JPH0727016B2 - Permeability measuring device and measuring method - Google Patents

Description

The present invention relates to an apparatus and method for measuring magnetic permeability of a magnetic material, and more particularly to an apparatus and method for measuring high frequency magnetic permeability using a magnetic flux detection coil and a magnetic field detection coil. Regarding

[Summary of the Invention] In the present invention, when a frequency characteristic of magnetic permeability is measured by using two coils, a magnetic flux detection coil and a magnetic field detection coil, a transfer function from the coil to the detection amplifier is measured to obtain a high frequency. It is intended to reduce the measurement error in.

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

FIG. 2 is a principle diagram for measuring magnetic permeability, which is a well-known measuring method. Magnetic flux detection coil 11 has the same cross-sectional area 2
It consists of two coils 11A and 11B.
1B is connected so that electromotive forces of opposite phases are generated at the input end of a detection amplifier (not shown) by an external magnetic field 12 generated by a drive coil (not shown) for generating an AC magnetic field. Therefore, even if a current is passed through the drive coil when there is no measurement sample 13, the signal output of the magnetic flux detection coil 11 detected by the detection amplifier is 0. So these two coils
When the measurement sample 13 is inserted into only one of 11A and 11B, the signal voltage VB generated in the magnetic flux detection coil 11 at this time is that the magnetic field in the magnetic flux detection coil 11 is Hi, its angular frequency is ω, and the measurement sample 13 Let SB be the cross-sectional area that crosses the magnetic flux detection coil surface of and the permeability of the sample be μ, which is given by VB = μ ・ SB ・ ω ・ Hi (1). However, it is assumed that the magnetic field in the sample 13 and the magnetic field in the magnetic flux detection coil 11 are equal.

Next, the magnetic field detection coil 14 is arranged in the vicinity of the coil 11B on the side where the sample is not inserted among the two coils of the magnetic flux detection coil 11. By arranging in this way, the measurement sample 13
Magnetic field detection coil 1 when is inserted into the magnetic flux detection coil 11A
The magnetic field in 4 is equal to Hi. Therefore, the magnetic field detection coil 14
The signal voltage VH generated at
If it is SH, it is given by VH = SH ・ ω ・ Hi (2). Therefore, by measuring VB, VH,
From formulas (1) and (2), μ = (SH / SB) · (VB / VH) (3) and μ can be calculated.

In an actual measurement device, if a current is passed through the drive coil when the measurement sample is not inserted, it is difficult to make the cross-sectional areas of the two coils forming the magnetic flux detection coil 11 completely equal. The applied voltage is not zero. When the voltage generated in the magnetic flux detection coil when the measurement sample is not inserted is VB0 and the voltage generated in the magnetic flux detection coil is VH0, the permeability μ is μ = (SH / SB) ・ (VB / VH-VB0 / VH0) (4) is calculated. The above is the measurement principle.

Next, a conventional measuring method will be described.

Conventionally, the output of the detection amplifier that measures the output of the magnetic flux detection coil (referred to as VBA) is used for VB of equation (1), and the output of the magnetic field detection coil is measured for VH of equation (2). Using the output of the detection amplifier (denoted as VHA), these values were substituted into the equation (3) or (4) to calculate the magnetic permeability.

[Problems to be Solved by the Invention] In the above-mentioned conventional method, there is no problem at low frequencies, but if the frequency becomes higher, VB and VBA, VH and VHA, etc. become unequal, which is a problem. This is because the transfer functions between VB and VBA and between VH and VHA have frequency characteristics due to the inductance of the detection coil and the stray capacitance at the input end of the detection amplifier. That is, the transfer functions are respectively GB and GH, the output of the detection amplifier that measures the output of the magnetic flux detection coil when the sample is not inserted is VB0A, the output of the detection amplifier that measures the output of the magnetic field detection coil is VH0A, and the transfer function of each Let GB0 and GH0 be VBA = GB ・ VB (5) VHA = GH ・ VH (6) VB0A = GB0 ・ VB0 (7) VH0A = GH0 ・ VH0 (8), and the true permeability μ is From formulas (4) to (8), μ = (SH / SB) {(VBA / VHA) (GH / GB)-(VB0A / VH0A) (GH0 / GB0)} (9) must be calculated. If this transfer function is ignored, that is, if it is assumed that the frequency characteristic is constant, the frequency characteristic of the transfer relationship is included in the calculation result of the magnetic permeability. That is, at a high frequency, a measurement error occurs due to the frequency characteristics related to transmission. Also, the transmission relation in equation (9)
Since GB 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 measured sample. Therefore, the measurement error also changes depending on the magnetic permeability.

