JPH0361879A - Magnetic flux detection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention A0 Object of the Invention (1) Industrial Application Field The present invention is directed to SQUID, Sup
ercond-ucttng Quatituw+I
The present invention relates to a magnetic flux detection device using a super (Yindo quantum interference magnetometer).

This type of magnetic flux detection device is used to detect magnetic fields with high precision in fields such as medicine and resource exploration.

Conventional technology: SQUID utilizes the phenomenon that the current flowing through the digo-Sefson element in a superconducting state depends extremely sensitively on changes in the magnetic field.
February 4th issue, pages 19-25 about r3QυID”,
The Institute of Electronics and Communication Engineers (19th edition) and the Institute of Electronics and Communication Engineers (19th edition)
82/6 VOL.

J65-CN0.6, pp. 475-482 "SQUIDm flux meter using niobium thin film bridge and its performance evaluation")
etc. are introduced. These publications describe magnetic flux detection devices using DCC SQUIDs and RF SQUIDs. The magnetic flux sensing device described therein detects magnetic flux in a sensing coil that is inductively coupled to a SQUID. The magnetic field where the detection coil is located is obtained by dividing the detected magnetic flux by the area of the detection coil.

Next, according to FIG. 3, the conventional RF described in the said publication
An example of a magnetic field detection device using a SQUID will be described.

In FIG. 3, a detection coil 01 for detecting a change in external magnetic flux Φ8 in the X direction is connected to an input coil 03 via a magnetic flux transmission section 02, and they form a closed circuit. This input coil 03 is arranged so as to be inductively coupled to the SQUID 04. This SQUID 04 is a ring made of a superconductor having a Josephson junction 04a in a part thereof. An RF coil 05 arranged to be inductively coupled to the SQUID 04 forms a resonant circuit 07 together with a capacitor 06. Also,
A feedback coil 08 is arranged to be inductively coupled to the SQUID 04. Said code 01~0
The components indicated by 8 are housed in a low temperature chamber 09 indicated by a dashed line and are maintained at a temperature rise of 3 or less. Further, the components indicated by the reference numerals 03 to 08 are housed in a shield case 09a indicated by a dashed line and are shielded from external magnetic fields.

The resonant circuit 07 receives weak high-frequency power from an RF bias current source 010 that oscillates at a high frequency (for example, 22M&), and resonates at 22M&.
The 22 MHz signal is amplitude-modulated by the SQUID 04 according to the sum of the magnetic fluxes of the input coil 03 and the feedback coil 08. This amplitude-modulated signal, that is, the magnetic flux detection signal is sent to the RF amplifier and detector 011.
The signal is amplified and detected and input to the lock-in amplifier 012.

The lock-in amplifier 012 is a banfa amplifier 0.
13, phase detector 014, and reference signal oscillator 015
The bottom of the tank has been removed from the water. And reference signal oscillator 015
is a reference signal (for example, 50 K
Hz), and this reference signal is applied to the feedback coil 08. The lock-in amplifier 012 is the RF amplifier and detector 011.
Among the input signals from the input signal, only the signal modulated at 50 KHz is detected and output to the integrating amplifier 016. The DC signal output from the integrating amplifier 016 passes through a feedback line 017, and the feedback coil 08 generates a feedback magnetic flux Φ8'. This feedback magnetic flux Φ8' has a magnitude and direction that cancels out the external magnetic flux Φ8.

Further, the output signal of the integrating amplifier 016 is taken out from both ends of the resistor R0 as a magnetic flux detection signal vo.

Next, the operation of the conventional magnetic flux detection device shown in FIG. 3 will be explained.

First, in FIG. 3, the total magnetic flux acting on the SQUID 04 is assumed to be Φ, and the case where this magnetic flux Φ changes will be considered.

In this case, the magnetic flux inside the SQUID 04 is a magnetic flux quantum Φ. (
-2,07 1. (See Figure 4) flows.

This shielding current ■ is the critical current ■ of SQUID 04. The magnetic flux flows in superconductivity until reaching the critical current 1c, but when it reaches the critical current 1c, it becomes normal conduction and magnetic flux flows in and out of the SQUID 04.

The magnitude of this shielding current Is is Φ/Φ. 4th for the value of
The relationship is as shown in the figure, and the magnetic flux quantum Φ. It is a periodic function whose unit is .

