Asim Egemen Yilmaz

Triangular-Shaped Single-Loop Resonator: A Triple-Band Metamaterial With MNG and ENG Regions in S/C Bands

A new metamaterial topology, called triangular-shaped single-loop resonator (SLR), is introduced with two distinct μ-negative (MNG) regions and one ε-negative (ENG) region over the S/C frequency bands. Transmission and reflection characteristics of the suggested subwavelength resonator are analyzed using full-wave electromagnetic solvers, Ansoft HFSS and CST Microwave Studio (MWS), to demonstrate the presence of four closely located resonance frequencies within the 3.3-5.1 GHz range. Effective permittivity and permeability parameters of the resulting composite medium are retrieved from simulated complex scattering parameters to verify the existence of fully developed MENG and ENG regions. Dependence of the resonance frequencies on the design parameters of the triangular SLR unit cell and on the presence of its gaps are also investigated in detail.

Distinguishing electronic devices using harmonic radar

A new approach to distinguishing electronic circuits using nonlinear/harmonic radar is presented in this paper. The radar transmits a single tone signal to the electronic circuits, consisting of nonlinear components, and exploits received harmonic response for separation. Unlike previous studies, the transmitted signal power is swept within a determined range so that the received powers at each harmonic are analyzed to capture the nonlinear characteristics. To predict the behavior of the nonlinear circuits such as diode clamper, diode limiter and full wave rectifier, certain statistical features of the received powers are analyzed. We show that the received power at the harmonics are distinctive for each circuit using Euclidean distances of features in feature space.

Data fusion for a surveillance system: addressing some practical problems

This paper presents solutions for some data fusion problems encountered in a real life command and control system and outlines the systems engineering approach used while addressing these problems. The systems engineering approach takes into account the functionality and the capabilities of the system, operational and user aspects, safety and security, subsystem interfaces, sustainability and design constraints. The system comprises several sensor points scattered around a vast region that collect radar plots and produce tracks and two central command points that receive these tracks and process them. The processing of tracks involve carrying the tracks obtained from geographically dispersed sensors onto a common reference point (e.g. coordinate conversion and registration), fusing the tracks originating from the same target provide full air picture of the surveillance region. Also, the proposed system reproduces the track states and corresponding covariance matrix from the track quality information.

Enhancement of Particle Swarm Optimization algorithms for the 3D crack reconstruction from ECT signals

This paper presents some strategies to enhance the efficiency of Particle Swarm Optimization (PSO) algorithms applied for the three-dimensional reconstruction of cracks from eddy current testing (ECT) signals. A fast forward FEM-BEM solver using database was adopted to simulate the ECT signals due to cracks with parallelepiped shape for various lengths, widths and depths. The inverse problem is formulated as an optimization problem, aiming to minimize the distance between the signal due to of the real crack and the signal due to a potential solution (crack). A novel technique which combines the features of PSO and local search methods is used in the inversion of ECT signals. The local search methods are specific to such kind of inverse problems. The points used in the local search are chosen in order to avoid local minimum in PSO algorithms. Numerical results of the 3D reconstruction of cracks from simulated 2D signals are presented and discussed.

PERFORMANCE COMPARISON OF VARIOUS HEXAHEDRAL ELEMENT QUALITY METRICS VIA PARAMETRIC DISTORTION OF AN IDEAL ELEMENT

In this study, by means of parametric distortion of an ideal hexahedral element, we investigate the accuracy and sensitivity of some hexahedral element quality metrics existing in the literature. We also investigate and compare the relative computational costs of each metrics. We try to identify the weaknesses and strengths of all metrics under interrogation, and come up with some proposals for practical use.

Adaptive desirability function for multiobjective design of thinned array antennas

The desirability function (DF) is widely used in multiobjective optimization problems especially when individual design objectives have conflicting responses. DF successfully transforms a complicated problem into a classical single parameter optimization problem by combining contradicting constraints. It can be applied to complex high-dimensional and multimodal problems where classical iterative methods are often insufficient to provide practical solutions. DF, however, requires prior knowledge about the trade-off parameter ranges and the preference parameters, namely, the target bound and shape. Thus, expert knowledge before optimization is often critical for convergence. In this work, multiobjective optimization problem is illustrated on thinned array antenna design. Single and two objective optimizations are compared with the all-active (no thinning) array. Adaptive desired function (ADF) is proposed, which requires no prior knowledge about the trade-off objectives. ADF is observed to provide faster convergence and better optimization results/behavior with its “fire, monitor, and update” approach when compared with the classical DF’s “fire, forget, and if it does not converge then restart” approach.

A comparison on the new electronic attack techniques against pulse compression radars

In this study, the mathematical models of Smeared and Chopping/Interleaving Spectrum techniques, which are recent electronic attack techniques against the pulse compression radars, are presented. Then, matched filter outputs are compared by means of a simulator. Moreover, the effect of the weighting filter in the radar receiver is also analyzed.

Similarity analysis method for structured statements and sentences in Turkish

In this study, a technique using a statistical approach without applying linguistic and syntactic techniques is presented for the similarity analysis of technical specifications and/or sofware requirements expressed in the natural language. For this purpose, a new and practical metric for the similarity of specification/requirement expressions is defined; and comparisons with other metrics in the literature are performed.

Grassmann and His Contributions to Electromagnetics [Historical Corner]

The main aim of this essay is to revisit and to remind the reader of the direct and indirect contributions of Hermann Gunther Grassmann to electromagnetics. Being ahead of his time, Grassmann did not have a chance to see that his mathematical ideas and studies were accepted and acclaimed. Acceptance and reception of his publications in applied sciences took more than a century. In this essay, we will try to revisit three major contributions of this genius scientist: his exterior algebra leading to the differential forms, his force law, and his law of optics.

Conformai dual-band frequency selective surface on Textile: Design, prototyping and expriment

In this study, a textile based dual band conformai frequency selective surface has been proposed in order to filter the electromagnetic waves. A commonly known split ring resonator (SRR) is used for unit cell design and an array with 4×6 elements used for planar design presented. The proposed array is bended on a sphere having a radius of 22.45 cm. The performance of the conformal structure is evaluated and compared with the planar one. Measurement results have also been presented.