Tag: fiber optic sensors

Chirped FBGs and Their Common Applications

Due to high demand, fiber optic sensing continues to evolve. The most well-known technology associated with fiber optic sensors is the fiber Bragg gratings. They have become an instrument for measuring thermal, mechanical and physical parameters, like other technologies.
The FBGs differ by the method of their inscription. For chirped FBGs, one of these methods is used. Chirped Fiber Bragg Gratings and Their Applications

What are the Chirped FBGs?

Chirped FBGs are fiber Bragg gratings with a variable period lengthwise. The most common type is the linear chirped grating, where the period of the grating varies according to a linear law. Such gratings are recorded with the help of special phase masks with a variable period. In the past decades, chirped FBGs have attracted a lot of interest from specialists. This is due to their main characteristics and grating structure.

Due to their reflective index, the chirped FBGs are different from the custom fiber Bragg gratings. The refractive index profile of a grating can be modified to add other features. One such feature is a linear change in the grating period, called chirp. The reflected wavelength changes with the grating period, broadening the reflected spectrum. A chirped grating has the property of adding dispersion. This means that different wavelengths reflected from the grating will experience different delays.

Common FBGs and chirped FBGs have another significant difference. The overall spectrum is a function of the temperature or strain that is registered in each individual section of the grating. Chirped FBG sensors are capable of detecting temperature or strain changes. In this way, they can locate the events, such as hot spots or strain deformations.

Applications of Chirped FBGs

Conventional FBGs are built on the basis of the periodic modulation of the refractive index in the core of the optical fiber. They have been proven to be the top of the line grating-based type of technology.

Structural engineering;
Medical devices;
Oil and gas industry;
Nuclear monitoring, etc.

The fiber Bragg gratings are used as in-fiber mirrors or optical filters with a narrow band optical spectrum. They are commonly applied as sensitive elements in various fiber optic sensing systems for measuring strain, temperature, and other parameters.

Chirped FBGs

Chirped FBGs, as well as traditional fiber Bragg gratings, have found a variety of applications in laser technology and distributed sensing systems. All chirped FBGs have the ability to use the full length of the grating for strain or temperature change monitoring. Chirped FBGs also have their own spectral properties and ability to detect profiles. All of these key features make them in demand, and even preferred, in a number of different areas.

Their main functions are as follows:

Heat detection and localization;
Measurements of strain;
Detection and estimation of the high-pressure events;
Location of structural damage and mechanical cracks;
Velocity measurement.

For example, there are several different applications, including the following:

Transmission line monitoring;
Medical treatments;
Aerospace and automobile industry;
Structural health monitoring;
Biosensing, etc.

Temperature Measurement for Cancer Care

Chirped FBG sensors are real-time temperature measurement devices. One of them is medical thermal ablation. It is based on the hyperthermia principle. This technique is widely applied in pain relief, correction of cardiac arrhythmias, interventional cancer care. Thermal ablation is a recently developed technology for the minimally invasive treatment of tumors. It has proven to be effective.

Based on the correctly selected thermal dose, medical personnel choose the most appropriate treatment method. The higher the temperature, the more human cells get affected. This is especially true when treating cancer, where high temperatures help kill tumors. Thermal ablation is a minimally invasive procedure performed through a small skin incision or needle. This helps avoid damage to healthy tissue.

Chirped FBGs have made a significant contribution to the implementation of real-time distributed monitoring systems. They have found a number of applications including structural health monitoring (SHM) where their ability to measure temperature and strain is useful.

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

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.

FBG sensors FBGs fiber Bragg grating sensors fiber Bragg gratings fiber optic 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. 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 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.

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

Distributed Sensing Systems for Leak Detection

The increasing role of the oil and gas industry has led to development of many related technologies including distributed sensing systems. Among other things, they have become a part of the leak detection technology that has proved to be one of the most powerful.

For development of the most cost-effective detection technology there should be a balance between three elements: well-trained staff, properly configured distributed monitoring systems and proper operations’ arrangement. By observing these conditions, the effective operation is achieved.

With distributed monitoring systems, the pipeline management leads to the fast detection of any accidents, thus, reducing the extent of damage, as well as unforeseen expenses. Distributed Sensing Systems for Leak Detection

The Most Common Classification of Distributed Sensing Systems

Distributed sensing is a continuous monitoring technique which operates across the whole fiber optic cable in real time.

