A One-Sided View of Acoustic Traps

Abstract

We demonstrate the trapping of elastic particles by the large gradient force of a single acoustical beam in three dimensions. Acoustical tweezers can push, pull and accurately control both the position and the forces exerted on a unique particle. Forces in excess of 1 micronewton were exerted on polystyrene beads in the submillimeter range. A beam intensity less than 50 W=cm 2 was required, ensuring damage-free trapping conditions. The large spectrum of frequencies covered by coherent ultrasonic sources provides a wide variety of manipulation possibilities from macroscopic to microscopic length scales. Our observations could open the way to important applications, in particular, in biology and biophysics at the cellular scale and for the design of acoustical machines in microfluidic environments.

Trapping of Aqueous Droplets under Surface Acoustic Wave-Driven Streaming in Oil-Filled Microwells

“…For the case of small objects satisfying the Rayleigh limit, the objects are subjected to either a streaminginduced drag force or the acoustic radiation forces due to the gradients of force fields in the liquid or a combination of both. 30 The manipulation of large droplets considered in the present study falls in the Mie-scattering regime, 25 where the objects experience significantly larger radiation forces due to the multiple reflection and transmission of waves within the droplets, distinct from small object manipulation. Moreover, the droplet trapping method demonstrated in this study is driven by traveling SAWs generated from a single interdigitated electrode (IDT) and hence is different from conventional trapping methods such as acoustic tweezers that utilize standing acoustic wave fields.…”

“…31−34 Single-source trapping methods are fundamentally different and offer greater flexibility compared to multiple-source trapping techniques as the former can trap particles or cells using traveling waves from only one side. 30 We first present the experimental details, including the design of the microwell and the working principle. Then, we experimentally demonstrate the trapping phenomenon for a single aqueous droplet and characterize the trapping phenomenon in terms of the operating power for different droplet sizes and densities.…”

“…In contrast to the trapping of particles/cells demonstrated earlier where the object size is much smaller than the wavelength of the vibration in liquid satisfying the Rayleigh limit, we illustrate here the trapping of droplets in the regime where the droplet size is much greater than the SAW wavelength. For the case of small objects satisfying the Rayleigh limit, the objects are subjected to either a streaming-induced drag force or the acoustic radiation forces due to the gradients of force fields in the liquid or a combination of both . The manipulation of large droplets considered in the present study falls in the Mie-scattering regime, where the objects experience significantly larger radiation forces due to the multiple reflection and transmission of waves within the droplets, distinct from small object manipulation.…”

An adjustable multi‐scale single beam acoustic tweezers based on ultrahigh frequency ultrasonic transducer

“…Preliminary analytical studies show that the feasibility of acoustic tweezers and trapping an arbitrarily located object mainly comes from the focused Gaussian ultrasound beam (Azarpeyvand and Azarpeyvand, ; Lee et al, ; Lee and Shung, ; Mitri, ; Wu and Du, ). These studies have shown that Gaussian beams can be used for trapping particles in both lateral and axial directions, although the latter is much harder due to the existence of the radiation force from scattering by pushing the particle away from the transducer (Hill, ; Marzo et al, ). To overcome this problem, single Bessel vortex beam was introduced into the study of SBAT, which can produce a negative axial radiation force (Mitri, , ,, ).…”

Micro-Acoustic-Trap (µAT) for microparticle assembly in 3D

“…b) polystyrene beads freely float in DI water, were propelled towards the focal plane by vortex beam created by AL28 . Motion of the particles is capture with high speed imaging system coupled to the optics of the inverted microscope.…”