JPH08129058A - Magnetic field sensor - Google Patents

Abstract

PURPOSE: To obtain a magnetic field sensor capable of detecting even a high frequency magnetic field in the GHz band, by forming a microstrip conductor at the front surface of a dielectric substrate having a grounded conductor formed at the rear surface thereof. CONSTITUTION: A grounded conductor 2 is formed at the rear surface of a dielectric substrate 3. A microstrip conductor 4 is formed one turn on the front surface of the dielectric conductor 3. A chip resistor 5 of an approximately equal resistance value to a value of the characteristic impedance of a microstrip line 40 is formed at the side of a terminal end of the conductor 4. One end of the chip resistor 5 is electrically connected to the conductor 4. The other end of the chip resistor 5 defines a slight gap from the conductor 4, and at the same time is electrically connected to the grounded conductor 2 through the substrate 3. The conductor 4 is thus terminated at the chip resistor 5. In a magnetic field sensor 1, a high frequency magnetic field is detected on the basis of an induced voltage in the microstrip line 40 induced when a magnetic field is interlinked with a coil formed of the microstrip line 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field sensor that can be used as a detection coil of a permeance measuring device, and more particularly to a magnetic field sensor using a microstrip line.

[0002]

2. Description of the Related Art As a conventional magnetic field sensor, a magnetoresistive element and a Hall element are generally known.

[0003]

However, the above-mentioned conventional magnetic field sensor has a low use frequency band, and for example, in the case of a Hall element, detection of a high frequency magnetic field of about 100 kHz is a limit, and detection of a high frequency magnetic field of the GHz band is performed. There was no magnetic field sensor capable of detecting a high frequency magnetic field in the GHz band.

An object of the present invention is to provide a magnetic field sensor capable of detecting a high frequency magnetic field in the GHz band.

[0005]

In order to achieve the above-mentioned object, a magnetic field sensor of the present invention comprises a dielectric substrate having a ground conductor formed on the back surface thereof, and approximately one turn formed on the surface of the dielectric substrate. And a resistor having a resistance value substantially equal to the resistance value of the characteristic impedance of the microstrip line and electrically connecting the tip end of the microstrip conductor to the ground conductor. Is characterized by.

[0006]

The magnetic field sensor of the present invention can detect a high frequency magnetic field based on the induced voltage of the microstrip line induced by interlinking the magnetic field with the coil formed by the microstrip line.

[0007]

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

FIG. 1 is a perspective view of an embodiment of a magnetic field sensor according to the present invention.

In the magnetic field sensor 1 of this embodiment, a microstrip conductor 4 of one turn is formed on the front surface of a dielectric substrate 3 having a ground conductor 2 formed on the back surface, and a microstrip conductor 4 is formed on the end side of the microstrip conductor 4. A chip resistor 5 having a resistance value substantially equal to the characteristic impedance value of the strip line 40.
To electrically connect one end of the chip resistor 5 to the microstrip conductor 4 and to form a small gap between the other end of the chip resistor 5 and the microstrip conductor 4 and to form a dielectric. Ground conductor 2 penetrating substrate 3
The microstrip conductor 4 is electrically connected to the microstrip conductor 4 and terminated by a chip resistor 5.

The microstrip conductor 4 is a dielectric substrate 3
The conductor formed above. Microstrip line 40
Is a microstrip conductor 4, a portion of the dielectric substrate 3 which is concentric with the microstrip conductor 4 and has a width several times the conductor width of the microstrip conductor 4, and a position where the portion of the dielectric substrate 3 is projected. It is a general term including a part of a certain ground conductor 2.

Generally, an approximate expression for obtaining the characteristic impedance Z ₀ of the microstrip line is given by Wheeler in the expressions (1) to (4).

[0012]

[Equation 1]

[0013]

[Equation 2]

[0014]

(Equation 3)

[0015]

[Equation 4]

In the equations (1) to (4), εr is the relative permittivity of the dielectric substrate 3, td is the film thickness of the dielectric substrate 3, tc is the film thickness of the conductor, that is, the film thickness of the microstrip line 40, wc is the width of the conductor, that is, the width of the microstrip conductor 4.

The width of the microstrip conductor 4 is determined by the equations (1) to (4) so that the characteristic impedance of the microstrip line 40 is 50Ω, and is processed into one turn shape by etching.

