EP2958116A1

EP2958116A1 - Annular magnetic core using iron-based nanocrystalline soft-magnetic alloy and magnetic component using said annular magnetic core

Info

Publication number: EP2958116A1
Application number: EP14751452.5A
Authority: EP
Inventors: Masamu Naoe; Yasuhiro Hamaguchi; Kazuhiro Hagiwara
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2013-02-15
Filing date: 2014-02-14
Publication date: 2015-12-23
Anticipated expiration: 2034-02-14
Also published as: CN105074843B; JP6075438B2; JPWO2014126220A1; EP2958116A4; CN105074843A; ES2775211T3; EP2958116B1; WO2014126220A1

Abstract

An annular magnetic core made of an Fe-based, nano-crystalline, soft-magnetic alloy, in which part of Fe is substituted by Ni and/or Co; having AC specific permeability µr_100k(50) of 4000 or more at a frequency of 100 kHz and DC magnetic field intensity of 50 A/m, AC specific permeability µr_100k(150) of 2500 or more at a frequency of 100 kHz and DC magnetic field intensity of 150 A/m, and the maximum permeability µ_Max of 8000 or less, and a magnetic flux density B₄₀₀ of 1.3 T or more, at DC magnetic field intensity of 400 A/m.

Description

FIELD OF THE INVENTION

The present invention relates to an annular magnetic core used in a noise filter, etc. disposed between a power supply and an electronic device to suppress noise in large current, and a magnetic device comprising it.

BACKGROUND OF THE INVENTION

In an electronic circuit comprising a power supply 201, an inverter 202, an electronic device 203, etc. as shown in Fig. 9, there are noises such as a high-frequency switching noise generated from a converter part of the power supply 201, a high-voltage pulse noise generated from the electronic device 203 such as a motor, etc., causing malfunctions. To prevent such noises, a noise filter 10 is disposed between the power supply 201 and the inverter 202 and the electronic device 203.
Fig. 10 shows the general structure of a noise filter 10 for a three-phase power supply. This noise filter 10 comprises interphase capacitors C11, C12, C 13, C21, C22, C23 for reducing a normal-mode noise, a common-mode choke coil 5 for reducing a common-mode noise, and grounded capacitors C31, C32, C33, between input terminals 101a on the power supply side and output terminals 101b on the electronic device side. A choke coil may be disposed in series to each power supply path to suppress a normal-mode noise.
Fig. 11 shows an example of common-mode choke coils 5. This common-mode choke coil 5 comprises, as described in JP 2000-340437 A , for example, an annular magnetic core 1 formed by Mn-Zn ferrite, an amorphous Fe-Si-B alloy, a nano-crystalline, soft-magnetic Fe-Si-B alloy, etc., pluralities of coils 7a, 7b, 7c wound around the annular magnetic core 1. The coil may be bifilar-wound. The common-mode choke coil 5 has large impedance to a common-mode noise in the power supply path, attenuating the common-mode noise from the power supply by the inductance of coils 7a, 7b, 7c and the grounded capacitors C31, C32, C33, and attenuating a normal-mode noise to input terminals by the interphase capacitors C11, C12, C13 connected between the input terminals, the interphase capacitors C21, C22, C23 connected between the output terminals, and the leak inductance of each coil, thereby preventing the noise of the power supply and the electronic devices from intruding each other.
Because noise suppression by a VCCI or CISPR standard, for example, determines the limit of noise terminal voltage in a frequency band of 150 kHz to 30 MHz, noise filters are required to reduce high-voltage noise, as well as noise in a wide frequency range. To suppress the high-voltage noise, the saturation magnetic flux density of a magnetic material used for cores of common-mode choke coils is important. To suppress the noise in a wide frequency band, the permeability of a magnetic material and its frequency characteristics are important.
JP 7-74419 B discloses an Fe-based, soft-magnetic alloy having a composition represented by the general formula of (Fe_1-aM_a)_100-X-Y-Z-αCu_XSi_YB_ZM'_α, wherein M is Co and/or Ni, M' is at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo, a, x, y, z and α meet 0 ≤ a ≤ 0.5, 0.1 ≤ x ≤ 3, 0 ≤ y ≤ 30, 0 ≤ z ≤ 25, 5 ≤ y + z ≤ 30, and 0.1 ≤ α ≤ 30; at least 50% of its structure being occupied by fine crystal grains having an average grain size of 100 nm or less, the balance being substantially amorphous. This Fe-based, soft-magnetic alloy has high permeability at high frequencies, but is easily magnetically saturated by large current, likely failing to exhibit sufficient function for choke coils. When a magnetic core is magnetically saturated by large current, its permeability decreases, resulting in low inductance. Therefore, when used for a noise filter, common-mode noise and normal-mode noise are less attenuated. When the magnetic core is provided with a magnetic gap to prevent decrease in the noise-attenuating performance, its core loss increases, and a magnetic flux leaks from the magnetic gap.
JP 2006-525655 A discloses a magnetic core formed by an ultrafine crystalline alloy having specific permeability µ of 500-15000, saturation magnetostriction λ of less than 15 ppm, and high operation characteristics in a linear B-H loop and at AC and DC; at least 50% of the ultrafine crystalline alloy being occupied by fine crystal particles having an average grain size of 100 nm or less; and the ultrafine crystalline alloy having a composition represented by the general formula of Fe_aCo_bNi_cCu_dM_eSi_fB_gX_h, wherein M is at least one of V, Nb, Ta, Ti, Mo, W, Zr, Cr, Mn and Hf, X is P, Ge, C and inevitable impurities, and a, b, c, d, e, f, g and h being expressed by atomic %, and meeting the conditions of 0 ≤ b ≤ 40, 2 < c < 20, 0.5 ≤ d ≤ 2, 1 ≤ e ≤ 6, 6.5 ≤ f ≤ 18, 5 ≤ g ≤ 14, 5 ≤ b + c ≤ 45, a + b + c + d + e + f = 100, and h < 5. It has been found, however, that magnetic cores having compositions specifically described in JP 2006-525655 A suffer the problem that high AC specific permeability µr cannot be easily kept in a DC magnetic field of 150 A/m or more.

