Plasmonic Security Element for Angle-Selective Image Switching
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Solution Overview
Problem
Conventional security elements using diffractive optically variable effect generating relief structures suffer from noise under diffuse lighting conditions and misregistration of colors, lacking precise optical variability.
Innovation Solution
A security element utilizing plasmonic nanostructures arranged in differently inclined sub-regions to display distinct images at different viewing angles, employing arrays of nanostructures such as nanopillars or nanoholes to generate color and provide optical variability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diffractive optically variable effect generating relief structures are used, then optical variability is achieved, but noise appears under diffuse lighting conditions
Solution Approach 1:
The patent changes the fundamental optical parameter from diffraction-based color generation to plasmonic resonance-based color generation. Plasmonic nanostructures generate color through resonant interactions between light and metallic nanostructures, where collective free-electron oscillations couple to electromagnetic fields, producing angular-independent colors that do not exhibit the noise characteristic of diffractive structures under diffuse lighting.
Solution Approach 2:
The patent replaces the mechanical relief structure system (diffraction gratings) with a plasmonic nanostructure system. This substitution eliminates the need for surface relief features that cause diffraction, thereby removing the source of noise under diffuse lighting while maintaining optical variability through plasmonic resonance effects.
2Adaptability or versatility
If printed inks are used to generate optically variable effect, then multiple colours can be produced, but misregistration between different colours occurs
Solution Approach 1:
The patent merges multiple color-generation functions into a single integrated plasmonic nanostructure layer. Instead of using separate printed ink layers for different colors (which suffer from misregistration), the invention uses arrays of plasmonic nanostructures with different geometries or compositions within the same layer to generate different colors simultaneously, ensuring perfect registration of multiple colors.
Solution Approach 2:
The patent changes from a multi-layer printing process to a single-layer plasmonic nanostructure process. By varying the geometric parameters (size, shape, spacing) or material composition of the plasmonic nanostructures, different colors are generated within the same layer, eliminating registration issues inherent in multi-color printing processes.
3Manufacturing precision
If diffractive structures are used, then integral register between different structures is achieved, but viewing under diffuse lighting conditions produces noisy appearance
Solution Approach 1:
The patent replaces the diffractive mechanical relief structure system with a plasmonic nanostructure system. This substitution maintains the advantage of integral register (since all structures are formed in a single process) while eliminating the harmful noise effect by using plasmonic resonance instead of diffraction for color generation.
Solution Approach 2:
The patent changes the optical mechanism from diffraction to plasmonic resonance. This parameter change eliminates the angle-dependent diffraction effects that cause noise under diffuse lighting, while plasmonic resonance provides angular-independent color generation that maintains a clean appearance under various lighting conditions.
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 solution achieves precise optical variability and image switching effects without angular dispersion, enhancing security and authenticity verification.
Implementation Method 1
Plasmonic nanostructures are structures that generate colour from the resonant interactions between light and metallic nanostructures where collective free-electron oscillations within the metallic nanostructure couple to electromagnetic fields in a neighbouring dielectric material.
Implementation Method 2
The first surface is arranged such that each sub-region has a respective average inclination and wherein the average inclinations of the first sub-regions are such that the first image is displayed at least at a first viewing angle and wherein the average inclinations of the second sub-regions are such that the second image is displayed at least at a second viewing angle
Data Source
AI summary
A security element includes a first layer having a first surface; an array of image regions across the first surface, each including a first and a second sub-region; a first array of plasmonic nanostructures in or on the first surface across the first sub-regions and defining in each first sub-region a portion of a first image; and a second array of plasmonic nanostructures in or on the first surface across the second sub-regions and defining in each second sub-region a portion of a second image. The first surface is arranged so the sub-regions have respective average inclinations. The average inclinations of the first sub-regions result in the first image being displayed at a first viewing angle. The average inclinations of the second sub-regions result in the second image being displayed at a different second viewing angle. The second image is substantially not displayed or only partially displayed at the first viewing angle.