Deep-collapse operation of capacitive micromachined ultrasonic transducers
Author
Olcum, S.
Yamaner F. Y.
Bozkurt, A.
Atalar, Abdullah
Date
2011Source 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
ArticleItem Usage Stats
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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 approachCapacitive 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