JPH02298878A - Superconducting device - Google Patents

Abstract

PURPOSE:To expand a dynamic range by directly connecting at least a part of a superconductor feedback loop to a pickup coil in one-chip type digital SQUID and also using the feedback loop as the pickup coil. CONSTITUTION:One-chip type digital SQUID is constituted of the SQUID sensor 4 magnetically coupled with a pickup coil 22, a resistor 5, a magnetic flux quantum writing gate 6 converting the positive or negative output pulse train from the sensor 4 to a magnetic flux quantum and the superconductor loop 21 directly connected to the coil 22. In this constitution, when input magnetic flux to be measured is negated by a feedback loop, since the loop 21 is directly connected to the coil 22, the interlinkage magnetic flux of the whole of the loop is always held to zero. That is, no loop current flows and the gate 6 is always normally operated and, therefore, the limitation of a dynamic range is eliminated.

Description

[Detailed Description of the Invention] [Summary] Regarding a superconducting device, the present invention provides a superconducting device that can obtain a large dynamic range with a small chip without using a large loop required to obtain a large dynamic range. A pink amplifier coil consisting of a superconducting loop that extracts the magnetic flux interlinked within the loop, and a superconducting quantum interference element that is magnetically coupled to the pickup coil and pulses the extracted magnetic flux with an alternating current bias. AC bias applying means for applying a predetermined AC bias to the superconducting quantum interference device; a flux quantum writing gate for converting pulses output from the superconducting quantum interference device into magnetic flux quanta; and storing the magnetic flux quanta. and a superconducting feedback loop that feeds back stored magnetic flux quanta to the pickup coil through magnetic field coupling, at least a part of the superconducting feedback loop being directly connected to the pickup coil, and the superconducting feedback loop feeding back stored magnetic flux quanta to the pickup coil. The loop is configured to also serve as the pickup coil.

[Industrial application field]

The present invention relates to a superconducting device, and in detail, SQU I
D (Superconducting Quantu
mInterferenceDevice: Superconducting quantum interference device) A superconducting device having a superconducting feedback circuit configured to operate a sensor in pulses and convert the pulses into magnetic flux quanta and store them in a superconducting loop in order to count the pulse output. .

In recent years, so-called multi-channel SQUIDs have been studied in order to form arrays of SQUIDs, which are highly sensitive magnetic field sensors, and measure magnetic field distribution. In order to create such a multi-channel system that uses a large number of SQUIDs, we used a superconducting circuit to realize the equivalent function of an external feedback circuit that previously consisted of room temperature electronics such as a lock-in amplifier. A one-chip digital SQUID integrated on a chip has been proposed by the present inventor.

When such a digital SQUID is used for various applications such as biomagnetism, it is required to be able to detect a wide range of magnetic field levels, just like conventional analog-operated SQUIDs, and the upper limit of measurable magnetic flux is The lower limit ratio, so-called dynamic range, requires a value such as 106, for example.

In other words, what you want to measure is generally IQ-1! While it is on the order of Stellar magnitude, the magnitude of the geomagnetic field is 3XIO-
'Since it is about the size of a Stella, there is a very small object to be measured on top of a very large object, and a dynamic range of about 106 is required.

[Conventional technology]

A conventional one-chip digital SQUID is shown in FIGS. 3 to 5, for example. In FIG. 3, ■ is a one-chip digital SQUID, and the one-chip digital SQUID 1 includes a pickup coil 2 that picks up the magnetic flux to be measured, a 5QUID sensor 4 magnetically coupled to the pickup coil 2, and a resistor 5. A magnetic flux quantum write gate 6 converts the positive or negative pulse train outputted from the 5QUID sensor 4 into magnetic flux quanta, and the magnetic flux converted by the magnetic flux quantum write gate 6 is stored, and the stored magnetic flux is passed through the magnetic field coupling 7 to the 5QUID sensor 4. Alternatively, as shown by the broken line in the figure, it is composed of a superconducting storage loop (superconducting feedback loop) 9 that feeds back to the big amplifier coil 2 through magnetic field coupling 8. 5QUI D sensor 4 has superconducting loop 10 and Josephson gate 11.1
2, and an AC bias 13 is applied to the 5QUID sensor 4. Similarly, flux quantum write gate 6
The superconducting loop 14 includes Josephson gates 15 and 16.

According to this configuration, the 5QUID sensor 4 is biased with alternating current and outputs a positive or negative pulse train depending on whether the total magnetic flux interlinking with the 5QUID sensor 4 is positive or negative. A flux quantum write gate 6 converts this pulse into flux quanta and stores them in a superconducting storage loop 9. The stored magnetic flux corresponds to the result of counting the number of pulses, which is calculated by 5QUI.
Feedback is provided to the D sensor 4 or the pickup coil 2 through magnetic field coupling. Due to this feedback, the total interlinkage magnetic flux applied to the 5QUID sensor 4 is maintained at zero, so the magnitude of the magnetic flux to be measured can be known from the amount of feedback that cancels it. Figure 4.5 is the third
It is a block diagram of the one-chip digital SQUID 1 shown in the figure, and the same members are given the same numbers.

