Serkan Alagoz

Sonic crystal acoustic switch device.

This study reports a wave-controlled sonic crystal switch device that exhibits a destructive interference-based wave to wave reverse switching effect. By applying control waves, this acoustic device, composed of a two-dimensional square lattice sonic crystal block, reduces acoustic wave transmission from input to output. The finite difference time domain simulation and experimental results confirm the wave-to-wave reverse switching effect at the peak frequencies of the second band. The proposed sonic crystal switch prototype provides a contrast rate of 86% at 11.3 kHz frequency. This wave-to-wave switching effect is useful for controlling wave propagation for smart structure applications.

Experimental observation of far-field and near-field focusing in a sonic crystal flat lens in air

This experimental study demonstrates intensity maps of far-field focusing using a two-dimensional triangular lattice sonic crystal and intensity maps of near-field focusing using a two-dimensional square lattice sonic crystal for various scatter materials. Besides, the paper presents an experimental method to estimate the effective refraction index of far-field flat lenses. The author introduces the experimental setup developed for the research and discusses the results obtained.

Opportunities for energy efficiency in smart cities

Rapid migration from rural to urban areas leads to the emergence of urbanization and sustainability problems. Management and monitoring of resources and infrastructures are getting more important today in crowded cities. Energy consumption is increasing with the growing population and intensified in highly populated parts of cities. This increased energy consumption results in high energy demand as well as the production of more pollutants and heat in these city parts. The management of pollution and heat problems leads to an additional energy demand. Therefore, energy efficiency is becoming central challenge for urban life similar to energy efficient structuring of living organisms. Practically, all activities arranging city life require energy. For instance, job activities, transportation, security, climate, catering, entertainment, commerce etc. In this study, we review active and passive approaches, which can be utilized for improvement of energy efficiency and thus sustainability of urbanization in todays cities. We give a discussion to present a vision for future smart cities in term of improvement of energy utilization and efficiency, and relieve of environmental issues. These approaches can be helpful for future cities for relieving issues originating from population increase.

Negative refractions by triangular lattice sonic crystals in partial band gaps

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.

Theoretical demonstration of the hybrid focusing points of sonic crystal flat lenses and possible applications

We demonstrate the hybrid focusing points of sonic crystals for a multi-source array applied to flat sonic crystal lenses. The contributions of different point source couples form hybrid focusing points. Ray-trace analyses are conducted for acoustic flat lenses with multi-source configurations. The finite-difference time-domain (FDTD) simulation of flat lenses with multi-source configurations demonstrates the establishment of pure and hybrid focusing points in a pyramidal constellation. The number of focusing points in the pyramidal constellation depends on the number of point sources. We propose an acoustic device for fine-tuning the location of a far-field hybrid focusing point and discuss its benefits for acoustic energy focusing application.

A space charge motion simulation with FDTD method and application in negative corona electrostatic field analysis

Abstract In this paper, a finite difference time domain based simulation method is presented for the spatio-temporal analysis of space charge motion and the proposed method is applied to negative corona electrostatic field analysis. Drifting and diffusion motion equations of space charges are numerically solved and used in the simulation of corona discharges considering effects of impact ionization, electron attachment, ion–ion recombination and ion–electron recombination. The results obtained from the simulation are discussed.

An Investigation of Ionic Flows in a Sphere-Plate Electrode Gap

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.

Modeling and analysis of dielectric materials by using gradient-descent optimization method

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.

Energy consumption analysis of motorized transportation in cities by considering average mobile mass

Ongoing migration trend to urban areas populates cities and leads to urbanization problems. A major problem of crowded cities is human mobility. Growing urban population and increase of personal automobiles in traffic lead to energy inefficiency in daily transportation activities and result in emission of more heat and pollutant in urban areas. Energy inefficiency in motorized transportation has negative effects on welfare of citizen, public health, air quality and economy of cities. More carbon emission and related global climate changes are global effects of energy inefficiency in transportation. This study presents an analysis of transportation energy consumption based on average mass mobility. Weighting average function is used to statistically represent transportation mode and social gender patterns of cities. Analysis examples are illustrated and solutions for improvement of energy efficiency are discussed in the aspect of human mobility in urban areas. The study can be useful for evaluation of transportation efficiency.

A distance-based dynamical transition analysis of time series signals and application to biological systems

This study demonstrates an application of distance-based numerical measures to the phase space of time series signals, in order to obtain a temporal analysis of complex dynamical systems. This method is capable of detecting alterations appearing in the characters of the deterministic dynamical systems and provides a simple tool for the real-time analysis of time series data obtained from a complex dynamical system even with black box functionality. The study presents a possible application of the method in the dynamical transition analysis of real EEG records from epilepsy patients.