Fiber Bragg grating strain sensors in prototype testing

FBG strain sensors in prototype testingStrain measurement is imperative during prototype design and testing. Strain measurements ensure that materials perform as they should and that the equipment is safe and durable. Measuring strain is crucial for testing complex structures, like aircraft, turbines, etc. There are multiple ways in which stress can be measured; however, it is widely accepted that FBG sensors are the most efficient way of strain measurement. FBG sensors provide multiple advantages over other methods: 1) high sensitivity; 2) small size; 3) ability to be mounted on any surface; 4) immunity to electromagnetic interference; 5) reliability even in harsh environments; 6) low sensitivity to vibration and heat.

FBG strain sensors are used in wing load testing to determine the structure’s performance and possible limitations under the lifting forces during flight. There are several benefits that FBG strain sensors offer to the aerospace field for this type of application. For instance, FBG technology provides strain measurement using a big number of continuous sensors which ensures maximum coverage from a single optical fiber. The immunity to electromagnetic interference, radio frequency interference, and other electrical influences makes FBG strain sensors ideal for use in hazardous environments, such as flight. Moreover, FBG sensors are less cumbersome to install. In addition, the FBG strain sensor prices are expected to decrease by 20% which will open up new opportunities for various markets.

The repeated loading and unloading of material causes fatigue. It is estimated that around 90% of structural failures are a result of fatigue. To determine the breaking point of a structure, fatigue tests are performed. The tests indicate the number of loading cycles until failure. FBG sensors are able to provide real-time data on strain fields and load distributions. The immunity to both low and high temperatures enables the sensors to be monitored during the high-temperature cure phase of composite fabrication. The fatigue life of an FBG strain sensor far surpasses that of other methods of strain measurement.

The tendency to build longer wind turbines with longer blades complicates the maintenance. The design of stronger, lighter materials is necessary, however small imperfections during the manufacturing process can cause failures. FBG strain sensors may provide real-time knowledge of load distributions and turbine blade shape. This data will provide valuable information on the needed adjustments to the blades manufacturing.

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. If you have any question about FBG strain sensors, please contact as info@optromix.com

Fiber optic well monitoring

The well integrity has become a critical concern after recent events in the oil industry, such as oil spills. The interaction of a salt layer with the cement and casting for Pre-salt wells is a concern for fiber optic well monitoring and the structural integrity of the well. The development of continuous monitoring tools for well structural integrity is an ongoing task for the oil industry.

Continuous fiber optic well monitoring has the advantage of allowing the quantification of the time needed for an event. Casting integrity logging operations may provide information regarding the damage location, however, the time in the life of the well when the damage happened or the process of the well degradation can not be determined. The logging operations can only provide information on the condition of the well at a particular time, not continuously. Continuous monitoring can help to correlate well damage and events that could be the cause of the damage, like outside intervention, allowing for corrective and preventive measures to take place.

The two main parameters that need to be measured are strain and temperature. The strain in fiber optic well monitoring can indicate the strain in the casting that is caused by the creep of the salt layer. Distributed temperature sensing may be used to indicate the positioning of the cement slurry, diagnose the curing process, and indicate the cementing failures.

The sensors need to be installed outside the production casing of the production liner. The size of the sensors, therefore, is required to be small. DTS sensors, in particular, are compact and are easy to install onto any surface. However, the mounting process of the sensors needs to be delicate as the casing properties may degrade. Fiber optic well monitoring solutions shouldn’t be intrusive as the sensors could potentially cause issues, like poor isolation.

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 info@optromix.com

Fiber Bragg grating sensors in chemical sensing

Chemical sensing is a developing field of fiber Bragg grating sensors. It is involved in the control of chemical processes, oil recovery, environment quality improvement. There are several factors that play a role in the implementation of chemical sensors – suitability for remote sensing, sensitivity, low costs, selectivity, ability to work consistently in harsh environments. The oil and gas applications require sensors that can withstand high temperatures and pressures, and environmental sensors must have a wide coverage area and limited signal fluctuations.