Further, in the magnetic field sensor 1, the dielectric substrate 3 is brought into close contact with the surface of the ground conductor 2, and the microstrip conductor 4 having a width such that the characteristic impedance is 50Ω is processed into one turn shape. It was done. In the microstrip conductor 4 of the present embodiment, the one-turn shape has a window width x, a window height y, and a coil end portion as shown in FIG.
That is, the gap length d between the chip resistor 5 and the adjacent line is formed. An example of the shape of the microstrip line 40 is shown in Table 1.
As shown in FIG.

[0019]

[Table 1]

A Teflon printed circuit board and a glass substrate are used as the dielectric substrate 3, and in the case of the Teflon substrate, when the window width x is varied from 4 to 32 mm while the gap length d is kept constant at 1 mm, and the window width x is 8 mm. It is shown that the air gap length d is changed to 1 to 8 mm while maintaining a constant value. Here, the conductor width was determined by ignoring the influence of adjacent lines.

In measuring the basic characteristics of the microstrip line 40, one end of the microstrip conductor 4 is set to H.
P8572A (manufactured by Hewlett-Packard Co.) network analyzer (input impedance 50 Ω) was connected, and the characteristics were measured by the reflection method.

The characteristic impedance Z ₀ of the microstrip line 40 is the input impedance when the end of the microstrip conductor 4 is short-circuited and opened, respectively.
If short and Zopen, it is calculated by the equation (5).

Z ₀ = √ (Zshort × Zopen) (5) When measuring the characteristic impedance of the microstrip line 40 in the present embodiment, the chip resistor 5 is removed, and the termination is opened and shorted to input impedance Zshort, Zop
Each en was measured and calculated by the equation (5). In this case, the characteristic impedance of the microstrip line 40 was 50Ω.

Before explaining the magnetic field detection by the magnetic field sensor 1, first, the basic characteristics of the microstrip line 40 when a Teflon substrate is used as the dielectric substrate 3 will be described.

Generally, it is said that the existence range of the electromagnetic field in the microstrip line 40 is about seven times the conductor width. In the microstrip line 40, FIG.
As shown in FIG. 3, there is a region where the microstrip conductors 4 are close to each other at the end portion of the microstrip conductor 4. Therefore, the behavior of the electromagnetic field in this portion will be described.

FIG. 2 illustrates the appearance of the terminal portion of the microstrip conductor 4. A hole was opened at the end of the microstrip conductor 4 to provide a chip resistor 5. Now, the window height y of the microstrip conductor 4 is 8 mm.
Therefore, when the void length d is 1 to 7 mm, it is as shown in FIG.
2A, the electrodes of the chip resistor 5 are oriented vertically in the drawing of FIG. 2A, while the gap length d is 8
In the case of 3 mm structure with mm, the electrodes of the chip resistor 5 are oriented in the left-right direction in the drawing of FIG. 2B as shown in FIG.

In the microstrip conductor 4 having a window width of 10 mm and a window height of 6 mm, when the air gap length d is changed, the characteristic impedance Z _0C of the microstrip line 40 increases as shown in FIG. Track 4
Although it is larger than the characteristic impedance Z _{0 of 0} , the change is about 10% at most. When the air gap length d is 8 mm, that is, when the structure has a three-sided structure as shown in FIG. 2B, the characteristic impedance Z _0C has a linear strip line 40.
Was almost equal to the value of the characteristic impedance Z ₀ . In this case, since the coupling between the upper and lower lines (the end portion of the microstrip line 40 and the microstrip line 40) in the plane of the microstrip line 40 is extremely small, it is presumed that the characteristic impedance was equal to that of the linear microstrip line. It

The reason why the tendency of the characteristic impedance is different between the case where the gap length d is 8 mm and the case where it is 1 to 7 mm is as shown in FIGS. 2 (a) and 2 (b). Figure 2 shows the direction to open the hole
It is considered that the difference between the case of (a) and the case of FIG. 2 (b) has an influence.

FIG. 4 shows the window width x and the microstrip line 4.
It shows the relationship with the characteristic impedance of 0.
FIG. 4 shows an example in which the window height y is 6 mm and the gap length d is 0.5 mm. The characteristic impedance increases as the window width x increases. Similar to the case of FIG. 3, the change in the characteristic impedance is about 10% at most in the case of the straight line.

