The present review (with 205 refs.) addresses the need for microdevices, presents the basic microfluidic equations and describes the relevant numerical and experimental approaches. Various types and designs of passive and active micromixers are presented. In addition, the relevant effective dimensionless or dimensional parameters and the fabrication technology for different micromixer types are introduced. Different general configurations of lamination, obstacle, convergence-divergence and curved-channel are discussed for passive micromixers. The active micromixers are categorized and described as pressure field driven, acoustic field driven, magnetic field driven, electric field driven and thermal field driven.

Active and passive micromixers: A comprehensive review

This communication presents a reconfigurable antenna capable of independently reconfiguring the operating frequency, radiation pattern and polarization A switched grid of small metallic patches, known as pixel surface, is used as a parasitic layer to provide reconfiguration capabilities to existing antennas acting as driven element The parasitic pixel layer presents advantages such as low profile, integrability and cost-effective fabrication A fully operational prototype has been designed, fabricated and its compound reconfiguration capabilities have been characterized The prototype combines a patch antenna and a parasitic pixel surface consisting of 6 $\,\times\,$ 6 pixels, with an overall size of $06 \lambda \times 06 \lambda$ and 60 PIN-diode switches The antenna simultaneously tunes its operation frequency over a 25% frequency range, steers the radiation beam over ${\pm 30^\circ}$ in E and H-planes, and switches between four different polarizations ( ${\mathhat{\rm x}},$ ${\mathhat{\rm y}}$ , LHCP, RHCP) The average antenna gain among the different parameter combinations is 4 dB, reaching 6–7 dB for the most advantageous combinations The distance between the driven and the parasitic layers determines the tradeoff between frequency tuning range (12% to 25%) and radiation efficiency (45% to 55%)

Frequency, radiation pattern and polarization reconfigurable antenna using a parasitic pixel layer

https://iopscience.iop.org/article/10.1149/1945-7111/ab77a0/pdf

Review—Recent Advances in Electrochemical Impedance Spectroscopy Based Toxic Gas Sensors Using Semiconducting Metal Oxides

This paper presents an analysis of the sol deposition process on porous silicon in order to produce highly sensitive gas detectors. Sol solutions were deposited within the dendrite structural pore regions of n-type silicon. The parameters for the structures, built of metal oxides (Fe, Ni, Sn), were analyzed. A morphological study of porous silicon, with embedded metal oxide nanocomposites, was carried out using atomic force microscopy. Cross-sections of porous silicon were examined using a scanning electron microscopy. Impedance spectroscopy was used to study the electrical properties of nanomaterials, based on porous silicon, with embedded metal oxide nanocomposites. Gas-sensitivity measurements of the synthesized samples were made. It turned out that, applying variable frequency interference to the sensory structures in a changing environment, changes the impedance response of gas. New perspectives for increasing sensitivity and selectivity are shown.

Porous silicon with embedded metal oxides for gas sensing applications

Slug flow in microchannels: Numerical simulation and applications

Porous silicon (PS) has many interesting and unique properties that make it a viable material in the field of MEMS. In this paper, we investigate the application of PS in improving the sensitivity of bulk micromachined piezoresistive pressure sensors. The property of a low Young's modulus of PS and its dependence on porosity have been exploited to obtain a higher sensitivity compared to pressure sensors with single crystalline silicon membranes. Simulation was carried out to represent the Si/PS composite membrane by two layers with Young's modulus corresponding to silicon and PS. The behavior of this membrane was studied for various values of porosity and thickness of the PS layer. Composite Si/PS membranes were fabricated by converting a part of the silicon membrane thickness into PS by electrochemical etching in an HF-based electrolyte. Polysilicon piezoresistors were formed on the membrane in the form of a Wheatstone bridge for the measurement of sensitivity. When compared to membranes of silicon, the sensitivity of the composite Si/PS membrane is found to be higher showing improvement with an increase in the porosity and thickness of the PS layer.