Fiber Bragg grating sensors have been used in numerous applications, including aircraft monitoring, structural health monitoring, strain, and temperature measurements. In the last decade, FBG sensors have been implemented as chemical sensors due to their ability to withstand high temperatures, immunity to electromagnetic interference, and the absence of electronics.

The main principle of FBG sensors for applications in chemical sensing is based on the axial strain of the fiber. The chemicals that surround the fiber causes it to shift and deform. The strain caused by the presence of a particular chemical causes the spectral pattern of reflected light to change; the shift in reflected wavelength is observed. To monitor the shift in wavelength FBG interrogators are used. The data gathered by the interrogator can then be converted to environmental concentrations.

The key component of fiber Bragg grating sensors for chemical sensing is a highly sensitive coating. The coating should be stiff and adhere easily and firmly to the glass fiber. Most often the coating is based on polymers. However, the coating needs to have a high modulus of elasticity that remains high at high temperatures and during analytes absorption. Most polymers are restricted by temperature due to softening and material relaxation.

Some ways of FBG sensors polymer coating include:

  1. improved coating processing;

The improvement of the coating process, like improved adhesion, may aid in the reduction of material relaxation and shifting. The glass fiber may be treated before the application of polymer coating for improved adhesion.

  1. improved data processing;

The use of two different coatings that respond in equal, but the opposite manner to environmental changes. The combination of the two responses limits the temperature drift.

  1. improved material properties.

Alternative coatings, like ones based on ceramic materials, may expand the temperature application range.

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. Optromix is a fast-growing vendor of fiber Bragg grating (FBG) products line: fiber Bragg grating sensors, FBG interrogators, and multiplexers, Distributed Temperature Sensing (DTS) systems. We create and supply a broad variety of top-notch fiber optic solutions for the monitoring of various facilities all over the world. If you would like to purchase FBG sensors, please contact us at info@optromix.com

Fiber Bragg Grating Sensors in biomedical science

Biomechanical engineering experiences rapid development as a result of FBG sensor application to strain and deformation measurements. The use of fiber Bragg grating sensors in biomedicine is a promising new method of enhancing biomechanical studies.

Fiber Bragg gratings were proposed for use in medical applications at the end of the 20th century. Some of the applications were monitoring ultrasound fields, monitoring the temperature inside nMRI devices, foot pressure monitoring in diabetic patients, etc.

One of the first uses of FBG sensors in biomedicine was an electrically assisted ventilation device triggered by an FBG sensor. A deformable strap was placed on the patient’s chest; the strap had FBG sensors embedded into it that were measuring chest deformations that were caused by air inspiration. A threshold level was set to produce a trigger signal to stimulate the phrenic nerve. Nowadays FBG sensors are used in medical-grade textiles for healthcare monitoring.

Fiber Bragg grating sensors provide several advantages over traditional methods of measuring ligament and tendon deformation and strain, namely an opportunity to record the deformations under several postures. For example, a foot pressure sensing system with embedded FBG was presented; it contains several carefully calibrated FBG sensors in an optical fiber strand. The distribution of transversal pressure and its analysis help to indicate abnormal standing gait in diabetic patients.

The research suggests that FBG sensors are superior to traditionally used strain gauges in soft tissue strain measurement. FBGS easily adhere to a bone or a curved surface; their dimensions are more compatible with bone size than those of the strain gauges; they are easily implantable, highly accurate, and less invasive.

The use of fiber Bragg grating sensors in intervertebral disc pressure measurements is very promising as it is significantly more sensitive than other measuring methods. Moreover, the FBG sensors are more compact which allows them to be inserted through a needle, and to be used for small discs, e.g. cervical or biodegenerated.

