Detection of weak magnetic signal for magnetic localization and orientation in capsule endoscope

A permanent magnet is embedded in the capsule endoscope to perform as an excitation source for tracking capsule´s position and orientation, and a magnetic sensor array is built around the capsule to capture the signals from magnet. However, the magnet-field signal is weak and attenuates dramatically when the spatial distance between the magnet and the sensor increases. How to detect this weak magnetic signal will be the key factor to influence the tracking accuracy, so a high stable, sensitive, anti-interference magnetic measurement system must be developed. In this paper, we present a weak magnetic signal detection system which is composed of Honeywell 3-axis magnetic sensors, high performance analog multiplexers, low noisy amplifiers, 16 bits A/D converter, and ARM controller. Especially, some processing measures are employed to reduce the sensors´ tolerance and enhance the sensitivity and dynamic range of localization system. The experimental results show that this detection system can be effectively applied for the cubic magnetic sensor array with the measurement space of 0.5 m times 0.5 m times 0.5 m.