Stretchable Capacitive Sensors of Torsion, Strain, and Touch Using Double Helix Liquid Metal Fibers

• Published in: Advanced functional materials Vol. 27; no. 20
• Main Authors: Cooper, Christopher B., Arutselvan, Kuralamudhan, Liu, Ying, Armstrong, Daniel, Lin, Yiliang, Khan, Mohammad Rashed, Genzer, Jan, Dickey, Michael D.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 25.05.2017
• Subjects: Alloys; Automation; Bundling; Capacitance; capacitive sensing; Capillaries; Casting; Deformation mechanisms; double helix; Elastomers; Elongation; Extreme values; Fibers; Industrial robots; Liquid metals; Manufacturing engineering; Materials science; Metal fibers; metallic wires; Robotics; room temperature fabrication; Sensors; Strain; Textiles; Torsion; Touch; Twisting
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201605630

Soft and stretchable sensors have the potential to be incorporated into soft robotics and conformal electronics. Liquid metals represent a promising class of materials for creating these sensors because they can undergo large deformations while retaining electrical continuity. Incorporating liquid metal into hollow elastomeric capillaries results in fibers that can integrate with textiles, comply with complex surfaces, and be mass produced at high speeds. Liquid metal is injected into the core of hollow and extremely stretchable elastomeric fibers and the resulting fibers are intertwined into a helix to fabricate capacitive sensors of torsion, strain, and touch. Twisting or elongating the fibers changes the geometry and, thus, the capacitance between the fibers in a predictable way. These sensors offer a simple mechanism to measure torsion up to 800 rad m−1—two orders of magnitude higher than current torsion sensors. These intertwined fibers can also sense strain capacitively. In a complementary embodiment, the fibers are injected with different lengths of liquid metal to create sensors capable of distinguishing touch along the length of a small bundle of fibers via self‐capacitance. The three capacitive‐based modes of sensing described here may enable new sensing applications that employ the unique attributes of stretchable fibers. Intertwined elastomeric fibers filled with liquid metal form stretchable sensors of torsion, strain, and touch. Sensing is enabled by capacitance changes between (1) adjacent fibers due to deformation or (2) fibers and fingers due to touch. The simplicity of the sensing mechanism, the versatile fiber geometry, and the soft properties offer potential applications in stretchable electronics, wearables, and soft robotics.