Asier Marzo

Holographic acoustic elements for manipulation of levitated objects

Sound can levitate objects of different sizes and materials through air, water and tissue. This allows us to manipulate cells, liquids, compounds or living things without touching or contaminating them. However, acoustic levitation has required the targets to be enclosed with acoustic elements or had limited manoeuvrability. Here we optimize the phases used to drive an ultrasonic phased array and show that acoustic levitation can be employed to translate, rotate and manipulate particles using even a single-sided emitter. Furthermore, we introduce the holographic acoustic elements framework that permits the rapid generation of traps and provides a bridge between optical and acoustical trapping. Acoustic structures shaped as tweezers, twisters or bottles emerge as the optimum mechanisms for tractor beams or containerless transportation. Single-beam levitation could manipulate particles inside our body for applications in targeted drug delivery or acoustically controlled micro-machines that do not interfere with magnetic resonance imaging.

LeviPath: Modular Acoustic Levitation for 3D Path Visualisations

LeviPath is a modular system to levitate objects across 3D paths. It consists of two opposed arrays of transducers that create a standing wave capable of suspending objects in mid-air. To control the standing wave, the system employs a novel algorithm based on combining basic patterns of movement. Our approach allows the control of multiple beads simultaneously along different 3D paths. Due to the patterns and the use of only two opposed arrays, the system is modular and can scale its interaction space by joining several LeviPaths. In this paper, we describe the hardware architecture, the basic patterns of movement and how to combine them to produce 3D path visualisations.

Realization of compact tractor beams using acoustic delay-lines

A method for generating stable ultrasonic levitation of physical matter in air using single beams (also known as tractor beams) is demonstrated. The method encodes the required phase modulation in passive unit cells into which the ultrasonic sources are mounted. These unit cells use waveguides such as straight and coiled tubes to act as delay-lines. It is shown that a static tractor beam can be generated using a single electrical driving signal, and a tractor beam with one-dimensional movement along the propagation direction can be created with two signals. Acoustic tractor beams capable of holding millimeter-sized polymer particles of density 1.25 g/cm3 and fruit-flies (Drosophila) are demonstrated. Based on these design concepts, we show that portable tractor beams can be constructed with simple components that are readily available and easily assembled, enabling applications in industrial contactless manipulation and biophysics.

JOLED: A Mid-air Display based on Electrostatic Rotation of Levitated Janus Objects

We present JOLED, a mid-air display for interactive physical visualization using Janus objects as physical voxels. The Janus objects have special surfaces that have two or more asymmetric physical properties at different areas. In JOLED, they are levitated in mid-air and controllably rotated to reveal their different physical properties. We made voxels by coating the hemispheres of expanded polystyrene beads with different materials, and applied a thin patch of titanium dioxide to induce electrostatic charge on them. Transparent indium tin oxide electrodes are used around the levitation volume to create a tailored electric field to control the orientation of the voxels. We propose a novel method to control the angular position of individual voxels in a grid using electrostatic rotation and their 3D position using acoustic levitation. We present a display in which voxels can be flipped independently, and two mid-air physical games with a voxel as the playable character that moves in 3D across other physical structures and rotates to reflect its status in the games. We demonstrate a voxel update speed of 37.8 ms/flip, which is video-rate.

EchoFlex: Hand Gesture Recognition using Ultrasound Imaging

Recent improvements in ultrasound imaging enable new opportunities for hand pose detection using wearable devices. Ultrasound imaging has remained under-explored in the HCI community despite being non-invasive, harmless and capable of imaging internal body parts, with applications including smart-watch interaction, prosthesis control and instrument tuition. In this paper, we compare the performance of different forearm mounting positions for a wearable ultrasonographic device. Location plays a fundamental role in ergonomics and performance since the anatomical features differ among positions. We also investigate the performance decrease due to cross-session position shifts and develop a technique to compensate for this misalignment. Our gesture recognition algorithm combines image processing and neural networks to classify the flexion and extension of 10 discrete hand gestures with an accuracy above 98%. Furthermore, this approach can continuously track individual digit flexion with less than 5% NRMSE, and also differentiate between digit flexion at different joints.

