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Yayın Volumetric ultrasound imaging using 2-D CMUT arrays(IEEE-Inst Electrical Electronics Engineers Inc, 2003-11) Oralkan, Ömer; Ergün, Arif Sanlı; Cheng, Ching-Hsiang; Johnson, Jeremy A.; Karaman, Mustafa; H. Lee, Thomas; Khuri-Yakub, Butrus ThomasRecently, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as a candidate to overcome the difficulties in the realization of 2-D arrays for real-time 3-D imaging. In this paper, we present the first volumetric images obtained using a 2-D CMUT array. We have fabricated a 128 x 128-element 2-D CMUT array with through-wafer via interconnects and a 420-mum element pitch. As an experimental prototype, a 32 x 64-element portion of the 128 X 128-element array was diced and flip-chip bonded onto a glass fanout chip. This chip provides individual leads from a central 16 X 16-element portion of the array to surrounding bondpads. An 8 x 16-element poition of the array was used in the experiments along with a 128-channel data acquisition system. For imaging phantoms, we used a 2.37-mm diameter steel sphere located 10 mm from the array center and two 12-mm-thick Plexiglas plates located 20 mm and 60 mm from the array. A 4 X 4 group of elements in the middle of the 8 X 16-element array was used in transmit, and the remaining elements were used to receive the echo signals. The echo signal obtained from the spherical target presented a frequency spectrum centered at 4.37 MHz with a 100% fractional bandwidth, whereas the frequency spectrum for the echo signal from the parallel plate phantom was centered at 3.44 MHz with a 91% fractional bandwidth. The images were reconstructed by using RF beamforming and synthetic phased array approaches and visualized by surface rendering and multiplanar slicing techniques. The image of the spherical target has been used to approximate the point spread function of the system and is compared with theoretical expectations. This study experimentally demonstrates that 2-D CMUT arrays can be fabricated with high yield using silicon IC-fabrication processes, individual electrical connections can be provided using through-wafer vias, and flip-chip bonding can be used to integrate these dense 2-D arrays with electronic circuits for practical 3-D imaging applications.Yayın DAG-SLODAR (SLOpe Detection And Ranging) Teleskobu(Türk Astronomi Derneği, 2020-12-11) Şatır, Onur; Yeşilyaprak, Cahit; Keskin, OnurAtmosferin astronomik gözlemlere olan olumsuz etkilerini alt etmek üzere geliştirilmiş ve DAG teleskobunda da kullanılacak olan Adaptif Optik (AO) sistemleri, türbülansın ayrıntılı bir şekilde karakterize edilmesine ihtiyaç duyar. SLODAR, atmosferik optik türbülansın dikey profilini, iki yakın yıldızın Shack-Hartmann dalgacephesi algılayıcısı (SH-WFC) ile yapılan dalgacephesi eğimi ölçümlerinin çapraz korelasyonundan elde eden bir yöntemdir. SLODAR sistemi, küçük çaplı (?50cm) bir teleskobun odak düzlemine yerleştirilen, iki SH-WFC barındıran SLODAR aygıtından oluşur. Paranal, La Palma, Mauna Kea ve SAAO gözlemevlerinde kurulan SLODAR teleskopları "yer katmanı (ground layer)" olarak adlandırılan ve yerleşkenin üzerindeki ilk kilometre içindeki türbülansı ölçmek amacıyla kullanılmışlardır. Bu sunumda DAG yerleşkesinde kurulmakta olan SLODAR sisteminden bahsedilecektir.Yayın OPAM tarafından üretilen derotator sistemi ve TROIA (Turkish Adaptive Optics System for Infrared Astronomy) adaptif optik sistemi(Türk Astronomi Derneği, 2020-12-11) Keskin, OnurDAG teleskopu için FMV Işık Üniversitesi Optomekatronik Uygulama ve Araştırma Merkezi’nde (OPAM) son tasarımı başarıyla bitirilerek, üretim aşamasına geçilen derotator ve adaptif optik (TROIA) sistemleri tanıtılacaktır.Yayın Adaptive optics for DAG telescope(Türk Astronomi Derneği, 2020-12-11) Keskin, Onur; Jolissaint, LaurentWhat we propose for DAG is therefore a natural guide star GLAO system, that can be turned into a highly efficient AO system. Thus the working principle and expected performance analysis will be shown. In this manner most DAG