Resumo em Inglês:

Abstract Electric field module for any isotropic multilayer thin film structure, is presented as analytical deduction. Analytic expressions for the electric field distribution are developed initially for a monolayer isotropic system based on Airy's formulae and boundary conditions, with an incident monochromatic source of light. The transfer matrix method 2×2, is used to deduce the distribution of the forward and backward electric field amplitudes on the inner layers in a general multilayer thin film structure. Analytical results are simulated in Transverse-Magnetic (TM) and Transverse-Electric (TE) modes making evident (when takes place) an electric field enhancement due to surface plasmons resonance. A graphical user interface is created to make steady simulations and create new structures as desired, minimizing time and optimizing resources.

Resumo em Inglês:

Abstract In this article, a circular patch microstrip antenna with a metamaterial resonator for 4G applications is proposed. For the design of the circular antenna patch, an approximate calculation was performed. The circular resonator is inserted into the patch for some antennas, in different positions for a parametric study. When incorporating the resonator, the performance of the antenna is improved and analyzed through some parameters, when compared with the antenna without the resonator. To verify the influence of the resonator and validate its performance, simulated results were performed with the ANSYS HFSS® software and compared with the experimental results, through prototypes, in which they showed a good agreement.

Resumo em Inglês:

Abstract In this paper, we design full-duplex (FD) medium access control (MAC) protocol for co-existing wireless local area networks (WLANs) in 5G cellular networks (WCFD-MAC). Our design considers some significant features of 5G networks, exceptionally, beamforming and FD capabilities at both, the base station and user equipment. FD communications may generate interferences, namely self-interference (SI) in bidirectional FD (BFD) and inter-user interferences in three-node FD (TNFD). Several efforts have been performed to mitigate the SI in BFD communications. However, the inter-user interferences in TNFD are still considered as a major drawback in FD networks. These interferences must be mitigated by an efficient MAC protocol design. WCFD-MAC protocol allows two neighboring users to simultaneously participate in TNFD communication without interfering with each other by using directional transmission and a three-node angle condition (TAC). Directional transmission combined with TAC increases system throughput. WCFD-MAC protocol allows a new half-duplex (HD) communication scheme referred to as three-node HD (TNHD). This scheme may occur when bidirectional FD (BFD) and TNFD communications cannot occur. TNHD scheme includes device-to-device (D2D) communication and allows energy efficiency, which is one of the keys requirements of 5G wireless networks. Simulations results show that WCFD-MAC protocol achieves higher throughput than existing works in the literature.

Resumo em Inglês:

Abstract Distributed sensor networks are becoming more and more widespread due to their substantial benefits to our daily lives. These sensors, in most cases, are distributed in nature and even may require mobility. This, in turn, implies omnidirectional collector units to collect the data from various sensors at arbitrary directions. This work summarizes the performance outcomes of various integrated wide-band antenna structures and solar power generation topologies to achieve equal gain in all directions. Purpose of the array in this instance is contrary to enhance the received signal levels in all directions. Low-cost solutions ranging from the planar helical printed circuit board (PCB) designs to vertical wire helical antennas were investigated. An optimum design structure for multiple ISM bands (868 MHz to 915 MHz) was proposed and characterized considering the cost, size, directional coverage and most significantly RF sensitivity and range of the overall design. The final water-resistant solar-powered wideband transceiver front-end has provided range improvement and omnidirectional radiation pattern. The system consists of a 190mm x 190mm low-cost FR4 substrate and a Wilkinson network to combine the power of 8 helical wire antennas sprinkled along with the solar cells. The self-contained, Sun-powered unit resulted in 4.5-dB sensitivity improvement in measurements.

Resumo em Inglês:

Abstract Maximum spatial eigenfiltering improves the accuracy of maximum likelihood direction-of-arrival estimators for closely-spaced signal sources but may interchangeably attenuate widely-spaced signal sources, producing a severe performance degradation. Although this behavior has been observed experimentally, it still lacks a mathematical explanation. In our previous work, we overcame these limitations using a differential spectrum-based spatial filter but this still caused a small degradation in the DOA estimate. In this paper, we develop a mathematical analysis of how the signal source separation and the Karhunen-Loève expansion affect the passbands of the maximum spatial eigenfilter. The farther the sources, the less significant is the maximum eigenvalue of the spatial correlation matrix and its corresponding eigenvector. Then, the magnitude response of the maximum spatial eigenfilter no longer approximates the spatial power spectrum and is not guaranteed to place multiple passbands around the signal sources. Consequently, we propose a spatial filter built from the eigenvectors of the entire signal subspace. This filter showed an overall runtime smaller than that of our previous work. It also provides a significant reduction in the threshold signal-to-noise ratio for closely-spaced signal sources and does not hamper the estimation for widely-spaced signal sources.