OBJECT OF THE INVENTION

Accordingly, an object of the present invention is to provide an annular magnetic core capable of keeping high permeability even in large current with high resistance to magnetic saturation, and a magnetic device such as a choke coil, etc. exhibiting an excellent noise reduction effect.

DISCLOSURE OF THE INVENTION

The annular magnetic core of the present invention is formed by an Fe-based, nano-crystalline, soft-magnetic alloy, in which part of Fe is substituted by Ni and/or Co, and having
AC specific permeability µr_100k(50) of 4000 or more at a frequency of 100 kHz and DC magnetic field intensity of 50 A/m; AC specific permeability µr_100k(150) of 2500 or more at a frequency of 100 kHz and DC magnetic field intensity of 150 A/m; and
the maximum permeability µ_Max of 8000 or less, and a magnetic flux density B₄₀₀ of 1.3 T or more at DC magnetic field intensity of 400 A/m.
The above annular magnetic core preferably has AC specific permeability µr_10k(150) of 4000 or more at a frequency of 10 kHz and DC magnetic field intensity of 150 A/m, and AC specific permeability µ_10k(200) of 2000 or more at a frequency of 10 kHz and DC magnetic field intensity of 200 A/m.
The above Fe-based, nano-crystalline, soft-magnetic alloy preferably comprises more than 75.5 atomic % in total of Fe and Ni and/or Co, Ni and/or Co being 6 atomic % or less, 0.1-2 atomic % of Cu, 0.1-4 atomic % of Nb, 8-12 atomic % of Si, and 9-12 atomic % of B. In the more preferable composition of the Fe-based, nano-crystalline, soft-magnetic alloy, Fe and Ni and/or Co are more than 75.5 atomic % in total, Ni and/or Co being 4-6 atomic %, Si is 10-11.5 atomic %, and B is 9.2-10 atomic %.
The above Fe-based, nano-crystalline, soft-magnetic alloy is preferably in the form of a ribbon as thick as 10-25 µm. The above ribbon is more preferably as thick as 14-25 µm.
The magnetic device of the present invention comprises the above annular magnetic core contained in a resin case, part of the annular magnetic core being fixed with an adhesive. In the first example, a conductor penetrates through a hollow portion of the annular magnetic core. In the second example, a conductor is wound around the annular magnetic core. The conductor is a conductive wire or a busbar.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view showing an example of the annular magnetic cores of the present invention (Example 1).
Fig. 2 is a graph showing a DC B-H loop of the annular magnetic core of Example 1.
Fig. 3 is a graph showing the relation between AC specific permeability µr and magnetic field intensity in the annular magnetic core of Example 1.
Fig. 4 is a graph showing the frequency characteristics of AC specific permeability µr in the annular magnetic core of Example 1.
Fig. 5 is a graph showing the frequency characteristics of impedance in the choke coil of Example 2.
Fig. 6 is a graph showing the DC current superimposition characteristics of inductance in the choke coils of Example 2 and Comparative Example 1.
Fig. 7 is a perspective view showing an example of three-phase common-mode choke coils.
Fig. 8 is a graph showing the frequency characteristics of impedance and inductance in the three-phase common-mode choke coil of Example 3.
Fig. 9 is a block diagram showing a circuit comprising a noise filter disposed between a power supply and an electronic device.
Fig. 10 is a view showing an example of the circuit structures of a noise filter for a three-phase power supply.
Fig. 11(a) is a front view showing an example of common-mode choke coils.
Fig. 11(b) is a front view showing another example of common-mode choke coils.
Fig. 12 is a schematic, exploded, perspective view showing an annular magnetic core disposed in an insulating core case.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be explained in detail below referring to the attached drawings, without intention of restricting the present invention thereto, and various modifications may be made within a scope of the present invention. Explanations of each embodiment will be applicable to other embodiments unless otherwise mentioned.

