Retroreflective Microcavity Security Element for Banknotes
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Solution Overview
Problem
Current security elements for documents of value, such as banknotes, lack effective anti-counterfeiting features that provide consistent color effects regardless of lighting conditions and viewing angles, relying heavily on the position and type of the lighting source and angle between the source and viewer.
Innovation Solution
A microcavity structure with two distinct areas within each microcavity, where radiation is reflected once in one area and multiple times in another, utilizing a color effect structure that changes with the angle of incidence, creating high contrast and allowing for mixed colors to be perceived as a single color pixel, even with varying depths and geometries of microcavities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional retroreflectors are used with simple reflective surfaces, then the structure is simple and easy to manufacture, but the visual appearance depends heavily on lighting conditions and viewing angle
Solution Approach 1:
The microcavity is divided into two distinct regions: a first region with a first surface that reflects incident radiation simply, and a second region with a second surface that reflects incident radiation multiple times. This segmentation creates different optical paths and color effects in different areas, making the overall color effect independent of viewing angle and lighting conditions.
Solution Approach 2:
Different regions of the microcavity are given different optical properties: the first region has a surface optimized for simple reflection, while the second region has a surface optimized for multiple reflections. This local differentiation ensures that each region contributes a consistent color effect, making the overall appearance reliable regardless of external conditions.
2Reliability
If microcavities with complex structures are used to achieve angle-independent color effects, then color consistency is improved, but the manufacturing complexity increases
Solution Approach 1:
The microcavity structure is segmented into two functional regions with different reflection characteristics. This segmentation achieves angle-independent color effects through a relatively simple geometric division rather than complex optical elements, maintaining manufacturability while improving reliability.
Solution Approach 2:
The microcavity utilizes a spherical or near-spherical geometry with different surface regions. The curvature of the spherical surface naturally creates different incident angles for the first and second regions, enabling multiple reflections without requiring complex additional structural elements.
3Device complexity
If single-region microcavities are used, then the manufacturing process is simple, but the visual impression depends on the type and position of the light source
Solution Approach 1:
The microcavity is segmented into regions that handle different aspects of light reflection: the first region handles simple reflection for direct viewing, while the second region handles multiple reflections for angled viewing. This segmentation eliminates dependence on lighting conditions by ensuring consistent color effects across all viewing angles.
Solution Approach 2:
The invention changes the optical parameters (number of reflections, incident angles) within the microcavity structure to create consistent color effects. By varying these parameters across different regions, the system achieves lighting-condition-independent appearance while maintaining a relatively simple overall structure.
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
This design enhances security against forgery by providing a consistent and easily perceivable color effect that is not dependent on lighting conditions, offering greater protection while being easier to produce and integrate into existing manufacturing processes.
Implementation Method 1
a microcavity structure (1) formed in a substrate (2), wherein on its upper surface a plurality of adjacent microcavities (3) designed as retroreflectors are formed
Implementation Method 2
the structure causing the color effect has an angle-of-incident dispersion, such that radiation once reflected from the top surface produces a different color effect at the first region than radiation multiply reflected at the second region
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
The invention relates to a security element (10) for producing value documents, such as banknotes, checks or the like, has an upper side on which a micro-cavity structure (1) is formed which has a multiplicity of micro-cavities (3) designed as retro-reflectors and located beside one another, wherein a structure (13) bringing about a color effect is formed on the micro-cavities (3) and the micro-cavities (3) are each formed in such a way that same have a first region (6), in which radiation (4) incident on the upper side is reflected singly, and a second region (7), in which radiation (5) incident on the upper side is reflected repeatedly, wherein the structure (13) bringing about the color effect exhibits dispersion as a function of the angle of incidence, so that radiation (4) reflected singly in the first region (6), seen from the upper side, exhibits a different color effect than radiation (5) reflected repeatedly in the second region (7).