Spacecraft structural health monitoring by fiber Bragg grating sensors

FBG sensors for spacecraft monitoringFiber 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. 

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

FBG accelerometers for railway structural health monitoring

FBG accelerometers for railway monitoringNew improved accelerometers based on fiber Bragg grating or FBG technology by fiber optic sensors allow performing railway structural health monitoring in both frequency and acceleration range. Such FBG accelerometers provide such advantage as immunity to electromagnetic interference, herewith, the fiber accelerometer offers multiplexed data information along very long lengths of a railway or pipeline for the in situ single-headend measurements of such parameters as vibration, strain, temperature, and fault locations or other challenges.

Thus, distributed sensors based on fiber optic technology are considered to be a better sensing device for structural health monitoring, compared to other sensing systems. It should be noted that FBG accelerometer systems are able to perform “perimeter security and other applications where events span frequencies <700 Hz and acceleration shock values of <30 G with sensitivities of about 16 pm/G” among various fiber optic sensing systems.

Nevertheless, the application in railway structural health monitoring requires optical fiber sensors that offer a higher level of acceleration peak value and broader frequency ranges. The developed optical fiber accelerometer offers the following parameters: >40 G acceleration values, 8 pm/G sensitivity for frequency values up to 1 kHz and the device is operable up to 2.5 kHz. The developed fiber optic sensor was already tested in a railway application and demonstrated successful results.

Additionally, it is possible to change the optical fiber cross-section to make the stress-induced measurement optimized, depending on the required parameters. For example, this FBG accelerometer has a commercially available length (about 0.35 m), a 15 mm diameter,  50/50 splitter (3 dB coupler), a 56 g stainless-steel mass (25 mm diameter, 15 mm height).

The principle of FBG accelerometer operation is based on the lateral forces cause birefringence changes that directly correlate with force parameters, such as vibration. Therefore, the FBG accelerometer installed on a moving train enables to monitor of the reflection spectrum in real-time to determine various problems with the track of a railway such as cracks, corrugations, or weak points. 

Finally, the developed microstructured optical fiber used in new types of FBG accelerometers increases the level of measurement sensitivity of available systems up to 5X, and it is planned to apply the optical fiber to manufacture additional FBG accelerometers for field tests. Herewith, the FBG accelerometer is regarded as a highly important sensing device in an all-optical fiber sensing network that offers a great amount of data information resulting in efficient structural health monitoring of railways.

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

High resolution distributed temperature sensing

high-resolution DTSThe fiber Bragg grating distributed temperature sensing on gas-insulated line spacer influences surfaces charge accumulation. Nevertheless, it is very difficult to perform the DTS measurement because the traditional electric sensors have huge dimensions, they are difficult to multiplex and highly sensitive to electromagnetic interference.

Thus, a distributed temperature sensing system of the GIL spacer based on the technology of the optical frequency domain reflectometry was designed to solve the challenges. The operation of the DTS system is based on the ultra-weak fiber Bragg grating or FBG technology to change single-mode optical fiber because of its higher signal-noise ratio.

It should be noted that the distributed temperature sensing also used the demodulation technique to compensate for the nonlinear frequency tuning errors caused by the unstable tunable laser. Therefore, the DTS system allows determining the connection between the space temperature and the wavelength shift during the calibration test.

Additionally, the distributed temperature sensing includes the application of the data processing technique for 3D surface temperature on a cone-type spacer. Finally, the DTS system based on FBG technology enables to obtain efficiently high-resolution temperature measurements on the spacer surface with the help of the optical frequency domain reflectometry, which is virtually impossible to perform with the traditional electric temperature sensing systems.

Nowadays the technology of direct current transmission with the gas-insulated line is an effective way due to its low electrical losses compared with, for example, AC transmission. That is why the distributed temperature sensing is considered to be a key factor that should be known first.

To be more precise, the disadvantages of traditional electric sensing systems such as dimensions, multiplexing, and sensitivity to EMI are solved by optical fiber sensing in electrical engineering. Fiber Bragg grating technology is a precise optical temperature sensing technique widely applied. But there are some limits in the multiplexing ability of conventional FBG sensors.

The new distributed temperature sensing system includes ultra-weak fiber Bragg gratings providing a reflectivity of only 0.1% compared to the conventional FBG sensors. Compared to the optical frequency domain reflectometry based on the Rayleigh technology, “ultra-weak FBG can achieve higher signal-noise ratio since the reflection of ultra-weak FBG sensor is much higher than the backscattering in the optical fiber”.

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

Fiber optic solutions for conveyor health monitoring

FBGs for conveyor monitoringA 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.

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

The development of fiber Bragg gratings using highly doped aluminosilicate glass optical fibers

FBGs made of doped fibersThe continuous development of high-temperature fiber Bragg grating technology (FBG technology) promotes a significant increase in novel applications. For instance, nowadays FBG applications include such fields as “the temperature profiling of high-temperature manufacturing equipment, monitoring of fuel combustion machinery, temperature regulation of large diesel engines in trains, as well as assessment the structural integrity of a building post-fire”.

Additionally, high-temperature FBG technology is used in oil and gas industries where the resistance to the temperatures higher than 500 °C is totally recommended. To be more precise, the sensors based on fiber Bragg gratings are able to stand temperature conditions below and above 800 °C. Herewith, the thermal stability of FBG sensors depends closely on the intrinsic thermal stability of the core-cladding materials.

This is the reason why the development of fiber optic technology with higher thermal resistance, for example, the molten core technique, is still required. Thus, it was decided to apply a circular core/cladding glass optical fiber containing a yttrium-doped aluminosilicate core and a silica cladding in FBG sensors that may withstand about 900 °C. 

The following types of FBG sensors are based on the nature of refractive index modifications induced by laser irradiation. The following types of FBGs  are distinguished:

  • The type I in fiber Bragg gratings produces a laser irradiation regime that emits an isotropic increase of the refractive index.
  • The type II in FBGs, in its turn, has a connection with the creation of an anisotropic index change upon irradiation, generally emitted by the presence of nanogratings, and leads to the observation of form birefringence.
  •  Ultra-high temperature regenerated fiber Bragg gratings are able to operate above 800 °C in silica optical fibers. Therefore, these FBGs find their application in such areas as the profiling of high-temperature manufacturing equipment, dual pressure/temperature sensing for gas turbines, sodium-cooled nuclear reactors, high-temperature air flow meters for internal combustion engines and train engine temperature regulation.
  • Femtosecond fiber Bragg gratings are made by ultrafast laser systems usually in the NIR spectral range, resulting in their use as temperature sensors for monitoring fluidized bed combustors, as well as for radiation-resistant temperature sensors.
  • Sapphire fiber Bragg gratings allow achieving even higher temperature operation by using materials with higher melting points.

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