JP2000065908A - Magnetic sensor and magnetic detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sensor capable of having an excellent linearity as against the magnetic field intensity of a detected output, decreasing the temperature dependency of a magnetic field detection sensitivity, and to provide a magnetic detection system capable of realizing magnetic field detecting circuit configuration simply. SOLUTION: A magnetic sensor 2 is provided with a magnet 23 which does not invert poles against an external magnetic field, and a piezoelectric element 21 which detects a magnetic field intensity applied to the magnet 23 as dynamic force. As a magnet 23, a rare earth cobalt magnet is used. As a piezoelectric element 21, a crystal is used. And this magnetic detection system 1 is provided with the magnetic sensor 2, an oscillation circuit 31A whose oscillation frequency varies according to dynamic force applied to the piezoelectric element 21 of the magnetic sensor 2, and a displaying means (a display circuit) 38 which measures the change of the oscillation frequency of the oscillation circuit 31A and displays a magnetic field intensity detected by the magnetic sensor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor for detecting the intensity of a magnetic field and a magnetic detection system provided with the magnetic sensor. In particular, the present invention relates to a magnetic sensor having excellent detection sensitivity and a magnetic field detection circuit having the magnetic sensor. The present invention relates to a magnetic field detection system that can be easily realized.

[0002]

2. Description of the Related Art A magnetic sensor (gauss meter) composed of a Hall element is generally used for detecting a magnetic field intensity. The Hall element is formed of a semiconductor thin plate. When a bias current is applied to the semiconductor thin plate, an output depending on an external magnetic field applied to the semiconductor thin plate can be obtained. That is, when a current flows through a semiconductor thin plate and an external magnetic field is applied in a direction perpendicular to the current direction, the Hall element generates a Hall electromotive force in a direction perpendicular to both the current direction and the external magnetic field direction by Lorentz force.

[0003]

In the magnetic sensor composed of the above-mentioned Hall element, no consideration is given to the following points.

(1) Since the magnetic sensor utilizes the Hall effect, it exhibits semiconductor-like behavior with respect to temperature. That is, the Hall element itself has temperature dependency. For this reason, the magnetic field detection sensitivity of the magnetic sensor changes according to the change in the environmental temperature.

(2) In order to correct the temperature dependency of the Hall element, a temperature compensation circuit is required in a magnetic detection system including a magnetic sensor. Since the temperature compensation circuit has a complicated circuit configuration and a relatively large circuit scale, the magnetic detection system becomes complicated and large.

(3) In the Hall element, a range in which the Hall electromotive force has linearity with respect to an external magnetic field (linear region)
Is narrow. Specifically, linearity is lost when the magnetic flux density of the external magnetic field is about 2 Tesla. For this reason, the detection range of the external magnetic field by the magnetic sensor is limited to a narrow range.

(4) In the magnetic detection system, a constant current generating circuit for supplying a constant current to the Hall element,
Further, a synchronous detection circuit or the like for detecting a small Hall electromotive force as a signal is essential. For this reason, especially the measurement circuit system of the magnetic detection system becomes complicated and large. Further, the complicated circuit configuration increases the manufacturing cost of the magnetic detection system.

The present invention has been made to solve the above problems. Therefore, an object of the present invention is to provide a magnetic sensor capable of improving the linearity of the detection sensitivity with respect to the magnetic field strength while reducing the temperature dependence of the magnetic field detection sensitivity.

It is a further object of the present invention to provide a magnetic sensor capable of improving the linearity of the detection sensitivity with respect to the magnetic field strength while reducing the temperature dependence of the magnetic field detection sensitivity.
Another object of the present invention is to provide a magnetic detection system that can easily realize a magnetic field detection circuit configuration.

In particular, an object of the present invention is to provide a magnetic detection system capable of realizing the miniaturization of the whole system and further reducing the manufacturing cost by simply realizing the configuration of the magnetic field detection circuit.

