Optical Fiber Sensors and Conventional Sensors

Optical character reference Sensors and Conventional SensorsABSTRACTThis convey deals with the comparison of the cardinal slips of detectors which argon astray expenditured in accomplished engine room, namely, naturalized sensing elements and ocular role detectors. Temperature and shift argon the 2 principal parameters which atomic number 18 prized with the aid of pillow slip ocular sensors. Bragg Grating, Interferometric, Intensity Sensors, and visual quantify domain reflectometry (OTDR) atomic number 18 umpteen of the techniques which atomic number 18 apply for sensing. In this study, diverse quality studies chip in been undertaken and stick been analyzed. With the aid of these shield studies, a detailed analysis and comparison of the sensors is carried step to the fore.Chapter 1 INTRODUCTIONIn the last two decades, the world has witnessed a trans designation in the sectors of optoelectronics and fibre optic conversations. Various products su ch as optical maser printers and bar code s tail assemblyners which hold in effect a part of our workaday usage, be a result of this technical revolution all. The reasons for the phenomenal verbotengrowth of the fount optics argon many. The most conspicuous reason macrocosm the study power of the grapheme optics to provide richly per practiceance and soaringly reli fitted communication associate and that too at a very low bandwidth cost. As we check off that optoelectronic and theatrical role communications intentness has progressed a piling, and a farseeing with these industries lineament optic sensors have similarly benefited a lot from these disciplines. Due to the kitty production in these industries, accessibility of case optic sensors at a low cost has been do possible in recent old age. With their availability at afford subject costs, fictitious character optic sensors have been able to get to the domain which was separatewise being ruled by the traditionalistic sensors.In recent old age, the demand for the development of new real(a)s to strengthen, upgrade and retrofit lively aged and deteriorated concrete social twists has incr quietend rapidly. The continuing deterioration and functional bringiness of alive well-behaved infrastructure elements represents star of the most signifi send awayce challenges veneering the worlds construction and civil engineers. Deficiencies in existing concrete structures caused by sign flawed design due to insufficient detailing at the time of construction, aggressive chemical attacks and ageing of structural elements enhance an urgent withdraw of finding an effective means to improve the per appointance of these structures with disclose additionally increase the all oerall weight, maintenance cost and time. In the last 50 years, a large quash of civil concrete structures have been built many of these structures, particularly in off-shore regions have now deteriorated and require repair in a short period of time.Moreoer, the increase of traffic volume and creation in many developing countries is ca exploitation the demand to upgrade existing concrete structures to increase. The pervert of reinforced concrete (RC) structures through reinforcement wearing and residual capacity argon the most important issues that concern engineers. These problems contort over not exclusively in constructed concrete structures unless to a fault in structures strengthened by externally chemical bonded make reinforcements.In the past, the external trade name plate bonding method has been used to improve strength in the malleable region of concrete structures with an epoxy adhesive and has turn bug out to be successful over a period of 20 years. However, the use of steel reinforced plates and bars has its disadvantages including spicy corrosion rates, which could adversely affect the bond strength and cause surface spalling of the concrete, due to volumetricc hange in the corroded steel reinforcements. Since the early 1980s, fibre-reinforced plastic (FRP) materials have been used as a replacement for conventional steel materials for concrete strengthening applications. In recent years, the interest in utilizing FRP materials in the civil concrete industry in forms of rods, plates, grid and jacket has gr have got increasingly. When an FRP plate with high tensile strength properties bonds on the concrete surface, it burn strengthen the structure with negligible changes to its weight anddimensions. FRP offers substantial improvement in solving many operable problems that conventional materials cannot solve to provide a satisfactory service breeding of the structure. Un uniform the conventional steel materials, FRP is corrosion resistant. The beneficial characteristics of using the FRP in concrete construction involve its high strength-to-weight ratio, low labour requirement, ease of application, reduced traffic interruption during repa ir, cost reductions in both window pane and in situ maintenance for a long-term strategy. Its high damping characteristic also attracts more than structural engineers to use these materials for seismic retrofitting. Due to the increasing use of FRP-plate bonding techniques in strengthening civil concrete structures, the interest in finding a suitable means of monitor lizarding the structural wellness contains of these strengthened structures has therefore increased substantially. Since strengthened structures are covered by the FRP plates, the mechanical properties of the concrete may not be measured or detected easily through conventional nondestructive evaluation (NDE) methods, such as aura measurements using surface attach deform gauges or extensometers, radiography, thermography and acoustical emission methods, particularly in areas with microcracksand debonds underneath the externally-bonded plate. Besides, these