CRAS - Indexed Articles in Journals

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    Accurate detection of spread-spectrum modulated signals in reverberant underwater environments
    ( 2015) Aparicio,J ; Jimenez,A ; Alvarez,FJ ; Urena,J ; De Marziani,C ; de Diego,D ; Nuno Cruz ; Campos,H
    In those positioning systems based on the detection of acoustic signals, an accurate detection of the arrival times is crucial for a correct estimation of the distance between nodes, and therefore, for the precise estimation of the node that wants to be located. In order to obtain this arrival time more accurately, acoustic signals can be coded using pseudorandom noise, but these coded signals are still affected by underwater channel phenomena. In this work, the detection of spread-spectrum modulated signals is analyzed in underwater environments that are highly affected by multipath and reverberation. A spread-spectrum signal, which consist of a modulated Kasami code, has been emitted through two different pools, reaching a receiver where it has been captured after following several line-of-sight and non-line-of-sight paths. Then, a correlation process has been performed offline to provide information about the arrival times (times-of-flight) that form the multipath structure. These times-of-flight are compared with those provided by an underwater acoustic propagation model, in order to test the performance of this model and its capacity to predict the outcome of signal detection in underwater environments with a strong multipath and reverberation component. That way, the validated propagation model could be later used in future studies to predict the detection of spread-spectrum signals and the performance of systems that use them in these adverse environments.
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    Analysis of Phase Interrogated SPR Fiber Optic Sensors With Bimetallic Layers
    ( 2014) Hamed Moayyed ; Leite,IT ; Luís Carlos Coelho ; José Luís Santos ; Diana Viegas
    An effective analytical model combining geometrical optics with the transfer-matrix theory for stratified optical media is applied to investigate the sensing properties of tapered optical fiber surface plasmon resonance (SPR) sensors incorporating Ag-Au bimetallic layers, particularly in the context of phase interrogation. The performance of the sensing structures is studied as a function of the tapering parameters and thickness of the metallic layers. It is shown that the Ag-Au bimetallic combination is capable of improving the resolution and tuning working region of SPR fiber-optic sensors and that by tapering the sensing structures enhanced sensitivity can be achieved when phase interrogation is considered.
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    Aptamer-based fiber sensor for thrombin detection
    ( 2016) Luís Carlos Coelho ; José Almeida ; José Luís Santos ; Pedro Jorge ; Martins,MCL ; Diana Viegas ; Queiros,RB
    The detection of thrombin based on aptamer binding is studied using two different optical fiber-based configurations: long period gratings coated with a thin layer of titanium dioxide and surface plasmon resonance devices in optical fibers coated with a multilayer of gold and titanium dioxide. These structures are functionalized and the performance to detect thrombin in the range 10 to 100 nM is compared in transmission mode. The sensitivity to the surrounding refractive index (RI) of the plasmonic device is higher than 3100 nmRIU(-1) in the RI range 1.335 to 1.355, a factor of 20 greater than the sensitivity of the coated grating. The detection of 10 nM of thrombin was accomplished with a wavelength shift of 3.5 nm and a resolution of 0.54 nM. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
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    Assessment of Robotic Picking Operations Using a 6 Axis Force/Torque Sensor
    ( 2016) Moreira,E ; Luís Freitas Rocha ; Andry Maykol Pinto ; António Paulo Moreira ; Germano Veiga
    This letter presents a novel architecture for evaluating the success of picking operations that are executed by industrial robots. It is formed by a cascade of machine learning algorithms (kNN and SVM) and uses information obtained by a 6 axis force/torque sensor and, if available, information from the built-in sensors of the robotic gripper. Beyond measuring the success or failure of the entire operation, this architecture makes it possible to detect in real-time when an object is slipping during the picking. Therefore, force and torque signatures are collected during the picking movement of the robot, which is decomposed into five different stages that allows to characterize distinct levels of success over time. Several trials were performed using an industrial robot with two different grippers for picking a long and flexible object. The experiments demonstrate the reliability of the proposed approach under different picking scenarios since, it obtained a testing performance (in terms of accuracy) up to 99.5% of successful identification of the result of the picking operations, considering an universe of 400 attempts. © 2016 IEEE.
