Now showing items 1-20 of 81

    • Acoustical tuning of CMUT receiver arrays 

      Taşdelen, Akif Sinan; Atalar, Abdullah; Enhoş, Kerem; Köymen, Hayrettin (IEEE, 2016)
      Cell placement in an element and structural modifications on the array baffle significantly change the bandwidth, band shape and signal to noise ratio of a CMUT receiver array. In this paper, optimum receiver performance ...
    • Analysis of mutual acoustic coupling in CMUT arrays using an accurate lumped element nonlinear equivalent circuit model 

      Oğuz, H.Kağan; Atalar, Abdullah; Köymen, Hayrettin (2012)
      We use an accurate nonlinear equivalent circuit model to analyze CMUT arrays with multiple cells, where every cell in the array is coupled to other cells at their acoustic terminals through a mutual radiation impedance ...
    • Assessment of information redundancy in ECG signals 

      Acar, Burak; Özçakır, Lütfü; Köymen, Hayrettin (IEEE, 1997-09)
      In this paper, the morphological information redundancy in standard 12 lead ECG channels is studied. Study is based on decomposing the ECG channels into orthogonal channels by an SVD based algorithm and then reconstructing ...
    • Bandwidth, power and noise considerations in airborne cMUTs 

      Şenlik, Muhammed N.; Olcum, Selim; Köymen, Hayrettin; Atalar, Abdullah (IEEE, 2009-09)
      Capacitive micromachined ultrasonic transducers (cMUTs) offer wider bandwidth in air due to their low mechanical impedances. The impedance mismatch between the air and transducer decreases with the smaller device dimensions ...
    • Beam steering in a half-frequency driven airborne CMUT transmitter array 

      Khan, Talha Masood; Taşdelen, Akif Sinan; Yılmaz, Mehmet; Atalar, Abdullah; Köymen, Hayrettin (IEEE Computer Society, 2019)
      An airborne Capacitive Micromachined Ultrasonic Transducer (CMUT) transmit array was designed using electromechanical modelling for unbiased airborne operation. The array elements are designed for maximum swing at 10V p-p ...
    • Bi-angular lens for material characterization 

      Yaralıoğlu, Göksen Göksenin; Atalar, Abdullah; Köymen, Hayrettin (IEEE, 1994)
      In this paper a new lens design is proposed for characterization of layered materials. Lamb wave lens employs Lamb waves for this purpose since these waves propagate along interfaces. However, below cut-off angle, the ...
    • Bilateral CMUT cells and arrays: equivalent circuits, diffraction constants, and substrate impedance 

      Köymen, Hayrettin; Atalar, Abdullah; Taşdelen, A. S. (Institute of Electrical and Electronics Engineers Inc., 2017)
      We introduce the large-signal and small-signal equivalent circuit models for a capacitive micromachined ultrasonic transducer (CMUT) cell, which has radiating plates on both sides. We present the diffraction coefficient ...
    • Calculation of transformer ratio in mason's equivalent circuit for cMUTs 

      Ölçüm, Selim; Atalar, Abdullah; Köymen, Hayrettin; Şenlik, Muhammed Niyazi (IEEE, 2006)
      We present a new method to calculate the transformer ratio of a cMUT in Mason's Equivalent circuit model. The effect of the spring softening capacitance is also included in the analysis. We use the existing turns ratio ...
    • Capacity analysis of a PMR system with DAB downlink 

      Şengül, Ersin; Can, B.; Akar, Nail; İder, Yusuf Ziya; Köymen, Hayrettin (IEEE, 2003)
      Several trunked private mobile radio (PMR) systems have been designed over the last decade, most of which have symmetric downlink and uplink channel capacities. These systems may not be spectrally efficient in case of group ...
    • Characterization and imaging with lamb wave lens at gigahertz frequencies 

