A matrix technique for the computation of the per-unit-length internal impedance of radially inhomogeneous cylindrical structures is presented. The cylindrical structure is conceptually divided into a number of layers, each layer being characterized by its constitutive parameters, conductivity, permeability, and permittivity. Within this general framework, compound conductors, compound capacitors, compound magnetic cores, or any other compound structures resulting from a mix of the above, can be analyzed by using the very same tool. The developed software program, MLCS, which implements the mentioned matrix technique, also permits the evaluation of the electric and magnetic fields intensity at the layers' interfaces. The MLCS program is validated by using several application examples.
This paper is devoted to a laser --- based diagnostic technique described as a method for solving an applied inverse problem in turbulent media using laser beam propagation. This problem consists of extracting local information about temperature fluctuations inside a hot turbulent jet of air, from the luminous photodiode trace produced by a laser beam, after having traversed the jet. A genetic algorithm is implemented in order to calculate the optimized laser beam directions corresponding to the whole luminous trace. An approximated ray equation which is proved from the geometrical optics is solved numerically by using those directions and enables to determine the variance of temperature fluctuations along the whole path of the laser beam. A good agreement coming from the comparison between the results obtained and the published experimental data proves the validity of the method.
^{}_{}A rigorous and efficient spectral domain formalism is presented of a plane wave-excited subwavelength circular aperture in a planar perfectly conducting metallic screen of infinitesimal thickness, based on the Bethe-Bouwkamp quasi-static model. The formulation utilizes a transmission line analogue of the medium, which facilitates the inclusion of planar multilayered material samples, where the latter may exhibit uniaxial anisotropy. The transmitted field components are expressed in terms of one-dimensional Hankel transform integrals, which can be evaluated by efficient numerical procedures. Sample results are presented showing the intensity profiles and polarization states of transmitted light penetrating into a semiconductor layer.
The fading phenomenon resulting from standing waves is a factor in quality deterioration in mobile communication technologies (e.g., cellular phones and television receivers). Suppression of this fading phenomenon is needed for many kinds of technologies. A single-feed planar antenna composed of two antenna components, a Planar Monopole Antenna (PMA) and a Planar Slot Antenna (PSA), is proposed for reducing deterioration of reception due to the fading phenomenon. Reflection coefficient and radiation patterns are analyzed by the Finite Difference Time Domain (FDTD) method and compared with measured results. Results indicate that the proposed antenna has a resonant frequency with functions of the PMA and the PSA. The results of a field experiment at 583.76MHz in the Ultra High Frequency (UHF) band indicate that the proposed antenna efficiently suppresses the fading phenomenon resulting from multipath propagation.
Non coaxial mutual inductance calculations, based on a Bessel function formulation, are presented for coils modelled by an explicitly finite number of circular turns. The mutual inductance of two such turns can be expressed as an integral of a product of three Bessel functions and an exponential factor, and it is shown that the exponential factors can be analytically summed as a simple geometric progression, or other related sums. This allows the mutual inductance of two thin solenoids to be expressed as an integral of a single analytical expression. Sample numerical results are given for some representative cases and the approach to the limit where the turns are considered to be smeared out over the solenoid windings is explored.
Recent research into very large, regularly shaped, geological structures has shown that in the 100 kHz to 10 MHz frequency range electromagnetic waveguide behaviour is observed when the material forming the structure is not too lossy (conductivity σ<0.0001). While mode formation and modal behaviour in electromagnetic waveguides is very well understood, much of the literature describes high frequency structures for which it can generally be assumed that the loss tangent of the wave guiding medium (tanδ) is very much less than unity. In this case wave attenuation is small and can generally be considered to be insignificant. This is not true for large low frequency waveguides, such as those formed by geological strata, and little seems to have been reported in the literature on the nature of modes in waveguides of this description. The paper takes the form of a parametric study aimed at ascertaining the limitations to modal formation in waveguides, for which tand is greater than unity, by revisiting the basic equations describing electromagnetic wave propagation in lossy media. The theoretical predictions are supported by modelling studies on large waveguide strata formed from material layers with dimensions typical of a geological structure such as a coal seam or oil-wet, strata-bound, petroleum reservoir.
Local multipoint distribution service (LMDS) is a broadband wireless access technology that operates at microwave frequencies above 25 GHz. However, severe attenuation due to excessive rain in tropical regions presents a major challenge for achieving reliable communication over such frequencies. To overcome this problem, cell-site diversity (CSD) can be deployed in cellular-type LMDS networks. In this paper, we address the problem of reliable communication for LMDS networks in heavy rain regions by proposing a fuzzy weight controller based cell-site diversity (FWC-CSD) scheme. Rain cells are randomly simulated in an LMDS network to analyze the system performance using the proposed FWC-CSD scheme. Simulation results show that the proposed scheme yields improved performance in terms of average outage probability and throughput while maintaining the overall quality of service.
