KR100399503B1 - Noise filter - Google Patents

Abstract

A noise filter in which a power source or signal line into which a noise to be removed is superimposed, or a power line or signal line to which an electric signal is input, is wound around a magnetic body to remove the noise, and the frequency characteristic of the impedance of the noise filter is specified. It has the same maximum value as the LC parallel circuit with respect to the frequency, and is characterized in that noise is removed in the magnetic resonance frequency band including the magnetic resonance frequency which is this specific frequency. This noise filter has an impedance frequency characteristic equivalent to that of an LC parallel circuit, and can effectively remove noise of a specific frequency.

Description

Noise filter

The present invention relates to a noise filter used for noise countermeasure of an electronic device.

Since electromagnetic noise (hereinafter referred to as "noise") causes malfunction of electronic equipment, noise countermeasure is a very important problem in society. With the recent miniaturization and high frequency of electronic devices, noise generated also occurs in a higher frequency band (hereinafter referred to as a "high frequency band"). Moreover, noise is generated everywhere due to the spread of portable electronic devices such as mobile phones, which causes malfunction of other electronic devices in the vicinity. In addition, the control device in the cockpit of the aircraft, the medical equipment in the hospital, and the pacemaker of the heart are known to cause malfunctions due to noise, and the use of electronic devices in the vicinity may be restricted. In this way, noise can sometimes threaten a person's life, which is a very important social problem. Currently, regulations on noise are independent and legal, which I think will become more stringent in the near future.

Various noise filters (noise counterparts) effective for noise countermeasures of electronic devices have been proposed and used so far. In general, noise is generated in a frequency band that is at least a positive integer multiple of the AC signal current. Therefore, the noise countermeasure parts are required to have high impedance in the frequency band in which noise occurs.

Representative noise countermeasures include resistive elements, coils, capacitors, LC composite parts, ferrite cores, and the like, and are used in many electronic devices.

(1) First, since the resistive element can convert the current into heat, it is possible to convert and remove even the current which is noise by heat. However, the resistance element works regardless of the frequency band and also acts as a resistance against direct current and alternating current. This affects not only the noise current but also the signal current. When acting as a resistance to the signal current, the waveform of the signal current is blunted or attenuated and affects the operation of the equipment. Recently, the spread of various portable electronic devices is remarkable, and how to lower the power consumption in order to prolong the continuous use time of these devices is an important technical problem. Therefore, acting as a resistance to the signal current increases the power consumption, so noise cancellation using a resistance element is undesirable.

(2) Next, the coil has a structure in which a conductor wire made of metal is wound and does not act as a resistance to a direct current (actually as much as a resistance of a conductor wire), and a resistance (impedance) to an alternating current. It is characterized by acting as. Here, the impedance has a frequency characteristic. That is, in the case of AC signal current, the impedance of the coil is Z = jωL (j is complex display, ω is angular frequency, L is impedance value, ω is 2πf [f is frequency, and L is the number of windings and cross-sectional area of the coil. Determined by the magnetic path length], and the impedance of the coil increases with increasing frequency.

Therefore, when the coil is used for noise countermeasure, it does not act as a resistance to the direct current signal current but acts as a resistance only to the noise, thereby making it possible to remove the noise. In addition, with respect to the AC signal current, the coil can be selected such that the impedance is lowered in the frequency band of the signal current and the impedance is increased in the frequency band where noise is generated. In this way, noise can be removed. As described above, in the case of the coil, it is less likely to affect the signal current as compared with the above-described resistance element, so that it is possible to suppress the power consumption, which is suitable for recent noise measures.

However, the coil has the following drawbacks. The impedance of the coil can prevent the noise from passing through, and the unpassed noise reflects off the coil and returns to the source of the noise. Since the noise returned to the generation source affects the operation of the circuit which is the source of generation, it may cause a malfunction of the electronic device itself as the source of noise. In addition, in order to increase the impedance of the coil, the number of turns may be increased, or the cross-sectional area and the magnetic path length of the coil may be increased. However, increasing the number of turns increases the resistance component of the winding, which is not preferable because the power consumption increases as with the resistance element.

