João L. Pinto

Optical Sensors Based on Plastic Fibers

The recent advances of polymer technology allowed the introduction of plastic optical fiber in sensor design. The advantages of optical metrology with plastic optical fiber have attracted the attention of the scientific community, as they allow the development of low-cost or cost competitive systems compared with conventional technologies. In this paper, the current state of the art of plastic optical fiber technology will be reviewed, namely its main characteristics and sensing advantages. Several measurement techniques will be described, with a strong focus on interrogation approaches based on intensity variation in transmission and reflection. The potential applications involving structural health monitoring, medicine, environment and the biological and chemical area are also presented.

Kinetics of conventional carbon coated-Li3V2(PO4)3 and nanocomposite Li3V2(PO4)3/graphene as cathode materials for lithium ion batteries

Recently, improvement on cycling stability and rate performance were reported when the electrode materials were supported by graphene. In this work, we report the approaches for fabricating a nano-structure Li3V2(PO4)3/carbon with conventional carbon-coating and Li3V2(PO4)3/graphene with graphene sheets supporting the composite. The crystal structure and morphology, the lithium diffusion behavior and high rates capacities of pure LVP, composites of LVP with conventional carbon and graphene sheets are studied in detail. The conventional carbon or some LVP particles are separately aggregated without effectively compounding with each other, but there is a more efficient carbon coating by graphene because the LVP nanoparticles are grown on or are enwrapped into a 2D network of graphene layers. Minor graphene contained in the Li3V2(PO4)3/graphene nanocomposite can result in a reduction of crystal size, a large surface area, an increase in conductivity (three orders of magnitude), and great improvement in the rate performance and cycling stability. We proposed an effective carbon coating (ECC) model of microstructure of LVP nanoparticles compounded with carbon or graphene to discuss the key roles of graphene on the great improvement of electrochemical performance. It should offer a new idea in the design and synthesis of battery electrodes based on carbon-coated technology.

Composite structure and properties of Mn3O4/graphene oxide and Mn3O4/graphene

Colloidal Mn3O4 nanocrystals supported by graphene oxide (GO) and reduced graphene oxide (RGO) (Mn3O4/GO and Mn3O4/RGO nanocomposites) have been fabricated through a facile synthetic route with ultrasonic-assisted in ethanol amine (ETA)-water system. It is proposed that in the formation mechanism of these intriguing nanocomposites, investigated by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), ultraviolet-visible absorption spectroscopy (UV-vis), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, the manganese ions are anchored on GO nanosheets (GOs) or enwrapped in curved RGO nanosheets (RGOs), followed by the nucleation and growth of Mn3O4 nanoparticles in ethanol ETA-water system via hydrolysis and oxidation, which in turn results in the exfoliation of GOs or RGOs. Based on the surface properties of GO and RGO, this work firstly explains how the synergetic compositing structure of Mn3O4/GO and Mn3O4/RGO nanocomposites plays a very important role in their properties for electrochemical capacitors (ECs) or lithium ion batteries (LIBs). The opinions we put forward may be readily extended to a strong basis for other classes of hybrids based on GOs or RGOs to make a wise choice between the ECs and LIBs applications.

Superimposed Bragg gratings in high-birefringence fibre optics: three-parameter simultaneous measurements

We used a pair of Bragg gratings written in high birefringence fibre optics to measure, simultaneously, longitudinal and transverse strain and temperature. The Bragg gratings are superimposed in the same position of the fibre optic, so as to behave as a punctual sensor. The sensitivity of the spectral response of the device to longitudinal strain, transverse strain and temperature are all characterized, and the results of its application as a three-parameter sensor are also presented.

Three-parameter optical fiber sensor based on a tilted fiber Bragg grating

A three-parameter optical sensor based on a tilted fiber Bragg grating is proposed. Through the monitoring of the wavelength shift of the core mode resonance and the ghost mode resonance, it is possible to discriminate strain and temperature. In addition, the refractive index can be determined by calculating the normalized transmission spectrum area. With the current approach, resolutions of up to 5.7×10−4, 4 μe, and 3.1 °C were achieved, for refractive index, strain, and temperature, respectively. The developed sensor can be an important tool in several areas of engineering, namely, biomedical, biological, and environmental sensing.

