Over the 45 months (45M) research and innovation action, ADD-ON was divided into two phases: an exploration phase (18M) and a consolidation phase (27 M). During this last period of the ADD-ON project, the following research activities have been developed:
• Low-cost sensors for delamination and damage detection based on waveguides inscribed into a sol-gel matrix were able to be deployed on a large surface.
1. Optimization of the grid structure
2. Preliminary reliability studies
3. Preliminary study on scaling on more complex surfaces
As a general conclusion of WP3/WP6 and the sol-gel sensor work, the ADD ON project allows us to demonstrate the feasibility to design sol-gel waveguide grids on large surface for damage detection as targeted by the proposal. Innovative techniques have been developed to achieve those results and to simplify the architecture of the sensor. Preliminary investigations were done regarding the reliability of those sol-gel based sensors to temperature change and to ensure the scaling of those types of sensors into more complex surfaces such as curved ones and the ones made of materials representative of aircraft (thanks to panel provided by our Topic Manager). These results have been published in international journals through four different articles (2 in MDPI Aerospace, 2 in MDPI Materials).
• Loading measurement chain based on FBG and using an integrated photonics system all-at-chip level adapted to the aircraft avionic needs.
In this activity a technology framework of relevance has been established in order to conceive aerospace compliant solutions for fiber optic sensing, based on integrated photonics technology. The framework encapsulates baselines and conditions towards successful implementation of fiber optic interrogation equipment as well as sensors themselves in the operational aircraft environment. This included:
1. Sensing performance aspects specified through the different damage detection (and data transfer) measurement approaches (resolution, sample speed, discrete or distributed, self-diagnostics, sensor installation)
2. Environmental compliance for shock and vibration, operating temperature ranges, humidity
3. Footprint as in mechanical dimensions, modular architecture, design aspects for mechanical and thermal stability, connectivity and interfacing, power consumption, cost analysis
4. Manufacturing, with regard to supply chain management, (volume) production capability and quality management.
During this last period, a demonstration was carried out on the impact detection capability of a FBG-sensing chain on an aircraft panel using a PIC-based interrogation operating at 20 kHz.
• Investigating the feasibility of self-diagnosis for the OSN.
During the exploration phase, the potential of different fiber sensing techniques, mainly Optical Time Domain Reflectometry (OTDR) and Optical Frequency Domain Reflectometry (OFDR) have been characterized in the WP4 ‘Self-Testing Connections” framework. We showed that these two techniques enable us to evaluate the quality of the connection within the OSN, measuring the associated optical losses and localizing the events, such as bad splices, connections or even bending issues. As the OFDR technique helps achieve better performances, during the last periods, we validate the potential of a commercial OBR to probe the network quality when implemented on the panel provided by the topic manager.
