Full-wave analysis and design of a realistic rail-track circuit based on loosely-coupled inductive loops

This Master Thesis approaches the analysis and design of a novel solution for the “Circuito di binario (CdB”) i.e., a railway track circuit, that is used as a detection system of the trains for track management and is integrated into the signalling and safety systems on board. The presented CdB exploits an inductive loop system coupled to an S-shaped joint (replacing the previously used mechanical joints) in the audio-frequency range (from 8 to 16 kHz). The tracks, therefore, constitute a transmission route similar to a transmission line equipped with a Transmitter (Tx) and a Receiver (Rx), and can be used to transmit information. As a starting point, different electromagnetic simulations of a prototype system of the CdB (scale 1:4), realized in the ARCES laboratories of the University of Bologna, have been carried out. A 3D replica of the CdB has been realized in CST and electromagnetically analysed. Afterward, the Rail Trak with its actual dimension (scale 1:1) has been simulated and the length of the S joint has been optimized in such a way that that the loops that are not in the Tx-Rx circuit are highly decoupled, whereas the coupling of those that are part of the communication circuit is maximum. Subsequently, with the purpose to lighten the whole CdB electromagnetic simulations, the rail-track has been analysed alone in order to extract an equivalent circuit to be used in AWR together with the outputs (scattering matrices) of the electromagnetic simulations of the S joint with loop (both Tx and Rx). The agile obtained optimization tool has allowed the design of the two matching networks with lumped components (one between the transmitting circuit and the Tx loop, the other between the Rx loop and the receiving circuit) for the maximization of the received power: the highest challenge of this project has been the satisfaction of the matching over such a broad frequency band (equal to one octave).