By applying equivalence principle in combination with PO and PTD, the boundary Integral Equation (BIE) on the opening of the first subdomain is established.

• 对于腔体开口面所在子域 ,应用等效原理 ,结合物理光学法 (PO)与物理绕射理论 (PTD) ,得到腔体开口面的边界积分方程 ;