Tag: fiber Bragg grating sensors

Constructions Where FBG Sensors Are Applied

FBG sensors have proven to be effective and useful during their implementations into different kinds of structures. They have become a necessary part of projects that aim to operate for long periods of time. Constructions Where Fiber Bragg Grating Sensors Are Applied

Fiber Bragg Grating Sensors Applications

There are various types of FBG sensors based on the parameters they monitor: temperature, strain, displacement, etc. They have a number of advantages that make them highly effective even in the most harsh environment. Compact size, fast response, immunity to electromagnetic interference and other factors usually play a critical role in many situations.

For example, fiber optic sensors are widely used for monitoring of long structures such as tunnels and pipelines. In addition to the ability of the remote control, they provide stable operation over a long period of time. Therefore, they don’t require any additional repairs.

The other advantage of fiber Bragg gratings is multiplexing. A single optical fiber can contain multiple FBGs at the same time. This fact makes it a cost-effective instrument even for large infrastructures. This is especially true when compared to techniques where each sensor is placed separately. Due to their size and weight, fiber optic sensors can be installed in most applications.

FBG Sensors for Strategic Buildings

FBG sensors are widely applied for structural health monitoring of various existing structures including critical facilities such as bridges, strategic buildings, etc. The main problem with this type of construction is related to the appearance of cracks. Cracks can cause many problems in the operation of the construction. They are dangerous because they can be invisible to specialists and unpredictable in terms of growth rate, both of size and speed. Unfortunately, there are a lot of examples where buildings have been ruined because of this, sometimes with tragic consequences.

When it comes to bridges in particular, real-time structural health monitoring is an effective tool for structural safety. Continuous monitoring is required for safety verification especially after extreme events.

Fiber Optic Sensors in Coal Mines

The other application field where fiber optic sensors are used is coal mining infrastructure. Electronic sensors can’t provide an effective structural health monitoring due to the extreme environment in coal mines. On the contrary, in most cases, FBG sensors are chosen for their ability to operate in harsh conditions such as darkness, vibration and for their immunity to electromagnetic interference. Coal mines are in need of a modern monitoring system for the fulfillment of the operating conditions of the tunnels and the transmission of the data to the control center. Structural health monitoring provides specialists with early warning of potential coal mine failures.

Fiber Bragg grating sensors build a safety control structure health monitoring system that accurately observes the processes. It can monitor various parameters but for the coal mines the most common sensors are FBG temperature sensors and FBG pressure sensors. Fiber optic sensors are embedded in the structure itself and function during the lifetime.

FBG sensors have gained increasing interest due to their ability to alert about any tiny or critical changes. The personnel can react to the alarm and prevent the possible disaster. And if it’s already happened, the fiber optic system can help in estimating the damage.

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

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. Fiber Bragg Grating Sensors for Concrete Constructions

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.

FBG interrogators FBG sensors fiber Bragg grating sensors fiber optic sensors structural health monitoring

Fiber Bragg Gratings for Civil and Geotechnical Engineering

Specialists have already found a series of applications where fiber Bragg gratings have shown to be profitable. FBG sensors have become a reliable distributed sensing solution for structural health monitoring. In addition to other applications, such as in the biomedical field, they are also used in civil engineering and geotechnical engineering.

All these areas have one thing in common – the environmental conditions. In such environments, it’s difficult to prevent the degradation processes such as aging and chemical effects. These factors should also be taken into account when implementing the traditional monitoring systems or equipment. In most cases, they have a short service life and require frequent replacement.

Alternatively, fiber optic sensors deliver modern fiber optic solutions that are able to work in extreme environments. FBGs for Civil and Geotechnical Engineering

Fiber Bragg Grating Sensors Common Characteristics

Since their first implementation, FBG sensors have been broadly deployed especially for distributed sensing of temperature, strain, and other characteristics that are particularly valuable in geotechnical and civil engineering. Fiber optic sensors have become world renowned for the features they offer. High sensitivity, immunity to electromagnetic interference are the most important parameters that are in demand.

