JP7531889B2 - Magnetic Oscillation Sensor - Google Patents

Description

The present invention relates to a fluxgate type magnetic sensor that measures magnetic fields by utilizing the nonlinear magnetic properties of a probe or sensor part that includes a ferromagnetic core, and in particular, to measures to suppress magnetic flux leakage from a magnetic oscillation sensor, and to miniaturization and density of excitation coils, etc.

Conventional fluxgate magnetic sensors have often been used to measure magnetic fields in natural spaces, facilities, equipment, structures, various devices, and other spaces that are much larger than the shape of the magnetic sensor. However, because fluxgate magnetic sensors release magnetic flux leaking from the excitation coil to the outside, when measuring magnetic fields near the magnetic sensor, measures to protect the magnetic environment from the leakage flux of the excitation coil and measures to suppress electromagnetic interference caused by magnetic sensors being placed close to each other remain unsolved.

The magnetic detection device described in Patent Document 1 is known as a conventional technique for environmental conservation of the measured magnetic field. The magnetic detection device described in Patent Document 1 uses a parallel coil method to counteract the magnetic flux leaking from the excitation coil of the magnetic sensing unit to the outside, by arranging an air-core coil in parallel next to the excitation coil, as a measure to protect the measured magnetic field environment near the magnetic oscillation sensor.

Patent No. 5521143

The problem with this method of the magnetic detection device described in Patent Document 1 is that the need for two coils makes the magnetic sensing part larger, and the magnetic field space disturbed by the excitation magnetic field can only be minimized to a cubic space with a side length of 20 mm. To reduce the size below this, a new technology was needed to reduce the size of the magnetic oscillation sensor itself and suppress electromagnetic interference between magnetic sensors.

The present invention uses a magnetic oscillation sensor to solve common technical problems in fluxgate type magnetic sensors, namely, 1) suppression of leakage magnetic flux from the excitation coil, 2) suppression of electromagnetic interference, 3) environmental conservation of the measured magnetic field in the vicinity of the magnetic sensor, and 4) miniaturization and density of the excitation coil.

The first solution to the problem is:
A magnetically sensitive basic element for detecting magnetism is constituted by a saturable magnetic body that serves as a magnetic core, an excitation coil that is wound around the saturable magnetic body and generates an excitation magnetic field until the excitation magnetic field reaches each of the positive and negative magnetic saturation points of the saturable magnetic body, and a ring-shaped current circuit that is provided on both ends of the excitation coil and suppresses leakage magnetic flux of the excitation magnetic field emitted from both end faces of the excitation coil,
In the magnetically-sensitive basic element, a through hole into which the saturable magnetic body is inserted is provided at the center of each of the components of the exciting coil and the ring-shaped current circuit;
The annular current circuit is formed by stacking and integrating disc-shaped conductors in a laminated state,
The magnetic oscillation sensor is used as a means for solving the problem, in which a sensor circuit section that outputs an excitation current whose polarity is reversed every time the saturable magnetic material becomes magnetically saturated is connected to the excitation coil of the magnetically sensitive basic element to form a magnetic oscillation circuit. This solution is the basic technology that forms the basis of the present invention.

The second solution to the problem is:
a dense magnetic sensing unit including a saturable magnetic body that serves as a magnetic core, a plurality of excitation coils wound around the saturable magnetic body to generate an excitation magnetic field that reaches each of the positive and negative magnetic saturation points of the saturable magnetic body, and a plurality of annular current circuits that suppress leakage magnetic flux of the excitation magnetic field emitted from the end faces of the excitation coils , the annular current circuits being formed by stacking and integrating disk-shaped conductors in a laminated state, a through hole through which the saturable magnetic body is inserted is provided in the center of each of the components of the excitation coils and the annular current circuits, the dense magnetic sensing unit being configured by closely arranging the excitation coils and the annular current circuits alternately ,
A sensor circuit unit is connected to each excitation coil, and outputs an excitation current whose polarity reverses each time the saturable magnetic material becomes magnetically saturated. This allows a magnetic oscillation sensor having multiple magnetic oscillation circuits to be used as a solution.
By realizing such a dense configuration of excitation coils, it has become possible to increase the density of magnetic oscillation sensors, something that was not possible with conventional technology.

