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- Monitorização para prevenção das úlceras por pressãoPublication . Azevedo, J. A. R.; Santos, C. L. A.; Santos, M. L. V. A.; Jardim, M. H. A. G.A permanência de pessoas em camas e cadeiras por períodos de 2 horas ou mais pode levar ao aparecimento de úlceras por pressão (UPP) nas zonas de contacto das proeminências ósseas. Este problema apresenta-se hoje com elevada magnitude afetando drasticamente a qualidade de vida dos indivíduos e das famílias e consequentemente da sociedade. Custos notáveis ao nível pessoal, familiar, social e económico solicitam respostas efetivas ao nível da sua prevenção. A elevada prevalência de UPP em pessoas com necessidade de cuidados de saúde, quer em hospitais, lares ou domicílios1 na Macaronésia suscitou o interesse de um grupo de investigadores para a sua prevenção. O trabalho aqui apresentado foi desenvolvido pelo projeto de Investigação Científica em Enfermagem2 no âmbito do programa MAC 2007-2013 (ICE2 MAC/1/A029). Trata-se de uma continuidade do estudo sobre sistemas de medição de pressão e de temperatura efetuado na Universidade da Madeira cujo objetivo foi criar um sistema automático de deteção precoce da lesão tecidular2. Ele expressa o esforço interdisciplinar de investigadores da área da engenharia e da enfermagem em prol de uma solução efetiva para apoiar os cuidadores a prevenir as UPP. O artigo começa por abordar a relação que a pressão e a temperatura têm no aparecimento da lesão tecidular, sugerindo-as como indicadores preditivos da mesma. Na segunda parte advoga a monitorização da pressão e da temperatura como mais-valias para uma eficaz prevenção das UPP e apresenta os resultados de um estudo com um sistema de monitorização de pressão e temperatura. Apresenta o protótipo em desenvolvimento, o sistema de monitorização para prevenção das UPP, constituído por matrizes de sensores, circuitos de aquisição de dados, sistema de transmissão sem fios e um software de visualização dos dados. Enfatiza-se como dado inovador o facto de cada matriz de sensores, aplicada numa superfície de contacto, cadeira ou cama, estar associada a um computador e a um nó sensor sem fios, permitindo que a informação relativa a cada superfície seja visualizada local e remotamente, constituindo-se uma ferramenta útil para o despiste precoce da lesão tecidular que origina uma úlcera por pressão.
- Energy harvesting from hydroelectric systems for remote sensorsPublication . Azevedo, Joaquim Amândio Rodrigues; Lopes, JorgeHydroelectric systems are well-known for large scale power generation. However, there are virtually no studies on energy harvesting with these systems to produce tens or hundreds of milliwatts. The goal of this work was to study which design parameters from large-scale systems can be applied to small-scale systems. Two types of hydro turbines were evaluated. The first one was a Pelton turbine which is suitable for high heads and low flow rates. The second one was a propeller turbine used for low heads and high flow rates. Several turbine geometries and nozzle diameters were tested for the Pelton system. For the propeller, a three-bladed turbine was tested for different heads and draft tubes. The mechanical power provided by these turbines was measured to evaluate the range of efficiencies of these systems. A small three-phase generator was developed for coupling with the turbines in order to evaluate the generated electric power. Selected turbines were used to test battery charging with hydroelectric systems and a comparison between several efficiencies of the systems was made. Keywords
- Adapted raised cosine window function for array factor control with dynamic range ratio limitationPublication . Santos, Filipe E. S.; Azevedo, Joaquim A. R.The use of window functions to improve the side lobe level of antenna arrays is hindered by high value of excitation currents dynamic range ratio. This paper proposes a fast and iterative window function generation strategy aimed at achieving improved side lobe level starting from a preset current dynamic range ratio. Based on this strategy a new window function is developed for standard set of conditions.
- Aplicação do processamento de sinal à análise e síntese de agrupamentosPublication . Azevedo, Joaquim Amândio Rodrigues; Casimiro, António Manuel Esteves Santos
- A model to estimate the path loss in areas with foliage of treesPublication . Azevedo, Joaquim A.; Santos, Filipe E.This paper presents an empirical model to predict attenuation in forest environments considering parameters related to vegetation. Typically, environmental parameters are only included in theoretical models, but they are more difficult to apply. The developed model uses tree density, average tree canopy diameter and foliage density as input parameters. The foliage density is very difficult to determine since it depends on the characteristics of trees. A simple metric of this parameter was obtained by measuring the background light silhouetted by the canopy. The model was developed with measurements obtained in different forest environments for two frequencies within the UHF band (Ultra High Frequency). A procedure was also applied to extend the operating frequency range of the model.