In contrast with the conventional sensors that were previously applied, distributed sensing systems use the whole optical fiber instead of the separate sensors that measure parameters in certain points. For this reason, fiber optic systems are easier to install even in heavy ambient conditions. With fiber optic cable, specialists have no need in defining particular locations where sensors should be placed. This fact makes the monitoring process more cost-effective.

The distributed sensing systems are different due to the data they require. So, there are distributed acoustic sensing (DAS) or distributed temperature sensing (DTS).

Distributed temperature sensing (DTS) uses a fiber optic cable that serves as linear temperature sensors. Eventually, specialists get the full temperature profile for the required period.
Operation principle of the distributed acoustic sensing (DAS) is similar to the DTS system. It applies a fiber optic cable as well, that provides the data. However, instead of registering temperature changes, they are relying on the acoustic and vibration changes in fibers.

Applications of the Leak Detection Systems

Leak detection fiber optic systems are installed to get the information about any appearing changes in parameters and leak possibilities. The distributed monitoring systems are able to find leaks almost instantly.

Here are a few examples where fiber optic sensing systems have found their applications:

One of the last well-known developments connected to fiber optic sensors is the monitoring of offshore Arctic fields. Pipelines are constructed for safe transportation of oil and gas avoiding any leaks. However, there are high risks of their deformation because of the severe environmental conditions like the effects of ice gouging, permafrost thaw settlement, or physical damage. The absence of fiber optic monitoring systems may result in severe environmental, and economic impacts.
Distributed sensing systems can be also applied for liquid sodium leaks monitoring. Fiber optic sensors can be implemented into various nuclear power plants and other facilities. Electromagnetic immunity, ability to resist high temperatures and operating in radioactive environments make fiber Bragg grating sensors a powerful instrument in monitoring.
Distributed monitoring systems are also used at wastewater treatment plants. The leak can lead to dangerous consequences such as spillage of contaminated fluids and therefore environmental damage.

Main Purposes of the Fiber Optic Technology Applications in Leak Detection

Fiber optic sensing systems bring many benefits while using. As a result, they have become useful instruments and can be applied for different purposes. Firstly, distributed monitoring systems are usually used for monitoring any changes that take place over long distances of the pipelines. Fiber optic sensors can monitor flow rates, temperature, pressure, ground strain, etc. All measured physical parameters are sent to the center where all the data is displayed with the help of the software.

Due to the received data from fiber optic monitoring systems, specialists are able to watch any changes or conduct the necessary calculations. In case of any changes, the operator or security personnel gets a signal that there are changes and sees their accurate site. So specialists can quickly respond to any changes and prevent any further possible damage.

The other purpose of distributed sensing monitoring is leak detection. Fiber optic monitoring systems can be installed both on buried and unburied pipelines. They can detect the precise location of the leakage in a short time. Moreover, they can discover other accidents like ground disturbances, theft, manual and machine excavation, etc.

Fiber optic monitoring systems designed for the oil and gas industry can also help in optimizing the lifetime of the wells. They are used as integrity monitoring instruments of the storage tanks, process vessels and other equipment. Considering all the information, specialists can make a decision on the maintenance programs as a means of extending the service life.

Due to all these possible applications, distributed sensing systems have found their place in the gas and oil industry. Fiber optic sensing systems have proved to be cost-effective in measurements of main parameters in pipes in the conditions of severe environmental and industrial equipment.

distributed acoustic sensing distributed monitoring systems distributed sensing systems distributed temperature sensing fiber optic monitoring systems fiber optic sensors

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.

FBGs fiber Bragg grating sensors fiber Bragg gratings fiber optic sensors fiber optic technology

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

Distributed Temperature Sensing Systems for Coal Mines

Distributed temperature sensing systems as well as fiber Bragg optic sensors are focused on the continuous monitoring of the constructions’ health condition and prevention of potential damages. The DTS system consists of a fiber optic cable, typically several kilometers long, that works as a temperature sensor. As a result, specialists can watch all dynamic temperature changes in a continuous temperature profile. DTS Systems for Coal Mines

DTS Systems as a Fire Detection Technology

In the mining industry, the risk of fires still remains very high. Conventional fire and heat alarm systems require constant and expensive maintenance and are not as effective as fiber optic monitoring systems. Thanks to modern DTS technology, both of these problems are now solved.

