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This paper presents the development of a compact monopole antenna bioinspired in the Opuntia ficus-indica plant-shape, generated by Gielis formula, built in fiberglass substrate, with hybrid feed by transmission line and probe, for wireless local area network band at 5 GHz. By using the plan-shape, it is possible to increase the perimeter of the design and thus reduce its total area, which can be employed in the development of compact antennas with larger electrical length. Results of the bioinspired plant-shape antenna is compared to the square-shape antenna, and the proposed antenna presents a more compact structure, with a reduction of 62.5% in the total area, with a value of 108.4 mm2, narrower bandwidth, and a directive radiation pattern, with a bandwidth of 1.44 GHz (4.41–5.85 GHz), which covers the 5 GHz WLAN band (5.15–5.85 GHz) and measured gain of 2.6 dBi, at the resonance frequency.

In this study, a new technique for circuit breaker diagnosis, based on broadband microstrip antennas, is presented. The diagnosis is based on the electromagnetic signals radiated by electric arcs in circuit breaker poles during opening operations. From each measured signal, several parameters are calculated, such as arc duration and signal energy, which are then processed by a statistical analysis routine, providing information that allows a correlation between the radiated signals and the degradation of the breaker contacts to be established. A current injection system was used in order to produce electric arcs. The technique was tested using nine contact samples, with different degradation levels. With the obtained results, it can be verified that the proposed technique is able to provide information regarding contact degradation level, arc duration, arc reignitions, and mechanical defects. The proposed technique is a simple and non-invasive solution, since the antenna can be placed far away from the equipment under evaluation. The use of antennas is a low-cost solution to circuit breaker monitoring, and since it provides a continuous monitoring system, a database containing the evolution history of contact degradation may be available.

This paper introduces a novel RFID method for accelerating the tag estimation performance in dynamic framed slotted ALOHA (DFSA) algorithms. Assuming a critical scenario where the number of tags in the interrogation zone is much greater than the initial frame size, the proposed Double-Approximation (DA) method uses, besides the backlog estimation to adjust the size of first frames, a second approximation that successively reduces the tags available to transmit until achieving a faster convergence to the first frame sizes. Once the convergence threshold is achieved, a more accurate tag estimation can be calculated and all temporarily disabled tags become able to transmit again. Simulation results show that all DFSA algorithms implemented with the DA method outperforms the traditional DFSA in terms of throughput and reduction of simultaneous tag signals.

The development of a microstrip patch antenna with a band-pass frequency selective surface superstrate for 5G New Radio applications at 3.5 GHz is presented in this paper. The frequency selective surface is based on the four-arms star geometry. The structure proposed was manufactured and measurements were performed and compared to simulations. The superstrate performance in function of the distance between the microstrip patch antenna and the FSS is analysed in detail. A measured gain improvement of 5.74 dB is achieved for a distance of 4.5 cm, approximately λ/2.

In this paper, it is presented a new modified structure of antipodal Vivaldi antenna (AVA). The structure is fed by a triple ridged substrate integrated waveguide (RSIW) on a single layer low-cost FR4 substrate. The ridges insertion allows a bandwidth enhancement due to the cut-off frequency decrease and consequently the miniaturization. The new structure is compared to an AVA fed by a classical SIW designed for a cut-off frequency around 4 GHz. Numerical simulations were performed and a bandwidth enhancement of 660 MHz was achieved with a gain of 2.06-7.59dBi within the frequency range.

The design of a bio-inspired butterfly-shaped patch antenna array, generated by polar transformations, covering the wireless local area network (WLAN) band at 2.4 GHz (2.400-2.483 GHz), with similar and dissimilar elements is presented in this paper. The dissimilar bio-inspired antenna presented a bandwidth of 96MHz covering the IEEE802.11b, g band, maximum gain of 8.64dBi, concentrated half power beamwidth of 52 degrees and front-to-back ratio of 15.21dB.

In this paper, a novel spiral multilayer frequency selective surface (MFSS) is proposed with element based on the concept of Baravelle spiral. A dual-band behavior at WLAN frequencies bands (2.4 GHz, 5.0 GHz or 5.8 GHz) has been obtained. The proposed structure is found to show stopband characteristics in the frequencies ranges from 1.67 GHz to 3.1 GHz and from 4.1 GHz to 5.9 GHz. In addition, the proposed MFSS shows an interesting characteristic of polarization stability.

