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A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (31 March 2020) | Viewed by 34702

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Special Issue Editor

Prof. Dr. Joost Lötters

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Guest Editor

1. Integrated Devices and Systems (IDS), University of Twente, 7500 AE Enschede, The Netherlands
2. Bronkhorst High-Tech BV, Nijverheidsstraat 1A, 7261 AK Ruurlo, The Netherlands
Interests: design, modeling, fabrication and application of microfluidic handling systems; MEMS thermal and Coriolis flow sensors and controllers; MEMS pressure sensors; MEMS control valves; micromachined flow analysis systems; multiparameter flow measurement systems; micro Wobbe index meters
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Special Issue Information

Dear Colleagues,

This Special Issue will publish both selected papers from the 4^th International Conference on Microfluidic Handling Systems (www.mfhs2019.org, 2–4 October, 2019, Enschede, The Netherlands) and external contributions. Manuscripts submitted to the journal Micromachines should be extended by at least 40% compared with that of the conference proceedings.

Worldwide, accurate handling—i.e., analysis, dosage, measurement and control—of small and extremely small mass flow rates of both gases and liquids is becoming more and more important, driven by numerous applications. Examples of economically and societally relevant applications are, e.g., improvement of medical infusion pump systems, nutrition supply and waste drainage in organ-on-a-chip systems, increasing the efficiency of processes that extract oil from oil wells (enhanced oil recovery), systems that measure the energy content (calorific value or Wobbe Index) of natural gas, biogas and Liquid Natural Gas (LNG), monitoring of ground water pollution, improving semiconductor equipment for e.g. etching and deposition, and the production of pharmaceuticals by means of flow chemistry.

Whether in analytical instrumentation, flow chemistry, energy, semiconductor industry, food and beverage or life sciences – microfluidic handling systems are facing four major trends: (1) a need for accurate measurement and calibration facilities; (2) a need for complete functional systems rather than for the individual components; (3) commercialisation of academic research results, and (4) standardisation of fabrication technology & materials, modules & connections, and quality assurance & test equipment. In the future, the impact of this field of research may become bigger and potentially large target markets may arise, especially when spin-off companies start manufacturing and selling their products, systems or pilot plants.

The 4^th International Conference on Microfluidic Handling Systems (MFHS 2019) focuses mainly on the technology, components, devices and systems that enable the application in microfluidic systems. We invite submission of papers on systems and devices for accurate handling (e.g., analysis, dosing, measurement and control) of (extremely) small mass flow rates of both gases and liquids, and corresponding measurement and control principles, including but not limited to:

Thermal, ultrasonic, Coriolis and other principles for flow measurement
Piezo-electric, electromagnetic, electrostatic and other principles for flow control
Electronic instrumentation, closed loop control systems
Innovative methods in calibration equipment and methodology
Micro- and nanomachining, 3D printing and other fabrication technologies
Device or wafer level characterization, packaging and testing
Application proposals

The topics include, but are not limited to:

Sensors: Flow, pressure, viscosity, temperature, conductivity, heat capacity, density, pH, refractive index
Actuators: Valves, pumps, mixers, dispensers, droplet generators
Interfaces: Electronic instrumentation, fluidic connections, assembly, packaging, testing
Fluidic control systems: Mass flow controllers, precision mixing, dosing and dispensing, calibration, multiparameter systems, evaporators
Applications: Gas chromatographs, liquid chromatographs, medical analyses, micro reaction systems, bio-analytical systems, flow chemistry, organ-on-a-chip, production of pharmaceuticals

Prof. Dr. Joost Lötters
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (10 papers)

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Research

8 pages, 2200 KiB

Open AccessArticle

Design and Analysis of a Slot Photonic Crystal Waveguide for Highly Sensitive Evanescent Field Absorption Sensing in Fluids

by Reyhaneh Jannesari, Gerald Pühringer, Thomas Grille and Bernhard Jakoby

Micromachines 2020, 11(8), 781; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11080781 - 15 Aug 2020

Cited by 5 | Viewed by 2749

Abstract

The design and modeling of a highly sensitive sensor based on a slot photonic crystal waveguide (slot-PCWG) is presented. The structure consists of cylindrical air rods drilled in a dielectric slab on a triangular lattice, which are filled with SiO₂. The waveguide is formed by removing elements from the regular photonic crystal grid in a row, and embedding a slot in the center position. This concept allows for a vast enhancement of the evanescent field ratio, leading to a strong overlap between the field of the waveguide mode and the analyte. In the present work, we show that the sensitivity at the constant slab thickness of the slot-PCWG modes is greatly enhanced, up to a factor of 7.6 compared with the corresponding PCWG modes or Si-slab WGs. The finite-difference time-domain (FDTD) technique and plane wave expansion (PWE) methods were used to study the dispersion and profile of the PCWG mode. The simulation results show the potential of this design, which will be fabricated and tested in the following steps of the project. Full article

