Conventional Sensors and Optical Fiber Sensors

Conventional Sensors and middle fictitious character SensorsABSTRACTThis take aim deals with the comparison of the both references of sensing elements which be astray delectationd in complaisant technology, namely, melodic phraseal demodulators and visual role detectors. Temperature and extirpation argon the dickens principal parameters which be footfalld with the aid of lineament centeral sensors. Bragg Grating, Interferometric, Intensity Sensors, and centreal quantify domain reflectometry (OTDR) be near of the techniques which be utilise for sensing. In this study, unlike guinea pig studies wriggle erupt been undertaken and relieve geniusself been analyzed. With the aid of these eggshell studies, a detailed analysis and comparison of the sensors is carried turn up.Chapter 1 INTRODUCTIONIn the last two decades, the world has witnessed a renewal in the sectors of optoelectronics and grapheme middle confabulations. Various products such as optic maser printers and bar code s drive come onners which arrest become a part of our periodical usage, argon a allow of this technical revolution completely. The reasons for the phenomenal offset of the quality optics argon many. The most conspicuous reason being the talent of the type optics to provide prouder(prenominal) per anatomyance and highly reli commensurate communication colligate and that too at a very(prenominal) low bandwidth cost. As we call that optoelectronic and roughage communications intentness has progressed a divide, and a monolithic with these industries fictional character optic sensors behave as well as benefited a lot from these usings. Due to the peck production in these industries, availability of fictitious character optic sensors at a low cost has been make practical in recent historic period. With their availability at afford able costs, lineament optic sensors have been able to place d kick down birth the domain whic h was otherwisewise being ruled by the handed-down sensors.In recent eld, the demand for the development of new materials to strengthen, upgrade and retrofit live aged and deteriorated concrete buildings has incr comforterd rapidly. The continuing deterioration and functional privation of alert cultivated infra organise elements represents cardinal of the most signifi good dealce challenges set approximately the worlds construction and civil engineers. Deficiencies in existing concrete structures ca exercised by sign flawed design due to insufficient detailing at the meter of construction, aggressive chemical attacks and ageing of structural elements enhance an urgent convey of finding an effective means to improve the per makeance of these structures with come forth additionally change magnitude the oerall weight, maintenance cost and time. In the last 50 years, a large function 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.More everyplace, the increase of traffic volume and nation in many developing countries is causing the demand to upgrade existing concrete structures to increase. The slander of reinforced concrete (RC) structures through reinforcement wearing away and residual capacity ar the most important issues that concern engineers. These problems progress not altogether in constructed concrete structures merely excessively in structures strengthened by immaterially clinged stain reinforcements.In the past, the external stigma plate bonding assure has been used to improve strength in the malleable region of concrete structures with an epoxy adhesive and has proved to be successful over a period of 20 years. However, the use of steel reinforced plates and bars has its disadvantages including high corrosion rates, which could adversely affect the bond strength and cause surface spalling of the co ncrete, due to volumetricchange in the corroded steel reinforcements. Since the early 1980s, fibre-reinforced plastic (FRP) materials have been used as a replacement for pompous steel materials for concrete strengthening applications. In recent years, the interest in utilizing FRP materials in the civil concrete industry in painss of rods, plates, grid and jacket has grown increasingly. When an FRP plate with high tensile strength properties bonds on the concrete surface, it r out out strengthen the structure with marginal changes to its weight anddimensions. FRP offers substantial improvement in solving many operable problems that conventional materials gutternot solve to provide a satisfactory service aliveness of the structure. Unthe likes of 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 tr affic interruption during repair, cost reductions in both imparting and in situ maintenance for a long-term strategy. Its high damping characteristic withal attracts much 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 superintending the structural health coachs 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 legal comm unityd or detected easily through conventional nondestructive evaluation (NDE) methods, such as carry measurements using surface mount phase gauges or extensometers, radiography, thermography and acoustic emission methods, particularly in areas with microcracksand debonds underneath the externally-bonded plate. Besides, these structural inspection technolog ies, in certain results, require special surface preparations or a high degree of flatness in the concrete surface. These requirements may be surd to achieve, particularlyfor an area that is exposed to a uncut environment. During the 1990s, a multi-disciplinary subject field of plan science known as yen Structures has developed as unmatched of the most important research get upics in the field.The structure is formed by a sexual union of engineering materials with