In this paper, the properties of the omnidirectional photonic band gap (OBG) realized by one-dimensional (1D) Fibonacci quasi-periodic structure which is composed of superconductor and isotropic dielectric have been theoretically investigated by the transfer matrix method (TMM). From the numerical results, it has been shown that this OBG is insensitive to the incident angle and the polarization of electromagnetic wave (EM wave), and the frequency range and central frequency of OBG cease to change with increasing Fibonacci order, but vary with the ambient temperature of system, the thickness of the superconductor, and dielectric layer, respectively. The bandwidth of OBG can be notably enlarged with increasing the superconductor thickness. Moreover, the frequency range of OBG can be narrowed with increasing the thickness of dielectric layer and ambient temperature. The damping coefficient of superconductor layers has no effect on the frequency range of OBG under low-temperature conditions. It is shown that Fibonacci quasi-periodic 1D superconductor dielectric photonic crystals (SDPCs) have a superior feature in the enhancement frequency range of OBG. This kind of OBG has potential applications in filters, microcavities, and fibers, etc.
In this paper we studied the effect of a chiral-substrate bianisotropy on the surface waves of the microstrip resonator. The effective technique used to formulate the characteristic equations of the surface waves in a medium equipped with a complex anisotropy is presented and detailed. The equations concerning an evaluation of the cut-off frequencies are given in more detailed forms. A simple approximate formula for estimating the wave number of the surface mode TM_{0} and TE_{1} are obtained. An estimated maximum value of chiral slab thickness without the excitation of surface waves is given. All of our original results are compared with those published in the literature.
In this paper, two different kinds of near-field measurement techniques are presented. The first one uses coaxial probes that do not give precise measurements on microelectronic devices. We saw in [1] that the spatial resolution of these probes reach 500 μm for monopole and is millimetric for dipole probe. The second one is based on the Pockels effect that converts an electromagnetic (EM) field into optical modulation. Our objective is to improve the Ex/Ey near-field measurement with this second technique. The performance of the electro-optic (EO) probe is compared with dipole probes of 2.5 and 5 mm with the use of simulations and measurements, on a wire above a ground plane and on coupled microstrip lines. At the end, a discussion about the technical limitations of the EO probe is made.
In this paper we propose a new algorithm called An Informative Differential Evolution with Self Adaptive Reclustering Technique to find the amplitude-phase excitation of a linear phased array to have the desired far field pattern. Here we consider three problems for three different far field patterns and each problem is optimized with this algorithm. This algorithm has a proper balancing of exploration and exploitation power which is achieved with the help of information exchange among the subpopulations. We also used an elitist local search algorithm for the fine tuning at the suspected optimal position, and that helps us from the unnecessary wastage of Function Evaluations (FEs).
Electric permittivity and magnetic permeability of linear passive dispersive medium were defined using the circuit equation of an electrically small antenna (scatterer) with resonant and antiresonant properties. It was shown that the average macroscopic energy stored by the scatterers is proportional to frequency derivative of the input admittance of corresponding antenna. It was found that the average macroscopic energy density of electric and magnetic fields in dispersive lossy medium is a function of frequency derivatives of its effective constitutive parameters in accordance with Poynting's theorem in dispersive lossy medium clarified for this case in the paper.
The dynamics of the onset of oscillations in a wave guide cavity based Gunn Oscillator (GO) has been critically examined through numerical simulations and experimental studies.The transition of the GO from a non-oscillatory to an oscillatory state and the same in the reverse direction occurs at different critical values of the dc bias voltage applied to the GO. In presence of a weak RF field in GO cavity, oscillations with broad band continuous spectrum and multiple discrete line spectrum are observed at the GO output for different values of dc bias below the above mentioned critical values. Analysing the numerically obtained time series data, chaos quantifiers have been obtained to prove the occurrence of the chaotic oscillations in the GO. Experimental results and observations of numerical simulation show good qualitative agreement.
