JP3248776B2 - Superconducting measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting measuring device for cooling a superconducting element exhibiting superconducting phenomena to a very low temperature by a cooler for cooling by a Stirling cycle system.

[0002] The present invention also relates to a small and highly sensitive superconductivity measuring apparatus which realizes the superconductivity phenomenon of a magnetoresistive element and utilizes the high sensitivity range of the superconducting magnetoresistance effect of the magnetoresistive element.

Further, the present invention can constitute a biomagnetism measuring device such as a magnetocardiograph for measuring a magnetic field from the heart generated on the chest wall, and can be used to measure electrical phenomena in the body such as the human heart, brain and lungs. The present invention relates to a superconducting measurement device capable of measuring a weak biomagnetic field generated thereby.

[0004]

2. Description of the Related Art The superconductivity phenomenon in which the electrical resistance becomes zero by cooling a certain kind of conductive material to an extremely low temperature has been well known. Utilizing this superconductivity phenomenon for a high-sensitivity sensor element, a switching element, a storage element, or the like has an excellent advantage as an application to the electronics field.

Conventionally, a magnetoresistive element using a semiconductor or a magnetic material has been generally used for measuring a magnetic field.
In particular, devices using the shape effect of InSb, InAs, etc., which are semiconductors with high electron mobility, and the orientation effect of Fe-Ni, Co-Ni, etc., which are ferromagnetic metals, have been put to practical use.

Further, a method for detecting and measuring a weak magnetic field utilizing the magnetoresistance effect of the superconductor due to the weak coupling of the oxide superconductor has been developed.

However, on the other hand, at present, superconducting phenomena can only be confirmed at cryogenic temperatures. Therefore, it is necessary to cool the superconducting elements to cryogenic temperatures in order to realize the superconducting phenomena. The fact is that it has not been used.

Conventionally, as an apparatus for cooling a superconducting element to a very low temperature, there is an apparatus in which the superconducting element is directly immersed in a refrigerant liquid such as liquid helium (He) or liquid nitrogen. In this apparatus, as shown in an example in FIG. 9, a liquid He 91 flows into a Dewar bottle 90, and is cooled while fixing a superconducting element 95 with a jig 92 in the Dewar bottle 90. .

However, in order to continuously cool the apparatus for a long time, it is necessary to supply a new refrigerant, and it is practically impossible to apply the apparatus to the electronics field which requires the continuous use for a long time. Met.

Further, in this apparatus, dew condensation occurs due to a rapid temperature change from room temperature to extremely low temperature by repeatedly immersing the superconducting element in liquid nitrogen or the like of a liquid refrigerant. Then, there is also a problem that the reliability of the superconducting element which is extremely weak to moisture is reduced by the repetition, and the life is shortened.

As another cooling device, the superconducting element is housed in a sample section without directly immersing the superconducting element in a coolant, and the flow of heat into and out of the sample section is controlled to reduce the temperature of the superconducting element. There is a device called a cryostat that controls and indirectly cools a superconducting element across an adiabatic space.

However, this device also requires a supply of refrigerant in order to continuously cool it for a long period of time, and the device is large and expensive, and needs to be downsized and durable for a long time and used continuously for a long period of time. Its use in certain electronics fields has been almost impossible.

Another cooling device is an electronic cooling device using the Peltier effect. In this apparatus, as shown in FIG. 8, a heat radiation electrode 83 is provided along with a jig 85 for connecting and fixing an n-type semiconductor element 81 and a p-type semiconductor element 82 via a thin insulating film. This heat radiation electrode 83
Are connected to side ends of the semiconductor elements 81 and 82. A lead wire 84 is connected to the heat radiation electrode 83. A cooling plate electrode 86 is provided at the front end of the semiconductor elements 81 and 82. The superconducting element 87 is fixed to the cooling plate electrode 86. The jig 85 serves as a support for the entire apparatus. Also,
The jig 85 is fixed to the heat radiating electrode 83 by a bonding method having good thermal conductivity for efficient heat radiation and cooling.

The electronic cooling device having the above-described structure is composed of a lead wire 84.
, The cooling plate electrode 86 is cooled at a low temperature based on the Peltier effect of the semiconductor elements 81 and 82, and the superconducting element 87 is cooled. On the other hand, the heat generated by the heat radiation electrode 83 is efficiently radiated to the outside via the jig 85.

However, in the electronic cooling device using the Peltier effect, a cryogenic temperature region where a superconducting phenomenon appears appears.
(Below 77K), there is no cooling capacity, and furthermore, the semiconductor device using the Peltier effect is made into a two-stage, and if necessary, a multi-stage cascade structure, and electronic cooling is attempted. Difficult and unrealistic. At this stage, most of the cooling temperatures at which the element exhibiting the superconductivity phenomenon has reached the practical level are around 77 K or less, so that there are still many problems in practical use by electronic cooling using the Peltier effect.

Further, another cooling device includes a compressor, a condenser and an evaporator, and operates in accordance with a vapor compression cooling cycle, and a high temperature cooler using a general refrigerant and a low temperature refrigerant. A low-temperature cooler used is provided, and a cooling device with a dual cooler having a cooling configuration in which heat is exchanged between a condenser of the low-temperature cooler and an evaporator of the high-temperature cooler is considered. Due to the problem that the specific volume of the steam becomes large, the problem that a high condensing pressure is required, and the like, there is still a problem that the cooling capacity at cryogenic temperature is insufficient, and there is a problem that the cooling equipment becomes large.

Further, the temperature at which the superconducting phenomenon appears differs depending on the variation in the characteristics of the superconducting element.
If possible, it is ideal to set the cooling temperature in accordance with the element, and the cooling is ideal. However, the conventional technique has a problem that the cooling temperature cannot be easily and easily changed.

In any of the above cooling devices,
In order to provide the cooling capacity of the cooler even if it is extremely low temperature, it was necessary to reduce the heat load around the cooling section and improve the heat conduction.

Further, since the cooling temperature required for the superconducting element is not easily handled by anyone in a cryogenic temperature range,
In applying superconducting elements to electronic components such as various sensors, realizing a sufficiently practical cooling device has become a very urgent problem.

In particular, when measuring biomagnetism, it is necessary to use a heat insulating material or the like between the magnetic field detection unit and the living body, and the distance between the magnetic field detection unit and the object to be measured becomes longer, and However, there is a problem that a separate detection coil or the like needs to be used since the loss of the input signal to the input terminal increases.

Further, in a measuring apparatus using a superconductor, there is a problem that the output signal of the superconductor has a low-frequency fluctuation of 10 Hz or less, and it is difficult to measure a weak magnetic field of a DC or a low-frequency magnetic field of 10 Hz or less. is there.

In a living body, a potential difference occurs due to the action potential of excitable cells such as nerve cells and muscle cells, and a current flows through the cells. At this time, a current called a volume current flows through the extracellular electric conductor, thereby generating a weak but magnetic field. Biomagnetic measurement for measuring these weak magnetic fields is currently being actively studied because it enables accurate diagnosis of diseases.

Among them, as a technique for measuring a magnetic field generated from the heart, a potential distribution is created in the thorax by a cardiac electromotive force accompanying excitation of the myocardium, a weak magnetic field generated around the thorax is detected, and a waveform similar to an electrocardiogram is detected. A device for displaying a certain magnetocardiogram is as follows.

A magnetocardiographic signal, which is a magnetic field signal from the heart, is 5
At present, it is at the research level because it is very weak, about ¹⁰ × 10 ^-10 T (Tesla), that is, about 5 × 10 ^-6 G (Gauss). A magnetic measuring device using an element to which the technique is applied is being developed. The device is called a SQUID (Super Conducting Quantum Interference Device), that is, a superconducting quantum interference device. The structure and principle of this SQUID will be briefly described with reference to FIG. The SQUID has a structure in which one or two Josephson junctions 301 of a weak coupling part are provided in a part of the superconducting ring 300. And this SQUI
A current is added to ID from a current source. When a magnetic flux from the outside penetrates the superconducting ring 300, a phase difference is generated between the phase of the current flowing on the right side of the superconducting ring 300 and the phase of the current flowing on the left side, and the current flowing on the right side , And the current flowing on the left side interfere with each other. Since this current changes periodically with respect to the magnetic flux, the output voltage of the element changes sensitively in synchronization with the penetration of the magnetic flux. Then, by performing waveform processing on this output voltage, a weak magnetic field can be captured as an image.

FIG. 30 schematically shows a magnetic measurement apparatus using the above SQUID. This device has a pickup coil section,
The magnetic flux transmission unit and the like are cooled to the extremely low temperature of liquid helium, and the signal processing unit performs magnetic measurement.

However, the magnetic measuring device has various problems as described below.

That is, since the magnetic measurement device needs to be cooled to an extremely low temperature of 4.2 K by directly immersing SQUID in a refrigerant liquid using liquid helium (He) as a refrigerant, it is necessary to perform magnetic measurement for a long time. Therefore, it is necessary to supply liquid helium. Therefore, FIG.
As shown in (1), a helium replenishing section is required as the helium replenishing means, and there is a problem that the apparatus becomes complicated. In addition, the SQUID, the pickup coil, and the like must be set in a low-temperature dewar to maintain a special operation state, and the low-temperature dewar itself has a complicated structure.

