Passive wireless respiratory sensor

Monitoring respiratory characteristics is an important method to monitor sleep respiratory diseases such as obstructive sleep apnea syndrome (OSAS). In this letter, a passive wireless respiratory sensor is developed, which is based on a surface acoustic wave (SAW) microsensor using graphene oxide as a sensitive layer. The developed sensor is placed on the upper lip below the nose, which monitors human's breathing by detecting the humidity changes while inhale and exhale. To meet the fast response requirement of human respiratory, the effect of the thicknesses of graphene oxide (GO) films is investigated. Results show that the response and recovery time of the sensor can achieve 0.4 and 1.4 s, respectively, with the optimized 70-nm thickness of GO. The respiratory rate that the sensing system can measure is greater than 33 breaths per minute, outcompeting the average number of breaths per minute from an adult (i.e. 16-20 breaths per minute). The new sensor proposed here paves the way for the fabrication of high-performance and low-cost respiratory sensors in human breathing monitoring in real life.