Planar GRIN lenses: Numerical modeling and experimental validation

Phononic Crystal (PnC) Gradient Index (GRIN) lenses have been intensively investigated in recent years for their promising applications in energy harvesting. Here we propose and verify, both numerically and experimentally, three designs of PnC GRIN lenses with amplification factors at the focal points of 4.33x, 7.35x and 7.49x. A design procedure based on the combination of two mechanisms of refraction index gradient formation is employed to boost the efficiency of the lens. Moreover, thanks to the planarity of the design and to the single-phase constitutive material, the proposed lenses are fully compatible with microfabrication processes and can be therefore employed as micro energy harvesters after proper miniaturization.