In this paper, we propose a generalized Wilkinson power divider operating at two arbitrary frequencies with unequal power dividing ratio. To achieve unequal power division and perfect matching at dual-frequency, a novel structure consisted of four dual-frequency transformers in two sections is proposed. For the compact power divider, the parallel and series RLC structures can be chosen to obtain effective isolation between the two outports according to different frequency ratios. Furthermore, the closed-form design equations of the unequal dual-frequency power divider are derived based on circuit theory and transmission line theory. Finally, simulation and experiment results of two examples including parallel and series RLC structures indicate that all the theoretical features of these unequal power dividers can be fulfilled at dual-frequency simultaneously.
Microwave methods require some sort of calibration before physical (thickness, flaw, etc.) and electrical (permittivity, permeability, etc.) measurements of materials. It is always attractive to devise a method which not only eliminates this necessity but also saves time before measurements. Microwave calibration-independent measurements can be utilized for this goal. However, in the literature, these measurements are only applied for electrical measurements of materials. In this research paper, we investigate the performance of microwave calibration-independent measurements for thickness evaluation of dielectric materials to increase the potential of available microwave techniques for thickness evaluation of dielectric materials. We derive an explicit expression for thickness estimation of dielectric materials from calibration-independent measurements for the adopted calibration-independent technique. We also propose a criterion for increasing the performance of measurements. We conducted thickness measurements of six dielectric specimens with different lengths to validate the derived expressions and the proposed criterion for thickness measurements.
This paper presents a diagnosis method for articular cartilage damage using polarization-sensitive optical coherence tomography (PS-OCT). Through signal analysis, the optical characteristics of intact cartilage and different types of mild lesions within cartilages can be quantified from measures such as the scattering coefficient (μs), effective anisotropy factor (geff), and birefringence coefficient (Δn). Our preliminary investigation using porcine articular cartilage indicated that both subsurface morphological changes and apparent variations in optical properties, which may be the early signs of cartilage degeneration, were found in three types of diseased cartilages.
In this work, frequency behavior of the multilayer structure comprised of double-negative (DNG) and dielectric slabs is presented in detail. The multilayer structure consists of N pieces DNG and dielectric slabs with different material properties and thicknesses. The incident electric field is assumed to be a monochromatic plane wave with any arbitrary polarization. The DNG layers are realized using the parameters of Lorentz/Drude type metamaterials. Transfer matrix method is used in the analysis to find the characteristics of the reflected and transmitted powers. Finally, the computations of the powers for two structures are demonstrated in numerical results for the application to design efficient filters at the microwave, millimeter wave, and optical frequency regions.
Dispersion characteristics of two types of two-dimension dielectric plasma photonic crystal are studied based on modified plane wave method. Firstly, the eigenvalue equations of TM mode of type-1 and type-2 structures are derived respectively; their dispersion curves are confirmed by the software simulation. Secondly, the influences of normalized plasma frequency, filling factor and relative dielectric constant on photonic band gap, and relative photonic band gap width are analyzed respectively, and some corresponding physical explanations are also given. These results would provide theoretical instructions for designing new photonic crystal devices using plasmadielectric structure.
Pulsed-current sensors require transducers constituted of magnetic materials with high magnetic permeability in a frequency range compatible with the period and the frequency of the current pulse. The use of ferrites in this application has the advantage of low cost and low losses in high frequencies. The aim of this work is to present a procedure for selection of the ceramic processing route of Ni-Zn ferrite for application in a pulsed-current sensor. The ferrite samples were prepared under different processing parameters and characterized in terms of microstructure, chemical analysis, complex magnetic permeability, and magnetic hysteresis. The chosen processing route included high energy milling of the pre-sintered powder, its disaggregation before sample forming, and sintering of the samples in air for 2h at 1300οC. Tests were performed and it was verified that using this processing route for the fabrication of the sensor's core it was possible to monitor pulses of 0.1-1.0 μs.