By the way, out of the magnetic flux acting on the SQUID 04,
When the feedback magnetic flux Φ8' is set to 0 and the alternating current magnetic flux due to the 50 KHz reference signal for improving detection accuracy is ignored, that is, the RF coil 0 is generated by the RF bias current source 010 as the magnetic flux acting on the SQUID 04.
AC magnetic flux Φ, sin generated by the high-frequency current flowing through 5
Consider a case where only ωt and the external magnetic flux (DC magnetic flux) Φ8 act. In this case, the alternating current magnetic flux Φ* si
The induced voltage (■) when the amplitude Φ of nωt is changed is the magnetic flux Φ and -O (and Φ8-nΦ, n=1.
2. . . ), the solid line in FIG. (and Φ8-n
Φ. +(1/2)Oos n-1, 2°...), the result is as shown by the broken line in FIG.

In FIG. 5, when Φ and -Φ are fixed, when the magnetic flux Φ8 generated in the implant coil 03 changes, the induced voltage V of the resonant circuit 07 becomes as follows. That is, Φ8−nΦ. When V-VA ΦK = (n + 1/2) Oo O) then V-VBnΦ. Φ<(n+1/2)Φ. or (n+1/2)Φ. kuΦ, < (n+1)Φ. When V, <V<V.

However, n-0, 1, 2,... In this case, with respect to the magnetic flux ΦX generated in the input coil 03, that is, the external magnetic flux detected by the detection coil 01, the induced voltage V of the resonance circuit o7 As shown in Fig. 6, the flux changes periodically between V and V in units of magnetic flux Φ0, forming a triangular wave pattern.

Actually, a feedback current flows through the feedback coil o8 so as to generate a feedback magnetic flux Φ' which is large enough to cancel out the change in the magnetic flux Φ generated in the input coil 03.

Therefore, the output signal of the integrating amplifier 016 and the magnetic flux detection signal vo are always applied to the input coil 03.
changes in response to changes in the magnetic flux Φχ.

By detecting the magnetic flux detection signal v0 with high precision, the magnetic flux quantum Φ. 1/1000 to 115000 of the unit
It is possible to detect changes in magnetic flux with a certain degree of accuracy. In this case, the flux quantum Φ. If the magnitude of the magnetic field obtained by dividing S by the area S of the detection coil is defined as the "unit magnetic field" of the detection device, changes in the external magnetic field can be detected with an accuracy of about 1/1000-115000 of the unit magnetic field. . Note that the unit magnetic field becomes smaller as the area S of the SQUID is increased, so by increasing the area S, the detection accuracy of the magnetic field can be improved.

Furthermore, the magnetic flux quantum Φ. If there is no need to detect the magnetic flux Φ with higher precision than the unit, that is, the change in the magnetic flux Φ8 is determined by the flux quantum Φ. When detecting in units (that is, when detecting changes in the external magnetic field with the precision of a unit magnetic field), there is no need to feed back the output signal of the integrating amplifier 016 shown in FIG. 3 to the feedback coil 08. The magnetic flux detection signal has the same shape as V shown in FIG. That is, as can be seen from FIG. 6, when the external magnetic flux Φ entering the detection coil O1 changes, the magnetic flux detection signal indicates that the magnetic flux within the detection coil 01 is nΦ.

Every time , it becomes VA (the peak value of the triangular wave pattern), and (n+1/2)Φ. The number of magnetic fluxes penetrating the detection coil 01 can be determined by recording the magnetic flux detection signal with a recorder or the like and counting the number of peaks or valleys of the triangular wave pattern. Change the magnetic flux quantum Φ. It is possible to measure the change in the external magnetic field in units (that is, the accuracy of the unit magnetic field).

(3) Problems to be Solved by the Invention In the magnetic flux detection device shown in FIG. 3, when detection is started, external magnetic flux Φ is already present in the detection coil 01. (
(see Figure 6), it is possible to detect only changes in the magnetic flux within the detection coil 01 from that state.
When counting the number m of peaks of the triangular wave up to Φ0), it is possible to detect the change in the magnetic flux at the location where the detection coil 01 is placed, and the magnitude of the magnetic flux (i.e., the magnitude of the magnetic flux with respect to 0) The problem is that it cannot be detected.

The above is an explanation regarding a magnetic flux detection device using an RF Squid.
Similarly, a magnetic flux detection device using a magnetic flux sensor (Hon 5QID) can only detect changes in the magnetic flux within the detection coil from that state if external magnetic flux has already entered the detection coil when detection is started. However, in this case, there is a problem in that the magnitude of the magnetic flux at the location where the detection coil is placed cannot be detected.

If there is a suitable means to keep the magnetic flux in the detection coil at O when the magnetic flux detection device starts magnetic flux detection, the thickness of the magnetic flux at the location where the detection coil is placed (with O as the standard) However, such an appropriate means is not yet known.

