Vibration-induced Flow Research Articles

Numerical investigation of induction of chaotic micromixing via vibration switching

Enhanced mixing in microfluidic systems is necessary in many applications such as chemical processing, biological assays, and diagnosis. We are developing a microfluidic system to efficiently mix minute reagents (down to several microliters) using vibration-induced flow (VIF), in which a net flow is generated around a micropillar by applying periodic vibration. In this study, we numerically investigate the enhancement in chaotic mixing using the VIF technique and periodic switching of vibrations. By extending our previous numerical simulation model, we investigate the flow field and trajectories of fluid particles in three-dimensional space. We demonstrate that chaotic advection characteristics can be observed by periodically switching the vibrational direction of a substrate using simple cylindrical pillars. In addition, using an appropriate interval for switching the vibration axes yields better mixing performance. The extent of chaotic advection is evaluated quantitatively using the Lyapunov exponent considering various vibration parameters, such as the vibration amplitude, separation distance between each pillar and pillar shape. The flow field induced by a large-amplitude and sharp-edged wall pillar provides excellent mixing results. Thus, VIF is successfully applied to obtain an efficient mixing strategy with the aid of the chaotic theory.

Vibration-Induced Flow and Streaming in Oscillatory Flow of Thermoacoustics

Induced acoustic streaming flow in thermoacoustic systems occurs due to acoustic vibrations, causing changes to the mean flow in the systems. This phenomenon creates a tendency to generate net fluid flow that can cause energy change within certain areas inside the system. However, the effects of the entire system’s vibrations on the flow streaming are not yet fully understood, yet it is important for a more effective operation. This study experimentally investigated the flow streaming resulting from vibration in a standing-wave thermoacoustic test rig with a flow frequency of 23.6 Hz. The existence of flow streaming due to vibration which was not counted in the theoretical formula is shown and indicated by experimental values. The result shows that there is a correlation between the amplitude of the drive ratio (DR) and the velocity of the oscillation of the flow. Upon examining both the theoretical and the practical evidence, it becomes clear that there exists a marginal flow velocity in directions other than the main flow due to the vibration of resonator’s wall as measured at the intake and outflow areas of the stack. This marginal flow velocity amplifies as the drive ratio of flow increases and it may potentially explain the observed difference between measured flow amplitude and the theoretical value.

Pneumatic Microballoons for Active Control of the Vibration-Induced Flow.

Vibration-induced flow (VIF), in which a mean flow is induced around a microstructure by applying periodic vibrations, is increasingly used as an active flow-control technique at the microscale. In this study, we have developed a microdevice that actively controls the VIF patterns using elastic membrane protrusions (microballoons) actuated by pneumatic pressure. This device enables on-demand spatial and temporal fluid manipulation using a single device that cannot be achieved using a conventional fixed-structure arrangement. We successfully demonstrated that the device achieved displacements of up to 38 µm using the device within a pressure range of 0 to 30 kPa, indicating the suitability of the device for microfluidic applications. Using this active microballoon array, we demonstrated that the device can actively manipulate the flow field and induce swirling flows. Furthermore, we achieved selective actuation of the microballoon using this system. By applying air pressure from a multi-input channel system through a connection tube, the microballoons corresponding to each air channel can be selectively actuated. This enabled precise control of the flow field and periodic switching of the flow patterns using a single chip. In summary, the proposed microdevice provides active control of VIF patterns and has potential applications in advanced microfluidics, such as fluid mixing and particle manipulation.

Miniature Amphibious Robot Actuated by Rigid-Flexible Hybrid Vibration Modules.

Amphibious robots can undertake various tasks in terrestrial and aquatic environments for their superior environmental compatibility. However, the existing amphibious robots usually utilize multi‐locomotion systems with transmission mechanisms, leading to complex and bulky structures. Here, a miniature amphibious robot based on vibration‐driven locomotion mechanism is developed. The robot has two unique rigid‐flexible hybrid modules (RFH‐modules), in which a soft foot and a flexible fin are arranged on a rigid leg to conduct vibrations from an eccentric motor to the environment. Then, it can run on ground with the soft foot adopting the friction locomotion mechanism and swim on water with the flexible fin utilizing the vibration‐induced flow mechanism. The robot is untethered with a compact size of 75 × 95 × 21 mm3 and a small weight of 35 g owing to no transmission mechanism or joints. It realizes the maximum speed of 815 mm s–1 on ground and 171 mm s–1 on water. The robot, actuated by the RFH‐modules based on vibration‐driven locomotion mechanism, exhibits the merits of miniature structure and fast movements, indicating its great potential for applications in narrow amphibious environments.

効率的なナノ粒子検出に向けた振動誘起マイクロ混合デバイスの開発

Detection of nanoparticles (NPs) plays an important role in a wide variety of fields such as medical diagnostics and environmental monitoring. We have been developing a simple system for detecting NPs in small samples using vibration-induced flow (VIF), in which a mean flow is induced around a micropillar by applying small periodic vibrations. The system can evaluate the presence and concentration of specific NPs in a minute sample from the extent of aggregation of affinity capture beads agitated by VIF. This technique eliminates the use of fluorescent labeling or expensive image analysis equipment. In this study, we investigated the relationship between various flow patterns and capture bead aggregation. It was found that large vortex flows induced by circular and elliptical vibration produce large aggregations, whereas small vortex flows induced by rectilinear vibration produce a large number of small aggregations with relatively uniform sizes. This result indicates that the size of aggregations depends on the size of the vortices in the flow field and that can be readily controlled by the flow pattern tuned with vibration conditions.

Switch of Cell Manipulations using Vibration-Induced Flow around Non-axisymmetric Structures

Switch of Cell Manipulations using Vibration-Induced Flow around Non-axisymmetric Structures

Model construction of microobject rotation using vibration-induced flow

Model construction of microobject rotation using vibration-induced flow

Angle control of microobject using vibration-induced flow

Angle control of microobject using vibration-induced flow

Evaluation of vibration-induced flow in high bandwidth frequency vibration

Evaluation of vibration-induced flow in high bandwidth frequency vibration

Evaluation of vibration-induced flow based on acoustic wave

Evaluation of vibration-induced flow based on acoustic wave

Vibration-induced flow design for reproducible cell spheroid production

Vibration-induced flow design for reproducible cell spheroid production

Evaluation of performance of micromixer based on vibration-induced flow with PIV

Evaluation of performance of micromixer based on vibration-induced flow with PIV

Concentration of nanoparticles based on vibration-induced flow

Concentration of nanoparticles based on vibration-induced flow

Cell spheroid formation based on vibration-induced flow and evaluate shape

Cell spheroid formation based on vibration-induced flow and evaluate shape

3D rotation of microparticle based on a vibration-induced flow

3D rotation of microparticle based on a vibration-induced flow

Generation of vibration-induced flow using by resonant structure

Generation of vibration-induced flow using by resonant structure

Evaluation of Fabrication Method of Cell Spheroid Based on a Vibration-Induced Flow

Evaluation of Fabrication Method of Cell Spheroid Based on a Vibration-Induced Flow

3D rotation of microobject based on a vibration-induced flow

3D rotation of microobject based on a vibration-induced flow

On-chip cell size separation method based on vibration-induced flow

On-chip cell size separation method based on vibration-induced flow

Micromixer based on vibration-induced flow

Micromixer based on vibration-induced flow