Optical Touch Sensors with Angular Filters for Moisture Discrimination
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Solution Overview
Problem
Existing touch sensors in electronic devices, such as capacitive touch sensors, face challenges in operating effectively in moist environments, including water exposure, which can lead to inaccurate input detection and operational failures.
Innovation Solution
The implementation of a two-dimensional optical touch sensor system that uses a display cover layer with integrated light sources and sensors, along with angular filters, to differentiate between user input and water droplets by controlling the angle of light emission and detection, ensuring accurate touch input even when the device is immersed in water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitive touch sensors are used in electronic devices, then touch input functionality is provided, but the sensors become inaccurate or fail when exposed to moisture or water
Solution Approach 1:
The patent replaces capacitive touch sensing with optical touch sensing. Instead of measuring electrical capacitance changes that are affected by moisture, the system uses light sources to illuminate the touch surface and light sensors to detect reflected or scattered light patterns. This substitution of the sensing mechanism with an optical-based system eliminates the harmful interaction between moisture and the sensor, allowing reliable operation in wet environments while maintaining accurate touch detection.
2Ease of operation
If optical touch sensors are used to detect touch input through light scattering, then touch detection is enabled, but water droplets can be mistakenly detected as touch input
Solution Approach 1:
The patent applies angular filters with specific directional characteristics to the light sensors. These filters are positioned and oriented to accept light scattering at specific angles that are characteristic of finger touch but reject light at angles characteristic of water droplets. By making the sensor response directional rather than omnidirectional, the system can distinguish between the optical signatures of different objects on the touch surface, enabling accurate discrimination between intended touch input and water droplet interference.
3Measurement precision
If angular filters are added to the optical touch sensor system, then discrimination between finger and water droplet is improved, but device complexity increases
Solution Approach 1:
The patent integrates the angular filtering functionality directly into the existing display structure. The same display layers and components that provide visual output also serve the touch sensing function with angular selectivity. By making the display system multi-functional—serving both as a visual display and as an angular-selective touch sensor—the patent avoids adding separate dedicated components, thereby reducing overall device complexity while maintaining the discrimination capability.
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 solution enables reliable touch input detection in wet conditions, preventing false registrations and maintaining device functionality even when submerged or exposed to moisture, while also allowing operation with gloved hands.
Implementation Method 1
One or more light sources may be included to 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.
Implementation Method 2
The angular filters may be on-axis light blocking angular filters that block light parallel to the surface normal of the display cover layer and pass light at high angles relative to the surface normal of the display cover layer. The angular filters may be off-axis light blocking angular filters that pass light parallel to the surface normal of the display cover layer and block light at high angles relative to the surface normal of the display cover layer.
Data Source
AI summary
An electronic device may have a touch sensitive display that is insensitive to the presence of moisture. The display may have a two-dimensional optical touch sensor that gathers touch input while the electronic device is immersed in water or otherwise exposed to moisture. The optical touch sensor may include light sources and light detectors. The light sources and the light sensors may be mounted on a common substrate with an array of image pixels. The image pixels may be formed by crystalline semiconductor light-emitting diode dies. Angular filters may be included over the light sources and/or the light detectors to improve discrimination between a user's finger and water droplets. The angular filters may be on-axis light blocking angular filters or off-axis light blocking angular filters.