Open Access
Sensitivity optimization of a microstructured optical fiber ammonia gas sensor by means of tuning the thickness of a metal oxide nano-coating
(IEEE, 2019) López Torres, Diego; López Aldaba, Aitor; Elosúa Aguado, César; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; López-Amo Sáinz, Manuel; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In this paper, the influence of the thickness of metallic-oxide coatings, ITO, and SnO2 on the sensitivity of a microstructured optical fiber Fabry–Pérot (FP) has been studied with the aim of developing ammonia gas fiber optic sensors. Also, the distribution of the optical power that can be coupled to the metallic-oxide sensing films is investigated in order to understand how the sensor’s sensitivity can be improved; the thickness of the coatings plays a relevant role on the sensitivity and response time. Films with thicknesses between 200 and 850 nm were experimentally examined resulting in an optimal thickness of 625 nm for a SnO2 film. The behavior of the sensors toward different concentrations of ammonia gas from 10 to 130 ppm was analyzed by measuring the phase shifts of the reflected signal using the fast Fourier transform of its optical spectrum. The registered response/recovery times of this sensor are below 90 s.
Open Access
Comparison between capacitive and microstructured optical fiber soil moisture sensors
(MDPI, 2018) López Aldaba, Aitor; López Torres, Diego; Campo-Bescós, Miguel; López Rodríguez, José Javier; Yerro Lizarazu, David; Elosúa Aguado, César; Arregui San Martín, Francisco Javier; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; López-Amo Sáinz, Manuel; Ingeniaritza Elektrikoa eta Elektronikoa; Landa Ingeniaritza eta Proiektuak; Institute of Smart Cities - ISC; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Ingeniería Eléctrica y Electrónica; Proyectos e Ingeniería Rural
Soil moisture content has always been an important parameter to control because it is a deterministic factor for site-specific irrigation, seeding, transplanting, and compaction detection. In this work, a discrete sensor that is based on a SnO2–FP (Fabry-Pérot) cavity is presented and characterized in real soil conditions. As far as authors know, it is the first time that a microstructured optical fiber is used for real soil moisture measurements. Its performance is compared with a commercial capacitive soil moisture sensor in two different soil scenarios for two weeks. The optical sensor shows a great agreement with capacitive sensor’s response and gravimetric measurements, as well as a fast and reversible response; moreover, the interrogation technique allows for several sensors to be potentially multiplexed, which offers the possibility of local measurements instead of volumetric: it constitutes a great tool for real soil moisture monitoring.
Open Access
Relative humidity multi-point optical sensors system based on Fast Fourier multiplexing technique
(SPIE, 2017) López Aldaba, Aitor; López Torres, Diego; Elosúa Aguado, César; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; Arregui San Martín, Francisco Javier; López-Amo Sáinz, Manuel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
In this paper, a new multipoint optical fiber system for relative humidity measurements based on Sn02-FP (Fabry-Pérot) sensing heads and an optical interrogator as single active device is presented and characterized. The interrogation of the sensing heads is carried out by monitoring the Fast Fourier Transform phase variations of the FP (Fabry-Pérot) interference frequencies. This method allows to multiplex several sensors with different wavelength spacing interference pattern. The sensors operate within a wide humidity range (20%-90% relative humidity) with low crosstalk between them. Five sensing heads have been measured using two different channels of the optical interrogator. The availability of four channels in the interrogator allows to multiplex a higher number of sensors, reducing proportionally the cost of each sensing point.
Open Access
SnO2-MOF-Fabry-Perot optical sensor for relative humidity measurements
(Elsevier, 2018) López Aldaba, Aitor; López Torres, Diego; Elosúa Aguado, César; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; Arregui San Martín, Francisco Javier; López-Amo Sáinz, Manuel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
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.
Open Access
Microstructured optical fiber sensor for soil moisture measurements
(Optical Society of America, 2018) López Aldaba, Aitor; López Torres, Diego; Campo-Bescós, Miguel; López Rodríguez, José Javier; Yerro Lizarazu, David; Elosúa Aguado, César; Arregui San Martín, Francisco Javier; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; López-Amo Sáinz, Manuel; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniería
A discrete sensor based on a Sn0₂-FP (Fabry-Pérot) cavity is presented and characterized in real soil conditions. Results are compared, for the first time to our knowledge, with a commercial capacitive sensor and gravimetric measurements.
Open Access
SnO2-MOF-Fabry-Pérot humidity optical sensor system based on Fast Fourier transform technique
(SPIE, 2016) López Aldaba, Aitor; López Torres, Diego; Ascorbe Muruzabal, Joaquín; Rota Rodrigo, Sergio; Elosúa Aguado, César; López-Amo Sáinz, Manuel; Arregui San Martín, Francisco Javier; Corres Sanz, Jesús María; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
In this paper, a new sensor system for relative humidity measurements based on a SnO2 sputtering deposition on a microstructured optical fiber (MOF) low-finesse Fabry-Pérot (FP) sensing head is presented and characterized. The interrogation of the sensing head is carried out by monitoring the Fast Fourier Transform phase variations of the FP interference frequency. This method is low-sensitive to signal amplitude variations and also avoids the necessity of tracking the evolution of peaks and valleys in the spectrum. The sensor is operated within a wide humidity range (20%-90% relative humidity) with a maximum sensitivity achieved of 0.14rad/%. The measurement method uses a commercial optical interrogator as the only active element, this compact solution allows real time analysis of the data.
Open Access
Real time measuring system of multiple chemical parameters using microstructured optical fibers based sensors
(IEEE, 2018) López Aldaba, Aitor; López Torres, Diego; Elosúa Aguado, César; Arregui San Martín, Francisco Javier; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; López-Amo Sáinz, Manuel; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
In this paper, a multiplexing system for simultaneous interrogation of optical fiber sensors which measure different parameters is presented and validated. The whole system has been tested with 6 different sensing heads with different purposes: one temperature sensing head, two relative humidity sensors and three VOCs leak sensors; all of them based on microstructured optical fibers. The interrogation system uses the FFT technique to isolate each sensor's interference, enabling their simultaneous interrogation. The system interrogates all the sensors at frequencies up to 1 KHz, showing a good performance of each measurement without crosstalk between sensors. The developed system is independent of the sensors' purpose or of the multiplexing topology.