JPH0580137A - Probe for squid - Google Patents

Abstract

PURPOSE:To decrease the amount of gas helium generation, suppress vibration due to gas passage, and reduce noise by forming each signal line connecting a superconductive quantum interferential element SQUID to a measuring circuit from a thin film conductor on a printed circuit board, and accomplishing a stratified twist pair structure. CONSTITUTION:Six signal lines connecting a SQUID element with a measuring circuit are formed from a conductive thin film wiring 4 on a printed circuit board 1, and three sets of twist pairs. That is, a plurality of substratum conductors 41, 41,... inclined in a specific direction are formed parallelly on the surface of the circuit board 1. Over it an insulative film 42 is formed, and thereover superstratum conductors 43, 43... are formed. The ends of these substrate and superstrate 41, 43 are connected with one another by contact holes 44, 44... penetrating the insulative film 42. The section areas of the wiring 4 and circuit board 1 can be lessened to a great extent, and the accomplished twist pair structure allows precise alignment of its loop areas. Accordingly heat influx from the ambient temperature lesser to a great extent to permit lessening of influence of the magnetic field on the signal lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe for SQUID used for biomagnetism measurement, magnetic susceptibility measurement and the like.

[0002]

2. Description of the Related Art In SQUID (superconducting quantum interference device), generally, a SQUID ring, an input coil and a modulation coil are formed on one chip, so-called SQUID.
It constitutes a QUID element and is connected to an external measurement circuit such as an amplifier or an RF oscillator by a signal line. The input coil forms a superconducting closed loop with the pickup coil outside the chip, and the magnetic flux to be measured is picked up by this pickup coil and transmitted to the SQUID ring via the input coil.

Of the above construction, the SQUID element and the pickup coil are inserted into a Dewar bottle containing liquid helium and cooled to the superconducting temperature. Therefore, normally, a probe is used, the SQUID element and the pickup coil are attached to the tip of the support body and inserted into the Dewar bottle, and a signal line is provided along this support body to connect to the measurement circuit outside the Dewar bottle. The structure is adopted.

FIG. 5 is a vertical cross-sectional view showing a usage state of a conventional SQUID probe. The support body 51 is a tubular body made of, for example, stainless steel or FRP, and a magnetic shield cylinder 52 accommodating the SQUID element is fixed to the tip end portion thereof, and a pickup coil 53 is further fixed to the tip end thereof. The support body 51 penetrates the flange portion F and is inserted into a Dewar bottle D containing liquid helium, and a measurement circuit C is connected to the base portion side. Then, an enamel-coated copper wire 54 is passed through the inside of the support body 51, and the wire is twisted to form the measurement circuits C and SQ.
It is used as a signal line for connecting to the UID element. The reason why the copper wire 54 is made into a twisted pair is to cancel the current induced by the magnetic field from the outside and reduce the influence thereof. The support 51 itself is held by fixing it to the flange portion F.

[0005]

By the way, in the structure of the conventional SQUID probe as described above, a large amount of heat from the atmosphere is transferred to the liquid helium through the copper wire 54,
In particular, when the number of channels is increased, the amount of helium vaporized becomes extremely large. Further, since the evaporated helium gas passes through the inside of the support body 51, the copper wire 54 serving as a signal wire
May vibrate and cause noise.

The present invention has been made for the purpose of solving such problems at once.

[0007]

In the SQUID probe of the present invention, the support is formed by an elongated printed wiring board, and the signal line connecting the SQUID element and the measurement circuit is formed by a thin film conductor on the printed wiring board. The thin film conductor is formed and has a layered twisted pair structure on the printed wiring board. Here, the twisted pair structure on a layer is one in which an insulating layer is interposed between two conductive thin films and contact holes are drilled at appropriate places on the insulating layer, and a printed wiring board is used as an insulating layer on the front and back sides. A conductive thin film is formed on each of the above, and through holes are formed at appropriate places on the printed wiring board.

[0008]

The cross-sectional area of the conductor thin film is much smaller than that of the copper wire, and the cross-sectional area of the support itself is also small, so that the evaporation amount of liquid helium can be suppressed. Further, since the signal line is fixedly formed on the substrate, vibration due to passage of helium gas is suppressed and noise is reduced.

[0009]

Embodiment FIG. 1 is an external perspective view of an embodiment of the present invention.
The SQUID element in which the SQUID ring, the input coil and the modulation coil are formed is housed in the magnetic shield tube 2 as in the conventional case, and the magnetic shield tube 2 is also provided.
Is fixed to the tip of the elongated printed wiring board 1. A pickup coil 3 is fixed to the tip of the magnetic shield tube 2.

On the printed wiring board 1, a total of six signal lines connecting the SQUID element and a measuring circuit (not shown) are formed by the conductor thin film wirings 4, and these form three twisted pairs. ing. That is, SQ
A pair of signal lines for applying a bias current and a pair of signal lines for extracting the output voltage of the SQUID ring are drawn out from both ends of the UID ring, and are connected to a measurement circuit from both ends of the modulation coil. A pair of signal lines are drawn out. Then, each of these pairs forms a twisted pair on the printed wiring board 1.

FIG. 2 shows an example of the structure of a twisted pair formed by the conductor thin film wiring 4. In this example, on the surface of the printed wiring board 1, a plurality of lower layer conductors 41 are formed in a pattern parallel to each other and inclined in a predetermined direction as shown in the drawing, and an insulating film 42 is formed above the lower layer conductors 41. On the membrane 42,
A contact is formed by forming a plurality of parallel upper layer conductors 43, ... 43 inclined in the opposite direction to the lower layer conductor 41, and penetrating the insulating film 42 at both ends of each lower layer conductor 41. The holes 44 are connected to each other by the holes 44.

