Tag: fiber optic solutions

Fiber Optic Sensor (FOS) Technology and its Applications

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

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

Bridges

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

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

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

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

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

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

Buildings

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

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

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

Mostly, fiber optic technology is used for:

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

Tunnels

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

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

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

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

Hydroelectric and Wind Power Plants

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

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

Dams

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

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

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

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

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

Fiber Bragg Grating Sensors for Railways

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

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

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

Fiber Optic Solutions for Monitoring Systems in the Railway Industry

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

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

Fiber Bragg Grating Sensors Characteristics

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

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

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

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

Fiber Bragg Grating Sensors in Field Projects

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

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

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

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

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Fiber Optic Sensors for the Structural Health Monitoring

Structural health monitoring or SHM is a crucial technique thanks to the development of architectural design. Its main goal is ensuring safety for the civil infrastructure. Due to the fiber optic sensors‘ benefits, a great number of the distributed sensing systems have found application in civil engineering as SHM systems.

What is a Structural Health Monitoring System?

Structural health monitoring is a technique of evaluating and monitoring structural health. Thanks to its capability to respond to unfavorable changes, this method is widely used in many fields including aerospace, civil, and energy sectors, etc.

Why is SHM necessary?

All structures are vulnerable to various internal and external factors that can lead to wear or malfunction. There are various reasons that can cause it. For instance, deterioration, problems in construction process, an accident or environmental load, etc. That’s why it is important to implement a monitoring system.

Damage identification systems monitor all the changes in rates in real time 24/7. It gives an opportunity to detect deviations quickly and react properly in a short period of time before significant damage is caused. Therefore, timely maintenance and repair actions reduce the repair time and operating costs.

The structural health monitoring systems provide the following benefits:

Increased security;
Detecting of the damages at an early stage of difficulties;
Continuous tracking;
Saving of operating costs and time;
Development of rational management and maintenance strategies, etc.

Typical Fiber Optic Sensors

In accordance with the increase of the number of buildings’ and bridges’ under construction, the health monitoring of the concrete structures has become a topical issue.

1. Temperature Sensors

Most of all, the health of the concrete structure depends on the temperature influence. Its monitoring influences the general quality and thermal resistance of the entire structure.

At early stages, the temperature shifts affect structure’ cracks and thermal stresses that are usually caused by hydration. Besides, with the help of the two crucial parameters, the maximum temperature and the temperature trend, specialists predict the future structural health.

In addition to that, there is a special system called Distributed Temperature Sensing (DTS) that helps to monitor the cracks that may appear in the concrete structures. Its low cost and well-considered technology are believed to be important advantages in measurement. Other advantages of the FBG temperature sensors are their accurate measurements and fast response. Besides, temperature sensors are perfect for hard-to-reach places and massive sensing networks.

2. Strain Sensors

Another popular type of the fiber optic sensors is FBG strain sensors. To find out the deformation degree, the structure’s density information is used. In fact, the stability of the structure depends on its strength. It is safe when the structure strength is greater than the applied pressure.

After calibration, the unit acquires the features of a force transducer. The strain sensor transfers the component strain accurately. Characteristics such as light phase, frequency, amplitude, or polarization state, allow operators to monitor the health of the structure. All these features change under the influence of deformation.

Due to the common features of the strain sensors, like small size, they are universal sensors for force and load control. They are often used in large machines and steel constructions where there are high loads.

3. Displacement sensors

The other type of sensors are displacement sensors the main task of which is displacement measurement. It becomes possible by the constant measurement of the distance between the sensor and an object.

These FBG sensors are frequently used because they are greatly resistant to external impacts like corrosion and electromagnetic interference. Moreover, they are applied where long term reliability and safety are demanded.

If we compare them to the strain sensors and temperature sensors, FBG displacement sensors can’t measure quantity using only fiber optic sensors. They utilize FBG response to its equivalent Bragg wavelength.

Displacement sensors are perfect for monitoring of the civil engineering structures 24/7. They are suitable for monitoring aircraft, concrete structures and other industrial applications.