(3) Since the capacitor has an impedance frequency characteristic with respect to an alternating signal current, like a coil, noise can be removed by selecting a capacitor whose impedance is large in the frequency band where noise occurs. However, as in the case of the coil, the noise is reflected by the capacitor, which may cause malfunction of the electronic device itself, which is the source of noise, and thus is not preferable. In addition, the capacitor is not suitable for direct current signal current because it does not conduct DC.

By the way, in the case of a grounded circuit, a method of bypassing noise from the circuit to GND using a capacitor is used. In this method, in order to easily bypass the generated noise to GND, a capacitor having a low impedance in the noise generating frequency band is used. That is, noise easily passes through a line using a low impedance capacitor and is bypassed to ground in front of it. However, noise bypassed to GND may affect other circuits through GND, cause GND to become unstable, or cause device malfunction. Therefore, even in this case, it is never a desirable noise countermeasure.

(4) As a noise countermeasure part, there is an LC composite part, which is a circuit composed of the above-described coils and capacitors, and may have a frequency characteristic of an arbitrary impedance by the method of connecting the coils and capacitors and the selection of the coils and capacitors. Therefore, it is possible to remove the noise by increasing the impedance in the frequency band to which the noise is to be removed. However, like the coils and capacitors described above, since noise is taken by reflecting noise, the noise is returned to the generation source, which is not preferable because it affects the operation of the circuit which is the generation source.

(5) In addition to the noise countermeasure parts using the above-described resistance elements, coils, capacitors, and LC composite parts, there are other effective noise countermeasure parts in which signal lines and the like are wound around a magnetic core (for example, a ferrite core). Ferrite is an oxide magnetic material, and as a noise countermeasure, a cubic ferrite (spinel type) mainly composed of Mn, Zn, Ni, Cu, Fe, etc. has been mainly used. Here, magnetic materials, including ferrite, have permeability. When a material having permeability is used as the core of the coil described in (2), the inductance can be increased with a small number of turns. Therefore, the impedance can also be increased with a small number of turns. As a result, it is possible to increase the impedance while suppressing the resistance component of the conductive wire, which increases as the number of turns increases, by decreasing the number of turns.

In addition, the magnetic permeability (μ) of ferrite, including ferrite is divided into real part component (μ ') and imaginary part component (μ "), represented by the relationship μ = μ'-μ", where μ "is a loss component, It acts as a resistance component when the magnetic material is wound as a core, and therefore, unlike in the case of a coil or a capacitor, it can be converted into heat without reflecting noise.

In addition, the noise countermeasure parts wound on the magnetic material, like the coil, with respect to the direct current signal current, the coil does not act as an impedance to the direct current, but as an impedance only to the noise, and selectively converts only the noise into heat.

As mentioned above, it can be said that the noise countermeasure parts wound on a magnetic body are more suitable for noise countermeasures than the above-mentioned resistance elements, coils, capacitors and LC composite parts. Such noise countermeasure parts include a ferrite core in a solenoid shape and a toroidal shape (divided or undivided), which are used by passing or winding a cable or the like. There is also a product of surface mount type (lamination type) in which a conductor is formed inside the ferrite. Ferrite cores are easily mounted and are inexpensive noise countermeasures (noise filters) that have been used in many electronic devices to date.

However, the noise filter wound on the conventional magnetic material has a high impedance in a wide frequency band, and there is a problem in that the property of selectively removing noise generated in a specific frequency band is insufficient. Moreover, the frequency characteristic of the spinel type ferrite mainly used conventionally follows the theory called "limit line of snake." In other words, the frequency dependence of the ferrite permeability is small at low frequencies, and the permeability gradually increases as the frequency increases, and then the permeability decreases in almost inverse proportion to the frequency. The frequency at which the permeability begins to fall (limit frequency) is inversely proportional to the permeability. This is the limit line of the snake (see FIG. 9, FIG. 9 based on theoretical values). In other words, the spinel type ferrite has a limit in a frequency band having a permeability, and even if the permeability is increased to a high frequency band, the permeability is lowered and the threshold value of the snake cannot be exceeded. Here, when the permeability is lowered, the impedance is also lowered, which makes it difficult to remove noise in the high frequency band. In the high frequency band, it is also possible to cope by increasing the number of turns in order to secure a high impedance. However, increasing the number of turns is not preferable because it increases the DC resistance of the coil as described above. In recent years, when the operating frequency of the electronic device tends to be high frequency, the higher frequency of the operating frequency is expected to proceed further, and the generated noise is also generated in the high frequency band. Therefore, it is expected that the use of spinel ferrite as a noise countermeasure will be difficult in the near future.

