Stretchable Capacitive Sensor With Variable Stiffness Reinforcement
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Solution Overview
Problem
Conductive wearable sensors, particularly capacitive force, pressure, and touch sensors, face reliability issues due to mechanical stress changes, especially when using conformable and flexible materials, leading to inconsistent performance and durability problems.
Innovation Solution
The design incorporates a flexible and stretchable capacitive sensor structure with a reinforcement structure that enhances resilience by varying the in-plane stiffness between different parts of the sensor, allowing for improved attachment and movement of conductive wires, and utilizing a compressible layer to distribute mechanical deformations effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conformable wiring with larger line width is used to connect to microelectronic chip input/output channels, then ease of manufacture is improved, but connection reliability deteriorates due to insufficient wiring separation and contact precision
Solution Approach 1:
A flexible circuit board is introduced as an intermediary component between the conformable sheet with thick wiring and the microelectronic chip. The flexible circuit board performs dual functions: at a first location, its wiring is sufficiently narrow to contact the input/output channels of the microelectronic chip with precision; at a second location, its wiring is separated to contact the wires of the conformable wiring. This intermediary resolves the contradiction by enabling both easy manufacture (through conformable sheet) and reliable connection (through flexible circuit board's precise wiring).
2Ease of operation
If flexible circuit board and conformable sheet are used to improve conformability and wiring flexibility, then ease of operation is improved, but mechanical reliability deteriorates when shape changes occur
Solution Approach 1:
The invention anticipates mechanical stress and shape changes by designing a layered structure with a flexible circuit board positioned between the rigid microelectronic chip and the conformable sheet. This structure beforehand cushions and distributes mechanical deformations, preventing direct stress transmission to the chip while maintaining electrical connections. The flexible circuit board's wiring can separate and flex without compromising the rigid chip, thus preserving mechanical reliability during shape changes.
3Reliability
If wiring line width is reduced to improve contact precision with input/output channels, then connection reliability is improved, but ease of manufacture deteriorates due to manufacturing limitations
Solution Approach 1:
The wiring system is segmented into two distinct parts: the conformable sheet with thicker, easier-to-manufacture wiring, and the flexible circuit board with narrower, precision wiring. This segmentation allows each component to be optimized independently - the conformable sheet for ease of manufacture and the flexible circuit board for contact precision. The two segments are then connected, combining the advantages of both approaches while avoiding their respective limitations.
Data Source
Figure 1~2d
Figure 3a1~3a4
Figure 3b1~3b4
AI summary
A capacitive sensor (100) comprising a first electrically conductive wire (222) that is flexible and stretchable, a compressible layer (310), an integral reinforcement structure (320), and a first electrode (224) for measuring a capacitance and coupled to the first electrically conductive wire (222). The first electrically conductive wire (222) is attached to a first joint (226) for connecting the first wire (222) to another electrically conductive structure (400), such as a flexible circuit board (410) or a connector (405). The capacitive sensor (100) is dividable to a first part (100a) of the capacitive sensor (100) and to a second part (100b) of the capacitive sensor (100), the first (100a) and second (100b) parts extending through the sensor (100) in a direction (Sz) of thickness of the sensor. The first electrically conductive wire (222) extends from the first joint (226) via the second part (100b) of sensor (100) to the first part (100a) of the sensor (100) and further to the first electrode (224). A resilience of the second part (100b) is improved. Therefore, [A] the second part (100b) of the sensor (100) comprises a second part (310b) of the compressible layer (310), wherein an in-plane stiffness of the second part (310b) of the compressible layer (310) is less than an in-plane stiffness of the first part (310a) of the compressible layer (310) or [B] the compressible layer (310) does not extend to the second part (100b) of the sensor (100).