Like traditional sensors, FBG interrogators face similar challenges. For example, they are usually required in extremely accurate equipment. That’s why there’s a high demand for maximum precision and high spectral resolution, down to picometer level. Fiber optic devices are also increasingly being used to deploy in rugged environments.

Fiber Bragg gratings are compact and can provide stable operation and durability in outdoor environments. For example, they are typically exposed to moisture influences, chemical reactions, temperature variations, etc. Distributed sensing systems should meet all the necessary requirements to ensure safety and proper operation of the entire system and to avoid the consequences of the interaction of the sensing element with the environment.

To ensure that, fiber optic systems should have robust materials and construction. In addition to complete, reliable fiber optic systems, fiber optic cables play a crucial role in creating the long-term FBG structural health monitoring systems. All fiber optic sensors should be able to withstand a certain level of thermal and mechanical loads at all times. The only way to provide customers with the best fiber optic solution is through testing of FBG sensors and application methods.

FBG Inscription Methods

Depending on the application and environmental conditions in which the FBGs are to be used, specialists can design FBG sensors for individual customer parameters.

A fiber Bragg grating is a fiber optic microstructure in which the index of refraction within the optical core changes along its length. The producing process of FBGs is usually called “writing”. Nowadays, there are three FBGs inscription methods:

The interferometric method is based on exposing a light sensitive area of the fiber to an interferometric fringe pattern to get the full grating. The pattern is achieved by illuminating an appropriate mask. In this case, the phase mask period defines the FBG period.
Continuous core-scanning method. Here, the FBG writing is provided by the motion of the translational frame where the fiber is fixed. In this technique, the period of the FBG is defined by the modulation frequency and the translation speed of the fiber.
And the last is the direct point-to-point method based on the absorption of a laser pulse. Each grating element is generated by controlling the laser parameters and moving the fiber. In this technique, the FBG period is determined by the fiber translation speed and the laser pulse repetition rate.

Applications of FBG Sensors

Fiber Bragg grating sensors are used in various fields where it is required to monitor structural health. In engineering, they are used to monitor the integrity of the entire structure and observe any deformation of its components. Such monitoring leads to the reduction of the risks and safety requirements. Fiber optic sensors are particularly useful for reinforced concrete structures because they can provide online data on the risk of corrosion.

When we talk about geotechnical and civil engineering, FBGs have also found their place for implementation.

Here are some examples of how fiber optic technology gets used:

Concrete structure monitoring;
Lateral deformation monitoring of embankment soft soil;
Pressure monitoring of tunnel’s rock and soil;
Structural health monitoring of bridges, dams, etc.

Nowadays, FBG sensors are also used to monitor landslides and slope failures and have shown good results. Distributed sensing systems have been applied to examine the landslide stability and deformation of landslides. Nevertheless, installing monitoring systems in complex environments and dealing with uncontrollable boundary conditions require careful consideration of potential issues.

Monitoring engineering and geotechnical structures with distributed sensing systems can improve profitability. Structural health monitoring methods are often preferred due to their ability to:

operate in chemically aggressive environments;
their feasibility in hard-to-reach areas of structures;
use fiber optic solutions which reduce equipment costs by utilizing a single fiber optic cable.

Overall, fiber Bragg gratings find extensive use in geotechnical and civil engineering applications. And, as with any technology, the successful implementation of fiber optic technology requires specialized experience and professionalism in designing and implementing the entire fiber optic system. Most of all, when there is a need for long-term measurements.

distributed sensing systems FBG interrogators FBGs fiber Bragg grating sensors fiber Bragg gratings structural health monitoring

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.

FBG Sensors for Li-ion Battery Cells

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.

distributed sensing systems distributed temperature sensing fiber Bragg grating sensors fiber optic sensors

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. SHM for the Aircraft Industry

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.

