magnetic detector

Abstract

To provide a magnetism detector that reduces a diamagnetic field of a magnetic thin film on a nonmagnetic board, is compact, and has high detection sensitivity.SOLUTION: A magnetism detector includes a segment-shaped magnetic thin film 10 disposed on a nonmagnetic board 1, an excitation thin-film coil 20 that is disposed in a layer differing from that of the magnetic thin film 10 and excites the magnetic thin film 10, and a detection thin-film coil 21 that is disposed in a layer differing from that of the magnetic thin film 10 and detects a change in magnetic flux appearing in the magnetic thin film 10 by a magnetic field to be measured, applies an excitation magnetic field to the magnetic thin film 10 by a high-frequency current energized to the excitation thin-film coil 20, and detects the amount of magnetic field to be measured applied to the magnetic thin film 10 as an electric signal synchronized with the high-frequency current by the detection thin-film coil 21.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic detector using a magnetic thin film formed on a non-magnetic substrate. [Background technology]

[0002] Parallel fluxgate magnetic detectors are known as elements for detecting magnetic field quantities. Parallel fluxgate magnetic detectors have high detection sensitivity and are used in applications such as direction sensors and for measuring magnetic field strength generated by electric currents.

[0003] A parallel fluxgate magnetic detector has an excitation coil and a detection coil wound around a magnetic core. When a high-frequency current is passed through the excitation coil, an excitation magnetic field is applied to the magnetic core. This excitation magnetic field saturates the magnetic core, causing it to repeatedly reverse its magnetization direction in synchronization with the high-frequency current cycle.

[0004] When the magnetic field to be measured is applied to the magnetic core, the magnetic field to be measured is added to the excitation magnetic field, causing a shift in the saturation point. The amount of change at this time can be converted into an electrical signal by a detection coil and processed to obtain the magnitude of the magnetic field to be measured.

[0005] Patent Document 1 describes a method for realizing this parallel fluxgate magnetic detector using a thin film. In Patent Document 1, an excitation magnetic field is applied to the magnetic core formed of a thin film in the direction perpendicular to the surface by an excitation coil wound around the magnetic material. A detection coil, wound around the magnetic material in the same way as the excitation coil, converts the amount of the detection magnetic field applied to the magnetic material into an electric signal. At this time, the magnetic field detection direction of the magnetic detector is also perpendicular to the surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-201061 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in Patent Document 1, an excitation magnetic field is applied perpendicular to the surface of a thin magnetic core formed from a thin film, resulting in a very large demagnetizing field in the thickness direction. A parallel fluxgate magnetic detector needs to saturate the magnetic core to drive it, but the demagnetizing field of the magnetic core is so large that it becomes difficult to saturate it. This also reduces the demagnetizing field of the magnetic core and the detection sensitivity. [Means for solving the problem]

[0008] In view of the above, the magnetic detector of the present invention comprises: a linear magnetic thin film disposed on a non-magnetic substrate; an exciting thin-film coil disposed in a layer different from the magnetic thin film and exciting the magnetic thin film; a detection thin-film coil disposed in a layer different from the magnetic thin-film and detecting a change in magnetic flux appearing in the magnetic thin-film due to a measured magnetic field; Equipped with applying an excitation magnetic field to the magnetic thin film by a high frequency current passed through the excitation thin film coil; The amount of the magnetic field to be measured applied to the magnetic thin film is detected by the detecting thin film coil as an electric signal synchronized with the high frequency current. [Effects of the Invention]

[0009] According to the present invention, the demagnetizing field of a magnetic thin film on a non-magnetic substrate can be reduced, and a small-sized magnetic detector with high detection sensitivity can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] Magnetic detector when the excitation coil and detection coil are on the same plane [Figure 2] An example of a circuit configuration for driving a magnetic detector and processing signals [Figure 3] An example of the waveform detected by a magnetic detector [Figure 4]An example of a circuit configuration for driving a magnetic detector, processing signals, and controlling negative feedback [Figure 5] A magnetic detector in which a first coil and a second coil are placed on a magnetic thin film [Figure 6] A magnetic detector having a first coil on one side of a non-magnetic substrate and a magnetic thin film and a second coil on the other side. DETAILED DESCRIPTION OF THE INVENTION

[0011] "First embodiment" The configuration of the magnetic detector according to the first embodiment of the present invention will be described below.