FIGS. 5A and 5B show the resistance and reactance of the measured input impedance when the microstrip conductor 4 is terminated with 50Ω. In FIG. 5, the window width x of the microstrip conductor 4 is 8
mm, the window height y is 8 mm, and the gap length d is 1 mm. For comparison, a two-terminal coil having the same dimensions as the coil made of the microstrip conductor 4 is also shown so that it can be measured and compared. From FIG. 5 (a), the resistance of the two-terminal coil changes greatly in the range of 12Ω to 210Ω due to the influence of resonance, whereas the resistance of the microstrip line 40 changes only 42 to 59Ω at a frequency of 1 MHz to 3 GHz. ing. In addition to this, the reactance of the line is smaller than that in the case of the two-terminal coil from FIG. 5B, and does not increase sharply due to LC resonance. From this, it can be seen that the impedance of the microstrip line 40 is substantially determined by the resistance component, the influence of resonance is small, and the high frequency characteristics are excellent.

Next, the magnetic field detection by the magnetic field sensor 1 will be described.

As shown in FIG. 6, a plate conductor having a thickness of 2 mm and a length of 70 mm for generating a magnetic field is 20 mm × 40 mm.
Of the exciting coil 10 having a rectangular cross section and a gap 11 is provided between the opposite ends of the rolled plate conductor so as to electrically insulate each other. The magnetic field sensor 1 is provided so as to project in a hollow rectangular tube forming the exciting coil 10 and the direction of the magnetic field generated by the exciting coil 10 and the coil surface of the microstrip line 40 are orthogonal to each other when energized. 1 is attached, the exciting coil 10 is excited from the network analyzer 12 (HP8752A) via the coaxial cable 13, an external magnetic field perpendicular to the coil surface of the microstrip line 40 is applied, and the induced voltage from the microstrip line 40 is applied. The measurement was conducted by introducing it to the network analyzer 12 via the coaxial cable 14.

The electrical equivalent circuit in the case of this magnetic field detection is as shown in FIG. In the magnetic field detection, the background voltage obtained by removing the microstrip line 40 as the detection coil was also measured, and the background voltage was subtracted from the induced voltage of the microstrip line 40 to obtain the induced voltage.

In this case, the resonance frequency of the exciting coil 10 was 700 MHz, and the uniformity of the magnetic field generated by the exciting coil 10 including the surface of the ground conductor 2 was within ± 8.9%.

The S21 of the voltage applied from the network analyzer 12 to the exciting coil 10 and the voltage induced in the microstrip line 40 was measured. The amplitude of the induced voltage was obtained from the gain of S21, and the phase difference of the induced voltage with respect to the magnetic field was obtained from the phase of S21. If the frequency is 100 MHz or less, the phase change in the coaxial cables 13 and 14 can be ignored, so that the phase of S21 can be considered as the phase difference between the magnetic field and the induced voltage.

FIG. 8 shows the window width x of the microstrip conductor 4.
5 shows the relationship between the applied voltage to the exciting coil 10 and the induced voltage when is changed. FIG. 8 illustrates the case where the window width x is 8 mm, the gap length d is 1 mm, and the frequency of the applied voltage is 100 MHz. Since the applied voltage and the induced voltage are almost proportional from FIG. 8, it is apparent that the magnetic field can be detected in this case as well. Further, the window width x of the microstrip conductor 4 and the induced voltage are substantially proportional to each other. Since the window height y is constant, the cross-sectional area of the coil and the induced voltage are proportional. In this sense, the microstrip line 40 has the same properties as the two-terminal magnetic field detection coil.

Furthermore, the phase change of the induced voltage with respect to the input voltage was sufficiently small. From the above results, it was found that the microstrip line 40 has the same magnetic field detection characteristics as those of a normal two-terminal coil.

On the other hand, FIG. 9 shows a microstrip line 40.
And a two-terminal coil. FIG. 9 shows an example in which the window width x of the microstrip line 40 is 8 mm, the window height y is 8 mm, the gap length d is 1 mm, and the frequency of the applied voltage is 100 MHz. In FIG. 9, the window width x has the same shape and size of the conductor line, and the two-terminal coil has a structure in which the ground conductor surface is removed from the microstrip line 40. The induced voltage of the microstrip line 40 is reduced to about 10% of that of the two-terminal coil. That is, the microstrip line 40 is characterized in that the input impedance is almost unaffected by resonance and is stable up to the frequency in the GHz band, while the induced voltage due to the alternating magnetic field is smaller than that of the two-terminal coil.

