Miniature flow cytometer models enable fast and cost-effective management of diseases in vulnerable and low-end settings. The single-line focusing of cell or particle samples is achieved using hydrodynamic forces in the microfluidic channels. The two common configurations among them are the single-sheath and dual-sheath flows wherein the sample is directed through the main channel, and the surrounding sheath fluids are directed into the main channel through inlets on either side of the main channel. Most models predict the width of the focused sample stream based on hydrodynamic focusing in the low Reynolds number regime (Re << 1), where the viscous forces dominate the inertial forces. In this work, we present comparative analysis of particle focusing by single-sheath and dual-sheath configurations for focusing of micron-sized cells/particles in the range 2 to 20 μm in the higher Re (10 < Re < 80) laminar regime. A quantitative analysis of the relative focused stream width (wf/wch) as a function of flow rate ratio (FRR = Sample flow rate/Sheath flow rate) for the two configurations is presented. The particle tracing results are also compared with the experimental fluorescent microscopy results at various FRR. The deviations of the results from the theoretical predictions of hydrodynamic focusing at Re << 1, are explained analytically. These findings clearly outline the range of flow parameters and relative particle sizes that can be used for cytometry studies for a given channel geometry. This is a highly predictive modeling method as it provides substantial results of particle positions across the microchannel width according to their size and FRR for single-line focusing of particles. Such information is crucial for one to engineer miniaturized flow cytometry for screening of desired cells or particles.
Suppression of overexpressed gene mutations in cancer cells through RNA interference (RNAi) technique is a therapeutically effective modality for oncogene silencing. In general, transfection agent is needed for siRNA delivery. Also, it is a tedious and time consuming process to analyze the gene transfection using current conventional flow cytometry systems and commercially available transfection kits. Therefore, there are two urgent challenges that we need to address for understanding and real time monitoring the delivery of siRNA to cancer cells more effectively. One, nontoxic, biocompatible and stable non-viral transfection agents need to be developed and investigated for gene delivery in cancer cells. Two, new, portable optofluidic methods need to be engineered for determining the transfection efficiency of the nanoformulation in real time. First, we demonstrate the feasibility of using gold nanorods (AuNRs) as nanoprobes for the delivery of Interleukin-8 (IL-8) siRNA in a pancreatic cancer cell line- MiaPaCa-2. An optimum ratio of 10:1 for the AuNRs–siRNA nanoformulation required for efficient loading has been experimentally determined. Promising transfection rates (≈88%) of the nanoprobe-assisted gene delivery are quantified by flow cytometry and fluorescence imaging, which are higher than the commercial control, Oligofectamine. The excellent gene knockdown performance (over 81%) of the proposed model support in vivo trials for RNAi-based cancer theranostics. In addition to cancer theranostics, our nanoprobe combination can be also applied for disease outbreak monitoring like MERS. Second, we present an optical fiber-integrated microfluidic chip that utilizes simple hydrodynamic and optical setups for miniaturized on-chip flow cytometry. The chip provides a powerful and convenient tool to quantitatively determine the siRNA transfection into cancer cells without using bulky flow cytometer. These studies outline the role of AuNRs as potential non-viral gene delivery vehicles, and their suitability for microfluidics-based lab-on-chip flow cytometry applications.
Damage monitoring is the need of the hour in this age of infrastructure. Many methods are being used for damage monitoring in different mechanical and civil structures. Some of them are strain based methods in which abruptly increased strain signifies the presence of damage in the structure. This article focuses on crack monitoring of a fixedfixed beam using fiber optic sensors which can measure strain locally or globally. The two types of fiber optic sensors used in this research are fiber Bragg grating (FBG) and fiber optic polarimetric sensors (FOPS). FBG and FOPS are used for local strain monitoring (at one point only) and global strain monitoring (in the entire specimen) respectively. At the centre of the specimen, a piezoelectric wafer active sensor (PWAS) is also attached. PWAS is used to obtain electromechanical admittance (EMA) signatures. Further, these EMA signatures are analysed to access the damage state in the beam. These multiple smart materials together provide improved information on damages in the specimen which is very valuable for the structural health monitoring (SHM) of the specimen.