users will be able to make some use of the DAG AO. Later, it will be possible to upgrade the system by changing th algorithm and adding 1 or 2 additional DM, and even laser guide stars.Yayın Forward-viewing CMUT arrays for medical Imaging(IEEE-INST Electrical Electronics Engineers Inc, 2004-07) Demirci, Utkan; Ergün, Arif Sanlı; Oralkan, Ömer; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasThis paper reports the design and testing of forward-viewing annular arrays fabricated using capacitive micromachined ultrasonic transducer (CMUT) technology. Recent research studies have shown that CMUTs have broad frequency bandwidth and high-transduction efficiency. One- and two-dimensional CMUT arrays of various sizes already have been fabricated, and their viability for medical imaging applications has been demonstrated. We fabricated 64-element, forward-viewing annular arrays using the standard CMUT fabrication process and carried out experiments to measure the operating frequency, bandwidth, and transmit/receive efficiency of the array elements. The annular array elements, designed for imaging applications in the 20 MHz range, had a resonance frequency of 13.5 MHz in air. The immersion pulse-echo data collected from a plane reflector showed that the devices operate in the 5-26 MHz range with a fractional bandwidth of 135%. The output pressure at the surface of the transducer was measured to be 24 kPa/V. These values translate into a dynamic range of 131.5 dB for I-V excitation in 1-Hz bandwidth with a commercial low noise receiving circuitry. The designed, forward-viewing annular CMUT array is suitable for mounting on the front surface of a cylindrical catheter probe and can provide Doppler information for measurement of blood flow and guiding information for navigation through blood vessels in intravascular ultrasound imaging.Yayın Integration of 2D CMUT arrays with front-end electronics for volumetric ultrasound imaging(IEEE-INST Electrical Electronics Engineers Inc, 2008-02) Wygant, Ira O.; Zhuang, Xuefeng; Yeh, David T.; Oralkan, Ömer; Ergün, Arif Sanlı; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasFor three-dimensional (3D) ultrasound imaging, connecting elements of a two-dimensional (2D) transducer array to the imaging system's front-end electronics is a challenge because of the large number of array elements and the small element size. To compactly connect the transducer array with electronics, we flip-chip bond a 2D 16 x 16-element capacitive micromachined ultrasonic transducer (CMUT) array to a custom-designed integrated circuit (IC). Through-wafer interconnects are used to connect the CMUT elements on the top side of the array with flip-chip bond pads on the back side. The IC provides a 25-V pulser and a transimpedance preamplifier to each element of the array. For each of three characterized devices, the element yield is excellent (99 to 100% of the elements are functional). Center frequencies range from 2.6 MHz to 5.1 MHz. For pulse-echo operation, the average -6-dB fractional bandwidth is as high as 125%. Transmit pressures normalized to the face of the transducer are as high as 339 kPa and input-referred receiver noise is typically 1.2 to 2.1 mPa/root Hz. The flip-chip bonded devices were used to acquire 3D synthetic aperture images of a wire-target phantom. Combining the transducer array and IC, as shown in this paper, allows for better utilization of large arrays, improves receive sensitivity, and may lead to new imaging techniques that depend on transducer arrays that are closely coupled to IC electronics.Yayın Observing with DAG: performance metrics of imaging and spectroscopy(Türk Astronomi Derneği, 2020-12-11) Jolissaint, Laurent; Zago, Lorenzo; Keskin, OnurDAG telescope will be designed as a telescope with adaptive optics and seeing limited modes of observation. Its primary mirror will be a thin meniscus, controlled in shape by an active optics system. This implies specific requirements for the mirrors manufacturing errors tolerancing, studied and defined in this