[1] Fe-based, nano-crystalline, soft-magnetic alloy

An Fe-based, nano-crystalline, soft-magnetic alloy used in the annular magnetic core of the present invention has a composition, in which part of Fe is substituted by Ni and/or Co. To have desired B-H characteristics, it preferably has a composition represented by the general formula of Fe_a(Ni, Co)_bCu_cNb_dSi_eB_f (atomic %), wherein 75.5 < a + b, b ≤ 6, 0.1 ≤ c ≤ 2, 0.1 ≤ d ≤ 4, 8 ≤ e ≤ 12, 9 ≤ f ≤ 12, and a + b + c + d + e + f = 100, except for impurities. In the above formula, (Ni, Co) means Ni and/or Co.

(1) Fe, and Ni and/or Co

Fe is an element dominating a saturation magnetic flux density Bs. To achieve a magnetic flux density B₄₀₀ of 1.3 T or more at DC magnetic field intensity of 400 A/m, Fe and Ni and/or Co are preferably more than 75.5 atomic % in total.
The substitution of part of Fe by Ni and/or Co can increase induction magnetic anisotropy. Accordingly, a heat treatment in a magnetic field can decrease specific permeability intentionally without drastically decreasing a saturation magnetic flux density, thereby providing the alloy with resistance to magnetic saturation in large current. In addition, the addition of Ni and/or Co decreases core loss Pcv. The amount of Ni and/or Co added is preferably 6 atomic % or less. More than 6 atomic % of Ni and/or Co reduce the permeability largely, making it difficult to achieve AC specific permeability µr_100k(50) of 4000 or more at a frequency of 100 kHz and DC magnetic field intensity of 50 A/m, and AC specific permeability µr_100k(150) of 2500 or more at a frequency of 100 kHz and DC magnetic field intensity of 150 A/m. To obtain necessary impedance, the number of winding should be increased, becoming unsuitable for a choke coil. The above permeability is obtained by applying a magnetic field in a direction perpendicular to the magnetic path of the magnetic core (width direction of the alloy) during the heat treatment.
Because Ni decreases a saturation magnetic flux density Bs, more than 6 atomic % of Ni added alone makes it difficult to achieve a magnetic flux density B₄₀₀ of 1.3 T or more. Because Ni is more effective than Co in inclining a B-H curve (decreasing specific permeability) in a range of 6 atomic % or less, the amount of Co added can be reduced.
Co slightly increases a saturation magnetic flux density Bs, but is disadvantageous in cost because it is more expensive than Ni. With Co added with Ni, decrease in a saturation magnetic flux density Bs is preferably suppressed depending on the percentage of Co.
Cu is an element necessary for precipitating fine crystal grains by a heat treatment. Less than 0.1 atomic % of Cu makes it difficult to obtain fine crystal grains having an average crystal grain size of 100 nm or less, which occupy 50% or more by volume of the alloy structure. Also, more than 2 atomic % of Cu makes a pre-heat-treated amorphous alloy ribbon brittle, thereby making winding and punching difficult. Accordingly, the amount of Cu added is preferably 0.1-2 atomic %, more preferably 0.5-1.5 atomic %.
Nb contributes to the precipitation of fine crystal grains together with Cu. With less than 0.1 atomic % of Nb, the above effect is not sufficiently obtained. On the other hand, even more than 4 atomic % of Nb does not largely change the effect of precipitating fine crystal grains, but decreases the amounts of other metal elements by its content, likely deteriorating magnetic properties. Accordingly, the amount of Nb added is preferably 0.1-4 atomic %, more preferably 1-3.5 atomic %. Part or all of Nb may be substituted by an element having the same function as that of Nb, such as Ti, Zr, Hf, Mo, W or Ta.
Both Si and B are amorphous-phase-forming elements. With 8 atomic % or more of Si, the amorphous phase is stably formed by quenching, resulting in low coercivity Hc and core loss Pcv. However, more than 12 atomic % of Si decreases a saturation magnetic flux density Bs. The induction magnetic anisotropy is influenced by the amount of Si in Fe crystal grains having a bcc structure. Accordingly, the amount of Si added is preferably 8-12 atomic %, more preferably 10-11.5 atomic %.
With 9 atomic % or more of B, the amorphous phase is stably formed by quenching, resulting in a uniform nano-crystalline phase after a heat treatment. However, more than 12 atomic % of B decreases a saturation magnetic flux density Bs. Accordingly, the amount of B added is preferably 9-12 atomic %. To prevent the saturation of permeability in a wide frequency range in large current (in a strong magnetic field), the amount of B added is more preferably 9.2-10 atomic %. The total amount of Si and B is preferably 22 atomic % or less, more preferably 21 atomic % or less.

