JPH07104044A - Magnetic permeability measuring device - Google Patents

Abstract

PURPOSE:To measure magnetic permeability with higher frequency more than that in the case of using a differential coil by an alternating field generating coil, and a coil, the piercing hole of which is concentric, and which is inserted in a magnetic field generating coil intersecting perpendicularly to the alternating field. CONSTITUTION:Voltage from a high frequency power supply 4 for exciting is applied to a magnetic field generating coil 2 to generate uniform alternating field parallel to the respective faces of the coil 2 in the interior surrounded by the coil 2. A measuring coil 20 is so constructed that a through hole 11 for inserting a magnetic permeability measuring sample 9 is provided on a glass epoxy base plate 10, and a one turn coil 12 where a microstrip line with fixed characteristic impedance is formed concentrically with the through hole 11 is formed on one surface of the base plate 10. With the sample 9 not inserted, the induced voltage of the coil 12 is measured, and further, with the sample 9 inserted in the through hole 11, the induced voltage of the coil 12 is measured, and according to both induced voltages, the magnetic permeability of the sample 9 is operated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic permeability measuring device for measuring the relative magnetic permeability of a thin film magnetic material at high frequencies and its real and imaginary parts.

[0002]

2. Description of the Related Art Conventionally, an inductance method, a yoke method and the like have been used to measure the magnetic permeability of a magnetic material. With these conventional methods, it is difficult to measure at a high frequency because of self-resonance caused by the coil's self-inductance and stray capacitance, and the upper limit of the measurable frequency is 10 MH.
It was about z. Therefore, instead of the method described above,
A magnetic permeability measuring method using a differential coil is known.

A magnetic permeability measuring device using a differential coil is disclosed in Japanese Unexamined Patent Publication No. 61-57871. As shown in FIG. 7, a magnetic permeability measuring apparatus using a differential coil generates a magnetic field by applying a voltage from a high frequency power supply 4 for excitation to a magnetic field generating coil 2 having a rectangular cross section to generate an alternating magnetic field. The magnetic field detection coil 8 and the measurement differential coil 6 wound in a figure 8 are provided in the magnetic field generation coil 2 so that the planes are orthogonal to the alternating magnetic field generated by the coil 2, and the measurement is performed. A magnetic permeability measurement sample (hereinafter also simply referred to as a sample) 9 is inserted into one coil of the differential coil 6 for magnetic field, and the magnetic permeability is calculated based on the induced voltages of the magnetic field detection coil 8 and the measurement differential coil 6. To do.

When the magnetic permeability measurement sample 9 is inserted
The induced voltage of the magnetic field detection coil 8 is V _{H (V)}, Permeability test
Magnetic field detection coil 8 in an air-core state in which no material is inserted
Induced voltage of V_{H0 (V)}, The state in which the magnetic permeability measurement sample 9 is inserted
Voltage V of the differential coil 6 for measurement in the stationary state_{B (V)}, Magnetic permeability
Difference for measurement in an air-core state in which the rate measurement sample 9 is not inserted
Induction voltage V of moving coil 6_{B0 (V)}Of the magnetic field detection coil 8
Effective area is S_H, The cross-sectional area of the magnetic permeability measurement sample 9 is S_MTosu
Then, the relative permeability μr of the magnetic permeability measurement sample 9_(V)Is

[0005]

[Equation 1]

Is calculated by

Here, the suffix (V) is used in this specification as a symbol indicating that it is a vector.

Now, the induced voltage V_{H (V)}, V_{H0 (V)},
V_{B (V)}, V_{B0 (V)}Measuring instrument with input impedance of 50Ω
If it is measured by, the measured induced voltage V
_{H (V)}′, V _{H0 (V)}′, V_{B (V)}′, V_{B0 (V)}′ Is

[0009]

[Equation 2]

(I = H (V), H0 (V), B (V),
It is represented by B0 (V)). Here, Z _{i (V)} is the impedance of the coil in each case, for example, Z _{i (V)
H (V)} is the impedance of the magnetic field detection coil 8 with the magnetic permeability measurement sample 9 inserted. It will be easily understood in other cases.

Therefore, considering the input impedance of the measuring instrument (here, 50Ω), the relative permeability μr _(V) is

[0012]

[Equation 3]

It will be calculated as follows.

[0014]

However, in the magnetic permeability measuring device using the above-mentioned measuring differential coil, self-resonance occurs at a frequency of 100 to 120 MHz due to the structural restriction of the measuring differential coil. ,As a result,
The magnetic permeability measuring device using the differential coil for measurement has a problem that the high frequency limit is 100 to 120 MHz and the magnetic permeability cannot be measured at frequencies higher than this.

