Category: FBG Sensors

FBG Sensors for Concrete Constructions

FBG sensors are used to monitor structures made of various materials, including concrete and metals. In particular, we are talking about structures that usually consist of metals such as aluminum, steel, copper, etc.

Concrete Constructions’ Main Issues

Reinforcement plays a major role in concrete structures. Its strength and durability can affect the appearance and growth of the cracks. One of the reasons for such a degradation is corrosion.

Corrosion occurs when a substance reacts with its surroundings, resulting in the material’s consumption or contamination by an environmental component. Corrosion can reduce the life and load-bearing capacity of a structure. Due to the chemical reactions caused by corrosion, it may change the reflection of the steel surface. The thicker the material, the more it will be subject to deformation. Here, structural health monitoring (SHM) delivers the results.

Structural Health Monitoring (SHM) is an important tool used to monitor the occurrence of corrosion. It is effectively used in constructions to detect and prevent any possible damage. Early corrosion monitoring is essential. Corrosion is dangerous because it causes high costs to repair, and it takes some time to be discovered. In the most extreme cases it can bring the collapse of the complete structure.

Types of Corrosion Monitoring Devices

Today, there are a number of inspection technologies that have been developed specifically for the purpose of detecting damage to constructions. These methods include acoustic emissions, ground penetrating radar systems, electromagnetic techniques, etc. However, they all have their shortcomings including susceptibility to electromagnetic disturbance and lack of continuous structural health monitoring.

Fiber optic sensors are an effective solution for structural health monitoring. They provide real-time monitoring and low-cost techniques that monitor and control the corrosion appearance. There are a variety of fiber optic solutions available such as fiber Bragg grating sensors, FBG interrogators, distributed sensing systems, etc.

Corrosion conditions may vary due to their structure. Therefore, there is a need for a great number of point sensors. This is where distributed fiber optic sensors really come into their own.

Fiber Optic Sensing for Structural Health Monitoring

FBG sensors are used as instruments for corrosion detection. Like any standard sensor, fiber optic sensors are built into the structure to collect all the data and transmit it to the unit. They directly or indirectly measure vibration, displacement, humidity, temperature and chemical changes. FBG sensors are divided into several types due to the parameters they measure: displacements, strain, temperature, etc. By displaying this data, they are able to predict the occurrence of corrosion and its future consequences.

Here is a list of the major features of the FBG sensors:

Portability;
High accuracy;
Simplicity;
Long life;
Easy to integrate;
Electromagnetic interference and corrosion resistance;
Ability to operate in harsh environments, etc.

FBG sensors are particularly indispensable for monitoring corrosion in the hidden areas that are usually inaccessible to specialists. Their compact size allows for high accuracy and resolution. However, fiber optic sensors do not detect corrosion appearance directly but by estimating the material layer deposited on an optical fiber. That’s why they should be located close to the structure, in the same conditions.

FBG sensors have shown promising future in interaction with the concrete structures. This expands the horizon of their applications, including critical facilities and civil engineering.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating sensors, for example, FBG strain sensors, FBG interrogators and multiplexers, Distributed Acoustic Sensing (DAS) systems, Distributed Temperature Sensing (DTS) systems. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in structural health monitoring systems and want to learn more, please contact us at info@optromix.com

Fiber Optic Sensors for Li-ion Battery Cells

Fiber optic sensors have found a number of applications where there is a strong need for temperature monitoring. The use of Li-ion batteries is no exception, and specialists have learned to use fiber optic sensors for them as well.

Temperature monitoring of Li-ion batteries is an essential aspect of their operation in the field, and the problems of temperature monitoring can be solved with the help of fiber optic sensors.

What are lithium-ion batteries?

Li-ion, or lithium-ion battery is the most common rechargeable battery that uses the reversible reduction of lithium ions to store energy. Each module consists of one or more individual cells, which are consistently connected to follow the necessary rates of voltage, energy demand and power.

Typical Li-Ion BMS includes a few thermistors to monitor on selected cells surface temperature. This means that there is a possibility that cells may heat up invisibly.

Due to the wide deployment and large number of cells in each module, there is a need for modern technologies that can monitor cell operation and prevent future catastrophic failures.

The most common problem is the significant increase in temperature and strain in the cells. The effect of high temperatures and heat production from the cell can induce a series of degradation processes, resulting in reduced capacity and performance degradation. This problem is perfectly monitored with modern distributed temperature sensing modules.

The Temperature Effect on Li-ion Batteries

Distributed temperature sensing is used because the operation of Li-ion batteries can be affected by the influence of low and high temperatures. That’s why it is necessary to maintain comfortable temperatures during operation, storage and charging.

Temperature deviations from the ideal values may occur. However, they should still be within the established operating range. In addition, the critical temperature points shouldn’t be reached. Because of the test fields, continuous use in marginal conditions leads to accelerated wear of the battery and deterioration of its technical parameters.

