Patent ID: 8413908

Claim:
An optical security mark is applied to at least part of an object, comprising at least one structure comprised by at least one metamaterial made up of a plurality of meta-atoms forming a structure, and having transverse dimensions in a plane on which meta-atoms are located, defined by the formula (b x , b y ) wherein: b x is a first transverse dimension in a first transverse extension of the metamaterial and b y is a second transverse dimension in a second transverse extension of the metamaterial, different from the first transverse dimension, wherein the metamaterial is selected from metamaterials generating magnetic responses with a relative magnetic permeability (μ r ) different from 1 at least at an incident radiation (I) selected from incident radiation with normal incidence or with oblique incidence and with at least a wavelength (λ) in a spectrum ultraviolet to near-infrared in a range of 0.15 micrometers to 1.1 micrometers, said magnetic responses produce a spectral signature when at least part of the metamaterial is subjected to said incident radiation (I) of the aforementioned wavelength or at wavelengths belonging to the same range, such that said spectral signature corresponds to at least one specific code assigned to said metamaterial, said specific code being: a value of the relative magnetic permeability at a wavelength (λ) of an incident radiation (I) according to formula μ r (λ) wherein μ r is the relative magnetic permeability and (λ) is the wavelength of the incident radiation, or the value of the wavelength (λ) at which the metamaterial has a particular relative magnetic permeability (μ r ) according to formula λ(μ r ) wherein λ and μ r have the meanings indicated above, and combinations of at least one specific permeability code and at least one specific wavelength code (λ), and in that said first transverse dimension and said second transverse dimension are each at least equal to the wavelength (λ) of the incident radiation.