Hernandez FU, Morgan SP, Hayes-Gill BR, Harvey D, Kinnear W, Norris A, Evans D, Hardman JG, Korposh S. Characterization and Use of a Fiber Optic Sensor Based on PAH/SiO
2 Film for Humidity Sensing in Ventilator Care Equipment.
IEEE Trans Biomed Eng 2016;
63:1985-1992. [PMID:
26829771 PMCID:
PMC7186042 DOI:
10.1109/tbme.2016.2521662]
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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 (SiO2) 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.
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