This work presents some considerations for the use of a Split Ring Resonator (SRR) and its dual structure, the Complementary Split Ring Resonator (CSRR), as permittivity sensing elements. The analytical circuit equivalents of both resonators are reviewed in the light of multilayer transmission lines and adjusted models are derived for the resonant frequencies when superstrates with finite thickness are included, thus accounting for the finite thickness of the Material Under Test (MUT) and the possible use of a sample container with its corresponding material and thickness. Validations of the proposed analytical models are performed by means of full-wave electromagnetic simulation using a SRR loaded microstrip line and a CSRR loaded Substrate Integrated Waveguide (SIW), as dielectric permittivity sensors.