Resumo em Inglês:

Abstract Determining the radiation efficiency of an antenna is a difficult task that becomes challenging when it is about electrically small antennas. This work investigates the applicability of the Wheeler cap method to measure the radiation efficiency of a UHF dual-band compact microstrip patch antenna. An overview of Wheeler method is presented. An adaptation to the original method is suggested to measure the efficiency of a small slitted microstrip patch antenna operating at two frequencies (400 MHz and 431 MHz). A third-order equivalent RLC circuit has been proposed. The measurements were performed using three metal shields of different sizes and shapes. Measured results agreed with the theoretical model. However, the metallic shield significantly interferes in the fringing fields, reducing the accuracy of the method. Despite the inaccuracy observed in the measurements, the method proved to be attractive due to its low cost and ease of measurement. The contribution of this work is to apply the method to an antenna under test with a high degree of miniaturization, low efficiency, and very narrow band, in addition to using a thick substrate. No previous work with this focus has been found in the literature, up to date.

Resumo em Inglês:

Abstract Semi-analytical equations are developed for aiding the process of designing terahertz graphene-based rectangular dipole antennas lying on glass substrates. It directly provides the dipole length required for obtaining resonance at a desired frequency since antenna width and graphene chemical potential are known. By using the finite-difference time-domain (FDTD) method, a large number of computational simulations were performed considering several combinations of antenna dimensions and chemical potential values. The simulation results were used along with graphene electrostatic scaling law combined with the least squares method to optimize the formulation coefficients. With the optimized coefficients, we obtain very satisfying accuracy levels. In the frequency range from 0.5 THz to 3.0 THz, the average relative absolute error is 1.50%, with maximum relative absolute error of 6.77%.

Resumo em Inglês:

Abstract The structural condition of the cable-stayed towers anchorage on power transmission lines requires constant monitoring. Maintenance routines must be able to identify faulty anchor rods and substitute them to avoid tower collapses and power delivery interruptions. Modern statistical diagnostic systems based on machine learning requires the generation of several distinct rod sample signals to be trained, which is a time-consuming process in typical electromagnetic solvers. Aiming to generate samples in a feasible time span, this paper presents a modeling strategy based on the cascade analysis of the transmission line composed by the anchor and the reference rods, interconnected by a dedicated high-frequency connector. Each distinct transmission line part is modeled by a quadrupole as a partial ABCD matrix. The complete response for each experimental setup is obtained from the cascaded-multiplying of the partial matrices. The proposed modeling proved to be accurate and provides a faster way to obtain the S-parameters from distinct faulty rods if compared to the traditional methodologies using electromagnetic tools.

Resumo em Inglês:

Abstract In this paper, a new procedure and topology of magnetic metasurface lens are proposed for improving the performance of Resonant Wireless Power Transfer systems. Firstly, three subwave-length unit cells are optimized in order to get negative magnetic permeability in the same frequency, each one with a different refractive index, and they are experimentally characterized. Then, the Transformation Optics technique is applied in order to find the unit cell arrangements which lead to the magnetic field focusing in a given direction. For this purpose, two coordinate transformations are proposed, and the effective electric permittivity and permeability that generate these profiles are calculated. It is shown from simulations and measurements that the refractive index gradient produced by the radial disposition of the unit cells can lead to a magnetic field manipulation similar to the optical converging and diverging lenses. Both metamaterials lenses are built, and the calculation of the magnetic flux density as a function of the measured induced voltage in a probe coil verifies their effects on the magnetic field. Finally, their performance in a resonant wireless power transfer system is tested, and improvements in terms of efficiency and range are presented. The proposed design method and the lenses that were developed demonstrate that metasurface lenses can improve efficiency without reducing the range, once these lenses are positioned close to the transmitter coil. Besides that, this method can reduce the losses due to misalignment between coils once the field can be collimated in a specific direction.

Resumo em Inglês:

Abstract This study presents a rigorous numerical analysis of the current in the cell membrane, subjected to a uniform electric field, and its impact in the pore formation. The numerical model considers a single cell composed of uniform membrane and cytoplasm, in a suspension medium. The current in the cell membrane is calculated using two different approaches. The first uses a lumped parameters approach based on the geometry of the pore, while the second describes the flow of ions through the pore considering the interaction with the pore walls as an energy barrier. The formation and growth of the pores is solved using an asymptotic approximation of the Smoluchowski’s equation. The electrical potential induced in the cell membrane, which is coupled with the current in the membrane, is resolved in spherical coordinates using the finite difference method. The two approaches have qualitatively similar results but significant quantitative differences in the number and radii of pores. The ionic flow approach has resulted in the formation of fewer pores and reduced pore growth. Approximately 38,000 fewer pores are created, a 21% difference, and the largest pores are approximately 8nm smaller, a 24% difference. Thus, this approach results in a less conductive membrane and smaller electroporated area.

Resumo em Inglês:

Abstract This paper features a step-by-step procedure for designing, simulate, and manufacture a bandpass filter using an inductive window topology within the substrate integrated waveguide (SIW) technology. We have chosen an operating frequency in the microwave range compatible with IoT circuits, employing a dielectric material, the FR-4, which is low cost and widely accessible. Even though it is not the most suitable material for microwave circuits operating above a few gigahertz, we propose to evaluate the challenges it poses on the filter design, in addition to performing a comparison between the results obtained directly from the analytical method, the computational simulations and measured results in the built prototype.

