Fiber-optic sensor system leads way toward smart composites

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, which 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 fiber 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. Then, together with the attached fiber sensor chain, the system was embedded in the blade of a tidal turbine by Airborne.

The silicon photonic integrated circuit, featuring an Arrayed Waveguide Grating (AWG) acting as a spectrometer, forms the core of the sensor system and allows interrogating the Fiber 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 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 enables lowering the cost of embedded strain sensors substantially.