Tag: fiber optic sensors

Fiber optic inclinometer demonstrates the versatility of FBG sensors

FBG inclinometer Fiber optic inclinometer is considered to be one of the most important optical fiber devices used in numerous fields of application. For example, in geophysical engineering, the inclinometer based on the fiber Bragg grating technology (FBG) allows monitoring the angle of inclination at regular intervals along the borehole to profile the land displacement.

Current fiber optic inclinometers utilizing FBG sensors demonstrate a high level of sensitivity and angle of measurement resolution of 0.006°. It should be noted that traditional inclinometers have disadvantages when it comes to their involuntary twist during the process of installation. And optical fiber sensors were widely thought to overcome these limitations due to the absence of moving parts.

Nevertheless, the combination of traditional inclinometers with FBG technology enables us to resolve the challenge and make the fiber optic inclinometers’ operation independent of twisting, therefore, the precision remains constant. Moreover, despite numerous fiber optic techniques that measure temperature, strain, pressure, and other parameters, new fiber optic inclinometer based on a fiber’s taper and a long-period fiber Bragg grating have been recently developed.

The principle of the fiber optic device is based on the use of conventional fiber Mach-Zehnder interferometer that allows dividing the incoming light between two optical fibers and recombining it at a second junction. To be precise, in a Mach-Zehnder system, a long-period fiber Bragg grating dissipates light at its resonant wavelength from the optical fiber core into the cladding, while a second-long period FBG takes light from the cladding back into the fiber core.

The novel fiber optic inclinometer is a simpler device that includes only a single long-period fiber Bragg grating. Moreover, it uses the taper that enables to increase the core field so that part of its light is coupled into the cladding. The fiber optic inclinometer offers the following advantages in its operation:

the immunity to electromagnetic interference;
the high sensitivity;
the compact size;
the multiplexing and remote interrogation abilities.

This optical fiber device based on the interferometer was tested in the measurement of angular displacement. During the experiment, the optical fiber on either side of the taper was sheathed in capillary tubes and then twisted accurately at the taper. Thus, such a bend influences the fringe visibility, but not the location of the fringes.

Optromix is a FBG sensor manufacturer that provides top of the line FBG sensing systems suitable for monitoring of the constructions’ inclination. If you have any questions or would like to buy a FBG product, please contact us at info@optromix.com

FBG pressure sensors for pipeline leakage detection

FBG pressure sensors for leak detection The technology of fiber Bragg grating or FBG is widely used in numerous sensing technology fields of application. For example, today FBG pressure sensors are installed to detect the leakage process of prestressed concrete cylinder pipe. This type of pressure sensor is based on the use of a Bourdon tube with two fiber Bragg gratings attached on its outside and inside surfaces.

Such a wider sensing application is caused by an increasingly large number of attractive characteristics of FBG sensors that include intrinsic safety, immunity to electromagnetic fields, remote sensing, and large multiplexing capabilities. Therefore, the pressure parameter remains the most important physical factor in the process industry.

Nevertheless, conventional pressure sensors based on electrical train gauge, vibration wire, mechanics have several disadvantages that include the absence of the ability to withstand harsh environmental conditions with critical electromagnetic interference, adventurous chemicals, or explosion matters. Moreover, such sensing systems do not allow making pressure’s multipoint measurement and online monitoring at a long distance.

It should be noted that the intrinsic pressure sensitivity of an FBG sensor is considered to be about 3.04 pm/MPa, which is quite a low index for the practical pressure measurement. Despite numerous ways proposed to increase the sensitivity factor of FBG pressure sensors, such as the installation of FBG in polymer, soldering metal-coated FBGs on a free elastic cylinder, and embedding the FBG fiber to a diaphragm, all these techniques propose relatively complex structures which are difficult to produce.

The thing is that the prestressed concrete cylinder pipe is widely used for water transportation in different areas, for example, municipal, industrial, and plant piping systems. Thus, the role of FBG pressure sensors for security monitoring and reliability management of huge cylinder pipes remains very important because now the sensing technology still faces numerous challenges.

