The unified theory of near-field-far-field transformation techniques with spiral scannings for quasi-spherical antennas is extended in this paper to the case of nonspherical ones, i.e., antennas with two dimensions very different from the third one. To this end, such a kind of antennas is no longer considered as enclosed in a sphere, but in a proper convex domain bounded by a rotational surface. The extension, heuristically derived by paralleling the rigorous procedure valid when adopting the spherical source modelling, allows the overcoming of its main and serious drawbacks. In fact, the corresponding near-field-far-field transformations with spiral scannings for nonspherical antennas make use of a reduced number of near-field measurements and, above all, allow one to consider measurement surfaces at a distance smaller than one half the antenna maximum size, thus remarkably reducing the error related to the truncation of the scanning zone. These are very important features, which make the spiral scannings more and more appealing from the practical viewpoint. Some examples of the application of this theory to spirals wrapping the conventional scanning surfaces employed in the near-field-far-field transformations are reported for various source modellings, and the accuracy and robustness of the far-field reconstructions are assessed.
The pump power and thulium-doped fiber (TDF) length for both single-pass and double-pass Thulium-Doped Fiber Amplifiers (TDFA) are theoretically optimized by solving differential equations. The 1050 nm pump is used to provide both ground-state and excitedstate absorptions for amplification in the S-band region. The TDFA is saturated at a shorter length with a higher gain value as the operating pump power increases. The double-pass TDFA allows double propagation of the test signal in the gain medium, which increases the effective TDF length and thus improves the gain of the TDFA compared to the single-pass configuration. Therefore, a small signal gain improvement of approximately 15 dB is obtained in the 1465 nm region. However, a noise figure penalty of approximately 1 dB is also obtained in this wavelength region. The theoretical result is in agreement with the experimental result.
This paper presents a class of ultra-thin metamaterial absorbers, which consists of periodic microstrip lines on top of a planar lossy substrate backed by a conducting metallic plate. A highly efficient full-wave analysis method was developed to solve the electromagnetic response of the absorbers. The in uence of electromagnetic properties of the substrate and physical dimensions of the microstrip lines were analyzed. Genetic algorithm was used to optimize the absorption bandwidth of the absorbers. Effective permeability and permittivity of the absorbers were retrieved to shed a new light on the absorption mechanism of the absorbers and to explain their ultimate bandwidth limit. It was found that the ultimate bandwidth limit of the metamaterial absorbers is the same as that of normal absorbers.
The present paper sets out to present a numerical electromagnetic (EM) method TWA for EM field modeling of planar structures. Combining both the benefits of TWA process and the modeling of planar excitation source, an optimization technique AMT is applied and evaluated in context of RF integratedcircuit applications. The computational complexity of TWA process is examined and the obtained simulation results are found to be in good agreement with literature.
In this paper we investigate boundary effects and other consequences of spatial dispersion by analyzing in detail the response of a metamaterial half-space to a monochromatic plane wave normally incident from free-space. The metamaterial is composed of an orthorhombic lattice of identical particles, each of which exhibits both an electric and magnetic response. Rather than relying on the conventional boundary conditions and the Clausius-Mossotti equations, we use instead the point-dipole interaction model and an expansion of polarization in eigenmodes to determine the structure's dispersion relation and electromagnetic response. Using the nearestneighbor approximation, we show how truncating the crystal lattice excites an "ordinary" mode and two "extraordinary" modes that are necessary to satisfy the boundary conditions at the interface. For most cases, the extraordinary modes are evanescent, and thus form a thin transition layer at the surface. However, under certain conditions, typically near particle resonances, either one or both of these modes can be propagating.
We present the theoretical development of the 3D multipole probability tomography applied to the electric Self-Potential (SP) method of geophysical exploration. We assume that an SP dataset can be thought of as the response of an aggregation of poles, dipoles, quadrupoles and octopoles. These physical sources are used to reconstruct, without a priori assumptions, the most probable position and shape of the true SP buried sources, by determining the location of their centres and critical points of their boundaries, as corners, wedges and vertices. At first, a few synthetic cases with cubic bodies are examined in order to determine the resolution power of the new technique. Then, an experimental SP dataset collected in the Mt. Somma-Vesuvius volcanic district (Naples, Italy) is elaborated in order to define location and shape of the sources of two SP anomalies of opposite sign detected in the northwestern sector of the surveyed area. The modelled sources are interpreted as the polarization state induced by an intense hydrothermal convective flow mechanism within the volcanic apparatus, from the free surface down to about 3 km of depth b.s.l..