http://iopscience.iop.org/article/10.1088/0960-1317/17/8/025/pdf

Enhancement of the sensitivity of pressure sensors with a composite Si/porous silicon membrane

Mercury (Hg2+) ion is one of the heavy metal ions present in water and highly poisonous to human consumption. Thus, developing an efficient sensor for detection of mercury ions at different concentration levels in the water down to nM is essential. Here, we report the development of fluorometric sensor using the fluidic MEMS device (i.e., microfluidic device) with high sensitivity and selective detection of Hg2+ in water using tiny quantity of sensing fluids ( $\sim 2.8~\mu \text{L}$ ). L-Arginine-capped gold nanoparticles functionalized with Rhodamine 6G allowed the on-chip fluorescence detection of Hg2+ ions concentration regime from 0 to 16 nM in water samples. The developed microfluidic device senses the presence of Hg2+ ions through the change in intensity of fluid fluorescence. The sensor response is found to be linear with respect to the Hg2+ ions concentration ranging from 2 to 12 nM.

Fluorometric Sensor for Mercury Ion Detection in a Fluidic MEMS Device

Abstract This paper deals with design, simulation, fabrication, analysis of mixing efficiency and thin film bonding stability of the micromixer devices with different flow rates used for lab on chip applications. The objective of the present study is to achieve complete mixing with low flow rate and less pressure drop in low cost polymer microfluidic devices. This paper emphasis the design, simulation and fabrication of straight channel micromixer, serpentine channel micromixer with and without quadrant shaped grooves to study the mixing behavior by the effect of structural dimensions of the microfluidic channel at different flow rates. The designed micromixers were tested with varying rates of flow such as 1, 10, 25, 50, 75 and 100 µL/min.

Study of Permissible Flow Rate and Mixing Efficiency of the Micromixer Devices

Abstract This paper deals with the design, analysis and optimization of micro-mixer for fluids having very low diffusivity (in the order of 10−12 m2/s) to be used in Lab on Chip (LOC) for medical diagnosis. As flow is laminar and the cross-sectional area is in microscale, the viscous forces are strong causing the fluids to be transported in streamline with minimum diffusion. The main objective in designing a micro mixer is to achieve complete mixing with minimum channel length and pressure drop. In this work a passive micro mixer with two inlets and one outlet (Y shaped passive micro mixer) with obstacles in various shapes and sizes is modelled, to study the effect of mixing. After a CFD analysis, Analysis of variance (ANOVA) of 3K design with 3 parameters as well as a 2K design with 4 parameters was performed to study the effect of parameters on mixing index (mixing length) and pressure loss. There is a negative correlation between the response obtained for mixing length and pressure loss while varying the parameters. This makes it difficult to predict the optimum configuration. Taguchi method is used to obtain an optimum configuration to overcome this negative correlatiozn.

Numerical Modeling and Parametric Optimization of Micromixer for Low Diffusivity Fluids

The presence of heavy metal ions such as Lead (Pb2+), Mercury (Hg2+), Cadmium (Cd2+), Arsenic (As3+) and Chromium (Cr3) in water cause serious and long-term effects on human health. In particular, they may cause kidney damage, liver damage, lung cancer, neurotic disorder, anemia, discoloration of hands and feet. Hence detection and quantification of these metal ions are important for health care and prevention of serious diseases. This paper aims at the design, analysis and fabrication of microfluidic device for improved mixing performance using herringbone type of micromixer for sensing of mercury ions in water.

L. Sujatha

Papers

Enhancement of the sensitivity of pressure sensors with a composite Si/porous silicon membrane

Fluorometric Sensor for Mercury Ion Detection in a Fluidic MEMS Device

Study of Permissible Flow Rate and Mixing Efficiency of the Micromixer Devices

Numerical Modeling and Parametric Optimization of Micromixer for Low Diffusivity Fluids

Design and fabrication of microfluidic device for mercury ions detection in water