Hayrettin Koymen | Bilkent University (original) (raw)

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Papers by Hayrettin Koymen

DergiPark (Istanbul University), Jul 1, 1987

Temporomandibular eklem sorunları son on yıl içerisinde gide rek önem kazanan ve yeni teşhis yönt... more Temporomandibular eklem sorunları son on yıl içerisinde gide rek önem kazanan ve yeni teşhis yöntemlerini de beraberinde getiren bir konu haline gelmiştir. Bunun nedeni erişkinlerde bu sorunlara % 28-86 oranında rastlanmasıdır (1). Son zamanlarda yapılan epidemiolojik çalışmalar ağrılı veya ağ rısız temporomandibular eklem seslerinin yaygın olduğunu, bu hasta ların % 28-65'inde bu semptomların görüldüğünü göstermiştir (2).

In this paper, we present the optimal use of coded signals in diverging wave transmission for fas... more In this paper, we present the optimal use of coded signals in diverging wave transmission for fast ultrasonic imaging. The performance of coded imaging with diverging waves, quantified by SNR, CNR, speckle power and target signal strength, is optimized in terms of code length, wave profile, aperture size and field of view. We obtained one frame in 200 microseconds using coded diverging wave transmission, equivalent to very high 5000 frames/s rate, where the imaging depth is 7.5 cm. The performances of coded diverging wave transmission and conventional single focused phased array imaging are compared on a single frame basis. Complementary Golay sequences with code lengths ranging from 2 to 10 bits are used to code the signal. The signal strength and SNR obtained using synthetic transmit aperture and conventional single focused phased array imaging techniques, respectively, are used as reference in the performance analysis. We present a method to determine the optimum diverging wave p...

2019 IEEE International Ultrasonics Symposium (IUS)

This study focuses on design, simulation, fabrication and measurement of transmitting CMUT arrays... more This study focuses on design, simulation, fabrication and measurement of transmitting CMUT arrays with unbiased mode of operation. We presented a design procedure considering the radiation pattern, Rayleigh distance and the parameters of the large signal equivalent circuit, which can be applied for different operation frequencies and applications. Large signal equivalent circuit model is used for lumped-element simulations. Harmonic balance and transient analyses are carried out with Gaussian enveloped tone burst, sinusoidal and pulse width modulation (PWM) signals with different duty cycles. Outputs of these simulations are fed in beamforming toolboxes for further verification. According to the design specifications transmitting CMUT arrays are fabricated. Corresponding experimental impedance measurements are conducted.

Electrical Engineering Handbook, 2006

2019 IEEE International Ultrasonics Symposium (IUS)

An airborne Capacitive Micromachined Ultrasonic Transducer (CMUT) transmit array was designed usi... more 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 unbiased drive, whereas conventional practice is to bias CMUT close to the collapsed voltage to achieve higher swing. The devices were fabricated using a customized single photolithographic process with a combination of wet and dry etching. The wafer level fabrication enabled the usage of 2x2 and 3x3 arrays. Driving CMUTs in an unbiased mode at half frequency drives the 'static pressure' depressed silicon membrane at a larger swing without letting it collapse. The 2x2 array displays 3.375 kHz bandwidth when characterized in air. The phase and amplitude differences due to the dispersion of resonance frequencies of the elements are compensated for beamformed and beamsteered airborne operation.

arXiv: Classical Physics, 2015

A polynomial approximation is proposed for the mutual acoustic impedance between uncollapsed capa... more A polynomial approximation is proposed for the mutual acoustic impedance between uncollapsed capacitive micromachined ultrasonic transducer (CMUT) cells with different radii in an infinite rigid baffle. The resulting approximation is employed in simulating CMUTs with a circuit model. A very good agreement is obtained with the corresponding finite element simulation (FEM) result.