This paper presents an analytical method based on the coulombian model of a magnet for studying a ferrofluid seal in ironless electrodynamic loudspeakers. Such an approach differs from the ones generally used for studying such geometries because the ferrofluid used is submitted to a magnetic field greater than $1$~T which saturates the ferrofluid. Consequently, its shape and its mechanical properties depend mainly on the magnetic field produced by the permanent magnets that constitute the ironless structure. The motor is constituted of outer stacked ring permanent magnets and the inner moving part is a piston. In addition, one ferrofluid seal is used for centering the moving part and ensuring the airtightness between the loudspeaker faces. The ferrofluid seal also exerts a pull back force on the moving piston. It is noted that this force depends on the lateral shape of the moving piston. Therefore, the piston profile is analytically studied in this paper. A peculiar attention is given to profiles that ensure the axial pull back force to be proportional to the piston displacement. Furthermore, a geometrical method is presented to design the shape of the ferrofluid seal according to the chosen piston profile. It can be noted that such a profile is elliptical in this study. Then, the magnetic energy of the ferrofluid seal is determined with the analytical expression of the magnetic energy density. Such an expression allows us to calculate the axial force created by the ferrofluid seal for a given profile.
The transmission line transfer matrix method (TLTMM) is proposed for the analysis of planar multilayer metamaterial (MTM) structures, where a transmission line model is developed by the transfer matrix method. This novel method may consider any oblique incident plane wave at any angle of incidence, any linear polarization (TE or TM with respect to the incidence plane), circular and elliptical polarizations, any frequency range (microwave or optical frequencies), any number of layers, any combination of common materials (DPS) and MTMs (such as DNG, ENG, MNG), any layer thickness, consideration of any dispersion relations for ε and μ, etc. A unified formulation is presented for both TE and TM polarizations, which lead to the evaluation of the fields and powers inside the layers and half spaces. The objective of the paper is to analyze and design several diverse problems of multilayered structures by TLTMM and a matrix method. The results of computations by TLTMM are agreed with the literature where possible and with the matrix method.
In this paper a new simple VHF-LB vest antenna is proposed, simulated, fabricated and tested. The simulation results for various user's positions such as standing, kneeling and prone on the ground are obtained and compared with conventional whip antenna mounted on mobile unit. It is shown that the proposed antenna outperforms the whip antenna in terms of gain and body energy absorption. The measurements results of proposed vest antenna confirm the simulation results.
Based on the equivalence principle and the reciprocity theorem, the multiple scattering up to $N$th-order by adjacent multi-particles is considered in this study. It is well known that the first-order solution can easily be obtained by calculating the scattered field from isolated targets when illuminated by a plane wave/Gaussian beam. However, due to the difficulty in formulating the couple scattered field, it is very difficult to find an analytical solution for the higher-order of the scattered field with considering the multiple scattering even for multi-canonical geometries, such as spheres, spheroids, and cubes. In order to overcome this problem, in this present work, the higher-order solutions of electromagnetic scattering for multi-particles are derived by employing the technique based on the reciprocity theorem and the equivalence principle. In specific, using the formulas of the composite scattering field obtained in this work, the bi-static scattering of plane wave/Gaussian beam by adjacent multi-spheres is calculated and the results are compared with those obtained from the numerical computations by the Time Domain Integral Equation Method (TDIEM).
A uniform asymptotic expression is developed for calculating the fields scattered by a perfect electrically conducting plate illuminated by a vectorial gaussian beam. This expression has been obtained under the physical optics approximation using the saddle point method. Some numerical applications are presented and compared with some reference methods such as a MoM. A brief parameter study of this solution is presented.
We evaluate effective dielectric permittivity and electric conductivity for water-saturated rocks based on a realistic model of a representative cell of the pore space which has periodical structure. We have applied the method of two-scale homogenization of the Maxwell equations, which results in up-scaling coupled equations at the microscale to equations valid at the macroscale. We have analyzed the interfacial Maxwell-Wagner dispersion effect and the Archie law as well.
We study theoretically the propagation of electromagnetic waves in an infinite and homogenous medium with both temporal and spatial dispersion included. We derive a partial differential equation connecting temporal and spatial dispersion to achieve negative group velocity. Exact solutions of the equation are found and shown to lead to the possibility of exciting constant negative group velocity waves. We then investigate the effect of spatial dispersion on the power flow and derive the first-, second-, and third-order corrections of power flow due to the nonlocality in the medium. This derivation suggests a path beyond the group velocity concept.
