Contents I. Introduction
With the progress of materials science and microelectronics manufacturing technology in recent years, flexible and stretchable electronic composite materials have facilitated the development of various smart devices with potential applications in sensors [1], [2], electronic skin [3], [4], soft robots [5], artificial limb [6] and supercapacitor [7], [8], etc. These aforementioned devices have received extensive attention as one of core components in the next-generation electronics. They can be directly attached to human skin or embedded in various fabrics to monitor the physiological and physical data [9]. The mechanical deformation produced by the body motion causes the change of the sensor output electrical signal, which can be applied in real-time human motion monitoring, human-machine interaction and healthcare [10]. In order to be able to expand the application of different human motion monitoring, the sensor usually needs to meet the requirements of high ductility, high sensitivity (high gauge factor (GF)), fast response/recovery, linear response, long-term stability and even self-healing [11]. The low detection limit of the sensor is necessary to monitor small deformations such as pulse [12], [13] and breath [14], and the wide detection range is useful for different kinds of joint bending.