Nevertheless, the use of a Bourdon tube in FBG pressure sensors as the spring element allows detecting spring elements. Herewith, the measurement sensitivity increases and becomes 1.414 pm/kPa in a range from 0 to 1 MPa while the correlative coefficient is 99.949%. That is the reason why the development of a totally new pressure sensor is planned, which probably finds new FBG sensing applications of pressure quasi-distributed measurement or online monitoring in industry and manufacture fields.

If you want to obtain a highly efficient sensing system, you should choose the Optromix company. Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber optic solutions for monitoring worldwide. Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line such as fiber Bragg grating sensors, FBG interrogators and multiplexers, distributed acoustic sensing (DAS) systems, distributed temperature sensing (DTS) systems. If you are interested in FBG sensors and want to learn more, please contact us at info@optromix.com

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NASA offers collaboration to companies providing fiber optic solutions

FBGs in fiber optic solutions The members of NASA company have decided to offer collaboration to companies providing fiber optic sensing solutions for monitoring of structures and asset management. The fact is fiber optic sensing technology unifies advanced optical fiber sensors and innovative algorithms that allow making precise and cost-efficient monitoring of numerous crucial parameters in real-time.

The mentioned abilities of fiber sensing solutions play a significant role in structural health monitoring and tank gauging applications. The following parameters are taken into consideration: position or deformation (2D and 3D displacement, twist, and rotation), the level of stiffness (bending, torsion, and vibration), operational loads (bending moments, shear loads, and torques), magnetic fields (different defects in safety-critical structures made from metal materials), and stress/strength parameters such as pressure or fatigue and breakage prediction.

Moreover, fiber optic sensing systems enable to provide not only the structural health monitoring of a tank but optical fiber technology is able to sense the inventory of the tank: for example, the level of the tank’s content, evaporation rate, temperature (that can varies from cryogenic up to 300 degrees Celsius), and stratification (oil vs. water, sediment vs. liquid, and thermal layers).

Fiber optic sensing solutions offer numerous advantages that include:

low cost opening new fields of application across industries;
low power consumption of fiber sensors due to highly efficient algorithms and high-speed processing platform enabling quick data processing and real-time analysis;
fast speed and high level of efficiency;
precise and adaptive fiber optic technology because of the ability of optical fiber sensors to automatically increase resolution where/when needed;
easy installation of fiber device;
high reliability of operation even in humid/liquid environments and harsh temperature conditions.

The numerous abilities of fiber optic sensing systems create a potential solution for a myriad range of monitoring applications. Structural health monitoring and integrity, tang gauging, active control, safety and protection area, non-destructive evaluation, and medical usage refer to potential optical fiber applications.

The principle of fiber sensor operation is based on the use of fiber Bragg grating sensors that are installed in an optical fiber at intervals as small as 0.25 inches (0.64 cm). Finally, such a fiber optic sensing system allows monitoring strain, stresses, structural instabilities, temperature distributions, and numerous other engineering parameters in real-time with a single instrumentation system which weight is less than 10 pounds (4.54 kg). Herewith, the fiber optic solution is able to differentiate between liquid and gas states in a tank or other container, offering precise measurements.

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Absolutely new optical gauge allows cutting well surveillance costs

FBG sensors for optical gauge Fiber optic technology is highly promising now, in spite of the fact that fiber optic solutions found their place in numerous fields of application, the optical fiber sphere still continues developing. Thus, recently a group of researchers from the UK demonstrated a novel optical pressure-temperature gauge of compact size.

The optical gauge is considered to enlarge the fiber optic application, especially when it comes to a well surveillance area. Moreover, this optical device allows cutting all the costs and offering a new alternative to conventional downhole fiber sensors and other electronic logging tools.

Also, it should be mentioned that it is possible to combine the optical gauge with other devices, for example, with a simple deployment mechanism and distributed sensing technology, adding new properties and offering savings of 50-90% compared to traditional logging techniques.