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    Characterization of zinc oxide coated optical fiber long period gratings with improved refractive index sensing properties
    ( 2016) Luís Carlos Coelho ; Diana Viegas ; José Luís Santos ; José Almeida
    A fiber-optic refractive index (RI) sensor based on a long period fiber grating (LPFG) coated with a zinc oxide (ZnO) thin film was fabricated and characterized. A method to overcoat the LPFG's with a homogeneous ZnO thin films was developed. Characterization of ZnO thin films, deposited simultaneously on silicon (Si) planar substrates, was performed using Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy and X-ray Photoelectron Spectroscopy. The LPFGs with ZnO coatings from 29 to 145 nm of thickness were characterized and compared in terms of the wavelength shift and the intensity of the attenuation bands changing the surrounding refractive index (SRI) from 1.300 to 1.600. An average wavelength sensitivity of similar to 7162 nm/RIU was achieved in the RI range from 1.440 to 1.456 and more than 12,000 nm/RIU at 1.440 RI. Using a ZnO film thickness of 116 nm and in the RI region between 1.320 and 1.360 the average sensitivity of similar to 806 nm/RIU was measured for a 145 nm thick film. Working as an intensity sensing device, the 87 nm coated LPFG shows a linear sensitivity of 216.4 dB/RIU in a wide range of RI from 1.340 to 1.420.
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    Collaborative Learning with Sustainability-driven Projects: A Summary of the EPS@ISEP Programme
    ( 2018) Manuel Santos Silva ; Benedita Malheiro ; Guedes,P ; Duarte,AJ ; Ferreira,P ; 5655 ; 5855
    This paper describes the collaborative learning environment, aligned with the United Nations Millennium Development Goals, provided by the European Project Semester (EPS). EPS is a one semester capstone project programme offered by eighteen European engineering schools as part of their student ex-change programme portfolio. In this international programme, students are organized in teams, grouping individuals from diverse academic backgrounds and nationalities. The teams, after choosing a project proposal, become fully responsible for the conduction of their projects. By default, project proposals refer to open multidisciplinary real problems. The purpose of the project is to expose students to problems of a greater dimension and complexity than those faced throughout the degree programme as well as to put them in con-tact with the so-called real world, in opposition to the academic world. EPS provides an integrated framework for undertaking capstone projects, which is focused on multicultural and multidisciplinary teamwork, communication, problem-solving, creativity, leadership, entrepreneurship, ethical reasoning and global contextual analysis. Specifically, the design and development of sustainable systems for growing food allow students not only to reach the described objectives, but to foster sustainable development practices. As a re-sult, we recommend the adoption of this category of projects within EPS for the benefit of engineering students and of the society as a whole.
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    Coordination of Marine Robots Under Tracking Errors and Communication Constraints
    ( 2016) Bruno Miguel Ferreira ; Aníbal Matos ; Nuno Cruz ; António Paulo Moreira
    This paper presents the development and the experimental validation of a centralized coordination control scheme that is robust to communication constraints and individual tracking errors for a team of possibly heterogeneous marine vehicles. By assuming the existence of a lower level target tracking control layer, a centralized potential-field-based coordination scheme is proposed to drive a team of robots along a path that does not necessarily need to be defined a priori. Furthermore, the formation is allowed to hold its position (the vehicles hold their positions with regard to a static virtual leader), which is particularly appreciated in several marine applications. As it is important to guarantee stability and mission completion in adverse environments with limited communications, the centralized control scheme for coordination is constructed in a way that makes it robust to tracking errors and intermittent communication links. The study and developments presented in this paper are complemented with field experiments in which vehicles have coordinated their operation to keep in formation over a dynamic path and static points. This work considers two types of communication technologies. Firstly, standard high rate radio communications are used to drive the formation and, secondly, acoustic communications are employed to assess the performance and the robustness of the proposed approach to degraded and highly variable conditions. Index Terms-Communication
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    Design, Modeling, and Simulation of a Wing Sail Land Yacht
    ( 2021) Vítor Tinoco ; Benedita Malheiro ; Manuel Santos Silva ; 5855 ; 5655 ; 8387
    Autonomous land yachts can play a major role in the context of environmental monitoring, namely, in open, flat, windy regions, such as iced planes or sandy shorelines. This work addresses the design, modeling, and simulation of a land yacht probe equipped with a rigid free-rotating wing sail and tail flap. The wing was designed with a symmetrical airfoil and dimensions to provide the necessary thrust to displace the vehicle. Specifically, it proposes a novel design and simulation method for free rotating wing sail autonomous land yachts. The simulation relies on the Gazebo simulator together with the Robotic Operating System (ROS) middleware. It uses a modified Gazebo aerodynamics plugin to generate the lift and drag forces and the yawing moment, two newly created plugins, one to act as a wind sensor and the other to set the wing flap angular position, and the 3D model of the land yacht created with Fusion 360. The wing sail aligns automatically to the wind direction and can be set to any given angle of attack, stabilizing after a few seconds. Finally, the obtained polar diagram characterizes the expected sailing performance of the land yacht. The described method can be adopted to evaluate different wing sail configurations, as well as control techniques, for autonomous land yachts.
