scholarly journals Visualization of Surface Acoustic Waves in Thin Liquid Films

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
R. W. Rambach ◽  
J. Taiber ◽  
C. M. L. Scheck ◽  
C. Meyer ◽  
J. Reboud ◽  
...  
Keyword(s):  
Liquid Film ◽  
Acoustic Waves ◽  
Low Cost ◽  
Thin Liquid Film ◽  
Surface Acoustic Waves ◽  
Liquid Films ◽  
Theoretical Description ◽  
Propagation Path ◽  
Microfluidic Channels ◽  
Potential Applications

Abstract We demonstrate that the propagation path of a surface acoustic wave (SAW), excited with an interdigitated transducer (IDT), can be visualized using a thin liquid film dispensed onto a lithium niobate (LiNbO3) substrate. The practical advantages of this visualization method are its rapid and simple implementation, with many potential applications including in characterising acoustic pumping within microfluidic channels. It also enables low-cost characterisation of IDT designs thereby allowing the determination of anisotropy and orientation of the piezoelectric substrate without the requirement for sophisticated and expensive equipment. Here, we show that the optical visibility of the sound path critically depends on the physical properties of the liquid film and identify heptane and methanol as most contrast rich solvents for visualization of SAW. We also provide a detailed theoretical description of this effect.

scholarly journals Double flow reversal in thin liquid films driven by megahertz-order surface vibration

2014 ◽  
Vol 470 (2169) ◽  
pp. 20130765 ◽  
Author(s):  
Amgad R. Rezk ◽  
Ofer Manor ◽  
Leslie Y. Yeo ◽  
James R. Friend
Keyword(s):  
Thin Films ◽  
Acoustic Waves ◽  
Surface Acoustic Waves ◽  
Intermolecular Forces ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Propagation Direction ◽  
Flow Reversal ◽  
Order Surface ◽  
Over Time

Arising from an interplay between capillary, acoustic and intermolecular forces, surface acoustic waves (SAWs) are observed to drive a unique and curious double flow reversal in the spreading of thin films. With a thickness at or less than the submicrometre viscous penetration depth, the film is seen to advance along the SAW propagation direction, and self-similarly over time t 1/4 in the inertial limit. At intermediate film thicknesses, beyond one-fourth the sound wavelength λ ℓ in the liquid, the spreading direction reverses, and the film propagates against the direction of the SAW propagation. The film reverses yet again, once its depth is further increased beyond one SAW wavelength. An unstable thickness region, between λ ℓ /8 and λ ℓ /4, exists from which regions of the film either rapidly grow in thickness to exceed λ ℓ /4 and move against the SAW propagation, consistent with the intermediate thickness films, whereas other regions decrease in thickness below λ ℓ /8 to conserve mass and move along the SAW propagation direction, consistent with the thin submicrometre films.

Rapid additive-free bacteria lysis using traveling surface acoustic waves in microfluidic channels

Lab on a Chip ◽  
2019 ◽  
Vol 19 (24) ◽  
pp. 4064-4070 ◽  
Author(s):  
Haiwei Lu ◽  
Kirk Mutafopulos ◽  
John A. Heyman ◽  
Pascal Spink ◽  
Liang Shen ◽  
...  
Keyword(s):  
Microfluidic Device ◽  
Acoustic Waves ◽  
High Efficiency ◽  
Surface Acoustic Waves ◽  
Microfluidic Channels ◽  
Wide Range

We introduce a microfluidic device that uses traveling surface acoustic waves to lyse bacteria with high efficiency. This lysis method should be applicable to a wide range of bacteria species and can be modified to analyze individual bacteria cells.

