1. Introduction
With the rapid advancement in MEMS technology, endoscopic systems have seen remarkable progress, particularly in the development of wireless capsule endoscopes for the human gastrointestinal tract. This innovation has marked a significant breakthrough in medical imaging and diagnostics. As research continues to expand around these miniature devices, challenges remain, especially regarding motion control and accurate positioning within the body. According to the 2004 European Technical Report, achieving reliable motion and posture control is crucial for effective diagnosis and treatment. Real-time location detection of these small capsules is essential for ensuring accurate medical outcomes. Traditional methods such as ultrasonic, nuclear medicine, and fluorescence-based imaging are often costly, complex, and may involve radiation, making them unsuitable for long-term dynamic monitoring inside the body. To address these limitations, researchers have explored simplified magnetic positioning models and advanced tracking technologies.
To enhance the accuracy of microcapsule localization in vivo, the author developed a three-axis magnetoresistive sensor module using HMC1022 and HMC1021. After signal amplification through a two-stage amplifier circuit, the system collects data from multiple points to determine the magnetic field strength of the capsule. This design improves sensitivity and measurement range compared to previous solutions, offering a more efficient and precise method for tracking the capsule’s position and orientation inside the body.
2. Capsule Positioning Detection Principle
Magnetic induction positioning relies on the Hall effect of magnetoresistive sensors, which detect changes in magnetic field distribution caused by variations in the direction and distance of a permanent magnet’s magnetic moment. By measuring these changes, it is possible to determine the spatial position of the magnet and, by extension, the capsule. In the human body, the capsule can be modeled as a rigid body with an internal cylindrical permanent magnet. Its position and orientation can be represented using coordinates and angles relative to a global coordinate system, allowing for accurate spatial mapping.
When the size of the cylindrical magnet is much smaller than the distance from the sensor, it can be approximated as a magnetic dipole. The magnetic field generated by the capsule at the sensor location is described mathematically, enabling real-time position calculation. Using multiple sensor modules allows for solving the five unknowns required to determine the capsule's exact location and orientation.
3. System Hardware Design
The system comprises four sets of three-axis magnetoresistive sensor modules, an amplifier circuit, and a data acquisition card. Each sensor module includes built-in set/reset circuits to reduce noise and improve stability. The amplifier boosts the weak signals from the sensors, while the data acquisition card processes the information for real-time analysis.
3.1 Magnetoresistive Sensor Module
The designed sensor module uses HMC1022 and HMC1021, arranged perpendicularly to measure magnetic fields in different directions. These components are optimized for high sensitivity and low drift, making them ideal for use in challenging environments like the human body.
3.2 Amplifying Circuit
As the magnetic field strength decreases with distance, a high-gain amplifier (such as AD620) is used to ensure signal clarity. In experiments, a gain of 1000x was applied to match the resolution requirements of the data acquisition system.
3.3 Data Collection
A PCI-1716 data acquisition card captures the amplified signals, which are then processed using LabVIEW software. This setup enables accurate signal acquisition, conversion, and real-time analysis of the capsule’s movement.
4. Experimental Steps
The experiment followed a structured process: first, the initial positions of the four sensor modules were recorded. Then, the capsule was moved along a path, and its position relative to each sensor was measured. The set/reset circuit helped improve sensor performance, and the resulting data was analyzed to verify the system’s accuracy.
5. Experiment and Result Analysis
In the experiment, the four sensor modules were placed at the corners of a cubic frame. As the capsule moved, the magnetic field readings from the sensors changed accordingly. The results showed that the error between experimental and calculated values was within ±10%, proving the system’s reliability. Further tests confirmed that the system could accurately track the capsule’s position and orientation, even when moving in complex paths.
6. Conclusion
This study presents a novel approach to capsule endoscope positioning using high-sensitivity magnetoresistive sensors. Both theoretical analysis and experimental results demonstrate the system’s ability to accurately determine the capsule’s spatial position and orientation. The findings indicate that this technology can significantly enhance the precision of medical diagnoses and improve clinical outcomes in gastrointestinal imaging.
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