Planar UWB Antenna with Modified Slotted Ground Plane

A compact coplanar waveguide-fed (CPW) monopole antenna for ultra-wideband wireless communication is presented. The proposed antenna comprises of a CPW-fed beveled rectangular patch with a modified slotted ground. The overall size of the antenna is 30 mm 27 mm 1.6 mm. The lower edge of the band is attained by properly decoupling the resonant frequencies due to the extended ground plane and the beveled rectangular patch of the antenna. The upper edge of the radiating band is enhanced by beveling the ground plane corners near the feed point. Experimental results show that the designed antenna operates in the 2.7–12 GHz band, for S11 10 dB with a gain of 2.7–5 dBi. Both the frequency domain and time domain characteristics of the antenna are investigated using antenna transfer function. It is observed that the antenna exhibits identical radiation patterns and reasonable transient characteristics over the entire operating band

Theoretical investigations of an annular elliptical ring microstrip antenna using Green‘s function technique

Analytical expressions for the Green’s function of an annular elliptical ring microstrip antenna (AERMA) are developed and reported. The modal, radiation and input impedance characteristics of the TM, modes are determined from these expressions. The resonant frequencies of odd modes are greater than that of the even modes for all TMnl modes (n = 1, 2, 3, ...) udke elliptical microstrip structures. The radiation pattern and input imedance curves of TMI2 mode on comparison with available experimental result shows good agreement whch provides an independent validation to this technique. The performance of the AERMA is then investigated as a function of thickness and substrate dielectric permittivity.

Arranjos Log-Periódicos Compactos em Microfita com Elementos Fractais de Koch

This work aims to present how the application of fractal geometry to the elements of a log-periodic array can become a good alternative when one wants to reduce the size of the array. Two types of log-periodic arrays were proposed: one with fed by microstrip line and other fed by electromagnetic coupling. To the elements of these arrays were applied fractal Koch contours, at two levels. In order to validate the results obtained some prototypes were built, which were measured on a vector network analyzer and simulated in a software, for comparison. The results presented reductions of 60% in the total area of the arrays, for both types. By analyzing the graphs of return loss, it was observed that the application of fractal contours made different resonant frequencies appear in the arrays. Furthermore, a good agreement was observed between simulated and measured results. The array with feeding by electromagnetic coupling presented, after application of fractal contours, radiation pattern with more smooth forms than the array with feeding by microstrip line

Determinação da freqüência de ressonância de antenas tipo microfita triangular e retangular utilizando redes neurais artificiais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da influência da flexibilidade dos discos nas rotações críticas de rotores

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Surface wave techniques for the study of engineering structures and materials

A wire drive pulse echo method of measuring the spectrum of solid bodies described. Using an 's' plane representation, a general analysis of the transient response of such solids has been carried out. This was used for the study of the stepped amplitude transient of high order modes of disks and for the case where there are two adjacent resonant frequencies. The techniques developed have been applied to the measurenent of the elasticities of refractory materials at high temperatures. In the experimental study of the high order in-plane resonances of thin disks it was found that the energy travelled at the edge of the disk and this initiated the work on one dimensional Rayleigh waves.Their properties were established for the straight edge condition by following an analysis similar to that of the two dimensional case. Experiments were then carried out on the velocity dispersion of various circuits including the disk and a hole in a large plate - the negative curvature condition.Theoretical analysis established the phase and group velocities for these cases and experimental tests on aluminium and glass gave good agreement with theory. At high frequencies all velocities approach that of the one dimensional Rayleigh waves. When applied to crack detection it was observed that a signal burst travelling round a disk showed an anomalous amplitude effect. In certain cases the signal which travelled the greater distance had the greater amplitude.An experiment was designed to investigate the phenanenon and it was established that the energy travelled in two nodes with different velocities.It was found by analysis that as well as the Rayleigh surface wave on the edge, a seoond node travelling at about the shear velocity was excited and the calculated results gave reasonable agreement with the experiments.

Desenvolvimento teórico e experimental de FSS com elementos fractais de Gosper em estruturas de multicamadas

The fractal self-similarity property is studied to develop frequency selective surfaces (FSS) with several rejection bands. Particularly, Gosper fractal curves are used to define the shapes of the FSS elements. Due to the difficulty of making the FSS element details, the analysis is developed for elements with up to three fractal levels. The simulation was carried out using Ansoft Designer software. For results validation, several FSS prototypes with fractal elements were fabricated. In the fabrication process, fractals elements were designed using computer aided design (CAD) tools. The prototypes were measured using a network analyzer (N3250A model, Agilent Technologies). Matlab software was used to generate compare measured and simulated results. The use of fractal elements in the FSS structures showed that the use of high fractal levels can reduce the size of the elements, at the same time as decreases the bandwidth. We also investigated the effect produced by cascading FSS structures. The considered cascaded structures are composed of two FSSs separated by a dielectric layer, which distance is varied to determine the effect produced on the bandwidth of the coupled geometry. Particularly, two FSS structures were coupled through dielectric layers of air and fiberglass. For comparison of results, we designed, fabricated and measured several prototypes of FSS on isolated and coupled structures. Agreement was observed between simulated and measured results. It was also observed that the use of cascaded FSS structures increases the FSSs bandwidths and, in particular cases, the number of resonant frequencies, in the considered frequency range. In future works, we will investigate the effects of using different types of fractal elements, in isolated, multilayer and coupled FSS structures for applications on planar filters, high-gain microstrip antennas and microwave absorbers

