Using Transfer Function Calculation and Extrapolation to Improve the Efficiency of the Finite-Difference Time-Domain Method at Low Frequencies

The finite-difference time-domain method (FDTD) needs a long computation time to solve low-frequency (LF) problems. In this paper, we suggest a new way to improve the efficiency of the FDTD method, especially for LF problems such as lightning indirect effects studies. The procedure consists in first calculating the system´s response to a quasi-impulse excitation. The quasi-impulse response is extrapolated using the matrix pencil method in order to obtain a totally damped waveform. Next, the system´s transfer function is calculated and the response to any excitation is deduced. Thus, this method allows for solving problems with a slow response. For instance, the tool is used to calculate currents induced on wires inside a composite aircraft struck by lightning. Very good agreements with FDTD complete simulations are found. Furthermore, the method allows an important computation time saving.