Cold and overheating are both undesirable and harmful for lithium-ion batteries. In cold temperatures, they can experience voltage drops, deterioration of current output and rapid discharge. However, these symptoms disappear as the temperature rises. Overheating is more dangerous to batteries. It shortens their life and reduces their performance characteristics. There is also a risk of fire in the power source.

Maintaining optimal temperature regimes during battery operation extends battery life and ensures safe use. That’s why monitoring with distributed temperature sensing is an essential element for the correct use of Li-ion batteries and the prevention of emergency situations.

Fiber Optic Sensors for Li-ion Batteries

For Li-ion batteries, fiber Bragg grating sensors have been used to obtain data on distributed temperature and strain on the battery surface in various operating conditions. Specialists use the data obtained from distributed sensing systems in real time to detect abnormal conditions and prevent battery failure.

According to the field experiments, FBG sensors have been proven to sense the temperature either in the cells or between the cells when they are placed between battery cells. As a result, fiber Bragg grating sensors are able to provide the thermal information of each cell in a battery.

Lithium-ion Battery Applications

The lithium-ion batteries are commonly used to provide uninterrupted power in data centers, factories, air and water vehicles, and other facilities. Compared with the other types of batteries, they are smaller and have a longer service life. However, there is one drawback that should be considered in its implementation. A battery contains an electrolyte that decomposes into flammable components. Today, specialists have greatly reduced the potential for explosion to the maximum, but there are still risks. That’s why fiber optic sensors are very useful for monitoring.

The commercial battery industry also includes primary batteries as one of the major segments. However, it has its peculiarities, including non-recyclable materials and hazardous components in the batteries, which also cause ecological problems.

All in all, the knowledge of the temperature distribution in a cell or between several cells is fundamental for the safety of the battery. Fiber optic sensors have proven to be suitable for both temperature and strain gradient monitoring.

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Structural Health Monitoring for the Aircraft Industry

Structural health monitoring has already found many applications in various industries and become a powerful instrument. Its purpose is measurement of the aircraft constructions’ conditions.

The real-time monitoring and review of the structure’s current state provides precise data about the state of the materials and the construction itself. The data received with the help of fiber optic technology can be applied whether by specialists that are responsible for flight safety while plane preparation or by pilots during the flights. Moreover, structural health monitoring is an up-to-date technique considering the increasing number of flying machines including drones.

Types of Structural Health Monitoring

A correctly customized SHM system tends to increase effective implementation, extend the service life of the equipment and reduce maintenance expenses.

There are two types of structural health monitoring that are applied in the design and operation of aircraft machines over many years: common structural condition monitoring that is responsible for damage determination and examination of the aircraft parts integrity, and load monitoring.

The monitoring of structure conditions and information about loads and damage location is proved to be extremely important, especially for the aerospace and aircraft industries. Usually, load monitoring is provided by measurement of the local deformations, and damage detection that is possible due to the acoustic signals of the distributed sensing systems.

FBG Sensors for Structural Health Monitoring in Aviation

To install structural health monitoring systems specialists carry out a range of calculations and estimations regarding FBGs and their integration into a process. Thanks to the factual flight data and a number of experiments, they have defined the vibration and load characteristics in aviation. This final information has been applied later for field projects.

Fiber Bragg grating sensors are particularly effective for monitoring and measurements of temperatures, pressures and strains. A variety of qualities make FBG sensors ideally suited for applications where the accuracy is important.

In addition to high accuracy, fiber Bragg grating sensors have compact sizes and light weight. These features apply both for cables and instrumentation. Moreover, they can be produced even smaller if the construction and clients require it. Therefore, FBG sensors have often been chosen as an appropriate monitoring instrument for the aviation industry as well as for various other spheres.

One more important advantage that specialists highly appreciate is the absolute explosion safety of the fiber optic sensors. This quality can provide safe engine operation even in conditions of laying cables along fuel tanks and lines.

Another issue that usually concerns aircraft specialists is susceptibility of metals to corrosion. To solve this, there is a need for monitoring of corrosion processes in real time. That’s why the development of specialized fiber optic sensors or corrosion sensor devices that are able to track its dynamics and transfer the data about it to the center plays a crucial role for aircraft construction.

Common Applications of the FBG Sensors

In aviation fiber optic sensors can be applied for measurement of different fundamental parameters that are necessary. Due to these numbers, there can be detected any appearing changes in construction. The standard FBG sensors measure temperature, pressure and strain. In aircraft engines, they can be applied in the hot and cold parts of the engine path. Fiber Bragg grating sensors for pressure and fuel consumption, vibration, and deformation at critical points can be used to evaluate their conditions even indirectly according to the deformations of the elements.

In addition to engine monitoring, FBG sensors are also applied to detect deformations of wings and fuselage parts, icing conditions, loads on the landing gear during takeoff and landing, etc. Structural health monitoring is proved to be essential, considering the wide range of details for airplanes that are made of polymer composites.

Fiber optic sensors may help specialists in detecting the problems during the flight that can be caused by difficult weather conditions. Moreover, they are able to highlight the existing problems during the creation of new aircraft or detect critical points under maneuvering modes. Both these applications are important and help in preventing huge catastrophes or at least will result in reducing their number.