Análise de superfícies seletivas em frequência com geometria multifractal

Frequency Selective surfaces are increasingly common structures in telecommunication systems due to their geometric and electromagnetic advantages. As a matter of fact, the frequency selective surfaces with fractal geometry type would allow an even bigger reduction of the electrical length which provided greater flexibility in the design of these structures. In this work, we investigated the use of multifractal geometry in frequency selective surfaces. Three structures with different multifractal geometries have been proposed and analyzed. The first structure allowed the design of multiband structures with greater flexibility in controlling the resonant frequencies and bandwidth. The second structure provided a bandwidth increase even with the rising of the fractal level. The third structure showed response with angle stability, dual polarization and provided room for a bandwidth increase with the rising of the structural multifractality. Furthermore, the proposed structures increased the degree of freedom in the multiband designs because they have multiple resonant frequencies ratios between adjacent bands and are easy to deploy. The validation of the proposed structures was initially verified through simulations in Ansoft Designer software and then the structures were constructed and the experimental results obtained

Dual-band Filtenna Array for WLAN Applications

This paper presents the design and results of a dual-band antenna array integrated with bandpass filters for WLAN applications. The array is fed with a single 50 Ω port and consists of two radiating elements; thereby having a 1x2 array structure. The two bands of the antenna array correspond to the two WLAN bands of 2.4 GHz and 5.8 GHz. A standalone array has first been designed. Other than the two fundamental resonant frequencies, the standalone array exhibits spurious harmonics at various other frequencies. For the suppression of these harmonics, the array has been integrated with two bandpass filters, centered at 2.4 GHz and 5.8 GHz. The resulting filtenna array was simulated, fabricated and measured. Obtained simulation and measurement results agree well with each other and have been presented to validate the accuracy of the proposed structure. Measured return loss of the structure shows dual-bands at 2.4 GHz and 5.8 GHz of more than 30 dB each and also a successful suppression of the spurious harmonics of the antenna array has been achieved. Radiation patterns have also been simulated and measured and both results shown. The gain and efficiency have also been presented; with the values being 6.7 dBi and 70% for the 2.4 GHz band and 7.4 dBi and 81% for the 5.8 GHz band respectively.

Soil characteristics in Doon Valley (north west Himalaya, India) by inversion of H/V spectral ratios from ambient noise measurements

Past and recent observations have shown that the local site conditions significantly affect the behavior of seismic waves and its potential to cause destructive earthquakes. Thus, seismic microzonation studies have become crucial for seismic hazard assessment, providing local soil characteristics that can help to evaluate the possible seismic effects. Among the different methods used for estimating the soil characteristics, the ones based on ambient noise measurements, such as the H/V technique, become a cheap, non-invasive and successful way for evaluating the soil properties along a studied area. In this work, ambient noise measurements were taken at 240 sites around the Doon Valley, India, in order to characterize the sediment deposits. First, the H/V analysis has been carried out to estimate the resonant frequencies along the valley. Subsequently, some of this H/V results have been inverted, using the neighborhood algorithm and the available geotechnical information, in order to provide an estimation of the S-wave velocity profiles at the studied sites. Using all these information, we have characterized the sedimentary deposits in different areas of the Doon Valley, providing the resonant frequency, the soil thickness, the mean S-wave velocity of the sediments, and the mean S-wave velocity in the uppermost 30 m.

Quality factor assessment of subwavelength resonant cavities at FIR frequencies

Subwavelength resonators at FIR are presented and studied. The structures consist of 1D cavities formed between a metallized (silver) surface and a metamaterial surface comprising a periodic array of silver patches on a silver-backed silicon substrate. The concept derives from recent discoveries of artificial magnetic conductors (AMC). By studying the currents excited on the metamaterial surface by a normally incident plane wave, the nature of the emerging resonant phenomena and the physical mechanism underlying the AMC operation are investigated. Full wave simulations, based on finite element method and time-domain transmission line modelling technique, have been carried out to demonstrate the effective AMC boundary condition and prove the possibilities for subwavelength cavities. The quality factor of the resonant cavities is assessed as a function of the cavity profile. It is demonstrated that the quality factor drops to about 1/8 of the half-wavelength value for lambda/8 resonant cavity.

A novel CDVM based high-voltage converter using low power solid-state switches and a tuned resonant circuit designed for pulsed power applications

A novel concept of producing high dc voltage for pulsed-power applications is proposed in this paper. The topology consists of an LC resonant circuit supplied through a tuned alternating waveform that is produced by an inverter. The control scheme is based on the detection of variations in the resonant frequency and adjustment of the switching signal patterns for the inverter to produce a square waveform with exactly the same frequencies. Therefore the capacitor voltage oscillates divergently with an increasing amplitude. A simple one-stage capacitor-diode voltage multiplier (CDVM) connected to the resonant capacitor then rectifies the alternating voltage and gives a dc level equal to twice the input voltage amplitude. The produced high voltage appears then in the form of high-voltage pulses across the load. A basic model is simulated by Simulink platform of MATLAB and the results are included in the paper.

A class E resonant inverter for use as electronic fluorescent lamp ballast

Class E Resonant Inverters are theoretically capable of delivering any power to a load and achieve 100% efficiency at any frequency of operation. In practice efficiency in the “high 90's” can be achieved into megahertz frequencies regardless of inverter output powers. The topology also allows the manipulation of output power through sub-optimal operation, with a negligible efficiency penalty. The 24W inverter discussed in this paper was specifically designed to harness the benefits, and discuss the shortcomings, of the Class E topology for use in the growing market for portable, battery powered lighting. It exhibits a peak recorded power efficiently of over 98%, and a conservatively measured efficiency of 95% across a range of dimming settings.