A new calibration method for magnetic sensor array for tracking capsule endoscope

To track the movement of wireless capsule endoscope in the human body, we design a magnetic localization and orientation system. In this system, capsule contains a permanent magnet as the movable object. A wearable magnetic sensor array is arranged out of the human body to capture the magnetic signal. This sensor array is composed of magnetic sensors, Honeywell product HMC1043. The variations of magnet field intensity and direction are related to the capsule position and orientation. Therefore, the 3D localization information and 2D orientation parameters of capsule can be computed based on the captured magnetic signals and by applying an appropriate algorithm. In order to initialize the system and improve the tracking accuracy, we propose a calibration technique based on high-accurate localization equipment, FASTRAK. The calibration method includes two steps. Firstly, we acquire the accurate reference data from FASTRAK tracking equipment, and transform them into the position and orientation parameters of the magnet. Secondly, we calculate three important parameters for the sensor calibration: the sensitivity, the center position, and the orientation. Based on the calibration, we can adjust the magnetic localization and orientation system quickly and accurately. The experimental results prove that the calibration method used in our system can improve the system with satisfactory tracking accuracy.