- Synthesis of planar arrays with elements in concentric ringsPublication . Azevedo, Joaquim A. R.The circular symmetry of concentric ring arrays becomes an advantage for situations where the radiation patterns are symmetric in the azimuthal direction. For planar arrays with elements in an equispaced grid, the fast Fourier transform can be applied in the calculations involved between the array factor and the source distribution. However, for circular arrays the elements are in a non-equispaced grid, making the application of fast computation algorithms difficult. Therefore, two techniques are proposed to synthesize circular arrays. The first one provides the control of the pattern by sampling the array factor. In this case, the fast Fourier transform can be applied. The windows technique is also utilized to control the sidelobe levels and the ripple structure of the shaped beam. The second technique considers the symmetric nature of concentric circular arrays and the control of the array factor is performed imposing some specific points of the pattern.
- An empirical propagation model for forest environments at tree trunk levelPublication . Azevedo, Joaquim A. R.; Santos, Filipe E. S.The estimation of the received signal strength inside forest environments is very dependent on the vegetation density. However, most published empirical models only provide calculation of the path loss as a function of distance and frequency. The importance of these models is their simplicity. This paper presents a model that was developed from an extensive measurement campaign carried out for different vegetation densities and types of trees. Noting the typical decaying behaviour of signal propagation, the objective was to estimate the main parameters of the log-normal model that fits the measured data. Since in many applications both the transmitter and the receiver are inside the forest, the propagation path is mainly characterized by tree trunks. In this case, it was found that the signal attenuation is dependent on the vegetation density, defined by the product of the tree density and the average diameter of the trunks. In addition to the measurements used to develop the model, other experiments were conducted to test it. The study also included a comparison with other methods in order to evaluate the performance of the model.
- Energy harvesting from wind and water for autonomous wireless sensor nodesPublication . Azevedo, J.A.R.; Santos, F. E. S.It is well-known that wireless sensor networks (WSNs) promise to revolutionise the way the authors can interact with the physical world. However, the deployment of these systems in practical environments is very limited because of power constraints. Systems based on solar, vibrational and thermal energy are the most used in WSN applications and only a few studies consider the wind for energy harvesting. Another important source of energy is the water flow. In the context of the WSN, it was found that there are practically no systems using such source. The purpose of this study is to evaluate the use of small-scale wind and hydro generators for energy harvesting to power wireless sensor nodes. For this purpose, the power coefficients and the output power of several horizontal-axis and Savonius wind turbines were determined. Systems based on Pelton and propeller turbines were constructed to evaluate the effect of some parameters in small-scale power generation.
- Sleeping ZigBee networks at the application layerPublication . Azevedo, Joaquim; Rodrigues, Maurício; Santos, Filipe; Aguiar, LuísZigBee/IEEE 802.15.4 is one of the most used standards for low-power applications. However, full function devices must be always active to route data in a mesh network. The objective of this work is to implement a sleeping technique at the application layer that enables sleep mode for all nodes of a ZigBee network. A time synchronisation mechanism to deal with the clock drift of the sensor nodes was developed. The technique also enables the recovery of lost messages. A large network is organised into smaller groups to reduce latency and packet collisions. The active interval of each node is dynamically adapted to the network operation to optimise the energy consumption. The proposed technique was applied to a real testbed and the increase in energy efficiency was evaluated. The results demonstrated energy savings of about 95% for networks containing up to 20 nodes per group and wake up periods longer than 2 min
- Impact of the antenna directivity on path loss for different propagation environmentsPublication . Azevedo, Joaquim Amândio; Santos, Filipe Edgar; Sousa, Tony Andres; Agrela, Jenny ManuelaLog-normal is a very common propagation model used to estimate the path loss introduced by a given environment. However, in most cases the parameters of the model are antenna specific. In this work, it is shown that the path loss exponent is highly dependent on the antenna pair used in the communication system. Large errors are introduced in the prediction of the path loss if the antennas are different from those used to obtain the parameters of the propagation model. An improved model is developed for the 2.4 GHz industrial, scientific and medical band to estimate the path loss exponent for different antenna directivities knowing the path loss exponent of a reference antenna. The model uses the antenna beamwidth and the antenna gain to obtain a parameter related to the path loss.