  A simple theoretical model which provides circuit parameters and resonance
frequency of metallic thick resonators is presented. Two different topologies
were studied: the original Pendry's SRR and spiral resonators of two and three
turns. Theoretical computations of resonant frequencies are in good agreement
with values obtained with a commercial electromagnetic solver. The model could
be helpful for designing thick frequency selective surfaces (FSS) based on this
types of resonators, so called metasurfaces.