In the prior art, the transfer relationship is ignored, or as shown in FIG. 3, in order to reduce this measurement error, a resistor is connected in series with the detection coil between the changeover switch 15 and the detection amplifier 16.
I tried to make the transfer function as constant as possible by inserting 17. However, in the method described above, the frequency characteristic of the transfer function is included in the calculation result of the magnetic permeability, and in the method described later, the output signal level in the detection amplifier is lowered by inserting the resistor, and the noise of the detection amplifier is reduced. S / N becomes worse. Therefore, the measurement accuracy becomes poor.

An object of the present invention is to reduce the measurement error caused by the frequency characteristic of the transfer function without deteriorating the S / N.

[Means for Solving the Problems] In order to achieve such an object, the measuring apparatus of the present invention includes an AC signal source, an AC magnetic field generation coil for applying an AC magnetic field to a measurement sample, and the AC magnetic field generation. Flux detection coil and magnetic field detection coil for respectively detecting the magnetic flux and magnetic field by the coil for use, amplifier for amplifying the detection output of the magnetic flux detection coil and magnetic field detection coil, and transmission from the magnetic flux detection coil and magnetic field detection coil to the amplifier A gain measuring coil wound around a toroidal high magnetic permeability material for measuring a function, and a first switch for switching and connecting a signal from the AC signal source to the AC magnetic field generating coil and the gain measuring coil. And a second switching device for switching and connecting the magnetic flux detecting coil and the magnetic field detecting coil to the amplifier. One of two wires connecting the switch and the amplifier is wired through the hollow portion of the toroidal high-permeability material.

In the measuring method of the present invention, a gain measuring coil is wound, and a wire having one end switchably connected to the magnetic field detecting coil and the magnetic flux detecting coil and the other end connected to the amplifier is arranged through the hollow portion. When a toroidal high magnetic permeability material is prepared; the material to be measured is inserted into the magnetic flux detecting coil, a signal current is passed through the gain measuring coil, and the wiring is connected to the magnetic field detecting coil. The output detected by the magnetic field detection coil and amplified by the amplifier is
1, VH1 / VB1 is the transfer function ratio GH / GB when the output detected by the magnetic flux detection coil and amplified by the amplifier when the connection of the wiring is switched to the magnetic flux detection coil is VB1; The sample to be measured is not inserted into the magnetic flux detection coil, a signal current is passed through the gain measurement coil, the output of the amplifier when the wiring is connected to the magnetic field detection coil, and the wiring is magnetic flux detected. GH0 / GB0 is the ratio with the output of the amplifier when it is switched and connected to the coil for
A sample to be measured is inserted into a magnetic field detection coil, a signal current is passed through the AC magnetic field generation coil, and when the wiring is connected to the magnetic field detection coil, it is detected by the magnetic field detection coil and amplified by the amplifier. Output VH,
VB / VH is VBA / VHA when the output detected by the magnetic flux detection coil and amplified by the amplifier is VB when the connection of the wiring is switched to the magnetic flux detection coil; Without inserting into the detection coil,
Between the output of the amplifier when the signal current of the AC magnetic field detection coil is passed and the wiring is connected to the magnetic flux detection coil, and the output of the amplifier when the wiring is switched and connected to the magnetic field detection coil. The ratio is VB0A / VH0A; the following formula μ = (SH / SB) {(VBA / VHA) (GH / GB)-(VB0A / VH0A) (GH0 / GB0)} where μ is the magnetic permeability and SB is the measured value. The magnetic permeability is obtained from the cross-sectional area of the sample that crosses the magnetic flux detection coil surface, SH is the cross-sectional area of the magnetic field detection coil.

[Operation] According to the present invention, the transfer function can be measured by a simple operation by inserting the gain measurement coil in the measurement circuit, and thereby the measurement error is corrected by correcting the permeability value. Can be reduced.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, which is a circuit diagram showing a signal detecting unit of a magnetic permeability measuring apparatus according to the present invention, an embodiment of the present invention is characterized by an AC magnetic field generating coil 1, a magnetic field detecting coil 2, and a magnetic field detecting 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 supply changeover switch 8. An AC signal source (not shown) is connected to the input terminal 9. Note that, in FIG. 1, for convenience, the magnetic flux detection coil 2 and the magnetic field detection coil 3 are shown in an arrangement different from the actual arrangement.

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

First, the transfer function ratios GB / GH and GB0 / GH0 in equation (9)
The measurement method of is explained.