4. Pressure sensors

FBG pressure sensors use reflected wavelength analysis. This kind of sensors measure various parameters under severe conditions like high temperature or pressure rates.

The fiber pressure sensor’ operational principle is based on the fact that external factors affect the Bragg wavelengths by influencing the pressure sensor. In such a case, changes of the FBG’s physical or geometrical properties are implicitly measured.

FBG pressure sensors have the same characteristics as the other fiber optic sensors. They are small, portable and provide the highest accuracy and stability.

Usually, fiber pressure sensors measure the levels of liquids and gas in pipelines or tanks. They are used for the indirect flow control in tanks and pipes. FBG pressure sensors are crucially essential in various industrial fields like liquid level monitoring in oil storage tanks, gas turbine engines, etc.

In conclusion, we should say that any of these fiber optic sensors can perform measurements as a structural health monitoring. According to the existing situation and characteristics, the specialists choose the suitable variant, thus ensuring safety for any kind of civil construction.

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Fiber Optic Sensing Systems for Oil and Gas Wells

Fiber optic sensing systems can greatly assist in the exploitation of oil and gas resources. During the downhole processing, technicians can face a variety of technical challenges resulting from difficult environmental conditions. Wellbore structural health monitoring is a substantial system that provides the profitability and reliability of these fields.

Fiber Bragg grating sensors have replaced traditional electronic sensors for reservoir monitoring and downhole production. In-well sensors are applied for measuring a range of parameters such as flow rate, pressure, temperature, fraction, seismic response, etc. Fiber Bragg gratings have proven themselves as reliable and accurate technology that can be applied in multilateral wells. These systems are installed in different operating environments all over the world.

Distributed Fiber Optic Monitoring Systems’ Elements

Thanks to all the benefits, including a wide range of working temperatures and pressures, immunity to electromagnetic interference, and the possibility of usage in an adverse environment, fiber optic solutions have found many applications.

Any fiber optic sensing system consists of three components:

Fiber optic cable is suited to measure some physical effects with high absolute and local accuracy. Usually, cables are produced in such a way that the scattering effects are minimized. That allows maximizing transmission distance and data rate.
Analyzer or control panel is connected to the fiber optic cable and is designed to capture and collect data.
The final step is the interpretation and analysis of the whole received sensor data with the usage of the software. The software allows users to visualize strain or temperature data from the system.

The Most Common Fiber Optic Sensing Systems

There are two main types of fiber optic sensing systems: distributed acoustic sensing systems and distributed temperature sensing systems. Both of them have proven to be the most cost-effective and reliable fiber optic solutions and found their applications, including in the oil and gas industry. The main advantage of these systems is the ability to measure at each position where the fiber optic cable is installed.

Distributed Acoustic Sensing

DAS systems are optoelectronic instruments based on fiber optic technology that measures acoustic interactions all over a fiber optic cable. In DAS there is also an attached optoelectronic device that processes all the data from the cable. This technique allows acoustic frequency strain signals to be detected in harsh environmental conditions and over large distances. The sensing fiber is usually built on single-mode fiber. However, multimode sensing fibers can be also applied in some customized applications.

Distributed Temperature Sensing

DTS systems are optoelectronic instruments based on fiber optic technology that measures temperature all over a fiber optic cable. One of its advantages is providing continuous temperature information along the whole sensing cable. Moreover, specialists can predetermine the discrete sensing points for the most accurate data.

Nowadays, scientists are working in other directions. Since the invention of fiber optic technology, significant improvements have been made in both technologies and sensors. But for now, it is complicated to project a system that would combine DAS and DTS systems with the same optical fiber because of the different operation principles.

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

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Fiber Bragg Grating (FBG) Sensors for Industrial Sensing

Recently, researchers have presented a new generation of fiber Bragg grating (FBG) sensors that are covered with aluminum and copper. These FBG sensors are compact and hermetically sealed. Depending on the applied coating, they are resistant to high or low temperatures and can be applied in harsh environmental conditions. As well as gold-coated fiber Bragg grating sensors, they are representatives of a modern generation of humidity-proof different sensors, for example, temperature sensors, strain sensors, pressure sensors, etc.

