Low-noise Magnetoresistive Sensor with Multi-layer Magnetic Modulation
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Solution Overview
Problem
Magnetoresistive sensors face high 1/f noise at low frequencies, which hinders accurate magnetic signal measurement, and existing solutions using MEMS technology with vibrating ferromagnetic flux concentrators increase complexity and size.
Innovation Solution
A low-noise magnetoresistive sensor with a multi-layer magnetic modulation structure, comprising a substrate with a multi-layer magnetic modulation structure array, a magnetoresistive sensing unit, and a two-port excitation coil, where the magnetoresistive sensing unit is positioned between the modulation structures, and an excitation current is applied to reduce 1/f noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a vibrating soft ferromagnetic flux concentrator structure is added to reduce 1/f noise, then measurement precision is improved, but device complexity and size increase
Solution Approach 1:
The patent replaces the mechanical vibrating flux concentrator structure with a magnetic modulation structure that uses magnetic field interaction instead of mechanical vibration. The modulation structure comprises alternating soft ferromagnetic layers and non-magnetic layers that create magnetic flux modulation without requiring mechanical movement, thereby eliminating the complexity of vibration drivers while maintaining noise reduction capability
Solution Approach 2:
The patent employs a composite magnetic modulation structure consisting of multiple layers with different magnetic properties (soft ferromagnetic layers alternating with non-magnetic or hard ferromagnetic layers). This composite structure creates effective magnetic flux modulation through the interaction between layers, achieving noise reduction without mechanical components
2Measurement precision
If a vibrating soft ferromagnetic flux concentrator structure is added to reduce 1/f noise, then measurement precision is improved, but the sensor size increases
Solution Approach 1:
The magnetic modulation structure replaces the mechanical vibrating system with a static multi-layer magnetic structure that achieves modulation through magnetic field interaction. This substitution eliminates the need for large mechanical components and vibration drivers, significantly reducing the overall sensor size while maintaining noise reduction performance
Solution Approach 2:
The modulation structure is designed as a compact multi-layer stack where soft ferromagnetic layers and non-magnetic layers are nested alternately. This nested configuration achieves effective magnetic flux modulation within a minimal volume, avoiding the space requirements of mechanical vibration structures
3Measurement precision
If frequency modulation is used to move measurement from low-frequency to high-frequency region, then 1/f noise energy density is reduced, but additional modulation structure is required
Solution Approach 1:
The patent uses a composite multi-layer magnetic structure where alternating soft ferromagnetic and non-magnetic layers create magnetic flux modulation. The differential magnetic properties of adjacent layers produce the frequency modulation effect needed to shift measurements away from the 1/f noise region, achieving noise reduction without complex additional components
Solution Approach 2:
The modulation function is merged into the sensor structure itself through the multi-layer magnetic modulation structure. The alternating layers inherently provide the frequency modulation capability, combining the modulation function with the sensing structure rather than requiring separate modulation components
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 solution effectively reduces the energy density of 1/f noise, improving magnetic signal measurement accuracy with a compact, simple, and sensitive sensor design.
Implementation Method 1
a magnetic signal is selectively pre-modulated into a high-frequency magnetic field, then it is measured by the magnetoresistive sensor to output a high-frequency voltage signal
Implementation Method 2
There is 1/f noise in a magnetoresistive sensor during normal use. Reducing the noise of the magnetoresistive sensor and developing a low-noise magnetoresistive sensor are of a great significance for improving accurate measurement of magnetic signals
Implementation Method 3
the magnetoresistive sensor has high 1/f noise at a low frequency, and mainly has thermal noise at a high frequency
Data Source
AI summary
A low-noise magnetoresistive sensor includes a substrate and an array of magnetic modulation structures on the substrate. The structure includes upper and lower soft ferromagnetic layers and a conductive metal layer in the middle. The two ends of the structure are connected to form a two-port excitation coil. Adjacent structures have opposite current directions. A magnetoresistive sensing unit is located above or below and is centered in the gap between the structures. The sensitive direction of the sensing units is perpendicular to a long direction of the structures. An array of sensing units is electrically connected to form a magnetoresistive sensor, and the sensor is connected to the sensor bond pads. When measuring an external magnetic field, an excitation current is applied to the excitation coil, and the output of the voltage or current signal of the magnetoresistive sensor is demodulated to produce a low-noise voltage signal.