MAGNETIC FIELD MEASUREMENT SYSTEM
First Claim
1. A magnetic field measurement system comprising:
- a magnetically shielding device having a cylindrical magnetic shield composed of a ferromagnetic material;
a plurality of sensing magnetometers having respective SQUIDs and respective pickup coils and arranged in two dimensions to sense a magnetic field component of a magnetic field emitted from a living body which is perpendicular to a center axis of said cylindrical magnetic shield;
a first reference magnetometer having a SQUID and a pickup coil to sense a magnetic field component of an external field which is parallel to said center axis;
a dewar for accommodating and cooling said plurality of sensing magnetometers and said first reference magnetometer, in which said plurality of sensing magnetometers are arranged in two dimensions on a first plane close to said center axis such that a plane of said pickup coils of said plurality of sensing magnetometers is parallel to said center axis and said reference magnetometer is positioned on a second plane perpendicular to said first plane in spaced apart relation to said first plane such that a plane of said pickup coil of said first reference magnetometer is perpendicular to said first plane;
a gantry for holding said dewar internally of said cylindrical magnetic shield;
a measurement circuit for driving said plurality of sensing magnetometers and said first reference magnetometer to sense said perpendicular magnetic field component and said parallel magnetic field component and outputting the sensed magnetic field components as measurement signals and a first reference signal;
a device for recording said measurement signals; and
an analyzing device for analyzing said measurement signals and displaying a result of analysis, wherein said analyzing device performs an arithmetic operation of subtracting a value obtained by multiplying said first reference signal sensed by said first reference magnetometer by a first specified factor from a difference between said measurement signals sensed by two of said sensing magnetometers disposed at different positions to determine a first corrected measurement signal under less influence of said external field.
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Accused Products
Abstract
A magnetic field measurement system for canceling an external field is provided, in which plurality of sensing magnetometers (3) for measuring a magnetic field signal in a direction perpendicular to the center axis of a cylindrical magnetic shield (1) are arranged in two dimensions on a plane parallel to the center axis and a reference magnetometer (4) for measuring the external field parallel to the center axis as a reference signal is disposed on a plane perpendicular to the plane parallel to the center axis. The reference signal multiplied by a specified factor is subtracted from a difference between signals from the adjacent sensing magnetometers (3). The magnetic field measurement system allows measurement of an extremely weak magnetic field by efficiently canceling the external field.
69 Citations
12 Claims
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1. A magnetic field measurement system comprising:
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a magnetically shielding device having a cylindrical magnetic shield composed of a ferromagnetic material;
a plurality of sensing magnetometers having respective SQUIDs and respective pickup coils and arranged in two dimensions to sense a magnetic field component of a magnetic field emitted from a living body which is perpendicular to a center axis of said cylindrical magnetic shield;
a first reference magnetometer having a SQUID and a pickup coil to sense a magnetic field component of an external field which is parallel to said center axis;
a dewar for accommodating and cooling said plurality of sensing magnetometers and said first reference magnetometer, in which said plurality of sensing magnetometers are arranged in two dimensions on a first plane close to said center axis such that a plane of said pickup coils of said plurality of sensing magnetometers is parallel to said center axis and said reference magnetometer is positioned on a second plane perpendicular to said first plane in spaced apart relation to said first plane such that a plane of said pickup coil of said first reference magnetometer is perpendicular to said first plane;
a gantry for holding said dewar internally of said cylindrical magnetic shield;
a measurement circuit for driving said plurality of sensing magnetometers and said first reference magnetometer to sense said perpendicular magnetic field component and said parallel magnetic field component and outputting the sensed magnetic field components as measurement signals and a first reference signal;
a device for recording said measurement signals; and
an analyzing device for analyzing said measurement signals and displaying a result of analysis, wherein said analyzing device performs an arithmetic operation of subtracting a value obtained by multiplying said first reference signal sensed by said first reference magnetometer by a first specified factor from a difference between said measurement signals sensed by two of said sensing magnetometers disposed at different positions to determine a first corrected measurement signal under less influence of said external field. - View Dependent Claims (2, 3, 4)
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5. A magnetic field measurement system comprising:
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a magnetically shielding device having a cylindrical magnetic shield composed of a ferromagnetic material;
a plurality of sensing magnetometers having respective SQUIDs and respective pickup coils and arranged in two dimensions to sense a magnetic field component of a magnetic field emitted from a living body which is perpendicular to a center axis of said cylindrical magnetic shield;
