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Frequently Asked Questions (FAQ)

Why should I choose fiber optic sensors over electronic sensors?


Fiber optic sensors have a lot of advantages over electronic sensors!

Fiber optic sensors are passive sensors:

  • Intrinsically safe
  • Immune to HV fields
  • No power at sensing location

Fiber optic sensors can withstand harsh environments:

  • Liquids/ moisture
  • Extreme temperatures
  • High robustness

Optical signal:

  • Immune to EM interferences
  • No pre-amps required
  • Remote operation over several km lengths without any lead.

Fiber optic sensors can withstand radiation environments

  • ​ATEX zones
  • Chemicals
  • Radiation hard
  • Electromagnetic Immunity: perfect for microwave environment, immune to radio frequency interference (RFI) and electromagnetic interference (EMI

More advantages:

  • Enable small sensor sizes, do not contaminate their surroundings and are not subject to corrosion.
  • Compact and Light; perfect match for surface mounting and embedding applications. Require small cable sizes and weights.
  • Wide dynamic range: ability to monitor a wide range of physical and chemical parameters and thus permit remote sensing
  • Integrated telemetry: fiber itself is a data link
  • Can be tailored to specific needs
    • Can be coated to modify/protect their surface and behaviour
  • Multiplexing and distribution capabilities of sensors are sole as they offer measurements at a greater number of points along a single optical cable: ideal for minimizing cable deployment and cable weight, or for monitoring extended structures like pipelines, dams etc.




How does a fiber optic sensor work?


An optical fiber is as thin as a human hair, and consists of two basic elements made of glass, the core, and the cladding. The core is the part of the fiber in which light is transmitted.

Fiber optic sensing uses an optical interrogator to send infrared light down the core as white light, in other words all colours of the spectrum.

The light passes through a fiber Bragg grating or FBG. A FBG is a series of optical filters that return a certain wavelength or colour while letting others pass through. The wavelength that is reflected is determined by the reflective index. External factors such as heat and strain will cause a shift in the wavelength of the reflective index, as seen in the picture below.

These variations can be translated to physical engineering units, such as amplitude, temperature, and strain.

Because al FBG sensors are based on measuring within a selected wavelength, it is possible to put multiple FBG sensors on one fiber. This way, one optical cable is enough for over 100 fiber optic sensors!




What is a fiber optic sensor?


A fiber optic sensor is a sensor that works using fiber optic technology. Such a sensor uses optical fiber as a sensing element to measure physical quantities such as temperature, acceleration, tilt, strain, pressure and many more. Fiber optic sensors have many advantages over electronic sensors!




Can fiber optic sensors be used to measure pressure?


Yes, a fiber optic sensor can be used to measure pressure! Check out our pressure sensors on the products page!

Optical fiber measurands:

  • Temperature
  • Pressure
  • Force
  • Vibration
  • Rotation/tilt
  • Strain
  • Hydrogen levels
  • Acceleration
  • Displacement
  • Flow
  • Velocity




Can fiber optic sensors be used to measure strain?


Yes, a fiber optic sensor can be used to measure strain! Check out our strain sensors on the products page!

Optical fiber measurands:

  • Temperature
  • Pressure
  • Force
  • Vibration
  • Rotation/tilt
  • Strain
  • Hydrogen levels
  • Acceleration
  • Displacement
  • Flow
  • Velocity




Can fiber optic sensors be used to measure hydrogen levels?


Yes, a fiber optic sensor can be used to measure hydrogen levels!

Hydrogen is one of the next generation energy sources and shows potential in aerospace applications and the chemical industries. Hydrogen leakage can however be very dangerous due to its low ignition energy and high combustion efficiency. The hydrogen molecules are so small that they can literally diffuse through metals!

This is where Somni is working on a solution! Somni develops fiber optic sensors to detect hydrogen leakages at low concentration (<4%). The sensing mechanism of these FBG based sensors relies on an ingenious interaction between hydrogen and the optical fiber such that hydrogen is detected with light travelling along the optical fiber.

Fiber optic hydrogen sensors have some unique advantages:
- Easy installation of many hydrogen sensors in an array
- No electronics inside the sensor
- Immune to intensity fluctuation caused by optical source fluctuation and/or fiber loss.
And many more!

Check out our hydrogen sensors on the products page!

Optical fiber measurands:

  • Temperature
  • Pressure
  • Force
  • Vibration
  • Rotation/tilt
  • Strain
  • Hydrogen levels
  • Acceleration
  • Displacement
  • Flow
  • Velocity




Can fiber optic sensors be used to measure acceleration?


Yes, a fiber optic sensor can be used to measure acceleration! Check out our acceleration sensors on the products page!