Main Fiber Bragg Grating Sensors advantages

It’s a well-known fact that FBG sensors are widely applied in various fields and spheres thanks to their advantages. A lot of measurements in harsh environmental conditions would become possible by the usage of fiber optic technology.

Here are the most common advantages of fiber Bragg grating sensors:

absolute temperature and other measurements in comparison with usual electric sensors;
rapid linear response in strain, pressure, or temperature measurements;
the compact size of the construction reduces the weight and allows to use of many sensing points on a single fiber strand;
measurements over long distances;
acceptable price, etc.

The new type of FBG Sensors

However, a usual FBG sensor with the glass fiber coating can have several limitations because of the high humidity, high temperatures, corrosion, etc. The new type of Fiber Bragg Gratings are embedded into optical fibers coated with aluminum, copper, or gold have much more applications.

Scientists have offered processes that allow providing two lays of metal coatings. It gives an opportunity to create different lengths of window stripping and make the second layer with the needed thickness and length.

In conclusion, we must say that scientists from all over the world keep finding new fiber optic solutions to solve the modern problems we face in real life. That means that fiber optic technology will be better and more effective every day.

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 Optic Sensors’ development as wearable

Over the last few decades, scientists could achieve considerable progress in creating wearable sensors. Wearable sensors are newly developed inventions that can detect physiological and biochemical markers for health monitoring. Fiber optic solutions such as fiber optic sensors were no exception and made a great contribution to this technology.

What are wearable sensors?

Wearable sensors have an enormous potential for the early detection of many diseases including Covid-19 by measuring numerous vital signs such as blood oxygen level, respiratory rate, etc. According to the studies on Covid-19, the most common symptoms are shortness of breath, fever, and fatigue. Moreover, the blood oxygen level of an infected patient is lower because it is a respiratory disease. That’s why it was important to create a fiber optic technology capable of providing accurate data that would be useful for specialists and non-specialists alike people in quarantine or self-isolated.

Fiber optic sensors for medicine

Fiber optic sensors have attracted attention by development as flexible sensors. They usually consist of optical gratings and optical fibers embedded into polymeric matrices. For example, wearable systems based on fiber Bragg grating (FBG) were developed for biomedical usage. Thanks to their small size, lightweight, and other advantages, they can be easily integrated into polymers or textiles.

FBGs were suggested as wearable sensors for respiratory measurement for the upper body like abdomen and chest movements. FBG output changes can show the respiratory rate and breathing pattern. Moreover, with the help of fiber optic sensors, specialists are able to receive information about cardiac activities. The suggested fiber optic system has high sensitivity and can respond to environmental factors, for instance, relative humidity, temperature, and water immersion. Researchers noticed that the temperature had more influence on them in comparison with water immersion and humidity. That means that this fiber optic system needs further investigation.

The new humidity sensors were also developed based on optical fibers. The humidity also influences the light intensity of the emitted light of optical fibers. This function was used for developing a fiber optic system to measure the level of the nasal exhaled breath for respiratory rate tracking. In this system, scientists have placed a Fiber Bragg grating in an agar substrate. This device with fiber optic sensors demonstrated reliable performance and nice sensitivity to relative humidity change.

Thanks to the newly designed wearable fiber optic sensors, it became possible to integrate the health data of each person and find the best option for him.

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FBG sensors application in VR technology

It is not a secret that fiber optic technology already has a wide range of different applications starting with medicine and ending with road monitoring. However, scientists still have a lot of spheres for FBG sensors implementation. And the VR ecosystem is one of them.

So one Korean company has developed motion capture suits based on fiber optic solutions. This company is a developer of virtual reality technologies that aims to create a fully integrated VR ecosystem with the usage of fiber Bragg grating sensors.

VR entertainment is becoming more popular and capturing the minds of consumers. Nowadays, VR equipment can be installed at homes and other VR-based devices. Its applications are very diverse and can be applied in many industries, including education and even defense.