This work proposes the application of a slot in the ground plane, Defected Ground Structure (DGS), of a microstrip patch antenna. The application of this technique aims to attenuate higher-order excited modes without deteriorating the antenna parameters in the fundamental mode. The methodology for the design of the slot in H-format is presented, based on the physical dimensions of the microstrip patch antenna. The positioning of the DGS concerning the feed line was determined from a detailed parametric analysis. The antenna was designed for the fundamental mode at 2.45 GHz frequency. Two antenna prototypes were built, with and without DGS, and measurements of reflection coefficient, gain, and radiation pattern were performed. The measured results show that the application of DGS considerably attenuated higher-order excited modes. A good agreement between simulated and measured results is achieved.

Conventional flexible and wearable antennas are currently fabricated with substrates which are neither biodegradable. Another negative point is the use of ecounfriendly processes to produce these circuits thus generating e-waste and causing environment contamination. In this paper, an eco-friendly metamaterial antenna for 2.4 GHz WLAN applications is presented. The rectangular patch antenna is composed of two copper tape layers, one as the radiating element and the other as the modified ground plane with Complementary Split Ring Resonators (CSRR). The substrate that separates these two layers is a mixture of polybutylene adipate-co-terephthalate (PBAT) and polyhydroxybutyrate (PHB) polymers, both biodegradable. The electrical characterizations of the mixture were performed using the probe method and the antenna simulations were performed using the commercial software ANSYSO Electronics Desktop. Convergent results were obtained with simulated and measured prototypes, with a measured resonant frequency in 2.44 GHz and bandwidth of 360 MHz, simulated gain of 4.01 dBi and half power beam width of $4\mathrm {S}.2^{\mathrm {o}}$, which shows great potential for WLAN applications.

This paper describes by the first time, at least of the authors’ knowledge, a frequency selective surface, FSS, based on the Matryoshka geometry, with dual-band band-pass frequency response, keeping the interesting features previously outlined: angular stability and polarization independence. Moreover, it is a single layer FSS and the reduction of the resonant frequencies, a characteristic of the Matryoshka geometry, was maintained. Initial design equations are proposed, providing good results, making easy the design of the FSS for other resonant frequencies and specific applications. Two FSS were designed, fabricated and characterized, verifying a good agreement between numerical and experimental results. The resonant frequencies remain almost constant for different incident angles, from 0° to 45°, confirming the angular stability.

In this article, the applicability of an UHF circular printed monopole antenna with slotted ground plane was evaluated in order to detect partial discharges in power transformers. To verify the applicability of the antenna, two measurement batteries were performed: reflection coefficient (bandwidth) and gain in an anechoic chamber, to avoid external interference; and PD sensitivity tests from the comparison with the conventional method of IEC 60270, using for this purpose an oil cell with immersed flat-tip electrodes. These analyzes were performed for the design of an antenna with optimized performance. The obtained values for the antenna's bandwidth, size, gain and PD detection sensitivity make it possible to classify the antenna as efficient in detecting partial discharges in power transformers.

In this paper is developed a transparent antenna, bioinspired in ingae edulis mart plants, build in Indio Tin Oxide film, and flexible transparent dielectric of low cost (cellulose acetate), generated by Gielis formula, for wireless local area network application in 5 GHz (5.15–5.85 GHz). The measured bioinspired transparent antenna presented bandwidth of 4.11 GHz (4.50-8.66 GHz), covering the WLAN band, with maximum gain of 5.44 dBi, and half power beamwidth of 126° at resonance frequency.

For fatigue life estimation as well as for fatigue testing analysis of welded structures by local stresses approaches, the stress concentration factor (SCF) at the weld must be known. Full penetration butt welded joints are extensively used in steel structures. Some empirical formulas to estimate SCFs are available in the literature, but their ranges of application are not always clearly defined, as well as the hypotheses on their local geometry. In this study, notch SCFs at steel butt welded joints under uniaxial tension are investigated by means of 2D plane strain linear elastic finite element analysis. The weld profile is modeled with splines. A detailed definition of the geometry is given. The influence of parameters such as the plate thickness, the weld reinforcement, the flank angle, the weld toe radius, the weld length and the presence of linear misalignment is assessed. Finally new parametric equations to estimate the SCFs at steel butt welded joints are proposed.

