Magnetic permeability measurement probe and magnetic permeability measurement device using the same

Abstract

Provided is a magnetic permeability measurement probe capable of accurately measuring the magnetic permeability, in particular the imaginary part of a complex permeability, of a magnetic material. The probe for measuring the magnetic permeability of a magnetic material comprises: a band-shaped strip conductor formed on the front surface of a dielectric substrate; a transmission line body having a grounding conductor formed on the front surface or the back surface of the dielectric substrate; a first connector that connects to one end of each of the strip conductor and the grounding conductor; and a second connector that connects to the other end of each of the strip conductor and the grounding conductor. The strip conductor is composed of a first length part including a portion that connects to the first connector at the one end side, a second length part including a portion that connects to the second connector at the other end, and a third length part that extends between the first length part and the second length part. The third length part has a current imbalance reducing means.

Description

[Technical Field]

[0001] The present invention relates to a probe for measuring the magnetic permeability of a magnetic body and a magnetic permeability measurement device using the same. [Background technology]

[0002] Currently, high-frequency applications using the GHz band, such as mobile phones and wireless communications, are becoming increasingly popular. High-frequency magnetic materials that are useful for further miniaturization and high integration of these components are highly desired, and magnetic thin films with high magnetic permeability are particularly essential for the magnetic materials used in circuits. At the same time, the establishment of a method for evaluating high-frequency magnetic permeability is becoming essential.

[0003] The present inventors have developed a magnetic permeability measurement device that does not require the effort of processing a sample. Patent documents 1 to 4 disclose probes and magnetic permeability measurement devices developed by the present inventors for measuring the magnetic permeability of magnetic materials, particularly film-like magnetic materials. The probe has a structure in which a dielectric layer is sandwiched between a strip conductor through which a high-frequency carrier signal is passed and a ground conductor, and the magnetic material to be measured is brought into contact with the conductor, and the permeability coefficient S of the magnetic material to be measured is measured. 21 By measuring this, the magnetic permeability of the magnetic material can be determined.

[0004] The permeability to be obtained is the complex permeability μ expressed by the following formula (1), where μ′ is the real part of the complex permeability μ and μ″ is the imaginary part of the complex permeability μ.

[0005]

number

[0006] The real part μ' of the complex permeability μ corresponds to the inductance component L of the magnetic material, and the imaginary part μ'' of the complex permeability μ is the loss component (resistance component) of the magnetic material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-060367 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-032165 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-172497 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-053569 Summary of the Invention [Problem to be solved by the invention]

[0008] 17 is a diagram showing a schematic diagram of a magnetic field region excited in a magnetic body to be measured, particularly in a magnetic body having a large area compared to the width of a strip conductor. The magnetic body 1 to be measured is excited by a high-frequency carrier signal (current) flowing through a strip conductor 2 of a probe that contacts the magnetic body. However, according to an electromagnetic field analysis by the inventors of the present application, when the strip conductor 2 is relatively thin and its width is relatively small compared to the width of the magnetic body 1, the entire magnetic body 1 is not excited, and only a localized region near the contact area with the strip conductor 2 is excited, resulting in an error in measuring the magnetic permeability.

[0009] When a magnetic body is locally excited, a demagnetizing field is generated inside the body outside the locally generated magnetic field. This demagnetizing field cancels out the magnetic flux of the excited magnetic field, resulting in an error in the actual permeability of the magnetic body being measured. More specifically, the resonant frequency of the imaginary part μ″ of the complex permeability μ in equation (1) above may shift, making it impossible to measure the permeability with high accuracy. Figure 18 is a graph showing an example of a measurement in which an error occurs in the imaginary part of the permeability due to the influence of a demagnetizing field. The graph shows measurements made using a probe equipped with a thin conductor microstrip line and measurements made using the Nicolson-Ross-Weir (NRW) method, a standard permeability measurement method that is not affected by demagnetizing fields. Figure 18(a) shows the imaginary part μ″ of the complex permeability μ, and Figure 18(b) shows the real part μ′ of the complex permeability μ. The magnetic material being measured was a NiZn ferrite thin film (3 mm × 1 mm × 100 μm thick), and as shown in Figure 18(a), the resonance frequency for the imaginary part μ'' of the complex permeability μ shifted to the higher frequency side by about 7 GHz compared to the values ​​measured by the NRW method, resulting in a large error in the measurement value. Note that the measured values ​​for the real part μ' of the complex permeability μ shown in Figure 18(b) appear to be roughly in line with the values ​​measured by the NRW method, but in reality the point of change should have shifted to the higher frequency side in the same way, and it is possible that this was buried in noise and made difficult to observe.

