At present, there are mainly two types of capacitive pressure sensors based on ordinary capacitance and electrical double layer (EDL) capacitance. However, few researchers have combined these two types of capacitors in pressure sensing to improve the dynamic range of a sensor under pressure. Here, we fabricated a capacitive pressure sensor with an asymmetric structure based on poly(vinylidene fluoride-co-hexafluoropropylene) using a simple electrospinning process. A layer of mixed ionic nanofiber membrane and a layer of pure nanofiber membrane were stacked and used as the dielectric layer of the sensor. Due to the porous structure and non-stickiness of the pure nanofiber membrane, it can be penetrated by the mixed ionic nanofiber membrane under pressure, realizing the reversible conversion from ordinary capacitance to EDL capacitance, thereby achieving a great change in the capacitance value. The sensitivities of the sensor are 55.66 and 24.72 kPa-1 in the pressure ranges of 0-31.11 and 31.11-66.67 kPa, respectively, with good cycle stability, fast loading-unloading response time, and an ultra-low pressure detection limit as low as 0.087 Pa. Finally, this sensor was used for the detection of human physiological signals, and the sensor would have potential applications in the fields of human tactile sensing systems, bionic robots, and wearable devices.
Keywords: capacitive sensor; electrostatic spinning; nanofiber membrane; pressure detection; wearable devices.