Structural health monitoring techniques using smart materials are on rise to meet the ever ending demand due to increased construction and manufacturing activities worldwide. The civil-structural components such as slabs, beams and columns and aero-components such as wings are constantly subjected to some or the other forms of external loading. This article thus focuses on condition monitoring due to loading/unloading cycle for a simply supported aluminum beam using multiple smart materials. On the specimen, fibre optic polarimetric sensor (FOPS) and fibre Bragg grating (FBG) sensors were glued. Piezoelectric wafer active sensor (PWAS) was also bonded at the centre of the specimen. FOPS and FBG provided the global and local strain measurements respectively whereas, PWAS predicted boundary condition variations by electromechanical admittance signatures. Thus these multiple smart materials together successfully assessed the condition of structure for loading and unloading tests.
A fibre optic sensor was developed for in-situ pressure measurement based on the principle of differential pressure in liquids. This sensor system is very simple and consists of fibre Bragg grating (FBG) done on a fibre with core diameter of 9 μm. A calibration study was carried out with a water column and the pressure sensitivity was found to be 1.636 × 10-2MPa-1. The results show that response of FBG to the rise of water level is linear and agrees well with the theoretical results. The reliability of the sensors is confirmed by repeating the measurements for three times. The sensor is useful in applications that involve in-situ resin pressure measurement in manufacturing of laminated composite materials.
Fiber Optics Polarimetric Sensors (FOPS), utilizing first fundamental frequency mode and its harmonics, have already been used as damage detection tool. The FOPS technology is attractive in damage detection as it facilitates us with real time non-destructive health monitoring of different mechanical and civil structures. In this paper, the effects of the size and the location of a single crack on the frequency of first fundamental mode of a cantilever beam have been studied. A relation between the relative size of a crack and relative change in the first fundamental frequency has been established theoretically and then verified experimentally. Further, it has been shown that the cracks, close to the fixed end of the cantilever beam, have significant effect on the frequency of first fundamental mode and as the crack moves away from the fixed end, the effect on the frequency starts becoming diminished. Also the sensitivity of Fiber Bragg Grating (FBG) sensor against a single crack has been studied along both the directions; parallel to the axis of FBG sensor and perpendicular to the axis of FBG sensor. Experimental results show that the range of sensitivity in both the directions is almost the same bur FBG is more efficient along its axis.
A stable dual-wavelength with a tunable wavelength spacing fiber laser based on a chirped two phase-shifted grating
filter is demonstrated. In the ring cavity, a chirped grating with two π-phase shifts servers as an ultra-narrow dualwavelength
transmission band filter. The grating is attached in a triangular cantilever for chirp rate tuning. A
semiconductor optical amplifier biased in low-gain regime is induced to reduce the gain competition of the two
wavelengths caused by erbium-doped fiber. And a feedback fiber loop working as a mode filter guarantees the laser in a
single-longitudinal-mode operation. Two lasing lines with different wavelength spacing from approximately 0.15 to 0.37
nm are experimentally demonstrated.
We report a liquid-level variation sensor based on a fiber Bragg grating (FBG) inscribed in a 6.5-μmdiameter
microfiber. The proposed microfiber Bragg grating (MFBG) in air has two separated reflection
peaks, which are caused by the fundamental mode reflection and the higher-order mode reflection. Each of
the two peaks will split into another two adjacent peaks when a fraction of the MFBG sensor immerses into
liquid. By measuring the reflectivity difference between the two original peaks and their respective adjacent
liquid-induced peaks, the liquid-level variation can be determined.
In this paper, we demonstrate that a prism coupling characterization technique can lead to simpler Waveguide Bragg
Grating (WBG) designs and easier fabrication process by avoiding channel transmission. The experimental results have
shown that the incident laser beam's collimation was maintained after coupling to a planar waveguide. A
characterization set-up using two prisms was designed for measuring transmission characteristics of integrated structures
and eventually planar waveguides in the visible or in the IR range. Since a reasonable overall optical efficiency of 10%
has been demonstrated for this set-up, the prism approach can be eventually utilized in Bragg Grating structures
characterization.