When the magnetic permeability measuring device using the measuring differential coil is used, the voltage generated from the magnetic permeability measuring sample is measured by the measuring differential coil, the signal lead wire, the connector,
A coaxial cable (50Ω or 75Ω) and a signal amplifier are transmitted in this order. In this case, since impedance matching cannot be achieved between the differential coil for measurement and the signal lead wire, it is usually 50Ω to 20Ω in series for the purpose of improving the mismatch.
A 0Ω resistor is connected. However, even if the resistors are connected in series, impedance matching cannot be perfectly achieved at each connection point, reflection of the measurement signal occurs, these act like resonance, and the signal level increases, and the input terminal of the signal amplifier increases. Appear in.

In particular, the reflection between the measuring differential coil and the signal lead wire determines the high frequency limit frequency of the magnetic permeability measuring device.

It is an object of the present invention to provide a magnetic permeability measuring device having a simple structure and capable of measuring the relative magnetic permeability at a high frequency as compared with the case where a measuring differential coil is used.

[0018]

A magnetic permeability measuring apparatus according to the present invention comprises a magnetic field generating coil for generating a substantially uniform alternating magnetic field and a substrate provided with a through hole for inserting a magnetic permeability measuring sample. A coil formed in a microstrip line concentrically with the through hole and inserted into the magnetic field generating coil so as to be orthogonal to the alternating magnetic field, wherein the magnetic permeability measurement sample is not inserted into the through hole. It is characterized in that the relative permeability of the magnetic permeability measurement sample is obtained based on the ratio of the induced voltage of the coil and the induced voltage of the coil when the magnetic permeability measurement sample is inserted into the through hole.

The magnetic permeability measuring apparatus of the present invention is characterized in that the coil has one turn.

The magnetic permeability measuring apparatus of the present invention is characterized in that the coil is terminated by a resistor having the same resistance value as the characteristic impedance of the microstrip line.

[0021]

According to the magnetic permeability measuring apparatus of the present invention, a coil formed by a microstrip line concentrically with a through hole in a substrate provided with a through hole in a substantially uniform alternating magnetic field generated by a magnetic field generating coil. Is inserted so as to be orthogonal to the alternating magnetic field, the ratio of the induced voltage of the coil when the magnetic permeability measurement sample is not inserted into the through hole and the induced voltage of the coil when the magnetic permeability measurement sample is inserted into the through hole. The relative permeability is obtained based on In this case, since the coil is formed by the microstrip line, it is possible to obtain a relative magnetic permeability at a high frequency that cannot be conventionally measured.

[0022]

EXAMPLES The present invention will be described below with reference to examples.

FIG. 1 is a schematic configuration diagram of an embodiment of a magnetic permeability measuring apparatus according to the present invention.

A voltage from an exciting high frequency power source 4 is applied to a magnetic field generating coil 2 composed of a strip coil having a rectangular cross section. By this application, a substantially uniform alternating magnetic field parallel to each surface of the magnetic field generating coil 2 is generated inside the magnetic field generating coil 2.

On the other hand, the measuring coil 20 is a T-shaped glass epoxy substrate 1 having a thickness of 0.5 mm as shown in FIG.
0 is provided with a through hole 11 for inserting the magnetic permeability measurement sample 9, and one turn formed by a microstrip line having a constant characteristic impedance (for example, 50Ω) concentrically with the through hole 11 on one surface of the substrate 10. The coil 12 is formed, the other surface of the substrate 10 is coated with a ground conductor 13 such as a copper plate, and the termination of the coil 12 is connected with a termination resistor 14 having the same value as the characteristic impedance (for example, 50Ω). The coil 12 is connected to the ground conductor 13 via 14
The starting end of is extended to the end of the substrate 10 for external connection. Here, the reason why the characteristic impedance of the microstrip line forming the coil 12 and the resistance value of the terminating resistor 14 are made the same is for impedance matching.

The substrate 10 is preferably a glass epoxy type substrate having a low magnetic permeability, and may be a Teflon type substrate.

As shown in FIG. 2, ground conductors 15A and 15B are electrically insulated from the coil 12 on one surface of the substrate 10 and electrically connected to the ground conductor 13 on the other surface of the substrate 10. May be worn. The ground conductors 15A and 15B are attached to facilitate the connection with the outside. Also, ground conductors 15A and 15B
A hole 16 for mounting the substrate 10 and a hole 17 for a through hole are provided in the portion (1).

The measuring coil 20 is bored so that the plane of the coil 12 is orthogonal to the alternating magnetic field generated by the excited magnetic field generating coil 2 and the coil 12 is positioned inside the magnetic field generating coil 2. 16 is provided.

