Wearable Flexible Strain Sensor Based on Three-Dimensional Wavy Laser-Induced Graphene and Silicone Rubber.

Lixiong Huang,Ziming Zhu,Wei Gao,Weimin Huang,Peixuan Wu,Rouxi Chen,Nian Cai,Feiyu Fang,Han Wang

doi:10.3390/s20154266

Abstract

Laser-induced graphene (LIG) has the advantages of one-step fabrication, prominent mechanical performance, as well as high conductivity; it acts as the ideal material to fabricate flexible strain sensors. In this study, a wearable flexible strain sensor consisting of three-dimensional (3D) wavy LIG and silicone rubber was reported. With a laser to scan on a polyimide film, 3D wavy LIG could be synthesized on the wavy surface of a mold. The wavy-LIG strain sensor was developed by transferring LIG to silicone rubber substrate and then packaging. For stress concentration, the ultimate strain primarily took place in the troughs of wavy LIG, resulting in higher sensitivity and less damage to LIG during stretching. As a result, the wavy-LIG strain sensor achieved high sensitivity (gauge factor was 37.8 in a range from 0% to 31.8%, better than the planar-LIG sensor), low hysteresis (1.39%) and wide working range (from 0% to 47.7%). The wavy-LIG strain sensor had a stable and rapid dynamic response; its reversibility and repeatability were demonstrated. After 5000 cycles, the signal peak varied by only 2.32%, demonstrating the long-term durability. Besides, its applications in detecting facial skin expansion, muscle movement, and joint movement, were discussed. It is considered a simple, efficient, and low-cost method to fabricate a flexible strain sensor with high sensitivity and structural robustness. Furthermore, the wavy-LIG strain senor can be developed into wearable sensing devices for virtual/augmented reality or electronic skin.

Highlights

We proposed a technique to fabricate a flexible strain sensor with high sensitivity and structural robustness, which was based on the 3D wavy Laser-induced graphene (LIG) and silicone rubber
With a laser to scan on PI film on the wavy surface of a mold, the 3D wavy LIG was synthesized
After LIG was transferred to silicone rubber substrate and package operation was finished, the wavy-LIG strain sensor was fabricated

Summary

Introduction

Flexible strain sensor with prominent performance is required to detect the interaction between the irregular object and tiny external stimuli, which has been extensively employed in a variety of Sensors 2020, 20, 4266; doi:10.3390/s20154266 www.mdpi.com/journal/sensors. There is a simple method to prepare a strain sensor with a 3D wavy structure by synthesizing the active material on the wavy surface of a mold and transferring it to an elastomeric substrate. LIG can be synthesized on a wavy surface by laser scanning and transferred to an elastomeric substrate (like PDMS). We have developed a flexible strain sensor based on the 3D wavy LIG and silicone rubber, which had high sensitivity and structural robustness. The PI film was attached fully to the wavy surface of a mold, and a CO2 infrared laser was used to scan on PI film for the synthesis of LIG. The wavy-LIG strain sensor was available with a laser to scan on PI film attached to the wavy surface of a mold and by transferring LIG to a silicone rubber substrate. The volume ratio of LIG/silicone was 33.55:3866.45

The Preparation of Wavy-LIG Strain Sensor

The Characterization of Properties

Results and Discussions

Applications

Conclusions