This paper presents the proposal and experimental demonstration of a microwave photonic bandpass filter structure based on a multiwavelength semiconductor optical amplifier (SOA) ring laser, an optical phase modulator, and a segment of single-mode fiber as a dispersive element. Experimental results show multiple-tap microwave photonic bandpass filter by using a power-equalized multiwavelength SOA ring laser as the optical source. Two laser configurations, one with a linearly chirped fiber Bragg grating (LCFBG) to compensate the dispersion of the laser cavity and one without the LCFBG, are compared for their multiwavelength laser outputs and the corresponding microwave photonic bandpass filters' response. The two microwave photonic bandpass filters have free spectral ranges (FSRs) ~1.26 GHz and 1.85 GHz. The maximal main-to-secondary sidelobe ratio of the microwave filter is above 10 dB.
A waveguide surface plasmon resonance (SPR) optical sensor based on wavelength modulation is presented. Strip waveguides are fabricated using MicroChem's SU-8 photoresist via UV lithography. Next, a bimetallic silver-gold film is deposited on the waveguides for exciting surface plasmon resonance. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. Experiments were conducted using various glucose concentrations as the analyte, and the normalized transmission output of the waveguide shows a good SPR curve for all the analytes. With a better evanescent field extension, the proposed waveguide SPR configuration extends the use of SPR, especially in bio-sensing, as longer ligands can be immobilized and bigger analytes can be monitored.
Applications involving fluorescence detection in point-of-care systems are both interesting and challenging in nature. The applications usually require a simple, compact, robust, highly sensitive yet affordable system. As a result, the system needs to be efficient in fluorescence detection by using practical and easily fabricated, hence inexpensive sensors. In this paper, a fluorescence sensor using an in-fiber microchannel has been developed and tested successfully. A blue LED, multimode PMMA or silica fiber, mini-PMT and fluorescein in PBS pH 7.4 buffer solution were used as the excitation source, light guide, fluorescence detector and sample, respectively. Microfluidic channels of 100μm width and 1cm length were fabricated in the optical fibers using a direct write CO2 laser system. The channels in the fibers were examined using a SEM and an optical microscope. Experimental results show that the sensor is highly sensitive, being able to detect 0.1 μg/L of fluorescein in the PBS buffer solution, with good signal to noise ratio and the results are reproducible. The data obtained using silica fibers as sensors when compared with the results from PMMA fibers show that the silica fiber sensor has better sensitivity than the PMMA fiber sensor. This could be due to the fouling effect created by the frosty layer at the bottom of the microchannel made within the PMMA fiber. Our future work will integrate the fiber sensor into microfluidic chips for lab-on-a-chip applications.
We propose a new and simple method to reconstruct the refractive-index modulation of a symmetric fiber Bragg grating (FBG) from its magnitude reflection spectrum (i.e., phase information is not required). The reconstruction method uses an FBG model based on some known parameters of the fabricated FBG (grating length, number of subgratings, and grating period) and an optimization technique, namely, the Quasi-Newton method, to find the local parameter values of the FBG. To our knowledge, this is the first time that the reconstruction of FBG is experimentally realized by an optimization technique. Compared with other reconstruction methods, the proposed method is so simple that it requires only the reflection spectrum of the fabricated FBG.
An erbium-doped fiber amplifier (EDFA) gain flattening technique using an embedded long period grating (ELPG) is proposed. By bending the ELPG, because the different bending curvature yields the different coupling strength, it is used for the dynamic gain flattening despite the different pump power on the EDFA. The flattened gain region of 35nm can be achieved with 1dB ripple.
