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Fibre-optic monitoring system embedded in composite mat'l

Posted: 01 Jul 2014     Print Version  Bookmark and Share

Keywords:Imec  Ghent University  fibre-optic  sensor  composite material 

Imec, Ghent University and their partners in the European FP7 project SMARTFIBER have revealed what they say is the world's first miniaturised fibre-optical sensor system than can be fully embedded in a composite material. According to them, this opens the path for smart composites that enable continued and automatic monitoring of the structural health of the composite material such as in tidal blades, wind turbines, airplanes (fuselage, wings, etc.) or marine structures (masts, antennas, hulls of sail yachts, navy ships, propellers).

The sensor system was assembled by Optocap on an electronic board designed by Xenics. The optical subsystem consists of a silicon photonics integrated circuit developed by Imec and photodiodes and read-out ICs provided by Xenics. Fraunhofer IIS was responsible for the wireless interface. It provides power to the embedded system and at the same time reads out the acquired data at high speed. After connecting the system to an optical fibre sensor chain manufactured by FBGS international, it was casted in an epoxy shape specifically designed by Ghent University to minimise the impact on the composite material. Finally, together with the attached fibre sensor chain it was embedded in the blade of a tidal turbine by Airborne.

The silicon photonic IC, featuring an arrayed waveguide grating (AWG) acting as a spectrometer, forms the core of the sensor system and allows interrogating the Fibre Bragg Grating (FBG) sensors connected to it with high accuracy. The advantages of these FBG sensors compared to other strain monitoring techniques (e.g. electrical strain gauges) are their compactness, light weight, immunity to electromagnetic interferences (EMI), high resistance to corrosion, high temperature operation and multiplexing capability. The FBG sensors, which exhibit a record small diameter and show unprecedented elongation at breakage, were specifically designed to minimally impact the strength of the composite material. Automatic techniques were developed to embed them in the composite. This, together with the use of silicon-based microfabrication processes on a well-established industrial infrastructure, will enable lowering the cost of embedded strain sensors substantially.

Interrogator after embedding in protective epoxy shell

Interrogator (diameter 10cm) after embedding in protective epoxy shell with shape optimised for minimal impact on composite structural strength.

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