Fig. 1. Schematic diagram of pressure sensor fabrication procedure. (a) The fabrication of microstructured PDMS sponge by mixing PDMS, NaCl, and CAM. (b) The preparation of CNTs/GNP Micro@Sponge by layer-by-layer electrostatic self-assembly. (c) The pressure sensor is packaged with ITO-PET film.

Fig. 2. SEM picture of PDMS sponge fabricated without sandpapers treatment (a) and PDMS sponge fabricated by sandpaper treatment (b), the red-circled area was an indentation induced by the convex structure of sandpaper on the sponge surface. SEM images of CNTs-coated sponge (c) and CNTs/GNP-coated sponge (d). (e-h) corresponding high magnification image. 3D profile of sponge surface without sandpaper treated (i) and with sandpaper-treated (j).

Fig. 3. (a-c) Schematic diagram of sensor loading tiny and high pressure. Circuit diagram of sensor mechanism for without pressure (d) and with pressure (e). RTC, RS and RBC correspond to the top contact resistance, the CNTs/GNP Micro@Sponge resistance and the bottom contact resistance, respectively.

Fig. 4. (a) Current response curve at a pressure range from 0 to 160 kPa, the inset was a partial enlargement of the pressure range of 50-110 kPa. (b) Response time at 50 kPa. (c) Contraction of current signals when loading 20 kPa and 50 kPa. (d) Different pressure detection range from 10 kPa to 40 kPa for a mutative current pulse. (e) Pressure testing at the pressure of 80 kPa, 120 kPa and 140 kPa. (f) The cyclic current response to 100 kPa at different frequencies, 0.125, 0.25, and 0.3 Hz, respectively. (g) Sensing stability test of cyclic current response for 1400 cycles at loading 40 kPa, inset: magnified view of 10 cycles for the (374-384 cycles) and (1080-1090 cycles) stages, respectively.

Fig. 5. The real-time response detection signal of the pressure sensor to the lighter weight object loading, (a) paper (9 mg), (b) screw (80 mg) and (c) rotor (4 g), (d) I-V changing curve when sensor loading different weights (0-100 g). Current responses of finger touching (e), breathing (f) and wrist pulse (g). (h) Current response for pressing the sponge at 0.7 MPa pressure for 6 cycles. (i) The sensitivity and sensing range of the CNTs/GNP Micro@Sponge pressure sensor are compared with other studies.

Fig. 6. Current signals of durability test for press (a), bending (b), twist (c) of the sensor. (d) Photographe of different fingertip force tests. (e) Display of different finger squeezing produced by different gestures. (f) Schematic diagram of 3 × 3 panel sensors arrays for space detection. (g) Photograph of 3 × 3 sponge integrated detection. (h) The corresponding pressure distribution mapping from the sensing responses.