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.

https://iopscience.iop.org/article/10.1088/0960-1317/15/2/R01/pdf

Micromixers?a review

Nanotechnology is the science of understanding matter and the control of matter at dimensions of 100 nm or less. Encompassing nanoscale science, engineering, and technology, nanotechnology involves imaging, measuring, modeling, and manipulation of matter at this level of precision. An important aspect of research in nanotechnology involves precision control and manipulation of devices and materials at a nanoscale, i.e., nanopositioning. Nanopositioners are precision mechatronic systems designed to move objects over a small range with a resolution down to a fraction of an atomic diameter. The desired attributes of a nanopositioner are extremely high resolution, accuracy, stability, and fast response. The key to successful nanopositioning is accurate position sensing and feedback control of the motion. This paper presents an overview of nanopositioning technologies and devices emphasizing the key role of advanced control techniques in improving precision, accuracy, and speed of operation of these systems.

/pdf/a-survey-of-control-issues-in-nanopositioning-1zgjre9s1l.pdf

A Survey of Control Issues in Nanopositioning

This article reviews acoustic microfiuidics: the use of acoustic fields, principally ultrasonics, for application in microfiuidics. Although acoustics is a classical field, its promising, and indeed perplexing, capabilities in powerfully manipulating both fluids and particles within those fluids on the microscale to nanoscale has revived interest in it. The bewildering state of the literature and ample jargon from decades of research is reorganized and presented in the context of models derived from first principles. This hopefully will make the area accessible for researchers with experience in materials science, fluid mechanics, or dynamics. The abundance of interesting phenomena arising from nonlinear interactions in ultrasound that easily appear at these small scales is considered, especially in surface acoustic wave devices that are simple to fabricate with planar lithography techniques common in microfluidics, along with the many applications in microfluidics and nanofluidics that appear through the literature.

/pdf/microscale-acoustofluidics-microfluidics-driven-via-5bet39j13p.pdf

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

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.

/pdf/microfluidic-mixing-a-review-3egj61w5ox.pdf

Microfluidic Mixing: A Review

The ability to tailor the chemical composition and structure of a surface at the sub-100-nm length scale is important for studying topics ranging from molecular electronics to materials assembly, and for investigating biological recognition at the single biomolecule level. Dip-pen nanolithography (DPN) is a scanning probe microscopy-based nanofabrication technique that uniquely combines direct-write soft-matter compatibility with the high resolution and registry of atomic force microscopy (AFM), which makes it a powerful tool for depositing soft and hard materials, in the form of stable and functional architectures, on a variety of surfaces. The technology is accessible to any researcher who can operate an AFM instrument and is now used by more than 200 laboratories throughout the world. This article introduces DPN and reviews the rapid growth of the field of DPN-enabled research and applications over the past several years.

Applications of dip-pen nanolithography.

High throughput, high resolution scanning probe microscopy

This paper demonstrates the use of a single right-angle prism for the optical readout of micro-electro-mechanical systems (MEMS) cantilever arrays. The non-linear reflectivity arisen from the internal reflection at the right-angle prism’s hypotenuse plane enables the measurement of cantilever deflections. The cantilever arrays used in the experiments are made of electroplated nickel structures and actuated at resonance by an external electro-coil. A laser beam illuminates multiple cantilevers, and then it is partially reflected by the prism. The prism reflectivity changes with the cantilever deflection and modulates the laser intensity at the photodetector. The detection sensitivity of the optical readout system is determined by the initial angle of incidence at the prism’s hypotenuse plane, numerical aperture of the illumination system and the polarization of the laser beam. In this paper, we showed both theoretically and experimentally that self-sustained oscillations of two MEMS cantilevers with simple rectangular geometry is achievable using only one actuator and one photodetector. The gain saturation mechanism for the oscillators was provided by the optical non-linearity in the prism readout, which eliminates the requirement for separate sensing electronics for each cantilever. Based on our analytical and experimental data, we found that the prism incident angle around 41.2° is desirable in the closed-loop system due to high responsivity. Finally, we demonstrated simultaneous self-sustained oscillations of two cantilevers in closed-loop with resonant frequencies in the range 25–30 kHz. It was shown that multiple oscillations are obtainable if the cantilever resonant frequencies are separated from each other by at least 3 dB bandwidth.

A prism-based non-linear optical readout method for MEMS cantilever arrays

This paper discusses improvements in the theoretical and experimental framework of capacitive micromachined ultrasonic Lamb wave transducers. Theoretically, a new method for the analysis of these Lamb wave devices is proposed using the electro-mechanical capabilities of ANSYS, a commercial finite element package. The model used in these simulations has been verified by comparing its predictions when configured as a clamped transducer to those predicted by the standard equivalent circuit model; the input impedances obtained using the two methods agree to within 1%. This method performs harmonic and transient analyses to predict device performance metrics in the presence of electrostatic forces. Experimentally, this paper introduces a new manufacturing process for the fabrication of Lamb wave devices using CMUT wafer bonding technology. Devices have successfully been built using this technique and preliminary results show significantly improved uniformity in membrane to membrane performance and successful Lamb wave propagation between transducers. The membranes fabricated are 1 cm long and 60 /spl mu/m wide have an insertion loss of 16.2 dB near 2.6 MHz.

http://ieeexplore.ieee.org/iel5/9075/28792/01293471.pdf

Improved modeling and fabrication techniques for capacitive micromachined ultrasonic Lamb wave transducers

MEMS array oscillators typically require a separate detector and feedback loop for each oscillator. We show that grating-based-optical-readout induces nonlinearity, which enables simultaneous operation of an array-of-oscillators using only one detector and single electronic feedback-loop

Cantilever array oscillators with nonlinear optical readout

A rotational sensor for measuring rotational acceleration is disclosed. The rotational sensor comprises a sense substrate; at least two proof masses, and a set of two transducers. Each of the at least two proof masses is anchored to the sense substrate via at least one flexure and electrically isolated from each other; and the at least two proof masses are capable of rotating in-plane about a Z-axis relative to the sense substrate, wherein the Z-axis is normal to the substrate. Each of the transducers can sense rotation of each proof mass with respect to the sense substrate in response to a rotation of the rotational sensor.

Goksen G. Yaralioglu

Papers

High throughput, high resolution scanning probe microscopy

A prism-based non-linear optical readout method for MEMS cantilever arrays

Improved modeling and fabrication techniques for capacitive micromachined ultrasonic Lamb wave transducers

Cantilever array oscillators with nonlinear optical readout

Mems rotation sensor with integrated electronics