Rotating Magnetometer for Magnetic Gradient Tensor Measurement
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Solution Overview
Problem
Existing magnetic gradiometers face challenges when used in boreholes for mining applications, particularly due to issues like sensor interactions and calibration difficulties, which affect the accuracy of magnetic field and gradient measurements.
Innovation Solution
A measuring instrument with a mechanism that rotates a single or dual uniaxial magnetometer(s) in a predetermined path, using a signal processing system to perform Fourier transforms and compare frequency components with predetermined paths to determine magnetic gradient tensor components, reducing interference and calibration needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple sensors are used to measure magnetic field components, then measurement completeness is improved, but sensor interactions and calibration difficulties increase
Solution Approach 1:
The patent divides the magnetic field measurement into sequential temporal segments using a single uniaxial magnetometer that rotates through different orientations. Instead of using multiple sensors simultaneously, the system segments the measurement process into multiple rotational positions, measuring different field components at different times. This eliminates sensor interactions while maintaining measurement completeness through time-separated measurements.
Solution Approach 2:
The patent adds the temporal dimension to the measurement process by rotating the sensor through space and time. The single sensor measures different spatial components of the magnetic field at different rotational positions and times. This transforms a spatial measurement problem (requiring multiple simultaneous sensors) into a temporal measurement problem (solved by sequential measurements), eliminating the need for multiple sensors and their complex calibration.
2Measurement precision
If a complex mechanism rotates the sensor along a predetermined path, then measurement accuracy is improved by isolating signals in frequency domain, but device complexity increases
Solution Approach 1:
The patent employs periodic rotational action of the uniaxial magnetometer along a predetermined path at a known frequency. This periodic motion creates distinct frequency signatures for different magnetic field components, allowing the signal processing system to isolate and identify each component through frequency domain analysis. The periodic rotation simplifies the mechanism compared to complex multi-sensor arrangements while achieving superior signal isolation.
Solution Approach 2:
The patent replaces complex mechanical multi-sensor systems with a simpler single-sensor rotational mechanism. Instead of mechanically aligning multiple sensors in precise spatial arrangements, the system uses a single sensor that rotates, with the rotation mechanics providing the spatial diversity needed for complete field characterization. The complexity is shifted from mechanical sensor arrays to rotational mechanics and signal processing.
3Measurement precision
If sensors are mounted on a rotating mechanism, then complete field component measurement is achieved, but motion noise and signal contamination increase
Solution Approach 1:
The patent introduces an intermediary frequency domain analysis step between the raw sensor measurements and the final field component determination. The rotational motion noise and signal contamination are separated from the desired magnetic field signals through frequency domain transformation. The known rotation frequency serves as a reference to identify and extract the magnetic field signal components while filtering out unrelated motion noise.
Solution Approach 2:
The patent changes the measurement parameters from static spatial readings to dynamic temporal-signal characteristics. By analyzing the frequency spectrum of the rotating sensor output, the system transforms the problem from one affected by motion noise in the time domain to one where noise and signal are separated by their frequency characteristics. This parameter transformation allows complete field measurement while mitigating motion contamination.
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 enhances the accuracy and reliability of magnetic field and gradient measurements by isolating field and gradient signals in the frequency domain, reducing contamination from sensor misalignment and motion noise.
Implementation Method 1
a sensor (110) mounted on a mechanism (120) to move the sensor (110) relative to the instrument (100)... determine one or more characteristics of a property of the local environment... The sensor may comprise a total magnetic intensity magnetometer, uniaxial magnetometer, or fluxgate magnetometer
Implementation Method 2
a signal processing system (130) to receive a sensor signal generated by the sensor (110), perform a Fourier transform on the sensor signal to identify frequency components of the sensor signal
Data Source
Figure 1
Figure 2A~2D
Figure 3A~3D
AI summary
Embodiments generally relate to a measuring instrument. The measuring instrument may comprise: a sensor to measure a property of the local environment; a mechanism configured to cause the sensor to move along a predetermined path relative to a fixed reference frame of the instrument; and a signal processing system configured to receive a sensor signal generated by the sensor, perform a Fourier transform on the sensor signal to identify frequency components of the sensor signal, and compare the frequency components of the sensor signal with frequency components associated with the predetermined path to determine a measurement of the property of the local environment. The mechanism may comprise a first member having a first axis and a second axis that is different from the first axis. The mechanism may be configured to cause the first member and the sensor to rotate about the first axis, and to cause the sensor to rotate about the second axis. The sensor may be spatially offset from the first axis. The sensor may be configured to measure one or more vector components of a local force field, such as a magnetic field, for example, and the measuring instrument may comprise a magnetometer or magnetic gradiometer, for example. The measuring instruments disclosed may be suited to downhole applications, such as in a measurement while drilling system, for example.