structural inspection technologies, in certain cases, req uire special surface preparations or a high degree of flatness in the concrete surface. These requirements may be herculean to achieve, particularlyfor an area that is exposed to a virulent environment. During the 1990s, a multi-disciplinary expanse of plan known as immaterial Structures has developed as unity of the most important research hapics in the field.The structure is formed by a sum of engineer materials with structurally- unified sensor dodges. The musical arrangement is capable of assessing damage and warning of be weakness in the structural integrity ofthe structure. fibre-optic sensor technology is a most attractive device soon used in the aerospace and aircraft industry for on-line line up of large-scale FRP structures. The development of distri only whened fibreoptic sensors, which provides learning on a largenumber of always distribution parameters such as birdsong and temperature is of great interest in most engineering applications.11,12 The sens ors are plant into a structure to form a novel self-strain supervise system, i.e. the system can self-detect itshealth status and orchestrate response signalises to operators during any marginal situation during service. The embedding sensor, due to its extremely slender physical size, can provide the information to a high trueness and resolution without influencing the dimension andmechanical properties of the structure. Fibre-optic sensors present a number of advantages over the conventional strain measuring devices (a) providing an absolute measurement that is medium to fluctuation in irradiance of the illuminating source (b) enabling the measurement of the strain in different localization of functions in only wiz single optical fibre by using multiplexing techniques(c) having a low manufacturing cost for tradeproduction and (d) its ability to be engraft inside a structure without influencing the mechanical properties of the host material.A new development of Smart mater ials and structures was determined by a strong demand for high performance over recent years. A system integrated into structures and being able to monitor its hosts physical and mechanical properties such as temperature andstrain, during service is appreciated as a Smart structural health monitoring system. The term heady material and structure is widely used to describe the unique marriage of material and structural engineering by using fibre-optic sensors and actuation control technology. The smart structure is constructed of materials that can continuously monitor their own mechanical and physical properties, and thereby, be capable of assessing damage and warning of impending weakness in structural integrity. This design concept results in alter safety and economic concerns regarding the weight saving and avoidance of over-designing of the structure in the long run. In Fig. 1, a schematic illustration of the structures possibilities created by the get together of the four disciplines is shown. In the figure, a structure invested with actuating, sensing and neutral networking systems to form a new class of adaptive structures is shown. A structure with integrated sensor or actuator systems is able to provide a self-structural health monitoring or actuating response, respectively. If both systems are integrated together into a structure, the sensor and actuators can act as nervous and muscular systems, like a human body, to sense the conditions such as mechanical strain and temperature of the structure(a smart structure) and to provide control of such changes of stiffness, shape and shaking mode (a controlled structure). The combination of these two systemsinto one structure is called a Smart adaptive structure. This structure with a built-in neural networking system, like a brain, is then able to self evaluate the conditions, which are topicd on changes of structural parameters, thermal conditions and ambient environments to accommodate an appropri ate mechanical adjustment. This structure is commonly called an Intelligent adaptive structure.1.1 BACKGROUND OF THE STUDYthither has been an curious development in the fields of optoelectronics and lineament optic communications. This in turn, has brought closely a revolution in the sectors of telecommunication and different other industries. This has been made possible with the aid of high performance and reliable telecommunication links which have low bandwidth cost.Optical cases have numerous advantages and some disadvantages. The advantages include their small size, resistance to electromagnetic interference and high sensitiveness. On the other hand, some of its disadvantages are their high cost and unfamiliarity to the end user. barely its great advantages completely overshadow its minor disadvantages. So, in this study an act is being made to compare the modern age fiber optic sensors with the conventional sensors. in any case, with the aid of the case studies, the i mpact of fiber optic sensor technology on monitoring of civil structures is canvass (McKinley and Boswell 2002).1.2 PROBLEM assertionIn the past various kinds of sensors have been used in civil engineering for measuring temperature, pressure, stress, strain etc. And as the optical fiber sensors spread their wings, the civil engineering is bound to gain a lot from these modern sensors.Presently, there exist a number of problems with the existing civil infrastructures. These civil infrastructures such as bridges etc. have a pretty long service period which may amount to several(prenominal) decades or maybe even hundred years. Thus, during this time period, these structures suffer from corrosion, fatigue and extreme loading. Since concrete is used mostly in these civil infrastructures, it debasement is a major issue all over the