Filter made of metamaterials
There is provided a filter for filtering electromagnetic radiation, wherein said filter is arranged to transmit electromagnetic radiation of a first predetermined wavelength and to block transmission of electromagnetic radiation of a second, different predetermined wavelength; said filter comprising a first metamaterial. Optionally, the metamaterial may be formed of a plurality of material elements wherein each material element is at least one-dimensional and the size of the material element along each dimension is no greater than the size of the second predetermined wavelength. The filter comprises a second metamaterial arranged to provide second filtering of electromagnetic radiation.
1. A filter for filtering electromagnetic radiation, said filter comprising:
a first artificial filtering layer comprising a plurality of structural features having a size in one dimension no greater than a first wavelength of the electromagnetic radiation, wherein the plurality of structural features are arranged to provide first filtering of electromagnetic radiation, the first filtering comprising blocking electromagnetic radiation at a first narrow frequency bandwidth about the first wavelength, the first wavelength being in the ultraviolet to infrared, the structural features of the first artificial filtering being a stack containing a plurality of layers of material having a pitch no greater than the first wavelength to form a Bragg reflector; and
a second artificial filtering layer comprising a plurality of second structural features that are different from the plurality of structural features of the first artificial filtering layer, wherein the plurality of second structural features are arranged to provide second filtering of electromagnetic radiation, the second filtering comprising blocking electromagnetic radiation at a second narrow frequency bandwidth about the first wavelength, the second narrow frequency band being substantially similar to the first frequency bandwidth, the second structural features of the second artificial filtering layer being nanoparticles, wherein the nanoparticles are made from a plasmonic metal and support plasmonic resonance at the first wavelength,
wherein the filter is comprised in a film, each of the first and second artificial filtering layers transmit electromagnetic radiation of wavelengths in the ultraviolet to infrared that are not in the first or second narrow frequency bandwidth about the first wavelength.
2. A filter as claimed in claim 1 wherein the film includes an adhesive.
3. A filter as claimed in claim 1 wherein the first artificial filtering layer and second artificial filtering layer are stacked layers of the filter.
4. A filter as claimed in claim 1 wherein the filter is comprised in or on a windscreen.
5. A filter as claimed in claim 1 wherein the filter is passive.
6. A filter as claimed in claim 1 wherein the filter appears substantially transparent to the human eye.
7. A filter as claimed in claim 1 wherein each narrow frequency bandwidth is between 5 and 10 nanometers around the first wavelength.
8. A filter as claimed in claim 1 , wherein the first artificial filtering layer is arranged to provide the first filtering to ultraviolet to infrared electromagnetic radiation incident at a first range of angles and the second artificial filtering layer of the layers is arranged to provide the second filtering to ultraviolet to infrared electromagnetic radiation incident at a second range of angles different from the first range of angles.
9. A filter as claimed in claim 8 wherein the first and second ranges of angles partially overlap.
10. A filter as claimed in claim 1 wherein the filter is comprised in or on an aircraft cockpit.
11. A filter as claimed in claim 1 , further comprising one or more third artificial filtering layers, each of the third artificial filtering layers comprising nanoparticles; and one or more fourth artificial filtering layers, each of the fourth artificial filtering layers being a Bragg reflector.