Superconducting detection coils

Abstract: First- or higher order-derivative bobbin-type superconducting detection coils. The accuracy of the areas of the coils, the shape accuracy, the accuracy of the positional relation between them, the accuracy of the degree of the parallelism between them, and other factors are improved. The magnetic field gradient sensitivity is improved. The coils are fabricated easily. A superconducting wiring pattern (2) is formed on a flexible printed wiring film (1). The flexible printed wiring film is bent into a cylinder.

Description: BACKGROUND OF THE INVENTION The present invention relates to the structure of detection coils used in a magnetic sensor employing superconducting quantum interference devices (SQUIDs) which are applied to high-sensitivity magnetic sensors. SQUIDs have been heretofore applied to detection of weak magnetic fields. Bobbin-shaped detection coils composed of superconducting wires are often used in SQUID fluxmeters. Fig. 10 shows conventional first-derivative detection coils of the bobbin type. Shown are a bobbin 11, a superconducting coil wire 12, electrodes 13, and a damping resistor 14. The superconducting coil wire 12 is so arranged in a groove formed in the bobbin 11 that upper and lower coils are wound in opposite senses. The superconducting coil wire 12 is connected with the electrodes 13 which are connected with the damping resistor 14. Fig. 11 shows the structure of conventional second-derivative detection coils of the bobbin type. Upper and lower coils are wound in the same sense. An intermediate coil is wound in the opposite sense with turns twice as many as the number of turns of the upper and lower coils. The wires of the first-derivative and second-derivative detection coils of the bobbin type are strands except for the coils to prevent magnetic flux from intersecting the wires. The first-derivative detection coil of the bobbin type detects the difference between the magnetic field signal detected by the upper coil and the magnetic field signal detected by the lower coil, i.e., the magnetic gradient is detected. The second-derivative detection coil of the bobbin type detects the difference between the magnetic field gradient detected by the upper and intermediate coils and the magnetic field gradient detected by the intermediate lower coils. Therefore, the accuracy of the areas of the coils, the shape accuracy, the accuracy of the positional relation between them, the accuracy of the degree of the parallelism between them, and other factors affect the magnetic gradient sensitivity. In the above-described conventional first-derivative detection coils of the bobbin type, the groove in the bobbin which accommodates the superconducting coil wire is required to be machined with high accuracy. Also, when the superconducting coil wire is laid, a triangular gap is formed at the boundary between each circular coil portion and the strand. This makes it difficult to improve the accuracy of the areas of the coils, the shape accuracy, the accuracy of the positional relation between them, and the accuracy of the degree of the parallelism between them. As a result, the magnetic field gradient sensitivity and the reproducibility of the characteristics are deteriorated. Furthermore, the coils are difficult to manufacture, because skilfulness is needed for the manufacture. In addition, when the damping resistor is connected in parallel with the detection coils, it is difficult to connect the resistor directly to the detection coils. Therefore, the resistor has been connected close to the locations in which the coils are connected with the SQUID. Hence the efficiency of the work has been low. In order to overcome the problems of conventional wire-laid superconducting detection coils, EP-A-0185186 discloses superconducting detection coils according to the preamble of claim 1. The superconductor gradiometer of EP-A-0 185 186 requires the gradiometer coils be placed in spaced position with connecting lines therebetween on a large planar body. The planar body is then formed into a three-dimensional gradiometer structure, which is then applied to a support body. As shown in Fig. 1 and described in the EP-A-0 185 186, the gradiometer coils 4 and 5 are preformed onto the planar flexible member before the planar flexible member is bent into a three-dimensional shape. Then, a relatively complex bending operation is required to dispose the coils 4 and 5 at appropriate relative positions. Summary of the invention It is an object of the present invention to provide an improved first or higher order-derivative bobbin-type superconducting detection coils for a magnetic sensor or the like. To achieve the foregoing object, the present invention offers superconducting detection coils according to claim 1. A resistor may or may not be formed on the film. The superconducting wiring pattern has a substantially U-shaped wiring portion formed in a portion thereof. The U-shaped wiring portion forms cylindrical wiring patterns. In the superconducting detection coil structure described above, the detection coil wiring pattern and the pattern of the resistor can be fabricated by ordinary printed wiring film conductive pattern fabrication techniques. The flexible film is merely bent into a cylinder. In this way, the superconducting detection coils can be easily fabricated. Consequently, the accuracy of the areas of the upper and lower coils, the shape accuracy, the accuracy of the positional relation between them, and the accuracy of the degree of the parallelism between them can be improved. Furthermore, the absolute accuracy of the resistance value and the absolute accuracy between the plural superconducting detection coils can be improved. