The following analysis assumes a general impedance surface. The general impedance boundary condition relates the tangential components of the electric and magnetic fields on the surface:
:<math> \mathbf{\hat{n} \times E(r)} = Z_s \mathbf{\hat{n} \times \mathbf{\hat{n} \times H(r)} </math>
where '''E(r)''' and '''H(r)''' are the electric and magnetic fields on the surface and '''n''' is the local outward normal unit vector as shown in the figure below. Z<sub>s</sub> is the surface impedance having units of Ohms.