A flexible pressure sensor array based on an ionic gel for pulse detection†

Flexible pressure sensors are widely applied in tactile sensing, gait testing, and wearable devices due to their flexibility and repeatability. However, measuring weaker signals needs ultrahigh sensitivity and an extensive detection range. Herein, we propose a novel ionic–electronic sensor featuring a cavity structure made up of Ag electrodes, a PDMS space layer, and an ionic gel. The latter was created by combining polyvinyl alcohol (PVA), chitosan (CS), and 1-ethyl-3-methylimidazole chloride (ionic liquid) after three freeze–thaw cycles. This sensor demonstrated remarkable maximum sensitivity of up to 48 584.56 kPa⁻¹ within the range of 1–10 kPa, a broad pressure range of 0.1–200 kPa, and excellent repeatability over 1000 loading–unloading cycles. Owing to a capacitive effect, a sensor and array sensor were used to detect pulse signals and space pressure distribution, respectively. The signals of each channel of the array sensor were collected through a data-acquisition system. The main peak of the pulse wave was represented by a histogram, and a three-dimensional (3D) pulse wave shape was reconstructed. The 3D pulse wave provides the possibility for the extraction of waveform characteristics. In conclusion, our sensor could be used in portable wearable and flexible smart electronics.