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The diffraction of plane electromagnetic waves by a perfect electromagnetic conductor (PEMC) semi-infinite sheet which is embedded in an anisotropic medium is examined. The anisotropic region is modeled by a dielectric matrix. The external uniform magnetic field is taken as parallel to the edge of the semi-infinite sheet. Upon considering the $H$ -polarized incident wave, the total scattered fields are obtained with the diffracted waves by using an integral theory which is associated with the scattered fields. The results are expressed in terms of the Fresnel functions. Thus, the wave behaviors at the transition boundaries are uniform. The solutions are compared numerically with the literature including limit values. [ABSTRACT FROM AUTHOR]

A new method is proposed for the antenna aperture illumination design on microwave wireless power transmission. Bezier curves are used to describe the aperture amplitude distributions. By optimizing the coordinates of the associated Bezier points, an aperture distribution yielding the maximum beam collection efficiency (BCE) can be achieved. Moreover, edge tapers can be easily controlled by the Bezier curves. The proposed method shows its effectiveness from carrying out extensive numerical experiments on different Fresnel parameters as well as edge taper constraints. The results show that larger aperture power coefficients obtain with a little sacrifice of BCEs when larger edge taper constraints are considered. Besides, the peak lobe irradiated outside the rectenna can be suppressed as well. [ABSTRACT FROM AUTHOR]

We have developed a new, fast, and simple 3-D imaging approach referred to as Simultaneous Azimuth and Fresnel Elevation (SAFE) compounding using a bias-sensitive crossed-electrode array. The principle behind this technique is to perform conventional plane-wave compounding with a back set of electrodes, while implementing a reconfigurable Fresnel elevation lens with an orthogonal set of front electrodes. While a Fresnel lens would usually result in unacceptable secondary lobe levels, these lobes can be suppressed by compounding different Fresnel patterns. The azimuthal and elevational planes can be simultaneously compounded to increase the beam quality with no loss in frame rate. A 10-MHz, $64 \times 64$ element crossed-electrode relaxor array was fabricated on an electrostrictive one-to-three composite substrate to demonstrate the SAFE compounding approach. The electrostrictive composite array has a measured electromechanical coupling coefficient ($k_{t}$) of 0.62 with a bias voltage of 90 V and a measured two-way pulse bandwidth of 60%. The electrical impedance magnitude of array elements on resonance was measured to be $90~\Omega$ with a phase angle of −35°. Radiation patterns were simulated showing a −6-dB beamwidth of $330~\mu \text{m}$ with secondary lobe levels suppressed more than −60 dB in the azimuth dimension, and a −6-dB beamwidth of $450~\mu \text{m}$ with secondary lobe levels suppressed to −50 dB in the elevation dimension after 64 compounds. Experimental radiation patterns were collected and found to be in good agreement with simulations. Experimental 3-D images of wire phantoms were collected using a Verasonics experimental ultrasound system. [ABSTRACT FROM AUTHOR]

In this paper, closed-form (Cf.) expressions for the backscattered radar cross section of cylindrically curved perfect electrically conducting plates have been derived. These Cf. expressions have been validated using full-wave integral equation-based solver for several radii (angles) of curvature of the curved plates. Here, the plane wave is incident symmetric with respect to the edges of the curved plate for both convex and concave side incidence cases. Cf. expressions include the contributions due to the reflected rays and the single edge diffracted rays for the convex side incidence case. In addition, the double edge diffracted rays have also been considered for the concave side incidence. The Cf. expressions have been demonstrated to be valid for all angles of curvature for the case of convex side incidence, whereas for the concave side incidence case, they are applicable up to 90° curvature, beyond which the higher order and surface diffracted rays become significant due to the concave nature of the curved plate. [ABSTRACT FROM AUTHOR]

In this paper, a current density convolution finite-difference time-domain method is extended to study the electromagnetic wave propagation and absorption in inhomogeneous magnetized plasmas. First of all, we analyze the wave propagation in homogeneous magnetized plasmas for arbitrary magnetic inclination angle. Then, we studied three types of plasma absorption, including plasma resonance, electron cyclotron resonance, and upper hybrid resonance in homogeneous and inhomogeneous magnetized plasmas. This model is applied to simulate the heating mechanism during ionospheric modification experiments by high-power high-frequency radio waves. These results have important implications for the interpretation of physical mechanisms for the interaction of high power radio waves with magnetized ionospheric plasmas and design of future experiments. [ABSTRACT FROM AUTHOR]

The propagation characteristics of a confocal waveguide are related to the radial spheroidal function, which is extremely complicated. A quadratic polynomial fitting (QPF) expression derived from numerical results by interpolation was successfully applied to the development of confocal gyrotrons. However, the QPF expression is valid only for a moderate spheroidal parameter. As a result, it cannot work well for confocal gyrotron travelling-wave tube (gyro-TWT) applications since the Fresnel parameter may be small for stable operations. For the first time, an efficient algorithm is developed to accurately calculate the spheroidal functions. Based on it, the MATLAB code with high accuracy and efficiency is developed to analyze the propagation characteristics of confocal waveguide. The calculated results and the QPF results are compared for different mirror apertures, and then demonstrated by high frequency structure simulator (HFSS). The calculated results show good agreement with the HFSS results for different mirror apertures while the QPF solution agrees with the HFSS results only for large apertures. The code is valid for arbitrary mirror apertures for both the confocal gyrotron and gyro-TWT applications. [ABSTRACT FROM AUTHOR]