In this paper is presented a rectangular Koch pre-fractal patch antenna until three iterations on wearable flexible polyamide dielectric operating in the ultrahigh frequency band for medical wireless applications. The antennas were implemented by MATLAB, with generated images simulated in commercial software ANSYS. The polyamide presents characteristics of mechanical and thermal resistance suitable for wearable applications that require high-temperature resistance and constant movement. The use of Koch pre-fractal geometries from square patch antenna provides a decrease of 20.3 % in resonance frequency, and 30° in half-power beamwidth, making it more directional (first iteration). The wearable patch antenna with Koch pre-fractal for the third iteration shows maximum a gain at the resonance frequency of 5.57 dBi, and a current density of 41 A/m2.

In this paper, the design and development of a bio-inspired UHF sensor for partial discharge detection in power transformers is presented. The UHF sensor was developed for external use in dielectric windows of power transformers. For this purpose, a microstrip antenna was designed with a radiating element shape based on the leaf of the Jatropha mollissima (Pohl) Baill plant. Then, an epoxy coating and an aluminium enclosure were developed to protect the antenna against corrosion and to provide mechanical support, external noise immunity, and a lifetime compatibility with power transformers. In order to verify the electrical parameters of the developed sensor, measurements of the gain and the reflection coefficient were performed in an anechoic chamber. Lastly, the antenna sensitivity for denominated partial discharge (PD) detection was compared with the IEC 60270 standard method. For this purpose, simultaneous tests were carried out in a partial discharge generator setup, composed of an oil cell with needle-plane electrodes. The experimental tests demonstrated the effectiveness of the sensor for detecting PD signals with apparent charge values higher than 35 pC.

Wearable antennas present flexible dielectric and microstrip antenna normally used in Wireless Body Area Network systems with medical and no-medical applications. This article presents a new wearable printed monopole antenna for second generation (2G), third generation (3G), and fourth generation (4G) systems on textile material and laminate cooper to flat cable. The bioinspired geometry of a gynkgo biloba leaf was generated by Gielis formula. The proposed antenna presents a bandwidth of 2.70 GHz, covering the ranges of 2G, 3G, and 4G systems, with an omnidirectional radiation pattern, 3.10 dBi gain, and a HPBW of 102°. Measurements were performed with the antenna nearly on the head, on hand and in the pocket of trousers. The biggest difference, in the resonance frequency, was observed with the antenna on hand, and the antenna nearly on head, showed greater difference in bandwidth. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2818–2823, 2016

Due to the increasing production of volatile new renewable energies as solar and wind, storage hydropower plants have to operate under harsh operation conditions in order to stabilize the electricity grid. As a result, highly transient water pressures occur in pressure tunnels and shafts more frequently. Non-intrusive monitoring techniques are therefore of special interest for these critical infrastructures. The propagation of a pressure wave generated actively by a cavitation bubble was experimentally investigated in a steel test pipe divided in several reaches. A local wall stiffness drop was simulated by replacing steel pipe reaches with less stiff materials as aluminum and PVC. Through the analysis of the pressure wave reflections due to the cavitation bubble explosion, recorded by two hydrophones placed at the extremities of the test pipe, the location of the weak reaches could be detected. An underwater spark generator was developed to produce cavitation bubbles in the pipe resulting in very steep shock waves. This allowed identifying very precisely the wave front and correspondingly the wave speed and the weak reach location. Compared to the wave analysis from water-hammer signals, the active cavitation bubble generation in the pipe is an innovative method that significantly increased the effectiveness of the detection of wall stiffness drops. (C) 2016 Elsevier Ltd. All rights reserved.

In this paper, a biologically inspired design methodology to develop directional leaf-shaped printed monopole antennas (PMA) for applications in the fourth-generation (4G) of mobile telecommunications technology is presented. Bio-inspired in the leaf shapes of a sugar cane plant, compact directional PMA are designed (with partial ground planes and flat rectangular reflectors) to cover the Brazilian 4G 700 MHz regulated band (698–806 MHz), with broadside radiation patterns and maximum directive gain up to 7.7 dBi. Simulated and measured results are presented for the proposed leaf-shaped antenna prototypes, and obtained results are compared with a square PMA. The use of bio-inspired leaf-shaped radiators and flat reflectors provides a fine tuning of ultra-wideband commonly presented by a conventional PMA, and the lowest resonant mode can be adjusted to cover the 700 MHz band. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1529–1533, 2016

