Anisotropic, Wrinkled, and Crack-Bridging Structure for Ultrasensitive, Highly Selective Multidirectional Strain Sensors

Abstract

Flexible multidirectional strain sensors are crucial to accurately determining the complex strain states involved in emerging sensing applications. Although considerable efforts have been made to construct anisotropic structures for improved selective sensing capabilities, existing anisotropic sensors suffer from a trade-off between high sensitivity and high stretchability with acceptable linearity. Here, an ultrasensitive, highly selective multidirectional sensor is developed by rational design of functionally different anisotropic layers. The bilayer sensor consists of an aligned carbon nanotube (CNT) array assembled on top of a periodically wrinkled and cracked CNT–graphene oxide film. The transversely aligned CNT layer bridge the underlying longitudinal microcracks to effectively discourage their propagation even when highly stretched, leading to superior sensitivity with a gauge factor of 287.6 across a broad linear working range of up to 100% strain. The wrinkles generated through a pre-straining/releasing routine in the direction transverse to CNT alignment is responsible for exceptional selectivity of 6.3, to the benefit of accurate detection of loading directions by the multidirectional sensor. This work proposes a unique approach to leveraging the inherent merits of two cross-influential anisotropic structures to resolve the trade-off among sensitivity, selectivity, and stretchability, demonstrating promising applications in full-range, multi-axis human motion detection for wearable electronics and smart robotics.

Flexible and highly‐sensitive pressure sensor based on controllably oxidized MXene

“…[24][25][26] Moreover, the orientations of the active materials significantly affect the sensing performance of the pressure sensor, as confirmed by the anisotropic arrangement of wrinkles. 27 Notably, the intrinsic electronic characteristics of the active sensitive materials play a critical role in determining the sensitivity of the sensors in addition to their nano/ microstructures. Studies have proven that an active material with proper conductivity is beneficial for enhancing the sensitivity of a pressure sensor, whereas excessive electrical conductivity limits the sensitivity.…”

“…For instance, the sensitivity of an MXene‐based pressure sensor can be improved by expanding the layer spacing between the nanosheets using compatible additive agents such as cellulose and silk protein, which mainly converts the 2D planar structure into a three dimensional (3D) porous structure 24–26 . Moreover, the orientations of the active materials significantly affect the sensing performance of the pressure sensor, as confirmed by the anisotropic arrangement of wrinkles 27 . Notably, the intrinsic electronic characteristics of the active sensitive materials play a critical role in determining the sensitivity of the sensors in addition to their nano/microstructures.…”

Textile-Based Mechanical Sensors: A Review

“…So far, a lot of work has been carried out on the developing and research of TMSs to improve the sensing performance of the devices, such as sensitivity, response range, response time, stability, etc., because these properties determine the practical application capabilities of the sensors [75]. Sensing performance can be improved by introducing special geometric structures, such as microarrays [76,77], microcracks [78], micropatterns [79,80], pleated structures [81,82], porous structures [83,84], spiral structures [85,86], etc. The innovation of materials is also a major key point to improve the sensing performance.…”

“…The formula for sensitivity is S = (∆X/X 0 )/Y, where S represents the sensitivity, X 0 represents the initial value of the electrical signal, resistance, capacitance, voltage, etc., ∆X represents the amount of change in the electrical signal, and Y represents the mechanical stimulus applied to the sensor, such as pressure, strain, etc. The usual methods to improve sensitivity include the introduction of microstructures [78], the use of new sensing materials [80], and the employment of multilayer structures [91]. Li et al [92] prepared a folded core-sheath structure fiber strain sensor by pre-stretching and releasing ultra-light MWCNTs/themoplasticelastomer (TPE) composite film wrapped TPE fiber core.…”

Scientific Developments and New Technological Trajectories in Sensor Research

“…One main example is smart sensors, which co-evolve through complex interaction with artificial intelligence technologies, Bluetooth technology, medical technologies, cloud computing, etc. [ 20 , 22 , 31 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ]. New studies show that smart sensors are crucial elements for the Internet of Things [ 43 , 45 , 46 , 47 , 48 , 49 , 50 ].…”