Willow-like portable triboelectric respiration sensor based on polyethylenimine-assisted CO2 capture

Real-time bio-signal detecting devices are critical for obtaining important physiological signals and recognizing respiratory diseases; the respiration sensor is one such important device. In this paper, human respiration is measured by using the triboelectric effect that converts the ambient mechanical energy into electrical energy by using a three-dimensional printed triboelectric respiration sensor (TRS). This TRS has a willow-like fluorinated ethylene propylene film between the right and left electrode plates; it generates electricity using a simple contact-separation motion. A 10 wt% solution of polyethylenimine, which enables carbon dioxide capturing, is coated and evaporated only on the right electrode of the TRS to distinguish the inspiration and expiration conditions. The distances between the adjacent electrodes, the air gap between the electrodes, and the top of the container in the TRS were systematically optimized by using the finite element method. The sensitivity to the air flow rate is characterized by different gradients of the output voltage. Analyzing the output voltage allows the TRS to identify four types of respirations: strong, weak, long, and short. This portable and self-powered respiration sensor will open new horizons for portable TRS devices because of its low cost and facile fabrication that uses three-dimensional printing technology. This device will also reduce the distress experienced by patients who are recovering from their respiratory disorders.