JPH01145589A - Drive method of ceramic superconductive magnetic sensor - Google Patents

Abstract

PURPOSE:To detect the strength of stable and high reliable magnetic field by applying a drive current whose certain value current always flows from a zero current condition on a magnetic sensor as drive current. CONSTITUTION:Ohmic current electrodes 2, 3 and voltage electrodes 4, 5 are formed by the use of a deposition film of titanium and silver paste on both the ends and the inside neighborhood of a ceramic superconductor element 1 respectively. The electrodes 2, 3 are connected to a constant current source 6 and the electrodes 4, 5 to a voltage detector 7. In the case where a magnetic field H is reduced as constant current is flowed in the element 1 from the current source 6, the result in which the superconductivity of weak connection which exists in grain boundaries of ceramic is preserved as it remains broken is supposed that hysteresis appears. Therefore, if current which has a property in which constant value current such as alternating current always returns to zero once in the element 1 flows to use a drive method of the element 1, hysteresis of output voltage for the change of a magnetic field does not completely appear and an stable and high reliable magnetic field can be detected.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a driving method for a highly sensitive superconducting magnetic sensor based on a new principle invented by the inventors.
More specifically, the present invention relates to a drive method for a superconducting magnetic sensor suitable for use in highly sensitive measurements in the industrial and medical fields that require highly accurate, reliable, and stable magnetic field measurements.

<Prior Art and its Problems> Conventionally, magnetoresistive elements using semiconductors or magnetic materials have been used for magnetic detection, but the magnetic field detection sensitivity has been on the order of several hundred Gauss. Further, since the increase in resistance of the magnetoresistive element is proportional to the square of the magnetic field in a certain region, the increase in resistance is extremely small for low values of the magnetic field.

Furthermore, there is a 5QUID magnetic flux sensor that uses superconductors.
It had a complex structure and required extremely low temperatures.

In order to solve the above-mentioned problems of conventional magnetic sensors, the present inventors first applied for a patent entitled "Superconducting Magnetic Detection Element" (1983).
As shown in FIG.
, 5 in contact with each other, and a detailed study of its operating characteristics as shown in Figure 2 revealed that a certain type of ceramic superconducting magnetic sensor can operate under a low magnetic field while a constant current is flowing. It was discovered that when the strength was changed, a hysteresis phenomenon as shown in FIG. 3 was exhibited.

This hysteresis phenomenon causes errors when detecting minute magnetic fields.

The present invention was created in view of the above points, and aims to propose a driving method for a ceramic superconducting magnetic sensor that enables stable magnetic field detection even when there is a hysteresis phenomenon. .

Means and operation for solving the above problems> In order to achieve the above object, the driving method of the ceramic superconducting magnetic sensor of the present invention is such that the magnetic sensor made of the ceramic superconductor is driven by a state in which the driving current is zero. The configuration is such that a drive current including .

When a magnetic field is applied to a ceramic superconductor while keeping it at a temperature below the critical temperature at which it becomes superconducting, the superconducting state is maintained until the magnetic field reaches about 0 to 5 degrees, as shown in Figure 2, and the resistance of the superconductor decreases. is zero. When the magnetic field exceeds 5 degrees, the superconducting state is broken and electrical resistance is exhibited. The inventors have discovered that the electrical resistance exhibits a steeper rise characteristic in response to the applied magnetic field than in conventional magnetoresistive elements.

The above-mentioned characteristics of a magnetic sensor using a ceramic superconductor are understood by the inventors as follows.

In other words, the above characteristics are caused by the fact that the ceramic sintered body is composed of many superconductor particles, and there is an extremely thin insulator at the grain boundaries, or the contact area between the particles is point-shaped. It can be regarded as an aggregate of weakly coupled superconductors, and is produced as a result of the superconducting state being broken by a weak magnetic field (critical magnetic field).In other words, it is produced as a result of the tunneling phenomenon at the contact interface between ceramic superconductor particles. I think of it as something.

However, a detailed study of the operating characteristics that show the steep rise characteristic in response to the magnetic field described above shows a nahysthesis phenomenon as shown in Figure 3.The degree of this hysteresis is extremely small overall, and it is difficult to detect large magnetic fields. Although this does not pose much of a practical problem, a large error will occur in the output voltage for a minute magnetic field of several tens of Gauss.

The inventors cut off the element current flowing through the superconductor for - degrees,
We confirmed that if we set the current to zero and then let the current flow, we could always detect a constant output for a constant magnetic field.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing a configuration example of a ceramic superconducting magnetic sensor to which the driving method of the present invention is applied.

Superconducting element 1 was prepared by weighing yttrium oxide y2o3, barium carbonate ABaCO3 + copper oxide CuO in a ratio of 1:2:3, and thoroughly dispersing and mixing fine particles at 900°C.