[2] Fe-based, nano-crystalline, soft-magnetic alloy ribbon

The Fe-based, nano-crystalline, soft-magnetic alloy ribbon is preferably as thick as 10-25 µm. With the thickness of less than 10 µm, the ribbon has not only insufficient mechanical strength, easily resulting in breakage during handling, but also high coercivity Hc. With the thickness of more than 25 µm, the ribbon does not stably have an amorphous structure, suffering large eddy current loss. Without considering the eddy current loss, the ribbon is preferably as thick as 14-25 µm.
Fig. 1 shows an example of annular magnetic cores 1 of the present invention, which is obtained by winding the Fe-based, nano-crystalline, soft-magnetic alloy ribbon 100. Apart from the wound magnetic core shown in Fig. 1, a magnetic core may be obtained by punching the ribbon to a doughnut shape, and laminating pluralities of the doughnut-shaped ribbons. The annular magnetic core 1 is not restricted to a circular shape, but may be in a racetrack shape, a rectangular shape, etc.

[3] Production method of annular magnetic core

(1) Production of Fe-based, nano-crystalline, soft-magnetic alloy ribbon

To obtain an Fe-based, nano-crystalline, soft-magnetic alloy ribbon, for example, an alloy melt having a predetermined composition is first quenched by a known single roll method, to form an Fe-based, amorphous alloy ribbon having a thickness of ten plus µm to about 30 µm, preferably 10-25 µm, more preferably 14-25 µm. The Fe-based, amorphous alloy ribbon may partially contain fine crystal grains in the structure. The Fe-based, amorphous alloy ribbon is wound or laminated to form an annular magnetic core. In this case, ribbons are preferably insulated.

(2) Heat treatment in magnetic field

The resultant annular magnetic core is heat-treated in a magnetic field at a temperature equal to or higher than the crystallization start temperature for 10 minutes or more, in an inert gas atmosphere such as a nitrogen gas, or in the air, to obtain an annular magnetic core of an Fe-based, nano-crystalline, soft-magnetic alloy, 50% by volume or more of whose structure is occupied by fine bcc-Fe crystal grains having an average crystal grain size of 100 nm or less. The temperature of precipitating bcc-Fe crystal grains (crystallization start temperature) is about 480-560°C, though variable depending on the composition of the Fe-based, nano-crystalline, soft-magnetic alloy. The crystallization start temperature is a heat generation start temperature measured by differential scanning calorimetry. When compound phases such as Fe₂B, etc. are precipitated, the coercivity Hc increases, losing constancy of permeability. Accordingly, the upper limit of the heat treatment temperature is preferably a temperature until which compound phases are not precipitated.
In the heat treatment in a magnetic field, the temperature and the keeping time are important. Because induction magnetic anisotropy is influenced by the amount of Si in Fe crystal grains having a bcc structure, Si should be sufficiently dissolved in Fe during crystallization. Accordingly, the highest-temperature-keeping time is preferably 10 minutes or more. A lower heat treatment temperature needs longer keeping time. Taking productivity into consideration, the upper limit is preferably 60 minutes.
When heat-treated in a magnetic field in a direction perpendicular to the magnetic path of the annular magnetic core (width direction of the ribbon), the B-H curve is inclined with improved linearity, resulting in low specific permeability, a low squareness ratio, and excellent constancy of permeability. The heat treatment in a magnetic field per se is a known method as disclosed, for example, in JP 7-74419 B . To saturate the alloy, a magnetic field applied is preferably at least 1000 A/m or more.
In an early stage of crystallization, Si is not sufficiently dissolved in a solid solution, failing to induce anisotropy. However, as more Si is dissolved, anisotropy is more rapidly induced. Accordingly, it is preferable to start applying a magnetic field at a temperature lower than the crystallization temperature.
A temperature-elevating speed until reaching the keeping temperature from the start of applying a magnetic field is preferably 5°C/minute or less. Too high a temperature-elevating speed provides early crystallization by heat generated by crystallization. Though anisotropy can be induced after the crystallization, it is insufficient as compared with that obtained during crystallization. In addition, crystallization may finish with insufficient Si dissolved. To obtain sufficient induction of anisotropy, the temperature-elevating speed is more preferably less than 1°C/minute.

