Desenvolvimento de técnicas ópticas avançadas de sensoriamento

Abstract

This PhD thesis describes the development and application of two different optical techniques. The first technique aims the at two-dimensional mapping of large surfaces (175 x 175) mm, using a new method for contact angle calculation named Top-Down Method. The contact angles measurements by Top-Down method have been validated and confirmed to be as good as traditional side-based measurements. A range of samples, including industrially relevant materials for roofing and printing, has been analyzed and the results compared to other introduced methods and literature. The surface mapping is performed by analyzing several surfaces such as: silicon wafer coated with silver nanoparticles (Ag) and Aspen paper printed. The potential of forensic and chemical analysis is shown to reveal regions of the surface of the printed paper Aspen black with a laser printer contaminated and non-contaminated by mineral oil. The method promises to be a viable solution for nanoscale characterization and industrial monitoring as well as chemical analyses by allowing rapid contact angle measurements over large areas or large numbers of samples in ways and times that have not been possible before. Besides the possibility of its use in embedded mobile and/or stand-alone electronic devices. The second technique has as objective the elaboration of a distributed optical sensor for acoustic monitoring – DAS. The system uses the φ-OTDR topology and a laser with ~2 kHz bandwidth and coherence length of 48 km. The high coherence of the laser allows the generation of coherent Rayleigh noise (CRN), which contributes to acoustic detection. On this thesis, is developed the processing methodology for the detection of frequencies and disturbances in DAS. The DAS processing methodology is confirmed by tests such as the detection of natural oscillation frequencies in a fixed optical fiber. Field tests are presented detecting the presence of a horse walking on an instrumented equestrian track. Finalizing the tests, is made "optical microphone" where it is possible to reconstruct the speech of the vowels "a e i o u".