Z. Y. Hong

Acoustic method for levitation of small living animals

Ultrasonic levitation of some small living animals such as ant, ladybug, and young fish has been achieved with a single-axis acoustic levitator. The vitality of ant and ladybug is not evidently influenced during the acoustic levitation, whereas that of the young fish is reduced because of the inadequacy of water supply. Numerical analysis shows that the sound pressures on the ladybug’s surface almost reach the incident pressure amplitude p0 due to sound scattering. It is estimated that 99.98% of the acoustic energy is reflected away from the ladybug. The acoustic radiation pressure pa on the ladybug’s surface is only 1%–3% of p0, which plays a compression role on the central region and a suction role on the peripheral region.Ultrasonic levitation of some small living animals such as ant, ladybug, and young fish has been achieved with a single-axis acoustic levitator. The vitality of ant and ladybug is not evidently influenced during the acoustic levitation, whereas that of the young fish is reduced because of the inadequacy of water supply. Numerical analysis shows that the sound pressures on the ladybug’s surface almost reach the incident pressure amplitude p0 due to sound scattering. It is estimated that 99.98% of the acoustic energy is reflected away from the ladybug. The acoustic radiation pressure pa on the ladybug’s surface is only 1%–3% of p0, which plays a compression role on the central region and a suction role on the peripheral region.

Acoustic levitation with self-adaptive flexible reflectors

Two kinds of flexible reflectors are proposed and examined in this paper to improve the stability of single-axis acoustic levitator, especially in the case of levitating high-density and high-temperature samples. One kind is those with a deformable reflecting surface, and the other kind is those with an elastic support, both of which are self-adaptive to the change of acoustic radiation pressure. High-density materials such as iridium (density 22.6 gcm(-3)) are stably levitated at room temperature with a soft reflector made of colloid as well as a rigid reflector supported by a spring. In addition, the containerless melting and solidification of binary In-Bi eutectic alloy (melting point 345.8 K) and ternary Ag-Cu-Ge eutectic alloy (melting point 812 K) are successfully achieved by applying the elastically supported reflector with the assistance of a laser beam.

Interaction of acoustic levitation field with liquid reflecting surface

Single-axis acoustic levitation of substances, such as foam, water, polymer, and aluminum, is achieved by employing various liquids as the sound reflectors. The interaction of acoustic levitation field with liquid reflecting surface is investigated theoretically by considering the deformation of the liquid surface under acoustic radiation pressure. Numerical calculations indicate that the deformation degree of the reflecting surface shows a direct proportion to the acoustic radiation power. Appropriate deformation is beneficial whereas excessive deformation is unfavorable to enhance the levitation capability. Typically, the levitation capability with water reflector is smaller than that with the concave rigid reflector but slightly larger than that with the planar rigid reflector at low emitter vibration intensity. Liquid reflectors with larger surface tension and higher density behave more closely to the planar rigid reflector.

A numerical simulation of acoustic field within liquids subject to three orthogonal ultrasounds

When one beam of ultrasound propagates along a single direction in liquids, the cavitation effect is always confined to a limited volume close to the ultrasonic source. This greatly limits the application of power ultrasound in liquid processing and materials fabrication. In this study, a methodology for applying three orthogonal ultrasounds within liquids has been proposed. By solving the Helmholtz equation, the sound field distribution characteristics are investigated in 1D (one dimensional), 2D (two dimensional) and 3D (three dimensional) ultrasounds at their resonant frequencies, which show that the coherent interaction of three beams of ultrasounds is able to strikingly promote the sound pressure level and reinforce the mean acoustic energy density as compared with that in 1D case. Hence, the potential cavitation volume is enlarged remarkably. This opens new possibilities for the design and optimization of ultrasonic technology in fabricating materials.

The near-field acoustic levitation of high-mass rotors.

Here we demonstrate that spherical rotors with 40 mm diameter and 0-1 kg mass can be suspended more than tens of micrometers away from an ultrasonically vibrating concave surface by near-field acoustic radiation force. Their rotating speeds exceed 3000 rpm. An acoustic model has been developed to evaluate the near-field acoustic radiation force and the resonant frequencies of levitation system. This technique has potential application in developing acoustic gyroscope.

Surface wave patterns on acoustically levitated viscous liquid alloys

We demonstrate two different kinds of surface wave patterns on viscous liquid alloys, which are melted and solidified under acoustic levitation condition. These patterns are consistent with the morphologies of standing capillary waves and ensembles of oscillons, respectively. The rapid solidification of two-dimensional liquid alloy surfaces may hold them down.

Dynamics of water drop detachment from a superhydrophobic surface induced by an ultrasonic field

We present the dynamics of sessile water drops during their detachment from a superhydrophobic surface induced by ultrasound. The superhydrophobic surface not only serves as a reflector of the ultrasound emitted from the source but also reduces the adhesive force between the drop and the solid surface. The drop is subject to an acoustic radiation force in the ultrasonic field due to the nonlinear effect of the latter. By shifting the reflector upward to approach the first resonance distance, the sessile drop is first elongated in the vertical direction, with its contact line and contact angle decreasing, and finally detaches from the superhydrophobic surface when the acoustic radiation force overcomes the sum of the gravitational and adhesive forces. The acoustic radiation pressure and acoustic radiation force are calculated by solving the acoustic field with the finite element method. The results indicate that the distribution of acoustic radiation pressure provides the upward force to make the drop detach. After its detachment from the reflector, the drop undergoes vertical vibration accompanied by shape oscillations. Oscillations of a water drop that is pinned on the reflector are also demonstrated.We present the dynamics of sessile water drops during their detachment from a superhydrophobic surface induced by ultrasound. The superhydrophobic surface not only serves as a reflector of the ultrasound emitted from the source but also reduces the adhesive force between the drop and the solid surface. The drop is subject to an acoustic radiation force in the ultrasonic field due to the nonlinear effect of the latter. By shifting the reflector upward to approach the first resonance distance, the sessile drop is first elongated in the vertical direction, with its contact line and contact angle decreasing, and finally detaches from the superhydrophobic surface when the acoustic radiation force overcomes the sum of the gravitational and adhesive forces. The acoustic radiation pressure and acoustic radiation force are calculated by solving the acoustic field with the finite element method. The results indicate that the distribution of acoustic radiation pressure provides the upward force to make the drop deta...

Note: Attenuation motion of acoustically levitated spherical rotor

Here we observe the attenuation motion of spherical rotors levitated by near-field acoustic radiation force and analyze the factors that affect the duration time of free rotation. It is found that the rotating speed of freely rotating rotor decreases exponentially with respect to time. The time constant of exponential attenuation motion depends mainly on the levitation height, the mass of rotor, and the depth of concave ultrasound emitter. Large levitation height, large mass of rotor, and small depth of concave emitter are beneficial to increase the time constant and hence extend the duration time of free rotation.