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows the wiring pattern on a flexible printed wiring film for first-derivative bobbin-type detection coils, showing example 1 of the present invention; Fig. 2 is a cross-sectional view showing the structure of the first-derivative bobbin-type detection coils, showing example 1 of the present invention; Fig. 3 shows the structure of first-derivative bobbin-type detection coils of one turn; Fig. 4 shows the structure of first-derivative bobbin-type detection coils of two turns; Fig. 5 shows the wiring pattern on a flexible wiring printed film for second-derivative bobbin-type detection coils, showing example 2 of the present invention; Fig. 6 shows the structure of second-derivative bobbin-type detection coils comprising an upper coil of one turn, an intermediate detection coil of two turns, and a lower detection coil of one turn; Fig. 7 shows the wiring pattern on a flexible printed wiring film for first-derivative bobbin-type detection coils, showing example 3 of the present invention; Fig. 8 shows the wiring pattern on a flexible printed wiring film for first-derivative bobbin-type detection coils showing example 4 of the present invention; Fig. 9 shows the wiring pattern on a flexible printed wiring film for first-derivative bobbin-type detection coils, showing example 5 of the present invention; Fig. 10 shows the structure of conventional first-derivative bobbin-type detection coils; and Fig. 11 shows the structure of conventional second-derivative bobbin-type detection coils. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is next described in detail with reference to its embodiment. Fig. 1 shows the pattern of wiring on a flexible printed wiring film for a first-derivative detection coil of the bobbin type, thus showing example 1 of the invention. Shown components are the flexible printed wiring film 1, a superconducting wiring pattern 2, electrodes 3, a resistive interconnect 4. The flexible printed wiring film 1 consists of polyimide. The superconducting wiring pattern 2 and the electrodes 3 are fabricated by plating of lead-zinc (Pb-Sn), sputtering of niobium (Nb), or deposition of lead-indium (Pb-In). Other wiring of a superconducting thin or thick film may also be used as the pattern 2 or as the electrodes 3. A buffer layer for the film of the Pb-Sn plating is used and consists of a resistive material such as copper (Cu) or palladium (Pd). Other high-resistivity materials can also be employed. The resistive interconnect 4 is made of a resistive material similar to the material used for the buffer layer for the Pb-Sn plating film. The flexible printed wiring film is rounded such that the portion indicated by A in Fig. 1 and the portion indicated by B overlap each other. In this way, first-derivative detection coils of one turn of the structure shown in Fig. 3 can be fabricated. The arrows of Fig. 3 indicate the directions of winding of the coils. Also, first-derivative detection coils of two turns of the structure shown in Fig. 4 can be fabricated by rounding the flexible printed wiring film two turns such that the portions A, C, and B of Fig. 1 overlap each other. The arrows of Fig. 4 indicate the directions of winding of the coils. Fig. 2 is a cross-sectional view showing the structure of the first-derivative bobbin-type detection coils, showing example 1 of the present invention. Shown are a bobbin 6 and a cover 7. The flexible printed wiring film 1 on which the superconducting wiring pattern shown in Fig. 1 is formed is wound around the bobbin 6. The cylindrical cover 7 is disposed. The bobbin 6 which may be a solid or hollow cylinder is made of FRP, glass, Teflon, or other material. The cover 7 that is cylindrical in shape is made of FRP, glass, Teflon, or other material. Fig. 5 shows the wiring pattern on a flexible printed wiring film for second-derivative bobbin-type detection coils, showing example 2 of the present invention. The flexible printed wiring film 1, the superconducting wiring pattern 2, the buffer layer for the Pb-Sn plating film, the electrodes 3, and the resistive interconnect 4 are made of the same materials as those of the counterparts of example 1. Electrical conduction is prevented at the intersection of wires indicated by A in Fig. 5. For example, after fabricating the lower superconducting film wiring, it is covered with an insulating material such as urethane. Second-derivative detection coils having one upper turn, two intermediate turns, and one lower turn, respectively, as shown in Fig. 6 can be fabricated by winding the device two turns