The adoption of microwave imaging as a tool for non-invasive monitoring of brain stroke has recently gained increasing attention. In this respect, the paper aims at providing a twofold contribution. First, we introduce a simple design tool to devise guidelines to properly set the working frequency as well as to choose the optimum matching medium needed to facilitate the penetration of the probing wave into the head. Second, we propose an imaging strategy based on a modified formulation of the linear sampling method, which allows a quasi real time monitoring of the disease's evolution. The accuracy of the design guidelines and performance of the imaging strategy are assessed trough numerical examples dealing with 2D anthropomorphic phantoms.
Network fade countermeasures for link budget can be better implemented based on the knowledge of seasonal variability of rainfall attenuation in a locality. Therefore, in this study, a seasonal approach is applied to estimate the effects of spatial rainfall attenuation in Durban (29^{o}52'S, 30^{o}58'E), South Africa using two-year rainfall data obtained from the RD-80 Joss-Waldvogel (J-W) distrometer. An analysis is undertaken for different seasons to obtain the rainfall rate exceedences at 0.001%, 0.01%, 0.1% and 1% of time. Consequently, rainfall drop-size distribution (DSD) models are developed for the control site at different seasons for the same period. The probability density analysis for each model indicates that the lognormal distribution best fits the summer and autumn season with percentage root-mean-square errors (RMS) of 30% and 26% respectively; gamma distribution fits winter season with RMS error of 16% and Weibull distribution fits spring season with RMS error of 26%. The results from the rainfall rate and rainfall DSD are combined to estimate the rainfall specific attenuation, by applying spherical droplet assumption for Mie scattering techniques, between 2 GHz and 1000 GHz. With this, the seasonal k and α coefficients for specific attenuation are derived from the best rainfall DSD models, using regression technique at 2.5 GHz, 25 GHz, 40 GHz and 100 GHz. At these frequencies, the results show that the predicted specific attenuation coefficients for all seasonal rainfall rates at the control site are lower, when compared to those from ITU-R models. It is concluded that specific attenuation levels may be similar and more intense in summer and autumn seasons, while, lower and less intense in autumn and winter seasons at similar rainfall rates.
Multiple signal classification (MUSIC) algorithm has been applied to localize small scatterers for super-resolution imaging. A problem associated with this application is the estimation of the number of scatterers in presence of noise and multiple scattering between targets. In this paper, we show that the mathematical model behind the scattering from the small objects is well compatible with the minimum description length (MDL) model. This leads us to use the MDL so as to estimate the number of scatterers before application of the MUSIC algorithm. As the MDL assumes the sources are independent, the nearby wave sources are grouped together to improve the independency criterion. The application of MDL to synthetic and experimental data verifies accurate estimation of the target number with low complexity, even if the data embodies significant noise and multiple scattering.
A coplanar rectangular slot antenna operating in the very wide frequency band from 0.27 to 3.1 GHz (bandwidth over 166%) has been designed for GPR applications. The antenna, which is supposed to be positioned on the soil surface, appears particularly compact (34 x 29 cm^{2}) and exhibits a low cross-polarization in the E-plane. 3D FDTD simulations have allowed to make a detailed parametric study associated with the antenna dimensional parameters in order to optimize the radiating performances. The slot antenna has also been studied with a shield to be further integrated in a bistatic subsurface radar positioned on the soil surface. Simulated results of the link in the presence of a homogeneous soil then including buried objects met in civil engineering structures are presented and discussed. First experimental results on a sandy soil have been compared to numerical ones.
We report the transmission response of generalized Fibonacci photonic crystal F_{l}(m,n) in microwave domain for normal incidence, where l is the generation number, and m and n are parameters of the Fibonacci distribution. The transmission spectra are calculated through the transfer matrix method and studied by varying the Fibonacci parameters. The structure is exploited to design a microwave mirror with large photonic band gap and polychromatic stop band filters. Therefore, other structure configurations based on the generalized Fibonacci system are proposed. A juxtaposition of p multilayer systems built according to Fibonacci distribution [F_{l}(m,n)]^{p} makes possible to have switches like property (off-on-off-on-off-on-…). Then, an hybrid structure which is obtained by sandwiching p stacks of generalized Fibonacci photonic crystal between two periodic photonic crystals is proposed to enlarge the photonic band gap in microwave domain.