[0011]

Means for Solving the Problems In order to solve the above problems, a first feature of the present invention is to detect a magnet which does not pole-reverse with respect to an external magnetic field and a magnetic field strength applied to the magnet as a mechanical force. That is, the magnetic sensor includes a piezoelectric element.

As the magnet, a compound of a rare earth metal and an iron group transition metal, more specifically, a rare earth cobalt magnet which is a ferromagnetic metal having high saturation magnetization and high crystal magnetic anisotropy, particularly, samarium cobalt (SmCo) ₅ or Sm ₂ Co ₁₇ ) is preferably used.

It is preferable to use quartz for the piezoelectric element. Further, the piezoelectric element includes a lanthanum tantalum gallium oxide (La ₃ Ga _5.5 Ta _0.5 O ₁₄ ) single crystal, a lanthanum gallium silicon oxide (La ₃ Ga ₅ SiO ₁₄ ) single crystal, and a lanthanum niobium gallium oxide. (La ₃ Ga _5.5 Nb _0.5 O ₁₄ ) single crystal can be used practically.

In the magnetic sensor thus configured, when the external magnetic field H acts on the magnet having the magnetic moment M, the outer product (H × H) of the magnetic moment M and the external magnetic field H is obtained.
M) A torque T acting on the axis acts. When the intensity of the external magnetic field H increases, the torque T, which is a mechanical force, increases. The torque T generated by the magnet generates a stress (torsional stress) on the piezoelectric element, and the external magnetic field H is converted into the stress.

A second feature of the present invention is that a magnetic sensor includes a magnet that does not pole-reverse with respect to an external magnetic field, and a piezoelectric element that detects a magnetic field strength applied to the magnet as a mechanical force.
An oscillation circuit whose oscillation frequency changes according to a mechanical force applied to the piezoelectric element of the magnetic sensor, and means for measuring the change in the oscillation frequency of the oscillation circuit and displaying the magnetic field strength detected by the magnetic sensor It is a magnetic detection system. As a piezoelectric element used in this magnetic detection system,
It is preferable to select a material having a small temperature dependence of the detection sensitivity and a relatively wide linear proportional range (linear range) between the amount of change in the external magnetic field and the amount of strain. As such a piezoelectric element,
Quartz is preferred. This is because the coefficient of thermal expansion of quartz is extremely small, and the error in quartz oscillation is extremely stable in the range of 10 ^-6 to 10 ^-7 . Further, when the magnetic flux density of the external magnetic field H is in the range of 1 Tesla to 10 Tesla, there is a linear proportional range between the amount of change in the external magnetic field and the amount of distortion. Therefore, it is possible to realize a magnetic sensor capable of improving the linearity of the detection output with respect to the magnetic field strength while reducing the temperature dependency of the detection output.

In the magnetic detection system configured as described above, in addition to the effects obtained by the first feature,
The strength of the magnetic field applied to the magnet of the magnetic sensor is detected as a mechanical force by a piezoelectric element, and the oscillation frequency of the oscillation circuit is changed based on the mechanical force detected by the piezoelectric element, and the change in the oscillation frequency is measured. In addition, the magnetic field intensity by the magnetic sensor can be displayed. Since the magnetic field strength can be measured by a simple method of measuring a change in the oscillation frequency of the oscillation circuit, the configuration of the magnetic field detection circuit can be easily realized. As described above, the magnetic field detection circuit configuration can be easily realized,
The size of the magnetic detection system can be reduced, and the manufacturing cost of the magnetic detection system can be reduced.

In particular, a position separated from the magnet on the piezoelectric element,
That is, it is preferable to further arrange a non-magnetic metal electrode at a position that is not affected by the stress due to the torque of the magnet. If the oscillation frequency of the oscillation circuit formed by the non-magnetic metal electrode is used as a reference frequency and a change in the oscillation frequency due to the strength of the magnetic field applied to the magnet is measured, more accurate measurement is possible.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a magnetic detection system including a magnetic sensor according to an embodiment of the present invention.
FIG. 3 is a perspective view of a magnetic sensor.

