An electro-magnetic tracking method was proposed. Putting several circular current loops on body surface

a well-designed receiving coil in the capsule can always keep its orientation. Through detecting the magnetic field strength by a receiving coil

and deducing the functional relationship between the position parameters of the coil and the magnetic field strength

the position of the capsule can be determined. This design not only simplifies the structure of the whole system compared with a common one

but also makes the arithmetic easy for ensuring its feasibility in application of capsule positioning. The transmitting and receiving system and a three-coordinate experimental device were constructed. A test including 38 points was carried out to verify the method and the system. The result shows that the maxim positioning errors of

x

y

z

coordinates are less than 4 cm

while the mean errors are less than 2 cm

which is better than current precision of other positioning methods for the capsule-typed device.