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

Highlights: • 3D printed triboelectric respiration sensor (TRS) detects the human breathing with a fluorinated ethylene propylene film. • Polyethylenimine solution was coated on the right electrode to distinguish expiration from inspiration. • Finite element method was employed to optimize the structure for enhancing the velocity intensity of the laminar flow. • Arduino sensing system was implemented to represent the respiration level as a practical application of the TRS. -- Abstract: 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.