WO1981000455A1 - Gyroscope a resonance magnetique nucleaire - Google Patents

Gyroscope a resonance magnetique nucleaire Download PDF

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Publication number
WO1981000455A1
WO1981000455A1 PCT/US1980/000972 US8000972W WO8100455A1 WO 1981000455 A1 WO1981000455 A1 WO 1981000455A1 US 8000972 W US8000972 W US 8000972W WO 8100455 A1 WO8100455 A1 WO 8100455A1
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WO
WIPO (PCT)
Prior art keywords
region
magnetic resonance
nuclear magnetic
atoms
enclosure
Prior art date
Application number
PCT/US1980/000972
Other languages
English (en)
Inventor
H Wang
Original Assignee
Hughes Aircraft Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hughes Aircraft Co filed Critical Hughes Aircraft Co
Publication of WO1981000455A1 publication Critical patent/WO1981000455A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/58—Turn-sensitive devices without moving masses
    • G01C19/60—Electronic or nuclear magnetic resonance gyrometers

Definitions

  • NUCLEAR MAGNETIC RESONANCE GYRO The present invention relates generally to gyros and more particularly to gyros of the nuclear magnetic resonance type.
  • Nuclear magnetic resonance gyros are presently known in the art, and existing designs have incorporated a single chamber, or gas cell, in which both optical pumping and observation of nucelar magnetic resonance take place.
  • atoms of a confined gas, or gases are generally excited by an intense resonant light source and/or an RF source.
  • the optical pumping creates nuclear polarization of the ground state atoms, and in addition, certain ions, electrons, metastable atoms, and other discharge products are also created.
  • certain ions, electrons, metastable atoms, and other discharge products are also created.
  • only the polarized ground state atoms are of interest in the observation region while the discharge products only serve to lower system performance and frequency resolution.
  • inter-atomic collisions between the discharge products and the polarized ground state atoms create unwanted frequency shifts and linewidth degradation (broadening of the resonance line) which lead to errors in the gyro readout.
  • a nuclear magnetic resonance gyro comprising an optically transmissive enclosure confining a mixture of two odd mass numbered isotopes of inert gas capable of undergoing nuclear magnetic resonance.
  • Pumping means for creating a population inversion in the inert gas is disposed adjacen to the enclosure and includes a light source for providing circularly polarized resonant light and an RF discharge source for providing RF energy.
  • the pumping means creates both polarized ground state atoms and discharge products during the pumping process.
  • Means for applying a magnetic field is disposed adjacent to the enclosure.
  • Sensing means for sensing the precession frequency of atoms undergoing nuclear magnetic resonance within the enclosure is disposed adjacent thereto.
  • the improvement comprises an enclosure having a first region, a second region, and a connecting region therebetween, the first region providing a volume in which the pumping of the isotopes occurs so as to create the population inversion therein.
  • the connector region provides filtering means wherein the pumped atoms diffused therethrough in a manner such that the polarized ground state atoms substantially diffuse into the second region having retained substantial polarization, while the discharge products decay by the process of interatomic collision with other atoms and with the walls of the connecting region.
  • the second region provides a volume thus containing a substantial quantity of polarized ground state atoms which undergo nuclear magnetic resonance, the second region further providing a volume in which nuclear magnetic resonance transitions occur which are sensed by the sensing means.
  • the pumping means are disposed adjacent to the first region while the sensing means is disposed adjacent to the second region.
  • the pumping means creates a population inversion in the atoms of the confined gas. This process creates both polarized ground state atoms and discharge products.
  • the pumped gases diffuse through the•connecting region and into the second region wherein the observation of the nuclear magnetic resonance takes place.
  • The- length of the connecting region is such that only the polarized ground state atoms can diffuse through the connecting region into the second region while retaining their polarization. This is due to the relatively long relax- ation time of the ground state nuclear polarization.
  • the discharge products are effectively prevented from reaching the second region due to their sensitivity to wall collision relaxation into a thermal equilibrium state in the connecting region.
  • the connecting region acts as a filter with respect to the unwanted discharge products.
  • the use of two isotopes of the inert gas compensates for variations in the applied magnetic field.
  • two nuclear magnetic resonance observations are made in the second region and the effective variations in the magnetic field may be substantially eliminated by comparing the two sets of data obtained.
  • FIGURE of the drawing is an illustration of a nuclear magnetic resonance gyro made in accordance with the principles of the present invention.
  • the gyro generally comprises a resonant light source 21, which may be a ' Xenon discharge lamp, or the like, which provides circu ⁇ larly polarized resonant light, and an RF discharge source 22, for providing RF energy.
  • the enclosure 20, which includes a first region 23, a second region 24, and a connecting region 25 therebetween, is disposed such that the first region 23 is adjacent to the resonant light source 21 and the RF source 22.
  • the enclosure 20 is generally comprised of an optically transmissive material, such as Pyrex, glass, or the like.
  • the first and second regions 23, 24 have an inner diameter on the order of two to three centimeters, while the connecting region 25 has an inner diameter of about three millimeters and a length of about two centimeters.
  • Means is provided adjacent to the enclosure 20, such- as a magnetic source 33, for applying a magnetic field (designated by arrow 32) to the enclosure 20.
