Thin films for energy efficient transparent electromagnetic shields

Multifunctional, radio frequency shielding, transparent in the visible and energy saving film, including an asymmetric and aperiodic superposition of three dielectric or semiconductor (D) layers alternated to two metal (M) nanometric layers, wherein the ratio of the thickness of the outermost metal layer to the inner one is between 1.4 and 1.7. Such a film can be applied on a transparent substrate to make a frequency selective screen characterized by having solar absorbance (Ae) always lower than 17% and one of the following combination of performances: - Shielding effectiveness (SE) higher than 32 dB from 30 kHz to 18 GHz, with optical visible transmittance (Tv) higher than 75%; - Shielding effectiveness higher (SE) than 36 dB from 30 kHz to 18 GHz, with optical visible transmittance (Tv) higher than 65%; - Shielding effectiveness (SE) higher than 38 dB from 30 kHz to 18 GHz, with optical visible transmittance' (Tv) higher than 50%.