first and second reference magnetometers having respective SQUIDs and respective pickup coils to sense a magnetic field component of an external field which is parallel to said center axis;
a dewar for accommodating and cooling said plurality of sensing magnetometers and said first and second reference magnetometers, in which said plurality of sensing magneto-meters are arranged in two dimensions on a first plane close to said center axis such that a plane of said pickup coils of said plurality of sensing magnetometers is parallel to said center axis, said first reference magnetometer is positioned on a second plane perpendicular to said first plane in spaced apart relation to said first plane such that a plane of said pickup coil of said first reference magnetometer is perpendicular to said first plane, and said second reference magnetometer is disposed on a fourth plane in parallel and spaced apart relation to said second plane such that a center axis of said pickup coil of said second reference magnetometer coincides with a center axis of said pickup coil of said first reference magnetometer;
a gantry for holding said dewar internally of said cylindrical magnetic shield;
a measurement circuit for driving said plurality of sensing magnetometers and said first and second reference magnetometers to sense said perpendicular magnetic field component and said parallel magnetic field component and outputting the sensed magnetic field components as measurement signals and first and second reference signals;
a device for recording said measurement signals and the reference signals; and
an analyzing device for analyzing said measurement signals and displaying a result of analysis, wherein said analyzing device performs an arithmetic operation of subtracting a value obtained by multiplying said first reference signal sensed by said first reference magnetometer by a first specified factor from a difference between said measurement signals sensed by two of said sensing magnetometers disposed at different positions to determine a first corrected measurement signal and subtracting, from said first corrected measurement signal, a value obtained by multiplying a difference between said first and second reference signals by a second specified factor to determine a second corrected measurement signal under less influence of said external field. - View Dependent Claims (6, 7, 8)
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9. A magnetic field measurement system comprising:
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a magnetically shielding device having a cylindrical magnetic shield composed of a ferromagnetic material;
a plurality of sensing magnetometers having respective SQUIDs and respective pickup coils and arranged in two dimensions to sense a magnetic field component of a magnetic field emitted from a living body which is perpendicular to a center axis of said cylindrical magnetic shield;
a first reference magnetometer having a SQUID and a pickup coil to sense a magnetic field component of an external field which is parallel to said center axis;
third and fourth reference magnetometers having respective SQUIDs and respective pickup coils to sense a magnetic field component of the external field which is perpendicular to said center axis;
a dewar for accommodating and cooling said plurality of sensing magnetometers and said first, third, and fourth reference magnetometers, in which said plurality of sensing magnetometers are arranged in two dimensions on a first plane close to said center axis such that a plane of said pickup coils of said plurality of sensing magnetometers is parallel to said center axis, said first reference magnetometer is positioned on a second plane perpendicular to said first plane in spaced apart relation to said center axis such that a plane of said pickup coil of said first reference magnetometer is perpendicular to said first plane, and said third and fourth reference magnetometers are disposed on a third plane in parallel relation to said first plane and in spaced apart relation to said center axis such that a plane of the pickup coils of said third and fourth reference magnetometers is parallel to said third plane and that said fourth reference magnetometer is positioned at a larger distance than said third reference magnetometer in a direction of said center axis of said cylindrical magnetic shield;
a gantry for holding said dewar internally of said cylindrical magnetic shield;
a measurement circuit for driving said plurality of sensing magnetometers and said first, third, and fourth reference magnetometers to sense said perpendicular magnetic field component and said parallel magnetic field component and outputting the sensed magnetic field components as measurement signals and first, third, and fourth reference signals;
a device for recording said measurement signals and said first, third, and fourth reference signals; and
an analyzing device for analyzing the recorded signals and displaying a result of analysis, wherein said analyzing device performs an arithmetic operation of subtracting a value obtained by multiplying said first reference signal by a first specified factor from a difference between said measurement signals sensed by two of said sensing magnetometers disposed at different positions to determine a first corrected measurement signal and subtracting, from said first measurement signal, a value obtained by multiplying a difference between said respective measurement signals sensed by said third and fourth magnetometers by a third specified factor to determine a third corrected measurement signal under less influence of said external field. - View Dependent Claims (10, 11, 12)
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Specification