Intelligent respiratory rate detection using disposable paper-based humidity sensor and precise peak-seeking algorithm

The traditional respiratory rate detection techniques, such as clinic monitor and ventilator, are often limited to specific application scenarios due to their complexity and high cost. In this work, we propose a disposable and cost-effective paper-based (PB) LiCl humidity sensor. The results show that the PB LiCl humidity sensor can detect a relative humidity (RH) range of 28.8–91.5 %, with alternating current impedance of 562.9 and direct current resistance response of 10,928.8 at 91.5 % RH (25°C). Notably, the incorporation of LiCl reduces the resistance of the paper material, which makes it easier for the circuit to obtain the resistance value. To achieve automatic recognition of respiratory rate, we propose a precise peak-seeking algorithm based on extreme value detection, addressing the baseline drift issue encountered in actual respiratory detection by humidity sensor. The corresponding circuit system is designed, which can accurately capture and analyze humidity changes caused by respiration, generate real-time respiratory response curves, and calculate respiratory rates, achieving intelligent respiratory rate detection. This work provides a useful reference for developing portable and low-cost respiratory detection equipment based on the disposable PB LiCl humidity sensor.