Abstract
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.
Highlights
IntroductionAcoustic waves can trap particles of different materials and a wide range of sizes of millimetre dimensions
Sound is a mechanical wave and as such it carries momentum that can act on particles due to acoustic radiation forces.[7,9,15,18] When the forces exerted on an object are strong enough and converge from all directions, the particles can be levitated and stably trapped.[6]Acoustic waves can trap particles of different materials and a wide range of sizes of millimetre dimensions
In the sections titled Design and Results, we show the procedures followed to design TinyLev and evaluate its performance
Summary
Acoustic waves can trap particles of different materials and a wide range of sizes of millimetre dimensions This is a significant difference with respect to optical trapping in which the particle size range is 0.01-10 μm and the materials need to be dielectric or optically transparent.[24]. Diamagnetic materials can be levitated by magnets that repel the sample;[14] a frog was levitated in this way[5] since water is slightly diamagnetic. This technique requires strong magnetic fields given the weak diamagnetism of most materials of interest. Other forms of levitation such as aerodynamic levitation[53] agitate and alter the samples in the process, and in electrostatic levitation,[23] the required control systems are complex and the sample materials are limited
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