JPH05312930A - Magnetic-field detecting device using amorphous magnetic film - Google Patents

Abstract

PURPOSE:To obtain a simple magnetic field detecting device having the sensitivity of about 10-100 times or more than a conventional device even if the device has about the same size as that of a conventional magnetism detecting element. CONSTITUTION:An exciting coil 2, a detecting coil 3, a high-frequency sine wave current source 4 for the exciting coil 2 and a detecting circuit 5, which detects the second higher harmonic of the voltage induced in the detecting coil, are provided in a double frequency type magnetic field detecting device. A saturable amorphous magnetic film 1, which is a cobalt-based thin film, is used as a magnetic core in this detecting device. The magnetic film has the size of the thickness of 1-3mum and the area of 50-150mm<2> and has the initial permeability of 1,500 or more at the exciting frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small magnetic field detecting device for detecting a minute magnetic field such as a earth porcelain.

[0002]

2. Description of the Related Art Conventionally, a Hall element or a magnetoresistive element is mainly used for detecting a magnetic field. Hall element
When a magnetic field is applied perpendicularly to a plate through which an electric current flows, an electric field is generated in a direction perpendicular to the two, and an electromotive force appears. The Hall effect is used, while the magnetoresistive element changes its electric resistance according to the magnetic field. Utilizing the phenomenon.

[0003]

A device using a Hall element and a magnetoresistive element has a low output sensitivity and requires a complicated circuit such as temperature compensation. It is an object of the present invention to provide a magnetic field detection device having a simple structure in which the magnetic field detection element is about the same size as the conventional element but has a sensitivity 10 to 100 times or more that of the conventional one.

[0004]

In order to achieve the above object, a magnetic field detecting device of the present invention includes an exciting coil wound around a magnetic core, a detecting coil wound in the same direction as the exciting coil, and an exciting coil. In a high frequency current source for supplying a sine wave high frequency current, and a double frequency type magnetic field detection device equipped with a detection circuit for detecting a second harmonic component of a voltage induced in a detection coil,
A saturable amorphous magnetic film, which is a cobalt-based thin film having a thickness of 1 to 3 μm and an area of 50 to 150 mm ² and an initial magnetic permeability at an excitation frequency of 1500 or more, is used for a magnetic core.

In order to enable high-sensitivity detection, it is important that the detector has a high inductance. In order to increase the inductance of the detection unit, one of them is to increase the number of turns of the detection coil. However, in this case, contradictory to the miniaturization, the area is increased. Therefore, in the present invention, the magnetic film area is defined as the lower limit value of 50 mm ² which is the minimum area capable of ensuring the minimum number of turns capable of realizing high sensitivity. The upper limit of the area is defined as 150 mm ² from the viewpoint of the size equivalent to that of the conventional element.

In the present invention, since the thickness corresponding to the inductance capable of realizing high sensitivity is 1 μm or more, the lower limit of the thickness of the magnetic film is defined as 1 μm.
In addition, when the thickness is 3 μm or more, the inductance reaches saturation and the upper limit of the thickness is defined as 3 μm from the viewpoint of shortening the time required for film formation. The lower limit of the initial magnetic permeability of the magnetic film is the minimum magnetic film magnetic core (thickness 1 μm,
In the magnetic field detection device using an area of 50 mm ² ), the minimum value 1500 that can confirm the realization of high sensitivity was defined.

[0007]

[Function] The excited amorphous magnetic film has an external magnetic field H
Is applied, a second harmonic component of the excitation frequency appears in the detection coil, and its voltage peak / peak value VP-P changes with a change in the magnitude of the magnetically biased state of the magnetic film. . The change tendency is linear with respect to a minute external magnetic field, and can be detected as a linear change with respect to a minute external magnetic field.

[0008]

FIG. 1 is a circuit diagram showing an embodiment of a magnetic field detecting device according to the present invention. An amorphous magnetic film magnetic core 1, an exciting coil 2 wound around it, and an exciting coil 2 wound in the same direction. The detection coil 3 is provided with a high frequency current source 4 for supplying a sinusoidal high frequency current to the excitation coil 2, and a detection circuit 5 for detecting the second harmonic component of the voltage induced in the detection coil 3.

The amorphous magnetic film has a thickness of 1 to 3 μm.
m is a cobalt-based thin film having an area of 50 to 150 mm ² and an initial permeability of 1500 or more at an excitation frequency. The high frequency current supplied to the exciting coil sufficiently saturates the magnetization of the amorphous magnetic film. With the device satisfying the above conditions, it is possible to provide a magnetic field detection device with high sensitivity and a simple configuration.

