Magnetic Field Sensor Stray Field Immunity Air Gap

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Solution Overview

Problem

Magnetic field sensors face interference from external stray fields and require increased air gap distances between the sensor and target magnet, which existing technologies fail to address effectively, impacting accuracy and operational reliability.

Innovation Solution

A magnetic field sensor system featuring a ring magnet with alternating magnetic segments and a substrate supporting four magnetic field sensing elements arranged in bridge circuits, with axes of maximum sensitivity parallel to the rotation axis, allowing for reduced sensitivity to stray fields and increased air gap operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If magnetic field sensing elements are positioned close to the target magnet to improve signal strength, then measurement precision is improved, but the sensor becomes more sensitive to external stray fields

Engineering Contradiction:

Improvesignal detection accuracyVSAvoidstray field sensitivity

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The sensor divides the detection function into multiple sensing elements (first set of four elements forming a first bridge circuit, and second set of four elements forming a second bridge circuit) with different sensitivity orientations. This segmentation allows the system to process magnetic field information from multiple directions, improving signal detection while canceling out stray field interference through differential measurement.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each magnetic field sensing element is oriented with its axis of maximum sensitivity parallel to the rotation axis of the target, creating local quality differentiation. This specific orientation arrangement ensures that each element responds optimally to the target's magnetic field while being less sensitive to external stray fields coming from other directions.

Inventive Principle:

Principle #3Local quality

2Reliability

If magnetic field sensing elements are positioned far from the target magnet to reduce stray field interference, then immunity to external fields is improved, but measurement precision deteriorates

Engineering Contradiction:

Improvestray field immunityVSAvoidsignal detection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The use of multiple bridge circuits with differently oriented sensing elements allows the system to maintain effective signal detection at larger distances. By combining outputs from multiple elements that are optimally oriented, the system preserves measurement precision even when positioned farther from the target, while the differential measurement approach simultaneously provides stray field rejection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent combines the outputs of multiple magnetic field sensing elements through bridge circuits to achieve both stray field immunity and accurate signal detection. The combined output from the first and second bridge circuits provides enhanced signal strength and stray field rejection, allowing reliable operation at increased air gap distances.

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If the sensor uses multiple bridge circuits with eight magnetic field sensing elements to improve stray field rejection, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improvestray field immunityVSAvoidsensor structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The sensor is segmented into two functional groups: a first set of four sensing elements forming a first bridge circuit, and a second set of four sensing elements forming a second bridge circuit. This segmentation into modular bridge circuits simplifies the overall design and fabrication process while maintaining the reliability benefits of multiple sensing elements with different sensitivity orientations.

Inventive Principle:

Principle #1Segmentation

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 provides improved immunity to stray fields and maintains accurate signal detection across larger air gap distances, enhancing the sensor's operational reliability and accuracy in various applications.

Implementation Method 1

A magnetic field sensor can be positioned within the magnetic field produced by the ring magnet to detect the rotation

Methodology Applied

Scientific EffectMagnetic field detection: Magnetic Field

Data Source

PatentUS11215681B2Magnetic field sensor with stray field immunity and large air gap performance

Publication Date: 2022.01.04 ALLEGRO MICROSYSTEMS LLC

AI summary

A system includes a ring magnet having magnetic segments and configured to rotate about an axis of rotation, wherein adjacent segments have different magnetic polarities, The system can further include a substrate positioned so that a top surface of the substrate is substantially parallel to the axis of rotation and a center plane passing through the ring magnet and perpendicular to the axis of rotation of the ring magnet intersects the top surface at an intersection line. The system can further include four magnetic field sensing elements supported by the substrate and electrically coupled to form a first bridge circuit, wherein two of the four magnetic field sensing elements are positioned on one side of the intersection line and the other two of the four magnetic field sensing elements are positioned on the other side of the intersection line.