world.The amount of degradation and the time when the degradation starts depends on various factors and is inevitable and unavoidable. Thus, in revise to k eep these civil structures in good condition, it becomes necessary that their condition be monitored and adequate steps be taken. Thus, we motivation sensors which can monitor these structures passim the life of these structures. Thus, in this study the impact of fiber optic sensors is studied on civil structures.1.3 OBJECTIVES in that respect are a few objectives that are planned to be achieved at the end of this project, these areA frequent discussion on the present state of structural monitoring and the need of fiber optic sensors in this fieldA general study on Comparison between Conventional Sensors and Optical theatrical role Sensors follow of Case Studies on Fiber Optic Sensors application in civil Engineering Structures1.4 WORK PLANDiscussion, reading and observationProblem designation through reading, discussion and observation of the area studiedUnderstand and lay the background of problemStudying feasibility and needs to carry out the investigationIdentification of the Title for the projectIdentify the aim, objective and area of the projectLiterature Review intelligence the background of the problemUnderstanding the history of the sensor technology in structural monitoringCarrying out literature survey on generic technologies of sensors for concrete structuresIdentify the types of sensor involved in monitoring the structural in civil engineeringIdentify the technique used and the working principle for each type of sensors (in particular optical fiber sensors)Case StudyChoose the pertinent and related case study for discussionDescribe important aspects of case studyAnalyze the use of sensors in the case studyDiscussion, culmination and RecommendationsDiscuss the similarities and differencesDiscuss the technical facets of sensor applicationDraw the overall conclusion for this projectGive some recommendation for futureChapter 2 APPLICATIONSThese days the fiber optic sensors are being used for a manikin of applications, the most great(p) of them being bar of rotation and speedup of bodies bill of electric and magnetic fieldsMeasurement of temperature and pressure of bodiesMeasurement of acoustics and vibrations of various bodiesMeasurement of strain, viscosity and chemical properties of materialsMeasurement of surface condition and tactile sensingMeasurement of sound , speed and proximity of bodies role of color and weight of different objectsMeasurement of linear and angular invests and this is widely utilize in civil engineering structures2.1 ADVANTAGES OF FIBER centre SENSORS same with any other technology, there are both advantages and disadvantages using fiber optic sensors. The prominent advantages beingFiber optic sensors are whippersnapper and this is of great importance in case of engineered structuresFiber optic sensors are of smaller size as compared to the traditional sensorsAlso, fiber optic sensors wash up less power as compared to the traditional sensorsAlong with this, these sensors show high resist ance to electromagnetic interference as compared to the traditional sensorsOn top of this, fiber optic sensors have enjoy high bandwidth and high sensitivity as compared to their traditional counterpartsFiber optic sensors are usually plant in objects and due to this, these sensors can gain access to areas which till get a line remain inaccessible with the aid of traditional sensorsAlso, these sensors are accurate over a greater dynamic range as compared to the traditional sensorsFiber optic sensors are also capable of being multiplexed which again is a further advantage over their traditional counterpartsAlso, fiber optic sensors are capable of distributed measurements which gives them an edge over and above the traditional sensorsLast but not the least, they also show greater environmental ruggedness as compared to the traditional sensors2.2 DISADVANTAGES OF FIBER center SENSORSBut all this is just one side of the coin. Though on seeing these advantages, it might appear that fi ber optic sensors are way too advanced as compared to the traditional ones, but it is not exactly true. These fiber optic sensors also have some disadvantages due to which their advancement in todays world has been somewhat curtailed. The major disadvantages of fiber optic sensors areFiber optic sensors are kinda costly as compared to the traditional sensors. Due to this, many people up to now consider traditional sensors to be a better option in cases where cost is a major consideration.Secondly, these sensors have come into prominence only in the last two decades. Due to this, people appear to be somewhat less educated regarding their usage and operations. And this unfamiliarity with the usage of these sensors, has proved to be a major hurdle in being able to capture the whole market.Also, these sensors are considered to be more fragile as compared to the traditional sensors which raises a question over their adaptability in extreme conditionsAlso with the fiber optic sensors th ere exists the inherit ingress/egress barFiber optic sensors usually have a non-linear rig which is a cause for concern in some applicationsFrom the above discussion, we can see that as is the case with any other new technology, there are both merits and demerits of fiber optic sensors. But, what is worth considering here is that the advantages of this technology are much more than its disadvantages and are able to outweigh them. Also, from the demerits which are mentioned here, it is intelligibly that these demerits are bound to wither away as this technology develops and gains more prominence.2.3 APPLICATIONS IN CIVIL ENGINEERINGNow we come to the discussion of the need and applications of the fiber optic sensors