The design of a novel Fractal planar inverted F antenna (F-PIFA) based on the self affinity property is presented in this paper. The procedure for designing a Fractal Planar Inverted F Antenna is explained and three different iterations are designed for use in cellular phones. The F-PIFA has a total dimension of 27 mm x 27 mm and has been optimized to be operational at GSM (Global System for Mobile Communication), UMTS (Universal Mobile Telecommunication System) and HiperLAN (High Performance Radio LAN) with the frequencies range from 1900 MHz to 2100 MHz, 1885 to 2200 MHz and 4800 MHz to 5800 MHz respectively. The antenna achieved -6 dB return loss at the required GSM, UMTS and HiperLan frequencies with and has almost omnidirectional radiation pattern. This antenna has been tested using realistic mobile phone model and has met the performance criteria for a mobile phone application. Simple semiempirical formulas of the operational frequency, numerical calculation and computational SAR of the antenna also has been presented and discussed.
The characteristics of guided modes in the planar waveguides which the core or cladding consists of chiral nihility meta-materials are studied theoretically. The dispersion curves, electromagnetic fields, energy flow distribution and the power of several low-order guided modes in the chiral nihility waveguides are presented. Some novel features such as anomalous dispersion curves, the power flows opposite to the wave vector propagation direction in the chiral nihility waveguides have been found.
A diversity monopulse antenna is presented in this paper. This monopulse antenna is based on a dual frequency dual mode rat-race coupler that has been designed by using Composite Right/Left Handed (CRLH) Transmission Lines (TL). The device has two input ports while the (Σ) and (Δ) outputs are interchangable at either of the two operating frequencies. In this way the monopulse antenna can work at two different frequencies with two sets of radiation patterns, Σ and Δ. In addition, there is no need of diplexing to separate the (Σ) and (Δ) radiation patterns since these patterns at either frequency are directly obtained at different ports. The dual frequency dual mode rat-race requires that the phase delay of the CRLH lines must be different at either working frequency. As an example of an application, a 950 MHz/1.8 GHz dual-band dual-mode rat-race coupler is shown.
The dynamic evolutions of full Gaussian and particularly the truncated Gaussian pulses in dispersive Lorentz media are studied numerically in detail. The observed qualitative phenomena lead to revised interpretation regarding both Sommerfeld and Brillouin precursors. Neither strict Sommerfeld nor Brillouin precursor is present for the case of an incident full Gaussian pulse for any finite propagation distance. In addition, the Brillouin effect can be separated into a tail and a forerunner depending on the turn-on point of the initial pulse. Moreover, the essence of an artificial precursor is discussed, which deserves caution when handling the high dynamic range problems by numerical algorithm.
Based on the deterministic Maxwellian framework, we investigate the ability of each of the dual fields (electric and magnetic) in carrying independent information in a multi-polarization MIMO system. We quantify the performance by using a well-defined power independent dimensionality (PID) metric. We present numerical results for 3 deterministic scenarios: a canonical free-space (near and far field exact solution), a canonical PEC corridor (using rigorous modal analysis) and a lossy-wall corridor (using image ray tracing). The deterministic results show that in a multi-path rich environment, the hexapole system (collocated polarized electric and magnetic point radiators) is almost guaranteed to provide more than 3 DOF. However, in the simulated scenarios, the maximum 6 DOF are never attained due to the inevitable coupling between the electric and magnetic fields. On the other hand, for a tripole system, the upper-limit of 3 DOF is achievable.
A comparative study using numerical models on the mutual coupling (MC) between two different heterogeneous beam steering dielectric resonator antennas (DRAs) and an omni-directional dielectric resonator antenna (DRA) is presented in this paper. The mutual coupling was investigated by varying the separation between the antennas and manipulating the far field radiation pattern of each antenna. Several arrangements with element separation ranging from 0.1 to 0.5 free space wave length were investigated at the design frequency of 10 GHz. Different configurations contributed to different isolation levels. It was found that a significant isolation (< -15 dB) between an array of heterogeneous DRAs can be obtained even with antennas placed in close proximity (0.1 free space wavelength separation). It was also shown that the resonant frequency and return loss are most affected at settings where the direction of the main lobe of antenna A overlaps with the direction of the main lobe of antenna B. The expected inverse proportionality between 'd' (the separation between two antennas) and the level of MC was also demonstrated.
This paper proposes a numerical model of soil ionization phenomena that can occur when earth electrodes are injected by high pulse transient currents, as the current associated with a direct lightning stroke. Based on finite difference time domain numerical scheme, this model ascribes the electrical breakdown in the soil to the process of discharge in the air. In fact, as soon as the local electric field overcomes the electrical strength, the air in the voids trapped among soil particles is ionized, and the current is conducted by ionized plasma paths locally grow. The dimension of these ionized air channels are strictly dependent upon the local temperature. Thus, a local heat balance is enforced in order to obtain the time variable conductivity profile of the medium. This model can be implemented both for concentrated and extended electrodes, since no hypothesis has to be enforced about the geometric shape of the ionized region. Validation of the proposed model is obtained by comparing simulation results with experimental data found in technical literature.