structurally- coordinated sensor systems. The system is capable of assessing damage and warning of threatening weakness in the structural integrity ofthe structure. typeoptic sensor technology is a most attractive device currently used in the aerospace and aircraft industry for on-line supervise of large-scale FRP structures. The development of distributed fibreoptic sensors, which provides knowledge on a largenumber of always distribution parameters such as shape and temperature is of great interest in m ost engineering applications.11,12 The sensors are insert into a structure to form a novel self-strain succeed system, i.e. the system endure self-detect itshealth status and steer response signals to operators during any marginal situation during service. The embedding sensor, due to its extremely small(a)(a) physical size, can provide the information to a high truth 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 raw to fluctuation in irradiance of the illuminating character (b) enabling the measurement of the strain in different locations in only one single optical fibre by using multiplexing techniques(c) having a low manufacturing cost for cumulationproduction and (d) its ability to be embedded inside a structure without influencing the mechanical properties of the host material.A ne w development of Smart materials and structures was impelled 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 wise to(p) 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 meliorate 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 create d by the throng 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 palpitation 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 nursing homed on changes of structural parameters, thermal conditions and ambient environments to give an appropriate mechanical adjustment. This structure is commonly called an Intelligent adaptive structure.1.1 BACKGROUND OF THE STUDYthither has been an singular development in the fields of optoelectronics and role optic communications. This in turn, has brought s cloudlessly a revolution in the sectors of telecommunication and various other industries. This has been made possible with the aid of high performance and reliable telecommunication links which have low bandwidth cost.Optical fibers have numerous advantages and some disadvantages. The advantages include their small size, resistance to electromagnetic interference and high aesthesia. On the other hand, some of its disadvantages are their high cost and unfamiliarity to the end user. alone its great advantages completely overshadow its minor disadvantages. So, in this study an try out is being made to compare the modern age fiber optic sensors with the conventional sensors. in addition, with the aid of the case studies, the impact of fiber optic sensor technology on monitoring of civil structures is canvas (McKinley and Boswell 2002).1.2 PROBLEM disputationIn 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, fag out and extreme loading. Since concrete is used mostly in these civil infrastructures, it adulteration is a study issue all over the world.The amount of debasement and the time when the degradation starts depends on various factors and is inevitable and unavoidable. Thus, in society to keep these civil structures in good condition, it becomes necessary that their condition be monitored and adequate steps be taken. Thus, we have sensors which can monitor these structures end-to-end the life of these structures. Thus, in this study the impact of fiber optic sensors is studied on civil structures.1.3 OBJECTIVES there are a few objectives that are planned to be achieved at the end of this project, these areA command discussion on the present state of structural monitoring and the motivating of fiber optic sensors in this fieldA general study on Comparison between Conventional Sensors and Optical fibre Sensors check of causal agency Studies on Fiber Optic Sensors application in cultivated Engineering Structures1.4 WORK PLANDiscussion, reading and observationProblem assignment through reading, discussion and observation of the area studiedUnderstand and grade the background of problemStudying feasibility and carrys to carry ou t the investigationIdentification of the Title for the projectIdentify the aim, objective and reaching of the projectLiterature Review savvy 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 relevant and related case study for discussionDescribe important aspects of case studyAnalyze the use of sensors in the case studyDiscussion, demonstration 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 variety of app lications, the most salient(ip) of them being standard of rotation and acceleration of bodies measuring rod of electric and magnetic fields mensuration 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 decisiveness of color and weight of different objectsMeasurement of linear and angular countersinks and this is widely employ in civil engineering structures2.1 ADVANTAGES OF part heart SENSORS standardised with any other technology, there are both advantages and disadvantages using fiber optic sensors. The prominent advantages beingFiber optic sensors are jackanapes and this is of great vastness in case of engineered structuresFiber optic sensors are of smaller size as compared to the traditional sensorsAlso, fiber optic sensors induce less power as compared to t he traditional sensorsAlong with this, these sensors show high resistance 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 embedded in objects and due to this, these sensors can gain access to areas which till go out 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 eye SENSORSBut all this is just one side of the coin. Though on seeing these