A modelling approach to design of ultrasonic tweezers devices

Abstract

Acoustic manipulators are devices designed to generate ultrasonic waves that alter the dynamics of small-scale objects which are applied to a wide range of applications. Acoustic tweezers are focused wave fields which enable high-contrast trapping forces and enhanced manipulation dexterity. In-plane closed devices manipulate particles in a contained two-dimensional acoustic chamber but may produce high-fidelity traps only in a narrow area. Devices built with complex manufacturing processes may render simplified models to predict accurately experimental results. Parts assembly may limit devices' performance whose simplified assumptions fails to predict. This work implements a modelling approach combining physics-based models to investigate system-wide responses applied to high-fidelity reproduction of acoustic traps in a new array transducer. Monolithic Ultrasonic Tweezers Device is proposed as a multi-electrode transducer with mechanically coupled elements for ultrasonic tweezing. An acoustic chamber surrounded by a backed monolithic piezoceramic is modelled by a unique interface which separates the internal acoustic from the external piezoelectric fields. This thesis presents numerical simulations of pressure fields and performances for various shapes, sizes and material properties. Three physics-based models investigate the system's response in alternative approximation levels. The Equivalent Source and the Finite Element methods solve for fluid and piezoelectric external domains, respectively. Two protocols are investigated based on the position of sources relative to the interface. Internal sources define internal wave incidence and reflection in the analysis protocol whereas external sources define wave scattering and internal transmission in the synthesis protocol. A simplified model associates analysis with synthesis performances. The inverse filtering technique is employed to pressure field synthesis. Mathematical models relate boundary data across protocols and correlate generating with solution waves in a performance-based parameter study. Mapping analysis performance between models is achieved by tuning electromechanical coefficients. A new wave superposition technique is employed to the reproduction of wide-area high-fidelity acoustic traps in a large-scale realistic model.

Date of Award	23 Jan 2020
Original language	English
Awarding Institution	The University of Bristol
Sponsors	CAPES
Supervisor	Bruce W Drinkwater (Supervisor) & Paul D Wilcox (Supervisor)