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Yayın Phased subarray imaging for low-cost, wideband coherent array imaging(IEEE, 2003) Johnson, Jeremy A.; Oralkan, Ömer; Ergün, Arif Sanlı; Demirci, Utkan; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasThe front-end hardware complexity of conventional full phased array (FPA) imaging is proportional to the number of array elements. Phased subarray (PSA) imaging has been proposed as a method of reducing the hardware complexity-and therefore system cost and size-while achieving near-FPA image quality. A new method is presented for designing the subarray-dependent interpolation filters suitable for wideband PSA imaging. The method was tested experimentally using pulse-echo data of a wire target phantom acquired using a 3.2-cm. 128-element capacitive micromachined ultrasonic transducer (CMUT) array with 85% fractional bandwidth at 3 MHz. A specific PSA configuration using seven 32-element subarrays was compared to FPA imaging, representing a 4-fold reduction in front-end hardware complexity and a 43% decrease in frame rate. For targets near the fixed transmit focal distance, the mean 6-dB lateral resolution was identical to that of FPA, the axial resolution improved by 4%, and the SNR decreased by 5 dB. Measurements were repeated for 10 different PSA configurations with subarray sizes ranging from 4 to 60. The lateral and axial resolutions did not vary significantly with subarray size; both the SNR and contrast-to-noise ratio (CNR) improved with increased subarray size.Yayın Co-array optimization of CMUT arrays for forward-looking IVUS(IEEE, 2009-09) Tekeş, Coşkun; Karaman, Mustafa; Değertekin, Fahrettin LeventThe ring annular array structure is a preferred configuration for implementing Forward-Looking IVUS (FLIVUS) catheters as it allows for volumetric imaging as well as use of a guidewire at the center. CMUT technology is promising for these arrays especially with the flexibility of locating array elements on the circular donut area efficiently. To take advantage of this flexibility, in this study, we introduce a new co-array sampling strategy that improves imaging performance while keeping the number of firings at a level suitable for real-time imaging. The presented co-array sampling strategy is based on the idea of adjusting the element density of the co-array rings in radial direction to suppress side lobes. In non-uniform sampling of the co-array with a given number of firings, the inter-element distances are adjusted both in radial and angular direction from inner ring to outer ring to fit a given apodization function. To test the imaging performance, we performed numerical simulations of the co-array with non-uniform sampling fitting to the raised-cosine apodization. The simulation results shows that sidelobe level can be reduced more than 10 dB by using non-uniform co-array sampling. This approach does use uniform weighting of all Tx and Rx elements in beamforming, and hence does not cause any SNR loss for apodization.Yayın A priority based packet scheduler with deadline considerations(IEEE Computer Soc, 2006) Dağ, Tamer; Gökgöl, OralQoS issues have become a focal point of research on Next Generation Networks (NGNs). In order to supply the various QoS requirement for different kinds of applications, new scheduling policies need to be developed and evaluated. This paper introduces a new kind of packet scheduler which tries to integrate an important QoS parameter (the delay) with the classical schedulers. The two sets of algorithms introduced; Static Priority with Deadline Considerations (SPD) and Dynamic Priority with Deadline Considerations (DPD); not only simplify the complexity and overhead of a classical Earliest Deadline First (EDF) or Static Priority (SP) algorithm, but also provide a better QoS based on the results of the simulations conducted.Yayın Parçacık süzgeçleme ile hedef izleme uygulamasında topak çizelgeleme(IEEE, 2007) Özfidan, Özgür; Bayazıt, Uluğ; Çırpan, Hakan AliBu çalışmada, uzaklık ölçer algılayıcılarla hedef takibi uygulamasında algılayıcı çizelgeleme problemi ele alınmıştır. Çok algılayıcılı uygulamalarda algılayıcıların yönetimi ürettikleri verilerin sınıflandırılması için olduğu kadar algılayıcıların verimli kullanımı için de gereklidir. Algılayıcı yönetimindeki önemli hususlardan biri algılayıcı çizelgelemesidir. Algılayıcıları çizelgeleyerek bant genişliği, güç, ve hesaplamada ciddi ölçüde kazanımlar sağlanabilir.Yayın Low complexity inter-mode selection for H.264(IEEE, 2006) Ba, Seydou Nourou; Altunbaşak, Yücel; Ateş, Hasan FehmiThe coding efficiency of the H.264/AVC standard enables the transmission of high quality video over bandwidth limited networks. Due to the use of multiple Macroblock (MB) partitions, the Motion estimation module has extremely high complexity that makes it unpractical for most real-time applications on resource-limited platforms such as hand held devices. In this paper we propose a novel algorithm that significantly reduces the encoding complexity while maintaining high rate distortion performance. The proposed method reduces the Motion estimation (ME) computational complexity by accurately predicting the optimal MB partitions and restricting the number of candidate modes based on a-priori probabilities computed from spatio-temporal information. The experimental results show that the speed up of UmHexagonS [1] (one of the most efficient ME algorithms) can be doubled while maintaining the coding efficiency of Full Search.Yayın A single matching network design for a dual band PIFA antenna via simplified real frequency technique(2006-10) Lindberg, Peter; Şengül, Metin; Çimen, Ebru Gürsu; Yarman, Bekir Sıddık Binboğa; Rydberg, Anders; Aksen, AhmetIn this paper, the matched performance of a dual band PIFA antenna is reported. The return loss of the antenna has been optimized over the popular