Accordingly, an object of the present invention is to provide a noise filter that effectively removes noise generated in a specific frequency band without blunting a signal. It is also an object of the present invention to provide a noise filter that effectively and enables noise removal in a high frequency band, which has been difficult to cope with conventional spinel ferrites.

1 is an impedance-frequency characteristic curve of a noise filter of the present invention, illustrating a magnetic resonance frequency band.

2 is a diagram showing an LC parallel circuit;

3 is a perspective view showing an example of the noise filter of the present invention;

4 is an impedance-frequency characteristic curve of the noise filter in the embodiment of the present invention (hexagonal ferrite),

5 is an impedance-frequency characteristic curve of the noise filter in the embodiment of the present invention (6 tetragonal ferrite),

6 is an impedance-frequency characteristic curve of the noise filter in the embodiment of the present invention (Ni-based ferrite),

7 is an impedance-frequency characteristic curve of the noise filter in the embodiment of the present invention (Ni-based ferrite),

8 is a diagram showing the magnetic permeability of each sample in the embodiment of the present invention.

9 is a diagram for explaining the limit line of the snake (theoretical value).

Coils made of a magnetic core are similar in shape to the noise filter used so far, but a stray capacitance (also called a distribution capacitance) is generated in the winding. The inventors have focused on the fact that this stray capacitance is generated so that the coil wound around the magnetic body becomes LC parallel circuit in the equivalent circuit.

That is, the present invention is a noise filter in which a power source or a signal line into which a noise to be removed is superimposed, or a signal line to which a signal current is input, is wound around a magnetic body to remove the noise, and the impedance of the noise filter is removed. The frequency characteristic of is the same as the LC parallel circuit with respect to the specific frequency, and the noise is removed in the magnetic resonance frequency band including the magnetic resonance frequency which is this specific frequency.

The coil wound around the magnetic material has a function of converting the noise into heat by the loss component of the magnetic material, thereby removing the noise without reflecting the noise to the generation source. In addition, since the stray capacitance is generated in the coil wound on the magnetic material, there is a magnetic resonance frequency with the maximum impedance. When the magnetic resonance frequency band including the magnetic resonance frequency and the frequency band of noise coincide or overlap, the noise is removed. The effect of becomes very high.

Here, parallel resonance refers to an LC parallel circuit of the coil L (inductance) and the capacitor C (see Fig. 2) when the angular frequency of the power source is _equal to ω ₀ = 1 / (LC) ^1/2. The impedance becomes maximum and the main current I is the minimum. This parallel resonance ω ₀ is called a parallel resonance frequency (corresponding to the magnetic resonance frequency described above). In addition, in the case where the resistance L is in the coil L, the impedance is when ω ₀ = ((1 + 2CR ² / L) ^1/2 / (LC)-(R / L) ² ) ^1/2 It is the maximum.

In the noise filter, the magnetic resonance frequency (see Fig. 1) in which the impedance becomes the maximum can be arbitrarily changed by changing the number of turns, the type of magnetic material used, or the like. Increasing the number of windings increases the stray capacitance generated in the coil and shifts the magnetic resonance frequency of the coil to the low frequency side. (L and C are preferably small to cause magnetic resonance on the high frequency side.) In addition, it is preferable that the frequency band of the signal (current) flowing through the signal line (power supply line) is different from the frequency band of the noise.

The magnetic resonance frequency of the noise filter is preferably 500 MHz or more. It is because the frequency band of the noise which generate | occur | produces also becomes high frequency according to the high frequency of the operating frequency in future electronic devices.

As a magnetic substance to be used, ferrite is preferable. The reason for this is that ferrite is used in all electronic devices, processing technology and the like are established and can be obtained at low cost. In addition, since the volume resistivity is high and can be treated as an insulator, the wire constituting the power supply line or the signal line can be wound directly on the ferrite element. Therefore, it is possible to obtain the noise filter of the present invention inexpensively and easily.

