Differential Magnetic Angle Sensor with Back Bias Magnet
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Solution Overview
Problem
Current magnetic field sensors require complex processing and additional components to determine the absolute relative rotational angle of a ferromagnetic target object, often employing multiple sensing elements or complexly shaped targets, which increases complexity and cost.
Innovation Solution
A magnetic field sensor system utilizing two magnetic field sensing elements and a differential amplifier to generate a difference signal related to the absolute relative rotation of a ferromagnetic target object, with specific target shapes creating a monotonic differential field for improved measurement accuracy and reduced post-processing requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple magnetic field sensing elements or complexly shaped target objects are employed, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The target object is segmented into multiple regions with different magnetic permeability (ferromagnetic and non-ferromagnetic regions), creating distinct magnetic field patterns that enable absolute angle measurement. This segmentation allows a single sensing element to resolve angular position without requiring multiple sensing elements or complex target geometries.
Solution Approach 2:
Different regions of the target object are assigned different magnetic properties (ferromagnetic vs. non-ferromagnetic), creating localized magnetic field variations. This local differentiation enables the sensing element to detect absolute angular position through the unique magnetic field signature produced by the specific combination of ferromagnetic and non-ferromagnetic regions.
2Measurement precision
If complex processing is used to determine rotational information, then measurement precision is improved, but manufacturing precision and cost increase
Solution Approach 1:
The target object's magnetic field distribution is designed to inherently encode absolute angular position information through its unique combination of ferromagnetic and non-ferromagnetic regions. The magnetic field pattern self-provides the necessary information for angle measurement, eliminating the need for complex signal processing or additional processing components.
3Device complexity
If a simple magnetic field sensor arrangement is used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The target object employs an asymmetric magnetic field distribution created by the specific arrangement of ferromagnetic and non-ferromagnetic regions. This asymmetric field pattern provides unique angular position information that enables a simple sensing element to achieve precise absolute angle measurement without requiring complex sensor arrays or processing.
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 measures absolute relative angular positions over a range of up to 180 degrees or 360 degrees with high linearity, reducing the need for complex processing and costly components, and achieving accurate rotational position detection.
Implementation Method 1
Magnetic field sensors provide information about a sensed ferromagnetic object by sensing fluctuations of the sensed magnetic field
Implementation Method 2
Various types of magnetic field sensing elements are known, including Hall Effect elements and magnetoresistance elements
Implementation Method 3
Some magnetic field sensors include a fixed permanent magnet in a so-called 'back bias' arrangement
Implementation Method 4
the magnetic field sensed by the magnetic field sensor varies in accordance with a shape or profile of the moving ferromagnetic object
Data Source
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Figure 1B
Figure 2
AI summary
A magnetic field sensor includes a back bias magnet to generate a DC magnetic field. First and second magnetic field sensing elements of the magnetic field sensor are disposed proximate to at least one ferromagnetic surface of a ferromagnetic target object. The first and second magnetic field sensing elements generate first and second electronic signals, respectively, in response to first and second sensed magnetic fields corresponding to the DC magnetic field but influenced by the at least one ferromagnetic surface. The magnetic field sensor generates a difference signal that is a difference of amplitudes of the first and second electronic signals. The difference signal is indicative of a rotation measurement of an absolute relative rotation of the ferromagnetic target object and the magnetic field sensor about a rotation axis.