Magnetometer Interference Detection Using Motion Sensor Comparison
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Solution Overview
Problem
Magnetometers in mobile devices face challenges in accurately measuring magnetic fields due to internal and external interference, leading to the need for recalibration, which can be resource-intensive and sometimes unnecessary, especially when dealing with transient interference sources.
Innovation Solution
A method that utilizes non-magnetometer sensors like accelerometers and gyroscopes to differentiate between internal and external interference, deferring recalibration until persistent interference is confirmed, and providing user indications to address transient interference by moving away from sources, thus optimizing recalibration and reducing resource consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If recalibration is performed frequently to maintain magnetometer accuracy, then measurement precision is improved, but use of energy and computing resources increases
Solution Approach 1:
The system continuously monitors magnetometer sensor data and compares it with expected motion data derived from accelerometer and gyroscope measurements. This feedback mechanism allows the system to detect discrepancies indicating magnetic interference and trigger recalibration only when necessary, rather than performing frequent recalibrations. The feedback loop includes: monitoring magnetometer readings, computing expected motion from other sensors, comparing actual vs expected motion, detecting interference when discrepancies exceed thresholds, and conditionally initiating recalibration based on interference persistence.
Solution Approach 2:
The system changes the parameter being monitored from raw magnetometer readings to computed motion characteristics. By transforming magnetometer data into motion parameters and comparing with reference motion data from other sensors, the system can identify when magnetic interference is present without directly measuring the interference itself. This parameter transformation enables intelligent detection of calibration needs.
2Measurement precision
If recalibration is performed immediately when interference is detected, then measurement precision is improved, but loss of time increases due to unnecessary recalibrations for transient interference
Solution Approach 1:
The system performs preliminary monitoring and analysis before initiating recalibration. It first detects potential interference by comparing magnetometer-derived motion with sensor-derived motion, then monitors whether the interference persists over time before committing to recalibration. This preliminary action phase includes detecting the interference condition and evaluating its persistence, allowing the system to avoid unnecessary recalibrations for transient interference while still responding promptly to genuine calibration needs.
3Reliability
If the system monitors magnetometer data continuously to detect interference, then reliability is improved, but use of energy increases
Solution Approach 1:
The system uses accelerometer and gyroscope data, collected for other navigation and motion-tracking purposes, to detect magnetic interference. By making these existing sensors serve the additional function of interference detection, the system achieves reliable monitoring without adding dedicated hardware or significantly increasing power consumption. The multi-functionality approach allows the same sensor data to support both primary navigation functions and magnetometer calibration monitoring.
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 efficiency of magnetometer data by minimizing unnecessary recalibrations, conserving computing and power resources, and improving user experience by reducing the frequency of recalibration prompts.
Implementation Method 1
A magnetometer is an instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument
Implementation Method 2
accelerometer operable to obtain accelerometer sensor data
Implementation Method 3
gyroscope operable to obtain gyroscope sensor data
Data Source
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AI summary
Methods and apparatus employing non-magnetometer navigational sensor data to assist in determining whether a change in a magnetic field detected by a magnetometer is likely due to a source of internal or external magnetic interference, and more generally, whether such interference is likely to be persistent or transient. If the magnetic field data detected by the magnetometer indicates a large change in magnetic field, but the non-magnetometer navigational sensor (e.g., gyroscope) data does not indicate a corresponding change in orientation of the mobile device contemporaneous with the change in magnetic field, then the cause of the magnetic field change may be determined as likely originating from a localized external interference source and the device may prompt the user to move away from the interference source, rather than initiating a recalibration of the magnetometer.