Gradiometer apparatus with compensation coils for measuring magnetic fields
First Claim
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1. An apparatus for measuring a very weak magnetic field such as that generated by a human body, comprising:
- a gradiometer for sensing the magnetic field;
a gradiometric field measuring circuit, operatively connected to said gradiometer, for outputting a signal indicative of the magnetic field sensed by said gradiometer;
at least three compensation coils for detecting uniform magnetic fields existing around said gradiometer, said three compensation coils being oriented in three different directions that are not in parallel with any one plane;
at least three magnetic field measuring circuits having sensitivity characteristics, operatively connected to said compensation coils, respectively, for outputting signals indicative of the uniform magnetic fields in the three different directions detected by said compensation coils; and
a magnetic noise eliminating circuit, operatively connected to said gradiometric and magnetic field measuring circuits, for eliminating magnetic noise in the signal indicative of the magnetic field output from said gradiometric field measuring circuit using scalar products of weight vectors containing weight factors predetermined by the sensitivity characteristics of said magnetic field measuring circuits and measured vectors containing, as vector components, magnetic fields previously measured by said magnetic field measuring circuits and said gradiometric field measuring circuit.
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Abstract
An apparatus is provided for measuring a very weak magnetic field generated by a human body, etc. External magnetic noise components coming from other magnetic sources and existing around an object whose magnetic field is to be measured are detected by compensation coils of the apparatus. The compensation coils are oriented in multiple dimensional directions. The detected noise components are weighted and added to each other to correctly find the noise components. Thereafter, the noise components mixed in the objective very weak magnetic field are removed, thereby correctly measuring the very weak magnetic field.
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Citations
17 Claims
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1. An apparatus for measuring a very weak magnetic field such as that generated by a human body, comprising:
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a gradiometer for sensing the magnetic field; a gradiometric field measuring circuit, operatively connected to said gradiometer, for outputting a signal indicative of the magnetic field sensed by said gradiometer; at least three compensation coils for detecting uniform magnetic fields existing around said gradiometer, said three compensation coils being oriented in three different directions that are not in parallel with any one plane; at least three magnetic field measuring circuits having sensitivity characteristics, operatively connected to said compensation coils, respectively, for outputting signals indicative of the uniform magnetic fields in the three different directions detected by said compensation coils; and a magnetic noise eliminating circuit, operatively connected to said gradiometric and magnetic field measuring circuits, for eliminating magnetic noise in the signal indicative of the magnetic field output from said gradiometric field measuring circuit using scalar products of weight vectors containing weight factors predetermined by the sensitivity characteristics of said magnetic field measuring circuits and measured vectors containing, as vector components, magnetic fields previously measured by said magnetic field measuring circuits and said gradiometric field measuring circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A multiple-point magnetic field measuring apparatus for detecting the distribution of a very weak magnetic field such as that generated by a human body, comprising:
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n gradiometers for sensing the magnetic field; n gradiometric field measuring circuits having sensitivity characteristics, operatively connected to said n gradiometers, respectively, to output signals indicative of the magnetic field sensed by said gradiometers; at least three compensation coils for measuring uniform magnetic fields existing around said gradiometers, said compensation coils being oriented in different directions, respectively, that are not in parallel with any one plane; at least three magnetic field measuring circuits having sensitivity characteristics, operatively connected to said compensation coils, respectively, for outputting signals indicative of the uniform magnetic fields in three different directions measured by said compensation coils; and n magnetic noise eliminating circuits, operatively connected to said n gradiometric field measuring circuits, respectively, each magnetic noise eliminating circuit also operatively connected to at least three of said magnetic field measuring circuits, for eliminating magnetic noise in the signals indicative of the magnetic field output from each of said gradiometric field measuring circuits using scalar products of weight vectors containing weight factors predetermined from the sensitivity characteristics of said magnetic field measuring circuits and one of said n gradiometric field measuring circuits and measured vectors containing, as vector components, magnetic fields previously measured by said magnetic field measuring circuits and said n gradiometric field measuring circuits.
