Moisture-Insensitive Optical Touch Sensor Metasurface Design
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Solution Overview
Problem
Existing electronic devices with capacitive touch sensors face challenges in operating effectively in moist environments, such as when immersed in water or exposed to moisture, as they are sensitive to moisture and may not function with gloved hands.
Innovation Solution
An optical touch sensor system utilizing a two-dimensional total internal reflection touch sensor with a metasurface grating that couples light at a specific angle into a display cover layer, ensuring total internal reflection is maintained even in moist conditions, and additional metasurface gratings redirect light to prevent edge-defeating, allowing the sensor to operate underwater or with moisture exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitive touch sensors are used in electronic devices, then touch input functionality is provided, but the sensors become sensitive to moisture and cannot function properly in wet conditions or with gloved hands
Solution Approach 1:
The patent replaces capacitive touch sensing (electrical field-based) with optical touch sensing (light-based). The optical system uses light sources, optical waveguides, and photodetectors to detect finger contact through changes in light propagation, eliminating sensitivity to moisture and electrical grounding issues while maintaining touch input functionality across diverse environments including wet conditions and gloved hand operation
Solution Approach 2:
The patent changes the fundamental operating parameter of the touch sensor from electrical capacitance detection to optical property detection. By measuring changes in light intensity, wavelength, or propagation characteristics when a finger contacts the surface, the system achieves environment-independent operation while maintaining reliable touch detection
2Loss of energy
If total internal reflection is used in the optical touch sensor, then light is trapped within the display cover layer, but moisture on the surface can defeat total internal reflection and reduce sensing accuracy
Solution Approach 1:
The patent introduces an optical waveguide structure as an intermediary between the light source and the external environment. The waveguide uses total internal reflection at controlled interfaces to guide light, while the coupling out of light at the touch detection surface is engineered to be insensitive to moisture presence, maintaining reliable sensing even when the surface is wet
Solution Approach 2:
The patent applies different optical properties to different regions of the display cover layer. The bulk of the cover layer maintains high optical confinement for efficient light guiding, while the external surface is engineered with specific optical characteristics that allow touch detection through moisture-insensitive coupling mechanisms, creating localized functional differentiation
3Loss of energy
If light is coupled into the display cover layer at a high angle to maintain total internal reflection, then light confinement is improved, but light may escape at edges and defeat total internal reflection
Solution Approach 1:
The patent divides the optical touch sensor into distinct functional segments: light sources positioned at specific locations, optical waveguide regions for light propagation, edge regions with modified optical properties to prevent leakage, and detection regions with photodetectors. This segmentation allows each component to be optimized independently for its specific function while working together as an integrated system
Solution Approach 2:
The patent addresses edge light escape by introducing additional spatial dimensions to the optical design. Instead of relying solely on angular control in two dimensions, the solution uses three-dimensional light guiding paths and vertical layering of optical components to maintain total internal reflection at edges while enabling effective touch detection at the surface
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 optical touch sensor system enables reliable touch input gathering in wet conditions and with gloved hands, as it is not impacted by moisture or grounding effects, providing a more versatile and user-friendly interface.
Implementation Method 1
A light source may illuminate an external object such as a finger of a user when the object contacts a surface of the display cover layer. This creates scattered light that may be detected by an array of light sensors. A metasurface grating may be used to couple light from the light source into the display cover layer at an angle such that total internal reflection within the display cover layer is sustained across the display cover layer even when the display cover layer is immersed in water or otherwise exposed to moisture.
Implementation Method 2
Additional metasurface gratings may be formed on the display cover layer to redirect light propagating within the display cover layer away from edges that might otherwise defeat total internal reflection.
Data Source
AI summary
An electronic device may have an optical touch sensor that is insensitive to the presence of moisture. The display may present images through a display cover layer. A light source may illuminate an external object such as a user's finger when the object contacts a surface of the display cover layer. This creates scattered light that may be detected by an array of light sensors. A metasurface grating may be used to couple light from the light source into the display cover layer at an angle such that total internal reflection within the display cover layer is sustained across the display cover layer even when the display cover layer is immersed in water or otherwise exposed to moisture. Additional metasurface gratings may be formed on the display cover layer to redirect light propagating within the display cover layer away from edges that might otherwise defeat total internal reflection.