The third solution to the problem is:
The control signal output from the signal generator is transmitted to the sensor circuit section via a transmission circuit configured with a series circuit of a diode and a capacitor, thereby preventing unwanted noise from being mixed into the output of the sensor circuit section. This solution is also a comprehensive performance improvement means with the mission of minimizing noise mixed into the output voltage of multiple sensor circuits having magnetic detection information and improving magnetic detection resolution overall.

The present invention provides the following benefits: suppression of leakage flux from the excitation coil, suppression of electromagnetic interference, environmental protection of the measured magnetic field in the vicinity of the magnetic sensor, and miniaturization and density of the excitation coil.

1 is a diagram showing a magnetically-sensitive basic element and a sensor circuit portion that constitute a magnetic oscillation sensor according to an embodiment of the present invention; 2A and 2B are diagrams for explaining the operating principle of the magnetic oscillation sensor (magnetic oscillation circuit) shown in FIG. 1, in which (a) is a graph of the B-H curve of a saturable magnetic material when the magnetic oscillation circuit shown in FIG. 1 is operating, and (b) is an explanatory diagram showing the relationship of the output voltage waveform of an operational amplifier. FIG. 2 is a diagram showing an example of a component configuration of a circular current circuit of the magnetic oscillation sensor shown in FIG. 1 . 5A and 5B are diagrams for explaining the magnetic flux distribution of adjacent excitation coils. FIG. 2 is a diagram showing a magnetic sensing part composed of a plurality of magnetic sensing basic elements. 1 is a diagram showing a configuration of a dense magnetic oscillation sensor according to an embodiment of the present invention;

(Embodiment)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic oscillation sensor according to an embodiment of the present invention will be described with reference to the drawings.
When using a fluxgate magnetic sensor, if one side of the object to be measured is approximately the same as or shorter than the length of the excitation coil, there is a high risk of disturbing the magnetic field to be measured, so it was necessary to determine whether or not to use it by taking into account the magnetic field measurement environment, the distance to the object to be measured, the shape and dimensions of the magnetic sensor, the measurement method, etc.

The main reasons for this are that part of the magnetic field that excites the magnetic core is emitted into the surrounding area as electromagnetic waves, that the magnetic environment in the measurement magnetic field space can be disturbed in the vicinity of the fluxgate magnetic sensor, that the demagnetizing effect of the magnetic sensor works when measuring the residual magnetism of a small object, so the measured value is small, and that when multiple magnetic sensors are closely spaced to measure the magnetic field, electromagnetic interference occurs between them, resulting in unreliable measurement data. With conventional fluxgate magnetic sensors, the miniaturization and close-packing of the excitation coil in particular remained a technical challenge that was nearly impossible to put into practical use.

To prevent or suppress leakage magnetic flux, magnetic materials are usually used for magnetic shielding. However, once a magnetic material is exposed to a strong magnetic field, residual magnetism remains in the magnetic material to a greater or lesser extent. From the perspective of the magnetic sensor, the effect of this residual magnetism is always added to the true value of the measured magnetic field, resulting in inaccurate magnetic field measurements, so it can be said that magnetic materials are completely unsuitable for use as magnetic shields in magnetic oscillation sensors.

Figure 1 shows a magnetic oscillation sensor 1 for explaining the connection relationship between a magnetically sensitive basic element 100 and a sensor circuit section A according to an embodiment of the present invention, with the power supply section omitted. The sensor circuit section A is not an oscillator, so it does not oscillate on its own. However, when a variable inductance excitation coil 20 with a saturable magnetic material 10 as its magnetic core is connected to the sensor circuit section A, a magnetic oscillation circuit (magnetic oscillation sensor 1) capable of magnetic detection is formed, and a magnetic oscillation phenomenon appears.