All in all, structural health monitoring has made a great contribution into the aviation industry, just like in other spheres. FBG sensors are proven to be cost-effective and powerful instruments that can improve operation of modern aircraft and drones.

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Structural Health Monitoring for Different Structures

This fiber optic technology has become a modern and advanced approach that attends several functions: diagnostic and simultaneous monitoring.

Structural Health Monitoring Operation Principle

The continuous structural health monitoring gives an opportunity to accumulate data about an object’s state. Thanks to the information obtained, specialists can use it to predict possible damage in the future and extend the service life. And fiber optic solutions provide a whole system that consists of fiber optic sensors, data collecting and transmitting units, etc.

Implementation of the fiber optic system involves review of the design processes of structural elements, a change of the processes, etc. For normal operation, parameters should stay at the allowable ranges that were previously determined and recorded in the program by specialists.

In fact, the factors that can influence the structural condition can be divided into two categories:

Negative external factors that have a constant impact on the material. This includes high or low temperatures, humidity, etc.;
Force-majeure circumstances, such as floods, volcanic eruptions, earthquakes, etc.

FBG Sensors for SHM Systems

Fiber optic sensors are proven to bring benefits to specialists as a part of the structural health monitoring system, including for civil construction. Compared to the electrical sensors, fiber optic sensors offer several advantages, including resistance to electromagnetic interference that is crucial in many applications.

Fiber optic technology can transmit data over several kilometers. Their other features such as long-term stability and reliability help them to function in severe environments. FBG sensors have been examined, for example, for implications in ice and snow. Fiber optic sensors are susceptible to the mechanical and chemical impacts of the concrete constructions. Despite that, they are mainly used in concrete environments for constructions such as bridges and dams. However, FBG sensors are able to effectively operate in such conditions for a considerable time.

Still scientists are going to design and experiment with fiber Bragg grating sensors further to find their limitations in new applications. Various types of fiber optic sensors were produced to provide measurements of diverse physical and chemical characteristics. Fiber Bragg grating temperature sensors are used for structural health monitoring of civil engineering structures, as it was mentioned above. In certain concrete based building structures there is a need for FBG strain sensors or FBG moisture sensors. From the other side, concrete structures are affected by formation of cracks and moisture ingress resulting in operation failure.

Fiber Optic Sensors for Sewage Tunnels

One of the fields where fiber optic sensors are used is a structural health monitoring system for sewage tunnels. The main reason for the sewage systems’ damages is excessive loading. It may be caused by constant physical effects like corrosion, penetration of plant roots, etc. The damage can be also caused by natural disasters such as landslides and floods. The consequences of all these impacts can greatly reduce the constructions’ operation life and lead to failures in operating.

That’s the reason why fiber Bragg grating sensors are essential in structural health monitoring systems. FBG sensors are able to constantly monitor and predict these events in advance. Thus, specialists have an opportunity to prevent great damage or at least minimize the economic losses.

Thanks to the fiber optic sensors that structural health monitoring includes, this technology is proved to be cost-effective in different applications. The modern approach provides quick and simple-in-use monitoring of various kinds of structures.

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Multicore Fiber Optic Sensors for 3D Shape Sensing

Multicore fiber optic sensors have found a range of applications in different fields. One of them is 3D shape sensing which has greatly risen in recent decades. Nowadays, 3D shape sensing can be produced for industrial necessities or for the area of research depending on the purposes of applications. Multicore fiber optic sensors have proved to be the most effective instruments for this technology in comparison with other methods. They are used particularly in the cases when there is a need for the most precise measurements and minimal invasive procedures.

What is 3D Shape Sensing?

Fiber optic 3D shape sensing is a fiber optic technology that applies a fiber optic cable for permanent monitoring of the objects’ 3D shape and position in real-time.

Shape sensing has a capability of finding and detecting all the deformation processes that take place at one or more locations along the fiber optic cable. This fiber optic technology can detect just one kind of deformations with certain types of fiber optic sensors or a range of deformations with the types of several distributed measurements.

Multicore optic fibers themselves have an ability to transmit the data at high speed. They also can be applied as fiber optic sensors, when they have fiber Bragg gratings (FBGs) in the cores. FBGs are reflective gratings that can filter specific wavelengths. Any changes of the form or position cause the wavelength changes.

As for the 3D shape sensing, there is a special way of fiber Bragg gratings’ inscription into multicore fibers. Firstly, they are spun while stretching. Then fiber Bragg gratings are written along the cores’ length. This technique makes it possible to identify the fiber’s rotation as well as three-dimensional changes.

The Most Common Advantages of the 3D Shape Sensing

Fiber optic sensors are proved to be effective in different technologies. They are especially suitable when there is a need for a complex measurement system. It usually involves the whole system with a number of fiber optic sensors and can provide the measurements of several characteristics simultaneously.

