Near-field Power Efficiency Maximization of a Bessel-shaped Beam Through Planar Layered Media

We discuss the problem of power transfer maximization through locally planar layered media of focused Bessel-shaped beams synthesized in the near-field region, by introducing a suitable spectral figure of merit able to quantify the amount of beam power that can be efficiently delivered through an arbitrary planar multilayer structure. Such an approach is quite novel in the Fresnel region of a beam launcher, since standard figures of merit normally adopted in the far-field region cannot be extended tout court to near-field, due to peculiar field distribution and wave-front curvature. The presented numerical results show that the adopted figure of merit is able to predict correctly the axicon angle for which Bessel-shaped beams, radiated by arrays of given length, maximize power transmission in near-field through planar multilayer structures, and also to maximize the Bessel-shaped beam wireless power transfer efficiency.