Fulya C. Kunter

Radially symmetric weighted extended b-spline model

In this paper, the weighted extended basis splines approach in the finite element method is applied to the electrostatic, electromagnetic wave and bioheat problems for inhomogeneous boundary conditions and radially symmetric structures. This new method, which does not need mesh generation, overcomes some of the drawbacks of using meshes and piecewise-uniform or linear trial functions. Two-dimensional radially symmetric electrostatic and electromagnetic wave equations are evaluated. We also attempt to propose a three-dimensional radially symmetric unexposed human eye model for simulating changes in corneal temperature using these new finite elements in conjunction with linear, quadratic and cubic b-splines. Our findings indicate that weighted extended basis spline solutions improve the standard finite element method. The simulation results which are verified using the values reported in the literature, point out to better efficiency in terms of the accuracy level.

WEB-SPLINE PREDICTION OF OCULAR SURFACE TEMPERATURE USING BIOHEAT EQUATION WITH EXTERNAL SOURCE EXPOSURE

In this paper, the finite element method (FEM) with web-spline computer modeling were applied to study corneal surface temperature increase during microwave irradiation. The heat conduction model of the microwave-irradiated eye, which assumed to be 3D, was constructed. The mechanism of heat transfer from the eye and the selection of the thermal parameters of the media of the eye are also discussed. The implementation of these parameters in the web-spline solution of heat conduction was then developed. Furthermore, temperature rise calculations were compared with the values found in the literature pertaining to microwave-induced cataract formation.

Radio propagation path loss prediction of UMTS for an urban area

In this paper, three path loss models were used to predict path loss for the UMTS, in Istanbul, Turkey. Used models are Advanced Okumura-Hata model and Algorithm 9999 from the empirical path loss model class and Advanced Walfisch-Ikegami model from the deterministic path loss model class. The study concentrates on comparative parametric analysis for propagation path loss in macro cell region using different models and contains comparative study with real measurements obtained from a WCDMA based wireless network. This study concluded that among three models, the Advanced Walfisch-Ikegami model gives the best result in the urban environment for Istanbul.

Use of web-splines for waveguide of arbitrary domain

This paper illustrates web-splines and their implementations for electromagnetic problems such as waveguide of arbitrary domain. The cutoff wave numbers of modes for the coaxial waveguides are studied for illustrating the two dimensional concept. The numerical results have been compared with the analytical results. The significance of web-splines is that the number of nodes and computing time is reduced and instability problem is solved by using web-splines. The analyses presented in this study show the suitability of proposed method to complex electromagnetic problems. The finite element method which uses web-splines is applied to coaxial waveguides. With different ratio of radius of coaxial waveguides, accurate results are obtained by using web-splines. Web-splines and extended b-splines are used to find the wave number of TM and TE mode respectively.

Modeling of snow attenuation at mobile frequencies

Snow attenuation depends on many factors which are hard to observe and identify or classify. Modeling of snow attenuation is relatively complex. There are two main classes of methods used in snow attenuation prediction: the empirical method and the physical method. Physical method which we used in this work focuses on reproducing the physical behavior of factors involved in the process. The attenuation in the frequencies of mobile communication due to snow is simulated using Discrete Propagation Model. For this modeling, certain ice-crystal categories are chosen to be investigated. Needles, plates and branches are the main 3 groups which are focused, and 13 different models of snow particles in total are chosen to represent snow. The element in each group is chosen according to similar physical characteristics of ice crystal. It was found that attenuation due to snow is higher than rain attenuation specifically due to differences in particle size. In our simulations, frequencies of GSM communication, 900MHz, 1800MHz and 2270MHz, are used for calculation of attenuation.

Optical propagation in a turbulent atmosphere using the split step method

It is well known that optical signals propagating through the atmosphere are subject to random fluctuations in phase and amplitude. These fluctuations are caused by random temperature distributions in the atmosphere, which manifests themselves as a random index of refraction changes along the propagation path. We introduce a simulation method for modeling atmospheric turbulence effects, which is based on a split-step approach to numerically solve the parabolic wave equation. Atmospheric turbulence effects are modeled by a number of phase screens. These phase screens are generated on a numerical grid of finite size, which corresponds to a narrow spatial area of atmospheric turbulence.

Multi-components mobile propagation model of park environment

This work extends a previously published theoretical propagation model to a park environment and compares measured and computed data for different types, size and shape of vegetation or trees. Horizontal and vertical attenuation values of leaves, trees and branches, as a contribution to total attenuation are separately obtained and effects of each element to total attenuation are assessed. Finally a comparison is done between 900 MHz, 1800 MHz and 2270 MHz. The difference in path loss between the three frequencies has been analyzed for park environment. The result shows that the loss from vegetation which depends on biophysical parameters is substantially higher for the higher frequencies.

Web-spline solution of axisymmetric cylindrical problems

Weighted extended (web) b-spline method is a new type of meshless finite elements without using mesh generation. The resulting web-method does not require any grid generation and, as a consequence, can be implemented very efficiently. This paper illustrates web-splines and their implementations for axisymmetrical formulation of electromagnetic problems for inhomogeneous boundary conditions in cylindrical coordinates. The error analysis of applications with respect to exact solution using standard FEM, linear, quadratic and cubic web-splines for different grid widths are illustrated.

Temperature and Specific Absorption Rate Distribution in the Human Head Exposed to RF Propagation at Different Distances and Angles

This paper presents specific absorption rate (SAR) obtained inside a human head and the thermal effects due to exposure to a cellular phone. The cellular phone radiating at 900 MHz and 1800 MHz frequencies was modeled by microstrip patch antenna and its output power was chosen according to the worst-case scenario. By the aid of finite element method (FEM) based COMSOL Multiphysics software program, not only the effect of distance between the antenna and the head model but also the effect of antenna’s angle relative to the head on SAR and the temperature distribution in the head model were investigated. It was shown in the study that the distance and the angle of the antenna to the head had significant importance on the SAR values and the temperature increase in the head. As a result of the simulation, it was found that SAR values at 900 MHz were under the safety limit values whereas at 1800 MHz were under the limits when the distance between the antenna and the head was 0.2 cm. Furthermore, it was noted that the temperature increase on the head was in good agreement with the other studies.

The effects of antenna position on RF exposed human head

The aim of this paper is to examine the effects of antenna position at different angles by measuring the specific absorption rate (SAR) using finite element method (FEM) in a human head (SAM Model). This model is created in COMSOL Multiphysics. In this study, a patch antenna is placed at the side of the head model at different angle positions. SAR and temperature increase simulations are performed.