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    Detection of Extra Virgin Olive Oil Thermal Deterioration Using a Long Period Fibre Grating Sensor Coated with Titanium Dioxide
    ( 2015) Luís Carlos Coelho ; Diana Viegas ; Santos,JL ; José Almeida
    A new sensing system for the detection of thermal deterioration of extra virgin olive oil based on long period fibre grating is reported. It is demonstrated the feasibility of long period fibre grating sensor for the analysis of high refractive index edible oils. The detection principle is the wavelength dependence of the attenuation bands of a TiO2-coated long period fibre grating on the changes in the refractive index of the medium surrounding the cladding surface of the optical fibre. The quality of the sensor was tested by measuring the wavelength shift of the attenuation bands in response to thermal deterioration of an edible oil (extra virgin olive oil) with refractive index higher than the fibre cladding. Absorption spectroscopy has allowed the effects of thermal deterioration to be detected, for example, in the decreasing of the absorption band at 677 nm, attributed to chlorophyll A. A detection limit of about 5 min at 180 A degrees C and of about 2 min at 225 A degrees C was observed for the sensing system. The proposed sensing system could lead to the realisation of a biochemical sensor for the food industry. The change in refractive index of extra virgin olive oil as a function of heating time and temperature was systematically measured for the first time.
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    Developing an aquaponics system to learn sustainability and social compromise skills
    ( 2015) Duarte,AJ ; Benedita Malheiro ; Ribeiro,C ; Manuel Santos Silva ; Ferreira,P ; Guedes,P
    The goal of this project, one of the proposals of the EPS@ISEP Spring 2014, was to develop an Aquaponics System. Over recent years Aquaponics systems have received increased attention since they contribute to reduce the strain on resources within 1st and 3rd world countries. Aquaponics is the combination of Hydroponics and Aquaculture, mimicking a natural environment in order to successfully apply and enhance the understanding of natural cycles within an indoor process. Using this knowledge of natural cycles, it was possible to create a system with capabilities similar to that of a natural environment with the support of electronics, enhancing the overall efficiency of the system. The multinational team involved in the development of this system was composed of five students from five countries and fields of study. This paper describes their solution, including the overall design, the technology involved and the benefits it can bring to the current market. The team was able to design and render the Computer Aided Design (CAD) drawings of the prototype, assemble all components, successfully test the electronics and comply with the budget. Furthermore, the designed solution was supported by a product sustainability study and included a specific marketing plan. Last but not least, the students enrolled in this project obtained new multidisciplinary knowledge and increased their team work and cross-cultural communication skills.