A new, bio-inspired printed monopole antenna (PMA) model is applied to monitor partial discharge (PD) activity in high voltage insulating systems. An optimized sensor was obtained by designing a PMA in accordance with the characteristics of the electromagnetic signal produced by PD. An ultra-wideband (UWB) antenna was obtained by applying the truncated ground plane technique. The patch geometry was bio-inspired by that of the Inga Marginata leaf, resulting in a significant reduction in size. To verify the operating frequency and gain of the PMA, measurements were carried out in an anechoic chamber. The results show that the antenna operating bandwidth covers most of the frequency range of PD occurrence. Moreover, the antenna presented a good sensitivity (mean gain of 3.63 dBi). The antenna performance was evaluated through comparative results with the standard IEC 60270 method. For this purpose, simultaneous tests were carried out in a PD generator arrangement, composed by an oil cell with point-to-plane electrode configurations. The developed PMA can be classified as an optimized sensor for PD detection and suitable for substation application, since it is able to measure PD radiated signals with half the voltage levels obtained from the IEC method and is immune to corona discharges.

International audience; In this paper, a low-cost patch antenna with circular polarization using a FR4 substrate is proposed. The antenna was developed to be used in US standard UHF RFID application, with better impedance matching at 915MHz. The design was concepted and optimized through simulations using the ANSYS HFSS software. The simulation results presented an absolute gain of 5.76dB, an axial ratio of 1.87dB and the return loss (S11) of 48dB at 915MHz. The antenna was manufactured and measurements of the return loss using the Keysight Vector Network Analyzer were made to compare with the simulation results. Furthermore, it was compared to a commercial antenna by reading a commercial tag using a RFID reader in order to validate the proposed antenna application.

Steel-lined pressure tunnels and shafts are constructed to convey water from reservoirs to hydroelectric power plants. They are multilayer structures made of a steel liner, a cracked backfill concrete layer, a cracked or loosened near-field rock zone and a sound far-field rock zone. Designers often assume isotropic behavior of the far-field rock, considering the most unfavorable rock mass elastic modulus measured in situ, and a quasi-static internal water pressure. Such a conventional model is thus axisymmetrical and has an analytical solution for stresses and displacements. However, rock masses often have an anisotropic behavior and such isotropic assumption is usually conservative in terms of quasi-static maximum stresses in the steel liner. In this work, the stresses and displacements in steel-lined pressure tunnels and shafts in anisotropic rock mass are studied by means of the finite element method. A quasi-static internal water pressure is considered. The materials are considered linear elastic, and tied contact is assumed between the layers. The constitutive models used for the rock mass and the cracked layers are presented and the practical ranges of variation of the parameters are discussed. An extensive systematic parametric study is performed and stresses and displacements in the steel liner and in the far-field rock mass are presented. Finally, correction factors are derived to be included in the axisymmetrical solution which allow a rapid estimate of the maximum stresses in the steel liners of pressure tunnels and shafts in anisotropic rock.

A double ring FSS with angular stability operating in the WLAN range is discussed in this paper. The Euclidean geometry of the proposed FSS is composed of a periodic array of metallic patches on a dielectric layer of FR4, which is designed and simulated using the commercial software ANSYS. Measurements and simulation of the proposed structure are compared to single ring FSS. An investigation of angular stability was performed in the WLAN range. The double ring FSS presents good response between simulated and measured results, in the 2.40 GHz band, the FSS presented angular stability from 0° to 40°, and for 5.30 GHz, the angular stability was observed from 0° to 20°.

The adaptation of dielectric windows as metamaterial superstrate over a bio-inspired Printed Monopole Antenna (PMA) was evaluated in order to improve the detection sensitivity of Ultra High Frequency (UHF) sensors designed for Partial Discharge (PD) measurement. For this purpose, rectangular and circular Split Ring Resonators (SRR) structures were designed and evaluated aiming to achieve a metamaterial superstrate that improves the characteristics of the bio-inspired PMA as the gain, bandwidth, and radiation pattern. Measurements of the PMA with metamaterial superstrate were carried out in an anechoic chamber and compared to the simulations performed. The results show that the metamaterial superstrate insertion did not impact the original operating bandwidth, covering most of the characteristic frequency range of PD activity. Moreover, this insertion resulted in a mean gain enhancement of 0.7 dBi regarding the reference PMA, resulting in an antenna with better sensitivity for PD detection (mean gain of 3.61 dBi). The PMA-metamaterial set PD detection sensitivity was evaluated through laboratory tests with a point-to-plane PD generator setup and in field with measurements from a 230 kV current transformer. The developed PMA-metamaterial set was able to detect, successfully, the activity of PD for both tests, being classified as an optimized sensor for PD detection through dielectric windows.