A novel microwave imaging approach to reconstruct the dielectric properties of targets hosted in partially known, noncanonical, scenarios is proposed and assessed. The method takes joint advantage of the recently introduced virtual experiments paradigm and exploits a new linear approximation developed within such a framework. Such an approximation implicitly depends on the unknown targets and, therefore, has a broader applicability as compared with the traditional distorted Born approximation. Being noniterative, the resulting distorted-wave inversion method is capable of quasi-real-time imaging and successfully images nonweak perturbations. The performances of the novel imaging method have been assessed with simulated data and validated experimentally against some of Fresnel data sets. [ABSTRACT FROM PUBLISHER]

We introduce the concept of spatially accelerating (curved) beam waves in the Fresnel region of properly designed antenna arrays. These are transversely localized EM waves that propagate in free space in a diffraction-resisting manner, while at the same time laterally shifting their amplitude pattern along a curved trajectory. The proposed beams are the radiowave analogue of Airy and related accelerating optical waves, which, in contrast to their optical counterparts, are produced by the interference of discrete radiating elements rather than by the evolution of a continuous wavefront. Two dyadic array configurations are proposed comprising 2D line antennas: linear phased arrays with a power-law phase variation and curved power-law arrays with in-phase radiating elements. Through analysis and numerical simulations, the formation of broadside accelerating beams with power-law trajectories is studied versus the array parameters. Furthermore, the abrupt autofocusing effect, that occurs when beams of this kind interfere with opposite acceleration, is investigated. The concept and the related antenna setups can be of use in radar and wireless communications applications. [ABSTRACT FROM AUTHOR]

An adaptive integration algorithm is presented for the computation of the Physical Optics (PO) electric and magnetic field scattered by electrically large objects modeled by Non-Uniform Rational B-Splines (NURBS). The algorithm is the customization of a more general-purpose result that has been recently published. By using a unique formulation both impenetrable (e.g., impedance surfaces, coated conductors) as well as transparent thin sheet materials (e.g., thin dielectric panels, or frequency selective surfaces) are treated, via their Fresnel reflection and transmission coefficients. The PO radiation integral is evaluated over the NURBS parametric domain. Since most of the computer-aided geometric design (CAGD) tools are based on NURBS, the proposed algorithm allows a straightforward electromagnetic analysis of the structures by exploiting the standard available geometrical description, with no need of generating new geometrical models. Furthermore, the proposed adaptive sampling requires a number of integration points that is found to be drastically smaller than that resulting from standard Nyquist-based sampling integration algorithms. Such reduction of the sampling points is achieved by resorting to high-frequency technique concepts and allows a significant reduction of the CPU computational burden. Therefore the algorithm is efficient and particulary suitable for the electromagnetic characterization of real-life electrically large objects. [ABSTRACT FROM PUBLISHER]

The computational time to evaluate the physical optics (PO) expression by numerical integration increases rapidly with the increase of electrical size of scattering surfaces. However, the computational time of PO integrals for electrically large object can be greatly reduced by using the stationary phase method, which is independent of the wavenumber. For this method, the theory and numerical implementations for isolated critical points have been well developed. However, for cases of nearby critical points, there are still a few issues to be considered, especially, in numerical implementations. In this paper, we mainly study the numerical implementations for several most common cases of nearby critical points. In particular, the cases of two nearby inner stationary phase points and complex inner stationary phase points are discussed in more details. Such cases occur frequently when the scattering surface includes convex-concave parts, but the numerical implementations to such cases have not been reported to our knowledge. The difficulty lies in how to identify whether two inner stationary points and complex inner stationary points on the surfaces with arbitrary shapes are close to each other or not. A strategy is designed to solve this difficulty. By validation in some typical examples, we find that the stationary phase method is robust enough to evaluate the PO integrals accurately. Finally, some interesting phenomena observed in numerical validations are interpreted. [ABSTRACT FROM PUBLISHER]

We apply the so-called multiplicative regularized Gauss–Newton inversion algorithm for solving three-dimensional electromagnetic microwave inverse problems. This inversion algorithm automatically adjusts the regularization parameter and when combined with the total variation type regularization function, it can provide inversion results with excellent edge-preserving characteristics. In addition, in order to deal with an extensive memory requirement for the Gauss–Newton method, we employ an implicit Jacobian calculation scheme. By using this scheme we do not have to explicitly store the Jacobian matrix. Hence, we are able to significantly reduce the memory requirement of the Gauss–Newton method albeit at an additional computational overhead. Furthermore, in order to be able to handle a large scale computational problem, both the forward and the inversion algorithms are parallelized using the MPI library, where we obtain a nearly linear speedup factor. We demonstrate efficiency and robustness of this algorithm by inverting synthetic data, Fresnel experimental data, and biomedical experimental data. [ABSTRACT FROM PUBLISHER]