FAOS

Flexible Artificial Optical Skin

The project contains 5 workpackages: 2 technology development workpackages, 1 workpackage for demonstrator development and 2 supporting workpackages dealing with valorisation and project management. The technical solutions that are being pursued are built on the existing experience with the 4 contributing partners.

Two complementary strategies will be developed within this proposed FAOS project :

1. The change of the reflection peak wavelength of the embedded silica fiber Bragg grating sensors (Distributed Fiber Sensors),

2. The change in coupling and scattering between polymer waveguides (Arrayed cross-waveguide couplers).

For the work on distributed fiber Bragg grating sensors, we will develop specialty microstructured Photonic Crystal Fibers (PCF) in such way that the fiber Bragg grating is sensing with a large mechanical sensitivity while exhibiting very low sensitivity to any temperature drifts. Traditional optical fiber sensors are not able to make such a distinction between stress and temperatures and require complex temperature compensation mechanisms. Within the FAOS project, these specialty fibers will be modelled, designed and fabricated. We will furthermore investigate how these fiber sensors can be embedded into a flexible sensing skin consisting of compliant polymer materials. At least flexible substrates are necessary, ideally the carrier substrate should also be elastic (stretchable) to some extent in order to follow all possible movements and deformations of the machine or body part onto which it is mounted. In practice, systems will have a mixture of substrate materials ranging from (small) rigid parts, over flexible parts and stretchable interconnection parts, all linked together in one system. Moreover, the necessary optics, electronics and packaging will be developed to allow for a compact read out of the measured signals. These fiber-based sensitive skins are well suited for large area applications, with a relatively low density of sensing points.

The second sensing principle will rely on the changing in coupling characteristics between low-cost polymer waveguides that are embedded in the photonic sensor skin. Optical waveguides can already be integrated into printed circuit boards but to integrate also active, sensing devices into flexible substrates will be a major challenge of the FAOS-project. These integrated waveguide-based sensing devices can be made more compact, will be easier to replicate in large numbers, but will not match the sensitivity and selectiveness of the PCF fibers. These waveguide-based sensitive skins will be better suited for smaller areas with a higher density of sensing points. Regarding the integration of the optoelectronic components and electronic circuitry, the route being followed in the FAOS-project is based on the expertise available on embedding electronic components into printed circuit boards. The new challenge faced in FAOS is the use of this technology also for optoelectronic components in which case alignment issues with the integrated sensing devices and waveguides is much more critical. Embedding these light sources into the flexible substrates and foils is required without jeopardizing the optical performances and coupling efficiency. New technology for the electrical interconnection between the different devices is required and the proposed route is making use of new fabrication tools such as laser-ablation to fabricate the micro-vias and advanced galvanic plating techniques for the electrical interconnections. Also reliable manufacturing technology (assembly, alignment, etc…) for this new type of flexible substrates has to be investigated.

The FAOS project will feed this new technology into 2 final demonstrators which will illustrate the potential of the technology. The embedded distributed optical sensor is a flexible surface in which optical sensors are integrated and can measure a specific parameter e.g. pressure. By integrating the distributed sensors in such a flexible foil, pressure and pressure variations can be measured over a whole surface. The application aimed at is robotics where such a sensitive skin can be applied on boots of robots to improve the walking behaviour.

The second demonstrator is an optical tactile sensor which has its main application area also in the robotics area, but in areas where high density of sensing points is required, e.g. on the finger-tips of the robots. Parameters such as optical coupling and reflection can be used to measure proximity and contact. A specific workpackage is also dedicated to the valorisation and these demonstrators will be used to advertise the project results.