Design of a 4.2-5.4 GHz differential LC VCO using 0.35 mu m SiGeBiCMOS technology for IEEE 802.11a applications

In this paper, a 4.2-5.4 GHz, -Gm LC voltage controlled oscillator (VCO) for IEEE 802.11a standard is presented. The circuit is designed with AMS 0.35 mu m SiGe BiCMOS process that includes high-speed SiGe Heterojunction Bipolar Transistors (HBTs). According to post-layout simulation results, phase noise is -110.7 dBc/Hz at 1 MHz offset from 5.4 GHz carrier frequency and -113.4 dBc/Hz from 4.2 GHz carrier frequency. A linear, 1200 MHz tuning range is obtained from the simulations, utilizing accumulation-mode varactors. Phase noise was also found to be relatively low because of taking advantage of differential tuning concept. Output power of the fundamental frequency changes between 4.8 dBm and 5.5 dBm depending on the tuning voltage. Based on the simulation results, the circuit draws 2 mA without buffers and 14.5 mA from 2.5 V supply including buffer circuits leading to a total power dissipation of 36.25 mW. The circuit layout occupies an area of 0.6 mm(2) on Si substrate, including DC and RF pads

Down-converter for GPS applications

An RF down/up converter system is presented for indoor GPS applications. Transmission of GPS signals directly into indoor environments are limited and in some cases prohibited for regular operation of GPS system. However, ISM frequency bands, especially 433MHz can be used to retransmit the GPS signals to indoors. In this paper, RF down-converter building blocks are designed and implemented for sending GPS signals in ISM band. The down-converter system has heterodyne architecture which has LNAs, mixer, oscillator and filters. Received signals from the satellites are amplified, downconverted, filtered and again amplified. The overall performance of the designed system is 54.3dB gain and 2 dB noise figure while it is drawing 78mA current with 3V supply

Modeling and characterization of capacitive micromachined ultrasonic transducers

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent Univ., 2000.Thesis (Ph.D.) -- Bilkent University, 2000.Includes bibliographical references leaves 79-83.The Capacitive Micromachined Ultrasonic Transducer (cMUT) is a device used for the generation and detection of ultrasonic sound waves. The device is constructed on a silicon substrate using a microfabrication process. Individual cells constituting the device are membranes which have dimensions in the order of tens of microns, and are made up of a mechanicalh^ strong compound of silicon. The transducer itself has dimensions measured in centimeters, thus the total number of cells that make up a transducer is in the order of thousands. The excitation/detection of acoustic waves relies on the capacitance between the substrate and membrane: The presence of acoustic waves induces a small -AlC variation on the DC bias on the device, which can be used for detection, while a small -A.C component added to the DC bias by the drive circuit changes the electro-static attraction force on the membrane causing it to vibrate, producing acoustic waves. Basic advantages of cMUT devices include easy patterning of array structures, integration of drive/detection electronics with mechanical structures, and low cost. In this study, basic theory describing the characteristics of cMUT devices were developed. The analytic formulation was used to test the validity of a Finite Element Method (FEM) model. The FEM model, then, was emplo3'ed in the analysis of structures for which no analytical models are present. Specific problems solved using the FEM model included the characterization of cMUT devices with judiciously patterned electrodes. A more specific study showed that the bandwidth of an immersion device with an active area of radius 25 /¿m can be increased by 100% by simply setting the electrode radius to 10 /rm. The FEM analysis was, then, extended to handle the effects of substrate loss, which required the incorporation of an Absorbing Boundary Condition (ABC) into the model. A Normal Mode Theory analysis was conducted to give better insight to the physical nature of the effect of substrate loss to device characteristics. The dominant wavemode for a transducer of central frequency 2.5 MHz was found to be the lowest order anti-symmetric lamb wave mode (AO), for a silicon substrate of thickness 500 //m. A microfabrication process was developed for the production of cMUT devices. Hexagonally shaped transducers of radius 40 p.m were fabrictated on a conducting silicon substrated with silicon nitride as the sacrificial la.j'er and amorphous silicon as the membrane material. Both the gap and membrane thicknesses are set to 0.5 //m. 8, 16, and 24 /im gold plates were deposited as top eletrodes. The total number of active cells were 24 thousand for a substrate size of 0.7x0.7 cm^. Some experimental results were obtained from the fabricated transducers to support the analytical cMUT model. The device is found to have a central frequency of 2 MHz.Bozkurt, AyhanPh.D