Fiber Bragg sensors proved to be useful in a femoral prosthesis. The multiplexing ability of FB sensors allows us to place several sensors on a prosthesis surface and connect them using a single optical link to interrogate all of them. The sensors aid in locating potential failure areas in the prosthesis under normal strain conditions.

Optromix is a fiber Bragg grating sensor vendor; we manufacture innovative fiber optic products for the global market. We are dedicated to delivering the best products and supports to all our customers, our engineers have extensive experience and strong technical expertise in creating fiber Bragg grating products. If you would like to buy FBG strain sensors, please contact us at info@optromix.com.

Types of gas flow measurement

Measurement of gas flow is a key point in the field of gas application. In recent decades, thermal mass flow (TMF) meters are widely used in measuring the mass of gas. The TMF meters have many advantages such as wide applicable fields it can be applied to many kinds of pipelines and different types of gasses), wide measurement range, and high measurement accuracy and repeatability.

Thermal mass flow meters generally use combinations of heated elements and temperature sensors to measure the difference between static and flowing heat transfer to a fluid and infer its flow with a knowledge of the fluid’s specific heat and density. The fluid temperature is also measured and compensated for. If the density and specific heat characteristics of the fluid are constant, the meter can provide a direct mass flow readout, and does not need any additional pressure temperature compensation over their specified range.

Today, thermal mass flowmeters are used to measure the flow of gasses in a growing range of applications, such as chemical reactions or thermal transfer applications that are difficult for other flow metering technologies. This is because thermal mass flow meters monitor variations in one or more of the thermal characteristics (temperature, thermal conductivity, and/or specific heat) of gaseous media to define the mass flow rate.

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Structural Deformations measurement using FBG sensors

Fiber Bragg Grating (FBG) sensors are widely used to measure various physical parameters; such as liquid level, weight, temperature, vibration, etc. They are also used in structural health monitoring systems and environmental conditions.

Structural deformations are one of the most significant factors that affect machine tool (MT) positioning accuracy. These induced errors are complex to be represented by a model, nevertheless, they need to be evaluated and predicted in order to increase the machining performance. The solution is based on the use of a multiplexed optical fiber sensor with a sufficient number of Bragg gratings for strains measuring embedded in the structure. The high sensitivity of the sensors ( 0.2 με ) suggests to employ them in the MT with high stiff structures. FBG sensors are suitable to measure both strains and temperature with very high accuracy and resolution. FBG sensors may offer many advantages since they ensure a dynamic performance up to 260 Hz, permitting the exposure and measurement of distortions acting during the working operations. The determination of the tooltip displacement is a complex process if it is directly extrapolated from the strains. For this reason, it is more convenient to employ FBG as a displacement sensor and to measure the overall integral effect of some critical point-to-point dimensions of the MT geometry.

The conventional approaches are based on models able to predict the MT deformations, studying a relationship between machine accuracy and undesired loads. Nevertheless, it is difficult to identify a general robust relation and these models need to be calibrated for every machine variant limiting their success, increasing costs, and the implementation time. In the first part of the experimental tests, the model was validated by applying a set of static loads. This analysis showed a good match between the real and the predicted position of the MT tool tip point. In the same way, the tests were replicated varying the environmental temperature over time.  Scientists highlight the significant advantages of applying FBG sensors in MT calibration such as their high sensitivity, geometrical versatility, lightweight, immunity to electromagnetic interference or chemical agents, high durability. Nevertheless, it also underlines the limits of this method. In particular, the accuracy of the model depends on the number and the position configuration of the sensors implemented in the structure. The choice of specific statistical methods may improve the accuracy of the model. In light of these results, the next steps of the research will be based on the fabrication of new prototypes changing the position configuration of the FBG sensors.

