Research on Flexible Sensors for Wearable Devices: A Review

Abstract

With the development of new materials and the trend of miniaturization of smart devices, wearable devices are playing an increasingly important role in people's lives and occupying a larger market share. Meanwhile, the operation of wearable devices is based on the flexible sensors inside them. Although the development of flexible sensors has been very rapid in the more than 20 years since entering the 21st century, facing the booming market and demand at present, the development of flexible sensors still faces many challenges such as more miniaturization, higher integration, greater sustainability, high precision, and more efficient energy saving. This paper aims to summarize the development of flexible sensors, look forward to the future development of such devices, and provide a reference for researchers.

Keywords: biosignal; flexible sensors; longtime monitoring; real-time feedback; smart devices; wearable devices.

Figure 1

Shows the application of flexible sensors. (a) Shows the profile view of a single micromirror [46]. (b) Includes the functionalities of wearable multi-functional sensors [4]. (c) The classification of acoustic sensors based on different principles [12]. (d) Typical applications of flexible sensors [37].

Figure 2

The diagram of mechanism of pressure sensor: (a) the diagram of working mechanism; (b) these curves show the sensitivity according to the different structures; (c) the new transfer technique [17].

Figure 3

The diagram of mechanisms of some bio-sensors. (a) The illustration of the fabrication process [24]. (b) The schematic overview of the sensor embedded in the tube [53]. (c) Change in strain and resistance caused by the movement of the wrist [56].

Figure 4

The diagram for some biosignals detection. (a) The different responses of sensor on different finger movements [6]. (b) Smart system for fall warning [6]. (c) Sweat analysis with mechanical deformation [79]. (d) Different curves within different sleep states [25].

Figure 5

The diagram for some mechanism of materials: (a) steps in the fabrication of the double-side EPS-PVDFnfs device [21]; (b) shows GO samples coated onto the surface of the silk [74].