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dc.contributor.advisorAtalar, Abdullahen_US
dc.contributor.authorŞenlik, Muhammed N.en_US
dc.date.accessioned2016-01-08T20:05:50Z
dc.date.available2016-01-08T20:05:50Z
dc.date.issued2010
dc.identifier.urihttp://hdl.handle.net/11693/17052
dc.descriptionAnkara : The Department of Electrical and Electronics Engineering and The Institute of Engineering and Science of Bilkent University, 2010.en_US
dc.descriptionThesis (Ph.D.) -- Bilkent University, 2010.en_US
dc.descriptionIncludes bibliographical references leaves 40-49.en_US
dc.description.abstractCapacitive micromachined ultrasonic transducers (cMUTs) are used to transmit and receive ultrasonic signals. The device is constructed from circular membranes fabricated with surface micromachining technology. They have wider bandwidth with lower transmit power and lower receive sensitivity compared to the piezoelectric transducers, which dominate the ultrasonic transducer market. In order to be commercialized, they must overcome these drawbacks or find new application areas, where piezoelectric transducers perform poorly or cannot work. In this thesis, the latter approach, finding a new application area, is followed to design wide band and highly efficient airborne transducers with high output power by maximizing the radiation resistance of the transducer. The radiation impedance describes the interaction of the transducer with the surrounding medium. The real part, radiation resistance, is a measure of the amount of the power radiated to the medium; whereas the imaginary part, radiation reactance, shows the wobbled medium near the transducer surface. The radiation impedance of cMUTs are currently not well-known. As a first step, the radiation impedance of a cMUT with a circular membrane is calculated analytically using its velocity profile up to its parallel resonance frequency for both the immersion and the airborne applications. The results are verified by finite element simulations. The work is extended to calculate the radiation impedance of an array of cMUT cells positioned in a hexagonal pattern. The radiation impedance is determined to be a strong function of the cell spacing. It is shown that excitation of nonsymmetric modes is possible in immersion applications. A higher radiation resistance improves the bandwidth as well as the efficiency and the transmit power of the cMUT. It is shown that a center-to-center cell spacing of 1.25 wavelength maximizes the radiation resistance for the most compact arrangement, if the membranes are not too thin. For the airborne applications, the bandwidth can be further increased by using smaller device dimensions, which decreases the impedance mismatch between the cMUT and the air. On the other hand, this choice leads to degradation in both efficiency and transmit power due to lowered radiation resistance. It is shown that by properly choosing the arrangement of the thin membranes within an array, it is possible to optimize the radiation resistance. To make a fair analysis, same size arrays are compared. The operating frequency and the collapse voltage of the devices are kept constant. The improvement in the bandwidth and the transmit power can be as high as three and one and a half times, respectively. This method may also improve the noise figure when cMUTs are used as receivers. A further improvement in the noise figure is possible when the cells are clustered and connected to separate receivers. The results are presented as normalized graphs to be used for arbitrary device dimensions and material properties.en_US
dc.description.statementofresponsibilityŞenlik, Muhammed Nen_US
dc.format.extentxv, 49 leavesen_US
dc.language.isoEnglishen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectCapacitive Micromachined Ultrasonic Transducer (cMUT)en_US
dc.subjectAnalytical Modelingen_US
dc.subjectFinite Element Method (FEM) Modelingen_US
dc.subjectRadiation Impedanceen_US
dc.subjectAirborne cMUTen_US
dc.subject.lccTK5982 .S465 2010en_US
dc.subject.lcshUltrasonic transducers.en_US
dc.subject.lcshImpedance (Electricity)en_US
dc.subject.lcshFinite element methods.en_US
dc.titleRadiation impedance of capacitive micromachined ultrasonic transducersen_US
dc.typeThesisen_US
dc.departmentDepartment of Electrical and Electronics Engineeringen_US
dc.publisherBilkent Universityen_US
dc.description.degreePh.D.en_US


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