Active Magnetic Noise Rejection Using Feedback Control
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Solution Overview
Problem
Conventional magnetic noise rejection methods, such as magnetic shield chambers and active magnetic shielding, are bulky and heavy, making them impractical for portable or wearable applications, and they often increase the noise component in magnetic field measurements due to mismatched sensor positions.
Innovation Solution
A magnetic noise rejection apparatus with multiple cancellation coils and sensors arranged near a target object, an adder circuit to sum sensor outputs, and a feedback control circuit to drive the coils with a common current, ensuring the sum of outputs equals zero under a zero magnetic field, effectively eliminating external magnetic noise and allowing for precise measurement of faint magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a magnetic shield chamber enclosed by permalloy is used to prevent external magnetic fields, then magnetic field shielding effectiveness is improved, but apparatus size and weight increase significantly
Solution Approach 1:
The patent replaces the passive mechanical magnetic shield chamber (permalloy enclosure) with an active magnetic noise rejection system using coils and sensors. The coils generate cancellation fields to actively counteract external magnetic fields, substituting the heavy passive shielding structure with a lighter active control system that achieves comparable shielding effectiveness without the weight penalty.
Solution Approach 2:
The invention changes the approach from static passive shielding to dynamic active control by using feedback from magnetic sensors to adjust coil currents in real-time. This parameter change enables the system to adapt to varying external magnetic field conditions while maintaining compact dimensions and reduced weight compared to fixed permalloy shields.
2Measurement precision
If the position of magnetic sensor measuring external magnetic field is separated from measurement magnetic sensor, then external magnetic field detection is improved, but magnetic noise component in measurement increases
Solution Approach 1:
The patent merges the functions of external magnetic field detection and target object measurement into a single integrated sensor array. Multiple magnetic sensors are positioned at different locations, and their outputs are combined through signal processing to simultaneously achieve external field detection and noise-free target measurement, eliminating the need for separate sensor positions that would increase noise.
Solution Approach 2:
The system uses feedback from the magnetic sensors to control the coils, creating a closed-loop active noise cancellation system. The sensor outputs are processed to determine the external magnetic field components, which then drive the coils to generate cancellation fields, thereby reducing the magnetic noise component reaching the measurement sensors while maintaining accurate external field detection capability.
3Measurement precision
If multiple magnetic sensors are arranged near target object with cancellation coils, then faint magnetic field measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent segments the magnetic measurement system into modular sensor-coil units that can be independently positioned near the target object. Each sensor-coil pair operates as a functional module, allowing the system to achieve high measurement precision for faint magnetic fields while maintaining manageable complexity through modular architecture and distributed sensing.
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
This configuration reduces the size and weight of the apparatus, prevents noise component increase, and enables accurate measurement of faint magnetic fields by using a reference sensor as the measurement sensor, making it suitable for portable and wearable applications.
Implementation Method 1
an external magnetic field entering from the outside is detected by a sensor, and the external magnetic field is canceled out by driving magnetic field cancellation coils provided around a measurement chamber
Implementation Method 2
a plurality of magnetic sensors disposed inside the respective cancellation coils
Data Source
AI summary
There is provided a magnetic noise rejection apparatus which includes: a plurality of cancellation coils arranged near a target object; a plurality of magnetic sensors disposed inside the respective cancellation coils; an adder circuit configured to take a sum of outputs of the plurality of magnetic sensors; and a feedback control circuit configured to supply the cancellation coils with such a common feedback drive current that the sum of the outputs of the magnetic sensors is equal to a sum of outputs of the magnetic sensors under a zero magnetic field.