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Öğe Effects of wave propagation anisotropy on the wave focusing by negative refractive sonic crystal flat lenses(Iop Publishing Ltd, 2012) Alagoz, S.In this study, wave propagation anisotropy in a triangular lattice crystal structure and its associated waveform shaping in a crystal structure are investigated theoretically. A directional variation in wave velocity inside a crystal structure is shown to cause bending wave envelopes. The authors report that a triangular lattice sonic crystal possesses six numbers of a high symmetry direction, which leads to a wave convergence caused by wave velocity anisotropy inside the crystal. However, two of them are utilized mostly in wave focusing by an acoustic flat lens. Based on wave velocity anisotropy, the pseudo ideal imaging effect obtained in the second band of the flat lens is discussed.Öğe An Investigation of Ionic Flows in a Sphere-Plate Electrode Gap(Iop Publishing Ltd, 2013) Alisoy, H. Z.; Alagoz, S.; Alisoy, G. T.; Alagoz, B. B.This paper presents analyses of ion flow characteristics and ion discharge pulses in a sphere-ground plate electrode system. As a result of variation in electric field intensity in the electrode gap, the ion flows towards electrodes generate non-uniform discharging pulses. Inspection of these pulses provides useful information on ionic stream kinetics, the effective thickness of ion cover around electrodes, and the timing of ion clouds discharge pulse sequences. A finite difference time domain (FDTD) based space-charge motion simulation is used for the numerical analysis of the spatio-temporal development of ionic flows following the first Townsend avalanche, and the simulation results demonstrate expansion of the positive ion flow and compression of the negative ion flow, which results in non-uniform discharge pulse characteristics.Öğe Modeling and analysis of dielectric materials by using gradient-descent optimization method(World Scientific Publ Co Pte Ltd, 2017) Alagoz, B. B.; Alisoy, H. Z.; Koseoglu, M.; Alagoz, S.This study presents a numerical method based on parallel RC equivalent circuit model fitting methodology for analysis and modeling of dielectric materials. The proposed method employs gradient-descent optimization method (GDOM) to estimate parallel RC equivalent circuit model from current waveforms by minimizing sum of squared difference (SSD) error. Estimation of parallel RC equivalent circuit parameters from measured current waveforms provides a useful tool for identification, simulation and analysis of dielectric materials. Moreover, applications of the proposed method for time and frequency analyses of dielectric materials are demonstrated numerically. Numerical simulations were presented to discuss efficiency of the proposed method for modeling, analysis and monitoring of insulator materials.Öğe Negative refractions by triangular lattice sonic crystals in partial band gaps(Iop Publishing Ltd, 2015) Alagoz, S.; Alagoz, B. B.; Sahin, A.; Nur, S.This study numerically demonstrates the effects of partial band gaps on the negative refraction properties of sonic crystal. The partial band gap appearing at the second band edge leads to the efficient transmissions of scattered wave envelopes in the transverse directions inside triangular lattice sonic crystal, and therefore enhances the refraction property of sonic crystal. Numerical simulation results indicate a diagonal guidance of coupled scattered wave envelopes inside crystal structure at the partial band gap frequencies and then output waves are restored in the vicinity of the output interface of sonic crystal by combining phase coherent scattered waves according to Huygens' principles. This mechanism leads to two operations for wavefront engineering: one is spatial wavefront shifting operation and the other is convex-concave wavefront inversion operation. The effects of this mechanism on the negative refraction and wave focalization are investigated by using the finite difference time domain (FDTD) simulations. This study contributes to a better understanding of negative refraction and wave focusing mechanisms at the band edge frequencies, and shows the applications of the slab corner beam splitting and SC-air multilayer acoustic system.Öğe A numerical method for the analysis of polydisperse aerosol particles charging in a coaxial electrode system(Elsevier Science Bv, 2012) Alisoy, H. Z.; Alagoz, S.; Alisoy, G. H.; Alagoz, B. B.In this paper, charging kinetics of polydisperse aerosol particles in a corona field of a coaxial electrode system is numerically analyzed for a logarithmic normal distribution of aerosol particle size. The particle charging and the particle current are calculated by using a charging model considering ion concentration and particle mobility. Particle charging profiles under varying ion density and electrical field intensity distributions of the charging chamber were revealed. A low charging profile in the transition region of bipolar corona field was demonstrated in the simulation results. (C) 2011 Elsevier B.V. All rights reserved.Öğe Spatio-spectral analyses of electromagnetic wave energy absorption and heating effect(Elsevier Gmbh, 2014) Alisoy, H. Z.; Alagoz, B. B.; Us, S. Barlaz; Deniz, F. N.; Alagoz, S.This study presents a theoretical analysis method to calculate electromagnetic (EM) wave power absorption spectrum of materials by using attenuation coefficients. The heating effect of EM waves is modeled to analyze spectral distribution of temperature rises inside material body as a result of EM wave power absorption. These analyses are very useful for the investigation of electromagnetic wave-material interaction on the bases of electro-physical material parameters (permittivity, permeability and conductivity). An illustrative analysis of spatio-spectral distribution of EM wave energy absorption and resulting heating effect were conducted for muscle tissues and the results are discussed. (C) 2014 Elsevier GmbH. All rights reserved.