As shown in FIGS. 1 and 2, the magnetic sensor 2 according to the embodiment of the present invention has at least a magnet 23 which does not pole-reverse with respect to an external magnetic field, and a magnetic field strength applied to the magnet 23, A piezoelectric element 21 for detecting as a force. The piezoelectric element 21 has a feature that the temperature sensitivity of the detection sensitivity is small, and a material having a relatively wide linear proportional range (linear range) between the amount of change in the external magnetic field and the amount of strain may be selected. For example, it is preferable to use a quartz (quartz) formed in a disk shape as the piezoelectric element 21. Quartz has a very low coefficient of thermal expansion, and the error range of quartz oscillation is 10 ^-6 to 10 ^-7
It is extremely stable. Further, the quartz has a linear proportional range between the amount of change in the external magnetic field and the amount of distortion when the magnetic flux density of the external magnetic field is in the range of 1 Tesla to 10 Tesla. Further, in the magnetic sensor 2 according to the embodiment of the present invention, the non-magnetic metal 24 is disposed on the surface of the piezoelectric element 21 at a position separated from the magnet 23 and in a region which is not affected by the stress due to the torque of the magnet 23. Have been.

The magnet 23 is disposed on the surface of the piezoelectric element 21 in a rectangular parallelepiped shape having an N pole on one side and an S pole on the other side. As the magnet 23, a compound of a rare earth metal and an iron group transition metal, more specifically, a rare earth cobalt magnet which is a ferromagnetic metal having high saturation magnetization and high crystal magnetic anisotropy can be practically used. Samarium-cobalt (SmCo ₅ or Sm ₂ Co ₁₇ ) can be practically used as the rare earth cobalt magnet. Samarium / cobalt is directly formed on the surface of the piezoelectric element 21 by, for example, a sputtering method so that the easy axis direction is present in the surface of the piezoelectric element 21, and is magnetized after the film formation. Note that the magnet 23 is also used as an electrode of a quartz oscillator that constitutes the oscillation circuit 31A. Therefore, FIG.
As shown in FIG. 7, a lead wire 25 is connected to the magnet 23. The nonmagnetic metal 24 is formed of, for example, copper (Cu) formed by a sputtering method in a rectangular parallelepiped shape having the same dimensions as the magnet 23, and also functions as an electrode of the crystal resonator. Therefore, the oscillation circuit 31 is also provided in the non-magnetic metal 24.
Lead wiring 25 for constructing B is connected.
A back electrode 22 of a quartz oscillator is provided on the back surface of the piezoelectric element 21, and a lead wire is connected to the magnet 23 (not shown in FIG. 2) in the same manner as a lead wire 25 connected to the non-magnetic metal 24. , And oscillation circuits 31A and 31B.

As shown in FIG. 1, the magnetic detection system 1 of the present invention comprises an oscillation circuit 31A whose oscillation frequency changes according to the above-mentioned magnetic sensor 2 and a mechanical force applied to the piezoelectric element 21 of the magnetic sensor 2. And a plurality of circuits for measuring a change in the oscillation frequency of the oscillation circuit 31A and displaying the magnetic field strength detected by the magnetic sensor 2. Oscillation circuit 31A
Is constructed by arranging the magnet 23 of the magnetic sensor 2, the piezoelectric element 21, and the CMOS inverter circuit 32 </ b> A in the feedback path, and has a predetermined oscillation frequency corresponding to the stress applied to the piezoelectric element 21, that is, the external magnetic field applied to the magnet 23. Is output from the CMOS inverter circuit 32A. Further, the non-magnetic metal 24 is disposed on the piezoelectric element 21 as described above, and the non-magnetic metal 2
4. An oscillation circuit 31B in which the piezoelectric element 21 and the CMOS inverter circuit 32B are arranged in the feedback path is provided. Since no torque is generated even when an external magnetic field is applied to the non-magnetic metal 24, the oscillation circuit 31B including the non-magnetic metal 24 and the piezoelectric element 21 in the feedback path always operates at the oscillation frequency where the external magnetic field is zero. It is the reference frequency at which it operates.

