Multiaxial and Transparent Strain Sensors Based on Synergetically Reinforced and Orthogonally Cracked Hetero‐Nanocrystal Solids

Abstract

Wearable strain sensors are widely researched as core components in electronic skin. However, their limited capability of detecting only a single axial strain, and their low sensitivity, stability, opacity, and high production costs hinder their use in advanced applications. Herein, multiaxially highly sensitive, optically transparent, chemically stable, and solution‐processed strain sensors are demonstrated. Transparent indium tin oxide and zinc oxide nanocrystals serve as metallic and insulating components in a metal–insulator matrix and as active materials for strain gauges. Synergetic sensitivity‐ and stability‐reinforcing agents are developed using a transparent SU‐8 polymer to enhance the sensitivity and encapsulate the devices, elevating the gauge factor up to over 3000 by blocking the reconnection of cracks caused by the Poisson effect. Cross‐shaped patterns with an orthogonal crack strategy are developed to detect a complex multiaxial strain, efficiently distinguishing strains applied in various directions with high sensitivity and selectivity. Finally, all‐transparent wearable strain sensors with Ag nanowire electrodes are fabricated using an all‐solution process, which effectively measure not only the human motion or emotion, but also the multiaxial strains occurring during human motion in real time. The strategies can provide a pathway to realize cost‐effective and high‐performance wearable sensors for advanced applications such as bio‐integrated devices.

Quantifying the Contributing Factors toward Signal Fatigue in Nanocomposite Strain Sensors

“…From the model presented, we can now understand on a fundamental level not only what causes conditioning in nanocomposite strain sensors but also why some materials, though not presenting any obvious signs of materials degradation, never report a steady signal. However, it can also be said that there are several examples of nanocomposites reporting little to no discernible tread in (R/R0)R,C with C. From this work, this can also now be attributed to their superior mechanical hysteresis as a result of fibre formation, [63][64][65][66] use of lament layers [63][64][65][66] and micro-structuring [67][68][69][70] which appears to quench effects of stress softening on electromechanical response. However, these morphologies, in particular the fibres, generally have larger values for Young's modulus which has been noted by the author in prior work as being a vital parameter of nanocomposites that must be minimised to facilitate applications as bodily sensors.…”

Quantifying the Piezoresistive Mechanism in High-Performance Printed Graphene Strain Sensors

“…Our best gauge factors (∼350) also compare favorably to polymer-based nanocomposite sensors. A 2019 study of 200 nanocomposite strain sensors ranked the reported G -values, which ranged from 0.01 to 2600 . Our best sensors would rank fifth on this scale.…”

“…A 2019 study of 200 nanocomposite strain sensors 12 ranked the reported G-values, which ranged from 0.01 to 2600. 22 Our best sensors would rank fifth on this scale. While nanosheet networks and nanocomposite films are cheap and easy to prepare, more sophisticated methods have been used to make the highest sensitivity published sensors.…”

Ultrasonically Patterning Silver Nanowire–Acrylate Composite for Highly Sensitive and Transparent Strain Sensors Based on Parallel Cracks

“…It can be inferred from these results that the AgNW strain sensor with a narrower straight line is more sensitive with a strain range tunable by the length. The strain sensor possesses the highest GF (10,486) among the previously reported transparent strain sensors in a relatively large strain range (8%) at high transparency (∼90%). ,,,,,,− Indeed, the GF is still predominant among other opaque strain sensors (Table S2), ,,,,,− as illustrated in Figure h. Actually, the GF of the strain sensor can be further increased by increasing the concentration of TEH in the composite due to the brittleness of TEH (Figure S6b).…”