Midair redirection of exhaled infectious aerosols toward the ceiling using upward acoustic streaming generated by reflected ultrasonic beams

Many contagious diseases, such as COVID-19, spread through aerosols that include pathogens. It has been demonstrated that avoiding exposure to those aerosols is important for suppressing pandemics. Conventional methods based on this strategy are the use of face masks, physical barriers, or personal ventilation (PV) systems. Besides those, the use of aerial acoustic streaming generated by ultrasound beams was proposed as another countermeasure with no physical constraints on users’ actions, which redirects the exhalations away from the opposing person to suppress direct exposure to aerosols. Although this method is valid, it is applicable to only two people facing each other because it requires a pair of ultrasound sources placed behind each user. In this study, we propose a countermeasure to aerosol infections, where ultrasound beams emitted from the phased array units of ultrasonic transducers mounted on the ceiling are reflected by the surface of tables or floors, and finally turn into upward acoustic streaming that redirects exhalations toward the ceiling before reaching other people there. This strategy does not limit the number of users or their positions because the upward acoustic streaming can aim at an arbitrary point between exhalations and the target people. In addition, the upward acoustic streaming is expected to expedite room ventilation as well, which was never addressed in the previous study. We experimentally demonstrated the effectiveness of our method for suppressing direct exposure to infectious aerosols in a manner that is robust to the positioning of both aerosol-exhaling and aerosol-receiving users.