Date of Award

1-1-2022

Publication Type

Thesis

Degree Name

M.A.Sc.

Department

Electrical and Computer Engineering

Keywords

3D FEA, Capacitive micromachined ultrasonic transducers, Electrostatic spring softening, Fluid Loading effect, Resonant frequency drift

Supervisor

Chowdhury, Sazzadur

Supervisor

E. Maeva

Rights

info:eu-repo/semantics/embargoedAccess

Abstract

This thesis presents a method to minimize the resonant frequency drift of Capacitive Micromachined Ultrasonic Transducers (CMUTs) due to fluid loading. A unified mathematical model for the resonant frequency of a CMUT that includes the electrostatic spring softening effect and the fluid loading effect due to the coupled fluidic layer has been developed that provides the basis of the proposed approach. The minimization method involves dynamic adjustment of the DC bias voltage to modify the electrostatic spring softening parameter to offset the effects of fluid loading. Analytical and COMSOL based 3D Finite Element Analysis (FEA) results show that the drift in the resonant frequency of a 6 MHz CMUT operated in water can be compensated by adjusting the bias voltage by 2% from its 75% pull-in voltage value to render an improvement of 4% in lateral and axial resolutions in imaging applications. A bias voltage adjustment of 9% of the 75% pull-in voltage value is necessary to achieve an improvement of 20.74% in glycerol medium. A microelectronics-based compensation scheme has been developed for dynamic voltage adjustment to offset the frequency drift. The developed scheme has been validated through simulation in MATLAB/Simulink.

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