[0010] The permeability of film-shaped magnetic materials, which are the target samples for measurement, is often evaluated using standard measurement methods such as the NRW method, but this requires precise machining of the sample into a doughnut shape and precise positioning in a coaxial tube, which is technically difficult and time-consuming. On the other hand, when evaluating using signal transmission lines such as microstrip lines with strip conductors, as mentioned above, when measuring magnetic materials with a large area compared to the width of the strip conductor, the demagnetizing field of the magnetic material forces localized magnetic field application, which causes a shift in the ferromagnetic resonance frequency and a decrease in permeability, making it difficult to accurately measure the intrinsic permeability of the material.

[0011] The inventors of the present invention have attempted to measure by expanding the width of the strip conductor or by increasing the distance between the strip conductor and the sample, but none of these attempts worked. In particular, when the width of the strip conductor was increased, the skin effect caused a bias in the current direction (outer periphery) of the conductor, making measurements difficult.

[0012] Therefore, an object of the present invention is to provide a magnetic permeability measurement probe and a magnetic permeability measurement device using the same that can measure the magnetic permeability with high accuracy even for magnetic materials that have an area large compared to the width of a strip conductor. [Means for solving the problem]

[0013] In order to achieve the above-mentioned object, the magnetic permeability measuring probe of the present invention is a probe for measuring the magnetic permeability of a magnetic material, and comprises a transmission line body having a band-shaped strip conductor formed on the surface of a dielectric substrate and a ground conductor formed on the surface or back surface of the dielectric substrate, a first connector connected to one end of each of the strip conductor and the ground conductor, and a second connector connected to the other end of each of the strip conductor and the ground conductor, wherein the strip conductor is composed of a first length portion including a portion that connects to the first connector at one end, a second length portion including a portion that connects to the second connector at the other end, and a third length portion extending between the first length portion and the second length portion, and the third length portion has a current bias suppression means. [Effects of the Invention]

[0014] According to the present invention, by providing a current bias suppression means in the strip conductor of the transmission line body, the bias of current in the conductor width direction due to the skin effect is suppressed and the influence of the demagnetizing field is reduced, thereby making it possible to measure the magnetic permeability (especially the imaginary part of the complex permeability) of a magnetic material with high accuracy. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram illustrating a schematic configuration example of a magnetic permeability measurement device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating a first configuration example of a probe according to the first embodiment of the present invention. [Figure 3] 10A and 10B are diagrams showing the pattern of a strip conductor constituting a probe. [Figure 4] 1 is a diagram schematically showing a magnetic field region excited in a magnetic body 1 to be measured by a wide strip conductor 11 provided with a slit 17 in the first embodiment of the present invention. FIG. [Figure 5] 10A and 10B are diagrams showing modified examples of the pattern of the strip conductor in the probe. [Figure 6] FIG. 4 is a diagram illustrating a second configuration example of the probe according to the first embodiment of the present invention. [Figure 7] FIG. 10 is a diagram showing a strip conductor according to a second embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing a strip conductor according to a third embodiment of the present invention. [Figure 9] FIG. 10 is a diagram showing a strip conductor according to a fourth embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing a strip conductor according to a fifth embodiment of the present invention. [Figure 11] 3 is a flowchart showing the procedure of a magnetic permeability measurement method according to an embodiment of the present invention. [Figure 12] FIG. 2 is a diagram schematically showing the shape of a magnetic thin film as a magnetic material to be measured. [Figure 13] 10 is a graph showing the results of measuring magnetic permeability by a magnetic permeability measurement device using a probe according to an embodiment of the present invention. [Figure 14] 10A and 10B are diagrams showing modified examples of the strip conductor 11 constituting the probe in the first embodiment of the present invention. [Figure 15] FIG. 10 is a diagram showing another modified example of the strip conductor 11 constituting the probe in the first embodiment of the present invention. [Figure 16] 10 is a diagram showing the measurement results of the current density flowing through the strip conductor 11. FIG. [Figure 17]FIG. 10 is a diagram schematically showing a magnetic field region excited in a magnetic body to be measured when a conventional probe is used. [Figure 18] 10 is a graph showing an example of measurement in which an error occurs in the imaginary part of magnetic permeability due to the influence of a demagnetizing field. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. However, the technical scope of the present invention is not limited to these preferred embodiments.

[0017] 1 is a diagram showing a schematic configuration example of a magnetic permeability measurement device according to an embodiment of the present invention. The magnetic permeability measurement device according to the embodiment of the present invention is configured to include a probe 10, a network analyzer (signal measuring instrument) 20, and an arithmetic processing device (e.g., a computer such as a personal computer) 30 (processing means) that executes numerical analysis processing.