TinyLev: A multi-emitter single-axis acoustic levitator

Acoustic levitation has the potential to enable novel studies due to its ability to hold a wide variety of substances against gravity under container-less conditions. It has found application in spectroscopy, chemistry, and the study of organisms in microgravity. Current levitators are constructed using Langevin horns that need to be manufactured to high tolerance with carefully matched resonant frequencies. This resonance condition is hard to maintain as their temperature changes due to transduction heating. In addition, Langevin horns are required to operate at high voltages (>100 V) which may cause problems in challenging experimental environments. Here, we design, build, and evaluate a single-axis levitator based on multiple, low-voltage (ca. 20 V), well-matched, and commercially available ultrasonic transducers. The levitator operates at 40 kHz in air and can trap objects above 2.2 g/cm3 density and 4 mm in diameter whilst consuming 10 W of input power. Levitation of water, fused-silica spheres, small insects, and electronic components is demonstrated. The device is constructed from low-cost off-the-shelf components and is easily assembled using 3D printed sections. Complete instructions and a part list are provided on how to assemble the levitator.

Three-dimensional ultrasonic trapping of micro-particles in water with a simple and compact two-element transducer

We report a simple and compact piezoelectric transducer capable of stably trapping single and multiple micro-particles in water. A 3D-printed Fresnel lens is bonded to a two-element kerfless piezoceramic disk and actuated in a split-piston mode to produce an acoustic radiation force trap that is stable in three-dimensions. Polystyrene micro-particles in the Rayleigh regime (radius λ/14 to λ/7) are trapped at the focus of the lens (F# = 0.4) and manipulated in two-dimensions on an acoustically transparent membrane with a peak trap stiffness of 0.43 mN/m. Clusters of Rayleigh particles are also trapped and manipulated in three-dimensions, suspended in water against gravity. This transducer represents a significant simplification over previous acoustic devices used for micro-particle manipulation in liquids as it operates at relatively low frequency (688 kHz) and only requires a single electrical drive signal. This simplified device has potential for widespread use in applications such as micro-scale manufac...

GauntLev: A Wearable to Manipulate Free-floating Objects

A tool able to generate remote forces would allow us to handle dangerous or fragile materials without contact or occlusions. Acoustic levitation is a suitable technology since it can trap particles in air or water. However, no approach has tried to endow humans with an intertwined way of controlling it. Previously, the acoustic elements were static, had to surround the particles and only translation was possible. Here, we present the basic manoeuvres that can be performed when levitators are attached to our moving hands. A Gauntlet of Levitation and a Sonic Screwdriver are presented with their manoeuvres for capturing, moving, transferring and combining particles. Manoeuvres can be performed manually or assisted by a computer for repeating patterns, stabilization and enhanced accuracy or speed. The presented prototypes still have limited forces but symbolize a milestone in our expectations of future technology.

Ultraino: An Open Phased-Array System for Narrowband Airborne Ultrasound Transmission

Modern ultrasonic phased-array controllers are electronic systems capable of delaying the transmitted or received signals of multiple transducers. Configurable transmit–receive array systems, capable of electronic steering and shaping of the beam in near real-time, are available commercially, for example, for medical imaging. However, emerging applications, such as ultrasonic haptics, parametric audio, or ultrasonic levitation, require only a small subset of the capabilities provided by the existing controllers. To meet this need, we present Ultraino, a modular, inexpensive, and open platform that provides hardware, software, and example applications specifically aimed at controlling the transmission of narrowband airborne ultrasound. Our system is composed of software, driver boards, and arrays that enable users to quickly and efficiently perform research in various emerging applications. The software can be used to define array geometries, simulate the acoustic field in real time, and control the connected driver boards. The driver board design is based on an Arduino Mega and can control 64 channels with a square wave of up to 17 Vpp and

SensIR: Detecting Hand Gestures with a Wearable Bracelet using Infrared Transmission and Reflection

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