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10. An apparatus for measuring a very weak magnetic field such as that generated by a human body, comprising:
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a gradiometer for sensing the magnetic field; a gradiometric field measuring circuit having sensitivity characteristics for outputting a signal indicative of the magnetic field sensed by said gradiometer; at least three compensation coils for detecting uniform magnetic fields existing around said gradiometer, said three compensation coils being oriented in different directions that are not in parallel with any one plane; at least three magnetic field measuring circuits having sensitivity characteristics, operatively connected to said compensation coils, respectively, for outputting signals indicative of the uniform magnetic fields in three different directions detected by said compensation coils; and a magnetic noise eliminating circuit operatively connected to said magnetic field measuring circuits, and magnetically coupled to aid gradiometer, for eliminating magnetic noise in the signal indicative of the magnetic field by feeding to said gradiometer, the scaler products of weight vectors containing weight factors predetermined from the sensitivity characteristics of said magnetic field measuring circuits and said gradiometric field measuring circuit, and measured vectors containing, as vector components, magnetic fields previously detected by said magnetic field measuring circuits and said gradiometric field measuring circuit. - View Dependent Claims (11)
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12. An appartus according to calim 11, wherein said gradiometric field measuring circuit comprises a superconducting quantum inteference device magnetically coupled to said gradiometer, and said feedback coil is magnetically coupled to said superconducting guantum interference device.
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13. A multiple-point magnetic field measuring apparatus for measuring the distribution of a very weak magnetic field such as that generated by a human body, comprising:
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n gradiometers for sensing the magnetic field; n gradiometric field measuring circuits, operatively connected to said n gradiometers respectively, for outputting signals indicative of the magnetic field sensed by said gradiometers; at least three compensation coils for detecting uniform magnetic fields existing around said gradiometers, said compensation coils being oriented in different directions that are not in parallel with any one plane; at least three magnetic field measuring circuits, operatively connected to said compensation coils, for outputting signals indicative of the uniform magnetic fields in three different directions detected by said compensation coils; and
a magnetic noise eliminating circuit, magnetically coupled to at least one of said n gradiometers and operatively connected to said magnetic field measuring circuits, for eliminating magnetic noise in the signal indicative of the magnetic field by feeding back to said at least one of n gradiometers, the scaler products of weight vectors containing weight factors predetermined from measured vectors containing, as vector components, magnetic fields previously measured by said magnetic field measuring circuits and said gradiometric field measuring circuit.
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14. A method of compensating a gradiometer for background magnetic noise using a correction circuit, said method comprising the steps of:
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(a) applying to the gradiometer and the correction circuit a first essentially uniform magnet field in a first direction; (b) measuring during said applying in step (a) a first, second and third magnetic field respectively sensed in different directions by the correction circuit and measuring a fourth magnetic field sensed by the gradiometer; (c) applying to the gradiometer and the correction circuit a second essentially uniform magnetic field in a second direction different than the first direction; (d) measuring during said applying in step (c) a fifth, sixth and seventh magnetic field respectively sensed in different directions by the correction circuit and measuring an eighth magnetic field sensed by the gradiometer; (e) applying to the gradiometer and the correction circuit a third essentially uniform magnetic field in a third direction different than the first and second directions, (f) measuring during said applying in step (e) ninth, tenth and eleventh magnetic fields respectively sensed in different directions by the correction circuit and measuring a twelfth magnetic field sensed by the gradiometer; (g) determining first, second and third weighing factors based on the first through twelfth magnetic fields; and (h) setting the correction circuit for correction by the first, second and third weighing factors. - View Dependent Claims (15, 16)
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17. A method of compensating a gradiometer for background magnetic noise using first, second and third magnetic field measuring circuits, said method comprising the steps of:
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(a) measuring a first, second and third magnetic field in different directions using the first, second and third magnetic field measuirng circuits to produce first, second and third signals, respectively; (b) measuring a fourth magnetic field sensed by the gradiometer when measuring in said step (a) to produce a fourth signal; (c) adjusting the first, second and third signals using scalar products of weight vectors containing weight factors predetermined by the sensitivity characteristics of said magnetic field measuring circuits and measured vectors containing, as vector components, magnetic fields previously measured by said magnetic field measuring circuits and said gradiometer to produce weighted first, second and third signals; and (d) subtracting the weighted first, second and third signals from the fourth signal to eliminate the background noise and produce a compensated gradiometer output signal.
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Specification