Vehicle Camera Prism Anti-Reflection Coating for Reflection Suppression
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Solution Overview
Problem
Modern vehicle windshields with a tilt angle of 20° to 30° cause significant interference from multiple reflections, which existing camera arrangements fail to effectively suppress, especially due to the high cost and mechanical sensitivity of polarization-rotating plates, and residual reflection issues with conventional anti-reflection coatings.
Innovation Solution
An anti-reflection coating is optimized to have lower reflectivity for s-polarized light than p-polarized light, particularly at large angles of incidence and within the camera's sensitivity spectrum, using materials like silicon dioxide, titanium dioxide, or magnesium fluoride, to minimize unwanted reflections by prioritizing reduced reflection for s-polarized light while allowing increased reflection for p-polarized light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional anti-reflection coating is used on the prism, then the total reflected light intensity is minimized, but the reflectivity for s-polarized light remains higher than for p-polarized light, causing residual reflections to persist
Solution Approach 1:
The patent applies parameter changes by optimizing the anti-reflection coating's reflectivity characteristics specifically for s-polarized light. The coating is designed with reflectivity Rs < Rp across the detection range, inverting the conventional approach where total reflection minimization is prioritized. This parameter optimization suppresses the harmful s-polarized reflections that cause multiple images while maintaining acceptable p-polarized light transmission.
2Object-generated harmful factors
If polarization-rotating plates are used to suppress reflections, then multiple images are reduced, but the cost increases significantly and mechanical sensitivity becomes a problem
Solution Approach 1:
The patent replaces expensive and mechanically sensitive polarization-rotating plates with a more economical anti-reflection coating solution. The coating, applied directly to the prism surface, provides durable and cost-effective suppression of multiple reflections without the mechanical sensitivity issues associated with polarization films and plates.
Solution Approach 2:
The patent substitutes the mechanical polarization-rotating system with an optical coating solution. Instead of using mechanically sensitive polarization films and rotating plates, the invention uses an anti-reflection coating with optimized optical properties (Rs < Rp) to achieve the same goal of suppressing multiple reflections, thereby eliminating mechanical sensitivity issues.
3Adaptability or versatility
If the camera is positioned to achieve a large image acquisition angle, then the detection range is improved, but the coupling area on the windshield becomes large, creating blind spots for the driver
Solution Approach 1:
The patent applies local quality by using a beam-guiding element with a prism that has non-parallel optical surfaces. This prism structure locally redirects light beams at different angles, enabling the camera to capture a wide detection range while the physical coupling area on the windshield remains compact. The prism's specific geometry (with surface angles differing by more than 10 degrees) creates the necessary beam guidance in a localized space.
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
This approach significantly reduces residual reflections, resulting in a more effective suppression of multiple images, with the intensity of unwanted reflections decreasing to 0.027% of the main image, compared to 0.93% without optimization and 0.13% with conventional coatings, thereby enhancing the camera's image quality.
Implementation Method 1
the reflectivity of the anti-reflective coating is smaller for s-polarized light than for p-polarized light, at least over a sub-range of the light incidence angles that form the detection range of the camera
Implementation Method 2
Because of the tilt of the windshield, the angle of incidence of the light is large and close to Brewster's angle. Therefore, without an anti-reflection coating, the reflected light is highly s-polarized.
Data Source
Figure 1~2
Figure 3~5
AI summary
The invention relates to a camera arrangement for a vehicle, said camera arrangement comprising a camera (7) arranged inside the vehicle behind a vehicle window (2), and a beam guidance element arranged between the vehicle window (2) and the camera (7), which has or forms a prism (3) and which has an anti-reflection coating (8, 8') on its reverse side, wherein the reflectivity of the anti-reflection coating (8, 8') is lower for s-polarised light than for p-polarised light over at least a portion of the entrance angles, which form the detection range of the camera (7), and at least over a partial region of the sensitivity spectrum of the camera (7).