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Humberto Xavier de Araujo

Bio: Humberto Xavier de Araujo is an academic researcher from Federal University of Tocantins. The author has contributed to research in topics: Antenna (radio) & Metamaterial. The author has an hindex of 5, co-authored 37 publications receiving 96 citations. Previous affiliations of Humberto Xavier de Araujo include State University of Campinas & Universidade Federal de São João del-Rei.

Papers
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Journal ArticleDOI
TL;DR: In this article, a dual-band patch antenna is developed for the Industrial, Scientific and Medical (ISM) bands of 2.4 GHz and 5.8 GHz with improved performance in terms of radiation pattern characteristics.
Abstract: In this paper, a dual-band patch antenna is developed for the Industrial, Scientific and Medical (ISM) bands of 2.4 GHz and 5.8 GHz with improved performance in terms of radiation pattern characteristics (antenna gain, front-to-back ratio and directivity) for both bands. For this purpose, a bandstop reflector based on Frequency Selective Surface (FSS) was designed and optimized. Simulation results show improved gain for the proposed structure for both frequency bands, with a gain of 7.54 dBi and 6.8 dBi at 2.4 GHz and 5.8 GHz, respectively. Measurement results showed a gain value of 7.46 dBi at 2.4 GHz. A bandwidth of 7% was obtained at the central frequency of 2.4 GHz (ranging from 2.37 to 2.56 GHz), while a bandwidth of 1.07 GHz (18.8% fractional bandwidth) was achieved at the frequency of 5.8 GHz. The measured experimental results were in agreement with those obtained by computational simulations and the satisfactory performance validate the proposed structure.

27 citations

Journal ArticleDOI
TL;DR: The results obtained by simulations and measurements show that it is possible to collect energy from two different types of sources in a complementary manner, using the rectenna design proposed, making it possible to feed low-power devices remotely.
Abstract: Combined solar and radio frequency (RF) harvesting systems are drawing attention by offering self-powered ability to low-power devices, an essential aspect to the success of the Internet of Things. One of the main challenges of these harvesting systems is to improve rectennas efficiency by optimizing the individual energy collection and conversion capacity of each source. To overcome this issue, this letter presents a novel 2.4-GHz rectenna structure for solar and radio frequency energy harvesting applications based on a coplanar antenna array integrated with multicrystalline solar cells, whose aluminum rear terminals are used as radiators for the antenna array. The results obtained by simulations and measurements show that it is possible to collect energy from two different types of sources in a complementary manner, using the rectenna design proposed, making it possible to feed low-power devices remotely.

23 citations

Journal ArticleDOI
TL;DR: In this article, the analysis, simulation and prototyping of radio frequency rectifier topologies for ambient energy harvesting applications are evaluated, highlighting the effects of input power levels below −10 dBm.
Abstract: In this paper the analysis, simulation and prototyping of radio frequency rectifier topologies for ambient energy harvesting applications are evaluated, highlighting the effects of input power levels below −10 dBm. The equivalent diode impedance model is taken into consideration for better interpreting its effects when attached to each rectifier topology. Furthermore, the output capacitance modeling and its effects over the rectifier efficiency are discussed for different capacitance types, including a radial stub. A prototype of the most prominent topology was built on a low cost FR-4 substrate for RF harvesting in the range of −10 to −20 dBm, resulting in an approximate efficiency between 40% and 25%, respectively.

18 citations

Journal ArticleDOI
TL;DR: The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectrics permittivity and loss tangent) in comparison to those of commercial substrates, indicating that the obtained ceramic substrates could be useful in the miniaturization of telecommunication devices.
Abstract: Titanium dioxide substrates have been synthesized by means of solid-state reactions with sintering temperatures varying from 1150 °C up to 1350 °C. X-ray diffraction and scanning electron microscopy (SEM) where employed to investigate the crystal structure, grain size and porosity of the resulting samples. The obtained ceramics are tetragonal (rutile phase) with average grain sizes varying from 2.94 µm up to 5.81 µm. The average grain size of samples increases with increasing temperature, while the porosity decreases. The effect of microstructure on the dielectric properties has been also studied. The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectric permittivity and loss tangent) in comparison to those of commercial substrates, indicating that the obtained ceramic substrates could be useful in the miniaturization of telecommunication devices.

