A flexible piezoresistive pressure sensor with micro-papillae structure for high sensitivity and wide detection range

Flexible pressure sensor is essential in various applications, including health monitoring, soft robots, and human machine interfaces. However, it is a challenge to fabricate high-performance flexible pressure sensor with high sensitivity and wide detection range. Herein, inspired by the microstructure of skin epidermis, a flexible piezoresistive pressure sensor with micro-papillae structure is proposed. Polydimethylsiloxane (PDMS) with rough surface molded from abrasive paper is utilized as the flexible substrate. Then, the conductive multiwalled carbon nanotube (MWCNT) film is deposited on the prepared substrate via spray-coating method to form MWCNT-PDMS membrane. A piezoresistive pressure sensor is obtained by putting two as-prepared membranes face-to-face. For comparison, a sensor with flat PDMS is prepared through the same method. Results show that the micro-papillae structure pressure sensor achieves a 5.79-fold increase in pressure sensitivity (11.93 kPa^-1) compared to that of the pressure sensor with flat PDMS (2.06 kPa^-1). Meanwhile, the structured pressure sensor exhibits a wide detection range (0.04-107 kPa), rapid response (179 ms), and excellent stability over 1000 cycles. Furthermore, finite element analysis (FEA) is conducted to investigate the influence of micropapillae structure on the sensing performance of sensor. Under force loading, a homogeneous stress distribution of the sensor with flat PDMS is observed, while the stress of the sensor with micro-papillae structure is concentrated on the micro-papillae, which enhances the sensitivity of sensor. Finally, the structured pressure sensor is utilized to monitor human physiological signals and different human motions, including breathing rate, feet movement, and finger bending.