A long-period grating (LPG) coated with gelatin was developed as a high relative humidity (RH) sensor. The resonance dip or coupling intensity of the LPG spectrum varies with humidity while the resonance wavelength remains constant. The principle of operation of the sensor is based on the effect of an external medium, with higher refractive index than that of silica or cladding, on the LPG spectrum. Experimental investigations on the sensor yield a sensitivity of 1.2dB/%RH with an accuracy of ±0.25%RH, and a resolution of ±0.00833%RH. The LPG RH sensor also offers repeatability, hysteresis and stability errors of less than ±0.877%RH, ±0.203%RH and ±0.04%RH respectively. In addition to the characterization of the LPG RH sensor, further studies were conducted to determine the effect of grating periodicities on the sensitivity. Results show that higher-order cladding modes from smaller grating periods enable the sensor to achieve higher sensitivity to humidity. This method is proposed to be more cost effective as compared to more complex spectroscopic methods based on wavelength detection. This sensor can also help to solve problems in measuring high humidity with existing relative humidity measurement systems.
A novel tunable multiwavelength erbium-doped fiber laser source based on a Sagnac loop filter is proposed and experimentally demonstrated. The filter, which is coupled together with the laser cavity, consists of a normal 3-dB fiber coupler, a polarization controller (PC1) and a segment of high-birefringence (Hi-Bi) fiber. The active gain medium, which is a polarization-maintaining erbium-doped fiber (PM-EDF) with an elliptical core, leads to possible multi-frequency lasing output at room temperature. In experiment, by changing the setting of the polarization controller (PC2), multiple frequency lasing lines with different wavelength spacing have been obtained. By applying some pressure to the PM-EDF, continuously tunable multiwavelength lasing output is achieved. Experimental results have shown several stable output lasing wavelengths with high extinction ratio at room temperature.
A novel spacing-tunable multiwavelength erbium-doped fiber laser source based on a Sagnac loop filter is proposed and experimentally demonstrated. The filter, which is coupled together with the laser cavity, consists of a normal 3-dB fiber coupler, a polarization controller (PC1), and a segment of high-birefringence (Hi-Bi) fiber. The active gain medium, which is a polarization-maintaining erbium-doped fiber (PM-EDF) with an elliptical core, leads to possible multifrequency lasing output at room temperature. In the experiment, by changing the setting of the polarization controller (PC2), multiple-frequency lasing lines with different wavelength spacing are obtained. Experimental results show several stable output lasing wavelengths with high extinction ratios at room temperature.
High resolution tunable optical filters are important in dense wavelength division multiplexing (DWDM) applications as channel spacing in optical communications systems can be as low as 0.4nm. The bandwidth of the filter must be narrow, to prevent filtering neighbouring channels. In this paper, a simple, low cost technique for the tuning of the Bragg wavelength of the FBG filter with high resolution and good repeatability is demonstrated. A FBG was embedded in a triangular carbon fiber composite package and aluminium plates were used to clamp the wider end of the package, leaving the thinner end free, like a cantilever beam. A micrometer was placed under the thinner end of the package and the vertical displacement of the micrometer will bend the carbon composite. This bending will produce compression and tension forces on the FBG depending on which side of the package is used, which will result in a shift of the Bragg wavelength. The total tuning range of the FBG filter is 2nm with a resolution of 1pm. The repeatability error was found to be 0.4% over the whole tuning range. The 3dB bandwidth of the reflected spectra from the FBG is 0.235nm, much less than channel spacing of 0.4nm.
A low cost, low complexity fiber optic humidity sensor is very desirable because of the various advantages fiber optic sensors have over conventional electrical sensors. In this paper a simple, low cost plastic optical fiber (POF) sensor based on cobalt chloride (CoCl2) and gelatin coating on the curved sensing point with a humidity sensing range from 60% to 95%RH is presented. An investigation into the effect of bending radii of the fiber at the sensing point as well as fiber core diameter on sensitivity of the humidity sensor is conducted to find the best way to improve sensing performance. The sensing mechanism of the POF humidity sensor is the attenuation of the evanescent wave at the bent portion of the fiber by absorption due to CoCl2. The sensor has a sensing range from 60%RH to 95%RH. The hysteresis error is negligible and a resolution of 0.01%RH is achieved. The repeatability error can be as low as 1.1% for the whole sensing range. Investigation of the effect of fiber diameter shows that the sensitivity of the sensor improves with larger fiber diameters. The sensitivity of the sensor increases when the sensing portion of the fiber is bent to a small radius.