Further, holding the low temperature dewar,
Since a dewar support base, a bed for the subject, signal processing peripheral devices, etc. are required to enable the dewar to be moved to the chest of the subject, the entire device is complicated and very large and expensive. There is a problem that becomes.

These problems become particularly serious problems when the above-mentioned apparatus is generally used in hospitals and the like. Further, since everything is affected by magnetism, it is needless to say that it is necessary to reduce the generation of magnetism from peripheral devices, and it is necessary to devise a system that does not use a paramagnetic material. This means that the larger the whole device,
Difficult to do. (For example, the low temperature dewar, not to mention the low temperature dewar holding support, it is necessary that the subject's bed does not include a paramagnetic material.) Thus, the magnetic measurement device, Since the SQUID has a sensitivity that can detect brain waves of the level of 10 ^-13 T, the magnetic signal from the heart has a sufficient sensitivity to detect it, but for cryogenic cooling up to 4.2K and maintenance of a special operating state In addition, there is a problem that the size and the size are complicated. Therefore, the magnetic measurement device has not yet been used for diagnosis in hospitals, and there are still many problems in practical use.

Applying a device capable of measuring weak magnetism to the medical field has great advantages and possibilities. Therefore, a device capable of measuring weak magnetism has high reliability and
There is a demand for a device that is small, easy to use for a long time, has high durability, and can be used by a simple operation.

At present, the magnetic measuring device using the SQUID is in a clinical research stage, and has not been generally used for diagnosis in hospitals. For this reason, at present, it is common practice to measure a biological signal from the heart by performing an electrocardiogram measurement using an electrocardiograph. The electrocardiograph detects a potential change generated in the rib cage by measuring a potential difference between two points on the body surface using electrodes. However, this electrocardiograph
There is a problem that the measurement is unstable due to the unstable coupling between the skin and the lead-out electrode due to sweating, and the problem that handling is not easy because sufficient consideration must be given to the point of contact with the living body. is there.

[0032]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned various problems. That is, an object of the present invention is to be able to easily cool down to around 77K or below, which is a cryogenic temperature, and to reproduce the superconducting phenomenon of a superconducting element whose characteristics still vary at this stage,
It is an object of the present invention to provide a compact superconducting measurement device capable of measuring a weak magnetic field with high sensitivity that can be generally used in the field of electronics as a high-sensitivity sensor as a high-sensitivity sensor and that can be used continuously for a long time.

Further, it is an object of the present invention that the superconducting element can be easily cooled to a cryogenic temperature range, is easy to handle, can be measured without contacting a subject, and can be used for medical examination diagnosis. It is an object of the present invention to provide a superconducting measurement device capable of realizing a compact biomagnetism measurement device that can be used for general purposes.

[0034]

According to a first aspect of the present invention, there is provided a superconducting measuring apparatus comprising a superconducting element comprising a magnetoresistive element mounted on a tip of a cooling section of a Stirling cycle cooler. A temperature sensor for controlling the Stirling cycle cooler, provided in a cooling unit of the Stirling cycle cooler, including a non-magnetic envelope surrounding the superconducting element and the cooling unit,
The signal line of the temperature sensor is taken out from a hermetic port provided on a side wall of the non-magnetic envelope.

According to a second aspect of the present invention, there is provided the superconducting measuring apparatus according to the first aspect, further comprising cooling control means for controlling a cooling capacity of the cooler based on a temperature signal from the temperature sensor. The signal line of the temperature sensor is characterized by being wound around a signal line relay section attached to the cooling section between the superconducting element and the hermetic port.

According to a third aspect of the present invention, in the superconducting measuring apparatus according to the first aspect, the superconducting element is a magnetoresistive element exhibiting a superconducting phenomenon, and the superconducting element is provided with a low frequency characteristic of the superconducting element. An electromagnetic coil for generating an alternating magnetic field arranged on the outer periphery of the envelope to apply an alternating magnetic field having a frequency higher than the fluctuation frequency of the magnetic field, a resistance value detecting means for detecting a resistance value of the magnetoresistive element, and A signal conversion device for converting a resistance value of the magnetoresistive element detected by the value detecting means into a magnetic field strength signal representing a magnetic field strength applied to the magnetoresistive element.

Further, the invention of claim 4 relates to claims 1 to 3
A superconducting measurement device according to any one of the above, receiving a magnetic field detection signal output by the superconducting element that has detected a weak magnetic field, and a signal conversion unit that converts the magnetic field detection signal into a visible image that can be viewed. It is characterized in that a weak biomagnetic field is measured.

[0038]

According to the first aspect of the present invention, since the cooling unit is provided with a temperature sensor for controlling the cooler, the temperature of the cooling unit can be precisely controlled, and the superconducting element reliably causes the superconducting phenomenon to occur. In addition, when the superconducting element alone fails, only the superconducting element alone needs to be replaced.

According to the second aspect of the present invention, the signal line of the temperature sensor is wound around the signal line relay section attached to the cooling section. The heat insulating effect on the heat transmitted through the wire is enhanced, and the temperature rise that breaks the superconducting state can be avoided.

According to the third aspect of the present invention, since the electromagnetic coil for generating the alternating magnetic field is arranged on the outer periphery of the envelope, the superconducting element is operated at a frequency higher than the fluctuation frequency inherent in the superconducting element, and the fluctuation is obtained. The influence of the frequency can be avoided, and the measurement sensitivity can be improved.

According to a fourth aspect of the present invention, since the signal conversion means converts the magnetic field detection signal into a visible image which can be visually recognized, a small and highly sensitive desktop size capable of visually recognizing a weak biomagnetic field. A superconducting measurement device can be realized.

According to the present invention, since the superconducting element is cooled by using the cooler that utilizes the state change of the refrigerant according to the Stirling cycle, it is possible to easily cool the superconducting element to the extremely low temperature range,
In addition, the size of the entire superconducting measurement device can be reduced.

The superconducting element is a magnetoresistive element composed of a superconductor having a weak coupling grain boundary. When a magnetic sensor including this magnetoresistive element is provided, a weak magnetic field can be measured with high sensitivity. It is possible to make a desktop handy size of the sensitivity weak magnetic field measuring device.

Further, since the non-magnetic envelope surrounds the superconducting element and the cooling section for heat insulation, the superconducting element can be cooled more effectively.

When the temperature sensor and cooling control means for controlling the cooling capacity of the cooler based on the temperature signal from the temperature sensor are provided, the cooling temperature is adjusted in accordance with the characteristics of each superconducting element. The temperature change of the superconducting element can be observed in the temperature drift after setting or cooling.

When the inside of the envelope is kept at a vacuum or the like, it is possible to prevent the occurrence of dew condensation by changing the set temperature of the cooler.

Further, when an alternating current having a frequency higher than the low-frequency fluctuation frequency inherent to the superconducting element is caused to flow through the alternating-current magnetic field generating electromagnetic coil disposed on the outer periphery of the envelope, the electromagnetic coil is activated. An alternating magnetic field having a frequency higher than the fluctuation frequency is generated. Then, the superconducting element is
Upon receiving the AC magnetic field from the electromagnetic coil, the superconducting element operates at a frequency higher than the fluctuation frequency inherent to the superconducting element. That is, the superconducting element outputs a voltage signal synchronized with the high frequency. When a magnetic field to be measured from the subject is applied to the superconducting element in this state, the voltage signal synchronized with the high frequency becomes a signal including a signal modulated by the magnetic field to be measured.
Therefore, by extracting and demodulating the modulated signal from the signal including the modulated signal, the measured magnetic field can be obtained.

According to the present invention, since the superconducting element is operated at a frequency higher than the fluctuation frequency inherent to the superconducting element to measure the magnetic field to be measured, a high frequency can be obtained without being affected by the fluctuation frequency. Accurate magnetic field measurement can be performed.

Further, the modulated signal can be easily extracted from the signal containing the modulated signal by the bandpass filter. Also, since the high-pass filter cuts off the geomagnetic or external fixed magnetic field that is a signal of a frequency lower than the frequency of the magnetic field to be measured,
The influence of geomagnetism can be eliminated.

The superconducting element is cooled to a cryogenic temperature at which superconductivity occurs by cooling means for changing the state of the refrigerant by a Stirling cycle. The superconducting element is driven by the driving means, detects a weak magnetic field, and outputs a magnetic field detection signal. Then, the signal conversion means converts the magnetic field detection signal into a visible image that can be viewed. Therefore, a weak biomagnetic field can be visually recognized. In addition, since the cooling means is a Stirling cycle system, it can be downsized to a desktop size.

The superconducting element is constituted by a magnetoresistive element including a superconductor having a weak coupling grain boundary. With this magnetoresistive element, a weak magnetic field from the heart can be measured with high sensitivity.

When the magnetic field converging means made of a high magnetic permeability material converges the magnetic field to be measured on the magnetic field detecting portion of the superconducting element, a weak magnetic field from the heart can be measured with particularly high accuracy. Further, since the magnetic field converging section is not in contact with the magnetic field detecting section, it does not hinder cooling of the superconducting element by the cooling means.

Further, a recording device for recording the time-dependent data of the magnetic field detection signal output from the superconducting element is provided, and a clinical examination and diagnosis of a living body can be performed based on the time-dependent change of the magnetic field detection signal. Detailed clinical examination and diagnosis can be performed by comparison.