Next, the induced voltage when the magnetic field of the microstrip line 40 is detected, comparison with the linear microstrip line, and the influence of the ground conductor surface will be described.

In this case, the basic dimensions of the microstrip line 40 are a window width x of 10 mm and a window height y of 6.0 m.
m, the gap length d is 0.5 mm, the height yg of the ground conductor 2 is 1
It was set to 2 mm and changed within the range shown in Table 2. As in the case of the example shown in Table 1, the line width wc of the microstrip conductor 4 is based on the formulas (1) to (4) and (5), and the characteristic impedance of the microstrip line 40 is 50Ω. So that it is 0.8 mm.

[0041]

[Table 2]

The induced voltage of the magnetic field sensor 1, that is, the microstrip line 40 will be described.

FIG. 10 shows the relationship between the induced voltage of the microstrip line 40 and the frequency.
Compared with terminal coil. FIG. 10 shows the microstrip line 40 having a window width x of 10 mm, a window height y of 6 mm, a gap length d of 0.5 mm, and a dielectric substrate 3 (εr = 5.0, substrate thickness td = 0.5 mm Teflon). Height of yg is 12m
This is an example in the case of m and an applied voltage of 0.5V. Figure 10 (a)
Represents the amplitude thereof, and FIG. 10 (b) represents the phase difference. FIG.
From 0 (a), the amplitude of the induced voltage increases in proportion to the frequency, and in the case of the microstrip line 40, the amplitude of the induced voltage is smaller than that of the two-terminal coil by about one digit. Further, it can be seen from FIG. 10 (b) that the phase of the induced voltage leads the applied magnetic field by about 90 °. However, in the microstrip line 40, 1 MHz to 10 MH
It is considered that the ground conductor surface has an effect on the point where the phase difference is smaller than 90 ° in z.

Next, the voltage generating mechanism will be described in relation to the induced voltage by changing the size of the microstrip conductor 4. The variables were the window width x, window height y, and gap length d of the microstrip conductor 4. In the measurement system of FIG. 6, the height yg of the ground conductor surface was fixed to 12 mm, and the dimensions of the microstrip line 40 were changed to detect the magnetic field. Figure 11
(A) shows the relationship between the window width x and the amplitude of the induced voltage with the window height y of the microstrip conductor 4 being constant, and both are proportional. Further, FIG. 11B shows the relationship between the window height y and the amplitude of the induced voltage with the window width x kept constant, and both are substantially proportional. However, when the distance between adjacent conductors becomes smaller and the influence of the coupled line becomes stronger, the proportional tendency is slightly deviated, and the magnetic field detection mechanism is considered to be complicated.

Further, in the case of the microstrip line 40, since there is always a gap between the end portion of the microstrip line 40 and the adjacent line, this effect will be described. FIG. 11C shows the relationship between the gap length d and the amplitude of the induced voltage. With respect to the void length d, even if d is increased to the point where one of the four sides of the microstrip conductor 4 is removed, the induced voltage does not change.

From the measurement results when the dimensions of the microstrip line 40 are changed, it can be seen that the amplitude of the induced voltage is almost proportional to the area surrounded by the microstrip conductor 4. Except for the fact that the amplitude of the induced voltage is about one digit smaller than that of the two-terminal coil, the induced voltage can be explained by Faraday's electromagnetic induction law. Further, the result shown in FIG. 11C shows that the current path when the induced voltage is generated passes through the ground conductor plane at the end portion where the one-turn microstrip conductor 4 is cut off.

Next, the relationship between the shape of the microstrip line 40 and the induced voltage will be clarified, and the presence or absence of the induced voltage in shapes other than the one-turn loop will be described.

FIG. 12 shows a linear microstrip line 2
0 is a schematic view of 0, in which a linear microstrip line 20 is formed on the surface of a dielectric substrate 22, one end of the linear microstrip line 20 is connected to a chip resistor 21, and the other end of the chip resistor 21 is a dielectric. The linear microstrip line 20 is terminated by a chip resistor 21 by connecting to a ground conductor 23 formed on the back surface of the substrate 22. In this case, the characteristic impedance of the linear microstrip line 20 is 50Ω, and the chip resistor 21 is a resistor of 50Ω. The magnetic field was applied in a direction perpendicular to the surface of the linear microstrip line 20 as shown in FIG.

