Browsing by Author "Bozkurt, A."

Now showing 1 - 6 of 6

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Equivalent circuit for capacitive micromachined ultrasonic transducers to predict anti-resonances
(Springer Nature, 2020-12) Kemal, Remzi Erkan; Bozkurt, A.; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Kemal, Remzi Erkan
Equivalent circuit models have been long used to evaluate the dynamics of the capacitive micromachined ultrasonic transducer (CMUT). An important parameter in the characterization of a CMUT is the anti-resonance frequency, which limits the immersion bandwidth. However, there is no equivalent circuit model that can accurately determine the anti-resonance frequency of a membrane. In this work, we present an improved lumped element parametric model for immersed CMUT. We demonstrate that the proposed equivalent circuit model accurately predicts anti-resonance and higher order mode frequencies, in addition to that of the fundamental mode. The proposed circuit model is in good agreement with device characteristics calculated using the finite element method and experimentally measured data.
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Mutual radiation impedance of circular CMUTs on a cylinder
(IEEE, 2016) Zangabad, R. P.; Bozkurt, A.; Yaralıoğlu, Göksen Göksenin; Bosch, J. G.; Soest, G. van; Steen, A. F. W. van der; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
In ultrasound imaging, cross coupling of transducer elements through the medium has significant effect on the frequency response, thus affecting the quality of the ultrasound image. In Side-Looking Intravascular Ultrasound (SL-IVUS) imaging a radial image of the vessel wall is formed using a transducer array in a cylindrical configuration. Recent advances in Capacitive Micromachined Ultrasound Transducer (CMUT) fabrication and integration techniques led to realization of CMUT arrays that can be wrapped into a cylinder shape and mounted on a catheter tip. In this paper, we present the calculation of radiation impedance of un-collapse CMUT arrays on a planar rigid baffle and on a cylinder using Finite Element Method (FEM) simulation. We link the crosstalk between planar CMUT elements with dips in frequency spectrum from experimental data and conclude that decreasing the cylinder radius causes downshift of the dips in frequency response. In the case of our device, these changes are too small to have detrimental effects on the array bandwidth.
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Portable low cost ultrasound imaging system
(IEEE, 2016) Sobhani, Mohammad Rahim; Ozum, H. E.; Yaralıoğlu, Göksen Göksenin; Ergun, A. S.; Bozkurt, A.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Sobhani, Mohammad Rahim
The applications of ultrasound in medicine have been increasing in the last decade either in diagnostics or in treatments. Ultrasound is routinely used in clinical examinations, such as pregnancy exams. On the other hand, a typical ultrasound system costs somewhere between 100k$ to 250k$ because of its (1) expensive ultrasound transducers, (2) large driving electronics, (3) processing and visualization units. High cost and large volume of the ultrasound systems prevent even wider usage of these systems. It is possible to extent the use of ultrasound in clinic environment like a stethoscope, if the size and cost had been reduced orders of magnitude. The aim of this work is to develop an ultraportable and very low cost diagnostic ultrasound imaging probe; by combining inertial sensors with the probes. The manual motion of the probe by the operator's hand movement enables scanning. The position of the probe is tracked using inertial sensors. Finally, the acoustic reflections are registered together by the help of position information of the probe to form an image.
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Receive-noise analysis of capacitive micromachined ultrasonic transducers
(IEEE, 2016) Bozkurt, A.; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
This paper presents an analysis of thermal (Johnson) noise received from the radiation medium by otherwise noiseless capacitive micromachined ultrasonic transducer (CMUT) membranes operating in their fundamental resonance mode. Determination of thermal noise received by multiple numbers of transducers or a transducer array requires the assessment of cross-coupling through the radiation medium, as well as the self-radiation impedance of the individual transducer. We show that the total thermal noise received by the cells of a CMUT has insignificant correlation, and is independent of the radiation impedance, but is only determined by the mass of each membrane and the electromechanical transformer ratio. The proof is based on the analytical derivations for a simple transducer with two cells, and extended to transducers with numerous cells using circuit simulators. We used a first-order model, which incorporates the fundamental resonance of the CMUT. Noise power is calculated by integrating over the entire spectrum; hence, the presented figures are an upper bound for the noise. The presented analyses are valid for a transimpedance amplifier in the receive path. We use the analysis results to calculate the minimum detectable pressure of a CMUT. We also provide an analysis based on the experimental data to show that output noise power is limited by and comparable to the theoretical upper limit.
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Signal to noise ratio optimization for a CMUT based medical ultrasound imaging system
(IEEE, 2015) Zangabad, R. P.; Bozkurt, A.; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
CMUTs offers key performance benefits compared to their piezoelectric counterparts. However, CMUTs are not widely adopted in commercial ultrasound imaging systems due to low signal to noise ratio (SNR) in the obtained images. Tunable parameters of the CMUT include the membrane material, radius, thickness, gap height, electrode size, and bias voltage. The aim of this work is to optimize these parameters to provide a solution for low SNR problem of CMUTs. In medical imaging, the device will be used in pulse echo mode for which both good receive sensitivity and high output pressure is required. Optimizing these performance metrics will end up in conflicting design parameters, such as a high gap for large pressure output whereas a small gap for better receive sensitivity. In this work, we develop a methodology for the investigation of the round-trip behavior of the transducer and try to co-optimize transmit and receive characteristics of the device to maximize the SNR of the received signal by tuning the bias voltage.
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Vertical cavity capacitive transducer
(American Institute of Physics Inc., 2021-04-01) Yaralıoğlu, Göksen Göksenin; Ergun, A. S.; Bozkurt, A.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
The capacitive micromachined ultrasonic transducer (CMUT) has inherent advantages, such as larger bandwidth and monolithic integration capability with electronics, when compared to the piezoelectric transducer. The most significant shortcoming of the device is the trade-off between input and output sensitivities. Adequate receive sensitivity requires an electric field intensity on the order of 105 V/m, which can be achieved by sub-micron gap heights. However, a small gap limits the device stroke and, consequently, the maximum output pressure. This paper addresses this problem by proposing a CMUT with a vertical cavity. The membrane of the device has a piston part that is surrounded by the sidewalls of a vertical cylinder formed in the substrate. The fringing electric field pulls the piston in the vertical direction; hence, the gap height remains fixed, which alleviates the hard limit on device stroke. The performance of the proposed device is compared to that of the conventional CMUT by theoretical and analytical methods, and a micro-fabrication method is devised. Additionally, a millimeter-scale device has been manufactured and tested as a proof of concept.