  We analyze the transmission and reflection data obtained through transfer
matrix calculations on metamaterials of finite lengths, to determine their
effective permittivity and permeability. Our study concerns metamaterial
structures composed of periodic arrangements of wires, cut-wires, split ring
resonators (SRRs), closed-SRRs, and both wires and SRRs. We find that the SRRs
have a strong electric response, equivalent to that of cut-wires, which
dominates the behavior of left-handed materials (LHM). Analytical expressions
for the effective parameters of the different structures are given, which can
be used to explain the transmission characteristics of LHMs. Of particular
relevance is the criterion introduced by our studies to identify if an
experimental transmission peak is left- or right-handed.