The FBG suits based on fiber optic technology are considered to be the fourth generation VR technologies. This generation intends to make VR more exciting and easily accessible. The previously created motion capture devices were much more expensive and required experience to work with. However, the company has solved both these problems with the help of fiber optic technology.

The company found out that there were some aspects that prevent VR adoption, for example, high installation costs and a long list of limitations. However, with the application of fiber optic sensors, the maintenance costs can be greatly reduced which will lead to greater adoption.

A lot of VR systems working on the principle of inertial sensor technology have a great number of cameras to detect a person’s movements. On the one hand, this method provides more accurate results. However, it also provides too much information that is needed to be handled. This factor makes it difficult to participate simultaneously for many users. Moreover, inertial sensor technology can be influenced by electromagnetic fields and cause an error.

The alternative design was developed with the usage of FBG sensors. This fiber optic technology is based on recognizing a person’s position through the refraction of light in the fiber optic cable. Fiber optic sensors precisely measure joint movement. Moreover, it can be used for a long perspective, providing no errors. According to scientists, this is a new implementation of FBG sensors into the existing products.

Now the company plans to deliver suites based on FBG sensors for VR applications in various fields and for different producers. And scientists hope to work in this direction further.

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FBG sensors for healthcare applications

A collaboration of scientists from different countries (China, Pakistan, and Hong Kong) have developed new 3D printed FBG sensors that can help in creating the ‘smart beds’. Scientists have worked to determine the main advantages of the innovative 3D printed FBG sensors and their applications in different spheres.

3D printing has demonstrated enormous results in different scientific fields. It helps to reduce the costs and makes the production process much easier for the developers. The university scientists have already applied it in their different devices with potential healthcare applications.

The main goal of this development based on the fiber Bragg grating sensors was to track sleeping patterns with high precision. First, the research team hopes that this fiber optic solution can be helpful for hospitals to monitor the well being of patients. Moreover, these fiber Bragg grating sensors are temperature-insensitive, lightweight, and high-accurate. That increases their chances to be installed in more hospitals and improves the quality of care because the staff could respond more quickly when the patients’ condition deteriorates.

Usually, FBGs are a microstructure that length is a few millimeters. It is implemented into a short optical fiber that can transform the light in response to temperature, strain, or vibration. FBG sensors are highly applied in mechanical engineering, textile, and medical spheres, thanks to their high thermal sensitivity.

Nowadays, the production of FBG sensors for healthcare still remains a time-consuming and equipment-intensive process that is hard to replicate. While 3D printing is an advanced technology that allows the creation of complex FBG sensing devices. Moreover, fiber Bragg grating sensors have never been applied to sleep-monitoring.

During the first experiments, the 3D printed FBG sensors were tested while putting under pressure loads. Each device demonstrated a number of consistent wavelengths which leads to the possibility of providing reliable readings. The final tests on fiber Bragg grating sensors were held by placing them under the mattress of a bed. A person demonstrated several sleeping positions while the FBG sensors were tracking his changes in posture.

According to the results, the FBG sensors’ readings were almost precise and had an error rate of less than 1%. Nevertheless, the research team considers that this fiber optic technology still has potential in the future. They could, for example, track a patient’s breathing and identify when the heart rate has begun to fall. And that is not the first time that fiber optic technology can prove beneficial to medicine.

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FBG sensors in monitoring road conditions

Scientists from Latvia made a number of experiments using fiber optic technology for monitoring the condition of the road surface. They chose special FBG sensors that can collect data about roadway changes, like changes in the strain and temperature. These fiber optic solutions that also include applying fiber Bragg gratings (FBGs) will help in designing reliable roads and planning for road repairs.

The process of pavement destroying can’t be completely stopped. However, we can apply more strong materials and repair small cracks in the structure at the early stages. That is why we require new monitoring methods and the most effective ways are fiber optic solutions.

According to the research, the fiber sensors could define the roadway defects and measure the load on the site. So with the help of fiber optic sensors, it will be possible to consider the pressure and vibration created by transport in the area and strengthen the coverage in the right places.

