We present a unique bubble generation technique in microfluidic chips using continuous-wave laser-induced heat and demonstrate its application by creating micro-valves and micro-pumps. In this work, efficient generation of thermal bubbles of controllable sizes has been achieved using different geometries of chromium pads immersed in various types of fluid. Effective blocking of microfluidic channels (cross-section 500 × 40 μm(2)) and direct pumping of fluid at a flow rate of 7.2-28.8 μl h(-1) with selectable direction have also been demonstrated. A particular advantage of this technique is that it allows the generation of bubbles at almost any location in the microchannel and thus enables microfluidic control at any point of interest. It can be readily integrated into lab-on-a-chip systems to improve functionality.
"Bubbles are now being used to reduce scattering cross section of modern submarines and new bubble-filled anechoic coating materials (metamaterial properties) are currently being developed . In other applications, microbubbles are used as bioactive food ingredients, green adjuncts for water or surface cleaning    , ultrasound contrast agents      and as efficient pumps or activators in the field of microtechnology . "
[Show abstract][Hide abstract] ABSTRACT: Single bubble sizing is usually performed by measuring the resonant bubble response using the Dual Frequency Ultrasound Method. However, in practice, the use of millisecond-duration chirp-like waves yields nonlinear distortions of the bubble oscillations. In comparison with the resonant curve obtained under harmonic excitation, it was observed that the bubble dynamic response shifted by up to 20 percent of the resonant frequency with bubble radii of less than 100 μm. In the case of low pressure waves (View the MathML source), an approximate formula for the apparent frequency shift is derived. Simulated and experimental bubble responses are analyzed in the time–frequency domain using an enhanced concentrated (reassigned) spectrogram. The difference in the resonant frequency resulted from the persistence of the resonant mode in the bubble response. Numerical simulations in which these findings are extended to pairs of coupled bubbles and to bubble clouds are also presented.
Journal of Sound and Vibration 11/2015; 356:48-60. DOI:10.1016/j.jsv.2015.06.038 · 1.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper describes a micro-pumping technology using laser induced thermal bubbles, which offers greater flexibility for selective control of flow directions in microfluidic chips. Without complicated fabrication, the bubble in the microchannel could be created by focusing a continuous-wave laser onto the patterned metal pad. Experiments demonstrate that the flow direction can be freely chosen at a T-junction and the flow velocity could be adjusted from 100 to 400 μm/s in real time by adjusting the laser power. This technology can be readily incorporated into the lab-on-a-chip systems for flexible microfluidic manipulation.
[Show abstract][Hide abstract] ABSTRACT: This work reports on optoelectronic-based heaters that can transduce low-power optical images into high-power heating to melt frozen liquids and form desired microfluidic circuitry. The mechanism of optoelectronic heating (OEH) was studied and characterized. OEH relies on photocurrent heating in the illuminated parts of actuating images. Resolution was affected by dark current heating. Photocurrents and dark currents were measured and related to the operating parameters. Successful melting of a frozen media within seconds with 2 mW light patterns and a 4 V operating voltage was demonstrated with feature sizes down to 200 μm × 200 μm. Strategies to increase resolution were addressed. It was shown that the size and location of heating areas can be reliably and rapidly reconfigured by changing the actuating image.
Advances in OptoElectronics 01/2011; 2011(5). DOI:10.1155/2011/237026
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