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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.