Characterization and Use of a Fiber Optic Sensor Based on PAH/SiO₂ Film for Humidity Sensing in Ventilator Care Equipment

Abstract

The user has requested enhancement of the downloaded file. IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING 1 Abstract-Objective: To develop a compact probe that can be used to monitor humidity in ventilator care equipment. A mesoporous film of alternate layers of Poly(allylamine hydrochloride) (PAH) and silica (SiO 2 ) nanoparticles (bilayers), deposited onto an optical fibre was used. The sensing film behaves as a Fabry-Perot cavity of low-finesse where the absorption of water vapour changes the optical thickness and produces a change in reflection proportional to humidity. Methods: The mesoporous film was deposited upon the cleaved tip of an optical fibre using the layer-by-layer method. The sensor was calibrated in a bench model against a commercially available capacitive sensor. The sensitivity and response time were assessed in the range from 5 % relative humidity (RH) to 95 %RH for different numbers of bilayers up to a maximum of nine. Results: The sensitivity increases with the number of bilayers deposited; sensitivity of 2.28 mV/%RH was obtained for nine bilayers. The time constant of the response was 1.13 s ± 0.30 s which is faster than the commercial device (measured as 158 s). After calibration, the optical fibre humidity sensor was utilised in a bench top study employing a mechanical ventilator. The fast response time enabled changes in humidity in individual breaths to be resolved. Conclusion: Optical fibre sensors have the potential to be used to monitor breath to breath humidity during ventilator care. Significance: Control of humidity is an essential part of critical respiratory care and the developed sensor provides a sensitive, compact and fast method of humidity monitoring.Index Terms-Humidity sensor, relative humidity, FabryPerot, layer-by-layer (LbL), intensive care unit, critical care, optical fibre sensor.

Highly sensitive volatile organic compounds vapour measurements using a long period grating optical fibre sensor coated with metal organic framework ZIF-8

“…for the occupational exposure, or any industrial monitoring, where a reference grating is necessary to subtract any temperature effect [45]. The cross-sensitivity to water vapour in highly humid environment should also be included to test the possibility of using this sensor in breath analysis [46].…”

Recent Developments in Fiber Optics Humidity Sensors

“…In addition, OFHSs have found new applications in clinical treatment due to the need for humidification of inspired gases in critical respiratory care [13,14]. …”

Simultaneous temperature and humidity measurements in a mechanical ventilator using an optical fibre sensor

“…Figure 3b plots the change in reflection intensity of the second local maximum (λ=1564.8 nm) after depositing each of 23 bilayers of PAH/SiO 2 . It is anticipated from Figure 3b that highest sensitivity to humidity would be observed in the region of thicknesses between 7 and 10 layers where the slope of the reflection change is highest 5 . Figure 4a compares the wavelength shift of the FBG (~1551 nm) written in the port1 of the fibre coupler and the readings from two thermocouples placed in the drying and heating chamber used for calibration (Fig.…”

“…One thermocouple and the capacitive sensor (iButton) were also inserted in the T-valve in order to corroborate the response of the fibre sensor. The HME was used to reduce moisture that could affect the performance of the humidity sensor probe 5 . All the devices involved in both experiments were synchronized (recording at the same sampling frequency of 1 Hz).…”

“…Our previous work aimed to characterise and calibrate an optical fibre humidity sensor probe (based on Fabry-Perot cavity), determining sensitivity to humidity, better response time than a commercially available capacitive sensor and feasibility to resolve individual breaths in a bench lung model using a mechanical ventilator 5 . The primary goal of this work is to present an extension of the optical fibre sensor through including a fibre Bragg grating (FBG) to measure temperature simultaneously and allow us to calculate absolute humidity levels.…”