(This article belongs to the Special Issue MFHS 2019)

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Graphical abstract

19 pages, 49126 KiB

Open AccessArticle

Heavily-Doped Bulk Silicon Sidewall Electrodes Embedded between Free-Hanging Microfluidic Channels by Modified Surface Channel Technology

by Yiyuan Zhao, Henk-Willem Veltkamp, Thomas V. P. Schut, Remco G. P. Sanders, Bogdan Breazu, Jarno Groenesteijn, Meint J. de Boer, Remco J. Wiegerink and Joost C. Lötters

Micromachines 2020, 11(6), 561; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11060561 - 31 May 2020

Cited by 3 | Viewed by 2347

Abstract

Surface Channel Technology is known as the fabrication platform to make free-hanging microchannels for various microfluidic sensors and actuators. In this technology, thin film metal electrodes, such as platinum or gold, are often used for electrical sensing and actuation purposes. As a result that they are located at the top surface of the microfluidic channels, only topside sensing and actuation is possible. Moreover, in microreactor applications, high temperature degradation of thin film metal layers limits their performance as robust microheaters. In this paper, we report on an innovative idea to make microfluidic devices with integrated silicon sidewall electrodes, and we demonstrate their use as microheaters. This is achieved by modifying the original Surface Channel Technology with optimized mask designs. The modified technology allows to embed heavily-doped bulk silicon electrodes in between the sidewalls of two adjacent free-hanging microfluidic channels. The bulk silicon electrodes have the same electrical properties as the extrinsic silicon substrate. Their cross-sectional geometry and overall dimensions can be designed by optimizing the mask design, hence the resulting resistance of each silicon electrode can be customized. Furthermore, each silicon electrode can be electrically insulated from the silicon substrate. They can be designed with large cross-sectional areas and allow for high power dissipation when used as microheater. A demonstrator device is presented which reached

119.4

^{\circ} C

at a power of

206.9

m

W

, limited by thermal conduction through the surrounding air. Other potential applications are sensors using the silicon sidewall electrodes as resistive or capacitive readout. Full article

(This article belongs to the Special Issue MFHS 2019)

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14 pages, 4213 KiB

Open AccessArticle

Parallel Droplet Deposition via a Superhydrophobic Plate with Integrated Heater and Temperature Sensors

by Marcus A. Hintermüller, Christina Offenzeller, Marcel Knoll, Andreas Tröls and Bernhard Jakoby

Micromachines 2020, 11(4), 354; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11040354 - 28 Mar 2020

Cited by 2 | Viewed by 2367

Abstract

A simple setup, which is suitable for parallel deposition of homogenous liquids with a precise volume (dosage), is presented. First, liquid is dispensed as an array of droplets onto a superhydrophobic dosage plate, featuring a 3 × 3 array of holes. The droplets rest on these holes and evaporate with time until they are small enough to pass through them to be used on the final target, where a precise amount of liquid is required. The system can be fabricated easily and operates in a highly parallel manner. The design of the superhydrophobic dosage plate can be adjusted, in terms of the hole positions and sizes, in order to meet different specifications. This makes the proposed system extremely flexible. The initial dispensed droplet mass is not significant, as the dosing takes place during the evaporation process, where the dosage is determined by the hole diameter. In order to speed up the evaporation process, microheaters are screen printed on the back side of the dosage plate. To characterize the temperature distribution caused by the microheaters, temperature sensors are screen printed on the top side of the dosage plate as well. Experimental data regarding the temperature sensors, the microheaters, and the performance of the setup are presented, and the improvement due to the heating of the dosage plate is assessed. A significant reduction of the total evaporation time due to the microheaters was observed. The improvement caused by the temperature increase was found to follow a power law. At a substrate temperature of 80 °C, the total evaporation time was reduced by about 79%. Full article

(This article belongs to the Special Issue MFHS 2019)

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12 pages, 7357 KiB

Open AccessArticle

2D Spatially-Resolved Depth-Section Microfluidic Flow Velocimetry Using Dual Beam OCT

by Jonathan M. Hallam, Evangelos Rigas, Thomas O. H. Charrett and Ralph P. Tatam

Micromachines 2020, 11(4), 351; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11040351 - 27 Mar 2020

