This article describes the process of formation of droplets and bubbles in microfluidic T-junction geometries. At low capillary numbers break-up is not dominated by shear stresses: experimental results support the assertion that the dominant contribution to the dynamics of break-up arises from the pressure drop across the emerging droplet or bubble. This pressure drop results from the high resistance to flow of the continuous (carrier) fluid in the thin films that separate the droplet from the walls of the microchannel when the droplet fills almost the entire cross-section of the channel. A simple scaling relation, based on this assertion, predicts the size of droplets and bubbles produced in the T-junctions over a range of rates of flow of the two immiscible phases, the viscosity of the continuous phase, the interfacial tension, and the geometrical dimensions of the device.

http://ichf.pong.pl/i/publications/29.pdf

Formation of droplets and bubbles in a microfluidic T-junction-scaling and mechanism of break-up.

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.

https://microfluidics.stanford.edu/Publications/Micropumps_Cooling/Laser%20Review%20of%20Micropumps%20in%20JMM.pdf

A review of micropumps

We review microfluidic platforms that enable the miniaturization, integration and automation of biochemical assays. Nowadays nearly an unmanageable variety of alternative approaches exists that can do this in principle. Here we focus on those kinds of platforms only that allow performance of a set of microfluidic functions—defined as microfluidic unit operations—which can be easily combined within a well defined and consistent fabrication technology to implement application specific biochemical assays in an easy, flexible and ideally monolithically way. The microfluidic platforms discussed in the following are capillary test strips, also known as lateral flow assays, the “microfluidic large scale integration” approach, centrifugal microfluidics, the electrokinetic platform, pressure driven droplet based microfluidics, electrowetting based microfluidics, SAW driven microfluidics and, last but not least, “free scalable non-contact dispensing”. The microfluidic unit operations discussed within those platforms are fluid transport, metering, mixing, switching, incubation, separation, droplet formation, droplet splitting, nL and pL dispensing, and detection.

/pdf/microfluidic-platforms-for-lab-on-a-chip-applications-2xenxmlmto.pdf

Microfluidic platforms for lab-on-a-chip applications

Micro total analysis systems. Recent developments.

Part I: Background and Fundamentals Introduction, Mohamed Gad-el-Hak, University of Notre Dame Scaling of Micromechanical Devices, William Trimmer, Standard MEMS, Inc., and Robert H. Stroud, Aerospace Corporation Mechanical Properties of MEMS Materials, William N. Sharpe, Jr., Johns Hopkins University Flow Physics, Mohamed Gad-el-Hak, University of Notre Dame Integrated Simulation for MEMS: Coupling Flow-Structure-Thermal-Electrical Domains, Robert M. Kirby and George Em Karniadakis, Brown University, and Oleg Mikulchenko and Kartikeya Mayaram, Oregon State University Liquid Flows in Microchannels, Kendra V. Sharp and Ronald J. Adrian, University of Illinois at Urbana-Champaign, Juan G. Santiago and Joshua I. Molho, Stanford University Burnett Simulations of Flows in Microdevices, Ramesh K. Agarwal and Keon-Young Yun, Wichita State University Molecular-Based Microfluidic Simulation Models, Ali Beskok, Texas A&M University Lubrication in MEMS, Kenneth S. Breuer, Brown University Physics of Thin Liquid Films, Alexander Oron, Technion, Israel Bubble/Drop Transport in Microchannels, Hsueh-Chia Chang, University of Notre Dame Fundamentals of Control Theory, Bill Goodwine, University of Notre Dame Model-Based Flow Control for Distributed Architectures, Thomas R. Bewley, University of California, San Diego Soft Computing in Control, Mihir Sen and Bill Goodwine, University of Notre Dame Part II: Design and Fabrication Materials for Microelectromechanical Systems Christian A. Zorman and Mehran Mehregany, Case Western Reserve University MEMS Fabrication, Marc J. Madou, Nanogen, Inc. LIGA and Other Replication Techniques, Marc J. Madou, Nanogen, Inc. X-Ray-Based Fabrication, Todd Christenson, Sandia National Laboratories Electrochemical Fabrication (EFAB), Adam L. Cohen, MEMGen Corporation Fabrication and Characterization of Single-Crystal Silicon Carbide MEMS, Robert S. Okojie, NASA Glenn Research Center Deep Reactive Ion Etching for Bulk Micromachining of Silicon Carbide, Glenn M. Beheim, NASA Glenn Research Center Microfabricated Chemical Sensors for Aerospace Applications, Gary W. Hunter, NASA Glenn Research Center, Chung-Chiun Liu, Case Western Reserve University, and Darby B. Makel, Makel Engineering, Inc. Packaging of Harsh-Environment MEMS Devices, Liang-Yu Chen and Jih-Fen Lei, NASA Glenn Research Center Part III: Applications of MEMS Inertial Sensors, Paul L. Bergstrom, Michigan Technological University, and Gary G. Li, OMM, Inc. Micromachined Pressure Sensors, Jae-Sung Park, Chester Wilson, and Yogesh B. Gianchandani, University of Wisconsin-Madison Sensors and Actuators for Turbulent Flows. Lennart Loefdahl, Chalmers University of Technology, and Mohamed Gad-el-Hak, University of Notre Dame Surface-Micromachined Mechanisms, Andrew D. Oliver and David W. Plummer, Sandia National Laboratories Microrobotics Thorbjoern Ebefors and Goeran Stemme, Royal Institute of Technology, Sweden Microscale Vacuum Pumps, E. Phillip Muntz, University of Southern California, and Stephen E. Vargo, SiWave, Inc. Microdroplet Generators. Fan-Gang Tseng, National Tsing Hua University, Taiwan Micro Heat Pipes and Micro Heat Spreaders, G. P. "Bud" Peterson, Rensselaer Polytechnic Institute Microchannel Heat Sinks, Yitshak Zohar, Hong Kong University of Science and Technology Flow Control, Mohamed Gad-el-Hak, University of Notre Dame) Part IV: The Future Reactive Control for Skin-Friction Reduction, Haecheon Choi, Seoul National University Towards MEMS Autonomous Control of Free-Shear Flows, Ahmed Naguib, Michigan State University Fabrication Technologies for Nanoelectromechanical Systems, Gary H. Bernstein, Holly V. Goodson, and Gregory L. Snider, University of Notre Dame Index