such that the portions A, B and C of Fig. 5 overlap each other. The arrows of Fig. 6 indicate the directions of winding of the coils. Also, second-derivative detection coils having two upper turns, four intermediate turns, and two lower turns, respectively, as shown in Fig. 5 can be fabricated by winding the device four turns such that the portions A, B, and C of Fig. 5 overlap each other. Fig. 7 shows the wiring pattern on a flexible printed wiring film for first-derivative bobbin-type detection coils, showing example 3 of the present invention. In Fig. 7, the wire portions B-D and E-F are equal in length. The flexible printed wiring film 1, the superconducting wiring pattern 2, the buffer layer for the Pb-Sn plating film, the electrodes 3, and the resistive interconnect 4 are made of the same materials as those of the counterparts of example 1. First-derivative detection coils of one turn and two turns, respectively, can be fabricated by rounding the flexible film in one turn and two turns, respectively, such that D is placed on the position C located midway between A and B of Fig. 7. The area of the upper coil can be made exactly coincident with the area of the lower coil of the finished detection coils by laying the wire portion A-E of the superconducting wiring pattern 2 of Fig. 7 at an angle such that the wire portions B-D and E-F agree in length. Noise produced laterally of the detection coils can be reduced by rounding the flexible film in such a way that the center of the wire portion D-F is placed on the center of the wire portion A-E of Fig. 7. Fig. 8 shows the wiring pattern on a flexible printed wiring film for first-derivative bobbin-type detection coils, showing example 4 of the present invention. The flexible printed wiring film 1, the superconducting wiring pattern 2, the buffer layer for the Pb-Sn plating film, the electrodes 3, and the resistive interconnect 4 are made of the same materials as those of the counterparts of example 1. The superconducting wiring pattern 2 is formed on both surfaces of the flexible printed wiring film 1 or on different layers. Electrical conduction between the portions formed on both surfaces of the flexible printed wiring film 1 or on the different layers is permitted by superconductors passed through contact holes 5 formed in the buffer layer and in the flexible printed wiring film 1. First-derivative detection coils of one turn and two turns, respectively, are fabricated by rounding the flexible film one turn and two turns, respectively, such that portion B is placed on portion A of Fig. 8. Fig. 9 shows the wiring pattern on a flexible printed wiring film of first-derivative bobbin-type detection coils, showing example 5 of the present invention. The flexible wiring printed film 1, the superconducting wiring pattern 2, the buffer layer for the Pb-Sn plating film, the electrodes 3, and the resistive interconnect 4 are made of the same materials as those of the counterparts of example 1. The superconducting wiring pattern 2 is formed on both surfaces of the flexible printed film 1 or on different layers in the same way as in example 4. As shown in Fig. 9, the wires of the superconducting wiring pattern extend from the electrodes 3 between portions A and B to the front and rear surfaces or to different layers of the flexible printed wiring film 1 in a staggered relation to each other to remove lateral noise caused by external magnetic disturbance. First-derivative detection coils of one turn and two turns, respectively, are fabricated by rounding the flexible film one turn and two turns, respectively, such that portion D is placed on position C located midway between portions A and B of Fig. 9. In the above-described structure of the superconducting detection coils, first- or higher order-derivative superconducting detection coils of any desired turns can be fabricated by shaping a flexible printed wiring film having a coil wiring pattern into a cylinder. The accuracy of the circular areas of the coils, the shape accuracy, the accuracy of the positional relation between them, and the accuracy of the degree of the parallelism between them can be extremely improved. Furthermore, the absolute accuracy of the damping resistor and the relative accuracy between plural superconducting detection coils can be improved. Thus, the magnetic filed gradient sensitivity and the reproducibility of the magnetic characteristics can be enhanced. As described thus far, in accordance with the present invention, superconducting detection coils can be easily fabricated by shaping a flexible printed wiring film having superconducting film wiring and a resistive interconnect into a cylinder. The accuracy of the circular areas of the upper and lower coils, the shape accuracy, the accuracy of the positional relation between them, and the accuracy of the degree of the parallelism between them can be extremely improved. Further, the absolute accuracy of the damping resistor and the relative accuracy between plural superconducting detection coils can be improved. Thus, the magnetic field gradient sensitivity and the reproducibility of the magnetic characteristics can be enhanced.