[0012] An example of the configuration of a magnetic detector in which an excitation coil and a detection coil are on the same plane will be described with reference to FIG.

[0013] Fig. 1(a) is a perspective view showing an example of a magnetic detector, and Fig. 1(b) is an exploded perspective view thereof, while Figs. 1(c) and 1(d) are exploded perspective views of a configuration according to another embodiment.

[0014] The magnetic detector 100 according to this embodiment is a parallel fluxgate type magnetic detector that converts the amount of a magnetic field to be measured that is applied to a magnetic thin film 10 as a magnetic body into an electric signal.

[0015] In the magnetic detector 100, a magnetic thin film 10 is disposed on a non-magnetic substrate 1, and an exciting coil 20 and a detecting coil 21 are disposed on the same plane above the magnetic thin film 10 via an insulating layer.

[0016] For the sake of explanation, the longitudinal direction of the magnetic thin film 10 is defined as the X direction, the direction perpendicular to the X direction in the plane on which the magnetic thin film is arranged as the Y direction, and the direction perpendicular to the X and Y directions as the Z direction. The magnetic sensing direction of the magnetic detector 100 is the longitudinal direction of the magnetic thin film 10.

[0017] (For non-magnetic substrates) The non-magnetic substrate 1 is made of a non-magnetic material such as ceramic or glass.

[0018] (Magnetic thin films) In this embodiment, the magnetic thin film 10 is made of a soft magnetic material with high magnetic permeability containing Fe, Co, etc., but the present invention is not limited to this and other soft magnetic materials can also be used.

[0019] The magnetic thin film 10 is formed on the non-magnetic substrate 1 by a method such as sputtering or vapor deposition, and then formed into any desired shape by a method such as ion milling. This method makes it possible to create a large number of magnetic thin films at once.

[0020] At least one magnetic thin film 10 is arranged in the form of a line segment. By arranging multiple magnetic thin films 10, the volume sensitive to the detection magnetic field increases, thereby improving detection sensitivity. Even when multiple magnetic thin films 10 are arranged, it is preferable that the end of one of the multiple magnetic thin films 10 is positioned at the center of the excitation coil 20 or detection coil 21, and the other magnetic thin films 10 are arranged side by side with that magnetic thin film, as will be described later.

[0021] To drive a parallel fluxgate magnetic detector, it is necessary to saturate the magnetic thin film 10. Therefore, if the magnetic thin film 10 is shaped so that the demagnetizing field is small, the amount of energy required to generate the excitation magnetic field can be reduced, and the drive current for the magnetic detector 100 can be made smaller. Note that although it is necessary to drive the magnetic thin film 10 so as to saturate it, generally, the areas near the ends where magnetic flux enters and exits do not become completely saturated. This is also true in the present invention; it is sufficient if the majority (central portion) of the magnetic thin film 10 is magnetically saturated, and this state can be considered to be the state in which the magnetic thin film 10 is saturated.

[0022] By making the magnetic thin film 10 thin and elongated, the demagnetizing field of the magnetic thin film 10 can be reduced. It is more preferable that the thickness of the magnetic thin film 10 be 3 μm or less and the width be 20 μm or less. It is also more preferable that the longitudinal direction of the magnetic thin film be longer, which is set to 15 μm in this embodiment.

[0023] If the magnetic thin film 10 is made elliptical, the magnetic poles at the ends in the X direction are dispersed, which is more preferable as it can further reduce the demagnetizing field (FIG. 1(d)).

[0024] In addition, if multiple magnetic thin films 10 are arranged in parallel and shifted in the Y direction, the volume of the magnetic thin films 10 can be increased, and the detection sensitivity can be further improved. In this embodiment, as shown in each diagram in Figure 1, three magnetic thin films are arranged at equal intervals near the center in the Y direction.

[0025] (Excitation coil and detection coil) The exciting coil 20 (exciting thin-film coil) and the detecting coil 21 (detecting thin-film coil) are arranged on the same plane above the magnetic thin film 10 via an insulating layer.