FBG sensors FBGs fiber Bragg grating sensors fiber optic sensors structural health monitoring

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. SHM for Different Structures

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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FBGs for Monitoring in Hydrogen and Radiation Environment

Fiber Bragg gratings (FBGs) are commonly applied in different fiber optic devices, for instance, in fiber lasers, sensors, etc. However, because of the harsh environmental conditions, where FBGs are operating, there are several important factors that should be taken into consideration.

According to the experiments and field results, FBGs’ characteristics can change with time. Negative environmental effects such as radiation and hydrogen effects can not only influence the parameters but also shorten the operation time of the fiber Bragg gratings. It is especially important to understand the radiation effects and other factors on essential dimensions of fiber optic systems during fiber optic technology manufacturing.

Fiber Bragg Gratings for Monitoring in Hydrogen and Radiation Environment

What are the Fiber Bragg Gratings (FBGs)?

Fiber Bragg grating is an optical fiber that has the refraction index changing along the fiber length. Due to its modulation, FBG acts as a mirror that reflects certain wavelengths and transmits the others.

FBGs have become significant tools of the fiber optic technology from the very first day of their creation. Specialists have drawn much attention to the fiber optic sensing because of its properties, for example, compact sizes, immunity to the electromagnetic interference, etc.

What are the applications of the FBGs?

Specialists have already applied fiber optic solutions in various industrial sectors: industrial and civil constructions, aerospace, etc. Fiber optic sensors are applied for measurement of different physical parameters including temperature, strain, pressure, etc. Nowadays, these abilities are effectively applied in such structures as a structural health monitoring device by fiber Bragg grating sensors.

However, implementing such a powerful instrument in difficult environmental conditions, where most tools can not be used at all, brings some troubles. Scientists have learned to deal with it and have improved fiber Bragg gratings greatly.

So, nowadays FBGs are capable of operating in high radiation conditions, as an example, for nuclear installations and space applications.

Fiber Bragg gratings (FBGs) for space

The most up-to-date fiber optic sensors can be used not only for spacecraft systems, but also for astronauts’ security and health. In space, the radiation level is very high, taking into consideration the periodic solar flares.

There is a need for an accurate system that is able to operate in radiation environments. Especially, considering the fact that it brings some troubles even to replace some equipment onboard not to tell about when a satellite is put into orbit.

That’s why fiber optic systems are highly suitable for applying in this industry and providing data about temperature, strain and radiation. Moreover, based on the received information, it can foresee possible malfunctions. They are able to operate in extreme conditions and survive during the entire mission.

These factors make all the difference in future space exploration and its colonization.

FBGs for the nuclear industry

Fiber Bragg grating sensors can be also implemented for the development of nuclear applications. It is well-known that the radiation affects the surrounding materials and consequently their features. It is about photonic and electronic components that are the most susceptible to nuclear radiation exposure.

Usually, in the nuclear industry there is no possibility to replace components or make any repairs of the already operating systems. That’s why it is required to monitor the systems’ maintenance in the radiation conditions.

There are two types of radiation that are always taken into consideration: gamma-rays and neutrons. Gamma-rays are radiated by the surrounding structures, and neutrons are relevant to the inner reactor core during its operation. FBGs can be implemented in different sensing operations. For example, monitoring of the temperature in the reactor core and observation of the underground nuclear waste storage facilities, mechanical stress measurements, etc.

FBGs in radiation environments

There are several types of FBGs that can be divided according to their diverse inscription processes, thermal and radiation resistances. In reality, fiber optic sensors can malfunction under the long-term exposure of radiation that leads to the future measurement errors. These malfunctions depend on the structure of distributed fiber optic sensors and the radiation environment.

Scientists have conducted a range of special studies to watch how fiber Bragg gratings are operating in radiation conditions. Space, high energy physics and nuclear facilities are able to apply fiber optic technology to their advantage.

Fiber optic sensors’ sensitivity to the radiation depends on their way of manufacturing and concentration. However, ionization is able to break the bonds. Moreover, there is a possibility of structural changes such as densification that causes further defects. These factors lead to the degradation of optical characteristics that are invisible to the eye.