      Bozkurt, Ayhan; Yaralıoğlu, Göksenin; Atalar, Abdullah; Köymen, Hayrettin; Kramer, K. (IEEE, 1994-10-11)
      Lamb wave lenses with conical refracting surfaces are fabricated for use at 400 MHz and 1 GHz. The conical surfaces are ground and polished with mechanical means and they are sufficiently smooth for the frequencies of ...
    • Characterization of layered materials by the lamb wave lens 

      Atalar, Abdullah; Köymen, Hayrettin; Değertekin, F. Levent (IEEE, 1990)
      The Lamb wave lens is a type of lens that can replace the conventional lens of an acoustic microscope for some applications. When it insonifies a layered solid structure, it excites a single mode in the structure, provided ...
    • Circuit theory based analysis of CMUT arrays with very large number of cells 

      Oguz, H. Kağan; Atalar, Abdullah; Köymen, Hayrettin (IEEE, 2013)
      We have recently developed a circuit theory based method to analyze large CMUT arrays and shown that mutual acoustic interactions significantly influence the transducer performance. We connect each cell in the array to a ...
    • CMUT array element in deep-collapse mode 

      Olcum, Semih; Yamaner F.Y.; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah (IEEE, 2011)
      Collapse and deep-collapse mode of operations have boosted the pressure outputs of capacitive micromachined ultrasonic transducers (CMUTs) considerably. In this work, we demonstrate a CMUT element operating in the deep-collapse ...
    • Comparison of various propagation models on real terrain: difficulties and remedies 

      Altıntaş, Ayhan; Aksun, İrşadi; Topçu, Satılmış; Köymen, Hayrettin; Yurchenko, V.; Yetginer, Emre; Yılmaz, Özgür (2000)
    • Compression of digital biomedical signals 

      Çetin, A. Enis; Köymen, Hayrettin (CRC Press, 2006)
      Computerized electrocardiogram (ECG), electroencephalogram (EEG), and magnetoencephalogram (MEG) processing systems have been widely used in clinical practice [1] and they are capable of recording and processing long records ...
    • Computer aided frequency planning for the radio and TV broadcasts 

      Altıntaş, Ayhan; Ocalı, O.; Topçu, Satılmış; Tanyer, S. G.; Köymen, Hayrettin (Institute of Electrical and Electronics Engineers, 1996-06)
      The frequency planning of the VHF and UHF broadcasts in Turkey is described. This planning is done with the aid of computer databases and digital terrain map. The frequency offset is applied whenever applicable to increase ...
    • Design and implementation of capacitive micromachined ultrasonic transducers for high power 

      Yamaner F.Y.; Ölçüm, Selim; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah (IEEE, 2011)
      Capacitive micromachined ultrasonic transducers (CMUTs) have a strong potential to compete piezoelectric transducers in high power applications. In a CMUT, obtaining high port pressure competes with high particle velocity: ...
    • The design of a wideband and widebeam piston transducer in a finite closed circular baffle 

      Şahin, Z.; Köymen, Hayrettin (2008-06-07)
      The design of a high power piezoelectric underwater transducer operating at frequency range 40 kHz-80 kHz with acoustic power capability in excess of 250W is described. The transducer consists of two back-toback elements. ...
    • Design of an emergency PMR network based on CDMA 450 in İstanbul metropolitan region 

      Kızılırmak, Çağlar; Topçu, Satılmış; Köymen, Hayrettin (TEHOSS, 2006)
      In this work, a complete design of PMR (Professional Mobile Radio) network based on CDMA 450 in ˙Istanbul metropolitan region is presented. Coverage and capacity analysis are performed by the developed simulation software ...
    • Designing circular CMUT cells using CMUT biasing chart 

      Köymen, Hayrettin; Atalar, Abdullah; Oğuz, H. Kağan (IEEE, 2012-10)
      A very accurate equivalent circuit model for circular CMUT cell is recently proposed. As a consequence of this model, the operating characteristics of the cell is derived and presented as a biasing chart for CMUTs. We ...