Researchers from India have presented a new development. Thanks to it the scientists can find toxic mercury in drinking water. The whole system is based on FBG sensors.
Fiber Bragg grating (FBG) sensors are utilized widely in industrial and commercial applications with the addition of fiber optic solutions. FBGS sensors are especially effective in stabilizing the wavelength of semiconductor lasers and are useful in extracting a single wavelength from the fiber. Fiber Bragg grating sensors are popular in different spheres, including aerospace, robotics, the oil and gas industry, etc. Achievements in creating fiber optic sensors and their applications make the Fiber Bragg grating sensors appropriate for other spheres and developments.
That’s why scientists from India decided to apply Fiber Bragg grating sensors to the mercury detecting system. We can find mercury particles everywhere in the environment. They can be produced not only by human-made causes, like industrial wastes but also by natural ones, for example, combustion of fossil fuels and volcanic eruptions. That’s why the creation of the mercury detection system with the help of FBG sensors was a very important step.
According to medical studies, mercury particles can easily enter the human body. The most common ways are water bodies and marine life. In the human gut, some microorganisms can turn mercury into organic and alkyl forms. These forms of mercury in the human blood-vascular system can lead to diseases of kidneys, nerves, endocrine, and other systems. So the mercury detection system based on fiber Bragg grating sensors plays a crucial role in health care activities.
The developed by the research team FBG sensors are portable in comparison with other traditional techniques. These techniques are gas chromatography and liquid chromatography methods were tested by time. They are considered to be precise and complicated. And they are not portable like fiber Bragg grating sensors. Moreover, they need much time and get more expenses because are made in special laboratories by professionals.
Scientists think that fiber Bragg grating sensors are an ideal decision for the developing mercury detection system. Fiber Bragg grating principles help to make this system cost-expensive and highly effective in comparison with the others. However, they agree that there is still a lot of work to do and Fiber Bragg grating sensors can be updated in the future.
Nowadays researchers tend to use fusion as a safe energy source at power plants. Nevertheless, this process is dangerous. It requires reliable fiber optic technology for structural health monitoring at power plants. Novel fiber optic sensors offer robust operation in the harsh conditions of a commercial fusion power plant.
To be more precise, these fiber sensors provide temperature sensing applying optical fibers with written fiber Bragg gratings (FBGs). The FBG operating principle is based on broadband light that is directed on it. Although most of the light goes through, one wavelength is reflected. Herewith, the reflected wavelength changes with both temperature and strain.
Therefore, the installation of several fiber Bragg gratings enables performing independent temperature sensing of each location. Standard FBGs are widely used in various industries for strain and temperature sensing. Herewith, compact superconducting cables use these optical fibers based on fiber optic technology.
Novel FBG sensors can maintain “the intense electrical, mechanical, and electromagnetic stresses of a fusion magnet’s environment.” The novel fiber optic technology supposes ultra-long fiber Bragg gratings of 9-millimeter located 1 mm apart. The FBG sensors operate as conventional long quasi-continuous systems.
Compared to standard systems, FBG sensors include such benefits as long grating length (meters instead of millimeters). Ultra-long FBGs allow for sensing simultaneously occurring temperature changes along their entire length. Thus, it is possible to determine fastly temperature variation, irrespective of the location of the heat source.
Additionally, it is possible to combine ultra-long FBGs and traditional FBGs to produce both spatial and temporal resolution. The fiber optic technology has been developed by a team of researchers from Switzerland. According to them, such a combination can be used on bigger cables.
These FBG sensors detect quickly and accurately even the smallest temperature changes under realistic operation conditions. Moreover, they demonstrate a better signal-to-noise ratio thanks to their high level of sensitivity and the opportunity to adjust the optical fiber response.
Thus, the fiber optic sensors locate quench events tens of seconds faster than voltage taps. Herewith, the application of FBG sensors for HTS magnets quenches detection is very potential. It allows for overcoming the current problem of HTS coils from damage during quenches.
Finally, such a fiber optic technology plays a crucial role in compact fusion processes, where practical, high-field, high-temperature superconducting magnets are important. FBG sensors are still under development and need some improvements to be used in new applications.