Fiber optic sensor (FOS) technologies based on situ strain and temperature monitoring for tunnel structures

FBG sensorss for tunnel structuresNowadays, numerous civil infrastructures have been built in metropolitan areas all over the world. The performance of these infrastructures during construction, operation, maintenance, and upgrading is a major concern for society. The use of smart sensing technologies for structural health monitoring has attracted much attention due to their exceptional benefits. These technologies have developed rapidly and some have found widespread applications in civil and geotechnical engineering practices, such as fiber optic sensing (FOS), time-domain reflectometry (TDR) and etc.

Based on fiber optic sensor technology, a quasi-distributed fiber optic sensing array can be established to perform accurate strain and temperature measurements. Besides FBG, another popular FOS technology is the fully distributed Brillouin optical time-domain reflectometry (BOTDR), which enables the measurement of strain and temperature profiles along with single-mode optical fiber.

Compared with electrical strain gauges, fiber Bragg grating (FBG) sensing technology is a relatively novel method for tunnel structural health monitoring, which has a number of advantages including high accuracy, multiplexing, electromagnetic interference resistance, and good repeatability. In order to study the internal force of the tunnel liner and detect the potential safety hazards, series of strain monitoring tests of a tunnel, taking into account the complex stress and strain variation during tunneling, were performed by employing the tandem linear FBG sensor arrays controlled by the wavelength division multiplexing (WDM) technology.

The length of the fiber, as well as the installation position of FBG sensors, depends on the size of the tunnel cross-section. For each test section, two layout methods could be employed: only using an independent fiber for the connection and signal transmission, or using two independent fibers according to the left and right sides of the tunnel cross-section.

 

BG sensors-based in situ monitoring on the internal force of the tunnel structure is of great environmental adaptability and performance stability. However, considering the cross effects of uncertain factors, such as special engineering properties, hydration heat of cement, and shrinkage and creep of concrete, the strain, and temperature collected through FBG sensors is influenced by composite factors. The stress and strain of liner concrete under the independent action of various factors cannot be analyzed accurately by using current ways. Therefore, it is necessary to conduct relevant studies to solve cross effect problems.

Optromix provides industry sensing solutions for Structural Health Monitoring (SHM) for different types of facilities. Optromix Company also offers a wide range of fiber optic temperature sensors for monitoring tunnel structures.  To learn more about SHM please contact us: info@optromix.com or +1 617 558 98 58

 

Fiber Optic Sensing and Cabling Technologies

Fiber optic sensors work well in tight spots and applications with a high degree of electrical noise, but care must be taken when specifying these critical components.

Sensing part presence in machines, in fixtures, and on conveyors is an important component of industrial automation. Error-proofing assembly and controlling sequence based on the presence or absence of a part is often required. Many types of sensors are available, including inductive, magnetic, capacitive, and photoelectric. Each has its own strengths and weaknesses depending on the application.

Photoelectric sensors come with a variety of light-emission types (infrared, visible red, laser Class 1 and 2), sensing technologies (diffuse, background suppression, reflective, through-beam), and housing configurations (photo-eye or fiber optic). Fiber cabling is immune to electrical noise, and the electronics can be mounted away from the noise in a shielded enclosure.

Another very common application is small part assembly. These operations tend to be fully automated, and thus require multiple sensors to confirm part placement (seated) and assembly verification to confirm completion of an operation. Typically, the parts are moving in and out of a stage quickly on carriers or an indexing table. Because travel tolerance is minimal, precise measurement of position becomes essential.

A common issue in fiber optic installations concerns excessive flexing of the fibers. Since the fiber cables are bundles of individual fibers, they typically feel quite pliable, allowing an installer to easily bend the fibers beyond their recommended maximum bend radius. This can cause irrecoverable plastic deformation of the fibers, which will reduce the light transmission or, in the worst case, sever it entirely. The maximum bend radius, listed with all fibers, varies depending on fiber material, bundle size, and fiber dispersion in the bundle—and it must be adhered to in all cases.

Regardless of the application, machine builders must select the proper sensor technology. If fiber-optic sensors are used, amplifiers and fiber-optic heads must be carefully selected for the application to provide robust sensing performance.