The magnetically sensitive basic element 100 has a saturable magnetic material 10 as a magnetic core, an excitation coil 20 wound in a manner that passes through the center, and a ring-shaped current circuit 30 having a through hole in the center at both ends of the excitation coil 20.
The saturable magnetic body 10 is made of a saturable magnetic material having high magnetic permeability and small coercive force, thereby stabilizing magnetic oscillation and improving magnetic detection sensitivity.
The saturable magnetic material 10 is magnetized from the positive magnetic saturation point through a magnetic unsaturated region to the negative magnetic saturation point by an excitation magnetic field created by an alternating excitation current flowing into the excitation coil 20, and at the moment of reaching the negative magnetic saturation point, the polarity of the excitation current is reversed, and the material is then excited from the negative magnetic saturation point through the magnetic unsaturated region toward the positive magnetic saturation point.

When the polarity of the excitation current is periodically reversed in this manner, the inductance value of the excitation coil 20 also changes from small (positive magnetic saturation point) - large (when passing through the magnetic unsaturated region) - small (negative magnetic saturation point) - large (when passing through the magnetic unsaturated region) with the positive or negative magnetic saturation point of the saturable magnetic body 10 as the boundary, and naturally, the absolute value of the voltage between terminals 21, 22 of the excitation coil 20 also changes from small - large - small - large in the same way as the inductance changes.
The absolute value of the voltage between terminals 21, 22 of excitation coil 20 is smallest at the timing of this positive and negative magnetic saturation, so if the moment when the voltage becomes small is detected by operational amplifier 40 as a reversal switching signal for the excitation current, the polarity of the output voltage and excitation current can be reversed at the timing of magnetic saturation.

FIG. 2 is an explanatory diagram showing the relationship between the BH curve of the saturable magnetic body 10 and the output voltage waveform of the operational amplifier 40 when the magnetic oscillation circuit (magnetic oscillation sensor 1) of FIG. 1 is in operation.
First, a case where no external magnetic field Hex is applied to the saturable magnetic body 10 will be described.
When the square wave voltage output from the output terminal 42 of the operational amplifier 40 shown in FIG. 1 is applied to the excitation coil 20, the saturable magnetic material 10 returns to its original position on the BH curve via the path P11-P12 (positive magnetic saturation point)-P13-P14 (negative magnetic saturation point)-P11, as shown in FIG. 2(a).
The time required to reach the positive magnetic saturation point P12 from P11 and the time required to reach the negative magnetic saturation point P14 from P13 are the same due to the symmetry of the BH characteristics. At this time, the output voltage waveform of the operational amplifier 40 becomes a voltage waveform in which the positive and negative half cycles have the same period length, as shown in the upper part of Figure 2(b), and the average value is zero.

However, when an external magnetic field Hex is applied to the saturable magnetic material 10, the original operating reference positions P11 and P13 on the BH curve are biased by the amount of Hex and move to positions P21 and P23. When a square wave voltage is applied in this state, the BH curve returns to the original position from the biased point P21 via the path P21-P22 (positive magnetic saturation point)-P23-P24 (negative magnetic saturation point)-P21.

As a result, the duty ratio of the output voltage waveform of the operational amplifier 40 changes due to the external magnetic field Hex, as shown in the lower waveform of Figure 2 (b), resulting in a difference in the duration of each positive and negative half cycle. Since this duration difference is caused by the external magnetic field Hex, by averaging the output voltage of the operational amplifier 40 in the low-pass filter 44 (see Figure 1) and inverting the polarity of the average voltage, information corresponding to the strength and polarity of the external magnetic field can be obtained.

An inversion reference voltage for comparison is required to identify the polarity reversal of the output voltage of the operational amplifier 40 shown in Fig. 1. The magnetic saturation point of the saturable magnetic body 10 is the moment when the absolute value of the voltage between the terminals 21 and 22 of the exciting coil 20 becomes the minimum voltage, so this voltage must be input in advance to the inversion terminal of the operational amplifier as an inversion reference voltage from a magnetically unsaturated state.
For this purpose, it is necessary to adjust the divided voltage at the voltage dividing terminal 43 when the output voltage of the operational amplifier 40 is divided by the resistor R2 and the variable resistor VR so that it coincides with the inverted reference voltage by the variable resistor VR. Then, this inverted reference voltage is input in advance to the inverted input terminal of the operational amplifier 40 via the resistor R3, and the timing of reversal is continuously monitored while comparing the magnitude relationship between this inverted reference voltage and the fluctuating voltage of the exciting coil 20 input to the non-inverted terminal.
Naturally, the polarity of the inverted reference voltage obtained by dividing the output voltage of the operational amplifier 40 is always the same as the output voltage of the operational amplifier 40, so that every time the polarity of the output voltage of the operational amplifier 40 is inverted, the polarity of the inverted reference voltage is also inverted in the same manner.