Calcined in air for 5 hours, crushed and dispersed again,
Uniform fine particles of perovskite oxide superconductor (1μ
mφ or less), and then pressurized into an optimal shape, for example, a circular pellet, at a pressure of 1toned, and then heated at 1000°C in air.

Ceramic superconducting magnetic sensors to which this can be applied are not limited to these, but include, for example, La-Ba-Cu-○ system, Y
lna group elements such as -5r-Ba-Cu-0 series.

It goes without saying that the same effect can be achieved even when the magnetic sensor is made of superconducting ceramics containing Ila group elements, copper (Cu) elements, and oxygen (0) elements and has hysteresis characteristics.

Next, a thin rectangular shape was cut out from the material produced as described above to produce a ceramic superconductor element 1.

Superconductor element 89 (Y (-Ba 2
-Cu 3 ) 06, and the magnetic field (critical magnetic field) at which the weakly coupled superconducting state is broken is approximately 5 oersteds.

Ohmic current electrodes 2, 3 and voltage electrodes 4, 5 are provided at both ends of this element 1 and near the inside thereof, respectively.
) and silver paste to form the current electrode 2.
．． 3 was connected to a constant current source 6, and voltage electrodes 4 and 5 were connected to a voltage detector 7.

In the above configuration, when the magnetic field H is decreased while a constant current is still flowing through the element 1 from the constant current source 6,
It is thought that hysteresis appears as a result of the superconductivity of the weak bonds that exist at the grain boundaries of ceramics remaining broken.

Therefore, in the element 1 shown in FIG.
As shown in Figure (a), the current starts flowing from -degree zero, and as shown in Figure 4 (
A current whose current value always returns to zero, such as a pulse current as shown in b), an alternating current as shown in Fig. 4(C), or a sawtooth current as shown in Fig. 4(d), that is, a current that always returns to zero. If we use an element drive method that allows a certain current value to flow from a zero state, no hysteresis will appear in the output voltage due to changes in the magnetic field, and stable and reliable magnetic field detection can be obtained as shown in Figure 5. . In addition, Fig. 4(c) t or (
When measuring a magnetic field by supplying a current with a waveform as shown in d), it is necessary to perform sampling measurement of the magnetic field at a predetermined value timing such as the peak value of the increasing current value.

As described above, in a magnetic sensor using a ceramic superconductor, by applying a driving current to the magnetic sensor such that a current of a certain value always flows from a current state of zero, it is possible to achieve extremely stable and highly reliable driving current. It is possible to detect the strength of the magnetic field.

<Effects of the Invention> As explained above, the present invention has a ceramic superconducting element that exhibits a large change in electrical resistance with respect to a magnetic field, eliminates the hysteresis phenomenon peculiar to superconductors, and extremely stably and reliably changes the magnetic field strength. It is a drive method that can perform detection, and it is extremely effective when applied to magnetic measurement technology for medical diagnosis or FA, which requires a high degree of precision, and has great industrial potential. It is something that contributes.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the element structure of a ceramic superconducting magnetic sensor to which the present invention is applied, and FIG. 2 is a diagram showing the characteristics of resistance change with respect to a magnetic field of the present sensor. FIG. 3 is a diagram showing the hysteresis characteristics of this sensor near a low magnetic field, and FIGS. 4(a) and (d) are diagrams for explaining the driving method of the present invention. FIG. 5, a diagram showing waveforms, is a diagram showing characteristics in which hysteresis is eliminated by the driving method of the present invention. 1... Ceramic superconducting magnetic sensor, 2, 3...
Current electrode, 4.5... Voltage electrode, 6... Constant current source,
7...Voltage detector. Agent Patent Attorney Takeshi Sugiyama (1 other person) Gen. 1 Figure 2 Figure 5 Procedural Amendment C Method) % Formula % [1 2. Title of Invention Ceramic Superconducting Magnetic Sensor Drive Method 3. Make Corrections Relationship with the case Patent applicant address 1IIr22-2 Nagaike, Abeno-ku, Osaka-shi, La 545
2) Name (504) Sharp Corporation Representative Haru Tsuji Shii 4, Agent ゛8

Claims (1)

[Claims] 1. A method for driving a ceramic superconducting magnetic sensor, characterized in that, in a magnetic sensor made of a ceramic superconductor, a driving current including a state where the current is zero is used as the driving current. 2. The driving method for a ceramic superconducting magnetic sensor according to claim 1, wherein the driving current is an alternating current. 3. The driving method for a ceramic superconducting magnetic sensor according to claim 1, wherein the driving current is a pulse current. 4. The driving method for a ceramic superconducting magnetic sensor according to claim 1, wherein the driving current is a sawtooth current.