JPH08240650A - Regulating device of phase of squid array - Google Patents

Abstract

PURPOSE: To provide a regulating device of a phase of a SQUID array which can make the phase coincident among discrete SQUIDs in the SQUID array. CONSTITUTION: This regulating device is equipped with a bias coil Li provided for each single dcSQUID Si of an SQUID array A1 or in other ways, a monitor signal source 3 and others for supplying a sine wave current or others to each bias coil Li independently and resistors Rt1-Rtn for current regulation, and the resistors Rt1 Rtn for current regulation are regulated so that every output voltage of each single dcSQUID Si of the SQUID array Al becomes maximum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to SQUID (Supercon
ducting Quantum Interference Device: A SQUID magnetometer for measuring a magnetic field using a superconducting quantum interference device, and in particular, an SQUID in which a plurality of SQUIDs are connected.
The present invention relates to a phase adjustment device for a D array. Where SQUID
Is a SQUID that is a superconducting loop that is maintained at a low temperature in a heat-insulating container (such as a cryostat) by liquid helium or liquid nitrogen and that includes a Josephson junction in the loop.
When a DC current is applied to the loop as a bias current to drive it and a magnetic flux from the outside is directly applied to this SQUID loop through a pickup coil, an input coil, etc., and applied, a circulating current is induced in the SQUID loop. The small magnetic flux change is measured by utilizing the fact that it acts as a transducer that converts a weak change in the applied external magnetic flux into a large change in the output voltage due to the quantum interference effect in the Josephson junction in the loop. It is an element.

[0002]

2. Description of the Related Art Conventionally, d including two Josephson junctions
As a magnetometer using the cSQUID, there are a dewar (or cryostat) which is an adiabatic storage container for storing liquid helium which is a coolant for maintaining a low temperature environment (cooling system), and an SQUID probe which operates in liquid helium. It is known that an SQUID probe in liquid helium and an amplifier at room temperature are connected to each other by a coaxial cable or a twist cable, and an amplifier and a controller that operate at room temperature are configured. Such a SQUID magnetometer has a magnetic flux resolution of 10 ^-5.
Φ 0 / Hz ^1/2 (Φ 0 represents unit flux quantum in the left equation), it has very high sensitivity, and the response of SQUID is very fast, from several GHz (GHz) to several tens GHz.
The feature is that it works with. However, the above-mentioned conventional SQU
The ID magnetometer has a drawback in that it has a very high magnetic flux resolution and is weak against external noise and induction noise. The SQUID is usually "FLL: Flux L
A feedback circuit for linear operation called "ocked loop" is provided and controlled so that the "zero-order method" is established. FLL is a method of amplifying the SQUID output and returning the SQUID output to the SQUID ring in the form of a magnetic flux in the form of a loop circuit. By this method, the magnetic flux in the SQUID ring is held at a specific value (magnetic flux lock), so the magnetic flux is kept at a specific value (operating point) in the SQUID ring, and with respect to the displacement magnetic flux from this operating point The SQUID will generate a voltage. In this case, if an external magnetic noise with a large amplitude or a high speed that cannot be followed by the FLL circuit is added to the SQUID, or if electrical pulse noise is added to the FLL circuit, the operating point of the FLL loop becomes out (referred to as “out of lock”). .), The subsequent linear movement was hindered. As a measure for solving the above problem, d
It is conceivable to connect n cSQUIDs in series (n: a positive integer satisfying n ≧ 2) to form an SQUID array. When SQUIDs are connected in an array like this,
If the phase of the output voltage (or current) with respect to the magnetic flux of each SQUID matches, the output amplitude will increase by n times.
The output characteristics of D are improved.

[0003]

However, in the above-mentioned conventional SQUID array, the phase of each SQUID is not always completely the same due to the influence of stray inductance, trap magnetic flux, etc. In some cases, the magnetic flux-voltage characteristic (φ-V characteristic) of the array becomes a slightly distorted sine wave, or the amplitude of the SQUID output voltage is not always n times. On the other hand, recently, S that becomes superconducting at liquid nitrogen temperature
Although QUID (high temperature superconducting SQUID) is being realized, there is a problem that the SQUID output voltage amplitude is small and the noise characteristic is poor, and the SQUID is caused by a manufacturing error.
Due to the large variations in output voltage amplitude and measurement sensitivity, and easy occurrence of magnetic flux traps, it is difficult to match the phases between SQUIDs even if an SQUID array is constructed with this high temperature superconducting SQUID. Yes, S
There is a problem that improvement of the output voltage amplitude characteristic of the QUID cannot be expected so much.