[Problem to be solved by the invention]

However, such conventional superconducting devices have a problem in that it is not necessarily easy to obtain a large guinamine range for reasons detailed below.

That is, the one-chip digital SQUID 1 operates to cancel the magnetic flux entering the pickup coil 2 by creating a magnetic field in the opposite direction using the superconducting storage loop 9. For example, when magnetic flux Φ enters, 5QUID
When Φ is positive, the sensor 4 continues to output a positive pulse value, and each time the magnetic flux enters, the SQUID sensor 4 increases in negative value, and when the positive magnetic flux is just canceled out, no pulse is output. The principle of this digital SQUID is to measure the original measurement based on the amount of feedback required to cancel the incoming magnetic flux, but when the thing you want to measure is large, the amount of cancellation is The upper limit of the magnetic flux that can be measured by this digital SQUID is the maximum number of magnetic flux quanta that can be stored in the superconducting storage loop 9, N va
Determined by ax.

Generally, when N magnetic flux quanta are accumulated, a current (2) expressed by the following equation (2) flows in the loop.

Here, Lf is the inductance of the superconducting storage loop, Φ
. represents a magnetic flux quantum (2,07×10−” Wb). When this loop current I reaches a certain maximum value I, ., the magnetic flux quantum write gate 6 cannot write a magnetic flux quantum even if any more pulses come. The maximum value ICO varies depending on the design of the magnetic flux quantum write gate 6, but is typically around 0.01 mA. Therefore, the maximum magnetic flux quantum Nmax is
,. It is determined as shown in the following equation (2), and the amount of feedback cannot be increased any further.

Therefore, if you try to increase Nmax in order to increase the dynamic range of the magnetometer,
Lf must be increased. For example, Nmax = 1
In the case of 0-, Lt = 200 μH (micro-Henry), which is a large value.

Attempting to realize such a large inductance with a thin film circuit would occupy a large chip area. 200μH
In the case of , for example, its size is several n squares, but 5QUI
Since the D sensor 4 and the magnetic flux quantum write gate 6 are several hundred μm square, the chip area is limited by the size of this loop. If the chip area is large, the number of chips obtained from one manufacturing process will decrease, and the yield will also decrease.

Therefore, an object of the present invention is to provide a superconducting device that can obtain a large dynamic range with a small chip without using a large loop that is required to obtain a large dynamic range.

[Means to solve the problem]

In order to achieve the above object, the superconducting device according to the present invention includes a pickup coil consisting of a superconducting loop that extracts magnetic flux interlinking within the loop, and a pickup coil that is magnetically coupled to the pickup coil and pulses the extracted magnetic flux using an alternating current bias. a superconducting quantum interference device; an alternating current bias applying means for applying a predetermined alternating current bias to the superconducting quantum interference device; and a magnetic flux quantum write gate for converting pulses output from the superconducting quantum interference device into magnetic flux quanta. , a superconducting device comprising a superconducting feedback loop that stores the magnetic flux quanta and feeds back the stored magnetic flux quanta to the pick amplifier coil through magnetic field coupling,
At least a portion of the superconducting feedback loop is directly connected to the pink-up coil, and the superconducting feedback loop also serves as the pickup coil.

[Effect]

In the present invention, at least a portion of the superconducting feedback loop is directly connected to the pickup coil, and the superconducting feedback loop is also used as the pickup coil.

Therefore, for example, when a positive magnetic flux enters the pickup coil, as a result of feedback, a negative magnetic flux quantum is written from the magnetic flux quantum writing gate, and when the balance is exactly balanced, it is canceled by the feedback written from the magnetic flux quantum writing gate. The flux linkage throughout the loop is kept at zero.

As a result, the loop current stops flowing at the point of cancellation, and the upper limit of the dynamic range disappears.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is an explanatory diagram of the present invention. Components that are the same as those of the conventional example shown in FIG. 4.5 are given the same numbers. Conventionally, the magnetic flux of the superconducting loop 9 was fed back by the magnetic coupling 8 or the magnetic coupling 7 as shown in Fig. 4.5, but in the present invention, as shown in Fig. 1, the magnetic flux of the superconducting loop (superconducting feedback The superconducting loop 21 is directly connected to the pickup coil 22, so that the pickup coil 22 serves as part or, in some cases, the entire superconducting loop 21. In this case, the pink amplifier coil serves as part or all of the loop, which not only reduces the chip area but also has the advantage that there is no limit to the dynamic range in terms of circuit operation.

The reason for this is that when the feedbank cancels out the manually applied magnetic flux to be measured, the superconducting loop 2
1 and the pickup coil 22 are directly connected, the interlinkage magnetic flux of the entire loop is always maintained at zero, so no loop current flows and the write gate always operates normally.