A mesh generation algorithm for the Method of Moments (MoM) is described. The algorithm, named CGSM, can mesh arbitrary planar shapes described with line segments and circular arcs into mixed triangular and rectangular cells. CGSM creates contours of the meshed shape and uses them to provide edge mesh (denser mesh near edges), creates an adaptive grid and uses it to insert axis-aligned rectangles in the interior, and finally, triangulates the remaining area (the Delaunay condition is imposed on the triangulation). CGSM is compared to two commercial applications (Designer® and IE3D™) on the example of a 2-GHz hybrid ring coupler. The same simulation results are obtained. However, with CGSM, simulation time is significantly reduced.
The design of wireless technology which involves radio frequency identification (RFID) and Bluetooth technology for tagging and transmission of data that will be applied to point of sale (POS) is presented. A complete POS circuitry system has been designed to allow certain item to be a tag easily identified and localized. This is implemented by using RFID technology which will communicate with personal computer (PC) either through Ethernet or Wifi connection. An Impinj RFID reader and Bluetooth mobile phone are selected in the proposed POS system. Matlab simulation has been performed for RFID transceiver part and Bluetooth data transmission. A prototype software is developed to interface the Impinj RFID reader through the Ethernet connection. Additionally, a data encryption from Bluetooth is paired with PC to achieve a secure and simple pairing feature when customer transaction is performed. It involves hardware and software implementation. Moreover, in simulation result, a double side band modulation is used to design the RFID reader for better item tagging. The results show the feasibility of using this design for POS and achieving very good read ranges. Finally, Bluetooth system enables fast transaction and makes purchase securely by using the proposed asymmetric algorithm.
We previously reported on the complex permittivity and dc conductivity of waste-activated sludge. The measurements, spanning a frequency range of 3 MHz to 40 GHz, were made using an open-ended coaxial transmission line. Although this technique is well established in the literature, we found that it was necessary to combine methods from several papers to use the open-ended coaxial probe to reliably characterize biological samples having a high dc conductivity. Here, we provide a set of detailed and practical guidelines that can be used to determine the permittivity and conductivity of biological samples over a broad frequency range. Due to the electrode polarization effect, low frequency measurements of conducting samples require corrections to extract the intrinsic electrical properties. We describe one practical correction scheme and verify its reliability using a control sample.
Fractal-shaped microwave passive circuits offer a great deal of promise for achieving good performance in small circuits. In this paper, isosceles right-angled triangular patch resonator with fractal hole is analyzed, and new single band and dual-band RF filters by using isosceles right-angled triangular patch resonators with fractal pattern are proposed. It is shown that with the assistance of a fractal, the right-angled triangular resonator can be miniaturized and filter performance is greatly improved, simultaneously, resonance of the resonator higher order mode is enhanced, which is helpful for a dual-band filter implementation. Two proposed fractal bandpass filters are fabricated, and their performance is verified by measurement. The proposed filters demonstrate the applications of right-angled triangular patch resonator and exhibit advantages of a simple structural topology and compactness, which are essential in RF circuit design.
A hybrid technique for the analysis of pyramidal and conical horn antennas is presented based on an exact vector Dirichlet to Neumann (DtN) mapping mathematical formalism. The transition from the feeding waveguide to the radiating aperture is analyzed by using the mode matching technique (MMT) employing a stepped-waveguide approach. Love's field equivalence principle is employed for the denition of equivalent electric and magnetic current densities at the horn aperture. Explicitly, these currents are located at a plane parallel to the aperture but slightly shifted inwards in order to implement an offset Moment Method for their discretization, which is free of integral singularities. The unbounded area field generated by these sources is enforced to be continuous with the internal mode matching field by strictly following DtN principles. Besides that, this procedure mimics a By-moment approach ensuring the decoupling of the required number of modes from that of the sources discretization degrees of freedom. Finally, the implemented hybrid method is validated against published experimental and numerical results for a number of pyramidal and conical horn antennas including various corrugated geometries.