The early identification of malignant tissue is one of the most significant factors in the successful treatment of breast cancer. Microwave imaging is an emerging breast screening modality based on the dielectric contrast between normal and cancerous tissues at microwave frequencies. When the breast is illuminated with an Ultrawideband (UWB) microwave pulse, the dielectric contrast between normal and cancerous tissues generates electromagnetic reflections. These reflected signals, containing tumor backscatter, are spatially focused using a beamformer which can compensate for attenuation and phase effects as the signal propagates through the breast. However, recent studies have shown the breast to be a dielectrically heterogeneous entity. High levels of heterogeneity reduce the dielectric contrast between normal and cancerous tissue, limiting the effectiveness of beamforming algorithms. One possible method to assist in the diagnoses of cancer in a heterogeneously dense breast is the use of contrast agents. Contrast agents modify the dielectric properties of a malignant tumor site in order to increase the dielectric contrast with fibroglandular tissue. In this paper, a number of beamforming algorithms are applied to MRI-derived models with endogenous and contrast enhanced malignant tissue properties. Two contrast agents are applied to heterogeneously dense breast phantoms and simulations are carried out prior and post contrast agent delivery. A range of tumor diameters are simulated and a number of beamforming algorithms are applied to the simulated data. The resulting differential scans are then compared across a range of appropriate metrics.
In implementing electromagnetic vulnerability (EMV) testing on operational helicopters fielding a variety of avionic, communication, and weapons systems, the testing levels as spelled out in MIL-STD-464A require most test labs to position the high power source antennas unreasonably close to the test item (sometimes within 2 m). Questions naturally arise concerning the efficacy of such testing with respect to both the manner of coupling of the fields to the helicopter systems as well as the levels required to achieve reasonable confidence in the coupling effects. This paper presents a comparison of the electric fields interior to an axially slotted circular cylinder and the fields in the slot aperture as a function of the distance from the source to the test item. Also, these measured interior and aperture fields are compared to two different mathematical/numerical models of the conducting cylinder with an axial slot running the length of the cylinder. Additional measurements are presented for the fields interior to a finite cylinder with conducting endcaps and a significantly reduced slot of finite length. Comparisons to one of the mathematical/numerical models for this finite length cylinder with finite length slot are presented also.
We investigate the localized surface plasmon resonances (LSPR) of a pair of dielectric-core/silver-shell nanospheres, with and without a silver nanobar connecting them, for different values of the permittivity of the dielectric core, using the finite element method. Results show that the structure of a pair of core shells with a nanobar possesses a distinct blue-shifted behavior that can be manipulated from near infrared to visible light. The near field intensity can be enhanced by several orders of magnitude and the working wavelengths depend on the shell thickness, dielectric medium in hollow metallic shell and the diameter of the nanobar. In addition, three or more pairs of nanospherical chain waveguides have also been investigated in our simulations.
A novel kind of room temperature terahertz photodetector based on Electromagnetically Induced Transparency (EIT) is presented. The main idea for room temperature and THz range operation is reduction of dark current which is done by converting of the incoming terahertz signal (long-wavelength Infrared signal) to short-wavelength field through EIT phenomena. For realization of this idea, we examine EIT phenomena in multi levels atomic system and quantum wells cascade structures. In the proposed structure the quantum interference between long wavelength and short-wavelength radiation modifies the absorption characteristic of short-wavelength probe field. By this means, the terahertz signal does not interact directly with ground state electrons, but affects on the absorption characteristics of the short-wavelength or visible probe optical field which directly interact with ground state electrons. Therefore, the important thermionic dark current in terahertz detection, can be strongly reduced. So, the proposed idea is appropriate for terahertz and room temperature applications.
Applying four-dimensional differential-form formalism, a novel class of electromagnetic media, labeled as that of P-media, is introduced in terms of a simple rule. It is shown that it is not possible to define the medium by expressing D and B in terms of E and H, whilst using 3D Gibbsian vectors and dyadics. Moreover, the basic properties of P-media are shown to be complementary to those of the previously known Q-media, which are defined in a somewhat similar manner. It is demonstrated that, for plane waves in a P-medium, there is no restriction to the wave one-form (corresponding to the k-vector). Importantly, the uniaxial P-medium half space also leads to another realization of the recently studied DB boundary conditions. Finally, a generalization of the class of P-media is brie y discussed. It is shown that the dispersion equation of a plane wave in the generalized Pmedium is decomposed into two conditions, each of which corresponds to a certain polarization condition. This occurrence resembles the behaviour of the generalized Q-medium.
We present an efficient way to generate the inverse synthetic aperture radar (ISAR) image of a target at an arbitrary aspect angle using the shooting and bouncing ray (SBR) method, which is much faster than the conventional approach by inverse Fourier transforming the computed scattered fields over frequency and aspect domain. We propose a general image-domain ray-tube integration formula, which contains aspect-dependent factors. The new formula can provide ISAR images of a target rapidly and conveniently in different image planes at different aspect angles in a world coordinate system. The ISAR images of a cube and an aircraft for several aspect angles and different image planes are presented to demonstrate the efficiency and accuracy of the general formula. The proposed method is more significant when large amount of ISAR images of a target are required to build the database for target recognition.
