Remzi Erkan Kemal - Ph.D, Electrical and Electronics Engineering
Prof. Taylan Akdoğan – Advisor
Asst. Prof.Göksenin Yaralıoğlu - Co-Advisor
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Improved modeling of Capacitive Micromachined Ultrasonic Transducers (CMUTs)
Prof. Taylan Akdoğan Özyeğin University
Assoc. Prof. Ayhan Bozkurt, Sabancı University
Assoc. Prof. Arif Sanlı Ergun, TOBB University of Economics and Technology
Dr. Ahmet Tekin, Ozyegin University
Dr. Cenk Demiroglu, Ozyegin Universtiy
Capacitive micromachined ultrasonic transducers (CMUTs) have been studied intensively in academia as well as in industry over the last two decades. Traditional ultrasound imaging technology mainly relies on piezoelectric transducers whereas CMUTs provide advantages such as providing wide bandwidth operation, ease of fabrication, potential to fabricate large 2D arrays, integration with IC and low cost.
With the design flexibility that CMUTs offer, it is possible to fabricate complex CMUT structures with different sizes and shapes including non-uniform membranes. This necessitates development of fast and accurate modeling tools for the medical imaging community. In this thesis, we demonstrate two methods that were developed to simulate the frequency of a CMUT, namely; Equivalent circuit models and finite element models (FEM). FEM provide very accurate calculations for various membrane geometries and evaluate the device performance. However, FEM analysis is much more time consuming compared to equivalent circuit models and it typically is not suitable for optimization where a series of simulations are required. Therefore, equivalent circuit models are preferred for the device optimization. There are several equivalent circuits models were presented previously. However, to be able to obtain frequency bandwidth accurately, anti-resonance of a CMUT must be included by the equivalent circuit. The first focus of the dissertation is to develop a new equivalent circuit model to simulate frequency bandwidth of a CMUT including anti-resonances.
The second aim of the dissertation is to design and simulate of ultra-wide bandwidth CMUTs for acoustic angiography applications. Currently, dual-frequency transducers are used for this application. In this process, two sets of transducers are used; one of them transmits ultrasonic waves at low frequencies and the other one receives the harmonic waves of the incident ultrasound, which is coming from the tissue. The process requires precise designing of the transducers bandwidths and hence is overly complex. Moreover, some of the information may be lost with undetected harmonics. Another difficulty arises due to the fact that it is difficult to align the transducers coaxially so that most of the generated ultrasound is detected by the receiver. However, if a transducer bandwidth can be increased enough, a single transducer can be used, and hence both the design complexity of the process is reduced and more harmonics can be detected. Therefore, the second part of this thesis focuses to optimize plate size and geometry as well as electrode area to obtain maximum frequency bandwidth. Within the framework of this dissertation, we demonstrated very high bandwidth transducers by introducing novel membrane geometries where we engineered the anti-resonance frequencies. Since the membrane geometry is not uniform the equivalent circuit model that was developed in the first part of the thesis is not accurate to estimate the bandwidth. Therefore, in the second part of the thesis, we used FEM analysis to design various membrane geometries to achieve very wide bandwidth.
R. Erkan Kemal is a PhD student at Ozyegin University Electrical and Electronics Department studying under the supervision of Prof. Taylan Akdoğan. He has completed the undergraduate program at Ankara University in the Department of Physics Engineering in 2010 and received his Master’s Degree in 2012 from Nanoelectronics Program of The University of Manchester, Manchester, UK. He worked as a visiting research assistant in North Carolina State University, USA in 2017. His current research focuses on developing devices and systems for ultrasound imaging and modeling of microelectromechanical systems.