Design Of Fiber Optic Sensor Research Articles

Electromagnetic Modelling of Fiber Sensors for Low-Cost and High Sensitivity Temperature Monitoring.

An accurate design of an innovative fiber optic temperature sensor is developed. The sensor is based on a cascade of three microstructured optical fibers (MOFs). In the first one a suitable cascade of long period gratings is designed into the core. A single mode intermediate and a rare-earth activated Fabry-Perot optical cavity are the other two sensor MOF sections. An exhaustive theoretic feasibility investigation is performed employing computer code. The complete set-up for temperature monitoring can be obtained by utilizing only a low cost pump diode laser at 980 nm wavelength and a commercial optical power detector. The simulated sensitivity S = 315.1 μW/°C and the operation range ΔT = 100 °C is good enough for actual applications.

Fiber Optic Temperature Sensor Design based on Fluorescent Lifetime

The temperature is measured by the fluorescent lifetime of fluorescent material. In this work, the analog switch was controlled by single chip to trigger exciting light emission of LED. In order to measure the fluorescent lifetime, pho- toelectric detector, amplifier and active power filter were used. The modulation frequency of fluorescent signal was de- tected by phase locking detection method. Therefore, the temperature measurement in the range of 0°C�450°C was real- ized. This sensor has advantages such as high accuracy, strong anti-electromagnetic interference and non-contact meas- urement.

Efficient design of Fiber Optic Polarimetric Sensors for crack location and sizing

The Fiber Optic Polarimetric Sensor (FOPS) is an attractive tool for damage monitoring in structures. However the system is not capable of identifying damage location and crack size, which would further assist in the assessment of the severity of damage. Also, the output signal from FOPS is very noisy because of the fact that the whole fiber is sensitive and picks up unwanted signals from its surroundings. In the current work, a new design of FOPS has been put forward for structural health monitoring (SHM). It has been shown that in this new design, only the central part of FOPS is sensitive keeping the “leading-in” and “leading-out” parts insensitive, allowing SHM using FOPS sensitive only to the region of interest. This design is then implemented to locate and estimate the size of a crack in a cantilever. Unlike previous studies, the current approach considers second vibrational mode along with the first vibrational mode to get better understanding of the damage size and location. In this paper, the location and sizing of a crack in a cantilever beam are studied theoretically and verified experimentally. • A new design of Fiber Optic Parametric Sensor (FOPS) is presented for its application in structural health monitoring. • This new design enables FOPS to remote sensing and local health monitoring in the field of structural health monitoring. • A methodology is proposed for crack location and sizing with this design of FOPS in cantilevers.

Frequency-shifted interferometry--a versatile fiber-optic sensing technique.

Fiber-optic sensing is a field that is developing at a fast pace. Novel fiber-optic sensor designs and sensing principles constantly open doors for new opportunities. In this paper, we review a fiber-optic sensing technique developed in our research group called frequency-shifted interferometry (FSI). This technique uses a continuous-wave light source, an optical frequency shifter, and a slow detector. We discuss the operation principles of several FSI implementations and show their applications in fiber length and dispersion measurement, locating weak reflections along a fiber link, fiber-optic sensor multiplexing, and high-sensitivity cavity ring-down measurement. Detailed analysis of FSI system parameters is also presented.

Design and characterization of a wearable macrobending fiber optic sensor for human joint angle determination

The work presented here describes the development and characterization of intensity fiber optic sensor integrated in a specifically designed piece of garment to measure elbow flexion. The sensing head is based on macrobending incorporated in the garment, and the increase of curvature number was studied in order to investigate which scheme provided a good result in terms of sensitivity and repeatability. Results showed the configuration that assured a higher sensitivity (0.644 dBm/deg ) and better repeatability was the one with four loops. Ultimately, this sensor can be used for rehabilitation purposes to monitor human joint angles, namely, elbow flexion on stroke survivors while performing the reach functional task, which is the most common upper-limb human gesture.

New statistical features for the design of fiber optic statistical mode sensors

Novel statistical features are proposed for the design of fiber optic statistical mode sensors. The statistical features are radial pth order moments, more precisely first and second order moments. These new features are compared with correlation and image difference features which were reported in the literature earlier. The fiber optic statistical mode sensor experiments are conducted for different applied loads and the corresponding images are captured using the CCD camera. Different statistical features such as image differencing, correlation, first moment and second moment are extracted from the captured images. These features are compared with each other in terms of different characteristics such as precision error, non-linearity, and hysteresis. It is shown that the first and second order moment statistical features are better alternatives for the design of statistical mode sensors, when precision and linearity characteristics are more important than the hysteresis characteristic.

Fiber optic sensor for the detection of ammonia, phosphate and iron in water

We report the design, development, and analysis of an evanescent wave fiber optic sensor, for detecting different chemical contaminants in water. The sensors are made up of a step index plastic multimode fiber. Different chemical contaminants in water like iron, phosphate and ammonia are determined using this sensor. The proposed measuring system with LED source is inexpensive and easily portable. The errors in measurement due to turbidity and other interferences are eliminated with the dual wavelength probing. Hence the proposed sensing method enhances sensitivity, selectivity and repeatability of measurement.

