Browsing by Subject "Fiber optics"

Now showing 1 - 7 of 7

Open Access
Asic implementation of high-throughput reed-solomon product codes
(2021-07) Sezer, Evren Göksu
A detailed ASIC implementation study of a decoder architecture for the prod-uct of two Reed-Solomon (RS) codes is presented. The implementation aims to achieve high throughput (more than 1 Tb/s) under low power and area consump-tion constraints while having more than 9 dB coding gain compared to uncoded transmission when concatenated with an inner polar code. The scope of work includes a comprehensive design space exploration for very high rate RS codes. Novel algorithms and architectures are introduced to achieve the design goals. High-throughput is achieved through a combination of pipelining and unrolling methods, while a fully-automated register balancing technique is used to mini-mize the implementation complexity. The implementation has been carried out using the 28nm TSMC library.
Open Access
Low power small size magnetic resonance imaging signal acquisition system with optical connections
(2022-12) Nuhoğlu, İlkcan
In Magnetic Resonance Imaging (MRI) systems echo signals received by a coil are sampled and subjected to digital signal processing. The physical link between the sampling system and the signal processor is coaxial cables in conventional applications. However, coaxial cables possess risks and limitations when placed in gradient and radio frequency fields, both of which are present in an MRI system. The complexity of issues related to coaxial cables increases rapidly as the number of channels scales up in parallel imaging applications. To overcome the drawbacks of coaxial cables, systems that employ fiber optic cables for the transmission of the analog signal have been proposed. In this work, we designed a system which transmits sampled and digitized analog signal through fiber optic cables, while the power required to perform acquisition and conversion operations is also delivered to the module using an optical link. To increase the number of channels that can be placed in a typical birdcage compartment, dimensions of the module are kept as small as possible. The module is designed to be used in a project with a 10.5 Tesla MRI system operating at 447 MHz which is currently available only at the University of Minnesota. The circuit design for one of the proposed approaches is completed at both the schematic and the layout levels to perform feasibility analysis. Theoretical estimations show that the power consumption is 263 mW and occupied cross-sectional area is 900 mm2 per channel while attaining more than 95 dBFS SNR figure using 65 MSPS sampling rate.
Open Access
Modeling of electrodes and implantable pulse generator cases for the analysis of implant tip heating under MR imaging
(Wiley-Blackwell Publishing, Inc., 2015) Acikel, V.; Uslubas, A.; Atalar, Ergin
Purpose: The authors purpose is to model the case of an implantable pulse generator (IPG) and the electrode of an active implantable medical device using lumped circuit elements in order to analyze their effect on radio frequency induced tissue heating problem during a magnetic resonance imaging (MRI) examination. Methods: In this study, IPG case and electrode are modeled with a voltage source and impedance. Values of these parameters are found using the modified transmission line method (MoTLiM) and the method of moments (MoM) simulations. Once the parameter values of an electrode/IPG case model are determined, they can be connected to any lead, and tip heating can be analyzed. To validate these models, both MoM simulations and MR experiments were used. The induced currents on the leads with the IPG case or electrode connections were solved using the proposed models and the MoTLiM. These results were compared with the MoM simulations. In addition, an electrode was connected to a lead via an inductor. The dissipated power on the electrode was calculated using the MoTLiM by changing the inductance and the results were compared with the specific absorption rate results that were obtained using MoM. Then, MRI experiments were conducted to test the IPG case and the electrode models. To test the IPG case, a bare lead was connected to the case and placed inside a uniform phantom. During a MRI scan, the temperature rise at the lead was measured by changing the lead length. The power at the lead tip for the same scenario was also calculated using the IPG case model and MoTLiM. Then, an electrode was connected to a lead via an inductor and placed inside a uniform phantom. During a MRI scan, the temperature rise at the electrode was measured by changing the inductance and compared with the dissipated power on the electrode resistance. Results: The induced currents on leads with the IPG case or electrode connection were solved for using the combination of the MoTLiM and the proposed lumped circuit models. These results were compared with those from the MoM simulations. The mean square error was less than 9%. During the MRI experiments, when the IPG case was introduced, the resonance lengths were calculated to have an error less than 13%. Also the change in tip temperature rise at resonance lengths was predicted with less than 4% error. For the electrode experiments, the value of the matching impedance was predicted with an error less than 1%. Conclusions: Electrical models for the IPG case and electrode are suggested, and the method is proposed to determine the parameter values. The concept of matching of the electrode to the lead is clarified using the defined electrode impedance and the lead Thevenin impedance. The effect of the IPG case and electrode on tip heating can be predicted using the proposed theory. With these models, understanding the tissue heating due to the implants becomes easier. Also, these models are beneficial for implant safety testers and designers. Using these models, worst case conditions can be determined and the corresponding implant test experiments can be planned.