Further, the temperature of the cooling means or the superconducting element is detected by the temperature sensor, and the cooling section control means controls the cooling capacity of the cooling means based on the temperature detection signal from the temperature sensor, and In the configuration having a superconducting transition temperature unique to the superconducting element, the superconducting element can be cooled in accordance with the superconducting transition temperature of each mounted superconducting element. Therefore, even if the superconducting element is replaced, a constant measurement sensitivity can be always maintained.

Further, the superconducting element and the cooling means on which the superconducting element is mounted are separated from the driving means and the signal converting means, so that the superconducting element can be freely moved with the driving means and the signal converting means stationary. If the object is measured by moving the sample, the handling at the time of measurement becomes more convenient. Therefore, in this case, in a state where the subject is in a free posture, and without imposing a burden on the examiner, the weak biomagnetism of the heart can be measured with high accuracy.
This eliminates the need for a bed for the subject and a support for the cooling unit.

[0056]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 5 is a block diagram of a first embodiment of the superconducting measuring apparatus according to the present invention. As shown in FIG. 5, the Stirling cycle cooler 11 is roughly divided into a compressor 12 of a compressor and a cooler 13 of an expander.

As shown in FIG. 5, this embodiment has a superconducting element 15 and a temperature sensor 16 for measuring a cooling temperature of the superconducting element 15.

As shown in FIGS. 2A and 2B, the superconducting element 15 is composed of a weakly-coupled aggregate in which minute oxide superconductor particles are coupled on a non-magnetic substrate 46 in a point-like manner. A superconducting film 47 is formed. This superconducting film 47 is made meandering by machining. Further, titanium (Ti) is vapor-deposited on the superconducting film 47 so that the current electrodes 40, 4
2 and voltage electrodes 41 and 43 are formed. The superconducting film 47 may be an aggregate of weak coupling in which the oxide superconductor particles are coupled via an extremely thin insulating film.

Further, in this embodiment, the superconducting element 15 is packaged as shown in FIG. 3 so as to reliably transmit the low-temperature heat from the cooling section 13 to the superconducting element 15 without loss. Are mounted on the cooling unit 13. The package constitutes the thermal coupling means. As shown in FIG.
The superconducting element 15 and the temperature sensor 16 are bonded to the package envelope 20 with an adhesive such as a silver paste having a high thermal conductivity. And, the package envelope 20
Is attached to the cooling plate 21 which is a good heat medium and has high thermal conductivity, so that the cooling effect can be improved. Furthermore, airtight sealing is performed with glass 50,
The package structure is such that the inside can be maintained in vacuum and thermally connected so that the heat of the cooling unit 13 is transmitted to the superconducting element 15 without loss.

In this embodiment, the temperature sensor 16
Was made into a plate-like CRC (E) thermocouple, but the temperature sensor 16
May be a platinum resistor or a thermistor. The cooling temperature of the superconducting element 15 can be monitored by the temperature sensor 16.

As shown in FIG. 6, the package element 44 is mounted on the cooling section 13, and the entire package element 44 and superconducting element 15 are surrounded and insulated by the non-magnetic envelope 14. . A signal line from the temperature sensor 16 constituted by a thermocouple is taken out from a hermetic port 23 attached to the envelope 14.

The signal of the temperature sensor 16 taken out of the non-magnetic envelope 14 is supplied to a signal conversion unit 17 shown in FIG.
Is input to Then, the signal conversion unit 17 converts the signal representing the temperature of the superconducting element 15 into a control signal for the cooler 11 and transmits the control signal to the control unit 10. The control unit 10 controls the cooler 11 to reduce the superconducting phenomenon. The cooling unit 13 is cooled to a temperature that appears. The control signal for controlling the control unit 10 is a signal amplified to the volt order by the signal conversion unit 17. The control unit 10 further controls the cooling capacity of the cooler 11 by raising or lowering the control signal by several volts, thereby varying the cooling temperature.

FIG. 7 shows a circuit diagram of the signal conversion unit 17. As shown in FIG. 7, in the signal conversion unit 17, the amplification unit and the shift unit are configured as a differential amplifier circuit using an operational amplifier.

As the superconducting element 15 and the means for driving the superconducting element 15 shown in FIG. 5, various known elements can be used. For example, the driving means described in “Superconducting Magnetic Field Measuring Apparatus” (Japanese Patent Application No. 1-130306) already applied for a patent can be used.

The operation of the embodiment having the above configuration will be described below with reference to the drawings.

The cooler 11 shown in FIG. 5 compresses the gas to a high pressure in the compression section 12 and adiabatically expands this compressed gas in the piston type expansion cylinder 34 of the cooling section 13 shown in FIG. The gas passed through the regenerator 32 incorporated in the displacer 31 is sent to the next cycle while exchanging heat. Then, the compressed gas is cooled by the regenerator 32 while being sent to the expansion cylinder 34, so that the temperature of the gas gradually decreases during the repetition of the cycle. In other words, the cooler 11 changes the state of each of the steps of isothermal compression, constant volume cooling, isothermal expansion, and constant volume heating of a very low boiling point refrigerant gas such as helium in accordance with a Stirling cycle that is repeated in this order. This is a Stirling cooler that cools the material to be cooled (superconducting element 15) by releasing the heat absorbed from superconducting element 15 as the substance to be cooled in the expansion process to the outside in the isothermal compression process.

As shown in FIG. 1, the cooling element 13 of the cooler 11 includes the package element 44 including the superconducting element 15.
It is equipped with. The process in which the superconducting element 15 is cooled by the cooling unit 13 will be described in more detail with reference to FIG. First, the cooling unit 13 includes a connecting pipe 35.
Is connected to the compression unit 12 (see FIG. 5). Then, helium He gas, which is a refrigerant gas as a working fluid, is sent to the cooling unit 13 through the pipe 35.
The He gas is compressed by the compression piston inside the compression cylinder of the compression unit 12 and sent to the cooling unit 13 in a pressurized state. The He gas is adiabatically expanded and cooled in the expansion low-temperature chamber 30 by the elevating movement of the displacer 31 having the shape of an elongated piston.

The upper end of the displacer 31 and the cooling unit 1
The space which is expanded and contracted between the front end portion 3 and the end portion 3 constitutes the expanded low-temperature chamber 30. The displacer 31 repeats the gas spring reciprocating motion while maintaining a certain phase difference with respect to the pressure fluctuation generated by the compression section 12 in the expansion cylinder 34.

The regenerator 32 is provided inside the displacer 31 as described above. And, the outer peripheral surface of the displacer 31 facing the expansion cylinder 34,
The gas through holes 3 are provided at the upper end face of the displacer 31 respectively.
3 are provided. Then, the pressurized He gas sent by the compression section 12 is cooled when passing through the regenerator 32 and sent out to the expansion low-temperature chamber 30.

Thereafter, when the displacer 31 returns to the original position (to the right in FIG. 1), the He
The gas is adiabatically expanded and cooled. The He gas cooled in the expansion low-temperature chamber 30 is sent back to the compression unit 12 through the connecting pipe 35 while cooling the regenerator 32. By continuously operating this movement as one cycle, the tip 13A (cold head) of the cooling unit 13 is cooled to a very low temperature. Thereby, the superconducting element 15 mounted on the cooling unit 13 is cooled to an extremely low temperature.

Further, the above-described embodiment is designed to achieve the purpose of cooling the cooling capacity to around 77 K or less, which is necessary for a superconducting element currently in practical use, and to achieve the purpose of preventing condensation. As shown in FIG. 6, the package element 44 including the cooling unit 13 and the superconducting element 15 is
It is surrounded by 4. As a result, it was possible to prevent widthwise heat radiation and improve the cooling capacity. Furthermore, by making the internal space 27 of the envelope 14 a vacuum state, the package element 44 containing the superconducting element 15 can be vacuum-insulated, and an excellent cooling effect can be realized.

The interior of the envelope 14 may be sealed with an atmosphere of an inert gas such as argon, nitrogen, neon, helium or the like.

FIG. 4 shows the cooling characteristics of this embodiment. The vertical axis in FIG. 4 shows a voltage drop value when a current of 0.1 mA flows through superconducting element 15, and the horizontal axis shows a cooling time. As shown in FIG. 4, the resistance value of superconducting element 15 is about 600 ohms (about 60 mV /
0.1 mA), but a superconductivity phenomenon appeared about 200 seconds after the start of cooling. About 360 seconds after the start of cooling, the resistance value of superconducting element 15 became about 2 ohms. The element temperature at this time was about 77K. As described above, according to the above-described embodiment, the resistance value of the superconducting element 15 reached about 0 ohm approximately 360 seconds after cooling, indicating that superconducting cooling is possible.

As shown in FIG. 6, an element driving signal line 24 and a temperature output signal line 25 are drawn out of the package envelope 20 of the package element 44. The element driving signal line 24 and the temperature output signal line 25 are taken out of the envelope 14 from the hermetic port 23 via the signal line relay unit 22. The signal output from the temperature output signal line 25 controls the cooling capacity of the cooler 11 by the signal converter 17 shown in FIG.

