Browsing by Subject "Quality Factor"

Now showing 1 - 4 of 4

Open Access
Characterization of photonic crystals at microwave frequencies
(1996) Temelkuran, Burak
VVe investigated the surface reflection properties of layer-by-layer photonic crystals, for dielectric and metallic based photonic crystals. By using a FabryPerot cavity analogy with the reflection-phase information of the photonic crystals, we predicted defect frequencies of planar defect structures. Our predictions were in good agreement with the measured defect frequencies. The Fabry-Perot cavity analogy was also used to relate the quality factors of the planar defect structures to the transmission of the mirrors of the cavity. A simple model was used to simulate the transmission spectra of planar defect structures, which agreed well with the experimental data. We also investigated the transmission and reflection properties of two different metallic crystal structures (face-centeredtetragonal and simple tetragonal). We obtained rejection rates of 7-8 dB per layer from metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations of metallic structures. Planar defect structures built around metallic structures resulted in higher quality factors (2250). We observed high reflection-rejection ratios (-80 dB) at defect frequencies for planar defect structures, which was explained by using the Fabry-Perot analogy. Finally, the enhanced field inside the defect volume was measured, by using a monopole receiver antenna inserted inside the defect. The maximum observed enhancement with respect to the incident field was around 200 for a planar defect structure. By placing a Schottky diode detector inside planar and box-like defects, we built resonant cavity enhanced (RCE) detectors and measured the enhanced field inside the defect.
Open Access
Design and fabrication of micromachined radio-frequency cavity resonators
(2006) Arslan, Cihan Hakan
Resonators are used almost in every wireless communications applications and play an important role in the performance of these systems. At radio frequencies, for high performance applications, realization of high-Q resonators is required. Furthermore, in the near future, integration of RF resonators with rest of the system is intended. This thesis describes the design and fabrication of a type of radio-frequency MEMS cavity resonator operating in the frequency range of 2-3 GHz. The fabricated resonators are small in size so that they allow the integration of a whole system on a single-chip. The cavity is realized by selectively removing (etching) silicon substrate using standard MEMS techniques. The resonator is based on creating a low-loss inductor by enclosing the inductor in a metal-coated cavity and then resonating it with either a fixed or tunable high-Q capacitor. In this thesis, formulas for the inductance and the Q-factor of the cavity are derived and a number of resonators are fabricated and measured. The Q-factors of the measured cavities were found to be in the range going up to 25- 30. The obtained results are promising and showed that on-chip resonators with Q-factors higher than 30 can be realized based on this design and fabrication technique at this frequency range.
Open Access
Fabrication and characterization of amorphous silicon microcavities
(1999) Tanriseven, Selim
In this thesis, planar amorphous silicon microcavities were fabricated and characterized at room temperature. Microcavities were realized by embedding the active amorphous silicon layer between distributed Bragg reflectors, which are composed of alternating silicon oxide and silicon nitride layers. All of the layers were grown by plasma enhanced chemical vapor deposition on silicon substrates. By tuning the cavity mode to emission maximum of amorphous silicon, a narrow and enhanced emission line is obtained. Device characterization was done by means of photoluminescence, and reflectance measurements. The experimental results compare favorably with the theoretical calculations performed by transfer matrix method.
Open Access
Fabrication and characterization of microelectromechanical resonators
(2006) Özer, Sevil
Micromachined mechanical resonators are of considerable interest because of their many important scienti c and technological applications. They can be used as a components of radio-frequency lters in communication systems, mechanical electrometer or magnetometer for sensitive detection of force, charge, pressure. This work is directed towards the fabrication and characterization of microelectromechanical resonators, cantilevers and bridges. The SOI cantilever and the silicon nitride cantilevers and bridges are fabricated by using surface micromachining techniques. They are fabricated in the Advanced Research Laboratory of Bilkent University. The center frequencies are ranging from 20 kHz to 270 kHz. The characterization of cantilevers and bridges are done by using the beam de ection method and the ber optic interferometer method. The dynamic response of the rst devices, such as the resonance frequencies and the quality factors will be reported. In addition, simple beam theory and some fundamental loss mechanisms will be discussed. The experimental results will also be compared with the theoretical ones.