http://www.mdpi.com/journal/micromachines Latest open access articles published in Micromachines at http://www.mdpi.com/journal/micromachines http://www.mdpi.com/2072-666X/4/2/197 This paper presents a microfluidic system for the active and precise control of microdroplet division in a micro device. Using two horizontal pneumatic valves formed at downstream of bifurcating microchannel, flow resistances of downstream channels were variably controlled. With the resistance control, volumetric ratio of downstream flows was changed and water-in-oil microdroplets were divided into two daughter droplets of different volume corresponding to the ratio. The microfluidic channels and pneumatic valves were fabricated by single-step soft lithography process of PDMS (polydimethylsiloxane) using SU-8 mold. A wide range control of the daughter droplets’ volume ratio was achieved by the simple channel structure. Volumetric ratio between large and small daughter droplets are ranged from 1 to 70, and the smallest droplet volume of 14 pL was obtained. The proposed microfluidic device is applicable for precise and high throughput droplet based digital synthesis. Micromachines 2013-05-07 4 2 Article 10.3390/mi4020197 197 205 2072-666X 2013-05-07 doi: 10.3390/mi4020197 Dong Yoon Junichi Ito Tetsushi Sekiguchi Shuichi Shoji http://www.mdpi.com/2072-666X/4/2/168 Beginning with a short historical sketch, electrodynamic energy harvesters with focus on vibration generators and volumes below 1dm3 are reviewed. The current challenges to generate up to several milliwatts of power from practically relevant flows and vibrations are addressed, and the variety of available solutions is sketched. Sixty-seven different harvester concepts from more than 130 publications are classified with respect to excitation, additional boundary conditions, design and fabrication. A chronological list of the harvester concepts with corresponding references provides an impression about the developments. Besides resonant harvester concepts, the review includes broadband approaches and mechanisms to harvest from flow. Finally, a short overview of harvesters in applications and first market ready concepts is given. Micromachines 2013-04-29 4 2 Article 10.3390/mi4020168 168 196 2072-666X 2013-04-29 doi: 10.3390/mi4020168 Clemens Cepnik Roland Lausecker Ulrike Wallrabe http://www.mdpi.com/2072-666X/4/2/157 This paper presents UV imprinting methods for fabricating a high-aspect-ratio pillar array. A polydimethylsiloxane (PDMS) mold was selected as the UV imprinting mold. The pillar pattern was formed on a 50 × 50 mm2 area on a polyethylene terephthalate (PET) film without remarkable deformation. The aspect ratios of the pillar and space were about four and ten, respectively. The mold was placed into contact with a UV-curable resin under a reduced pressure, and the resin was cured by UV light irradiation after exposure to atmospheric pressure. The PDMS mold showed good mold releasability and high flexibility. By moderately pressing the mold before UV-curing, the thickness of the residual layer of the imprinted resin was reduced and the pattern was precisely imprinted. Both batch pressing and roll pressing are available. Micromachines 2013-04-17 4 2 Article 10.3390/mi4020157 157 167 2072-666X 2013-04-17 doi: 10.3390/mi4020157 Hidetoshi Shinohara Hiroshi Goto Takashi Kasahara Jun Mizuno http://www.mdpi.com/2072-666X/4/2/149 Micrometer order magnetophotonic crystals with periodic arranged metallic glass and oxide glass composite materials were fabricated by stereolithographic method to reflect electromagnetic waves in terahertz frequency ranges through Bragg diffraction. In the fabrication process, the photo sensitive acrylic resin paste mixed with micrometer sized metallic glass of Fe72B14.4Si9.6Nb4 and oxide glass of B2O3·Bi2O3 particles was spread on a metal substrate, and cross sectional images of ultra violet ray were exposed. Through the layer by layer stacking, micro lattice structures with a diamond type periodic arrangement were successfully formed. The composite structures could be obtained through the dewaxing and sintering process with the lower temperature under the transition point of metallic glass. Transmission spectra of the terahertz waves through the magnetophotonic crystals were measured by using a terahertz time domain spectroscopy. Micromachines 2013-04-02 4 2 Article 10.3390/mi4020149 149 156 2072-666X 2013-04-02 doi: 10.3390/mi4020149 Soshu Kirihara Maasa Nakano http://www.mdpi.com/2072-666X/4/2/138 This paper presents improvements in flow detection by electrical cross-correlation spectroscopy. This new technique detects molecular number fluctuations of electrochemically active analyte molecules as they are transported by liquid flow through a nanochannel. The fluctuations are used as a marker of liquid flow as their time of flight in between two consecutive transducers is determined, thereby allowing for the measurement of liquid flow rates in the picoliter-per-minute regime. Here we show an enhanced record-low sensitivity below 1 pL/min by capitalizing on improved electrical instrumentation, an optimized sensor geometry and a smaller channel cross section. We further discuss the impact of sensor geometry on the cross-correlation functions. Micromachines 2013-04-02 4 2 Article 10.3390/mi4020138 138 148 2072-666X 2013-04-02 doi: 10.3390/mi4020138 Klaus Mathwig Serge Lemay http://www.mdpi.com/2072-666X/4/2/128 Microfibers composed of azobenzene-based photochromic amorphous molecular materials, namely low molecular-mass photochromic materials with a glass-forming property, could be fabricated. These fibers were found to exhibit mechanical bending motion upon irradiation with a laser beam. In addition, the bending direction could be controlled by altering the polarization direction of the irradiated light without changing the position of the light source or the wavelength of the light. In-situ fluorescence observation of mass transport induced at the surface of the fiber doped with CdSe quantum dots suggested that the bending motions were related with the photoinduced mass transport taking place near the irradiated surface of the fiber. Micromachines 2013-03-27 4 2 Article 10.3390/mi4020128 128 137 2072-666X 2013-03-27 doi: 10.3390/mi4020128 Hideyuki Nakano Ryoji Ichikawa Riku Matsui http://www.mdpi.com/2072-666X/4/1/116 We presented an overview of improvements in detection limit and responsivity of our biomimetic hair flow sensors by electrostatic spring-softening (ESS). Applying a DC-bias voltage to our capacitive flow sensors improves the responsively by up to 80% for flow signals at frequencies below the sensor’s resonance. Application of frequency matched AC-bias voltages allows for tunable filtering and selective gain up to 20 dB. Furthermore, the quality and fidelity of low frequency flow measurements can be improved using a non frequency-matched AC-bias voltage, resulting in a flow detection limit down to 5 mm/s at low (30 Hz) frequencies. The merits and applicability of the three methods are discussed. Micromachines 2013-03-19 4 1 Article 10.3390/mi4010116 116 127 2072-666X 2013-03-19 doi: 10.3390/mi4010116 Harmen Droogendijk Christiaan Bruinink Remco Sanders Gijs Krijnen http://www.mdpi.com/2072-666X/4/1/103 This paper presents work on the development of a microfluidic device using super-paramagnetic beads for sampling and mixing. The beads are manipulated via an external rotating permanent magnet in a microfluidic channel. Efficient mixing is achieved in a short distance with this method. Modeling shows the variables which influence the mixing are flow rate, bead rotation speed and the bead number density. Displacement of the bead relative the rotating magnetic field sets an upper limit on the bead rotation speed due to viscous drag. Future work will examine optimization of this system for capture of pathogens from a complex mixture. Micromachines 2013-03-19 4 1 Article 10.3390/mi4010103 103 115 2072-666X 2013-03-19 doi: 10.3390/mi4010103 Drew Owen Wenbin Mao Alex Alexeev Jennifer Cannon Peter Hesketh http://www.mdpi.com/2072-666X/4/1/90 Here we present new applications for silicon nitride (SiN) membranes to evaluate biological processes. We determined that 50-nanometer thin films of SiN produced from silicon wafers were sufficiently durable to bind active rotavirus assemblies. A direct comparison of SiN microchips with conventional carbon support films indicated that SiN performs equivalent to the traditional substrate to prepare samples for Electron Microscopy (EM) imaging. Likewise, SiN films coated with Ni-NTA affinity layers concentrated rotavirus particles similarly to affinity-coated carbon films. However, affinity-coated SiN membranes outperformed glow-discharged conventional carbon films 5-fold as indicated by the number of viral particles quantified in EM images. In addition, we were able to recapitulate viral uncoating and transcription mechanisms directed onto the microchip surfaces. EM images of these processes revealed the production of RNA transcripts emerging from active rotavirus complexes. These results were confirmed by the functional incorporation of radiolabeled nucleotides into the nascent RNA transcripts. Collectively, we demonstrate new uses for SiN membranes to perform molecular surveillance on life processes in real-time. Micromachines 2013-03-14 4 1 Article 10.3390/mi4010090 90 102 2072-666X 2013-03-14 doi: 10.3390/mi4010090 Brian Gilmore Justin Tanner Allison McKell Crystal Boudreaux Madeline Dukes Sarah McDonald Deborah Kelly http://www.mdpi.com/2072-666X/4/1/80 We present a continuous-flow active micromixer based on channel-wall deflection in a polydimethylsiloxane (PDMS) chip for volume flows in the range up to 2 μL s−1 which is intended as a novel unit operation for the microfluidic Braille pin actuated platform. The chip design comprises a main microchannel connected to a series of side channels with dead ends aligned on the Braille pins. Computer-controlled deflection of the side-channel walls induces chaotic advection in the main-channel, which substantially accelerates mixing in low-Reynolds number flow. Sufficient mixing (mixing index MI below 0.1) of volume flows up to 0.5 μL s−1 could be achieved within residence times ~500 ms in the micromixer. As an application, continuous dilution of a yeast cell sample by a ratio down to 1:10 was successfully demonstrated. The mixer is intended to serve as a component of bio-analytical devices or as a unit operation in the microfluidic Braille pin actuated platform. Micromachines 2013-03-14 4 1 Article 10.3390/mi4010080 80 89 2072-666X 2013-03-14 doi: 10.3390/mi4010080 Yawar Abbas Junichi Miwa Roland Zengerle Felix von Stetten http://www.mdpi.com/2072-666X/4/1/67 Silica glass is frequently used as a device material for micro/nano fluidic devices due to its excellent properties, such as transparency and chemical resistance. Wet etching by hydrofluoric acid and dry etching by neutral loop discharge (NLD) plasma etching are currently used to micromachine glass to form micro/nano fluidic channels. Electro-osmotic flow (EOF) is one of the most effective methods to drive liquids into the channels. EOF mobility is affected by a property of the micromachined glass surfaces, which includes surface roughness that is determined by the manufacturing processes. In this paper, we investigate the effect of micromaching processes on the glass surface topography and the EOF mobility. We prepared glass surfaces by either wet etching or by NLD plasma etching, investigated the surface topography using atomic force microscopy, and attempted to correlate it with EOF generated in the micro-channels of the machined glass. Experiments revealed that the EOF mobility strongly depends on the surface roughness, and therefore upon the fabrication process used. A particularly strong dependency was observed when the surface roughness was on the order of the electric double layer thickness or below. We believe that the correlation described in this paper can be of great help in the design of micro/nano