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    Development of an Electrohydraulic Variable Buoyancy System
    ( 2019) Carneiro,JF ; Pinto,JB ; Nuno Cruz ; de Almeida,FG ; 5155
    The growing needs in exploring ocean resources have been pushing the length and complexity of autonomous underwater vehicle (AUV) missions, leading to more stringent energy requirements. A promising approach to reduce the energy consumption of AUVs is to use variable buoyancy systems (VBSs) as a replacement or complement to thruster action, since VBSs only require energy consumption during limited periods of time to control the vehicle's floatation. This paper presents the development of an electrohydraulic VBS to be included in an existing AUV for shallow depths of up to 100 m. The device's preliminary mechanical design is presented, and a mathematical model of the device's power consumption is developed, based on data provided by the manufacturer. Taking a standard mission profile as an example, a comparison between the energy consumed using thrusters and the designed VBS is presented and compared.
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    Engineering Education for Sustainable Development: The European Project Semester Approach
    ( 2020) Benedita Malheiro ; Guedes,P ; Fuentes Dura,P ; Manuel Santos Silva ; Perat,I ; Duarte,AJ ; Arno,E ; Ferreira,P ; 5655 ; 5855
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    Enhanced refractive index sensing characteristics of optical fibre long period grating coated with titanium dioxide thin films
    ( 2014) Luís Carlos Coelho ; Diana Viegas ; José Luís Santos ; José Almeida
    A new type of fibre-optic refractive index sensor based on a long period fibre grating (LPFG) coated with a titanium dioxide (TiO2) thin film was demonstrated. The wavelength shift of the attenuation bands of this LPFG sensor to changes in the refractive index of the external media from 1.30 to 1.64 RIU was investigated. In order to optimize the sensor the TiO2 thin film thickness deposited around the LPFGs was varied from 10 to 80 nm. It was found that the TiO2 thin film increases the wavelength sensitivity of the LPFG to changes in the surrounding refractive index for values lower and higher than the cladding refractive index. As opposed to the bare LPFG it was shown the possibility to monitor refractive indices lower and higher than cladding refractive index tailoring the TiO2 thickness. An average wavelength sensitivity of 5250 nm/RIU was achieved in the range 1.444 to 1.456 RIU for a TiO2 thickness of 50 nm. In the region between 1.46 and 1.48 RIU the average sensitivity of about 825 nm/RIU was measured for a 40 nm thick film.
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    Enhancing dynamic videos for surveillance and robotic applications: The robust bilateral and temporal filter
    ( 2014) Andry Maykol Pinto ; Paulo José Costa ; Miguel Velhote Correia ; António Paulo Moreira
    Over the last few decades, surveillance applications have been an extremely useful tool to prevent dangerous situations and to identify abnormal activities. Although, the majority of surveillance videos are often subjected to different noises that corrupt structured patterns and fine edges. This makes the image processing methods even more difficult, for instance, object detection, motion segmentation, tracking, identification and recognition of humans. This paper proposes a novel filtering technique named robust bilateral and temporal (RBLT), which resorts to a spatial and temporal evolution of sequences to conduct the filtering process while preserving relevant image information. A pixel value is estimated using a robust combination of spatial characteristics of the pixel's neighborhood and its own temporal evolution. Thus, robust statics concepts and temporal correlation between consecutive images are incorporated together which results in a reliable and configurable filter formulation that makes it possible to reconstruct highly dynamic and degraded image sequences. The filtering is evaluated using qualitative judgments and several assessment metrics, for different Gaussian and Salt Pepper noise conditions. Extensive experiments considering videos obtained by stationary and non-stationary cameras prove that the proposed technique achieves a good perceptual quality of filtering sequences corrupted with a strong noise component.
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    Estimation Approach for AUV Navigation Using a Single Acoustic Beacon
    ( 2010) Nuno Cruz ; Bruno Miguel Ferreira ; Aníbal Matos
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    The European Project Semester at ISEP: the challenge of educating global engineers
    ( 2015) Benedita Malheiro ; Manuel Santos Silva ; Ribeiro,MC ; Guedes,P ; Ferreira,P
    Current engineering education challenges require approaches that promote scientific, technical, design and complementary skills while fostering autonomy, innovation and responsibility. The European Project Semester (EPS) at Instituto Superior de Engenharia do Porto (ISEP) (EPS@ISEP) is a one semester project-based learning programme (30 European Credit Transfer Units (ECTU)) for engineering students from diverse scientific backgrounds and nationalities that intends to address these goals. The students, organised in multidisciplinary and multicultural teams, are challenged to solve real multidisciplinary problems during one semester. The EPS package, although on project development (20 ECTU), includes a series of complementary seminars aimed at fostering soft, project-related and engineering transversal skills (10 ECTU). Hence, the students enrolled in this programme improve their transversal skills and learn, together and with the team of supervisors, subjects distinct from their core training. This paper presents the structure, implementation and results of the EPS@ISEP that was created in 2011 to apply the best engineering practices and promote internationalisation and engineering education innovation at ISEP. © 2014 SEFI.