For an embedded LPG bending sensor, in which the its resonance coupling strength changes with bending curvature, cross-talk issues between temperature and bending curvature arises if it is to be deployed in non-controlled environments. A 2 x 2 matrix method was thus employed for simultaneous measurement of bending curvature and temperature for the embedded LPG bending sensor. The matrix is made up of bending and temperature coefficients from 2 different fiber-types LPG; one is H2-loaded and the other is Bo/Ge co-doped. To find out the percentage error, a random test has to be carried out and the matrix was deployed for calculation. From the test results, the percentage error achieved for curvature measurement yields less than 6%. For temperature measurement, the percentage error fluctuates between 1.56% and 5.4%. The use of simultaneous measurement of both bending curvature and temperature enables researchers and engineers to measure bending of structures more accurately.
The use of LPG embedded in carbon-fiber composite laminates (ELPG), in a 4-3 configuration, for bending measurement has been demonstrated. With increased bending curvatures on the 4 layers side, the coupling strength of the cladding mode decreases while the resonance wavelength remains relatively constant. A reduction in coupling strength leads to a reduction of the resonance amplitude depth. From the bending test covering the range of curvatures from 0m-1 to 2m-1, the ELPG yields a sensitivity of 5.065dB/m-1 and a repeatability of 98.1%. In another investigation, the ELPG ability to determine direction of bend has also been demonstrated by applying bending at the 3 layers side of the laminate. Despite having a short curvature range between 0m-1 and ~0.626m-1, the test demonstrates an increase of the cladding mode coupling strength with an increase in bending curvature, thus showing the ELPG ability to differentiate bending directions. By exploiting the unique characteristics of ELPG, two ELPGs can be exploited for 2-axis measurement of structures. Hence the overall cost and complexity of the bending sensor system can be greatly reduced.
Fiber gratings have been studied for their applications in sensing and communications. Many sensing applications of the uniform fiber Bragg grating, chirped fiber grating and long period grating have been studied, proposed and commercialized. Sampled chirped gratings have been studied for multichannel dispersion compensation in DWDM systems. In this paper, we show that the sampled chirped fiber grating can be used as a distributed pressure sensor. The chirp provides ease of manufacture of many gratings. The sampling results in many small, uniform grating-like structures. This fact can be used to simulate a distributed sensor over the length of the sampled chirped grating. When a surface comes into contact with the sensor, the distribution of the pressure determines the shift in central wavelength of the various sub-gratings. The sub-grating that experiences the maximum pressure will show maximum wavelength shift whereas adjacent sub-gratings will show less shift. This can also give the location of the pressure. The sensor design comprises of a sampled chirped grating embedded in unidirectional fiber-reinforced composite prepreg. The prepreg enhances the mechanical strength and the unidirectional embedding reduces birefringence. The number of layers in the prepreg stack varies the sensitivity. Such distributed pressure sensors can be applied in robotics, ergonomics, and in the biomedical field.
The paper describes the design features and characteristics of an embedded fiber Bragg grating (FBG) pressure sensor that has been developed to measure forces applied in the direction perpendicular to the fiber axis. This FBG-based pressure sensor provides an absolute measurement in terms of wavelength shift, which avoids problems of signal intensity fluctuation often encountered by conventional intensity-modulated or phase-modulated pressure sensors. The initial outcome of our study indicates that direct sensing using bare-FBG is infeasible for real applications due to its non-linearity and limited range of force sensing. However, when the FBG is embedded into some composite material, the sensor exhibits excellent linearity, high stability and reliability over a wider force-sensing range, making it a potentially viable sensing element. When an FBG is embedded into some fiber-reinforced composites, a level of sensing force of up to 60N with a sensitivity of 3.96 pm/N and resolution of 1pm (equivalent to 0.8με) is achievable without causing permanent deformation to the FBG.
