Christopoulos, Giorgos;
(2025)
Modelling, Computing and Prototyping Acoustic Holograms.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Acoustic holograms are devices that encode and synthesise multiple target acoustic fields based on the complex (amplitude and phase) activation of their individual source elements. Phased arrays of ultrasonic transducers (PATs) or diffraction limited passive holograms like monolithic plates or acoustic metasurfaces, have been shown to manipulate acoustic waves for impressive mixed reality, multimodal mid-air displays as well as contactless additive manufacturing and tissue engineering. In this thesis, I present advances in the theory and practice of acoustic holography with contributions that cover all aspects of modelling, computing and prototyping acoustic holograms. I first interpret the widely used Gerchberg-Saxton (GS) phase retrieval algorithm as a gradient descent method, which maximises amplitudes at target locations, and accordingly present state-of-the-art solutions for different holograms and applications. Second, I numerically and experimentally validate reflective spatial ultrasound modulator prototypes that address reconfigurability in passive holograms. Third, I present an efficient boundary element method reformulation for high-speed holography in an environment including static rigid obstacles. Combined with a simplified acoustic potential objective, this approach allows the interaction between physical objects and digital content generated by PATs in real time. Finally, I develop temporal phase retrieval algorithms that both succeed target amplitudes and suppress transducers' phase changes, preventing fluctuations in their emission. From fast GS based hardware implementations to introducing saddle point optimisation in computer generated holography, my algorithms address the conflicting amplitude and phase objectives and enable dynamic 3D content delivery with minimum geometric restrictions. I experimentally demonstrate independent motion of multiple levitated particles that depict different parts of a human body. Beyond its specific software or hardware contributions, my work provides an end-to-end guide for prototyping acoustic holographic devices and applications, paving the way for their widespread use.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Modelling, Computing and Prototyping Acoustic Holograms |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/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 > Dept of Computer Science |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10206874 |
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