A novel interrogation system for fiber Bragg grating sensor array

Interrogation techniques for fiber Bragg grating sensor arrays need particular attention in the case of structural health monitoring applications involving dynamic strain measurement. Typically the performance of the sensing system is dependent on both the sensor type and the interrogation method employed. A novel interrogation system is proposed here that consists of different interrogation units for each sensor in the array, each unit comprising of a circulator, chirped grating and a Mach-Zehnder interferometer. We present an analysis that consists of tracking the spectral changes as the light passes through various elements in the interrogation system. This is expected to help in the optimization of sensor and interrogation elements leading to improved performance of the health monitoring system.

Calibration of etched fiber bragg grating sensor arrays for measurement of molecular surface adsorption

Etched Fiber Bragg Grating (EFBG) sensors are attractive from the point of the inherently high multiplexing ability of fiber based sensors. However, the strong dependence of the sensitivity of EFBG sensors on the fiber diameter requires robust methods for calibration when used for distributed sensing in a large array format. Using experimental data and numerical modelling, we show that knowledge of the wavelength shift during the etch process is necessary for high-fidelity calibration of EFBG arrays. However as this approach requires the monitoring of every element of the sensor array during etching, we also proposed and demonstrated a calibration scheme using data from bulk refractometry measurements conducted post-fabrication without needing any information about the etching process. Although this approach is not as precise as the first one, it may be more practical as there is no requirement to monitor each element of the sensor array. We were able to calibrate the response of the sensors to within 3% with the approach using information acquired during etching and to within 5% using the post-fabrication bulk refractometry approach in spite of the sensitivities of the array element differing by more than a factor of 4. These two approaches present a tradeoff between accuracy and practicality.

Detection limit of etched fiber bragg grating sensors

While Fiber Bragg Grating (FBG) sensors have been extensively used for temperature and strain sensing, clad etched FBGs (EFBGs) have only recently been explored for refractive index sensing. Prior literature in EFBG based refractive index sensing predominantly deals with bulk refractometry only, where the Bragg wavelength shift of the sensor as a function of the bulk refractive index of the sample can be analytically modeled, unlike the situation for adsorption of molecular thin films on the sensor surface. We used a finite element model to calculate the Bragg wavelength change as a function of thickness and refractive index of the adsorbing molecular layer and compared the model with the real-time, in-situ measurement of electrostatic layer-by-layer (LbL) assembly of weak polyelectrolytes on the silica surface of EFBGs. We then used this model to calculate the layer thickness of LbL films and found them to be in agreement with literature. Further, we used this model to arrive at a realistic estimate of the limit of detection of EFBG sensors based on nominal measurement noise levels in current FBG interrogation systems and found that sufficiently thinned EFBGs can provide a competitive platform for real-time measurement of molecular interactions while simultaneously leveraging the high multiplexing capabilities of fiber optics.

CO2 sensing at room temperature using carbon nanotubes coated core fiber Bragg grating

The sensing of carbon dioxide (CO2) at room temperature, which has potential applications in environmental monitoring, healthcare, mining, biotechnology, food industry, etc., is a challenge for the scientific community due to the relative inertness of CO2. Here, we propose a novel gas sensor based on clad-etched Fiber Bragg Grating (FBG) with polyallylamine-amino-carbon nanotube coated on the surface of the core for detecting the concentrations of CO2 gas at room temperature, in ppm levels over a wide range (1000 ppm-4000 ppm). The limit of detection observed in polyallylamine-amino-carbon nanotube coated core-FBG has been found to be about 75 ppm. In this approach, when CO2 gas molecules interact with the polyallylamine-amino-carbon nanotube coated FBG, the effective refractive index of the fiber core changes, resulting in a shift in Bragg wavelength. The experimental data show a linear response of Bragg wavelength shift for increase in concentration of CO2 gas. Besides being reproducible and repeatable, the technique is fast, compact, and highly sensitive. (C) 2013 AIP Publishing LLC.

pH Induced switching in hydrogel coated fiber bragg grating sensor

In this paper we report a novel hydrogel functionalized optical Fiber Bragg Grating (FBG) sensor based on chemo-mechanical-optical sensing, and demonstrate its specific application in pH activated process monitoring. The sensing mechanism is based on the stress due to ion diffusion and polymer phase transition which produce strain in the FBG. This results in shift in the Bragg wavelength which is detected by an interrogator system. A simple dip coating method to coat a thin layer of hydrogel on the FBG has been established. The gel consists of sodium alginate and calcium chloride. Gel formation is observed in real-time by continuously monitoring the Bragg wavelength shift. We have demonstrated pH sensing in the range of pH of 2 to 10. Another interesting phenomenon is observed by swelling and deswelling of FBG functionalized with hydrogel by a sequence of alternate dipping between acidic and base solutions. It is observed that the Bragg wavelength undergoes reversible and repeatable pH dependent switching.