In this way, the external magnetic field applied to the saturable magnetic material directly below the excitation coil 20 is detected from the change in duty ratio of the output voltage waveform of the operational amplifier 40 caused by the external magnetic field Hex, and the strength and direction of the external magnetic field are converted into a voltage and its polarity, making it possible to obtain external magnetic field information from the output voltage of the sensor circuit section A.
Incidentally, although a normal wire-wound coil cannot measure a DC magnetic field, it can detect an AC magnetic field. In a wire-wound coil, a magnetic material with high magnetic permeability is used for the magnetic core of the coil to make it small and increase the inductance value. The excitation process region used with this magnetic material is the magnetic unsaturation region where the permeability value does not change much, and the AC magnetic field to be detected is also in the high frequency band from around 5 Hz onwards.

Generally speaking, wound coils are inductor components that are often used as linear components with a large inductance whose value hardly changes. Due to the magnetization characteristics of wound coils, they cannot normally be used in the magnetic saturation region. Needless to say, it is impossible to send a switching signal that reverses the current flowing through the wound coil from the magnetization state of the winding coil itself, and there is absolutely no need for this in terms of the intended use of the winding coil itself.

However, in the magnetized region of the excitation coil 20 in this embodiment, the excitation period of the entire magnetized region from the positive magnetic saturation region through the magnetic unsaturation region to the negative magnetic saturation region is utilized, and magnetic detection is performed by repeating this excitation period. There are no ordinary winding coils that utilize such a phenomenon, and there is a technical difference between the present invention and magnetic field measurement using ordinary winding coils that can be said to be polar opposites.
The excitation coil 20 in the magnetic oscillation sensor 1 has a different operating range and magnetization characteristics from those of a normal wire-wound coil, and the present invention utilizes the nonlinear characteristics that are a problem with normal wire-wound coils as its greatest advantage.

Next, it will be explained that the circular current circuit 30, which is one of the components of the magnetic sensing basic element 100, plays an important role.
The first purpose of adopting the circular current circuit is to block or suppress the magnetic flux of the excitation magnetic field emitted from the excitation coil 20 to the outside with the circular current circuit 30 of the conductor arranged on both ends of the excitation coil 20, so that the magnetic field generated by the magnetized body to be measured can be measured with high accuracy while preserving the natural magnetic field environment, without disturbing the magnetic field space formed by the magnetized body to be measured as much as possible. As a result, it has become possible to preserve the magnetic field environment and to make the sensor smaller and more densely packed.

To accurately describe the circular current circuit 30 of this embodiment, it is a conductor that has a hole near the center through which a saturable magnetic material passes, and which forms an electrically short-circuited closed circuit with no open circuits.
The looped current circuit 30 is made of a hollow non-magnetic conductor. When the looped current circuit 30 is placed in close contact with the end face of the excitation coil 20 so as to efficiently capture the magnetic flux of the excitation magnetic field emitted from the excitation coil 20, the looped current circuit 30 is electromagnetically coupled closely with the magnetic flux emitted from the excitation coil 20, and an induced current is generated in the looped current circuit.
When this induced current flows through the circular current circuit 30 , which is a ring-shaped closed circuit, the newly generated magnetic field blocks or suppresses the magnetic flux emitted from the exciting coil 20 .
The material of the circular current circuit 30 is preferably a conductor having a low resistance value, such as copper or aluminum.

