Wearable and Transparent Capacitive Strain Sensor with High Sensitivity Based on Patterned Ag Nanowire Networks

Abstract

In this study, a transparent and stretchable thin-film capacitive strain sensor based on patterned Ag nanowire networks (AgNWs) was successfully fabricated. The AgNWs were patterned using a capillary force lithography (CFL) method and were embedded onto the surface of the polydimethylsiloxane substrate. The strain (ε) sensitivity of the capacitive strain sensor was controlled and enhanced by patterning the AgNWs into electrodes with an interdigitated shape. The interdigitated capacitive strain sensor (ICSS) is expected to have -1.57 gauge factor (GF) at 30% ε by calculation, which is much higher than the sensitivity of typical parallel-plate-type capacitive strain sensors. Because of the interdigitated pattern of the electrodes, the GF of the ICSS was increased up to -2.0. The ICSS had no hysteresis behavior up to ε values of 15% and showed stable ε sensing performance during the repeated stretching test at ε values of 10% for 1000 cycles. Furthermore, there was no cross talk between ε and pressure sensing in the AgNW-based ICSS, which was found to be insensitive to externally applied pressure. The ICSS was then used to detect the finger and wrist muscle motions of the human body to simulate its application to large and small ε sensing.

Significance of Nanomaterials in Wearables: A Review on Wearable Actuators and Sensors

“…A typical capacitive sensor is composed of a dielectric layer sandwiched between two electrodes, whose thickness varies upon stretching. [135][136][137] In order to obtain higher mechanical sensitivity, higher stretchable dielectric layer materials with smaller mechanical modulus are needed, such as PDMS, PU, and Ecoflex. In order to achieve conformal skin attachment, the electrodes of the sensor must meet the requirement of being stretchable.…”

“…2019, 31, 1805921 Figure 7. [137] Copyright 2017, American Chemical Society. Reproduced with permission.…”

“…[136] Furthermore, multidimensional strain sensor based on uniform prestrained Ag NW percolation network films with sandwich-structure achieved excellent capacitive response in the axial and perpendicular directional strain. [137] When compared with resistant strain sensors, the capacitive strain sensors are more suitable for large strain monitoring because of their lower sensitivity. It is noticeable that the sensor embedded in a glove can distinguish and map the strain distribution at the joint for hand grip motion.…”

“…[134] Particularly, various AgNW composites with advanced structures are intensively utilized in stretchable capacitive sensors by virtue of their cost effectiveness, high length-diameter ratio, ultrahigh conductivity, and good transparency. [135][136][137] In order to obtain higher mechanical sensitivity, higher stretchable dielectric layer materials with smaller mechanical modulus are needed, such as PDMS, PU, and Ecoflex. Using as the wearable .…”

Emerging Novel Metal Electrodes for Photovoltaic Applications

“…[157] Meanwhile, the as-coated metal NWs without any posttreatment generally have weak adhesion with the substrate, which allows the metal NWs can be selectively removed or transferred to another substrate by a patterned tape or stamp. [362] By using the photomask, patterned metal nanowire transparent electrode can also be achieved through direct exposure by high pulse laser, contributed by the photothermal effect. Under the irradiation of pulse laser with proper power, the metal NWs will be welded together and gradually embedded into the polymer substrate, while the metal NWs without light irradiation can easily be removed by solvent or tape due to the poor bonding between nanowire and polymer substrate.…”