Blood pressure evaluation using sphygmomanometry assisted by arterial pulse waveform detection by fiber Bragg grating pulse device

We report a blood pressure evaluation methodology by recording the radial arterial pulse waveform in real time using a fiber Bragg grating pulse device (FBGPD). Here, the pressure responses of the arterial pulse in the form of beat-to-beat pulse amplitude and arterial diametrical variations are monitored. Particularly, the unique signatures of pulse pressure variations have been recorded in the arterial pulse waveform, which indicate the systolic and diastolic blood pressure while the patient is subjected to the sphygmomanometric blood pressure examination. The proposed method of blood pressure evaluation using FBGPD has been validated with the auscultatory method of detecting the acoustic pulses (Korotkoff sounds) by an electronic stethoscope. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)

Real time monitoring of petroleum leakage detection using etched fiber Bragg grating

Detection of petroleum leakages in pipelines and storage tanks is a very important as it may lead to significant pollution of the environment, accidental hazards, and also it is a very important fuel resource. Petroleum leakage detection sensor based on fiber optics was fabricated by etching the fiber Bragg grating (FBG) to a region where the total internal reflection is affected. The experiment shows that the reflected Bragg's wavelength and intensity goes to zero when etched FBG is in air and recovers Bragg's wavelength and intensity when it is comes in contact with petroleum or any external fluid. This acts as high sensitive, fast response fluid optical switch in liquid level sensing, petroleum leakage detection etc. In this paper we present our results on using this technique in petroleum leakage detection.

Carbon nanotube coated fiber Bragg grating for photomechanical optic modulator

We have demonstrated novel concept of utilizing the photomechanical actuation in carbon nanotubes (CNTs) to tune and reversibly switch the Bragg wavelength. When fiber Bragg grating coated with CNTs (CNT-FBG) is exposed externally to a wide range of optical wavelengths, e. g., ultraviolet to infrared (0.2-200 mu m), a strain is induced in the CNTs which alters the grating pitch and refractive index in the CNT-FBG system resulting in a shift in the Bragg wavelength. This novel approach will find applications in telecommunication, sensors and actuators, and also for real time monitoring of the photomechanical actuation in nanoscale materials. (C) 2013 AIP Publishing LLC.

Fiber Bragg Grating Sensor Instrumentation for Parking Space Occupancy Management

This work aims at providing an effective parking management system by reducing the drivers' searching time for vacant car-parking space, in turn improving the traffic flow in the car park areas. This is achieved by the use of Fiber Bragg Grating Sensor (FBG) sensor instrumentation in vehicle parking management system. Present work involves embedding an array of FBG sensors underground in the parking space, then determining the strain changes on the FBG sensor due to load applied by the vehicle parked in the parking space, occupancy of the parking space is determined. To validate the FBG sensor parking management system, three most common cases have been considered. This closed loop FBG parking management system can give real-time feed-back to space-guidance display board helping the driver in maneuvering the vehicle to the appropriate parking space. The proposed technique offers optimized usage of parking space for the various segments of cars and also facilitates in a conjoined automated billing system, as compared to conventional method of parking systems.