Then, as shown in FIG. 6, a thermocouple as the temperature sensor 16 is wound around the signal line relay section 22,
From the external temperature output signal line 25 to the hermetic port 23
The amount of heat flowing into the envelope 14 through the superconducting element 15
Is not transmitted to the package element 44 having the built-in. This means that, even when an element other than a thermocouple is used as the temperature sensor 16, when a signal line required for the temperature sensor is wound around the signal relay unit 22 as described above,
There is an effect that the cooling temperature of superconducting element 15 can be easily lowered. The drive signal line 2 of the superconducting element 15
The same applies to the signal line 25 for the signal line 25.
In this way, by adopting the structure as shown in FIG. 6, the superconducting element 15 can be more effectively cooled by the cooler 11, and the superconducting element 15 can be cooled down to an extremely low temperature in a short time and reliably. It became possible to cool.

As described above, according to the above embodiment, the superconducting element 15 can be reliably cooled to the cryogenic temperature region in a short time.

Therefore, according to the above embodiment, it is possible to overcome the hurdles such as the downsizing and continuous driving required for applying the superconducting element to the electronics field, and the superconducting element will be widely used in the future. Is expected.

In the above embodiment, the cooler 11 is of a split type in which the compressor section of the compressor 12 and the cooling section 13 of the expander are separated by a connecting pipe 35. However, an integrated type cooler may be used. Good. However, when the cooler 11 is of a split type, the measuring unit including the cooling unit 13 and the superconducting element 15 has a size that can be put on a hand, and has an effect of approaching practical use as a small superconducting sensor. .

Next, FIG. 10 shows a second embodiment of the present invention. In FIG. 10, reference numeral 101 denotes a superconducting magnetoresistive element,
02 is a sensor signal processing unit that processes the output signal of the superconducting magnetoresistance element 101, 103 is a high-pass filter circuit,
Reference numeral 104 denotes a display unit for displaying a magnetic field signal to be measured; 105, a temperature sensor; 106, a signal conversion unit for converting a signal from the temperature sensor 105; 107, a control unit for controlling a cooler 112 which is a Stirling cycle cooler; Is a compressor, 109 is a connecting pipe, 110 is a cold finger or cooling unit, 111 is an envelope, 1
Reference numeral 13 denotes an AC magnetic field generating coil mounted on the outer periphery of the envelope 111, and reference numeral 114 denotes a correction magnetic field generating coil mounted on the outer periphery of the envelope 111. The AC magnetic field generating coil 113 and the correction magnetic field generating coil 114 are driven by a coil driving unit 115.

The output voltage signal of the superconducting magnetoresistive element 101 is input to the sensor signal processing unit 102. As shown in FIG. 18, the sensor signal processing unit 102 includes an amplifier 132 to which the output voltage signal of the element 101 is input, a bandpass filter 133, an amplifier 134, a demodulator Z, and a low-pass filter 131. The demodulator Z receives a synchronization signal g. The demodulator Z and the low-pass filter 131 constitute a lock-in amplifier.

The cooling system including the Stirling cycle cooler of this embodiment includes a cooler 112 and a control unit 107.
, A temperature sensor 105, and a signal converter 106. The cooler 112 includes a compressor 108, a connecting pipe 109, and a cold finger 110.
It is composed of

The temperature sensor 105 is attached to the tip of the cold finger 110 and
Monitor the temperature at the 0 tip. The output signal of the temperature sensor 105 is converted by the temperature signal conversion unit 106 into a signal suitable for input to the control unit 107. Control unit 107
Supplies a compressor control current to the compressor 108. The compressor control current controls the output of the compressor 108 so that the temperature at the tip of the cold finger 110 becomes a predetermined temperature at which nitrogen becomes a liquid.

In the initial stage of the operation of the above embodiment, the output signal of the temperature sensor 105 has not reached the predetermined value representing the predetermined temperature (liquid nitrogen temperature) and has been separated from the predetermined value. Therefore, in the initial operation, the control unit 1
The compressor control current supplied from 07 to the compressor 108 is larger than when the output signal of the temperature sensor 105 is near the predetermined value. Then, as the temperature of the tip of the cold finger 110 approaches the predetermined temperature (liquid nitrogen temperature), the compressor control current decreases. And the above cold finger 11
When the temperature at the leading end of the temperature 0 coincides with the predetermined temperature and the temperature represented by the output signal of the temperature sensor 105 coincides with the predetermined temperature, the control unit 107 sends a signal to the compressor 10.
The compressor control current output to 8 becomes zero.

The above-described embodiment incorporating the Stirling cycle cooler is operated as described above, and a long-time continuous operation can be realized without supplying a refrigerant.

In FIG. 11, a superconducting magnetoresistive element 101 and a temperature sensor 105 are mounted on a cold finger 110, and an AC magnetic field generating coil 113 and a correction magnetic field generating coil 114 are mounted on the outer periphery of a nonmagnetic envelope 111. It is an entity schematic diagram showing a state. Cold finger 1
Since the diameter of 10 is at most about 1 cm, the envelope 111 can be downsized, and the magnetic detection unit can be downsized.

The magnetic field to be measured is input to the superconducting measuring apparatus of this embodiment, as indicated by an arrow 116 shown in FIG. The gap between the envelope 111 and the superconducting magnetoresistive element 101 is maintained in a vacuum state. The gap can be set to be considerably small, the distance between the superconducting magnetoresistance element 101 and the object can be shortened, and the loss until the magnetic field generated from the object reaches the element 101 can be reduced. Therefore, the measured magnetic field from the measured object can be measured with high sensitivity.

FIG. 12 shows a detailed shape of the superconducting magnetoresistive element 101. As shown in FIG. 12B, which is a cross-sectional view, the superconducting magnetoresistive element 101 includes a nonmagnetic substrate 121.
And a superconducting film 122 composed of a weakly-coupled aggregate in which minute oxide superconducting particles are coupled in a point form via an extremely thin insulating film (not shown) on the non-magnetic substrate 121. ing. The superconducting film 122 is processed in a meandering shape by machining or electrodeposition. In addition, as shown in FIG.
Current electrodes 123a, 123b and voltage electrodes 124a, 124b are formed on the second electrode 2 by vapor deposition of titanium (Ti).

As shown in FIG. 12A, the current electrode 12
A current source 125 is connected to 3a and 123b, and a voltage electrode 124
The output voltage measuring device 126 is connected to a and 124b. By driving the current source 125 and the output voltage measuring device 126, the superconducting magnetoresistive element 101 is driven to a state in which magnetism can be measured.

When a magnetic field having a strength not less than a certain value is applied, the superconducting magnetoresistance element 101 transits to a normal conductor,
An electric resistance proportional to the strength of the applied magnetic field appears. Therefore, when a constant current is applied to the superconducting magnetoresistance element 101 from the current electrode 123, an output voltage corresponding to the strength of the applied magnetic field is output from the voltage electrode 124.

The output characteristics of the superconducting magnetoresistive element 101 are measured as shown in FIG. That is, an external magnetic field applying coil 127 is arranged around the element 101,
A current is applied to the coil 127 to apply a magnetic field (external magnetic field) to the element 101 from the coil 127.

One example of the output characteristics of the element 101 is shown in FIG.
3 is shown. The characteristic shown in FIG. 13 is such that when an external DC magnetic field is applied to the element 101 from the coil 127 for applying an external magnetic field while a constant current of 10 mA flows from the current electrode 123 to the element 101, the superconducting magnetoresistive element 101 This is the characteristic of the output voltage to be output. That is, in FIG.
The vertical axis represents the value of the output voltage from the voltage electrode 124 of the element 101, and the horizontal axis represents the strength of the external magnetic field.

Also, as shown in FIG.
FIG. 15 shows the magnitude of noise included in the output voltage of the element 101 when the intensity of the external DC magnetic field applied to the element is changed. In FIG. 15, the vertical axis indicates the magnitude of noise. As can be seen from FIG. 15, the noise of the output voltage of the element 101 hardly changes even when the strength of the externally applied magnetic field changes. That is, no matter what the value of the externally applied magnetic field is, the value is several H higher than the high frequency noise.
Low frequency noise below z is large. This generally means that
This indicates that high-precision measurement of a weak magnetic field such as a DC or low-frequency magnetic field is difficult.

Therefore, in this embodiment, a high-frequency magnetic field is applied in advance to the superconducting magnetoresistive element 101 surrounded by the coil 113 by applying an alternating current to the alternating magnetic field generating coil 113, separately from the magnetic field to be measured. I am trying to do it. Thus, the superconducting magnetoresistive element 101 is operated in a high-frequency region, so that when measuring a low-frequency weak magnetic field, measurement accuracy is not reduced by low-frequency noise. This will be described in detail below while explaining the operation of this embodiment.

First, a constant current is applied to the superconducting magnetoresistance element 101 from the current electrode 123 shown in FIG.
Then, an AC current is applied to the AC magnetic field generating coil 113 shown in FIG. 11 to apply a high frequency (about 1 KHz) AC magnetic field to the superconducting magnetoresistive element 101. Then, the electric resistance of the superconducting magnetoresistive element 101 changes according to the magnetic field change of the AC magnetic field, and the voltage electrode 24 of the element 101 changes.
Thus, an output voltage waveform synchronized with the applied waveform of the AC magnetic field is obtained.

In this state, as shown in FIG. 11, when a measured magnetic field having a frequency lower than the AC applied magnetic field is applied to the element 101 from the outside, the resistance change of the element 101 due to the AC magnetic field causes the low resistance. The resistance change of the element 101 due to the frequency measurement magnetic field is superimposed. The superposition of the low frequency magnetic field and the high frequency magnetic field will be described in detail below.

