Dual-Range Capacitive MEMS Force Sensor for Touch Screens
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Solution Overview
Problem
Capacitive touch screens are limited in measuring touch force magnitude and are dependent on the conductive nature of the human body, restricting use with gloved hands or non-conductive styluses, and face challenges with sensitivity to electromagnetic fields and sensor size.
Innovation Solution
A dual-range capacitive force sensor with two types of elastic spacers, one highly flexible and the other stiffer, is used to measure touch forces over a wide range, allowing for pressure-responsive touch recognition independent of conductive materials and enabling multiple touch detection without increasing device dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single elastic spacer is used in a capacitive force sensor, then the sensor can measure forces in one range, but it cannot simultaneously provide high sensitivity for light touches and durability for heavy forces
Solution Approach 1:
The elastic spacer is divided into multiple segments with different stiffness values. The first segment has higher stiffness to withstand heavy forces, while the second segment has lower stiffness to detect light touches with high sensitivity. This segmentation allows the sensor to operate effectively across a wide force range without requiring separate sensors for different force magnitudes.
Solution Approach 2:
Different portions of the elastic spacer are assigned different mechanical properties (stiffness values). The first segment is designed with higher stiffness to provide structural support and durability, while the second segment is designed with lower stiffness to enhance sensitivity for light touch detection. This local differentiation of properties enables the sensor to simultaneously achieve both durability and sensitivity.
2Measurement precision
If the capacitive touch screen uses small capacitance changes for sensing, then it achieves high sensitivity, but it becomes highly sensitive to electromagnetic fields and limits the maximum screen size
Solution Approach 1:
The patent introduces a force sensing mechanism as an intermediary between the touch input and the capacitive sensing system. Instead of directly measuring small capacitance changes that are susceptible to electromagnetic interference, the system measures force through the deformation of elastic spacers. This intermediary force measurement approach provides robust sensing that is less sensitive to electromagnetic fields while maintaining the ability to detect touch inputs accurately.
3Adaptability or versatility
If a force sensing layer is added to the capacitive touch screen, then touch force magnitude can be measured, but the device complexity and electronic integration complexity increase
Solution Approach 1:
The patent combines the force sensing function with the existing capacitive touch screen structure by integrating elastic spacers into the current electrode assembly. Rather than adding a completely separate force sensing layer with its own independent reading circuit, the system utilizes the deformation of the elastic spacers to modulate the capacitance between existing electrodes, thereby measuring force through the existing capacitive sensing infrastructure and reducing electronic integration complexity.
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 sensor provides high sensitivity for light touches and durability for heavy forces, enabling capacitive touch screens to recognize inputs from non-conductive objects and reduce sensitivity to electromagnetic noise, while maintaining transparency and minimizing thickness.
Implementation Method 1
The sensor includes two types of the elastic spacers with different values of stiffness... The deformation of the elastic spacer minimizes the gap between the sensor electrodes and leads to a change in the nominal capacitance value of the sensor
Implementation Method 2
This change of capacitance is used to measure the magnitude of the touch force... the nominal capacitance value of the sensor is known and any changes due to an applied touch is predictable
Data Source
AI summary
A capacitive MEMS force sensor for touch recognition and force measurement in touch screens is provided. The sensor includes two planar conductive electrodes separated by a predetermined distance using an elastic spacer to define an initial capacitance value of the sensor. An applied external force deforms the elastic spacer and minimizes the gap between sensor electrodes to alter the nominal capacitance value. This change in capacitance is monitored to measure the magnitude of the touch force. The sensor includes two types of the elastic spacers with different values of stiffness to overcome the trade-off between sensitivity and dynamic range of force measurement. These elastic spacers are interposed between sensor electrodes and are offset with a height difference to provide two ranges of force measurement.