[4] Characteristics of annular magnetic core

As a result of investigation to solve problems occurring when the Fe-based, nano-crystalline, soft-magnetic alloy is used for a magnetic device (particularly a choke coil), to exhibit excellent noise suppression effects while keeping excellent magnetic properties such as a high saturation magnetic flux density, low loss, and low magnetostriction, it has been found that (a) AC specific permeability µr_100k(50) at a frequency of 100 kHz and DC magnetic field intensity of 50 A/m should be 4000 or more, that (b) AC specific permeability µr_100k(150) at a frequency of 100 kHz and DC magnetic field intensity of 150 A/m should be 2500 or more, and that (c) the maximum permeability µ_Max should be 8000 or less, and a magnetic flux density B₄₀₀ should be 1.3 T or more, at DC magnetic field intensity of 400 A/m.
The AC specific permeability µr is permeability determined from the effective self-inductance of a coil having a closed-magnetic-path magnetic core with negligible magnetic flux leakage, by the following formula (1): $μr = (L \times C 1) / (μ_{0} \times N^{2})$

L: Effective self-inductance (H),
N: Number of winding,
µ₀: Permeability of vacuum (4 x π x 10^-7), and
C1: Magnetic core constant (mm^-1).

The effective self-inductance L was measured by an LCR meter (4284A available from Agilent Technologies, Inc.), and an impedance/gain-phase analyzer (4194A available from Agilent Technologies, Inc.).
The relation between a magnetic field and specific permeability µr was determined by measuring DC-current-superimposed inductance by a combination of an LCR meter 4284A and a bias current source (42841A available from Agilent Technologies, Inc.) capable of providing superimposing DC current of up to 20 A. The AC specific permeability µr was determined from effective self-inductance L at a predetermined frequency (for example, 100 kHz) by the above formula (1). The bias current I generating a predetermined DC magnetic field intensity H (for example, 50 A/m) was determined by the following formula (2): $H = I \times N / Le$

H: DC magnetic field intensity (A/m),
I: Bias current (A),
N: Number of winding, and
Le: Average line length (m).

The frequency characteristics of AC specific permeability µr were measured at an operational magnetic field of 0.05 A/m and a frequency of 10 kHz to 10 MHz, by an impedance/gain-phase analyzer 4194A. The maximum permeability µ_Max, a magnetic flux density B₄₀₀ and coercivity Hc at DC magnetic field intensity of 400 A/m were measured by a DC magnetization tester (SK-110 available from METRON, Inc.).
Considering noise-containing surge current, the present invention requires AC specific permeabilities µr_100k(50) and µr_100k(150) of 4000 or more and 2500 or more, respectively, at a frequency of 100 kHz and DC magnetic field intensities of 50 A/m and 150 A/m. With the AC specific permeability µr_100k(50) of 4000 or more and the AC specific permeability µr_100k(150) of 2500 or more, decrease in the attenuation performance of common-mode noise and normal-mode noise due to lowered permeability is suppressed, making it possible to exhibit an excellent noise suppression effect. The AC specific permeability µr_10k(150) at a frequency of 10 kHz and DC magnetic field intensity of 150 A/m is more preferably 4000 or more, and the AC specific permeability µr_10k(200) at a frequency of 10 kHz and DC magnetic field intensity of 200 A/m is more preferably 2000 or more.
When the maximum permeability µ_Max is 8000 or less, and a magnetic flux density B₄₀₀ is 1.3 T or more, at DC magnetic field intensity of 400 A/m, high-voltage noise is reduced, and magnetic saturation is avoided even with large current generated by transient current peak increase, thereby preventing extreme decrease in inductance.
Because the Fe-based, nano-crystalline, soft-magnetic alloy used in the annular magnetic core of the present invention exhibits higher permeability than those of other magnetic materials at high frequencies, a noise filter using a magnetic device (choke coil) comprising the annular magnetic core of the present invention is also excellent not only in high-voltage noise reduction but also in noise reduction in wide frequency bands.

[5] Magnetic device

The magnetic device of the present invention is obtained by (a) a penetrating conductors through a hollow portion of an annular magnetic core, or (b) winding conductors around an annular magnetic core, after the above annular magnetic core is contained in an insulating core case or provided with an insulating coating. Fig. 11 (a) shows a three-phase common-mode choke coil comprising three conductors a, b, c penetrating through an annular magnetic core 5', as an example of magnetic devices comprising conductors penetrating through a hollow portion of the annular magnetic core. Fig. 11(b) shows a three-phase common-mode choke coil comprising three conductors a, b, c wound around an annular magnetic core 5', as an example of magnetic devices comprising conductors wound around an annular magnetic core. Fig. 12 shows the annular magnetic core 5' contained in an insulating core case constituted by an upper case 11 and a lower case 12.
The present invention will be explained in more detail by Examples below without intention of restricting the scope of this invention.