11 citations


Cited by
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01 Jan 2013
TL;DR: From the experience of several industrial trials on smart grid with communication infrastructures, it is expected that the traditional carbon fuel based power plants can cooperate with emerging distributed renewable energy such as wind, solar, etc, to reduce the carbon fuel consumption and consequent green house gas such as carbon dioxide emission.
Abstract: A communication infrastructure is an essential part to the success of the emerging smart grid. A scalable and pervasive communication infrastructure is crucial in both construction and operation of a smart grid. In this paper, we present the background and motivation of communication infrastructures in smart grid systems. We also summarize major requirements that smart grid communications must meet. From the experience of several industrial trials on smart grid with communication infrastructures, we expect that the traditional carbon fuel based power plants can cooperate with emerging distributed renewable energy such as wind, solar, etc, to reduce the carbon fuel consumption and consequent green house gas such as carbon dioxide emission. The consumers can minimize their expense on energy by adjusting their intelligent home appliance operations to avoid the peak hours and utilize the renewable energy instead. We further explore the challenges for a communication infrastructure as the part of a complex smart grid system. Since a smart grid system might have over millions of consumers and devices, the demand of its reliability and security is extremely critical. Through a communication infrastructure, a smart grid can improve power reliability and quality to eliminate electricity blackout. Security is a challenging issue since the on-going smart grid systems facing increasing vulnerabilities as more and more automation, remote monitoring/controlling and supervision entities are interconnected.

1,036 citations

01 Jan 2016
TL;DR: This rfid handbook fundamentals and applications in contactless smart cards and identification helps people to read a good book with a cup of coffee in the afternoon instead of juggled with some malicious bugs inside their laptop.
Abstract: Thank you for reading rfid handbook fundamentals and applications in contactless smart cards and identification. As you may know, people have search numerous times for their chosen novels like this rfid handbook fundamentals and applications in contactless smart cards and identification, but end up in malicious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they juggled with some malicious bugs inside their laptop.

570 citations

Journal ArticleDOI
01 Apr 1985
TL;DR: In this article, the authors present an overview of the active components in integrated circuits, including Diodes, Resistors, and Capacitors, as well as passive components such as Bias Circuits, Oscillators, and Timers.
Abstract: Integrated-Circuit Fabrication. Active Devices in Integrated Circuits. Passive Components: Diodes, Resistors, and Capacitors. Bias Circuits. Basic Gain Stages. Analog Design with MOS Technology. Operational Amplifiers. Wideband Amplifiers. Analog Multipliers and Modulators. Voltage Regulators. Integrated-Circuit Oscillators and Timers. Phase-Locked-Loop Circuits. Integrated-Circuit Filters. Data Conversion Circuits: Digital-To-Analog Converters. Data Conversion Circuits: Analog-To-Digital Converters. Index.

281 citations

Book ChapterDOI
01 Jan 2003
TL;DR: In this paper, an expanded and thoroughly revised edition of Thomas H. Lee's acclaimed guide to the design of gigahertz RF integrated circuits features a completely new chapter on the principles of wireless systems.
Abstract: This expanded and thoroughly revised edition of Thomas H. Lee's acclaimed guide to the design of gigahertz RF integrated circuits features a completely new chapter on the principles of wireless systems. The chapters on low-noise amplifiers, oscillators and phase noise have been significantly expanded as well. The chapter on architectures now contains several examples of complete chip designs that bring together all the various theoretical and practical elements involved in producing a prototype chip. First Edition Hb (1998): 0-521-63061-4 First Edition Pb (1998); 0-521-63922-0

207 citations