Scientists chose fiber optic systems because fiber optic sensors are highly sensitive and do not require a power supply. Fiber sensors can be installed in an existing fiber optic network and receive data remotely. The basis of fiber optic sensors contains fiber Bragg gratings (FBGs). It is a section in the middle of an optical fiber, where the refractive index of light has been changed using ultraviolet radiation. As a result, such a section always reflects radiation only in a very small part of the spectrum and transmits the rest of the light without loss. The fiber Bragg grating (FBG) can be formed so that the wavelength of the reflected light depends on changes in temperature, pressure, or other physical aspects. Because of these parameters, fiber Bragg grating sensors are effective for application.

Scientists placed two types of fiber optic sensors on one of the highways during its renovation. The first one measured deformations in construction, the other detected temperature. Since unprotected fiber sensors are quite fragile, they were packed in composite and ceramic tubes. The first test demonstrated that the most precise strain measurements are possible when the load is placed exactly at the location of the fiber optic sensors. Researchers also specified that temperature plays a crucial role in the deformations of the asphalt. And the final key aspect of the tests with fiber optic technology was monitoring real traffic and defining the truck’s quantity.

Finally, the experiments demonstrate that fiber optic sensors can measure the deformations of the roadway with sufficient accuracy. By applying FBG sensors specialists can determine the moment when the limit of permissible deformations will be exceeded in the selected area. That will definitely help in designing new roads and repairing the existing ones.

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Fiber Optic Technology and its recent advances

During the last 60 years, fiber optic technology has been applied to improve the efficiency of developed systems in various spheres like medicine, vehicles, and other industries. Modern fiber optic solutions expand the abilities by implementing levels of data and sensing technology in the energy, medical field, and even aerospace. There are various fiber optic solutions that help researchers improve their development and make new discoveries in science.

Intrinsic and extrinsic fiber optic sensors are two wide categories of fiber optic sensors. Extrinsic fiber optic sensors utilize the fiber to manage the light to a sensing region. Then the optical signal is modulated in another environment. Talking about the intrinsic fiber optic sensors, the light remains within the waveguide. So it measures the influence of the optical fiber signal.

Intrinsic fiber optic sensor technology, where the fiber optic sensor is the fiber optic cable itself, has improved significantly during recent years. There are two main technologies connected to intrinsic fiber optic sensors: scattering and FBG. FBG methods can be fully distributed or have many sensing points. With the help of FBG sensors, scientists can define the changes by getting precise measurements. Scattering techniques depend on natural imperfections occurring in the fiber optic cable. The FBGs have a high signal-to-noise ratio in comparison with scattering techniques.

Both scattering and FBGs use different demodulation techniques. Scattering techniques get the information by observing changes in naturally back-scattering patterns. For FBG based technology, wavelength division multiplexing is the most prevalent demodulation technique. However, in certain circumstances, optical frequency domain reflectometry can become the most useful method.

Wavelength division multiplexing is able to spread to large distances and get the data rapidly. This technology can also support multiple fiber Bragg gratings on a fiber. It observes critical points more than the whole field of the data. That is why it is mostly applied in automobile crash testing as a monitoring instrument.

The scattering techniques can cover long distances and give a distributed profile of the data. They obtain information all over the entire fiber optic cable. Many systems on the market measure temperature or acoustics and are called Distributed Temperature Sensing (DTS) or Distributed Acoustic Sensing (DAS). These techniques are usually applied in monitoring a pipeline for tampering, for example, where there is no need for high-speed acquisition.

Optical frequency domain reflectometry is another demodulation technique that is mostly applied with FBG sensors where fiber Bragg gratings are placed really close and create a fully distributed sensing fiber. It has many advantages like the combination of high spatial resolution, a bunch of fiber optic sensors, a quick refresh rate, and a full distribution set. Apart from distributed sensing of a strain and temperature, this technology allows defining 2D deflection, liquid level, magnetic fields, etc.

Nowadays, thanks to fiber optic technology, scientists have an opportunity to solve any problems in their designs by using fiber optic systems. And there are still many possibilities for fiber optic technology in the future.

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