[0018] The magnetic body 1 to be measured is a film-like magnetic body with a film thickness of, for example, about 100 μm. The probe 10 is placed in contact with or close to the magnetic body 1, and is connected to a network analyzer 20 via a non-magnetic coaxial cable 3. The network analyzer 20 measures the transmission coefficient S 21 The signal data is input to a control personal computer 30, and the complex permeability of the magnetic material is calculated by a predetermined numerical analysis process (for example, optimization process). In addition, to magnetically saturate the magnetic material 1, a magnet (magnetic field application unit) consisting of a double-yoke electromagnet 40 is used.

[0019] FIG. 2 is a diagram showing a first configuration example of a probe according to the first embodiment of the present invention, and FIG. 3 is a diagram showing a pattern of a strip conductor that constitutes the probe.

[0020] Probe 10 comprises transmission line 14, which constitutes a microstrip line having a structure in which a dielectric substrate 13 is sandwiched between strip conductor 11 and ground conductor 12, and connectors 15 and 16, which are electrically connected to both ends of transmission line 14 in the longitudinal direction. Transmission line 14 comprises dielectric substrate 13, band-shaped strip conductor 11 formed on its surface, and ground conductor 12 formed on the back surface of dielectric substrate 13. A 50 Ω coaxial cable 3 is connected to connectors 15 and 16, which are connected to network analyzer 20. Transmission line 14 is fabricated, for example, by etching a printed circuit board made of fluororesin (e.g., polytetrafluoroethylene (PTFE)).

[0021] The strip conductor 11 is composed of a first length portion 11a including a portion at one end of its length that connects to the connector 15, a second length portion 11b including a portion at the other end of its length that connects to the connector 16, and a third length portion 11c extending between the first length portion 11a and the second length portion 11b, and the third length portion 11c has at least one slit 17 extending in the length direction.

[0022] The strip conductor 11 is formed relatively wide (for example, 1.2 mm wide) to match the width direction length of the magnetic body 1 to be measured, and is designed to have dimensions equal to or greater than the width direction length of the magnetic body 1 to be measured. By forming the strip conductor 11 relatively wide, it becomes possible to bring the entire surface of the magnetic body 1 to be measured into contact with the third length portion 11c of the strip conductor 11.

[0023] On the other hand, when the strip conductor 11 is designed to be relatively wide, it has been found that most of the high-frequency carrier signal (current) flowing through the strip conductor 11 flows through both end regions (left and right ends) of the strip conductor 11 in the width direction, and almost none flows through the central part between them.Therefore, in the present invention, a slit 17 is provided as a current imbalance suppression means so that the high-frequency carrier signal (current) flows almost uniformly throughout the entire width direction of the wide strip conductor 11.

[0024] The slits 17 are elongated gap regions extending along the length of the strip conductor 11 into the region of the third length portion 11c, and by providing the slits 17, the region of the third length portion 11c of the strip conductor 11 is divided from a single wide strip conductor portion into multiple elongated strip conductor portions 18 extending in parallel, allowing current to flow uniformly through each of the elongated strip conductor portions 18 divided by the slits 17. Preferably, multiple slits 17 are formed extending parallel to each other in the length direction.

[0025] Taking into account the skin effect of a conductor for high-frequency current, the width h of each narrow strip conductor portion 18 that allows a uniform current to flow through it is determined based on the skin depth, which represents the skin effect of the strip conductor 11 (the skin depth may be determined by an approximate calculation). The width s and number of slits 17 are determined based on the relationship between the width w of the third length portion 11c and the width h of the narrow strip conductor portion 18. By shortening the width s of the slits 17, forming a greater number of slits 17, and forming a greater number of narrow strip conductor portions 18 within the limits of manufacturing technology, the current distribution in the width direction of the third length portion 11c of the strip conductor 11 can be made more uniform.

[0026] The width s of the slit 17 and the width h of the narrow strip conductor portion 18 of the present invention are preferably about 0.1 μm to 100 μm, and more preferably 1 μm to 10 μm. The width of the slit 17 and the width of the narrow strip conductor portion 18 may be the same or may be different as described below. The narrower the slit width, the more uniform the current and excitation can be, even in the high frequency band. Known methods, such as sputtering and electrodeposition, can be used for fabrication.

[0027] 2 and 3, the slits 17 have the same width s and are spaced at equal intervals, and the narrow strip conductor portions 18 also have the same width h and are spaced at equal intervals. The width h of the narrow strip conductor portions 18 corresponds to the spacing between the slits 17, and the width s of the slits 17 corresponds to the spacing between the narrow strip conductors 18.

[0028] 4 is a diagram showing a magnetic field region excited in the magnetic body 1 to be measured by a wide strip conductor 11 provided with a slit 17 according to the first embodiment of the present invention. By forming the strip conductor 11 (the third length portion 11c with which the magnetic body 1 contacts) wide enough to correspond to the size of the magnetic body 1 to be measured and providing the above-mentioned slit 17, the bias of the current in the conductor width direction due to the skin effect is suppressed, and a uniform current flows throughout the entire strip conductor 11 (the third length portion 11c with which the magnetic body 1 contacts). As a result, the magnetic body 1 to be measured is not excited locally, but is excited as a whole. As a result, even if the magnetic body 1 to be measured has a large area, the influence of the demagnetizing field can be reduced, and the magnetic permeability of the magnetic body to be measured can be measured with high accuracy.

