Hall Sensor Circuit for MRI Interference Detection in Implantable Devices
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Solution Overview
Problem
Implantable medical devices (IMDs) face interference from electromagnetic fields during medical procedures like MRI scans, which can affect their operation and therapy delivery.
Innovation Solution
A magnetic field detection circuit using Hall sensors and a chopper-amplifier to determine the presence of a magnetic field, allowing the IMD to enter a safe mode and protect itself from interference, without the need for offset voltage correction, using low power excitation currents and multiple Hall sensors for accurate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electromagnetic field shielding or filtering is added to protect the IMD, then the device reliability improves, but the device complexity increases
Solution Approach 1:
The patent applies preliminary action by detecting the presence of electromagnetic fields (e.g., MRI fields) before they can interfere with IMD operation. The Hall sensor continuously monitors the environment, and when a magnetic field is detected, the IMD proactively enters a safe mode to prevent interference. This approach improves reliability by preventing harmful interactions before they occur, rather than trying to shield or filter the electromagnetic interference after it has affected the device.
2Measurement precision
If continuous magnetic field monitoring is performed, then the detection precision improves, but the energy consumption increases
Solution Approach 1:
The patent implements periodic action by having the Hall sensor continuously monitor for the presence of magnetic fields rather than performing continuous measurements. The system periodically checks for magnetic field presence and only activates full detection and safe mode when needed. This approach maintains detection precision for safety-critical functions while significantly reducing average power consumption compared to continuous monitoring.
3Measurement precision
If offset voltage correction circuits are added to the Hall sensor, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent applies the taking out principle by extracting only the essential function needed for MRI safety detection. Instead of implementing full offset voltage correction circuits that would provide complete measurement accuracy, the system uses a simplified approach that only detects the presence or absence of magnetic fields above threshold levels. This extraction of the critical detection function maintains sufficient precision for safety applications while avoiding the complexity of complete correction circuits.
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
Enables IMDs to accurately detect magnetic fields and safely enter a protective mode, minimizing interference and ensuring continuous operation during magnetic field exposure.
Implementation Method 1
a chopper circuit amplifies and demodulates a voltage generated at a first set of terminals of a first Hall sensor due to modulated current applied through an orthogonal second set of terminals of the first Hall sensor
Data Source
AI summary
Techniques are described for magnetic field detection using a plurality of Hall sensors and chopper-amplifier circuit. Determination that a magnetic field is present from measurement from one of the Hall sensors may trigger confirmation or confirmation and reconfirmation of the presence of the magnetic field from measurements from one or more of the other Hall sensors.