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Title: ACES Journal July 2017 Cover
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
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Title: ACES Journal July 2017 Front/Back Matter
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
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Title: ACES Journal July 2017 Full
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
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Title: Electromagnetic Diffraction Modeling: High Frequency Asymptotics vs. Numerical Techniques
Abstract: Electromagnetic diffraction modelling and recent numerical simulation approaches, on the canonical 2D non-penetrable wedge scattering problem, are reviewed in this introduction paper.
Author(s): L. Sevgi
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
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Title: Computational Design of Optical Couplers for Bended Nanowire Transmission Lines
Abstract: We present computational analysis, optimization, and design of optical couplers that can be useful to improve the transmission along bended nanowires. After demonstrating the deteriorated energy transmission due to sharp bends, which lead to out-ofphase nanowires and diffraction, we use a rigorous simulation environment to design efficient couplers made of spherical particles. For this purpose, an optimization module based on genetic algorithms is combined with the multilevel fast multipole algorithm, leading to a full-wave environment for precise designs of couplers. Numerical examples involving silver nanowires are presented to demonstrate the effectiveness of the optimization mechanism.
Author(s): Y. E. Tunçyürek, B. Karaosmano?lu, Ö. Ergül
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 1964 KB

Title: Baffle Diffraction in Interferometric Detectors of Gravitational Waves
Abstract: This paper presents an efficient highfrequency analysis framework for studying diffraction occurring at irises, or baffles, in the arms of a Fabry- Perot optical interferometer, relevant to the design and operation of interferometric detectors of gravitational waves like LIGO and Virgo.
Author(s): G. Pelosi, L. Possenti, S. Selleri, I. M. Pinto
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
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Title: Finite Difference Time Domain Modeling of Fringe Waves
Abstract: A novel method is introduced for calculating fringe currents and fringe waves around the tip of a perfectly reflecting wedge under line source illumination. The time-domain fringe (non-uniform) currents are extracted with the finite-difference time-domain (FDTD) method. These currents are then fed into a free-space FDTD and fringe waves are excited. Alternatively, fringe waves are also obtained using the Green’s function approach. The validation of the proposed method and the verification of the results are done against the physical theory of diffraction (PTD) as well as the method of moments (MoM). The factors affecting the accuracy are also discussed.
Author(s): M. A. Uslu, G. Apaydin, L. Sevgi
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 1806 KB

Title: An Improved Shooting and Bouncing Ray Method for Outdoor Wave Propagation Prediction
Abstract: An improved algorithm for shooting and bouncing ray tracing (SBR) is proposed in this paper. The conventional SBR method has to launch a large number of rays or ray tubes to guarantee the accuracy, which increases the calculation time significantly. This paper presents a novel adaptive ray launching (ARL) method based on the pattern of transmitting antenna, which reduces the launched rays greatly while maintaining the computation accuracy. Some examples of applying the proposed method to calculate the outdoor radio wave propagation are presented, and the results are compared with the measurements and simulations. The good agreements between them validate the proposed approach. The method has a high gain in terms of computational efficiency (about 480% speedup compared with 10 uniform ray launching).
Author(s): D. Shi, N. Lv, N. Wang, Y. Gao
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 1647 KB

Title: A Top-down Approach to S-UTD-CH Model
Abstract: Free space electromagnetic wave propagation is an excessively pretty simple. However, in the reality, there are obstructions like buildings and hills blocking the electromagnetic waves and leading diffraction and reflection, and these obstructions can be modeled as a knife edge or wedge due to using of UHF. Hence, the vital problem is how an electromagnetic wave propagates in multiple diffraction scenario including buildings, trees, hills, cars etc. In order to estimate the field strength or relative path loss of the waves at the receiver, so many electromagnetic wave propagation models have been introduced throughout the century. Ray tracing and numerical integration based propagation models are introduced. In this paper, detailed information is provided about S-UTD-CH (Slope UTD with Convex Hull) model. Particularly, in the transition zone, the S-UTD-CH model can be applied to multiple diffraction scenarios. In addition, Fresnel zone concept, convex hull and slope UTD models are fundamentals of the S-UTD-CH model. Moreover, in terms of computation time and accuracy, the S-UTD-CH model is conceived an optimum model. Furthermore, verification of S-UTD-CH model is made by means of FEKO, which is a comprehensive electromagnetic simulation software tool by Altair.
Author(s): M. B. Tabakcioglu
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
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Title: Modeling of Diffraction Effects in Urban Radiowave Propagation
Abstract: A comparative study of some theoretical and numerical models is presented in the solution of twodimensional urban radiowave propagation problems. The path loss is computed by GO+UTD (geometric optics + uniform theory of diffraction), two-way SSPE (split step parabolic equation) and the diffracting screens models, and the results are compared through numerical simulations. The diffracted fields that are obtained by the GO+UTD model are demonstrated. Computational aspects of the models are briefly discussed.
Author(s): O. Ozgun
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 2260 KB