Therefore, the magnitude of the magnetic flux ΦX penetrating the detection coil 01 (
A possible method for detecting the value (value based on 0) is to use a combination of a highly accurate magnetic flux detection device using SQUID 04 as shown in Figure 3 and another less accurate magnetic flux detection device. It will be done. In this method, the coarse magnetic flux detection device detects the true value of magnetic flux nΦ in units of magnetic flux quantum Φ0.
. and (n+1)Φ. The magnitude of the magnetic flux ΦX can be detected with high precision by detecting that the magnetic flux Φ However, such a method has a problem in that a magnetic flux detection device with rough precision must be separately prepared.

Further, in the conventional magnetic flux detection device, it is not easy to completely shield the SQUID from external magnetic flux, and there is also a problem that detection accuracy is reduced due to external magnetic flux penetrating into the shield case 09a.

In view of the above-mentioned circumstances, an object of the present invention is to enable highly accurate magnetic flux detection by making the magnetic flux in the detection coil zero when a magnetic flux detection device starts magnetic flux detection.

B0 Structure of the Invention (1) Means for Solving the Problems In order to solve the above problems, the magnetic flux detection device of the present invention includes:
A core made of a superconductor and a SQUID for magnetic field detection made of a superconductor having a higher critical temperature than the core, which is disposed on the surface of this core with an insulating layer interposed therebetween, is configured to detect an external magnetic field. In the magnetic flux detection device of the present invention having the above-described configuration, the core of the superconductor is held at a temperature lower than its critical temperature. The magnetic flux penetrating the inside of the magnetic flux detection SQUID becomes zero.

The temperature of the superconductor core is then varied from below its critical temperature to above the core's critical temperature and below the critical temperature of the SQUID for magnetic flux detection. As a result, the core changes from a superconducting state to a normal conducting state, and the magnetic flux passing through the SQUID for magnetic flux detection changes from zero to the magnitude of the external magnetic flux. This change in magnetic flux within the SQUID is extracted as an electrical signal by conventionally known means and processed. Changes in the magnetic flux passing through the SQUID for detecting magnetic flux are detected based on the state where the passing magnetic flux is O.

The conventional means for extracting the magnetic flux change in the SQUID for magnetic flux detection as an electrical signal is also described in the above-mentioned magazine.For example, when the SQUID is a DCC SQUID, it is divided by a pair of Josephson junctions. There is a means for directly extracting the voltage generated by the DC current flowing through the Josephson junction between the two arc-shaped superconductors, and when the SQUID is an RF SQUID, there is a means for directly extracting the voltage generated by the DC current flowing between the two arc-shaped superconductors. There are RF coils arranged to couple.

(3) Embodiment Next, an embodiment of the magnetic flux detection device of the present invention will be described.

FIG. 1 is an explanatory diagram of a first embodiment of the magnetic flux detection device of the present invention.

In FIG. 1, a SQUID 3 for detecting magnetic flux is disposed on the upper surface of a cylindrical core l made of a superconductor with a thin insulating layer 2 interposed therebetween. This SQUID 3 is an RF SQUID formed by a superconductor ring having one Josephson junction, and is formed by thin film technology. Further, the SQUID 3 is made of a superconductor having a higher critical temperature than the core 1, for example, the core 1 is made of 5n of tin.
(Tcc=3.7'K), niobium Nb (T, -90K) is used for the RF SQUID 3.

Further, a heater 4 serving as heating means for the core 1 is disposed on the lower surface of the core 1 via a thin insulating layer (not shown). This heater 4 is connected to a heating power source B via a switch SW. Further, the switch SW is turned on and off by a core temperature control device S that operates based on the detected temperature of the core 1.

An RF coil 5 arranged to be inductively coupled to the SQUID 3 constitutes a resonant circuit 7 together with a capacitor 6. Further, a feedback coil 8 is arranged so as to be inductively coupled to the SQUID 3. The components indicated by 1 to 8 are placed in a low temperature chamber 9 indicated by a dashed line and maintained at a temperature below the critical temperature.

Components designated by reference numerals 10 to 17 and Ro in FIG. 1 are respectively designated by reference numerals 010-01 in FIG.
Since there is no difference from the conventional components shown by 7 and Ro, the explanation will be omitted.

Note that also in the embodiment shown in FIG.
Similar to the conventional example shown in the figure, the output signal of the integrating amplifier 16 is the magnetic flux detection signal V from both ends of the resistor R0. It is taken out as.

Next, the operation of the first embodiment will be explained.

First, let Tcc and Tck be the critical temperatures of the core 1 and the SQUID 3 for detecting magnetic flux, respectively, and T be the temperature of the core 1, SQUID 3, etc. cooled by the low temperature chamber 9.

(1) Turn off switch SW under external magnetic field B.
Leave it at F, then T<Tcc T. By doing so, the core 1 is transposed to a superconducting state, and the magnetic flux within the area surrounded by the SQUID 3 is eliminated. This is the so-called Meissner effect.