Example 1

According to a single roll method, a melt having a composition of Fe_70.7Ni_5.0Cu_0.8Nb_2.8Si_10.9B_9.8 (atomic %) was rapidly quenched by ejection from a nozzle onto a copper roll rotating at a high speed, to obtain 53-mm-wide alloy ribbons as thick as 16 µm, 18 µm and 23 µm, respectively. It was confirmed by X-ray diffraction measurement that these alloy ribbons had a substantially amorphous structure. The crystallization temperature Tx of this alloy measured by differential scanning calorimetry was 490°C.
Each ribbon was slit to obtain two 25-mm-wide ribbons. Each ribbon was wound to obtain a toroidal core (space factor: 0.9) having an outer diameter of 24.5 mm, an inner diameter of 21 mm and a height/width of 25 mm. Each toroidal core was placed in a heat treatment furnace controlled to a nitrogen atmosphere, and subjected to a heat treatment comprising temperature elevation from 420°C to the highest temperature of 550°C at a speed of 0.54°C/minute, keeping at the highest temperature for 20 minutes, and then leaving it to cool in the furnace, thereby obtaining a toroidal core of the Fe-based, nano-crystalline, soft-magnetic alloy shown in Fig. 1. While elevating the temperature and keeping the highest temperature, a magnetic field of 280 kA/m was applied to the annular magnetic core in a height direction (width direction of the ribbon). By heat treatment in a magnetic field, substantially 70% by volume of fine crystal grains having average grain size of 100 nm or less were formed in any ribbons.
Each annular magnetic core was contained in an insulating case, provided with 10 turns of winding on the primary side and 10 turns of winding on the secondary side, to measure the maximum permeability µ_Max, a magnetic flux density B₄₀₀, coercivity Hc, and a squareness ratio at 25°C, by a DC magnetization test machine SK-110. The results are shown in Table 1. As a typical example, a direct current B-H loop of an annular magnetic core of a 16-µm-thick ribbon is shown in Fig. 2.
Each annular magnetic core was contained in an insulating case and provided with 10 turns of winding, to determine the relation of AC specific permeability µr to a DC magnetic field (intensity: 50 A/m, 150 A/m, and 200 A/m) at frequencies of 10 kHz and 100 kHz, and at 25°C, by an LCR meter 4284A. Table 1 shows AC specific permeability µr_100k(50) at a frequency of 100 kHz and DC magnetic field intensity of 50 A/m, AC specific permeability µr_100k(150) at a frequency of 100 kHz and DC magnetic field intensity of 150 A/m, AC specific permeability µr_10k(150) at a frequency of 10 kHz and DC magnetic field intensity of 150 A/m, and AC specific permeability µr_10k(200) at a frequency of 10 kHz and DC magnetic field intensity of 200 A/m. Fig. 3 shows the relation between AC specific permeability µr and magnetic field intensity (frequency: 10 kHz) in the annular magnetic core of a 16-µm-thick ribbon.

Each of the annular magnetic cores (Samples 1-5) was contained in an insulating case and provided with 1 turn of winding, to measure AC specific permeability µr_10k and µr_100k at a voltage amplitude of 0.5 Vrms, at frequencies of 10-100 kHz, and a temperature of 25°C, by an impedance/gain-phase analyzer 4194A. Also measured was a frequency f50, at which specific permeability µr corresponding to 50% of specific permeability µr10k at a frequency of 10 kHz was obtained. The results are shown in Table 1. Fig. 4 shows the frequency characteristics of specific permeability µr of a 16-µm-thick ribbon.

Table 1-1

Samples	Thickness (µm)	Coercivity Hc (A/m)	Magnetic Flux Density B₄₀₀ (T)	Squareness Ratio (%)
1-1	16	1.6	1.30	0.8
1-2	18	1.4	1.32	0.7
1-3	23	0.8	1.33	0.4
1-4	18	1.4	1.30	0.8
1-5	18	1.4	1.30	0.6

Table 1-2

Samples	µ_Max ⁽¹⁾ (x 10³)	AC Specific Permeability µr (x 10³)
		At Frequency of 10 kHz		At Frequency of 100 kHz
		µr_10k(150) ⁽²⁾	µr_10k(200) ⁽³⁾	µr_100k(50) ⁽⁴⁾	µr_100k(150) ⁽⁵⁾
1-1	5.1	4.9	2.7	4.2	2.9
1-2	5.0	4.5	2.5	4.0	2.5
1-3	5.0	4.7	2.7	4.1	2.9
1-4	5.0	4.7	2.2	4.2	3.0
1-5	5.0	4.2	1.4	4.7	3.7

[0071] Note: (1) The maximum permeability at DC magnetic field intensity of 400 A/m.
[0072] (2) Measured at a frequency of 10 kHz and DC magnetic field intensity of 150 A/m.
[0073] (3) Measured at a frequency of 10 kHz and DC magnetic field intensity of 200 A/m.
[0074] (4) Measured at a frequency of 100 kHz and DC magnetic field intensity of 50 A/m.
[0075] (5) Measured at a frequency of 100 kHz and DC magnetic field intensity of 150 A/m.

