Optimization of Acoustic Fields Advances towards its use for Matter Manipulation and Contactless Fabrication
Authors:   , Ezcurdia Aguirre Íñigo Fermín 
Published: April 2023

Acoustic pressure fields are capable of patterning and levitating particles of a wide range of ma-terials and sizes through air, water or biological tissue. This has applications in crystallography, cell manipulation, lab-on-a-chip scenarios, pharmacology, containerless transportation and even levitation of living things. Overall, the research domain of acoustic pressure fields has seen signif-icant advances in recent years. Its flexibility and potential applications have been greatly increased with the development of holographic techniques and the use of optimizers. However, there is still room for improvement, as limitations hinder the application of acoustic fields in various research scenarios. For example, there is no unified hardware platform that can flexibly support exploratory research in acoustic holography applications. Most commercial or DIY devices lack the resolution or power that researchers require, so they need to fabricate more complex, cumbersome and ex-pensive devices. Moreover, previous research has focused on the levitation and manipulation of small particles and droplets; however, a full prototype for contactless fabrication has yet to be de-veloped since there is no existing work on trapping elongated objects in position and orientation. Furthermore, microfluidics is limited in terms of three-dimensional (3D) manipulation, droplet size and cross-contamination. This thesis provides a comprehensive introduction to the optimization of acoustic fields, re-viewing its importance in applications across multiple research and industry domains. This thesis also examines the previously stated limitations and shortcomings of the design and application of acoustic fields. Novel algorithms are proposed to generate desired target fields and to significantly improve their resolution and power through spatial and temporal multiplexation. An open and affordable hardware platform is presented to facilitate customisation for experimental require-ments by researchers exploring novel applications for ultrasonic holograms. Optimum acoustic traps are designed and evaluated to lock elongated elements in position and orientation. Contact-less fabrication using full acoustic trapping of elongated parts is demonstrated through additive manufacturing based on levitated particles, sticks and UV resin; the addition on top of other ob-jects and building inside containers is also illustrated. Finally, a 3D digital microfluidics system is proposed based on focused ultrasound through a hydrophobic mesh. Able to handle a large num-ber of liquid droplets (> 40μL), and capable of merging/splitting them or vertically propelling them, this system significantly improves already existing EWOD systems generating less surface contamination. This thesis presents these achievements and their related works, models, methodologies, pro-cedures and conclusions. I hope that these pieces of work are a significant advancement in the research of acoustic fields and may inspire and facilitate future novel applications of acoustic holo-grams by researchers in various domains of academia and industry.