Thispaperisconcerned withthedesign ofan AL efficient, widebandanda wide-beamwidth resonant acoust... more Thispaperisconcerned withthedesign ofan AL efficient, widebandanda wide-beamwidth resonant acoustic transducer forhighfrequency use.The general transducer Water structure whichhastwo back-to-back quarter wave thick W..te 1 - 3 composite ceramic elements atresonancefrequency is l-oad-l-

2003 IEEE International Symposium on Electromagnetic Compatibility, 2003. EMC '03., 2003

We propose capacitive micromachined ultrasonic transducers (CMUTs) as a candidate for underwater ... more We propose capacitive micromachined ultrasonic transducers (CMUTs) as a candidate for underwater acoustic applications, in this paper. We have designed and fabricated CMUT membranes by utilizing anodic bonding technology and tested them underwater. We developed a nonlinear electrical equivalent circuit for immersed CMUTs and compared the model with transient finite element analysis (FEA) and measurements. FEA reveals that the radial distribution of both the fundamental component and the harmonics in the membrane displacement can be modeled as clamped radiators. CMUTs, operating in conventional regime, are designed by deriving the force and current equations for a clamped radiator and implemented using a harmonic balance simulator. A mechanical LC section and the radiation impedance of a clamped radiator are used in the model. A 380 µm thick silicon wafer is chosen as the membrane and 3.2 mm thick glass is used as the substrate. The performance of the transducer is measured in an open water testing facility and approximately 40% bandwidth is achieved around 25 KHz with a single underwater CMUT cell.

IEEE 1991 Ultrasonics Symposium

2014 IEEE International Ultrasonics Symposium, 2014

This study focuses on modeling collapsed mode operation of CMUT arrays, and obtaining a small sig... more This study focuses on modeling collapsed mode operation of CMUT arrays, and obtaining a small signal lumped element model for collapsed mode operation. Having the large signal model for single CMUT from previous studies, the mutual radiation impedance is presented for the collapsed mode, and a large signal model for a CMUT array is obtained for simulating the operation in both uncollapsed and collapsed modes. For faster computation, a small signal model for a CMUT cell is derived by linearizing the collapsed mode operation at a given bias point, and the computation time is reduced significantly. Using this model we are able to simulate a large array of collapsed CMUT cells.

2006 IEEE Ultrasonics Symposium, 2006

In this study, we explore the limits of cMUTs in airborne applications. First we investigate the ... more In this study, we explore the limits of cMUTs in airborne applications. First we investigate the ways of increasing the bandwidth of a single cMUT cell in air. The effect of array operation is also considered in order to increase the radiation resistance seen by the transducer. We calculate the bandwidth of a stagger tuned cMUT array. It is shown in this paper that more than 60% bandwidth can be obtained by three staggered frequencies.

2006 IEEE Ultrasonics Symposium, 2006

DergiPark (Istanbul University), Jul 1, 1987

Temporomandibular eklem sorunları son on yıl içerisinde gide rek önem kazanan ve yeni teşhis yönt... more Temporomandibular eklem sorunları son on yıl içerisinde gide rek önem kazanan ve yeni teşhis yöntemlerini de beraberinde getiren bir konu haline gelmiştir. Bunun nedeni erişkinlerde bu sorunlara % 28-86 oranında rastlanmasıdır (1). Son zamanlarda yapılan epidemiolojik çalışmalar ağrılı veya ağ rısız temporomandibular eklem seslerinin yaygın olduğunu, bu hasta ların % 28-65'inde bu semptomların görüldüğünü göstermiştir (2).

In this paper, we present the optimal use of coded signals in diverging wave transmission for fas... more In this paper, we present the optimal use of coded signals in diverging wave transmission for fast ultrasonic imaging. The performance of coded imaging with diverging waves, quantified by SNR, CNR, speckle power and target signal strength, is optimized in terms of code length, wave profile, aperture size and field of view. We obtained one frame in 200 microseconds using coded diverging wave transmission, equivalent to very high 5000 frames/s rate, where the imaging depth is 7.5 cm. The performances of coded diverging wave transmission and conventional single focused phased array imaging are compared on a single frame basis. Complementary Golay sequences with code lengths ranging from 2 to 10 bits are used to code the signal. The signal strength and SNR obtained using synthetic transmit aperture and conventional single focused phased array imaging techniques, respectively, are used as reference in the performance analysis. We present a method to determine the optimum diverging wave p...

2019 IEEE International Ultrasonics Symposium (IUS)

This study focuses on design, simulation, fabrication and measurement of transmitting CMUT arrays... more This study focuses on design, simulation, fabrication and measurement of transmitting CMUT arrays with unbiased mode of operation. We presented a design procedure considering the radiation pattern, Rayleigh distance and the parameters of the large signal equivalent circuit, which can be applied for different operation frequencies and applications. Large signal equivalent circuit model is used for lumped-element simulations. Harmonic balance and transient analyses are carried out with Gaussian enveloped tone burst, sinusoidal and pulse width modulation (PWM) signals with different duty cycles. Outputs of these simulations are fed in beamforming toolboxes for further verification. According to the design specifications transmitting CMUT arrays are fabricated. Corresponding experimental impedance measurements are conducted.