A large class of angle sensors uses a small permanent magnet attached to the rotor. The magnet is polarized perpendicularly to the axis of rotation, and a magnetic field sensor is placed ahead on the axis. The sensor circuit consists of two full bridges at 45^{o}, each having four anisotropic magneto-resistive (AMR) elements. Even though the electronic system may be calibrated to have nearly no errors like offset, nonlinearity, and mismatch, still significant angle errors may result from assembly tolerances of the magnet and the sensor. This work gives an analytical description of the angle error caused by tilts and eccentricities of magnet and sensor elements against the axis of rotation. Particular emphasis is given to worst case combinations of all tolerances. One part of the angle error can be cancelled by an optimized layout of the AMR-resistors. The remaining part is identical to the case of giant magneto-resistive (GMR) angle sensors. Errors of both AMR and GMR angle sensors are effectively reduced by identical optimization of the shape of magnets. One such optimized shape is disclosed.
The effect of 850 MHz electromagnetic radiation on diabetic blood at 2 W and 60 W power levels was investigated and compared with normal blood cells. The power levels respectively represent radiations from a cell phone and the cell phone tower, both operating 850 MHz. A GTEM cell was designed for the tests to generate the desired uniform electromagnetic field and power in a shielded environment. Blood samples, having normal and high glucose concentrations, were placed in the usable area inside the GTEM cell for 10, 30, 60 minutes and the glucose levels and red and white blood cell viabilities were monitored and compared with the controls. Results show that the 850 MHz exposure significantly influences the blood cell counts and the glucose level in both normal and high glucose blood samples. In cell survivability analysis in normal blood samples it was found that the white blood cells are significantly higher than the control at 60 min exposure from cell phone radiation, while both the white and red blood cell are significantly higher following a 30 min exposure from tower radiation. For high glucose blood tests at 30 and 60 min exposure times, the tower radiation for 60 min and the cell phone radiation at both the exposure times show significantly changes in white blood cell counts, whereas there was no effect in red blood cells. Also, for 30 and 60 min exposure times, the glucose level in normal blood samples increased from cell phone radiation and decreased due to tower radiation. Finally, in high glucose blood samples, the glucose level decreased significantly for a 30 minute tower exposure, while the glucose level increased significantly for the cell phones exposure duration of 60 min and for tower exposure duration of 10 min. Electromagnetic radiation effects on cells can be better analyzed through a combination of the frequency, power and test duration as a single factor as opposed to the effects of frequency alone.
In this paper, mathematical analysis supported by computer simulation is used to investigate the impact of both system and propagation loss parameters on the performance of cellular wireless network operating at microwave carrier frequencies greater than 2 GHz, where multiple tier of co-channel interfering cells are considered to be active. The two-slope path loss model and the uplink information capacity of the cellular network is used for the performance analysis. Results show that for carrier frequencies greater than 2 GHz and smaller cell radius multiple tier of co-channel interfering cells become active as compared to carrier frequencies lesser than 2 GHz. The multiple tier of co-channel interfering cells, leads to a decrease in the information capacity of the cellular wireless network. The results also show that the system performance is sensitive to most of the propagation model parameters such as the basic and extra path loss exponent.
Axial permanent magnetic couplings are composed of two discs with a small air-gap in-between. Each disc consists of several segments in the shape of slices of cakes. The segments are polarized in axial direction with alternating polarity. In this work the homogeneous magnetization in the segments is replaced by equivalent currents on the surface of the segments (Amperean model). In a simplified model we consider only radial currents whereas azimuthal currents along the perimeter of the discs are discarded. This corresponds to the arrangement where one of the discs has much larger diameter than the other disc. Compared to the case of two equal discs it leads to a notable error in the magnetic field near the perimeter, yet it has only a small effect on the torque, especially for the case of optimum couplings. This trick allows for summing up the fields of all segments in closed form. A concise double integral over the radial magnetic field component describes the torque. An investigation of this integral reveals many properties of axial magnetic couplings: A diagram is introduced and areas in this diagram are identified where the torque shows overshoot, rectangular pulse shape or sinusoidal dependence versus twist angle between bothdiscs. The diagram contains also a curve for maximum torque and one point on this curve is of considerable economic significance: It denotes the global maximum of torque over magnet mass.