Simultaneous in situ temperature and relative humidity monitoring in mechanical ventilators using an array of functionalised optical fibre long period grating sensors

An array of optical fibre long period gratings (LPGs) has been demonstrated for biomedical application to monitor temperature and relative humidity (RH) changes in the air delivered by a mechanical ventilator operating in different modes. The LPG array consists of two gratings, where one was kept bare to monitor the temperature change and the second was modified with 10 layers of silica nanoparticles to measure relative humidity. A mesoporous film was deposited on the surface of an optical fibre LPG using the layer-by-layer method. The sensor was calibrated in a bench model against a commercially available temperature and relative humidity sensor and sensitivity of the sensor was 0.46 ± 0.01 nm/ oC and 0.53 nm/RH%, respectively. The tip of the sensor array was modified with reflection mirror and placed inside an endotracheal tube (ETT) and tested in typical clinical equipment to enable the in-situ real-time monitoring of humidity and temperature. Temperature and RH changes associated with the breathing frequency of 8 and 15 breaths per minute were successfully monitored using developed sensor array