In addition, as a ferrite using a magnetic substance, hexagonal ferrite is preferable. When the hexagonal ferrite is used, the permeability increases to the high frequency region than the Ni-based ferrite, so that loss components also occur in the high frequency region than the Ni-based ferrite. Therefore, use in the high frequency band becomes possible rather than the case where Ni-based ferrite is used.

Among the hexagonal ferrites, W-type, Y-type, and Z-type hexagonal ferrites, called perox sprayers, are preferable because the permeability extends to a high frequency band. It is more preferable because the permeability increases to the high frequency band while having a high transmittance.

Ferrite is the main component in oxide conversion,

Fe ₂ O ₃ : 68-74 mol%

MO: 15-22 mol%

MeO: 4-13 mol%

Secondary ingredients

PbO: 0-10 wt%

SiO ₂ : 0 ~ 5wt%

With respect to the composition in the range of, the sintered body density is high and the resistance ratio is increased, so that the mechanical strength can be improved, and the signal lines and the like can be wound without subjecting the core to the core.

In addition, M is at least one of Ba and Sr, and Me is at least one of Co, Ni, Zn, and Cu. In addition, a subcomponent is an optional component.

In addition, the present invention proposes an electronic apparatus which has made noise measures by attaching the noise filter to a power supply line or a signal line of the electronic apparatus. It is possible to easily remove noise at low cost simply by attaching a noise filter to a signal line or the like. In addition, since the GND is not required for mounting the noise filter, the design of the substrate of the electronic device is also very easy and can be performed at low cost.

<Example>

EMBODIMENT OF THE INVENTION Embodiment of this invention is described in detail with reference to drawings suitably.

<< Configuration of noise filter >>

An example of the structure of a noise filter is shown in FIG. The noise filter NF is configured by winding the wire 2 around the magnetic body 1. This configuration is the same as the conventional noise filter. In addition, the noise filter NF is suitably attached to a power supply line or a signal line, such as an electronic device which is a noise generating source.

The shape of the magnetic body 1 may be either a troidal type constituting the closed furnace or a solenoid type constituting the open furnace. In addition, other shapes can be selected. As the magnetic material constituting the magnetic body 1, conventional magnetic material such as ferrite or the like can be used. Ferrites are widely used in electronics, and their varieties are abundant. As the magnetic material used as the magnetic material 1, it is preferable to select and use a material having a high permeability and a high impedance in the frequency band to which noise is to be removed.

If the noise is removed in the high frequency band of 500 MHz or more, hexagonal ferrite is preferable as the magnetic material. That is, since hexagonal ferrite has a high investment up to a high frequency band exceeding the limit line of the snake, it can be used in a high frequency band of about 4 to 5 GHz.

In addition, the magnetic material constituting the magnetic body 1 preferably has a high resistance ratio. This is because a signal line or the like can be wound directly on the magnetic body 1 without performing special insulation treatment. In addition, since the resistivity of the Ni-based ferrite conventionally used without performing an insulation treatment is 10 ⁶ Ω / cm or more, the resistivity of the magnetic material constituting the magnetic body 1 is the same as that of the Ni-based ferrite. It is enough to have.

Moreover, it is preferable that the magnetic body material which comprises the magnetic body 1 is a material which has high mechanical strength. The mechanical strength does not directly affect the electromagnetic properties of the magnetic body 1, but if the mechanical strength is small, the magnetic body 1 (i.e., the noise filter NF) when the noise filter NF is mounted on the substrate of the electronic device is used. ) Can collapse. In addition, the density and the resistance ratio of the magnetic material constituting the magnetic body 1 are related to each other, and when the density decreases, the resistance ratio tends to be increased. Therefore, in view of the resistance ratio, it is preferable that the density of the magnetic material is low. However, since the lowering of the density of the magnetic material causes a decrease in the mechanical strength of the magnetic material 1, it is not a preferable means to increase the resistance ratio by lowering the density of the magnetic material.

The wire 2 is composed of a conductor. The wire 2 is mounted on a power line or a signal line of an electronic device or the like, and a noise current flows through the wire 2 (a signal current flows, etc.). In addition, the number of turns of the wire 2 to the magnetic body 1 greatly affects the characteristics of the noise filter NF as described later.

The noise to be removed is superimposed on an electric signal or the like on a power supply line or a signal line, and this noise corresponds to a recent increase in the processing speed of electronic equipment. In addition, noise is often generated in the high frequency band of 500 MHz or more.

