Capacitive Sensor Electrode Shape Optimization for Linear Force Response
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Solution Overview
Problem
Capacitive force sensors in input devices, such as touchpads and touchscreens, face challenges in accurately detecting low levels of applied force due to the exponential displacement response function when using uniformly rectangularly shaped electrodes, leading to undetectable changes in capacitance.
Innovation Solution
Optimizing the electrode shape by using slice lengths corresponding to gap distances between sensor electrodes, which are determined through a capacitive function optimization process, to define a sensor electrode pattern that matches a selected displacement response, thereby enhancing the detection of applied force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniformly rectangularly shaped electrodes are used, then the device structure is simple and easy to manufacture, but the displacement response becomes exponential causing low force levels to be undetectable
Solution Approach 1:
The electrode is divided into multiple slices along the gap distance direction, with each slice having a different length. This segmentation allows the electrode to achieve a linear displacement response function while maintaining manufacturability through standardized slicing processes.
Solution Approach 2:
Different portions of the electrode have different local properties - specifically, the slice lengths vary at different positions along the gap distance to achieve uniform displacement response across the electrode surface, rather than the exponential response of uniform rectangular electrodes.
2Ease of manufacture
If uniformly rectangularly shaped electrodes are used, then the manufacturing process is straightforward, but the displacement response function becomes exponential reducing detectability
Solution Approach 1:
The electrode pattern is segmented into multiple slices with progressively varying lengths, transforming the exponential displacement response into a linear one. This maintains ease of manufacture through systematic slicing while significantly improving force detection reliability across the full range of applied forces.
Solution Approach 2:
The electrode geometry parameters are changed from uniform dimensions to progressively varying slice lengths. This parameter modification transforms the displacement response function from exponential to linear, ensuring reliable detection of force levels throughout the operating range.
3Measurement precision
If the electrode shape is optimized with varying slice lengths, then the displacement response becomes linear improving force detection accuracy, but the electrode design complexity increases
Solution Approach 1:
The electrode is segmented into standardizable slices that can be manufactured using conventional processes. While the overall shape is optimized for linear response, the segmentation approach maintains design simplicity by breaking down the complex geometry into manageable, repeatable units.
Solution Approach 2:
The electrode design uses local quality variations in slice lengths to achieve linear displacement response. This localized optimization improves force detection accuracy without requiring complete redesign of the entire electrode system, maintaining reasonable design complexity.
4Ease of manufacture
If uniformly rectangular electrodes are used, then the manufacturing process is simple, but changes in capacitance at low force levels become undetectable
Solution Approach 1:
By segmenting the electrode into varying slice lengths, the capacitance response to applied force becomes linear rather than exponential. This transformation ensures that even small capacitance changes at low force levels produce detectable signals, while the segmented structure remains manufacturable.
Solution Approach 2:
The electrode employs local quality variations in slice lengths to enhance sensitivity at different force levels. This localized optimization ensures detectable capacitance changes across the full force range, particularly improving detection capability at low force levels while maintaining straightforward fabrication.
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 optimized sensor electrode pattern allows for more accurate response to applied force, improving the usability of input devices by ensuring detectability at low force levels and achieving a linear displacement response function.
Implementation Method 1
Capacitive force sensors include force sensor electrodes, a compressible layer, and an input surface. The force sensor electrodes, compressible layer, and input surface are arranged such that when force is applied to a surface, the compressible layer compresses. Compressing of the compressible layer causes a change in capacitance to be detected by the force sensor electrodes.
Data Source
AI summary
A method includes obtaining a capacitive function of ground plane displacement and gap distance, and optimizing, using the capacitive function, an optimization function to obtain multiple slice lengths. The slice lengths correspond to multiple gap distances between a first sensor electrode and a second sensor electrode. The method further includes defining a sensor electrode shape using slice lengths and gap distances, defining a sensor electrode pattern based on the sensor electrode shape, and storing the sensor electrode pattern.