Thin and Flexible Polymer Photonic Sensor Foils for Monitoring Composite Structures

Abstract

Thin and flexible photonic sensor foils are proposed, fabricated, and tested as a promising alternative for monitoring composite structures. Sensor foils are implemented using two different optical polymers and as such optimized for multi‐axial sensing and embedding within composite materials, respectively. It is first shown that those sensor foils allow multi‐axial strain sensing by multiplexing a multitude of Bragg grating sensors in a rosette configuration. Secondly, those sensors can be realized in very thin foils (down to 50 µm) making them suitable for embedding in composite materials during their production. This is proven by visually inspecting and by testing the functionality of the embedded sensors. Finally, owing to their low Young's modulus and flexibility, polymer sensor foils can be bent to small curvature radii and withstand large elongations. Herein, the sensors are bent down to a radius of 11 mm, and elongated by 1.4% without losing functionality.

Comparison of different polymers and printing technologies for realizing flexible optical waveguide Bragg grating strain sensor foils

“…The operating wavelength is set by choosing the grating pitch  for a chosen material and waveguide design with a certain n eff . In this paper, polymer WBG sensor foils operating around 1550 nm [1] and 850 nm [7] are discussed.…”

“…The strain sensitivities were determined employing tensile tests. More details on the sensor characterization methods can be found in [1,7]. Table 4 gives an overview of the realized sensors and their temperature and (axial) strain sensitivity.…”

“…However, fibers are sometimes difficult to handle during the installation, especially when they need to be placed under a specific orientation or when they need to be closely spaced. For this reason, we have previously introduced the concept of using a thin polymeric sensor foil, in which multiple grating sensors can be incorporated, having a well-defined orientation [1]. These sensor foils can be made thin enough so that they can be embedded in materials, such as composites, and are flexible allowing bending them down to small curvature radii and withstanding large elongations.…”

An imprinted polymer-based guided mode resonance grating sensor

“…The grating structures can be realized in polymer materials on a very thin foil, which can be integrated in thin membranes [1]. By applying a strain to the sensor, the GMR grating is stretched out, leading to an increase in the pitch of the sensor and therefore a resonance shift.…”

“…Various sensors based on different resonance structures such as Fabry-Perot etalons, Bragg gratings and micro-ring resonators have already been demonstrated in literature. In [1], a multi-axial strain Bragg grating sensor is described. These sensors are realized in very thin foils to make them suitable for embedding in composite materials.…”