Improved efficiency of wireless power transfer by tilting coils for wireless data communication

Accurate detection of train position is critical for successful operation of intelligent railroad transportation system. In order to get high precision position information of railroad vehicles, modules and subsystems such as GPS module, wheel sensors, and RFID tags are used for various detection methods. Among the detection methods, position detection based on RFID tags placed onto the sleepers of the track is examined in this paper. Position information of each tag is transmitted to the reader installed at the bottom of railroad vehicle, following the wireless power transfer from the reader coil to the tag coil. By the wireless power transfer, the energy required for the position information transmission is harvested by each tag. The wireless power transfer mechanism from the reader coil to the tag coil is the magnetic induction, so power transfer efficiency is substantially affected by the relative location and relative tilting direction of the reader coil to the tag coil. From this viewpoint, improved power transfer efficiency can be achieved by tilting coils. Two tilting coils, with their tilting angles favorable to the reader coil position, which is slightly off the axial position, and a leveled coil are combined. The power transfer efficiency obtained from these three coils is compared with the one by the conventional leveled reader coil. Due to tilting directions of the reader coils, significant gain is obtained even at off-axis positions of them. Simulation to show the improved efficiency by tilting coils is executed and the results are shown.