There are many forces in mines that can cause a fire. The possibility of fire is especially high in certain locations due to the complicating factors such as:

geological settings;
presence of the vehicles, heat-generating and mobile equipment;
conveyor failures;
lighting faults, etc.

Distributed temperature sensing systems have been proven to outperform standard fire detection systems in a range of aspects including efficiency and high level of safety.

The DTS system includes a single fiber optic cable and a DTS unit. The traditional system includes many components and devices. The distinction of DTS results in lower installation and maintenance costs due to less equipment, and in improved system reliability. Therefore, there is no need in its regular service that can be complicated because of the difficulty of access and huge size of the mine. Moreover, the conducted field projects have demonstrated that fiber optic sensors inform the operators about the heat significantly earlier than a fire starts.

All these advantages have made DTS technology one of the main methods for the detection of potential fires or other abnormal conditions.

Fiber Optic Sensors for Detection of Faulty Conveyor Belt Rollers

The conveyor belts are cost-effective instruments for continuous transporting of dry bulk materials over various distances. Due to the latest technologies, the accidents related to the problems with conveyor belts are relatively rare in modern underground coal mines. However, to this day there is a possibility of causing damage related to the conveyor belt accidents that can result in the interruption of the production process.

The reliability of the whole conveyor belt depends on the robustness of its separate components. Distributed temperature sensing (DTS) system helps to monitor the thermal conditions of each idler and detect the malfunctions. DTS systems use the latest advancements of fiber optic technology. They have proven to be a safe method of application in underground mines.

There are some aspects to consider when choosing the suitable monitoring system. Firstly, it is not easy to obtain data from a vast area. It requires the setting up of thousands of sensor elements. Secondly, the data transmission can be challenging due to the underground mine environment. Therefore, some types of equipment are prohibited for usage, such as electrical cables. Fiber optic monitoring systems have been able to solve a number of such issues that engineers usually face during underground mining.

The DTS system consists of a DTS unit and a fiber optic cable. The system measures temperature along the entire length of the cable and transmits the data to the operators who can detect any mechanical failures of the rolling components at an early stage. The specialists see real-time data of the conveyor structure and the surrounding area.

The specialists conducted a range of experiments to find the most effective placement of the fiber optic monitoring system. The problem is that fiber optic sensors can’t be located over the idlers because they will interrupt the operation. So they are attached to the frame of the idler, as close to the bearing as possible. This affects the results because fiber optic sensors take longer to capture the heat. However, they still have better results compared to the traditional methods.

Fiber Optic Sensing for Monitoring of Roof Activity

According to statistics, there are many causes that can lead to mine accidents including dust explosions, mine support deterioration, etc. However, the most common cause of the accidents that take place in underground coal mines is mine collapse.

Design and functioning of the underground mines creates a number of complicated factors for operation. The dynamism of mining operations and increasing depth can lead to the associated risks and jeopardize an acceptable level of safety. At the same time, there are always natural risks to the mine structures, such as seismic shocks which can also lead to roof stratum displacements.

Roof activity monitoring can be used for a variety of purposes, including structural health construction monitoring of the underground openings and design optimization. For the majority of projects, fiber optic monitoring systems are applied due to their ease of use in harsh environments compared to other conventional methods.

Fiber optic sensing monitoring is able to help in reduction of the mine roof displacement and thus avoid severe consequences. There are different types of fiber Bragg grating sensors that are used to monitor displacement, temperature or strain in underground openings or nearby them depending on the purposes. FBG sensors have proved to be reliable and accurate monitoring equipment of roof activities in underground coal mining. Modern fiber optic monitoring systems have made it possible to display all changes of the required parameters on the screen almost instantly and prevent any accidents in underground mines.

The conducted projects on the mining sites have demonstrated the benefits of fiber optic sensors. The fiber optic monitoring systems can detect the slight roof displacement during the progressive face advance. The received data is usually used for roadway support and design of the mine.

In conclusion, thanks to the latest state-of-the-art technologies nowadays there is an opportunity to monitor structural health constantly. That is why distributed temperature sensing systems are widely applied for structural health monitoring of different constructions including mines. The fiber optic sensing has found many spheres of applications due to the qualities it has.

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

DTS DTS systems fiber optic cable fiber optic monitoring systems fiber optic sensing fiber optic sensors