We present a review of the different coupling schemes in a planar array of terahertz metamaterials. The gap-to-gap near-field capacitive coupling between split-ring resonators in a unit cell leads to either blue shift or red shift of the fundamental inductive-capacitive (LC) resonance, depending on the position of the split gap. The inductive coupling is enhanced by decreasing the inter resonator distance resulting in strong blue shifts of the LC resonance. We observe the LC resonance tuning only when the split-ring resonators are in close proximity of each other; otherwise, they appear to be uncoupled. Conversely, the higher-order resonances are sensitive to the smallest change in the inter particle distance or split-ring resonator orientation and undergo tremendous resonance line reshaping giving rise to a sharp subradiant resonance mode which produces hot spots useful for sensing applications. Most of the coupling schemes in a metamaterial are based on a near-field effect, though there also exists a mechanism to couple the resonators through the excitation of lowest-order lattice mode which facilitates the long-range radiative or diffractive coupling in the split-ring resonator plane leading to resonance line narrowing of the fundamental as well as the higher order resonance modes. 1. Introduction The interaction of electromagnetic waves with unstructured bulk matter is mainly governed by the inherent chemistry of material, and its properties are usually described in terms of permittivity and permeability. Recently developed electromagnetic metamaterials allow engineered material at the unit cell level, which has enabled novel methods to manipulate the electromagnetic properties [1]. Metamaterials have attracted a tremendous amount of interest because of their exotic properties such as negative refractive index [2], perfect focusing [3], cloaking [4, 5], and resonance modulation in the active and passive modes [6–29]. The electromagnetic responses offered by metamaterials are unique and are not found in naturally occurring materials. The fundamental building blocks of metamaterials are mainly comprised of a metallic split-ring resonators (SRRs) fabricated on a dielectric/semiconducting substrate. The operation of most metamaterial devices depends on the designs employed to control the fundamental resonances of SRRs, since the major tuning of material permittivity and permeability is enabled by these resonances [6–29]. Apart from the single-SRR approach, several research groups have explored lateral coupling between nearest neighbor SRRs and its
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