Design and development of Fiber Bragg Grating sensing plate for plantar strain measurement and postural stability analysis

This paper describes an ab initio design and development of a novel Fiber Bragg Grating (FBG) sensor based strain sensing plate for the measurement of plantar strain distribution in human foot. The primary aim of this work is to study the feasibility of usage of FBG sensors in the measurement of plantar strain in the foot; in particular, to spatially resolve the strain distribution in the foot at different regions such as fore-foot, mid-foot and hind-foot. This study also provides a method to quantify and compare relative postural stability of different subjects under test; in addition, traditional accelerometers have been used to record the movements of center of gravity (second lumbar vertebra) of the subject and the results obtained have been compared against the outcome of the postural stability studies undertaken using the developed FBG plantar strain sensing plate. (C) 2013 Elsevier Ltd. All rights reserved.

pH sensing by single and multi-layer hydrogel coated Fiber Bragg Grating

In this paper we show a novel chemo-mechanical-optical sensing mechanism in single and multi-layer hydrogel coated Fiber Bragg Grating (FBG) and demonstrate specific application in pH activated processes. The sensing device is based on the ionizable monomers inside the hydrogel which reversibly dissociates as a function of the pH and consequently resulting in osmotic pressure difference between the gel and the solution. This pressure gradient causes the hydrogel to deform which in turn induces secondary strain on the FBG sensor resulting in shift in the Bragg wavelength. We also report on the sensitivity factor of single and multilayer hydrogel coated FBG at various different pH.

Evaluation of airline exercises prescribed to avoid deep vein thrombosis using fiber Bragg grating sensors

Various leg exercises have been recommended to prevent deep vein thrombosis (DVT), a condition where a blood clot forms in the deep veins, especially during long-haul flights. Accessing the benefit of each of these exercises in avoiding the DVT, which can be fatal, is important in the context of suggesting the correct and the most beneficial exercises. Present work aims at demonstrating the fiber Bragg grating (FBG)-based sensing methodology for measuring surface strains generated on the skin of the calf muscle to evaluate the suggested airline exercises to avoid DVT. As the dataset in the experiment involves multiple subjects performing these exercises, an inertial measurement unit has been used to validate the repetitiveness of each of the exercises. The surface strain on the calf muscle obtained using the FBG sensor, which is a measure of the calf muscle deformation, has been compared against the variation of blood velocity in the femoral vein of the thigh measured using a commercial electronic-phased array color Doppler ultrasound system. Apart from analyzing the effectiveness of suggested exercises, a new exercise which is more effective in terms of strain generated to avoid DVT is proposed and evaluated. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)

Reversible and irreversible pH induced conformational changes in self-assembled weak polyelectrolyte multilayers probed using etched fiber Bragg grating sensors

Polyelectrolytes are charged polymer species which electrostatically adsorb onto surfaces in a layer by layer fashion leading to the sequential assembly of multilayer structures. It is known that the morphology of weak polyelectrolyte structures is strongly influenced by environmental variables such as pH. We created a weak polyelectrolyte multilayer structure (similar to 100 nm thick) of cationic polymer poly-allylamine hydrochloride (PAH) and an anionic polymer poly-acrylic acid (PAA) on an etched clad fiber Bragg grating (EFBG) to study the pH induced conformational transitions in the polymer multilayers brought about by the variation in charge density of weak polyelectrolyte groups as a function of pH. The conformational changes of the polyelectrolyte multilayer structure lead to changes in optical density of the adsorbed film which reflects in the shift of the Bragg wavelength from the EFBG. Using the EFBG system we were able to probe reversible and irreversible pH induced transitions in the PAH/PAA weak polyelectrolyte system. (C) 2014 Elsevier B.V. All rights reserved.

A Brief Overview of the Recent Bio-Medical Applications of Fiber Bragg Grating Sensors

Fiber Bragg Grating (FBG) sensors have become one of the most widely used sensors in the recent times for a variety of applications in the fields of aerospace, civil, automotive, etc. It has been recently realized that FBGs and etched FBGs can play an important role in biomedical applications. This article provides a brief overview of the recent advancements in the application of FBG sensors in bio-mechanical, bio-sensing and bio-medical fields.

Radial arterial compliance measurement by fiber Bragg grating pulse recorder

In the present work, we report a novel, in vivo, noninvasive technique to determine radial arterial compliance using the radial arterial pressure pulse waveform (RAPPW) acquired by fiber Bragg grating pulse recorder (FBGPR). The radial arterial compliance of the subject can be measured during sphygmomanometric examination by the unique signatures of arterial diametrical variations and the beat-to-beat pulse pressure acquired simultaneously from the RAPPW recorded using FBGPR. This proposed technique has been validated against the radial arterial diametrical measurements obtained from the color Doppler ultrasound. Two distinct trials have been illustrated in this work and the results from both techniques have been found to be in good agreement with each other.