Printed Piezoelectric Foil for Multi-Touch Pressure Sensing
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Solution Overview
Problem
Current touch sensing technologies, such as optical, resistive, capacitive, and piezoelectric devices, face limitations in accurately tracking pressure, distinguishing between touch and pen inputs, and providing multi-touch and pressure sensing capabilities simultaneously.
Innovation Solution
A pressure-sensing input device utilizing a ferroelectric material with both piezoelectric and pyroelectric effects, featuring a sandwich structure of four layers that can be printed on flexible substrates, combining with high-resolution optical sensing foils to enable efficient tracking of hand and pen inputs, pressure changes, and hovering interactions, while reducing ghost points in multi-touch scenarios through orthogonal electrode grids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If resistive array-based sensors are used, then the device is inexpensive and energy-efficient, but the tracking resolution is limited to the space between the sensing lines
Solution Approach 1:
The sensor is divided into multiple independent sensing lines arranged in a grid pattern, where each line can independently detect touch events. This segmentation allows for high resolution tracking by creating numerous discrete sensing points across the surface, overcoming the limitation of conventional resistive sensors while maintaining cost-effectiveness through simplified manufacturing processes.
2Stability of the object's composition
If plane-type conductors with well-defined resistivity are used, then the electrodes provide stable conductivity, but the standard resistive touch panel concept is not suitable for pressure sensing
Solution Approach 1:
The sensing lines are designed to serve multiple functions: they act as both electrodes for capacitive touch detection and as pressure-sensing elements through their resistive properties. This multi-functionality allows the same structural element to enable both touch location detection and pressure measurement, eliminating the need for separate pressure sensing layers.
3Measurement precision
If capacitive touch sensors are used, then the device can detect touch location with high resolution, but it cannot measure pressure and relies on dielectric properties of the human body
Solution Approach 1:
The patent combines capacitive sensing lines with resistive pressure-sensing lines into a unified sensor structure. The capacitive lines provide high-resolution touch location detection, while the resistive lines measure pressure through changes in resistance. By merging these two sensing mechanisms, the system achieves both high-resolution positioning and pressure measurement capabilities simultaneously.
4Measurement precision
If state-of-the-art piezoelectric sensing devices are used, then pressure can be detected, but the devices are expensive due to inorganic piezoelectric materials and costly assembling processes
Solution Approach 1:
The patent changes the material parameter from inorganic piezoelectric ceramics to organic conductive polymer lines. These polymer lines exhibit piezoelectric properties and can be deposited using low-cost printing techniques on flexible substrates. This parameter change maintains pressure detection accuracy while dramatically reducing manufacturing costs and enabling flexible, wearable applications.
5Measurement precision
If state-of-the-art piezoelectric sensing devices are used, then pressure can be detected, but the devices provide only limited user interaction as motion-less finger detection is impossible
Solution Approach 1:
The sensing lines are designed to detect dynamic changes in both position and pressure simultaneously. By continuously monitoring resistance and capacitance changes along the lines, the system can distinguish between static pressure (finger resting on surface) and dynamic interactions (pen writing, multi-touch gestures). This dynamic sensing capability enables comprehensive user interaction detection including motionless finger detection through subtle pressure variations.
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 provides accurate and energy-efficient pressure sensing, effective separation of pen and touch inputs, and reliable multi-touch recognition, with enhanced sensitivity and durability, suitable for large-area, flexible surfaces, and various user interactions, including haptic and acoustic feedback.
Implementation Method 1
the piezoelectric material can be used for sensing pressures changes on large, flat and/or bended surfaces
Implementation Method 2
A pressure-sensing input device utilizing a ferroelectric material with both piezoelectric and pyroelectric effects
Data Source
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AI summary
There is provided an sensing device, comprising: a substrate; a sensor ink printed onto the substrate; a conductive polymer ink printed onto the sensor ink; a conductive carbon paste formed on the polymer ink; and a conductive silver ink printed on the conductive carbon paste. There is also provided a sensing device for processing a signal generated by the input device, the sensing device comprising: an operational amplifier to amplify the signal; a filter to filter signal noise from the signal; an adder to apply an offset and attenuation to the signal; a microcontroller comprising an analogue to digital converter to convert the signal into a digital output signal.