Date of Award

1-10-2024

Publication Type

Thesis

Degree Name

M.A.Sc.

Department

Electrical and Computer Engineering

Keywords

CMUT, MEMS, Planar Fresnel Lens

Supervisor

Sazzadur Chowdhury

Rights

info:eu-repo/semantics/openAccess

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

This thesis presents a Microelectromechanical Systems (MEMS) planar Fresnel lens for use with a Capacitive Micromachined Ultrasonic Transducer (CMUT) array for high-resolution cardiac diagnostic imaging applications. The research exploited the excellent sound propagation and thermal properties of cross-linked silica aerogel, a nano-porous, nano-networked ultra-light-weight material, to design a planar thinfilm lens that can be easily microfabricated or integrated with a CMUT array. The designed lens, comprised of 32 various width concentric rings, was optimized to operate with a 256 element 6 MHz CMUT array. The 4 µm thick lens was designed to generate a 1.9 mm focal spot at a focal depth of 30.13 mm, which is the typical distance between the skin surface and the heart of an adult person. Two-dimensional (2D) axisymmetric Finite Element Analysis (FEA) was conducted in COMSOL Multiphysics design environment to validate the design. The focal spot exhibits a focal gain of 27.08 decibels (dB) and the efficiency of the lens was calculated from COMSOL Multiphysics simulated results to be 52.82%. The developed design methodology can be used to design Fresnel lenses operating at other frequencies and intensities suitable for High Intensity Focused Ultrasound (HIFU) applications, such as thermal ablation and acoustic cavitation-based tissue removal. The lens can be microfabricated in a standard microfabrication facility.

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