[0026] The excitation coil 20 and detection coil 21 are spiral planar coils made of non-magnetic conductive material such as copper or gold. These coils are preferably thin-film coils formed by forming a film using a method such as sputtering or vapor deposition, and then molding the film into a desired shape using a method such as ion milling.

[0027] It is preferable that the center of the excitation coil 20 and one longitudinal end of the magnetic thin film 10 are positioned approximately in the X and Y directions (in-plane positions), and it is preferable that the other longitudinal end of the magnetic thin film 10 is positioned approximately in the center of the detection coil 21 (FIGS. 1(a) and 1(b)), although the other end may extend beyond the center of the detection coil 21 (FIG. 1(c)). The center of the excitation coil 20 may also be positioned not to be positioned in the same position as one end of the magnetic thin film 10, but to extend beyond it, but it is preferable that the distance between the center of the detection coil 21 and the other end of the magnetic thin film 10 is no greater than the distance between the center of the detection coil 21 and the other end of the magnetic thin film 10.

[0028] The excitation coil 20 and the detection coil 21 each have electrodes for electrical connection to a drive unit, a detection unit, etc. Specifically, electrodes 51 and 52 are provided for inputting an excitation current (drive current) to the excitation coil 20, and electrodes 53 and 54 are provided for extracting an output from the detection coil 21.

[0029] The excitation coil 20 may also function as the detection coil 21. That is, by configuring the detection coil 21 in Fig. 2 so that a drive current from a drive unit is applied between it and a band limiting unit and providing a high-pass filter in the band limiting unit, it is possible to extract an output waveform (magnetic flux change) resulting from the magnetic field to be measured, which appears at twice the frequency of the high-frequency current serving as the drive current, as will be described later.

[0030] (Magnetic detector drive and signal processing) Fig. 2 shows a circuit block diagram for driving and processing signals from the magnetic detector 100. The circuit block diagram in Fig. 2 may be configured with an analog circuit, a digital circuit, or a combination of these.

[0031] A high frequency current is applied from a driving unit to the exciting coil 20. The waveform of this high frequency current is preferably a sine wave or a triangular wave, and may also be a square wave.

[0032] The frequency of the high frequency current is preferably in the band of several hundred kHz to about 20 MHz.

[0033] A high-frequency current is passed through the excitation coil 20, which generates an excitation magnetic field. The direction in which the excitation magnetic field is generated and the longitudinal direction (X direction) of the magnetic thin film 10 are perpendicular to each other, but the excitation magnetic field easily passes through the magnetic thin film, which has high magnetic permeability, and the magnetic field passes along the longitudinal direction. This excitation magnetic field causes the magnetic thin film to alternately saturate in the longitudinal direction with positive and negative polarities.

[0034] As mentioned above, the exciting coil 20 and the magnetic thin film 10 are arranged with an insulating layer between them. Because the insulating layer is very thin, at only a few micrometers, the exciting coil 20 and the magnetic thin film 10 can be placed close to each other, and the exciting magnetic field generated by the exciting coil 20 can be applied to the magnetic thin film 10 very efficiently.

[0035] When a measured magnetic field is applied longitudinally to the magnetic thin film 10, which is in a state of alternating positive and negative saturation in the longitudinal direction, a signal with an amplitude corresponding to the amount of the measured magnetic field can be obtained from the detection coil 21 at twice the frequency of the drive signal, corresponding to the change in magnetic flux that occurs due to the magnetic bias being applied to the magnetic thin film 10. This operation will be described in detail using Figure 3.

[0036] Fig. 3 shows the detection signals of the magnetic detector 100 configured in this embodiment when a measured magnetic field of a certain intensity is biased to the magnetic thin film 10. Two detection signals output at timings roughly synchronized with the excitation signal (excitation current) shown in Fig. 3a are shown in Fig. 3b and 3c. Fig. 3b is the output signal from the magnetic thin film 10 when there is no measured magnetic field, and Fig. 3c is the detection signal from the magnetic thin film 10 when the measured magnetic field is applied. Fig. 3d shows the difference between Fig. 3b and 3c, and the detection signal from the detector appears at twice the frequency of the excitation signal.

