Fiber Bragg Grating Measuring System for Simultaneous Monitoring of Temperature and Humidity in Mechanical Ventilation

Abstract

During mechanical ventilation, the humidification of the dry air delivered by the mechanical ventilator is recommended. Among several solutions, heated wire humidifiers (HWHs) have gained large acceptance to be used in this field. The aim of this work is to fabricate a measuring system based on fiber Bragg grating (FBG) for the simultaneous monitoring of gas relative humidity (RH) and temperature, intended to be used for providing feedback to the HWHs’ control. This solution can be implemented using an array of two FBGs having a different center wavelength. Regarding RH monitoring, three sensors have been fabricated by coating an FBG with two different moisture-sensitive and biocompatible materials: the first two sensors were fabricated by coating the grating with a 3 mm × 3 mm layer of agar and agarose; to investigate the influence of the coating thickness to the sensor response, a third sensor was developed with a 5 mm × 5 mm layer of agar. The sensors have been assessed in a wide range of RH (up to 95%) during both an ascending and a subsequent descending phase. Only the response of the 3 mm × 3 mm-coated sensors were fast enough to follow the RH changes, showing a mean sensitivity of about 0.14 nm/% (agar-coated) and 0.12 nm/% (agarose-coated). The hysteresis error was about <10% in the two sensors. The contribution of temperature changes on these RH sensors was negligible. The temperature measurement was performed by a commercial FBG insensitive to RH changes. The small size of these FBG-based sensors, the use of biocompatible polymers, and the possibility to measure both temperature and RH by using the same fiber optic embedding an array of two FBGs make intriguing the use of this solution for application in the control of HWHs.

SnO2-MOF-Fabry-Perot optical sensor for relative humidity measurements

“…Another key feature in RH sensors is the hysteresis error. Usually metal oxide sensitive layers present low hysteresis effects in comparison with the polymeric ones [50] . In the MOF-FP-SnO2 this tendency is also followed.…”

Analysis of the Sensor of Temperature and Humidity Measurement Based on the Optical Fiber

“…It is called the Bragg wavelength (λ B ), and located in the middle of the waves which is the lumen of the filter to achieve the light spectrum that can satisfy the requirements of Bragg [3].…”

“…Nowadays, there are many digital sensors that use physical principles. At the present time, there are sensors that measure the humidity and temperature in the unit [1][2][3][4]. The humidity and temperature sensor based on optical fibers have such qualities as high sensitivity, fast response, small in volume and electro-magnetic interference.…”

“…[10]. Measuring system based on sensitivity of optic fiber Bragg grating (OFBG) [10][11][12][13], Fabry-Perot interferometers (FPI) [14,15], homogeneous optical fibers [16] were discussed in publications.…”

A compact low-power wireless system for in vivo evaluation of heat and moisture exchanger performance

“…To date, the evaluation of HME performances described in the literature have been performed in vitro and ex vivo [11,12] with various methodologies ranging from dew point to optical fiber sensors [13,14], reaching best accuracies of ±2% RH (range 0%-80% RH) and ±0.3 °C (from −40 °C to 115 °C) [15], and response times down to 0.1-0.2 s for the fastest heated capacitive hygrometer [16,17]. However, due to the clinical scenario discussed above, accuracy and fast response times should be combined in a portable stand-alone device that could be integrated with all the ICU instrumentation, providing an easily interpretable feedback.…”