Ultra‐Stretchable Porous Fiber‐Shaped Strain Sensor with Exponential Response in Full Sensing Range and Excellent Anti‐Interference Ability toward Buckling, Torsion, Temperature, and Humidity

Abstract

transistors, [5,6] flexible displays, [7,8] energy devices, [9][10][11] mechanical sensors, [12][13][14][15][16] etc. Stretchable conductive fibrous composites as a vital part of stretchable devices are very promising for wearable electronics in the near future as they can be easily manufactured in abundance and facilely knitted into garments. [17,18] Currently, stretchable fibers are requested to possess high sensitivity and stretchability to meet the applications such as health monitoring, and e-skins. [19,20] Here, the main arguments accounting for the properties of strain sensors are sensitivity, stretchability, and stability.Fibrous strain sensors have gained great development on the tuning of microstructure and sensing properties, recently. [21] Zhang et al. prepared a carbonized silk fiber as the main component of a wearable and ultra-stretchable strain sensor (500% workable strain). [22] Compared with the natural stretchable fibers, wet-spinning is a universal method for industrial manufacture of serial fibers for many decades, providing a general strategy for producing high performance fibers. [23] Previously, Tang et al. constructed an Ecoflex/multi-walled carbon nanotubes (MWCNTs) coresheath fiber, which exhibited high stretchability (above 300% strain), good stability (over 10 000 cycles), low hysteresis, and favorable hydrophobicity. [20] Lee et al. fabricated a thermoplastic As a crucial element for wearable devices, high-performance strain sensors have been spotlighted as an ideal strategy to develop machine-human interfaces and healthcare systems. It still remains a huge challenge to construct flexible strain sensors with equational response in a broad range. Herein, highly stretchable multi-walled carbon nanotubes (MWCNTs)-decorated thermoplastic polyurethane (TPU) fibers with a porous microstructure are produced through a scalable and facile strategy by wet-spinning and ultrasonication. The fiber is composed of pure TPU fibers with MWCNTs decorated on the surface. The porous fiber is then assembled as a strain sensor. Interestingly, the effective MWCNTs distribution on the TPU fiber enables exponential sensing over the whole strain range. The sensor possesses a high gauge factor (GF, 102 at 300% strain), very large workable sensing range (300% strain), excellent durability (10 000 cycles), light weight (0.85 g cm −3 ), and fast response (200 ms). The as-prepared strain sensor exhibits excellent insensitive properties toward buckling, torsion, temperature, and humidity stimuli. Based on the high sensing performance, the fiber-shaped strain sensor detects human movements precisely by directly attaching to skin or embedding in garments, demonstrating huge potential in human-machine interfaces, health monitoring application, etc.Recently, stretchable devices have attracted lots of researchers on the basis of their significant impact and promotion in various fields, including wearable electronics, [1,2] actuators, [3,4] Adv.

Materials, Electrical Performance, Mechanisms, Applications, and Manufacturing Approaches for Flexible Strain Sensors

“…Our group proposed a highly sensitive strain sensor for sensing of facial muscle stretch [ 95 ]. In addition, other low strain motions, such as swallowing, [ 134 , 179 , 191 ] voice vibrations, [ 164 , 192 , 193 ] pulsing, [ 29 , 135 ] blowing, [ 194 , 195 ] and neck joint motion [ 196 , 197 ] biomedical test have also been presented by different composites. On the other hand, large strain movements, including finger [ 198 , 199 ] and knee bending [ 200 , 201 ], wrist [ 60 ] and elbow motions [ 202 , 203 ], plantar distribution [ 204 ], respiration rate [ 205 ], and some derived sports behaviors requires high stretchability and better sensitivity of the sensors.…”

Tunable and Nacre‐Mimetic Multifunctional Electronic Skins for Highly Stretchable Contact‐Noncontact Sensing

“…Thermogravimetric analysis (TGA) of pure TPU nanofiber mats and the e‐skin is performed to investigate the filler concentration and thermal stability of the material. Here, the conductive filler content is calculated through the formula as follows: [ 44 ] where m t , m s , and m p represent the weight of the e‐skin, conductive filler, and TPU mats, respectively; a and b are the weight ratios of the residual of e‐skin and TPU nanofiber mats, respectively. Based on these formulas, the conductive filler content ω s in e‐skin is calculated: …”

Fiber‐Shaped Electronic Devices

“…The use of MWCNTs on the TPU fiber provided great sensing capabilities with a high gauge factor and a large workable sensing range at 300% strain, a very good durability of 10 000 cycles, a light weight of 0.85 g cm −3 , and a fast response of 200 ms, while being insensitive to torsion, temperature, and humidity changes. [ 268 ] A fibrous strain sensor for detecting various human movements was recently developed via coaxial wet‐spun approach by Yue et al. It exhibited a stretchable black/thermoplastic PU with porous and core–sheath structure.…”