Method for measuring magnetic properties

Abstract

To provide a method for measuring magnetic characteristics capable of measuring complex magnetic permeability with high accuracy.SOLUTION: A method of measuring a magnetic property includes measuring a first inductance and a first resistance value by applying a current between both ends of a rod-shaped conductor inserted into a center hole of a substantially ring-shaped magnetic body, measuring a second inductance and a second resistance value by applying a current between both ends of the rod-shaped conductor from which the magnetic body is removed, and calculating a complex magnetic permeability of the magnetic body from a difference between the first inductance and the second inductance and a difference between the first resistance value and the second resistance value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for measuring magnetic properties. [Background technology]

[0002] For example, Patent Document 1 describes a method for measuring magnetic properties by providing an excitation winding and a detection winding on a sample to be measured that has been processed into a doughnut shape. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-139717 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when measuring the complex permeability of a magnetic material using the above method, the stray capacitance of the windings strongly affects the impedance in the high frequency band, which may result in a decrease in measurement accuracy.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a method for measuring magnetic properties that can measure complex permeability with high accuracy. [Means for solving the problem]

[0006] The method for measuring magnetic properties of the present invention measures a first inductance and a first resistance value by passing current between both ends of a rod-shaped conductor inserted into the center hole of an approximately ring-shaped magnetic body, measures a second inductance and a second resistance value by passing current between both ends of the rod-shaped conductor with the magnetic body removed, and calculates the complex permeability of the magnetic body from the difference between the first inductance and the second inductance and the difference between the first resistance value and the second resistance value.

[0007] In the above measuring method, the maximum frequency of the current passed through the rod-shaped conductor may be 1 MHz or higher.

[0008] In the above-described measuring method, the main component of the rod-shaped conductor may be copper. [Effects of the Invention]

[0009] According to the present invention, complex permeability can be measured with high accuracy. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of a system for measuring magnetic properties. [Figure 2] FIG. 2 is a diagram showing an example of a measurement system when the magnetic core is removed. [Figure 3] FIG. 3(a) is a diagram showing an example of changes in calculated inductance values ​​relative to frequency, and FIG. 3(b) is a diagram showing an example of changes in calculated resistance values ​​relative to frequency. [Figure 4] 4(a) and 4(b) are diagrams showing the real part and the imaginary part of the complex permeability measured by the measuring methods of the example and the comparative example, respectively. [Figure 5] FIG. 5 is a flowchart showing an example of a procedure for measuring complex permeability. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Measurement system configuration) Fig. 1 is a diagram showing an example of a magnetic property measurement system SYS. The measurement system SYS includes a magnetic core 1, a rod-shaped conductor 2, an impedance measuring instrument 3, a computer 5, lead wires 31 and 32, and support members 40 to 42. Fig. 1 shows a perspective view of the assembled magnetic core 1, rod-shaped conductor 2, and support members 40 to 42.

[0012] The support members 40 to 42 are placed, for example, on a surface 90 of a base 9. The support member 40 supports the magnetic core 1, and the support members 41 and 42 support the rod-shaped conductor 2. The support members 40 to 42 are formed of an insulating material such as resin.

[0013] The magnetic core 1 is an example of a magnetic material and is the object for measuring complex permeability. The magnetic core 1 is obtained by processing a magnetic material, such as a nanocrystalline material, into a roughly ring shape. The magnetic core 1 has, as an example, a cylindrical shape and has a roughly circular center hole 1a when viewed from the front. The center hole 1a is defined by an inner wall surface. For example, the difference between the inner diameter and the outer diameter of the magnetic core 1 is about 10 mm, and the height (thickness) of the magnetic core 1 is about 20 mm.

[0014] The magnetic core 1 is used, for example, for reducing EMC (Electro Magnetic Compatibility) noise caused by switching elements. By measuring the complex permeability using a magnetic property measurement method described later, it is possible to determine whether the magnetic core 1 is suitable for the above-mentioned application.

[0015] The support member 40 has a disk shape in top view, and the center of the disk is recessed in a saucer shape. The lower part of the magnetic core 1 is in contact with the saucer-shaped part of the support member 40.

[0016] The rod-shaped conductor 2 is a flat metal plate mainly composed of copper, for example. The rod-shaped conductor 2 is inserted into the central hole 1a of the magnetic core 1. Lead wires 31 and 32 are electrically connected to the ends 21 and 22 of the rod-shaped conductor 2, respectively, by tape or the like. The ends of the lead wires 31 and 32 opposite to the rod-shaped conductor 2 are connected to an impedance measuring instrument 3.

[0017] The support members 41 and 42 support the rod-shaped conductor 2 substantially horizontally on both sides of the magnetic core 1. The centers of the support members 41 and 42 are recessed so as to sandwich the rod-shaped conductor 2 from above and below. The shapes of the support members 41 and 42 are adjusted so that the center position of the vertical cross section of the rod-shaped conductor 2 substantially coincides with the center position of the center hole 1a of the magnetic core 1.

