To track a capsule endoscope, a novel measuring method based on alternating magnetic field is presented. The signal-to-noise ratio of the magnetic sensor decreases sharply with the increasing tracking distance. Thus, a magnetic generator with automatic gain regulation is designed to improve the localization precision. It is composed of a microcontroller, a DA converter, a timer, a waveform synthesis circuit, a power amplifier, a sequence control circuit and excitation coils. First, the wireless magnetic sensor measures the strength of the magnetic field produced by the magnetic generator. Via radio frequency communication, the measured result is feedback to the comparator of the microcontroller. According to a deviation obtained by comparing the measured results with the reference value, the microcontroller outputs a digital signal to the DA converter to control the magnitude of the exciting current. The prototype of the system was developed and the experiment was performed. The experiment shows that the magnetic field generator can automatically adjust the strength of the exciting signal.
Measuring relative positions and orientations of the tibia with respect to the femur using one-channel 3D-tracked A-mode ultrasound tracking system: A cadaveric study