This paper presents the feasibility assessment for the adoption of a rectenna with basic structure elements as energy source in wireless sensor networks (WSN) nodes. For that matter, a rectenna that harvests energy from 2.45 GHz was designed by the application of a tuning technique on the dimensions of its elements. In the design, the CST Microwave Studio and a SPICE based software were used. The DC-DC boost converter was selected among several commercial options. The limitations of the rectenna were evaluated using the power consumption of different nodes. Results show that the total maximum conversion efficiency for the rectenna was 34.08% at 20 dBm. The distance ranges between the designed rectenna and the wireless energy source were from 0.03 m to 0.20 m in the indoor scenario and from 0.26 m to 2.03 m in the outdoor scenario. The rectenna can supply the required power for the nodes CC2538 and CC1350 in the full range of distances, but for the nodes Z1 and Sky the range of distances is reduced.
This work proposes an objective function to optimize an ultra wideband antenna for adjusting the bandwidth and coupling with other elements, based on the performance comparison of several objective functions from the literature. The optimal dimensions of a printed rectangular monopole antenna were obtained with the Particle Swarm Optimization method to compare such functions. In the results of the comparison, the linear functions had a mean value of S11 magnitude near the threshold, but they presented a smaller standard deviation than the rest of the functions. The logarithmic and cubic functions showed a mean value of S11 magnitude higher than the double of the threshold, but they had superior standard deviation values, which did not happen with the quadratic function. Hence, the proposed function is the mean of a logarithmic expression with the quadratic argument. With this function, a bandwidth adjustment of 130%, a mean S11 magnitude of -22.1 dB and a standard deviation equal to 6.7 dB were obtained on the resonant band for the designed antenna. In this way, the proposed function can be used to avoid interference with other wireless systems and to obtain a uniform coupling of the antenna.
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