JPH0419584A - Instrument and method for magnetic permeability measurement - Google Patents

Abstract

PURPOSE:To reduce the measurement error of high frequency by inserting a coil for gain measurement into a measuring circuit and correcting a value of magnetic permeability with a measured transfer function. CONSTITUTION:Only when a signal source changeover switch 8 is placed on the side of the coil 7 for gain measurement and a sample to be measured is inserted into a magnetic flux detection coil 2, a detection coil changeover switch 4 is switched between a magnetic field detection coil 3 and the coil 2 to supply a signal to an input terminal 9. The ratio of outputs of an output terminal 10 in those cases is found. Then the ratio of outputs is fond similarly without inserting the sample to be measured into the coil 2. Further, the switch 8 is switched to the side of a coil 1 for AC magnetic field generation and the ratio of outputs when the sample to the measured is inserted into the coil 2 and not inserted is found similarly. Those four ratios are substituted in a specific equation to find corrected magnetic permeability, thereby reducing the measurement error.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an apparatus and method for measuring the magnetic permeability of magnetic materials, and particularly to a high-frequency magnetic permeability measuring apparatus and measuring method using a magnetic flux detection coil and a magnetic field detection coil. Regarding.

[Summary of the Invention 1 This invention provides a high-frequency This makes it possible to reduce measurement errors in the measurement.

[Prior Art 1] First, the principle of measuring magnetic permeability using a magnetic permeability measuring device using a magnetic flux detection coil and a magnetic field detection coil will be described.

Figure 2 is a principle diagram for measuring magnetic permeability, which is a well-known measurement method.The magnetic flux detection coil 11 is composed of two coils IIA and IIB with equal cross-sectional areas. IIB is connected in such a way that electromotive forces having opposite phases are generated at the input end of a voltage detection amplifier (not shown) by an external magnetic field 12 generated by a drive coil (not shown) for generating an alternating magnetic field.Therefore, the measurement sample 13 Even if current is applied to the drive coil when there is no current, the 8 signals of the magnetic flux detection coil 11 detected by the detection amplifier are O. Therefore, the measurement sample 13 is inserted into only one of these two coils 11A and 11B. Then, the signal voltage VB generated in the magnetic flux detection coil 11 at this time is
Assuming that the magnetic field within l is H1, its angular frequency is ω, the cross-sectional area across the magnetic flux detection coil surface of the measurement sample 13 is SB, and the magnetic permeability of the sample is μ, VB=μ・SB・ω・Hi (1) is given by However, it is assumed that the magnetic field within the sample 13 and the magnetic field within the magnetic flux detection coil II are equal.

Next, of the two coils of the magnetic flux detection coil 11, the magnetic field detection coil 14 is placed near the coil 11B on the side into which the sample is not inserted. When inserted into the magnetic field detection coil 14, the magnetic field in the magnetic field detection coil 14 becomes equal to Hi.Therefore, the signal voltage VH generated in the magnetic field detection coil 14 is as follows, where SH is the cross-sectional area of the magnetic field detection coil 14.VH=SH・ω・Hi (2). Therefore, by measuring VB and VH, (
1), (μ from formula 21: (SH/SB)・(VB/VH)
(3) and μ can be calculated.

Note that in an actual measurement device, if a current is applied to the drive coil when no measurement sample is inserted, it is difficult to make the cross-sectional areas of the two coils that make up the magnetic flux detection coil 11 completely equal; The voltage applied is not O. If the voltage generated in the magnetic flux detection coil when no measurement sample is inserted is vao, and the voltage generated by the field pressure detection coil is VHO, then the magnetic permeability μ is u = (St(/SB) - (VB/VH-VBO) /
VHO) (4) is calculated. The above is the measurement principle.

Next, a conventional measurement method will be described.

Conventionally, the output of a detector amplifier (denoted as VBA) that measures the output of the magnetic flux detection coil is used for VB in equation (1), and the output of the magnetic field detection coil is used for VH in equation (2). The magnetic permeability was calculated by substituting the output (Vl (denoted as A)) of the detection amplifier into equation (3) or (4).