FIG. 13A shows the relationship between the excitation frequency and the amplitude of the induced voltage, and FIG. 13B shows the relationship between the excitation frequency and the phase difference of the induced voltage with respect to the magnetic field.

Compared with the case of the microstrip line 40, the amplitude of the induced voltage is not proportional to the frequency, and the phase difference between the magnetic field and the induced voltage is 0 to 30 °.
It is clear that the principle of magnetic field detection is different because it is different from 90 ° in the case of the microstrip line 40.

Next, the wide band property of the microstrip line 40 will be described.

In order to use the microstrip line 40 in a wide band, it is desirable to keep the characteristic impedance near 50Ω. Here, microstrip line 4
The change in the characteristic impedance when the dimension of 0 is changed will be described. In FIG. 14, the characteristic impedance Z _0C of the microstrip line 40 having different window heights y is obtained by measurement, and the characteristic impedance Z ₀ of the linear microstrip line 20 is obtained.
It is shown standardized by _C. In FIG. 14, the window width x of the microstrip line 40 is 10 mm and the gap length d is 0.
This is an example in which the height yg of the ground conductor 2 is 5 mm and the height yg is 12 mm. If the distance between adjacent conductors is less than 3 mm, line coupling occurs and the characteristic impedance decreases. Assuming a lossless line, the characteristic impedance is Z ₀ = √ (La / Ca) due to the inductance La and the capacitance Ca as the linear constant of the line. Here, when parallel lines in which current flows in the opposite direction approaches, negative mutual inductance increases, La decreases, and Ca increases, so the result of FIG. 14 is qualitatively valid. The deviation of the characteristic impedance can be solved by setting the line width such that the characteristic impedance becomes 50Ω in consideration of the influence of the coupled line.

Although not shown, when the distance between the parallel strip conductors is 3 mm or more, and when one of the four sides of the coil is cut out from the gap length d of 0.3 mm, 3
The characteristic impedance was almost constant in all cases where the edge structure was changed.

FIG. 15 compares the input impedances of the microstrip line 40 and a normal two-terminal coil. Window width x and window height y of the microstrip conductor 4
Are 10.0 mm and 6.0 mm, respectively, the size of the two-terminal coil is 10.0 mm × 6.0 mm, and a resistance of 50Ω is connected in series to the two-terminal coil. FIG.
(A) shows the resistance component, and the two-terminal coil is
While it fluctuates greatly in the range of 0Ω to 180Ω, it is 40Ω to 60 in the case of the microstrip line 40.
It is kept at Ω. Further, FIG. 15B shows the reactance component. Since the reactance component of the microstrip line 40 is 1/10 or less of the resistance component, the input impedance can be regarded as almost pure resistance.

It is well known in the circuit theory of transmission lines that wide bandwidth can be obtained by the input resistance being a pure resistance of about 50Ω, and it is explained as follows. In FIG. 7, which shows a circuit diagram of a measurement system for magnetic field detection, Vc is a voltage generated by an alternating magnetic field, and Vr is a terminal voltage of a 50Ω resistance observed inside the network analyzer 12. In the case of the microstrip line 40, since the input impedance Z _in looking at the microstrip line 40 is matched with the transmission characteristic impedance Z ₀ , the voltage Vr observed over a high frequency is V
r≈Vc / 2. This is an advantage in measuring the induced voltage in a wide band.

Next, the influence of the ground conductor surface will be described.

