In order to non-invasively track a medical micro-device in gastrointestinal tract,a novel telemetric method based on alternating magnetic fields was presented.In the telemetric method,several cylindrical energizing coils are located on the abdomen.All the coils are excited by time-sharing sinusoidal signals to generate alternating magnetic fields.And a wireless magnetic sensor is used to measure the magnetic field strength at the location of the micro-device.According to the relationship between the magneti...