A system includes a device that is swallowed, passed through a subject, and includes a magnetic field generator generating a constant magnetic field; and a position transducer. The position transducer includes a plurality of magnetic detectors detecting intensities of a magnetic filed, first and second...http://www.google.ca/patents/US7509158?utm_source=gb-gplus-sharePatent US7509158 - System for detecting position of capsule endoscope in subject