A fiber optic gauge is a special tool that is based on fiber Bragg gratings without using electronics, external connections, or power supply equipment. Herewith, optical gauges provide the following advantages that include:

Immunity to electromagnetic fields;
Potential application in highly explosive environments;
Ability to withstand high vibration loads without any mechanical failure of sensor material;
Reduced number of connection lines and consequently, less impact on test purposes;
Low interconnection is required because of the possibility to include numerous sensors with different fiber Bragg grating wavelengths in one optical fiber.

The novel optical gauge can be installed in the fiber optic line and used in harsh atmospheres. Moreover, this fiber optic device is able to measure up to 10,000 psi (689 bar) and 150°C (302°F), optionally enlarged to 20,000 psi (1,379 bar) and 300°C (572°F).

Herein, the size of the optical gauge is about 10 cu mm, that is why the device can be easily implemented in various optical sensors and even installed in narrow access wells to log data during descent and to capture bottom hole temperature and pressure over time.

Finally, the optical pressure-temperature gauge is able to operate several months without human control, streaming real-time, live well information along with the optical fiber back to the surface. Usually, fiber optic sensors are applied in complex surveillance systems that have a high cost, sometimes they need either batteries or electrical power as well as special equipment compared to the novel optical gauges. Nevertheless, FBG sensors remain number one in the market today due to their lightweight, simple installation and relatively low cost.

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FBG sensors: a comprehensive review

FBG sensors A fiber Bragg grating is an optical interferometer embedded in an optical fiber. At the same time, fiber optics combined with certain substances (usually germanium) can change its refractive factor when the fiber is exposed to ultraviolet light. If such a fiber is illuminated with ultraviolet light with a specific spatial periodic structure, the optical fiber becomes a kind of diffraction grating. In other words, this optical fiber will almost completely reflect the light of a certain, predetermined range of wavelengths, and transmit light of all other wavelengths.

Application of FBG sensors

The FGB application includes the following fields:

Point sensors (that is able to measure deformation, temperature, pressure, tilt, displacement), embedded in composite materials and others;
Laser systems and amplifiers (filters, mirrors);
Telecommunications (dispersion compensation modules, WDM technology);
Research and development.

Difference between electrical and fiber sensors

For decades, electrical sensors (tensor-resistive, string, potentiometric, etc.) have been the main method of measuring physical and mechanical phenomena. Despite their widespread use, electrical sensors have several disadvantages, such as loss during signal transmission, sensibility to electromagnetic interference, the need to organize a spark-resistant electrical circuit (if there is a danger of explosion). These mentioned above limitations make electrical sensors unsuitable or difficult to use for a number of applications.

The use of fiber optic sensors is an excellent solution to these problems. In fiber optic sensors, the signal is light in the optical fiber instead of electricity in the copper wire at traditional electrical sensors.

Over the past twenty years, a huge number of innovations in optoelectronics and in the field of fiber optic telecommunications has led to a significant reduction in prices for optical components and to a significant improvement in their quality. This factor allows fiber optic sensors to move from the category of experimental laboratory tools to the category of widely used devices in various areas.

Operating principle of Bragg gratings

A fiber Bragg grating or FBG acts as a sensitive element of point fiber optic sensors, which is capable to reflect certain wavelengths of light and transmit all others. This effect is achieved by periodically changing the refractive index in the core of the fiber optics.

When the laser light passes through an optical fiber, a part of it is reflected from the fiber grating at a certain wavelength. This peak of reflected light is registered by measuring equipment. As a result of the numerous parameters influence, the interval between the FBG bundles and the refractive index of the fiber optics change.

Consequently, the wavelength of the light reflected from the fiber Bragg grating changes. In addition, it is possible to determine the exact characteristics of the changes by changing the wavelength. In fiber optic sensors based on Bragg gratings, the measured value is converted to a Bragg wavelength offset. The recording system converts the wavelength offset into an electrical signal.