We present a practical and simple method for calculating the mutual inductance between two non-coaxial circular coils with parallel axes. All possible circular coils such as coils of rectangular cross section, thin wall solenoids, thin disk coils (pancakes) and circular filamentary coils are taken into consideration. We use Grover's formula for the mutual inductance between two filamentary circular coils with parallel axes. The filament method is applied for all coil combinations, for coils of the rectangular cross section and for thin coils. We consider that the proposed method is very simple, accurate and practical for engineering applications. Computed mutual inductance values obtained by the proposed method have been verified by previously published data and the software Fast-Henry. All results are in a very good agreement. This method can be used in various electromagnetic applications such as coil guns, tubular linear motors, transducers, actuators and biomedical implanted sensors.
In this paper, the design, simulation, and fabrication of a double-ridged antenna is presented. The designed double-ridged antenna is most suitable as a feed element in reflectors of the radar systems and EMC applications. The designed antenna has a voltage standing wave ratio (VSWR) less than 2 for the frequency range of 8-18 GHz. Moreover, the proposed antenna exhibits satisfactory far-field radiation characteristics in the entire operating bandwidth. A coaxial line to rectangular double-ridged waveguide transition is introduced for coaxial feeding of the designed antenna. The proposed antenna is simulated with commercially available packages such as CST microwave studio and Ansoft HFSS in the operating frequency range. Simulation results for the VSWR, radiation patterns, and gain of the designed antenna over the frequency band 8-18 GHz are presented and discussed.
A through-wall imaging problem is tackled by means a linear inverse scattering approach described and numerically analyzed in previous works by the same authors. Here, such an approach is checked for against experimental data. To this end, a CW-SF ultrawideband radar system is used to take measurements in a controlled environment as well as for in situ experiments. Different types of scatterers and of obscuring walls are considered.
In this paper, we present a demodulation structure suitable for a reader receiver in a passive Radio Frequency IDentification (RFID) environment. In a passive RFID configuration, undesirable DC-offset phenomenon may appear in the baseband of the reader receiver. As a result, this DC-offset phenomenon can severely degrade the performance of the extraction of valid information from a received signal in the reader receiver. To mitigate the DC-offset phenomenon, we propose a demodulation structure to reconstruct a corrupted signal with the DC-offset phenomenon, by extracting useful transition information from the corrupted signal. It is shown that the proposed method can successfully detect valid data from a received signal, even when the received baseband signal is distorted with the DC-offset phenomenon.
The construction and comprehensive electromagnetic analysis of a novel class of WLAN layouts is presented in this paper. The main purpose is to construct a wireless system according to the 802.11 a/b/g standards, which enables significantly larger and more reliable data transfer rates, making use of a new largescale field prediction technique, based on the parabolic equation with finite differences. Thus, four distinct structures, based on two different operating systems and two different hardware architectures, are proposed and elaborately examined. On the other hand, for the prediction algorithm a 3D wide-angle parabolic equation scheme is devised and a recursive approximation of the forward wave equation is accomplished. Unlike existing methods that characterize obstacles by means of surface impedance boundary conditions, a more rigorous approach, by treating them as penetrable objects with known material features is utilized. In this manner, the "interface" problem is systematically formulated and high levels of accuracy are attained. Moreover, the proposed technique is proven to be sufficiently faster and numerically more efficient, as the lattice, so constructed, along with the numbering of degrees of freedom remain unchanged from a parabolic equation plane to another. Extensive results and measurements certify the aforementioned merits for various realistic exterior and interior configurations.
This paper presents a novel compact "via-less" UWB filter derived from a quarter-wavelength short-circuited stubs model. In this compact "via-less" UWB filter, there is no connecting vias as short circuit elements. Unlike its previous model that has 5 short-circuited stubs, this novel shape consists of two pairs of stubs which are joint together to share on the same microstrip patch and thus reduces total size of the UWB filter itself making it more compact in nature. With proper width optimization, the microstrip patch is able to decouple and provides low impedance to the ground in the UWB frequencies range. The filter delivers 3.85 GHz to 10.44 GHz frequency range with 92.23% of fractional bandwidth. The magnitude of insertion loss is below than 0.53 dB and the return loss is lower than -14.8 dB in the passband frequencies. The -3 dB bandwidth is from 3.85 GHz to 10.44 GHz with 92.23% of fractional bandwidth. The group delay only varied by 0.47 ns in the passband, which makes it suitable for radio communication systems.