The V-Groove lens

Ankara : The Department of Electrical and Electronics Engineering and Institute of Engineering and Sciences of Bilkent University, 1994.Thesis (Master's) -- -Bilkent University, 1994.Includes bibliographical refences.Primarily designed for imaging purposes, the acoustic microscope finds application in the qualitative evaluation of materials, too. The lens response as a function of defocus, which is known as the V{z) curve, is formed by the interference of various wave components reflected from the material surface. Leaky wave velocities of the material can be extracted from this interference pattern. The accuracy of the measurement is heavily influenced by the leaky wave contribution to the V(z) curve. Hence, lens geometries capable of efficiently exciting leaky wave modes need to be designed. If a particular geometry is to be used for measurements on materials exhibiting crystalographic anisotropies, it must be able to couple to modes only in a single direction, as well. The proposed V-Groove lens, combines the directional sensitivity of the Line Focus Beam lens and the efficiency of the Lamb Wave lens. The geometry is able to accurately measure the direction dependent leaky wave velocities of anisotropic materials. A new model based approach improves the accuarcy of the extracted velocities. In this study, the V-Groove lens has been analyzed theoretically. A mathematical model describing the lens response has been developed. The performance of the V-Groove lens has been tested by simulations. A new leaky wave velocity extraction algorithm based on fitting the model curve to actual curves using Nelder-Meade search has been proposed. A prototype lens has been manufactured and performance figures have been verified experimentally. The accuracy of the lens has been compared with those of other various geometries.Bozkurt, AyhanM.S

A Librarian in Oxford: An Experience of Erasmus Staff Mobility Programme

Bu çalışmanın amacı, Erasmus Personel Hareketliliği kapsamında 19-23 Kasım 2018 tarihleri arasında Oxford Brookes Üniversitesi Kütüphanesi’nde aldığım 5 günlük eğitim hakkında bilgi aktarmaktır. Aktarılan bilgiler, hazırlanan eğitim programı çerçevesinde günlük olarak paylaşılmıştır. Eğitim programı sonunda yazar tarafından Özyeğin Üniversitesi Kütüphanesindeki kütüphanecilik uygulamalarını anlatan bir sunum yapılmıştır Bu çalışmada ayrıca Oxford Üniversitesi Bodleian Kütüphanesi, tarihi kolejler, kültürel mekânlar ve Oxford şehri gözlemlerime de kısaca değinilmiştir.The aim of this study is to give information about the 5-day training that I received at Oxford Brookes University Library between 19-23 November 2018 within the scope of Erasmus Staff Mobility. The information was shared on a daily basis within the framework of the prepared training program. At the end of the training program, a presentation has been made by the author about the practices of librarianship in Özyeğin University Library. In this study, the Bodleian Library of Oxford University, historical colleges, cultural visits and the city of Oxford are briefly mentioned as well

PMMA-based wafer-bonded capacitive micromachined ultrasonic transducer for underwater applications

This article presents a new wafer-bonding fabrication technique for Capacitive Micromachined Ultrasonic Transducers (CMUTs) using polymethyl methacrylate (PMMA). The PMMA-based single-mask and single-dry-etch step-bonding device is much simpler, and reduces process steps and cost as compared to other wafer-bonding methods and sacrificial-layer processes. A low-temperature (<180 ◦ C) bonding process was carried out in a purpose-built bonding tool to minimize the involvement of expensive laboratory equipment. A single-element CMUT comprising 16 cells of 2.5 mm radius and 800 nm cavity was fabricated. The center frequency of the device was set to 200 kHz for underwater communication purposes. Characterization of the device was carried out in immersion, and results were subsequently validated with data from Finite Element Analysis (FEA). Results show the feasibility of the fabricated CMUTs as receivers for underwater applications

Fabrication of capacitive micromachined ultrasonic transducers for underwater applications using thermocompression wafer-bonder

Capacitive Micromachined Ultrasonic Transducers (CMUTs) are the prospective alternative to the traditional piezoelectric ultrasonic transducers. CMUTs are essentially parallel plate capacitors produced using Microelectromechanical Systems (MEMS) technology. The production of CMUTs is broken down into sacrificial underetching and wafer bonding methods. The sacrificial release-based techniques are complex and require several adjustments in terms of optimizing fabrication steps and material selections. Further, the sacrificial release-based processes need ultimate control over the gap height and membrane thickness. On the contrary, the wafer bonding fabrication processes are not only simpler than the sacrificial release methods but also provide a very good parametric control over the membrane thickness and gap height. Besides its advantages, the wafer bonding methods are very sensitive to contamination and surface roughness. The surface roughness problems are addressed by either using the costly Silicon-on-Insulator (SOI) wafers or by using complex Chemical Mechanical Polishing (CMP) method. This article presents a simple and economical CMUTs wafer bonding fabrication method. A thermocompression based metal bonded technique is adopted to successfully fabricate low frequency CMUTs to be used for underwater applications

