Variable permeability magnetometer systems and methods for aerospace applications
원문보기
IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
G01R-033/028
G01V-003/10
G01R-033/022
G01V-003/08
출원번호
US-0676172
(2015-04-01)
등록번호
US-10036784
(2018-07-31)
발명자
/ 주소
Shams, Qamar A.
Sutton, John F.
출원인 / 주소
THE UNITED STATES OF AMERICA AS REPRESENTED BY THE ADMINISTRATOR OF NASA
대리인 / 주소
Warmbier, Andrea Z.
인용정보
피인용 횟수 :
0인용 특허 :
7
초록▼
A magnetometer configured to measure low field strength magnetic fields is provided. Certain embodiments of the magnetometer include a cylindrical coil assembly having a variable permeability core and terminals disposed at both ends. A current source circuit may be operably connected to the terminal
A magnetometer configured to measure low field strength magnetic fields is provided. Certain embodiments of the magnetometer include a cylindrical coil assembly having a variable permeability core and terminals disposed at both ends. A current source circuit may be operably connected to the terminals and configured to apply a voltage controlled current across the terminals. A voltage readout circuit may be operably connected to the terminals and configured to measure a voltage across the terminals due to the applied current from the current source. An inductance of the coil assembly directly varies as an ambient magnetic field strength varies a permeability of the variable permeability core, and a voltage across the terminals varies directly with the inductance such that the measured voltage across the terminals is a direct measure of the ambient magnetic field strength.
대표청구항▼
1. A magnetometer comprising: a cylindrical coil assembly extending from a first end to an opposing second end, having a variable permeability core configured to measure low strength magnetic fields having a frequency response range between 0 and 700 hertz, the cylindrical coil assembly further comp
1. A magnetometer comprising: a cylindrical coil assembly extending from a first end to an opposing second end, having a variable permeability core configured to measure low strength magnetic fields having a frequency response range between 0 and 700 hertz, the cylindrical coil assembly further comprising terminals, including at least a first terminal at the first end and a second terminal at the second end of the coil assembly, wherein the variable permeability core includes a plastic coil form and a foil strip constructed of a variable permeability magnetic material that is wrapped within the plastic coil form, the variable permeability core further including a search coil having a sense winding that is wound over the plastic coil form, the search coil further including a secondary winding configured for feedback control or calibration of the magnetometer, the secondary winding being disposed over the sense winding;a current source circuit operably connected to the terminals, and including a crystal oscillator configured to provide a high-frequency clock signal to drive the current source circuit and thereby apply a plurality of electric currents to the cylindrical coil assembly, including a voltage-controlled sense current across the terminals, a feedback current applied to the secondary winding to cancel out variation in the Earth's field caused by a change in orientation of the cylindrical coil assembly, and a biasing current across the terminals; anda voltage readout circuit operably connected to the terminals and configured to measure a voltage across the terminals, with direct current offsets eliminated, due to the applied voltage-controlled currents from the current source circuit,wherein an inductance of the cylindrical coil assembly directly varies as an ambient magnetic field strength varies a permeability of the variable permeability core, and a voltage across the terminals varies directly with the inductance such that the measured voltage across the terminals is a direct measure of the ambient magnetic field strength. 2. The magnetometer of claim 1, wherein the foil strip is comprised of a cobalt-alloy magnetic material. 3. The magnetometer of claim 1, wherein the sense winding is comprised of an enameled copper wire having at least 500 turns. 4. The magnetometer of claim 1, wherein the voltage readout circuit includes a double synchronous demodulator, a low pass filter, and an integrator, and wherein the feedback current is fed to the secondary windings through each of the double synchronous demodulator, the low pass filter, and the integrator. 5. The magnetometer of claim 1, wherein the current source circuit further includes a digital frequency divider configured to divide the clock signal of the crystal oscillator from 1 MHz to a lower frequency of 10 kHz. 6. The magnetometer of claim 5, wherein the current source circuit further includes a signal shaper configured to shape the lower frequency signal of the digital frequency divider into a sinusoidal form. 7. The magnetometer of claim 1, wherein the current source circuit is configured to adjust the applied biasing current across the terminals to bias the variable permeability core to an optimum location of a core permeability curve. 8. A method of measuring a low magnetic field strength having a frequency response range of between 0 and 700 hertz comprising: applying a plurality of currents to a winding of a coil assembly having a variable permeability core, including a sinusoidal, voltage-controlled current across two opposing terminals of the coil assembly having the variable permeability core, the variable permeability core including a foil strip constructed of a variable permeability magnetic material wrapped within the plastic coil form, and a search coil wound over the plastic coil form;measuring a voltage applied across the terminals due to the sinusoidal, voltage-controlled current;calculating the low magnetic field strength from the measured voltage; anddetecting a presence of a geophysical or atmospheric event using the calculated low magnetic field strength. 9. The method of claim 8 further comprising: applying a feedback signal to the winding of the coil assembly as one of the plurality of currents;enhancing a receiving cross section of the coil assembly; andmeasuring an adjusted voltage across the terminals. 10. The method of claim 9, further comprising removing, by the feedback signal, variations in ambient magnetic field strength due to a change in a coil assembly orientation. 11. The method of claim 8, wherein measuring the voltage includes applying a double synchronous detector for detecting a measured voltage that substantially eliminates l/f noise, switch noise, and the direct current offsets. 12. The method of claim 11, wherein measuring the voltage further includes applying a low pass filter. 13. The method of claim 8, wherein applying the sinusoidal, voltage-controlled current source includes providing a clock signal, by a crystal oscillator, to drive a high-output impedance current source. 14. The method of claim 13, wherein applying the sinusoidal, voltage-controlled current source further includes: dividing the clock signal of the crystal oscillator to a lower frequency signal; andshaping the lower frequency signal into a sinusoidal form. 15. The method of claim 8, further comprising: enclosing each of a pair of the coil assemblies in a corresponding wooden box;burying the enclosed coil assemblies to a depth of six to nine inches below a ground surface a minimum distance of 2,000 miles apart; andwirelessly transmitting the measured voltage to a remote readout screen located above the ground surface. 16. The method of claim 8, wherein the foil strip of a variable permeability magnetic material is constructed of cobalt-alloy magnetic material. 17. The method of claim 8, wherein applying the plurality of currents includes applying each of: a 10 kHz sine oscillator signal as the sinusoidal, voltage-controlled current;a variable biasing current operable for biasing the core to a predetermined location of a core permeability curve; anda feedback current applied directly to the search coil.
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이 특허에 인용된 특허 (7)
Kim Nam H. (Glendale CA) Hawks Timothy (Stanford CA), Digital compass and magnetometer having a sensor coil wound on a high permeability isotropic core.
Arnaud Jean-Louis (Verrieres-le-Buisson FRX) Floret Michel (Gennevelliers FRX), Process and device for the detection of cracks in riveted joints using an eddy current probe.
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