[0018] The impedance measuring instrument 3 measures impedance by passing a current between the ends (both ends) 21, 22 of the rod-shaped conductor 2. The computer 5 is connected to the impedance measuring instrument 3. The computer 5 controls the impedance measuring instrument 3 (calibration and impedance measurement), calculates the complex permeability, and performs other operations in accordance with a predetermined program (software).

[0019] (impedance measurement) Zca = Rca + jωLca (1) Za=Ra+jωLa (2) Zc = Zca - Za (3)

[0020] The above formula (1) represents the impedance Zca when the magnetic core 1 is present in the measurement system SYS, and the above formula (2) represents the impedance Za when the magnetic core 1 is not present in the measurement system SYS. Furthermore, the above formula (3) represents the impedance Zc of the magnetic core 1 alone. In formulas (1) to (3), j is the imaginary unit, and ω is the angular frequency of the AC current during measurement. Furthermore, Rca and Ra are resistance values, and Lca and La are inductances.

[0021] In the measurement system SYS, the impedance measuring instrument 3 measures the impedance Zca by passing a current between the ends 21 and 22 of the rod-shaped conductor 2. The impedance measuring instrument 3 passes AC currents of multiple frequencies (=2πω) through the rod-shaped conductor 2 and measures the resistance Rca and inductance Lca for each frequency. The frequencies are, for example, 1 kHz, 10 kHz, 100 kHz, 1000 kHz, 10,000 kHz, and 30,000 kHz. The user sets the frequency at the start of measurement (1 kHz) and the frequency at the end of measurement (30,000 kHz) in the impedance measuring instrument 3 via the computer 5. The computer 5 acquires the resistance Rca and inductance Lca from the impedance measuring instrument 3 and stores them in a memory or the like. Next, the magnetic core 1 is removed from the rod-shaped conductor 2.

[0022] Fig. 2 is a diagram showing an example of the measurement system SYS when the magnetic core 1 is removed. In Fig. 2, components common to Fig. 1 are given the same reference numerals and their explanations are omitted. The magnetic core 1 is indicated by a dotted line.

[0023] In the measurement system SYS without the magnetic core 1, the impedance measuring instrument 3 measures the impedance Za by passing a current between the ends 21, 22 of the rod-shaped conductor 2. At this time, the support member 40 is also removed along with the magnetic core 1, and only air is present around the rod-shaped conductor 2. The impedance measuring instrument 3 passes currents of each of the above frequencies through the rod-shaped conductor 2 and measures the resistance value Ra and inductance La for each frequency. The computer 5 obtains the resistance value Ra and inductance La from the impedance measuring instrument 3 and stores them in a memory or the like.

[0024] Zc=(Rca-Ra)+jω(Lca-La)=Rc+jωLc ···(4)

[0025] Next, the computer 5 calculates the impedance Zc of the magnetic core 1 for each frequency from the resistance values ​​Rca and Ra and the inductances Lca and La. The impedance Zc is the difference between the measured impedances Zca and Za as shown in equation (3), and is therefore expressed by the above equation (4).

[0026] The computer 5 calculates the resistance value Rc (=Rca-Rc) of the magnetic core 1 from the difference between the resistance values ​​Rca and Rc for each frequency, and calculates the inductance Lc (=Lca-La) of the magnetic core 1 from the difference between the inductances Lca and La for each frequency. The resistance values ​​Rca and Ra are examples of first and second resistance values, respectively, and the inductances Lca and La are examples of first and second inductances, respectively.

[0027] Fig. 3(a) is a graph showing an example of changes in the calculated value of inductance Lc (nH) with respect to frequency f (kHz), and Fig. 3(b) is a graph showing an example of changes in the calculated value of resistance Rc (mΩ) with respect to frequency f (kHz). The solid line indicates the value (logarithmic) calculated by computer 5 based on the measurement results of impedance measuring instrument 3, and the dotted line indicates the theoretical value (logarithmic).

[0028] The frequency f ranges, for example, from 1 to 30,000 kHz. Because calculated values ​​close to the theoretical values ​​are obtained over the entire range of frequency f, the above measurement method makes it possible to measure the inductance Lc and resistance Rc with high accuracy.

[0029] (Calculation of complex permeability) Next, the computer 5 calculates the complex permeability of the magnetic core 1 from the inductance Lc and the resistance value Rc.

[0030] μ=μ'+jμ'' (5) μ'=(Lc·l) / (S·N 2 ) ···(6) μ''=(Rc·l) / (ω·S·N 2 ) ···(7)

[0031] As shown in the above formula (5), the complex permeability μ of the magnetic core 1 includes a real part μ' and an imaginary part μ''. The computer 5 calculates the real part μ' from the inductance Lc using the above formula (6), and calculates the imaginary part μ'' from the resistance value Rc using the above formula (7).

[0032] In equations (6) and (7), l is the magnetic path length of the magnetic core 1, S is the cross-sectional area of ​​the magnetic core 1, and N is the number of turns of the magnetic core 1. The magnetic path length l is the circumference of a circle with a radius midway between the inner and outer diameters when viewed from the front of the center hole 1a of the magnetic core 1. The area S is the cross-sectional area of ​​an approximately rectangular shape when the magnetic core 1 is cut vertically. The number of turns N is 1. The computer 5 stores the magnetic path length l, area S, and number of turns N in advance in a storage means such as a memory.