[0037] The magnetic field detection direction (magnetic sensing direction) of the magnetic detector 100 is the longitudinal direction of the magnetic thin film 10. In this way, in the parallel fluxgate system, the magnetic field detection direction and the direction of the excitation magnetic field in the magnetic thin film 10 are parallel to each other.

[0038] One end of the detection coil 21 is connected to a reference potential, and the other end is connected to a band limiting unit (FIG. 2). The signal flowing from the band limiting unit to the detection unit side is set to a band that allows the detection signal detected by the detection coil 21 to pass.

[0039] In this embodiment, a resonance capacitor C1 is arranged in parallel with the detection coil 21. By achieving resonance between the detection coil 21 and the resonance capacitor C1, it is possible to extract a detection signal more efficiently.

[0040] The band limiting section consists of a band pass filter (BPF) and a high pass filter (HPF) that use resistors and capacitors.

[0041] The detection signal that passes through the band limiting section is shaped by the detection section, and then input to the amplification section where it is amplified to a predetermined potential. This amplified signal becomes an output signal that corresponds to the amount of magnetic field to be measured.

[0042] Furthermore, negative feedback control may be performed to cancel the magnetic field to be measured that is applied to the magnetic thin film 10. By performing negative feedback control, it is possible to obtain effects such as linearity of magnetic field detection, temperature stability, and a wider detection range.

[0043] Figure 4(a) shows a configuration diagram in which the detection coil and negative feedback coil are implemented in one coil. The negative feedback signal output from the amplifier section acting as a negative feedback driver via the detection section is input to the contact point between the band limiting section and the detection coil via resistor R. At this time, the negative feedback signal is limited to a band that cannot pass through the band limiting section to the detection section. The amount of magnetic field to be measured can be detected by detecting the amount of current in the negative feedback signal via resistor R.

[0044] A negative feedback coil 24 may be further wound around the magnetic thin film 10 (FIG. 4(b)). The negative feedback coil 24 may be wound around the magnetic detector 100 in a solenoid shape, or may be arranged in parallel to the detection coil 21 in a thin-film spiral shape. In this case, a negative feedback signal output from the amplifier section acting as a negative feedback driver via the detection section is connected to one end of the negative feedback coil 24 via resistor R. The other end of the negative feedback coil 24 is connected to a reference potential.

[0045] The resistor R may be connected between the negative feedback coil 24 and the reference potential (not shown), in which case the amplifier section serving as the negative feedback driver is directly connected to one end of the negative feedback coil 24. The amount of the magnetic field to be measured can be detected by detecting the amount of current of the negative feedback signal via the resistor R.

[0046] So far, in this embodiment, an example has been described in which there are three magnetic thin films 10, but it is clear that the number of magnetic thin films 10 is not limited to this, and the number of turns of the excitation coil 20 and detection coil 21 does not have to be limited to those shown in the figure.

[0047] "Second embodiment" Next, a second embodiment will be described with reference to Fig. 5. This embodiment differs from the first embodiment in that an excitation coil and a detection coil are disposed between two magnetic thin films; the same reference numerals are used for the common components, and their description will be omitted.

[0048] The magnetic detector 100 shown in FIG. 5(a) has a lower magnetic thin film 11, a lower coil 22, an upper coil 23, and an upper magnetic thin film 12 laminated in this order on one surface of a non-magnetic substrate 1, with insulating layers interposed between them.

[0049] However, the present invention is not limited to this configuration, and two non-magnetic substrates each having a magnetic thin film and a lower coil arranged thereon may be used, and the two substrates may be bonded together so that the coil surfaces are in contact with each other.

[0050] Alternatively, the lower magnetic thin film, lower coil, and upper coil may be arranged on a non-magnetic substrate, and the upper magnetic thin film may be arranged on another non-magnetic substrate, and these may then be bonded together using adhesive, solder, or other means.

[0051] (Regarding the lower and upper coils) The lower coil 22 is either an excitation coil or a detection coil, and the upper coil 23 is the other.

[0052] The lower coil 22 and the upper coil 23 are each composed of a first lower coil 221 and a first upper coil 231, and a second lower coil 222 and a second upper coil 232, which are wound in opposite directions on the same plane, and the respective first coils and second coils are electrically connected.