Moreover, FBG sensors have a range of other benefits in comparison with other traditional sensors. So, fiber optic sensors are:

highly sensitive to temperature and strain modifications that lead to the high levels of accuracy;
immune to external electromagnetic interference;
lightweight and small sized;
easy to attach and reliable;
corrosion resistance;
resistant to the harsh environmental conditions such as humidity, high temperatures, etc.

Due to their compact size, fiber optic sensors can be embedded in small devices and objects. Moreover, they can be implemented into distributed sensing systems so the FBG interrogator units can be installed at some other place and send all the data remotely without any wiring.

Fiber Optic Sensors Applications in 3D Shape Sensing

3D shape sensing technology has recommended itself as an effective and even preferable instrument.

This technology has a significant use in the structural health monitoring of different constructions such as buildings, bridges, etc. Besides, fiber optic sensors are produced for aircraft monitoring. Fiber optic solutions are also utilized for damage detection, deformation monitoring and structural fatigue life evaluation. Moreover, intelligent material deformation and intelligent robot posture monitoring are of the applications where fiber optic technology is used.

3D Shape Sensing in Medicine

As for the medicine and biomedical fields, fiber Bragg gratings (FBGs) as well as 3D shape sensing have got a special place. This technique has significantly decreased the healing and rehabilitation time and resulted in minimum functional and cosmetic damage to the body. Here are some examples where fiber optic sensors have proved to be an effective option:

FBG sensors have found a wide range of applications connected to cardiac activities and cardiovascular diseases. They are applied in artery pressure detection, intra-aortic balloon pumping, etc.
In surgery, they are applied as surgical instruments that, among all other options, help in visualization. If we are talking about laparoscopic or robotic surgery, the process of visualization has become more simple due to the fiber endoscopes.
Endourology is another field that uses shape sensing technology’s advantages. One of the endourological procedures is cystoscopy that means the treatment of bladder and tumors. Sensing technology makes the device navigation and localization process better. As a result, specialists can carry out operations faster and safer, therefore, conducting the procedures more effectively.
3D shape sensing was able to improve another medical field called colonoscopy. A common colonoscope coupled with the fiber optic technology makes the navigation better and allows preventing most challenges that specialists usually face. Due to the benefits of the fiber optic solutions, including shape reconstruction over the whole device, specialists can get the data about the procedure in real time. As a result, medical procedures become safer and more comfortable.
Epidural anesthesia is getting popular in difficult operations where pain management methods are required. The insertion procedure is conducted with a thin needle that makes it impossible to use most of the sensors due to their size. However, fiber optic sensors based on the distributed sensing principle are able to solve this problem. Specialists have conducted accurate calculations to provide a navigation system that is able to make the correct penetration into the tissue easier. So, it also helps the operators in determination whether the epidural space has been reached.

All in all, 3D shape sensing is a fiber optic technology that has found many applications and become an indispensable tool in medicine, for example, as needles and catheters. Fiber optic sensors, being cost-effective tools, are especially irresistible when there is a requirement in detecting small deformations.

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High-Temperature Measurements with FBG Temperature Sensors

Fiber optic sensors, in particular FBG temperature sensors, are relatively new technical applications in optoelectronics, fiber and integrated optics. The reason for their popularity is the optical signal itself. It simultaneously provides information about the change in phase, amplitude, wavelength and polarization in space and time.

Fiber Bragg grating temperature sensors are better suited for solving many issues than conventional sensors and measurement systems. For example, fiber optic sensors are applied for preventive diagnostics and forecasting of emergency situations. FBG sensors can be built into critical structures such as bridges, dams, ships, aircraft, power plants and other structures. By continuously monitoring the structural integrity of objects, fiber optic solutions prevent possible catastrophic failures and accidents.

FBG Temperature Sensors in Measurements of High Temperatures

The measurements of high temperatures, especially over 1000 °C, were always difficult to conduct in harsh environments. However, high temperatures are essential in a number of processes and widely applied in such fields as metallurgical industry, aerospace, and nuclear energy production. Due to the FBG temperature sensors, the problems with high pressures, temperatures and strong electromagnetic radiation that conventional temperature sensors used to have, were solved.

Here are some examples of fiber optic technology applications:

Distributed fiber optic sensors are proved to be effective for pipeline protection and safe operation of the deep underground wells;
In metallurgy, fiber Bragg grating temperature sensors measure the internal temperature of high-temperature boilers for monitoring of the combustion efficiency and enhancement the safety;
FBG temperature sensors monitor the combustion chambers and turbines of an aircraft. For example, scientists are working on the implementation of fiber optic sensors into an aircraft gas turbine engine. Its monitoring helps in the extension of durability and is difficult because the temperature and pressure rates are constantly changing. So to prevent all the emergency and undesirable situations, there is a need for a large amount of control and measuring equipment. Moreover, fiber optic sensors have to operate at temperatures of 400-1800 °C and provide data in real time.

Advantages of the FBG Sensors

Fiber Bragg grating temperature sensors have got close attention because of their inherent benefits in comparison with usual electronic sensors. Due to specialists’ continuous scientific work, sensors have built a reputation based on successful field projects.

