Ayhan Altintas
Bilkent University, Ee, Faculty Member
We present a whispering-gallery-mode resonance-enhanced microwave-detected photoconductivity-decay method for contactless measurement of recombination lifetime in highresistivity semiconductor layers. We applied the method to undoped... more
We present a whispering-gallery-mode resonance-enhanced microwave-detected photoconductivity-decay method for contactless measurement of recombination lifetime in highresistivity semiconductor layers. We applied the method to undoped Silicon wafers of high resistivity at 5 and 30 kOhm*cm and measured the conductivity relaxation times of 10 and 14 microseconds, respectively. In wafers being considered, they are supposed to be defined by the electron-hole diffusion from the bulk to the wafer surfaces.
Research Interests:
We analyze the interplay of two different types of electromagnetic behavior demonstrated by a 2-D dielectric prism: Geometrical Optics and resonance. As it is shown, the first is responsible, for instance, for enhanced reflection from an... more
We analyze the interplay of two different types of electromagnetic behavior demonstrated by a 2-D dielectric prism: Geometrical Optics and resonance. As it is shown, the first is responsible, for instance, for enhanced reflection from an isosceles 90-degree prism of arbitrary epsilon and size, if illuminated from the base. The second is responsible for the peaks in the total scattering and absorption cross-sections (RCS) at the natural-mode frequencies. The numerical model is based on Nystrom discretization of Muller-type integral equations that provides guarantied convergence.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
This paper describes our theoretical and experimental investigation on light scattering from individual murine red blood cells (RBCs). Based on measured cell morphologies at different ionic strength and osmolarity conditions, we simulated... more
This paper describes our theoretical and experimental investigation on light scattering from individual murine red blood cells (RBCs). Based on measured cell morphologies at different ionic strength and osmolarity conditions, we simulated the light scattering characteristics of the cells by using the Muller boundary integral equation (MBIE) method. The calculated cross section values showed good agreement with our experimental data obtained with conventional and imaging-based flow cytometries.
Research Interests:
The electromagnetic 2-D scattering from a single biological cell is analyzed by using Muller boundary integral equation (MBIE) method. The accuracy and smoothness of the solution are improved by applying Nystrom-type discretization. We... more
The electromagnetic 2-D scattering from a single biological cell is analyzed by using Muller boundary integral equation (MBIE) method. The accuracy and smoothness of the solution are improved by applying Nystrom-type discretization. We present numerical results on a single biological cell during the different major phases of mitosis. The simulations show that the cell shape, as well as the cell orientation, have a large influence on the scattering properties of biological cell models.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
We present experimental investigation of light-controlled photonics-enhanced quasi-optical mm-wave beam switch operating at a resonant frequency in the mm-wave band of 75 to 110 GHz. The switch is implemented as a Bragg structure with a... more
We present experimental investigation of light-controlled photonics-enhanced quasi-optical mm-wave beam switch operating at a resonant frequency in the mm-wave band of 75 to 110 GHz. The switch is implemented as a Bragg structure with a resonant layer of high-resistivity silicon that creates a narrow transmission peak within the mm-wave propagation gap. The peak amplitude is sensitive to the intensity of light pulses illuminating the structure. When using a silicon wafer of 30 KOhm · cm resistivity and light pulses created by a 400W LED-array light source, we achieved mm-wave transmission peak modulation exceeding 15 dB.
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
Research Interests:
Research Interests:
Research Interests:
For the original article see ibid., vol.23, no.20, p.1097-8 (1987). In a recent letter Snyder, Ankiewicz and Altintas stated, without justification according to the commenter, that the recent coupled mode theory of Hardy and Streifer (see... more
For the original article see ibid., vol.23, no.20, p.1097-8 (1987). In a recent letter Snyder, Ankiewicz and Altintas stated, without justification according to the commenter, that the recent coupled mode theory of Hardy and Streifer (see J. Lightwave Technol., vol.LT-3, no.5, p.1135-46, 1985) (hereafter H-S) is fundamentally in error, and claimed that the prior theory is superior. To support this contention they published two misleading graphs, which on more careful scrutiny indicate that the H-S theory is in fact more accurate than the prior theory. In reply the original authors show that the H-S full perturbation result is consistently less accurate than the standard first-order result for describing polarisation phenomena, and also show how this is corrected.
Research Interests:
Research Interests:
Research Interests:
A high-frequency analysis of electromagnetic modal reflection and transmission coefficients is presented for waveguide discontinuities formed by joining different waveguide sections. The analysis uses an extended version of the concept of... more
A high-frequency analysis of electromagnetic modal reflection and transmission coefficients is presented for waveguide discontinuities formed by joining different waveguide sections. The analysis uses an extended version of the concept of geometrical theory of diffraction based equivalent edge currents in conjunction with the reciprocity theorem to describe interior scattering effects. If the waveguide modes and their associated modal rays can
Research Interests:
Research Interests:
Research Interests:
Research Interests:
A full-wave analysis technique based on the method of moments solution of the electric field integral equation is presented to evaluate the MIMO channel matrix accurately by including majority of electromagnetic effects. Effects of mutual... more
A full-wave analysis technique based on the method of moments solution of the electric field integral equation is presented to evaluate the MIMO channel matrix accurately by including majority of electromagnetic effects. Effects of mutual interactions among the array elements through space and surface waves (in the case of printed arrays) are included in the channel matrix. Besides achieving the
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT Mobile radio planning requires the accurate prediction of electromagnetic field strengths over large areas and in a wide variety of environments. This present approaches to predicting field patterns present a similar behavior... more
ABSTRACT Mobile radio planning requires the accurate prediction of electromagnetic field strengths over large areas and in a wide variety of environments. This present approaches to predicting field patterns present a similar behavior about the main trend in field attenuation. However, they do not give numerically or analytically exact results. The spectral acceleration forward-backward (FB/SA) is an integral equation based numerical method that obtains the exact scattering data over very undulating terrain profiles with a computational cost of O(N). In this paper, the propagation and coverage analysis problem over different terrain profiles is explored using the FB/SA. In addition, the exact solution is compared with some popular propagation models.
Research Interests:
... Thus the original problem is reduced to the search for the sur-face current density function X(q. By using the boundary condi-tion (3) we ... and hence the condition (4). Note that the leading con-tribution to the coefficient ZC,... more
... Thus the original problem is reduced to the search for the sur-face current density function X(q. By using the boundary condi-tion (3) we ... and hence the condition (4). Note that the leading con-tribution to the coefficient ZC, given by (17) comes from the term ikaZ which remains ...