Abstract:Acoustic manipulation by an ultrasonic phased array provides an entirely new approach to processes such as coalescence, mixing, separation, and evaporation occurring in the generation of new materials, physical property measurement, the biomedical industry, etc. However, to date, ultrasonic phased arrays have not been fully investigated for applications in fluid manipulation. This paper provides contactless coalescence and mixing techniques for droplets in air by controlling the acoustic potential by using an … Show more
“…As described in the literature, [40][41][42] the acoustic radiation force acting on the droplets can be approximated by the restoring force of a spring and the oscillations can be described by making an analogy with a damped harmonic oscillator. The merging operation was achieved by a procedure similar to that described by Watanabe et al, 28 but instead of generating the focal points by rapidly switching the phases of all the transducers, our focusing scheme divided the transducers into two sets to obtain two simultaneous and independent focus points; i.e. Watanabe et al employed time multiplexing whereas we have used spatial multiplexing.…”
Section: Resultsmentioning
confidence: 99%
“…22 In the recent years, different acoustic approaches have been proposed to manipulate liquid droplets. 14,[23][24][25][26][27][28] Koyama and Nakamura 23 developed a levitation system formed by a plane reflector and a metal plate attached to transducers at its ends. By changing the relative phase between the a) Author to whom correspondence should be addressed: marcobrizzotti@ gmail.com transducers, they could transport ethanol droplets.…”
Section: Introductionmentioning
confidence: 99%
“…Ochiai et al 24 employed four arrays arranged in a cube to manipulate small solid objects and liquid droplets in three-dimensions. Recently, Watanabe et al 28 used a 7 × 7 square array of 40 kHz transducers and an opposing reflector to levitate and merge two liquid droplets. In their system, the horizontal positions of the droplets were controlled by rapidly multiplexing (i.e.…”
Section: Introductionmentioning
confidence: 99%
“…Despite the recent progress in manipulating liquid droplets by acoustic levitation methods, a remaining issue is how to insert and remove the samples from the levitator. In the state-of-the-art levitation systems, 11,14,22,23,28 samples are manually inserted and removed with a syringe, requiring a skilled person to avoid sample losses and preventing the automation of the processes. Therefore, executing different fluidic operations such as injection, 19,29,30 transportation, 14,23,24 merging 14,26,28 and ejection 31 in a single levitation device would open up multiple possibilities, enabling the automatic processing of droplets in mid-air.…”
We present an acoustic levitation system that automatically injects, transports, merges and ejects liquid droplets in mid-air. The system consists of a phased array operating at 40 kHz on top of a plane reflector. The phase array generates multiple focal points at independent positions that form standing waves between the array and the reflector. In the reflector there is an inlet for a piezoelectric droplet injector which automatically inserts liquid droplets at the lower pressure nodes of the standing waves, and a hole that serves as an outlet for ejecting the processed droplets out of the system. Simulations of the acoustic radiation potential acting on the levitating droplets are in good agreement with the experiments. High-speed footage captured the functioning of the system in four fluidic operations: injection, transport, merging and ejection of liquid droplets. Having these operations integrated reliably into a single automatic system paves the way for the adoption of mid-air acoustophoretic processing in biological, chemical and pharmaceutical applications.