[0029] FIG. 5 is a schematic diagram showing a modified pattern of the strip conductor 11 in the probe. In the example shown in FIG. 5(a), the first length portion 11a and the second length portion 11b of the strip conductor 11 are narrower than the third length portion 11c, and the first length portion 11a and the second length portion 11b only need to have widths that allow connection to the connectors 15 and 16, respectively. The third length portion 11c tapers on both sides and narrows to the widths of the first length portion 11a and the second length portion 11b. FIG. 5(a) illustrates a pattern in which the width of the third length portion 11c tapers, but the third length portion 11c may also be tapered at a right angle or connected smoothly by a curve. Note that the third length portion 11c only needs to be wider than the first length portion 11a and the second length portion 11b, and may be circular overall.

[0030] The example shown in Figure 5(b) shows a pattern in which the spacing between the slits 17 is different from one another in the width direction. Specifically, the multiple slits 17 are arranged at different spacings so that the narrow strip conductor portions 18 are more sparsely spaced from both ends toward the center in the width direction. In this case, the width dimension h of the narrow strip conductor portions 18 increases from both ends toward the center. The width dimension s of each slit 17 is the same.

[0031] As described above, in a wide conductor, larger currents flow at both ends in the width direction and smaller currents near the center. Therefore, in order to allow larger currents to flow near the center according to the current distribution, the narrow strip conductor portion 18 is made thicker in the center compared to the both ends, and the width dimension h of the narrow strip conductor portion 18 is made thinner at both ends and wider in the center, thereby correcting the bias in the current distribution and achieving a more uniform current distribution.

[0032] Simulation analysis by the inventors of the present application revealed that the current distribution decreases exponentially from both ends of the wide conductor toward the center, specifically, according to 1 / e (natural logarithm). Therefore, it is preferable that the width h of the multiple elongated strip portions 18 separated by slits 17 is set so that it increases by, for example, the natural logarithm e from both ends toward the center. The multiplier value may be 2 to 3 times the natural logarithm e.

[0033] The example shown in Figure 5(c) shows a pattern in which the width dimension s of the slits 17 varies in the width direction. As in Figure 5(b), the width dimensions s of the multiple slits 17 are formed and arranged to be different from each other so that the narrow strip conductor portions 18 are more sparsely spaced from both ends toward the center in the width direction. In this case, the width dimension s of the slits 17 increases from both ends toward the center. The width dimension h of each narrow strip conductor portion 18 is the same.

[0034] In the pattern example of Figure 5(c), by arranging the elongated strip conductor portion 18 so that it is sparser in the central portion compared to both ends, the bias in the current distribution can be corrected and a more uniform current distribution can be achieved.

[0035] Alternatively, the slits 17 may have different widths s and different intervals between the slits 17 (corresponding to the width h of the narrow strip conductor portions 18).

[0036] Furthermore, the pattern of the slits 17 does not have to be limited to a rectangle as explained above. Any shape, such as a long, thin oval, is acceptable. Any shape is acceptable as long as it prevents large currents from being concentrated at both ends in the width direction of the conductor.

[0037] FIG. 6 illustrates a second exemplary configuration of a probe according to an embodiment of the present invention. Probe 10 in the second exemplary configuration differs from the probe in the first exemplary configuration in that transmission line 14 constitutes a coplanar waveguide and includes a band-shaped strip conductor 11 formed on the surface of dielectric substrate 13 and two ground conductors 12 spaced apart on either side of strip conductor 11 on the same surface. Probe 10 includes transmission line 14 constituting the coplanar waveguide and connectors 15 and 16 electrically connected to both ends of transmission line 14 in the longitudinal direction. The pattern of strip conductor 11 in transmission line 14 can be the same as the pattern shown in FIG. 3 or FIG. 5. Transmission line 14 is not limited to the microstrip line or coplanar line illustrated above, and may have other transmission line structures.

[0038] Next, an example of the configuration of a probe according to a second embodiment of the present invention will be described below. Fig. 7 is a diagram showing the pattern of a strip conductor constituting the probe according to the second embodiment of the present invention.

[0039] The difference from the probe 10 in the first embodiment is that the third length portion of the strip conductor 11 is made up of conductors made of multiple materials with different electrical resistance values ​​as a means for suppressing current bias, instead of or in addition to providing slits 17.

