Fiber Bragg Grating Based Chemical Sensors

Chemical FBGsFiber Bragg grating (FBG) can be used as miniature, inexpensive, and lightweight strain, temperature, and pressure sensors for applications such as real-time health monitoring of aircraft, space vehicles, and smart materials and structures. Nowadays only a few applications of FBGs in chemical sensing have been reported.

The key to a chemical sensor using an FBG lies in the transfer of stress from a swelling material, such as a polymer, to the FBG, resulting in a measurable strain via the shift in resonant Bragg wavelength.

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 cause 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.

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.

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 Optic Sensing: Fiber Bragg Grating Sensor Interrogation Systems

FBG sensors for interrogation systemsFBG sensor interrogator systems can be deployed into a variety of fields. These products feature high reliability, advanced command and data output control, and incredible speed and sensing range.

Fiber Bragg grating (FBG) sensors have been well known and widely used for around 20 years for the following reasons: they are light, compact, easy to install, require very low maintenance, can be used in highly explosive atmospheres, and are immune to electromagnetic interference. Fiber optic sensors have a wide range of possible applications, which include temperature sensing, strain and bending measurements, medium refractive index measurement.

Despite numerous advantages of fiber optic sensors, it is important to install an FBG interrogator to retrieve accurate data and measurements from the sensors. Here is the main principle of how the fiber optic interrogator works: after the light has been sent into the fiber and has been reflected from the FBG, it travels to the interrogator – it’s photodetectors – which then compares it to the wavelength reference artifacts; after that, the interrogator determines the position of the FBG center wavelength. This information is later converted to some measurement units.

There are multiple types of FBG interrogators; each type offers different advantages over others, for example, the number of optical channels and Wavelength range. For example, high-frequency FBG interrogators provide an opportunity to work with dozens of fiber optic sensors at high speed. This characteristic also provides an opportunity to use multiple fiber optic interrogators at once.

The wavelength range of the FBG interrogator plays an important role when it comes to how many wavelengths or bandwidth information from an FBG sensor it can process. Some FBG interrogators have a very limited wavelength range, only around a few nm, however, this is not ideal for most FBG systems. The broad wavelength range of the interrogator provides better measurements.

Another important characteristic of FBG interrogator is the number of optical channels. Each channel represents an optical line, therefore, the bigger the number of optical channels, the more optic lines the interrogator can handle at once. Most interrogators have one optical channel and dedicated to one particular optic line.

Other approaches to FBG sensor interrogating, some of which include:

  1. Broadband source, Dispersive element, Diode Array;

This method is less reliable than the aforementioned ones due to limited resolution, which is a result of the inherent limitations of commercially available diodes.

2.Broadband source, Optical Spectrum Analyzer/Multi-line wavelength meter;

optical spectrum analyzers are large and expensive, which makes them less desirable in a laboratory setting. They are also not able to perform optimally under some temperatures.

3.OTDR/TDM systems;

The system cannot handle a large number of sensors on the fiber as its data acquisition rates scale down with increasing sensor counts.

4.External Cavity Tunable Laser, Power Meter, Wavelength Meter;

External cavity tunable lasers have low speed and do not have a wide operating temperature range. Moreover, they are expensive and do not have the required mechanical robustness.

Optromix interrogators can control up to 8 optical channels. The interrogator operates with the 20 maximum sensors per channel. The device is controlled by the PC with the specialized software for sensors monitoring. The system contains a broadband source of radiation and it can carry out spectrum analysis.

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 devices.

If you have any questions, please contact us at info@optromix.com

 

 

 

 

Optical Pressure Detector for Improving Robot Skin, Wearable Devices, and Touch Screens

FBG sensors for touch screensA new type of fbg pressure sensor based on light could allow the creation of sensitive artificial skins to give robots a better sense of touch. The silicone sheet can be placed on display panels to enable touch screens or can be wrapped on robot surfaces as an artificial skin layer for tactile interactions. In addition to this, such a new sensor could allow the creation of optically transparent touch screens and devices and wearable blood-pressure monitors for humans.

