boundary conditions for D and H

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Let us consider the boundary conditions for \mathbf{D}\, and \mathbf{H}\, across the interface between two materials when fields are constant in time. Integrating Maxwell's equations over cylinders and loops straddling the interface gives

\boldsymbol{\nabla} \cdot \mathbf{D} = \rho_f, implies \hat\mathbf{n} \cdot \left( \mathbf{D}_{out} - \mathbf{D}_{in} \right) = \sigma_f\,,
\boldsymbol{\nabla} \times \mathbf{E} = 0\, implies \hat\mathbf{n} \times \left( \mathbf{E}_{out} - \mathbf{E}_{in} \right) = 0\,,

and

\boldsymbol{\nabla} \cdot \mathbf{B} = 0, implies \hat\mathbf{n} \cdot \left( \mathbf{B}_{out} - \mathbf{B}_{in} \right) = 0\,,
\boldsymbol{\nabla} \times \mathbf{H} = \mathbf{J} implies \hat\mathbf{n} \times \left( \mathbf{H}_{out} - \mathbf{H}_{in} \right)  = \mathbf{K}_f \,,
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