[0040] In this case, to prevent the current from being concentrated at both ends of the conductor in the width direction, the strip conductor 11 is formed of conductors 11-1 made of a material with high electrical resistance at both ends in the width direction, and conductor 11-2 made of a material with low electrical resistance in the center. The conductor may be made of two or more materials, and one of the materials may be the same as the material used for the first and second length portions. The example in Figure 7 is an example using three conductor materials, with conductor 11-3 made of a material with an intermediate electrical resistance between conductor 11-1 made of a material with high electrical resistance and conductor 11-2 made of a material with low electrical resistance.

[0041] Moreover, the strips of different materials may be in close contact with each other, or may be spaced apart by providing slits as in the first embodiment.

[0042] In this way, by using conductors made of multiple materials with different electrical resistance values, large currents are not concentrated at both ends of the wide part of the strip conductor, making it possible to measure accurately even samples with a large area.

[0043] Next, an example of the configuration of a probe according to the third embodiment of the present invention will be described below. Fig. 8 is a diagram showing the pattern of a strip conductor constituting the probe according to the third embodiment of the present invention.

[0044] The difference from the probe 10 in the first embodiment is that a conductor 11-4 having a higher conductivity than the strip conductor is laminated on the central part of the strip conductor in place of or in addition to the slit 17 as a means for suppressing current bias in the third length portion of the strip conductor 11.

[0045] As shown in Figure 8, when a highly conductive conductor 11-4 is layered on a strip conductor, it is preferable to form the top surface of the strip conductor so that it is flat after layering. (The original strip conductor is formed so that the center is thinner, or the center is removed after the strip conductor is formed.) This is because the magnetic material 1 to be measured is often flat, and in such cases, it is difficult to place the measurement object horizontally unless the top of the strip conductor is horizontal. However, depending on the sample to be measured, it may be simply layered on the strip conductor.

[0046] Since the conductor 11-4 having a higher conductivity than the strip conductor is provided in the center of the strip conductor, the current is not concentrated to both ends in the width direction of the conductor.

[0047] The conductor 11-4 with higher conductivity may be formed by stacking a plurality of conductors with higher conductivity toward the center.

[0048] Here, we have described an example in which conductor 11-4, which has a higher conductivity than strip conductor 11, is applied to the central part of strip conductor 11, but the same effect can be achieved by providing conductors with a lower conductivity than strip conductor 11 at both ends of the strip conductor 11 in the width direction.

[0049] The method for providing the highly conductive conductor 11-4 may be any known method, such as applying silver paste, forming it by sputtering, or depositing it by electrodeposition.

[0050] In this way, by providing conductors with different conductivities on the strip conductor, large currents are not concentrated at both ends of the width of the wide part of the strip conductor, making it possible to measure accurately even samples with a large area.

[0051] Next, an example of the configuration of a probe according to the fourth embodiment of the present invention will be described below: Fig. 9 is a diagram showing the pattern of a strip conductor constituting the probe according to the fourth embodiment of the present invention.

[0052] The difference from the probe 10 in the first embodiment is that in the third length portion of the strip conductor 11, a current bias suppression means is provided, instead of or in addition to the slits 17, by making the film thickness of the strip conductor thicker at the center and thinner toward both ends in the width direction. Fig. 9(a) shows an example of a configuration in which the film thickness of the strip conductor is made different without providing the slits 17, and Fig. 9(b) shows an example of a configuration in which the film thickness of the strip conductor is made different with the slits 17 provided.

[0053] 9(a) and 9(b), when the film thickness is increased, it is preferable to form grooves of different depths in the dielectric substrate 13 and embed the strip conductor in them so that the top surface of the strip conductor is flat. This is because the magnetic body 1 to be measured is often flat, and in such cases, it is difficult to place the measurement object horizontally unless the top of the strip conductor is horizontal. However, depending on the sample to be measured, the film thickness may be increased on the flat dielectric substrate 13.

[0054] The thickness of the strip conductor is thick in the center and becomes thinner toward both ends in the width direction, so that current flows more easily in the center part where the electrical resistance is low, and large currents do not tend to flow to both ends in the width direction of the conductor.

[0055] As shown in FIG. 9(b), it is more effective to combine a configuration in which the film thickness of the central portion of the strip conductor is thicker than that of both ends with a configuration in which slits 17 are provided.

[0056] In this way, by providing conductors with different conductivities on the strip conductor, large currents are not concentrated at both ends of the width of the wide part of the strip conductor, making it possible to measure accurately even samples with a large area.

[0057] Next, an example of the configuration of a probe according to the fifth embodiment of the present invention will be described below. Fig. 10 is a diagram showing the pattern of a strip conductor constituting the probe according to the fifth embodiment of the present invention.

[0058] The difference from the probe 10 in the first embodiment is that the third length portion of the strip conductor 11 is doped with a substance 11-5 that improves the conductivity of the central portion of the strip conductor 11 as a means for suppressing current imbalance, so that the conductivity of the central portion of the strip conductor 11 is high.