Beamforming front-ends are an attractive technology because it concentrates its radiated power in one direction, which can improve energy efficiency and reduce undesirable interference. In this context, electronic beamforming systems have lower cost than mechanical ones. Knowing the uses of directive antennas and power dividers in electronic beamforming systems, this work aims at the design, simulation and measurements of these components at 5.8 GHz. Measurements with Power Divider showed very good return and insertion losses at 5.8 GHz: S 11 = −23.5 dB and S 21 = −3.8 dB. A printed dipole antenna was then fabricated, presenting −14.6 dB of return losses and a 2.82 dBi gain. Later, a 2-antenna beamforming front-end was implemented, proving the beamforming capability with the proposed devices. It also presented S 11 = −15.7 dB, and a high directive gain (10.3 dBi). Since this is still a preliminary work, the results presented are very promising.

The aim of this work is to implement electronic beam-steering systems. More specifically, we propose systems working at 2.45 GHz. For that, power dividers (PD), phase shifters (RTPS), and printed antennas are used. The main advantage of electronic beam-steering systems is related to the simple realization and low cost, when compared with mechanical ones. For some devices, a small shift in frequency is observed from 2.45 to 2.40 GHz. At 2.40 GHz, PD and RTPS show very low losses: 0.10 dB for the PD and between 0.55 and 1.40 dB for the RTPS; as well as good return losses (−30.19 dB and −2.85 dB, respectively). The RTPS enables to perform 360° of phase-shift with a 0.5–2.72 pF varactor. With the proposed topologies, a simulated 2-antenna array beam-steering of ±85° has been shown with return loss of −12.88 dB. Since inclination angle F also varied, no relevant measured results were obtained in the available anechoic chamber, which works only in the Φ = 0 plane. A 4-antenna array was then measured. Results reach gains up to 5.58 dBi with −11.07 dB of return losses at 2.40 GHz. Since this is still a preliminary work, the results presented are very promising.

International audience; A new simple Ultra-Wideband (UWB) monocycle pulse generator based on step recovery diode is presented. This pulse generator uses nonlinear components with a single power supply and microstrip transmission lines. It is made up of three parts: a Gaussian pulse generator, an impulse-shaping network, and a monocycle-pulse forming circuit. The proposed circuit allows to generate ultra-short Gaussian monocycles of 270-ps pulse duration with a bandwidth of 9-GHz and a pulse repetition rate of 100-MHz.

A microstrip leaf-shaped printed monopole antenna bioinspired on the Inga marginata leaves is presented in this paper for UWB applications. A parametric study of the proposed antenna bioinspired geometry was conducted in order to verify their resonant properties. The antenna was designed with a rectangular slitted ground plane for impedance matching and fabricated on inexpensive glass fiber substrate and fed by a 50 Ω microstrip line. Numerical and experimental results were obtained. The results show an impedance bandwidth superior to 10.26 GHz, greater than the bandwidth considered UWB (7.5 GHz). Antenna dimensions were optimized with the computer program Ansys Designer® used to simulate the electromagnetic behavior of the antennas by the method of moments.

When for steel liners of pressure tunnels and shafts high-strength steels are used, welded joints are subject to the risk of hydrogen induced cold-cracking in the base material. Longitudinal butt welded joints are critical regions as they are loaded transversely. For an accurate engineering fatigue and fracture assessment, solutions for stress intensity factors (SIF) are required, considering the weld shape and the global behavior of the liner (i.e., geometrical imperfections and interaction with surrounding concrete and rock). In this study, SIF for axial semi-elliptical surface cracks and embedded elliptical cracks at longitudinal butt welded joints of steel liners are studied by means of the finite element method. At first the applicability of published parametric equations for SIF of elliptical cracks in plates is validated. Then the influence of the weld shape is assessed through a systematic parametric study. It is shown that the weld profile has a significant influence on SIF for semi-elliptical surface cracks while it has no significant influence on SIF for embedded elliptical cracks within the studied range of relative crack depth. Finally, a new parametric equation is proposed to estimate the weld shape correction factor for semi-elliptical surface cracks.