Observation of a single-beam gradient force acoustical trap for elastic particles: acoustical tweezers

TL;DR

This paper demonstrates a novel acoustical tweezers technique that uses a single-beam gradient force to trap elastic particles in three dimensions, enabling precise manipulation with safe ultrasonic intensities.

Contribution

It introduces a new method for three-dimensional trapping of elastic particles using a single acoustic beam with high force and low intensity, expanding potential applications.

Findings

Achieved trapping of elastic particles with forces over 1 micronewton.

Used ultrasonic beam intensity below 50 W/cm² for damage-free manipulation.

Demonstrated wide frequency spectrum for macro- to microscopic control.

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 sub-millimeter range. A beam intensity less than 50 Watts/cm$^2$ was required ensuring damage-free trapping conditions. The large spectrum of frequencies covered by coherent ultrasonic sources provide a wide variety of manipulation possibilities from macro- 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.