Ferromagnetic Tag Sensing System for Medical Tracking
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Solution Overview
Problem
Existing electromagnetic tracking methods for medical procedures, such as those using permanent magnets or AC magnetic fields, are limited by the need for large magnetic volumes, susceptibility to external fields, and inability to track multiple targets accurately.
Innovation Solution
A sensing system utilizing high aspect ratio ferromagnetic tags with selection coils to generate a spatially-varying DC magnetic field and interrogation coils to generate and receive AC magnetic fields, allowing for the determination of the location and orientation of the tag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If permanent magnets are used for tracking, then location can be determined, but the magnet volume must be several cubic millimetres and the system is susceptible to external magnetic fields
Solution Approach 1:
The patent changes the fundamental tracking parameter from permanent magnet field magnitude to AC magnetic response harmonics. By using ferromagnetic material with non-linear magnetisation properties and applying AC magnetic fields, the system detects harmonics generated by the material's non-linear response, enabling tracking with much smaller tag volumes while improving resistance to external DC magnetic fields.
2Measurement precision
If permanent magnets are used for tracking, then location can be determined, but the system cannot track multiple targets accurately
Solution Approach 1:
The patent employs periodic AC magnetic fields at specific frequencies to excite the ferromagnetic tags. Each tag responds at the same frequency but with unique amplitude and phase characteristics determined by its location and orientation. By using frequency-domain analysis and detecting harmonics, the system can distinguish and track multiple tags simultaneously, overcoming the limitation of permanent magnet systems.
3Measurement precision
If search coils are used for AC magnetic field tracking, then location can be determined, but voltages must be retrieved from the search coil and operation frequency is limited by eddy current distortion
Solution Approach 1:
The patent extracts the tracking function from complex search coil systems with voltage retrieval requirements and simplifies it by using passive ferromagnetic tags that naturally generate detectable harmonic signals through their non-linear magnetisation. This eliminates the need for active electronics in the tag and simplifies the external sensing system.
4Measurement precision
If spherical magnetic particles are used, then AC field harmonics can be detected, but very large heavy interrogation coils are required and sample volume is small
Solution Approach 1:
The patent uses ferromagnetic material with high aspect ratio (non-spherical geometry) instead of spherical particles. This asymmetric shape enhances the non-linear magnetisation response to AC fields, generating stronger harmonics that can be detected with smaller, lighter interrogation coils while providing sufficient sample volume for surgical applications.
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 system achieves accurate location and orientation tracking of medical devices within the body, enabling real-time guidance during procedures while using tags that are easily integrated into medical components and are significantly smaller than current systems.
Implementation Method 1
the selection coils are arranged to generate a spatially-varying DC magnetic field from which the location of the tag can be determined in use
Implementation Method 2
at least some of the interrogation coils are arranged to generate one or more AC magnetic fields
Implementation Method 3
at least some of the interrogation coils are arranged to receive harmonics, intermodulation products or time dependent variations of the AC magnetic fields
Implementation Method 4
A sensing system utilizing high aspect ratio ferromagnetic tags
Data Source
AI summary
A sensing system for determining the location and orientation of an object which comprises a magnetic tag. The sensing system comprises selection coils and interrogation coils. The selection coils are arranged to generate a spatially varying DC magnetic field from which the location of the tag can be determined in use. At least some of the interrogation coils are arranged to generate one or more AC magnetic fields and at least some of the interrogation coils are arranged to receive harmonics, intermodulation products or time dependent variations of the AC magnetic fields, from which the orientation of the tag is determined in use.