Ramasawmy, Danny Raj;
(2020)
Modelling the Directional Response of Fabry-Pérot Ultrasound Sensors.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Fabry-Pérot ultrasound sensors offer an alternative to traditional piezoelectric sensors for clinical and metrological applications, for example, measuring high intensity focused-ultrasound (HIFU) fields. In this thesis, a model of the frequency dependent directional response was developed based on the partial-wave method, treating the sensor as a multi-layered elastic structure. An open-source MATLAB toolbox called ElasticMatrix was developed to model acoustic and elastic-wave propagation in multi-layered structures with anisotropic material properties. The toolbox uses an object-oriented framework, giving it a simple scripting interface and allowing it to be expanded easily. The toolbox is capable of calculating and plotting reflection and transmission coefficients, slowness profiles, dispersion curves and displacement and stress fields. An additional MATLAB class is included to model the frequency-dependent directional response of Fabry-Pérot ultrasound sensors. The model was validated, tested and compared with directional response measurements made on two glass-etalon sensors: an air-backed cover-slip sensor with well-known acoustic properties, and an all-hard-dielectric sensor. Features of the directional response were investigated and attributed to the critical angles of the substrate backing, and Lamb- and Rayleigh-modes propagating in the sensor. The directional response of two sensors with Parylene C (a commonly used soft-polymer) were also investigated: a sensor with a Parylene C spacer, and a glass-etalon sensor with a thick Parylene C coating. X-ray diffraction and transmission electron microscope measurements indicated Parylene has a crystal structure and impedance measurements indicated that Parylene is acoustically anisotropic. Using the measured impedance values, the modelled and measured directivity had improved agreement compared with isotropic values based on the phase-speeds of guided modes. The developed modelling tools allow detailed analysis of the physical mechanisms affecting the frequency-dependent directional response of planar Fabry-Pérot sensors. This knowledge can be used to inform future sensor design, to aid with material selection, and for deconvolution of the sensor response from acoustic measurements.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Modelling the Directional Response of Fabry-Pérot Ultrasound Sensors |
| Event: | UCL (University College London) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10094177 |
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