Differential-form formalism has been often applied, in stead of the more commonplace Gibbsian vector calculus, to express the basic electromagnetic equations in simple and elegant form. However, representing higher-order equations has met with unexpected difficulties, in particular, when dealing with general linear electromagnetic media. In the present study, wave equations involving scalar operators of the fourth order are derived for the electromagnetic two-form and the potential one-form, for the general linear bi-anisotropic medium. This generalizes previous coordinate- free approaches valid for certain special classes of media. The analysis is based on some multivector and dyadic identities derived in the Appendix.
A rigorous solution to the Neumann boundary value problem (BVP) for semicircular trough in a perfectly electrically conducting (PEC) ground plane is presented. The known Rayleigh's method expansion of a solution by eigensolutions of the Helmholtz equation in cylindrical coordinates coupled with partial orthogonality of trigonometric functions is used. In contrast to previous works on this theme, a Fredholm 2nd kind matrix equation for modal coefficients is obtained, which permits one to derive very fast convergent approximate solution for any incidence angle and trough dimension. The method solution permits one to consider a dielectric loading as well. A strong broadband fall-off of backscattering from apertures loaded with lossy dielectric is theoretically revealed.
This paper presents an innovative inverse scattering approach based on a fuzzy-logic strategy aimed at fully exploiting the information content of the scattered data in a microwave imaging system. The effectiveness of the proposed method is assessed through the results of a numerical analysis concerned with the reconstruction of single as well as multiple dielectric targets in various noisy environments. For comparison purposes, the obtained performance are compared with those of a standard method in terms of reconstruction accuracy and computational load to point out the improvement induced by the proposed approach.
Scattering by pulsating objects is discussed. In the case of the pulsating cylinder, its surface vibrates time-harmonically in the radial direction. The formalism is based on first-order v/c relativistic approximations, and on the assumption that the ambient media are not affected by the mechanical motion of the interface. This is conducive to simpler and amenable approximations. The cases analyzed display the modulation effect due to the mechanical motion at frequency Ω, creating new spectral components in the scattered wave, peaking at the sideband frequencies ωex ± nΩ around the excitation frequency. To put such phenomena in a quasi-relativistic and electromagnetic context, and account for the boundary-condition problem and the representation of the scattered wave is the subject of the present investigation. Such effects can be used to remotely sense the properties of the scatterer, especially its motion.
The present paper concerns the design, numerical analysis, and measurement for simple metal-plate lens structures. The power of electromagnetic waves can be concentrated by arranging flat strips parallel to one another and adjusting the transverse and longitudinal length of the waveguide regions. The simple designing procedures are described for the lenses with plane, concave, and convex profiles. These steps are practically applied to construct the lenses for the X band. In order to discuss the dependence of focusing properties on the lens and source types, we numerically analyze the scattering problems using the integral equations combined with the moment method. The lenses are made up by aluminum plates, and the field amplitude in the transmission region is measured. We confirm the formation of the focus near the design point.
In this paper, the electromagnetic field in air from a radiating horizontal electric dipole located in the homogeneous isotropic spherical electrically earth coated with N-layered dielectrics is investigated anew. The starting point is based on the formulas for the electromagnetic fields in air from vertical electric and magnetic dipoles situated in air above the surface of the earth coated with N-layered dielectrics. The complete explicit formulas are derived for the electromagnetic fields in the earth due to vertical electric and magnetic dipoles located in air. By using reciprocity theorem, the formulas are readily obtained for the six components of the electromagnetic field in air radiated by a horizontal electric dipole located in the earth.
From a very roughly random surface the backscattering enhancement is predicted due to the constructive interference of multiple surfaces scattering. For specialized surfaces involving roughness large compared with the incident wavelength, the backscattering enhancement takes place. The phenomenon of backscatter enhancement becomes evident for both larger normalized surface height and surface rms slope. In this paper we take further study to predict the backscattering enhancement mainly comes from upward multiple scattering. On the contrary the downward multiple scattering has no contributions to the scatter strength of backscattering enhancement. The model developed in this paper is based upon the integral equation method and able to predict this phenomenon of multiple scattering and backscattering enhancement. The depolarized multiple scattering makes much contribution along the plane of incidence from random rough surfaces, but depolarized single scattering makes little contributions. The total multiple scattering strength is the summation of upward and downward multiple scattering strength. In comparison of model prediction of total multiple scattering strength with measured data along the specular plane, excellent agreement is obtained.
Knowledge of the current distribution on a radome can be used to improve radome design, detect manufacturing errors, and to verify numerical simulations. In this paper, the transformation from near-field data to its equivalent current distribution on a surface of arbitrary material, i.e., the radome, is analyzed. The transformation is based on the scalar surface integral representation that relates the equivalent currents to the near-field data. The presence of axial symmetry enables usage of the fast Fourier transform (FFT) to reduce the computational complexity. Furthermore, the problem is regularized using the singular value decomposition (SVD). Both synthetic and measured data are used to verify the method. The quantity of data is large since the height of the radome corresponds to 29-43 wavelengths in the frequency interval 8.0-12.0 GHz. It is shown that the method gives an accurate description of the field radiated from an antenna, on a surface enclosing it. Moreover, disturbances introduced by copper plates attached to the radome surface, not localized in the measured near field, are focused and detectable in the equivalent currents.