Claims: Superconducting detection coils for a superconducting quantum interference device, said coils comprising a flexible printed wiring film (1) on which a superconducting wiring pattern (2) is formed and which is shaped into a cylinder, CHARACTERIZED IN THAT , the superconducting wiring pattern (2) comprises a substantially U-shaped wiring portion which forms at least a pair of upper and lower cylindrical wiring patterns when the flexible printed wiring film (1) is formed into the cylinder shape, the substantially U-shaped wiring portion having two leg portions interconnected by a base portion, each leg portion having opposed ends which overlap each other to form the cylindrical wiring patterns when the flexible printed wiring film (1) is formed into the cylindrical shape; and electrodes (3) each connected to the respective leg portion of the substantially U-shaped wiring portion for coupling the cylindrical wiring patterns to at least one superconducting quantum interference device. Superconducting detection coils according to claim 1, further comprising a resistor (4) electrically connected in parallel with the superconducting wiring pattern (2). Superconducting detection coils according to claim 1, wherein the superconducting wiring pattern (2) has at least two substantially U-shaped wiring portions for forming at least three cylindrical wiring patterns when the flexible printed wiring film (1) is fcrmed into the cylinder shape. Superconducting detection coils according to claim 1, wherein the two leg portions are of equal length so that an area of a cylindrical wiring pattern formed by one leg portion is the same as an area of a cylindrical wiring pattern formed by the other leg portion when the flexible printed wiring film (1) is formed into the cylinder shape. Superconducting detection coils according to claim 1, wherein the superconducting wiring pattern (2) has a front surface and a back surface, and has through-holes (5) between the back surface and the front surface; and the superconducting wiring pattern is formed on both the front surface and the back surface and electrically connected through the through-holes (5). Superconducting detection coils according to claim 5, wherein the two leg portions are formed on one of the front surface and the back surface, one leg portion being connected to a portion of the superconducting wiring pattern formed on the other of the front surface and the back surface through the through-holes (5). Superconducting detection coils according to claim 5, wherein the two leg portion are formed on one of the front surface and the back surface; and the superconducting wiring pattern (2) includes a first connecting portion formed on both the front surface and the back surface and connected through through-holes (5) and a second connecting portion formed on both the front surface and the back surface and connected through through-holes (5), the first and second connecting portions overlapping each other with the flexible printed wiring film (1) between them, and the first connecting portion being connected between one of the electrode (3) and one leg portion and the second connecting portion being connected between the other electrode (3) and the other leg portion so that the overlapping first and second connecting portions effectively remove noise caused by external magnetic disturbance. Superconducting detection coils according to claim 1, wherein the two leg portions are parallel and the base portion is perpendicular to the two leg portions.

Inventors: CHIBA NORIO, NAKAYAMA SATOSHI, ODAWARA AKIKAZU, YABE SATORU, CHIBA, NORIO, NAKAYAMA, SATOSHI, ODAWARA, AKIKAZU, YABE, SATORU
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 1992
Main classification: G01R33
IPC codes: G01R33