FIG. 16A shows the waveform of the AC magnetic field generated by the AC magnetic field generating coil 113. That is, FIG.
The signal a shown in (A) is the AC applied magnetic field. In this embodiment, the signal a is a sine wave having a frequency of about 1 KHz. The signal b shown in FIG. 16B is output from the superconducting magnetoresistance element 101 when the alternating magnetic field shown by the signal a is applied to the superconducting magnetoresistance element 101 and the magnetic field to be measured is zero. Output voltage signal. This signal b
Is a signal having a waveform obtained by folding a sine wave around the 0 V level, and a signal having a frequency that is twice the frequency of the signal a.

The signal c shown in FIG.
1. In addition to the AC applied magnetic field, an external DC magnetic field
When (+ ΔB) is applied, the superconducting magnetoresistive element 10
1 is a signal to be output. As shown in FIG. 16C, when a positive external DC magnetic field (+ ΔB) is applied to the element 101, the output voltage signal of the element 101 becomes an output signal whose peak value is shifted to the positive side.

The signal d shown in FIG.
01 is an output voltage signal output from the element 101 when the external DC magnetic field applied to the element 01 is negative (−ΔB). Therefore, as shown in FIG. 16D, the signal d is a signal whose phase is shifted by 180 ° from the signal c.

Now, an arbitrary magnetic field having a frequency considerably lower than the frequency of the AC applied magnetic field generated by the AC magnetic field generating coil 113 is externally applied in the direction indicated by the arrow 116 in FIG.
When applied to the element 101, the superconducting magnetoresistive element 1
The output voltage signal output from 01 is also a signal that is turned back to the positive side at the 0 V level.

A magnetic field signal B (t) shown in FIG. 17A indicates a measured magnetic field signal applied to the element 101 from outside. The signal shown in FIG. 7B is an output voltage signal output from the element 101 in the driving state to which the above-mentioned magnetic field signal to be measured is applied and the AC applied magnetic field is applied from the coil 113.

Here, if the AC applied magnetic field signal is represented by A cosωt and the magnetic field signal to be measured is represented by B (t), the output voltage signal V (t) output from the superconducting magnetoresistive element 101 becomes Given by In Equation 1, A is the amplitude of the AC applied magnetic field, and a ₀ is a proportional constant.

[0103]

V (t) = a ₀ | A cos ωt + B (t) | The output voltage signal V (t) can be transformed as shown in the following Expression 2.

[0104]

V (t) = a ₀ | A cos ωt + B (t) | = a ₀ ((A cos ωt + B (t)) ² ) ^1/2 = a ₀ (A ² cos ² ωt + 2A · B (t) cos ωt + B ² (t)) ^1/2 = a ₀ ((1/2) · A ² + B ² (t) + (1/2) · A ² cos2ωt + 2A · B (t) cosωt) ^1/2 As can be understood by referring to FIG.
01 is included in the measured magnetic field signal B (t).
And cosωt proportional to the AC applied magnetic field signal.
(t) cosωt term is included.

This indicates that the measured magnetic field signal B (t) is a signal that can be processed as a signal of the angular frequency ω by the AC applied magnetic field signal Acosωt.

Therefore, the externally measured magnetic field signal B (t)
However, signal processing can be performed as a signal that is not affected by low-frequency noise. From another viewpoint, it can be considered that the AC applied magnetic field signal Acosωt is used as a carrier, and the carrier is balanced-modulated with the measured magnetic field signal B (t). Therefore, FIG.
By passing the output voltage signal of the element 101 shown in FIG. 7 (B) through the bandpass filter 133 shown in FIG. 18 and passing only the AC applied magnetic field signal Acosωt and the measured magnetic field signal B (t), FIG. As shown, the AC applied magnetic field signal Aco
Only a modulation signal f (see 9 in FIG. 17C) obtained by modulating sωt with the magnetic field signal B (t) to be measured is output from the bandpass filter 33 via the amplifier 34.

The modulated signal f is supplied to the demodulation circuit 13
Input to 0. The measured magnetic field signal B (t) is synchronously demodulated from the modulation signal f by the lock-in amplifier shown in FIG.

The synchronization signal g shown in FIG. 18 is a signal synchronized with the signal a, which is an AC applied magnetic field signal, and is a signal obtained by shifting the phase of the signal a. This signal g is input to the demodulator Z, similarly to the signal f. The demodulator Z synchronously demodulates the signal f using the signal g. By this demodulation, a signal h obtained by demodulating the signal f is obtained (see FIG. 17D). The demodulated signal h passes through the low-pass filter 131, so that the carrier component (about 1 KHz) is cut off, and the measured magnetic field signal is reproduced to become the signal i shown in FIG. This signal i is a signal obtained by accurately restoring the waveform of the measured magnetic field signal B (t).

FIG. 19 shows the relationship between the output signal i of the lock-in amplifier and the measured magnetic field signal B (t). In the drawing, the vertical axis represents the output voltage of the lock-in amplifier. The horizontal axis is the intensity of the magnetic field to be measured from the outside.

As described above, according to this embodiment, a low-frequency magnetic field signal to be measured can be accurately measured without being affected by low-frequency noise of the superconducting magnetoresistance element 101.

Finally, the signal flow of this embodiment will be described briefly. When the superconducting magnetoresistive element 101 shown in FIG. 10 reaches a predetermined operating temperature (for example, liquid nitrogen temperature) by the cooling operation of the Stirling cycle cooler, the superconducting magnetoresistive element 101 enters an operating state. In this operating state, coarse adjustment of the superconducting measurement system of this embodiment is performed. In other words, if any large external magnetic field exists, the magnetic field exceeds the magnetic field measurement range of the element 101. Therefore, a DC magnetic field is applied to the element 101 by the correction magnetic field generating coil 114 to offset the large external magnetic field to some extent. Accordingly, the magnetic field intensity reaching the element 101 shifts the signal level within the measurement range of the element 101. The correction magnetic field generating coil 114 for generating the correction magnetic field and the AC magnetic field generating coil 113 are driven and controlled by a coil driving unit 115. Then, the measurement starts after the magnetic field intensity reaching the element 101 shifts to a range where the element 101 can be measured. When the measured magnetic field signal is input in the direction of arrow 116, the superconducting magnetoresistive element 1
From 01, the output voltage signal to the sensor signal processing unit 102 changes. The signal processing operation in the sensor signal processing unit 102 is as described above. Further, the output signal of the sensor signal processing unit 102 is passed through the high-pass filter 103 and displayed on the display unit 104. Since the change frequency of the geomagnetism is a low frequency of 0.1 Hz or less, if the high-pass filter 103 is set so as to cut off the signal of the frequency of 0.1 Hz or less, the influence of the geomagnetism upon measuring the biomagnetic field is reduced. Can be eliminated.

Next, a third embodiment of the present invention will be described. This embodiment is a biomagnetism measuring device for measuring a weak biomagnetic signal from the heart.

As shown in FIG. 20, this embodiment has a superconducting element 207 for detecting biomagnetism and a superconducting element 207.
Superconducting element 2 up to cryogenic temperature at which superconductivity occurs
And a Stirling cycle cooler 214 that cools the 07. This Stirling cycle cooler 214
Includes a compression unit 202 and a cooling unit 203, and utilizes a change in the state of the refrigerant due to a Stirling cycle.

The superconducting element 207 is made of, for example, ceramic-based particles and weakly-coupled superconductor particles having crystal grain boundaries. This superconducting element 20
Reference numeral 7 indicates that the electric resistance R is completely zero under the condition where the magnetic field is not applied while being in the superconducting phenomenon region. Under the condition that the superconducting element 207 is in a superconducting phenomenon region and a certain critical magnetic field B is applied to the superconducting element 207, the superconducting element 207 has a positive electric resistance and the magnetic field B As the resistance increases, the electric resistance of the superconducting element 207 sharply increases. This embodiment is an application of the above phenomenon, and utilizes the ratio of the initial electric resistance R when the superconducting element 207 is cooled to the resistance change ΔR changed by applying a magnetic field to the superconducting element 207. Thus, it is intended to measure a weak biomagnetic field with high accuracy.

FIG. 27 shows the structure of the superconducting element 207 in detail. In the superconducting element 207, a superconducting film 82 made of an aggregate of weakly coupled points is formed on a non-magnetic substrate 281, and this film 82 is formed into a meander shape by machining or electrodeposition. Titanium (T
i) is deposited by a vapor deposition method to form current electrodes 284a and 284b and voltage electrodes 283a and 283b.

The superconducting element 207 may be formed by forming minute oxide superconducting particles on the nonmagnetic substrate 281 via an extremely thin insulating film.

As shown in FIG. 27A, this element 207
Is used, a current source 285 is connected between the current electrodes 284a and 284b, and an output voltage measuring device 286 is connected between the voltage electrodes 283a and 284b.

Further, in this embodiment, as shown in FIG. 21B, the package element 222 produced by packaging the
1 As the package element in which the superconducting element is packaged, various known elements can be used. For example, the element described in "Superconducting Package Element" (Japanese Patent Application No. 4-31650), which has already been applied for a patent, can be used.