Design and Fabrication of 2D Phononic Crystals in Surface Acoustic Wave Micro Devices

2005 ◽  
Author(s):  
Kebin Gu ◽  
Chien-Liu Chang ◽  
Jyh-Cherng Shieh
Keyword(s):  
Silicon Substrate ◽  
Acoustic Waves ◽  
Surface Acoustic Waves ◽  
Phononic Crystals ◽  
Two Dimensional ◽  
Central Frequency ◽  
Potential Applications ◽  
Specific Incident ◽  
Lift Off ◽  
Propagation Of Elastic Waves

In this paper, we present the design and fabrication of innovative phononic crystals integrated with two sets of interdigital (IDT) electrodes for frequency band selection of surface acoustic waves (SAW). The potential applications of this device include performance improvement of SAW micro-sensors, front-end components in RF circuitries, and directional receptions of high frequency acoustic waves. Analogous to the band-gap generated by photonic crystals, the phononic crystals, two dimensional repetitive structures composed of two different elastic materials, can prohibit the propagation of elastic waves with either specific incident angles or certain bandwidth. In this paper, the prohibited bandwidth has been verified by fabricating the phononic crystals between a micromachined SAW resonator and a receiver. Both the resonator and receiver are composed of IDT electrodes deposited and patterned on a thin piezoelectric layer. To confine the prohibited bandwidth on the order of hundred MHz, the diameter of the circular pores in phononic crystals is designed to be 6 micron and the aspect ratio of each pore is 3:1. To maximize the power transduction from IDT electrodes to SAW, the spacing between two inter-digits is one-fourth the wavelength of SAW. Specifically, the spacing ranges from 3.4 microns to 9.0 microns, depending on the central frequency. Both surface and bulk micromachining are employed and integrated to fabricate the crystals as well as SAW resonator and receiver altogether. Firstly, a 1.5-micron zinc oxide, which provides well-defined central frequency, is sputtered and patterned onto silicon substrate. Second, the IDT electrodes are evaporated and patterned by lift-off technique. Then the exposed silicon substrate is etched using DRIE to generate two dimensional phononic crystals. To tune the prohibited SAW bandwidth, the crystal pores are filled with copper or nickel by electroless plating. The insertion loss of the fabricated devices is characterized and is found to agree with simulation results.

The Influence of Evaporation in Shear-Driven Liquid Film on Heat Removal From Local Heater

2006 ◽  
Author(s):  
Elizaveta Gatapova ◽  
Oleg Kabov
Keyword(s):  
Liquid Film ◽  
Thin Liquid Film ◽  
Heat Removal ◽  
Film Surface ◽  
Numerical Data ◽  
High Heat ◽  
Liquid Films ◽  
High Heat Flux ◽  
Maximal Surface ◽  
High Heat Transfer

The present work focuses upon shear-driven liquid film evaporative cooling of high heat flux local heater. Thin evaporating liquid films may provide very high heat transfer rates and can be used for cooling of high power microelectronic systems. Thermocapillary convection in a liquid film falling down a locally heated substrate has recently been extensively studied. However, non-uniform heating effects remain only partially understood for shear-driven liquid films. The combined effects of evaporation, thermocapillarity and gas dynamics as well as formation of microscopic adsorbed film have not been studied. The effect of evaporation on heat and mass transfer for 2D joint flow of a liquid film and gas is theoretically and numerically investigated. The convective terms in the energy equations are taken into account. The calculations reveal that evaporation from film surface essential influences on heat removal from local heater. It is shown that the thermal boundary layer plays significant role for cooling local heater by evaporating thin liquid film. Measured by an infrared scanner temperature distribution at the film surface is compared with numerical data. Calculations satisfactorily describe the maximal surface temperature value.

