Optical Pumping Magnetometer with Active Noise Cancellation
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Solution Overview
Problem
Current magnetic field measurement systems face challenges in accurately detecting biomagnetic signals due to environmental noise interference, particularly with the use of SQUID and optical pumping magnetometers, which require costly shielding and coolant, and pose risks to pacemakers from oscillating magnetic fields.
Innovation Solution
The system employs fluxgate magnetometers to detect and cancel environmental noise in three axial directions, using a metal tube with a vapor cell, Helmholtz coil, and RF coil, and a magnetic shield case made of high permeability materials like Permalloy or Mumetal to stabilize magnetic fields and reduce noise interference, allowing for accurate biomagnetic measurements without a magnetic shield room.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetic shield room is used to shield environmental magnetic noise, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the magnetic shielding function from a large-scale magnetic shield room and concentrates it into a compact magnetic shield case made of high-permeability material that surrounds only the vapor cell and RF coil, achieving noise shielding without the complexity of a full magnetic shield room
Solution Approach 2:
The patent introduces a fluxgate magnetometer as an intermediary device that detects environmental magnetic noise and enables active cancellation through feedback control, thereby reducing the shielding requirements and allowing for a more compact shield case design
2Measurement precision
If SQUID magnetometer is used for biomagnetic measurement, then measurement precision is improved, but loss of substance increases due to liquid helium consumption
Solution Approach 1:
The patent replaces the SQUID magnetometer (which requires cryogenic cooling with liquid helium) with an optical pumping magnetometer using a vapor cell that operates at room temperature, eliminating the need for liquid helium and its associated loss and maintenance requirements
Solution Approach 2:
The patent changes the operating temperature parameter from cryogenic (liquid helium temperature) to room temperature by using an optical pumping magnetometer with a vapor cell, thereby eliminating continuous coolant consumption
3Measurement precision
If optical pumping magnetometer is used for environmental noise measurement, then measurement precision is improved, but object-affected harmful factors increase due to oscillating magnetic field impact on pacemakers
Solution Approach 1:
The patent applies magnetic shielding selectively only to the vapor cell and RF coil region rather than the entire measurement system, creating a localized shielded zone that protects against environmental noise while minimizing the volume of oscillating magnetic field generation to reduce pacemaker interference
Solution Approach 2:
The patent creates a localized magnetic shield case with high-permeability material that provides concentrated shielding exactly where needed (around the vapor cell and RF coil), achieving effective noise rejection while minimizing the overall oscillating field exposure to pacemakers
4Device complexity
If fluxgate magnetometer is used for environmental noise detection, then device complexity is reduced, but measurement precision worsens due to low detection sensitivity
Solution Approach 1:
The patent implements a feedback control system where the fluxgate magnetometer detects environmental magnetic noise and the signal is fed back through a current converter to the magnetic field generating coil, which generates a canceling magnetic field to actively neutralize the noise, thereby compensating for the fluxgate's lower intrinsic sensitivity
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 approach enhances the sensitivity and accuracy of biomagnetic measurements, reduces the need for expensive shielding and coolant, and minimizes the risk to pacemakers by effectively canceling environmental noise and stabilizing magnetic fields, thereby downsizing the measurement system and lowering maintenance costs.
Implementation Method 1
a magnetometer such as a fluxgate magnetometer for detecting the environmental magnetic noise
Implementation Method 2
a magnetic field generating coil disposed between the magnetometer and the hold in the optical axis direction of the light source, and a magnetic field in a phase opposite to the environmental magnetic noise detected with the magnetometer is applied
Implementation Method 3
a magnetic shield case made of high permeability materials like Permalloy or Mumetal to stabilize magnetic fields and reduce noise interference
Implementation Method 4
Helmholtz coil, and RF coil
Implementation Method 5
RF coil, and a magnetic field in a phase opposite to the environmental magnetic noise
Data Source
AI summary
Provided is a highly accurate optical pumping magnetometer, in which a static magnetic field and an oscillating field to be applied to a vapor cell are stabilized. To this end, the optical pumping magnetometer includes: Helmholtz coils for applying a constant static magnetic field to a vapor cell serving as a magnetic field detector; fluxgate magnetometers for detecting environmental magnetic noise in two directions of X-axis direction and Y-axis direction other than Z-axis direction which is a direction for detecting a magnetic field coming out of a measurement object while locating the vapor cell in the center thereof; magnetometer drive circuits for driving the fluxgate magneotometers; current converters for converting outputs of the magnetometer drive circuits into amount of currents; and magnetic field generating coils for generating a magnetic field in a phase opposite to the environmental magnetic noise in the two directions.