Extremely Elastic Wearable Carbon Nanotube Fiber Strain Sensor for Monitoring of Human Motion

Abstract

The increasing demand for wearable electronic devices has made the development of highly elastic strain sensors that can monitor various physical parameters an essential factor for realizing next generation electronics. Here, we report an ultrahigh stretchable and wearable device fabricated from dry-spun carbon nanotube (CNT) fibers. Stretching the highly oriented CNT fibers grown on a flexible substrate (Ecoflex) induces a constant decrease in the conductive pathways and contact areas between nanotubes depending on the stretching distance; this enables CNT fibers to behave as highly sensitive strain sensors. Owing to its unique structure and mechanism, this device can be stretched by over 900% while retaining high sensitivity, responsiveness, and durability. Furthermore, the device with biaxially oriented CNT fiber arrays shows independent cross-sensitivity, which facilitates simultaneous measurement of strains along multiple axes. We demonstrated potential applications of the proposed device, such as strain gauge, single and multiaxial detecting motion sensors. These devices can be incorporated into various motion detecting systems where their applications are limited to their strain.

Extremely Stretchable Strain Sensors Based on Conductive Self‐Healing Dynamic Cross‐Links Hydrogels for Human‐Motion Detection

“…The high stretchability of both SWCNT/hydrogel and VHB tape allowed the self‐healing strain sensor to remain intact up to 1000% strain, the highest value for electronic strain sensor so far, to the best of our knowledge 43, 44, 45. The excellent performances of the device are derived from all parts of the device or their coordination with each other.…”

Nanomaterial‐Enabled Wearable Sensors for Healthcare

“…Wearable strain sensors based on the disconnection (sliding) have been fabricated in a number of ways such as depositing AuNPs onto PDMS, [115] embedding AgNWs into PDMS, [111] electrospinning Au nanotroughs onto PDMS, [116] mixing SWCNTs with self-healing hydrogel, [117] sandwiching SWCNTs between two PU-PEDOT:PSS electrodes, [46] aligning CNTs onto a substrate, [53,118] growing well-aligned ZnO NWs on the textile substrate, [119] laser-scribing graphene coated on PET substrate, [113] encapsulating graphene-nanocellulose nanopaper in PDMS, [51] and infusing graphene into rubber. [120] Tensile strain can decrease the overlapped area between nanomaterials and decrease the number of conductive pathways, leading to an increase in resistance.…”

“…Strain sensors fabricated by dry-spinning CNT fibers onto a prestrained (100%) Ecoflex substrate exhibited a GF of 0.54 for strain below 400% and 64 for strain between 400% and 960% (Figure 4a). [53] Very recently, SWCNT/hydrogel was reported to be able to detect strain as large as 1000% owing to the self-healing capability of the hydrogel. [117] GF of 0.24 for strain within 100% and 1.51 at 1000% strain was realized.…”

“…[23,[36][37][38] Solution based processing methods such as spray coating, [25,39,40] drop casting, [41][42][43][44][45] spin coating, [46,47] dip coating, [48] vacuum filtration, [49][50][51] and layer-by-layer assembly [52] were commonly used for fabrication of nanomaterial-based sensors. Direct spinning of CNTs onto a substrate or into yarns [53][54][55] and electrospinning of nanofibers or NWs were reported to produce fiber-like nanomaterials. [56][57][58][59] In addition, novel direct printing or writing techniques [60,61] such as inkjet printing, [62] gravure printing, [63,64] screen printing, [65][66][67] nozzle jet printing, [26] and direct writing [68,69] enabled the fabrication of wearable sensors that possess complex patterns with high resolution.…”

Ultrastretchable Fiber Sensor with High Sensitivity in Whole Workable Range for Wearable Electronics and Implantable Medicine

“…However, currently, very few stretchable strain sensors based on these materials simultaneously possess a large workable strain range and high sensitivity, which severely limits their applications. For example, an elastic wearable carbon nanotube fiber strain sensor can be maximally stretched over 900%; however, over a 0–400% strain range, and the gauge factor (GF) was only 0.54 16. On the contrary, a graphite‐based strain sensor achieved a high GF of 536.6, which was mainly attributed to the generated cracks and overlaps of contacting areas between graphite‐slices.…”