The sensing element of such FBG sensor does not contain electronic components and therefore it is completely passive, which means it can be used in the area of increased explosiveness, aggressiveness, strong electromagnetic interference. Numerous fiber Bragg gratings can be installed on a single fiber, each of which gives a response at its own wavelength. In this case, instead of a point sensor, we get a distributed sensing system with multiplexing along the wavelength.

The use of the light wavelength as an information parameter makes the FBG sensor insensitive to the long-term changes of the parameters of the source and radiation detector, as well as random attenuation of power in the optical fiber.

Common types of FBG sensors

The following types of fiber optic sensors based on FBG technology are used for automated monitoring:

FBG strain sensors;
FBG displacement sensors;
FBG temperature sensors;
FBG pressure sensors;
Fiber optic tilt sensors;
Fiber optic acceleration and vibration sensors;
Data recorders for fiber optic sensors;
Additional equipment for data recorders.

The principle of FGB sensor operation is based on the modulation of one or several properties of a propagating light wave (intensity, phase, polarization, frequency), which change occurs with a change in the measured physical quantity.

The basis of fiber-optic sensing technology is an optical fiber – a thin glass thread that transmits light through its core. The optical fiber consists of three main components: core, shell, and coating. The shell reflects the scattered light back into the core, allowing light to pass through the core with minimal loss.

It can be achieved by a higher refractive index in the core relative to the shell, resulting in a complete internal reflection of light. The outer coating protects the fiber optics from external influences and physical damage. It can consist of several layers depending on the required protection.

Benefits of fiber sensors based on Bragg gratings

The advantages of FBG sensors include:

Wide sensing range;
Possibility to integrate the FBG sensing system into the object structure;
Full fire and explosion safety;
Long-distance signal transmission;
Integration of several fiber optic sensors in one channel;
Insensitiveness to electromagnetic and radio frequency influences;
No need for recalibration (stable over time under constant external conditions).

Bridge, Australia, Bridge At the moment, most of the sensors used in the world are electrical sensors. As it was mentioned above, in optical sensors based on fiber Bragg gratings, the signal is light passing through an optical fiber (instead of an electric current passing through a copper wire). This fundamental difference allows FBG sensors to overcome many problems typical for electrical sensors.

Features of fiber optic sensors

Optical fibers and sensors are non-conductive, electrically passive, and immune to electromagnetic interference. Monitoring with a tunable high-power laser system allows sensing over long distances with virtually no signal loss. In addition, each optical channel is able to monitor a variety of FBG sensors unlike the electrical channel, which significantly reduces the size and complexity of such a sensing system.

Optical sensing systems are ideal for use in conditions where conventional electrical sensors (strain gauge, string, thermistor, etc.) can be difficult to use (long distances, EM fields, explosion safety, etc.). It is easy to switch to fiber optic solutions since the installation and operation of optical sensors are similar to traditional electrical sensors.

Understanding the principles of FBG operation and the benefits of Bragg grating sensor applications can greatly facilitate the solution of various problems in the field of sensing measurement (for example, monitoring of structures).

Nowadays FBG sensors are applied in various fields that require precise and fast measurements. Fiber Bragg sensing systems can be used in aeronautic, automotive, civil engineering structure monitoring, undersea oil exploration, in the mining industry, geotechnical engineering, structural engineering, tunnel construction engineering, etc.

Bragg sensors in medicine

The most promising application of FBG sensors is medicine. Now FBG technology is highly used for fiber-based biomedical sensing including biosensing, safety or security, and structural health monitoring. FBG sensors offer a new and effective way of real-time measurements. They can be applied in laser systems, medical tiny intra-aortic probes, and body sensors for biochemical analysis making.

For example, today fiber Bragg gratings apply optical-fiber sensing probes that are able to dissolve due to such ability as controlled solubility in a physiological environment. Thus, FBG technology enables safer diagnostic of sensitive human organs and there is no need for a surgical extraction. The development of FBG continues, and it is possible that very soon new FBG sensors with improved characteristics appear.

