NMR Gyroscope Bias Error Compensation Using Three Noble Gases
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Solution Overview
Problem
Nuclear magnetic resonance (NMR) gyroscopes face bias errors due to differences in effective magnetic fields experienced by noble gas species caused by collisions with alkali atoms, leading to inaccuracies in measuring angular rotation rates.
Innovation Solution
Incorporating a third nuclear species and modifying the equations to account for local collisional fields, allowing for the determination of unique solutions for the magnetic field, alkali density, and rotation rate by using additional equations that relate the collisional fields to the alkali density and spin polarization, which can be calibrated and measured.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two noble gas species are used for detection, then the gyroscope can measure rotation rates based on Larmor precession frequency differences, but bias errors occur due to different effective magnetic fields experienced by each species from collisions with alkali atoms
Solution Approach 1:
The patent segments the detection system by adding a third noble gas species, creating three separate detection channels. Each species experiences collisions with alkali atoms independently, allowing the system to separate and measure the collisional field effects for each species. This segmentation enables the calculation of individual collisional fields (h1, h2, h3) that can be used to correct bias errors in the rotation rate measurement.
Solution Approach 2:
The patent introduces the third noble gas species as an intermediary element that helps mediate the measurement of collisional field effects. By adding this intermediate detection channel, the system can better isolate and measure the effects of alkali atom collisions on the noble gas species, providing additional information needed to calculate and correct the effective magnetic field differences that cause bias errors.
2Measurement precision
If optical pumping is used to align atomic magnetic moments, then a macroscopic magnetic moment is produced for detection, but the alignment and signal strength depend on light intensity which introduces additional variables
Solution Approach 1:
The patent applies feedback control to the optical pumping process by continuously monitoring the spin polarization of the alkali atoms and adjusting the light intensity accordingly. This feedback mechanism maintains optimal alignment conditions and compensates for variations in light source intensity, ensuring consistent macroscopic magnetic moment production while reducing the need for frequent manual recalibration.
Solution Approach 2:
The patent systematically varies light intensity parameters during operation to optimize the alignment of atomic magnetic moments. By controlling and adjusting the light intensity parameter, the system can maximize the macroscopic magnetic moment signal while accounting for the thermal and light intensity dependencies mentioned in the patent, thereby improving detection precision without excessive complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate calibration and reduction of gyro bias errors by accounting for the thermal and light intensity dependencies, resulting in improved precision in measuring angular rotation rates.
Implementation Method 1
The NMR cell is illuminated by a beam of circularly polarized light that originates from a source such as a rubidium lamp and which passes through the cell at an angle with respect to the steady magnetic field. Absorption of some of this light causes the atomic magnetic moments of the rubidium atoms to be partly aligned in the direction of the steady magnetic field.
Implementation Method 2
This alignment is partly transferred to the nuclear magnetic moments of the noble gases, and these moments are caused to precess about the direction of the steady magnetic field, which in turn creates magnetic fields that rotate at the respective Larmor precession frequencies of the two noble gases.
Implementation Method 3
These rotating fields modulate the precessional motions of the rubidium magnetic moments, which in turn produce corresponding modulations of the transmitted light, thereby making it possible to optically detect the Larmor precession frequencies of the two noble gases.
Implementation Method 4
The modulations of the light intensity are converted into electrical signals by a photodetector, and these signals are then electronically demodulated and filtered to provide signals at the Larmor precession frequencies of the two noble gases.
Data Source
AI summary
A method comprises the steps of providing a nuclear magnetic resonance cell (102) with first, second, and third nuclear moment gases (106,108,110) and at least one optically pumpable substance; obtaining first, second, and third measured precession frequencies that correspond to the first, second, and third nuclear moment gases, wherein the first, second, and third measured precession frequencies are altered from corresponding first, second, and third Larmor precession frequencies by a rotational rate and corresponding first, second, and third local magnetic fields; and determining the rotational rate with compensation for the first, second, and third local magnetic fields through employment of the first, second, and third measured precession frequencies.