fluidic devices. Micromachines 2013-03-13 4 1 Article 10.3390/mi4010067 67 79 2072-666X 2013-03-13 doi: 10.3390/mi4010067 Yosuke Koga Reiko Kuriyama Yohei Sato Koichi Hishida Norihisa Miki http://www.mdpi.com/2072-666X/4/1/49 We present a novel pneumatic actuation system for generation of liquid metal droplets according to the so-called StarJet method. In contrast to our previous work, the performance of the device has been significantly improved: the maximum droplet generation frequency in continuous mode has been increased to fmax = 11 kHz (formerly fmax = 4 kHz). In addition, the droplet diameter has been reduced to 60 μm. Therefore, a new fabrication process for the silicon nozzle chips has been developed enabling the production of smaller nozzle chips with higher surface quality. The size of the metal reservoir has been increased to hold up to 22 mL liquid metal and the performance and durability of the actuator has been improved by using stainless steel and a second pneumatic connection to control the sheath flow. Experimental results are presented regarding the characterization of the droplet generation, as well as printed metal structures. Micromachines 2013-03-11 4 1 Article 10.3390/mi4010049 49 66 2072-666X 2013-03-11 doi: 10.3390/mi4010049 Nils Lass Lutz Riegger Roland Zengerle Peter Koltay http://www.mdpi.com/2072-666X/4/1/34 We present an active droplet merging device, which can merge various sizes of micro droplets in different numbers by using pneumatically controlled horizontal PDMS microvalves. The merging part consists of a main and side channels separated by a pillar array. The pillar array structure is contained within a microfuidic channel. The function of the pillar array provides a bypass path to the continuous flow (oil) inside the merging chamber. Droplets are successfully generated within the channel and achieve merging by controlling the selective different numbers and diameters of droplets through varying the flow resistance of main and side channel. In the merging chamber, a droplet will enter and slow down its movement. It will wait and then merge with the sequential droplets. These experiments demonstrate that such a merging device can controllably select and adjust the distance between the different adjacent micro droplets without any generation of sister droplets in the side channel. The device has no desynchronization problems. Thus, it can be applied for efficiently mixing the droplets in various diameters and numbers without changing the structure of the merging chamber. Hence, this device can be a more effective choice when applying microfluidics to chemical and biological applications. Micromachines 2013-03-08 4 1 Article 10.3390/mi4010034 34 48 2072-666X 2013-03-08 doi: 10.3390/mi4010034 Afshan Jamshaid Masaya Igaki Dong Yoon Tetsushi Sekiguchi Shuichi Shoji http://www.mdpi.com/2072-666X/4/1/22 In this paper we demonstrate a compact ready-to-use micro Coriolis mass flow meter. The full scale flow is 1 g/h (for water at a pressure drop < 1 bar). It has a zero stability of 2 mg/h and an accuracy of 0.5% reading for both liquids and gases. The temperature drift between 10 and 50 °C is below 1 mg/h/°C. The meter is robust, has standard fluidic connections and can be read out by means of a PC or laptop via USB. Its performance was tested for several common gases (hydrogen, helium, nitrogen, argon and air) and liquids (water and isopropanol). As in all Coriolis mass flow meters, the meter is also able to measure the actual density of the medium flowing through the tube. The sensitivity of the measured density is ~1 Hz.m3/kg. Micromachines 2013-03-01 4 1 Article 10.3390/mi4010022 22 33 2072-666X 2013-03-01 doi: 10.3390/mi4010022 Wouter Sparreboom Jan van de Geest Marcel Katerberg Ferry Postma Jeroen Haneveld Jarno Groenesteijn Theo Lammerink Remco Wiegerink Joost Lötters http://www.mdpi.com/2072-666X/4/1/9 We present a disposable, normally closed, non-contact dispensing valve for the sub-µL range. The miniaturized solenoid valve (diameter: 8 mm, height: 27.25 mm) is compatible to standard Luer-Lock interfaces. A highly dynamic actuation principle enables opening times down to 1 ms. The dispensing performance was evaluated for water (η = 1.03 mPas) and a 66% (w/w) glycerol/water solution (η = 16.98 mPas), at pressures varying from 200 to 800 mbar. The experimentally determined minimal dispensing volume was 163 nL (CV 1.6%) for water and 123 nL (CV 4.5%) for 66% (w/w) glycerol/water. The low-cost polymer valve enables high precision dispensing of liquid volumes down to the lower end of the sub-µL range comparable to high-end non-disposable micro-dispensing valves. Micromachines 2013-02-28 4 1 Article 10.3390/mi4010009 9 21 2072-666X 2013-02-28 doi: 10.3390/mi4010009 Stefan Bammesberger Sabrina Kartmann Laurent Tanguy Dong Liang Klaus Mutschler Andreas Ernst Roland Zengerle Peter Koltay http://www.mdpi.com/2072-666X/4/1/1 Self-driven microfluidic devices enable fully autonomous handling of very small volumes of liquid samples and reagents. However, many applications require an active control mechanism to trigger self-driven flow in microchannels. Here, we report on capillary soft valves (CSVs), which enable stopping a liquid filling front at a precise location inside a microchannel and can resume flow of liquid upon simple actuation. The working mechanism of a CSV is based on a barrier of capillary pressure induced by an abruptly expanding microchannel. We discuss the influence of wetting conditions on the performance of a CSV and the effect of elevated temperatures on a CSV in its closed state. We introduce design features such as pillars and cavities, as well as fabrication techniques for rounded microchannels, which all may broaden the applicability and robustness of CSVs in microfluidic devices. Finally, we present CSV having multiple inlet channels. CSVs further diversify the toolbox of microfluidic functionalities and yet are simple to implement, fabricate and actuate. Micromachines 2013-01-24 4 1 Article 10.3390/mi4010001 1 8 2072-666X 2013-01-24 doi: 10.3390/mi4010001 Martina Hitzbleck Emmanuel Delamarche http://www.mdpi.com/2072-666X/3/4/615 Despite the advancements made in drug delivery systems over the years, many challenges remain in drug delivery systems for treating chronic diseases at the personalized medicine level. The current urgent need is to develop novel strategies for targeted therapy of chronic diseases. Due to their unique properties, microelectromechanical systems (MEMS) technology has been recently engineered as implantable drug delivery systems for disease therapy. This review examines the challenges faced in implementing implantable MEMS drug delivery systems in vivo and the solutions available to overcome these challenges. Micromachines 2012-11-14 3 4 Review 10.3390/mi3040615 615 631 2072-666X 2012-11-14 doi: 10.3390/mi3040615 Danny Tng Rui Hu Peiyi Song Indrajit Roy Ken-Tye Yong http://www.mdpi.com/2072-666X/3/4/604 Femtosecond laser irradiation followed by chemical etching (FLICE) with hydrogen fluoride (HF) is an emerging technique for the fabrication of directly buried, three-dimensional microfluidic channels in silica. The procedure, as described in literature, consists of irradiating a silica slab followed by chemical etching using hydrogen fluoride. With aqueous HF the etching process is diffusion-limited and is self-terminating, leading to maximum microchannel lengths of about 1.5 mm, while the use of low-pressure gaseous HF etchant can quickly produce 3 mm long channels with an aspect ratio (Length/Diameter) higher than 25. By utilizing this methodology the aspect ratio is not constant, but depends on the length of the channel. When the microchannel is short the aspect ratio increases quickly until it reaches a maximum length at around 1400 µm. Thereafter the aspect ratio starts to decrease slowly. In this paper we present a variation of the low-pressure gaseous HF etching method, which is based on the dynamic displacement of the etchant. This method results in a 13% increase in the aspect ratio (L/D = 29) at the expense of a low etching speed (4 µm/min). Micromachines 2012-09-28 3 4 Article 10.3390/mi3040604 604 614 2072-666X 2012-09-28 doi: 10.3390/mi3040604 Francesco Venturini Maurizio Sansotera Rebeca Martinez Vazquez Roberto Osellame Giulio Cerullo Walter Navarrini http://www.mdpi.com/2072-666X/3/3/582 A distributed modeling approach has been developed to describe the dynamic behavior of ring resonators. The model includes the effect of large amplitudes around primary resonance frequencies, material and electrostatic nonlinearities. Through a combination of geometric and material nonlinearities, closed-form expression for third-order nonlinearity in mechanical stiffness of bulk-mode ring resonators is obtained. Moreover, to avoid dynamic pull-in instability, the choices of the quality factor, ac-drive and DC-bias voltages of the ring resonators, with a given geometry are limited by a resonant pull-in condition. Using the perturbation technique and the method of harmonic balance, the expressions for describing the effect of nonlinearities on the resonance frequency and displacement are derived. The results are discussed in detail, showing the effect of varying operating conditions and the quality factor on the harmonic distortions and third-order intermodulation distortion. The detailed nonlinear modeling and distortion analysis are applied as appropriate tools to design bulk-mode ring resonators with low motional resistance and high linearity. Micromachines 2012-08-22 3 3 Article 10.3390/mi3030582 582 603 2072-666X 2012-08-22 doi: 10.3390/mi3030582 Abolfazl Bijari Sayyed-Hossein Keshmiri Farshad Babazadeh http://www.mdpi.com/2072-666X/3/3/574 Here we present an electrical lysis throughput of 600 microliters per minute at high cell density (108 yeast cells per ml) with 90% efficiency, thus improving the current common throughput of one microliter per minute. We also demonstrate the extraction of intracellular luciferase from mammalian cells with efficiency comparable to off-chip bulk chemical lysis. The goal of this work is to develop a sample preparation module that can act as a stand-alone device or be integrated to other functions already demonstrated in miniaturized devices, including sorting and analysis, towards a true lab-on-a-chip. Micromachines 2012-08-16 3 3 Communication 10.3390/mi3030574 574 581 2072-666X 2012-08-16 doi: 10.3390/mi3030574 Guillaume Mernier Rodrigo Martinez-Duarte Rajwinder Lehal Freddy Radtke Philippe Renaud http://www.mdpi.com/2072-666X/3/3/550 Microfabrication has greatly matured and proliferated in use amongst many disciplines. There has been great interest in micromachined flow sensors due to the benefits of miniaturization: low cost, small device footprint, low power consumption, greater sensitivity, integration with on-chip circuitry, etc. This paper reviews the theory of thermal flow sensing and the different configurations and operation modes available. Material properties relevant to micromachined thermal flow sensing and selection criteria are also presented. Finally, recent applications of micromachined thermal flow sensors are presented. Detailed tables of the reviewed devices are included. Micromachines 2012-07-23 3 3 Review 10.3390/mi3030550 550 573 2072-666X 2012-07-23 doi: 10.3390/mi3030550 Jonathan T. W. Kuo Lawrence Yu Ellis Meng http://www.mdpi.com/2072-666X/3/3/542 This paper compares the design and performance of kink actuators, a modified version of the bent-beam thermal actuator, to the standard chevron-shaped designs. A variety of kink and chevron actuator designs were fabricated from polysilicon. While the actuators were electrically probed, these designs were tested using a probe station connected to a National Instruments (NI) controller that uses LabVIEW to extract the displacement results via image processing. The displacement results were then used to validate the thermal-electric-structural simulations produced by COMSOL. These results, in turn, were used to extract the stiffness