Three-dimensional phenomena in microbubble acoustic streaming

Ultrasound-driven oscillating micro-bubbles have been used as active actuators in microfluidic devices to perform manifold tasks such as mixing, sorting and manipulation of microparticles. A common configuration consists on side-bubbles, created by trapping air pockets in blind channels perpendicular to the main channel direction. This configuration consists of acoustically excited bubbles with a semi-cylindrical shape that generate significant streaming flow. Due to the geometry of the channels, such flows have been generally considered as quasi two-dimensional. Similar assumptions are often made in many other microfluidic systems based on \emph{flat} micro-channels. However, in this paper we show that microparticle trajectories actually present a much richer behavior, with particularly strong out-of-plane dynamics in regions close to the microbubble interface. Using Astigmatism Particle Tracking Velocimetry, we reveal that the apparent planar streamlines are actually projections of a \emph{streamsurface} with a pseudo-toroidal shape. We therefore show that acoustic streaming cannot generally be assumed as a two-dimensional phenomenon in confined systems. The results have crucial consequences for most of the applications involving acoustic streaming as particle trapping, sorting and mixing.Comment: 5 pages, 4 high quality figures. Accepted for Publication in Phys. Rev. Applied, March 201

Three-dimensional streaming flow patterns in confinement

Steady streaming flow exited by oscillating bubbles is an intriguing tool for transport, mixing, sorting, or force actuation applications in microfluidics. Often the geometry of the set-up is intended to encourage two-dimensional (2D) flows, keeping the flow pattern across the channel depth uniform. This condition cannot always be ideally fulfilled, and three-dimensional (3D) streaming effects may be greatly beneficial, e.g., in mixing applications. We demonstrate that a weak 3D streaming component can be combined with existing 2D streaming theory, resulting in a systematic description of 3D streaming flow patterns. We show that these patterns can indeed be observed in bubble microstreaming, using 3D trajectory tracking by astigmatic particle tracking velocimetry

Size-dependent particle migration and trapping in 3D microbubble streaming flows

Acoustically actuated sessile bubbles can be used as a tool to manipulate microparticles, vesicles and cells. In this work, using acoustically actuated sessile semi-cylindrical microbubbles, we demonstrate experimentally that finite-sized microparticles undergo size-sensitive migration and trapping towards specific spatial positions in three dimensions with high reproducibility. The particle trajectories are successfully reproduced by passive advection of the particles in a steady three-dimensional streaming flow field augmented with volume exclusion from the confining boundaries. For different particle sizes, this volume exclusion mechanism leads to three regimes of qualitatively different migratory behavior, suggesting applications for separating, trapping, and sorting of particles in three dimensions.Comment: 12 pages, 7 figure

Sediment electric conductivity profiles of benthic EM profiler NERIDIS during HEINCKE cruise HE537, profile HE537_82NE_P2

Sediment-physical properties of the seabed mapped with the MARUM benthic EM profiler NERIDIS III during HEINCKE cruise HE537. The profiler was towed in contact with the seabed at speeds of 2-4 kn (1-2 m/s) along 11 parallel, 2.5 km long survey lines with 50 m line-spacing at salt diapir Berta. A half-space inversion method (Müller et al., 2012) was used to convert 75 Hz and 10 kHz inphase and quadrature data into apparent electric conductivity and magnetic susceptibility of the shallow subsurface (approx. 0-1 m below seafloor)

Physical properties measured on 23 sediment cores from METEOR cruise M34/1

During METEOR Cruise M 34/1 all recovered gravity cores were subject to laboratory geophysical studies. A routine shipboard measurement of three physical parameters was carried out on the segmented sediment cores, comprising the determination of - the compressional (P-) wave velocity vp, - the electric resistivity Rs, and - the magnetic volume susceptibility K. These properties are closely related to the grain size, porosity and Iithology of the sediments and provide high-resolution core logs (spacing 3, 3 and 1 cm, respectively) available prior to all other detailed investigations. In addition, oriented sampies for later shore based paleo- and rockmagnetic studies were taken at intervals of 10 cm

Sediment electric conductivity profiles of benthic EM profiler NERIDIS during HEINCKE cruise HE537, profile HE537_82NE_P3

Sediment-physical properties of the seabed mapped with the MARUM benthic EM profiler NERIDIS III during HEINCKE cruise HE537. The profiler was towed in contact with the seabed at speeds of 2-4 kn (1-2 m/s) along 11 parallel, 2.5 km long survey lines with 50 m line-spacing at salt diapir Berta. A half-space inversion method (Müller et al., 2012) was used to convert 75 Hz and 10 kHz inphase and quadrature data into apparent electric conductivity and magnetic susceptibility of the shallow subsurface (approx. 0-1 m below seafloor)

Sediment electric conductivity profiles of benthic EM profiler NERIDIS during HEINCKE cruise HE537, profile HE537_82NE_P1

Sediment-physical properties of the seabed mapped with the MARUM benthic EM profiler NERIDIS III during HEINCKE cruise HE537. The profiler was towed in contact with the seabed at speeds of 2-4 kn (1-2 m/s) along 11 parallel, 2.5 km long survey lines with 50 m line-spacing at salt diapir Berta. A half-space inversion method (Müller et al., 2012) was used to convert 75 Hz and 10 kHz inphase and quadrature data into apparent electric conductivity and magnetic susceptibility of the shallow subsurface (approx. 0-1 m below seafloor)

Physical properties measured on 75 sediment cores from METEOR cruise M38/2

The complete sediment series recovered during METEOR Cruise M38/2 with the gravity corer were subject to laboratory geophysical studies. Shipboard measurements on the segmented cores routinely comprised three basic physical parameters: - compressional (p-) wave velocity vp, - electric resistivity Rs (as a measure of density and porosity), and, - magnetic volume susceptibility K. These properties are closely related to lithology and grain size of the sediments and provide high-resolution core logs (spacing 1 cm for p-wave velocity, 2 cm for electric resistivity and magnetic volume susceptibility) available prior to all other detailed investigations. In addition, oriented samples for subsequent shore based rock and paleomagnetic studies were taken at typically 5 cm intervals

Physical properties measured on 83 sediment cores from METEOR cruise M46/3

The sediment series recovered during R/V METEOR Cruise M46/3 with the gravity corer were subject to laboratory geophysical studies. Shipboard measurements on the segmented cores routinely comprised three basic physical parameters: compressional (p-) wave velocity vp, electric resistivity Rs (as a measure of density and porosity) and magnetic volume susceptibility K. These properties are closely related to lithology and grain size of the sediments and provide high-resolution core logs (spacing 1 cm for p-wave velocity, 2 cm for electric resistivity and magnetic volume susceptibility) available prior to all other detailed investigations. In addition, oriented samples for subsequent share based rock and paleomagnetic studies were taken at typically 5 cm intervals