We demonstrated the improvements of an optical biosensor system using a long range surface plasma resonance technique. As preliminary simulation results, we present the prism-based biosensor system with a broader operating range to improve the sensitivity for a wider the measurable reflective index range and a narrower absorbing peak. This proposed optical biosensor system could be used to implement a compact immunoassay device.
An effective method to implement room temperature operation of multiwavlength erbium-doped fiber ring laser (MW-EDFL) employing equivalent low frequency shift feedback (ELFSF) is presented. Simultaneous multiwavelength lasing with 0.5nm wavelength spacing is experimentally demonstrated by applying a sawtooth signal of the order of 10kHz to a phase modulator inserted in the ring cavity to prevent single-wavelength oscillation. A LiNbO3 multifunction chip of fiber gyro has been used as the phase modulator, the output coupler, and the polarizer of Lyot periodic filter. The MW-EDFL output is linearly polarization light that meets the requirement of external modulation for WDM applications.
Over past few years, the concept of structural health monitoring has been emerging as a new area of research. Fiber Bragg grating (FBG) based sensor offers a new sensing approach with a number of advantages over conventional sensors. This new sensing technology is suitable for the harsh environment of construction industry due to its robustness, ruggedness and ease of installation. Two unique advantages of FBG based sensors are immunity to electromagnetic interference and multiplexing capability. This paper reports some of the results of a multi-disciplinary program on the FBG based sensors involving the School of Electrical and Electronic Engineering and the School of Civil and Environment Engineering at Nanyang Technological University, Singapore.
In this paper, the application of fiber interferometry in the nano-scale displacement measurement of microelectromechanical system (MEMS) device is being presented. Fiber optic interferometry combines the benefits of the optical fiber such as lightweight, small size and wide bandwidth with the high resolution, high sensitivity capability of the interferometry. It also provides easier setup and offers lower energy loss than the conventional free-spaced interferometry. The fiber optic interferometric system comprises a laser source and a 2 X 2 fiber coupler. The reference arm and the sensing arm of the interferometer are formed within a single output of the coupler. The resultant interference intensity is measured at one of the fiber coupler input. The fiber optic interferometry could be used for the MEMS with moving structure. A case study is being carried out to investigate the displacement of the micromirror in the MEMS Fabry-Perot Filter. The mirror is being driven by the comb drive actuator under the effect of applied voltage. It selectively reflects certain wavelengths while allows others to pass through determined by the air cavity length. The displacement under different applied voltages will be measured using the fiber optic interferometry. The experiment and the result will be demonstrated.
In recent years, fiber optic sensors have been used for structural health monitoring because of the advantages they have over conventional strain gauges, such as multiplexing capability and immunity to electromagnetic interference (EMI). In addition, they have ability to monitor multiple parameters simultaneously, which is of significant benefit to researchers. However, this diverse sensitivity can cause "cross coupling" leading to imprecision in measurement. In this paper, we report our results on the development and testing of a temperature compensated fiber Bragg grating strain sensor. Results show that the proposed sensor structure can be used to effectively compensate for temperature variations in strain measurement.
We demonstrate the development of tunable optical filters based on fiber bragg gratings (FBGs). A distributed on fiber resistive heater consisting of a thin metal film is deposited by means of an Electron Beam Evaporator onto the outer surface of an uniform FBG. The physics of heat flowand diffusion in these structures leads to resistive heating of the metal film that follow, to a remarkably good approximation, the local resistance of the coating. This generated heating induces changes in the fiber’s refraction index (thermo-optic effect), which together with the thermal expansion effect of fiber causes a shift in the Bragg wavelength thereby achieving the tunability. Experimental results show a dc tuning range of 4.284 nm (nickel as thin film) with a corresponding electrical power of 569 mW. A maximum efficiency of 8.133 nm/W (gold as thin film) was obtained for dc tuning.