Table 1-3

Samples	Frequency Characteristics of AC Specific Permeability µr (x 10³)
Samples	µr_10k	µr_100k	f50 (MHz)
1-1	4.5	4.5	1.7
1-2	4.5	4.5	1.5
1-3	4.5	4.5	0.8
1-4	4.6	4.3	1.0
1-5	4.9	4.8	1.0

It is clear that the annular magnetic core of the present invention has a small squareness ratio, excellent constancy of permeability, and small change of AC specific permeability with frequency, while keeping a high magnetic flux density. It also has AC specific permeability µr_100k(50) of 4000 or more at a frequency of 100 kHz and DC magnetic field intensity of 50 A/m, AC specific permeability µr_10k(150) of 4000 or more at a frequency of 10 kHz and DC magnetic field intensity of 150 A/m, AC specific permeability µr_100k(150) of 2500 or more at a frequency of 100 kHz and DC magnetic field intensity of 150 A/m, and AC specific permeability µr_10k(200) of 2000 or more at a frequency of 10 kHz and DC magnetic field intensity of 200 A/m. Thus, the annular magnetic core of the present invention has high AC specific permeability in a range from a low magnetic field to a high magnetic field. Further, the annular magnetic core formed by the thin ribbon has excellent frequency characteristics, with less decrease in AC specific permeability.

Comparative Example 1

A ribbon (thickness: 18 µm) of an Fe-based, nano-crystalline, soft-magnetic alloy (FT-3KL available from Hitachi Metals, Ltd.) was formed into a toroidal core having an outer diameter of 36.0 mm, an inner diameter of 17.5 mm and a width of 25 mm, and charged into a case, around which an enameled wire having a diameter of 2.5 mm was wound 8 turns to produce a choke coil.

Example 2

The ribbon (thickness: 18 µm) produced in Example 1 was formed into a toroidal core having an outer diameter of 36.0 mm, an inner diameter of 17.5 mm and a width of 25 mm, and charged into a case, around which an enameled wire having a diameter of 2.5 mm was wound 17 turns to produce a choke coil. The impedance of the choke coil is shown in Fig. 5. As is clear from Fig. 5, the choke coil of Example 2 exhibited excellent impedance performance in a range from a low frequency to a high frequency.
The choke coils of Example 2 and Comparative Example 1 were evaluated with respect to DC current superimposition characteristics of inductance. The results are shown in Fig. 6. As is clear from Fig. 6, the choke coil of Example 2 was better than that of Comparative Example 1 in DC current superimposition characteristics of inductance.

Example 3

The ribbon (thickness: 18 µm) produced in Example 1 was formed into a toroidal core having an outer diameter of 17.8 mm, an inner diameter of 13.8 mm and a width of 25 mm, which was then used to produce a three-phase common-mode choke coil shown in Fig. 7. The annular magnetic core was inserted into an insulating case 6, into which a center partition plate 8 for dividing wiring regions was inserted. A 3-turn winding 7a, 7b, 7c of each phase was formed by winding an enameled wire having a diameter of 2.5 mm. The frequency characteristics of impedance and inductance in the three-phase common-mode choke coil are shown in Fig. 8. In the figure, a solid line indicates inductance, and a broken line indicates impedance. As is clear from Fig. 8, the three-phase common-mode choke coil of Example 3 exhibited excellent impedance performance from a low-frequency band to a high-frequency band.

Example 4

The three-phase common-mode choke coil produced in Example 2 was used to produce a noise filter shown in Fig. 9. The resultant noise filter exhibited excellent attenuation to low-frequency noise, high-frequency noise and pulse noise, as well as remarkable reduction of noise terminal voltage in a wide frequency range from 150 kHz to 30 MHz.