Optical fiber measurands:

  • Temperature
  • Pressure
  • Force
  • Vibration
  • Rotation/tilt
  • Strain
  • Hydrogen levels
  • Acceleration
  • Displacement
  • Flow
  • Velocity




Can fiber optic sensors be used to measure angle/tilt?


Yes, a fiber optic sensor can be used to measure tilt! Check out our tilt sensors on the products page!

Optical fiber measurands:

  • Temperature
  • Pressure
  • Force
  • Vibration
  • Rotation/tilt
  • Strain
  • Hydrogen levels
  • Acceleration
  • Displacement
  • Flow
  • Velocity




Can fiber optic sensors be used in civil engineering structures?


Yes, definitely! Fiber optic sensors can be used for structural health monitoring and condition monitoring of civil engineering structures.

For example, Somni installed low frequency fiber optic accelerometers to monitor the vibrations and movements of the tuned mass damper in the Taipei 101. By monitoring the vibrations, information is extracted to identify changes in the behaviour of the structure which is indicative of a developing fault. But monitoring the vibrations also gives information about the way the structure reacts to wind or for example an earthquake. Therefore, condition monitoring is a major part of predictive maintenance and increases knowledge about the behaviour of the structure.

Somni has also installed fiber optic sensors on the Genoa bridge to monitor the structural health of the structure.

Read more about this on our applications and projects page.




Can fiber optic sensors be used in biomedical instrumentation?


Yes, fiber optic sensors can be used in biomedical instrumentation. Fiber optic sensors have some unique properties that make usage in the biomedical field possible:

  • Small dimensions.
  • Light weight.
  • Non-electrical connection to patients.
  • Ability to monitor multiple measurands.
  • Biocompatibility with MRI and CT.
  • Usage in high EM (Electromagnetic) or RF (Radiofrequency) environments, due to its high immunity to EM interferences.
  • Minimally invasive or non-invasive technique, because of the inherent penetrating properties of light signal.
  • Fast speed since light is used.




What type of interrogator do I need for the fiber optic sensors?


Our fiber optic sensors are compatible with the following interrogators:





How reliable are fiber optic sensors?


Fiber optic sensors should last as long as they are needed, provided that they are installed correctly. so far, fiber cables don’t seem to degrade like other infrastructure. It’s likely that the future of fiber optics will even outlast the next generation of devices and industrial requirements.




What are the main differences between strain gauges and fiber optic sensing?


The working principle of strain gauges is based on the change in electrical resistance of the foil material as a result of mechanical elongation. This principle has been used for a long time, but it has a few limitations in comparison to fiber optic sensing.

Firstly, one strain gauges needs 2/3- conductor wire connected to the DAQ unit or signal conditioner. This makes it very impractical to establish high-density distributed strain gauge systems. Fiber optics however do not have this issue. Fiber optic sensors use optical fibers to measure strain, but the fiber itself is also the data link. This means that to establish a high-density network of strain measurements, less cable is needed, and therefore less weight. These weight savings are substantial when high density-strain measurements are needed for large structures, as for example, building, bridges, or pipes.

A second limitation is that strain gauges require specific installation techniques which can generally only be performed by a professional. Furthermore, to ensure a good connection between the gauges and the wires, excellent soldering is needed. If done incorrectly, the measurements may not be accurate.

Soldering in strain gauges is comparable to splicing in fiber optics. Nevertheless, splicing only has to be done ones for each fiber supporting thousands of strain measurement points.

Lastly, strain gauges are very sensitive to electromagnetic interference (EMI). This means that every electrical device that consumes, generates, or transmits power is likely to cause noise in strain gauge circuits. Fiber optic sensors however, are immune to electromagnetic interference.




Can you place the sensor far away from the interrogator?


Yes, it is possible to place the sensors far away (up to 2 km) from the interrogator. If you want to know more about this, please contact us.




Can you have multiple connection points along a fiber line/How many FBGs sensors can be installed on one fiber?


Yes, it is possible to connect multiple points along one fiber. FBG sensors can be installed in series by using FC/APC patch cords.




Are fiber optic sensors embeddable?


Yes, fiber optic sensors can be embedded in composite materials. Please go to our “embedding sensors in composite materials” page for more information.




Can fiber optic sensors be used to measure temperature?


Yes, a fiber optic sensor can be used to measure temperature! Check out our temperature sensors on the products page!

Optical fiber measurands:

  • Temperature
  • Pressure
  • Force
  • Vibration
  • Rotation/tilt
  • Strain
  • Hydrogen levels
  • Acceleration
  • Displacement
  • Flow
  • Velocity





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