Design and Implementation of Miniature 3-Axial Fiber Optic Rate Sensor

The key design and implementation methods of Miniature 3-axial Fiber Optic Rate Sensor are described in detail. Based on plenty of theoretical analysis and experimental validation, effective measures and key technology on optical components, fiber coil technics, assembly methods, control circuits and structure solidity are adopt and summarized. Finally, its main engineering performance is tested and listed detailedly. From experimental results and engineering practice, we can conclude that Miniature 3-axial Fiber Optic Rate Sensor has the performance of high reliability, radiation resistance, low air pressure resistance, temperature resistance and high reliability, and can be widely used in some special and professional fields. More importantly, it greatly promotes the development of fiber optic sensing and inertial technology application of China.

Localized active-cladding optical fiber bend sensor

We present the design and fabrication of a novel fiber optic multiparameter bend sensor. Unlike current intrinsic fiber optic multiparameter bend sensors that depend on multiple cores or multiple fibers, the new sensor is based on three circumferential active-cladding point modifications on a single optical fiber at specific axial locations along the length of the fiber. A commercial 30-W CO2 laser is used to cut three point modifications in the plastic cladding of the fiber. Each of the three defects is filled with fluorophores (quantum dots) with different peak emission wavelengths. A 405-nm laser (operating at 10-mW) is used to excite the quantum dots, while a spectrometer, coupled to the fiber, measures the emission signals of each of the three fluorophores simultaneously. Results show that bending direction and degree of curvature at a single localized modification region can be expressed as a function of the three fluorescence intensities.

Package and installation of embeddable fiber optic sensors

The issues related with design of pre-embedded white light interferometric fiber optic steel, epoxy and concrete bar sensors for use in concrete structures in construction are discussed in this paper. The shapes are designed as spindle for steel and epoxy bar sensors and the simple cylinder or rectangular shape has been used in the cement-based concrete bar sensor. The manufacture procedures of the pre-embedded fiber optic sensors are described in detail. Finally, the issues on the installation of the fiber optic pre-embedded bar sensor into host structures are also considered.

Design and development of a temperature-compensated fiber optic polarimetric pressure sensor based on photonic crystal fiber at 1550 nm

Use of photonic crystal fibers (PCFs) in the field of sensing is relatively new. We propose the application of a PCF for pressure sensing. The fiber analyzed is a polarization-maintaining PCF that has negligible sensitivity to temperature, making it an ideal candidate for pressure sensing in harsh environments. On the basis of theoretical and experimental analysis, PCF is proposed to be applied as a temperature-compensated pressure sensor. Detailed theoretical analysis and the experiment carried out are described to show the concept of the sensor.

Fiber optic based gas sensor with nanoporous structure for the selective detection of NO 2 in air samples

A fiber optic based sensor (FOS) system for the selective detection of NO 2 in air samples has been developed. In the present design, a signal transduction mechanism based on the spectroscopic changes at the nanopores of a sol–gel element has been utilized. The sensor is prepared by uniformly immobilizing NO 2 sensing reagents at the pores during the sol–gel process. This facilitates an easy tailoring of the transducer element to build different optical designs. In the present paper, we describe two different fiber optic sensor designs, which are operating in extrinsic and intrinsic configurations. The extrinsic design is based on the fiber optic transflection probe geometry with its sensor element placed at the distal end of the fiber bundle. A part per billion (ppb) level detection has been achieved with the intrinsic sensor design with an active sol–gel fiber core as a sensor element. The two different optical designs improve the NO 2 detection level and sensitivity of detection. The nitrogen dioxide mediated coloration reaction ensures the high specificity of detection when tested in a mixture of gas samples. The test results indicate the potential use of the fiber optic sensor for real time detection of NO 2 in air samples.

Ratiometric fiber optic sensors for the detection of inter- and intra-cellular dissolved oxygen

A sensor platform was developed for the detection of inter- and intra-cellular dissolved oxygen, using a fiber optic probe. The design and fabrication of the oxygen fiber optic sensor are based on the excellent luminescence quenching properties of the near-infrared oxygen sensitive platinum(II) octaethylporphine ketone (PtOEPK) dye. Together with a reference dye, octaethyl porphyrin (OEP) or bodipy maleimide 577/618, the dye was entrapped, in an easily renewable liquid polymer matrix, made of polyvinyl chloride, including the plastisizing agent bis(2-ethylhexyl) sebacate (DOS). Multi-mode fibers were pulled down to submicron dimensions and a dip coating procedure was used to apply the sensing membrane film to the tip. This sensor was fully characterized and exhibits excellent reversibility, minimal photobleaching and leaching, and fast response times. The resulting oxygen sensor is one of the most sensitive optical oxygen sensors to date, with good linearity in the Stern–Volmer plot calibrations. This sensor is ultimately intended for biological inter- and intra-cellular measurements.