Medical fiber optic sensing products and technologies

The range of medical devices incorporating optical fibers has taken a slow technological growth, with the bulk of the industry focused on endoscopy and various methods of optical power delivery for cutting, dissecting, and ablating. These technologies utilize an optical fiber’s mechanism—the ability to guide light from one location to another.

Fiber sensing technologies offer significantly advanced functionality by utilizing their inherent sensitivity to temperature, strain, and pressure. During the last five years, the medical industry has taken significant steps to adapt historic fiber-optic sensing methods to enable them to be used within in vivo environments.

The main area for recent technological developments driving fiber sensors into the medical industry has focused on minimally invasive surgery (MIS). The benefits of MIS are now well-founded, encouraging surgical-tool manufacturers to invest their money in new technology developments to pioneer new MIS procedures or to further improve existing procedures. Three exciting recently developed fiber optic sensing technologies for MIS are focused on here: haptic feedback, 3D shape sensing, and pressure sensing.

By utilizing multiple FBGs or manipulating the FBG structure, it is possible to obtain a spatially distributed strain profile. Such FBGs can be applied along the length of a surgical tool to enable haptic feedback at the regions of most concern. A prime example of this is to add haptic sensing to a grasping tool, where both the grasping and spreading forces can be measured and fed back to the surgeon to indicate how tightly they are grasping or how much force they are applying to pry tissues apart.

Fiber optic 3D shape sensing has been developed by several commercial groups to enable a dramatic reduction in the need for prolonged exposure to the visualization methods, as the optical fiber can track itself in three dimensions and thus if laid within a catheter, can recreate the shape of the catheter. This technique relies on a mixture of FBG and fiber technology, where a very special fiber has been developed specifically for this application. Optical fibers also can be optimized to be sensitive to the hydrostatic pressures experienced within the body. These new applications are being opened up by a mixture of economic desire and technology development. Specialty optical-fiber manufacturers continue to pioneer new fiber designs that medical-device manufacturers can exploit. This enables a greater diversification of medical-device product ranges and opens up new procedures that were not previously possible with minimally invasive surgery.

 

FBG structural health monitoring

FBG has been considered as an excellent sensor element, which is currently receiving more and more research interest. In order to measure strain/temperature variations with high accuracy, the ability to detect small shifts in Bragg wavelength becomes an essential requirement for an FBG sensing system.

With the construction of high buildings and bridges, etc., in recent years, the importance of structural health monitoring technologies to assess building safety is being re-examined. In previous systems using electrical strain sensors, every sensor required power supply, and the installed sensors were easily affected by electromagnetic noise, thunderstorms, etc., causing noise components in the electrical signal measured by remote sensing and presenting a risk of degraded accuracy. Optical fibers have been used as sensors to solve these problems with a focus on optical sensing technology. Since optical sensing technology does not require supplying power to the sensor itself, it offers many advantages including long life spans with excellent corrosion resistance, excellent explosion-proofs, easy remote measurement at distances of more than 10 km with no concerns about electromagnetic noise effects, etc. In addition, the characteristics of optical fibers lend them to linear and sheet designs for extreme environments, making them ideal for disaster monitoring and structural health monitoring systems.

Some of the well-known technologies in optical fiber sensing rely on measuring changes in the frequency of Brillouin backscatter occurring in optical fibers to determine structural deformations and temperature changes. Another method uses a Fiber Bragg Grating (FBG) forming a diffraction grating at the optical fiber core as a sensor to measure changes in the center wavelength of the optical spectrum reflected from the FBG sensor as an index of the amount of strain impressed on the fiber and temperature changes.  Since FBG sensor monitors are used mainly for natural disaster and structural health monitoring they are designed to be convenient for installation, small, and lightweight. Additionally, to be able to measure small strain and temperature changes quickly, they require a high responsivity of better than 1 kHz as well as better measurement accuracy than commercially available FBG sensor monitors and our previously developed model.