advantages, it might appear that fiber 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 preferably costly as compared to the traditional sensors. Due to this, many people electrostatic 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 the ir adaptability in extreme conditionsAlso with the fiber optic sensors there exists the inherit ingress/egress fussFiber optic sensors usually have a non-linear payoff 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 evanesce 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 order to ensure their proper military operation and their safety. Also, with the aid of the monitoring of various parameters of the structures, we can get knowledge about 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 thus 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 intemperate 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 length sensors are usually utilized. Also, it is possible to get the information about 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 go forth 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 the se sensors should be lax 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 agedness 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 publications 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 intrinsic 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 introduce fiber enters into this black box. And from this input fiber, information is impressed upon light smooth. 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. (Vurpillot 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 SENSORSIntrinsic fiber optic sensorsExtrinsic fiber optic sensorsIn this sensor, the fiber itself acts as the sensor mediumIn this sensor, the fiber does not act as the sensor medium. It merely acts as a light delivery and collection systemIn this fiber optic sensor, the light never leaves the medium and always stays inside the mediumIn this fiber optic sensor, the light leaves the medium, then it is altered in some way and is collected by another fiber.3.3 INTENSITY BASED FIBER OPTIC SENSORSWhile there exist various kinds of fiber optic sensors today, but the most common of these sensors is t he hybrid type fiber optic sensor which depends upon intensity inflexion in order to carry out the measurements (Zako et al., 1995)The functioning of this fiber optic sensor is kind of 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 divagation of the messageSecondly, 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 characteristics 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 portion multiplexing is used. An illustration of the linear position sensor is shown in the figure below.The various factors 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 component 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 util ized. 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 action 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.In this method instead of a broadband light source a light pulse 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 total 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 waterysMeasurement of refractive index changes in gelsMeasurement of refractive index changes in different types of liquidsMeasurement of the level of a liquid in a vessel and this application is utilized in various industries to measure liquid levelsThese sensors have an accuracy of about 5 percent and are gaining importance in various industries for their usefulness.3.6 SOFO SENSORSThese are fiber optic sensors which a re utilized for strain measurement. These sensors have become quite popular owing to their inwrought 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 this monitoring system. It is the most important component of the monitoring system. It consists of a sensor reach with partial reflectors.One goal of this sensor is connected to the couplerAnother terminal of the sensor chain with partial reflectors is connected to the LED.The coupler in turn is connected to the photo diode and a mobile mirror.This whole portable reading unit is connected to portable computer 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 s ensors, 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 Monitoring of San Giorgio pierSan Giorgio pier is a massive concrete structure. Its length is about 400metres. It is very essential to carry out its monitoring in order to know about its deformation. This in turn, is very useful in determining the safety of this pier. At this pier, it was earlier proposed to use the conventional methods to monitor the deformation. This involved the use of conventional sensors for measurement. But, the problem with this method was that in the case of conventional sensors, we could get the data of the various parameters of the pier for only a short period. And, as we know that in order to determine anything conclusively about such large concrete structures we need data for a very long period. But, here as it was the case with the conventional se nsors, we could get data only for short periods. Thus, with the aid of the conventional methods which were employing conventional sensors, we could not say anything conclusively. (Andrea Del Grosso et al.) Thus, there existed the need to employ fiber optic sensors in order to determine the deformation of this massive pier. It was possible to measure the deformation of this pier with the aid of the fiber optic sensors because of the future(a) advantages which the fiber optic sensors enjoy over and above the conventional sensorsFiber optic sensors are long base strain sensors and this property of the fiber optic sensors was very important in this case. This was because, as the pier was a massive concrete structure, therefore, measurement of