Electrical sensing systems (strain sensors, string-based, potentiometric, etc.) have been the main method of measuring physical and mechanical phenomena for decades. Despite their widespread application, electric sensing systems have a number of disadvantages, such as loss of signal transmission, susceptibility to electromagnetic interference, the need to organize an intrinsically safe electrical circuit (if there is a danger of explosion).
These inherent limitations make electrical sensors unsuitable or difficult to use for a number of tasks. The application of fiber optic sensing solutions is an excellent way to overcome these problems. The signal in fiber optic sensors is light in the optical fiber used instead of electricity in the copper wire of standard electrical sensors.
Over the past twenty years, a huge number of innovations in optoelectronics and in the field of fiber optic telecommunications have led to a significant reduction in the price of fiber sensorcomponents and to a significant improvement in the quality of fiber optic systems. These improvements allow fiber optic sensors to move from the category of experimental laboratory devices to the category of widely used devices in such areas as monitoring of buildings and structures, etc.
The most widespread type of sensors
One of the most commonly used fiber optic sensors is considered to be fiber Bragg grating sensors (FBG). The fiber Bragg gratings in these sensors reflect a light signal whose spectral characteristic (wavelength) shifts along with changes in the measured parameter (temperature and/or deformation). During the manufacture of gratings, a region with a periodic change in the refractive index is created inside the optical fiber core, herewith, this region is directly called the FBG.
Optical fibersand fiber sensors are non-conductive, electrically passive, and immune to EM interference. The interrogation using a tunable high-power laser allows measurements to be made over long distances with virtually no signal loss. Additionally, in contrast to the electrical sensing system, each optical fiberchannel can interrogate a variety of FBG sensors, which significantly reduces the size and complexity of such afiber optic system.
the best weight and overall dimensions, small size;
high noise immunity, insensitivity to electromagnetic interference, such as microwave field, spark discharge, magnetic fields, electromagnetic pulses of various nature and any intensity;
absolute electrical safety due to the absence of electrical circuits between the fiber optic sensor and the recording module;
full electrical, explosion and fire safety, high chemical resistance of sensor elements.
Extreme environmental conditions
The conditions of the environment and controlled conditions in which one or more external factors — radiation, temperature, electromagnetic field, aggressiveness, humidity, pressure, and deformation — have the maximum possible constant values are regarded as extreme.
In such conditions, primary converters of control systems for dangerous technological processes (oil production, transportation, and processing of oil and gas, nuclear power generation, storage of radioactive waste), monitoring and diagnostics systems for complex construction and engineering structures (dams, bridges, mines, etc.), and military and emergency management systems operate.
Compared to fiber sensors, the lack of power supply at the location of electrical sensing systemsdoes not prevent continuous remote monitoring of dangerous objects, such as nuclear power plants, in an emergency beyond design situations. For instance, the well-known events at the Japanese nuclear power plant “Fukushima-1” in 2011 were characterized by the fact that during the two weeks when the nuclear power plant was completely de-energized, there was no information from electronic sensors, which was extremely important for monitoring the technical condition of the emergency station.
Application in extreme temperatures
Problems of standard sensing systems control of tightness of tanks with liquid hydrogen, which is the fuel of modern rocket engines, has a temperature of -253 °C and very high fluidity, due to the fact that at such temperatures, most materials become very fragile, and the sensitivity of palladium sensors quickly decreases.
It is problematic to measure the pressure and dryness of superheated steam in gas generators and superheated gas in jet engine nozzles at temperatures up to + 600 °C since piezoelectric sensors quickly degrade at temperatures above + 300 °C. Modern FBG sensorsof physical quantities are heat-resistant (up to +2300 °C) and cold-resistant (up to -270 °C). This provides reliable and long-term monitoring of the technical condition of high-temperature and cryogenic objects.
Operation during electromagnetic interference
Measurements of physical quantities using electrical sensing systems in conditions of high-power electromagnetic interference, including guidance on coaxial electrical cables and sensors from lightning discharges, in conditions of monitoring the patient’s pulse in a medical nuclear magnetic resonance facility, as well as measurements of high voltages and high currents in electrical engineering, are highly problematic.