commercial wireless communication bands of 824-960 MHz and 1710-1990 MHz using only one matching network. The network was synthesized using the Simplified Real Frequency Technique, which yields an "easy to implement circuit topology" and realizable component values. With the implemented matching network, a simultaneous measured bandwidth enhancement of 58% and 127% has been achieved in the low and high frequency band, respectively, without significant reduction of radiation efficiency.Yayın Evaluation of CMUT annular arrays for side-looking IVUS(IEEE, 2009) Şişman, Alper; Zahorian, Jaime S.; Gürün, Gökçe; Karaman, Mustafa; Balantekin, Müjdat; Değertekin, Fahrettin Levent; Hasler, Paul E.Side-looking (SL) IVUS probes are extensively used for management of cardiovascular diseases. Currently SL-IVUS imaging probes use either a single rotating transducer element or solid-state arrays. Probes with single rotating piezoelectric transducer have simple front-end, but have fixed focused operation, and suffers from motion artifacts. Solid-state SL-IVUS imaging probes use piezoelectric transducer arrays and electronic beam-forming. Synthetic phased array processing of signals detected with small-sized elements in these arrays limits the SNR achievable with these probes. In this study, we explore a new SL-IVUS probe architecture employing rotating phased annular CMUT arrays. We tested and compared imaging performance of the existing and proposed probe configurations through simulated point spread functions. We also two fabricated sample annular array designs operating at 20-MHz and 50-MHz. Our experimental measurements on the 20-MHz array in oil shows 105% fractional bandwidth. The 50-MHz array with parylene coating shows approximately 40% fractional bandwidth measured in water. We also present imaging results acquired from wire-targets to test the experimental point-spread functions.Yayın An Analog beamformer for integrated high-frequency medical ultrasound imaging(IEEE, 2011) Gürün, Gökçe; Zahorian, Jaime; Tekeş, Coşkun; Karaman, Mustafa; Hasler, Paul E.; Değertekin, Fahrettin LeventWe designed and fabricated a dynamic receive beamforming integrated circuit (IC) in 0.35-mu m CMOS technology. This beamformer is suitable for integration with an ultrasound annular array for high-frequency (30-50 MHz) intravascular ultrasound (IVUS) imaging. The beamformer IC is capable of buffering, delaying and preamplification for 8 receive channels. We explored an analog delay cell based on a currentmode first-order all-pass filter, which is used as the basic building block to form an analog dynamic delay line. We also explored a bandwidth enhancement method on the delay cell that improved the overall bandwidth of the delay line by a factor of 6. Each delay cell consumes 2.1 mW of power and is capable of generating a tunable delay between 1.75 ns to 2.5 ns, enabling dynamic receive beamforming over a focal range from 1.4 mm to 2 mm. We successfully integrated the fabricated beamformer IC with an 8-element annular array. Our experimental test results demonstrated the desired buffering, preamplification and delaying capabilities of the beamformer.Yayın An endoscopie imaging system based on a two-dimensional CMUT array: real-time imaging results(IEEE, 2005) Wygant, Ira O.; Zhuang, Xuefeng; Yeh, David T.; Vaithilingam, Srikant; Nikoozadeh, Amin; Oralkan, Ömer; Ergün, Arif Sanlı; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasReal-time catheter-based ultrasound imaging tools are needed for diagnosis and image-guided procedures. The continued development of these tools is partially limited by the difficulty of fabricating two-dimensional array geometries of piezoelectric transducers. Using capacitive micromachined ultrasonic transducer (CMUT) technology, transducer arrays with widely varying geometries, high frequencies, and wide bandwidths can be fabricated. A volumetric ultrasound imaging system based on a two-dimensional, 16×l6-element, CMUT array is presented. Transducer arrays with operating frequencies ranging from 3 MHz to 7.5 MHz were fabricated for this system. The transducer array including DC bias pads measures 4 mm by 4.7 mm. The transducer elements are connected to flip-chip bond pads on the array back side with 400-?m long through-wafer interconnects. The array is flip-chip bonded to a custom-designed integrated circuit (IC) that comprises the front-end electronics. Integrating the front-end electronics with the transducer array reduces the effects of cable capacitance on the transducer's performance and provides a compact means of connecting to the transducer elements. The front-end IC provides a 27-V pulser and 10-MHz bandwidth amplifier for each element of the array. An FPGA-based data acquisition system is used for control and data acquisition. Output pressure of 230 kPa was measured for the integrated device. A receive sensitivity of 125 mV/kPa was measured at the output of the amplifier. Amplifier output noise at 5 Mhz is 112 nV/?Hz. Volumetric images of a wire phantom and vessel phantom are presented. Volumetric data for a wire phantom was acquired in real-time at 30 frames per second.Yayın Cluster based sensor scheduling in a target tracking application with particle filtering(IEEE, 2007) Özfidan, Özgür; Bayazıt, Uluğ; Çırpan, Hakan AliIn multi-sensor applications management of sensors is necessary for the classification of data they produce and for the efficient use of sensors as well. One of the important aspects in sensor management is the sensor scheduling. By scheduling the sensors, serious reductions can be achieved in the cost of bandwidth, power, and computation. In this work a simple solution for the problem of sensor scheduling in a multi-sensor target tracking application is presented. Due to non-linearity of the problem itself, proposed solution is presented in the framework of non-linear Bayesian estimation.