How to choose the right fiber optic product?

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Fiber optic solutions for fire detection and temperature measurement

FBGs for fire detection Proper fire detection in the mining area is the number one priority because fire can evoke damages to valuable assets, downtime in operation, and even loss of lives. Herewith, the installation of fire protection devices can be complicated by harsh environmental conditions of the mining area because industrial equipment produces dirt, dust, humidity, and corrosive atmospheres in the production, storage, or transport of goods. Nevertheless, the application of modern fiber optic sensors based on distributed temperature sensing or DTS is considered to be a proven and efficient technology for fire detection and temperature measurement.

The fact is DTS technology provides precise temperature measurement along the length of a conveyor belt due to the use of autonomous fiber optic cables, therefore, even very long conveyor routes can be efficiently monitored. Thus, cases of fires and overheating during mining operations can be quickly and easily identified and localized to within one-meter precision by distributed temperature sensors, enabling to activate the safety countermeasures. Also, it should be mentioned that it is required the proper installation of the fiber optic sensor cables and adjustment of the alarm zones for heat detection of industrial rollers.

Nowadays mining industry applies fiber optic linear heat detection systems for these purposes, however, the new distributed sensing technology may significantly improve and increase the protection of assets in combination with the one mentioned above. The principle of DTS technology operation is based on the use of optical fibers as a distributed microphone, moreover, it means that fiber optic sensors allow measuring not only the temperature but also the acoustics. Such additional information is important because it helps to determine potential sources of danger and improves the whole purpose of fire prevention. To be precise, the DTS is highly important in hot roller detection that is the main reason for conveyor fires.

Also, it is difficult to identify the initial smoldering stage with traditional techniques, herewith, the majority of common gas detecting systems do not work properly because of high air currents. An optical fiber-based on distributed temperature sensing technology, in its turn, provides numerous benefits during both normal operation and dangerous situation that include:

Reliable fiber optic cable that is resistant to dirt and dust;
Long-distance (up to 10 km) and up to 4 measurement channels monitor several conveyors with one DTS system;
Practically maintenance-free;
Accurate localization of fires and hot rollers;
DTS is able to detect fires in spite of unfavorable environmental conditions.

Optromix is a DTS system manufacturer that provides top of the line distributed temperature sensing systems suitable for monitoring of 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 sensors provide groundwater flow sensing

FBG sensors for flow sensing Groundwater flow sensing is highly important when it comes to the extraction of drinking water because it allows for avoiding well clogging and pollution. Nevertheless, fiber Bragg grating sensors with optical fibers are considered to be a promising new technique for monitoring of groundwater flow.

The fact is that FBG sensors enable us to identify even tiny changes in temperature, pressure, and fiber shape taking into account the sensitivities influenced by the packaging. Thus, fiber Bragg grating sensors are able to create a multiplexed sensor for the groundwater flow direction and magnitude.

It should be mentioned that the fiber-optic technology of FBG sensors has numerous application range, for example, in aerospace (load monitoring and shape sensing), in civil engineering (structural health monitoring), and in the oil and gas industry (temperature and pressure monitoring).

Today the technology of fiber Bragg grating sensing is also used for groundwater flow monitoring. FBG sensors allow measuring various physical properties, strain, or temperature variations such as pressure, vibrations, and curvature of the optical fiber, herewith, fiber sensors make instant and precise measurements.

One more technique that can be used for monitoring is distributed temperature sensing, and the intended application influences directly the choice of technology – fiber Bragg grating or DTS sensing. DTS uses conventional single-mode or multimode fibers that find various applications in the telecom industry, that is why DTS fibers are available in large lengths.

Moreover, the FBG sensors are possible to be written in traditional and specialty fiber optics, and consequently, their price increases per sensor number. However, the cost of fiber interrogators that are required for the DTS sensing data collection is five times more expensive than FBG units.

