HUD Windshield Coating with Single-Silver P-Polarized Reflection
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Solution Overview
Problem
Head-up display (HUD) projection assemblies face challenges with ghost images due to reflection on windshields, and existing solutions using wedge films are costly, while reflection coatings for p-polarized radiation can affect color neutrality and sensor compatibility.
Innovation Solution
A projection assembly using a reflection coating with a single silver layer and high-refractive-index dielectric layers, optimized for p-polarized radiation reflection, eliminating ghost images and ensuring color neutrality and sensor compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflection coating with high reflectivity for p-polarized radiation is used, then ghost images are eliminated and HUD image intensity is improved, but the reflection spectrum becomes curved and wavelength-dependent, affecting color neutrality
Solution Approach 1:
The patent applies parameter changes by carefully controlling the thickness of the silver layer (5-9 nm) and the optical thickness of dielectric layers to flatten the reflection spectrum. By adjusting these parameters, the coating achieves high reflectivity for p-polarized radiation while maintaining color neutrality across the visible spectrum.
Solution Approach 2:
The patent uses composite materials by combining a thin silver layer with dielectric layers having specific refractive indices (≥1.9). This composite structure leverages the high reflectivity of silver for p-polarized radiation while the dielectric layers modify the spectral characteristics to achieve a flat reflection spectrum, resolving the color neutrality issue.
2Illumination intensity
If a reflection coating is applied to the windshield, then p-polarized radiation is reflected effectively for HUD projection, but transmittance for sensors behind the glazing is reduced
Solution Approach 1:
The patent optimizes the silver layer thickness to 5-9 nm, which is thin enough to allow sufficient light transmittance for sensors while still providing effective reflection of p-polarized radiation for HUD projection. This precise parameter control resolves the contradiction between HUD intensity and sensor transmittance.
Solution Approach 2:
The reflection coating is applied selectively to specific regions of the windshield (HUD projection areas) rather than uniformly across the entire surface. This localized application ensures high HUD projection intensity where needed while maintaining sensor transmittance in regions where sensors are positioned.
3Object-affected harmful factors
If wedge films are used to eliminate ghost images, then ghost image problem is solved, but production cost increases significantly
Solution Approach 1:
The patent replaces expensive wedge films with a cost-effective thin-film reflection coating consisting of a 5-9 nm silver layer and dielectric layers. This alternative solution achieves the same ghost image elimination function at a lower production cost, making the technology economically viable for mass production.
Solution Approach 2:
Instead of using wedge-shaped geometry to eliminate ghost images, the patent changes the approach by using a flat reflection coating with optimized optical parameters (layer thicknesses, refractive indices). This parameter optimization achieves ghost image elimination without the manufacturing complexity and cost of wedge films.
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 provides a high-intensity, color-neutral HUD image without ghost images, compatible with camera systems, and maintains high transmittance for sensors, reducing manufacturing costs and complexity.
Implementation Method 1
the radiation of the projector is predominantly p-polarized and the reflection coating is suitable for reflecting p-polarized radiation
Implementation Method 2
The problem arises that the projector image is reflected on both external surfaces of the windshield... near Brewster's angle for an air/glass transition (56.5° for soda lime glass)
Implementation Method 3
The upper and the lower dielectric layer or layer sequence have in each case a refractive index that is at least 1.9
Implementation Method 4
the ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is between 2.10 and 3.20
Implementation Method 5
The reflection coating comprises an electrically conductive layer (21) based on silver
Implementation Method 6
Proposed, among other things, as a reflecting structure is a single metallic layer with a thickness of 5 nm to 9 nm, made, for example, of silver or aluminum
Data Source
AI summary
A projection assembly for a head-up display (HUD), includes a windshield with an HUD region, inner and outer panes joined via a thermoplastic intermediate layer, and a projector directed at the HUD region having a radiation predominantly p-polarized. The windshield has a reflection coating for reflecting p-polarized radiation. The reflection coating has exactly one electrically conductive layer based on silver. A lower dielectric layer or layer sequence with a refractive index of at least 1.9 is arranged below the electrically conductive layer. An upper dielectric layer or layer sequence with a refractive index of at least 1.9 is arranged above the electrically conductive layer. The ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is between 2.10 and 3.20. The reflection coating includes no dielectric layers with a refractive index less than 1.9.