Jr-Hung Tsai

Bio: Jr-Hung Tsai is an academic researcher from University of Michigan. The author has contributed to research in topics: Micropump & Bubble. The author has an hindex of 5, co-authored 7 publications receiving 671 citations. Previous affiliations of Jr-Hung Tsai include University of California, Berkeley.

Active microfluidic mixer and gas bubble filter driven by thermal bubble micropump

Abstract: A microfluidic mixer with a gas bubble filter activated by a thermal bubble actuated nozzle-diffuser micropump is successfully demonstrated. The oscillatory flow generated by the micropump can induce wavy interface to increase the contact area of mixing fluids to accelerate the mixing process. The microfluidic mixing channels are 200 μm wide, 50 μm deep and the speed of the mixing liquids are measured at 6.5 μl/min. The optimal mixing result is found when the actuating frequency of thermal bubble reaches 200 Hz. Normalized gray-scale values that correspond to the completeness of the mixing effect are observed to be proportional to the one-third power of the input pulse frequency. Furthermore, a gas bubble filter is integrated and successfully demonstrated in the microfluidic mixing system. A model based on the principle of threshold pressure with respect to the geometry of microchannels is established.

A thermal-bubble-actuated micronozzle-diffuser pump

Abstract: A thermal-bubble-actuated micropump by the principles of liquid/vapor phase transition and nozzle-diffuser flow regulation is successfully demonstrated. The micropump consists of a resistive heater, a pair of nozzle-diffuser flow controller and a 1 mm in diameter, 50 /spl mu/m in depth pumping chamber. The actuation mechanism comes from periodically nucleating and collapsing thermal bubbles. A net flow is generated from the nozzle to the diffuser by the nozzle-diffuser flow controller. Two heater designs, single-bubble and dual-bubble actuation mode, have been investigated. In the single-bubble pumping mode, a maximum flow rate of 5 /spl mu/l/min is measured when the driving pulse is 250 Hz at 10% duty cycle under an average power consumption of 1 W. A similar flow rate of 4.5 /spl mu/l/min is achieved in the dual-bubble pumping mode, at the driving pulse of 5% duty cycle at 400 Hz with lower average power consumption, 0.5 W. The static pumping pressure is measured at a maximum value of 377 Pascal when the net volume flow rate is zero. As an application example in a microfluidic device, this valve-less micropump is used in a microfluidic system to enhance the fluid mixing by agitating the flows.

Micro-to-macro fluidic interconnectors with an integrated polymer sealant

Abstract: This paper presents the design, fabrication and testing results of inserting a polymer sealant (Mylar) into a micro-to-macro fluidic interconnection. Two processes, discrete and integrated Mylar sealant, have been developed by means of post-fabrication after the mircofluidic components such as micro-channels and micro-chambers are constructed. The integrated process utilizes microfabrication techniques such that batch processing is feasible and the sealant dimensions can be precisely controlled. The discrete process takes advantage of easy and simple processing and is compatible with most microfluidic systems without any extra wafer-level micromachining process. In both processes, macroscale capillary tubes with a diameter of 320 µm have been successfully connected to microscale channels with the help of the Mylar. Both leakage and pull-out tests are conducted and successfully demonstrate the functionality of the interconnectors. The leakage test shows that no leakage is observed up to 190 kPa and the pull-out test proves 100% survival rate under a pulling force of 2 N. (Some figures in this article are in colour only in the electronic version)

A thermal bubble actuated micro nozzle-diffuser pump

Abstract: A valve-less micropump using the principles of thermal bubble actuation and nozzle-diffuser flow regulation is successfully demonstrated. The pump consists of a meander-shaped resistive heater, a pair of nozzle-diffuser flow controllers, and a 1 mm in diameter, 50 /spl mu/m in depth pumping chamber. Liquid is actuated by periodically expanding and collapsing thermal bubbles via resistive heating and a net flow is induced by the nozzle-diffuser flow regulator. Both single-bubble and dual-bubble actuation modes have been investigated. In the single-bubble pumping mode, a maximum flow rate of 5 /spl mu/l/min is measured at the driving pulse of 10% duty cycle at 250 Hz under an average power consumption of 1 W. A similar flow rate of 4.5 /spl mu/l/min is measured in the dual-bubble pumping mode, at the driving pulse of 5% duty cycle at 400 Hz with 0.5 W of average power consumption. The highest measured pumping pressure is 377 Pascal at zero volume flow rate.

Transient Thermal Bubble Formation on Polysilicon Micro-Resisters

Abstract: Transient bubble formation experiments are investigated on polysilicon micro-resisters having dimensions of 95 μm in length, 10 μm or 5 μm in width, and 0.5 μm in thickness. Micro resisters act as both resistive heating sources and temperature transducers simultaneously to measure the transient temperature responses beneath the thermal bubbles. The micro bubble nucleation processes can be classified into three groups depending on the levels of the input current. When the input current level is low, no bubble is nucleated. In the middle range of the input current, a single spherical bubble is nucleated with a waiting period up to 2 sec while the wall temperature can drop up to 8°C depending on the magnitude of the input current. After the formation of a thermal bubble, the resister temperature rises and reaches a steady state eventually. The bubble growth rate is found proportional to the square root of time that is similar to the heat diffusion controlled model as proposed in the macro scale boiling experiments. In the group of high input current, a single bubble is nucleated immediately after the current is applied

A review of micropumps

Abstract: We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

Micromixers?a review

Abstract: This review reports the progress on the recent development of micromixers. The review first presents the different micromixer types and designs. Micromixers in this review are categorized as passive micromixers and active micromixers. Due to the simple fabrication technology and the easy implementation in a complex microfluidic system, passive micromixers will be the focus of this review. Next, the review discusses the operation points of the micromixers based on characteristic dimensionless numbers such as Reynolds number Re, Peclet number Pe, and in dynamic cases the Strouhal number St. The fabrication technologies for different mixer types are also analysed. Quantification techniques for evaluation of the performance of micromixers are discussed. Finally, the review addresses typical applications of micromixers.

Microfluidic Mixing: A Review

Abstract: The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either “active”, where an external energy force is applied to perturb the sample species, or “passive”, where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers.

A review of microvalves

Abstract: This review gives a brief overview of microvalves, and focuses on the actuation mechanisms and their applications. One of the stumbling blocks for successful miniaturization and commercialization of fully integrated microfluidic systems was the development of reliable microvalves. Applications of the microvalves include flow regulation, on/off switching and sealing of liquids, gases or vacuums. Microvalves have been developed in the form of active or passive microvalves employing mechanical, non-mechanical and external systems. Even though great progress has been made during the last 20 years, there is plenty of room for further improving the performance of existing microvalves.

Lab-on-chip technologies: making a microfluidic network and coupling it into a complete microsystem : a review

Abstract: Microfluidics is an emerging field that has given rise to a large number of scientific and technological developments over the last few years. This review reports on the use of various materials, such as silicon, glass and polymers, and their related technologies for the manufacturing of simple microchannels and complex systems. It also presents the main application fields concerned with the different technologies and the most significant results reported by academic and industrial teams. Finally, it demonstrates the advantage of developing approaches for associating polymer technologies for manufacturing of fluidic elements with integration of active or sensitive elements, particularly silicon devices.