[0033] 4(a) and 4(b) are diagrams showing the real part μ' and imaginary part μ'' of complex permeability μ measured by the measurement methods of the example and the comparative example, respectively. In FIGS. 4(a) and 4(b), the horizontal axis represents frequency f (kHz). The solid lines represent the real part μ' and imaginary part μ'' measured by the measurement method of the example, and the two-dot chain lines represent the real part μ' and imaginary part μ'' measured by the measurement method of the comparative example based on the above-mentioned Patent Document 1. The dotted lines represent the theoretical values ​​of the real part μ' and imaginary part μ''.

[0034] In the frequency range f=1 to 1000 (kHz), the real part μ' and imaginary part μ'' of the examples and comparative examples substantially match the theoretical values. On the other hand, in the frequency range f≧1000 (kHz), the real part μ' and imaginary part μ'' of the examples substantially match the theoretical values, but in the comparative examples, the error of the real part μ' and imaginary part μ'' from the theoretical values ​​increases as the frequency f increases.

[0035] |Z|=|1 / {1 / (ω·L)-ω·C}| ···(8)

[0036] In the comparative example, impedance Z is measured by winding a wire (e.g., a copper wire) around the magnetic core 1 and passing a current through it. In this case, impedance Z includes not only inductance L but also stray capacitance C generated by the winding, as shown in the above equation (8). Since impedance Z depends on the product of stray capacitance C and angular frequency ω, the measurement error of impedance Z increases as frequency f (=2πω) increases.

[0037] In contrast, in the embodiment, no winding is provided around the magnetic core 1, and therefore the stray capacitance C has substantially no effect on the measurement. In the embodiment, as described above, the impedance Zca when the rod-shaped conductor 2 is inserted into the center hole 1a of the magnetic core 1 and the impedance Za when the magnetic core 1 is removed from the rod-shaped conductor 2 are measured, and the real part μ' and imaginary part μ'' are calculated from the difference between the impedances Zca and Za (resistance value Rc, inductance Lc), making it possible to measure the complex permeability μ with higher accuracy than in the comparative example, particularly in the high frequency band.

[0038] Therefore, as described above, particularly good measurement results can be obtained by setting the maximum frequency of the current passed from the impedance measuring instrument 3 to the rod-shaped conductor 2 to 1 MHz or higher. In addition, in this example, the rod-shaped conductor 2 is mainly composed of copper, which has high conductivity, and therefore more accurate measurement results can be obtained than when a rod-shaped conductor 2 with low conductivity is used, but the main component of the rod-shaped conductor 2 may be another metal. In addition, the shape of the rod-shaped conductor 2 is not limited to a flat plate, and may be another shape, such as a round bar.

[0039] (Measurement procedure) 5 is a flowchart showing an example of a procedure for measuring complex permeability μ. First, in a measurement system SYS that includes a magnetic core 1, the inductance Lca and the resistance Rca are measured by passing a current between both ends of a rod-shaped conductor 2 from an impedance measuring instrument 3 (step St1). Next, in a measurement system SYS that does not include a magnetic core 1, the inductance La and the resistance Ra are measured by passing a current between both ends of the rod-shaped conductor 2 from an impedance measuring instrument 3 (step St2). In steps St1 and St2, the frequency f of the AC current is changed within a predetermined range, and the resistances Rca and Rc and the inductances Lca and La are measured at each of a plurality of frequencies f.

[0040] Next, the computer 5 calculates the resistance value Rc, which is the difference between the resistance values ​​Rca and Rc, for each frequency, and calculates the inductance Lc, which is the difference between the inductances Lca and La, for each frequency (step St3). Next, the computer 5 calculates the complex permeability μ of the magnetic core 1 from the inductance Lc and the resistance value Rc (step St4). Measurement is performed in this manner.

[0041] As described above, according to the above-mentioned method for measuring magnetic properties, the complex permeability μ can be measured with high accuracy from the resistance values ​​Rca, Rc and inductances Lca, La measured without winding the magnetic core 1.

[0042] The above-described embodiment is a preferred example of the present invention, but the present invention is not limited to this and can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0043] 1 magnetic core (magnetic material), 1a central hole, 2 rod-shaped conductor, 21, 22 end portions (both ends), 3 impedance measuring instrument, SYS measurement system

Claims

1. measuring the first inductance and the first resistance value by passing a current between both ends of a rod-shaped conductor inserted into a center hole of a substantially ring-shaped magnetic body; measuring a second inductance and a second resistance value by passing a current between both ends of the rod-shaped conductor from which the magnetic body has been removed; calculating a complex permeability of the magnetic body from a difference between the first inductance and the second inductance and a difference between the first resistance value and the second resistance value; Methods for measuring magnetic properties.

2. The maximum frequency of the current passing through the rod-shaped conductor is 1 MHz or more. The method for measuring magnetic properties according to claim 1 .

3. The main component of the rod-shaped conductor is copper. The method for measuring magnetic properties according to claim 1 .

Images