Acoustic levitator for contactless motion and merging of large droplets in air

Abstract

Flow and noise predictions for the tandem cylinder aeroacoustic benchmark Phys. Fluids 24, 036101 (2012) Acoustic cloak for airborne sound by inverse design Appl. Phys. Lett. 99, 074102 (2011) Influence of gases on Lamb waves propagations in resonator Appl. Phys. Lett. 95, 223505 (2009) Sound control by temperature gradients Appl. Phys. Lett. 95, 204102 (2009) Quenching of acoustic bandgaps by flow noise Appl. Phys. Lett. 94, 134104 (2009) Additional information on J. Appl. Phys.Large droplet transport in a line-focussed acoustic manipulator in terms of maximum droplet size is achieved by employing a driving voltage control mechanism. The maximum volume of the transported droplets in the order of few microliters is thereby increased by three orders of magnitude compared to the constant voltage case, widening the application field of this method significantly. A drop-on-demand droplet generator is used to supply the liquid droplets into the system. The ejected sequence of picoliter-size droplets is guided along trajectories by the acoustic field and accumulates at the selected pressure node, merging into a single large droplet. Droplet movement is achieved by varying the reflector height. This also changes the intensity of the radiation pressure during droplet movement, which in turn could atomise the droplet. The acoustic force is adjusted by regulating the driving voltage of the actuator to keep the liquid droplet suspended in air and to prevent atomisation. In the herein presented levitation concept, liquids with a wide range of surface tension (water and tetradecane were tested) can be transported over distances of several mm. The aspect ratio of the droplet in the acoustic field is shown to be a good indicator for radiation pressure intensity and is kept between 1.1 and 1.4 during droplet transport. Despite certain limitations with volatile liquids, the presented acoustic levitator concept has the potential to expand the range of analytical characterisation and manipulation methods in applications ranging from chemistry and biology. V C 2012 American Institute of Physics. [http://dx.

Automatic contactless injection, transportation, merging, and ejection of droplets with a multifocal point acoustic levitator

“…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.…”

“…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.…”

Non-contact droplet manipulation and its dynamics based on acoustic levitation

“…Gonzalez-Avila等人 [151] , 进而实现悬浮液滴的空间移 动. Bjelobrk等人 [154] 通过改变声场尺寸实现了多个势 阱的合并与劈裂. Min等人 [155] 用3个发射端形成声驻 波场, 同时改变腔室的长度可以实现声场模式的切换.…”

Droplet manipulation in a microfluidic chamber with acoustic radiation pressure and acoustic streaming

“…The manipulation of droplets in microuidic devices involves techniques to overcome forces that prevent the droplets from moving and deforming such as frictional forces and capillary forces. The two common methods for droplet manipulation by acoustic actuation are acoustic levitation of droplets in air [1][2][3][4][5][6][7][8][9][10][11][12][13] and surface acoustic wave (SAW) for droplets on a planar surface or in a microuidic device. [14][15][16][17][18][19][20][21][22][23][24][25][26][27] Evaporation is a major problem for the above two methods as droplets are manipulated in an open environment.…”

“…1,9 The levitation of droplets has found applications in contactless transport and handling in air. [11][12][13] Adjusting the driving voltage of the piezoelectric transducer controls the levitation potential and allows for continuous planar transport. This method is useful for contact free handling of solids with different shapes and contact free handling (transportation, merging and atomization) of reactive or under-cooled liquids.…”