Induction of the dimensions of the microstrip conductor 4 when the window width x is 10.0 mm, the window height y is 3.0 mm, the gap length d is 0.5 mm, and the dimensions of the ground conductor surface are changed. The voltage and the input impedance will be described. FIG. 16 is an explanatory diagram of the dimensions of the ground conductor surface.
16A is the surface on the microstrip line 40 side, and FIG. 16B is the ground conductor surface side. yg is the height of the ground conductor surface, and h is the height of the opening 30 provided inside the pattern of the microstrip conductor 4. The width of the opening 30 was 10.0 mm, which was equal to the window width x of the microstrip conductor 4. This is to investigate the influence of the opening 30 in the detection coil for the permeance measuring device. Further, wg in FIG. 16B represents the width of the ground conductor surface when there is the opening 30. In the measurement, the dimensions of the ground conductor surface were successively reduced in the following three steps. (A) The height yg of the ground conductor surface is from 12.0 mm to 5.
It was reduced to 0 mm. (B) The width of the inside of the microstrip conductor 4 is 10.
The opening 30 having a height of 0 mm and a height of 0 mm was made, and the height h of the opening 30 was increased from 0 mm to 3.0 mm. (C) Width wc 0.8 mm of the microstrip conductor 4
On the other hand, the width wg of the ground conductor surface was reduced from 1 mm to 0.3 mm. Table 3 shows the range of dimensions changed by this procedure.

[0058]

[Table 3]

(B) The influence of the height yg of the ground conductor surface will be described.

FIG. 17 shows the relationship between the height yg of the ground conductor surface and the amplitude of the induced voltage in the microstrip line 40. The value of the voltage is the induced voltage due to the two-terminal coil having the same size as the microstrip conductor 4. The value V ₀ was standardized and shown. FIG. 17 shows an example in which the frequency of the voltage applied to the exciting coil 10 is 10 MHz, 5 MHz, and 1 MHz.
As shown in FIG. 17, when the height yg of the ground conductor surface decreases, the induced voltage in the microstrip line 40 increases almost inversely. This suggests that reducing the height yg of the ground conductor surface reduces the eddy current circulating in the ground conductor surface.

Based on this consideration, the amount of magnetic flux interlinking with the coil pattern of the microstrip conductor 4 is obtained from the three-dimensional electromagnetic field analysis by the T-Ω method, and the induced voltage V _C is V _C.
The result calculated by = (dφ / dt) / 2 is shown in FIG. The reason why dφ / dt is divided by 2 is to divide the voltage by the terminal resistance 5 (50Ω) and the input resistance of the network analyzer 12. The relationship between the height yg of the ground conductor surface and the amplitude of the induced voltage in the microstrip line 40 shown in FIG. 17 is in good agreement with the measurement result, and the analysis result shows that an eddy current is generated on the ground conductor surface and the end of the conductor portion. It was found to be localized in the area. From this, it was quantitatively clarified that an eddy current is generated by the application of the alternating magnetic field, and the magnetic field strength interlinking the microstrip conductor 4 is reduced. On the other hand, in the input impedance corresponding to FIG. 17, as shown in FIG. 18, the resistance component is dominant, and the change due to the height yg of the ground conductor surface remains within the range of 40Ω to 60Ω, and there are few problems in impedance matching. I understand. (B) The influence of the height h of the opening will be described.

FIG. 19 shows the height h of the opening 30 on the ground conductor surface.
And the amplitude of the induced voltage in the microstrip line 40 are shown. Even if the height h of the opening 30 is changed, the amplitude of the induced voltage in the microstrip line 40 does not change. This is because the eddy current is concentrated on the end portion in the ground conductor surface.

FIG. 20 shows the frequency dependency of the input impedance of the magnetic field sensor 1, that is, the microstrip line 40 when the height h of the opening 30 is changed. The change in input impedance increases as the value increases. When the height h of the opening 30 is 3 mm, that is, the width wg of the ground conductor surface is the width wc of the microstrip conductor 4 as shown in FIG.
In case of 1mm which is almost equal to, the input resistance is 35Ω ~ 70Ω
Changes greatly in the range of. (C) The influence of the width wg of the ground conductor surface will be described.

FIG. 21 shows the relationship between the width wg of the ground conductor surface and the amplitude of the induced voltage in the microstrip line 40. When the width wg of the ground conductor surface is reduced, the induced voltage in the microstrip line 40 increases. To do. The value in which the width wg of the ground conductor surface is 0 mm indicates the induced voltage of the microstrip line 40 in the case of the two-terminal coil.

FIG. 22 shows the frequency dependence of the input impedance of the magnetic field sensor 1. The width wg of the ground conductor surface is 1 mm, 0.8 mm, 0.6 mm, 0.3 mm and the two terminal coil. This is an example of the case. When the width wg of the ground conductor surface decreases, the change in the input impedance of the magnetic field sensor 1 increases. The width wg of the ground conductor surface is 0.3 mm
If it is made smaller, the induced voltage of the magnetic field sensor 1 increases to about 50% of that of the two-terminal coil, while the change of the input impedance greatly changes in the range of 30Ω to 100Ω.