The plurality of circuits constituting the magnetic detection system 1 include a counter circuit 33A, 33B, a subtraction circuit 34, a compensation circuit 35, a calibration coefficient generation circuit 36, a multiplication circuit 37, and a display device 38. The counter circuit 33A counts the number of pulses per unit time output from the oscillation circuit 31A. Similarly, the counter circuit 33B includes the oscillation circuit 3
The number of pulses per unit time output from 1B is counted. The subtraction circuit 34 calculates a difference between the number of pulses counted by the counter circuit 33A and the number of pulses counted by the counter circuit 33B.

When the external magnetic field is zero, the oscillation circuits 31A, 31A
B, the number of pulses output from each of them is the same, and the subtraction output of the subtraction circuit 34 should be zero.
There is a difference in the number of pulses output from both sides due to variations in the thickness of the two. The compensation circuit 35 compensates for such a difference in the number of pulses, and makes the output when the external magnetic field is zero (the output from the compensation circuit 35) zero. The calibration coefficient generation circuit 36 outputs a calibration coefficient for displaying the output from the compensation circuit 35 as a value of the external magnetic field. The multiplication circuit 37 multiplies the output from the compensation circuit 35 by the calibration coefficient from the calibration coefficient generation circuit 36. The display circuit 38 displays the value of the external magnetic field detected by the magnetic sensor 2 based on the output from the multiplication circuit 37.

Next, the magnetic detection operation of the magnetic sensor 2 and the magnetic detection system 1 will be described.

As shown in FIG. 3, the magnet 2 of the magnetic sensor 2
When the external magnetic field H acts on 3, a torque acts on the axis of the direction of the outer product (H × M) of the magnetic moment M of the magnet 23 and the external magnetic field H. The surface of quartz as the piezoelectric element 21 and the magnet 2
3 are mechanically joined to each other, the torque T
Causes stress (torsional stress) in the crystal.

As the strength of the external magnetic field H increases, the torque T, which is a mechanical force, increases. The stress causes the crystal of the piezoelectric element 21 to be distorted, and the oscillation frequency of the oscillation circuit 31A including the piezoelectric element 21 in the feedback path changes according to the amount of distortion. Although the change in the oscillation frequency is slight, for example, the oscillation frequency of the piezoelectric element 21 is set to the order of 10 MHz,
By appropriately selecting the shapes of the magnet (electrode) 23 and the back electrode 22, the oscillation frequency can be freely set in the range of 10 MHz to 100 MHz.

As described above, the stress generated in the piezoelectric element 21 causes the crystal of the piezoelectric element 21 to be distorted, and the oscillation circuit 31A shown in FIG. 1 outputs a pulse signal at an oscillation frequency corresponding to the stress. This pulse number is counted by the counter circuit 33A. On the other hand, although the external magnetic field H is also applied to the non-magnetic metal 24, no stress is generated in the piezoelectric element 21.
The oscillation circuit 31B shown in FIG. 1 outputs a pulse signal at an oscillation frequency when no stress occurs. This pulse number is counted by the counter circuit 33B. The subtraction circuit 34 calculates the difference between the number of pulses counted by the counter circuit 33A and the number of pulses counted by the counter circuit 33B. The output of the subtraction circuit 34 is passed through a compensation circuit 35 to a multiplication circuit 37.
The multiplication circuit 37 multiplies the output of the compensation circuit 35 by the calibration coefficient from the calibration coefficient generation circuit 36.
Then, based on the output from the multiplication circuit 37, the display circuit 38
Indicates the value of the external magnetic field detected by the magnetic sensor 2.

In the magnetic sensor 2 configured as described above, the external magnetic field is converted into a mechanical force by the magnet 23 and the piezoelectric element 21, and the piezoelectric element 21 itself has little temperature dependency of the magnetic field detection sensitivity. Since the piezoelectric material having high linearity of the sensitivity with respect to the magnetic field intensity is used, it is possible to improve the linearity of the magnetic field detection sensitivity with respect to the magnetic field intensity while reducing the temperature dependence of the magnetic field detection sensitivity.