[Problem to be solved by the invention l The conventional method described above has no problem at low frequencies, but at high frequencies (VB and VBA, VH and VHA, etc. are no longer equal, and this becomes a problem. This is because the inductance of the detection coil and the detection Due to the stray capacitance at the input end of the amplifier,
This is because the transfer functions between VB and VBA and between VH and VHA have frequency characteristics. That is, the transfer functions are GB and GH, respectively, the output of the detection amplifier that measures the output of the magnetic flux detection coil when no sample is inserted is VBOA, and the output of the voltage detection amplifier that measures the output of the magnetic field detection coil is VH.
Assuming that OA and their respective transfer functions are GBO and GHQ, VBA = GB・VB (5
)Vl(A = GH-VH(6) VBOA = GBflVBO(7) VHOA = GHQ・VHO(8) There is a relationship as follows, and the true magnetic permeability μ is expressed by formulas (4) to (8)%
Formula %) must be calculated. If this transfer function is ignored, that is, if it is assumed that the frequency characteristics are constant, the frequency characteristics related to the transfer will be included in the magnetic permeability calculation result. That is, at high frequencies, measurement errors occur by the amount of frequency characteristics related to transmission. Furthermore, since the transfer relationship GB in equation (9) is related to the inductance of the magnetic flux detection coil when the sample is inserted, it changes depending on the magnetic permeability of the measurement sample. Therefore, the measurement error also changes depending on the magnetic permeability.

In the prior art, either the transfer relationship is ignored or, as shown in FIG. I was trying to keep the transfer function as constant as possible. However, in the method described above, the frequency characteristics of the transfer function are included in the magnetic permeability calculation result, and in the method described later, the output signal level at the detection amplifier is lowered by inserting a resistor, which reduces the noise of the detection amplifier. The S/N ratio is poor (as a result, the measurement accuracy becomes poor).

An object of the present invention is to reduce measurement errors caused by the frequency characteristics of the transfer function without worsening the S/N ratio.

[Means for Solving the Problems 1] In order to achieve such an object, the measuring device of the present invention includes an alternating current signal source, an alternating current magnetic field generating coil for applying an alternating magnetic field to a measurement sample, and an alternating current magnetic field generating coil for applying an alternating magnetic field to a measurement sample. a magnetic flux detection coil and a magnetic field detection coil that respectively detect the magnetic flux and magnetic field caused by the magnetic flux detection coil and the magnetic field detection coil; an amplifier that amplifies the detection output of the magnetic flux detection coil and the magnetic field detection coil; and a transmission from the magnetic flux detection coil and the magnetic field detection coil to the amplifier. a gain measuring coil wound in a toroidal high permeability material for measuring the function; and a first switch for switching and connecting a signal from the alternating current signal source to the alternating current magnetic field generating coil and the gain measuring coil. a second switch for switchingly connecting the magnetic flux detection coil and the magnetic field detection coil to the amplifier, one of the two wires connecting the second switch and the amplifier to the toroidal shape. It is characterized by being wired through a hollow part of a high magnetic permeability material.

The measurement method of the present invention includes a magnetic flux detection coil that detects the magnetic flux and magnetic field from an AC magnetic field generating coil for applying an AC magnetic field to a measurement sample, a magnetic field detection coil, and an amplifier that amplifies the detection outputs of the two detection coils. The present invention is characterized in that the magnetic permeability of the measurement sample determined from the output of the amplifier is corrected by the transfer function.

[Function j] According to the present invention, the transfer function can be measured with a simple operation by using a simple configuration in which a gain measurement coil is inserted into the measurement circuit, and the measurement can be performed by correcting the magnetic permeability value. Error can be reduced.

[Example 1] Examples of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, which is a circuit diagram showing the signal detection section of the magnetic permeability measuring device according to the present invention, the embodiment of the present invention has an AC magnetic field generation coil 1, a magnetic flux detection coil 2, a magnetic field detection coil 3, , a detection coil changeover switch 4, a detection amplifier 5, a toroidal ferrite 6, a gain measurement coil 7 wound around the ferrite 6 a plurality of times, and a signal power changeover switch 8. An AC signal source (not shown) is connected to the input terminal 9. In addition, in FIG. 1, for convenience, the magnetic flux detection coil 2 and the magnetic field detection coil 3 are shown in a different arrangement from the actual arrangement.

Next, the measurement procedure according to the present invention will be explained with reference to FIG.

