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Acoustic holograms are the keystone of modern acoustics. They encode three-dimensional acoustic fields in two dimensions, and their quality determines the performance of acoustic systems. Optimisation methods that control only the phase of an acoustic wave are considered inferior to methods that control both the amplitude and phase of the wave. In this paper, we present Diff-PAT, an acoustic hologram optimisation platform with automatic differentiation. We show that in the most fundamental case of optimizing the output amplitude to match the target amplitude; our method with only phase modulation achieves better performance than conventional algorithm with both amplitude and phase modulation. The performance of Diff-PAT was evaluated by randomly generating 1000 sets of up to 32 control points for single-sided arrays and single-axis arrays. This optimisation platform for acoustic hologram can be used in a wide range of applications of PATs without introducing any changes to existing systems that control the PATs. In addition, we applied Diff-PAT to a phase plate and achieved an increase of > 8 dB in the peak noise-to-signal ratio of the acoustic hologram.

This paper presents a method for generating dynamic caustic patterns by utilising dual-optimised holographic fields with Phased Array Transducer (PAT). Building on previous research in static caustic optimisation and ultrasonic manipulation, this approach employs computational techniques to dynamically shape fluid surfaces, thereby creating controllable and real-time caustic images. The system employs a Digital Twin framework, which enables iterative feedback and refinement, thereby improving the accuracy and quality of the caustic patterns produced. This paper extends the foundational work in caustic generation by integrating liquid surfaces as refractive media. This concept has previously been explored in simulations but not fully realised in practical applications. The utilisation of ultrasound to directly manipulate these surfaces enables the generation of dynamic caustics with a high degree of flexibility. The Digital Twin approach further enhances this process by allowing for precise adjustments and optimisation based on real-time feedback. Experimental results demonstrate the technique’s capacity to generate continuous animations and complex caustic patterns at high frequencies. Although there are limitations in contrast and resolution compared to solid-surface methods, this approach offers advantages in terms of real-time adaptability and scalability. This technique has the potential to be applied in a number of areas, including interactive displays, artistic installations and educational tools. This research builds upon the work of previous researchers in the fields of caustics optimisation, ultrasonic manipulation, and computational displays. Future research will concentrate on enhancing the resolution and intricacy of the generated patterns.

The need for the accurate generation of acoustic holograms has increased with the prevalence of the use of acoustophoresis methods such as ultrasonic haptic sensation, acoustic levitation, and displays. However, experimental results have shown that the actual acoustic field may differ from the simulated field owing to uncertainties in the transducer position, power and phase, or from nonlinearity and inhomogeneity in the field. Traditional methods for experimentally optimizing acoustic holograms require prior calibration and do not scale with the number of variables. Here, we propose a digital twin approach that combines feedback from experimental measurements (such as a microphone and an optical camera) in the physical setup with numerically obtained derivatives of the loss function, using automatic differentiation, to optimize the loss function. This approach is number of transducers times faster and more efficient than the classical finite difference approach, making it beneficial for various applications such as acoustophoretic volumetric displays, ultrasonic haptic sensations, and focused ultrasound therapy. Fushimi and colleagues report a digital twin based method to correct the discrepancies between simulation and experimental states for acoustic hologram optimization. This method reduces the number of experimental measurements needed, thus more efficient as compared to classical finite difference based approaches.

Abstract Applications in chemistry, biology, medicine, and engineering require the large-scale manipulation of a wide range of chemicals, samples, and specimens. To achieve maximum efficiency, parallel control of microlitre droplets using automated techniques is essential. Electrowetting-on-dielectric (EWOD), which manipulates droplets using the imbalance of wetting on a substrate, is the most widely employed method. However, EWOD is limited in its capability to make droplets detach from the substrate (jumping), which hinders throughput and device integration. Here, we propose a novel microfluidic system based on focused ultrasound passing through a hydrophobic mesh with droplets resting on top. A phased array dynamically creates foci to manipulate droplets of up to 300 μL. This platform offers a jump height of up to 10 cm, a 27-fold improvement over conventional EWOD systems. In addition, droplets can be merged or split by pushing them against a hydrophobic knife. We demonstrate Suzuki-Miyaura cross-coupling using our platform, showing its potential for a wide range of chemical experiments. Biofouling in our system was lower than in conventional EWOD, demonstrating its high suitability for biological experiments. Focused ultrasound allows the manipulation of both solid and liquid targets. Our platform provides a foundation for the advancement of micro-robotics, additive manufacturing, and laboratory automation.

Mid-air acoustic streaming, where ultrasound induces steady fluid motion, could significantly affect the perception of haptic sensations, stability of levitation systems, and enable controlled transfer of odors (smells) through air by directing volatile compounds to specific locations. Despite its importance, the streaming behavior in airborne phased-array transducers remains poorly understood. Here, we use particle image velocimetry and numerical simulations to investigate streaming dynamics in single- and multi-focus acoustic fields. Experimental measurements reveal streaming velocities exceeding 0.4 m/s in single-focus configurations and up to 0.3 m/s in multi-focus setups, with distinct grating lobe-induced lateral jets. While multi-physics finite-element models effectively capture central streaming, they exhibit subtle differences and perform poorly in capturing flow in the side lobes. These findings provide valuable insights into the interplay between acoustic field design and streaming dynamics, offering guidance for optimizing ultrasonic technologies in haptics and levitation applications.