for both actuator types. The data extracted show that chevron actuators can have larger stiffness values with increasing offsets, but at the cost of lower amplification factors. In contrast, kink actuators showed a constant stiffness value equivalent to the chevron actuator with the highest amplification factor. The kink actuator also had larger amplification factors than chevrons at all designs tested. Therefore, kink actuators are capable of longer throws at lower power levels than the standard chevron designs. Micromachines 2012-07-06 3 3 Article 10.3390/mi3030542 542 549 2072-666X 2012-07-06 doi: 10.3390/mi3030542 Ehab Rawashdeh Ayman Karam Ian G. Foulds http://www.mdpi.com/2072-666X/3/2/529 Single-cell studies of phenotypic heterogeneity reveal more information about pathogenic processes than conventional bulk-cell analysis methods. By enabling high-resolution structural and functional imaging, a single-cell three-dimensional (3D) imaging system can be used to study basic biological processes and to diagnose diseases such as cancer at an early stage. One mechanism that such systems apply to accomplish 3D imaging is rotation of a single cell about a fixed axis. However, many cell rotation mechanisms require intricate and tedious microfabrication, or fail to provide a suitable environment for living cells. To address these and related challenges, we applied numerical simulation methods to design new microfluidic chambers capable of generating fluidic microvortices to rotate suspended cells. We then compared several microfluidic chip designs experimentally in terms of: (1) their ability to rotate biological cells in a stable and precise manner; and (2) their suitability, from a geometric standpoint, for microscopic cell imaging. We selected a design that incorporates a trapezoidal side chamber connected to a main flow channel because it provided well-controlled circulation and met imaging requirements. Micro particle-image velocimetry (micro-PIV) was used to provide a detailed characterization of flows in the new design. Simulated and experimental results demonstrate that a trapezoidal side chamber represents a viable option for accomplishing controlled single cell rotation. Further, agreement between experimental and simulated results confirms that numerical simulation is an effective method for chamber design. Micromachines 2012-06-15 3 2 Article 10.3390/mi3020529 529 541 2072-666X 2012-06-15 doi: 10.3390/mi3020529 Wenjie Zhang David H. Frakes Haithem Babiker Shih-hui Chao Cody Youngbull Roger H. Johnson Deirdre R. Meldrum http://www.mdpi.com/2072-666X/3/2/509 This paper reports on design, fabrication and characterization of high-Q MEMS resonators to be used in optical applications like laser displays and LIDAR range sensors. Stacked vertical comb drives for electrostatic actuation of single-axis scanners and biaxial MEMS mirrors were realized in a dual layer polysilicon SOI process. High Q-factors up to 145,000 have been achieved applying wafer level vacuum packaging technology including deposition of titanium thin film getters. The effective reduction of gas damping allows the MEMS actuator to achieve large amplitudes at high oscillation frequencies while driving voltage and power consumption can be minimized. Exemplarily shown is a micro scanner that achieves a total optical scan angle of 86 degrees at a resonant frequency of 30.8 kHz, which fulfills the requirements for HD720 resolution. Furthermore, results of a new wafer based glass-forming technology for fabrication of three dimensionally shaped glass lids with tilted optical windows are presented. Micromachines 2012-06-06 3 2 Article 10.3390/mi3020509 509 528 2072-666X 2012-06-06 doi: 10.3390/mi3020509 Ulrich Hofmann Joachim Janes Hans-Joachim Quenzer http://www.mdpi.com/2072-666X/3/2/492 In the last seven years, optoelectronic tweezers using optically-induced dielectrophoretic (ODEP) force have been explored experimentally with much success in manipulating micro/nano objects. However, not much has been done in terms of in-depth understanding of the ODEP-based manipulation process or optimizing the input physical parameters to maximize ODEP force. We present our work on analyzing two significant influencing factors in generating ODEP force on a-Si:H based ODEP chips: (1) the waveforms of the AC electric potential across the fluidic medium in an ODEP chip based microfluidic platform; and (2) optical spectrum of the light image projected onto the ODEP chip. Theoretical and simulation results indicate that when square waves are used as the AC electric potential instead of sine waves, ODEP force can double. Moreover, numerical results show that ODEP force increases with increasing optical frequency of the projected light on an ODEP chip following the Fermi-Dirac function, validating that the optically-induced dielectrophoresis force depends strongly on the electron-hole carrier generation phenomena in optoelectronic materials. Qualitative experimental results that validate the numerical results are also presented in this paper. Micromachines 2012-05-16 3 2 Article 10.3390/mi3020492 492 508 2072-666X 2012-05-16 doi: 10.3390/mi3020492 Wenfeng Liang Shue Wang Zaili Dong Gwo-Bin Lee Wen J. Li http://www.mdpi.com/2072-666X/3/2/480 Flexible structures are the main components in many precision measuring and research systems. They provide miniaturization, repeatability, minimal damping, low measuring forces, and very high resolution. This article focuses on the modeling, development, and comparison of three typical flexible micro- nano-structures: flexible helicoids, atomic force microscopy (AFM) cantilevers, and concave notch hinges. Our theory yields results which allow us to increase the accuracy and functionality of these structures in new fields of application such as the modeling of helicoidal DNA molecules’ mechanics, the definition of instantaneous center of rotation in concave flexure notch hinges, and the estimation of the increase of spring constants and resolution at higher mode vibration in AFM cantilevers with an additional concentrated and end extended mass. We developed the original kinetostatic, reverse conformal mapping of approximating contours, and non-linear thermomechanical fluctuation methods for calculation, comparison, and research of the micromechanical structures. These methods simplify complicated solutions in micro elasticity but provide them with necessary accuracy. All our calculation results in this article and in all corresponding referenced author’s publications are in a good agreement with experimental and finite element modeling data within 10% or less. Micromachines 2012-05-16 3 2 Article 10.3390/mi3020480 480 491 2072-666X 2012-05-16 doi: 10.3390/mi3020480 Yakov Tseytlin http://www.mdpi.com/2072-666X/3/2/462 This paper presents a novel, highly sensitive and ultra-small fluorescent detection system, including an autonomous capillary fluid manipulation chip. The optical detector integrates a LED light source, all necessary optical components, and a photodiode with preamplifier into one package of about 2 cm × 2 cm × 2 cm. Also, the low-cost and simple pumpless microfluidic device works well in sample preparation and manipulation. This chip consists of capillary stop valves and trigger valves which are fabricated by lithography and then bonded with a polydimethylsiloxane-ethylene oxide polymer polydimethylsiloxane (PEO-PDMS) cover. The contact angle of the PEO-PDMS can be adjusted by changing the concentration of the PEO. Hence, the fluidic chip can achieve functionalities such as timing features and basic logical functions. The prototype has been tested by fluorescence dye 5-Carboxyfluorescein (5-FAM) dissolved into the solvent DMSO (Dimethyl Sulfoxide). The results prove a remarkable sensitivity at a pico-scale molar, around 1.08 pM. The low-cost and miniaturized optical detection system, with a self-control capillary-driven microfluidic chip developed in this work, can be used as the crucial parts in portable biochemical detection applications and point of care testing. Micromachines 2012-05-10 3 2 Article 10.3390/mi3020462 462 479 2072-666X 2012-05-10 doi: 10.3390/mi3020462 Mingjin Yao Girish Shah Ji Fang http://www.mdpi.com/2072-666X/3/2/442 Hydrodynamically confined flow device technology is a young research area with high practical application potential in surface processing, assay development, and in various areas of single cell research. Several variants have been developed, and most recently, theoretical and conceptual studies, as well as fully developed automated systems, were presented. In this article we review concepts, fabrication strategies, and application areas of hydrodynamically confined flow (HCF) devices. Micromachines 2012-05-10 3 2 Review 10.3390/mi3020442 442 461 2072-666X 2012-05-10 doi: 10.3390/mi3020442 Alar Ainla Gavin Jeffries Aldo Jesorka http://www.mdpi.com/2072-666X/3/2/427 In this paper, a low-cost yet effective method of irreversible bonding between two elastomeric polydimethylsiloxane (PDMS) interfaces using Piranha solution is investigated. Piranha solutions at a weight ratio of 3:1 using different acids and hydrogen peroxide were attempted. The average tensile strengths of the device bonded with concentrated sulfuric acid-based piranha solution and nitric acid-based piranha solution were found to be 200 ± 20 kPa and 100 ± 15 kPa respectively. A PDMS surface treated with Piranha Solution demonstrated an increase in hydrophilicity. In addition, relatively straightforward swelling studies of PDMS using a weight loss method with common organic solvents were also investigated. Experimental results show that hexane, toluene, ethyl acetate, n-propyl alcohol and acetone swell PDMS significantly over a duration of up to 1 h and above; PDMS samples reached a steady state of swelling only after 5 min of immersion in other solvents. This will enable researchers to develop devices for the future according to the interaction between the material and the solvents in contact. Micromachines 2012-05-04 3 2 Article 10.3390/mi3020427 427 441 2072-666X 2012-05-04 doi: 10.3390/mi3020427 Kai-Seng Koh Jitkai Chin Joanna Chia Choon-Lai Chiang http://www.mdpi.com/2072-666X/3/2/413 Temperature induced frequency shifts may compromise the sensor response of polymer coated acoustic wave gas-phase sensors operating in environments of variable temperature. To correct the sensor data with the temperature response of the sensor the latter must be known. This study presents and discusses temperature frequency characteristics (TFCs) of solid hexamethyldisiloxane (HMDSO) polymer coated sensor resonators using the Rayleigh surface acoustic wave (RSAW) mode on ST-cut quartz. Using a RF-plasma polymerization process, RSAW sensor resonators optimized for maximum gas sensitivity have been coated with chemosensitive HMDSO films at 4 different thicknesses: 50, 100, 150 and 250 nm. Their TFCs have been measured over a (−100 to +110) °C temperature range and compared to the TFC of an uncoated device. An exponential 2,500 ppm downshift of the resonant frequency and a 40 K downshift of the sensor’s turn-over temperature (TOT) are observed when the HMDSO thickness increases from 0 to 250 nm. A partial temperature compensation effect caused by the film is also observed. A third order polynomial fit provides excellent agreement with the experimental TFC curve. The frequency downshift due to mass loading by the film, the TOT and the temperature coefficients are unambiguously related to each other. Micromachines 2012-05-02 3 2 Article 10.3390/mi3020413 413 426 2072-666X 2012-05-02 doi: 10.3390/mi3020413 Karekin D. Esmeryan Ivan D. Avramov Ekaterina I. Radeva http://www.mdpi.com/2072-666X/3/2/396 Precise mass flow control is an essential requirement for novel, small-scale fluidic systems. However, a small-volume, low-leakage proportional control valve for minute fluid flows has not yet been designed or manufactured. A survey is therefore made of the primary design considerations of a micromachined, proportional control valve. Performance