After being modulated by a periodic signal, the pulse compression result of the modulated LFM (Linear Frequency Modulation) may have many isolated and sharp peaks. According to this phenomenon, we developed a strip-map SAR (Synthetic Aperture Radar) jammer which modulated both the SAR's fast and slow time LFMs with periodic waveforms. This kind of jamming can forge isolated and bright points in the SAR image, and may confuse the SAR's image processing. The structure of this kind of jammer is simple and easy to be designed comparing to that of a traditional jammer utilizing the coherent jamming. Also it only needs much lower transmitted power than a noise jammer. Finally, the jamming experiences were conducted by utilizing a railway SAR, and the SAR imaging results showed the effectiveness of this kind of jamming.
In this paper, we analyze the behaviour of a switched mode power supply (SMPS) regarding the radiated magnetic nearfield through an initial understanding of the electrical working of the converter, particularly during switchings. We propose a method based on impedance analysis at each state of the converter in order to predict the resonances of currents and/or voltages in the SMPS at the origin of the magnetic radiated near-field.
In this paper, we describe the design of a hybrid 24 GHz RADAR array for termite detection and imaging. The array uses MIMO techniques to provide transmit beam steering and null steering in conjunction with the Matrix Enhanced Matrix Pencil (MEMP), which provides direction of arrival processing. We describe the selection of our MIMO orthogonal codes and test their suitability. Simulated results are shown for our array design and MIMO processing in a range of applications MIMO enables us to produce flexible nulling and beam steering for our transmitter array as well as reducing multipath re°ections and narrowband interference. MIMO processing also produces large time savings, enabling longer, more accurate acquisitions which can increase SNR. Transmitter beam-forming, produces an SNR improvement of 18.2 dB and can be used to reject clutter by up to 20 dB. Flexible nulling can reject interferers still further.
A fully-integrated bandpass filter using Q-enhanced and semi-passive inductors is design, implemented, and verified experimentally in a standard 0.18-μm CMOS process. The inductors achieve high-Q factors by using a tapped-inductor feedback technique to produce negative resistances. Compared with conventional transformer feedback, the proposed technique not only compensates resistive losses with low-power consumption but also provides a high-inductance inductor which is suitable for low-frequency applications. The 2-pole Chebyshev series-C coupled bandpass filter provides a frequency tuning range of 300 MHz around 2.65 GHz. Measurements shown that it consumes 2.4 mW to achieve 1.0-dB insertion loss, 12-dB return loss, 6.3-dB noise figure, and --- 2.5-dBm input P_{1dB} with a 950-MHz bandwidth at 2.8 GHz. And it consumes 5.6 mW to achieve 1.5-dB insertion loss, 10-dB return loss, 7.9-dB noise figure, and --- 4-dBm input P_{1dB} with a 700-MHz bandwidth at 2.5 GHz. The overall chip size of the filter is 0.7 mm×0.9 mm including all testing pads.
Forward scattering effects have been studied and compared when nonhomogeneous medium is illuminated by coherent and quasi-noise sources operating in mm-wave and microwave ranges. Double-layers dielectric structure simulating Fabry-Perot resonator properties was employed to develop a relevant model used for comparing transmittances of both coherent and noise signals. Experiments with nonhomogeneous materials such as coal, wood chips, sand and others have proved the basic modeling predictions and the role of noise bandwidth in averaging process important for material characterizations. It was found out that efficient averaging associated with noise nature of probing signal can be reached for the relative noise bandwidth of 25% and more.
This paper studies the surface modes at the interface of finite size Electromagnetic Band Gap (EBG) woodpile structures. The impact of different types of woodpile terminations on the properties of these surface modes is analyzed. For all the studied terminations there exist surface modes which must be taken into account when designing components based on this EBG structure.
Recently, the use of the particle swarm optimization (PSO) technique for the reconstruction of microwave images has received increasing interest from the optimization community due to its simplicity in implementation and its inexpensive computational overhead. However, the basic PSO algorithm is easily trapping into local minimum and may lead to the premature convergence. When a local optimal solution is reached with PSO, all particles gather around it, and escaping from this local optima becomes difficult. To overcome the premature convergence of PSO, we propose a new hybrid algorithm of particle swarm optimization (PSO), simulated annealing (SA) and tabu search algorithm (TS) for solving the scattering inverse problem. The incorporation of tabu search (TS) and simulated annealing (SA) as local improvement approaches enable the hybrid algorithm to overleap local optima and intensify its search ability in local regions. Reconstructions of dielectric scatterers from experimental inverse-scattering data are finally presented to demonstrate the accuracy and efficiency of the hybrid technique.