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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, Abdullah
      Date
      2011
      Source Title
      IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
      Print ISSN
      0885-3010
      Publisher
      IEEE
      Volume
      58
      Issue
      11
      Pages
      2475 - 2483
      Language
      English
      Type
      Article
      Item Usage Stats
      139
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      126
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      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.
      Keywords
      Analytical approach
      Capacitive micromachined ultrasonic transducer
      Collapse voltage
      Electrical energy
      Electrical force
      Electrical pulse excitation
      FEM simulations
      Finite element method simulation
      Fractional bandwidths
      High signal-to-noise ratio
      Mechanical energies
      Output power
      Piezoelectrics
      Pulse amplitude
      Restoring forces
      Static deflections
      Therapeutic ultrasound
      Ultrasound imaging
      Bandwidth
      Fading
      Finite element method
      Power quality
      Pulse amplitude modulation
      Signal to noise ratio
      Ultrasonics
      Electric Capacitance
      Ultrasonic therapy
      Ultrasonography
      Permalink
      http://hdl.handle.net/11693/21738
      Published Version (Please cite this version)
      http://dx.doi.org/10.1109/TUFFC.2011.2104
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      • Department of Electrical and Electronics Engineering 3597
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