Glass Projection Screen Waveguide Effect Reduction
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Solution Overview
Problem
Glass-based writeable/erasable marker boards have poor contrast when used as projection screens, making them unsuitable for effectively communicating information, especially with small features and a white background.
Innovation Solution
A glass-based front projection screen with a transparent glass sheet and a diffusing element on its back surface, where the glass sheet thickness is reduced to less than 0.2 millimeters to minimize the waveguide effect, and the diffusing element is used to reflect image light back through the glass, creating a writable/erasable user-facing surface with high contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a glass-based writeable/erasable marker board is used as a projection screen, then the board provides writable and erasable functionality, but the contrast is poor and information communication is detracted
Solution Approach 1:
The patent applies parameter changes by precisely controlling the glass sheet thickness to 0.05-0.2mm and adjusting the refractive index mismatch between glass and adhesive to minimize the waveguide effect. This parameter optimization resolves the contradiction by enabling both writeable/erasable functionality and high contrast projection performance to coexist
Solution Approach 2:
The patent converts the harmful waveguide effect into a beneficial feature by using it to enhance the writeable/erasable functionality while controlling it to maintain projection contrast. The waveguide effect is harnessed to improve marker board functionality while its negative impact on projection is minimized through parameter control
2Illumination intensity
If the glass sheet thickness is reduced to less than 0.2 millimeters, then the waveguide effect is minimized and contrast is improved, but the structural strength may be compromised
Solution Approach 1:
The patent resolves this contradiction by changing the glass thickness parameter to an optimized range (0.05-0.2mm) that balances optical performance and structural strength. This parameter optimization ensures sufficient contrast improvement while maintaining adequate structural integrity for practical use
Solution Approach 2:
The patent uses composite material construction with multiple layers including glass sheets, adhesive layers, and diffusing elements. This composite structure provides both the thin glass needed for high contrast and the overall structural strength through the combined properties of different materials
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 contrast levels of at least 75%, comparable to white printer paper, significantly improving the usability of glass-based writeable/erasable marker boards as projection screens by reducing the waveguide effect and enhancing light absorption.
Implementation Method 1
the diffusing element reflects a portion of that light back through the glass sheet (13) to a user
Implementation Method 2
the glass sheet thickness is reduced to less than 0.2 millimeters to minimize the waveguide effect
Data Source
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AI summary
High contrast, glass-based, writeable/erasable front projection screens are provided. The screens include a transparent glass sheet which has a front surface and a back surface separated by a distance d. The back surface is in optical contact with a diffusing element. During use of the projection screen, the glass sheet transmits image light from a projector to the diffusing element and the diffusing element reflects a portion of that light back through the glass sheet to a user. The screens have a user-facing surface that is a writable/erasable surface. In embodiments, the distance d is less than or equal to 0.2 millimeters, the whiteness W of the projection screen is less than or equal to 0.5, and/or the contrast C of the projection screen is at least 75%.