Magnetic Sensor Stray Field Immunity via Asymmetric Magnetoresistive Layout

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Solution Overview

Problem

Magnetic sensors used in magnetic encoders face errors due to stray fields generated by voice coil motors, which affect the accuracy of position detection.

Innovation Solution

The magnetic sensor is designed with a specific layout of magnetoresistive elements and resistors, where the positions of the resistors and the magnetization directions of the magnetization pinned layers are optimized to minimize the impact of stray fields.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a magnetic sensor is used to detect position in a magnetic encoder system, then position detection capability is provided, but detection accuracy deteriorates due to stray fields from voice coil motors

Engineering Contradiction:

Improveposition detection accuracyVSAvoidstray field interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies differential measurement techniques where the stray field interference is detected simultaneously with the target magnetic field, and the interference component is subtracted through differential calculation. This converts the harmful stray field into a detectable signal that can be mathematically eliminated, improving position detection accuracy in the presence of motor-generated magnetic interference

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces additional magnetic sensors or reference measurement points as intermediaries to detect the stray field component separately. These intermediary sensors provide reference data that mediates between the target magnetic field signal and the stray field interference, enabling separation and elimination of the harmful interference component through signal processing

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If magnetoresistive elements are arranged to detect magnetic field components, then detection capability is improved, but sensitivity to stray fields increases

Engineering Contradiction:

Improvemagnetic field detection capabilityVSAvoidstray field sensitivity

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent employs magnetoresistive elements with different magnetization orientations (e.g., in-plane and out-of-plane magnetization) positioned at specific locations. Each element has optimized local properties to detect specific magnetic field components while being less sensitive to stray fields in certain directions, achieving selective detection capability that reduces overall stray field interference

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses asymmetric arrangements of magnetoresistive elements with different magnetization directions and positions. This asymmetric configuration creates differential response characteristics where the combined output of multiple elements cancels out symmetric stray field components while preserving sensitivity to the target magnetic field gradient

Inventive Principle:

Principle #4Asymmetry

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 configuration reduces errors in the magnetic sensor's detection signals caused by stray fields, leading to improved accuracy in position detection and reduced noise in the magnetic encoder's output.

Implementation Method 1

a first resistor, a second resistor, a third resistor, and a fourth resistor each configured to change in resistance with change in strength of the magnetic field component

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS20250155529A1Magnetic sensor, magnetic encoder, lens position detection device, distance measuring device, and manufacturing method for magnetic sensor

Publication Date: 2025.05.15 TDK CORP

AI summary

In a magnetic sensor, first and second resistors are provided in a path that connects a power supply port and a first output port, and third and fourth resistors are provided in a path that connects a ground port and the first output port. In a direction parallel to an X direction, both of a distance between the first resistor and the second resistor and a distance between the third resistor and the fourth resistor are λ/2, and a distance between the first resistor and the third resistor is zero. A magnetization of a magnetization pinned layer in the first and fourth resistors contains a component in a −X direction. The magnetization of the magnetization pinned layer in the second and third resistors contains a component in the X direction.