Resumo em Inglês:

Abstract For massive multiple-input multiple-output (m-MIMO) uplink, the performances of the linear minimum mean-square error (MMSE) detector are considered near optimal, and they occupy benchmark place for most linear iterative detectors. However, the MMSE algorithm is known by its load computational complexity due to the implication of large-scale matrix inversions, and in other hand, iterative methods are often preferred in signal detection because of its low complexity. In this paper, we propose a New Damped Jacobi (NDJ) detector in order to improve the performance of the classical Jacobi linear algorithm. Starting from the classical Jacobi technique to our new proposal, we go through the development of two variants; one uses a damping factor and the other uses a stair-matrix. However, the NDJ incorporates a damping factor in its construction and basing also on stair matrix instead of diagonal matrix. The performances in terms of convergence and low complexity of each Jacobi variant studied in this paper are analyzed. Finally, some simulation examples are given to illustrate the advantages of the new proposed algorithm.

Resumo em Inglês:

Abstract In this article, bandwidth enhancement of a microstrip patch antenna using a new kind of metasurface is discussed. This new geometry is used to generate new resonances in antenna and with an optimal position of the metasurface in relation to antenna we can overlap the resonances and obtain a large bandwidth. The proposed antenna showed a bandwidth from 5.1 GHz to 8.0 GHz what can it able to be applied in WiFi 5 and 6. Numerical results were obtained with Ansys HFSS software. A prototype was built and measurements for S11, Smith chart and gain were performed. Numerical and experimental results are in good agreement.

Resumo em Inglês:

Abstract In this paper, a configuration of a passive Q-switched Erbium-doped fiber laser (EDFL) using a Lutetium Oxide (Lu2O3) thin film as a saturable absorber (SA) is experimentally implemented to generate high pulse energy with a high signal to noise ratio. A stable Q-switched pulse train is initiated at the input pump power of 30.442mW, and a maximum pulse energy of 16.11 nJ is obtained at an output power of 0.97 mW, which confirms the stability of the pulses. It was possible to increase the repetition rate of the Q-switched laser from 31.25 to 60.2 kHz as the pump power was raised from 30.442 mW to 71.652 mW. Moreover, the pulse width decreased from 11.4 µs to 4.27 µs and 66.4 dB of the received signal-to-noise ratio at the radio frequency spectrum was achieved.

Resumo em Inglês:

Abstract While the amount of telecommunications services grows rapidly in the whole world, humans get potentially more exposed to Non-Ionizing Radiation (NIR) from a number of different sources. Measurements of NIR levels are relevant in order to compare the results with national and international standards, aiming at the preservation of human health. Thus, it is of great interest to explore a variety of topics regarding this subject. Based on this need, this paper has a number of goals, including monitoring radiation levels in an everyday situation, an investigation of how national and international regulations organs address NIR levels and a demonstration of scientific production trends regarding this topic. The work also presents a bibliometric study about the main scientific productions and trends related to NIR measurements, with focus on the field of Telecommunications. The analysis is based on the databases of Web of Science (WOS) and Scopus, computing publications in the last 10 and 3 years, showing a trend evaluation. Among the main results from this exploratory investigation, there is an exponential growth in the number of publications about NIR, ranging from research in physics to medicine. The way research contribution in different countries is also shown, in order to support the relevance of the topic in defining new tendencies for new investigations. Furthermore, the NIR exposure limits and measurement criteria are presented both in Brazilian and in international norms, demonstrating how different national regulations can be when compared to international guidelines. Another contribution is a case study in Natal, Brazil, where NIR levels were monitored in four distinct locations over a period of 24 hours each and compared to the current regulations. The result is a quantitative analysis of the amount of radiation that some populations might be exposed to in distinct moments of the day. Measurements were carried out in the proximity of an antenna spot, since it could represent a source of high NIR levels (a worst case of human exposure). This campaign differs from older studies by including a more intense usage of microwaves frequencies due to operating 4G and pre-5G systems in Brazil. Finally, a statistical study involving the measurements is conducted, concluding the analysis of how some population groups might be affected by NIR.