Fiber optic sensors are capable of stable operation for a considerable period of time in harsh conditions. High temperatures and pressures, poisonous or corrosive environments negatively affect the measurement results. However, all these factors have little effect on the FBG sensors, especially in comparison with electrical sensors. Moreover, it is easier and cheaper to replace fiber optic sensors if necessary.

Considering all the above, FBG temperature sensors are able to provide the most accurate data despite bad environmental conditions.

Types of the High-Temperature Measurement Systems

There are different types of high-temperature measurement systems due to their installation and detection techniques. There are contact and non-contact measuring systems:

Contact temperature measurement systems include thermocouple sensors. Despite simplicity of use, they have a number of disadvantages such as poor corrosion resistance and exposure to electromagnetic interference. Moreover, high temperatures greatly shorten their service life. They are getting damaged and, as a result, provide inaccurate measurement rates.
Infrared thermography (IRT) as a non-contact temperature measurement excludes the direct contact between the equipment and high-temperature sections. However, it works only for the surface temperature measurements, so the internal structure can’t be measured.

The most common fiber optic sensors are fiber Bragg grating (FBG) sensors and distributed temperature sensors. Due to the material of the fiber and laser inscription technique, the maximum temperature can be increased.

Fiber Bragg gratings are units that have found different applications, especially as they are effective in distributed sensing devices. FBG sensors are proved to be useful as fiber optic sensing instruments. They are able to provide high stability, multiplexing and other features that are widely produced in a number of industrial and scientific applications.
Distributed temperature sensors as a part of DTS systems measure temperature along the whole fiber optic cable. Their main goal is providing the most accurate temperature data in space and over a long distance. As a result, specialists get a distributed profile of the temperature conditions along the whole fiber optic cable.

All in all, the latest developments in fiber optic sensing have gotten a great amount of attention due to their capability of operating in environments with high temperatures. FBG temperature sensors can make up a continuous optic line that provides accurate and reliable data in real time that can be stored and compared with the previous data in the future.

Optromix is a DTS system manufacturer that provides top of the line distributed temperature sensing systems suitable for monitoring commerce networks. If you have any questions or would like to buy a DTS system, please contact us at info@optromix.com

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Fiber Optic Sensors for Underground Coal Mines

Thanks to the fiber optic sensors, a number of fields and industries have found new approaches in safety and production processes. As a part of fiber optic technology, fiber Bragg grating sensors have proved to be an effective technique of monitoring and security insurance.

Fiber Optic Sensing Applications in Underground Mining

Underground extraction of the minerals continues to be a high-risk industry. This industry has become highly dangerous because of the permanent presence of difficult challenges. Such factors as dynamic changes, hidden defaults and seismic tremors can lead to disastrous consequences.

Due to the advancement of fiber optic technology, there is an opportunity of constant monitoring with the help of fiber optic sensing systems. Fiber Bragg grating (FBG) sensing has already demonstrated its abilities in other directions like for monitoring of the dams and bridges. For mining, the deployment of FBG sensors has become possible because of the properties they have such as high and long-term sustainability and high resistance to electromagnetic events.

This article presents the most common applications of the fiber Bragg grating (FBG) sensing in the coal industry.

Fiber Optic Sensors for Structural Safety of the Mines

Distributed sensing can be called a crucial component in the structural health monitoring of the underground mines. Previously, devices for the structural health construction monitoring couldn’t allow watching the data 24/7, and thus, respond quickly in such environmental conditions. However, today’s fiber optic monitoring systems make all this possible.

Due to the fiber Bragg grating sensors’ qualities, like reliability, they are able to constantly track the extractive activities. Moreover, thanks to their high level of sensitivity, there is a possibility to detect the slight modifications in equipment functioning and prevent severe damages at an early stage. So, fiber optic sensors are fit for mine structural monitoring as a proactive damage detection system and as one of the accident prevention strategies.

Therefore, fiber Bragg grating (FBG) sensing is able to ensure the necessary level of safety in mines. It provides the estimation of the mines’ present environment when FBG sensors collect and transmit the data remotely.

Fiber Optic Sensing for Coal Dressing Chamber Bottom Plate

Apart from safety monitoring of the roof activity, there is an opportunity to monitor changes in the coal dressing chamber bottom plate with the fiber optic monitoring systems. However such monitoring has a range of aspects that should be taken into account.

Firstly, huge equipment occupies most of part of the chamber. During the coal production it produces vibrations that may influence the stability of the mine country rock. This fact should be considered while installing fiber optic technology.
Secondly, monitoring systems should be immune to electronic interference. That is a great benefit of the fiber optic sensing, especially for the chamber, where electromagnetic interference phenomenon is strong.
Thirdly, the system shouldn’t interfere with the operation of the equipment.
Fourthly, due to the constant production around the coal separation chamber it is complicated to get accurate information.

