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Due to a nearby lightning return stroke, the coupled electromagnetic (EM) fields inside a rectangular shielding enclosure, on the finitely conducting ground, with an aperture in one wall are calculated numerically by using the finite-difference time-domain (FDTD) method. First, the near fields generated by the return stroke are obtained in two-dimensional (2-D) cylindrical coordinates by the FDTD method. Then, the coupled fields inside a rectangular shielding enclosure are calculated in three-dimensional (3-D) rectangular coordinates through the total field-scattered field connecting boundary, with the sources obtained by coordinates transformations of the return stroke near fields. Index Terms--Finite-difference time-domain (FDTD) method, lightning return stroke, shielding enclosure, total field-scattered field connecting boundary.

A memory-efficient scalar wave finite-difference time-domain (FDTD) algorithm, using a two dimensional (2-D) mesh is proposed in this letter. The proposed algorithm requires one memory element per cell, instead of the usual three of the conventional 2-D Yee algorithm. This leads to a direct memory reduction of 66 % in the storage of fields. Furthermore, the computational efficiency of this algorithm is higher than that of previous scalar wave approaches. A numerical example is given to show the validity of the proposed algorithm, in which the Liao absorbing boundary condition (ABC) is implemented directly. Index Terms--Finite-difference time-domain (FDTD) method, memory-efficient, scalar wave.