In recent years, RFID solutions are finding an increasing number of applications in a wide variety of industries. There are some natural limitations when applying RFID technology in the steel industry, because the tags do not function well in metallic environments. Even though some commercial RFID metal tags are available in the market, they are found to be too expensive by steel companies. This paper proposes a useful and practical RFID tag design for management applications involving steel-bar and wirerod products manufactured by the steel industry. The dual-function metallic RFID tag, comprising of both an RFID code and a barcode, involves technology advancement in RFID design, and named Window-Tag (WinTag). The maximum read range of this tag can reach about 5.7m for the radiated power of 4.0W EIRP in free space. In the practical application, the maximum read ranges are about 2.3m and 5.0m for the worst and best case, respectively. The design methodology as well as simulation and measurement results of the WinTag are presented in this paper. The low profile and low cost features of the WinTag makes the RFID tag well suited for metallic type tag of labeling system that requires integration of RFID technology.
This study introduces the notion of 2-D and 3-D Phase Projection in our search for a simple and elegant solution to further reduce noise during InSAR post-processing steps with multiple baselines. Projection is a powerful tool to reduce noise in a system of more than two satellites. It does so by noting that the geometry of the satellite configuration restricts the range of values over which the wrapped phases can assume. Projection in general reduces noise in the system by utilizing the information provided by the configuration of the satellites to reduce the set of allowed phase points, thereby improving the robustness of the system in the presence of noise. Our results show that, for most cases, whether with the extremely small baseline distance or non-integer baseline ratios, using 3-D Projection gives better height inversion results.
This paper presents an efficient approach for analyzing the longtime response of high-speed dispersive and lossy interconnects terminated with nonlinear loads. In this approach, a fast real-time convolution algorithm with computational cost st O(N log2N) is suggested to tackle the long-time analysis of the high-speed dispersive and lossy interconnects, which are modeled by S-parameters. In addition, the acquirement of the S-parameters is recommended to adopt wideband closed-form formulas. The time response of a microstrip line with a nonlinear load is shown as a practical example. The dominant parameters affecting the response of this microstrip line is observed and discussed in detail. The approach demonstrates its efficiency and accuracy in the analysis.
A simple approach for evaluation of the reciprocity of materials using raw scattering parameter measurements is proposed. This approach not only reduces the overall measurement time but also eliminates the need for calibrating the measurement system since it uses calibration-independent measurements. We have derived a metric function for reflecting and nonreflecting cells, which are used to house the sample under test. This function does not depend on electrical properties of materials and their lengths, and whether the cell is reflecting. We have also investigated the effects of the sample length and air pockets between sample external surfaces and cell inner walls on the performance of the evaluation of sample reciprocity.
A promising microwave method has been proposed to accurately determine the complex permittivity of thin materials. The method uses amplitude-only scattering parameter measurements at one frequency for this purpose. It resolves the problems arising from any offset of the sample inside its cell in complex reflection scattering parameter measurements and from any uncertainty in sample thickness in transmission scattering parameter measurements. The method determines unique permittivity since, for thin samples, multi-valued trigonometric terms can be linearized. It uses higher order approximations to extract highly accurate permittivity values. It works very well in limited frequency-band applications or for dispersive materials since it is based upon point-bypoint or (frequency-by-frequency) measurements. For validation of the method, we measured the complex permittivity of two thin polytetrafluoro-ethylene (PTFE) samples.
Deterministic propagation models are typically validated by performing comparisons between real and simulated E-field envelope distributions. These distributions correspond to straight spatial segments and, occasionally, also surfaces. This approach is correct to study large scale fading for relatively large distances. However, in a real environment and shorter distances, there are too many details to consider. As a result, it is almost impossible to reach a point by point match in a minimally realistic experiment. There are two ways to deal with this problem. The first one is to model every minor detail everywhere around us, keeping the point by point metric. The second one is to change that metric in order to admit, at least in part, that we can not take into account of all the details. If uncertainty can not be eliminated, we should learn to take advantage of it by using a statistical metric like the one proposed here. This paper uses such a kind of metric to validate several structural and geometrical simplifications of a model for the transition between outdoor and indoor propagation that has been recently published. Furthermore, we demonstrate that this metric has helped us to improve and understand better this model, while revealing unexpected model properties at the same time.
