This is a repository copy of Lithium-Ion battery state-of-charge estimator based on FBG-based strain sensor and employing machine learning.

A fibre-cavity design based on highly reflective gold coatings, vapour deposited to the two end faces of a large core multimode waveguide, is presented. In contrast to common fibre-cavity approaches, the laser pulses are not coupled through the reflective coatings into the cavity but through a micro hole in one of the fibre end faces, which reduces the commonly very high coupling loss to less than 1%. Accordingly, lower demands on the source power and the sensitivity of the receiver circuit result in lower costs of ring-down sensor approaches. The scope of the paper is on the proof of principle and the characterization of the novel fibre-cavity design. Nevertheless, potential applications are briefly addressed at the end of the paper.

This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link:

Effective strain in composites as well as potential rupture and debonding of composite materials play a crucial role in predicting the strength of retrofitted reinforced concrete (RC) beams.However, only limited experimental data on these phenomena is available, mainly due to the inadequacy of traditional monitoring systems. This paper presents a comparative analysis of different instrumentation for monitoring retrofitted RC elements. In particular, the paper addresses beams retrofitted with composite materials (FRP and FRCM) and considers strain gauges (SG), fibre-optic Bragg grating (FBG) sensors, linear variable differential transformer (LVDT), digital image correlation (DIC) and acoustic emission (AE) sensors for monitoring strain, displacement, cracking and debonding. Experiments on six beams were carried out and the measured data from the monitoring devices was compared. The accuracy of DIC for strain and displacement monitoring, as well as the ability of using AE for detecting cracks and debonding, were shown to match the performance of traditional methods, with the added benefit of providing full-field and depth monitoring. This is of particular interest for compositestrengthened concrete elements in which the accurate measurements of effective strain and debonding of the composite material can lead to developing more precise design formulae.

We demonstrate evanescent-wave fiber cavity-enhanced spectroscopy in the liquid phase using a near-infrared frequency comb. Exploiting strong fiber-dispersion effects, we show that liquid absorption spectra can be recorded without any external dispersive element. The fiber cavity is used both as sensor and spectrometer. The resonance modes are frequency locked to the comb teeth while the cavity photon lifetime is measured over 155 nm, from 1515 nm to 1670 nm, where absorption bands of liquid polyamines are detected as a proof of concept. Our fiber spectrometer lends itself to in situ, real-time chemical analysis in environmental monitoring, biomedical assays, and micro-opto-fluidic systems.