Nowadays, fiber Bragg grating sensors can not always be applied for monitoring of the coal dressing chamber bottom plate. Still, there are some challenges that specialists can face. The lack of space, chances of inaccurate data and other difficulties can make fiber optic sensors’ setup harder or even impossible. As well as wet environments, FBG sensors are often applied in heavy environmental conditions, and specialists got used to developing such projects.

Microseismic Monitoring System as Part of the Fiber Optic Technology

Microseismic monitoring technology is an important instrument designed to prevent any dangerous accidents with the help of seismic assessment and alert about any changes.

Fiber optic sensing has also been successfully applied as a microseismic monitoring system for coal mines. The sensors were suggested to use because of their significant advantages such as large dynamic range, high sensitivity, etc.

Due to the conducted experiments, fiber Bragg grating sensors were installed in the tunnels. During the field projects they have proved to be effective by providing all the data about dynamic activities in the mine accurately. Such level of accuracy is possible due to the fact that the microseismic data are tracked over the full length of the installed fiber optic cable. The interrogation system collects the data, provides the seismic interrogation and transfers the received data. It allows improving the dynamic range and installing more fiber optic sensors. Both these factors increase the positioning accuracy of seismic events.

All in all, monitoring with fiber optic sensors in combination with the automatic processing of data can bring major benefits to identification of any changes, malfunction of mine operation and damage prevention.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating sensors, for example, fbg strain sensors, FBG interrogators and multiplexers, Distributed Acoustic Sensing (DAS) systems, Distributed Temperature Sensing (DTS) systems. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in structural health monitoring systems and want to learn more, please contact us at info@optromix.com

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Fiber Bragg Grating Sensors for Weigh-in-Motion strips

Nowadays, road safety has advanced to a new level with the use of fiber Bragg grating sensors. Due to its characteristics, fiber optic technology has become part of the other technologies. For example, FBG sensors are applied in WIM systems (or Weigh-In-Motion systems) for that purpose.

There are several types of WIM systems and one of them is based on fiber Bragg grating sensors. Such systems provide specialists with the most accurate and detailed data around the clock, monitoring traffic flow. They are able to detect the vehicles and in the meantime determine their weight during the regular traffic. The traffic monitoring in real time allows improving the enhancement of traffic management.

Moreover, fiber Bragg gratings (FBGs) are used in WIM systems for the structural health monitoring, for example, of the bridges or rails.

What is Weigh-in-Motion (WIM) Technology?

Weigh-in-motion (WIM) systems are based on technology that allows providing reliable weight measurements of the vehicles. The systems can be applied whether for specific road or rail vehicles such as trucks and trains, or for public applications like be set on the rail or road tracks to monitor the traffic. Weigh-in-motion systems built on fiber Bragg grating sensors measure the traffic flow and supply all the information from it. Thanks to the durability and quality of FBG sensors, the necessary data is provided using one of the most cost-effective methods.

The whole fiber optic system consists of a range of sensors and a roadside unit with all the data devices. According to the application purposes, there is an opportunity to add other fiber optic sensors to this weigh-in-motion system, for instance, temperature sensors. Moreover, to receive more data about the vehicles, it is possible to use cameras for license plate photos.

What Information do the Weigh-in-Motion Systems Provide?

Fiber optic sensors follow two basic physical principles. The first principle that belongs to fiber Bragg gratings is the diffraction changes under the deformations. The second one is the changes of the optical fibers and their characteristics under the influence of the deformation. Therefore, the WIM systems provide all the characteristics that fiber optic technology offers.

The reliable data on weight from fiber optic sensors give an understanding of the loading of heavy goods vehicles and traffic flow. FBG sensors will help in estimation, avoiding any inaccuracy in the future. This, in turn, will allow improving the goods transportation and infrastructure management.

Except for the usual weight parameters that fiber optic systems provide, there are other available options, such as date-time, speed and classes of vehicles. To efficiently operate, the fiber optic systems can be installed on the specific vehicle or placed by the road for the entire traffic flow monitoring.

Advantages and Disadvantages of the Fiber Optic Sensors

As any technology based on fiber optic sensors, WIM systems possess all the features that FBG sensors have. Such characteristics as light weight, small size and insensitivity to the electromagnetic fields and weather conditions are really important in monitoring systems. Moreover, WIM systems have an ability to identify the underinflated or double tires in the traffic stream.

Weigh-in-motion systems help in providing very short response time in operations. However, there is a possibility of some inaccuracy of weighting, especially in motion. That’s why specialists are aiming at enhancing the same level of accuracy in motion as in static. And sometimes there is no use in enhancing the fiber Bragg grating sensors’ accuracy level, but increasing the number of sensors or making the automatic calibration processes better. There is a range of external factors that influence fiber optic sensors’ operation such as vehicle suspension, road roughness, etc. Moreover, they can influence the accuracy level in a bad way.

The most commonly agreed disadvantage is relatively high cost for electronic equipment. However, due to the long service life of fiber optic sensors, WIM systems seem to be a cost-effective technique by operating for at least 10 years.