  • the orientation of the magnetic field 32 is not critical, but is generally parallel to the major axis of the connecting region 25, and may have a field strength on the order of about 1 Gauss.
  • the enclosure 20 confines a mixture of two odd mass numbered isotopes of an inert gas, such as Xenon, or the like, which are capable of undergoing nuclear magnetic resonance. Typical of these isotopes is Xe and 131Xe.
  • the enclosure 20 is generally sealed and evacuated prior to the introduction of the two isotopes, so as to lessen the amount of contamination therein.
  • Sensing means is provided for sensing the precession frequency of atoms undergoing nuclear magnetic resonance within the enclosure 20.
  • the sensing means generally comprises two substantially identical sensing circuits
  • the first sensing circuit 26 generally includes a resonant tank circuit comprising an induction coil 27, a capacitor 28, and an amplifier 30 assembled to form a nuclear magnetic resonance controlled oscillator, such as a marginal oscillator, or the like.
  • the first sensing circuit 26 is tuned to respond to the precession frequency of the first isotope, while the second sensing circuit 34 is tuned to respond to the precession frequency of the second isotope.
  • Signal processor means 31 such as a microcomputer, or the like, is coupled to the two sensing circuits 26, 34 for processing signals received therefrom in accordance with data processing methods well known in the nuclear magnetic resonance gyro art.
  • the resonance light source 21 applied circularly polarized resonant light to the first region 23 of the enclosure 20.
  • the RF discharge source 22 applied RF energy, by means of weak RF discharge, to the first region 23.
  • the two isotopes of Xenon confined within the enclosure 20 are initially in an equilibrium ground state condition.
  • the RF discharge pumps these isotopes into an excited state, thus creating a mixture of ground state atoms, metastable atoms, electrons and ions within the first region 23.
  • the metastable atoms subsequently transfer angular momentum to the ground state atoms confined within the first region 23 which causes a population inversion therein.
  • the ground state atoms are put in a polarization state wherein the nuclear spins of the atoms are oriented in a direction substantially parallel to the magnetic field 32.
  • isotopes of Xenon are used, namely 129Xe and 131Xe.
  • isotopes of Xenon are particularly useful because they have long nuclear magnetic relaxation time in that the nuclear polarization in the ground state atoms is retained for a relatively long period of time. For example, the ground state nuclear polarization of the Xenon isotopes continues to exist for periods up to 24 minutes.
  • ⁇ acts as an observation region for the nuclear magnetic resonance.
  • the connecting region 25 acts as a filter which allows only the polarized ground state atoms to diffuse into the second region 24.
  • the magnetic field 32 is applied to the enclosure 20.
  • the applied magnetic field 32 is essential to the nuclear magnetic resonance process in that it defines the orientation of the polarized nuclear spins in the two isotopes.
  • the polarized ground state atoms Once the polarized ground state atoms have diffused into the second ' region 24, they are stimulated to make a radiative transition in response to the radio frequency field provided by the two sensing circuits 26, 34.
  • Each sensing circuits 26, 34 responds to the nuclear magnetic resonance signal of one of the two isotopes, in that the two sensing circuits are tuned to resonate at the magnetic resonance frequency of the respective isotopes.
  • the radiative transition leads to an observable signal which is detected by the sensing circuits 26, 34.
  • the sensing circuits 26, 34 are nuclear magnetic resonant controlled oscillators whose oscillation frequen ⁇ cies are the Larmor precession frequencies of the nuclear spins of the polarized ground state atoms of the two isotopes in the applied magnetic field 32.
  • the inertial rotation rate of practical systems are relatively small, being on the order of one part in 100 million of the nuclear Larmor precession frequency in a 1 Gauss field.
  • frequency measure ⁇ ments of one part in ten to the fourteenth are easily detected by the present state of the art devices.
  • the frequencies of the nuclear magnetic resonance are detected by the sensing circuits 26, 34, and are applied to the signal processor means 31, such as a micro-computer, or the like.
  • the signal processor means 31 may, for example, integrate the changes in frequency * over time to attain an angular rate of change which is indicative of the rotational motion of the gyro. This manner integration is well known to those skilled in the nuclear magnetic resonance gyro art.
  • the applied magnetic field 32 generally fluctuates with time, and in accordance with the present invention, the use of two isotopes of Xenon compensates therefore. Accordingly, two nuclear magnetic resonances are measured which provides a means for eliminating any fluctuations in the magnetic field 32.
  • the use of two isotopes of Xenon provides for two equations and two unknowns thus elimina ⁇ ting the magnetic field from the equations, and as such the rotational frequency of the enclosure 20 may be easily calculated by the signal processor means 31.
  • the present invention has incorporated the use of two isotopes of Xenon so as to circumvent the practical problem of a fluctuating magnetic field 32.
  • the invention is in principle operational when using only one isotope.
  • other elements may be used, such as mercury or rubidium.
  • these elements have polarization relaxation times on the order of one second or so, which would require a very short connecting region and a consequent reduction in signal to noise ratio due to losses in nuclear polarization.
  • the nuclear magnetic resonance frequency resolution is reduced, thus providing a less effective gyro.
  • certain inert gases cannot be used, since they have no odd mass number isotopes. Such a gas is argon.
  • neon may be used, but it has only one odd mass number isotope.
  • the magnetic field fluctuations could become a problem in gyros incorporating neon.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