Traditional fiber Bragg grating sensors already possess a sufficient temperature resolution for the measurement of groundwater temperature changes without additional packaging. In addition, this FBG system has been recently tested to demonstrate its benefits for groundwater flow monitoring.

Thus, the experiment has shown that the use of FBG sensors enables to measure the relative temperature with a precision of 0.85 ℃ for the differential measurements. Also, the used fiber Bragg grating system is able to make a multiple-sensor interrogation with the possibility of an expansion into a larger distributed sensing network.

Finally, the data results presented that fiber Bragg grating sensors can be employed as a temperature sensing system in the subsurface environment, but in this case, they did not demonstrate any benefits over the existing fiber sensing technologies. Nevertheless, multiplexed fiber Bragg grating pressure or strain sensors would possibly find their application in groundwater flow monitoring.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line such as fiber Bragg grating 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 FBG sensors and want to learn more, please contact us at info@optromix.com

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Quasi-distributed fiber optic sensor based on fiber Bragg gratings

Quasi-distributed FBG sensors At the present time distributed optical fiber sensors based on Raman, Brillouin, and Rayleigh scattering play a crucial role in the area of monitoring due to their ability to measure strain or temperature distributions. Nevertheless, weak signals within optical fibers cause numerous challenges, such as limited spatial resolution, low measurement speed, high system complexity, or high cost of the system. That is why new technology that replaces the previous one and is called a quasi-distributed fiber optic sensing based on fiber Bragg gratings is developed now.

The fact is that over the last decades, fiber optic sensors have become one of the fastest-growing and promising areas of modern sensing technologies. Thus, distributed fiber optic sensing has been successfully employed in numerous strain- or temperature-sensing applications because of the multiple benefits of many sensing points and a long sensing range. Nevertheless, weak signals create new difficulties in the monitoring process.

The use of fiber Bragg grating (FBG) sensors is the only solution to the problem because FBG sensors have stronger reflection signals within an optical fiber. As a result, it is possible to use the technology for obtaining numerous physical and chemical parameters from discretized local points of a few millimeters along with a single optical fiber. Moreover, these fiber optic sensors based on fiber Bragg grating can be easily multiplexed for assurance of high measurement speeds.

Unfortunately, at the moment fiber Bragg grating sensors have several drawbacks. The first is the limit of fiber optic sensors for FBG interrogation systems based on multiplexing. Thus, the maximum available number of sensors is considered to be a few tens or less. The second drawback of FBG sensors is the relatively high cost of the writing of periodic grating that is needful for the assurance of high reflectivity at different Bragg wavelengths. This is the reason why fiber optic sensors based on fiber Bragg grating are not suitable for mass production.

Herewith, a novel real-time quasi-distributed fiber optic sensor with weak fiber Bragg gratings allows increasing the number of FBG sensors up to 31 for the successful and efficient process of interrogation. Such a system does not require special maintenance, has a long lifetime because its most components are optical fibers and semiconductor tools that can be easily found in the optical industry.

Finally, this FBG system offers the following advantages that can find numerous applications in the near future:

high linearity;
high speed;
high stability against harsh environmental factors such as vibration, temperature, and humidity.

Optromix is a manufacturer of innovative fiber optic products for the global market. The company provides the most technologically advanced fiber optic solutions for the clients. Optromix produces a wide range of fiber optic devices, including cutting-edge customized fiber optic Bragg grating product line and fiber Bragg grating sensor systems. Moreover, Optromix is a top choice among the manufacturers of fiber Bragg grating monitoring systems. If you have any questions, please contact us at info@optromix.com

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New long-gauge FBG sensor allows detecting corrosion damage

FBG sensors for corrosion detection Nowadays the process of main steel reinforcement corrosion is one of the most frequent problems that evokes structural deterioration and reduces its durability. However, the development of a new kind of long-gauge fiber Bragg grating sensor enables us to detect and quantify corrosion damage via a two-level strategy.

