Eddy Current Angle Sensor with Quadrature Magnetoresistance Detection
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Solution Overview
Problem
Magnetic field sensors face challenges in accurately detecting the angular position of a target with symmetric gradient reflected magnetic fields, particularly in non-destructive testing and motion/position sensing applications, where existing sensors are sensitive to stray fields and require complex normalization techniques.
Innovation Solution
A magnetoresistance-based angle sensor system utilizing a coil to generate eddy currents in a rotatable target, with first and second magnetoresistance elements positioned to detect quadrature components of the reflected magnetic field, and a processing module to compute the angular position using the ratio of signals from these elements, minimizing direct coupled magnetic fields and stray field immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetoresistance elements are used to detect reflected magnetic fields, then measurement precision is improved, but sensitivity to stray fields increases causing measurement errors
Solution Approach 1:
The sensing system is divided into multiple magnetoresistance elements (first and second elements) that detect different quadrature components of the magnetic field. By segmenting the detection function across multiple elements and processing their signals differentially, the system achieves precise angular position measurement while rejecting common-mode stray field interference.
Solution Approach 2:
The system uses feedback processing where the outputs from multiple magnetoresistance elements are combined through signal processing circuitry. The differential processing of quadrature components provides feedback that cancels out stray field effects while preserving the desired angular position information.
2Measurement precision
If complex normalization techniques are used to compensate for stray fields, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent employs magnetoresistance elements with specific local magnetic properties and orientations tailored to detect particular quadrature components. Each element is locally optimized with specific magnetization directions and geometric arrangements to inherently distinguish between reflected magnetic field signals and stray field interference, eliminating the need for complex global normalization algorithms.
Solution Approach 2:
Instead of applying complex normalization techniques to correct stray field effects after detection, the patent inverts the approach by designing the sensing element geometry and magnetization patterns to inherently reject stray fields. The quadrature detection scheme is structured so that stray field contributions naturally cancel out in the differential measurement, turning a post-processing problem into a design-level solution.
3Ease of operation
If direct coupled magnetic fields are present in the sensing structure, then ease of operation is improved, but measurement precision deteriorates due to field interference
Solution Approach 1:
The patent employs asymmetric arrangements of magnetoresistance elements with different orientations and positions relative to the coil axis. This asymmetric configuration creates differential sensitivity patterns where the first and second magnetoresistance elements respond differently to direct coupled fields while maintaining equal sensitivity to the reflected magnetic field quadrature components. The asymmetry enables simple operation without requiring additional shielding or complex compensation circuits.
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
The system effectively determines the angular position of the target with improved sensitivity and reduced impact from stray fields, achieving accurate angle detection without the need for complex normalization or direct coupled field subtraction.
Implementation Method 1
a coil configured to generate a magnetic field that induces an eddy current in a rotatable target
Implementation Method 2
a reflected magnetic field generated by the eddy current induced in the target
Implementation Method 3
at least one first magnetoresistance element positioned proximate to the coil and configured to detect a reflected magnetic field
Data Source
AI summary
A magnetic field angle sensor includes a coil configured to generate a magnetic field that induces an eddy current in a rotatable target, a first magnetic field sensing structure positioned proximate to the coil and configured to detect a reflected magnetic field generated by the eddy current induced in the target, a second magnetic field sensing structure positioned proximate to the coil and configured to detect the reflected magnetic field generated by the eddy current induced in the target, wherein the first and second magnetic field sensing structures are configured to detect quadrature components of the reflected magnetic field, and a processing module configured to process the reflected magnetic field detected by the first and second magnetic field sensing structures for determining an angular position of the target.