FIG. 2 is a magnetization curve of the amorphous magnetic film when the external magnetic field H is zero and the amorphous magnetic film is excited by a high frequency current sufficient to saturate the magnetization of the amorphous magnetic film. The amorphous magnetic film excited in this way has an external magnetic field H
3 is applied, a demagnetized state is generated as shown in FIG. 3, a second harmonic component of the excitation frequency appears in the detection coil, and its voltage peak / peak value VP-P is the magnitude of the demagnetized state of the magnetic film. It changes with the change in size. The change tendency is linear with respect to a minute external magnetic field, and can be detected as a linear change with respect to a minute external magnetic field. When the saturation due to the excitation is insufficient, the linear change region decreases.

In order to enable highly sensitive detection in this principle, it is important that the detector has a high inductance. In order to increase the inductance of the detection unit, the number of turns of the detection coil may be increased as one.
However, this is contradictory to miniaturization, but it involves an increase in area. Therefore, in the present invention, the lower limit of the magnetic film area is defined by the minimum area of 50 mm ² which can ensure the minimum number of turns for which the realization of high sensitivity can be confirmed. The upper limit of the area is defined as 150 mm ² from the viewpoint of the size equivalent to that of the conventional element.

Further, the thickness of the magnetic film determines the magnitude of the inductance. FIG. 4 shows the change tendency of the inductance with respect to the change of the thickness of the magnetic film. In the present invention, the thickness corresponding to the inductance capable of realizing high sensitivity is 1 μm or more. Therefore, in the present invention, the lower limit of the thickness of the magnetic film is defined as 1 μm. Further, the inductance reaches saturation at 3 μm or more, and the upper limit of the thickness is defined as 3 μm from the viewpoint of shortening the time required for film formation.

FIG. 5 shows the detection characteristics with respect to an external magnetic field in the case where the magnetic film has an initial permeability of 4800, which exhibits the highest sensitivity in the minimum magnetic film magnetic core of the present invention. An example of the configuration conditions of the sensor unit of the magnetic field detection device in this case is as follows.

In the present invention, all the influences of the above-mentioned sensor section constituent conditions on the detection characteristics were investigated. Therefore, FIG. 6 shows the magnetic field detection characteristics under the condition that shows the highest sensitivity among them. The configuration conditions are as follows.

[00015]

As described above, according to the present invention, 100
A magnetic field of about mG can be detected with an output of 10 to 100 mV or higher, and the sensitivity is 10 to 100 times higher than that of a conventional magnetic field detection element, so that extremely efficient detection of geomagnetism can be performed. Furthermore, it has many excellent effects such as nondestructive flaw detection, checking of environmental magnetic and magnetic shield effects, and application to various magnetic measurements in a steel plant.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a device of the present invention.

FIG. 2 is a magnetization curve of an amorphous magnetic film when an external magnetic field is not applied.

FIG. 3 is a magnetization curve of an amorphous magnetic film when an external magnetic field is applied.

FIG. 4 is a relationship diagram between the thickness of an amorphous magnetic film and the inductance.

FIG. 5 is a magnetic field detection characteristic diagram when the highest sensitivity is shown in the device using the minimum magnetic film magnetic core according to the present invention.

FIG. 6 is a magnetic field detection characteristic diagram showing the magnetic field detection characteristics under the sensor unit configuration conditions that show the highest sensitivity within the scope of the present invention.

[Explanation of symbols]

 1 Amorphous magnetic film magnetic core 2 Excitation coil 3 Detection coil 4 High frequency current source 5 Detection circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mineo Asada, 383 Takada, Toyama City, Toyama Prefecture, Toyama Prefectural Industrial Technology Center (72) Inventor, Katsumi Yano, 383, Takada, Toyama City, Toyama Prefecture Industrial Technology Center ( 72) Inventor Makoto Takashima 1-643 Kamikae-cho, Toyama City, Toyama Prefecture Eruko Co., Ltd. (72) Inventor Tetsuo Koshihama, 20 Ishigane, Toyama City, Toyama Prefecture

Claims (1)

[Claims] 1. An exciting coil wound around a magnetic core, a detecting coil wound in the same direction as the exciting coil, a high-frequency current source for supplying a sinusoidal high-frequency current to the exciting coil, and a voltage induced in the detecting coil. In a frequency doubler type magnetic field detection device equipped with a detection circuit for detecting a second harmonic component, a thickness of 1 to 3 μm,
A magnetic field detection device, characterized in that a saturable amorphous magnetic film, which is a cobalt-based thin film having an area of 50 to 150 mm ² and an initial permeability at an excitation frequency of 1500 or more, is used as a magnetic core.