“…As described in the literature, [40][41][42] the acoustic radiation force acting on the droplets can be approximated by the restoring force of a spring and the oscillations can be described by making an analogy with a damped harmonic oscillator. The merging operation was achieved by a procedure similar to that described by Watanabe et al, 28 but instead of generating the focal points by rapidly switching the phases of all the transducers, our focusing scheme divided the transducers into two sets to obtain two simultaneous and independent focus points; i.e. Watanabe et al employed time multiplexing whereas we have used spatial multiplexing.…”
Section: Resultsmentioning
confidence: 99%
“…22 In the recent years, different acoustic approaches have been proposed to manipulate liquid droplets. 14,[23][24][25][26][27][28] Koyama and Nakamura 23 developed a levitation system formed by a plane reflector and a metal plate attached to transducers at its ends. By changing the relative phase between the a) Author to whom correspondence should be addressed: marcobrizzotti@ gmail.com transducers, they could transport ethanol droplets.…”
Section: Introductionmentioning
confidence: 99%
“…Ochiai et al 24 employed four arrays arranged in a cube to manipulate small solid objects and liquid droplets in three-dimensions. Recently, Watanabe et al 28 used a 7 × 7 square array of 40 kHz transducers and an opposing reflector to levitate and merge two liquid droplets. In their system, the horizontal positions of the droplets were controlled by rapidly multiplexing (i.e.…”
Section: Introductionmentioning
confidence: 99%
“…Despite the recent progress in manipulating liquid droplets by acoustic levitation methods, a remaining issue is how to insert and remove the samples from the levitator. In the state-of-the-art levitation systems, 11,14,22,23,28 samples are manually inserted and removed with a syringe, requiring a skilled person to avoid sample losses and preventing the automation of the processes. Therefore, executing different fluidic operations such as injection, 19,29,30 transportation, 14,23,24 merging 14,26,28 and ejection 31 in a single levitation device would open up multiple possibilities, enabling the automatic processing of droplets in mid-air.…”
We present an acoustic levitation system that automatically injects, transports, merges and ejects liquid droplets in mid-air. The system consists of a phased array operating at 40 kHz on top of a plane reflector. The phase array generates multiple focal points at independent positions that form standing waves between the array and the reflector. In the reflector there is an inlet for a piezoelectric droplet injector which automatically inserts liquid droplets at the lower pressure nodes of the standing waves, and a hole that serves as an outlet for ejecting the processed droplets out of the system. Simulations of the acoustic radiation potential acting on the levitating droplets are in good agreement with the experiments. High-speed footage captured the functioning of the system in four fluidic operations: injection, transport, merging and ejection of liquid droplets. Having these operations integrated reliably into a single automatic system paves the way for the adoption of mid-air acoustophoretic processing in biological, chemical and pharmaceutical applications.
“…Additionally, Andrade et al [12] experimentally presented a manipulation method for a target sample for injection, levitation, transportation, coalescence, and ejection in midair. Watanabe et al [13] investigated the mixing of droplets with an ultrasonic phased array system. After the successful merging of droplets, a single droplet was effectively mixed by inducing the 6th mode oscillation on its surface.…”
The contactless coalescence of a droplet is of paramount importance for physical and industrial applications. This paper describes a coalescence method in mid-air via acoustic levitation using an ultrasonic phased array system. Acoustic levitation using ultrasonic phased arrays provides promising lab-on-a-drop applications, such as transportation, coalescence, mixing, separation, evaporation, and extraction in a continuous operation. The mechanism of droplet coalescence in mid-air may be better understood by experimentally and numerically exploring the droplet dynamics immediately before the coalescence. In this study, water droplets were experimentally levitated, transported, and coalesced by controlling acoustic fields. We observed that the edge of droplets deformed and attracted each other immediately before the coalescence. Through image processing, the radii of curvature of the droplets were quantified and the pressure difference between the inside and outside the droplet was simulated to obtain the pressure and velocity information on the droplet surface. The results revealed that the sound pressure acting on the droplet clearly decreased before the impact of the droplets. This pressure on the droplets was quantitatively analyzed from the experimental data. Our experimental and numerical results provide deeper physical insights into contactless droplet manipulation for futuristic lab-on-a-drop applications.
High‐quality acousto‐holographic patterns and images, integral to applications like 3D displays, acoustophoresis, and midair haptics, require precise distribution of ultrasound waves to achieve. Essential tools for this task are spatial sound modulators (SSMs), which control constituent elements to enable dynamic distribution of sound pressure. However, current ultrasonic SSMs face limitations due to high costs and the intricate actuation of numerous small, closely spaced units. This study introduces “segmented SSMs,” novel devices that combine traditional acoustic metasurface pixel units into custom‐shaped segmented elements. These segmented SSMs reduce actuation costs and complexity while retaining pressure distribution quality. This approach includes a custom phase agglomeration algorithm (PAA), that offers a hierarchy of potential segmentation solutions for user selection. An SSM fabrication method is detailed using off‐the‐shelf 3D printers and bespoke control electronics, completing an end‐to‐end methodology from conception to realization. This approach is validated with two prototype SSM devices that focus sound waves and levitate polystyrene beads using dynamic segmented elements. Further enhancements to the technique are explored through hybrid SSM devices with both static and dynamic elements. The pipeline facilitates efficient SSM construction across diverse applications and invites the inception of future devices with varying sizes, uses, and actuation mechanisms.
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