  We present frequency tunable metamaterial designs at terahertz (THz)
frequencies using broadside-coupled split ring resonator (BC-SRR) arrays.
Frequency tuning, arising from changes in near field coupling, is obtained by
in-plane horizontal or vertical displacements of the two SRR layers. For
electrical excitation, the resonance frequency continuously redshifts as a
function of displacement. The maximum frequency shift occurs for displacement
of half a unit cell, with vertical displacement resulting in a shift of 663 GHz
(51% of f0) and horizontal displacement yielding a shift of 270 GHz (20% of
f0). We also discuss the significant differences in tuning that arise for
electrical excitation in comparison to magnetic excitation of BC-SRRs.
