Bio-inspired mask filters with breathing resistance control*

As the COVID-19 pandemic progresses, awareness of airborne virus-contamination and the importance of wearing a mask have increased dramatically. To minimize viral exposure for a long time, masks should be able to filter out sufficiently small droplets and have less breathing resistance. In this study, we proposed a 3D tortuous mask filter inspired by animal's nasal cavity. Based on Stokes number, our proposed filter with a 1 mm-width channel of a 1.8 tortuosity can capture small droplet particles of 5 µm or larger. Also, we demonstrated a system that monitors the user's breathing by a pressure sensor and controls an additional mask filter that opens and closes according to the level of breathing. When the pressure sensor catches the exceeding threshold, the regulator opens the additional filter to make human breathing easier. The performance of the mask filters and breathing regulator system was evaluated through a piston setup that imitated the human respiratory. Using this robotic system, the respiratory resistance and face-seal leakage rate were measured at the normal human breathing rate (15~100 LPM).