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    Fabrication and Characterization of Metal Oxide-Coated Long-Period Fiber Gratings
    ( 2016) Luís Carlos Coelho ; José Luís Santos ; Diana Viegas ; José Almeida
    Sensors based on long-period fiber gratings (LPFGs) over coated with metal oxide were fabricated and characterized for refractive index (RI) sensing. Oxidation of Ni, Ti, Al, and Cr was monitored in real time by following the features of the LPFG attenuation band. Themetals were deposited simultaneously on top of Si substrates for further chemical and morphological analysis. Wavelength sensitivities (nm/RIU) of about 10 437 at 1.432, 1150 at 1.400, 20 125 at 1.448, and 875 at 1.420 were achieved for LPFGs coated, with 68 nm of Ni, 60 nm of TiO2, 50 nm of Al2O3, and 62 nm of Cr2O3, respectively. For surrounding RI higher than the cladding RI, the wavelength sensitivities are 1937, 6801, 5762, and 3051 nm/RIU at 1.457 for the Ni, Ti, Al, and Cr oxides, respectively. Working as intensity sensing devices sensitivities up to 167 dB/RIU were measured. Metal oxide coated LPFGs leads to wavelength sensitivity enhancement comparing to bare LPFGs and may be used in systems with RI higher than the fiber cladding, a region where bare LPFGs are insensitive.
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    Fiber optic hydrogen sensor based on an etched Bragg grating coated with palladium
    ( 2015) Luís Carlos Coelho ; José Almeida ; José Luís Santos ; Diana Viegas
    A study of a sensor for hydrogen (H-2) detection based on fiber Bragg gratings coated with palladium (Pd) with self-temperature compensation is presented. The cladding around the gratings was reduced down to 50 mu m diameter by a chemical etching process. One of the gratings was left uncoated, and the other was coated with 150 nm of Pd. It was observed that palladium hydride has unstable behavior in environments with high humidity level. A simple solution to overcome this problem based on a Teflon tape is presented. The sensing device studied was able to respond to H-2 concentrations in the range 0%-1% v/v at room temperature and atmospheric pressure, achieving sensitivities larger than 20 pm/% v/v. Considering H-2 concentrations in nitrogen up to 1%, the performance of the sensing head was characterized for different thicknesses of Pd coating ranging from 50 to 200 nm. (C) 2015 Optical Society of America
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    A Flow-based Motion Perception Technique for an Autonomous Robot System
    ( 2014) Andry Maykol Pinto ; António Paulo Moreira ; Miguel Velhote Correia ; Paulo José Costa
    Visual motion perception from a moving observer is the most often encountered case in real life situations. It is a complex and challenging problem, although, it can promote the arising of new applications. This article presents an innovative and autonomous robotic system designed for active surveillance and a dense optical flow technique. Several optical flow techniques have been proposed for motion perception however, most of them are too computationally demanding for autonomous mobile systems. The proposed HybridTree method is able to identify the intrinsic nature of the motion by performing two consecutive operations: expectation and sensing. Descriptive properties of the image are retrieved using a tree-based scheme and during the expectation phase. In the sensing operation, the properties of image regions are used by a hybrid and hierarchical optical flow structure to estimate the flow field. The experiments prove that the proposed method extracts reliable visual motion information in a short period of time and is more suitable for applications that do not have specialized computer devices. Therefore, the HybridTree differs from other techniques since it introduces a new perspective for the motion perception computation: high level information about the image sequence is integrated into the estimation of the optical flow. In addition, it meets most of the robotic or surveillance demands and the resulting flow field is less computationally demanding comparatively to other state-of-the-art methods.