FIG. 3 shows an example of the component configuration of the circular current circuit 30.
In the figure, 30a is an example of a circular current circuit 30 configured as an assembly of multiple independent disc-shaped conductors, in which a circular current circuit 30 using a disc-shaped conductor flows, and in which an induced current generated by the magnetic flux emitted from the excitation coil 20 flows. When actually incorporating it into a magnetic sensing unit, each disc-shaped conductor is stacked and used as an integrated circular current circuit.
In order to make the direction of the current flowing in the circular current circuit 30 as parallel and uniform as possible, in other words, to make the circuit through which the induced current generated by the magnetic flux emitted from the excitation coil 20 flows function as a collection of multiple distributed and independent circuits, it is also possible to electrically separate and independent each disk-shaped conductor by providing an insulating layer between each disk-shaped conductor or by using a disk-shaped conductor coated with an insulator.

Reference numeral 30b denotes a tape-shaped conductor that is wound and overlapped, and it is also possible to configure a plurality of such wound conductors by closely arranging them in the axial direction.
Reference numeral 30c denotes a rod-shaped conductor having a hole in the center through which a saturable magnetic body passes. In this configuration, it is also possible to combine thin pipes with different diameters to form a multiple pipe configuration.

The shape of the circular current circuit is not limited to the example, and may be any shape suitable for the purpose. In addition, the conductor portion (lead wire) of the circular current circuit 30 shown in Figure 3 can be configured as the terminals 210, 220 of the exciting coil 20 of the magnetically sensitive basic element 100 as shown by the dashed lines.
Both are structurally very simple, but through the present invention, they are technologies that have provided a clue to simultaneously suppressing the electromagnetic induction phenomenon between spatially adjacent magnetic sensing basic elements 100, and solving the various issues of miniaturization and density of the magnetic sensing basic elements 100 themselves.

A second purpose of using the loop current circuit 30 is to suppress the demagnetizing effect caused by the magnetic flux emitted from the end face of the exciting coil 20 .
In particular, residual magnetism remaining in small objects is often a weak magnetism of several tens of mG or less, and when a conventional fluxgate sensor is brought close to the object to be measured, the alternating magnetic flux emitted from the sensor demagnetizes the residual magnetism of the object to be measured, to the point where it becomes impossible to reproduce the original residual magnetism that existed before the measurement, which is a fatal problem in magnetic measurement. This phenomenon was a common unsolved technical issue for all conventional fluxgate type magnetic sensors.
However, in the magnetic oscillation sensor 1 according to the embodiment of the present invention, this problem is solved by bringing the circular current circuit 30 made of a conductor having a disk shape or the like as close as possible to the end face of the excitation coil 20, so that the AC magnetic flux emitted from the end face of the excitation coil 20 is suppressed by the circular current circuit 30, making it possible to measure the residual magnetism possessed by the object to be measured as it is, without demagnetizing the residual magnetism of the object to be measured.

Next, the function of the sensor circuit portion A will be described.
It has a function of supplying an AC excitation current to the excitation coil 20 shown in Figure 1 to excite the saturable magnetic material 10, a function of identifying the timing of polarity reversal of the excitation current, and a function of outputting information about the external magnetic field Hex applied to the saturable magnetic material 10 as a voltage.
The components are an operational amplifier 40, resistors R1, R2, R3, and R4, a variable resistor VR, and a low-pass filter 44.
The output voltage of the operational amplifier 40 is divided by the terminal voltage of resistor R1 and the exciting coil 20, and the voltage of the exciting coil 20 at the divided terminal 41 (terminal 22) is input to the non-inverting input terminal of the operational amplifier 40 via resistor R4 as a voltage that varies greatly due to the inductance change in the magnetization process of the exciting coil 20. The absolute value of this voltage changes and becomes a minimum each time the magnetic saturation point is reached. The voltage of the exciting coil 20 at the non-inverting input terminal when magnetically saturated also coincides with the reference voltage value of the inversion timing at the inverting input terminal side described later.

