Browsing by Subject "Current distribution"

Now showing 1 - 4 of 4

Open Access
Distributed contact flip chip InGaN/GaN blue LED; comparison with conventional LEDs
(Elsevier, 2019) Genç, M.; Sheremet, Volodymyr; Elçi, M.; Kasapoğlu, A.; Altuntaş, İ.; Demir, İ.; Eğin, G.; İslamoğlu, Serkan; Gür, E.; Muzafferoğlu, N.; Elagöz, S.; Gülseren, Oğuz; Aydınlı, A.
This paper presents high performance, GaN/InGaN-based light emitting diodes (LEDs) in three different device configurations, namely Top Emitting (TE) LED, conventional Flip Chip (FC) and Distributed Contact (DC) FC. Series resistances as low as 1.1 Ω have been obtained from FC device configurations with a back reflecting ohmic contact of Ni/Au/RTA/Ni/Ag metal stack. A small shift has been observed between electroluminescence (EL) emissions of TE LED and the FC LEDs. In addition, FWHM value of the EL emission of DCFC LED has shown the minimum value of 160 meV (26.9 nm). Furthermore, DCFC LED configuration has shown the highest quantum efficiency and power output, with 330 mW at 500 mA current injection, compared to that of traditional wire bonded TE LEDs and the conventional FC LEDs.
Open Access
Fourier transform magnetic resonance current density imaging (FT-MRCDI) from one component of magnetic flux density
(IOP Publishing, 2010-05-17) Ider, Y. Z.; Birgul, O.; Oran, O. F.; Arıkan, Orhan; Hamamura, M. J.; Muftuler, L. T.
Fourier transform (FT)-based algorithms for magnetic resonance current density imaging (MRCDI) from one component of magnetic flux density have been developed for 2D and 3D problems. For 2D problems, where current is confined to the xy-plane and z-component of the magnetic flux density is measured also on the xy-plane inside the object, an iterative FT-MRCDI algorithm is developed by which both the current distribution inside the object and the z-component of the magnetic flux density on the xy-plane outside the object are reconstructed. The method is applied to simulated as well as actual data from phantoms. The effect of measurement error on the spatial resolution of the current density reconstruction is also investigated. For 3D objects an iterative FT-based algorithm is developed whereby the projected current is reconstructed on any slice using as data the Laplacian of the z-component of magnetic flux density measured for that slice. In an injected current MRCDI scenario, the current is not divergence free on the boundary of the object. The method developed in this study also handles this situation.
Open Access
Integral equation based method for the fast analysis of irregularly contoured large finite phased arrays
(Institution of Engineering and Technology, 2007) Ertürk, Vakur B.; Çivi, Ö. A.
A fast and accurate integral equation based hybrid method that can investigate electrically large, arbitrarily contoured finite planar arrays of printed elements is developed. The method is a hybridization of the Galerkin type method of moments (MoM) and generalized forward backward method (GFBM) with the grounded dielectric slab's Green's function; and the acceleration of the resultant hybrid method by a discrete Fourier transform (DFT) based acceleration algorithm. Numerical results in the form of array current distribution are given for arbitrarily contoured as well as thinned arrays of probe fed microstrip patches where current on each element expanded by more than one subsectional basis function.
Open Access
Magnetic resonance electrical impedance tomography (MREIT) based on the solution of the convection equation using FEM with stabilization
(Institute of Physics Publishing, 2012-07-27) Oran, O. F.; Ider, Y. Z.
Most algorithms for magnetic resonance electrical impedance tomography (MREIT) concentrate on reconstructing the internal conductivity distribution of a conductive object from the Laplacian of only one component of the magnetic flux density (∇ 2B z) generated by the internal current distribution. In this study, a new algorithm is proposed to solve this ∇ 2B z-based MREIT problem which is mathematically formulated as the steady-state scalar pure convection equation. Numerical methods developed for the solution of the more general convectiondiffusion equation are utilized. It is known that the solution of the pure convection equation is numerically unstable if sharp variations of the field variable (in this case conductivity) exist or if there are inconsistent boundary conditions. Various stabilization techniques, based on introducing artificial diffusion, are developed to handle such cases and in this study the streamline upwind Petrov-Galerkin (SUPG) stabilization method is incorporated into the Galerkin weighted residual finite element method (FEM) to numerically solve the MREIT problem. The proposed algorithm is tested with simulated and also experimental data from phantoms. Successful conductivity reconstructions are obtained by solving the related convection equation using the Galerkin weighted residual FEM when there are no sharp variations in the actual conductivity distribution. However, when there is noise in the magnetic flux density data or when there are sharp variations in conductivity, it is found that SUPG stabilization is beneficial.