The main effect applied in this technology is radiation-induced attenuation. It depends on various parameters including:

Harsh environments;
Qualities of the optical fibers like manufacturer process, etc;
Testing environment.

Due to the composition of the optical fibers, they will react in radiation environments differently. That’s why except for the accurate calculations, specialists take tests on the fiber radiation response in conjunction with temperature. They watch fiber optic sensors’ possible reactions before applications in the real-world environment.

Fiber Bragg gratings have many capabilities and can be applied for prevention of disasters and accidents. With a proper coating and method of inscription, FBGs are able to detect any changes and, due to it, define the concentration of the hydrogen, etc. The quick and accurate location of the resulting leakage can prevent crucial damages, unexpected expenses, and danger to human life.

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FBG Interrogators and Other Fiber Optic Technologies

Fiber optic technology has become a solution that takes its place in many processes due to its benefits and stable performance it provides. It contains a wide range of tools such as fiber Bragg grating sensors, FBG interrogator, etc. All equipment contributes to distributed sensing and plays its own different role. FBG Interrogators and Other Fiber Optic Technologies

FBG Technology Principle

Fiber Bragg grating is a microstructure. It might be integrated into the optical fiber’s core. FBG is usually approximately a few millimeters in length. The interference pattern in the core is done with the help of the UV laser beam and a phase mask.

According to the technology, the index of reflection changes along the length in the fiber core. Its modulation makes a fiber Bragg grating play as a selective mirror that is able to reflect certain wavelengths and transmit the others. The light that continues to pass through the optical fiber to the following fiber Bragg grating travels without any loss. The reflected wavelength is defined by the microstructure interval and the index of refraction of the core.

The FBG system contains two main elements: FBG interrogator and a range of fiber Bragg grating sensors.

FBG Interrogators

FBG interrogators are optoelectronic units playing a role of measurement and data collection systems. FBG interrogator is an important part of the distributed monitoring system that enables instant figures of fiber Bragg grating (FBG) sensors and data transmission.

An FBG interrogator is able to provide data from the network of sensors. Fiber optic sensors can be presented by different types of sensors that measure different parameters, for example, temperature, strain, displacement, etc. They are connected into one distributed monitoring system that acquires information simultaneously.

During the data acquisition, FBG interrogator acts as a radar, sending pulses into the fiber and getting the signals back. The interrogator registers the received wavelengths and then transfers them into engineering units. With highly accurate FBG interrogators, fiber optic sensing systems are able to provide reliable data over a wide distance. FBG interrogators efficiently provide precise measured data twenty-four hours a day using computer software. Due to the software, data can be stored and later analyzed.

Fiber Bragg Grating Sensors

The other element of every sensing system, except for FBG interrogator, is fiber Bragg grating sensors. FBG sensors are sensors based on the same principle of fiber optic technology. They usually present a chain of sensors creating a single optical fiber. This chain commonly consists of up to 30 fiber Bragg grating sensors per fiber.

Fiber optic sensors proved to be the best solution compared to traditional electrical sensors. They have proven to be highly accurate, relatively simple instruments capable of operating in severe environments. In contrast with conventional electrical sensors, fiber Bragg grating sensors are immune to electromagnetic influences (EMI) and mechanical fatigue.

The diversity of FBG sensors is quite wide. The most common types of sensors are:

Temperature sensors;
Strain sensors;
Displacement sensors;
Pressure sensors, etc.

Fiber optic sensors can be implemented in different field projects. Depending on the purposes, multiple fiber optic sensors or array of sensors can be installed. They are able to take measurements for one or several parameters in different places. The FBG sensors can be embedded into the structures or surface mounted.

FBG systems that contain fiber Bragg grating sensors and FBG interrogators have found their applications in many areas. They are proven to help in development and monitoring of different constructions, vessels, systems, etc. Fiber optic technology has proven to be cost-effective and efficient.

distributed monitoring systems FBG interrogators FBG systems fiber Bragg grating sensors fiber Bragg gratings fiber optic sensors

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. FOS for Underground Coal Mines

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. FBG Sensors for Weigh-in-Motion strips

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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