A Wide-Range-Response Piezoresistive–Capacitive Dual-Sensing Breathable Sensor with Spherical-Shell Network of MWCNTs for Motion Detection and Language Assistance

Abstract

It is still a challenge for flexible electronic materials to realize integrated strain sensors with a large linear working range, high sensitivity, good response durability, good skin affinity and good air permeability. In this paper, we present a simple and scalable porous piezoresistive/capacitive dual-mode sensor with a porous structure in polydimethylsiloxane (PDMS) and with multi-walled carbon nanotubes (MWCNTs) embedded on its internal surface to form a three-dimensional spherical-shell-structured conductive network. Thanks to the unique spherical-shell conductive network of MWCNTs and the uniform elastic deformation of the cross-linked PDMS porous structure under compression, our sensor offers a dual piezoresistive/capacitive strain-sensing capability, a wide pressure response range (1–520 kPa), a very large linear response region (95%), excellent response stability and durability (98% of initial performance after 1000 compression cycles). Multi-walled carbon nanotubes were coated on the surface of refined sugar particles by continuous agitation. Ultrasonic PDMS solidified with crystals was attached to the multi-walled carbon nanotubes. After the crystals were dissolved, the multi-walled carbon nanotubes were attached to the porous surface of the PDMS, forming a three-dimensional spherical-shell-structure network. The porosity of the porous PDMS was 53.9%. The large linear induction range was mainly related to the good conductive network of the MWCNTs in the porous structure of the crosslinked PDMS and the elasticity of the material, which ensured the uniform deformation of the porous structure under compression. The porous conductive polymer flexible sensor prepared by us can be assembled into a wearable sensor with good human motion detection ability. For example, human movement can be detected by responding to stress in the joints of the fingers, elbows, knees, plantar, etc., during movement. Finally, our sensors can also be used for simple gesture and sign language recognition, as well as speech recognition by monitoring facial muscle activity. This can play a role in improving communication and the transfer of information between people, especially in facilitating the lives of people with disabilities.

Sensitivity–stability trade-off in conductive foam-based pressure sensors

“…We have summarized some recent research results on flexible pressure sensors (Table S2, ESI†). In comparison to other foam-based pressure sensors reported 31,36–42 in the literature (Fig. 5i), the PMM pressure sensor possessed a high sensitivity of 14.16 kPa −1 , a fast response time and extraordinary durability showing great feasibility and practicability in the field of tactile sensors.…”

Ultra-wide range tri-mode flexible pressure sensor

“…A detailed parameter comparison is shown in table S1, listing the different modes of single-mode and dual-mode sensors. In terms of response range, the three-mode sensor exceeds the pressure range listed in the table and is only slightly less sensitive than the other sensors [40][41][42][43][44][45][46][47]. The range from 0.91 Pa to 30 MPa is achieved by integrating the triboelectric effect, piezoresistive effect, and ML effect (figure 5(b)).…”

Flexible Strain Sensors for Walking Gait Monitoring

“…Zhang S.M. et al [35] proposed a simple and scalable porous piezoresistive/capacitive dual-mode sensor with a porous structure of polydimethylsiloxane (PDMS) with a porosity of 53.9% and multi-walled carbon nanotubes (MWCNTs) embedded on the inner surface to form a conductive network with a three-dimensional spherical shell structure. Due to the unique spherical shell conductive network and uniform elastic deformation compression of the cross-linked PDMS porous structure, the sensor provides piezoresistive/capacitive strain sensing capability, a vast pressure response range (1-520 kPa), and linear response region (95%), good response stability and durability (98% of initial performance after 1000 compression cycles).…”