requirements are identified based on various applications. Valve operating principles and actuation schemes presented in the literature are evaluated with respect to functionality and technological feasibility. Proceeding from these analyses, we identify the design concepts and actuation schemes that we think are best suited for the fabrication of the intended microvalve. Micromachines 2012-04-27 3 2 Article 10.3390/mi3020396 396 412 2072-666X 2012-04-27 doi: 10.3390/mi3020396 Maarten S. Groen Dannis M. Brouwer Remco J. Wiegerink Joost C. Lötters http://www.mdpi.com/2072-666X/3/2/379 This paper presents a low-power hybrid thermopneumatic microvalve with an electrostatic hold and integrated valve plate position sensing. This combination of actuators in a single structure enables a high throw and force actuator with low energy consumption, a combination that is difficult to otherwise achieve. The completed 7.5 mm × 10.3 mm × 1.5 mm valve has an open flow rate of 8 sccm at 600 Pa, a leak rate of 2.2 × 10−3 sccm at 115 kPa, a open-to-closed fluidic conductance ratio of nearly one million, an actuation time of 430 ms at 250 mW, and a required power of 90 mW while closed. It additionally requires no power to open, and has a built-in capacitive position sensor with a sensitivity of 9.8 fF/kPa. The paper additionally presents analytical models of the valve components, design tradeoffs, and guidelines for achieving an optimized device. Micromachines 2012-04-27 3 2 Article 10.3390/mi3020379 379 395 2072-666X 2012-04-27 doi: 10.3390/mi3020379 Joseph A. Potkay Kensall D. Wise http://www.mdpi.com/2072-666X/3/2/364 Shock/boundary layer interaction (SBLI) is an undesirable phenomenon, occurring in high-speed propulsion systems. The conventional method to manipulate and control SBLI is using a bleed system that involves the removal of a certain amount of mass of the inlet flow to control boundary layer separation. However, the system requires a larger nacelle to compensate the mass loss, larger nacelles contribute to additional weight and drag and reduce the overall performance. This study investigates a novel type of flow control device called micro-ramps, a part of the micro vortex generators (VGs) family that intends to replace the bleed technique. Micro-ramps produce pairs of counter-rotating streamwise vortices, which help to suppress SBLI and reduce the chances of flow separation. Experiments were done at Mach 5 with two micro-ramp models of different sizes. Schlieren photography, surface flow visualization and infrared thermography were used in this investigation. The results revealed the detailed flow characteristics of the micro-ramp, such as the primary and secondary vortices. This helps us to understand the overall flow physics of micro-ramps in hypersonic flow and their application for SBLI control. Micromachines 2012-04-26 3 2 Article 10.3390/mi3020364 364 378 2072-666X 2012-04-26 doi: 10.3390/mi3020364 Mohd R. Saad Hossein Zare-Behtash Azam Che-Idris Konstantinos Kontis http://www.mdpi.com/2072-666X/3/2/345 We have investigated the selective epitaxial growth of GeSi bulk material on silicon-on-insulator substrates by reduced pressure chemical vapor deposition. We employed AFM, SIMS, and Hall measurements, to characterize the GeSi heteroepitaxy quality. Optimal growth conditions have been identified to achieve low defect density, low RMS roughness with high selectivity and precise control of silicon content. Fabricated vertical p-i-n diodes exhibit very low dark current density of 5 mA/cm2 at −1 V bias. Under a 7.5 V/µm E-field, GeSi alloys with 0.6% Si content demonstrate very strong electro-absorption with an estimated effective ∆α/α around 3.5 at 1,590 nm. We compared measured ∆α/α performance to that of bulk Ge. Optical modulation up to 40 GHz is observed in waveguide devices while small signal analysis indicates bandwidth is limited by device parasitics. Micromachines 2012-04-26 3 2 Article 10.3390/mi3020345 345 363 2072-666X 2012-04-26 doi: 10.3390/mi3020345 Ying Luo Xuezhe Zheng Guoliang Li Ivan Shubin Hiren Thacker Jin Yao Jin-Hyoung Lee Dazeng Feng Joan Fong Cheng-Chih Kung Shirong Liao Roshanak Shafiiha Mehdi Asghari Kannan Raj Ashok V. Krishnamoorthy John E. Cunningham http://www.mdpi.com/2072-666X/3/2/331 Increasing world-wide energy use and growing population growth presents a critical need for enhanced energy efficiency and sustainability. One method to address this issue is via waste heat scavenging. In this approach, thermal energy that is normally expelled to the environment is transferred to a secondary device to produce useful power output. This paper investigates a novel MEMS-based boiler designed to operate as part of a small-scale energy scavenging system. For the first time, fabrication and operation of the boiler is presented. Boiler operation is based on capillary action that drives working fluid from surrounding reservoirs across a heated surface. Pressure is generated as working fluid transitions from liquid to vapor in an integrated steamdome. In a full system application, the steam can be made available to other MEMS-based devices to drive final power output. Capillary channels are formed from silicon substrates with 100 µm widths. Varying depths are studied that range from 57 to 170 µm. Operation of the boiler shows increasing flow-rates with increasing capillary channel depths. Maximum fluid mass transfer rates are 12.26 mg/s from 170 µm channels, an increase of 28% over 57 µm channel devices. Maximum pressures achieved during operation are 229 Pa. Micromachines 2012-04-26 3 2 Article 10.3390/mi3020331 331 344 2072-666X 2012-04-26 doi: 10.3390/mi3020331 Suvhashis Thapa Emmanuel Ogbonnaya Christopher Champagne Leland Weiss http://www.mdpi.com/2072-666X/3/2/325 A time of flight sensor has been equipped with a sensing wire parallel to the flow direction (flow parallel wire, FPW). A heat pulse is generated with a coil in the flow channel. The FPW has a center tap allowing its upstream and downstream parts to join in a half bridge. When a heat pulse passes the FPW, a large output peak is generated. The time between heat pulse generation and recording the peak maximum is only marginally affected by the properties of the fluid. With a combination of two FPWs, a measuring range of approximately 0.01–0.5 m/s can be achieved. Micromachines 2012-04-26 3 2 Article 10.3390/mi3020325 325 330 2072-666X 2012-04-26 doi: 10.3390/mi3020325 Christof Gerhardy Werner Karl Schomburg http://www.mdpi.com/2072-666X/3/2/315 A novel capacitive tactile sensor using a polyurethane thin film is proposed in this paper. In previous studies, capacitive tactile sensors generally had an air gap between two electrodes in order to enhance the sensitivity. In this study, there is only polyurethane thin film and no air gap between the electrodes. The sensitivity of this sensor is higher than the previous capacitive tactile sensors because the polyurethane is a fairly flexible elastomer and the film is very thin (about 1 µm). The polyurethane film is formed by spin-coating and etched back from 6 µm to 1 µm using 48% sulfuric acid. As a result of evaluation, the sensitivity of the developed sensor (diameter is 1 mm) is 1.3 pF/Pa (800 pF/N considering the sensing area). Young’s modulus of the thin polyurethane film was estimated to be 20 kPa. Micromachines 2012-04-10 3 2 Article 10.3390/mi3020315 315 324 2072-666X 2012-04-10 doi: 10.3390/mi3020315 Masato Suzuki Tomokazu Takahashi Seiji Aoyagi http://www.mdpi.com/2072-666X/3/2/295 Flow sensors are the key elements in most systems for monitoring and controlling fluid flows. With the introduction of MEMS thermal flow sensors, unprecedented performances, such as ultra wide measurement ranges, low power consumptions and extreme miniaturization, have been achieved, although several critical issues have still to be solved. In this work, a systematic approach to the design of integrated thermal flow sensors, with specification of resolution, dynamic range, power consumption and pressure insertion loss is proposed. All the critical components of the sensors, namely thermal microstructure, package and read-out interface are examined, showing their impact on the sensor performance and indicating effective optimization strategies. The proposed design procedures are supported by experiments performed using a recently developed test chip,including several different sensing structures and a flexible electronic interface. Micromachines 2012-04-10 3 2 Article 10.3390/mi3020295 295 314 2072-666X 2012-04-10 doi: 10.3390/mi3020295 Paolo Bruschi Massimo Piotto http://www.mdpi.com/2072-666X/3/2/279 This paper presents an integrated digitally controllable microfluidic system for continuous solution supply with a real-time concentration control. This system contains multiple independently operating mixing modules, each integrated with two vortex micropumps, two Tesla valves and a micromixer. The interior surface of the system is made of biocompatible materials using a polymer micro-fabrication process and thus its operation can be applied to chemicals and bio-reagents. In each module, pumping of fluid is achieved by the vortex micropump working with the rotation of a micro-impeller. The downstream fluid mixing is based on mechanical vibrations driven by a lead zirconate titanate ceramic diaphragm actuator located below the mixing chamber. We have conducted experiments to prove that the addition of the micro-pillar structures to the mixing chamber further improves the mixing performance. We also developed a computer-controlled automated driver system to control the real-time fluid mixing and concentration regulation with the mixing module array. This research demonstrates the integration of digitally controllable polymer-based microfluidic modules as a fully functional system, which has great potential in the automation of many bio-fluid handling processes in bio-related applications. Micromachines 2012-03-29 3 2 Article 10.3390/mi3020279 279 294 2072-666X 2012-03-29 doi: 10.3390/mi3020279 Raymond H. W. Lam Wen J. Li http://www.mdpi.com/2072-666X/3/2/270 We propose a concept of a flexible sensor array using a novel capacitive force sensor not having a vulnerable electrode on the force applied site. It has a polymer domed structure inside which silicone oil is contained. When the force is applied, the oil is pushed into the surrounding thin channels, where the change in capacitance due to the inflowing dielectric oil is measured between two electrodes on the top and bottom surfaces of the channel. Since the channel does not have a directly applied external force to it, the electrodes do not suffer from damage problems. The change in capacitance was simulated using a simplified flow model. The first trial device of the sensing element has been fabricated. A sensitivity of 0.05 pF/gf was achieved. Micromachines 2012-03-28 3 2 Article 10.3390/mi3020270 270 278 2072-666X 2012-03-28 doi: 10.3390/mi3020270 Tomokazu Takahashi Masto Suzuki Shota Iwamoto Seiji Aoyagi http://www.mdpi.com/2072-666X/3/2/255 A thermally-actuated micro-electro-mechanical (MEMS) device based on a vibrating silicon membrane has been proposed as a viscosity sensor by the authors. In this paper we analyze the vibration mode of the sensor as it vibrates freely at its natural frequency. Analytical examination is compared to finite element analysis, electrical measurements and the results obtained through real-time dynamic optical surface profilometry. The vertical movement of the membrane due to the applied heat is characterized statically and dynamically. The natural vibration mode is determined to be the (1,1) mode and good correlation is found between the analytical predictions, the simulation analysis, the observed mechanical displacement and the electrical measurements. Micromachines 2012-03-28 3 2 Article 10.3390/mi3020255 255 269 2072-666X 2012-03-28 doi: 10.3390/mi3020255 Ivan Puchades Mustafa Koz Lynn Fuller http://www.mdpi.com/2072-666X/3/2/244 With the commercial availability of integrated microreactor systems, the numbers of