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- A more efficient technique to power home monitoring systems using controlled battery chargingPublication . Azevedo, Joaquim Amândio; Santos, Filipe EdgarHome energy monitoring has recently become a very important issue and a means to reduce energy consumption in the residential sector. Sensors and control systems are deployed at various locations in a house and an intelligent system is used to efficiently manage the consumed energy. Low power communication systems are used to provide low power consumption from a smart meter. Several of these systems are battery operated. Other systems use AC/DC adapters to supply power to sensors and communication systems. However, even using low-power technology, such as ZigBee, the power consumption of a router can be high because it must always be powered on. In this work, to evaluate power consumption, a system for monitoring energy usage and indoor air quality was developed. A technique is proposed to efficiently supply power to the components of the system. All sensor nodes are battery operated, and relays are used to control the battery charging process. In addition, an energy harvesting system based on solar energy was developed to power the proposed system.
- Performance evaluation of directional antennas in ZigBee networks under NLOS propagation conditionsPublication . Azevedo, Joaquim Amândio; Santos, FilipeMany authors suggest directional antennas to enhance the transmission performance of ZigBee networks. For line-of-sight propagation, directional antennas can extend the transmission range or reduce the transmit power. Directional antennas may also reduce interference between networks operating in the same frequency channel. However, these antennas may not perform similarly under non-line-of-sight propagation conditions. This work presents a study with ZigBee modules comparing the performance of a directional antenna with an omnidirectional one. The measurements were conducted on a university campus for different propagation outdoor environ ments. A deconvolution technique was applied to estimate the received signal as a function of the azimuth angle. The results demonstrated that the received power followed the gain difference between antennas only for paths with low attenuation. Considering the same Effective Isotropic Radiated Power (EIRP), the system with directional antennas started to lose packets at the same distance as the omnidirectional antennas. The directional antenna did not allow the increase in the link range compared to the omnidirectional antenna. The power consumption was also measured for different transmit power levels of the ZigBee radio. The study showed that the control circuits of directional antennas typically consume more power than omnidirectional antennas operating at a higher transmit power level.
- 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.
- Implementation of a hydric energy harvesting system for wireless sensor networksPublication . Santos, Filipe; Azevedo, Joaquim