Planar Retroreflector With High-Index Dielectric Coating Without Air Gaps
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Solution Overview
Problem
Existing retroreflectors based on microprismatic structures either have a metallic appearance due to mirrored surfaces or require air gaps for total internal reflection, which complicates manufacturing and affects long-term stability, limiting their applicability and visibility.
Innovation Solution
A planar retroreflector with a microprismatic relief structure coated with a high-index dielectric coating that facilitates total internal reflection without air gaps, allowing for a non-metallic appearance and improved long-term stability, while maintaining high retroreflection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a metallic mirror coating is applied to the relief structure, then retroreflection efficiency is improved, but the retroreflector acquires a metallic appearance which is undesirable for many applications
Solution Approach 1:
The patent changes the material parameter of the coating from metallic to dielectric with high refractive index. This parameter change enables total internal reflection at the dielectric-air interface, achieving high retroreflection efficiency without the metallic appearance, thus resolving the contradiction between reflection efficiency and appearance control.
Solution Approach 2:
The patent replaces the metallic mirror coating system with a dielectric coating system that utilizes total internal reflection. This substitution eliminates the need for metallic materials while maintaining or improving retroreflection performance, and simultaneously resolves the appearance issue by providing a non-metallic, transparent, or translucent coating.
2Loss of energy
If air gaps are provided for total internal reflection, then retroreflection efficiency is improved, but manufacturing complexity increases and long-term stability is affected
Solution Approach 1:
The patent extracts the air gap requirement from the system by providing air gaps only in specific regions where they are most needed for optical performance, while filling other regions with encapsulant material. This selective extraction reduces manufacturing complexity and improves long-term stability by eliminating air pockets in critical areas, while still maintaining total internal reflection where required.
Solution Approach 2:
The patent introduces an encapsulant material as an intermediary substance that fills the spaces between and around the lens elements. This intermediary material provides structural support, eliminates problematic air gaps in non-critical regions, and maintains the optical performance by allowing total internal reflection at the dielectric-coating interfaces while simplifying the overall manufacturing process.
3Ease of manufacture
If the relief structure is completely embedded in plastic, then manufacturing is simplified, but the retroreflective properties are reduced due to loss of total internal reflection at the air interface
Solution Approach 1:
The patent applies local quality by providing dielectric coatings with high refractive index specifically on the light-incident surfaces of the relief structure, while allowing air gaps to exist in other regions. This localized application of the dielectric coating ensures that total internal reflection occurs at the critical interfaces where light enters and exits the lens elements, maintaining high retroreflection efficiency while still allowing complete embedding for manufacturing simplicity.
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 high retroreflection values without a metallic appearance and enhances manufacturing ease, enabling transparent or semi-transparent designs that maintain the visibility of the underlying substrate, suitable for applications requiring non-reflective coatings and improved durability.
Implementation Method 1
a dielectric coating with a high refractive index is provided on the light-incident surfaces of the relief structure... facilitates total internal reflection without air gaps
Data Source
Figure 1A~1B
Figure 2A~3
Figure 4A~4B
AI summary
The invention relates to a retroreflector which comprises a retroreflecting, microprismatic relief structure (3b) formed in a transparent plastics material (3a) and retroreflects, by means of total reflection, optical radiation which is incident from an incidence face and through the plastics material (3a). The microprismatic relief structure (3b) is coated with a dielectric coating (3d) and the dielectric coating (3d) is covered with a cover layer (3c). A refractive index of the dielectric coating (3d) is greater than a refractive index of the cover layer (3c).