chemical processes that are performed nowadays in a continuous flow is growing rapidly. The control over mixing efficiency and homogeneous heating in these reactors allows industrial scale production that was often hampered by the use of large amounts of hazardous chemicals. Accurate actuation and in line measurements of the flows, to have a better control over the chemical reaction, is of added value for increasing reproducibility and a safe production. Micromachines 2012-03-27 3 2 Article 10.3390/mi3020244 244 254 2072-666X 2012-03-27 doi: 10.3390/mi3020244 Sebastiaan A. M. W. van den Broek René Becker Kaspar Koch Pieter J. Nieuwland http://www.mdpi.com/2072-666X/3/2/225 Application fields of micromachined devices are growing very rapidly due to the continuous improvement of three dimensional technologies of micro-fabrication. In particular, applications of micromachined sensors to monitor gas and liquid flows hold immense potential because of their valuable characteristics (e.g., low energy consumption, relatively good accuracy, the ability to measure very small flow, and small size). Moreover, the feedback provided by integrating microflow sensors to micro mass flow controllers is essential to deliver accurately set target small flows. This paper is a review of some application areas in the biomedical field of micromachined flow sensors, such as blood flow, respiratory monitoring, and drug delivery among others. Particular attention is dedicated to the description of the measurement principles utilized in early and current research. Finally, some observations about characteristics and issues of these devices are also reported. Micromachines 2012-03-26 3 2 Review 10.3390/mi3020225 225 243 2072-666X 2012-03-26 doi: 10.3390/mi3020225 Sergio Silvestri Emiliano Schena http://www.mdpi.com/2072-666X/3/2/218 We present the fabrication and evaluation of microdebubblers that are able to remove large bubbles while keeping a very low dead volume. The devices use a polytetrafluoroethylene membrane that is permeable to air in order to filter air bubbles out of an aqueous sample. The dead volume of the devices is less than one microliter, but bubbles as large as 60 microliters can be removed. This simple solution can be very useful for microfluidic devices for chemical or biological analysis that suffer from channel clogging due to the presence of bubbles in their sample. One embodiment is particularly suited for buffer solutions with living cells. Micromachines 2012-03-23 3 2 Communication 10.3390/mi3020218 218 224 2072-666X 2012-03-23 doi: 10.3390/mi3020218 Harald van Lintel Guillaume Mernier Philippe Renaud http://www.mdpi.com/2072-666X/3/2/204 Simple and efficient approaches for filter design at optical frequencies using a large number of coupled microcavities are proposed. The design problem is formulated as an optimization problem with a unique global solution. Various efficient filter designs are obtained at both the drop and through ports. Our approaches are illustrated through a number of examples. Micromachines 2012-03-23 3 2 Review 10.3390/mi3020204 204 217 2072-666X 2012-03-23 doi: 10.3390/mi3020204 Mohamed A. Swillam Osman S. Ahmed Mohamed H. Bakr http://www.mdpi.com/2072-666X/3/1/194 We have realized a micromachined single chip flow sensing system with an ultra-wide dynamic flow range of more than five decades, from 100 nL/h up to more than 10 mL/h. The system comprises both a thermal and a micro Coriolis flow sensor with partially overlapping flow ranges. Micromachines 2012-03-15 3 1 Article 10.3390/mi3010194 194 203 2072-666X 2012-03-15 doi: 10.3390/mi3010194 Joost C. Lötters Theo S.J. Lammerink Jarno Groenesteijn Jeroen Haneveld Remco J. Wiegerink http://www.mdpi.com/2072-666X/3/1/180 New and novel sensing schemes require optical functions with unconventional spatial light distributions, as well as complex spectral functionality. Micro-optical elements have shown some flexibility in their ability to spatially encode phase information using surface relief dielectrics. In this paper, we present a novel optical component that exploits the properties of optically resonant structures to make an azimuthally spatially varying spectral filter. The dispersive properties are quite unique with an angular resonance shift of 28 Deg/nm. This device is fabricated using techniques that are compatible with standard micro-electronic fabrication technologies. Micromachines 2012-03-15 3 1 Article 10.3390/mi3010180 180 193 2072-666X 2012-03-15 doi: 10.3390/mi3010180 Zachary A. Roth Pradeep Srinivasan Menelaos K. Poutous Aaron J. Pung Raymond C. Rumpf Eric G. Johnson http://www.mdpi.com/2072-666X/3/1/168 We present a new effective permittivity (EP) model to accurately calculate surface plasmons (SPs) using the finite-difference time-domain (FDTD) method. The computational representation of physical structures with curved interfaces causes inherent errors in FDTD calculations, especially when the numerical grid is coarse. Conventional EP models improve the errors, but they are not effective for SPs because the SP resonance condition determined by the original permittivity is changed by the interpolated EP values. We perform FDTD simulations using the proposed model for an infinitely-long silver cylinder and gold sphere, and the results are compared with Mie theory. Our model gives better accuracy than the conventional staircase and EP models for SPs. Micromachines 2012-03-14 3 1 Article 10.3390/mi3010168 168 179 2072-666X 2012-03-14 doi: 10.3390/mi3010168 Naoki Okada James B. Cole http://www.mdpi.com/2072-666X/3/1/150 In this paper, a general methodology for the dynamic study of electrostatically actuated droplets is presented. A simplified 1D transient model is developed to investigate the transient response of a droplet to an actuation voltage and to study the effect of geometrical and fluid-thermal properties and electrical parameters on this behavior. First, the general approach for the dynamic droplet motion model is described. All forces acting on the droplet are introduced and presented in a simplified algebraic expression. For the retentive force, the empirically extracted correlations are used, and for the electrostatic actuation force, results from electrostatic finite element simulations are used. The dynamic model is applied to electrowetting induced droplet motion between parallel plates in the case of a single actuation electrode and for an array of electrodes. Using this methodology, the influence of the switching frequency and actuation voltage is studied. Furthermore, a linearized equivalent damped mass—spring model is presented to approximate the dynamic droplet motion. It is shown that the optimal switching frequency can be estimated by twice the natural frequency of the linearized damped mass—spring system. Micromachines 2012-03-14 3 1 Article 10.3390/mi3010150 150 167 2072-666X 2012-03-14 doi: 10.3390/mi3010150 Herman Oprins Bart Vandevelde Martine Baelmans http://www.mdpi.com/2072-666X/3/1/137 Flexible and high-sensitive capacitive sensors are demanded to detect pressure distribution and/or tactile information on a curved surface, hence, wide varieties of polymer-based flexible MEMS sensors have been developed. High-sensitivity may be achieved by increasing the capacitance of the sensor using solid dielectric material while it deteriorates the flexibility. Using air as the dielectric, to maintain the flexibility, sacrifices the sensor sensitivity. In this paper, we demonstrate flexible and highly sensitive capacitive sensor arrays that encapsulate highly dielectric liquids as the dielectric. Deionized water and glycerin, which have relative dielectric constants of approximately 80 and 47, respectively, could increase the capacitance of the sensor when used as the dielectric while maintaining flexibility of the sensor with electrodes patterned on flexible polymer substrates. A reservoir of liquids between the electrodes was designed to have a leak path, which allows the sensor to deform despite of the incompressibility of the encapsulated liquids. The proposed sensor was microfabricated and demonstrated successfully to have a five times greater sensitivity than sensors that use air as the dielectric. Micromachines 2012-03-13 3 1 Article 10.3390/mi3010137 137 149 2072-666X 2012-03-13 doi: 10.3390/mi3010137 Yasunari Hotta Yuhua Zhang Norihisa Miki http://www.mdpi.com/2072-666X/3/1/126 This paper presents an integrated sensor/actuator device with multi-input and multi-output designed on the basis of a standard control representation called a distributed port-Hamiltonian system. The device is made from soft material called an ionic polymer-metal composite (IPMC). The IPMC consists of a base film of a polyelectrolyte gel and a double layer of plated metal electrodes. The electrodes of the experimental IPMC are sectioned, and it is implemented as a control system with four pairs of inputs/outputs. We stabilize the system, and detect changes in dynamics by using the control representation. Micromachines 2012-02-29 3 1 Article 10.3390/mi3010126 126 136 2072-666X 2012-02-29 doi: 10.3390/mi3010126 Gou Nishida Motonobu Sugiura Masaki Yamakita Bernhard Maschke Ryojun Ikeura http://www.mdpi.com/2072-666X/3/1/114 We describe how the amorphous fluoropolymer CYTOP can be advantageously used as a waveguide cladding material in integrated optical circuits suitable for applications in integrated biophotonics. The unique refractive index of CYTOP (n = 1.34) enables the cladding material to be well index-matched to an optically probed sample solution. Furthermore, ultra-high index contrast waveguides can be fabricated, using conventional optical polymers as waveguide core materials, offering a route to large-scale integration of optical functions on a single chip. We discuss applications of this platform to evanescent-wave excitation fluorescence microscopy, passive and/or thermo-electrically-controlled on-chip light manipulation, on-chip light generation, and direct integration with microfluidic circuits through low-temperature bonding. Micromachines 2012-02-29 3 1 Article 10.3390/mi3010114 114 125 2072-666X 2012-02-29 doi: 10.3390/mi3010114 Kristjan Leosson Björn Agnarsson http://www.mdpi.com/2072-666X/3/1/101 A thin-film grating on a curved substrate functions as a highly reflective and wavelength sensitive mirror for a diverging wave that has the same curvature as the substrate. In this paper we propose a cylindrical cavity surrounded by a curved resonant grating wall, and describe its resonance characteristics. Through finite-difference time-domain (FDTD) simulation we have clarified that this type of cavity supports two resonance modes: one is confined by Fresnel reflection and the other by resonance reflection of the wall. We have also demonstrated that the latter mode exhibits a Q factor several orders of magnitude higher than that of the former mode. Micromachines 2012-02-27 3 1 Article 10.3390/mi3010101 101 113 2072-666X 2012-02-27 doi: 10.3390/mi3010101 Yasuo Ohtera Shohei Iijima Hirohito Yamada http://www.mdpi.com/2072-666X/3/1/78 Prognostics is seen as a key component of health usage monitoring systems, where prognostics algorithms can both detect anomalies in the behavior/performance of a micro-device/system, and predict its remaining useful life when subjected to monitored operational and environmental conditions. Light Emitting Diodes (LEDs) are optoelectronic micro-devices that are now replacing traditional incandescent and fluorescent lighting, as they have many advantages including higher reliability, greater energy efficiency, long life time and faster switching speed. For some LED applications there is a requirement to monitor the health of LED lighting systems and predict when failure is likely to occur. This is very important in the case of safety critical and emergency applications. This paper provides both experimental and theoretical results that demonstrate the use of prognostics and health monitoring techniques for high power LEDs subjected to harsh operating conditions. Micromachines 2012-02-24 3 1 Article 