As shown in FIG. 23, the superconducting element 20
The package element 222 in which the package 7 is packaged and the cooler 203 are surrounded by a non-magnetic envelope 215. The envelope 215 is used to radiate heat from the superconducting element 207 and the cooler 2.
03 can be prevented, and the cooling capacity can be improved. Further, the inner space 2 of the envelope 215
In a case where 44 is in a vacuum state, superconducting element 207 can be thermally insulated in vacuum from outside air, and an excellent cooling effect can be achieved. Further, the inside of the envelope 215 may be sealed with an inert gas atmosphere such as helium, nitrogen, argon, or neon.

As shown in FIG. 23, superconducting element 2
07 and a temperature output signal line 243 of the temperature sensor 204 from the package element 222 and the temperature sensor 204 via the signal line relay 245 to the hermetic port 241, 24
1 is drawn out of the envelope 215. The signal output from the temperature output signal line 243 is fed back to the signal converter 208 shown in FIG. 20 and used to control the cooling capacity of the Stirling cycle cooler 214.

In this embodiment, in order to efficiently converge the biomagnetism to the superconducting element 207, as shown in FIG. 21B, the superconducting element 207 was made of a material having a high magnetic permeability above the detection surface. A truncated-cone permalloy 220 having a truncated-cone shape is arranged. The frustoconical permalloy 220 is arranged so as not to contact the cooling plate 221 and the superconducting element 207 so as not to be a load for cooling the cooling section 203. That is, in this embodiment, as shown in FIG. 23, a truncated conical permalloy 220 is attached to the front inner peripheral surface 215a of the envelope 215, and
0 is opposed to the superconducting element 207, and the frusto-conical permalloy 220 does not touch the package element 222.

In this embodiment, the frustoconical permalloy 2 is used.
Although permalloy (relative permeability μs 10 ⁴ ) is used as the high permeability material forming 20, a material having a high relative permeability such as silicon steel may be used as the high permeability material. However, it should be noted that the high permeability material may be magnetized during the measurement and its characteristics may fluctuate. Therefore, use the material in a state where the strong magnetic field is canceled by the correction coil 205. Therefore, it is necessary not to expose the permalloy 220 to a strong magnetic field higher than the biomagnetism.

In this embodiment, the temperature sensor 204
Is disposed between the cooling unit 203 and the superconducting element 207 so that the cooling temperature of the cooling unit 203 can be monitored.
07. However, the temperature sensor 2
It is necessary to arrange so that low-temperature heat can be reliably transmitted from the cooling section 203 to the element 04 and the element 207 without loss.

This embodiment is similar to that of FIGS.
As shown in FIG. 7, a correction coil 205 for performing magnetic correction so that terrestrial magnetism, urban magnetic noise and the like does not reach the superconducting element 207 is provided.

The correction coil 205 and the AC magnetic field coil 206, which are electromagnetic coils, are mounted on the outer surface of the envelope 215 surrounding the superconducting element 207. Correction coil 2
05 is caused by an external magnetic field such as terrestrial magnetism or urban noise magnetism.
It is provided to prevent the magnetic field applied to the superconducting element 207 from exceeding the measurement range. That is, the correction coil 205 generates a correction magnetic field that cancels out an external magnetic field such as the terrestrial magnetism or the urban noise magnetism, and converts the DC magnetic field input to the superconducting element 207 into a signal level within a range in which the superconducting element 207 can measure. Shift up to

The AC magnetic field coil 206 applies a high frequency AC magnetic field to the superconducting element 207 which is not affected by the low frequency fluctuation inherent to the superconducting element 207. Due to the AC magnetic field generated by the AC magnetic field coil 206, the superconducting element 207
A signal synchronized with the AC magnetic field is output.

When a biomagnetic signal having a frequency lower than the AC magnetic field applied to the superconducting element 207 is applied to the superconducting element 207, the output signal of the superconducting element 207 changes. The output signal of the superconducting element 207 includes a signal component obtained by modulating an AC magnetic field signal generated by the AC magnetic field coil 206 with a biomagnetic signal.

In order to process a signal output from the superconducting element 207, a magnetic signal processing section 210, a filter section 211, an image section 212, and an output section 213 are connected to the superconducting element 207 in this order. The image section 212
Converts the biomagnetic signal from the heart captured from the superconducting element 207 into a waveform and displays it as a visible image.

In order to allow visual observation of the biomagnetism from the heart, the image section 212 may be configured as shown in FIG. In FIG. 24, reference numeral 250 denotes a storage oscilloscope for imaging a biomagnetic signal.
1 and the computer 251 analyzes the signal to perform a test diagnosis based on the biomagnetic signal. Also, the disk device 252 and the output device 2
53 is used to record diagnostic data. With this configuration, it is possible to compare and examine many measurement data. Also, the image section 212 is
The configuration shown in FIG. In FIG. 25, the biomagnetic signal input to the storage oscilloscope 250 is converted into a video signal by a video signal converter 261 and input to a television monitor 262. The television monitor 262 converts the biomagnetic signal by imaging. Project on the screen. And
The image is recorded on the VCR 263, and the image data is stored on the VTR tape 264. The image data can be output from the video printer 265 as needed.

On the other hand, as shown in FIG. 20, the cooler 214 of the Stirling cycle system is roughly divided into a compression section 202 as a compressor and a cooling section 20 as an expander.
3 is comprised. In order to reliably transmit the low-temperature heat from the cooling unit 203 to the superconducting element 207 mounted on the cooling unit 203 without loss, the cooling unit 203 includes an envelope 215.
Surrounded by The cooling unit 203 is vacuum-insulated by the envelope 215. Needless to say, the envelope 215 is made of a non-magnetic material that is not affected by magnetism in order to measure biomagnetism with the superconducting element 207. Further, a temperature sensor 204 is mounted on the cooling unit 203. This temperature sensor 204
The temperature of the cooling unit 203 is detected and a temperature detection signal is output to the signal conversion unit 208. The signal conversion unit 208 converts the temperature detection signal into a control signal, and converts the control signal into the control unit 20 that controls the Stirling cycle cooler 214.
Transmit to 1. The control unit 201 controls the temperature sensor 204
In response to the control signal fed back from the controller, the compressor 202 is controlled to cool the cooling unit 203 to an extremely low temperature. The extremely low temperature is a temperature at which the cooling unit 203 can cool the superconducting element 207 to a temperature at which a superconducting phenomenon occurs. The control signal from the signal conversion unit 208 can control the control unit 201. It has been amplified to the volt order.

The control unit 201 further controls the cooling capacity of the cooler 214 by outputting a signal obtained by increasing or decreasing the control signal by several volts to the cooler 214, The cooling temperature can be varied.

FIG. 26 is a circuit diagram of the signal conversion unit 208. As shown in FIG. 26, the signal conversion unit 208
An amplification unit and a temperature shift unit are included. The amplifying unit is an inverting amplifying circuit including an operational amplifier, and the temperature shifting unit is a differential amplifying circuit including an operational amplifier. In this embodiment, the temperature sensor 204 shown in FIG.
However, the temperature sensor 204 may be formed of a platinum resistor or a thermistor capable of measuring low temperature.

The operation of the above embodiment will be described in detail below with reference to the drawings.

First, referring to FIG.
Operation 3 will be described. The cooling section 203 is connected to the compression section 202 shown in FIG. 20 by a connecting pipe (not shown).

Then, helium (He) gas as a refrigerant gas as a working fluid is sent from the compression section 202 through the connecting pipe to the cooling section 203. The He gas is compressed by the compression piston inside the compression cylinder of the compression unit 202 and sent to the cooling unit 203 in a pressurized state. Then, the He gas is adiabatically expanded and cooled in the expansion low-temperature chamber 230 by the elevating movement of the displacer 231 having the shape of an elongated piston. The expansion low-temperature chamber 230 is a space that is expanded and contracted between the upper end of the displacer 231 and the cooling tip 235. The displacer 231 repeats the gas spring reciprocating motion in the expansion cylinder 234 while maintaining a certain phase difference with respect to the pressure fluctuation generated by the compression unit 202.

Inside the displacer 231, a regenerator 232 is provided. Gas holes 233 are provided on the outer peripheral surface of the displacer 231 facing the expansion cylinder 234 and on the upper end surface of the displacer 231. I have. Then, the pressurized He gas sent by the compression unit 202 is cooled when passing through the regenerator 232 and sent out to the expanded low-temperature chamber 230. Thereafter, when the displacer 231 returns to the original position (to the left in FIG. 22), the He gas is adiabatically expanded and cooled in the expanded low-temperature chamber 230. The He gas cooled in the expansion low-temperature chamber 230 is sent back to the compression unit 202 through the connecting pipe while cooling the regenerator 232. By continuously operating this movement as one cycle, the cooling tip 235 is cooled to an extremely low temperature.

That is, the cooling unit 203 compresses the helium extremely low-boiling refrigerant gas at a constant temperature, cools at a constant volume, expands at a constant temperature,
The state is changed by a Stirling cycle in which each process of constant volume heating is repeated in this order, and the heat absorbed from the superconducting element 207, which is a substance to be cooled in the above isothermal expansion step, is released to the outside in the above isothermal compression step. To cool.

Adjustment of the cooling temperature of cooling section 203 is performed by a temperature shift section (see FIG. 26) included in signal conversion section 208 shown in FIG.

