Fig. 1. (a) Molecular structure of graphene monolayer^[12]; (b) Schematic diagram of carbon nanotube decompression to obtain graphene; (c) Schematic diagram of epitaxial growth method; (d) Schematic diagram of graphene preparation by Redox process^[21].

Fig. 2. Manufacturing process of LC-MEMS pressure sensor. (a) Silicon substrate; (b) KOH etching and PMMA/Gr film transfer; (c) Upper plate aluminum sputtering; (d) Glass substrate; (e) Sputtering and curing of microcoils; (f) Silicon-glass bonding^[20].

Fig. 3. (a) Process of graphene-based sensors with paper substrate^[32]; (b) Biological microstructure of the human epidermis, and the spines beneath the epidermis being a key factor in high sensitivity;(c) Surface of the spinous body shown by epidermal microscope; (d) Three-dimensional morphology of sandpaper; (e) Manufacturing process of graphene pressure sensors; (f) ‍Optical micrographs of patterned PDMS; (g) Optical micrograph of GO coating on PDMS; (h) Optical micrograph of No.150 sandpaper after high temperature reduction^[40].

Fig. 4. (a) Preparation process of biomimetic porous graphene-SBR pressure sensor; (b,c) Folded and twisted photos of biomimetic porous graphene-SBR pressure sensor; (d) Photo of biomimetic porous graphene-SBR pressure sensor^[45].

Fig. 5. 3D structure of the sensor^[46]

Fig. 6. Step by step synthesis of rGO/α-Fe₂O₃ nanocomposites^[47]

Fig. 7. Characteristic description of pressure response. (a) I-V curves under different pressures; (b) Relative conductivity changes with pressure, the dotted line is the fitting result;(c) Response to pulse pressure, the response rise time (t_r) was 2 μs, and the relaxation decline time (t_f) was 3 μs; (d) Stability of pressure response during 4 000 cycles of loading-unloading at a pressure of 28 Pa, the operating voltage was 5 V^[9].

Fig. 8. Human motion monitoring applications of flexible pressure sensors reported in various research articles, such as finger flexion^[61], elbow flexion^[57], knee flexion^[59], vocal cord vibration^[60], cheek movement^{[63, 65]}, swallowing^[59], exhaling or inhaling ^[63], walking and running^[7].

Fig. 9. Schematic diagram of structure and mechanis of reduced GO textiles deposited by electrostatic discharge^[68]

Fig. 10. A sensor attached to the femur joint of the toy robot monitors the response of the sensor through wireless communication on the mobile phone when the sensor is touched by the hand^[73]

Fig. 11. Dynamic response of GO/Gr composite films. (a) Response of output current under loading pressure of 100 Hz; (b) High frequency voltage response of GO/Gr composite bilayer with loading frequencies of 2, 8, 10 kHz, respectively. The curve follows the input pressure signal^[28].