Investigation of fibre optic sensing techniques for the measurement of physical-chemical properties of liquids

Single-mode optical fibre (SMF) sensors have been extremely useful in biomedical applications because of their small size and chemical inertness. Many optical fibre techniques have been used to measure the surface tension () of liquids. However, due to the cylindrical shape and small size of the optical fibre used, the contact angle (θ) was either ignored or supposed to be equal to zero by other researchers, affecting the measurement by ~20%. In this thesis, the contact angle is practically measured via two methods.The first method is via the critical meniscus height (CMH) measurement with a SMF for liquid volumes up to 5 μL. In addition, the light used to enlighten (1550 nm) the optical fibre could be absorbed by some liquids, which would increase the temperature of the said liquids, and could be affected. Therefore, a halogen light source has been filtered with an optical fibre coupler (centred at 850 nm), and the liquids that do not absorb those wavelengths resulted in a CMH comparable with the results from the new setup. Differently, the CMH value was increased with the new setup for liquids that absorb light at 1550 nm. For example, the CMH of water increased by ~10 μm, and the overall sensitivity increased by ~15%. Moreover, the CMH varies with different and dynamic viscosity of the liquid.The second method started with measuring the meniscus height (MH) from the liquid profile on the fibre and finished with the MH measurement on the fibre surface. In fact, the θ could be calculated once the MH is known, and by measuring the force on the fibre, the surface tension can be determined. The MH is measured using a cleaved and side polished SMF attached to an SMF with a known separation distance between their fibre-tips. The MH seems to increase as the surface tension decreases, and the variation of the mass measured by the scale increases with the increase of the surface tension. This sensor was also used to measure the interfacial surface tension at the liquid/liquid interface since the θ could be measured, which is useful for biomedical applications.In conclusion, both methods could be used for measuring the surface chemistry properties of liquids. The advantage in comparison with other methods is the decrease in the amount of liquid needed for the measurement, i.e., up to 5 μL. In addition, using the cleaved and side polished fibre attached to an SMF gives contemporaneous knowledge about the force and the contact angle of different liquids on the fibre. Therefore, the proposed technique modifies the commonly used method to provide valuable information on surface tension

An urban bikeway network design model for inclusive and equitable transport policies

Abstract This study suggests an optimization framework to plan and design a network of bike lanes in an urban context, based on equity principles and subject to a given available budget. The novelty of the proposal consists in an objective function that aims at minimizing the existing inequities among different population groups in terms of accessibility/opportunity to the bikeways. The proposed methodology represents a reliable decision support system tool that could help transport authorities/managers to select the priority areas of their future investments related to the cycling infrastructures. To prove the effectiveness and value of the methodology, an application with relevant analysis to a test case study is presented

Graphene-Oxide and Hydrogel Coated FBG-Based pH Sensor for Biomedical Applications

A hydrogel coated fibre grating-based pH sensor for biomedical applications has been realised, where Graphene Oxide (GO) had been used to enhance the bonding between the coating and the fibre. Two methods of deposition of GO were analysed i.e., evaporation and co-electroplating. The paper concludes that the system of GO evaporated on the fibre + the hydrogel has a sensitivity much higher, (6.1 ± 0.5) pm/pH, than the system of Cu and GO co-electroplated + the hydrogel, (1.9 ± 0.1) pm/pH, for a pH range between 2 to 10. The other conclusion is that the first system has a less coating bonding energy with the optical fibre whereas the second system has a stronger bonding energy, with better durability

Evaluation of Viscosity Dependence of the Critical Meniscus Height with Optical Fiber Sensors

Conventional means of data extraction using optical fiber interrogators are not adequate for fast-paced detection of a target parameter. In this instance, the relationship between the critical meniscus heights (CMH) of several liquids to the extraction speed of a rod submerged in them, have been analyzed. A limitation of a previous interrogator used for the purpose had been light absorption by the liquid due to the used bandwidth of the readily-available light source, i.e., C-band. The newly proposed technique addresses this limitation by utilizing a broadband light source instead, with a Si-photodetector and an Arduino. In addition, the Arduino is capable of extracting data at a relatively faster rate with respect to the conventional optical interrogator. The use of a different operational wavelength (850 nm instead of 1550 nm) increased the r2 and the sensitivity of the sensor. The new setup can measure surface chemistry properties, with the advantage of being comparatively cheaper than the conventionally available interrogator units, thereby providing a suitable alternative to conventional measurement techniques of liquid surface properties, while reducing material waste, i.e., in terms of the required volume for detection of a target parameter, through the use of optical fiber

Simultaneous Measurement of Temperature and Relative Humidity Using a Dual-Wavelength Erbium-Doped Fiber Ring Laser Sensor

A fiber ring laser sensor setup utilizing FBGs (Fiber Bragg Gratings) for simultaneous measurement of ambient temperature and relative humidity (RH) is presented. Two FBGs are incorporated as tunable filters for a dual-wavelength laser emission, where one FBG was coated with Polyimide (PI) in order to achieve sensitivity to RH changes, while the other bare FBG was used for temperature sensing. An increase in RH would induce a strain on the grating, which results in a variation in the resonance wavelength of the PI-coated FBG. This causes a shift in the laser emission wavelength. Being insensitive to RH changes, the bare FBG was employed to measure temperature. The dual-wavelength fiber ring laser sensor created thus allows to determine simultaneous measurement of RH and temperature. The RH sensitivities observed by the PI coated FBG to RH and temperature are 3.6 pm/%RH and 12.15 pm/°C respectively. The temperature sensitivity of the bare FBG was observed to be 9.6 pm/°C. The main advantage of the proposed setup is an optical signal to noise ratio (OSNR) higher than 55 dB and a 3 dB-bandwidth less than 0.02 nm, which points out efficient capabilities for both precise sensing and remote detection applications