Second Implementation Examples will be described below based on the above basic principle. Second
The figure is a diagram showing an embodiment of a superconducting device according to the present invention, and the same components as those of the conventional example shown in FIG. In Figure 2, 3
1 is a one-chip digital SQUID (superconducting device)
The one-chip digital SQUID 31 has a part directly connected to the superconducting loop 21, a big amplifier coil 22 that picks up the magnetic flux to be measured, a 5QUID sensor 4 magnetically coupled to the pickup coil 22, and a resistor 5. 5 A magnetic flux quantum writing gate 6 that converts the positive or negative pulse train output from the QUID sensor 4 into magnetic flux quanta.
and a superconducting loop 21 directly connected to a pickup coil 22.

In the above configuration, in the past, magnetic flux was once stored in the superconducting storage loop 9 and magnetically coupled to the 5QUID sensor 4 or the pickup coil 2 by magnetic field coupling 7.8, but in this embodiment, the magnetic flux to be measured is transferred to the pickup coil 22. When the current enters the 5QUID sensor 4, a current flows accordingly, and a predetermined pulse is output from the 5QUID sensor 4 via the magnetic field coupling 3.

For example, when positive magnetic flux comes in, 5QUID sensor 4
outputs a positive pulse. The pulse causes the magnetic flux quantum write gate 6 to apply magnetic flux, and the applied magnetic flux enters the same loop as the incoming magnetic flux. For example, when a positive flux enters the pink amplifier coil into the pickup coil 22, as a result of feedback, a negative magnetic flux quantum is written from the magnetic flux quantum writing gate 6, and when the balance is exactly balanced, a negative magnetic flux quantum is written from the magnetic flux quantum writing gate 6. This is canceled out by the written feedback, and the positive magnetic flux that has entered the entire loop consisting of the pickup coil 22 and the superconducting loop 21 is canceled out by the negative magnetic flux, and the magnetic flux becomes zero. That is,
By integrating them, a feedback circuit is created in which no current flows through the loop made up of the pickup coil 22 and the superconducting loop 21 at the time of cancellation.

The Josephson gates 15 and 16 have a characteristic that they will not operate if a current exceeding a certain value flows through them, but since the device of this embodiment has a circuit in which no current flows when the current is canceled, no matter how much current flows in the pickup coil 22, Even if a large magnetic field is applied, no current flows when it is canceled, resulting in a circuit with no dynamic range limitations.

As explained above, since the superconducting loop 21 and the pickup coil 22 are directly connected by magnetic coupling, the upper limit of the dynamic range limited by the operation of the write gate is removed, and other causes such as the superconducting critical magnetic field are removed. This makes it possible to measure magnetic flux over a wide range without being limited by anything other than an extremely large upper limit.

In addition, the one-chip digital SQUID 3 of this embodiment
1, the big amplifier coil 22 also serves as the superconducting loop 21, so although inductance is written in the superconducting loop 21 on the circuit diagram in Figure 2, in reality, the inductance of the superconducting loop 21 is picked up. The inductance of the coil 22 can be used for both purposes, and the chip area can be reduced. Therefore, a digital SQUID with a small chip area and a large dynamic range can be realized.

〔Effect of the invention〕

According to the present invention, a large dynamic range can be obtained with a small chip without using the large loops required to obtain a large dynamic range.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the present invention. FIG. 2 is an overall configuration diagram showing an embodiment of a superconducting device according to the present invention. FIGS. 3 to 5 are diagrams showing conventional superconducting devices. Figure 3 is its overall configuration diagram, and Figure 4.5 is its block configuration diagram. 3... Magnetic field coupling, 4...5 QUID sensor (superconducting quantum interference device), 5... Resistance, 6... Magnetic flux quantum writing gate, 10 , 14...Superconducting loop, 11.12.1
5.16...Josephson Gate, 13...
...AC bias, 21...Superconducting loop (superconducting feedback loop), 22...Pick amplifier coil, 31
...One-chip digital SQUID (superconducting device). Diagram for explaining the principle of the present invention. Figure 1. Block diagram of a conventional example. Figure 4. Block diagram of a conventional example. Figure 5.

Claims (1)

[Scope of Claims] A pickup coil consisting of a superconducting loop that extracts magnetic flux interlinking within the loop; a superconducting quantum interference element that is magnetically coupled to the pickup coil and pulses the extracted magnetic flux with an alternating current bias; AC bias applying means for applying a predetermined AC bias to the superconducting quantum interference device; a flux quantum write gate for converting pulses output from the superconducting quantum interference device into magnetic flux quanta; and a magnetic flux quantum write gate for storing the magnetic flux quanta and , a superconducting feedback loop that feeds back stored magnetic flux quanta to the pickup coil through magnetic field coupling, wherein at least a part of the superconducting feedback loop is directly connected to the pickup coil, and the superconducting feedback loop A superconducting device characterized in that a loop is configured to also serve as the pickup coil.