Wide Linear Range Strain Sensor Enabled by the Non‐Newtonian Fluid for Bio‐Signals Monitoring

Abstract

Wearable strain sensors with a wide linear range (i.e., sensors established on piezoresistive materials) are highly desirable in detection of human motion, as well as for the evaluation of physical rehabilitation. However, most piezoresistive devices possess poor linearity in the working range due to the exponential collapse of the solid conductive structures under high strain, thus limiting their batch applications. Herein, a strain sensor with a broad linear detection range by virtue of a non‐Newtonian fluid (NNF) is reported. Graphitized carbon black (GCB) is employed to create the conductive network and subsequently embedded in defatted cellulose nanofiber (CNF)‐insulating framework. After the GCB/CNF liquid is encapsulated into the elastic polymer, the conductivity shows excellent response to tensile strain (gauge factor = 5.47). The conductivity does not drop sharply under large deformation, and the device reveals a linear response in the whole sensing range up to 100%. The sensor, which exhibits a stable performance with excellent sensitivity, durability, and low hysteresis, is applicable for real‐time monitoring bio‐signals, including pulse, muscle, and joint movements. All these results inspire a simple but promising route to design high‐performance wearable devices.

Tough, anti-drying and thermoplastic hydrogels consisting of biofriendly resources for a wide linear range and fast response strain sensor

“…7,8 Most of these strain sensors are resistive sensors, which present the advantages of low cost, easy readout, and anti-interference. 9,10 Many recent studies focus on enhancing their sensitivity and stretchability to have a wider working range. [11][12][13][14] However, as their working range is extended, nonlinearity, which is one of the fundamental drawbacks of resistive sensors, becomes increasingly severe.…”

Thermoplastic charge-transfer hydrogels for highly sensitive strain and temperature sensors

“…15 Most hydrogel sensors are resistive sensors, which are anti-interference and low-cost. 16,17 The sensing mechanism of hydrogel resistive sensors is the breaking and deformation of the conductive hydrogel network by external stimuli, which affects electron or ion migration and changes the resistance. 18 Therefore, the ease of breaking or deforming the conductive networks has a significant impact on the sensitivity of resistive hydrogel sensors.…”

A self-compensating stretchable conductor based on a viscous fluid for wide-range flexible sensors

“…GCB and NaCl, resulting in a more favorable conductivity (30.6 S m −1 ). Moreover, when the conductivity of GCB becomes weak due to its piezoresistive effect under stretching, 30 the ionic carriers from NaCl will enhance the conductivity because of the shutter effect. 31 Therefore, the SCD was achieved in keeping a stable conductivity over a large tensile range.…”