As shown in FIG. 23, the temperature sensor 204 is constituted by a thermocouple (E), and this thermocouple is wound around the signal relay section 245. By doing so, the hermetic port 241 is connected to the external temperature output signal line 243.
The heat is prevented from flowing into the thermocouple through the thermocouple.
As a result, the amount of heat flowing into the envelope 215 is absorbed by the signal relay unit 245, and the amount of heat is
7 is not transmitted to the package element 222 having the built-in 7. In addition, elements other than the thermocouple are
Even in the case of 4, the cooling temperature of the superconducting element 207 can be easily lowered by winding the wire portion of the temperature sensor 204 around the signal relay portion 245 as described above. Note that the same can be said for the element driving signal line 242 for driving the superconducting element 207 as for the temperature output signal line 243.

As described above, by adopting the structure as shown in FIG.
The cooling effect of the superconducting element 14 can be improved, and the superconducting element 207 can be reliably cooled to the cryogenic temperature region in a short time.

Further, even if a biomagnetic subject or measurer touches the envelope 215, the low temperature of the cooling section 203 can be prevented from being transmitted to the subject or measurer. Compared to a device that cools a superconducting element with a liquid refrigerant,
The degree of freedom of the measurement style is improved. That is, as shown in FIG. 32, the biomagnetism of the subject 1134 can be measured with the subject 1134 in a comfortable style. This also has the effect of reducing the disturbance of the biological signal of the subject due to the stimulus or the like that the subject receives from vision.

In the above embodiment, since the superconducting element 207 is cooled in the configuration shown in FIG. 23, the superconducting element 207 can be cooled to around 77 K or less, which is necessary for the superconducting element 207, and the chest of the subject can be cooled. And the superconducting element 207 is cooled to an extremely low temperature, and the exposed surface of the above embodiment is kept at a temperature at which there is no problem even if the subject and the measurer touch it. In addition to the above, condensation can be prevented.

FIG. 31 shows the output characteristics of the superconducting element 207. This characteristic is obtained when a constant current of 1 mA is applied to the element 207 shown in FIG. 27 through the current electrodes 284a and 284b and the correction coil 20 shown in FIGS.
Reference numeral 5 indicates a change in the output voltage of the element 207 when an external DC magnetic field is applied to the element 207 and the external DC magnetic field is changed. Therefore, in FIG. 31, the vertical axis represents the output voltage from the voltage electrodes 283a and 283b of the element 207, and the horizontal axis represents the intensity of the external DC magnetic field. Various known devices can be used for the superconducting element 207 (superconducting magnetoresistive element) exhibiting this characteristic and a device for driving the superconducting magnetoresistive element. For example, those described in “Superconducting Magnetoresistance System” (Japanese Patent Application No. 62-233369) and “Superconducting Magnetic Field Measuring Device” (Japanese Patent Application No. 1-130306) which have already been applied for patents can be used.

The output signal of the superconducting element 207 is shown in FIG.
0 is input to the magnetic signal processing unit 210. The magnetic signal processing section 210 includes a band elimination filter and a lock-in amplifier. Then, the output signal of the superconducting element 207 is input to the band elimination filter, and then to the lock-in amplifier.

The band elimination filter covers the frequency of a signal for generating a magnetic field in the AC magnetic field coil 206 and the frequency of the biomagnetic signal. That is, the band elimination filter is used for the AC magnetic field coil 206.
Selectively pass the frequency of the signal for generating a magnetic field and the frequency of the biomagnetic signal. Further, the lock-in amplifier synchronously demodulates the biomagnetic signal from a signal component obtained by modulating the AC magnetic field signal generated by the AC magnetic field coil 206 with the biomagnetic signal. In order to perform the synchronous demodulation, the lock-in amplifier includes an AC magnetic field coil 20.
A signal having the same frequency as the AC magnetic field generated by the coil 6 is transmitted from the coil driving unit 209 shown in FIG.

That is, by passing the output signal of the superconducting element 207 through the band elimination filter, only the signal component obtained by modulating the AC magnetic field signal with the biomagnetic signal is selected from the output signals of the superconducting element 207. And output from the band elimination filter. The modulated signal output from the band elimination filter is input to the lock-in amplifier, and the lock-in amplifier synchronously demodulates the biomagnetic signal.

Since there is a great deal of random noise superimposed on a regular magnetic signal generated from the heart, in order to avoid the influence of the random noise, in this embodiment, the averaging process of the demodulated biomagnetic signal is performed. Is repeated. Then, an inspection and diagnosis are performed using the averaged biomagnetic signal.

Further, since this embodiment is a biomagnetism measuring apparatus for measuring weak magnetism from the heart, the filter section 211 is used to cut low frequency geomagnetism of 0.1 Hz or less. Includes a 0.5 Hz Butterworth high pass filter. The signal that has passed through the filter unit 211 is input to the image unit 212 and is converted into an image signal that can be visually observed by being imaged.

In this embodiment, the image part 212 is
As shown in FIG. 1, a storage oscilloscope 250 as a digital storage scope is provided. The image unit 212 uses a function generally called a roll mode to rewrite the low-frequency waveform of the biomagnetic signal,
The waveform is sequentially displayed on the digital storage scope. Specifically, according to this embodiment, the biomagnetism from the heart is measured, and the demodulated biomagnetic signal is
A sample averaging process is performed 100 times. Thus, the signal waveform output from the output unit 213 shown in FIG. 20, that is, the biomagnetic signal is shown in FIG. FIG. 28 (B)
Is a magnetocardiogram. The vertical axis of FIG. 28B represents the strength of biomagnetism, and the horizontal axis represents time. Note that FIG.
Is an electrocardiogram, which shows a waveform measured by a conventional electrocardiograph. As can be seen by comparing FIGS. 28A and 28B, the peak waveform point based on the magnetocardiogram has a time lag compared to the peak waveform point based on the electrocardiogram. This time delay is
It is caused by contraction of the heart muscle after an electric signal flows to the heart due to the action potential of the excitable cells. The magnetocardiogram in FIG. 28B shows one cycle after averaging in 100 cycle measurements in order to reduce random noise superimposed on a regular signal.

FIG. 3 shows the appearance of this embodiment and the actual measurement state.
It is shown in FIG. As shown in FIG. 32, according to this embodiment,
The subject cooler 1135 has the element cooler 1130 and the subject 1
By approaching the chest at 134, biomagnetism from the heart can be measured. The element cooler 1130
Includes an envelope 215 surrounding the cooling unit 203 and the superconducting element 207 and a Stirling cycle cooler 214.

As described above, according to this embodiment, it is possible to measure the weak magnetism from the heart with high sensitivity, and to obtain a clear biomagnetic signal by reducing the influence of geomagnetism or an external magnetic field. A simple biomagnetism measuring device can be realized.

[0152]

As is apparent from the above description, in the superconducting measuring apparatus according to the first aspect of the present invention, the temperature sensor for controlling the cooler is provided in the cooling unit, so that the temperature of the cooling unit can be precisely controlled. In addition, the superconducting element can reliably cause the superconducting phenomenon to improve the measurement sensitivity, and when the superconducting element alone fails, only the superconducting element alone needs to be replaced.

According to the second aspect of the present invention, the signal line of the temperature sensor is wound around the signal line relay section attached to the cooling section. The heat insulating effect on the heat transmitted through the wire is enhanced, and the temperature rise that breaks the superconducting state can be avoided.

According to the third aspect of the present invention, since the alternating current magnetic field generating electromagnetic coil is arranged on the outer periphery of the envelope, the superconducting element is operated at a frequency higher than the fluctuation frequency inherent to the superconducting element, and the fluctuation is obtained. The influence of the frequency can be avoided, and the measurement sensitivity can be improved.

According to a fourth aspect of the present invention, since the signal conversion means converts the magnetic field detection signal into a visible image which can be visually recognized, a small and highly sensitive desktop size capable of visually recognizing a weak biomagnetic field. A superconducting measurement device can be realized.

According to the present invention, the cooler for cooling the cooling section on which the superconducting element is mounted is a Stirling cooler for cooling the cooling section by changing the state of the refrigerant according to the Stirling cycle. The superconductivity measuring device can be cooled down to a very low temperature range and the entire superconducting measuring device can be downsized. Therefore, according to the present invention, the superconducting element can be applied to the electronics field.

Further, when the superconducting element is a magnetoresistive element constituted by a superconductor having a weak coupling grain boundary and a magnetic sensor including this magnetoresistive element is provided, a highly sensitive magnetometer can be realized.

[0158] Further, there are provided thermal connection means for thermally connecting the superconducting element to the cooling section, and heat insulating means including a non-magnetic envelope for heat insulation surrounding the superconducting element and the cooling section. The cooling unit can be connected to the superconducting element so that the low-temperature heat of the cooling unit is transmitted to the superconducting element without loss, and the cooling effect can be further improved.

When a temperature sensor and cooling control means for controlling the cooling capacity of the cooler based on a temperature signal from the temperature sensor are provided, the cooling temperature is set in accordance with the characteristics of each superconducting element. In addition, the temperature change of the superconducting element can be observed in the temperature drift after cooling, and the cooler can be controlled so that the superconducting element itself has an ideal cooling temperature.

In the case where the superconducting element and the cooling section are hermetically sealed in a vacuum or an inert gas atmosphere by the non-magnetic envelope, the set temperature of the cooler was changed. This can prevent condensation from occurring. Therefore, the superconducting element can be protected from dew condensation, and the reliability can be improved.