In this embodiment constructed as described above,
In the state in which the magnetic permeability measurement sample 9 is not inserted, the induced voltage of the coil 12 is measured, and in the state in which the magnetic permeability measurement sample 9 is inserted in the through hole 11, the induced voltage of the coil 12 is measured and both The magnetic permeability of the magnetic permeability measurement sample 9 is calculated based on the induced voltage.

In this embodiment, the cross-sectional area of the magnetic permeability measurement sample 9 is S _M and the effective area of the coil 12 is S _HT . The coil 12 acts as both the measuring differential coil 6 and the magnetic field detecting coil 8, and the effective area S _HT corresponds to the cross-sectional area S _H.

In the state where the magnetic permeability measurement sample 9 is not inserted,
That is, the induced voltage of the coil 12 measured by a measuring instrument having an input impedance of 50Ω at the time of air core is V _{HT (V)} ′,
If the induced voltage of the coil 12 measured with a measuring instrument having an input impedance of 50Ω in the state where the magnetic permeability measurement sample 9 is inserted in the through hole 11, is V _{BT (V)} ′, then V _{HT (V)} ′
Is the induced voltage V of the magnetic field detection coil 8 during air core
_{B0 (V)} 'and the induced voltage V _{H0 (V)} ' of the differential coil 6 for measurement.

If the impedance of the coil 12 in the air core is Z _{HT (V)} , Z _{HT (V)} is the impedance Z _{B0 (V)} of the magnetic field detecting coil 8 in the air core and the differential coil 6 for measurement. Impedance Z _{H0 (V)} .

Therefore, in this embodiment (Equation 3)
The second term in the parentheses on the right side is “1”, and the relative permeability μr _(V) according to this embodiment using the coil 12 is

[0034]

[Equation 4]

It is calculated by

Now, when the magnetic permeability measurement sample 9 is not inserted, that is, when the magnetic permeability measurement sample 9 is inserted into the through hole 11, the impedance change of the coil 12 is small, and When the change can be ignored, the relative permeability μr _(V) is

[0037]

[Equation 5]

Is calculated by

Since the relative permeability μr _(V) >> 1,
The second term (+1) on the right side of (Equation 5) is often omitted.

Here, the voltages V _{BT (V)} 'and V _{HT (V)} ' are complex quantities, and the relative permeability μr _(V) is also a complex quantity.

Therefore, the relative permeability μr _(V) is

[0042]

[Equation 6]

It can be expressed as Where | μr | is the absolute value of μr _(V) , and θ is the relative permeability μr at DC.
It is the phase difference from _(V) .

Next, each measurement example in the above-mentioned embodiment will be described.

In the above embodiment, the magnetic field generating coil 2 has a width of 36 mm, a height of 16 mm, and a length of 68.7 mm, and the magnetic field generating coil 2 is equivalently regarded as a series circuit of a resistance and an inductance. The frequency characteristics of the value R (Ω) and the inductance value L (nH) are as shown in FIG. 3, and the solid line shows the resistance value and the broken line shows the inductance value, and the first resonance occurs at about 850 MHz.

Next, the frequency characteristic of the resistance value (Ω) of the coil 12 is as shown by the solid line in FIG. 4. For reference, the frequency characteristic of the resistance value (Ω) of the measuring differential coil 6 at the time of mismatch is shown. This is indicated by the broken line in FIG. In FIG. 4, the resistance values of the terminating resistors 14 are both 50Ω. As is apparent from FIG. 4, the resistance value of the coil 12 has less change with respect to the frequency as compared with the resistance value of the measuring differential coil 6.

The absolute value | Z | of the impedance of the coil 12 and the frequency characteristics of the phase when the measuring coil 20 is inserted into the magnetic field generating coil 2 and when it is not inserted are as shown in FIG. In FIG. 5, the solid line and the dotted line show the absolute value of the impedance, the solid line shows the case of being inserted in the magnetic field detection coil 8, and the dotted line shows the case of not inserting it in the magnetic field detection coil 8. In FIG. 5, 1
The dashed-dotted line and the broken line show the phase, and the dashed-dotted line shows the case where the magnetic field detection coil 8 is inserted, and the dashed line shows the case where the magnetic field detection coil 8 is not inserted.

It is apparent from FIGS. 4 and 5 that the impedance of the coil 12 has a small variation with respect to frequency and the frequency characteristic is considerably improved.

Next, the magnetic field generating coil 2 has a width of 36 mm, a height of 16 mm and a length of 68.7 mm as in the above case, and a sputtered permalloy film having a thickness of 0.3 μm and a diameter of 17 mm is used as a magnetic permeability measurement sample. As for the forward transmission coefficient S ₂₁ of the S parameter when the magnetic permeability measurement sample 9 is inserted into the coil 12 and the S parameter when the magnetic permeability measurement sample 9 is not inserted into the coil 12 by a network analyzer (HP8752A type) manufactured by Hewlett Packard. Forward transfer coefficient S ₂₁
FIG. 6 shows the relative permeability μr calculated from both forward transfer coefficients S ₂₁ by measuring and.