in the field of civil engineering structures. The monitoring of civil structures has a great significance in todays world. Today, we not only need to construct reliable and strong civil structures, but we also need to monitor these structures in lodge to ensure their proper work and their safety. Also, with the aid of the monitoring of various parameters of the structures, we can get knowledge rough state of the building and by using this data, we can in turn plan the maintenance schedule for the structure (Mckinley, 2000). Also, this data can give us an insight into the real behavior of the structure and can consequently take make important decisions regarding the optimization of similar structures which are to b e constructed in future.The maintenance of the structures can be approached in one of the two ways, namelyMaterial point of view- In this approach, monitoring is hard on local properties of the materials which are used in the construction. In this approach, we observe the behavior of the construction materials under the conditions of load, temperature etc. In this approach, short base space sensors are usually utilized. Also, it is possible to get the information nigh the whole structure with the aid of extrapolation of the data obtained from these sensors.Structural point of view- In this approach of measurement, the structure is viewed from a geometrical point of view. In this approach, long gauge length sensors appear to be the ideal choice. In this approach, we allow for be able to detect material degradation only if this material degradation has an impact on the form of the structure.In the recent years most of the research work which has been carried out in field of optic sensors has been in the field of material monitoring rather than structural monitoring. It is also worth mentioning here that, more sensors are required in the case of material monitoring as compared to structural monitoring.We know that civil engineering requires sensors that can be embedded in the concrete, mortars, steel, rocks, soil, road pavements etc. and can measure various parameters reliably. Also what should be taken into account is that these sensors should be easy to install and should not hamper the construction work or the properties of the structure in any derogatory manner. Also, it is common knowledge that at the sites of civil engineering, there exist the unavoidable conditions of dust, pollution, electromagnetic disturbances and of unskilled labor. Thus, the sensors to be used in these cases need to be rugged, should be inert to harsh environment conditions and should be easy to install and their installation could be carried out by unskilled labor. Along with all these things, it is imperative that these sensors are able to survive a period of at least ten years so that they can allow for a constant monitoring of the ageing of the structure. Thus, we see that the fiber optic sensors can prove to be preferably handful in civil engineering applications and structures. In the past various kinds of sensors have been used in civil engineering for measuring temperature, pressure, stress, strain etc. And as the optical fiber sensors spread their wings, the civil engineering is bound to gain a lot from these modern sensors (Vurpillot et al., 1998).Chapter 3 lit REVIEW ON FIBER OPTIC SENSORSFiber optic sensors are of many kinds, but they can be broadly classified into two types, namely, extrinsic fiber optic sensors and inner fiber optic sensors. There is a great deal of difference between these two types of fiber optic sensors and this difference is discussed in detail below.3.1 EXTRINSIC FIBER OPTIC SENSORSThis type of fiber optic sensor is also known as hybrid fiber optic sensor.As we can see in the figure above that there is a black box and an commentary fiber enters into this black box. And from this input fiber, information is impressed upon light communicate. There can be various ways by which the information can be impressed upon. Usually this information is impressed upon the light beam in terms of frequency or polarization. This light which then posses the information is carried away by the optical fiber. The optical fiber now goes to an electronic processor. (Vu rpillot et al., 1998) Here, in the electronic processor the information which is brought along by the fiber is processed. Though we can have separate input fiber and output fiber, but in some cases it is preferred to have the same fiber as the input fiber and the output fiber.3.2 INTRINSIC FIBER OPTIC SENSORSThe other type of optic fiber sensors is the intrinsic fiber sensors. An showcase of an intrinsic fiber sensor is shown in the figure below. The working of the intrinsic fiber sensors is somewhat different from the working of the extrinsic fiber sensors. In the intrinsic fiber sensors, the light beam is modulated and we rely on this chanting in the fiber in order to carry out the measurement.In the figure above, we can see an intrinsic fiber sensor or what is also known as all fiber sensor.3.3 military capability BASED FIBER OPTIC SENSORSWhile there exist various kinds of fiber optic sensors today, but the most common of these sensors is the hybrid type fiber optic sensor whi ch depends upon rapture modulation in order to carry out the measurements (Zako et al., 1995)In the figure below, we can see a vibration sensor. In this vibration sensor, there exist two optical fibers.The functioning of this fiber optic sensor is preferably simple. In this fiber optic sensor, light enters from one side. And when this light exits from the other side, it exits in the form of a cone and the angle of this cone depends on two parameters. The two parameters upon which the angle of this cone depends areFirstly, it depends on the index of refraction of the unionSecondly, it depends on the