User studies are crucial for meeting user needs. In user studies, real experimental scenarios and participants are constructed and recruited. However, emerging and unfamiliar studies face limitations, including safety concerns and iterative efficiency. To address these challenges, this study utilises a Generative Artificial Intelligence (GenAI) to create GenAI-generated scenarios for user experience (UX). By recruiting real users to evaluate this experience, we can collect feedback that enables rapid iteration in the early design phase. The air taxi is particularly representative of these challenges and has been chosen as the case study for this research. The key contribution was designing an Air Taxi Journey (ATJ) using Large Language Models (LLMs) and AI image and video generators. Based on the GPT-4-generated scripts, key visuals were created for the air taxi, and the ATJ was evaluated by 72 participants. Furthermore, the LLMs demonstrated the ability to identify and suggest environments that significantly improve participants' willingness toward air taxis. Education level and gender significantly influenced participants' the difference in willingness and their satisfaction with the ATJ. Satisfaction with the ATJ serves as a mediator, significantly influencing participants' willingness to take air taxis. Our study confirms the capability of GenAI to support user studies, providing a feasible approach and valuable insights for designing air taxi UX in the early design phase.

Acoustic levitation is a powerful method which enables objects to be levitated in mid-air using sound waves. The introduction of phased array levitator (PAL) has expanded the capability of acoustic levitation. The PAL allowed the levitated objects to be manipulated more dynamically in a three-dimensional field and opened up avenues for new applications of acoustic levitation. Whilst the interest in the acoustic levitation is high, the dynamic behaviour of the levitated spherical particles has not been explored in-depth, and a linear stiffness model of remains standard in the field. Therefore, this thesis aims to understand the underlying dynamics of a particle levitated in a PAL, and thereby improve the positioning performance of the particle. A single-axis PAL with two opposed emitting arrays was utilised for this thesis, and a numerical model was developed to predict the acoustic radiation force inside the levitator. A one-dimensional dynamic model was constructed using the numerical model to simulate the dynamic motion of particle in the PAL, and it was experimentally validated. It was found that there are positioning inaccuracies in the PAL, and was found to affect the dynamic response of the system. The effects and implications of these inaccuracies were demonstrated via the development of numerical simulations, and calibration schemes were developed to minimise the effect of the deviation. Both the numerical models and calibration methods in this thesis can be generalised to be applied to other forms of acoustic levitation, and the results presented here will lay the foundation for the current development of acoustic levitators. This case was confirmed by the application of the findings to the practical development of acoustophoretic volumetric display and will continue to aid the development of future application in the field of acoustic levitation.

Phased array transducers can shape acoustic fields for versatile manipulation; however, generating multiple focal points typically involves complex optimization. This study demonstrates that Dammann gratings - binary phase gratings originally used in optics to generate equal-intensity spot arrays - can be adapted for acoustics to create multiple equal-strength focal points with a phased array transducer. The transducer elements were assigned phases of 0 or , based on a Dammann grating defined by its transition points. Simulations show that simple gratings with two transition points can generate fields with up to 12 focal points of nearly equal acoustic pressures. Compared to conventional multi-focus phase optimization techniques, the Dammann grating approach offers computational efficiency and facile reconfiguration of the focal pattern by adjusting the grating hologram. We tested this approach in numerical simulations with a hypothetical high-resolution array, achieving up to 12 focal points, and validated the efficacy of the Dammann grating in a conventional 16x16 transducer array through both simulations and experiments. This comparison highlights that while Dammann gratings effectively generate multi-focus fields, the recreation ability of these gratings in a conventional array shows a lower resolution than the hypothetical array. This study underlines the potential of adapting binary phase functions from photonics to enhance ultrasound-based acoustic manipulation for tasks requiring parallel actuation at multiple points.

Accurate vibration measurement is vital for analyzing dynamic systems across science and engineering, yet noncontact methods often balance precision against practicality. Event cameras offer high-speed, low-light sensing, but existing approaches fail to recover vibration amplitude and frequency with sufficient accuracy. We present an event topology-based visual microphone that reconstructs vibrations directly from raw event streams without external illumination. By integrating the Mapper algorithm from topological data analysis with hierarchical density-based clustering, our framework captures the intrinsic structure of event data to recover both amplitude and frequency with high fidelity. Experiments demonstrate substantial improvements over prior methods and enable simultaneous recovery of multiple sound sources from a single event stream, advancing the frontier of passive, illumination-free vibration sensing.

Ultrasonic phased array technology, while versatile, often requires complex computing resources and numerous amplifier components. We present a Manually Reconfigurable Phased Array that physically controls transducer position and phase, offering a simpler alternative to traditional phased array transducers (PAT). Our system uses a conductor rod-connected transducer array with an underlying plate that modulates the phase state through its shape and electrode arrangement. This approach enables variable phase reconstruction with reduced computational demands and lower cost. Experimental results demonstrate the device's capability to focus ultrasonic waves at different spatial locations. The system's design facilitates the creation of acoustic fields without extensive digital control, potentially broadening applications in areas such as aerial haptics, audio spotlighting, and educational demonstrations of acoustic phenomena. This work contributes to the development of more accessible and computationally efficient acoustic phased array systems.