Magnetoresistive Sensor System with Asymmetric Biasing Magnet
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Solution Overview
Problem
Existing magnetic field sensor systems face challenges with sensitivity and reliability due to external magnetic fields, particularly in automotive applications where sensors like crankshaft position detection are affected by nearby starter motors.
Innovation Solution
A magnetic field sensor system with a biasing magnet generating a symmetric magnetic field, combined with a magnetoresistive sensor arrangement in an x-y plane, which maintains high sensitivity and immunity to external fields by optimizing the placement and orientation of magnetoresistive sensor elements within the Wheatstone bridge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional magnetic field sensor system uses a biasing magnet to magnetize the wheel, then the sensor can detect magnetic field changes for position determination, but external magnetic fields negatively impact the sensitivity and reliability of the sensor system
Solution Approach 1:
The patent applies asymmetry by strategically positioning the biasing magnet offset from the center of the magnetic wheel. This asymmetric placement creates a non-uniform magnetic field distribution that allows the sensor to distinguish between field changes caused by wheel rotation and those caused by external magnetic fields. The offset position generates a characteristic field pattern that maintains sensitivity while providing immunity to external interference.
Solution Approach 2:
The patent introduces an intermediary evaluation unit that processes sensor signals to separate useful information from interference. This evaluation unit acts as a mediator between the raw sensor output and the final position determination, filtering out external magnetic field effects while preserving the rotational position signal. The evaluation unit may use reference signals or algorithms to compensate for external field disturbances.
2Measurement precision
If AMR sensors are used to achieve high sensitivity, then the sensor requires more fabrication steps and cannot easily be integrated monolithically, making the total sensor system more expensive
Solution Approach 1:
The patent combines multiple sensor elements into a single integrated sensor arrangement that functions as a unified component. By merging several magnetoresistive elements with different orientation angles into one assembly, the system achieves high measurement precision while enabling monolithic integration. This combined structure can be fabricated as a single unit using standard semiconductor processes, reducing overall system complexity and cost.
Solution Approach 2:
The patent changes the orientation parameters of magnetoresistive sensor elements within the integrated arrangement. By varying the magnetization directions and measurement axes of individual elements in a controlled manner, the system achieves enhanced sensitivity and external field immunity. This parameter variation allows the use of standard AMR technology while optimizing performance through geometric configuration rather than complex fabrication.
3Measurement precision
If GMR sensors are used to achieve higher sensitivity than AMR sensors, then the fabrication technology becomes considerably more complicated and expensive, and the operating temperature range is limited
Solution Approach 1:
The patent employs a simpler sensor technology (AMR) that can be manufactured more easily and at lower cost, accepting that individual sensor elements may have limited operational lifetimes in harsh environments. By using robust AMR elements with appropriate protective measures and redundancy in the sensor arrangement, the system achieves reliable performance without requiring the complex, temperature-sensitive GMR structure.
Solution Approach 2:
The patent uses composite structures within the magnetoresistive sensor elements, combining ferromagnetic layers with non-magnetic spacer layers and protective coatings. This composite approach enhances the thermal stability and mechanical robustness of the sensor elements, allowing AMR technology to operate reliably at higher temperatures without requiring the complex multilayer GMR structure.
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 achieves high sensitivity and robustness against external magnetic fields, allowing for accurate position detection and reduced production costs through a compact design with minimized semiconductor die area, offering improved performance compared to traditional sensor concepts.
Implementation Method 1
a biasing magnet configured for generating a biasing magnetic field
Implementation Method 2
the magnetic wheel can be magnetized by the biasing magnetic field
Implementation Method 3
magnetoresistive sensor arrangement comprising four magnetoresistive sensor elements being connected with each other in a Wheatstone bridge
Data Source
AI summary
A magnetic field sensor system for measuring rotational movements of a shaft is disclosed. The sensor system includes a biasing magnet configured for generating a biasing magnetic field and a magnetic wheel having a wheel axis and a circumferential surface which comprises a regular structure of teeth and gaps arranged in an alternating manner. The magnetic wheel is attachable to the shaft and is magnetizable by the biasing magnetic field. A magnetoresistive sensor arrangement comprising four magnetoresistive sensor elements being connected with each other in a Wheatstone bridge, respectively two of the magnetoresistive sensor elements being assigned to one half bridge of the Wheatstone bridge. The four magnetoresistive sensor elements are arranged within an x-y plane.