A highly sensitive and flexible pressure sensor with electrodes and elastomeric interlayer containing silver nanowires

Abstract

The next-generation application of pressure sensors is gradually being extended to include electronic artificial skin (e-skin), wearable devices, humanoid robotics and smart prosthetics. In these advanced applications, high sensing capability is an essential feature for high performance. Although surface patterning treatments and some special elastomeric interlayers have been applied to improve sensitivity, the process is complex and this inevitably raises the cost and is an obstacle to large-scale production. In the present study a simple printing process without complex patterning has been used for constructing the sensor, and an interlayer is employed comprising elastomeric composites filled with silver nanowires. By increasing the relative permittivity, εr, of the composite interlayer induced by compression at high nanowire concentration, it has been possible to achieve a maximum sensitivity of 5.54 kPa(-1). The improvement in sensitivity did not sacrifice or undermine the other features of the sensor. Thanks to the silver nanowire electrodes, the sensor is flexible and stable after 200 cycles at a bending radius of 2 mm, and exhibits outstanding reproducibility without hysteresis under similar pressure pulses. The sensor has been readily integrated onto an adhesive bandage and has been successful in detecting human movements. In addition to measuring pressure in direct contact, non-contact pressures such as air flow can also be detected.

Nanomaterial‐Enabled Wearable Sensors for Healthcare

“…Another strategy to increase the effective dielectric constant is to add conductive fillers into the dielectric just below the percolation threshold. [153] Compression shortens the distance between the fillers, leading to an increased dielectric constant under pressure. AgNWs, for example, were added into PU as the filler.…”

“…AgNWs, for example, were added into PU as the filler. [153] Using AgNW/PU composite as the dielectric layer, ultrahigh capacitive sensitivity of 5.54 kPa −1 for pressure Reproduced with permission. [142] c) Schematic illustration of a single pixel of the active matrix pressure sensor for instantaneous pressure visualization.…”

“…[41,121,153] Figure 10a highlights a CNT based strain sensor used for detection of various knee motions during extending, flexing, marching, squatting, and jumping. [121] Both intensity and frequency of the motions can be identified.…”

“…Substantial efforts were devoted to improving the pressure sensitivity by using a softer material as the dielectric, or a dielectric that can show increasing dielectric constant under pressure. [152][153][154] Highly deformable dielectric materials can be realized by using commercial porous tapes, [43] creating microstructures in elastomers using a mold (e.g., the surface of matte glass, [155] a micromachined Si mold, [131] or the surface of lotus leaf [156] ), creating porous elastomers using sugar cubes as the template, [157] or fabricating buckled structures through prestretching and releasing. [158] When the air gap is compressed, the effective dielectric constant is increased under pressure, as the dielectric constant of air is smaller than that of the dielectric material used for the sensor.…”

“…Wearable strain sensors with a large strain detection range are widely used to monitor body motions, including finger bending, [41,52,120,123,126] forearm muscle movements, [21,44,52,103,120,123,153] and knee motions. [41,121,153] Figure 10a highlights a CNT based strain sensor used for detection of various knee motions during extending, flexing, marching, squatting, and jumping.…”