The main advantage of the novel long-gauge FBG sensor compared with the conventional strain sensors is the possibility to use it for both local and global structural monitoring. The principle of FBG technology operation is based on the measurement of the averaged strain within a long gauge length.

It should be noted that the new FBG system is based on the dynamic macro strain responses of FBG sensors. The technology of the strain flexibility detects the location of the corrosion process, and then it quantifies the corrosion by analyzing the sensitivity of strain flexibility.

Moreover, the technology of fiber Bragg grating sensors provides the following benefit that lies in highly accurate and effective corrosion quantification that is possible to be performed in a reduced domain. Herewith, the FBG sensing system has shown great results while testing in the marine environment.

The FBG technology is highly effective in the detection of structural corrosion, but unfortunately, fails to determine the corrosion process unless the apparatus covers the corroded part. Nevertheless, the FBG-based strain sensor remains the most popular due to the use of small, lightweight optical fibers that allow being easily attached to the surface of any steel reinforcement.

The main difference between the new fiber Bragg grating sensors and traditional ones is that civil structures with a large scale and complex shapes very often contain a high quantity of unknown factors that make the process of analysis slower and more complicated. Also, compared to long-gauge FBG sensors, most damage detection techniques are able to detect damage, but can not quantify the severity.

Thus, the distributed long-gauge fiber Bragg grating sensor is a very promising technology for the efficient and precise location of the corrosion damage and further structural long-term performance estimation. Herein, researchers have developed a step-by-step strategy that would help to detect and quantify the process of corrosion, and even proved it by a solid theoretical basis.

Finally, the novel two-level corrosion detection by the FBG sensing system provides a decisive superiority because the corrosion detection significantly reduces the number of unknown factors in the sensitivity equations and increases the success of the corrosion quantification.

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Fiber optic cables for earthquake monitoring

FBG sensors for earthquake monitoring Nowadays researchers from California are planning to use “dark fiber optic cables”, i.e. unused fiber cables, for underground monitoring of sound waves or signals came from earthquakes. It should be noted that today millions of fiber optic cable miles remain unused underground in spite of the fact that they have numerous applications.

Thus, the researchers have developed a new technique of fiber optic underground monitoring that allows higher-resolution measurements of the Earth’s crust movement than the seismic detector networks could offer at the present time. Herewith, in traditional seismology the number of optical sensors for earthquake detection is limited but this technology makes each couple of meters a separate sensor.

Also, today’s problem is the measurement of the Earth’s surface vibrations because, in some seismically active places, there are a lot of fiber optic sensors while the areas that are far from tectonic plates have only a few. That is why it remains difficult to take measurements in places with fracking-induced earthquakes.

The new technique is based on distributed acoustic sensing that includes laser pulses with the aim of vibration detection along with the fiber. Moreover, the researchers use FBG interrogators that are placed along the fibers that transmit and detect short infrared laser signals.

The principle of the interrogator operation includes the detection of tiny strains caused by seismic activity on the fiber, then they force the laser light to reflect and bounce back to the fiber sensor. Thus, the researchers are able to determine light changes scattering over time by analyzing the rapid pulses, and this information shows where the seismic activity occurred.

The technology of distributed acoustic sensing was tested in real-world conditions and enable to extract information about the speed of waves traveling through the Earth’s surface. Moreover, the researchers succeeded in the earthquake measurement that happened in Mexico due to the distributed acoustic method and used fiber optic cables.

The potential application of DAS technology is the determination of groundwater location, nevertheless, the tests were not successful although the researchers could measure passing trucks and trains. Unfortunately, this experimental method is not ready for application beyond research yet because there are a lot of limitations. For example, now a single sensing location along the line is less sensitive than a single seismometer and is able to measure the fiber strain only in one direction. The second problem of fiber optic cables is a huge amount of data that are difficult to manage, store, and organize. Herewith, the new DAS technique cannot be used yet on underwater lines.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line such as fiber Bragg grating 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 acoustic measurement systems and want to learn more, please contact us at info@optromix.com

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