document.Yayın Wind disturbance cancellation for smaller alt-azimuth telescopes(Universidad Nacional Autonoma de Mexico, 2019-10) Ünal, Ali Cem; Kararsız, Gökhan; Yılmaz, Cemal Tuğrul; Keskin, Onur; Yeşilyaprak, CahitThis study focuses on eliminating unknown amplitude wind disturbance for 2-DOF alt-azimuth configuration small telescopes. An adaptive controller is designed to overcome wind disturbance as a set and forget system. The mathematical model is derived based on 2-DOF alt-azimuth configuration. The wind disturbance is modeled as a sum of sinusoidal with unknown amplitude, frequency and phase by using Wind-Gust model. The controller aims to cancel the effect of the disturbance on the altitude and azimuth angles of the telescope while positioning or staying static on a dedicated configuration. The asymptotic stability is proven with the Lyapunov approach. The numerical study is illustrated to success of the proposed controller.Yayın Coherent array imaging using phased subarrays. Part II: Simulations and experimental results(IEEE-INST Electrical Electronics Engineers Inc, 2005-01) Johnson, Jeremy A.; Oralkan, Ömer; Ergün, Arif Sanlı; Demirci, Utkan; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasThe basic principles and theory of phased subarray (PSA) imaging imaging provides the flexibility of reducing I he number of front-end hardware channels between that of classical synthetic aperture (CSA) imaging-which uses only one element per firing event-and full-phased array (FPA,) imaging-which uses all elements for each firing. The performance of PSA generally ranges between that obtained by CSA and FPA using the same array, and depends on the amount of hardware complexity reduction. For the work described in this paper, we performed FPA, CSA, and PSA imaging of a resolution phantom using both simulated and experimental data from a 3-MHz, 3.2-cm, 128-element capacitive micromachined ultrasound transducer (CMUT) array. The simulated system point responses in the spatial and frequency domains are presented as a means of studying the effects of signal bandwidth, reconstruction filter size, and subsampling rate on the PSA system performance. The PSA and FPA sector-scanned images were reconstructed using the wideband experimental data with 80% fractional bandwidth, with seven 32-element subarrays used for PSA imaging. The measurements on the experimental sector images indicate that, at the transmit focal zone, the PSA method provides a 10% improvement in the 6-dB lateral resolution, and the axial point resolution of PSA imaging is identical to that of FPA imaging. The signal-to-noise ratio (SNR) of PSA image was 58.3 dB, 4.9 dB below that of the FPA image, and the contrast-to-noise ratio (CNR) is reduced by 10%. The simulated and experimental test results presented in this paper validate theoretical expectations and illustrate the flexibility of PSA imaging as a way to exchange SNR and frame rate for simplified front-end hardware.Yayın İstabul Üniversitesi gözlemevi odak düzlemi aygıtı test ve karakterizasyon laboratuvarı(Türk Astronomi Derneği, 2020-12-11) Aliş, Sinan; Güver, Tolga; Erol, Ayşe; Ege, Ergün; Kay, Burak; Yelkenci, Korhan; Yeşilyaprak, Cahit; Keskin, Onur; Yerli, Sinan Kaan; Sercan, Fahreettin; Fişek, SüleymanDoğu Anadolu Gözlemevi Odak Düzlemi Aygıtları ve Adaptif Optik Sistemi başlıklı, 2016K121370 numaralı T.C. Kalkınma Bakanlığı projesi ve İstanbul Üniversitesi Rektörlüğü desteğinde yürüyen çalışmalar kapsamında İstanbul Üniversitesi Astronomi ve Uzay Bilimleri Bölümü’nde teleskop odak düzlemi aygıtı test ve karakterizasyon laboratuvarı kurulum çalışmaları başlatılmıştır. Başta DAG Teleskobu olmak üzere ülkemizdeki tüm gözlemevlerine hizmet verebilecek şekilde tasarlanan laboratuvar, CCD kamera, filtre ve odak düzlemi aygıtları için bir test masasına sahip olacaktır. Bu sunumda, laboratuvarın kurulumu ve alımlarında gelinen son noktanın yanı sıra, İstanbul Üniversitesi Fizik Bölümü Nano-Optoelektronik Araştırma Laboratuvarları ile birlikte yapılması planlanan çalışmalar sunulacaktır.
