JP2002189067A - Method for applying bias of magnetic field sensor and strain sensor, and the magnetic field sensor and strain sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for applying bias for a magnetic field sensor and for a strain sensor, whereby the bias can be applied using a simple arrangement, in place of a magnetic field bias by a winding wire, and to provide a magnetic field sensor and a strain sensor. SOLUTION: There are provided the magnetic field sensor 1, a PZT piezoelectric element 3, attached to a rear face of the magnetic field sensor 1 for generating primary strain, and a power supply 4 for impressing a voltage on the PZT piezoelectric element 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field sensor in which application of a magnetic field bias is indispensable, a bias applying method for a strain sensor, and a magnetic field sensor and a strain sensor.

[0002]

2. Description of the Related Art When a magnetic material is energized with a high-frequency current and its magnetic anisotropy is controlled in advance, its impedance changes sensitively to an external magnetic field or externally applied strain. It can be used as a magnetic field sensor or a high-sensitivity strain sensor. In particular, the magnetic field sensor is well known by its name such as MI sensor and high-frequency carrier type sensor.

[0003]

However, since these sensors can realize high sensitivity only under a certain applied DC magnetic field, a mechanism for applying a bias magnetic field such as a winding or a permanent magnet is indispensable around the sensor. In addition, there are problems such as an increase in size, an increase in power consumption, and generation of a leakage magnetic field to the outside. G that requires a bias magnetic field
The MR sensor uses a method called SAL that uses a magnetic field that generates a current flowing in the vicinity because the sensor thickness is extremely thin. However, this sensor is not applicable because the sensor thickness is as thick as several microns. It was possible.

It is known that when a magnetic material is distorted, the direction of the internal magnetization changes in accordance with the distortion (inverse magnetostriction effect).
By controlling the direction of the internal magnetization of the magnetic field sensor, bias application without winding was realized. This method is a completely new method that has not been used before.

In view of the above circumstances, the present invention provides a magnetic field sensor, a bias applying method for a strain sensor, and a magnetic field sensor and a strain sensor capable of applying a bias with a simple configuration instead of a magnetic field bias by a winding. The purpose is to.

[0006]

According to the present invention, there is provided a method for applying a bias to a magnetic field sensor and a strain sensor, wherein a bias utilizing an inverse magnetostriction effect is applied to the sensor element. Thus, a bias is applied instead of the magnetic field bias by the winding.

[2] A magnetic field sensor and a strain sensor are characterized in that they include a sensor element, a piezoelectric element that causes primary distortion and is attached to the back surface of the sensor element, and a power supply that applies a voltage to the piezoelectric element. And

[3] In the magnetic field sensor and the strain sensor according to the above [2], a groove is formed in the piezoelectric element that generates the primary distortion, and a primary distortion is generated along the groove. And

[4] The magnetic field sensor and strain sensor according to [2], further comprising a circuit for converting a signal detected by the sensor element into a voltage via a feedback circuit and applying the voltage to a piezoelectric element.

[0010]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a schematic diagram of a magnetic field sensor showing an embodiment of the present invention.

In FIG. 1A, 1 is a magnetic field sensor made of a magnetic thin film formed on a glass substrate, 2 is a glass substrate, 3 is a PZT piezoelectric substrate (hereinafter simply referred to as a piezoelectric substrate), 4 is a power supply, and 5 is a power supply. This is a groove provided on the piezoelectric substrate 3. The PZT piezoelectric substrate 3 is grooved on the back surface as shown in FIG. 1B, and generates uniaxial distortion in the groove longitudinal direction.

FIG. 2 is a system configuration diagram of the magnetic field sensor according to the present invention.

In this figure, H ₁ is a minute magnetic field, 6 is a magnetic field sensor, 7 is a PZT piezoelectric substrate, 8 is a power supply, 9 is a detection circuit, and _So is an output.

According to FIGS. 1 and 2, the magnetic field sensors 1, 6
Is mechanically adhered to the piezoelectric substrates 3 and 7, so that when a voltage is applied to the piezoelectric substrates 1 and 6,
Strain is applied to the magnetic field sensors 1 and 6 via the magnetic field sensors, thereby changing the anisotropy inside the magnetic material forming the magnetic field sensors 1 and 6 and changing the sensor characteristics. This makes it possible to determine the operating point at the point where the sensor has the highest sensitivity.

FIG. 3 is a diagram showing an experimental result of the magnetic field sensor showing the embodiment of the present invention, and FIG. 4 is a diagram showing an operation of the magnetic field sensor showing the embodiment of the present invention.

FIG. 3 shows an output signal with respect to a magnetic field, where a is a large output signal, b is an optimal DC magnetic field, c is a minute AC magnetic field, and no electric field is applied to the piezoelectric material (V = V). In order to operate at the point showing the maximum magnetic field detection sensitivity at 0), it is clear that application of a DC magnetic field is necessary, as shown in FIG. Is added, the operating point changes accordingly, and by giving some optimal distortion (V =
V ₃ ), it is clear that the maximum magnetic field detection sensitivity can be obtained without applying an external DC magnetic field.

As described above, it has been clarified that a method utilizing distortion can be applied as a bias method of a magnetic sensor. In addition, this method has a number of advantages over the bias method using a DC magnetic field. For example, although an electric field is applied to a piezoelectric material, generally, the piezoelectric material is an insulator and therefore has a high resistance and no current flows, and the power required for bias application is extremely small. This is an extremely great advantage as compared with a DC magnetic field bias in which a current is continuously supplied. Furthermore, in order to achieve linearity that is as important as sensitivity for the sensor, a method of feedback of the output is generally used. Since this is a voltage feedback, the circuit is simple and not only easy to manufacture, but also contributes to miniaturization of the entire circuit. Needless to say, the piezoelectric material is extremely small in size as compared with the size of the bias magnetic field generating coil, so that the size of the sensor element itself can be reduced.