[0053] The lower coil 22 and the upper coil 23 are made of a non-magnetic conductive material such as copper or gold. These coils may be formed into any desired shape by ion milling or the like after being formed into a film by a method such as sputtering or vapor deposition.

[0054] The centers of the first coils and the centers of the second coils of the lower coil 22 and the upper coil 23, respectively, are approximately aligned in the in-plane direction, and are also approximately aligned with the longitudinal ends of the lower magnetic thin film 11 and the upper magnetic thin film 12, respectively.

[0055] The lower coil 22 and the upper coil 23 are provided with electrodes 61, 63 and electrodes 62, 64, respectively, for electrical connection with a driving unit, a detecting unit, and the like.

[0056] Here, the distribution of the excitation magnetic field when the lower coil 22 is used as the excitation coil will be explained using Fig. 5(b). For simplicity of explanation, the non-magnetic substrate is omitted in Fig. 5(b), and the lower magnetic thin film and the upper magnetic thin film are treated as one line.

[0057] When a current is passed in the direction shown in Figure 5(b), a magnetic field is generated from the first coil toward the lower magnetic thin film, and a magnetic field is generated from the second coil toward the upper magnetic thin film. The magnetic fields generated by each coil form a magnetic path in which the lower and upper magnetic thin films form part of the magnetic path, causing the magnetic field to flow counterclockwise in Figure 5(b). At this time, the magnetic resistance seen from the first and second coils becomes small, making it possible to saturate the magnetic thin film with a small excitation energy, and therefore allowing the excitation current to be reduced.

[0058] The excitation current is a high-frequency current, and if a current in the opposite direction to that shown in Figure 5(b) is passed through the coil, the flow of the magnetic field will also be reversed.

[0059] The same effect can be obtained when the second coil 23 serves as an exciting coil.

[0060] It is also possible to form a magnetic path using only one of the lower magnetic thin film 11 and the upper magnetic thin film 12, without providing either one.

[0061] "Third embodiment" Next, a configuration in which a back coil is disposed on the back surface of a non-magnetic substrate on which a magnetic thin film and a surface coil are disposed will be described with reference to Fig. 6. Note that, except for the location where they are disposed, the back coil corresponds to the lower coil 22 described in the second embodiment, and the surface coil corresponds to the second coil 23, so in the following description, the same reference numerals are used to refer to the back coil 22 and the surface coil 23.

[0062] A magnetic thin film 10 is disposed on the surface (one side) of the non-magnetic substrate 1, and a surface coil 23 is disposed on the magnetic thin film 10 via an insulating layer. Furthermore, a back coil 22 is disposed on the back side (other side) of the non-magnetic substrate 1 opposite to the surface on which the magnetic thin film 10 is disposed.

[0063] The surface coil 23 and the back coil 22 are made of a non-magnetic conductive material such as copper or gold. These coils may be formed into any desired shape by ion milling or the like after being formed into a film by a method such as sputtering or vapor deposition.

[0064] The back coil 22 may be arranged on a non-magnetic substrate separate from the non-magnetic substrate 1 on which the magnetic thin film 10 is arranged, and may be attached to the non-magnetic substrate 1. The attachment can be achieved by means of adhesive, solder, or the like.

[0065] Either the back coil 22 or the surface coil 23 is an excitation coil, and the other is a detection coil. However, if the surface coil 23 is a detection coil, it is preferable because it is closer to the magnetic thin film and can improve detection sensitivity.

[0066] The back coil 22 and the surface coil 23 are provided with electrodes 71, 73 and electrodes 72, 74, respectively, for electrical connection with a driving unit, a detecting unit, and the like.

[0067] By adopting the configurations of the above-described embodiments, it is possible to reduce the demagnetizing field of the magnetic thin film with a side of about several mm, and to realize a small magnetic detector.

[0068] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, in the magnetic detector 100 described in FIG. 1, only one of the excitation coil 20 and the detection coil 21 may be provided, and the other may also serve as the function of the other. In this case, as described above, by providing a driving unit and a band-limiting unit for one planar coil and providing a high-pass filter in the band-limiting unit, it is possible to extract an output waveform resulting from the measured magnetic field, which appears at twice the frequency of the high-frequency current used as the driving current.