As described above, due to the eddy current circulating in the ground conductor surface from (a) to (c), the magnetic field strength interlinking the loop formed by the microstrip conductor 4 is reduced as compared with the two-terminal coil, and the induced voltage is reduced. Decrease. Since the eddy current concentrates on the end portion of the ground conductor surface, the induced voltage does not change even if the opening portion is provided on the ground conductor surface. The change in input impedance is greatly affected by the width of the ground conductor surface. If the input impedance is allowed to change within a range of ± 20% with respect to 50Ω, the amplitude of the induced voltage is approximately 3 when the amplitude of the two-terminal coil is
It can be increased up to 7%. The dimension of the ground conductor surface at this time is such that the height yg of the ground conductor surface is approximately the same as the loop outer shape of the microstrip conductor 4.

Next, the case of a microstrip line made of a thin film will be described.

Copper was sputtered to a thickness of 1 μm on a cover glass substrate having a thickness of 150 μm and processed into one turn shape by ion trimming to form a microstrip line 40.
The width of the microstrip conductor 4 was 0.31 mm, which was obtained from the equations (1) to (4) so that the characteristic impedance of the microstrip line 40 was 50Ω.

FIG. 23 shows the magnetic field detection characteristic of the microstrip line 40 having the four-sided structure shown in FIG. 2A, in which both the window width x and the window height y of the microstrip conductor 4 are 3 mm. The excitation frequency was 100 MHz as in the case of the Teflon substrate. The applied voltage to the exciting coil 10 and the induced voltage of the microstrip line 40 are almost proportional to each other, and it can be seen that the magnetic field can be detected also in the microstrip line 40 made of a thin film. In addition, the induced voltage per unit area was reduced to about 30% as compared with the case where a Teflon substrate having a four-sided structure was used.

However, based on the above results (see FIG. 17), assuming that the height yg of the ground conductor surface and the amplitude of the induced voltage are in inverse proportion to each other, the size of the ground conductor surface can be reduced to obtain a wide band. It is considered that the induced voltage can be increased at least four times or more without impairing the property.

[0071]

As described above, according to the magnetic field sensor of the present invention, a macrostrip conductor of approximately one turn is formed on the surface of a dielectric substrate having a ground conductor formed on the back surface, and the characteristic impedance of the microstrip line is formed. Since the tip end of the microstrip conductor is electrically connected to the tip end of the microstrip conductor by a resistor having a resistance value substantially equal to that of the microstrip conductor,
An induced voltage is generated in the microstrip line by the magnetic field interlinking with the surface surrounded by the microstrip conductor, and this induced voltage has an effect of detecting the magnetic field.

Further, according to the present invention, it is possible to obtain the effect that the induced voltage substantially proportional to the area surrounded by the microstrip conductor can be obtained and the magnetic field can be detected.

According to the magnetic field sensor of the present invention, the magnetic field can be similarly detected even when the microstrip conductor is formed of a thin film or a printed board.

Further, according to the magnetic field sensor of the present invention, there is an effect that a substantially constant induced voltage can be obtained even if the gap length between the end portion of the microstrip line and the opposing microstrip line is changed.

According to the present invention, the ground conductor surface has a constant characteristic impedance (50Ω) of the microstrip line.
, And can be used as a high frequency magnetic field sensor up to GHz band.

Further, according to the magnetic field sensor of the present invention, when the width and height of the ground conductor surface are reduced, the magnetic field strength of the coil pattern by the microstrip line increases, so that an induced voltage with a large amplitude can be obtained. .

According to the present invention, the characteristic impedance of the ground conductor surface is specified as described above ((50Ω in the embodiment).
Has the role of both the effect (desired effect) and the effect of reducing the voltage induced in the microstrip line by the in-plane eddy current (undesirable effect). Therefore, the optimum design guideline is to optimize the dimensions of the ground conductor surface (to reduce the width and height) while keeping the characteristic impedance at the specified value.

