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      • Department of Electrical and Electronics Engineering
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      Deep - collapse operation of capacitive micromachined ultrasonic transducers

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      Author
      Olcum, S.
      Yamaner F. Y.
      Bozkurt, A.
      Atalar, A.
      Date
      2011
      Journal Title
      IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
      ISSN
      0885-3010
      Publisher
      IEEE
      Volume
      58
      Issue
      11
      Pages
      2475 - 2483
      Language
      English
      Type
      Article
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      Please cite this item using this persistent URL
      http://hdl.handle.net/11693/21738
      Abstract
      Capacitive micromachined ultrasonic transducers (CMUTs) have been introduced as a promising technology for ultrasound imaging and therapeutic ultrasound applications which require high transmitted pressures for increased penetration, high signal-to-noise ratio, and fast heating. However, output power limitation of CMUTs compared with piezoelectrics has been a major drawback. In this work, we show that the output pressure of CMUTs can be significantly increased by deep-collapse operation, which utilizes an electrical pulse excitation much higher than the collapse voltage. We extend the analyses made for CMUTs working in the conventional (uncollapsed) region to the collapsed region and experimentally verify the findings. The static deflection profile of a collapsed membrane is calculated by an analytical approach within 0.6% error when compared with static, electromechanical finite element method (FEM) simulations. The electrical and mechanical restoring forces acting on a collapsed membrane are calculated. It is demonstrated that the stored mechanical energy and the electrical energy increase nonlinearly with increasing pulse amplitude if the membrane has a full-coverage top electrode. Utilizing higher restoring and electrical forces in the deep-collapsed region, we measure 3.5 MPa peak-to-peak pressure centered at 6.8 MHz with a 106% fractional bandwidth at the surface of the transducer with a collapse voltage of 35 V, when the pulse amplitude is 160 V. The experimental results are verified using transient FEM simulations.
      Published as
      http://dx.doi.org/10.1109/TUFFC.2011.2104
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