Measurements of physical quantities of chemically aggressive media, long — term measurements of deformation of dynamically loaded objects and structures, as well as multi-sensor measurements-with the number of control points in several hundred and thousands, are also problematic for electrical sensing systems since the volume of measuring electrical cables is unacceptably increasing.
A serious problem of electrical sensing systems embedded in objects (in the concrete of hydraulic dams and bridges, in the pylons and walls of high-rise buildings, etc.) presents the practical difficulty of their periodic calibration (metrological verification).
Modernfiber sensorshave the function of metrological self-monitoring (FMSM) due to the multimodality of the optical signal, which allows for self-calibration of fiber optic sensors in real-time without stopping the controlled processes and without verification standards.
In the last decade, there were implemented many similar applications of modern fiber sensorsand systems in extreme environments of nuclear, oil and gas, and aerospace industries, shipbuilding, hydraulic engineering, energy, construction, military, and natural emergencies.
Moreover, the durability of FBG sensors in these extreme conditions creates an obvious advantage of their use in the energy, oil and gas, aerospace, construction, and transport industries in comparison with non-optical types of measuring systems.
Thus, the extreme operating conditions of fiber Bragg grating sensors, for example in wells (extreme parameters, flammable, aggressive and abrasive environments) or power plants (ultra-high currents and discharges, voltages and fields, significant ionizing radiation), actually belong to the usual operating conditions of fiber optic sensors.
Nowadays fiber Bragg gratings are actively applied in the aerospace industry. The thing is that fiber optic multiplexing abilities of sensors based on FBG technology allow performing structural health monitoring of airborne vehicles resulting in an increase of their lifetime. Thus, fiber Bragg grating sensors play a crucial role in the spacecraft industry where mistakes and damage can lead to death.
It should be noted that fiber Bragg gratings are considered to be a thin optical fiberdevice that includes a physical “grating” area at its core. Herewith, the FBG core is not homogeneous, and the fiber optic sensor has a periodic variation in the refractive index of the material. Also, there is a dependency between the wavelength of light (reflected vs transmitted) and the periodic spacing of the grating.
FBG sensors can block specific wavelengths and transmit others like in laser cavities during the mode choice. Additionally, such factors as pressure and strain also influence the qualities of FBGs and the wavelengths resulting in stretching or compressing the grating period while temperature leads to thermo-optic effects. These and some other effects (for instance, vibration and displacement) promote the application of fiber Bragg grating sensors to monitor various physical effects.
FBG sensors enable to determine ultrasonic and acoustic wave signals that are important in structural health monitoring of aerospace vehicles. For instance, acoustic-ultrasonic determination provided FBG technology helps to find out damage when the spacecraft is not mobile.
The detection offered by fiber optic sensors is regarded as highly accurate and quantitative because it is possible to monitor both the form function of the waves and the repetition of measurements. Nevertheless, the resolution and the bandwidth limitation of conventional tools employed with fiber Bragg gratings (for example, optical spectrum analyzers) do not enable accuracy in high-frequency determination.
The fact is that accurate determination of ultrasonic waves requires a demodulation method to interpret the detected signals. Four demodulation methods are distinguished in FBG technology both in practice and in laboratory testing: “a broadband light source (power detection), laser light source (edge-filter detection), Erbium-Doped Fiber Laser (EDFL), and modulated lasers.” Moreover, it is necessary to pay careful attention to the installation technique of the FBGs.
Finally, specialists apply several various techniques to employ fiber Bragg grating sensors into a vehicle or craft. The fiber optic sensors have been already tested at their installation into composite materials (inside of a fiber honeycomb sandwiches.) However, the technique can cause signal distortion, that is why an ideal wayfor spacecraft is gluing fiber Bragg gratings on with some adhesive.
Nowadays distributed fiber optic sensors remain a subject of great interest for constant structural health monitoring of huge structures, for instance, bridges or dams. Herewith, the more sensing points there are, the more effective monitoring the sensing system offers. Thus, newly improved distributed sensors with 1 million sensing points provide prominently faster detection of structural problems that are now accessible.
Fiber optic sensors allow accurately detecting of erosion or cracking before a dam fails. Therefore, earlier detection of a problem by fiber optic sensing systems may lead to its possible prevention from later deformation or provision of sufficient time for evacuation procedures. Fiber sensors are considered to be perfect for controlling infrastructure since they suit for use in harsh environmental conditions and in areas that lack nearby power supply.
