Surface Relief Microstructures for Rainbow-Free Image Flip Security
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Solution Overview
Problem
Existing optical devices for security applications lack the ability to display images with scattering effects, positive-negative image flip without rainbow colors, and achieve distinct, saturated color appearances, while being susceptible to counterfeiting due to the widespread availability of hologram technology.
Innovation Solution
The invention introduces surface relief microstructures with non-periodic lateral transitions and equal relief modulation depth across the surface, featuring top and bottom regions in distinct plateaus, which are anisotropic and have a specific autocorrelation length, allowing for vivid graphical designs and color appearances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If holographic technology is used for security devices, then the devices can display images with scattering effects and positive-negative image flips, but the devices exhibit rainbow colors and are susceptible to counterfeiting due to widespread availability of hologram technology
Solution Approach 1:
The patent changes the fundamental parameters of the optical structure by using non-periodic surface relief microstructures with specific autocorrelation lengths instead of traditional periodic holographic structures. This parameter change produces distinct color appearances without rainbow effects while maintaining manufacturing feasibility through established replication techniques.
Solution Approach 2:
The invention introduces asymmetric non-periodic patterns in the surface relief microstructures, where the lateral transitions and autocorrelation lengths create unique optical signatures that differ fundamentally from symmetric periodic holographic structures. This asymmetry provides both aesthetic distinction and enhanced security.
2Illumination intensity
If thin interference films are used to achieve colorshift effects, then the devices can change color with viewing angle, but the devices cannot display high-resolution images with distinct saturated colors without rainbow effects
Solution Approach 1:
The patent segments the surface into multiple regions with different non-periodic patterns, each having specific autocorrelation lengths and transition frequencies. This segmentation allows different areas to contribute to various color and image components, achieving both high resolution and saturated colors through the collective effect of many small structured elements.
Solution Approach 2:
The invention adds a vertical dimension to the surface structure by creating relief microstructures with controlled modulation depths and plateaus. This third dimension (z-height) works in conjunction with the lateral dimensions to produce distinct color appearances and high-resolution imaging capabilities that cannot be achieved with planar thin films alone.
3Adaptability or versatility
If anisotropic scattering surfaces are used to generate viewing angle sensitive devices, then the devices can display images with positive-negative flips, but the devices cannot achieve distinct saturated color appearances without rainbow colors
Solution Approach 1:
The patent replaces traditional mechanical or chemical coloration methods with optical structuring. By carefully designing the geometric parameters of the non-periodic surface relief structures, including autocorrelation lengths and transition densities, the device generates color through interference and scattering physics rather than pigments or dyes, achieving saturated colors without rainbow artifacts.
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 enables optical devices to exhibit pronounced color shifts, high-resolution images, and positive-negative image flips without rainbow colors, enhancing security features by providing a distinct and saturated color appearance.
Implementation Method 1
Colorshift effects due to the interference of light at thin optical films
Implementation Method 2
The use of isotropic and even more anisotropic scattering effects in OVDs can enhance the optical attractiveness significantly
Data Source
Figure 1.1~1.2
Figure 2~3
Figure 4.1~4.3
AI summary
The present invention relates to an element comprising a surface area with an anisotropic optically effective surface relief microstructure (12), which has a surface modulation of transitions from top regions (13) to bottom regions (14) and from bottom regions (14) to top (13) regions. The element is obtained by first generating a mask with a microstructure comprising first and second zones, wherein the microstructure of the mask has in a first lateral direction in average at least one transition from said first to said second zone or vice versa within every 20 micrometer and the lateral arrangement of the transitions is non-periodic in this direction. Due to anisotropic scattering, the surface relief microstructures of the elements of the invention are suitable to display images with a positive-negative image flip, which advantageously have a distinct and saturated color appearance but at the same time do not show any rainbow colors.