The MEMS Handbook

A new type of a flow sensor is presented which is based on a thermal principle. The combination of two detecting methods results both in a considerable increase in measuring range (0.1 to 150 mm/s) and in a shorter reaction time of less than 2 ms. Furthermore, the sensor is relatively insensitive to pollution. Devices were manufactured and successfully tested for liquids and gases.

Thermal flow sensor for liquids and gases based on combinations of two principles

This paper reports the surface micromachined gyroscopes realized by HSG-IMIT according to the patented decoupling principle DAVED (DECOUPLED ANGULAR VELOCITY DETECTOR). The DAVED prototypes show a rms noise below 0.05/sup o///sub s/ and a bias stability of /spl plusmn/2.5 /sup o///sub s/ over the temperature range and thus meet the target specification comparable to ESP requirements. Further, a novel and advanced concept is presented which can be viewed as a doubly decoupling scheme. The goal of decoupling is to reduce the so-called quadrature signal and thus improve the sensor performance, especially, the temperature sensitivity. This advancement will be necessary to meet the demands of future applications, like, ADASs (Advanced Driver Assistance System) or partially replace fiber optic gyroscopes, for example, within autonomous guided vehicles.

Decoupled microgyros and the design principle DAVED

An investigation on thermal inclinometers working with free convective flow is presented. This type of sensors shows high sensitivity and good baseline stability. Thermal time constants of 110 ms are achieved. Due to the free convection working principle, the housing has a direct influence on the sensor function. Experiments with different sorts of sensor caps are presented, the system composition and the sensor housing are discussed.

Micromachined inclinometer with high sensitivity and very good stability

In this paper, a method for the fabrication of convex corners in (100) silicon in KOH etchant is presented. Based on the identification of the planes occurring at convex corners during etching in this solution and the determination of the etching rate ratio of these planes in relation to the {100} planes, special structures suited for the compensation of the under-cutting in the case of very narrow contours have been developed. With the help of these structures it is feasible to realize bent V-grooves or structures with a very low ratio between lateral expansion and etching depth, e.g., a discrete truncated pyramid, formed by {111} planes or {411} planes, with minimum dimensions on the wafer surface.

Methods for the fabrication of convex corners in anisotropic etching of (100) silicon in aqueous KOH

We present a new device, the VAMP, which is both an active microvalve and a forward-and reverse-working micropump (VAMP=Valve And MicroPump). Driven by a d.c. voltage, the VAMP operates in its valve mode and is able to control fluid flow in both directions. Driven by a square wave or a sinusoidal voltage, the VAMP operates in its pump mode and is able to pump fluids in both directions. The direction of fluid transport can be changed by varying the driving frequency of the actuator. We discuss two new mechanisms, which in combination are responsible for this frequency-dependent pump effect. The VAMP has been successfully tested for liquids (water, oil) and air. Using water we have achieved maximum pump rates of more than 2000 μl min−1 in the forward direction and 1200 μl min−1 in the reverse direction. The maximum back pressure is 17 kPa (1.7 mH2O) at a supply voltage of 200 V. Pumping air, we have achieved a maximum flow rate of 8000 μl min−1 in both directions. The VAMP has been manufactured in a small-lot production and is now available for industrial evaluation.

Hermann Sandmaier

Papers

Thermal flow sensor for liquids and gases based on combinations of two principles

Decoupled microgyros and the design principle DAVED

Micromachined inclinometer with high sensitivity and very good stability

Methods for the fabrication of convex corners in anisotropic etching of (100) silicon in aqueous KOH

The VAMP — a new device for handling liquids or gases