The measurement sample is inserted into the magnetic flux detection coil 2, the signal source changeover switch 8 is tilted to the gain measurement coil 7 side, the detection coil changeover switch 4 is tilted to the magnetic field detection coil 3 side, and a signal is supplied to the input terminal 9 for detection. The output of the output terminal 10 of the amplifier 5 is measured, and this is VH1. Next, turn down the detection coil changeover switch 4 to the magnetic flux detection coil 2 side, and set the others to VH.
Measure the output of output terminal 10 in the same way as when 1 was measured, and set this as VB1. Let VB1 / VH1 be the transfer function ratio GB / GH. In addition, the same measurement is performed without inserting the measurement sample into the magnetic flux detection coil 2, and the detection amplifier 5 is set to
The output ratio of the output terminal 10 when connected to and to the magnetic field detection coil 3 is GB0 / GH0.

Next, the method for measuring VBA / VHA and VB0A / VH0A in the formula (9) will be described.

Insert the measurement sample into the magnetic flux detection coil 2, tilt the signal source changeover switch 8 to the AC magnetic field generation coil 1 side, and tilt the detection coil changeover switch 4 to the magnetic field detection coil 3 side,
A signal is sent to the input terminal 9, the output of the output terminal 10 is measured, and this is VH. Next, the detection coil changeover switch 4 is tilted to the magnetic flux detection coil 2, and otherwise the output of the output terminal 10 is measured in the same manner as when measuring VH, and this is designated as VB. Let VB / VH be VBA / VHA. In addition, the same measurement is performed without inserting the measurement sample into the magnetic flux detection coil 2, and the output ratio of the output terminal 10 when the detection amplifier 5 is connected to the magnetic flux detection coil 2 and the magnetic field detection coil 3 is VB0A. / VH0A
And

GB / GH, GB0 / GH0, VBA / VHA and V thus obtained
Substituting B0A / VH0A into the equation (9), the magnetic permeability is obtained.

Next, the reason why the ratio of transfer functions can be measured by measuring VH1 and VB1 will be described 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 portion of the toroidal ferrite 6 form an n: 1 transformer. If the transformer is ideal, when an input signal ei is passed through the gain detection coil 7, an electromotive force of ei / n is generated in the wiring passing through the core, and its impedance Zt is from the gain detection coil 7 to the signal generator side. Let Zs be the impedance seen by, then Zt = Zs / n ² . Therefore, if n is designed so that Zt is sufficiently smaller (Zt << ZC, and Zt << ZA) than the impedance (ZC) of the detection coil or the impedance (ZA) of the detection amplifier, the internal impedance is almost zero. May be considered to occur in the wiring. A practical transformer is not ideal, and the electromotive force generated in the wiring is k · ei. Here, k is determined by the characteristics of the coil itself, such as the number of turns n of the coil 7, the winding method, the magnetic permeability of the toroidal material 6, and the like, and has frequency characteristics due to these characteristics.
However, if n is designed as described above, the impedance can be regarded as almost 0, and k can be regarded as a coefficient irrelevant to the impedance of the detection coil or the detection amplifier. From the viewpoint of measurement accuracy, the number of turns n is preferably 10 or more.

The voltage eo in 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) (11), so if the impedance of the magnetic flux detection coil is ZB and the impedance of the magnetic field detection coil is ZH, GB = ZA / ( ZB + ZA) (12) GH = ZA / (ZH + ZA) (13). According to the above measurement procedure, the relationship of VB1 = ZA / (ZB + ZA) · k · ei (14) VH1 = ZA / (ZH + ZA) · k · ei (15) is established by the equation (10). From (12) to (15), VB1 / VH1 = GB / GH (16), and the transfer function ratio can be measured by measuring VH1 and VB1.

The magnetic permeability measurement result according to the present invention will be described in comparison with the result by the conventional method.

FIG. 5 shows the measurement of the magnetic permeability of a thin film having a thickness of 0.2 μm by the conventional technique of calculating without considering the transfer function. The horizontal axis shows the frequency from 500 kHz to 120 MHz on a logarithmic scale. The vertical axis is the magnetic permeability, which is displayed on a logarithmic scale from 10 to 5000. The solid line is the effective and ineffective part of permeability,
The dotted line represents the absolute value.

FIG. 6 shows the same thin film used for the measurement by the conventional method of FIG. 5 measured by the method of the present invention.

Comparing Fig. 5 and Fig. 6, there is almost no difference up to about 50MHz, but at higher frequencies, the absolute value of magnetic permeability increases in Fig. 5, whereas it decreases in Fig. 6. You can see it going. It is considered that such a measurement result is obtained because the transfer function is not taken into consideration in the conventional method shown in FIG. On the other hand, it can be said that the measurement by the method of the present invention does not give the result as in the conventional technique, and the result with less measurement error than the conventional technique is obtained.

