Rotating Disk Magnetic Probe for Low-Noise 3D Field Sensing
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Solution Overview
Problem
Magnetoresistive sensors face challenges with high 1/f noise at low frequencies, leading to increased complexity and size in high-frequency magnetic signal measuring apparatuses, which complicates the measurement of magnetic signals.
Innovation Solution
A rotating disk magnetic field probe with 4N first soft ferromagnetic sectors and M second soft ferromagnetic sectors on a non-magnetic disk, modulating external magnetic fields into high-frequency components measurable by X-axis, Y-axis, and Z-axis magnetoresistive sensors, along with a reference signal generator to demodulate signals and improve signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic signal measurement is performed at low frequency using magnetoresistive sensors, then measurement simplicity is maintained, but 1/f noise increases significantly
Solution Approach 1:
The patent applies periodic action by rotating a disk with soft ferromagnetic sectors at a specific frequency to modulate the magnetic field. This periodic rotation transforms the static or low-frequency magnetic signal into a high-frequency AC signal, allowing measurement at frequencies where 1/f noise is minimized. The modulation frequency is determined by the rotation speed and the number of soft ferromagnetic sectors on the disk.
Solution Approach 2:
The patent introduces a soft ferromagnetic sector disk as an intermediary element between the magnetic field source and the magnetoresistive sensor. This intermediary modulates the magnetic field by concentrating and redirecting magnetic flux lines during rotation, enabling frequency transformation without requiring complex electronic modulation circuits or high-frequency sensor operation.
2Measurement precision
If high-frequency modulation is applied to reduce 1/f noise, then signal-to-noise ratio improves, but device complexity and size increase
Solution Approach 1:
The patent replaces complex electronic or optical modulation systems with a simple mechanical rotation system. The soft ferromagnetic sector disk rotates mechanically to provide magnetic field modulation, eliminating the need for complex modulators, mixers, or high-frequency signal generation circuits. This mechanical approach achieves frequency transformation with minimal added complexity.
Solution Approach 2:
The patent changes the operating parameters by rotating the soft ferromagnetic disk at a controlled frequency to shift the measurement from low-frequency DC/AC regime to a higher frequency regime. This parameter change (rotation frequency) enables the system to operate in a noise-optimal frequency range while maintaining simple sensor hardware.
3Measurement precision
If a rotating member with flux concentrators is used to modulate magnetic flux, then magnetic signal modulation is achieved, but structure complexity and size increase
Solution Approach 1:
The patent merges the modulation function with the existing magnetoresistive sensor assembly by integrating a soft ferromagnetic sector disk that can rotate in close proximity to the sensor. This combined structure achieves magnetic field modulation without requiring separate, bulky modulation components, thereby minimizing the increase in overall assembly size.
Solution Approach 2:
The soft ferromagnetic disk is segmented into multiple sectors with different magnetic properties or orientations. This segmentation allows for efficient magnetic flux modulation with a compact disk structure, as each sector contributes to the modulation pattern. The segmented design achieves effective modulation with reduced material and smaller overall disk size compared to a solid ferromagnetic structure.
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 noise caused by DC offsets, simplifies the measurement structure, and enhances the signal-to-noise ratio for three-dimensional magnetic field measurements, while reducing the complexity and size of the measurement apparatus.
Implementation Method 1
An external magnetic field H is modulated by the first soft ferromagnetic sector into magnetic field sensed components Hx and Hy having a frequency of 4N×f, and the external magnetic field H is further modulated by the second soft ferromagnetic sector into a magnetic field sensed component Hz having a frequency of M×f
Implementation Method 2
The three magnetic field sensed components Hx, Hy, and Hz are converted into output signals by means of the X-axis, Y-axis and Z-axis magnetoresistive sensors, respectively
Data Source
AI summary
A type of rotating disk magnetic field probe (1) comprising: a non-magnetic rotating disk (2), 4N first soft ferromagnetic sectors (3), M second soft ferromagnetic sectors (4), a reference signal generator, an X-axis magnetoresistive sensor (7, 8), a Y-axis magnetoresistive sensor (5,6), and a Z-axis magnetoresistive sensor (9). Both the first soft ferromagnetic sectors (3) and the second soft ferromagnetic sector (4) are located on the non-magnetic rotating disk (2). In operation, the non-magnetic rotating disk (2) rotates about a Z-axis at a frequency f. An external magnetic field is modulated by the first soft ferromagnetic sector (3) into an X-axis magnetic field sensed component and a Y-axis magnetic field sensed component having a frequency of 4N×f, and is modulated by the second soft ferromagnetic field sectors into a Z-axis magnetic field sensed component having a frequency of M×f. The X-axis sensed magnetic field component, the Y-axis sensed magnetic field component, and the Z-axis sensed magnetic field component respectively are converted into output signals by means of the X-axis magnetoresistive sensor (7, 8) the Y-axis magnetoresistive sensor (5, 6) and the Z-axis magnetoresistive sensor (9). The reference signal generator respectively outputs a first reference signal having a frequency of 4N×f and a second reference signal having a frequency of M×f. The first reference signal, the second reference signal, and the measurement signals are demodulated by an external processing circuit to output magnetic field values Hx, Hy and Hz.