Magnetic Sensor Cross Field Design for Sensitivity

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Solution Overview

Problem

Magnetic sensor devices face challenges in detecting subtle magnetic patterns due to the saturation of anisotropic magnetoresistance effect elements at high magnetic field strengths and the distance between the object and the magnetoresistance effect element, leading to reduced detection sensitivity.

Innovation Solution

The magnetic sensor device employs a configuration with two permanent magnets positioned to create a cross magnetic field, ensuring the anisotropic magnetoresistance effect element operates within a strong magnetic field, and uses a multilayer board and metal carrier to maintain sensitivity even when the object and magnetoresistance effect element are spaced apart, with meander-shaped resistors for enhanced sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the object to be detected and the magnetoresistance effect element are spaced apart by a predetermined distance, then non-contact detection is enabled, but the output signal becomes small and detection sensitivity deteriorates

Engineering Contradiction:

Improvenon-contact detection capabilityVSAvoiddetection sensitivity

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent divides the magnetic field generation into two separate permanent magnets (first and second permanent magnets) positioned on opposite sides of the conveyance path. This segmentation allows the magnetic field to be applied across the gap between the object and sensor without requiring direct contact, while maintaining sufficient field strength through the combined effect of both magnets

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses the first and second permanent magnets to create opposing magnetic fields that counterbalance each other in the spacing direction while reinforcing the magnetic field in the conveyance direction. This counterweight approach allows the magnetic field to penetrate through the gap without saturation, enabling non-contact detection while maintaining sensitivity

Inventive Principle:

Principle #8Anti-weight (Counterweight)

2Measurement precision

If the magnetic field strength is increased to improve detection sensitivity, then the anisotropic magnetoresistance effect element becomes saturated, making it difficult to maintain high sensitivity

Engineering Contradiction:

Improvedetection sensitivityVSAvoidmagnetic field saturation

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent creates a localized magnetic field environment where the magnetic field strength is optimized in the conveyance direction (parallel to the object surface) while keeping the spacing direction (perpendicular to object surface) field component controlled. The first and second permanent magnets are positioned and oriented to generate magnetic field lines that run parallel to the object surface in the detection region, ensuring the AMR element operates in its high-sensitivity range without saturation

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent transitions from considering only magnetic field strength magnitude to considering the directional components of the magnetic field. By orienting the permanent magnets to create magnetic field lines primarily in the conveyance direction (X-axis) rather than in the spacing direction (Z-axis), the patent exploits the anisotropic nature of the AMR element to achieve high sensitivity without saturation

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 maintains detection sensitivity and stability by applying a strong magnetic field across the object, even at larger distances, and reduces assembly complexity, ensuring accurate detection of magnetic patterns without external interference.

Implementation Method 1

the magnetic sensor device uses an anisotropic magnetoresistance effect element, which has a higher detection sensitivity than a semiconductor magnetoresistance effect element

Methodology Applied

Scientific EffectAnisotropic magnetoresistance effect: Magnetoresistance

Implementation Method 2

the position of a permanent magnet is adjusted so that the bias magnetic field strength in the magnetic sensing direction of the ferromagnetic thin-film magnetoresistance element applied by a detecting magnetic field by the permanent magnet

Methodology Applied

Scientific EffectMagnetic field generation: Magnetism

Data Source

PatentEP2711728B1Magnetic sensor device

Publication Date: 2021.03.17 MITSUBISHI ELECTRIC CORP

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AI summary

A magnetic sensor device comprises a first magnet (6) and a second magnet (7) that are disposed on mutually opposing sides of a conveyance path (2), and one of poles of the first magnet (6) faces an opposite pole of the second magnet (7). The first magnet (6) and the second magnet (7) generate a cross magnetic field whose strength in a spacing direction, which is orthogonal to a conveying direction, is within a predetermined range. An AMR element (10) is located in a magnetic field in which the strength of the cross magnetic field in the spacing direction is within a predetermined range, and detects, as a change in a resistance value, a change in the cross magnetic field caused by an object (5) to be detected. A multilayer board (9) outputs the change in the resistance value detected by the AMR element (10) to a processing circuit (15).