Security Element Double Line Grating Color Effects
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Solution Overview
Problem
Existing security elements for value documents, such as banknotes, lack effective color-changing properties when viewed through and tilted, and are not easily machine-readable due to their polarizing effects.
Innovation Solution
A double line grating structure composed of two superposed line grating structures that are complementary and phase-shifted by 90°, made of metal or semiconductor materials, with a specific layer structure and modulation depth, allowing for angle-dependent color filtering and polarization properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sub-wavelength gratings with non-continuous surface are used, then color filter properties are pronounced, but angle tolerance is large and hue hardly changes when tilted
Solution Approach 1:
The invention divides a single grating structure into two separate superimposed gratings with different orientations. Each grating has lines running in a specific direction (e.g., first grating with horizontal lines, second grating with vertical lines), and their superposition creates the desired optical effect while reducing angle tolerance limitations
Solution Approach 2:
The invention combines two grating structures with different line orientations and optical properties into a composite security element. The first and second gratings are superimposed with their respective lines perpendicular to each other, creating a composite structure that exhibits both color filter properties and controlled angle dependence
2Ease of manufacture
If single line grating structure is used, then manufacturing is simpler, but color effect in transmission is weak and requires absorbent base
Solution Approach 1:
The invention merges two line grating structures into a single superimposed configuration. The first grating with lines in one direction and the second grating with lines in a perpendicular direction are combined in the same plane, creating enhanced optical effects in both reflection and transmission without requiring absorbent bases
3Illumination intensity
If gratings are made of metal or semiconductor, then color saturation is high, but polarizing effect is strong reducing machine readability
Solution Approach 1:
The invention introduces asymmetry by superimposing two gratings with perpendicular line orientations. This asymmetric configuration modifies the polarizing effect while maintaining color saturation, making the security element both visually striking and machine-readable through specialized verification systems
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 security element provides reproducible and striking color effects in both reflection and transmission, enabling machine-readable authenticity verification using polarized light, with color changes observable when tilted or rotated, enhancing security features.
Implementation Method 1
A double line grating is used, which consists of two superposed line grating structures that are complementary to one another... provides reproducible and easily perceptible color effects both in reflection and in transmission
Implementation Method 2
The line grating structures are made of metal or semiconductors or of a multilayer structure... provides reproducible and easily perceptible color effects
Implementation Method 3
These structures have a strong polarizing effect on the reflection or transmission of an incident light beam
Data Source
Figure 1~2b
Figure 2c~3
Figure 4
AI summary
The invention relates to a security element for producing value documents, such as banknotes, checks, or the like, said security element having: a dielectric substrate (1); a first line grid structure (2) which is embedded into the substrate (1), said structure consisting of multiple first grid webs (3) which run along a longitudinal direction, which are arranged on a plane (L), and which consist of metal or a semiconductor; and a second line grid structure (6) which is embedded into the substrate (1), said structure consisting of second grid webs (7) which run along the longitudinal direction, and which consist of metal or a semiconductor, wherein the second line grid structure is located above the first line grid structure (2) with respect to the plane (L). Each first grid web (3) has a width (b), and the webs lie next to one another at a distance (a) from one another such that first grid gaps (4), which runs along the longitudinal direction and which have a width that corresponds to the distance (a), are formed between the first grid webs (3). The second line grid structure (6) is inverted with respect to the first line grid structure (2) and is displaced by half a period with respect to the first line grid structure (2) such that the second grid webs (7) lie above the first grid gaps (4), and second grid gaps (8), which are produced between the second grid webs (7), lie above the first grid webs (3) in a plan view of the plane. The width of the first grid webs (3) and the second grid gaps (8), the width of the second grid webs (7) and the first grid gaps (4), and a thickness (t) of the first grid webs (3) and the second grid webs (7) are each less than 300 nm.