[Effects of the Invention] As described above, in the present invention, since the magnetic permeability is measured in consideration of the transfer function, the magnetic permeability can be evaluated correctly as compared with the prior art.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a magnetic permeability measuring device according to the present invention, FIG. 2 is a diagram showing a principle of measuring magnetic permeability, and FIG. 3 is a structural example of a magnetic permeability measuring device according to a conventional technique. Fig. 4 is a diagram showing a part of an equivalent circuit of the measuring device, Fig. 5 is a diagram showing an example of the result of measuring the permeability according to the prior art, and Fig. 6 is a diagram showing an example of the result of the permeability according to the present invention. Is. 1 ... AC magnetic field generating coil, 2 ... Magnetic flux detecting coil, 3 ...
Magnetic field detection coil, 4 ... Detection coil changeover switch, 5
... detection amplifier, 6 ... toroidal high magnetic permeability material, 7 ... gain measurement coil, 8 ... signal source selector 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, 17 ... Resistance.

Claims (4)

[Claims] 1. An AC signal source, an AC magnetic field generating coil for applying an AC magnetic field to a measurement sample, and a magnetic flux detecting coil and a magnetic field detecting coil for respectively detecting a magnetic flux and a magnetic field by the AC magnetic field generating coil, An amplifier for amplifying the detection output of the magnetic flux detection coil and the magnetic field detection coil,
A gain measuring coil wound around a toroidal high-permeability material for measuring a transfer function from the magnetic flux detecting coil and the magnetic field detecting coil to the amplifier, and the AC magnetic field generating coil for generating a signal from the AC signal source. And a second switcher for switching and connecting the magnetic flux detection coil and the magnetic field detection coil to the amplifier, and a second switcher for switching between the gain measuring coil and the gain measuring coil. A magnetic permeability measuring device, wherein one of two wirings connecting to an amplifier is wired through the hollow portion of the toroidal high magnetic permeability material. 2. When the number of turns of the gain detection coil is n and the impedances of the AC signal generation source, the magnetic flux detection coil and the magnetic field detection coil are Z1, ZB and ZH, respectively, n ² > Z
The magnetic permeability measuring apparatus according to claim 1, wherein 1 / ZH and n ² > Z1 / ZB. 3. The magnetic permeability measuring device according to claim 1, wherein the number of turns of the gain detecting coil is 10 or more. 4. A wire around which a gain measuring coil is wound, one end of which is switchably connected to a magnetic field detecting coil and a magnetic flux detecting coil, and the other end of which is connected to an amplifier is arranged through the hollow portion. When a toroidal high magnetic permeability material is prepared; a sample to be measured is inserted into the magnetic flux detecting coil, a signal current is passed through the gain measuring coil, and the wiring is connected to the magnetic field detecting coil. The output detected by the magnetic field detection coil and amplified by the amplifier is VH1,
VH1 / VB1 is the transfer function ratio GH / GB, where VB1 is the output detected by the magnetic flux detection coil and amplified by the amplifier when the connection of the wiring is switched to the magnetic flux detection coil; A sample is not inserted into the magnetic flux detecting coil, a signal current is passed through the gain measuring coil, and the output of the amplifier when the wiring is connected to the magnetic field detecting coil,
The ratio of the output of the amplifier when the wiring is switched and connected to the magnetic flux detection coil is GH0 / GB0; the sample to be measured is inserted into the magnetic field detection coil, and a signal current is passed through the AC magnetic field generation coil, When the wiring is connected to the magnetic field detection coil, the output detected by the magnetic field detection coil and amplified by the amplifier is VH, and when the connection of the wiring is switched to the magnetic flux detection coil, the magnetic flux detection coil is used. When the output detected and amplified by the amplifier is VB, VB / VH is VBA / VHA; the sample to be measured is not inserted into the magnetic flux detection coil, and a signal current is passed through the AC magnetic field generation coil. , The ratio of the output of the amplifier when the wiring is connected to the magnetic flux detecting coil and the output of the amplifier when the wiring is switched and connected to the magnetic field detecting coil is VB0A / VH0A; μ = (SH / SB) {(VBA / VHA) (GH / GB)-(VB0A / VH0A) (GH0 / GB0)} where μ is the magnetic permeability and SB is the cut across the magnetic flux detection coil surface of the DUT. Area, SH is the cross-sectional area of the magnetic field detection coil, and the permeability is calculated from