The noise filter NF is mounted on a power line or a signal line of an electronic circuit or the like during use, and the noise filter NF has a configuration in which the wire 2 is wound around the magnetic body 1 as described above (see FIG. 3). Since the stray capacitance occurs in the noise filter NF having such a configuration, the equivalent circuit of the noise filter NF is an LC parallel circuit (see Fig. 2). Therefore, this noise filter NF has a magnetic resonance frequency in which the impedance corresponding to the parallel resonance frequency in the LC parallel circuit is maximized (Fig. 1). Since the magnetic resonance frequency band including the magnetic resonance frequency has a high impedance, when the magnetic resonance frequency band and the frequency band of noise coincide or overlap, the noise can be converted into heat and removed.

<< Operation of Noise Filter >>

For example, when noise overlaps a signal line of an electronic device together with a signal, a noise filter NF is attached to this signal line so as to remove the noise so that the noise is connected to the wire 2 of the noise filter NF. To pass through. If the frequency band of the noise coincides or overlaps with the magnetic resonance frequency band of the noise filter NF, the noise can be effectively removed. At this time, if the frequency band of the signal and the magnetic resonance frequency band of the noise filter NF are different, the signal is not attenuated by the noise filter NF. Therefore, only noise can be selectively removed. In addition, mounting means that the signal line (power line) and the wire 2 are connected, or the signal line (power line) is wound directly on the magnetic body 1 as the wire 2 so that the signal and the noise are the wires of the noise filter NF. We say to let you pass (2).

When the magnetic resonance frequency band of the noise filter NF is narrow, only noise can be selectively removed even when the frequency band of the signal and the frequency band of the noise are close. On the contrary, when the self-resonant frequency band of the noise filter NF is wide, the noise generated over the wide frequency band can be removed at once. The magnetic resonance frequency band of the noise filter NF can be arbitrarily adjusted by the type and material of the magnetic material constituting the magnetic body 1 or the number of turns of the wire 2.

For example, when the number of turns of the wire 2 to the magnetic body 1 is reduced, the magnetic resonance frequency shifts to the high frequency side, and when the number of turns to the magnetic body 1 is increased, the magnetic resonance frequency shifts to the low frequency side. In addition, when the number of turns of the wire 2 to the magnetic body 1 is increased, the impedance tends to increase.

The magnetic resonance frequency band can be, for example, a peak portion appearing in the impedance-frequency characteristic curve. Note that the peak portion may be, for example, a frequency band protruding upwardly fitted to the rising portion from the base line in the impedance-frequency characteristic curve (see Fig. 1). The magnetic resonance frequency band may be a portion whose impedance exceeds 100 Ω, for example.

<< magnetic material material >>

The magnetic material of the magnetic material 1 constituting the noise filter NF of the present invention will be described in more detail. As a magnetic material which comprises the magnetic body 1, ferrite, a polymer magnetic body, etc. which have a high permeability are mentioned. Among them, for the noise generated in the high frequency band, it is preferable to configure the magnetic body 1 with hexagonal ferrite. Since the hexagonal ferrite has a high permeability up to the high frequency band exceeding the limit line of the snake as described above, the noise filter using the hexagonal ferrite has a high impedance even in the high frequency band and can remove the noise generated in the high frequency band. Because there is. Among these hexagonal ferrites, W-type, Y-type, and Z-type hexagonal ferrites called peroxsprayers are preferable because the permeability increases to a higher frequency band. In addition, the use of a hexagonal ferrite mainly composed of Z-type has a higher permeability and more preferable because the permeability increases to a high frequency band. In addition, hexagonal ferrite is present in a band having a loss component μ ″ of 500 MHz or more.

In addition, hexagonal ferrite is M type (MFe ₁₂ O ₁₉ ), W type (MMe ₂ Fe ₁₆ O ₂₇ ), Y type (M ₂ Me ₂ Fe ₁₂ O ₂₂ ), Z type (M ₃ Me ₂ Fe ₂₄ O ₄₁ ) Are known (M: alkali metal ion, Me: divalent metal ion). Form Z is disclosed in Japanese Patent Application Laid-open No. 33-736, wherein M is Ba, Ca, Sr, Pb, and Me is Co. Further, Japanese Patent Publication No. 34-6778 discloses Me is Fe, A composition consisting of Mn, Co, Ni, Zn, Mg, Cu is disclosed. In the present invention, any ferrite can be used as the magnetic material 1 for the noise filter NF.