A Tabu Search (TS) algorithm, to our knowledge, for the first time, is introduced into the optimized design of Fiber Bragg gratings (FBGs). By combining the Transfer Matrix Method (TMM) for calculating the reflection spectrum and the TS algorithm, we obtained a new method for synthesis the FBGs with advanced characteristics. A new appodization profile is proposed as an example to demonstrate the effectiveness of the method that is general to be useful for inverse problems in FBGs application.
This paper reports our work on the applications of fiber Bragg grating-based strain sensors for the vibration tests and mode analysis on concrete structures. The arrayed fiber grating strain sensors, which were wavelength-division-multiplexed along the fibers, were attached onto the reinforced bars (rebars) before concrete was poured in to form a 5.5m long, 0.3m wide, 0.15m deep reinforced concrete beam. The embedded sensors will provide quasi-distributed real-time dynamic strain information along the length of the beam. For verification with the FBG strain sensors, some electrical accelerometers were also placed on the top surface of the concrete beam. All the data from FBG sensors and electrical accelerometers were recorded and analyzed by a computer. In the experiments, a hammer and an electrical shaker were used to excite the structure. The experimental results obtained with the FBG sensors show good consistency with the theoretical analysis.
Development in sensing technologies and data acquisition systems is making it possible for engineers to acquire the actual state of strains and stresses in structures at construction stage and during their service life. The knowledge of actual internal forces in a structure is key to identification of parameters such as stiffness and support conditions enabling the structural performance to be accurately estimated. This paper reports on the theoretical and experimental work carried out using fibre Bragg gating (FBG) strain sensors, embedded into and attached onto the concrete beam, to obtain the strain distribution of the concrete beam, therefore deduce the information of the applied load.
Fiber Bragg grating (FBG)-based strain and temperature sensor array were embedded into the concrete structure in order to provide real-time information on its strain and temperature distribution. The sensors were wavelength- multiplexed along a single fiber. The temperature and strain sensors were specially designed and optimized for their measurands. The calibration experiments of those FBG sensors, and parameter monitoring during the structural curing processes were also presented in this paper. These fiber optic strain and temperature sensor show many advantages over the traditional electrical strain gauges and thermocouples.
Initially developed for applications in the aerospace industry, fiber-optic Bragg grating sensors (FBG) have attracted attention in the civil engineering community. The interest in FBG sensors has been motivated by the potential advantages they can offer over existing sensing technologies. They are, immune to electromagnetic interference, small in size and can be easier to install than traditional electrical resistance strain gauges. They can also be multiplexed, that is, a single fiber may have more than one change. Although field test of FBG sensors have been reported in literature, there is a dearth of information on their installation procedures, their precision in quantifying strains of concrete structures, and robustness requirements for embedment in concrete structures. In particular the harsh environment during the construction of concrete structures is a great challenge in the installation of these fragile sensors. The paper reports on our experiences with FBG sensors in concrete structures. FBG sensor have been sued to quantify strain, temperature and to capture vibration signals. Th result of these studies indicate that, if properly installed, FBG sensors can survive the sever conditions associated with the embedment process and yield accurate measurements of strains and vibration response, so it is possible to benefit from their potential advantages.
KEYWORDS: Sensors, Fiber Bragg gratings, Telecommunications, Control systems, Signal attenuation, Signal detection, Fiber optics sensors, Multiplexing, Data acquisition, Metals
We report on the use of fiber Bragg grating (FBG) foot sensors to study the reaction of human being subjected to floor vibration. The entire testing system comprises the multiplexed FBG foot sensors, the communication link between the sensors and the vibrating slab, the control and synchronization software, the graphical user interface, and the data acquisition and analysis system. The pressure distributions over different parts of the foot are obtained at different floor vibrating frequencies and with different distances from the vibrating source. These results show great potential in the application of the FBG foot sensors to study the biomechanics of balancing on a vibrating floor. It has also been demonstrated that the system is robust and able to work under harsh conditions. Further development towards practical implementation of the system is proposed.