Design and fabrication of optical code generating devices based on plastic optical fiber (POF) for security access-card system is presented. The POF waveguide coupler will utilize two basic designs: 1 × 2 Y-branch coupler as the main device structure and 1 × 2 asymmetric coupler which allows non-symmetric optical power splitting. The Y-branch coupler are based on two designs: A metalbased POF coupler with a hollow taper waveguide and an acrylicbased POF coupler with optical glue for the taper waveguide region. The Y-branch device is composed of input POF fiber, middle taper waveguide and output POF fibers. Simulation based on non-sequential ray tracings have been performed on both types of POF couplers. Low cost aluminum and acrylic based materials are used for the substrates. Fabrications of the POF couplers are done by producing the device mold insert using CNC machining tool and POF fibers are then slotted into the Y-branch coupler mold insert. The insertion loss for both devices are about 8 dB.
An analytical investigation of the lightwave propagation through dielectric optical fibers with helical clads is presented with the emphasis on their field patterns. The helical clad section is effectively realized by introducing conducting windings on the core-clad boundary. Using Maxwell's equations, a rigorous analytical approach is implemented to determine the field patterns in such fibers. For simplicity, two particular values of the helix pitch angle are considered, viz. 0°and 90°. The nature of fields is presented in both the situations corresponding to different allowed values of the propagation constants and the fiber diameters. The radial distributions of fields are presented under different situations, which exhibit the patterns like spikes. The observed smooth match of the fields at the core-clad interface validates of our analytical approach. The presence of a little higher amount of field in the fiber clad section is essentially attributed to the helical windings introduced over the fiber core. Further, the existence of considerable amount of evanescent waves in such fibers opens up the possibility of their applications in optical sensing.
This paper presents some improved three-dimensional expressions of the magnetic field created by tile permanent magnets uniformly and radially magnetized for the design of ironless loudspeaker structures. All the expressions determined have been reduced to compact forms. We use these expressions for the optimization of ironless loudspeaker structures in which the radial field must be radially uniform. Indeed, as ring permanent magnets radially magnetized are rather difficult to manufacture, these magnets are replaced by assemblies of tile permanent magnets radially and uniformly magnetized. We present an example of ironless loudspeaker structure that has been optimized with our threedimensional approaches.
Scattering from a two-dimensional (2-D) perfectly electrically conducting (PEC) cylinder partially embedded in a random dielectric rough surface interface is studied using the method of moments (MoM) with pulse basis functions and the point matching technique, for the case of horizontal polarization. The random rough surface is modeled using Gaussian statistical characteristic for the rough surface height and surface correlation function, and generated by the spectralmethod. The tapered plane-wave incidence is used to avoid artificial edge diffraction due to the truncation of the rough surface into finitelength rough surface in the numerical simulations. With the developed algorithms, the interactions between the dielectric rough surface and the partially buried PEC cylinder are investigated using the Monte Carlo simulation, and are expressed as a function of the root mean square (rms) height of a random dielectric rough surface and the moisture content of the soil. The numerical results show that the bistatic scattering coefficients are dependent upon the moisture content, the rms height of a rough surface, and other parameters.
We study the radio wave propagation at VHF frequencies in a forested environment using a three-layer anisotropic slab model. The analytical solution to the slab model is implemented numerically to generate broadband data. The data are then transformed into the time domain. The various propagation mechanisms including the direct wave, the lateral wave, the multi-reflected slab waves and the multi-bounce lateral waves are investigated based on their respective times-of-flight. Our results show that the dominant propagation mechanisms are highly dependent on the effective permittivity and conductivity of the forest layer. We then utilize the numerical solution to extract the effective medium parameters of the forest based on the published measurement data of Hicks et al. Good agreement between the fitted model and the measurement data is achieved. The extracted effective permittivity and conductivity of the forest layer show considerable anisotropy and frequency dependence.
This work presents a new indoor localization method based on the fingerprinting technique. The proposed method uses a ray-tracing model that provides information about multipath effects. This information is stored in a dataset during the first stage of the fingerprinting method. The direction of arrival (DOA) and received signal strength (RSS) are used in the fingerprinting technique as a hybrid system. The localization estimation is calculated while taking into account the Euclidian distance between the DOA and the RSS from each unknown position and the information of the fingerprints. Numerical calculations were performed to show the mean and the standard deviation of the estimated error.