Lourdes S. M. Alwis

Bio: Lourdes S. M. Alwis is an academic researcher from Edinburgh Napier University. The author has contributed to research in topics: Fiber Bragg grating & Fiber optic sensor. The author has an hindex of 12, co-authored 44 publications receiving 581 citations. Previous affiliations of Lourdes S. M. Alwis include City University London.

Fibre optic long period grating-based humidity sensor probe using a Michelson interferometric arrangement

Abstract: Long period gratings (LPG)-based sensors are widely used due to their high sensitivity to a range of suitable measurands. However, a typical configuration involving a single grating-based LPG sensor system frequently has the disadvantage of the probe being used in transmission mode. Further, the broad bandwidth of the attenuation bands formed by the propagation mode coupling between the core and the cladding modes constitutes a difficulty when the device is used as a conventional sensor probe. To overcome these limitations, a Michelson interferometer-type sensor configuration has been developed, using a LPG grating pair formed by coating a mirror at the distal end of the LPG. This sensor configuration is more convenient to use and is able to overcome the limitations of the single LPG sensor due to the shifts in the attenuation bands being more easily detectable. As part of work to develop an optimum configuration for the probe, a series of tests has been carried out to determine the most suitable distance between the LPG and the mirror coating for a typical grating (LPG) of period 250 μm. The sensor thus developed was then calibrated for use for temperature and refractive index measurement. In this paper, the design of a LPG coated with polyvinyl alcohol (PVA) as a relative humidity (RH) sensor and used in the Michelson interferometer configuration is reported. PVA, which swells with the increase of RH in its surroundings, causes a change in the refractive index of the coated polymer layer which was observed by tracking the response of the resonance loss band of the LPG to varying RH levels. The distal end of the fibre containing the LPG has been coated with a silver mirror in order to track the shift of the resonance loss band in reflection and to achieve a high resolution. The sensor was evaluated by being subjected to humidity changes over a RH range from 20% to 85% and an excellent detection performance was obtained while retaining the sensitivity of the PVA coated sensor.

[INVITED] Developments in optical fibre sensors for industrial applications

Abstract: It can be seen that optical fibre sensing technology has huge potential to address industrial applications. They offer various advantages over the conventional electrical systems and are increasingly becoming cost effective. Different types of fibre structure and configurations can be utilised to tailor specific applications. The paper aims to highlight the developments in optical fibre sensors for industrial applications.

Structural Health Monitoring Using Textile Reinforcement Structures with Integrated Optical Fiber Sensors.

Abstract: Optical fiber-based sensors "embedded" in functionalized carbon structures (FCSs) and textile net structures (TNSs) based on alkaline-resistant glass are introduced for the purpose of structural health monitoring (SHM) of concrete-based structures. The design aims to monitor common SHM parameters such as strain and cracks while at the same time acting as a structural strengthening mechanism. The sensor performances of the two systems are characterized in situ using Mach-Zehnder interferometric (MZI) and optical attenuation measurement techniques, respectively. For this purpose, different FCS samples were subjected to varying elongation using a tensile testing machine by carefully incrementing the applied force, and good correlation between the applied force and measured length change was observed. For crack detection, the functionalized TNSs were embedded into a concrete block which was then exposed to varying load using the three-point flexural test until destruction. Promising results were observed, identifying that the location of the crack can be determined using the conventional optical time domain reflectometry (OTDR) technique. The embedded sensors thus evaluated show the value of the dual achievement of the schemes proposed in obtaining strain/crack measurement while being utilized as strengthening agents as well.

