【摘 要】
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Background, Motivation and Objective The low mechanical impedance of Capacitive Micromachined Ultrasonic Transducers (CMUTs) results in a high bandwidth and receive sensitivity (RX), but consequently
【机 构】
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Department of Micro- and Nanotechnology, Technical University of Denmark, Denmark
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Background, Motivation and Objective The low mechanical impedance of Capacitive Micromachined Ultrasonic Transducers (CMUTs) results in a high bandwidth and receive sensitivity (RX), but consequently also a low output pressure (TX). This is particularly inhibiting for harmonic imaging where high pressure is needed to generate sufficient harmonics. The electrostatic force of the CMUT is proportional to the sum of the bias (VDC) and excitation voltages (VAC) squared, hence maximizing TX can be achieved by increasing both voltage levels. Applying a VDC close to pull-in increases the risk of collapsing the cells, but also for encountering potential intrinsic charging effects within the CMUT. Increasing VAC will, due to the nonlinear driving term, inherently increase the unwanted intrinsic generation of second harmonics of the CMUT. The optimal voltage levels for driving a CMUT are ultimately a compromise between TX, RX, and intrinsic harmonic generation.
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