Overall design of open-mask respiratory rate sensor: (A) inside, (B) outside.|@|~(^,^)~|@|Demonstration of the sensor being worn by a person: (A) front, (B) side.|@|~(^,^)~|@|Working mechanism of the sensor: (A) before exhalation, (B) during exhalation.|@|~(^,^)~|@|Respiration rate measured using the sensor.|@|~(^,^)~|@|Sensor data while nodding and shaking the head side- to-side.|@|~(^,^)~|@|Sensor data while turning the head side-to-side.