Magnetic Sensor Bias Field Stabilization for Sensitive Pattern Detection
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Solution Overview
Problem
Existing magnetic sensors using anisotropic magnetoresistance elements face challenges in maintaining sensitivity without saturating, as they require precise alignment and uniform magnetic fields, leading to inconsistent output and difficulty in detecting small magnetic patterns on sheet-like media like paper currency.
Innovation Solution
A magnetic sensor design that includes a magnet and a magnetic carrier with yokes to create a uniform magnetic field, positioning the anisotropic magnetoresistance element to receive a bias magnetic field within a specific range, minimizing fluctuations, and using a shielded substrate to enhance sensitivity and consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an anisotropic magnetoresistance element is used to detect small magnetic patterns, then sensitivity is improved, but the element saturates at a magnetic flux density of approximately 10 mT, making it difficult to dispose multiple elements in areas where sensitivity rises without saturation
Solution Approach 1:
A permanent magnet is introduced as an intermediary component to generate a bias magnetic field. This bias field shifts the operating point of the anisotropic magnetoresistance element to a region where high sensitivity exists without saturation. The permanent magnet acts as a mediator that enables multiple sensor elements to operate simultaneously in the optimal sensitivity range, resolving the contradiction between sensitivity and device complexity.
2Measurement precision
If a permanent magnet is disposed to impart a bias magnetic field to ferromagnetic thin film magnetoresistance elements, then sensitivity is improved, but the bias magnetic field strength must be precisely controlled to avoid exceeding saturation magnetic field
Solution Approach 1:
The invention changes the magnetic field parameter by introducing a permanent magnet that generates a bias magnetic field. This bias field shifts the operating point of the magnetoresistance elements to an optimal region. By carefully selecting the position and strength of the permanent magnet, the system achieves high sensitivity while maintaining operation below saturation, resolving the contradiction between sensitivity improvement and manufacturing precision requirements.
3Ease of operation
If the object of detection is moved between a magnet and a magnetoresistance element, then detection is enabled, but the magnetic field strength varies significantly in the magneto-sensing direction, causing inconsistent output
Solution Approach 1:
The permanent magnet is positioned in advance to establish a uniform bias magnetic field in the magneto-sensing direction before the object of detection enters the detection region. This preliminary action ensures that all magnetoresistance elements receive a consistent bias field, eliminating variations in magnetic field strength and ensuring reliable, consistent output throughout the detection process.
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 design achieves consistent and sensitive detection of magnetic patterns on sheet-like media by stabilizing the bias magnetic field, allowing for loose assembly tolerances and improved output across multiple channels.
Implementation Method 1
a magnetoresistance element having a property in which the resistance varies according to magnetic field strength. The magnetization of a magnetic pattern included in a sheet-like medium such as paper currency is typically small. For this reason, particularly in a line-type magnetic sensor that detects multiple channels simultaneously, an anisotropic magnetoresistance element is often used in order to detect a magnetic pattern with high sensitivity.
Implementation Method 2
a permanent magnet is disposed with the position adjusted so that the bias magnetic field strength in the magneto-sensing direction of ferromagnetic thin film magnetoresistance elements (anisotropic magnetoresistance elements) simultaneously imparted by a detecting magnetic field from the permanent magnet reaches a magnetic flux that is not greater than the saturation magnetic field.
Data Source
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AI summary
The purpose of the present disclosure is to detect consistently and with good sensitivity the magnetic pattern of an object of detection in a contactless state in which the object of detection having the magnetic pattern is separated from a magnetoresistance element by a minute distance. A magnet (6) is disposed on one face of a hollow section (2) which is the conveyance path of an object of detection (5), and has a magnetic pole of designated length along the conveyance direction of the object of detection (5). A magnetic body (8) is disposed along the conveyance direction opposite the magnet (6) with the hollow section (2) therebetween, and generates a cross magnetic field that crosses the hollow section (2) formed between the magnetic body (8) and the magnet (6). An anisotropic magnetoresistance element (10) is disposed on the side of the magnetic body carrier (8) facing the hollow section (2), and has magneto-sensing action in the conveyance direction.