Superelastic, Sensitive, and Low Hysteresis Flexible Strain Sensor Based on Wave-Patterned Liquid Metal for Human Activity Monitoring

Abstract

Flexible strain sensors have been widely used in wearable electronic devices for body physical parameter capturing. However, regardless of the stretchability of the sensing material, the resolution of small strain changes or the hysteresis between loading/unloading states has always limited the various applications of these sensors. In this paper, a microfluidic flexible strain sensor was achieved by introducing liquid metal eutectic gallium indium (EGaIn) embedded into a wave-shaped microchannel elastomeric matrix (300 μm width × 70 μm height). The microfluidic sensor can withstand a strain of up to 320%, and the hysteresis performance was also improved from 6.79 to 1.02% by the wave-patterned structure which can restrain the viscoelasticity of the elastomer effectively. Moreover, an enhanced wave-shaped strain sensor was fabricated by increasing the length of the microfluidic channel; it has high sensitivity (GF = 4.91) and resolution, and even as low as 0.09% strain change could be detected, which is capable of resolving microdeformation; besides, the enhanced wave-shaped strain sensor exhibits quick response time (t = 116 ms), long-term stability, and durability under periodic dynamic load. As an example of potential applications, the enhanced flexible sensor showed excellent mechanical compliance and was successfully applied as a conceptual wearable device for distinctively monitoring various kinds of human body and robot activities, such as the different states of the finger, neck, breathing chest, robot's joint, and so forth. The flexible waveshaped strain sensor has great promising applications for wearable electronics, motion recognition, healthcare, and soft robotics.

Nacre‐Inspired, Liquid Metal‐Based Ultrasensitive Electronic Skin by Spatially Regulated Cracking Strategy

“…The combination of these two cracking strategies contributed to a much improved sensor performance. Compared with previously reported liquid metal‐based counterparts (Figure 1f; Table S2, Supporting Information), [ 17,29,35–40 ] this sensor design resulted in two orders of magnitude of sensitivity amplification in term of maximum and overall gauge factor ( GF , Note 1, Supporting Information), while maintaining a wide working range (>85%). As shown in Figure 1g, to our knowledge, this is the first liquid metal‐based sensor that rivals the state‐of‐art counterparts on sensitivity.…”

“…Working range can be regulated by adjusting liquid metal pattern configurations. f,g) Compared with previous liquid metal‐based counterparts, [ 17,29,35–40 ] the proposed sensor improves the sensitivity by two orders of magnitude. By this improvement, liquid metal‐based sensors rival the state‐of‐art counterparts.…”

Printable, Highly Sensitive Flexible Temperature Sensors for Human Body Temperature Monitoring: A Review

“…The fabricate of flexible sensors requires the sensor itself to be flexible, stretchable, and ductile and the substrates and circuits on which it depends. Specific stretch and stretch characteristics to adapt to the adhesion on the human body surface, common flexible substrates are usually processed into a film, such as polydimethylsiloxane (PDMS) [ 17 – 20 ], polyimide (PI) [ 21 , 22 ], polyurethane (PU) [ 23 ], polyethylene terephthalate (PET) [ 24 , 25 ], polyvinyl alcohol(PVA) [ 26 ], polyvinyl butyral(PVB) [ 27 ], paper [ 28 , 29 ], silicone rubber [ 5 , 30 , 31 ], and more skin-friendly biodegradable materials can also be used, such as pectin [ 32 ], cotton, silk [ 33 ], and other cellulose materials [ 34 , 35 ].…”

Ready-to-wear strain sensing gloves for human motion sensing

“…Progress in the development of soft and conformable strain sensors has used conductive materials including metal nanowires ( Amjadi et al., 2014 ; Gong et al, 2015 ), carbon nanotubes ( Ryu et al., ; Yamada et al., 2011 ), metal films ( Filiatrault et al., 2015 ), graphene ( Li et al., 2016 ; Wang et al., 2014 ), liquid metal ( Chen et al., 2020 ; Gao et al., 2019 ; Li and Lee, 2017 ), and ionic liquid ( Choi et al., 2017 ; Chossat et al, 2015 ; Zhang et al., 2017 ) on stretchable substrates such as siloxane elastomers ( Ryu et al., ; Wang et al., 2018 ), latex ( Gong et al, 2015 ), and polyurethane ( Ding et al., 2016 ; Jeon et al., 2017 ). Strain sensors can employ resistive, capacitive, or optical sensing mechanisms, where a change in one of these properties can be correlated to strain ( Souri et al., 2020 ).…”