Researchers from the Electronics and Telecommunications Research Institute (Daejeon, South Korea) and Hanyang University (Seoul, South Korea) developed a flexible, transparent fiber optic device that detects pressure by analyzing changes in the amount of light traveling through tiny tunnels embedded in polydimethylsiloxane (PDMS), a common type of silicon. This device is sensitive to even gentle pressure and is less prone to failure compared to previous types of fbg pressure sensors. It also should be feasible to incorporate the embedded optical sensors across a large surface area.

The fiber optic device works by measuring the flow of light through a precisely arranged pair of optical waveguides called a photonic tunnel-junction array. The waveguides run parallel to each other and are embedded in PDMS. PDMS is a very well-known biocompatible, non-toxic material, so the sensor sheet may even be applied on or inside the human body, for example, to monitor blood pressure.

Several steps are needed to move the sensor from a laboratory demonstration to a practical device. In developing the prototype, the research team used precision alignment tools, which would be too expensive and time-consuming to use in most commercial applications. An alternative approach, pigtail fibers, which telecommunications companies use to couple fibers in their systems, should make the process easier.

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

 

 

Strain Measurement with Fiber Bragg Grating Sensors

FBG sensors for strain measurementScientists and engineers can perform through the implementation of optical sensors measurements that were previously impractical or, in some cases, impossible with vibrating wire or foil gases. Many applications will require a hybrid approach using the benefits of both electrical and optical measurements together. Fiber Bragg gratings are often used in strain sensing especially in such places where the environment is harsh (for instance, high-EMI, high-temperature, or highly-corrosive). Strain 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.

Fiber Bragg grating strain sensors have been infrastructure monitoring of smart structures like bridges, dams, pipelines. By monitoring load, strain, temperature, vibration, and even liquid of gas flow, structural integrity can be assessed and tracked on a real-time basis. There various ways in which stress can be measured, but it is widely accepted that FBG sensors are the most efficient way of strain measurement.

There are two types of applications of the fiber Bragg grating strain sensors:

  • Long-term Static Strain Sensing. The main issue in the long-term static strain test is an interest in measuring the long-term static strain of the component in question. In order to carry out the above operation, it is necessary to set up the grating on the structure, find out what the initial wavelength is, and then within a set period of time to detect and record the changes that have occurred. Also, it is possible to return to the structure, reattach, and refer back to the initial wavelength. As a result, it becomes possible to obtain the determination of what this strain is from the initial condition at that time. The ability to disconnect your monitoring instrumentation and return for results after a large amount of time such as months or even years is a very great advantage of fiber Bragg grating sensors. For instance, in the case of bridges, it is common for engineers to visit the bridge and conduct the impact testing using an impact hammer on the different parts of the bridge. This is time-consuming and even hazardous because of the height of some bridge structures. The distribution of a number of FBG sensors throughout the bridge and the attachment of the instrumentation to this bridge on a periodic basis is a much more efficient solution. This is only one of the good examples to demonstrate the effectiveness of the fiber Bragg grating strain sensors. Besides bridges, other examples of using FBG for long-term static strain testing are buildings, piers, and structures in high earthquake-prone areas.
  • Dynamic Strain Sensing. The different structures may have very-low-frequency modes, and they may also have higher modes due to the effects of wind and tide. Most earthquakes and other earth tremors are low-frequency events.  Fiber Bragg gratings can be attached to the structures and monitored for the vibrations during the earth’s tremors and earthquakes. The low-frequency dynamic strain testing can help in determining the reaction of high-rise buildings to the wind. In addition to this, FBG sensors create connections with peers and other shore structures to determine their vibrations during the ebb and flow of tides. Dynamic strain testing can also be performed on transportation vehicles like automobiles, trains, and airplanes. In addition to civil structures and vehicles, there are a number of other applications for dynamic strain testing and vibration stress testing using fiber Bragg gratings. FBG sensors can be attached to industrial machinery to determine the frequency and amplitude of the stress vibrations.  

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 would like to purchase Optromix FBG Strain Sensors, please contact us: info@optromix.com or +1 617 558 98 58