Capacitive Touch Sensor Light Guide for Interference-Free Illumination
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Solution Overview
Problem
Capacitive touch-sensitive systems face challenges in providing user feedback due to interference between electrical signals and light sources, particularly when trying to illuminate capacitive sensing pads, which increases costs and complexity.
Innovation Solution
A capacitive sensing apparatus with a light guide that separates the light source from the capacitive sensing area, using a light scattering means to guide light to the sensing area, thereby minimizing interference and allowing for uniform illumination without disrupting the capacitive sensing field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a light source is placed close to the capacitive sensing area for illumination, then illumination intensity is improved, but electrical interference with the capacitive sensing field increases
Solution Approach 1:
The device is divided into separate functional zones: the light source is positioned at a distance from the capacitive sensing area, with the light guide acting as an intermediary structure. This spatial segmentation allows the light source to illuminate the sensing area without its electrical components interfering with the capacitive field.
Solution Approach 2:
The light guide serves as an intermediary element between the light source and the capacitive sensing area. It transports light from the spaced-apart light source to the sensing region without allowing electrical interference to reach the sensitive capacitive field.
2Illumination intensity
If transparent capacitive sensing pads are used on a separate substrate for backlighting, then illumination is achieved, but manufacturing complexity and connection difficulty increase
Solution Approach 1:
The light guide is integrated directly with the capacitive sensing pad structure, combining the illumination function with the sensing substrate. This eliminates the need for separate transparent pads on different substrates and simplifies the electrical connections between the light source and sensing elements.
Solution Approach 2:
The capacitive sensing pad substrate serves dual functions: it acts as both the sensing element and the light guide structure. This multi-functionality reduces the number of separate components and simplifies manufacturing while maintaining both sensing and illumination capabilities.
3Reliability
If the light source is spaced apart from the capacitive sensing area, then electrical interference is reduced, but direct illumination efficiency decreases
Solution Approach 1:
The light guide utilizes three-dimensional light propagation paths including internal reflections and refraction to efficiently transport light from the spaced-apart source to the sensing area. This dimensional approach to light guidance maintains high efficiency despite the increased source-to-target distance.
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 effective user feedback through uniform illumination while maintaining the integrity of the capacitive sensing field, reducing costs and complexity by avoiding direct electrical connections and interference, and allowing for robust and attractive design options in touch-sensitive displays.
Implementation Method 1
the light guide is arranged to guide light from the light source to the light scattering means
Data Source
AI summary
A capacitive sensing apparatus is described that incorporates a light guide having a light scattering means for illumination of the apparatus. The apparatus has a capacitive sensor mounted on a substrate that provides a capacitive sensing area for generating an electric field that emanates from the apparatus. A light source is arranged in optical communication with the light scattering means via the light guide. This arrangement acts to mitigate the effects of interference between the capacitive sensor and the light source. When an opaque substrate is employed an air gap is located between the substrate and the light guide so as to provide a substantially uniform illumination across the light guide. Appropriate selection of the refractive indices of the light guide, ng, and a transparent substrate, ns, provides the same desired uniform illumination in alternative embodiments. The capacitive sensing apparatus finds particular application within a touch sensitive display.