Three-axis magnetoresistive sensor upstream modulation for 1/f noise reduction
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Solution Overview
Problem
Magnetoresistive sensors exhibit high 1/f noise at low frequencies, which affects the accuracy of magnetic field measurements. Existing solutions, such as MEMS technology with vibrating structures, increase complexity and size.
Innovation Solution
A three-axis upstream-modulated low-noise magnetoresistive sensor is developed, which includes X, Y, and Z-axis magnetoresistive sensors with soft ferromagnetic flux concentrators and modulator wire arrays. These sensors output high-frequency signals, reducing 1/f noise through stationary soft ferromagnetic structures and alternating current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a MEMS vibrating structure with soft ferromagnetic flux concentrator is added to modulate the magnetic field, then the 1/f noise is reduced, but the device complexity and size increase greatly
Solution Approach 1:
The patent applies mechanical vibration by driving the soft ferromagnetic flux concentrator to vibrate periodically at a high frequency (e.g., 100 Hz or higher) using a driving electrode. This vibration modulates the static external magnetic field into a high-frequency alternating magnetic field, which is then detected by the magnetoresistive sensor. By converting the low-frequency magnetic signal to high-frequency, the measurement moves away from the 1/f noise region, achieving noise reduction without requiring complex additional structures.
Solution Approach 2:
The patent implements periodic action by applying a periodic driving voltage to the driving electrode, which causes the soft ferromagnetic flux concentrator to vibrate periodically. This periodic vibration creates a time-varying magnetic field that modulates the external magnetic field signal. The periodic modulation allows the use of lock-in detection or synchronous demodulation techniques to extract the magnetic signal from the noise, improving measurement precision while maintaining a relatively simple device structure.
2Measurement precision
If a MEMS vibrating structure with soft ferromagnetic flux concentrator is added to modulate the magnetic field, then the 1/f noise is reduced, but the manufacturing process complexity increases
Solution Approach 1:
The patent merges multiple functions into a single integrated structure. The soft ferromagnetic flux concentrator serves both as a magnetic flux concentrating element and as a vibratory modulator. The driving electrode is integrated directly onto the flux concentrator, eliminating the need for separate driving mechanisms. This integration simplifies the manufacturing process by reducing the number of discrete components and assembly steps required, while still achieving the noise reduction benefit.
Solution Approach 2:
The patent replaces a complex mechanical vibration system with an electrostatic actuation system. Instead of using mechanical motors or actuators to drive the flux concentrator, the patent uses an electric field applied through the driving electrode to induce vibrational motion. This substitution of mechanical systems with electrical control simplifies the manufacturing process and enables easier integration with electronic circuits, while maintaining the periodic modulation function needed for noise reduction.
3Measurement precision
If high-frequency modulation is applied to shift measurement signal to high-frequency region, then the 1/f noise is reduced, but the device structure becomes more complex
Solution Approach 1:
The patent achieves multi-functionality with the soft ferromagnetic flux concentrator, which simultaneously performs magnetic flux concentration and mechanical vibration for signal modulation. The same structure that concentrates magnetic flux also serves as the vibrating element that modulates the signal frequency. This universal design eliminates the need for separate modulation mechanisms, reducing structural complexity while maintaining the high-frequency modulation capability needed for noise reduction.
Solution Approach 2:
The patent introduces the soft ferromagnetic flux concentrator as an intermediary element between the external magnetic field and the magnetoresistive sensor. This intermediary serves multiple purposes: it concentrates the magnetic flux to enhance signal strength, and when driven to vibrate, it modulates the magnetic field frequency. The intermediary approach allows the system to achieve high-frequency modulation without directly complicating the sensor structure, as the modulation function is performed by the intermediary flux concentrator.
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 sensor achieves low-noise measurement signals by shifting the measurement signal from low-frequency to high-frequency, simplifying the structure, reducing size, and streamlining the manufacturing process.
Implementation Method 1
a soft ferromagnetic flux concentrator is driven such that it vibrates periodically on the surface of the magnetoresistive sensor for modulating a static external magnetic field
Implementation Method 2
the soft ferromagnetic flux concentrator is driven such that it vibrates periodically on the surface of the magnetoresistive sensor for modulating a static external magnetic field
Implementation Method 3
a magnetoresistive sensor has high 1/f noise at low frequency, while a magnetoresistive sensor mainly has thermal noise at a high frequency; the noise energy density of the latter is much lower than that at the low frequency
Data Source
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AI summary
A three-axis upstream-modulated low-noise magnetoresistive sensor, comprising an X-axis magnetoresistive sensor (100), a Y-axis magnetoresistive sensor (110), and a Z-axis magnetoresistive sensor (120), wherein the X, Y, and Z-axis magnetoresistive sensors respectively comprise X, Y, and Z-axis magnetoresistive sensing unit arrays, X, Y, and Z-axis soft ferromagnetic flux concentrator arrays, and X, Y, and Z-axis modulator wire arrays. The X, Y, and Z-axis magnetoresistive sensing unit arrays are electrically interconnected into X, Y, and Z-axis magnetoresistive sensing bridges respectively. The X, Y, and Z-axis modulator wire arrays are electrically interconnected into individual two-port X, Y, and Z-axis excitation coils. In order to measure external magnetic fields, the two-port X, Y, and Z-axis excitation coils separately supplied with high-frequency alternating current at a frequency f, from a current supply. The X-axis magnetoresistive sensor (100), Y-axis magnetoresistive sensor (110), and Z-axis magnetoresistive sensor (120) each output harmonic signal components having a frequency of 2f, which are then demodulated to obtain the X, Y, and Z-axis low-noise signals. This device is small in size, has low noise, and a simple structure.