The present invention shows that it is possible to apply a bias using distortion, and it is considered that the applicable range is wide.

First, a sensor using a wire as a magnetic material and a sensor using a thin film are currently used, but the present invention is applicable to both.

In the above experiment, a piezoelectric material (PZT) was used as a means for imparting distortion. However, the present invention is not limited to this. Further, the shape of the sensor is not limited to bulk or thin film, and sufficient distortion can be applied to the sensor. Applicable if given.

The magnetic sensor is used for a very wide range of applications, and the economic ripple effect on the development of the magnetic sensor is extremely large. For example, it is widely used in the medical field such as magnetoencephalogram and magnetocardiogram measurement, the transportation field such as highway automatic driving system, and the industrial fields such as banknote recognition, geomagnetic compensation for CRT, and magnetic recording. Is eagerly awaited. The present invention satisfies those expectations.

Next, a second embodiment of the present invention will be described.

In this embodiment, a strain sensor will be described.

FIG. 5 is a schematic diagram of a strain sensor according to a second embodiment of the present invention, and FIG. 6 is an explanatory diagram of the operation of the strain sensor.

In these figures, 10 is a base, 11
Is a strain sensor, 12 is a cantilever, 12A is a cantilever tip, 13 is a PZT piezoelectric substrate, and 14 is a convex surface portion.

As shown in FIG. 6, when an external force is applied to the tip portion 12A of the cantilever 12 by the convex portion 14, the cantilever 12 is distorted, and an output signal is output from the distortion sensor 11. This output signal is output to P through a feedback circuit.
When a voltage is applied to the ZT piezoelectric substrate 13, the piezoelectric substrate 1
3 is thereby bent and deforms until the contact pressure of the cantilever tip 12A becomes zero. Therefore, by monitoring the voltage applied to the PZT piezoelectric substrate 13,
The contact pressure of the tip 12A can be detected.

In addition, if the above mechanism is used, even if the surface contacting the cantilever 12 has irregularities, the cantilever 1
By always keeping the contact pressure of the tip 12A of the second at zero,
Alternatively, by applying an offset to the feedback circuit, it is possible to control the contact pressure of the cantilever tip 12A to a certain constant force. If this is used, it can be applied to an AFM (atomic force microscope) probe, an arm holding a magnetic recording head, and the like. That is, in a cantilever-shaped actuator, the present invention can be applied to a case where it is desired to always maintain a constant contact pressure even if an object to be contacted at the tip has irregularities.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible based on the gist of the present invention, and these are not excluded from the scope of the present invention.

[0030]

As described above, according to the present invention, the following effects can be obtained.

The reason why the MI sensor requires a DC bias magnetic field is to control the magnitude of anisotropy that fixes the direction of internal magnetization in a certain direction. Therefore, instead of the method of applying a magnetic field from the outside, energy for rotating the internal magnetic field (anisotropic energy) may be given by another method. The present invention is based on this concept, and uses energy due to the inverse magnetostriction effect.

In order to generate the inverse magnetostriction effect, for example,
A voltage was applied to the piezoelectric element attached to the back surface of the sensor to apply a distortion to the sensor, thereby obtaining the same effect as applying a bias magnetic field by flowing a current through the winding. In this case, since the strain needs to be uniaxial strain, a groove is formed in the piezoelectric element, and uniaxial strain is generated only along the groove.

According to the present invention, a bias can be applied with a voltage while maintaining the sensitivity of the sensor alone, so that the feedback circuit is simplified, the power consumption is reduced, and the overall size of the sensor element can be reduced.

Further, the strain sensor of the present invention is suitable for a cantilever-shaped actuator in which it is desired to always maintain a constant contact pressure even if an object whose tip comes into contact has irregularities.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a magnetic field sensor showing an embodiment of the present invention.

FIG. 2 is a system configuration diagram of a magnetic field sensor according to the present invention.

FIG. 3 is a diagram showing experimental results of a magnetic field sensor showing an example of the present invention.

FIG. 4 is a diagram illustrating an operation of the magnetic field sensor according to the embodiment of the present invention.

FIG. 5 is a schematic view of a strain sensor according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram of an operation of a strain sensor according to a second embodiment of the present invention.

[Explanation of symbols]

1,6 Magnetic field sensor made of a magnetic thin film formed on a glass substrate 2 Glass substrate 3,7,13 PZT piezoelectric substrate 4,8 Power supply 5 Groove 9 Detection circuit 10 Base 11 Strain sensor 12 Cantilever 12A Cantilever tip 14 Convex part

Claims (4)

[Claims] 1. A method of applying a bias to a magnetic field sensor and a strain sensor, wherein a bias is applied to the sensor element instead of a magnetic field bias by a winding by applying a bias utilizing an inverse magnetostriction effect to the sensor element. Method for applying a bias to a magnetic field sensor and a strain sensor. (A) a sensor element; (b) a piezoelectric element which causes primary distortion and is attached to the back surface of the sensor element;
A magnetic field sensor and a strain sensor, comprising: a power supply for applying a voltage to the piezoelectric element. 3. The magnetic field and strain sensor according to claim 2, wherein a groove is formed in the piezoelectric element that generates the primary distortion, and a primary distortion is generated along the groove. Sensors and strain sensors. 4. The magnetic field sensor and strain sensor according to claim 2, further comprising a circuit for converting a signal detected by the sensor element into a voltage via a feedback circuit and applying the voltage to a piezoelectric element. Strain sensor.