Abstract
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.
Highlights
Sound can levitate objects of different sizes and materials through air, water and tissue
We introduce the holographic acoustic element framework based on interpreting the phase delays as a holographic plate that combines the encoding of identifiable acoustic elements
The Gor’kov Laplacian function at one position in space can be expressed as a nonlinear infinitely differentiable function with the phase delays applied to the transducers as the only variables. With this function and the gradient of its variables, we employ a Broyden–Fletcher–Goldfarb–Shanno (BFGS) optimizer[25] to obtain the phase modulations for the transducers so that when driven with a reference signal the generated acoustic field exerts maximum trapping forces on a particle situated at the target point
Summary
Sound can levitate objects of different sizes and materials through air, water and tissue. Acoustic waves can exert radiation forces[1] and form acoustic traps at points where these forces converge permitting the levitation of particles of a wide range of materials and sizes[2] through air[3], water[4] or biological tissues[5]. This is of paramount importance for crystallography[6], cell manipulation[7], lab-on-a-chip scenarios[8], biomaterials[9], containerless transportation[3,10] and even the levitation of living things[11]. Controlled 3D trapping, translation and rotation with a single-sided array would enable acoustic tweezers to become the larger-scale counterparts of optical tweezers[24], opening up applications in materials processing, micro-scale manufacturing and biomedicine
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