Applications of the Weigh-in-Motion Systems

Fiber optic solutions are applied for many purposes as WIM systems. If it is needed, WIM unit can provide several data parameters at once. Usually, such data is applied in the following spheres:

Vehicle and traffic loading. As it was mentioned before, the information on the traffic flow helps in optimization and planning of the road network in the future. Or the researchers frequently apply it for carrying out the studies. However, there is another implementation that can be used for the already existing infrastructure – for example, for the review of the traffic flow over the road network and its future development with time.
Weight enforcement is aimed at complying with loading regulations. This will lead to the decline of the overloading numbers that have negative implications. These WIM systems based on the FBG principles provide the most effective instrument of weight enforcement.
WIM systems based on the FBGs can also be applied for industrial use like in logistic centers or at ports. They are most commonly needed in the weight check and defining of the trucks’ axle loads. All these measures are aimed at avoiding overloads and their possible future consequences of entering the road network.
WIM systems with fiber optic sensors for the railway industry are as well effective as DAS systems described in previous articles. The most common ways of application in this sphere are the total track loading and dynamic wheel loads. In practical terms, the provided data helps in design and maintenance of the rail tracks.

In the future WIM systems with fiber optic sensors will allow creating one of the base elements of the “Smart City” concept. The FBG sensors are able to provide the system that with different types of sensors will form a complex and reliable technology. Moreover, the improvement of the weigh-in-motion systems based on the fiber Bragg grating sensors will lead to the decrease of overloaded trucks on roads.

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Fiber Optic Sensor (FOS) Technology and its Applications

Thanks to all the advantages of the fiber optic sensor (FOS) technology and its diversity of instruments, described in the previous article, there are a range of applications. Structural health monitoring of the concrete constructions is proved to be the most effective tool for management of the infrastructure, due to the latest results.

Here is a list of the most common applications where fiber Bragg grating sensors can be installed.

Bridges

The lifetime of every large bridge is several decades or hundreds of years, including the period of construction and repair stages. Despite the improved quality of the bridges’ planning, it is still difficult to accurately predict its lifetime because of the complex structures and external influence like corrosion or the natural disasters like earthquake, flood, etc.

The structural health monitoring in real time gives an insurance of the safety of bridges. According to the researchers, this fiber optic system can be applied on the different stages of the bridge construction. Most of all, these fiber optic monitoring systems are used in the operation or safety phase of bridges and extend their lifespan.

The FBG structural health monitoring systems include fiber optic sensors, multiplexers, FBG interrogators, local and remote computers.

All in all, the fiber optic monitoring systems provide the following advantages:

Control of state of metal structures;
Control of the bridge oscillation frequency;
Notifications for the personnel on screen;
Extending the bridge’s lifetime, etc.

Moreover, when we talk about the railroad bridges, it is also possible to evaluate the lower bridge beam condition.

Buildings

The state of the load-bearing structure and building foundation is a crucial element of safety. And fiber optic sensors have made a great contribution to it.

The structural health monitoring can be applied whether for the buildings under construction or for the old houses when there is a severe level of damage and degradation of materials. Unfortunately, the majority of the houses that were built before, mostly in the previous century, are particularly vulnerable to environmental actions. Basically, because there was no specific constructive detailing that would provide the age resistance of the constructions.

The degradation usually includes steel corrosion, debonding of concrete, etc. It becomes visible when the damage is greatly extended on the elements of the structure. If the moment for the structural repair is missed, it often leads to its more complex and expensive modernization. At worst, there is a need for demolition.

Mostly, fiber optic technology is used for:

Control of the strain-stress state of metal basic structures and foundations;
Monitoring of the cracks and foundation shrinkage in reinforced concrete structures;
Snow load control.

Tunnels

The structural health monitoring systems have also made a great contribution into tunnel construction.

The most important safety factor in tunnels, as in many civil structures, is the deformations. Fiber optic sensors can monitor and provide the useful data both within the construction phases and over the long term. In the long term, monitoring calls a very stable and precise system that can compare deformation measurements over long periods. In the short term, the monitoring system can measure deformations that occur for relatively short periods.

The structural health monitoring system influences the tunnels’ management and security by providing in-time maintenance and restoration. There is a problem of excessive deformations which can seldom affect the structural security, but can cause durability problems.

For example, such fiber optic monitoring systems can be applied during the highway tunnel’ construction to measure the tunnel load or to monitor railway tunnels. Besides, the knowledge of the tunnel’s behavior helps while the introduction of the modern building techniques or for the prolongation of its service life in the future.

Hydroelectric and Wind Power Plants

Fiber optic solutions have found their applications for nuclear, hydroelectric, wind power plants. Aging management of the components is directly related to their operation. Safety requirements guarantee their safe operation but still are difficult for operators to track fully. All kinds of power plants require the accurate and qualified assessment of the thermomechanical loads and other parameters that can lead to the early aging of the equipment.

Fiber optic sensing is one of the best monitoring and maintaining systems for the plants. Structural health monitoring (SHM) of hydroelectric plants, wind turbines and others gives operators real-time information of the components’ condition.