Ferrite is made by mixing the amounts of materials such as Fe ₂ O ₃ to a predetermined composition, shaping them and firing (sintering) them. Regarding the composition of the ferrite, when M is at least one of Ba and Sr, and Me is at least one of Co, Ni, Zn, and Cu, the composition of the main component in terms of oxide is Fe ₂ O ₃ : 68 to 74 mol%, MO Hexagonal ferrite (Z-type) in the range of 15 to 22 mol%, MeO: 4 to 13 mol%, and subcomponents of PbO: 0 to 10 wt% and SiO ₂ : 0 to ₅ wt% has high mechanical strength and high frequency band. It is desirable to have a high permeability of.

Within the range of the above composition, the magnetic body 1 having the hexagonal ferrite as the main layer can have a magnetic permeability range of 5 to 25, a density of 4.6 g / cc or more, and a resistance ratio of 10 ⁶ Ω / cm or more. The magnetic body 1 suitable for the noise filter NF of this invention can be comprised.

A subcomponent is an optional component and hexagonal ferrite can be comprised without including this subcomponent. However, since SiO ₂ and PbO are added to glass at the time of firing, the resistivity of the hexagonal ferrite produced can be increased, which is preferable. Further, SiO ₂ is effective to increase the resistance ratio of each generated by adding at least 0.04wt%, PbO is at least 0.02%.

<< How to remove noise >>

According to another embodiment of the present invention, there is provided a noise removing method for removing the noise by a noise filter in which a magnetic body is wound around a core body from a power source line or a signal line into which noise is superimposed or an electric signal is input.

For example, when noise overlaps with a signal on a signal line of an electronic device, a noise filter obtained by winding the magnetic material as a core is mounted on the signal line to remove noise by passing the noise and a signal through the winding. .

That is, when the frequency band of the noise and the magnetic resonance frequency band of the noise filter coincide or overlap, the noise can be effectively removed. On the other hand, if the frequency band of the signal and the magnetic resonance frequency band of the noise filter are different, the signal is not attenuated by the noise filter NF. Therefore, only noise can be selectively removed.

EXAMPLES

Next, the present invention will be described in detail with reference to Examples (see Table 1 and Table 2 and FIGS. 4 to 7). In addition, this invention is not limited to a present Example.

<< production of noise filter >>

First, No. 1 to 8, No. Various raw material powders were weighed so as to obtain an oxide conversion composition shown in 60 to 65, wet mixed for 4 hours by a ball mill, and then dried. Next, the dried product was calcined in the air at the temperature shown in Table 1, wet milling with a ball mill for 20 hours, and then dried. Subsequently, the binder was added and molded to the dried product, and then calcined in the air at the temperatures shown in Table 1 to obtain a troidal ferrite core (magnetic body (1)) shown in FIG. 3. Then, a wire 2 was wound around the magnetic material 1 to make a noise filter NF. The number of turns is shown in Table 1.

In addition, No. 1 to 8 are noise filters (NF) in which the magnetic body 1 is made of hexagonal ferrite. 60 to 65 are noise filters (NF) made of Ni-based ferrite.

<< Evaluation of noise filter >>

[impedance]

Each manufactured noise filter (NF) measured the frequency characteristic of the impedance in the frequency range of 1 MHz-1.8 GHz using the impedance analyzer (Hewlett-Packard Co., HP-4291A). The measurement results are as shown in the impedance-frequency characteristic curves of FIGS. 4 to 7.

4 and 5, which are impedance-frequency characteristic curves for the noise filter NF having the hexagonal ferrite as the magnetic material 1, No. It can be seen that 1 to 8 show clear maximum values (magnetic resonance frequencies) on the impedance-frequency characteristic curve, causing magnetic resonance. The impedance has a high value of 1000 to 10000 Ω or more in the frequency band of 200 MHz or more. In addition, it has a high impedance of more than 1000Ω up to 1GHz.

