PHOSFOS

PhoSFOS is a research and technology development project co-funded by the European Commission.

Project Description

Figure 1: Flexible skin concept

Figure 2: Photograph of a real flexible skin with embedded sensors made at the University of Gent

The PHOSFOS (Photonic Skins For Optical Sensing) project is developing flexible and stretchable foils or skins that integrate optical sensing elements with optical and electrical devices, such as onboard signal processing and wireless communications, as seen in Figure 1. These flexible skins can be wrapped around, embedded in, and anchored to irregularly shaped or moving objects and allow quasi-distributed sensing of mechanical quantities such as deformation, pressure, stress, and strain. This approach offers advantages over conventional sensing systems, such as increased portability and measurement range.

The sensing technology is based around sensing elements called Fiber Bragg Gratings (FBGs) that are fabricated in standard single core silica fibers, highly birefringent Microstructured fibers (MSF) and Plastic optical fibers (POF). The silica MSFs are designed to exhibit almost zero temperature sensitivity to cope with the traditional temperature cross-sensitivity issues of conventional fiber sensors. These specialty fibers are being modeled, designed, and fabricated within the programme. FBGs implemented in plastic optical fiber are also being studied because plastic fibers can be stretched up to 300% before breaking, permitting use under conditions that would result in catastrophic failure of other types of strain sensors.

Once optimized, the sensors are embedded into a flexible skin and interfaced with peripheral optoelectronics and electronics (see Figure 2).

The photonic skins developed by PHOSFOS have potential application in real-time remote monitoring of behavior and integrity of various structures such as in civil engineering (buildings, dams, bridges, roads, tunnels and mines), in aerospace (aircraft wings, helicopter blades), and in energy production (windmill blades). Applications in healthcare are also being investigated.

There is a movie describing the technology on YouTube.

Key results

Figure 3: Scattering of HeNe laser light from noise gratings recorded in PMMA using a 325 nm HeCd laser

A summary of the key developments can be found on the PhoSFOS EU webpage [1] and include the demonstration of a fully flexible opto-electronic foil.

Figure 3 shows the scattering of HeNe laser light from noise gratings recorded in PMMA using a 325 nm HeCd laser.

One of the early results from the project was in developing a repeatable method for joining polymer fiber to standard silica fiber — a major development that enabled using POF Bragg gratings in applications outside an optics lab. One of the first uses for these sensors was in monitoring strain in tapestries shown in Figure 4,. In this case conventional electrical strain sensors and silica fiber sensors were shown to be strengthening the tapestries in areas where they were fixed. Because polymer fibre devices are much more flexible they did not distort the textiles as much, permitting more accurate measurement of strain.