The present invention has been made in order to solve the above-mentioned problems, and each SQ in the SQUID array is
An object of the present invention is to provide a phase adjustment device for an SQUID array that can match the phases between UIDs.

[0005]

In order to solve the above-mentioned problems, the phase adjusting device of the SQUID array according to the invention of claim 1 comprises n (n: a positive integer satisfying n ≧ 2) dcS.
Each dc of the SQUID array in which the QUIDs are connected in series
A phase adjusting device for an SQUID array for adjusting the phase of an SQUID, the single dcSQ of the SQUID array.
A coil provided for each UID or a plurality of dcSQUIDs, a current source for independently supplying a variable current to each coil, and a current adjusting unit capable of adjusting the value of the variable current for each coil. The current adjusting means is adjusted so that the output voltage of each single dcSQUID or plural dcSQUIDs of the SQUID array is maximized.

Further, the SQUI according to the invention of claim 2
The SQUID according to claim 1, wherein the phase adjusting device of the D array is provided.
In the phase adjusting device of the array, the bias magnetic flux applied from the coil to the single dcSQUID or the plurality of dcSQUIDs is configured to have a magnetic flux amplitude of ± φ0 / 4 (φ0: unit magnetic flux quantum) or less.

[0007]

The S according to the invention of claim 1 having the above construction
According to the phase adjusting device of the QUID array, when the current adjusting means adjusts the output voltage of each single dcSQUID or plural dcSQUIDs of the SQUID array to be maximum, a single dcSQ is output from each coil.
The bias flux applied to a UID or multiple dcSQUIDs is centered on the slope of the input flux-output voltage curve for all dcSQUIDs. Therefore, all dcS
The phases of the QUIDs match.

According to the phase adjusting device of the SQUID array of the present invention having the above structure, the center position of the amplitude of the bias magnetic flux to be added is SQUID.
Array single dcSQUID or multiple dcSQUIS
The magnetic flux range is φ0 / 2 (φ0: unit magnetic flux quantum) or less in the slope portion on the input magnetic flux-output voltage conversion curve for each D. This magnetic flux range is the same as the narrowest range in which the SQUID operates linearly.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a phase adjustment device for an SQUID array which is an embodiment of the present invention. As shown in the figure, the phase adjusting device 100 of this SQUID array includes n (n: a positive integer of n ≧ 2) dcSQUIs connected in series.
SQUID array A consisting of IDS1 to Sn, and SQUID array A
Input / output terminals T1 and T2 to the QUID array A, n bias coils L1 to Ln, n current adjusting resistors Rt1 to Rtn connected to each bias coil, a changeover switch 1, and a bias magnetic flux. Power source 2 and monitor signal source 3
And a monitoring resistor R. In FIG. 1, a bias current source for observing the output of the SQUID array A, an amplifier, a negative feedback circuit, a FLL circuit and the like are not shown.

J1 and J2 are dcSQUIDS1 to Sn, respectively.
It is a Josephson junction provided in. The bias coils L1 to Ln are arranged in the vicinity of the dcSQUIDS1 to Sn. The mutual inductance (coupling capacitance) connecting one dcSQUIDSi and one bias coil Li is Mt. This bias coil L1
One end of each of the bias coils L1 to Ln is connected to one end of each of the current adjusting resistors Rt1 to Rtn, and the other end thereof is grounded. The bias magnetic flux power source 2 has a voltage value Vb and is a power source for supplying the bias magnetic flux of the bias coils L1 to Ln. The monitor signal source 3 is a current source having a voltage value Vs and a variable amplitude characteristic, and adjusts the bias magnetic flux of the bias coil. A voltage or current is injected into the input / output terminals T1 and T2, or an SQUID output is taken out. The currents from the monitor signal source 3 and the monitor resistor R are switched by the changeover switch 1 so that the bias magnetic flux current can be supplied to each bias coil Li independently. Although not shown, each dcSQ
UIDS1 to Sn are shunted with shunt resistors.