Bragg gratings in normal and reduced diameter high birefringence fibre optics

Fibre optic Bragg gratings (FBGs) written in normal and reduced diameter high birefringence (HiBi) fibres are studied. Chemical etching is used to reduce the diameter of fibres while the optical properties of the FBG spectrum are measured. The results obtained agree qualitatively with the stress enhanced chemical etching. The birefringence of the fibre is determined as a function of the diameter. Optical characterization of the FBG under transverse strain and temperature is also performed. The results obtained show the feasibility of the simultaneous measurement of those parameters with a HiBi FBG sensor.

Application of Bragg Grating Sensors in Dental Biomechanics

This paper describes the use of fibre Bragg grating (FBG) sensors to measure strains at a mandible surface that are caused by static or impact loads on a dental implant. The measuring apparatus uses a fixed optical filter reference scheme and is able to detect dynamic signals with frequency components of up to 10 kHz. A dried implanted cadaveric mandible was used with strain gauges and FBG sensors placed at the outer surface in the direction of the longitudinal axis of the implant. The implants were loaded statically and dynamically and uniaxial strains recorded. The study demonstrates the ability of the FBG as a biomechanical sensor.

Determination of setting expansion of dental materials using fibre optical sensing

The use of fibre Bragg grating sensors to study dental materials like resin-based composite and gypsum products is reported. Two commercially available composite resins and three types of gypsum products were tested in order to determine polymerization contraction and setting expansion. Temperature and strain evolution during the hardening phase of the material were also obtained. The presented technique can be a good tool for dentists in order to better manipulate a material and predict how it will behave in vivo.

Feasibility studies of Bragg probe for noninvasive carotid pulse waveform assessment.

Abstract. The arterial stiffness evaluation is largely reported as an independent predictor of cardiovascular diseases. The central pulse waveform can provide important data about arterial health and has been studied in patients with several pathologies, such as diabetes mellitus, coronary artery disease and hypertension. The implementation and feasibility studies of a fiber Bragg grating probe for noninvasive monitoring of the carotid pulse are described based on fiber Bragg grating technology. Assessment tests were carried out in carotids of different volunteers and it was possible to detect the carotid pulse waveform in all subjects. In one of the subjects, the sensor was also tested in terms of repeatability. Although further tests will be required for clinical investigation, the first studies suggest that the developed sensor can be a valid alternative to electromechanical tonometers.

Large-scale preparation of shape controlled SnO and improved capacitance for supercapacitors: from nanoclusters to square microplates

Here, we first provide a facile ultrasonic-assisted synthesis of SnO using SnCl2 and the organic solvent of ethanolamine (ETA). The moderate alkalinity of ETA and ultrasound play very important roles in the synthesis of SnO. After the hydrolysis of the intermediate of ETA-Sn(II), the as-synthesized SnO nanoclusters undergo assembly, amalgamation, and preferential growth to microplates in hydrothermal treatment. The as-synthesized SnO was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible absorption spectroscopy (UV-vis) and X-ray diffraction (XRD). To explore its potential applications in energy storage, SnO was fabricated into a supercapacitor electrode and characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge measurements. The as-synthesized SnO exhibits remarkable pseudocapacitive activity including high specific capacitance (208.9 F g(-1) at 0.1 A g(-1)), good rate capability (65.8 F g(-1) at 40 A g(-1)), and excellent cycling stability (retention 119.3% after 10,000 cycles) for application in supercapacitors. The capacitive behavior of SnO with various crystal morphologies was observed by fitted EIS using an equivalent circuit. The novel synthetic route for SnO is a convenient and potential way to large-scale production of microplates which is expected to be applicable in the synthesis of other metal oxide nanoparticles.