First, the ratio GB/GH of the transfer function in equation (9), and G
The method for measuring BO/GHQ will be explained.

Insert the measurement sample into the magnetic flux detection coil 2, turn the signal source changeover switch 8 to the gain measurement coil 7 side, turn the detection coil changeover switch 4 to the magnetic field detection coil 3 side, send a signal to the input terminal 9, and perform detection. The output of the output terminal 10 of the amplifier 5 is measured, and this is defined as ①old. Next, turn the detection coil changeover switch 4 to the magnetic flux detection coil 2 side, do the other things the same as when measuring the old case, measure the output of the 8 terminals 10, and set this as VBl. Let VBI/VH1 be the ratio GB/GH of the transfer function. In addition, similar measurements were made without inserting the measurement sample into the magnetic flux detection coil 2, and the detection amplifier 5
The ratio of the output of the output terminal 10 when connected to the magnetic flux detection coil 2 and when connected to the magnetic field detection coil 3 is GBO/G
HQ.

Next, VBA/VHA and VBOA/VHO in equation (9)
The method for measuring A will be explained.

Insert the measurement sample into the magnetic flux detection coil 2, turn the signal source changeover switch 8 to the AC magnetic field generation coil 1 side, turn the detection coil changeover switch 4 to the magnetic field detection coil 3 side,
A signal is applied to the input terminal 9, the output of the output terminal 1O is measured, and this is set as VH. Next, set the detection coil changeover switch 4 to the magnetic flux detection coil 2, and otherwise do the same as when measuring VH, measure the output of the output terminal 10, and set this as VB. Let VB/VH be VBA/VHA. In addition, the same measurement was performed without inserting the measurement sample into the magnetic flux detection coil 2, and the output terminal 10 when the detection amplifier 5 was connected to the magnetic flux detection coil 2 and when it was connected to the magnetic field detection coil 3.
Let the ratio of the output of VBOA/VHOA be VBOA/VHOA.

GB/GH, GBO/GHD obtained in this way,
Substitute VBA/VHA and VBOA/VHOA into equation (9) to find the magnetic permeability.

Next, the reason why the ratio of transfer functions can be measured by measuring VHI and VBI will be explained using the equivalent circuit shown in FIG.

When the number of turns of the gain detection coil 7 is n, the gain detection coil 7 and the wiring passing through the hollow part of the toroidal ferrite 6 form an n:1 transformer. If the transformer is ideal, when the input signal ei is passed through the gain detection coil 7, an electromotive force ei/n will be generated in the wiring passing through the core, and the impedance 21 will be connected from the gain detection coil 7 to the signal generator side. If the impedance seen is Zs, then Zt=Zs
/n2. Therefore, 21 is sufficiently small compared to the impedance of the detection coil (ZC) and the impedance of the detection amplifier (ZA).
If n is designed as shown in ZA), it can be assumed that a voltage source with an internal impedance of approximately O is generated within the wiring. The transformer that can actually be created is not ideal, and the electromotive force generated in the wiring is also a key factor. Here, k is determined by the characteristics of the coil itself, such as the winding method and the magnetic permeability of the toroidal material 6, in addition to the number of turns n of the coil 7, and has frequency characteristics caused by these characteristics.

However, if n is designed as described above, the impedance can be regarded as approximately 0, and k can be regarded as a coefficient unrelated to the impedance of the detection coil or detection amplifier. From the viewpoint of measurement accuracy, the number of turns n is preferably 10 or more.

The voltage eo at the detection amplifier is eo=zA/(zC+zA)·k·ei (10). On the other hand, the transfer function G from the detection coil to the detection amplifier is G = ZA/(ZC+ZA) (1
1), the impedance of the magnetic flux detection coil is Z
B. If the impedance of the magnetic field detection coil is ZH, then GB=ZA/(ZB+ZA)
(12) GH=ZA/(ZH+ZA)
(13). According to the above measurement procedure, VBCZA/(ZB+ZA) ・k−ei
(14) VHCZA/ (ZH+ZA) ・k
-ei (15) holds true. From (12) to (15), VBI/VH1=GB/G)
l (16), ■Old and VB
By measuring I, the ratio of the transfer functions can be measured.