Resumo em Inglês:

Abstract This paper presents measurements at a mock-up medium voltage network to verify the feasibility of Broadband Power Line Communication (BPLC). We use the data extracted within the frequency range 2 − 30 MHz to characterize a MIMO PLC network using different phase combinations, defining the best and worst use case scenarios. The empirical data shows that not only phases directly connected for input-output can be used, but also that we can exploit the coupling between phases to transmit and receive data, therefore creating a dynamic PLC network which will depend on the characteristics of the power grid. By making use of transmission line theory, we also demonstrate how we can mitigate the reflections by measuring the input impedance of the network to allow better use of the bandwidth available for BPLC operation.

Resumo em Inglês:

Abstract To achieve a high gain and low first side-lobe level, variants of linear and planar series fed circular and hexagonal microstrip antenna arrays using the binomial distribution, are proposed around 3000 MHz frequency band, on thinner Arlon substrate (h ~ 0.027λg). The linear 7 × 1 array of circular patches, yields first side-lobe level of −25 dB with a gain of 12.7 dBi, whereas using hexagonal patches, respective values are, −28 dB and 12.9 dBi. The planar 5 × 3 and 5 × 5 arrays using half wavelength and wavelength spacing are presented. An optimum response is obtained in 5 × 5 array for the wavelength inter-element spacing. Here, using circular patches, first side lobe level in the E and H-planes is −29 and −14 dB, respectively, with a peak gain of 17.6 dBi, whereas that using hexagonal patches, the respective first side lobe level in the E and H-planes is −26 and −17 dB, with a peak broadside gain of nearly 19 dBi. Thus using a thinner substrate, proposed series feed binomial planar arrays offer a gain of more than 15 dBi with a lower first side lobe level.

Resumo em Inglês:

Abstract In this work, a new model of high selectivity dual-mode bandpass filter is presented. The proposed filter consists of a set of coupled lines with a dual-mode adjustable response in its design process. An improvement in selectivity is presented by combining the dual-mode element with a classic band rejection structure, thus making it possible to introduce transmission zeros near the transmission band. A modeling is presented based on the traditional analysis of even and odd excitation circuit. Circuit and microstrip line simulations are carried out via ADS and Ansoft HFSS, and their results are compared with measurements made on a fabricated prototype. Its results were consistent with those of the process of analysis and synthesis of the high selectivity filter.

Resumo em Inglês:

Abstract The growth of urban centers has a major impact on our lives and on our society, one of which is the increase in the vehicle fleet, which in turns is a major offender in increasing road congestion, pollution, accidents, theft of vehicles, among others. With a focus on minimizing problems with theft of vehicles in an urban environment this paper proposes a low cost Internet of Things for smart surveillance system. The central element of the system is attached to a vehicle that travels in an urban environment making Automatic License Plate Recognition of the vehicles license plates in front of it. The information collected is forwarded to a cloud service that is responsible for monitoring restricted vehicle license plates to view positioning, time, date and statistics related to restricted vehicle license plates. Experimental results obtained in test paths in an urban environment show promising results. The low cost of implementing the system allows it to be scaled to a fleet of vehicles, making it possible to build a mobile intelligent surveillance network, amplifying the monitoring capacity of an urban area.

Resumo em Inglês:

Abstract This paper presents the Multiphysics Analysis of a High-Power Microwave Window for a Ka-Band Klystron providing 16MW of peak power. After the optimization of the electromagnetic performances, we analyze the effect of RF heating effect and the stress of the pressure on the window. We also analyze the multipactor effect, that is a common cause of window failure. Using such approach, it is possible to realize a virtual prototype capable to represent in a complete way the real prototype to be manufactured.

Resumo em Inglês:

Abstract This paper presents a method to cancel the constant phase loading and transmission line that are added to the S-parameters of coupled resonant networks. Thus, the phase-corrected S-parameters may be used to obtain a rational model together with its representative coupling matrix. This method is applicable to lossy and lossless coupled resonator networks with two ports, such as microwave filters. In addition, it has the advantage of not requiring S-parameters with wide frequency ranges, and offers less computational effort than other approaches. Examples including simulations of microwaves passband filters are provided in order to demonstrate the effectiveness of this new technique.

Resumo em Inglês:

Abstract In this article, antennas for the 60 GHz ISM band designed to be integrated to a new high-frequency, low-cost interposer technology called Membrane-nanowire-Membrane (MnM) are discussed, manufactured, and measured. Also, an antenna characterization system under development at the Microelectronic Laboratory (LME-USP) is introduced, showing promising results for the deployment of mmW systems.

Resumo em Inglês:

Abstract Solar cells integrated with antennas have aroused scientific interest as an attractive energy source alternative in low power devices for IoT and Wireless Sensor Network applications. Since the space for all components in the systems is scarce, different integration ideas have been proposed in this field. However, further analysis of the performance of photovoltaic modules used as structural components of antennas is still lacking. In this context, this work experimentally extracts the necessary parameters to create an equivalent circuit model of a modified solar cell used as a radiator of a 2.4 GHz coplanar patch antenna. The obtained model is then used in the numerical characterization of the Current- Voltage (I-V) curves under temperature variations. Antenna design and performance are described, and the physical modifications of a commercial solar cell used in the prototype are presented. The I-V curves were generated for temperatures ranging from 243 to 325 K. The obtained simulation results within this temperature range showed a 150 mV shift of the optimal operation point, decreasing in approximately 20 mW the supported power with the temperature rise. A predictive methodology is introduced to estimate the possible values for the fill factor, energy conversion efficiency, and current density in a modified solar cell under temperature variations, allowing a fully operational photovoltaic antenna design.