Transmission characteristics of SMS fiber optic sensor structures

We examine theoretically the transmission characteristics of the Single mode–Multimode–Single mode (SMS) fiber structures when the spot sizes of the fundamental modes of the single and multimode fibers do not match. It is observed that in such cases, the transmitted power becomes highly sensitive to the wavelength of operation and the length of the multimode fiber used. The study should be useful in the design of efficient fiber optic microbend sensors and novel wavelength filters using SMS structures.

A microbent fiber optic pH sensor

Optical fiber sensors developed for measuring pH values usually employ an unclad and unstrained section of the fiber. In this paper, we describe the design and fabrication of a microbent fiber optic sensor that can be used for pH sensing. In order to obtain the desired performance, a permanently microbent portion of a plastic optic fiber is coated with a thin film of dye impregnated sol–gel material. The measurements are simultaneously carried out in two independent detection schemes viz., the bright field detection configuration for detecting the core modes and dark field detection configuration, for detecting the cladding modes. The results of measurements of core mode-power and cladding mode-power variation with change in pH of a solution surrounding the coated portion of the fiber is presented. This paper thus demonstrates how a bare plastic fiber can be modified for pH sensing in a simple and cost effective manner.

In vitro and in vivo measurements of fiber optic and electrochemical sensors to monitor brain tissue pH

We report herein the development of fiber optic and electrochemical pH sensors that could become part of an arsenal to quickly and aggressively treat people undergoing a stroke as well as people who have suffered traumatic brain injury. The fiber optic pH sensor design consists of the immobilization of a pH sensitive dye, seminaphthorhodamine-1 carboxylate (SNARF-1C) within a silica sol–gel matrix. A miniature optoelectronics package was developed to acquire data from the fiber optic sensor. The electrochemical sensor consists of a thin film multilayer coating sputtered on a kapton substrate. The sensors were tested in vitro and in vivo. For both sensors, the in vitro results show linear and reproducible responses in human blood in the pH range 6.8–8.0. The results of the in vivo studies which were performed in Spraque–Dawley rats indicate that both the fiber optic and electrochemical sensors monitor pH with very little drift. It was concluded that both types of sensors would be useful in tracking brain tissue pH.

Development of fiber optic and electrochemical pH sensors to monitor brain tissue.

This article describes fiber optic and electrochemical pH sensors that could become part of a therapeutic arsenal to quickly and aggressively treat stroke victims as well as people who have suffered brain trauma. The fiber optic sensor design was based on the immobilization of a pH-sensitive dye, seminaphthorhodamine-1 carboxylate (SNARF-1C), onto the end of a 125-microm-diameter silica optical fiber using the sol-gel method. A miniature bench-top fluorimeter system was developed for use with the optical fiber to obtain pH measurements. The electrochemical sensor was based on sputter-coated iridium oxide thin films. Linear and reproducible responses for both sensors were obtained in human blood with pH varying between 6.8 ato 8.0, which encompasses the clinically relevant range. In vivo studies were also performed and results indicated that both types of sensors tracked pH with very little drift.

Optimal design of IRIS-based polarimetric intrinsic fiber optic current sensors

Performance of reciprocity-compensated polarimetric fiber optic current sensors are analyzed for typical low-birefringence fibers. The intensity-based reciprocity-insensitive structure (IRIS) can effectively balance the birefringent and lossy influences in intrinsically low-birefringence fiber-based current sensors, while supplementary techniques such as wavelength control and pole-zero cancellation are needed to eliminate the strong polarization coupling effect in spun fiber-based sensors. It is shown from simulation that the stability of the sensor can be maximized by using the IRIS and a suitable initial birefringence.

Optimal design of fiber optic sensors for control of flexible structures

This paper presents methods for designing fiber optic sensors for control of flexible structures. The sensors are designed so that a first-order observer, instead of a high-order state estimator, can be used to construct feedback control laws based on distributed or high-order finite-dimensional models of the structure. Design methods for the sensors and the observers are developed for two types of problems: 1) where the sensors extend over the entire structure, and 2) where the sensors extend over one or more subregions.

Design of bioluminescence-based fiber optic sensors for flow-injection analysis

A fiber optic sensor based on enzyme-catalyzed light-emitting reactions has been developed and integrated in a flow-injection analysis (FIA) system. The firefly luciferase, specific for ATP, and the bacterial oxidoreductase/luciferase system, specific for NADH, have been immobilized on preactivated polyamide membranes. ATP and NADH analysis could be performed in the range from 0.1 pmol to 3 nmol and from 0.5 pmol to 1 nmol, respectively. By co-immobilizing these two bioluminescence systems on the same membrane, a multi-function biosensor has been designed allowing the alternate determination of ATP or NADH with the same sensitivity as that obtained with the two different monofunctional biosensors. A partly self-contained biosensor has been also developed for the flow injection analysis of NADH. For this purpose, FMN (one of the substrates of the bacterial bienzymatic system) has been embedded in a synthetic matrix. Different supports have been tested for the non-covalent immobilization of this substrate and its release in the immediate vicinity of the bound enzymes. Using a photo-crosslinked poly(vinyl alcohol) support, 40 reliable assays ( cv = 4.5% ) could be performed without changing or reloading the matrix.