[0069] Furthermore, although an example has been described in which the excitation coil and detection coil are configured as uniformly spiral-shaped thin-film coils, it is sufficient that the thin-film coils are arranged in a layer above the magnetic thin-film and are configured so that they can be saturated by applying a magnetic field to the magnetic thin-film, and it is merely preferable that the thin-film coils are formed in a generally spiral shape.

[0070] Furthermore, as shown in Figure 1, when the excitation coil and detection coil are formed from one spiral thin-film coil, the configuration in which they are arranged on the same plane (on the same layer) has been described, but this is not limited to this, and the excitation coil and detection coil may also be arranged on different planes. [Explanation of symbols]

[0071] 1 Non-magnetic substrate 10 Magnetic thin film 11 Lower magnetic thin film 12 Upper magnetic thin film 20 Excitation coil 21 Detection coil 22 Lower coil 221 First lower coil 222 Second lower coil 23 Upper coil 231 First upper coil 232 Second lower coil

Claims

1. a linear magnetic body disposed on a non-magnetic substrate; an exciting planar coil disposed on a layer different from the magnetic body and exciting the magnetic body; a detection planar coil disposed on a layer different from the magnetic body and detecting a change in magnetic flux occurring in the magnetic body due to a measured magnetic field; A parallel fluxgate type magnetic detector comprising: an excitation magnetic field is applied to the magnetic body by a high frequency current passed through the excitation planar coil, causing magnetic saturation; the amount of the magnetic field to be measured applied to the magnetic body is detected by the detection planar coil as an electric signal synchronized with the high frequency current; A magnetic detector characterized in that the center of the exciting planar coil and an end of the magnetic body in the longitudinal direction are arranged at positions that coincide with each other in the in-plane direction of the non-magnetic substrate.

2. 2. The magnetic detector according to claim 1, wherein the center of the detection planar coil and an end of the magnetic body in the longitudinal direction are arranged at positions that coincide with each other in the in-plane direction of the non-magnetic substrate.

3. 3. The magnetic detector according to claim 1, wherein the exciting planar coil and the detecting planar coil are arranged on the same plane.

4. A linear magnetic body disposed on a non-magnetic substrate; an exciting planar coil disposed on a layer different from the magnetic body and exciting the magnetic body; a detection planar coil disposed on a layer different from the magnetic body and detecting a change in magnetic flux occurring in the magnetic body due to a measured magnetic field; A parallel fluxgate type magnetic detector comprising: an excitation magnetic field is applied to the magnetic body by a high frequency current passed through the excitation planar coil, causing magnetic saturation; the amount of the magnetic field to be measured applied to the magnetic body is detected by the detection planar coil as an electric signal synchronized with the high frequency current; the excitation planar coil is formed by a first planar coil formed in a spiral shape with its center located on one end side of the magnetic body, and a second planar coil formed in a spiral shape with a reverse winding to the first planar coil with its center located on the other end side of the magnetic body, the detection planar coil is formed by a third planar coil formed in a spiral shape with its center located on the one end side of the magnetic body, and a fourth planar coil formed in a spiral shape with a reverse winding to the third planar coil with its center located on the other end side of the magnetic body, a magnetic detector, characterized in that the planar excitation coil, the planar detection coil, and the magnetic body are stacked on the non-magnetic substrate, each as a different layer;

5. 5. The magnetic detector according to claim 4, wherein the magnetic body is composed of a lower magnetic body and an upper magnetic body, and the excitation planar coil and the detection planar coil are provided in a layer between the lower magnetic body and the upper magnetic body.

6. 5. The magnetic detector according to claim 4, wherein the magnetic body is provided on one surface of the non-magnetic substrate, one of the exciting planar coil and the detecting planar coil is provided on the one surface side, and the other of the exciting planar coil and the detecting planar coil is provided on the other surface side of the non-magnetic substrate opposite the one surface.

7. 7. The magnetic detector according to claim 1, wherein a plurality of the magnetic bodies are arranged at predetermined intervals.

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