Magnetic Sensor With Exchange-Coupled Bias Field Stability
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Solution Overview
Problem
Magnetic sensors using hard magnetic materials for bias magnetic field generation are susceptible to changes in magnetization direction when exposed to external magnetic fields exceeding the coercivity of the hard magnetic material, leading to unstable output signals.
Innovation Solution
A magnetic sensor design incorporating soft magnetic yokes and ferromagnetic-antiferromagnetic exchange-coupled magnetic field generators to stabilize the bias magnetic field, using ferromagnetic and antiferromagnetic materials to resist disturbances and maintain signal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hard magnetic material is used for bias magnetic field generation, then the bias magnetic field can be maintained under normal conditions, but the magnetization direction changes when external magnetic field exceeds coercivity
Solution Approach 1:
The patent uses a composite structure consisting of a soft magnetic material yoke and a hard magnetic material bias magnetic field generation section. The soft magnetic yoke concentrates the magnetic field while the hard magnetic section provides stable magnetization. This composite approach allows the system to maintain bias magnetic field stability under normal conditions while the soft magnetic yoke helps resist changes when external magnetic fields are applied.
2Measurement precision
If soft magnetic yoke is used to concentrate magnetic field, then sensitivity is improved, but hysteresis occurs in output signal
Solution Approach 1:
The patent applies a bias magnetic field to the soft magnetic yoke in advance to prevent hysteresis effects. By pre-magnetizing the soft magnetic material with a controlled bias field from the hard magnetic section, the yoke operates in a linear region of its magnetization curve, eliminating hysteresis loops and ensuring that the output signal accurately reflects the applied magnetic field without memory effects.
3Stability of the object's composition
If bias magnetic field generation section is made of hard magnetic material, then magnetic field direction is stable, but external magnetic field can permanently change magnetization direction
Solution Approach 1:
The soft magnetic yoke acts as an intermediary between the hard magnetic bias field generation section and the measurement target. The hard magnetic section provides a stable, fixed magnetization direction that generates the bias field, while the soft magnetic yoke concentrates and directs this field toward the sensor element. This intermediary structure allows the system to maintain stable magnetization direction while protecting against permanent changes from external fields.
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 proposed design effectively resists changes in the output signal due to external magnetic field disturbances, ensuring stable bias magnetic fields and consistent sensor performance.
Implementation Method 1
an antiferromagnetic portion made of an antiferromagnetic material and exchange-coupled with the ferromagnetic portion
Implementation Method 2
a soft magnetic body that converges the magnetic field of the measurement target on the magnetoresistive element
Implementation Method 3
a spin-valve magnetoresistive element including a magnetization pinned layer having a magnetization pinned in a certain direction, a free layer having a magnetization whose direction is variable depending on the direction of a target magnetic field
Data Source
AI summary
A magnetic sensor includes an MR element, at least one yoke, and at least one magnetic field generator. The at least one yoke includes a magnetic layer made of a soft magnetic material, and is adjacent to the MR element and spaced at a distance apart from each other. The at least one magnetic field generator includes a ferromagnetic portion made of a ferromagnetic material and an antiferromagnetic portion made of an antiferromagnetic material and exchange-coupled with the ferromagnetic portion, and is configured to generate a magnetic field to be applied to the at least one yoke.