[0059] Since the central portion of the strip conductor 11 has high conductivity, current flows more easily through the central portion where electrical resistance is low, and large currents do not tend to flow to both ends in the width direction of the conductor.

[0060] The same effect can be obtained by doping the conductor near both ends in the width direction with a substance 11-5 that reduces the conductivity, thereby increasing the electrical resistance at both ends in the width direction.

[0061] In this way, by performing various dopings on the strip conductor, large currents are not concentrated at both ends of the wide part of the strip conductor in the width direction, making it possible to measure accurately even samples with a large area.

[0062] The embodiment of the present invention is not limited to the above, and any configuration is possible as long as a large amount of current flows in the central portion.

[0063] The measurement procedure using the magnetic permeability measurement device equipped with the probe 10 of the present invention will be described below.

[0064] 11 is a flowchart showing the steps of a magnetic permeability measurement method according to an embodiment of the present invention. The transmission line member 14 of the probe 10 is brought into contact with the magnetic body 1 to be measured (S100). Then, the probe 10 is placed in the pole gap of a double-yoke electromagnet 40, a strong DC magnetic field (for example, about 20 kOe) is applied, the magnetic body 1 is saturated, and calibration is performed with the network analyzer 20 (S102). This eliminates the electrical length of the probe 10 and the coaxial cable 3, the DC impedance of the magnetic body, non-magnetic signals, etc. Then, the DC magnetic field is removed, and the permeability coefficient S 21 (S104) The transmission coefficient S is calculated using the following equation (2).21 is converted into the impedance Z of the magnetic body 1 (S106).

[0065]

number

[0066] Specifically, the permeability coefficient S 21 is measured by the network analyzer 20. The probe 10 is brought into contact with the magnetic body 1, and the magnetic body 1 is saturated by an electromagnet, which is the background, and the transmission coefficient at this time is used as the reference signal. Next, the transmission coefficient is measured when the magnetic field of the electromagnet is removed. The transmission coefficient at this time is a differential signal from the reference signal, i.e., the difference between the transmission coefficients with and without the magnetic field, which reflects the magnetic properties of the magnetic body 1. This difference in the transmission coefficients is the impedance component contributed by the magnetic body 1.

[0067] According to equation (2), impedance Z is the difference value of the permeability coefficient, and its real part is the loss (resistance component) R of the magnetic body 1, and its imaginary part is the inductance component L of the magnetic body 1. The inductance component L corresponds to the real part μ' of the permeability of the magnetic body 1, and the resistance component R corresponds to the imaginary part μ'' of the permeability of the magnetic body 1. The permeability (complex permeability) μ of the magnetic body 1 is expressed by the following equation (3). Note that equation (3) is the same as equation (1) in the background art section above.

[0068]

number

[0069] 12 is a diagram schematically showing the shape of a magnetic thin film as a magnetic body to be measured. As the frequency of a current flowing through a strip conductor 11 increases, the current flows only on the surface of the magnetic body (magnetic thin film) 1 due to the skin effect. Assuming that the impedance Z is determined by the current being biased in the film thickness direction due to the skin effect as shown in FIG. 12, as a numerical analysis process, for example, using the above equation (3) and the following equations (4) and (5), μ′ and μ″ are obtained by repeated calculations using the Newton-Raphson method, and the complex permeability is obtained by optimization process so as to minimize a predetermined evaluation function value (S108).

[0070]

number

[0071]

number

[0072] where Z is impedance, ρ is resistivity, l is sample length, w is sample width, t is film thickness, f is frequency, and μ is complex permeability.

[0073] FIG. 13 is a graph showing the results of measuring magnetic permeability using a magnetic permeability measurement device using a probe according to an embodiment of the present invention. The sample being measured was a NiZn ferrite thin film (3 mm × 1 mm × 100 μm thick), and the results were compared with the values ​​measured using the NRW method, a standard magnetic permeability measurement method that is not affected by demagnetizing fields. The transmission line 14 provided with the slit 17 was the microstrip line shown in FIG. 2. The magnetic permeability measured using the probe according to the embodiment of the present invention roughly corresponded to the values ​​measured using the NRW method, demonstrating that the effects of demagnetizing fields could be suppressed and that both the real part μ' and the imaginary part μ'' of complex magnetic permeability (μ = μ' - jμ'') could be measured with high accuracy over the entire frequency range up to the high frequency band.