Electrical Engineering Handbook, 2006

2019 IEEE International Ultrasonics Symposium (IUS)

An airborne Capacitive Micromachined Ultrasonic Transducer (CMUT) transmit array was designed usi... more 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 unbiased drive, whereas conventional practice is to bias CMUT close to the collapsed voltage to achieve higher swing. The devices were fabricated using a customized single photolithographic process with a combination of wet and dry etching. The wafer level fabrication enabled the usage of 2x2 and 3x3 arrays. Driving CMUTs in an unbiased mode at half frequency drives the 'static pressure' depressed silicon membrane at a larger swing without letting it collapse. The 2x2 array displays 3.375 kHz bandwidth when characterized in air. The phase and amplitude differences due to the dispersion of resonance frequencies of the elements are compensated for beamformed and beamsteered airborne operation.

arXiv: Classical Physics, 2015

A polynomial approximation is proposed for the mutual acoustic impedance between uncollapsed capa... more A polynomial approximation is proposed for the mutual acoustic impedance between uncollapsed capacitive micromachined ultrasonic transducer (CMUT) cells with different radii in an infinite rigid baffle. The resulting approximation is employed in simulating CMUTs with a circuit model. A very good agreement is obtained with the corresponding finite element simulation (FEM) result.

Thispaperisconcerned withthedesign ofan AL efficient, widebandanda wide-beamwidth resonant acoust... more Thispaperisconcerned withthedesign ofan AL efficient, widebandanda wide-beamwidth resonant acoustic transducer forhighfrequency use.The general transducer Water structure whichhastwo back-to-back quarter wave thick W..te 1 - 3 composite ceramic elements atresonancefrequency is l-oad-l-

2003 IEEE International Symposium on Electromagnetic Compatibility, 2003. EMC '03., 2003

We propose capacitive micromachined ultrasonic transducers (CMUTs) as a candidate for underwater ... more We propose capacitive micromachined ultrasonic transducers (CMUTs) as a candidate for underwater acoustic applications, in this paper. We have designed and fabricated CMUT membranes by utilizing anodic bonding technology and tested them underwater. We developed a nonlinear electrical equivalent circuit for immersed CMUTs and compared the model with transient finite element analysis (FEA) and measurements. FEA reveals that the radial distribution of both the fundamental component and the harmonics in the membrane displacement can be modeled as clamped radiators. CMUTs, operating in conventional regime, are designed by deriving the force and current equations for a clamped radiator and implemented using a harmonic balance simulator. A mechanical LC section and the radiation impedance of a clamped radiator are used in the model. A 380 µm thick silicon wafer is chosen as the membrane and 3.2 mm thick glass is used as the substrate. The performance of the transducer is measured in an open water testing facility and approximately 40% bandwidth is achieved around 25 KHz with a single underwater CMUT cell.

IEEE 1991 Ultrasonics Symposium

2014 IEEE International Ultrasonics Symposium, 2014

This study focuses on modeling collapsed mode operation of CMUT arrays, and obtaining a small sig... more This study focuses on modeling collapsed mode operation of CMUT arrays, and obtaining a small signal lumped element model for collapsed mode operation. Having the large signal model for single CMUT from previous studies, the mutual radiation impedance is presented for the collapsed mode, and a large signal model for a CMUT array is obtained for simulating the operation in both uncollapsed and collapsed modes. For faster computation, a small signal model for a CMUT cell is derived by linearizing the collapsed mode operation at a given bias point, and the computation time is reduced significantly. Using this model we are able to simulate a large array of collapsed CMUT cells.

2006 IEEE Ultrasonics Symposium, 2006

In this study, we explore the limits of cMUTs in airborne applications. First we investigate the ... more In this study, we explore the limits of cMUTs in airborne applications. First we investigate the ways of increasing the bandwidth of a single cMUT cell in air. The effect of array operation is also considered in order to increase the radiation resistance seen by the transducer. We calculate the bandwidth of a stagger tuned cMUT array. It is shown in this paper that more than 60% bandwidth can be obtained by three staggered frequencies.

2006 IEEE Ultrasonics Symposium, 2006