HUD Windshield Reflection Coating for Ghost-Free Color Neutrality
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Solution Overview
Problem
Current head-up display (HUD) projection assemblies face challenges with ghost images due to the reflection of projector images on both surfaces of windshields, leading to increased costs with the use of wedge films, and existing reflection coatings have wavelength-dependent reflectance, affecting color neutrality.
Innovation Solution
A projection assembly using p-polarized radiation with a reflection coating comprising a single silver layer and high-refractive-index dielectric layers, optimized to reflect p-polarized radiation with a smooth spectral response, eliminating ghost images and ensuring color neutrality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a reflection coating is used to reflect p-polarised radiation, then ghost images are eliminated, but the reflectance becomes wavelength dependent affecting color neutrality
Solution Approach 1:
The reflection coating uses a composite structure with multiple dielectric layers having different refractive indices arranged in a specific sequence. This composite material approach enables wavelength-independent reflectance for p-polarised radiation, eliminating the color distortion problem while maintaining ghost image suppression.
Solution Approach 2:
The patent optimizes the optical thicknesses of individual dielectric layers and their refractive indices to achieve a flat reflectance spectrum. By carefully controlling these parameters, the coating reflects p-polarised radiation uniformly across the visible spectrum, ensuring color neutrality in the HUD display.
2Object-affected harmful factors
If wedge films are used to prevent ghost images, then reflection issues are resolved, but production costs increase significantly
Solution Approach 1:
The patent replaces expensive wedge films with a more cost-effective reflection coating consisting of standard dielectric layers. This coating can be applied using conventional vacuum deposition techniques, significantly reducing manufacturing costs while achieving the same ghost image elimination function.
Solution Approach 2:
Instead of using wedge-shaped geometry to prevent ghost images, the patent changes the approach by using a flat coating with optimized optical parameters (refractive indices and thicknesses) that selectively reflects p-polarised radiation, thereby eliminating the need for expensive wedge films.
3Illumination intensity
If the reflection coating reflects p-polarised radiation effectively, then HUD image intensity increases, but transmittance of the windshield decreases
Solution Approach 1:
The reflection coating is designed to exhibit selective optical properties: it strongly reflects p-polarised radiation in the HUD wavelength range while maintaining high transmittance for other polarizations and wavelengths. This local optimization of optical quality ensures bright HUD images without significantly compromising overall windshield transparency.
Solution Approach 2:
By optimizing the thickness and refractive indices of individual dielectric layers, the coating achieves high reflectance for p-polarised light at the specific angle of incidence used in HUD systems, while maintaining good overall transmittance. The parameters are tuned to create a balance between HUD image intensity and windshield transparency.
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 high-intensity, color-neutral HUD images without the need for expensive wedge films, maintaining high transmittance and reflectivity, and preventing ghost images, while ensuring the windshield can be used as intended.
Implementation Method 1
the reflection coating is provided as a reflection surface for the radiation incident thereon, in particular as a reflection surface for predominantly p-polarised radiation
Implementation Method 2
the angle of incidence of about 65° typical for HUD projection assemblies is relatively close to Brewster's angle for an air/glass transition (56.5°, soda lime glass), the p-polarised radiation is hardly reflected by the pane surfaces
Implementation Method 3
The ratio according to the invention of the optical thicknesses of the upper and lower dielectric layer sequence causes a smoothing of the reflective spectrum such that a colour-neutral display is ensured
Implementation Method 4
images are projected onto the windshield, reflected there, and perceived by the driver as a virtual image behind the windshield
Data Source
AI summary
A projection assembly for a head-up display (HUD), includes a windshield, including outer and inner panes that are joined to one another via a thermoplastic intermediate layer and having an HUD region; and a projector aimed at the HUD region. The radiation of the projector is predominantly p-polarised, and the windshield is provided with a reflection coating that is suitable for reflecting p-polarised radiation. The reflection coating has exactly one electrically conductive layer based on silver, a lower dielectric layer or layer sequence whose refractive index is at least 1.9 is arranged beneath the electrically conductive layer, an upper dielectric layer or layer sequence whose refractive index is 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 at least 1.7.