Detecting and monitoring varieties of human activities is one of the most essential functions and design purposes of different kinds of wearable sensors. Apart from excellent sensitivity and durability, limited by the materials, most of the sensors reported in the literature are capable of detecting signals only on the basis of a sole mechanism. In this work, a dual-mode flexible sensor derived from a high-temperature-pyrolysized 3D carbon sponge (C-Sponge) was proposed as a peculiar sensor material that is able to detect human activities based on fundamentally different mechanisms, by either the triboelectric effect or the piezoresistive effect. The sensor generated an average open circuit voltage up to ∼2 V and short circuit current up to ∼70 nA when being used as self-powered triboelectric sensor, which was sufficiently sensitive for detecting finger touching and plantar pressure distribution of human feet. On the other hand, by incorporating MWCNT into the 3D structure, the sensor at piezoresistive mode exhibited a sensitivity improvement of nearly 20-fold, from less than 40% to more than 800%, and a durability improvement of more than 22-fold (240 000 cycles) compared with those of original C-Sponge fabricated at 1000 °C (10 800 cycles). All the experimental results indicated that the proposed flexible dual-mode sensor is potentially applicable as wearable sensors for human activity monitoring.
Keywords: 3D architecture; dual-mode; piezoresistive; tactile sensor; triboelectric self-power.