Gyroscope a resonance magnetique nucleaire comprenant une enceinte (20) composee d'une premiere region (23), d'une deuxieme region (24) et une region de connexion (25), cette enceinte (20) renfermant une certaine quantite de gaz inerte avec deux isotopes de masse atomique impaire capables de subir une resonance magnetique nucleaire. Un champ magnetique (32) est applique a l'enceinte (20), et le gaz dans la premiere region (23) est pompe jusqu'a un etat d'excitation pour produire des atomes polarises a l'etat fondamental et des produits de decharge a l'interieur, les atomes etant ensuite diffuses a travers la region de connexion (25), faisant office de filtre par rapport aux produits de decharge non desires, vers la deuxieme region (24) ou seulement des atomes polarises a l'etat fondamental, qui ont garde leur polarisation, peuvent se propager. Des transitions dans la resonance magnetique nucleaire ont lieu dans la deuxieme region 824) et les changements de frequence et la precession des atomes polarises autour du champ magnetique applique (32) dus au mouvement de rotation de l'enceinte (20) sont detectes par des circuits de detection (26, 21, 34).
PCT/US1980/000972 1979-08-01 1980-07-31 Gyroscope a resonance magnetique nucleaire WO1981000455A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US6266279A 1979-08-01 1979-08-01
US62662 1979-08-01

Publications (1)

Publication Number Publication Date
WO1981000455A1 true WO1981000455A1 (fr) 1981-02-19

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EP (1) EP0033340A1 (fr)
WO (1) WO1981000455A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8600691B2 (en) 2011-01-21 2013-12-03 Northrop Grumman Guidance and Electronics, Inc. Gyroscope system magnetic field error compensation
EP3290863A1 (fr) * 2016-09-02 2018-03-07 Commissariat à l'énergie atomique et aux énergies alternatives Dispositif de détection de résonance magnétique nucléaire de type seop à double cellule
CN110068320A (zh) * 2019-05-05 2019-07-30 中国工程物理研究院总体工程研究所 一种零偏自校准原子陀螺仪
DE102022202228A1 (de) 2022-03-04 2023-09-07 Robert Bosch Gesellschaft mit beschränkter Haftung Gyroskop-Sensor mit Dampfzelle

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3049662A (en) * 1957-06-01 1962-08-14 Commissariat Energie Atomique Method and device for the measurement of magnetic fields by magnetic resonance
US3206671A (en) * 1962-04-09 1965-09-14 Texas Instruments Inc Atomic collision influenced gaseous helium-3 quantum resonance magnetometer apparatus
US3281709A (en) * 1963-02-05 1966-10-25 Varian Associates Apparatus for optical alignment and detection of atomic energy states
US3350632A (en) * 1964-08-25 1967-10-31 Varian Associates Optically pumped atomic diffusion maser with separate pumping and observation regions

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3049662A (en) * 1957-06-01 1962-08-14 Commissariat Energie Atomique Method and device for the measurement of magnetic fields by magnetic resonance
US3206671A (en) * 1962-04-09 1965-09-14 Texas Instruments Inc Atomic collision influenced gaseous helium-3 quantum resonance magnetometer apparatus
US3281709A (en) * 1963-02-05 1966-10-25 Varian Associates Apparatus for optical alignment and detection of atomic energy states
US3350632A (en) * 1964-08-25 1967-10-31 Varian Associates Optically pumped atomic diffusion maser with separate pumping and observation regions

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8600691B2 (en) 2011-01-21 2013-12-03 Northrop Grumman Guidance and Electronics, Inc. Gyroscope system magnetic field error compensation
EP3290863A1 (fr) * 2016-09-02 2018-03-07 Commissariat à l'énergie atomique et aux énergies alternatives Dispositif de détection de résonance magnétique nucléaire de type seop à double cellule
FR3055699A1 (fr) * 2016-09-02 2018-03-09 Commissariat A L'energie Atomique Et Aux Energies Alternatives Dispositif de detection de resonance magnetique nucleaire de type seop a double cellule
CN110068320A (zh) * 2019-05-05 2019-07-30 中国工程物理研究院总体工程研究所 一种零偏自校准原子陀螺仪
CN110068320B (zh) * 2019-05-05 2024-02-06 中国工程物理研究院总体工程研究所 一种零偏自校准原子陀螺仪
DE102022202228A1 (de) 2022-03-04 2023-09-07 Robert Bosch Gesellschaft mit beschränkter Haftung Gyroskop-Sensor mit Dampfzelle

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Publication number Publication date
EP0033340A1 (fr) 1981-08-12

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