Abstract
This paper describes an approach to develop and deploy low-cost plastic optical fiber sensors suitable for measuring low concentrations of pollutants in the atmosphere. The sensors are designed by depositing onto the exposed core of a plastic fiber thin films of sensitive compounds via either plasma sputtering or via plasma-enhanced chemical vapor deposition (PECVD). The interaction between the deposited layer and the gas alters the fiber's capability to transmit the light, so that the sensor can simply be realized with a few centimeters of fiber, an LED and a photodiode. Sensors arranged in this way exhibit several advantages in comparison to electrochemical and optical conventional sensors; in particular, they have an extremely low cost and can be easily designed to have an integral, i.e., cumulative, response. The paper describes the sensor design, the preparation procedure and two examples of sensor prototypes that exploit a cumulative response. One sensor is designed for monitoring indoor atmospheres for cultural heritage applications and the other for detecting the presence of particular gas species inside the RPC (resistive plate chamber) muon detector of the Compact Muon Solenoid (CMS) experiment at CERN in Geneva.
Highlights
Fiber optic sensors are being employed for various sensing applications, e.g., optical fiber sensors are used for detecting the presence of air pollutants in the atmosphere [1,2], as well as being employed in the biomedical field [3,4] and in environmental sensing [5,6]
Both compositions lead to a thin coating, which is attacked by the fluoride ions, but the layer obtained in the presence of oxygen, and much less organic, results in an increased sensitivity that changes from less than 0.01%/(ppm · hour), in the case of the sensor obtained without oxygen, to about 0.02%/(ppm · hour) for the sensor obtained with oxygen presence, doubling the sensor sensitivity
Sensors based on the measurement of the fiber transmittance change, even though less accurate than solutions based, for example, on fiber Bragg grating, are extremely inexpensive, have very low energy consumption and, in addition, do not require bulky interrogation systems
Summary
Fiber optic sensors are being employed for various sensing applications, e.g., optical fiber sensors are used for detecting the presence of air pollutants in the atmosphere [1,2], as well as being employed in the biomedical field [3,4] and in environmental sensing [5,6]. By measuring the fiber light attenuation, it is very easy to directly arrange bending and pressure sensors, but the measurement of chemical quantities requires a chemical modification of the fiber core surface in order to make it reactive with respect to different chemical species with high sensitivity and selectivity [7]. This latter solution has great potentialities, and it can be employed for many different quantities by changing the nature of the sensitive coating. The sensor assemblies employ a light amplitude measurement, which requires only an LED and a photo-diode and are arranged by taking advantage of vacuum deposition techniques to make the fiber sensitive to the quantity of interest
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