Acoustic impedance-based manipulation of elastic microspheres using travelling surface acoustic waves

Abstract

We present a method for size-independent manipulation of elastic polystyrene (PS), poly(methyl methacrylate) (PMMA), and fused silica (FS) microspheres that uses travelling surface acoustic waves (TSAWs). Normally incident TSAWs originating from an interdigitated transducer (IDT) were used to separate similar-sized pairs of PS and PMMA or PS and FS elastic particles by producing distinct lateral deflections across laminar streamlines in a continuous flow microfluidic channel. Elastic particles with similar diameters but different acoustic impedances exhibit significantly different deflection characteristics when exposed to TSAW-based acoustic radiation forces (ARFs). For instance, exposing a mixture of PS and PMMA particles with similar diameters ($5 mm) to TSAWs with frequencies of 140MHz and 185 MHz produces larger deflections of the PS and PMMA particles, respectively. This difference arises because of the resonance of the elastic particles with the incoming acoustic waves at certain frequencies. Similar particle deflection characteristics were observed for mixtures of PS and FS particles with comparable diameters (3/3, 4.8/5, 10/10 mm). This difference in deflection distances was used to experimentally characterize the non-linear behavior of the ARFs acting on particles (3-10 mm) exposed to a range of TSAW frequencies (120-205 MHz). Our experimental results can be explained by plotting the acoustic radiation force factor (F F ) against the TSAW frequency (f TSAW ) and the dimensionless Helmholtz number (1 < k < 4), which is calculated by using a theoretical model of an elastic microsphere suspended in a fluid.

Acoustic Microfluidic Separation Techniques and Bioapplications: A Review

“…As shown in Figure 3 c, the right IDT with frequency -generated radiation force deflected the largest diameter particles to the left side, and the left IDT with frequency -created radiation force drove medium-sized particles to the right side, leaving the smallest particles in the middle of the microchannel; thus, triple separation was realized. In a follow-up of this work, they developed a method for size-independent separation of polymethyl methacrylate (PMMA), elastic polystyrene (PS), and fused silica (FS) particles using acoustic radiation force [ 64 ]. They found that PS, PMMA, and FS particles have different peak acoustic radiation forces under different wavenumbers ( ).…”

“…For ≅ 1.69, PMMA particles are expected to experience a higher acoustic radiation force than PS and FS particles. They also calculated acoustic impedance ( ) of these particles by combining the particle density ( ) and speed of longitudinal waves within the particle ( ), which will significantly influence the deflection characteristics of particles when they are exposed to TSAW-based ARFs [ 64 ]. For FS particles, since they have higher acoustic impedance than PMMA and PS particles, they are hardly influenced by the acoustic radiation force.…”

“…( e ) Different acoustic radiation force for same-sized particles. Reprinted with permission from reference [ 64 ]. ( f ) Tilted-angled TSAW (TaTSAW)-induced radiation force for particle focusing and particle separation.…”

Contactless, programmable acoustofluidic manipulation of objects on water

“…11 The combination of microfluidics and acoustics provides versatile, contactless manipulation platforms based on acoustofluidics. 12,13 Various acoustofluidic functions, including particle translation (i.e., acoustic tweezers), [14][15][16][17][18][19][20] liquid handling (e.g., pumping, mixing, wetting), [21][22][23][24][25] model organism manipulation, 26,27 particle separation [28][29][30][31] and sorting, 32,33 have been realized. Recently, there has been growing interest in small-object manipulation in open space using acoustic waves due to its contactless operation, label-free nature, and high biocompatibility.…”

3D Manipulation and Imaging of Plant Cells using Acoustically Activated Microbubbles

“…Acoustics provide a noninvasive and robust transduction mechanism that has been widely used in micromixing, micropumping, particle or cell separation, and manipulation, protein crystal patterning, microfluidic switches, droplet production, drug delivery, and actuation of micro‐ and nanoswimmers . Acoustic wave–induced microvortices around solid structures and bubbles have been used to perform manipulation of small objects .…”