It is known that certain design consideration must be given to the concrete structures to cater for possible ambient temperature variations. The thermal stress that results from these changes can cause damage in concrete structures ifthey are restrained or ignored in the design stage. The thermal effects in concrete structures are mainly due to the surrounding environmental conditions and some other special effects, such as the heat of hydration during construction and casting of the bitumen. In this paper, we present our preliminary results on monitoring the non-linear temperature profiles of simulated bridge decks due to various environmental contributing factors using fiber Bragg grating (FBG) sensors and thermocouples. We will also present the data on the variations of the temperature profiles in the concrete due to different thickness of the bitumen topping.
In concrete curing process, the temperature and the volume of the structure, and the inner pressure/stress exerted on the rebars will change in a fashion that depends on the composition of the concrete mixture. The temperature, strain and pressure changes at various points of a 3m long concrete structure with a mixture of cement, water and aggregate were monitored over a period of several days. Fiber Bragg grating based sensors were used to monitor these parameters in vivo. These sensors were designed and optimized to measure the temperature, strain and pressure respectively.
In this paper, we report the development of an Er3-doped dual-wavelength fiber laser constructed from a
quasi-ring structure incorporated with two cascaded fiber Bragg gratings (FBGs). A total output power of
8.5 dBm and a mode suppression ratio of more than 50 dB have been obtained in the cw operation case.
The mode competition phenomenon for dual wavelengths lasing has been investigated by reducing the
wavelength spacing of the two FBGs. With mode locking, switching from one wavelength to the other, and
between single- and dual- wavelength lasing has been demonstrated by adjusting the rf frequency of an
intensity modulator in the laser cavity.
In this paper, we present our work on the fiber Bragg grating (FBG) sensors for structural health monitoring in 5m long concrete structures. Two sets of sensors were securely fastened onto the surfaces of the top and bottom reinforced bars respectively before concrete was poured in. Another set of the sensors was mounted onto the slab surface. These sensors were then monitored to observe the strain experienced at different locations within concrete slab. Loading and unloading cycle tests and failure test were performed on the completed structure. From the results obtained using the FBG sensors, we were able to correlate t he load-strain behavior of the slabs to the failure state as observed on the slab surface. These data are useful in determining the maximum allowable load before failure sets in. At the same time, we made comparisons of the data obtained using our FBG sensors with those obtained with electrical strain gauges. The two sets of data show a similar trend during the loading and unloading tests as well as during the failure tests.
A Fiber Optic Pressure Sensor utilizing a Fiber Bragg Grating (FBG) as a sensing element has been demonstrated. In the experiment, a broad band LED source with a wavelength range of 1520 nm to 1570 nm was launched into a single mode optical fiber within which the FBG was written. With no applied force, the fiber grating reflects light strongly at a wavelength of 1549.92nm. When the FBG was subjected to a range of forces (from 0.0N to 18.0N), applied perpendicularly to its axis, the reflected light from the FBG was found to be wavelength shifted in proportion to the applied force, but in a non- linear manner. The shift in wavelength is detected using fiber Fabry-Perot interferometric technique. With the FBG embedded in carbon fiber material, the test results showed an excellent linear relationship between the wavelength shift and the applied force (pressure). In addition, force sensing range of up to 60N was obtained with the pressure sensor still remaining in good condition.
A two-fiber laser Doppler anemometer was built and tested with the fiber probe placed parallel to the flow. Nine combinations of fiber diameters and fiber separations were tested, and the dominant and maximum shift frequencies were plotted as a function of the unperturbed (or freestream) flow velocity. For both the forward (toward the fiber tip) and reverse (away from the fiber tip) flow directions, the graph of the flow velocity against the maximum shift frequency shows better linearity and approaches closer to the theoretical line than the graph of the flow yelocity against the dominant shift frequency. For the forward flow, the Doppler frequency is close to that predicted and linear above 20 cm/s, but for the reverse flow the slope is only one-quarter of that predicted. Analysis of the data showed that the region of flow perturbation decreases towards the fiber tips in the forward flow, whereas it extends away from the fiber tips in the reverse flow. In its present form, the two-fiber system cannot then be used for accurate blood velocity measurements, since linear calibration between the forward and reverse flow velocities cannot be achieved.
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