The operating principle of distributed sensors is based on “changes in the structure at any of the sensing points along with the optical fiber that causes detectable changes in the light traveling down the fiber”. Despite the high popularity of distributed fiber optic sensors, the main applications of sensors include the detection of leaks in oil pipes and structural health monitoring for landslides along railroads.
It should be noted that the novel fiber optic sensing system enables tracing train and temperature changes from 1 million sensing points over a 10-kilometer optical fiber in less than 20 minutes, while the strain parameter demonstrates deformation or mechanical stress on an object of interest. Herewith, the new distributed sensor is regarded as to be about 4.5 times faster than previous fiber sensors with 1 million sensing points. A larger number of sensing points require fewer optical fiber units for structural health monitoring of an entire structure resulting in cost reduction.
A large density of sensing points makes distributedfiber optic sensors suitable for such applications as avionics and aerospace, where every inch of a plane wing has to be controlled properly. According to researchers, the conventional technique of generating the continuous signal in fiber sensors undertakes distortions in the fiber optic system at higher laser powers. This problem has been solved by using the approach known as Brillouin optical time-domain analysis.
The fiber optic sensor has been already tested and showed the opportunity to measure the temperature of a hot spot to within 3 degrees Celsius from the end of a 10-kilometer long optical fiber. Additionally, it is planned to improve the distributed sensor and make it even faster resulting in the further reduction of the acquisition time. Future enlargement of sensing point density will promote the fiber sensors being used in new fields, for example, biomedical applications.
Fiber Bragg gratings or FBGs are considered to offer a markworthy application in the fastly growing aerospace industry. The FBG benefits such as phenomenal optical multiplexing make them possible to use as smart fiber optic sensors that allow them to perform structural health monitoring of airborne vehicles and maintain and lengthen their lifetime. Thus, FBG technology plays a crucial role in the spacecraft industry where tiny errors and damage can lead to death for the crew aboard.
To be more precise, fiber Bragg grating is regarded as a thin, tubular optical fiber device that includes a physical “grating” area at its core. Herewith, the core of fiber Bragg gratings is not homogeneous, it has a periodic variation in the refractive material index. The principle of FBG technology operation is based on the change in the core refractive index because of which “some light will be reflected and some will be transmitted through the tube.” Additionally, the periodic spacing of the grating influences the reflected vs transmitted wavelength of light.
FBGs demonstrate efficient operation as narrow bandwidth light filters. The FBG application includes a block of specific wavelengths and transmission of others that is similar to the mode selection that appears in laser cavities. Nevertheless, such features as pressure and strain as well as vibration and displacement also influence the wavelengths of fiber Bragg gratings, while the temperature may lead to thermo-optic effects in the silica material that conventional FBG sensors are made from. Therefore, the mentioned FBG properties allow using them as fiber optic sensors to measure various physical effects at the same time.
FBG technology opens an opportunity to use FBG sensors to determine ultrasonic and acoustic wave signals, with a unique application in structural health monitoring of aerospace vehicles. The thing is that acousto-ultrasonic detection by fiber Bragg grating sensors is highly effective in damage detection if the spacecraft is not mobile (on the ground). Herewith, an ultrasonic actuator is required to produce the ultrasonic signals. It should be noted that the damage detection by FBG sensors is very accurate and quantitative because it allows controlling both the waveform function and the repetition of measurements.
Nevertheless, the limitations in resolution and bandwidth of conventional tools applied with fiber Bragg grating sensors, for example, optical spectrum analyzers, do not provide accuracy in high-frequency detection. It is necessary to use a demodulation method to interpret the detected signals for accurate detection of ultrasonic waves. Herewith, the installation technique of the fiber Bragg gratings is also important in ultrasonic detection. The installation of the fiber Bragg grating sensors into an aerospace vehicle or craft requires the use of various techniques. For example, it is possible to place FBGs into composite materials, however, it may cause signal distortion. This is the reason why a better way is gluing FBG sensors on with some adhesive, such as epoxy.
A company from Australia offers a novel fiber optic solution that allows providing conveyor health monitoring by applying real-time data to rationalize production and on-site performance, improve occupational health, hygiene, and safety management, and implement new predictive maintenance and support capabilities to control management.