Dams

As for the dams, fiber optic technology helps in detection of the seepage flow changes in a dam structure. Dams usually face different problems connected to external loads such as water level changes, seismic disturbances, etc. Any changes in numbers can be a sign of erosion which is the most common cause of the dam failure.

Fiber optic system allows operators to get the data from all over the dam as measurements are taken along the full length of the cable. Distributed sensing detects the tiniest changes in rates that otherwise can lead to the operational failures.

Fiber optic sensors are able to measure various parameters and quantities in structural health monitoring. Depending on the required operating principles, specialists discuss which type of FBG sensor is the best suitable and their way of embedding and surface mounting. All in all, their final goal is to find the most effective fiber optic solution for the operating principle and potential applications in SHM.

The short list of applications can be also found on our website.

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Fiber Bragg Grating Sensors for Railways

Fiber Bragg grating (FBG) sensors have already been applied in various applications and still arouse great production interest. They are commonly used in structural health monitoring for aerospace, civil engineering, oil & gas, etc.

As for the railway industry, fiber optic technology has made a substantial contribution to its development. It is anticipated that within a few years the number of goods that will be transported by railways will be increased, as well as the number of passengers. This, in turn, will lead to the growth of the axle load and trains’ faster speeds operating.

That’s why there is a great need for a full understanding of the rails’ structural and operating conditions as well as for providing safe and reliable operating conditions. So modern innovative technologies are required.

Fiber Optic Solutions for Monitoring Systems in the Railway Industry

In railways, common monitoring systems use strain gauge sensors. The sensors constantly measure resistance caused by the stress transmitted by the rail when the train runs through it. This fiber optic technology is already prominent due to its effectiveness. However, it still has several shortcomings. For example, it is expensive, huge and has difficulties in usage, in comparison with modern FBG sensors. Moreover, the most important disadvantage is that they can be affected by electromagnetic interference. FBG sensors are immune to the external interference such as electromagnetic interference, lightning and many other external disturbances.

Because of this, fiber Bragg grating sensors are getting more and more applications in high-speed railway networks. Applications are train weight estimation, measurement of train speed for real time, wheel imbalance detection, etc. It is clear from experiments that FBG sensors are more appropriate as railway monitoring systems compared to electrical ones.

Fiber Bragg Grating Sensors Characteristics

FBG sensors provide many crucial features for unique operational conditions in railways. In comparison with usual electrical sensors, fiber Bragg grating sensors have EMI/RFI immunity, multiplexing capability and can offer interrogation for long distances. In FBGs the data is wavelength-encoded, which makes the signals less susceptible to intensity fluctuations. Moreover, the fiber optic cable can be interrogated from either end, offering redundancy to FBG sensing networks. Plus, FBGs have a self-calibration capability. The strain and temperature measured findings is an absolute parameter. So there is no dependency on the measurement value and losses between the interrogation unit and the FBGs. To fabricate FBG sensors, FBGs are packaged and transformed into different types of transducers. That makes it possible to install them on the rail track fasteners, clips, bogie, train body, chassis, and axle boxes of a train to provide ongoing inspection for health checking.

In addition to that, FBG sensors can be interrogated at very high-speeds.

Providing reliable operational conditions, fiber optic designs can measure a wide range of other parameters such as inclination and acceleration through the modulation of light in reaction to the environment. Therefore, one FBG interrogator can work with a lot of FBG sensors to measure many options at the same time at different locations over the vast territory. The sensing signals can be read at distances more than 100 km away.

These features are especially useful for the railway industry because they allow simplifying the installations a lot and reducing costs.

Fiber Bragg Grating Sensors in Field Projects

Over the past few years, specialists have safely held a number of field trial railway projects involving FBG sensors. For example, in 2007, about fifty FBG-based vibration sensors were installed along the East Rail Link that connects Hong Kong and Mainland China. Then fiber optic solutions were applied in metro lines of Hong Kong, part of the Beijing-Shanghai High-speed Rail Link, and in Delhi Airport Metro Express Line.

In Hong Kong this fiber optic technology was applied on a passenger rail system as a structural health monitoring system. The FBG sensors were attached to the bottom of the carriages. The goal was temperature and strain measurement. The fiber optic system supplied all the necessary data including rail tracks’ and carriages’ deformation. The acquired information helped to assess the rates of the corrosion and bearing wear.

According to the results, due to FBG sensors, costs of maintenance were greatly reduced. Moreover, it helped to avoid or prevent problems at early stages due to the early detection of excessive vibrations. All these works showed that FBG sensors are superior in comparison with conventional sensors in many essential aspects.

Nowadays, fiber optic solutions are regarded as one the most cost-effective technology that helps in monitoring the condition and structural health of the carriages, tracks, and under frame equipment in railway systems. There are still some parameters that need to be improved, like the lack of proprietary and custom specifications. However, in the future major railway operators can apply modern FBG sensors, gaining more field experience.

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