In this measurement, as shown by the broken line in FIG. 1, a DC bias magnetic field of 5 Oersted or 10 Oersted is applied in the direction orthogonal to the magnetic field generated by the magnetic field generating coil 2.

In FIG. 6, the alternate long and short dash line and the broken line are theoretical values in consideration of eddy current loss and self-resonance, showing the real part μr ′ and the imaginary part μr ′ of the complex relative permeability, and the white circles and black circles indicate the measured values. The real part μr 'of the complex relative permeability is shown, and the white squares and the black squares show the imaginary part μr' of the complex relative permeability measured. Also, the alternate long and short dash line, the black circles and the black squares represent the case where a bias magnetic field of 5 Oersted was applied, and the broken line, the white circles and the white squares represent the case where a bias magnetic field of 10 Oersted was applied. From FIG. 6, it is shown that the theoretical value and the measured value are in good agreement, and the relative permeability up to 700 MHz which is the excitation limit frequency of the magnetic field generating coil 2 can be measured.

Further, instead of the network analyzer (HP8752A type) manufactured by Hewlett-Packard, the network analyzer (6 manufactured by Anritsu Corporation is used.
20J type), manufactured by Advantest Corporation (R3763A
Type) or the like may be used, and the same applies in this case.

The coil 1 is used in the above-described embodiment.
Although 2 has illustrated the case of one turn, it may be a plurality of turns.

[0054]

As described above, according to the magnetic permeability measuring apparatus of the present invention, the substrate having the through holes is concentric with the through holes in the substantially uniform alternating magnetic field generated by the magnetic field generating coil. Insert the coil formed by the microstrip line so as to be orthogonal to the alternating magnetic field, the induced voltage of the coil when the permeability measurement sample is not inserted into the through hole and the permeability measurement sample when inserted into the through hole Since the relative permeability is obtained based on the ratio with the induced voltage of the coil,
There is an effect that a relative magnetic permeability at a high frequency, which cannot be measured conventionally, can be obtained.

According to the magnetic permeability measuring apparatus of the present invention,
The coil configuration is simple and effective. Further, when the coil has one turn, the coil can be more easily constructed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a magnetic permeability measuring apparatus according to the present invention.

FIG. 2 (a) and FIG. 2 (b) are a front view and a back view showing a configuration of a measuring coil according to an embodiment of the present invention.

FIG. 3 is a frequency characteristic diagram of an equivalent resistance and an equivalent inductance of a magnetic field generating coil according to an embodiment of the present invention.

FIG. 4 is a resistance-frequency characteristic diagram of a coil in an example of the present invention.

FIG. 5 is an impedance-frequency characteristic diagram of a coil in an example of the present invention.

FIG. 6 is a relative magnetic permeability-frequency characteristic diagram showing theoretical values of relative magnetic permeability and calculated values by measurement in one example of the present invention.

FIG. 7 is a schematic configuration diagram of a conventional magnetic permeability measuring apparatus.

[Explanation of symbols]

2 ... Coil for magnetic field generation 4 ... High frequency power supply 6 ... Differential coil for measurement 8 ... Coil for magnetic field detection 9 ... Permeability measurement sample 10 ... Substrate 11 ... Through hole 12 ... Coil 13, 15A, 15B ... Ground conductor 14 ... Termination Resistance 20 ... Measuring coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Itagaki 48 Minami-timberly-machi, Wakabayashi-ku, Sendai-shi, Miyagi Ryowa Electronics Co., Ltd. Wade Electronics Co., Ltd.

Claims (3)

[Claims] 1. A magnetic field generating coil for generating a substantially uniform alternating magnetic field, and a substrate provided with a through hole for inserting a magnetic permeability measurement sample, which is formed by a microstrip line concentrically with the through hole. And a coil that is inserted into the magnetic field generating coil so as to be orthogonal to the alternating magnetic field, the permeability measurement sample in the through voltage and the induced voltage of the coil when the permeability measurement sample is not inserted into the through hole. A magnetic permeability measuring apparatus, characterized in that a relative magnetic permeability of the magnetic permeability measuring sample is obtained based on a ratio with an induced voltage of the coil when inserted. 2. The magnetic permeability measuring device according to claim 1, wherein
A magnetic permeability measuring device characterized in that the coil has one turn. 3. The magnetic permeability measuring device according to claim 1,
The magnetic permeability measuring device, wherein the coil is terminated by a resistor having the same resistance value as the characteristic impedance of the microstrip line.