and a composite magnetic body mainly composed of a Si—Fe-based magnetic powder is arranged between the outer conductor and the inner conductor. A through-type EMI filter characterized by being provided. 2. The through-type EMI filter according to claim 1, wherein both ends of the cylindrical outer conductor are closed by insulating lids that support the inner conductor in a penetrating state. 3. The through-hole type E according to claim 1, wherein a ferrite bead is further provided around the inner conductor.
MI filter.