“…The theoretical analysis of scattering from cavities was well investigated (see, for example, [3,4,43]). A variety of numerical methods, including finite difference method [7,[13][14][15][16][17]41,42], finite element method [2,28,31,32,38,40,[48][49][50], boundary element method [21,44,47] and hybrid method [25,30,36,47] have been developed for solving the cavity problem.…”