Non-Conductive Mirror Opaque White Coating for Capacitive Sensors
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Solution Overview
Problem
Capacitive sensors in portable digital devices face performance issues due to the high dielectric constant of titanium dioxide pigments in thick white coatings, which affect sensitivity and accuracy, especially when contamination and particle voids are present.
Innovation Solution
A thin opaque non-conductive white coating stack is implemented, featuring a mirror structure with interleaved dielectric layers of low dielectric constant materials like silicon oxide and niobium pentoxide, reducing the thickness of the white coating and improving sensor sensitivity by reflecting light and minimizing the distance between the sensor and the object being sensed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thick white coating with high percentage of titanium dioxide pigment is used to achieve adequate optical density and conceal the sensor, then the optical opacity is improved, but the sensor sensitivity deteriorates due to increased distance and high dielectric constant affecting capacitive performance
Solution Approach 1:
The white coating is segmented into multiple thin layers (first white coating layer, second white coating layer) with a mirror structure inserted between them. This segmentation allows the total thickness to be reduced while maintaining optical opacity, as each layer is thinner and the mirror structure provides additional light reflection to enhance concealment of the sensor.
Solution Approach 2:
A non-conductive mirror structure is introduced as an intermediary element between the sensor and the white coating layers. This mirror structure serves dual purposes: it reflects light to enhance optical opacity and concealment, while being non-conductive it does not interfere with the capacitive sensor performance, thus resolving the contradiction between opacity and sensitivity.
2Object-affected harmful factors
If the thickness of the white coating is increased to improve optical density, then the concealment of sensor is improved, but the sensor sensitivity deteriorates due to increased distance between sensor and sensed object
Solution Approach 1:
The white coating structure is segmented into multiple thin layers with a mirror structure in between, replacing a single thick coating. This segmentation achieves the same or better concealment effect while reducing the overall thickness and distance from the sensor to the outer surface, thereby maintaining sensor sensitivity.
Solution Approach 2:
The optical concealment function is achieved not by increasing mechanical thickness of the white coating, but by introducing a mirror structure that uses light reflection (optical mechanism) to enhance opacity. This substitution allows thin coating layers to provide adequate concealment without increasing distance and compromising sensor sensitivity.
3Object-affected harmful factors
If a thick white coating is used to achieve adequate optical density, then the optical opacity is improved, but the sensor signal quality deteriorates due to high dielectric constant of titanium dioxide pigment
Solution Approach 1:
A non-conductive mirror structure is introduced as an intermediary that provides the necessary light reflection for optical opacity without introducing high dielectric constant materials. This mirror structure replaces or supplements the need for thick titanium dioxide-based white coating, thereby maintaining signal quality while achieving adequate opacity.
Solution Approach 2:
The dielectric constant parameter of the coating structure is changed by reducing the thickness of titanium dioxide-based white coating layers and replacing some of their optical function with a mirror structure. This parameter change reduces the overall dielectric constant impact on the capacitive sensor while maintaining optical opacity through the combined effect of thin white layers and mirror reflection.
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 solution enhances the sensitivity and signal quality of capacitive sensors by reducing the thickness of the white coating to 20-25 μm, making the sensor more responsive to touch and improving the overall performance while maintaining adequate optical density.
Implementation Method 1
The non-conductive mirror structure reflects light and may help reduce the thickness of the white coating
Implementation Method 2
The non-conductive mirror structure includes a number of first dielectric layers having a first refractive index interleaved with second dielectric layers having a second refractive index
Data Source
AI summary
An opaque cover is provided for a capacitive sensor. The cover includes a transparent substrate, and at least one white coating layer including white pigments disposed over at least one portion of the transparent substrate. The cover also includes a non-conductive mirror structure disposed over the at least one white coating layer. The non-conductive mirror structure includes a number of first dielectric layers having a first refractive index interleaved with second dielectric layers having a second refractive index. The first and second dielectric layers have dielectric constants below a threshold.