10.3390/mi3010078 78 100 2072-666X 2012-02-24 doi: 10.3390/mi3010078 Thamo Sutharssan Stoyan Stoyanov Chris Bailey Yasmine Rosunally http://www.mdpi.com/2072-666X/3/1/62 Fabrication and performance of a functional photonic-microfluidic flow cytometer is demonstrated. The devices are fabricated on a Pyrex substrate by photolithographically patterning the microchannels and optics in a SU-8 layer that is sealed via a poly(dimethylsiloxane) (PDMS) layer through a unique chemical bonding method. The resulting devices eliminate the free-space excitation optics through integration of microlenses onto the chip to mimic conventional cytometry excitation. Devices with beam waists of 6 μm and 12 μm in fluorescent detection and counting tests using 2.5 and 6 μm beads-show CVs of 9%–13% and 23% for the two devices, respectively. These results are within the expectations for a conventional cytometer (5%–15%) and demonstrate the ability to integrate the photonic components for excitation onto the chip and the ability to maintain the level of reliable detection. Micromachines 2012-02-15 3 1 Article 10.3390/mi3010062 62 77 2072-666X 2012-02-15 doi: 10.3390/mi3010062 Benjamin R. Watts Thomas Kowpak Zhiyi Zhang Chang-Qing Xu Shiping Zhu Xudong Cao Min Lin http://www.mdpi.com/2072-666X/3/1/55 Collimated Gaussian beams are efficiently localized at the apex of a metal-coated axicon prism by surface plasmon excitations. We observed the light scattered at the apex and the light reflected by the prism. Intense scattered light was observed with the radial polarization incidence. Further, each incidence of the radial, azimuthal, and linear polarizations provided field distributions of bright and dark intensities in the reflected images according to the surface plasmon excitation. We have demonstrated that surface plasmon waves are excited at the sides of the prism in the Kretschmann configuration and that they converge to its apex. Micromachines 2012-02-08 3 1 Article 10.3390/mi3010055 55 61 2072-666X 2012-02-08 doi: 10.3390/mi3010055 Atsushi Ono Hiroki Sano Wataru Inami Yoshimasa Kawata http://www.mdpi.com/2072-666X/3/1/45 The dispersion of the fundamental super mode confined along the boundary between a multilayer metal-insulator (MMI) stack and a dielectric coating is theoretically analyzed and compared to the dispersion of surface waves on a single metal-insulator (MI) boundary. Based on the classical Kretschmann setup, the MMI system is experimentally tested as an anisotropic material to exhibit plasmonic behavior and a candidate of “metametal” to engineer the preset surface plasmon frequency of conventional metals for optical sensing applications. The conditions to obtain artificial surface plasmon frequency are thoroughly studied, and the tuning of surface plasmon frequency is verified by electromagnetic modeling and experiments. The design rules drawn in this paper would bring important insights into applications such as optical lithography, nano-sensing and imaging. Micromachines 2012-02-01 3 1 Article 10.3390/mi3010045 45 54 2072-666X 2012-02-01 doi: 10.3390/mi3010045 Ruoxi Yang Xiaoyue Huang Zhaolin Lu http://www.mdpi.com/2072-666X/3/1/36 A novel angle detector for laser beams is designed in this paper. It takes advantage of grating coupling to couple the incident light into a slab waveguide; and, the incident light’s angle can be determined by reading the outputs of light detectors within the waveguide. This device offers fast-responding on-chip detection of laser beam’s angle. Compared to techniques based on quadrant photodiodes or lateral effect photodiodes, the device in this paper has far greater detectable range (up to a few degrees, to be specific). Performance of the laser angle detector in this paper is demonstrated by finite-difference-time-domain simulations. Numerical results show that, the detectable angle range can be adjusted by several design parameters and can reach [−4°, 4°]. The laser beam angle detector in this paper is expected to find various applications such as ultra-fast optical interconnects. Micromachines 2012-02-01 3 1 Article 10.3390/mi3010036 36 44 2072-666X 2012-02-01 doi: 10.3390/mi3010036 Tapas Kumar Saha Mingyu Lu Zhenqiang Ma Weidong Zhou http://www.mdpi.com/2072-666X/3/1/28 This paper presents a new tuning mechanism for millimetre-wave BPF based on deflection of the BCB membrane of BCB packaging cap. A 3-pole parallel-coupled microstrip filter operating at 60 GHz is first implemented on 30 µm-thick BCB polymer substrate and then BCB-capped through our new anti-adhesion layer assisted wafer-level transfer technique. Gold electrodes are fabricated on top of the BCB cap for DC actuation. The implemented BCB capped BPF showed the tuning range of 1.49 GHz from 63.36 GHz to 64.85 GHz with the associated insertion losses of −9.7 dB and −9.4 dB and the return losses better than −11 dB over the tuning range. Micromachines 2012-01-06 3 1 Article 10.3390/mi3010028 28 35 2072-666X 2012-01-06 doi: 10.3390/mi3010028 Seonho Seok Janggil Kim Nathalie Rolland Paul-Alain Rolland http://www.mdpi.com/2072-666X/3/1/21 We prepared high-density plasmonic nanostructures on a glass substrate. By using soft UV nanoimprint lithography, gold nanodisks with a diameter of 65 nm were obtained on an area of 1 mm2. We tested these gold nanosensors in the biotin/streptavidin system to study their selectivity and sensitivity of detection. The prepared gold nanodisks could detect streptavidin at 10 pM. Micromachines 2012-01-06 3 1 Article 10.3390/mi3010021 21 27 2072-666X 2012-01-06 doi: 10.3390/mi3010021 Grégory Barbillon http://www.mdpi.com/2072-666X/3/1/10 We present a switchable thermal interface based on an array of discrete liquid droplets initially confined on hydrophilic islands on a substrate. The droplets undergo reversible morphological transition into a continuous liquid film when they are mechanically compressed by an opposing substrate to create low-thermal resistance heat conduction path. We investigate a criterion for reversible switching in terms of hydrophilic pattern size and liquid volume. The dependence of the liquid morphology and rupture distance on the diameter and areal fraction of hydrophilic islands, liquid volumes, as well as loading pressure is also characterized both theoretically and experimentally. The thermal resistance in the on-state is experimentally characterized for ionic liquids, which are promising for practical applications due to their negligible vapor pressure. A life testing setup is constructed to evaluate the reliability of the interface under continued switching conditions at relatively high switching frequencies. Micromachines 2012-01-06 3 1 Article 10.3390/mi3010010 10 20 2072-666X 2012-01-06 doi: 10.3390/mi3010010 Yanbing Jia Gilhwan Cha Yongho Sungtaek Ju http://www.mdpi.com/2072-666X/3/1/1 We describe two novel centrifugal microfluidic platform designs that enable passive pumping of liquids radially inward while the platform is in motion. The first design uses an immiscible liquid to displace an aqueous solution back towards the center of the platform, while the second design uses an arbitrary pumping liquid with a volume of air between it and the solution being pumped. Both designs demonstrated the ability to effectively pump 55% to 60% of the solution radially inward at rotational frequencies as low as 400 rpm (6.7 Hz) to 700 rpm (11.7 Hz). The pumping operations reached completion within 120 s and 400 s respectively. These platform designs for passive pumping of liquids do not require moving parts or complex fabrication techniques. They offer great potential for increasing the number of sequential operations that can be performed on centrifugal microfluidic platforms, thereby reducing a fundamental limitation often associated with these platforms. Micromachines 2011-12-22 3 1 Communication 10.3390/mi3010001 1 9 2072-666X 2011-12-22 doi: 10.3390/mi3010001 Matthew C. R. Kong Adam P. Bouchard Eric D. Salin http://www.mdpi.com/2072-666X/2/4/431 We report in this paper a novel, inexpensive and flexible method for fabricating micrometer- and nanometer-scale three-dimensional (3D) polymer structures using visible light sources instead of ultra-violet (UV) light sources or lasers. This method also does not require the conventional micro-photolithographic technique (i.e., photolithographic masks) for patterning and fabricating polymer structures such as hydrogels. The major materials and methods required for this novel fabrication technology are: (1) any cross-linked network of photoactive polymers (examples of fabricated poly(ethylene glycol) (PEG)-diacrylate hydrogel structures are shown in this paper); (2) an Optically-induced Dielectrophoresis (ODEP) System which includes an “ODEP chip” (i.e., any chip that changes its surface conductivity when exposed to visible light), an optical microscope, a projector, and a computer; and (3) an animator software hosted on a computer that can generate virtual or dynamic patterns which can be projected onto the “ODEP chip” through the use of a projector and a condenser lens. Essentially, by placing a photosensitive polymer solution inside the microfluidic platform formed by the “ODEP chip” bonded to another substrate, and applying an alternating current (a.c.) electrical potential across the polymer solution (typically ~20 Vp-p at 10 kHz), solid polymer micro/nano structures can then be formed on the “ODEP chip” surface when visible-light is projected onto the chip. The 2D lateral geometry (x and y dimensions) and the thickness (height) of the micro/nano structures are dictated by the image geometry of the visible light projected onto the “ODEP chip” and also the time duration of projection. Typically, after an image projection with intensity ranging from ~0.2 to 0.4 mW/cm2 for 10 s, ~200 nm high structures can be formed. In our current system, the thickness of these polymer structures can be controlled to form from ~200 nanometers to ~3 micrometers structures. However, in the in-plane dimensions, only ~7 μm resolution can be achieved now, due to the optical diffraction limit and the physical dimensions of DMD mirrors in the projector. Nevertheless, with higher quality optical components, the in-plane resolution is expected to be sub-micron. Micromachines 2011-12-13 2 4 Article 10.3390/mi2040431 431 442 2072-666X 2011-12-13 doi: 10.3390/mi2040431 Shue Wang Wenfeng Liang Zaili Dong Vincent G. B. Lee Wen J. Li http://www.mdpi.com/2072-666X/2/4/410 Recent progress in data processing, communications and electronics miniaturization is now enabling the development of low-cost wireless sensor networks (WSN), which consist of spatially distributed autonomous sensor modules that collaborate to monitor real-time environmental conditions unobtrusively and with appropriate levels of spatial and temporal granularity. Recent and future applications of this technology range from preventative maintenance and quality control to environmental modelling and failure analysis. In order to fabricate these low-cost, low-power reliable monitoring platforms, it is necessary to improve the level of sensor integration available today. This paper outlines the microfabrication and characterization results of a multifunctional multisensor unit. An existing fabrication process for Complementary Metal Oxide Semiconductor CMOS-compatible microelectromechanical systems (MEMS) structures has been modified and extended to manufacture temperature, relative humidity, corrosion, gas thermal conductivity, and gas flow velocity sensors on a single silicon substrate. A dedicated signal conditioning circuit layer has been built around this MEMS multisensor die for integration on an existing low-power WSN module. The final unit enables accurate readings and cross-sensitivity compensation thanks to a combination of simultaneous readings from multiple sensors. Real-time communication to the outside world is ensured via radio-frequency protocols, and data collection in a serial memory is also made possible for diagnostics applications. Micromachines 2011-11-03 2 4 Article 10.3390/mi2040410 