On the other hand, an inverting reference voltage is required on the inverting input terminal side of the operational amplifier 40 to identify the timing for reversing the excitation current, and this voltage is set by dividing the output voltage of the operational amplifier 40 using resistor R2 and variable resistor VR, which are separate circuits that are not affected by changes in the voltage of the excitation coil 20.
Specifically, since this inversion reference voltage value is used to identify the magnitude relationship with the minimum voltage value at the timing when the absolute value of the voltage between the terminals 21 and 22 of the exciting coil 20 is smallest, the inversion reference voltage value is set by adjusting the divided voltage, obtained by dividing the output voltage of the operational amplifier 40 by resistor R2 and variable resistor VR, with variable resistor VR so that it coincides with the minimum voltage value. The adjusted divided voltage is input as an inversion reference voltage from voltage dividing terminal 43 through resistor R3 to the inverting terminal of the operational amplifier 40. The time when this inversion reference voltage and the exciting coil voltage input to the non-inverting terminal become equal becomes the timing for reversing the exciting current, and the polarity of the exciting current is automatically reversed.

FIG. 4 shows the distribution of the exciting magnetic field when exciting coils 20 are arranged adjacent to the saturable magnetic body 10. As shown in FIG.
In Fig. 4(a), when excitation currents flow from the respective operational amplifiers 40 (see Fig. 1) into the excitation coils 20a and 20b, leakage magnetic fluxes emitted to the outside from the excitation coils 20a and 20b overlap considerably near the end faces of the adjacent excitation coils 20a and 20b, and a complex electromagnetic coupling state occurs between the two excitation coils 20a and 20b. Note that in Fig. 4(a), the winding state of the excitation coils 20a and 20b is omitted.
As a result, the voltage of each exciting coil 20a, 20b is disturbed, affecting the time to reach the saturation point of the magnetic oscillation sensor, disturbing and making the oscillation frequency of the magnetic oscillation circuit unstable, and finally causing noise and errors in the magnetic detection voltage.

As a measure to prevent this phenomenon, in this embodiment, as shown in Fig. 4(b), a looped current circuit 30 is placed between the exciting coils 20. In this way, the magnetic field formed by the induced current generated in the looped current circuit 30 cancels the leakage magnetic flux of the exciting magnetic field, making it possible to prevent unnecessary electromagnetic coupling.
Figure 4 (b) shows that when the circular current circuit 30 is inserted between the excitation coils, the magnetic field distribution area of the excitation magnetic field becomes smaller. By closely contacting each excitation coil 20 with the circular current circuit 30, the electromagnetic induction between adjacent excitation coils 20 is suppressed, making it possible to configure a dense magnetic sensing section. In other words, the magnetic field space occupied by each excitation coil itself is reduced, and each excitation coil 20 can measure the magnetic field within its own occupied space with high accuracy and sensitivity.

5 shows a magnetic sensing section 1000 composed of a plurality of magnetically-sensing basic elements 100. The magnetically-sensing section 1000 is an example of an assembly of magnetically-sensing basic elements in which the saturable magnetic body 10 of the magnetically-sensing basic element 100 is elongated, and a plurality of exciting coils 20 and a ring-shaped current circuit 30 formed by stacking a plurality of disk-shaped conductors are alternately arranged and densely packed. In the example shown in the figure, the ring-shaped current circuits 30 of the magnetically-sensing basic elements 100 are in close contact with each other when densely packed, so it is also possible to omit the ring-shaped current circuit 30 on one side of the magnetically-sensing basic element 100 to achieve dense packing.
6, by connecting the sensor circuit sections A1 to An and the control circuit section 70 to the magnetic sensing section 1000, a so-called dense magnetic oscillation sensor 2 is constructed.

The function of the cylindrical support 60 incorporating the saturable magnetic material 10 is to protect the saturable magnetic material 10 so that its magnetic properties do not change due to external stress, and to support the weight of the circular current circuits 300 to 300+n and the exciting coils 201 to 200+n. A non-magnetic, non-metallic insulator is used for the support 60.
6 shows an example of a linear magnetic sensing part 1000, but the magnetic sensing part 1000 is not limited to a bent, curved, etc. It is also possible to change the shape according to the magnetic field components to be measured, and the magnetic field measurement can be performed in response to the environmental conditions of the magnetic field measurement.
FIG. 6 shows an example of the configuration of a dense magnetic oscillation sensor 2 as a composite body in which the magnetic sensing part 1000 shown in FIG. 5 and the sensor circuit parts A1 to An are combined and connected.

