From the divergence theorem the volume integral of div ⁡ ⁡ ( E 1 × × H 2 ) equals the surface integral of E 1 × × H 2 over the boundary. ∫ ∫ V ( H 2 ⋅ ⋅ j ω ω B 1 + E 1 ⋅ ⋅ j ω ω D 2 + E 1 ⋅ ⋅ J 2 ) d V = − − ∮ ∮ S ( E 1 × × H 2 ) ⋅ ⋅ d S ^ ^ .