At the tip of the printed wiring board 1,
As shown in the enlarged perspective view of FIG. 3, each conductor thin film wiring 4 and SQ
A socket portion 5 for connecting each portion of the UID element is provided to facilitate connection with the SQUID element side. Further, in the probe of this embodiment, as shown in the enlarged perspective view of the pickup coil 3 and the bottom of the dewar bottle D in FIG. 4, a concave portion 31 is formed on the tip surface of the pickup coil 3 and the dewar bottle is formed. A protrusion 6 is formed on the bottom of D, and positioning of the probe in the Dewar bottle D is performed by fitting the recess 31 and the protrusion 6. The concave portion 31 is, for example, a cylindrical hole, and the protrusion 6 has a columnar shape with an upper end portion having a hemispherical shape. When the probe is inserted from above, the tip of the hemispherical portion of the protrusion 6 is initially in the concave portion 31. The structure is such that it enters and guides the probe to a fixed position. In this case, in consideration of the thermal expansion coefficients of the material forming the pickup coil 3 and the material forming the protrusions 6, the protrusions 6 do not rattle in the recess 31 at an extremely low temperature, which is the operating temperature of the probe. Need to

According to this positioning method, the position of the pickup coil 3 in the Dewar bottle D is always constant,
Positioning can be performed with good reproducibility. That is, in the conventional method of positioning and fixing the probe at the flange F portion at the upper end portion of the Dewar bottle D, the position of the pickup coil at the most distal end is not constant due to various causes such as the fixing method and contraction of the support. However, there was a problem in terms of reproducibility, but in the above positioning method, the position of the pickup coil 3 itself is regulated by the projection 6, and the reproducibility of position is improved.

In the above-mentioned embodiment of the present invention, the point to be particularly noted is that the SQUID element in the Dewar bottle D and the external measuring circuit are connected by the conductor thin film wiring 4 on the printed wiring board 1, and the conductor thin film wiring 4 Has a remarkably small cross-sectional area as compared with a conventional signal line made of copper wire, and this printed wiring board 1 can have a remarkably small cross-sectional area as compared with a conventional tubular support. The twisted pair structure with a conductive thin film is that it is possible to accurately align each loop area by the method of photolithography,
As a result, the inflow of heat from the atmosphere is significantly reduced, and the influence of the magnetic field on each signal line can be reduced.

In the above embodiment, the conductor thin film wiring 4
Although the twisted pair structure is obtained by a two-layer structure in which an insulating film is sandwiched on the printed wiring board 1, a conductor is patterned on the front and back of the printed wiring board 1 without using the insulating film, and these are printed. The structure may be such that they are connected to each other by a through hole drilled in the. Also,
The twisted pair pattern formed by the conductor thin film wiring 4 is not limited to the above-mentioned embodiment, and can be any pattern.

[0016]

As described above, according to the present invention, in the SQUID probe in which the pickup coil and the SQUID element are fixed to the tip and the base is connected to the measurement circuit, the support such as the SQUID element is printed wiring. In addition to being formed by a board, this printed wiring board is provided with a conductor thin film wiring as a signal line for connecting the SQUID element and the measurement circuit, and further, this conductor thin film wiring has a twisted pair structure. Compared to a probe that uses a signal line made of a support and a copper wire, the cross-sectional area of the signal line is significantly smaller and the cross-sectional area of the support is also smaller, so the evaporation of liquid helium due to heat introduction from the atmosphere The amount of liquid helium can be significantly reduced, and in particular, it is possible to suppress the enormous vaporization of liquid helium that is expected in the case of multiple channels.

Further, since the twisted pair structure formed by the conductor thin film wiring is formed by using the photolithography method, the alignment can be performed with an accuracy of the order of μm.
The area of each loop can be very accurate. Since the twisted pair structure is intended to cancel the current induced by the magnetic field in the adjacent loops, the configuration of the present invention reduces the influence of the magnetic field as compared to the conventional twisted pair twisted copper wire. The effect is significantly improved.

Further, by forming the signal line as a conductor wiring on the printed wiring board, fluctuation of the signal line due to evaporation of helium gas is prevented, and noise of the device is also reduced.

[Brief description of drawings]

FIG. 1 is an external perspective view of an embodiment of the present invention.

FIG. 2 is an explanatory view of an example of a twisted pair structure by the conductor thin film wiring 4.

FIG. 3 is an enlarged perspective view of a front end portion of the printed wiring board 1 according to the embodiment of the present invention.

FIG. 4 is also a pickup coil 3 according to the embodiment of the present invention.
And enlarged perspective view near the bottom of Dewar bottle D

FIG. 5 is a vertical cross-sectional view showing a usage state of a conventional SQUID probe.

[Explanation of symbols]

 1 ... Printed wiring board 2 ... Magnetic shield cylinder 3 ... Pickup coil 31 ... Recess 4 ... Conductor thin film wiring 41 ... Lower conductor 42 ... Insulation Membrane 43 ・ ・ ・ ・ Upper layer conductor 44 ・ ・ ・ ・ Contact hole 5 ・ ・ ・ ・ Socket 6 ・ ・ ・ ・ Protrusion D ・ ・ ・ ・ Dewar bottle

Claims (1)

[Claims] 1. A probe having a pickup coil and an SQUID element fixed to the tip of a support, and a signal line for connecting the SQUID element and a measurement circuit along the support, wherein the support is provided. Is formed of an elongated printed wiring board, the signal line is formed of a thin film conductor on the printed wiring board, and the thin film conductor has a layered twisted pair structure on the printed wiring board. Characterized by S
QUID probe.