Next, the operation of the phase adjusting device 100 for the SQUID array of this embodiment will be described. First, as described above, by connecting the n dcSQUIDS1 to Sn in series to form the SQUID array A,
If the phases of the dcSQUIDs match, the output voltage of the QUID array A increases in proportion to the number n of the dcSQUIDs and becomes n times.

However, since the stray inductance and the trap magnetic flux individually enter each dcSQUID ring, the relationship between the input magnetic flux of the SQUID and the output voltage is as shown in FIG. 2 when negative feedback is applied. Becomes, S
A deviation occurs for each SQUID that constitutes the QUID array. Therefore, the output voltage amplitude of the SQUID array A is not a simple addition value of the output voltages of the dcSQUIDS1 to Sn. In this case, each SQUI shown in FIG.
If the output voltage of D can be independently phase-shifted, S
Set the output voltage of the QUID array A to dcSQUIDS1 ~
It can be an added value of the output voltage of Sn.

In the phase shift adjusting device 100 for the SQUID array shown in FIG. 1, first, an appropriate bias current is applied to the input / output T1 and T2. In that state, when the changeover switch 1 is changed to any one, a variable current signal such as a sine wave or a triangular wave is output from the monitor signal source 3 and the monitor resistance R to the bias coil Li changed by the changeover switch 1. It The center point of the amplitude of the bias magnetic flux due to this variable current must satisfy the condition of the following equation: Mt x (Vs / R) ≤ φ0 / 2 (1).

If the conditional expression of the above expression (1) is satisfied, Vs / R in the above expression (1) indicates the DC component of the variable current (the center point of the amplitude of the variable current). The above equation (1) means that the center point of the amplitude of the bias magnetic flux is controlled so as to fall within the magnetic flux range of φ0 / 2 or less.
This is done because the linear operating range of the SQUID input flux-output voltage conversion curve is usually (when negative feedback is not applied to the SQUID array) the slope portion on the SQUID input flux-output voltage conversion curve. This is because the range is 1/2 or less of the unit magnetic flux quantum φ 0, and therefore, when the bias magnetic flux injection position exceeds the linear operation range on the input magnetic flux-output voltage conversion curve of the SQUID, adverse effects such as generation of high frequency occur. . However, the output current of the SQUID array A is supplied as a negative feedback current to a negative feedback coil (not shown), and each dcSQUIDSi or S is fed from the negative feedback coil.
When the negative feedback magnetic flux is fed back for every several groups of QUID, the linear range of the magnetic flux of the SQUID array A can be expanded to the range of less than the unit magnetic flux quantum φ0 at the slope on the input magnetic flux-output voltage conversion curve of the SQUID. Therefore, when negative feedback is applied to the SQUID array, the equal sign in the above equation (1) may be an inequality sign, and the right side of the above equation (1) may be φ0.

In this case, the above-mentioned input / output terminals T1 and T2
From the bias coil Li depending on the bias current from the bias current, the monitor current signal of the AC wave from the monitor signal source 3 and the monitor resistor R, and the current adjusting resistor Rti.
A bias magnetic flux is applied to SQUIDSi. Observing the output of dcSQUIDSi at this time, as shown in FIG. 2, the added bias magnetic flux shows that this dcSQUIDSi.
When reaching the center P of the slope of the input flux-output voltage curve of DSi, the amplitude of the output voltage of the dcSQUID becomes maximum and the distortion becomes minimum. Therefore, each dcS
While monitoring the output voltage of the QUIDSi at the input / output terminals T1 and T2, the corresponding current adjustment resistor Rti is adjusted so that the output voltage of the dcSQUIDSi becomes maximum, and this adjustment is performed for all dcSQUIDS1 in the SQUID array A.
.About.Sn, all the phases of dcSQUIDS1.about.Sn in the SQUID array A can be matched. The current adjusting resistors Rt1 to Rtn correspond to current adjusting means.

In the above description, the current adjusting resistor Rti is not adjusted for each SQUID, but several adjacent SQUIDs are set as one group, and a bias coil and a current adjusting resistor are provided for each SQUID group.
It may be adjusted for each group. Several adjacent SQUs
Since the ID has a stronger phase correlation than the distant SQUIDs, even if the bias magnetic flux is adjusted for several groups of SQUIDs in this way, the same effect as that of the device shown in FIG. 1 (phase matching of each SQUID is obtained). ) Can be obtained.