Here, the dense magnetic oscillation sensor 2 will be described in detail with reference to FIG.
The dense magnetic sensing part 2000 (magnetic sensing part 1000) is configured by alternately passing n exciting coils 201 to 200+n and n+1 circular current circuits 300 to 300+n through a single elongated saturable magnetic body 10. n is an integer (n≧2).
The circular current circuits 300, 300+n at both ends of the dense magnetic oscillation sensor 2 may be omitted on one side or both sides depending on the purpose of the magnetic field measurement.

In the dense magnetic sensor 2000, each magnetic sensor basic element 101-100+n is connected to a sensor circuit A1-An consisting of resistors R1, R2, R3, R4, a variable resistor VR, and a low-pass filter 44 attached to an operational amplifier 40, and each individually constitutes a magnetic oscillation circuit (magnetic oscillation sensor 1 (see Figure 1)). The low-pass filter 44 averages the oscillation voltage output from the output terminal 42 of the operational amplifier 40, converts information about the strength and polarity of the magnetic field into a voltage, and the magnetic information detected by each magnetic oscillation circuit is individually and simultaneously output from the output terminals E1-En.

In the figure, reference numeral 70 denotes a control circuit section, which controls the non-uniformity of the oscillation frequencies of the magnetic oscillation circuits to prevent unwanted noise from being mixed into the outputs of the sensor circuits A1 to An.
The control circuit section 70 is composed of a signal generator, a diode, and a capacitor.
A control signal is output from a signal generator OSC, which outputs a voltage waveform such as a square wave or a pulse waveform, and is transmitted to each of the sensor circuit sections A1 to An via a plurality of (here, n) transmission circuits L1 to Ln, each of which is composed of a series circuit of diodes D1 to Dn and capacitors C1 to Cn.
Specifically, capacitors C1 to Cn are connected in series to the other end terminals of diodes D1 to Dn, respectively, and a control signal for controlling the oscillation frequency is output from the other terminal of each capacitor (output terminals S1 to Sn of transmission circuits L1 to Ln) to the inverting input terminal of each operational amplifier 40 in the sensor circuit sections A1 to An.

There is an optimum range for the voltage of the control signal output from the control circuit section 70. If the voltage of the control signal is too high, the oscillation waveform of the magnetic oscillation circuit will almost match the frequency and phase of the signal generator, causing a very small change in the duty ratio of the output waveform of the operational amplifier due to an external magnetic field, resulting in a significant decrease in magnetic detection performance.
On the other hand, if the voltage of the control signal is too low, the oscillation frequencies of the magnetic oscillation circuits cannot be unified and will remain uneven, resulting in output voltages containing a lot of noise at the terminal voltages of the output terminals E1 to En of the sensor circuit parts A1 to An. The same is true for increasing or decreasing the capacitance of the capacitor.
Therefore, it is necessary to find an optimum value by adjusting the voltage value of the control signal and selecting the capacitance of the capacitor so that the coupling between the control circuit section 70 and the sensor circuit sections A1 to An is loosely coupled.
As a transmission circuit other than that shown in the figure, it is also possible to configure a transmission circuit by replacing the diode with a resistor.

The features of the dense magnetic oscillation sensor 2 are:
By constructing a magnetic sensing unit 1000 by attaching multiple excitation coils 201 to 200+n and circular current circuits 300 to 300+n to a single, elongated saturable magnetic body 10, the magnetic sensing basic elements 1000 are closely packed together, thereby increasing the density of magnetic field measurement points.
By increasing the density of the magnetic oscillation sensors per unit length, it has become possible to measure the magnetic field in a small space using a plurality of magnetic oscillation sensors 1 (see FIG. 1) while maintaining high spatial resolution.
Numerically, the length of a conventional magnetic core is at least about 20 mm, and the length of the exciting coil 20 is also of approximately the same dimension, so the magnetic field space could be minimized to about 20 mm cubic.
However, it has been confirmed that in the dense magnetic oscillation sensor of the present invention, magnetic detection can be performed normally even if the length of the exciting coil wound around the saturable magnetic material is reduced to 2 mm.