410 430 2072-666X 2011-11-03 doi: 10.3390/mi2040410 Mathieu Hautefeuille Brendan O’Flynn Frank H. Peters Conor O’Mahony http://www.mdpi.com/2072-666X/2/4/394 In this paper, we describe our all-titanium microelectrode array (tMEA) fabrication process and show that uncoated titanium microelectrodes are fully applicable to measuring field potentials (FPs) from neurons and cardiomyocytes. Many novel research questions require custom designed microelectrode configurations different from the few commercially available ones. As several different configurations may be needed especially in a prototyping phase, considerable time and cost savings in MEA fabrication can be achieved by omitting the additional low impedance microelectrode coating, usually made of titanium nitride (TiN) or platinum black, and have a simplified and easily processable MEA structure instead. Noise, impedance, and atomic force microscopy (AFM) characterization were performed to our uncoated titanium microelectrodes and commercial TiN coated microelectrodes and were supplemented by FP measurements from neurons and cardiomyocytes on both platforms. Despite the increased noise levels compared to commercial MEAs our tMEAs produced good FP measurements from neurons and cardiomyocytes. Thus, tMEAs offer a cost effective platform to develop custom designed electrode configurations and more complex monitoring environments. Micromachines 2011-10-28 2 4 Article 10.3390/mi2040394 394 409 2072-666X 2011-10-28 doi: 10.3390/mi2040394 Tomi Ryynänen Ville Kujala Laura Ylä-Outinen Ismo Korhonen Jarno M.A. Tanskanen Pasi Kauppinen Katriina Aalto-Setälä Jari Hyttinen Erja Kerkelä Susanna Narkilahti Jukka Lekkala http://www.mdpi.com/2072-666X/2/4/385 This paper introduces a simple theoretical model for the response time of thermal flow sensors. Response time is defined here as the time needed by the sensor output signal to reach 63.2% of amplitude due to a change of fluid flow. This model uses the finite-difference method to solve the heat transfer equations, taking into consideration the transient conduction and convection between the sensor membrane and the surrounding fluid. Program results agree with experimental measurements and explain the response time dependence on the velocity and the sensor geometry. Values of the response time vary from about 5 ms in the case of stagnant flow to 1.5 ms for a flow velocity of 44 m/s. Micromachines 2011-10-21 2 4 Article 10.3390/mi2040385 385 393 2072-666X 2011-10-21 doi: 10.3390/mi2040385 Safir Issa Hannes Sturm Walter Lang http://www.mdpi.com/2072-666X/2/4/369 A 16 × 16 digital microfluidic multiplexer is demonstrated. The device makes use of dual-phase AC activation in a bi-layered electrode structure for actuating microdrops independently. A switching arrangement is employed to localize two out-of-phase AC waveforms in one overlapped region of the two-dimensional multiplexer grid. The superimposed AC waveforms overcome the threshold voltage for motion of a local microdrop. The demonstrated dual-phase activation and nonlinear threshold-based motion overcomes the previously-reported microdrop interference effect, as it successfully actuates individual microdrops in systems with multiple neighbouring microdrops. The device is demonstrated with an integrated centre-tap transformer using a 10.0 Vrms input voltage and minimal power consumption. Micromachines 2011-09-28 2 4 Article 10.3390/mi2040369 369 384 2072-666X 2011-09-28 doi: 10.3390/mi2040369 Christopher M. Collier Michael Wiltshire Jacqueline Nichols Brandon Born Emily L. Landry Jonathan F. Holzman http://www.mdpi.com/2072-666X/2/3/356 We report the design, fabrication and characterization of micromachined Parylene structures for self-sealing liquid encapsulation applications. Automatic sealing is enabled through the use of an integrated annular-plate stiction valve which greatly reduces device footprint over in-plane configurations. We achieve automatic wafer-level liquid entrapment without using adhesives or processing at elevated pressures or temperatures. The ability to track changes to the internal liquid volume through the use of electrochemical impedance measurements is also presented. Micromachines 2011-09-08 2 3 Article 10.3390/mi2030356 356 368 2072-666X 2011-09-08 doi: 10.3390/mi2030356 Christian A. Gutierrez Ellis Meng http://www.mdpi.com/2072-666X/2/3/345 This paper presents the fabrication process of a single-chamber planar valveless micropump driven by an external electromagnetic actuator. This micropump features a pair of micro diffuser and nozzle elements used to rectify the fluid flow, and an elastic magnetic membrane used to regulate the pressure in the enclosed fluid chamber. Polydimethylsiloxane (PDMS) is used as the main construction material of this proposed micropump, including the structural substrate and the planar actuation membrane embedded with a thin micro magnet. Both the Finite Element Method and experimental analysis are used to assess the PDMS-membrane actuation under the applied electromagnetic forces and characterize the pump performance at variable working conditions. The resonant frequency of this micropump is identified experimentally and de-ionized (DI) water is loaded to account for the coupling effects of the working fluid. The experimental data was used to demonstrate the reliability of flow rates and how it can be controlled by consistently adjusting the driving frequencies and currents. The proposed micropump is capable of delivering a maximum flow rate of 319.6 μL/min and a maximum hydrostatic backpressure of 950 Pa (9.5 cm H2O). The planar design feature of the pump allows for potential integration of the pump with other PDMS-based microfluidic systems for biomedical applications. Micromachines 2011-07-27 2 3 Article 10.3390/mi2030345 345 355 2072-666X 2011-07-27 doi: 10.3390/mi2030345 Yu Zhou Farid Amirouche http://www.mdpi.com/2072-666X/2/3/344 We have discovered a mistake in our original derivation related to the definition of the apparent conductivity due to orientation averaging. Micromachines 2011-07-25 2 3 Correction 10.3390/mi2030344 344 344 2072-666X 2011-07-25 doi: 10.3390/mi2030344 Jan Stránský Jan Vorel Jan Zeman Michal Sejnoha http://www.mdpi.com/2072-666X/2/3/319 Blood, a complex biological fluid, comprises 45% cellular components suspended in protein rich plasma. These different hematologic components perform distinct functions in vivo and thus the ability to efficiently fractionate blood into its individual components has innumerable applications in both clinical diagnosis and biological research. Yet, processing blood is not trivial. In the past decade, a flurry of new microfluidic based technologies has emerged to address this compelling problem. Microfluidics is an attractive solution for this application leveraging its numerous advantages to process clinical blood samples. This paper reviews the various microfluidic approaches realized to successfully fractionate one or more blood components. Techniques to separate plasma from hematologic cellular components as well as isolating blood cells of interest including certain rare cells are discussed. Comparisons based on common separation metrics including efficiency (sensitivity), purity (selectivity), and throughput will be presented. Finally, we will provide insights into the challenges associated with blood-based separation systems towards realizing true point-of-care (POC) devices and provide future perspectives. Micromachines 2011-07-20 2 3 Article 10.3390/mi2030319 319 343 2072-666X 2011-07-20 doi: 10.3390/mi2030319 Han Wei Hou Ali Asgar S. Bhagat Wong Cheng Lee Sha Huang Jongyoon Han Chwee Teck Lim http://www.mdpi.com/2072-666X/2/2/306 A set of newly synthesized aryl-substituted amides of 16-mercaptohexadecanoic acid (R = 4-OH; 3,5-di-OH) are self-assembled on Au(111) substrate. Self assembled monolayers (SAMs) formed by these molecules are studied by ellipsometry from infrared to visible spectral range. Best fit calculations based on the three-phase optical model are employed in order to determine the average tilt angle of the hydrocarbon chains. The data revealed that the SAMs reside in a crystalline-like environment as the long methylene chains predominantly exist in all-trans conformation. The calculated tilt angle of the hydrocarbon chain is decreased by approximately 12° in comparison with the one for the correspondent long-chain n-alkyl thiols. Strong hydrogen bonded networks were detected between the amide proton and the carbonyl oxygen as well as between hydroxyl groups in the end aryl substituents. The transition dipole moments of the C=O, N-H and O-H modes are oriented almost parallel to the gold surface. Micromachines 2011-06-22 2 2 Article 10.3390/mi2020306 306 318 2072-666X 2011-06-22 doi: 10.3390/mi2020306 Dimiter Tsankov Irena Philipova Kalina Kostova Karsten Hinrichs http://www.mdpi.com/2072-666X/2/2/295 Microrobotics is a rapidly growing field with promising applications in microsurgery and microassembly. A challenge in these systems is providing power and control signals to the robot. This project explores crawling robots that are powered and controlled through a global mechanical vibration field. Structures within the robot will cause it to respond to particular frequencies with different motion modalities. A prototype, dubbed the “jitterbot”, was cut out of a 0.75 mm sheet of steel using electric discharge machining (EDM), and has a total footprint of approximately 30 mm × 20 mm in the xy-plane. The “robot” has a tripod body (8 mm × 16 mm) with three small legs, and two suspended masses that are designed for specific resonance frequencies. The robot was tested on a plate that was vibrated vertically at frequencies ranging from 20 to 2,000 Hz. For particular resonant frequencies, the robot moves forward and turns in either a clockwise or counterclockwise direction. Finite element modeling confirms that the mechanism for motion is a rocking mode that is influenced by two arms that are suspended mass springs tuned to different frequencies. This lays the groundwork for further miniaturization. Micromachines 2011-06-15 2 2 Communication 10.3390/mi2020295 295 305 2072-666X 2011-06-15 doi: 10.3390/mi2020295 Samara Firebaugh Jenelle Piepmeier Elizabeth Leckie John Burkhardt http://www.mdpi.com/2072-666X/2/2/274 This paper aims at providing an up-to-date review of nonlinear electronic interfaces for energy harvesting from mechanical vibrations using piezoelectric coupling. The basic principles and the direct application to energy harvesting of nonlinear treatment of the output voltage of the transducers for conversion enhancement will be recalled, and extensions of this approach presented. Latest advances in this field will be exposed, such as the use of intermediate energy tanks for decoupling or initial energy injection for conversion magnification. A comparative analysis of each of these techniques will be performed, highlighting the advantages and drawbacks of the methods, in terms of efficiency, performance under several excitation conditions, complexity of implementation and so on. Finally, a special focus of their implementation in the case of low voltage output transducers (as in the case of microsystems) will be presented. Micromachines 2011-06-03 2 2 Review 10.3390/mi2020274 274 294 2072-666X 2011-06-03 doi: 10.3390/mi2020274 Daniel Guyomar Mickaël Lallart http://www.mdpi.com/2072-666X/2/2/258 Digital microfluidic has recently been under intensive study, as an effective method to carry out liquid manipulation in Lab-On-a-Chip (LOC) systems. Among droplet actuation forces, ElectroWetting on Dielectric (EWOD) and Liquid DiElectroPhoresis (LDEP) are powerful tools, used in many LOC platforms. Such digital microfluidic transductions do not require integration of complex mechanical components such as pumps and valves to perform the fluidic operations. However, although LDEP has been proved to be efficient to carry and manipulate biological components in insulating liquids, this microfluidic transduction requires several hundreds