FTIR and Capacitive Touch Force Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Touch devices often cannot accurately determine the amount of force applied by a user, limiting their ability to provide advanced functions such as differentiated interactions through varying touch forces, which can reduce their effectiveness and value.
Innovation Solution
Incorporating force-sensitive sensors into touch devices using infrared techniques like frustrated total internal reflection (FTIR) and capacitive sensing, allowing for the detection of force and its changes by measuring infrared light reflection and capacitive coupling, enabling more precise determination of touch location and force applied.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If touch devices use basic touch detection methods, then device simplicity is maintained, but the ability to determine force applied is lost
Solution Approach 1:
The patent combines FTIR optical sensing and capacitive sensing into a single integrated sensor system. The FTIR component uses infrared LEDs and photodetectors to detect force through light reflection changes, while the capacitive component uses conductive layers to detect touch and force through capacitance changes. Merging these two sensing mechanisms allows the device to achieve precise force measurement capability while sharing common structural elements like the cover glass and sensor layers, thereby reducing overall system complexity compared to using separate independent sensing systems.
Solution Approach 2:
The integrated sensor system performs multiple functions simultaneously: it detects touch location, determines force applied, identifies contact area size, and distinguishes between different types of contact (finger vs. stylus). The FTIR and capacitive sensing components work together to provide comprehensive touch information, making the sensor system universal in its capability to handle various touch interaction scenarios without requiring separate specialized sensors for each function.
2Measurement precision
If multiple sensing techniques are integrated to improve force detection, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent implements a nested sensor architecture where the capacitive sensing layers are integrated within the same structure as the FTIR sensing components. The conductive layers for capacitive sensing are positioned between the cover glass and the FTIR photodetectors, allowing both sensing mechanisms to occupy overlapping spatial regions. This nesting approach enables dual sensing functionality while minimizing the overall thickness and structural footprint of the sensor system.
Solution Approach 2:
The sensor system employs different sensing mechanisms in different regions or for different purposes within the same touch surface. The FTIR component is particularly effective for detecting force magnitude through optical reflection changes, while the capacitive component excels at detecting touch location and contact area. By allowing each sensing technique to operate optimally in its suitable regime, the system achieves high overall measurement precision without requiring every region to use every sensing method, thereby managing complexity.
3Adaptability or versatility
If force-sensitive sensors are added to touch devices, then device functionality is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent utilizes parameter changes in existing materials and components to enable force sensing without adding fundamentally new material types. The FTIR system changes the refractive index parameter at the cover glass interface to detect force, while the capacitive system changes capacitance values based on proximity and contact. By leveraging parameter changes in conventional materials rather than requiring exotic new materials, the manufacturing process remains compatible with existing semiconductor and display manufacturing techniques.
Solution Approach 2:
The sensor structure employs asymmetric layering where the FTIR and capacitive sensing components are positioned at different depths and orientations within the touch panel structure. The infrared LEDs and photodetectors are arranged in specific asymmetric patterns to optimize light path geometry, while the capacitive conductive layers are positioned asymmetrically relative to the FTIR components. This asymmetric design allows each sensing mechanism to function independently without interference while facilitating modular manufacturing assembly.
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
Enables touch devices to provide additional functions based on the amount of force applied, enhancing user interaction and device capabilities by accurately measuring force and its variations, thereby improving user experience and device effectiveness.
Implementation Method 1
Transmission of the infrared light is substantially totally reflected when the interface at the top surface is between the cover glass and air, while transmission is substantially attenuated when the interface at the top surface is between the cover glass and a user's finger
Implementation Method 2
infrared techniques, including frustrated total internal reflection (FTIR)
Implementation Method 3
capacitive sensing, including capacitive location sensing
Data Source
AI summary
Detecting force and touch using FTIR and capacitive location. FTIR determines applied force by the user's finger within infrared transmit lines on a touch device. A pattern of such lines determine optical coupling with the touch device. Capacitive sensing can determine (A) where the finger actually touches, so the touch device more accurately infers applied force; (B) whether finger touches shadow each other; (C) as a baseline for applied force; or (D) whether attenuated reflection is due to a current optical coupling, or is due to an earlier optical coupling, such as a smudge on the cover glass. If there is attenuated reflection without actual touching, the touch device can reset a baseline for applied force for the area in which that smudge remains. Infrared transmitters and receivers are positioned where they are not visible to a user, such as below a frame or mask for the cover glass.