Analysis of Polyimide-Coated Optical Fiber Long-Period Grating-Based Relative Humidity Sensor

Abstract: A long-period grating (LPG)-based relative humidity (RH) sensor is developed, based on using a tailored layered polyimide coating on the grating region at the distal end of the fiber probe and allowing it to respond to humidity changes. The attenuation band of the coated LPG, on which the sensor is based, responds to the varying RH (in this case, over the region from 20% to 80% RH) through changes in the characteristic wavelength of the LPG. The experimental results confirm that the sensor created shows a linear response to the variation of RH levels. The sensitivity of the sensor is estimated to be 0.10 nm/%RH with negligible hysteresis (<; 1% RH). An advantage of the sensor design is that the probe is configured in reflection mode where the distal end of the fiber (containing the LPG) is coated with a silver mirror to monitor the wavelength shift at the same end of the fiber at which the light is launched (and to directly relate this to the RH change). The results obtained are compared with those from other probe designs (which often are in the less convenient transmission mode) and are seen to exhibit excellent overall performance and repeatability, showing the value of the probe for practical RH measurement, for example, in structural monitoring applications, a key area where effective monitoring of moisture and humidity change is important.

Fiber-Optic Chemical Sensors and Biosensors (2013-2015).

Abstract: Xu-dong Wang*,† and Otto S. Wolfbeis*,‡ †Department of Chemistry, Fudan University, 200433 Shanghai, P. R. China ‡Institute of Analytical Chemistry, Chemoand Biosensors, University of Regensburg, D-93040 Regensburg, Germany ■ CONTENTS Books, Reviews, and Articles of General Interest 204 Sensors for (Dissolved) Gases and Vapors 204 Hydrogen 204 Hydrocarbons 206 Oxygen 206 Carbon Dioxide 208 Nitrogen Oxides 208 Other Gases 208 Ammonia 209 Ethanol 209 Other Volatile Organic Compounds (VOC)s 210 Sensors for Humidity, Water Fractions, Hydrogen Peroxide, and Hydrazine 211 Humidity 211 Water Fractions in Organic Solvents 212 Hydrogen Peroxide 213 Sensors for pH Values, Ions, and Salinity 213 pH Values 213 Ions 214 Salinity and Ionic Strength 215 Sensors for Organic Species 216 Glucose Sensing 216 Sucrose 217 Oils 217 Other Organics 217 Biosensors 218 Nucleic Acid-Based Biosensors (DNAand Aptamer-Based) 218 Immunosensors 218 Enzymatic Biosensors 219 Other Biosensors 220 New Schemes and Materials 220 New Sensing Schemes 220 Molecularly Imprinted Polymer (MIP)-Based Sensors 221 Photonic Crystals 223 Author Information 223 Corresponding Authors 223 Notes 223 Biographies 223 Acknowledgments 223 References 223

Ultrafast response humidity sensor using supramolecular nanofibre and its application in monitoring breath humidity and flow

Abstract: Measuring humidity in dynamic situations calls for highly sensitive fast response sensors. Here we report, a humidity sensor fabricated using solution processed supramolecular nanofibres as active resistive sensing material. The nanofibres are built via self- assembly of donor and acceptor molecules (coronene tetracarboxylate and dodecyl methyl viologen respectively) involved in charge transfer interactions. The conductivity of the nanofibre varied sensitively over a wide range of relative humidity (RH) with unprecedented fast response and recovery times. Based on UV-vis, XRD and AFM measurements, it is found that the stacking distance in the nanofibre decreases slightly while the charge transfer band intensity increases, all observations implying enhanced charge transfer interaction and hence the conductivity. It is demonstrated to be as a novel breath sensor which can monitor the respiration rate. Using two humidity sensors, a breath flow sensor was made which could simultaneously measure RH and flow rate of exhaled nasal breath. The integrated device was used for monitoring RH in the exhaled breath from volunteers undergoing exercise and alcohol induced dehydration.

Toward a New Generation of Photonic Humidity Sensors

Abstract: This review offers new perspectives on the subject and highlights an area in need of further research. It includes an analysis of current scientific literature mainly covering the last decade and examines the trends in the development of electronic, acoustic and optical-fiber humidity sensors over this period. The major findings indicate that a new generation of sensor technology based on optical fibers is emerging. The current trends suggest that electronic humidity sensors could soon be replaced by sensors that are based on photonic structures. Recent scientific advances are expected to allow dedicated systems to avoid the relatively high price of interrogation modules that is currently a major disadvantage of fiber-based sensors.