Capacitive Touch Screen Sealing Frame and Refractive Index Matching
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Solution Overview
Problem
Capacitive touch screens face issues with precise control of electrode spacing, leading to potential misinterpretation of control signals and visibility of electrodes due to reflections, which affect the appearance and readability of portable devices.
Innovation Solution
A capacitive touch screen design featuring two transparent dielectric substrates joined rigidly by a sealing frame along the outer perimeter, with a filling fluid matching the refractive index of the substrates to minimize visibility and maintain constant spacing, and spacers for additional rigidity and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the substrates are joined rigidly by a sealing frame to maintain constant spacing, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The sealing frame is divided into multiple segments that can be independently positioned and secured to the substrates. This segmentation allows for easier assembly and adjustment, reducing the overall complexity while maintaining the rigid connection and constant spacing required for precise capacitance measurement.
Solution Approach 2:
The sealing frame acts as an intermediary element between the two substrates, providing a rigid connection that maintains constant spacing. This intermediary structure simplifies the overall device by consolidating the spacing maintenance function into a single component rather than requiring multiple adjustment mechanisms.
2Object-affected harmful factors
If a filling fluid with matching refractive index is used to optimize optical appearance, then harmful factors are reduced, but manufacturing precision requirements increase
Solution Approach 1:
The refractive index of the filling fluid is specifically selected to match the refractive index of the substrate material. This parameter change (matching refractive indices) eliminates the optical contrast that makes electrodes visible, thereby reducing the harmful effect of electrode visibility without requiring complex manufacturing adjustments.
Solution Approach 2:
The system uses a composite structure combining the substrate and filling fluid with matched refractive indices. This composite material approach creates optical homogeneity that hides the electrodes, reducing harmful visual effects while maintaining manufacturing simplicity through the use of standard optical matching techniques.
3Reliability
If spacers are added to enhance rigidity and control spacing, then reliability is improved, but device complexity increases
Solution Approach 1:
The spacers are integrated into the sealing frame structure rather than being separate components. This merging of the spacer function into the sealing frame reduces the total number of components and simplifies assembly, while still providing the necessary rigidity and spacing control to ensure reliable capacitance measurement.
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
Ensures accurate capacitance measurement and optical compensation, making electrodes invisible and preventing distortion from user pressure, thus enhancing the reliability and appearance of touch screens.
Implementation Method 1
a filling fluid whose optical refractive index is substantially equal to that of the first substrate
Implementation Method 2
the reflections of the ambient light on the touch screen
Implementation Method 3
the first and second substrates are joined together in such a way rigid by means of a sealing frame which extends along the outer perimeter of these two substrates to maintain constant the spacing between the two substrates
Implementation Method 4
Screens with capacitive touch zones operate on the principle of the variation in capacitance observed when the user brings his finger near the desired electrode
Data Source
Figure 1~4
AI summary
The touchscreen (20) has substrates (2, 4) made of a transparent dielectric material, and extended parallely and remote from one another. A set of electrodes (6) is arranged on a face (2a) of the substrate (2). Maintaining units i.e. sealing frames (8), maintain a constant spacing between the substrates. Another set of electrodes (22) is arranged on a face of the substrate (4). The electrodes are made of transparent and electrically conductive material e.g. indium-tin oxide. Intermediate layers (12, 24) are arranged on the faces to cover the electrodes, respectively.