Sensors and Actuators B: Chemical
2018
A. LÓPEZ ALDABA; D. LÓPEZ-TORRES; C. ELOSUA; J.-L. AUGUSTE; R. JAMIER; P. ROY; F.J. ARREGUI; M. LÓPEZ-AMO
Highlights
• The proposed humidity and real time human breathe sensor combines sputtering deposition method and photonic crystal fiber.
• Sputtering deposition time is studied in order to optimize the thin film thickness and therefore the sensor’s sensitivity.
• The thin film penetration inside the fiber holes is measured through the optical backscatter reflectometer (LUNA 4600).
• Fast Fourier Transform is applied to monitor the sensor’s performance towards humidity variations showing linear response in the whole humidity range (20%–90%).
• The sensor shows a sensitivity of 0.14 rad/% with less than 5% of error and rising and recovery times of 370 ms and 380 ms respectively.
Abstract
In this paper, a new optical fiber sensor for relative humidity measurements is presented and characterized. The sensor is based on a SnO2 sputtering deposition on a microstructured optical fiber (MOF) low-finesse Fabry-Pérot (FP) sensing head. The feasibility of the device as a breathing sensor is also experimentally demonstrated. The interrogation of the sensing head is carried out by monitoring the Fast Fourier Transform phase variations of the FP interference frequency. This method substitutes the necessity of tracking the optical spectrum peaks or valleys, which can be a handicap when noise or multiple contributions are present: therefore, it is low-sensitive to noise and to artifacts signal amplitude. The sensor shows a linear behavior in a wide relative humidity range (20%–90% relative humidity) in which the sensitivity is 0.14 rad/%; the maximum observed instability is 0.007 rad, whereas the highest hysteresis is 5% RH. The cross correlation with temperature is also considered and a method to lower its influence is proposed. For human breathing measurement, the registered rising and recovery times are 370 ms and 380 ms respectively.
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Sensing material
… A SnO2 (the sputtering target was purchased in ZhongNuo Advanced Material Techonology Co) thin film was deposited onto the low-finesse FP interferometer sensor head using a sputtering machine (Pulsed DC sputtering System, Nadetech Innovations). The sputtering process was performed with a partial pressure of Argon of 5 × 10−2 mb, a current of 160 mA and a voltage of 190 V. The distance between the sensor head and the SnO2 target was set to 2 cm.