Touch Sensor Back Surface Capacitance Suppression
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Solution Overview
Problem
Wearable devices that are thin and designed for direct skin contact face malfunctions due to changes in capacitance detected from the back surface, limiting the sensor's space and functionality.
Innovation Solution
A touch sensor with a sensor electrode layer, a front surface protective layer, and a back surface protective layer, where the back surface protective layer includes a suppressing member to prevent detection of changes in capacitance from the opposite side, using an insulating portion with a thickness at least three times that of the front surface protective layer or lower permittivity than the front surface protective layer, and a conductive portion connected to ground to block electrostatic actions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the device is made thin for direct skin contact, then wearability and comfort are improved, but the sensor space is limited and capacitance detection from the back surface causes malfunctions
Solution Approach 1:
The device is segmented into distinct functional layers: a front surface protective layer, a sensor electrode layer, and a back surface protective layer with suppressing members. This segmentation allows each layer to perform its specific function - the suppressing members in the back surface protective layer specifically block capacitance detection from the back surface, while maintaining the overall thin profile for wearability.
Solution Approach 2:
The back surface protective layer acts as an intermediary between the sensor electrode layer and the external environment. By incorporating suppressing members (insulating portions or conductive portions connected to ground) in this intermediate layer, the patent blocks the harmful capacitance detection from the back surface before it reaches the sensor electrodes, thereby preventing malfunctions.
2Measurement precision
If the sensor electrode layer is exposed, then touch sensitivity is improved, but the sensor becomes vulnerable to external force such as extension and contraction
Solution Approach 1:
The patent uses flexible protective layers (front surface protective layer and back surface protective layer) that can withstand extension and contraction forces. These flexible protective layers enclose and protect the sensor electrode layer, maintaining touch sensitivity while providing mechanical strength and resistance to external forces during wearable use.
Solution Approach 2:
The protective layers are constructed using composite materials that combine flexibility, durability, and protective properties. The front surface protective layer and back surface protective layer are made of materials that can resist external forces while maintaining the flexibility needed for wearable applications, thereby protecting the sensor electrode layer without compromising touch sensitivity.
3Reliability
If a suppressing member with large thickness is used to block back surface capacitance detection, then malfunction prevention is improved, but the overall device thickness increases
Solution Approach 1:
The patent optimizes the thickness parameter of the suppressing members (insulating portions) to achieve effective capacitance blocking while maintaining a thin overall device profile. By carefully controlling the thickness parameter and using materials with appropriate permittivity, the suppressing members effectively prevent back surface capacitance detection without significantly increasing device thickness.
Solution Approach 2:
The suppressing members are strategically positioned and sized to provide capacitance blocking only where needed - on the back surface protective layer opposite the sensor electrodes. This localized approach ensures effective malfunction prevention without requiring the entire device to be thick, maintaining wearability while preventing malfunctions.
4Ease of manufacture
If metal members are used for the touch sensor, then manufacturing is simplified, but the device generates electrostatic actions that interfere with capacitance detection
Solution Approach 1:
The patent converts the potentially harmful electrostatic actions into a beneficial configuration by using conductive portions connected to ground. These grounded conductive portions act as electrostatic shields that actively manage and dissipate electrostatic charges, preventing interference with capacitance detection while still allowing the use of metal members for manufacturing simplicity.
Solution Approach 2:
The conductive portions connected to ground serve as intermediaries that manage electrostatic actions. By providing a controlled path to ground, these conductive portions mediate between the metal members and the sensor electrodes, preventing harmful electrostatic interference while maintaining the manufacturing advantages of metal components.
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 reduces malfunctions by distinguishing signals from the front and back surfaces, ensuring accurate input operations even when the device is in contact with the body, thereby enhancing the reliability of wearable touch sensors and bracelet-type devices.
Implementation Method 1
the back surface protective layer includes a suppressing member configured to prevent easy detection of a change in capacitance from the opposite side of the operation surface
Implementation Method 2
the suppressing member may include an insulating portion having a permittivity lower than a permittivity of the front surface protective layer
Implementation Method 3
a conductive portion connected to ground to block electrostatic actions
Data Source
AI summary
A touch sensor includes a sensor electrode layer having a plurality of sensor electrodes, a front surface protective layer disposed on an operation surface side, and a back surface protective layer disposed on an opposite side of the operation surface, the front surface protective layer and the back surface protective layer being stacked together. In the touch sensor, the back surface protective layer includes a suppressing member configured to prevent easy detection of a change in capacitance from the opposite side of the operation surface.