Cited by 1 | Viewed by 2695

Abstract

A dual beam optical coherence tomography (OCT) instrument has been developed for flow measurement that offers advantages over microscope derived imaging techniques. It requires only a single optical access port, allows simultaneous imaging of the microfluidic channel, does not require fluorescent seed particles, and can provide a millimetre-deep depth-section velocity profile (as opposed to horizontal-section). The dual beam instrument performs rapid re-sampling of particle positions, allowing measurement of faster flows. In this paper, we develop the methods and processes necessary to make 2D quantitative measurements of the flow-velocity using dual beam OCT and present exemplar results in a microfluidic chip. A 2D reference measurement of the Poiseuille flow in a microfluidic channel is presented over a spanwise depth range of 700 μm and streamwise length of 1600 μm with a spatial resolution of 10 μm, at velocities up to 50 mm/s. A measurement of a more complex flow field is also demonstrated in a sloped microfluidic section. Full article

(This article belongs to the Special Issue MFHS 2019)

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11 pages, 5965 KiB

Open AccessArticle

A Flow-Through Microfluidic Relative Permittivity Sensor

by Yaxiang Zeng, Remco Sanders, Remco Wiegerink and Joost Lötters

Micromachines 2020, 11(3), 325; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030325 - 20 Mar 2020

Cited by 1 | Viewed by 2568

Abstract

In this paper, we present the design, simulation, fabrication and characterization of a microfluidic relative permittivity sensor in which the fluid flows through an interdigitated electrode structure. Sensor fabrication is based on an silicon on insulator (SOI) wafer where the fluidic inlet and outlet are etched through the handle layer and the interdigitated electrodes are made in the device layer. An impedance analyzer was used to measure the impedance between the interdigitated electrodes for various non-conducting fluids with a relative permittivity ranging from 1 to 41. The sensor shows good linearity over this range of relative permittivity and can be integrated with other microfluidic sensors in a multiparameter chip. Full article

(This article belongs to the Special Issue MFHS 2019)

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22 pages, 7952 KiB

Open AccessArticle

A Multiparameter Gas-Monitoring System Combining Functionalized and Non-Functionalized Microcantilevers

by Christof Huber, Maria Pilar Pina, Juan José Morales and Alexandre Mehdaoui

Micromachines 2020, 11(3), 283; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030283 - 10 Mar 2020

Cited by 5 | Viewed by 2330

Abstract

The aim of the study is to develop a compact, robust and maintenance free gas concentration and humidity monitoring system for industrial use in the field of inert process gases. Our multiparameter gas-monitoring system prototype allows the simultaneous measurement of the fluid physical properties (density, viscosity) and water vapor content (at ppm level) under varying process conditions. This approach is enabled by the combination of functionalized and non-functionalized resonating microcantilevers in a single sensing platform. Density and viscosity measuring performance is evaluated over a wide range of gases, temperatures and pressures with non-functionalized microcantilevers. For the humidity measurement, microporous Y-type zeolite and mesoporous silica MCM48 are evaluated as sensing materials. An easily scalable functionalization method to high-throughput production is herein adopted. Experimental results with functionalized microcantilevers exposed to water vapor (at ppm level) indicate that frequency changes cannot be attributed to a mass effect alone, but also stiffness effects dependent on adsorption of water and working temperature must be considered. To support this hypothesis, the mechanical response of such microcantilevers has been modelled considering both effects and the simulated results validated by comparison against experimental data. Full article

(This article belongs to the Special Issue MFHS 2019)

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28 pages, 25023 KiB

Open AccessArticle

Disposable DNA Amplification Chips with Integrated Low-Cost Heaters ^†

by Henk-Willem Veltkamp, Fernanda Akegawa Monteiro, Remco Sanders, Remco Wiegerink and Joost Lötters

Micromachines 2020, 11(3), 238; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030238 - 25 Feb 2020

Cited by 11 | Viewed by 5464

Abstract

Fast point-of-use detection of, for example, early-stage zoonoses, e.g., Q-fever, bovine tuberculosis, or the Covid-19 coronavirus, is beneficial for both humans and animal husbandry as it can save lives and livestock. The latter prevents farmers from going bankrupt after a zoonoses outbreak. This paper describes the development of a fabrication process and the proof-of-principle of a disposable DNA amplification chip with an integrated heater. Based on the analysis of the milling process, metal adhesion studies, and COMSOL MultiPhysics heat transfer simulations, the first batch of chips has been fabricated and successful multiple displacement amplification reactions are performed inside these chips. This research is the first step towards the development of an early-stage zoonoses detection device. Tests with real zoonoses and DNA specific amplification reactions still need to be done. Full article