Realization of a ROIC for 72x4 PV-IR detectors

Silicon Readout Integrated Circuits (ROIC) for HgCdTe Focal Plane Arrays of 1x4 and 72x4 photovoltaic detectors are represented. The analog circuit blocks are completely identical for both, while the digital control circuit is modified to take into account the larger array size. The manufacturing technology is 0.35μm, double poly-Si, three-metal CMOS process. ROIC structure includes four elements TDI functioning with a super sampling rate of 3, bidirectional scanning, dead pixel de-selection, automatic gain adjustment in response to pixel deselection besides programmable four gain setting (up to 2.58pC storage), and programmable integration time. ROIC has four outputs with a dynamic range of 2.8V (from 1.2V to 4V) for an output load of 10pF capacitive in parallel with 1MΩ resistance, and operates at a clock frequency of 5 MHz. The input referred noise is less than 1037 μV with 460 fF integration capacitor, corresponding to 2978 electrons

Indoor positioning based on global positioning system signals

The Global Positioning System (GPS) is highly reliable and accurate when used outdoors.However, in indoor environments, due to the additional signal loss incurred by the walls of the buildings, the detection and decoding of GPS signals becomes a difficult task. As a solution to the indoor area coverage problem, an indoor positioning system based on GPS repeaters and a modified positioning algorithm is proposed, designed, and tested. A prototype indoor positioning system for 1D/2D positioning is built using directional GPS antennas and low-noise amplifiers (LNA). The modified positioning algorithm is used for the real time processing of captured live GPS data. All the system components are integrated and positioning is obtained for the evaluation of the system performance. Results of the experiments show that the proposed system can be used for indoor positioning in locations where there is no GPS signal reception. The proposed system facilitates the continuation of GPS services indoors with hardware additions to the buildings and only a software update to a standard GPS receiver

Baykan Sezer as the possibility of native sociology

19. yüzyılda Batı’da yaşanan sorunlara çözüm getirme çabalarıyla sosyoloji bilimi ortaya çıkmıştır. Batı’da ortaya çıkan yeni toplumsal sorunlar ve bu sorunlara karşı düzen arayışı ve dünya egemenliğinin meşruluğu problemlerinin çözümü için sosyoloji araçsal bir şekilde kullanılmıştır. Ülkemizde Batı’nın sorunlarına karşı geliştirilen çözüm reçeteleri alınıp Türk toplumunun sorunlarına hazır reçete olarak sunulmuştur. Ancak Türk sosyolojisi bütünüyle bu taklitçi ve nakilci yaklaşımdan ibaret olmamıştır. Bu yöndeki özgün/yerli katkılardan biri Baykan Sezer’dir. Sezer, Türk toplumunun sorunlarını Doğu-Batı ilişkileri ve çatışması çerçevesinde ele alıp değerlendiren, sosyal bünyemizi açıklayan, düşünce geleneğimiz ve tarihimizle ilişki kuran bir “Türk Sosyolojisi” inşa etme kaygısında olmuştur. Sezer, Kemal Tahir’den etkilenerek sosyoloji biliminin merkezine tarihselliği koyarak Doğu-Batı ikilemi içerisinde Türk toplumunu anlamaya çalışmış, Türk sosyolojisinde yerlilik üzerinde durmuştur. Bu çalışmada Türk sosyolojisinin bir imkânı olarak Sezer’in görüşleri ele alınacaktır.In the 19th century, sociology emerged with the efforts to solve the problems in the West. Sociology has been used instrumentally for the new social problems that emerged in the West, the search for order against these problems and the solution of the problems of legitimacy of world sovereignty. Sociology emerged as a product of the West's own internal dynamics. But in our country, Sociology presented as a prescription for the problems of Turkish society by taking the recipes developed against the problems of the West. However, Turkish sociology did not consist entirely of this imitator and transporter approach. One of the original / local contributions in this direction is Baykan Sezer. Sezer pointed out the necessity of building a, Turkish Sociology that is appropriate to the conditions of the Turkish society, by taking and evaluating our problems within the framework of East-West relations and conflict, explaining our social structure and establishing a relationship with our tradition of thought and our history. Sezer, influenced by Kemal Tahir, tried to understand the Turkish society and its problems within the East-West dilemma by putting historicity in the center of sociology.The study will try to discuss the views of Sezer as an opportunity of Turkish sociology