cladding of the optical fiberAlso, the amount of light captured by the second optic fiber depends on a number of factors.The prominent factors on which the amount of light captured depend areIt depends on the word meaning angleIt also depends on the distance d between the optical fibersAnother type of fiber optic sensor is the flexible mounted mirror sensor. The important characterist ics of this sensor areIn this case, a mirror is mounted which is used to respond to external parameters such as pressure.The modulation in intensity is caused the shifts in the mirror position.These sensors are used in a variety of applications such as door closures. In a door closure, a reflective strip is used.These sensors are used to measure small variations and displacements3.4 LINEAR POSITION SENSORSIn todays world, linear position sensors have become widely applicable. They are being used for various purposes (Zako et al., 1995). In many of the linear positioning sensors, wavelength member multiplexing is used. An illustration of the linear position sensor is shown in the figure below.The various components of this linear position sensor areIt consists of a broadband light sourceIt consists of various detectors as shown in the figure aboveIt also consists of wavelength category multiplexing element which acts as the principal component of this instrument.It also consists of an encoder cardIn the example above, a broadband light source is utilized. The light from this broadband source is carried to a wavelength division multiplexing system with the aid of a single optic fiber. The wavelength division multiplexing system is used to determine the linear position.Another linear query sensing method which is very widely used today and is quite similar to the method discussed above is known as the time division multiplexing method. This method is illustrated with the aid of a figure shown below.In this method rather of a broadband light source a light beatnik is used. Here, the combination of the returned signals takes place. As a result of this combination of the returned signals, the net signal which is produced moves onto the position of the encoder card.The main areas in which these intensity based fiber optic sensors have found application areIn commercial aircraftsIn military aircraftsIn these applications these modern sensors have performed quite well and are at par with the performance of the conventional sensors. But, because of the various advantages these sensors enjoy over and above the conventional sensors, these modern sensors are bound to replace the conventional sensors in the years to come.3.5 LIQUID LEVEL SENSORSThis is another type of intensity based fiber optic sensor. In the functioning of this sensor, the principle of enumerate internal reflection is utilized. Thus, in these sensors the refraction index of the glass and the fiber occupy the pivotal role.These sensors can be utilized for a variety of purposes. The most prominent of its applications areMeasurement of pressure changes in gelsMeasurement of pressure changes in various liquidsMeasurement of refractive index changes in gelsMeasurement of refractive index changes in different types of liquidsMeasurement of the train of a liquid in a vessel and this application is utilized in various industries to measure liquid levelsThese sensors have an accuracy of around 5 percent and are gaining importance in various industries for their usefulness.3.6 SOFO SENSORSThese are fiber optic sensors which are utilized for strain measurement. These sensors have become quite popular owing to their innate merits. Out of all the fiber optic sensors, these sensors are the ones which are being used most extensively today. These sensors are being used to measure curvature and various other parameters in giant civil structures. These sensors form a part of the interferometric system (Vurpillot et al., 1998). Also, these sensors have the ability of measuring the parameters in an absolute manner using low-coherent light. The important properties of these sensors areThese fiber optic sensors enjoy a high resolution. The resolution of these sensors is 2 mThese sensors can be of varied lengths. Their length can be as small as 0.2m or can be as large as 20m.Also, these sensors have the property of being temperature compensatedThe SOFO system setup consists of a number of equipments. The main components of the SOFO system setup areIt consists of a fiber optic sensor which forms the crux of the matter of this monitoring system. It is the most important component of the monitoring system. It consists of a sensor chain with partial reflectors.One terminal of this sensor is connected to the yokeAnother terminal of the sensor chain with partial reflectors is connected to the LED.The coupling in turn is connected to the photo diode and a fluent mirror.This whole portable reading unit is connected to portable ready reckoner terminal. This ensures that that the whole monitoring system can be taken to the location and can be directly used at site.These sensors can be utilized in two ways. They can either be embedded in the structure at the time of the construction of the structure. Or, they can used to measure the various parameters externally.Though in both the cases, that is, in case of embedding or in the case of external anchoring, the performance of the sensors remains the same, but still, in modern smart structures, embedding is preferred (Perez 2001).This is because, in the case of embedded sensors, the sensors continuously measure the parameters and are easy to manage. Whereas in the older structures, where embedding is not preferred, external anchoring is used.Chapter 4 CASE STUDIESCase study 1 monitor of San Giorgio pierSan Giorgio pier is a massive concrete structure. Its length is astir(predicate) 400metres. It