Method for sorting of items and an assembly for categorizing an item
A method for sorting of items ( 1 ) based on material type, comprising: —depositing an array of nanostructures ( 3 ) onto a surface portion of an item ( 1 ) to form a material identification tag ( 2 ), the nanostructures having an optical response dependent on the material type of the item onto which they are deposited, —illuminating the material identification tag using a light source ( 30 ), —determining at least one optical extinction and/or reflectance peak of the illuminated material identification tag, which peak is dependent on a material type of the item, —categorizing the item based on the detected optical extinction and/or reflectance spectrum, and —sorting the item in accordance with the categorization.
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.
2. The method according to claim 1 , wherein the nanostructures are metallic, dielectric, or semiconducting.
3. The method according to claim 1 , wherein illuminating the material identification tag comprises illuminating the material identification tag with light from a spectral range including ultraviolet light, and/or visible light, and/or near-infrared light.
4. The method according to claim 1 , wherein detecting the optical extinction and/or reflectance spectrum of the illuminated array of nanostructures comprises determining at least one of a peak position, a peak width, and a peak height of at least one optical extinction and/or reflectance peak of the spectrum.
5. The method according to claim 1 , wherein depositing the array of nanostructures comprises applying a liquid containing the nanostructures onto the surface portion.
6. The method according to claim 5 , further comprising:
producing the nanostructures on a flat substrate by a lithographic method, and subsequently lifting them into the liquid.
7. The method according to claim 6 , wherein the flat substrate comprises a thin film on which the nanostructures are supported, and wherein flakes of the thin film with the nanostructures supported thereon are subsequently transferred to the liquid.
8. The method according to claim 5 , further comprising:
synthesizing the nanostructures by a chemical synthesis method in the liquid.
9. The method according to claim 5 , wherein depositing the array of nanostructures comprises spraying the liquid containing the nanostructures onto the surface portion.
10. The method according to claim 5 , wherein depositing the array of nanostructures comprises drop casting of the liquid containing the nanostructures onto the surface portion.
11. The method according to claim 1 , wherein the nanostructures have a mean equivalent diameter of 10-500 nm, or 20-400 nm, or 30-200 nm, as measured in a plane parallel with a surface on which the nanostructures are provided.
12. The method according to claim 1 , wherein the nanostructures are metal rings having an outer diameter of 100-300 nm, an inner diameter of 10-100 nm as measured in a plane parallel with a surface on which the metal rings are provided, and a height of 5-50 nm as measured in a direction perpendicular to said plane.
13. The method according to claim 1 , wherein the plurality of categories are selected as material categories for material recycling, and wherein sorting the item comprises sorting the item for recycling purposes.
14. The method according to claim 13 , wherein the plurality of material categories comprise at least two categories selected from the group of metals, plastics, cardboard, glass, and paper.
15. An assembly for categorizing items of varying material types based on the material type of each item, comprising:
a liquid containing nanostructures,
deposition means for depositing an array of the nanostructures contained in the liquid onto a surface portion of each item to form a material identification tag respectively on each item, wherein:
the nanostructures are plasmonic and have an optical response dependent on the material type of the item onto which the nanostructures are deposited,
an optical extinction and/or reflectance spectrum of the material identification tag is dependent on an 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 optical extinction and/or reflectance spectrum being a signature of the material identification tag and item material combination, and
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,
a light source for illuminating the material identification tag of one of the items underdoing characterization,
a spectrometer for detecting the optical extinction and/or reflectance spectrum of the illuminated material identification tag of the item undergoing characterization,
means for categorizing the item undergoing characterization into one of plural predetermined categories category 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.
16. The assembly according to claim 15 , wherein the deposition means is configured for spraying of the liquid onto the item.
17. The assembly according to claim 15 , wherein the assembly is configured for automated deposition, illumination, spectrum detection, and categorization.
18. The assembly according to claim 15 , wherein the assembly is configured as a hand-held device.