Template:Frequency domain equations for the radiation modes

The body boundary condition for a radiation mode [math]\displaystyle{ m }[/math] is just

[math]\displaystyle{ \partial_{n}\phi=\mathbf{n}_m,\ \ \mathbf{x}\in\partial\Omega_{\mathrm{B}}, }[/math]

where [math]\displaystyle{ \mathbf{n}_m }[/math] is the normal derivative of the [math]\displaystyle{ m }[/math] mode