split of the SRR. As in an LC circuit, the charge separation generated over the capacitive split relaxes as a circulating current, hence giving rise to a magnetic dipole $\bm{m}=(0,0,\alpha_{HE}^{zx}E_x)$ in the $z$ direction, in response to a driving E-field along $x$ [@Burresi09]. The same is valid vice versa: an applied magnetic field along $z$ induces a magnetic dipole moment $\bm{m}=(0,0,\alpha_{HH}^{zz} H_z)$ along the $z$ direction. The associated current accumulates at the gap, giving rise to an electric dipole moment $\bm{p}=(\alpha_{HE}^{xz}H_z,0,0)$ driven by $H_z$. If we assume that the LC resonance really only involves $\bm{p}_x$ and $\bm{m}_z$, we find that the polarizability tensor is filled with zeros, except for the four contributions described above. Hence $$\boldsymbol{\alpha}_{SRR} = \left(
\begin{array} {c c c c c}
\alpha_{EE}^{xx} & 0 & ... & 0 & \alpha_{EH}^{xz}\\
0 &  &  &  & 0\\
\vdots &  & \ddots &  & \vdots\\
0 &  &  &  & 0\\
\alpha_{HE}^{zx} & 0 & ... & 0 & \alpha_{HH}^{zz}
\end{array} \right). \label{Eq:SRRsymmetry}$$ The symmetry constraints that set which elements of $\boldsymbol{\alpha}_{SRR}$ are zero, are valid both for the electrodynamic and electrostatic polarizability of split rings.

Quasi-electrostatic RLC model
-----------------------------

We will now construct the electrodynamic polarizability by starting 