Optical fibre thermometry using ratiometric green emission of an upconverting nanoparticle- polydimethylsiloxane composite

The thermally coupled green band emission from excited Er 3+ ions has been used in the past to create optical thermometers, by doping the material in various types of media, particularly glasses. Glasses are known to be excellent hosts for Er 3+ ions: however, high temperatures (>900 K) are usually required for doping these ions into glasses and a non-linear temperature response is often produced. In this work, the frequently encountered drawbacks of glass-based temperature sensors have been addressed by developing a temperature sensor created at a lower temperature (543 K), by dip-coating chemically synthesized upconverting nanoparticles (UCNP-NaYF4:(18%) Yb 3+ , (2%) Er 3+) embedded in polydimethylsiloxane (PDMS) onto the tip of a 1000 μm optical fibre, to create the actual fibre probe. The sensor shows an excellent linear response (R 2 = 0.991) over a very useful temperature range of 295 K-473 K, with a sensitivity of 2.9 ×10-3 K-1 , a temperature resolution of ± 2.7 K and response time of ~ 5 seconds. Additionally, a probe was investigated 2 where a pure upconverting nanoparticle powder was coated on the tip of optical fibre and its spectral and temperature response was obtained (and cross compared with that of UCNP-PDMS composite). The results obtained from the probe development work show that the UCNP-PDMS-coated optical fibre temperature sensor developed offers a better alternative to more conventional Er 3+ doped glass-based temperature sensors, in terms of the thermal budget, the synthesis process and the ease of coating, creating as a result, a very linear device response

Optical Fiber-Based Heavy Metal Detection Using the Localized Surface Plasmon Resonance Technique

An innovative, reflection-based localized surface plasmon resonance (LSPR) fiber-optic sensor has been developed and demonstrated to detect the concentration of several heavy metal lead ions in an aqueous solution. By using a self-assembling technique, gold nanoparticles (Au NPs) have been immobilized on an optical fiber surface and functionalized with 1,1-Mercaptoundecanoic acid (MUA; HS(CH2)10CO2H) in order to make the fiber selective to each the important heavy metal ion, Pb2+ or Cd2+. The concentration of the heavy metal then can be determined from the link between binding rate and the shift of the LSPR resonance wavelength. The Pb2+ ion sensitivity of the sensor thus created has been determined to be 0.28 nm/mM, with a typical response time of 30 seconds. Importantly, the probe has been shown to be reversible through a simple process involving the use of Ethylenedinitrilotetraacetic acid (EDTA;(HO2CCH2)2NCH2 CH2N(CH2CO2H)2) chelator to remove the bound heavy metal ion

Monitoring of the Critical Meniscus of Very Low Liquid Volumes Using an Optical Fiber Sensor

A novel sensing system based on single mode optical fiber in reflective configuration has been developed to measure the critical meniscus height (CMH) of low volumes of liquids, which is then used to calculate the contact angle. The sensing system has been designed especially for very low volumes of liquids (e.g. bio-liquids) and the work has demonstrated that measurements are possible with a minimum liquid volume of 5 µL. The sensing system is based on monitoring the spectral variation induced by the difference in the refractive index regions surrounding the fiber tip, at the air-liquid or liquid-liquid interfaces. From the experiments performed in water, (by immersing and extracting the fiber sensor in the liquid sample), it can be concluded that the CMH forming on the fiber decreases as the temperature increases. The change of temperature (in this experiment from 22 to 60 ℃) does not influence the CMH of the sample used in the evaluation (P3 mineral oil), giving an indication of its thermal stability. In addition, a fixed fiber was used to measure the variation in the liquid level when another fiber is immersed in the liquid. The error in the liquid level obtained in the work was small, at 0.34 ± 0.04 %. Such a sensor, allowing accurate measurements with very small quantities is especially useful where liquid sample volumes are limited e.g. biologically sourced liquids or specialized, expensive industrial material in the liquid phase

Novel Technique for Meniscus Height Measurement of Liquids Using Optical Fibers

A novel technique was designed to measure the meniscus height (MH) of liquids on a standard single mode fiber (SMF) using fiber optics. Once the MH is known, the contact angle could be calculated, and the surface tension of liquids can be determined. In this paper, the MH is measured using a cleaved and side polished optical fiber attached to a SMF with a known separation distance between their fiber tips. When the liquid reaches the SMF, the liquid meniscus rises on the vertical wall of the SMF, which also causes a variation in mass (measured by a μg scale). At this point, the liquid moves upwards until the liquid meniscus touches the side polished fiber, which registers a variation of the reflected optical power. The MH seems to increase as the surface tension decreases, and the variation of the mass measured by the scale increase with the increase of the surface tension. This sensor was also used to measure the interfacial surface tension of the air-liquid and liquid-liquid interface since the contact angle could be measured. In addition, the small dimension of the sensor is adequate for applications where using small amounts of liquid is critical, i.e., biomedical applications