In other words, it was confirmed that the spatial resolution performance was improved by about 10 times compared to the conventional method. In addition, it became possible to manufacture a linear magnetic sensing part in which 10 magnetically sensitive basic elements 101-110, including the circular current circuits 300-310, are densely arranged in a section of the saturable magnetic body 10 having a length of 60 mm.
In other words, the intervals between the excitation coils 201 to 200+n can be narrowed, making it possible to increase the density of measurement points and ensure the simultaneity of data. For example, when the magnetic field in the measurement target space fluctuates violently, the simultaneity of measurement data becomes an issue. Even in this case, by using the dense magnetic oscillation sensor of the present invention, the spatial resolution of the measurement magnetic field space can be increased and the simultaneity of measurement data can be ensured by simultaneously measuring the measurement magnetic field space divided into multiple parts.

The present invention can be suitably used for measuring magnetic fields in small magnetic spaces by increasing the density of magnetic measurement points.

1 Magnetic oscillation sensor 2 Dense magnetic oscillation sensor 10 Saturable magnetic material
20, 201 to 200+n Excitation coil 21, 22, 210, 220 Terminal 30, 300 to 300+n Ring-shaped current circuit 40 Operational amplifier 41 Divided terminal 42 Output terminal 43 Voltage dividing terminal 44 Low-pass filter 60 Support 70 Control circuit section 100, 101 to 100+n Magnetic sensing basic element 1000 Magnetic sensing section 2000 Dense magnetic sensing section A, A1 to An Sensor circuit section C1 to Cn Capacitors D1 to Dn Diodes E, E1 to En Output terminals of sensor circuit section L1 to Ln Transmission circuit OSC Signal generator R1, R2, R3, R4 Resistors S1 to Sn Output terminals of transmission circuit VR Variable resistor

Claims (3)

A magnetically sensitive basic element for detecting magnetism is constituted by a saturable magnetic body that serves as a magnetic core, an excitation coil that is wound around the saturable magnetic body and generates an excitation magnetic field until the excitation magnetic field reaches each of the positive and negative magnetic saturation points of the saturable magnetic body, and a ring-shaped current circuit that is provided on both ends of the excitation coil and suppresses leakage magnetic flux of the excitation magnetic field emitted from both end faces of the excitation coil,
In the magnetically-sensitive basic element, a through hole into which the saturable magnetic body is inserted is provided at the center of each of the components of the exciting coil and the ring-shaped current circuit;
The annular current circuit is formed by stacking and integrating disc-shaped conductors in a laminated state,
The magnetic oscillation sensor has a magnetic oscillation circuit formed by connecting a sensor circuit section that outputs an excitation current whose polarity is reversed every time the saturable magnetic body becomes magnetically saturated to an excitation coil of the magnetically sensitive basic element. a dense magnetic sensing unit including a saturable magnetic body that serves as a magnetic core, a plurality of excitation coils wound around the saturable magnetic body to generate an excitation magnetic field that reaches each of the positive and negative magnetic saturation points of the saturable magnetic body, and a plurality of annular current circuits that suppress leakage magnetic flux of the excitation magnetic field emitted from the end faces of the excitation coils , the annular current circuits being formed by stacking and integrating disk-shaped conductors in a laminated state, a through hole through which the saturable magnetic body is inserted is provided in the center of each of the components of the excitation coils and the annular current circuits, the dense magnetic sensing unit being configured by closely arranging the excitation coils and the annular current circuits alternately ,
A magnetic oscillation sensor in which multiple magnetic oscillation circuits are formed by connecting each of the excitation coils to a sensor circuit unit that outputs an excitation current whose polarity reverses each time the saturable magnetic material becomes magnetically saturated. 3. A magnetic oscillation sensor as described in claim 2, wherein a control signal output from a signal generator is transmitted to the sensor circuit section via a transmission circuit composed of a series circuit of a diode and a capacitor , thereby preventing unnecessary noise from being mixed into the output of the sensor circuit section .

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