Example 5

Each alloy melt having the composition (atomic %) shown in Table 2 was formed into a ribbon having a thickness of 16 µm and a width of 53 mm, in the same manner as in Example 1. Each ribbon was slit to two 25-mm-wide ribbons. Each ribbon was wound to obtain a toroidal core (space factor: 0.9) having an outer diameter of 24.5 mm, an inner diameter of 21 mm and a width of 25 mm. Each toroidal core was subjected to the same heat treatment in a magnetic field as in Example 1, to obtain a toroidal core of an Fe-based, nano-crystalline, soft-magnetic alloy. The AC specific permeabilities µr_100k(50), µr_100k(150), µr_10k(150) and µr_10k(200) of each toroidal core were measured in the same manner as in Example 1. The results are shown in Table 2.

Table 2-1

Samples	Alloy Composition (atomic %)
Samples	Fe	Ni	Cu	Nb	Si	B
5-1	70.96	5.04	0.85	2.81	10.9	9.44
5-2	70.95	4.95	0.85	2.77	11.0	9.48
5-3	70.79	4.91	0.85	2.77	10.9	9.78
5-4	70.90	5.03	0.85	2.78	11.0	9.44
5-5	71.22	4.93	0.86	2.77	10.9	9.32
5-6	70.87	5.03	0.85	2.77	11.0	9.48
5-7	70.96	5.04	0.85	2.81	10.9	9.44

Table 2-2

Sample	AC Specific Permeability µr (x 10³)
	At Frequency of 10 kHz		At Frequency of 100 kHz
	µr_10k(150) ⁽¹⁾	µr_10k(200) ⁽²⁾	µr_100k(50) ⁽³⁾	µr_100k(150) ⁽⁴⁾
5-1	4.9	2.7	4.2	2.9
5-2	4.9	2.6	4.1	2.6
5-3	4.2	1.4	4.7	3.7
5-4	4.5	2.4	4.0	2.5
5-5	4.6	2.5	4.0	2.7
5-6	4.7	2.1	4.1	2.9
5-7	4.7	2.2	4.2	3.0

Note: (1)-(4) The same as in Notes (2)-(5) under Table 1-2.

As is clear from Table 2, good AC specific permeability characteristics were obtained particularly when B was in a range of 9.32-9.78 atomic %.

EFFECT OF THE INVENTION

Because the annular magnetic core of the present invention is resistant to magnetic saturation, keeping high permeability at large current, it has high performance of reducing voltage noise and excellent pulse attenuation characteristics, suitable for small, light-weight choke filters for reducing noise in a wide frequency band. Also, it does not need a magnetic gap necessary when an Fe-based, nano-crystalline, soft-magnetic alloy having high permeability is used, resulting in the reduced number of working steps. Further, it advantageously does not suffer the change of characteristics by magnetostriction, unlike Fe-based, amorphous alloys.

Claims

A annular magnetic core made of an Fe-based, nano-crystalline, soft-magnetic alloy, in which part of Fe is substituted by Ni and/or Co; which has
AC specific permeability µr_100k(50) of 4000 or more at a frequency of 100 kHz and DC magnetic field intensity of 50 A/m;
AC specific permeability µr_100k(150) of 2500 or more at a frequency of 100 kHz and DC magnetic field intensity of 150 A/m; and
the maximum permeability µ_Max of 8000 or less, and a magnetic flux density B₄₀₀ of 1.3 T or more, at DC magnetic field intensity of 400 A/m.
The annular magnetic core according to claim 1, which has AC specific permeability µr_10k(150) of 4000 or more at a frequency of 10 kHz and DC magnetic field intensity of 150 A/m, and AC specific permeability µr_10k(200) of 2000 or more at a frequency of 10 kHz and DC magnetic field intensity of 200 A/m.
The annular magnetic core according to claim 1 or 2, wherein said Fe-based, nano-crystalline, soft-magnetic alloy comprises more than 75.5 atomic % in total of Fe and Ni and/or Co, Ni and/or Co being 6 atomic % or less, 0.1-2 atomic % of Cu, 0.1-4 atomic % of Nb, 8-12 atomic % of Si, and 9-12 atomic % of B.
The annular magnetic core according to claim 3, wherein in said Fe-based, nano-crystalline, soft-magnetic alloy, Fe and Ni and/or Co are more than 75.5 atomic % in total, Ni and/or Co being 4-6 atomic %, Si is 10-11.5 atomic %, and B is 9.2-10 atomic %.
The annular magnetic core according to any one of claims 1-4, wherein said Fe-based, nano-crystalline, soft-magnetic alloy is in the form of a ribbon as thick as 10-25 µm.
The annular magnetic core according to claim 5, wherein said ribbon has a thickness of 14-25 µm.
A magnetic device comprising the annular magnetic core recited in any one of claims 1-6 contained in a resin case, part of said annular magnetic core being fixed by an adhesive.
The magnetic device according to claim 7, wherein a conductor penetrates through a hollow portion of said annular magnetic core.
The magnetic device according to claim 7, wherein a conductor is wound around said annular magnetic core.