(This article belongs to the Special Issue MFHS 2019)

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14 pages, 15196 KiB

Open AccessFeature PaperArticle

μ-Coriolis Mass Flow Sensor with Resistive Readout

by Thomas Schut, Remco Wiegerink and Joost Lötters

Micromachines 2020, 11(2), 184; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11020184 - 11 Feb 2020

Cited by 9 | Viewed by 3116

Abstract

This paper presents a

μ

This paper presents a

μ

-Coriolis mass flow sensor with resistive readout. Instead of measuring a net displacement such as in a capacitive readout, a resistive readout detects the deformation of the suspended micro-fluidic channel. It allows for actuation at much higher amplitudes than for a capacitive readout, resulting in correspondingly larger Coriolis forces in response to fluid flow. A resistive readout can be operated in two actuation vibrational modes. A capacitive readout can only be operated in one of these two modes, which is more sensitive to external disturbances. Three types of devices have been realized. We present measurement results for all three devices. One device clearly outperforms the other two, with a flow sensitivity of 2.22 °/(g·h⁻¹) and a zero-flow stability of 0.02 g·h⁻¹ over 30 min. Optimization of the metal strain gauges and/or implementation of poly-Silicon strain gauges could further improve performance. Full article

(This article belongs to the Special Issue MFHS 2019)

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15 pages, 2207 KiB

Open AccessArticle

Proportional Microvalve Using a Unimorph Piezoelectric Microactuator

by Arun Gunda, Gürhan Özkayar, Marcel Tichem and Murali Krishna Ghatkesar

Micromachines 2020, 11(2), 130; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11020130 - 24 Jan 2020

Cited by 15 | Viewed by 3731

Abstract

Microvalves are important flow-control devices in many standalone and integrated microfluidic applications. Polydimethylsiloxane (PDMS)-based pneumatic microvalves are commonly used but they generally require large peripheral connections that decrease portability. There are many alternatives found in the literature that use Si-based microvalves, but variants that can throttle even moderate pressures (1 bar) tend to be bulky (cm-range) or consume high power. This paper details the development of a low-power, normally-open piezoelectric microvalve to control flows with a maximum driving pressure of 1 bar, but also retain a small effective form-factor of 5 mm × 5 mm × 1.8 mm. A novel combination of rapid prototyping methods like stereolithography and laser-cutting have been used to realize this device. The maximum displacement of the fabricated piezoelectric microactuator was measured to be 8.5 μm at 150 V. The fabricated microvalve has a flow range of 0–90 μL min⁻¹ at 1 bar inlet pressure. When fully closed, a leakage of 0.8% open-flow was observed with a power-consumption of 37.5 μW. A flow resolution of 0.2 μL min⁻¹—De-ionized (DI) water was measured at 0.5 bar pressure. Full article

(This article belongs to the Special Issue MFHS 2019)

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15 pages, 4418 KiB

Open AccessFeature PaperArticle

A Versatile Capacitive Sensing Platform for the Assessment of the Composition in Gas Mixtures

by Jörgen Sweelssen, Huib Blokland, Timo Rajamäki, Risto Sarjonen and Arjen Boersma

Micromachines 2020, 11(2), 116; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11020116 - 21 Jan 2020

Cited by 7 | Viewed by 3239

Abstract

The energy market is facing a major transition, in which natural gas and renewable gasses will play an important role. However, changing gas sources and compositions will force the gas transporters, gas engine manufacturers, and gas grid operators to monitor the gas quality in a more intensive way. This leads to the need for lower cost, smaller, and easy to install gas quality sensors. A new approach is proposed in this study that is based on the chemical interactions of the various gas components and responsive layers applied to an array of capacitive interdigitated electrodes. For Liquid Natural Gas (LNG), containing a relative high concentration of higher hydrocarbons, an array of ten capacitive chips is proposed, that is sufficient to calculate the full composition, and can be used to calculate energy parameters, such as Wobbe Index, Calorific Value, and Methane Number. A first prototype was realized that was small enough to be inserted in low and medium pressure gas pipes and LNG engine fuel lines. Adding the pressure and temperature data to the chip readings enables the determination of the concentrations of the various alkanes, hydrogen, nitrogen, and carbon dioxide, including small fluctuations in water vapor pressure. The sensitivity and selectivity of the new sensor is compared to a compact analyzer employing tunable filter infrared spectrometry. Full article

(This article belongs to the Special Issue MFHS 2019)

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