Therefore, first, with respect to dcSQUIDSi in the SQUID array, the input magnetic flux of the SQUID-
The bias magnetic flux injection position on the output voltage conversion curve is changed by trial and error, and after the high frequency component is not mixed in the SQUID output, the SQ is operated by the same operation as described above.
If a control program that matches the phases of all dcSQUIDs in the UID array is used, the phase adjustment of all dcSQUIDs in the SQUID array can be automatically performed.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention, and any device having the same function and effect can be realized by the present invention. It is included in the technical scope of the invention.

For example, in the above embodiment, an example in which a plurality of SQUID arrays connected in series are connected in parallel to form a matrix has been described, but the present invention is not limited to this. Matrix SQUID
A plurality of structures may be connected in series and used.

Further, in the above embodiment, an example is explained in which one end of the bias coil is commonly connected to the bias magnetic flux power supply 2 via the current adjusting resistor Rti, and the other end of the bias coil is commonly grounded. However, the present invention is not limited to this, and one bias magnetic flux power source is connected to one end of each bias coil via the current adjusting resistor Rti, and the other end of the bias coil is individually grounded. However, the circuits that apply the bias magnetic flux to each SQUID may be separated.

[0021]

As described above, according to the phase adjusting device of the SQUID array of the present invention having the above-mentioned structure, the current adjusting means allows the single dcSQUID or the plurality of dcSQUIDs of the SQUID array. If the output voltages of all are adjusted to be maximum, a single dcSQUID or multiple dcs from each coil
The bias magnetic flux added to the SQUID is all dcS
It comes to the center of the slope on the input flux-output voltage curve of the QUID. Therefore, the phases of all dcSQUIDs match. Further, according to the phase adjusting device of the SQUID array of the present invention having the above-mentioned configuration, the center position of the amplitude of the bias magnetic flux to be added is input for each single dcSQUID or a plurality of dcSQUIDs of the SQUID array. Φ 0 / at the slope of the magnetic flux-output voltage conversion curve
The magnetic flux range is 2 (φ 0: unit magnetic flux quantum) or less. Since this magnetic flux range is the same as the narrowest range in which the SQUID operates linearly, the SQUID does not deviate from the linear operation range, and the SQUID output is not adversely affected.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a phase adjustment device for an SQUID array which is an embodiment according to the present invention.

FIG. 2 SQUIDs with SQUIDs whose phases do not match
It is a figure which shows the output voltage characteristic of an array.

[Explanation of symbols]

 1 Change-over switch 2 Bias magnetic flux power source 3 Monitor signal source A SQUID array J1, J2 Josephson junction L1 to Ln Bias coil Mt Mutual inductance R Monitor resistor Rt1 to Rtn Current adjusting resistor S1 to Sn dcSQUID T1, T2 I / O Terminal 100 SQUID magnetometer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kunio Kazami 2-1200 Inzai Gakuendai, Inzai-cho, Inba-gun, Chiba Prefecture Superconducting Sensor Laboratory Co., Ltd. (72) Atsushi Kawai Inzai-gun, Inzai-gun, Chiba Prefecture Tai 2-1200 Co., Ltd. Superconducting Sensor Laboratory (72) Inventor Gen Uehara Takeshi Gakuen, Inzai-cho, Inba-gun, Chiba Tai 2-1200 Superconducting Sensor Laboratory (72) Inventor Hisashi Kado Tsukuba, Ibaraki Prefecture Umezono 1-4-1 Industrial Technology Research Institute, Industrial Technology Institute

Claims (2)

[Claims] 1. n (n: a positive integer satisfying n ≧ 2) dc
Each d of SQUID array with SQUIDs connected in series
A phase adjusting device for an SQUID array for adjusting the phase of a cSQUID, comprising: a coil provided for each single dcSQUID or a plurality of dcSQUIDs of the SQUID array; and a current source for independently supplying a variable current to each coil. And a current adjusting unit capable of adjusting the value of the variable current for each of the coils, and the current adjusting so that the output voltage for each single dcSQUID or a plurality of dcSQUIDs of the SQUID array is maximized. SQ characterized in that the means are adjusted
Phase adjustment device for UID array. 2. The single dcSQUID from the coil
2. The phase adjusting device for an SQUID array according to claim 1, wherein the bias magnetic flux added to the plurality of dcSQUIDs has a magnetic flux amplitude of ± φ 0/4 (φ 0: unit magnetic flux quantum) or less.