The magnetic permeability measurement results according to the present invention will be explained in comparison with the results according to the conventional method.

FIG. 5 shows a measurement of the magnetic permeability of a thin film with a thickness of 0.2 μm using a conventional technique in which the magnetic permeability is calculated without considering the transfer function. The horizontal axis is the frequency from 500kHz to 120MHz
It is displayed on a logarithmic scale. The vertical axis represents magnetic permeability, which is expressed on a logarithmic scale from 10 to 5000. The solid line represents the effective and reactive components of magnetic permeability, and the dotted line represents the absolute value.

FIG. 6 shows the same thin film used in the measurement using the conventional method shown in FIG. 5, but measured using the method according to the present invention.

Comparing Figures 5 and 6, there is almost no difference up to about 50 MHz, but at frequencies above that, the absolute value of magnetic permeability increases in Figure 5, while it decreases in Figure 6. I can see it going. It is thought that the conventional method shown in FIG. 5 produced such a measurement result because the transfer function was not considered. On the other hand, the measurement according to the method of the present invention does not give the same results as the conventional technique, and it can be said that a result with less measurement error than the conventional technique is obtained.

[Advantageous Effects of the Invention 1] As explained above, in the present invention, since magnetic permeability is measured in consideration of a transfer function, magnetic permeability can be evaluated more accurately than in the prior art.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of a magnetic permeability measuring device according to the present invention. Fig. 2 is a diagram showing the principle of measuring magnetic permeability, Fig. 3 is a diagram showing an example of the configuration of a magnetic permeability measuring device according to the prior art, Fig. 4 is a diagram showing a part of the equivalent circuit of the measuring device, and Fig. 5 is a diagram showing a part of the equivalent circuit of the measuring device. FIG. 6 is a diagram showing an example of magnetic permeability measurement results according to the prior art, and FIG. 6 is a diagram showing an example of magnetic permeability measurement results according to the present invention. DESCRIPTION OF SYMBOLS 1... AC magnetic field generation coil, 2... Magnetic flux detection coil, 3... Magnetic field detection coil, 4... Detection coil changeover switch, 5... Detection amplifier, 6... Toroidal high transparency Magnetic material, 7... Gain measurement coil, 8... Signal source changeover switch, 9... Input terminal, 10... Output terminal, 11... Magnetic flux detection coil, 12... External magnetic field, 13 ... Measurement sample, 14... Magnetic field detection coil, 15... Changeover switch, 16... Detection amplifier, F... Resistor. Figure 2 shows the magnetic permeability of 0.

Claims (1)

[Claims] 1) An AC signal source, an AC magnetic field generation coil for applying an AC magnetic field to a measurement sample, and a magnetic flux detection coil and magnetic field detection that respectively detect the magnetic flux and magnetic field generated by the AC magnetic field generation coil. a coil, an amplifier for amplifying the detection output of the magnetic flux detection coil and the magnetic field detection coil, and a toroidal-shaped high permeability material for measuring a transfer function from the magnetic flux detection coil and the magnetic field detection coil to the amplifier. a first switch that switches and connects a signal from the AC signal source to the AC magnetic field generation coil and the gain measurement coil, and connects the magnetic flux detection coil and the magnetic field detection coil to the amplifier; and a second switch for switching connection, and one of the two wires connecting the second switch and the amplifier is routed through a hollow part of the toroidal high magnetic permeability material. Characteristic magnetic permeability measuring device. 2) When the number of turns of the gain detection coil is n, and the impedances of the AC signal generation source, magnetic flux detection coil, and magnetic field detection coil are Z1, ZB, and ZH, respectively, n^2
The magnetic permeability measuring device according to claim 1, characterized in that >Z1/ZH and n^2>Z1/ZB. 3) The magnetic permeability measuring device according to claim 1, wherein the number of turns of the gain detection coil is 10 or more. 4) A magnetic flux detection coil that detects the magnetic flux and magnetic field from the alternating current magnetic field generating coil for applying an alternating magnetic field to the measurement sample, respectively, and transmission between the magnetic field detection coil and an amplifier that amplifies the detection outputs of the two detection coils. A method for measuring magnetic permeability, comprising: measuring a function, and correcting the magnetic permeability of the measurement sample determined from the output of the amplifier using the transfer function.