S-parameters are widely utilized for characterizing circuit components and systems. Although they only contain the frequency domain responses with a limited range, the time domain characteristics of the circuit systems can be estimated using processing methods for extracting the causal impulse response from the S-parameter. This paper presents an efficient extrapolation method (EM) for the accurate transient simulation of circuit systems using band-limited S-parameters. The proposed method constructs the extrapolation function of the given S-parameter for ensuring the causality of its impulse response, with higher accuracy over the measured frequency range, and without computationally intensive iteration. We implemented this method using the noniterative approach for extracting coefficients of the extrapolation function, and the optimal selection scheme for its input parameters. To verify the proposed method, 2-port network using the Chebyshev band-stop filters and 4-port network using the coupled transmission line were designed. In the first case, the proposed method had a normalized mean square error of -71.32 dB, a noncausal error of below system resolution, and the computation time of 0.17 s. Under the similar accuracy and causality conditions, the conventional methods, such as the iterative extrapolation and the vector fitting, required 122.45 and 3.98 s, respectively. In the second case, the proposed EM also ensured the causality of the time domain response with higher accuracy and computational efficiency.

Wireless power transfer (WPT) is being developed to supply electric power to electric trains, using a source coil in/on the railway track and a pick-up coil on the train. A number of benefits can be obtained by eliminating the catenary and pantograph currently used for railway electric power supply. However, the WPT employs coils, and the electromagnetic field generated by the WPT can interfere with conventional train detection methods, such as track circuits and RFID, installed on the tracks. Train position information is critical for railway operation, especially for high speed trains. This paper proposes a novel system which provides train position information using a source coil segment. It consists of onboard sensor coils, ferrite blocks designed using specific position information, and a detector. The proposed system can be implemented using the source coil and load coil of the WPT. Information about the train's relative position is obtained by the detection of ferrite blocks distributed within the source coil segment. The train position information provided by the ferrite components is detected by onboard sensor coils and a detector. The proposed ferrite position identification (FPID) system provides accurate train position information and is not affected by WPT electromagnetic interference. The operating principles of the FPID system are presented in detail. The performance of the proposed FPID system was measured by simulations and experiments.