Piezoelectric Layer Touch Panel Pressure Sensing
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Solution Overview
Problem
Projected capacitance touch panels cannot sense pressure, failing to distinguish between light taps and heavy presses, and existing solutions for pressure sensing often require bulky electronics, complex production processes, or material fatigue.
Innovation Solution
A projected capacitance touch panel with a layer of piezoelectric material between electrodes, using a voltage-controlled signal source and front-end module with frequency-dependent filters to separate pressure and capacitance signals, allowing for simultaneous capacitive and pressure sensing without separate electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If projected capacitance touch panel uses glass exterior layer for durability, then surface hardness and scratch resistance are improved, but pressure sensing capability deteriorates
Solution Approach 1:
The patent combines capacitive touch sensing and pressure sensing into a single integrated system. The piezoelectric material layer is positioned between the glass exterior layer and the capacitive electrodes, allowing simultaneous detection of both touch position (via capacitance) and applied pressure (via piezoelectric signal), resolving the contradiction between maintaining hard glass surface and enabling pressure sensing
Solution Approach 2:
The piezoelectric material acts as an intermediary layer between the glass exterior and the sensing electrodes. This intermediary converts mechanical pressure into electrical signals that can be processed alongside capacitive touch data, enabling pressure sensing without compromising the glass surface integrity
2Measurement precision
If separate force sensors are used behind the touch panel, then pressure sensing capability is improved, but device complexity and bulk increase
Solution Approach 1:
The patent merges pressure sensing and capacitive touch sensing into a single integrated structure. The piezoelectric material layer is positioned between the glass exterior layer and the capacitive electrodes, allowing simultaneous detection of both touch position (via capacitance) and applied pressure (via piezoelectric signal), eliminating the need for separate force sensor systems
Solution Approach 2:
The piezoelectric material layer serves multiple functions: it acts as a structural component between the glass and electrodes, a pressure sensor that generates electrical signals under mechanical stress, and an integral part of the touch sensing system. This multi-functionality reduces overall device complexity while maintaining pressure sensing capability
3Measurement precision
If discrete pressure sensors are placed around the periphery, then pressure detection is improved, but ability to distinguish multiple touch pressures deteriorates
Solution Approach 1:
The patent segments the pressure sensing capability across multiple piezoelectric material locations corresponding to different electrode positions. Each electrode-piezoelectric interface independently detects local pressure, enabling the system to distinguish pressure at multiple separate touch points simultaneously, unlike periphery sensors that would require complex interpolation
4Measurement precision
If piezoelectric material is used for pressure sensing, then pressure measurement accuracy is improved, but signal separation from capacitance changes becomes difficult
Solution Approach 1:
The patent employs periodic scanning of electrodes to generate time-varying signals. By scanning electrodes in a systematic sequence, the system creates distinct temporal patterns for capacitive signals versus piezoelectric signals, enabling frequency-domain separation and accurate distinction between touch position and pressure information
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
Enables accurate pressure and capacitance measurement using a single input signal, integrating seamlessly into existing touch panels and reducing material fatigue, while maintaining a transparent and durable surface.
Implementation Method 1
a layer of piezoelectric material disposed between a plurality of first electrodes and at least one second electrode
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
An apparatus for combined capacitance and pressure sensing is described. The apparatus includes a multiplexer (75) having a plurality of inputs (76) and an output (F), a touch panel (29), and a front end module (3). The touch panel includes a layer structure (5; Fig.15) comprising one or more layers, each extending perpendicularly to a thickness direction, the one or more layers including a layer of piezoelectric material (10; Fig.15), the layer structure having first (6) and second (7; Fig.15) opposite faces, and the layer(s) arranged between the first and second faces such that the thickness direction of each layer is perpendicular to the first and second faces. The touch panel also includes a plurality of first electrodes (8) disposed on the first face, each first electrode connected to a respective input of the multiplexer. The touch panel also includes at least one second electrode (9) disposed on the second face.