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Chapter 7 – Application of Graphene composites: Raman Strain Sensors 7. APPLICATION OF GRAPHENE COMPOSITES: RAMAN STRAIN SENSORS2 7.1. INTRODUCTION The monolayered nature of graphene makes it of particular promise for sensor applications as every atom is present at both surfaces, increasing its sensitivity to environmental changes. For example, the Hall Effect has been used to detect the absorption of single NO2 and NH3 gas molecules.35 Graphene has also been used as a photo detector.297, 432 Micro-engineered vibrating beam sensors have taken advantage of graphene’s high stiffness and low density to act as mass sensors with detection limits reported of up to 2 zeptograms.296 Graphene has also shown promise as a peizorestivity based strain sensor, with studies based on MC graphene,276, 308 CVD-grown graphene 309, 310, 314, 319, 433 and graphene-composites.316, 317 CVD graphene on PDMS was found to have a GF of 6.1310 whilst MC graphene on PDMS had a GF ~ 2 for applied strains up to 30 %.276 In a recent study, thin films, produced by spray coating of LPE graphene, on a plastic substrate were used to demonstrate strain sensitive coating with a tuneable gauge factor based on the stretching of a percolated graphene network.311 These sensors are analogous to the conventional foil strain gauges (GF 2-5) which give high accuracy single- point measurements.434 In addition to high accuracy, single-point, deformation measurements, there is a need to be able to measure local strain at multiple points over a structure. Whilst this can be achieved with electronically-based sensors, every point of interest needs to be individually wired, leading to a significant amount of infrastructure. Thus it is preferable to measure the strain using optical measurements based upon the photoelastic properties of either the material itself or an active coating upon it. A classic example of such a system is the birefringence measurements made on PMMA and polystyrene (PS) structures. There are already commercially available photoelasticity-based sensors, such as the Grey-field Polariscope from Stress Photonics and PhotoStress® from Vishay 2 Sections of 7.1 and 7.3 of this chapter are based upon a paper of “Wide-Area Strain Sensors based upon Graphene-Polymer Composite Coatings Probed by Raman Spectroscopy” in Adv. Funct. Mater. 2014, 24, 2865-2874. DOI: 10.1002/adfm.201302869. 195PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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