According to the present invention, a maintenance-free compact superconducting magnetic field measuring device can be realized, and a magnetic field measuring device with much higher sensitivity than a conventional magnetic field measuring device can be realized. Therefore, it can be used in various fields such as medical treatment and nondestructive inspection. In addition, since it is small and maintenance-free, it can be applied as a home health care device, which was not suitable in the past, and it will be an application to the electronics field of superconductivity.

Further, in the present invention, the means for cooling the superconducting element is a Stirling cooler for cooling the cooling section by changing the state of the refrigerant according to the Stirling cycle, so that the superconducting element can be cooled down to the cryogenic temperature region easily in a short time. Since the cooling unit is small, a small biomagnetometer can be realized.

Further, according to the present invention, not only the liquid refrigerant (liquid helium or the like) is not required, so that it can be used continuously for a long time, but also a detection unit such as a complicated pickup coil by SQUID measurement is unnecessary. Therefore, a handy type magnetic field measuring device can be realized by paying attention to the magnetic field measuring position. Therefore, the present invention not only allows the superconducting element to be applied to the medical field, but also enables biomagnetic measurement from clinical research to use in hospital diagnosis, which has advanced one step. In addition, in the past, the subject may be disturbed in response to visual stimuli due to an unusual sight of a large device, a complex device, or the like at the time of measurement, and the subject may become unclear, and accurate data may be obtained. However, the apparatus of the present invention can perform measurement even while asking a patient while sitting down, so that disturbance to the subject due to vision or the like can be reduced. This can be expected as a major effect of the present invention in the medical field.

It should be noted that the present invention has an advantage in that biomagnetism can be measured without bringing it into contact with the body, unlike an electrocardiograph which is currently in practical use and generally used in medical treatment.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of the vicinity of a cooling unit of an embodiment of a superconducting measurement device of the present invention.

FIG. 2 is a diagram showing a superconducting element of the above embodiment.

FIG. 3 is a view showing a package element in which the superconducting element of the embodiment is packaged.

FIG. 4 is a diagram showing a change in resistance of the superconducting element of the embodiment.

FIG. 5 is a block diagram of the embodiment.

FIG. 6 is a schematic cross-sectional view showing a state where the cooling unit of the embodiment is surrounded by an envelope.

FIG. 7 is a circuit diagram of a signal converter of the embodiment.

FIG. 8 is a sectional view showing an example of a superconducting cooling method including a conventional cryostat cooling device.

FIG. 9 is a sectional view of a cooling device of a system in which a superconducting element is directly immersed in a refrigerant.

FIG. 10 is an overall block diagram of a second embodiment of the present invention.

FIG. 11 is a sectional view showing the structure of a superconducting magnetoresistive element, a cold finger, an alternating magnetic field generating coil, a correction magnetic field generating coil, and an envelope of the second embodiment.

FIG. 12 is a structural diagram of the superconducting magnetoresistive element of the second embodiment.

FIG. 13 is an output characteristic diagram of the superconducting magnetoresistive element with respect to a DC applied magnetic field.

FIG. 14 is a view showing a state in which characteristics of the superconducting magnetoresistive element are measured.

FIG. 15 is a noise characteristic diagram of the superconducting magnetoresistance element with respect to a DC applied magnetic field.

FIG. 16 is a diagram showing an output signal waveform when an AC magnetic field is applied to the superconducting magnetoresistive element.

FIG. 17 is a waveform diagram including a waveform of an external magnetic field signal applied to the second embodiment, a modulation waveform of an AC magnetic field by the external magnetic field signal, and a demodulated waveform of the external magnetic field signal.

FIG. 18 is a block diagram of a sensor signal processing unit according to the second embodiment.

FIG. 19 is a characteristic diagram showing a relationship between a magnetic field to be measured and an output signal of a lock-in amplifier in the second embodiment.

FIG. 20 is a system block diagram of a biomagnetism measuring apparatus according to a third embodiment of the present invention.

FIG. 21 includes a block diagram and a layout diagram of a portion for detecting biomagnetism according to the third embodiment.

FIG. 22 is a sectional view of the vicinity of a cooling unit of the third embodiment.

FIG. 23 is a schematic sectional view showing a structure of a main part of a magnetic measurement including a superconducting element mounted on a cooling unit of the third embodiment.

FIG. 24 is a block diagram showing a configuration for recording temporal measurement data according to the third embodiment.

FIG. 25 is a block diagram showing a configuration for recording temporal measurement data of the third embodiment.

FIG. 26 is a circuit diagram of a signal conversion unit according to the third embodiment.

FIG. 27 is a view showing the structure of the superconducting element of the third embodiment.

FIG. 28 is a diagram including a magnetocardiogram showing a biomagnetic signal from the heart measured by the biomagnetometer of the third embodiment and a conventional electrocardiogram.

FIG. 29 is a simple principle diagram of a conventionally used SQUID.

FIG. 30 is a block diagram showing an example of a conventionally used SQUID-based biomagnetism measurement apparatus.

FIG. 31 is an output characteristic diagram with respect to a DC applied magnetic field of the superconducting magnetoresistive element of the third embodiment.

FIG. 32 is a schematic diagram showing a measurement state of biomagnetism according to the third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Control part 11 Cooler 12 Compression part 13 Cooling part 14 Envelope 15 Superconducting element 16 Temperature sensor 17 Signal conversion part 20 Package enclosure 21 Cooling plate 22 Signal line relay part 23 Hermetic port 24 Element drive signal line 25 Temperature Output signal line 27 Internal space 30 Expansion low temperature chamber 31 Displacer 32 Regenerator 33 Gas through hole 34 Expansion cylinder 35 Connecting pipe 50 Glass 41 Electrode 101 Superconducting magnetoresistive element 102 Sensor signal processing unit 103 High pass filter 104 Display unit 105 Temperature sensor 106 signal Conversion unit 107 Control unit 108 Compression unit 109 Connecting pipe 110 Cooling unit 111 Enclosure 112 Cooler 113 AC magnetic field generating coil 114 Correction magnetic field generating coil 115 Coil driving unit 116 Arrow 121 Substrate 122 Conductive film 123 current electrode 124 voltage electrode 125 current power supply 126 voltmeter 127 magnetic field application coil 130 demodulator 131 low-pass filter 132 amplifier 133 band-pass filter 134 amplifier 201 control unit 202 compression unit 203 cooling unit 204 temperature sensor 205 correction coil 206 AC magnetic field Coil 207 Superconducting element 208 Signal conversion section 209 Coil driving section 210 Magnetic signal processing section 211 Filter section 212 Image section 213 Output section 214 Cooler 215 Enclosure 220 Frustoconical permalloy 221 Cooling plate 222 Package element 230 Expansion low temperature chamber 231 Displacer 232 Cool storage unit 233 Gas through hole 234 Expansion cylinder 235 Cooling tip 241 Hermetic port 242 Element driving signal line 243 Temperature output signal line 244 Internal vacuum space 24 5 Signal line relay unit 250 Storage oscilloscope 251 Computer 252 Disk device 253 Output device 261 Video signal converter 262 TV monitor 263 Video deck 264 VTR tape 265 Video printer 271 Temperature detection unit 281 Non-magnetic substrate 282 Superconducting film 283 Voltage electrode 284 Current electrode 285 Current source 286 Voltage measuring device 300 Superconducting ring 301 Josephson junction

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-98979 (JP, A) JP-A-2-298765 (JP, A) JP-A-4-25780 (JP, A) JP-A-4-98 61843 (JP, A) JP-A-63-276281 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 39/04 H01L 39/00 H01L 39/22 H01L 39/24 G01R 33/00-33/18 F25B 9/14

Claims (4)

(57) [Claims] 1. A superconducting element comprising a magnetoresistive element is mounted on a tip of a cooling section of a Stirling cycle cooler, and is provided in a cooling section of the Stirling cycle cooler.
A temperature sensor for controlling the Stirling cycle cooler, comprising a non-magnetic envelope surrounding the superconducting element and the cooling unit, and a temperature from a hermetic port provided on a side wall of the non-magnetic envelope. A superconducting measuring device characterized by taking out a signal line of a sensor. 2. The superconducting measuring apparatus according to claim 1, further comprising: cooling control means for controlling a cooling capacity of the cooler based on a temperature signal from the temperature sensor, wherein a signal line of the temperature sensor is A superconducting measuring device, wherein the superconducting element is wound around a signal line relay unit attached to the cooling unit between the superconducting element and the hermetic port. 3. The superconducting measuring device according to claim 1, wherein the superconducting element is a magnetoresistive element exhibiting a superconducting phenomenon, wherein the superconducting element has a frequency higher than a low-frequency fluctuation frequency inherent to the superconducting element. An electromagnetic coil for generating an alternating magnetic field arranged on the outer periphery of the envelope to apply an alternating magnetic field, a resistance value detecting means for detecting a resistance value of the magnetoresistive element, and a resistance value detecting means for detecting the resistance value. A signal converter for converting a resistance value of the magnetoresistive element into a magnetic field strength signal representing a magnetic field strength applied to the magnetoresistive element. 4. The superconducting measurement apparatus according to claim 1, wherein the superconducting element detects a weak magnetic field, receives the magnetic field detection signal output from the superconducting element, and visualizes the magnetic field detection signal. A superconducting measurement apparatus comprising: a signal conversion unit for converting a visible image; and measuring a weak biomagnetic field.