[0074] Figure 14 shows a modified example of the strip conductor 11 constituting the probe in the first embodiment of the present invention. Figure 14(a) shows the pattern of the strip conductor 11 similar to that of Figure 5(a), and Figure 14(b) is an enlarged view of the area A enclosed by the dotted line in Figure 14(a). The strip conductor 11 shown in Figure 14 has a third length portion 11c that is wider in the width direction than the first length portion 11a and the second length portion 11b, and a plurality of slits 17 are provided in parallel across the width direction of the third length portion 11c. Preferably, the lengths of the plurality of slits 17 in the length direction are the same. The third length portion 11c is formed with a tapered shape such that its widthwise extending edge (widthwise edge) 11e becomes thinner toward both widthwise ends, and thus the distance d extending in the lengthwise direction from the lengthwise end 17e of each slit to the widthwise edge 11e of the third length portion 11c is designed to become shorter from the center toward both widthwise ends.

[0075] 14(b), for the first slit 17-1 located relatively closer to both ends in the width direction and the second slit 17-2 located closer to the center in the width direction than the first slit 17-1, the first distance d1 extending in the length direction from the longitudinal end 17-1e of the first slit 17-1 to the widthwise edge 11e of the third length portion 11c is designed to be shorter than the second distance d2 extending in the length direction from the longitudinal end 17-2e of the second slit 17-2 to the widthwise edge 11e of the third length portion 11c. By making the distance d smaller toward both ends in the width direction of the strip conductor 11, the path of the current flowing through the strip conductor 11 becomes narrower toward both ends, thereby increasing the electrical resistance at both ends, suppressing bias in the current flowing toward both ends, and enabling a more uniform current to flow throughout the strip conductor 11. The shorter the length of the narrowest distance d (first distance d1), the better. However, due to constraints on the manufacturing precision of design and microfabrication technology, it is preferable to set the length to, for example, about 2 to 10 μm.

[0076] Figure 15 shows another modified example of the strip conductor 11 constituting the probe in the first embodiment of the present invention. Figure 15(a) shows the pattern of the strip conductor 11, and Figure 15(b) is an enlarged view of the area B enclosed by the dotted line in Figure 15(a). The strip conductor 11 shown in Figure 15 has a third length portion 11c that is wider in the width direction than the first length portion 11a and the second length portion 11b, and a plurality of slits 17 are provided in parallel across the width direction in the third length portion 11c. The lengths of the plurality of slits 17 in the length direction are different, and are designed to be longer at both ends in the width direction.

[0077] The third length portion 11c has widthwise edge portions 11e that rise at right angles from the strip-shaped first length portion 11a and second length portion 11b toward both widthwise ends, giving the third length portion 11c a rectangular shape as a whole. As a result, since the lengths of the multiple slits 17 are different, the interval d extending in the lengthwise direction from the lengthwise end portion 17e of each slit to the widthwise edge portion 11e of the third length portion 11c becomes shorter from the center toward both widthwise ends, and the conductor width becomes narrower toward the ends, thereby suppressing the skin effect at the ends.

[0078] 14(b), the first slit 17-1 located at both ends in the width direction and the second slit 17-2 located closer to the center in the width direction than the first slit 17-1 are designed such that the first distance d1 extending in the length direction from the longitudinal end 17-1e of the first slit 17-1 to the widthwise edge 11e of the third length portion 11c is shorter than the second distance d2 extending in the length direction from the longitudinal end 17-2e of the second slit 17-2 to the widthwise edge 11e of the third length portion 11c. By reducing the distance d toward both ends in the width direction of the strip conductor 11, the path of the current flowing through the strip conductor 11 becomes narrower toward both ends, thereby increasing the electrical resistance at both ends, suppressing bias in the current flowing toward both ends, and enabling a more uniform current to flow throughout the strip conductor 11. In the example shown in Figure 15, the position and width of the slits may be adjusted so that the conductor width (the width between the slits and the outermost conductor width) becomes narrower from the central portion toward both ends, in order to make it difficult for current to flow to both ends.

[0079] 14 and 15 may be combined with the structure shown in Fig. 5(b) in which the spacing between the slits 17 is different between the center and both ends, or the structure shown in Fig. 5(c) in which the width dimension s of the slits 17 is different between the center and both ends in the width direction. Furthermore, the structure shown in Figs. 9(a) and 9(b) in which the film thickness is made thicker at the center and both ends, or the structure shown in Fig. 10 in which the conductivity is made different between the center and both ends, may be combined with the structure shown in Figs. 14 and 15 to enhance the effect.

[0080] Fig. 16 shows the measurement results of the current density flowing through the strip conductor 11, and Fig. 16(d) shows the current density at each position in the width direction for the three shape patterns of the third length portion 11c (upper half shape only) of the strip conductor 11 shown in Fig. 16(a), (b), and (c). The three shape patterns shown in Fig. 16(a), (b), and (c) have in common that the length of the third length portion 11c is 1.2 mm, the length of the slit 17 is 1 mm, and the width direction length (upper half only) is 2 mm. Fig. 16(a) is a pattern in which no tapered portion is provided at the width direction edge 11e, Fig. 16(b) is a pattern in which a tapered portion is formed from a position 1.6 mm into the rise of the width direction edge 11e, and Fig. 16(c) is a pattern in which a tapered portion is formed from a position 0.8 mm into the rise. As shown in the graph in Figure 16(d), the longer the tapered portion is provided, i.e., the shorter the distance d becomes from the center in the width direction toward both ends, the smaller the current density at the ends becomes, which makes it clear that this is an effective means of suppressing current bias (concentration) at the ends in the width direction and making the current density more uniform.