Further, the configuration of the magnetic field detection circuit can be easily realized. In particular, the use of a constant current generation circuit that supplies a constant current to the Hall element and a synchronous detection circuit for detecting a small Hall electromotive force, which were conventionally required, have been eliminated.
Since the magnetic field strength can be basically detected by the simple oscillation circuit 31A and the counter circuit 33A, the configuration of the magnetic field detection circuit of the magnetic detection system 1 can be greatly simplified. Further, downsizing of the magnetic detection system 1 can be realized. Furthermore, the manufacturing cost of the magnetic detection system 1 can be significantly reduced, and a very inexpensive magnetic detection system 1 can be provided.

The distance between the magnet 23 and the non-magnetic metal 24 on the surface of the piezoelectric element 21 needs to be a distance that is not affected by the stress caused by the torque of the magnet 23. That is, a fixed distance is required between the magnet 23 and the non-magnetic metal 24 in order to perform high-accuracy magnetic measurement (this distance is determined by empirical rules). Therefore, in order to realize a more compact magnetic sensor, the magnet 23 and the nonmagnetic metal 24 are required.
The piezoelectric element 21 is divided into two in the middle (center line) of
If the magnet 23 and the non-magnetic metal 24 are arranged in the respective areas of the adjacent semi-circular plates, even if the magnet 23 and the non-magnetic metal 24 are brought close to each other, the influence of the stress due to the torque of the magnet 23 is reduced. The non-magnetic metal 24 can be prevented from reaching the piezoelectric element side on which the non-magnetic metal 24 is provided. Further, a groove may be provided in the middle (center line) between the magnet 23 and the non-magnetic metal 24 shown in FIG. Such a structure that is not affected by the stress due to the torque of the magnet 23 has the disadvantage of slightly increasing the number of steps, but can provide a more accurate and compact magnetic sensor. Since the spatial resolution is improved by bringing the magnet 23 and the non-magnetic metal 24 close to each other, it is possible to measure the spatial distribution of the magnetic field with high accuracy.

[0031]

According to the present invention, it is possible to provide a magnetic sensor capable of improving the linearity of the detection sensitivity with respect to the magnetic field strength while reducing the temperature dependence of the magnetic field detection sensitivity.

Further, according to the present invention, there is provided a magnetic sensor capable of improving the linearity of the detection sensitivity with respect to the magnetic field strength while reducing the temperature dependence of the magnetic field detection sensitivity,
In addition, it is possible to provide a magnetic detection system that can easily realize a magnetic field detection circuit configuration.

In particular, according to the present invention, the size of the magnetic detection system can be reduced, and the manufacturing cost of the magnetic detection system can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a magnetic detection system including a magnetic sensor according to an embodiment of the present invention.

FIG. 2 is a perspective view of the magnetic sensor according to the embodiment of the present invention.

FIG. 3 is a principle view showing a magnet side of the magnetic sensor according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic detection system 2 Magnetic sensor 21 Piezoelectric element 22 Back electrode 23 Magnet 24 Non-magnetic metal 31A, 31B Oscillation circuit 32A, 32B Inverter circuit 33A, 33B Counter circuit 34 Subtraction circuit 35 Compensation circuit 36 Calibration coefficient generation circuit 37 Multiplication circuit 38 Display circuit

Claims (2)

[Claims] 1. A magnetic sensor, comprising: a magnet that does not pole-reverse with respect to an external magnetic field; and a piezoelectric element that detects a magnetic field strength applied to the magnet as a mechanical force. 2. A magnetic sensor comprising: a magnet that does not undergo pole reversal with respect to an external magnetic field; a piezoelectric element that detects a magnetic field intensity applied to the magnet as a mechanical force; and a mechanical sensor that applies a piezoelectric element to the magnetic sensor. An oscillation circuit whose oscillation frequency changes according to a force, and a means for measuring a change in the oscillation frequency of the oscillation circuit and displaying a magnetic field strength detected by the magnetic sensor. system.