  Detection of vehicle position is critical for successful operation of
intelligent transportation system. In case of railroad transportation systems,
position information of railroad vehicles can be detected by GPS, track
circuits, and so on. In this paper, position detection based on tags onto
sleepers of the track is investigated. Position information stored in the tags
is read by a reader placed at the bottom of running railroad vehicle. Due to
limited capacity of battery or its alternative in the tags, power required for
transmission of position information to the reader is harvested by the tags
from the power wirelessly transferred from the reader. Basic mechanism in
wireless power transfer is magnetic induction and power transfer efficiency
according to the relative location of the reader to a tag is discussed with
simulation results. Since power transfer efficiency is significantly affected
by the ferromagnetic material (steel) at the bottom of the railroad vehicle and
the track, magnetic beam shaping by ferrite material is carried out. With the
ferrite material for magnetic beam shaping, degradation of power transfer
efficiency due to the steel is substantially reduced. Based on the experimental
results, successful wireless power transfer to the tag coil is possible when
transmitted power from the reader coil is close to a few watts.