Thus, the fiber optic technology was tested in surface and sub-surface environments of some of the world’s largest mining companies and bulk material handling the equipment resulting in the accessibility of optical fiber sensing for present sale all over the world. The fact is that efficient conveyor systems are highly important because the profitability of mining companies depends fully on such fiber optic sensing systems.
Additionally, the mining industry has always a huge challenge of conveyor maintenance, and traditional sensing technologies for advanced conveyor failure detection are often precarious, subjective, they require many time and labors. The new fiber sensing system combines the technology of optical fiber detection with a sensing technology platform, “advanced signal processing algorithms and predictive analytics” enabling to acoustically monitor and check conveyor health.
The advantages of presented fiber optic solution include the provision of accurate data to maintenance technicians, site personnel, regional operational hubs, and global headquarters, the opportunity to obtain daily asset reliability reports from every conveyor, at every site worldwide due to the connection of the fiber system to
a wireless Internet.
The operation of the fiber optic system is based on the transmission process of short laser beam pulses along a single optical fiber cable installed along the length of a conveyor, while acoustic disturbances from the conveyor sensing system lead to tiny changes in the backscattered laser beam light, which is then classified into distinguished parameters.
Also, the obtained data is then processed, the following information is gathered:
the detection of a damaged ball or a broken cage in a ball race;
monitoring and “tracking idler bearings as they progressively wear”;
the prediction of potential bearing seizures and establishment of roller replacement priorities at the next maintenance shut down.
Finally, the fiber optic technology of distributed acoustic sensing is considered to be “the way of the future for conveyor health monitoring”. Such fiber optic solution successfully optimizes conveyor operation and provides essential cost savings for operators. Herewith, this fiber sensing system monitors the condition of every conveyor roller that can contain 7.000 bearings per kilometer.
Fiber Bragg grating sensors are highly useful fiber optic sensing devices that help carry out the monitoring of temperature and strain characteristics even during a nanosatellite mission. FBG sensors present highly attractive reliable fiber optic solutions for process monitoring in a spacecraft. Additionally, it is possible to install these fiber sensors in composite structures or attached on their surface for structural health monitoring during the entire life cycle of a satellite.
To be more precise, space application of fiber optic sensors requires the use of two fiber Bragg gratings to measure temperature and strain characteristics during one space mission. The main aim of the mission is the validation and demonstration of the suitability and reliability of fiber optic technologies when it comes to a small area with numerous restrictions in terms of mass and power consumption.
Despite the fact that FBG sensors offer great performance in various fields of application, especially in industry, engineering and science, however, the use of fiber sensors in space application is not so popular, although fiber optics are presented more than 30 years in space but typically applied to transmit data or to guide the light for illumination purposes.
Fiber sensors based on fiber Bragg grating technology have numerous benefits such as electromagnetic immunity, the possibility of multiplexing, and weight-saving by taking copper harness away. This is the reason why fiber sensing technology is perfect for the harsh space environment.
Also, FBG sensors are better than other optical fiber sensors because their optical response does not depend on the optical power of the light source the eventual loss of energy transmitted along with the optical fiber, and of the response of the photodetector, thus, the response of the fiber sensor is considered to be wavelength-coded.
The used FBG technology has been successfully tested and the tests presented the capability and reliability of fiber optic sensors based on fiber Bragg gratings in space environmental conditions. In spite of the high restrictions in terms of mass, volume, and power consumption, FBG sensors offer an optimal performance of all-optical fiber components after their 3 years’ application in the space environment.
Finally, during the whole space mission crucial attenuation proving the degradation of fiber optic components because of harsh environmental conditions (as well as radiation and vacuum conditions) has not been registered. Herewith, the used tunable laser system for telecommunications purposes also presented excellent results in the space environment. It is possible that these FBG sensors contribute to the creation of more complex sensor arrays with a more complex FBG interrogator unit that will enable better resolution and operation in a wider temperature range.