Resumo em Inglês:

Abstract This article presents an experimental analysis of the use of signals transmitted by Wireless Local Area Networks (WLAN) based on the IEEE 802.11b/g standards for Radio Frequency Energy Harvesting (RFEH) applications in indoor environments employing a Quasi-Yagi Rectenna (QYR) topology. This analysis is a crucial point to distinguish the use of the IEEE 802.11b/g standards for ambient RFEH applications and contributes to the debate on the use of different types of energy available for free in modern society. For it, a dedicated setup, developed in a controlled environment to avoid any external interference, was built to carry out the programmed measurements. The results obtained indicate that IEEE 802.11b/g standards have great potential for applications in RFEH, with the IEEE 802.11b average power four times higher than IEEE 802.11g at the rectifier output.

Resumo em Inglês:

Abstract Recently a surface plasmon resonance (SPR) optical sensor, based on the Otto configuration — the Otto chip — has been developed. One essential step in the quality control of the fabrication process is characterization of the active region of several devices in a batch. Characterization is done by measuring the angular spectrum of the optical re ectance on several points across the active region of the device, and determining parameters by regression analysis of the data. Traditional gradient methods used in the regression process are extremely dependent on an initial guess and are not very efficient for batch analysis of curves, when those include poorly defined SPR spectra, where an initial guess may be hard to infer. An alternative approach for the regression problem is to model the analysis as an optimization problem and using an efficient stochastic algorithm. In this paper one discusses the use of Particle Swarm Optimization (PSO) for characterization of Otto chip devices. From comparative studies carried out in an existing Otto chip, it is observed that PSO can be a very efficient approach for batch analysis and yields better results when compared with the traditional gradient-based regression method.

Resumo em Inglês:

Abstract In this paper, we have designed a low-overhead low-complexity carrier phase tracking scheme for OFDM-based superchannel transmission system enabled by optical frequency combs. In this scheme, taking advantage of the broadband phase coherence provided by optical frequency combs among the OFDM-bands, the carrier phase retrieved from pilot-subcarriers of the OFDM-band on the central wavelength channel is reused for the OFDM-bands on the other wavelength channels. In this case, the overall pilot-subcarrier overhead and DSP complexity is significantly reduced since the pilot-subcarriers occupy a small fraction of the overall OFDM bandwidth. The feasibility of this joint-carrier phase tracking scheme has been verified successfully via comprehensive simulation, where results show that the BER threshold for soft-decision FEC could be achieved for 50GHz-spaced 5-band 4-QAM, 8-QAM, 16-QAM and 32-QAM OFDM-based superchannel signals with zero guard-band and both laser and nonlinear phase noise effects after 7000km, 4000km, 3000km and 2000km SSMF transmission respectively. The simulation results show that there exist chromatic dispersion-induced differential phase offset among the OFDM-bands whose impact on joint-carrier phase tracking depends on the modulation format, channel count and fiber length. Finally, we demonstrate experimentally the feasibility performance of the designed master-slave carrier phase tracking technique for comb-based OFDM-based superchannels.

Resumo em Inglês:

Abstract This paper presents a general methodology based on the description of the inductive channel as virtual magnetic transmission-lines (VMGTLs). In comparison with other existing methods, VMGTL approach presents a better physical insight of the channel behavior since the model correctly preserves the energy flow between the transmitting and receiving coils. Besides that, it facilitates the integration into the analysis of highly nonlinear and dispersive structures such as metamaterial (MTM) lenses. Particularly, the virtual-TL analogy clarifies that the enhancement of the transmission gain between any two coils assisted by MTM is not due to an enhanced coupling between the drivers, as usually claimed, but to the emergence of propagating near-field modes supported by the MTM. This approach, by means of a parametric study, also indicates, for the first time, that MTMs could be employed not only for the increasing of power but also of data transfer due to the emergence of a sub-resonant region of minimum distortion. Nonetheless, since both effects are mutually exclusive, no passive MTM structure could simultaneously improve power and data transmission.

Resumo em Inglês:

Abstract In this paper, it is demonstrated that the efficiency and ability to transfer power to the load in three-coil wireless power transfer (WPT) systems are always higher than in equivalent four-coil ones. On the other hand, it is shown that there are features attainable in four-coil WPT system that are not in three-coil ones. For instance, in a four-coil WPT system, which can be divided into source, two communication, and load circuits, it is possible to devise a method for which the maximum power transferred to the load circuit or the maximum efficiency do not depend on the mutual inductance between the two communication coils, independently of the load resistance value. The necessary conditions to achieve the above feature together with the overall circuit analysis are discussed in details and practical results presented.