Browsing by Subject "Theoretical calculations"

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    All-chalcogenide glass omnidirectional photonic band gap variable infrared filters
    (AIP Publishing, 2009) Kondakci, H. E.; Yaman, M.; Koylu, O.; Dana, A.; Bayındır, Mehmet
    We report on the design, fabrication, and characterization of spatially variable infrared photonic band gap filter that consists of thermally evaporated, high refractive indexcontrast, amorphous chalcogenide glass multilayers. Due to graded thickness structure, the filter exhibits a position dependent stop band and a cavity mode ranging from 1.8 to 3.4 μm3.4 μmwavelengths. Reflection measurements on the variable filter agree well with theoretical calculations. These results pave the way to low-loss infrared mirrors, filters, spectral imaging, and miniaturized spectrometers at infrared region.
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    Digital microfluidics for reconfigurable antennas
    (IEEE, 2014) Damgaci, Y.; Çağatay, Engin; Bıyıklı, Necmi; Cetiner, B. A.
    Usage of fluids (microfluidic or otherwise) in antennas provides a conceptually easy reconfiguration mechanism in the aspect of physical alteration. However, a requirement of pumps, valves, etc. for liquid transportation makes the antenna implementations rather impractical for the real-life scenarios. This work reports on the theoretical calculations and experiments conducted to evaluate the electrowetting on dielectric (EWOD) driven digital microfluidics as a reconfiguration mechanism for antennas and RF circuits. © 2014 European Association on Antennas and Propagation.
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    Theoretical modeling of the doping process in polypyrrole by calculating UV/Vis absorption spectra of neutral and charged oligomers
    (2008) Okur, S.; Salzner, U.
    Changes in absorption spectra during doping of oligopyrroles were investigated with time-dependent density functional theory on optimized structures of neutral, singly, and doubly charged pyrrole oligomers with up to 24 rings. In the absence of counterions, defects are delocalized. Counterions induce localization. For dications two polarons on the same chain are preferred over a bipolaren. Intragap absorptions arise in charged species, no matter whether defects are localized or delocalized. Cations and dications give rise to two sub-band transitions. The cation peaks have lower energies than those of dications. The first excitations of cations have lower oscillator strengths than the second; for dications the second peak is weaker than the first. For very long oligomers, the second sub-band absorption vanishes and a third one appears at higher energy. The behavior of pyrrole oligomers is analogous to that of thiophene oligomers. Theoretical UV spectra for cations and dications of short oligomers (six to eight rings) match experimental spectra of polypyrrole at low and at high doping levels, respectively. The error in the theoretical calculations is about 0.4 eV, slightly larger than for thiophene oligomers at the same level of theory. © 2008 American Chemical Society.