JP2561219B2 - SQUID - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for medical diagnosis for measuring a magnetic field generated from a human body or a living body, physical property measurement for measuring magnetic permeability of a material, and an interface for magnetic signal transmission. SQUID used for communication, etc.
(Superconducting Quantum Interference Device).

[0002]

2. Description of the Related Art Conventionally, relaxation oscillation (relaxation oscillation: relaxation oscillation)
Oscillation) type SQUID (hereinafter referred to as "ROS")
It has been known. As an example of the configuration, as shown in FIG. 4, the SQUID loop S installed in an ultra-low temperature environment
And a shunt circuit having a shunt resistor Rs and a shunt inductor Ls connected in parallel to the SQUID loop S is known. Above SQUID
Loop S has two Josephson junctions JJ.
The loop inductance of the SQUID loop S is L
sq, SQUID loop S and shunt inductance Ls
The mutual inductance between them is Ms. When a DC bias Ib is applied to the above ROS, a critical current Ic flows through the SQUID loop S, and the ROS is stored under appropriate conditions.
Oscillates. At that time, the oscillation frequency f is changed by the external magnetic flux Φ entering the SQUID loop S. Therefore, this ROS functions as a magnetic field sensor that converts the external magnetic flux Φ into the frequency f. During the above oscillation, the current is S
It flows so as to vibrate on the QUID loop S side and the shunt circuit side. The oscillating current value flowing in the shunt circuit is Is. Then, a current of 1/2 Ic flows through each Josephson junction.

[0003]

However, the conventional R
In the OS, when in the oscillating state, the current oscillates between the SQUID loop S and the shunt circuit. Therefore,
The SQUID loop S of the ROS receives not only the external magnetic flux Φ but also the self-magnetic field Φs generated by the oscillating current Is flowing in the shunt circuit, and this self-magnetic field Φs affects the ROS itself. Due to the influence of this self-magnetic field Φs, R
Since the oscillation spectrum of the OS spreads, the characteristics of the magnetic field sensor deteriorate. That is, the spread of the spectrum means fluctuation of the output frequency f of the ROS and becomes noise. In the conventional ROS, this phenomenon was a fate due to its structure. The present invention has been made to solve the above problems, and an object of the present invention is to provide a relaxation oscillation SQUID capable of preventing deterioration of magnetic field detection characteristics.

[0004]

In order to solve the above problems, an SQUID according to the present invention has an SQUID loop having two Josephson junctions, a first shunt resistor and a first shunt inductance, and In a relaxation oscillation type SQUID including a first shunt circuit connected in parallel to an SQUID loop, a second shunt circuit having a second shunt resistance and a second shunt inductance is connected in parallel to the SQUID loop. to, and connected so that the first shunt circuit and symmetrical with respect to said SQUID loop, said first sheet
The self-magnetic field generated by the
Strike by the self-magnetic field generated by the shunt inductance
Oscillation spectrum of output frequency
To prevent the spread of.

[0005]

According to the present invention having the above-mentioned structure, in the conventional relaxation oscillation type SQUID, the self magnetic field opposite to the self magnetic field generated by the relaxation oscillation is generated to cancel the self magnetic fields. .
Accordingly, the oscillation spectrum of the output frequency by the self-magnetic field is expanding want it is prevented, it can prevent the characteristics of the magnetic field sensor is deteriorated.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an equivalent circuit diagram showing the configuration of a ROS that is an embodiment of the present invention.

As shown in the figure, this ROS is composed of an SQUID loop S installed in an ultralow temperature environment and an SQUID loop S.
Some include two shunt circuits having a shunt resistor Rs and a shunt inductor Ls connected in parallel and symmetrically to the loop S. The above SQUID loop S
Has two Josephson junctions JJ. Also, S
The loop inductance of the QUID loop S is Lsq.

When a DC bias Ib is applied to the above ROS, a critical current Ic flows through the SQUID loop S, and the ROS oscillates under appropriate conditions. At that time, the oscillation frequency f is changed by the external magnetic flux Φ entering the SQUID loop S.

In the ROS shown in FIG. 1, when in the oscillating state, the current oscillates between the SQUID loop S and each shunt circuit. Therefore, not only the external magnetic flux Φ but also two self-magnetic fields generated by the oscillating current Is flowing in the shunt circuit enter the SQUID loop S of the ROS, and the respective self-magnetic fields act so as to cancel each other out.

Therefore, unlike the conventional ROS, the oscillation spectrum of the ROS does not spread due to the influence of the self-magnetic field Φs from the shunt circuit, and it is possible to prevent the characteristics of the magnetic field sensor from deteriorating.

In the spectrum of the output frequency f at this time, as shown in FIG. 2, the spectrum center frequency f0,
Letting Δf be the spectral width at a point 3 dB below the center of the spectrum, the Q value is defined by the following equation: Q = f0 / Δf (1) This Q value is a parameter indicating the sharpness of oscillation.

In the conventional ROS, the Q value is about 30. However, in the ROS having the configuration shown in FIG.
This Q value was a value of about 300 or more, showing an improvement of about 10 times or more.

FIG. 3 is a plan view showing a specific structure of the ROS of this embodiment. As shown in FIG. 3, this ROS is
A SQUID loop 2 having two Josephson junctions 1 and 1 and a shunt circuit are connected to the SQUID loop 2 in parallel and symmetrically. Each of the shunt circuits has a shunt resistor 3 and a shunt inductance 4. 5 is a bonding pad.

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.

[0015]

As described above, according to the present invention having the above-mentioned structure, in the conventional relaxation oscillation type SQUID, by generating the self magnetic field which is completely opposite to the self magnetic field generated by the relaxation oscillation, The magnetic fields can be canceled. Accordingly, the oscillation spectrum of the output frequency by the self-magnetic field is expanding want it is prevented, it can prevent the characteristics of the magnetic field sensor is deteriorated
It

[Brief description of drawings]

FIG. 1 is a relaxation oscillation type SQUID according to an embodiment of the present invention.
It is an equivalent circuit diagram showing the configuration of.

FIG. 2 is a diagram illustrating an operation of the relaxation oscillation type SQUID shown in FIG.

FIG. 3 is a plan view showing a specific configuration of the relaxation oscillation type SQUID shown in FIG.

FIG. 4 is an equivalent circuit diagram showing a configuration of a conventional relaxation oscillation type SQUID.

[Explanation of symbols]

 1 Josephson junction 2 SQUID loop 3 Shunt resistance 4 Shunt inductance 5 Bonding pad S SQUID loop Ls Shunt inductance Rs Shunt resistance

Claims (1)

(57) [Claims] 1. An SQU having two Josephson junctions.
A relaxation oscillation type SQUID comprising an ID loop and a first shunt circuit having a first shunt resistance and a first shunt inductance and connected in parallel to the SQUID loop, wherein a second shunt resistance and A second shunt circuit having a second shunt inductance is connected in parallel with the SQUID loop and symmetrically with respect to the SQUID loop with the first shunt circuit to provide the first shunt circuit .
The self magnetic field generated by the shunt inductance is applied to the second
By the self-magnetic field generated by the shunt inductance of
Oscillation spectrum of output frequency configured to cancel each other
The SQUID is characterized by preventing the spread of the cable.