Fiber optic products were invented to carry big amounts of voice data over long distances very efficiently. Improvements in fiber optic pipeline monitoring have led to the fact that now we know fiber optic cables as an actual sensor. This fbg sensor is equipped with the ability to measure parameters such as acoustic energy, temperature, strain, vibration, and suchlike. The capability of continuously gathering data about these parameters over several kilometers of fiber simultaneously is called distributed monitoring. Fiber pipeline leak detection and prevention, asset and perimeter security, and precise fluid flow measurements.
Pipelines are very efficient and safe means of transportation. The number of leaks could be reduced since the early ’70s of the last century due to improved design and maintenance procedures as well as improved materials, but leaks still appear. Most of these are originated by external causes such as digging excavators or slope movements despite intensive pipeline right of way surveillance by foot, car, and out of the air. These events are a clear sign for a monitoring gap. The technical evolution of fiber optic products allows closing large parts of this monitoring gap.
Pipelines are part of the backbone of modern communities’ lifestyles and are absolutely indispensable for the transportation of water, gas, oil, and all kinds of products. Fiber optic devices are standard equipment for the transmission of voice, video, and other data. Fiber optic systems are frequently installed along pipelines and often used to enable communication between and remote control of the individual station of the system. The same standard optical fibers are suitable to measure several physical effects with high absolute and local accuracy.
Fiber optic products are almost ideal for many types of fiber optic pipeline monitoring applications and several of these applications have been implemented during recent years all over the industry. So here are some examples:
Ground movement detection and Structural health monitoring
Power cable and Transformer monitoring
Status monitoring of water mains
Pig position detection
In other words, many different applications have already been implemented in the industry and constantly ideas for new applications are being created.
Optromix, Inc. is a U.S. manufacturer of innovative fiber optic products for the global market, based in Cambridge, MA. Our team always strives to provide the most technologically advanced fiber optic solutions for our clients. Our main goal is to deliver the best quality fiber optic products to our clients. We produce a wide range of fiber optic devices, including our cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Optromix, Inc. is a top choice among the manufacturers of fiber optic monitoring systems. If you have any questions, please contact us at email@example.com
FBG sensors give the opportunity to measure a variety of parameters in conditions where other sensor technologies fail or simply cannot operate. Such FBG sensors have intrinsic advantages, including resistance to electromagnetic interference, non-electrical conductivity, passive measurements, small size and small weight, and the option of multipoint measurements. the reflection wavelength of the FBG (Bragg wavelength) depends on the grating characteristics (period, modulation) and is influenced by the ambient conditions such as strain and temperature. The development of fiber optic devices based on fiber optic sensors for operation in harsh environments (such as for temperatures of up to 1000°С) is becoming an increasingly important field. In the case of temperature sensing the Bragg wavelength is a function of the temperature. This temperature dependence results from changes in the refractive index of the fiber as well as from thermal expansion of the glass material. Many material properties show strong temperature dependence. Examples of such temperature dependencies are dew point, density, electrical conductivity, refractive index, rigidity, and diffusion. Temperature measurement also plays an important role in the health monitoring of electric circuits or civil structures.
The main advantages of FBG sensors are their measurement of reflected light, wavelength-encoded sensing, and multiplexing capability. Nowadays there are many types of FBG sensors used for measuring temperature: intrinsic and extrinsic.
Three major types exist:
The intensity-modulated sensors
Intensity-modulated FBG sensors are based on the principle of letting a physical disturbance such as temperature cause a change in the received light through an optical fiber;
The phase-modulated sensors
The phase-modulated FBG sensors are based on the principle of comparing the phase of light in the sensing fiber with a reference fiber in an interferometer;
The wavelength modulated sensors
Wavelength modulated FBG sensors are based on the principle that a physical disturbance such as temperature or strain changes the reflected wavelength of the light.
In general, it should be noted, phase modulated and wave modulated FBG sensors are providing much more accurate measurements than intensity-modulated sensors but at the cost of much more expensive interrogators.
Optromix, Inc. is a U.S. manufacturer of innovative fiber optic products for the global market, based in Cambridge, MA. Our team always strives to provide the most technologically advanced fiber optic solutions for our clients. Our main goal is to deliver the best quality fiber optic products to our clients. We produce a wide range of fiber optic devices, including our cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Optromix, Inc. is a top choice among the manufacturers of fiber Bragg grating monitoring systems. If you have any questions, please contact us at firstname.lastname@example.org