Title: Diffraction at Rounded Wedges: MoM Modeling of PTD Fringe Waves
Abstract: The paper examines diffraction at rounded wedges with perfectly conducting faces. This topic was a subject of many publications which investigated mainly the total diffracted waves. In the present paper, we calculate specifically their fringe components to illustrate their sensitivity to the edge curvature. Such fringe waves provide substantial contributions to the scattered field in certain directions and represent a key element in extension of the physical theory of diffraction (PTD) for objects with rounded edges.
Author(s): G. Apaydin, L. Sevgi, P. Y. Ufimtsev
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 2064 KB

Title: A Diffraction Ray Tracing Method Based on Curved Surface Ray Tube for Complex Environment
Abstract: A self-adaptive ray tracing method for predicting radio propagation based on the curved surface ray tube (CSRT) model is proposed in this paper. The CSRT model is implemented in the ray tracing method to reduce the unnecessary consume compared with the four-ray tube model in complex environments. Both the theoretical calculation and the practical simulation were applied to verify the high efficiency of the CSRT model. The radio wave propagation in a complex scene was calculated by the CSRT model and the four-ray tube model, and the theoretical analytical result demonstrated that the CSRT model achieved a speed up of 4 times compared to the four-ray tube model. Moreover, the wave propagations in several different environments were simulated with our developed software based on the CSRT and four-ray tube tracing method, and the comparisons of the simulation time spent by the two methods proved the high efficiency of the CSRT model. In addition, the correct prediction of the propagation paths and E-field also validates the accuracy of the CSRT model.
Author(s): D. Shi, N. Lv, Y. Gao
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 1794 KB

Title: A GPU Implementation of a Shooting and Bouncing Ray Tracing Method for Radio Wave Propagation
Abstract: Shooting and bouncing ray tracing method (SBR) is widely adopted in radio wave propagation simulations. Compared with the center-ray tube model, the lateral-ray tube model is more accurate but more time consuming. As a result, we use graphics processing unit (GPU) to accelerate the lateral-ray tube model. In this paper, we proposed a GPU-Based shooting and bouncing lateral-ray tube tracing method that is applied to predicting the radio wave propagation. The numerical experiment demonstrates that the GPU-based SBR can significantly improve the computational efficiency of lateral-ray tube model about 16 times faster, while providing the same accuracy as the CPU-based SBR. The most efficient mode of transferring the data of triangle faces is also discussed.
Author(s): D. Shi, X. Tang, C. Wang, M. Zhao, Y. Gao
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 2125 KB

Title: An Optimized Microwave Absorber Geometry Based on Wedge Absorber
Abstract: Low reflectivity of microwave absorbers is important to improve the performance of anechoic chamber measurements. The shape of the absorber as well as the material used are among the main components to provide desired low reflection performance. Pyramidal and wedge-shaped absorbers are two of the most wellknown microwave absorber types. We discuss the effect of a convex shape on reflection performance of microwave absorbers and show that convex shape structure has significantly performance by absorbing most of the electromagnetic energy of the incident wave. We used a concavity theorem based design method to obtain a function for a convex shape. Absorbing structures have been analyzed by using the periodic moment method (PMM). An optimization method is employed to find coefficients of the convex function, which provides better absorption performance than the wedge type absorber. Reflection performances of the wedge and convex absorbers for the 212 GHz frequency band are compared. Their reflection performances at 2 GHz for different angles of incidence are presented. An important implication of this study is that the alternative absorber shapes other than the wedge shape are demonstrated by using simple mathematical methods to have the optimal reflection characteristics.
Author(s): I. Catalkaya, S. Kent
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 1791 KB

Title: A Novel AGEI Solution of Parabolic Equation for EM Scattering Problems
Abstract: Parabolic equation (PE) has been widely used for EM propagating and scattering problems for its high efficiency. By using the finite differential (FD) method, the calculation can be taken in a series of transverse planes in a marching manner. In this paper, the alternating group explicit iterative (AGEI) method is applied to solve the alternating direction implicit based parabolic equation (ADI-PE). As a result, the CPU time can be further saved when compared with the CN-PE and ADI-PE methods. Numerical results are shown for demonstrating the accuracy and efficiency.
Author(s): S. Tao
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 1483 KB

Title: Design, Modeling, and Numerical Characteristics of the Plasmonic Dipole Nano-Antennas for Maximum Field Enhancement
Abstract: In this paper, we investigate the near-field enhanced optical absorption and far-field radiation characteristics of plasmonic dipole nano-antenna with different geometries which are rectangular, square, circular, and ellipse dipoles. Localized E-field enhancement at the excitation gap and reflection profile in an infinite 2D array of each nano-antenna are characterized and optimized at the resonant frequency of 375 THz, which corresponds to the incident wavelength of 800 nm. Numerical results show that the ellipse nano-antenna produces the most enhanced electric field at the excitation gap whereas the circular nano-antenna yields the best reflection and far-field radiation characteristics. This research is useful for the researchers and designers in choosing appropriate plasmonic dipole nano-antennas when incorporating with a photoconductive antenna for terahertz radiation enhancement.
Author(s): T. T. K. Nguyen, Q. M. Ngo, T. K. Nguyen
File Type: Journal Paper
Issue:Volume: 32      Number: 7      Year: 2017
Download Link:Click here to download PDF     File Size: 2228 KB