Resonant sub-wavelength devices to achieve enhanced transmission through electrically small apertures

In this contribution we review some of our recent result in achieving power transmission enhancement through sub-wavelength apertures at both microwaves and optical frequencies. We aim at exciting highly localized magnetic resonances in order to design devices whose size is comparable to that of the aperture and suitable, thus, for practical applications. The proposed approaches may be applied indeed to the design of ultra-diffractive imaging systems, high-resolution spatial filters, high-precision lithography systems.