2D Periodic Colour Filtering Grating for Security Documents
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Solution Overview
Problem
Two-dimensional periodic subwavelength gratings with pronounced color filter properties have high angular tolerance but are complex and costly to produce, making them unsuitable for large-scale production in security documents.
Innovation Solution
A two-dimensional, color-filtering grid with a high-refractive index base layer and metallic surface elements, arranged in a periodic pattern with specific dimensions and materials, allowing for cost-effective production and integration into security elements like banknotes and ID cards, using a dielectric substrate and UV varnish for enhanced optical effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If two-dimensional periodic subwavelength gratings with pronounced color filter properties are used, then angular tolerance and color saturation are improved, but production complexity and cost increase significantly
Solution Approach 1:
The grating structure is segmented into two distinct components: a continuous base layer and discrete surface elements arranged in a periodic pattern. This segmentation allows the continuous base layer to provide angular tolerance while the discrete surface elements create the color filtering effect, simplifying the overall production process compared to fully continuous two-dimensional gratings
Solution Approach 2:
A dielectric intermediate layer is introduced between the metallic base layer and the metallic surface elements. This intermediary layer enables cost-effective production by allowing standard deposition techniques while maintaining the optical properties needed for color filtering and angular tolerance
2Adaptability or versatility
If two-dimensional periodic subwavelength gratings with pronounced color filter properties are used, then angular tolerance is improved, but production complexity and cost increase significantly
Solution Approach 1:
Different regions of the grating structure are assigned different functions: the continuous base layer provides angular tolerance through its extended structure, while the discrete surface elements provide color filtering. This local differentiation allows each component to be optimized independently for its specific function, simplifying production
Solution Approach 2:
The grating combines multiple materials with different properties: a metallic base layer for structural continuity and angular tolerance, a dielectric intermediate layer for isolation and optical control, and metallic surface elements for color filtering. This composite structure achieves both angular tolerance and color saturation while remaining manufacturable
3Manufacturing precision
If fine structuring capabilities are enhanced to achieve true color images, then color filtering performance is improved, but manufacturing difficulty increases
Solution Approach 1:
The fine structuring is segmented into the periodic arrangement of discrete surface elements on the continuous base layer. This segmentation allows the fine periodic structure to be created using standard photolithography and deposition techniques, avoiding the need for complex nanofabrication processes while still achieving the required subwavelength periodicity for color filtering
Solution Approach 2:
The continuous base layer is formed first as a preliminary structure before adding the surface elements. This preliminary action establishes the angular tolerance foundation early in the manufacturing process, allowing subsequent steps to focus only on creating the color-filtering surface elements with precise periodicity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The grid achieves high color saturation and angular tolerance with fine structuring capabilities, enabling true color images and secure authenticity features in documents, overcoming production complexities and costs of previous technologies.
Implementation Method 1
They can exhibit color filter properties in the subwavelength range if the grating profile is designed such that resonance effects occur in the visible wavelength range
Implementation Method 2
A two-dimensional, color-filtering grid with a high-refractive index base layer and metallic surface elements, arranged in a periodic pattern with specific dimensions and materials
Implementation Method 3
using a dielectric substrate and UV varnish for enhanced optical effects
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
The invention relates to a two-dimensionally periodic, colour-filtering grating comprising a continuous, more particularly metallic, base layer (3) having a high refractive index, said base layer defining a grating plane, and above the base layer (3) a two-dimensionally regular pattern (6) composed of individual, more particularly metallic, surface elements (5) having a high refractive index, which each extend parallel to the grating plane and are each spaced apart from the base layer (3) by an intermediate dielectric (4) by a distance (h) that is greater than the thickness of the base layer (3) and of the surface elements (5), wherein the regular pattern (6) has a periodicity (p1, p2) of between 100 nm and 800 nm, preferably between 200 nm and 500 nm, in at least two directions running parallel to the grating plane.