Further, according to the magnetic field sensor of the present invention, it is possible to obtain a large amplitude induced voltage by increasing the distance between the microstrip conductor and the ground conductor surface while maintaining the characteristic impedance at the design value. There is also.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an embodiment of a magnetic field sensor according to the present invention.

FIG. 2 is a plan view showing a positional relationship between a terminal end portion of a microstrip line and a chip resistor in an embodiment of a magnetic field sensor according to the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the air gap length and Z _0C / Z ₀ in one embodiment of the magnetic field sensor according to the present invention.

FIG. 4 is a characteristic diagram showing a relationship between a window width and Z _0C / Z ₀ in an example of the magnetic field sensor according to the present invention.

FIG. 5 is a frequency characteristic diagram of input impedance in one embodiment of the magnetic field sensor according to the present invention.

FIG. 6 is a schematic view of a measurement system for magnetic field detection according to an embodiment of a magnetic field sensor according to the present invention.

FIG. 7 is an equivalent circuit diagram of a measurement system for magnetic field detection according to an embodiment of a magnetic field sensor according to the present invention.

FIG. 8 is a characteristic diagram of an applied voltage versus an induced voltage when a window width is used as a parameter in one embodiment of the magnetic field sensor according to the present invention.

FIG. 9 is a characteristic diagram of applied voltage vs. induced voltage showing magnetic field detection characteristics of a microstrip line and a two-terminal coil in one embodiment of a magnetic field sensor according to the present invention.

FIG. 10 is a comparison diagram of induced voltages in a microstrip line and a two-terminal coil in one embodiment of the magnetic field sensor according to the present invention.

FIG. 11 is a characteristic diagram showing the relationship between the size of the microstrip line and the amplitude of the induced voltage in one embodiment of the magnetic field sensor according to the present invention.

FIG. 12 is a perspective view of a linear microstrip line.

FIG. 13 is a frequency vs. induced voltage characteristic diagram of a linear microstrip line.

FIG. 14 is a characteristic diagram showing the relationship between the window height of the microstrip line and the characteristic impedance in one embodiment of the magnetic field sensor according to the present invention.

FIG. 15 is a frequency characteristic diagram of input impedance of a microstrip line in an example of the magnetic field sensor according to the present invention.

FIG. 16 is a plan view for explaining the shape of a ground conductor surface in an embodiment of the magnetic field sensor according to the invention.

FIG. 17 is a characteristic diagram showing the relationship between the height of the ground conductor surface and the amplitude of the induced voltage in one embodiment of the magnetic field sensor according to the present invention.

FIG. 18 is a characteristic diagram showing the relationship between the height of the ground conductor surface and the input impedance in one embodiment of the magnetic field sensor according to the present invention.

FIG. 19 is a characteristic diagram showing the relationship between the height of the opening and the amplitude of the induced voltage in one embodiment of the magnetic field sensor according to the present invention.

FIG. 20 is a characteristic diagram showing the relationship between the height of the opening and the input impedance in one embodiment of the magnetic field sensor according to the present invention.

FIG. 21 is a characteristic diagram showing the relationship between the width of the ground conductor surface and the amplitude of the induced voltage in one embodiment of the magnetic field sensor according to the invention.

FIG. 22 is a characteristic diagram showing the relationship between the ground conductor surface and the input impedance in one embodiment of the magnetic field sensor according to the present invention.

FIG. 23 is a characteristic diagram showing the relationship between the amplitude of the induced voltage and the applied voltage of the thin film microstrip line in one embodiment of the magnetic field sensor according to the present invention.

[Explanation of symbols]

 1 ... Magnetic field sensor 2 ... Ground conductor 3 ... Dielectric substrate 4 ... Microstrip conductor 5 ... Chip resistance 10 ... Excitation coil 40 ... Microstrip line

Claims (3)

[Claims] 1. A dielectric substrate having a ground conductor formed on the back surface thereof, a microstrip conductor having substantially one turn formed on the surface of the dielectric substrate, and a resistance value substantially equal to the resistance value of the characteristic impedance of the microstrip line. Have
A magnetic field sensor comprising a resistor electrically connecting the tip of the micro-strip conductor and the ground conductor. 2. The magnetic field sensor according to claim 1, wherein the microstrip line is formed of a thin film or a printed board. 3. The magnetic field sensor according to claim 1, wherein the resistor is a chip resistor formed on the surface of a dielectric substrate.