Open Access
Numerical and experimental investigation of the stability of a drop in a single-axis acoustic levitator
(American Institute of Physics, 2019) Brizzotti Andrade, Marco Aurélio; Marzo Pérez, Asier; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika
Acoustic levitation can be employed to hold liquid drops in midair, enabling novel applications in X-ray scattering of proteins, amorphous crystallization of solutions, or contactless mixing. Multiple studies have characterized the physical behavior of a levitated drop inside an acoustic field. Here, we present a numerical and experimental study on the acoustic levitation of water drops in a single-Axis acoustic levitator consisting of an ultrasonic transducer and an opposing reflector. Instead of modeling an abstract incident acoustic field, our model considers the shape of the drop as well as the real geometry of the levitator. We also use a high-speed camera to observe the disintegration and the undesired oscillations of the drops. Our results show that the insertion of a drop in the levitator provokes a shift in its resonant frequency that depends on the shape of the drop. Second, the levitation behavior depends on whether the levitator operates slightly below or above the resonance. Third, if the levitator is driven above the resonant frequency, it is possible to levitate with more strength and avoid disintegration of the drop. This research provides an insight on how to achieve more stable experiments that avoid the bursting and undesired oscillations of the levitated sample. We hope that it will facilitate numerous experiments involving acoustically levitated liquid drops.
Open Access
Contactless pick-and-place of millimetric objects using inverted near-field acoustic levitation
(American Institute of Physics, 2020) Brizzotti Andrade, Marco Aurélio; Ramos, Tiago S.; Adamowski, Julio C.; Marzo Pérez, Asier; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika
We model and realize an ultrasonic contactless pick-and-place device capable of picking, self-centering, self-orienting, translating, and releasing flat millimetric objects. The device is an ultrasonic Langevin transducer operating at 21 kHz that radiates into air through a tapered tip. Objects are trapped few micrometers below the tip due to the near-field acoustic levitation phenomenon. We first investigate the conditions to achieve an attractive force on the object depending on its size and the device operating frequency. Second, we use a 3D acoustic model that describes the converging forces and torque that provide the self-centering and self-orienting capabilities. Third, a more advanced Computational Fluid Dynamics model based on the Navier-Stokes equations explains the small gap between the tip and the trapped object. The contactless manipulation capabilities of the device are demonstrated by picking, transporting, and releasing a Surface Mount Device in air. The presented manipulation concept can be an interesting alternative for manipulating delicate objects such as microelectromechanical devices, silicon dies, or micro-optical devices.
Open Access
Nonlinear trapping stiffness of mid-air single-axis acoustic levitators
(American Institute of Physics, 2018) Fushimi, Tatsuki; Hill, Thomas L.; Marzo Pérez, Asier; Drinkwater, Bruce W.; Estadística, Informática y Matemáticas; Estatistika, Informatika eta Matematika
We describe and experimentally explore a nonlinear stiffness model of the trapping of a solid particle in a single-axis acoustic levitator. In contrast to the commonly employed linear stiffness assumption, our nonlinear model accurately predicts the response of the system. Our nonlinear model approximates the acoustic field in the vicinity of the trap as a one-dimensional sinusoid and solves the resulting dynamics using numerical continuation. In particular, we predict a softening of stiffness with amplitude as well as period-doubling bifurcations, even for small excitation amplitudes of 2% of the wavelength. These nonlinear dynamic features are observed experimentally in a single-axis levitator operating at 40 kHz and trapping millimetre-scale expanded polystyrene spheres. Excellent agreement between the observed and predicted behaviour is obtained suggesting that this relatively simple model captures the relevant physical phenomena. This new model enables the dynamic instabilities of trapped particles to be accurately predicted, thereby benefiting contactless transportation and manipulation applications

Marzo Pérez, Asier

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