Characteristics of a single-layer, dual-frequency microstrip patch antenna, which uses a T-strip loaded rectangular microstrip patch, are studied. This antenna is easy to achieve good impedance matching at both frequencies by tuning the feed position and other design parameters. Another advantageous aspect is that it has high polarization purity. A detailed parameter study is performed and the theoretical analysis is based on the finite-difference time-domain (FDTD) method. The FDTD programs are developed and validated by measurement results. The effects of various antenna parameters on two resonant frequencies, frequency ratio, and radiation pattern characteristics of the antenna are analyzed and discussed. It is shown that various frequency ratios (1.5-2.49) can be obtained by varying the design parameters of this antenna. Similar radiation patterns with same polarization are obtained at two resonant frequencies. Several design curves are presented.
The reconstruction capabilities of a microwave imaging algorithm can be enhanced by exploiting a multi-view measurement set-up. In the past, different researches have proved that collecting scattering data by probing the unknown scenario from different incidence angles, it allows to acquire more information on the scenario under test. This paper is aimed at verifying such an assumption in a real scenario when the Iterative Multi-Scaling Approach (IMSA) is used to fully exploit multi-view data. In fact, unlike synthetic data, in a real environment more measurements introduce larger systematic errors that could affect the physical constraints used in the inversion procedure and, consequently, the reconstruction process. Thus, the analysis is carried out by considering a set of experimental data concerning different scattering configurations involving single and multiple dielectric scatterers.
The scattering problem from the random interface with the Dirichlet boundary condition can be formulated as an integral equation x = K̂y with respect to surface sources y (here, K̂ is the integral operator). Starting with an approximate operator K̂0, for which the inverse operator M̂=K̂âˆ’10 is known, the series in powers of the operator Ẑ=M̂(K̂0âˆ’K̂) is derived. As an approximate kernel, we consider the kernel depending only on the difference of arguments: K0=K0(r-r´), for which the kernel of the operator M̂ can be found in terms of generalized functions. The norm of the difference operator ||Ẑ|| is found; the conditions of convergency ||Ẑ||≤ 1 were obtained.
The intra-channel collision of optical solitons, with power law nonlinearity, is studied in this paper with the aid of quasi-particle theory. The perturbation terms that are considered in this paper are of Hamiltonian type. The suppression of soliton-soliton interaction, in presence of these perturbation terms, is achieved. The numerical simulations support the quasi-particle theory.
In this paper a novel antenna is presented. This antenna, employing microstrip circular disc as radiator is seen to perform over a large impedance bandwidth (130 MHz to 876 MHz). The disk resonator is loaded with L-C-R circuit across a selective location in the disk via a thin shorting pin. The theoretical modeling predicts TM01 mode of operation. Therefore the beam pattern shows a null in the broadside direction. The said antenna is proposed to be developed for end use in coal mine where the antenna can be flush mounted on coal strata. Thus it will be able to measure the angle of arrival of any reflective component due to presence of waterbed at a distance. The measured as well as simulated results regarding impedance bandwidth and beam pattern agrees well. The simulated efficiency using IE3D is 48% whereas measured efficiency is nearly 45%.
New possibilities to design artificial magnetic materials for microwave frequencies are considered. Such composites can be used in microwave engineering at frequencies where no natural low-loss magnetic materials are available. A new magnetic particle (metasolenoid) formed by a stack of many parallel and very closely spaced single broken loops is proposed and analyzed analytically, numerically, and experimentally. It is shown that the effective permeability can reach reasonably high values over a wide frequency range when using such inclusions.
A fast technique based on the Poggio, Miller, Chang, Harrington and Wu (PMCHW) formulation and the precorrected-FFT method is presented for accurate and efficient analysis of electromagnetic transmission through dielectric radomes of arbitrary shape (including airborne radomes). The method of moments is applied to solve the integral equations in which the surfaces of the radomes are modeled using surface triangular patches and the integral equations are converted into a linear system in terms of the equivalent electric and magnetic surface currents. Next, the precorrected-FFT method, a fast approach associated with O(N 1.5 log N) or less complexity, is used to eliminate the requirement of generating and storing the square impedance matrix and to speed up the matrix-vector product in each iteration of the iterative solution. Numerical results are presented to validate the implementation and illustrate the accuracy of the method.
This paper describes the performance of different loaded wire antennas (e.g., inverted L, T, I and C-shaped antennas) as electromagnetic interference (EMI) sensors. Loaded wire antennas in transmitting mode are widely used for low frequency communication. However, while using these antennas as EMI sensors, the extra loading is likely to introduce the reception of cross-polarized component of incident electric field and investigation on this has not yet been performed. This paper highlights the results of the initial investigation on the performance of these loaded antennas as EMI sensors in terms of the Antenna Factor for the desired and cross-polarized component of incident electric field. The Method of Moments with Pulse basis function and Point-matching technique has been used to evaluate the current distribution on the antenna surface and hence the Antenna Factor.
Abstract-In this paper, a two-dimensional inverse scattering problem dealing with microwave tomography is considered. To solve this non linear and ill-posed problem, an iterative scheme based on the Modified Gradient Method (MGM) is used. The object to be estimated is represented by a complex function, and some modifications of the MGM formulation have been considered. This algorithm leads to an efficient regularization scheme, based on edge preserving functions which act separately on the real and imaginary parts of the object. In order to show the interest of this regularized MGM, the algorithm is tested against laboratory-controlled microwave data.