[0081] The present invention is not limited to the above-described embodiments, and it goes without saying that the present invention also includes design changes within the scope of the gist, including various modifications and alterations that would be conceivable to a person with ordinary knowledge in the field of the present invention. [Explanation of symbols]

[0082] 1: magnetic material, 3: coaxial cable, 10: probe, 11: strip conductor, 12: ground conductor, 13: dielectric substrate, 14: transmission line body, 15: connector, 16: connector, 17: slit (current bias suppression means), 18: thin strip conductor portion, 20: network analyzer (signal measuring instrument), 30: arithmetic processing unit, 40: double yoke electromagnet

Claims

1. A probe for measuring the magnetic permeability of a magnetic material, a transmission line having a strip conductor formed on a surface of a dielectric substrate and a ground conductor formed on the surface or rear surface of the dielectric substrate; a first connector connected to one end of each of the strip conductor and the ground conductor; a second connector connected to the other end of each of the strip conductor and the ground conductor, The strip conductor is composed of a first length portion including a portion that connects to the first connector at one end, a second length portion including a portion that connects to the second connector at the other end, and a third length portion that extends between the first length portion and the second length portion, and the third length portion has a current bias suppression means.

2. 2. The probe according to claim 1, wherein the transmission line element is a microstrip line or a coplanar line.

3. 2. The probe according to claim 1, wherein the current bias suppressing means comprises at least one slit extending in the longitudinal direction of the strip conductor.

4. 4. The probe according to claim 3, wherein the slit comprises a plurality of slits extending parallel to one another in the longitudinal direction of the strip conductor.

5. The probe according to claim 4 , wherein the plurality of slits are arranged at equal intervals in the width direction.

6. The probe according to claim 4 , wherein the plurality of slits are arranged at different intervals in the width direction.

7. The probe according to claim 6, wherein the plurality of slits are arranged such that the intervals between the slits become wider from both ends toward the center in the width direction.

8. 8. The probe according to claim 7, wherein the strip conductor is formed so that the thickness of the central portion is greater than that of both ends in the width direction.

9. 5. The probe according to claim 4, wherein the plurality of slits are formed to have the same width dimension.

10. The probe according to claim 4 , wherein the plurality of slits are formed to have different widths.

11. The probe according to claim 10, wherein the plurality of slits are formed and arranged such that the width dimension increases from both ends toward the center in the width direction.

12. the third length portion is wider in a width direction than the first length portion and the second length portion; the plurality of slits include first slits located relatively closer to both ends in the width direction and second slits located closer to the center in the width direction than the first slits, 5. The probe of claim 4, wherein a first distance extending longitudinally from a longitudinal end of the first slit to a widthwise edge of the third length portion is shorter than a second distance extending longitudinally from a longitudinal end of the second slit to a widthwise edge of the third length portion.

13. the first slit and the second slit have the same length; 13. The probe according to claim 12, wherein widthwise edges of the third length portion are tapered, and the length dimension of the third length portion becomes shorter from the center side toward both ends in the width direction.

14. The length dimension of the third length portion is the same from the center side to both end sides in the width direction, The probe according to claim 12, wherein the first slit has a length dimension longer than that of the second slit.

15. 2. The probe according to claim 1, wherein the current bias suppression means is configured so that electrical resistance decreases from the end toward the inside in a width direction perpendicular to the longitudinal direction of the strip conductor of the third length portion.

16. 16. The probe according to claim 15, wherein the current bias suppressing means comprises the strip conductor made of a plurality of materials having different electrical resistances.

17. 16. The probe according to claim 15, wherein the current bias suppression means comprises a material provided on the strip conductor with a conductivity different from that of the strip conductor.

18. 16. The probe according to claim 15, wherein the current bias suppressing means is configured such that the inner film thickness of the strip conductor is greater than the end film thickness.

19. 16. The probe according to claim 15, wherein the current bias suppressing means is formed by doping the strip conductor with a substance that changes the conductivity.

20. a probe according to any one of claims 1 to 19, and a magnetic field applying unit for applying a magnetic field to the magnetic body; a signal measuring device connected to the probe via a cable and configured to measure a signal of a transmission coefficient both with and without application of a magnetic field by the magnetic field applying unit; and processing means for determining the magnetic permeability of the magnetic body by numerical analysis calculation processing based on the signal of the permeability coefficient measured by the signal measuring instrument.

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