Thiago V. N. Coelho

An Optical Fiber Sensor and Its Application in UAVs for Current Measurements

In this paper, we propose and experimentally investigate an optical sensor based on a novel combination of a long-period fiber grating (LPFG) with a permanent magnet to measure electrical current in unmanned aerial vehicles (UAVs). The proposed device uses a neodymium magnet attached to the grating structure, which suffers from an electromagnetic force produced when the current flows in the wire of the UAV engine. Therefore, it causes deformation on the sensor and thus, different shifts occur in the resonant bands of the transmission spectrum of the LPFG. Finally, the results show that it is possible to monitor electrical current throughout the entire operating range of the UAV engine from 0 A to 10 A in an effective and practical way with good linearity, reliability and response time, which are desirable characteristics in electrical current sensing.

Mathematical modelling for correlation between temperature and mechanical strain in long period gratings

Optical fiber sensors based on long period grating (LPG) are effective devices in sensing simultaneously temperature and mechanical strain. It was shown that different shifts in the resonant bands for the transmitted spectrum of an LPG sensor can be correlated with variation in temperature or mechanical strain. This paper presents the effects of non-linearity and cross-sensibility in the LPG resonance condition arising from combined effects of temperature and mechanical strain, proposing an adjustment coefficient in order to compensate these effects in a simple and effective way, reducing uncertainties in simultaneous measurements of temperature and mechanical strain.

A numerical and experimental study of the remote long-period grating fiber sensor with Raman Amplification

In this paper, we analyze numerically and experimentally a remote optical sensor system based on Raman Amplification, composed by one long period grating operating as a sensor head separated by 50 km from the optical source and the interrogation unit composed by two fiber Bragg gratings. Since the active components of the system and the sensor head are separated over such a large distance, it is necessary to consider optical amplification to strengthen the optical signal. The use of Raman amplification allows reaching the desirable gain bandwidth by changing the pump lasers parameters such as the power, number of pumps and spectral position. We present the obtained measurement results of the environmental temperature for two different setups that was analyzed a priori by the numerical model. We show that the power ratio between the two central wavelengths of the FBG has a linear relation with the change of LPG resonance with temperature.

Modulador Digital Educacional em FPGA para uso em Aulas de Laboratório de Telecomunicações

This article presents a generator of digital modulations in FPGA for the teaching and the practice in Telecommunication laboratory. With the increasing demand for technological tools to be used in practical classes, this generator is an alternative to the use of commercial measurement equipments, it presents great flexibility, but at a high cost; and also, to the use of specific laboratory kits, which have a lower cost but have little flexibility. The design, its implementation and tests are showed in this work. Finally, the results are compared to a commercial kit, showing the viability of using this project for laboratory practice.

A novel experimental set-up for turbidity sensing based on plastic optical fibre

Abstract A novel set-up for remote sensing the turbidity of a solution using plastic optical fibres together with a mirror is proposed. The authors have estimated turbidity of a liquid in terms of the nephelometric turbidity unit – NTU, a standard unit that relates the solution appearance with its turbidity for two proposed set-ups. Its performance was also investigated using clay sample measurements over a concentration range of 0–10 g/L. The proposed set-ups are useful for detection of suspended particles in a solution even in small quantities due to its high sensitivity, simplicity and robustness.

Autonomous Quadrotor for accurate positioning

Surveillance missions in vast, difficult access environments are responsible for logistic difficulties in comparison to using an in loco monitoring team. For this and many other reasons, solutions with robotic platforms such as unmanned aerial vehicles (UAVs), present economic advantages.

PMD Emulator based on PZTs attached to pieces of an Hi-Bi fiber

In this paper we demonstrate the development of an adjustable and compact polarization mode dispersion (PMD) emulator device, based on piezoelectric actuators that squeezes a defined pieces of an Hi-Bi fiber. Using this device, the first and second order PMD (SOPMD) can be reproduced in a controlled and compact way, allowing its use as a reliable metrological reference for PMD compensators and for the study of several polarizations phenomena that can represent impairments to the high data transmission networks. This emulator was used to perform an analysis of the correlation between the PMD and SOPMD under different climate chamber temperature.

Considerations about the number of coefficients used in Volterra series models for RF Power Amplifiers

This article discusses further about the number of coefficients used in the many implementations of Volterra series models, performing a fair comparison between them, using measured data and known figures of merit found in the literature. Among the models implemented, a model that uses sub-sampling techniques allied to Volterra series in a parallel cascade structure aiming accuracy outperforms other variations of Volterra series models, with the drawback of using a higher number of coefficients. Based on the many figures of merit results, this article suggests new trends to be used in RF power amplifier behavioral models.

Evolution of Black-Box Models Based on Volterra Series

This paper presents a historical review of the many behavioral models actually used to model radio frequency power amplifiers and a new classification of these behavioral models. It also discusses the evolution of these models, from a single polynomial to multirate Volterra models, presenting equations and estimation methods. New trends in RF power amplifier behavioral modeling are suggested.

A new experimental approach to second-order polarization mode dispersion analysis for optical communications systems

This article analyzes the polarization mode dispersion (PMD) in optical fibers and presents a new approach for its measurement. This approach permits the combined analysis of the first-order PMD and the second-order polarization mode dispersion (SOPMD) in optical systems for different values of temperature. The relation between SOPMD and the differential group delay (DGD) in a single-mode fiber is discussed. The analysis is based on time/wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long-term statistical characteristics of SOPMD acquired by a PMD emulator constructed with some pieces of high birefringence fiber, and the correlation between the SOPMD, depolarization (Depol) and polarization-dependent chromatic dispersion (PCD) was investigated. A new interpretation of SOPMD is presented to analyze the problem of the temperature spectral stability. The actual techniques for SOPMD determination, consequently Depol and PCD, use the variation with time and/or wavelength. In some studies, the results obtained for SOPMD are correlated to first-order PMD. We demonstrate experimentally that the temperature is an important factor for the correlation between SOPMD and PMD and cannot be neglected in the optimization of high-speed optical communications links.