Sculpting and Aerosolizing Pinned Liquid Films With Localized Acoustic Pressures of Surface Acoustic Waves

2012 ◽  
Author(s):  
Daniel Taller ◽  
Hsueh-Chia Chang ◽  
David B. Go
Keyword(s):  
Contact Angle ◽  
Numerical Modeling ◽  
Contact Line ◽  
Acoustic Waves ◽  
Acoustic Pressure ◽  
Surface Acoustic Waves ◽  
Liquid Films ◽  
Solid Substrate ◽  
Planar Surface ◽  
Bulk Film

Due to viscous decay, a planar surface acoustic wave (SAW) diffracting from a solid substrate into a liquid film produces a time-averaged, exponentially decaying acoustic pressure in the film. We show that if the film is pinned against a bounding wall, the localized acoustic pressure generates a sequence of surface drops at the contact line, whose dimensions decay in the same exponential manner as the localized acoustic pressure. The undulating interfacial profile near the contact line also inherits this exponential decay, such that the averaged contact angle is exponentially small. The bulk film topology and the aerosolization mechanism are hence insensitive to the wettability of the surface but are controlled only by the localized acoustic pressure and the decaying undulations it produces at the contact line. The size distribution of surface drops is collapsed under the exponential scaling that depends only on the SAW decay rate and amplitude. Numerical modeling based on the Young-Laplace equation is used to model the liquid profile and to predict two aerosolization regimes.

Temporal Effect and Transient Simulation of Thin Liquid Film in Micro Channels

2013 ◽  
Author(s):  
Yu-Yan Jiang ◽  
Da-Wei Tang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Film ◽  
Flow Boiling ◽  
Thin Liquid Film ◽  
Liquid Films ◽  
Transient Simulation ◽  
Governing Equations ◽  
Flash Evaporation ◽  
Micro Channels

The evaporation and heat transfer of thin liquid film are crucial factors affecting on the heat transfer performance of boiling bubbles or slugs. For boiling in micro-channels, the flash evaporation of the liquid film may give rise to boiling instability, and the dry-out of the film leads to serious deterioration of the heat transport. The thin liquid film has multi-scale transitions, and hence the phase change and fluid dynamics need to be solved by special governing equations and numerical algorithm. The numerical studies to date have solved the steady state distribution of the film, but the difficulty consists in the transient simulation of time-variant liquid films. In the present study, unsteady form governing equations are developed. With inclusion of the temporal terms, we conducted transient simulations for flat liquid films formed during the flow boiling in micro-channels. The model predicts the developing of drying spot during growth of elongated bubbles. The results show that the film thickness and distribution change quickly in a growth period, which are functions of the heat flux, mass flow rate and the other parameters. The quantitative assessment of these effects helps to clarify the mechanism of boiling instability and the conditions for the occurrence of critical heat flux (CHF). The simulation needs special numerical scheme for time marching and stabilization treatment for the nonlinear terms, where the numerical accuracy and the significance of the temporal effects are also discussed.

scholarly journals Shaping liquid films by dielectrophoresis

Flow ◽  
2021 ◽  
Vol 1 ◽  
Author(s):  
Israel Gabay ◽  
Federico Paratore ◽  
Evgeniy Boyko ◽  
Antonio Ramos ◽  
Amir D. Gat ◽  
...  
Keyword(s):  
Liquid Film ◽  
Thin Liquid Film ◽  
High Surface ◽  
Liquid Films ◽  
Digital Holographic Microscopy ◽  
Electrode Pair ◽  
Liquid Form ◽  
High Surface Quality ◽  
Air Interface ◽  
Set Up

Abstract We present a theoretical model and experimental demonstration of thin liquid film deformations due to a dielectric force distribution established by surface electrodes. We model the spatial electric field produced by a pair of parallel electrodes and use it to evaluate the stress on the liquid–air interface through Maxwell stresses. By coupling this force with the Young–Laplace equation, we obtain the deformation of the interface. To validate our theory, we design an experimental set-up which uses microfabricated electrodes to achieve spatial dielectrophoretic actuation of a thin liquid film, while providing measurements of microscale deformations through digital holographic microscopy. We characterize the deformation as a function of the electrode-pair geometry and film thickness, showing very good agreement with the model. Based on the insights from the characterization of the system, we pattern conductive lines of electrode pairs on the surface of a microfluidic chamber and demonstrate the ability to produce complex two-dimensional deformations. The films can remain in liquid form and be dynamically modulated between different configurations or polymerized to create solid structures with high surface quality.

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