Open Access
Modeling of thermal sensitivity of a fiber optic gyroscope coil with practical quadrupole winding
(SPIE, 2017) Ogut, Serdar; Osunluk B.; Özbay, Ekmel
Thermally induced bias error is one of the main performance limits for the fiber optic gyroscopes (FOGs). We reviewed the thermal sensitivity of FOG in detail and created a simulation environment by the Finite Element Method (FEM). Thermal sensitivity analysis is based on Shupe and elastooptic effects. Elastooptical interactions are modeled by using the two different FEM simulations and homogenization-dehomogenization processes. FEM simulations are validated by comparing the results with a laboratory FOG setup. We report the changes in the error characteristics for practical quadruple winding patterns. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
Open Access
Silicon nanocrystal doped polymer nanowire arrays
(2013) Çelebi, Muhammet
In this thesis, we successfully produced silicon nanocrystal embedded polymer micro and nanowire arrays by using a new top—to—bottom nanofabrication approach. Silicon nanocrystal (Si-Nc) quantum dots are photoluminescent materials that give bright optical illumination under UV light excitation. Si-Ncs were used to fabricate large area luminescent thin polymer ﬁlms before production of the ﬁbers. Among many of Si—Nc fabrication methods that are available, we chose a chemical route which takes the advantage of high product yield and ease of production steps, although the resultant size distribution is not uniform as other methods such as electrochemical treatment of Si wafers. Dopant Si—Ncs in polymer sheets shows some improved properties compared to free standing silicon nanocrystals, like longer luminescent life time in normal atmospheric conditions and in high temperatures as high as 300 °C. With utilizing these properties, thermal drawing of Si—Nc doped polymer ﬁbers is possible without harming the luminescence properties. Hence, throughout the work, different types of ﬁlms were investigated and polycarbonate ﬁlms were chosen for both their thermal and optical properties such as durable luminescence at high temperatures and low absorption at visible wavelengths. Consequently, with combining these properties with our iterative thermal size reduction method, we successfully produced silicon nanocrystal doped polymer micro and nanowire arrays. In literature, there are similar works treating the same idea of producing luminescent ﬁbers, which were realized with different techniques and material sets, like dye/QD doped nanoﬁbers or ﬁbers produced with conjugated polymers. However, the methods used to produce these type of geometries lacks in some aspects such as limited length, uniformity, alignment, reproducibility, etc. On the other hand, our iterative thermal drawing method is very successful for producing indeﬁnitely long, uniform and easily aligned ﬁbers. Our production steps can be summed in ﬁve steps which are: Si—Nc synthesis, ﬁlm preparation, ﬁlmrolling, consolidation, and two consecutive ﬁber drawing. Keeping the track of characterization of the product in each step is important. Hence, for silicon nanocrystals, we took photoluminescence (PL) intensity measurements, SEM/TEM images and temperature dependent PL measurements. Also for doped ﬁlms, we performed temperature dependent PL measurements and for the resultant ﬁbers we carried out cross—section SEM and PL characterizations. Silicon nanocrystal embedded micro and nanowires can be utilized as ﬁber gain medium, single photon source, directional emitter, light emitting diodes and optical sensing elements. Also, they increases light extraction efﬁciencies with guiding advantages and this can result to ﬂuorescence enhancement for luminescent active material dopants.
Open Access
Thermally induced bias errors for a fiber coil with practical quadrupole winding
(Institute of Electrical and Electronics Engineers Inc., 2017) Osunluk, Berk; Ogut, Serdar; Özbay, Ekmel
This paper presents an advanced thermal modeling of a fiber optic gyroscope (FOG) coil. We extended the current models to practical quadrupole winding. Model covers homogenization/dehomogenization parameters of fiber coil. A simulation environment is created by the Finite Element Method (FEM). Simulation environment is validated by comparing the results with laboratory FOG experiments.
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Türk Telekom tarihi
(Bilkent University, 2020) Gözdemir, Almina; Gedik, Berkan; Tütüncü, Can; Kaymak, Cemre; Çelik, Ekim
Bu çalışmada, Türkiye’nin telekomünikasyon sektöründeki en önemli temsilcilerinden biri olan Türk Telekom’un, 1980li yıllardan itibaren telekomünikasyondaki modernleşme çalışmaları ile başlayıp PTT bünyesinden ayrılması ve daha sonra özelleştirilmesi ile biten süreç ele alınmıştır. Bu araştırmada Türk Telekom A.Ş.’nin Türkiye telekomünikasyon alanına olan katkıları ve bu alanın gelişimindeki rolü incelenmiştir.