Next, from Figs. 6 to 7, which are impedance-frequency characteristic curves for the noise filter NF having the Ni-based ferrite as the magnetic material 1, No. It can be seen that the magnetic resonance is caused from the impedance-frequency characteristic curve of 60 to 63 degrees. The impedance also shows a relatively high value of about 1000 to 2000 Ω.

On the other hand, No. Although 64 and 65 have relatively high impedance values, the maximum values are not recognized in the impedance-frequency characteristic curve shown in Fig. 7, and almost constant impedance values are shown from the low frequency band to the high frequency band.

In addition, No. causing magnetic resonance 63 and No. which do not cause magnetic resonance The difference from 64 and 65 is the difference in the number of turns.

In addition, No. The noise filters NF of 1 to 8 are Nos. 60 to Nos. In the high frequency band of 500 MHz or more. Compared with the noise filter using the Ni-based ferrite of 65, it can be seen that it has a much higher impedance.

[Resistance Ratio, Density, Permeability]

No. shown above. In addition to 1-8, No. 10 to 32 and no. 66-68 were made into the composition and conditions of Table 2, and magnetic permeability, sintered compact density, and resistance ratio were measured. In addition, regarding the manufacturing method, No. It is the same as 1-8.

The resistance ratio was made by using a disk-shaped sample having an outer diameter of about 25.4 mm and a height of about 2 mm, applying In-Ga electrodes to both ends (front and rear) of the sample, and measuring the voltage with a voltage of 100 V using an insulation resistance meter (MEGRO, MEGOHMMETTER). It calculated from the measured value and the external dimension of the measurement sample.

The density of the sintered compact (magnetic body) was computed by measuring the external dimension of the produced sample by caliper, and measuring the weight of the sample by the electronic balance.

The magnetic permeability is obtained by preparing a sample of a troidal shape of 18mm in outer diameter, 10mm in inner diameter and 6mm in height, winding it, and measuring the impedance value of 100kHz and the external diameter measured by an LCR meter (HP-4284A). It calculated | required by calculating according to JIS).

These results are summarized in Table 2.

From the results in Table 2, it can be seen that the characteristics of the resistance ratio of 10 ⁴ to 10 ⁸ Ω / cm and the sintered compact density of 4.5 to 4.9 g / cc are obtained. With this resistance ratio and sintered body density, no special mechanical strength is required, the voltage used is not very high, and when used at a high voltage, there is no problem in use if sufficient insulation treatment is performed for the winding.

In order to have a value of 10 ⁶ Ω / cm or more of Ni-based ferrite with respect to the resistance ratio, It is more preferable if it is 1-3 because it has a value more than equivalent.

In addition, No. 1-32 has a value of 4.6 g / cc or more also with respect to a sintered compact density, and mechanical strength is also fully acquired.

As shown in Fig. 8, the magnetic permeability is No. 1 and No. 5 exceeds the limit of the snake.

This invention is not necessarily limited to the said embodiment and Example, It is possible to change suitably in the range which achieves the objective of this invention, and has the effect of this invention.

The noise filter of the present invention has an impedance-frequency characteristic equivalent to that of an LC parallel circuit, and can effectively remove noise of a specific frequency. In addition, noise can be removed in the high frequency band of 500 MHz or more. By using the hexagonal ferrite core as a magnetic material, it becomes possible to remove noise in the high frequency band which was not possible with the conventional ferrite core. In addition, since the mounting is easy, it is possible to easily and inexpensively prevent the noise of the electronic device.

Claims (31)

It consists of winding the power line or signal line to which noise is superimposed to be removed, or the input power line or signal line to which the electric signal is input, with the magnetic body as the core, and the maximum frequency characteristic of impedance is the same as the LC parallel circuit which is equivalent circuit for a specific frequency. In the noise filter for removing the noise in the self-known frequency band of this specific frequency, The core is a hexagonal ferrite, the composition of the ferrite is composed of the main component in terms of oxide, Fe ₂ O ₃ : 68 ~ 74 mol% MO: 15 to 22 mol% MeO: 4 ~ 13 mol% In the range of PbO: 0 to 10 wt% SiO ₂ : 0 ~ 5 wt% Wherein M is at least one material selected from the group consisting of Ba and Sr, and Me is at least one material selected from the group consisting of Co, Ni, Zn and Cu. delete The noise filter as claimed in claim 1, wherein the resonance frequency is 500 MHz or more. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete