Miniature fibre optic sensor can be embedded

01 July 2014

Breakthrough paves the way towards smart composites that continually and automatically monitor material’s structural health.

Nanoelectronics research center imec, Ghent University, and partners in the European FP7 project, SMARTFIBER, have demonstrated the world’s first miniaturised fibre-optical sensor system than can be fully embedded in a composite material. This paves the way toward smart composites that enable continued and automatic monitoring of the structural health of the composite material in, for example, tidal blades, wind turbines, airplanes (fuselage, wings) or marine structures (masts, antennae, 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 IC 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 cast 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 the Fibre Bragg Grating (FBG) sensors connected to it to be integrated. Compared to other strain monitoring techniques (e.g. electrical strain gauges)the FBGs are compact, light weight, immune to EMI, resistant to corrosion, operate at high temperatures and have multiplexing capability. They also have a small diameter and show unprecedented elongation at breakage, says the project partners, and 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 the cost of embedded strain sensors to be substantially reduced.

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