(2) Next, heat the core 1 using the heater 4 and
N.T. By causing the core 1 to transition from a superconducting state to a normal conducting state, the excluded external magnetic flux Φ wing attempts to enter the SQUID 3. At this time, the external magnetic flux Φ8° in the direction that cancels the external magnetic flux Φ that tries to enter the SQUID 3
An output voltage v0, that is, a magnetic flux detection signal v0 is obtained. This magnetic flux detection signal■. By reading with high precision the magnetic flux quantum Φ. Changes in magnetic flux can be detected with an accuracy of 1/1000 of a unit. Note that the magnetic flux detection signal ■. If not fed back to the feedback coil 8,
Alternatively, if the feedback coil 8 is omitted, the excluded external magnetic flux Φ8 becomes a magnetic flux quantum Φ. Enter Squid 3 in units. At this time, a magnetic flux detection signal V having a triangular wave pattern as shown in FIG. 6 described above is output. By counting the number of peaks or valleys in this triangular wave pattern, we calculate the magnetic flux quantum Φ. Magnetic flux can be detected in units.

Then, by dividing the detected external magnetic flux Φ8 by the area of the SQUID 3, the magnitude of the external magnetic field can be detected.

Next, a second embodiment of the present invention will be explained with reference to FIG.

This second embodiment differs from the first embodiment in that the constituent elements indicated by numerals 1 to 4 in the first embodiment are configured as indicated by numerals 1' to 4'. They are the same in some respects.

In Figure 2, a cylindrical core 1' made of superconductor
A SQUID 3' for detecting magnetic flux is disposed on the side surface of the magnetic flux sensor with a thin insulating layer 2' interposed therebetween. This SQUID 3' is an RF SQUID formed by a superconductor ring with one Josephson junction, and is formed using thin film technology. Further, a superconductor having a higher critical temperature than the core 1' is used for the SQUID 3'.

Further, a thin insulating layer (not shown) is provided on the upper surface of the core 1'.
A heater 4', which is heating means for the core 1', is disposed through the core 1'.

This second embodiment also has the same effect as the first embodiment.

According to each of the embodiments of the present invention described above, the SQUID itself is used as the detection coil, and the conventional detection coil and the magnetic flux transmission section provided between the detection coil and the conventional SQUID are omitted, so the configuration is simplified. At the same time, the influence of residual magnetic flux penetrating the magnetic flux transmission section and the detection coil at the start of magnetic flux detection work can be removed. Therefore, the magnitude of the magnetic flux itself can be detected with high precision.

Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications can be made.

For example, the cores 1, 1' can be made into a prismatic shape instead of a cylinder, and the magnetic flux detecting SQUID 3'3' can be made not only by vapor deposition but also by simply winding a superconducting wire. It is also possible to form a superconducting ring having a Josephson junction on the surface of a thin disk-shaped insulator such as ceramic, and attach this to the surface of a core made of superconductor. Furthermore, the heater 4.4' can be disposed at a suitable position other than the core 1.4', or can be omitted. And heater 4
．． If 4' is omitted, the temperature T in the cryostat 9 can be set to T <
What is necessary is to increase Tcc from Tcc<Tck to T<Tck and maintain that state. Furthermore, by arranging three SQUIDs 3 in the directions of three orthogonal axes, it is possible to detect the direction and magnitude of the magnetic field in a three-dimensional space. Furthermore, it is also possible to omit the feedback coil 8 and connect the feedback line 17 to the RF coil 5.

C1 Effects of the Invention As described above, the magnetic flux detection device of the present invention not only can detect changes in external magnetic flux with high precision using a simple configuration using SQUID elements, but also can detect the magnitude of the external magnetic flux itself with high precision. It can be detected in a wide variety of fields, such as medicine and resource exploration.

[Brief explanation of drawings]

Fig. 1 is a block diagram of one embodiment of the magnetic flux detection device of the present invention, Fig. 2 is a block diagram of main parts of another embodiment of the present invention, and Fig. 3 is a block diagram of a conventional magnetic flux detection device using a SQUID. Explanatory diagrams, Figures 4 and 6 are explanatory diagrams of the operation of a magnetic flux detection device using a SQUID. 1.1'...Core, 2,2'...Insulating layer, 3,3'
...Magnetic flux detection SQUID, 4.4'...Converter, 9
...low temperature chamber

Claims (1)

[Claims] A core made of a superconductor and a SQUID for magnetic field detection made of a superconductor having a higher critical temperature than the core, which is disposed on the surface of this core with an insulating layer interposed therebetween, is configured to detect an external magnetic field. Magnetic flux detection device placed in a cryogenic chamber with no shielding.