| CPC B07C 5/3427 (2013.01) | 18 Claims |
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1. A method for sorting a plurality of items of varying material types based on the material type of each item, comprising:
for each item, depositing an array of nanostructures onto a surface portion of the item to form a material identification tag, the nanostructures being plasmonic so as to have an optical response dependent on the material type of the item onto which the nanostructures are deposited,
for one of the items undergoing sorting, illuminating the material identification tag,
for the item undergoing sorting, detecting an optical extinction and/or reflectance spectrum of the illuminated material identification tag, which optical extinction and/or reflectance spectrum is dependent on the influence that the material type of the item has on a refractive index of the optical extinction and/or reflectance peak of the array of nanostructures of the material identification tag, the detected optical extinction and/or reflectance spectrum being a signature of the material identification tag and item material combination,
for the item undergoing sorting, categorizing the item into one category of a plurality of predetermined categories according to material type based on the detected optical extinction and/or reflectance spectrum, wherein categorizing the item comprises comparing at least peak positions and/or peak widths and/or peak heights of the detected optical extinction and/or reflectance spectrum to predetermined ranges or threshold values, which have been determined beforehand for the varying material types, and
for the item undergoing sorting, sorting the item according to material type of the item in accordance with the categorization, and
wherein the nanostructures in each deposited array of nanostructures comprises a single nanostructure type so that, for each material type and within deposition tolerances, the signature of the material identification tag is identical.
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