Airborne cmut cell design

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buir.advisorKöymen, Hayrettin
dc.contributor.authorYılmaz, Aslı
dc.date.accessioned2016-01-08T18:27:52Z
dc.date.available2016-01-08T18:27:52Z
dc.date.issued2014
dc.departmentDepartment of Electrical and Electronics Engineeringen_US
dc.descriptionAnkara : The Department of Electrical and Electronics Engineering and The Graduate School of Engineering and Science of Bilkent University, 2014.en_US
dc.descriptionThesis (Ph. D.) -- Bilkent University, 2014.en_US
dc.descriptionIncludes bibliographical references leaves 60-64.en_US
dc.description.abstractAll transducers used in airborne ultrasonic applications, including capacitive micromachined ultrasonic transducers (CMUTs), incorporate loss mechanisms to have reasonably wide frequency bandwidth. However, CMUTs can yield high efficiency in airborne applications and unlike other technologies, they offer wider bandwidth due to their low characteristic impedance, even for efficient designs. Despite these advantages, achieving the full potential is challenging due to the lack of a systematic method to design a wide bandwidth CMUTs. In this thesis, we present a method for airborne CMUT design. We use a lumped element circuit model and harmonic balance (HB) approach to optimize CMUTs for maximum transmitted power. Airborne CMUTs have narrowband characteristic at their mechanical part, due to low radiation impedance. In this work, we restrict the analysis to a single frequency and the transducer is driven by a sinusoidal voltage with half of the frequency of operation frequency, without any dc bias. We propose a new mode of airborne operation for CMUTs, where the plate motion spans the entire gap. We achieve this maximum swing at a specific frequency applying the lowest drive voltage and we call this mode of operation as Minimum Voltage Drive Mode (MVDM). We present equivalent circuit-based design fundamentals for airborne CMUT cells and verify the design targets by fabricated CMUTs. The performance limits for silicon membranes for airborne applications are derived. We experimentally obtain 78.9 dB//20Pa@1m source level at 73.7 kHz, with a CMUT cell of radius 2.05 mm driven by 71 V sinusoidal drive voltage at half the frequency. The measured quality factor is 120. CMUTs can achieve a large bandwidth (low quality factor level) as they can be manufactured to have thin plates. Low-quality-factor airborne CMUTs experience increased ambient pressure and therefore a larger membrane deflection. This effect increases the stiffness of the plate material and can be considered by nonlinear compliance in the circuit model. We study the interaction of the compliance nonlinearity and nonlinearity of transduction force and show that transduction overwhelms the compliance nonlinearity. To match the simulation results with the admittance measurements we implement a very accurate model-based characterization approach where we modify the equivalent circuit model. In the modified circuit model, we introduced new elements to include loss mechanisms. Also, we changed the dimension parameters used in the simulation to compensate the difference in the resonance frequency and amplitude.en_US
dc.description.degreePh.D.en_US
dc.description.statementofresponsibilityYılmaz, Aslıen_US
dc.format.extentxviii, 64 leaves, graphicsen_US
dc.identifier.itemidB147580
dc.identifier.urihttp://hdl.handle.net/11693/15976
dc.language.isoEnglishen_US
dc.publisherBilkent Universityen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectAirborne Capacitive Micromachined Ultrasonic Transducersen_US
dc.subjectCircular CMUTen_US
dc.subjectMEMSen_US
dc.subjectLumped Element Modelen_US
dc.subjectEquivalent Circuit Modelen_US
dc.subjectUnbiased Operationen_US
dc.subjectHigh Efficiencyen_US
dc.subject.lccTK5982 .Y55 2014en_US
dc.subject.lcshUltrasonic transducers.en_US
dc.subject.lcshElectroacoustic transducers.en_US
dc.subject.lcshElectroacoustic transducers--Design and construction.en_US
dc.titleAirborne cmut cell designen_US
dc.typeThesisen_US

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