of volts at relatively high frequencies (kHz to MHz). With the purpose to develop integrated microsystems µ-TAS (Micro Total Analysis System) or Point of Care systems, the goal here is to reduce such high actuation voltage, the power consumption, though using standard dielectric materials. This paper gives key rules to determine the best tradeoff between liquid manipulation efficiency, low-power consumption and robustness of microsystems using LDEP actuation. This study leans on an electromechanical model to describe liquid manipulation that is applied to an experimental setup, and provides precise quantification of both actuation voltage Vth and frequency fc thresholds between EWOD and LDEP regimes. In particular, several parameters will be investigated to quantify Vth and fc, such as the influence of the chip materials, the electrodes size and the device configurations. Compared to current studies in the field, significant reduction of both Vth and fc is achieved by optimization of the aforementioned parameters. Micromachines 2011-06-03 2 2 Article 10.3390/mi2020258 258 273 2072-666X 2011-06-03 doi: 10.3390/mi2020258 Raphaël Renaudot Vincent Agache Bruno Daunay Pierre Lambert Momoko Kumemura Yves Fouillet Dominique Collard Hiroyuki Fujita http://www.mdpi.com/2072-666X/2/2/221 Research in recent years has greatly advanced the understanding and capabilities of multi-beam interference (MBI). With this technology it is now possible to generate a wide range of one-, two-, and three-dimensional periodic optical-intensity distributions at the micro- and nano-scale over a large length/area/volume. These patterns may be used directly or recorded in photo-sensitive materials using multi-beam interference lithography (MBIL) to accomplish subwavelength patterning. Advances in MBI and MBIL and a very wide range of applications areas including nano-electronics, photonic crystals, metamaterials, subwavelength structures, optical trapping, and biomedical structures are reviewed and put into a unified perspective. Micromachines 2011-06-03 2 2 Review 10.3390/mi2020221 221 257 2072-666X 2011-06-03 doi: 10.3390/mi2020221 Guy M. Burrow Thomas K. Gaylord http://www.mdpi.com/2072-666X/2/2/179 This review presents an extensive overview of a large number of microvalve and micropump designs with great variability in performance and operation. The performance of a given design varies greatly depending on the particular assembly procedure and there is no standardized performance test against which all microvalves and micropumps can be compared. We present the designs with a historical perspective and provide insight into their advantages and limitations for biomedical uses. Micromachines 2011-05-24 2 2 Review 10.3390/mi2020179 179 220 2072-666X 2011-05-24 doi: 10.3390/mi2020179 Anthony K. Au Hoyin Lai Ben R. Utela Albert Folch http://www.mdpi.com/2072-666X/2/2/167 In the present work, the design and the environmental conditions of a micromachined thermal accelerometer, based on convection effect, are discussed and studied in order to understand the behavior of the frequency response evolution of the sensor. It has been theoretically and experimentally studied with different detector widths, pressure and gas nature. Although this type of sensor has already been intensively examined, little information concerning the frequency response modeling is currently available and very few experimental results about the frequency response are reported in the literature. In some particular conditions, our measurements show a cut-off frequency at −3 dB greater than 200 Hz. By using simple cylindrical and planar models of the thermal accelerometer and an equivalent electrical circuit, a good agreement with the experimental results has been demonstrated. Micromachines 2011-05-23 2 2 Article 10.3390/mi2020167 167 178 2072-666X 2011-05-23 doi: 10.3390/mi2020167 Alexandra Garraud Philippe Combette Johann Courteaud Alain Giani http://www.mdpi.com/2072-666X/2/2/157 Ultrasonic hot embossing is a new process for fast and low-cost production of micro systems from polymer. Investment costs are on the order of 20.000 € and cycle times are a few seconds. Microstructures are fabricated on polymer foils and can be combined to three-dimensional systems by ultrasonic welding. Micromachines 2011-05-11 2 2 Article 10.3390/mi2020157 157 166 2072-666X 2011-05-11 doi: 10.3390/mi2020157 Werner Karl Schomburg Katharina Burlage Christof Gerhardy http://www.mdpi.com/2072-666X/2/2/150 Employing numerical simulations, we investigate the possibility of using curved guided-mode resonance (GMR) elements to focus light in reflection. We treat GMR reflectors with a parabolic shape and show that they are capable of focusing light effectively across wavelength bands that extend several hundred nanometers. The spatially infinite reflector model is simulated with a finite-element method, whereas the spatially finite reflector is treated with a finite-difference-time-domain method. The numerical results demonstrate that light intensity at the focal point is 8.6 dB stronger than the incident intensity when the GMR reflector’s size is on the order of 10 wavelengths. The results indicate potential applicability of wideband-focusing devices in electromagnetics and photonics using compact resonance elements. Micromachines 2011-04-28 2 2 Article 10.3390/mi2020150 150 156 2072-666X 2011-04-28 doi: 10.3390/mi2020150 Mingyu Lu Huiqing Zhai Robert Magnusson http://www.mdpi.com/2072-666X/2/2/129 The purpose of this paper is to present a simple micromechanics-based model to estimate the effective thermal conductivity of macroscopically isotropic materials of matrix-inclusion type. The methodology is based on the well-established Mori-Tanaka method for composite media reinforced with ellipsoidal inclusions, extended to account for imperfect thermal contact at the matrix-inclusion interface, random orientation of particles and particle size distribution. Using simple ensemble averaging arguments, we show that the Mori-Tanaka relations are still applicable for these complex systems, provided that the inclusion conductivity is appropriately modified. Such conclusion is supported by the verification of the model against a detailed finite-element study as well as its validation against experimental data for a wide range of engineering material systems. Micromachines 2011-04-15 2 2 Article 10.3390/mi2020129 129 149 2072-666X 2011-04-15 doi: 10.3390/mi2020129 Jan Stránský Jan Vorel Jan Zeman Michal Šejnoha http://www.mdpi.com/2072-666X/2/2/116 We present a novel integrated device for preparing metaphase chromosomes spread slides (FISHprep). The quality of cytogenetic analysis from patient samples greatly relies on the efficiency of sample pre-treatment and/or slide preparation. In cytogenetic slide preparation, cell cultures are routinely used to process samples (for culture, arrest and fixation of cells) and/or to expand limited amount of samples (in case of prenatal diagnostics). Arguably, this expansion and other sample pretreatments form the longest part of the entire diagnostic protocols spanning over 3–4 days. We present here a novel device with an integrated expansion chamber to culture, arrest and fix metaphase cells followed by a subsequent splashing protocol leading to ample metaphase chromosome spreads on a glass slide for metaphase FISH analysis. The device provides an easy, disposable, low cost, integrated solution with minimal handling for metaphase FISH slide preparation. Micromachines 2011-04-04 2 2 Article 10.3390/mi2020116 116 128 2072-666X 2011-04-04 doi: 10.3390/mi2020116 Pranjul Shah Indumathi Vedarethinam Dorota Kwasny Lars Andresen Søren Skov Asli Silahtaroglu Zeynep Tümer Maria Dimaki Winnie E. Svendsen http://www.mdpi.com/2072-666X/2/2/82 A wealth of current research in microengineering aims at fabricating devices of increasing complexity, notably by (self-)assembling elementary components into heterogeneous functional systems. At the same time, a large body of robotic research called swarm robotics is concerned with the design and the control of large ensembles of robots of decreasing size and complexity. This paper describes the asymptotic convergence of micro/nano electromechanical systems (M/NEMS) on one side, and swarm robotic systems on the other, toward a unifying class of systems, which we denote Smart Minimal Particles (SMPs). We define SMPs as mobile, purely reactive and physically embodied agents that compensate for their limited on-board capabilities using specifically engineered reactivity to external physical stimuli, including local energy and information scavenging. In trading off internal resources for simplicity and robustness, SMPs are still able to collectively perform non-trivial, spatio-temporally coordinated and highly scalable operations such as aggregation and self-assembly (SA). We outline the opposite converging tendencies, namely M/NEMS smarting and robotic minimalism, by reviewing each field’s literature with specific focus on self-assembling systems. Our main claim is that the SMPs can be used to develop a unifying technological and methodological framework that bridges the gap between passive M/NEMS and active, centimeter-sized robots. By proposing this unifying perspective, we hypothesize a continuum in both complexity and length scale between these two extremes. We illustrate the benefits of possible cross-fertilizations among these originally separate domains, with specific emphasis on the modeling of collective dynamics. Particularly, we argue that while most of the theoretical studies on M/NEMS SA dynamics belong so far to one of only two main frameworks—based on analytical master equations and on numerical agent-based simulations, respectively—alternative models developed in swarm robotics could be amenable to the task, and thereby provide important novel insights. Micromachines 2011-03-31 2 2 Review 10.3390/mi2020082 82 115 2072-666X 2011-03-31 doi: 10.3390/mi2020082 Massimo Mastrangeli Grégory Mermoud Alcherio Martinoli http://www.mdpi.com/2072-666X/2/1/69 Self-assembly is a promising technique to overcome fundamental limitations with integrating, packaging, and general handling of individual electronic-related components with characteristic lengths significantly smaller than 1 mm. Here we describe the use of magnetic and capillary forces to self-assemble 280 µm sized silicon building blocks into interconnected structures which approach a three-dimensional crystalline configuration. Integrated permanent magnet microstructures provided magnetic forces, while a low-melting-point solder alloy provided capillary forces. A finite element model of forces between the magnetic features demonstrated the utility of magnetic forces at this size scale. Despite a slight departure from designed dimensions in the actual fabricated parts, the combination of magnetic and capillary forces improved the assembly yield to 8%, over approximately 0.1% achieved previously with capillary forces alone. Micromachines 2011-03-01 2 1 Article 10.3390/mi2010069 69 81 2072-666X 2011-03-01 doi: 10.3390/mi2010069 Christopher J. Morris Brian Isaacson Michael D. Grapes Madan Dubey http://www.mdpi.com/2072-666X/2/1/49 New surface mounting and packaging technologies, using self-assembly with chips having cavity structures, were investigated for three-dimensional (3D) and hetero integration of complementary metal-oxide semiconductors (CMOS) and microelectromechanical systems (MEMS). By the surface tension of small droplets of 0.5 wt% hydrogen fluoride (HF) aqueous solution, the cavity chips, with a side length of 3 mm, were precisely aligned to hydrophilic bonding regions on the surface of plateaus formed on Si substrates. The plateaus have micro-channels to readily evaporate and fully remove the liquid from the cavities. The average alignment accuracy of the chips with a 1 mm square cavity was found to be 0.4 mm. The alignment accuracy depends, not only on the area of the bonding regions on the substrates and the length of chip periphery without the widths of channels in the plateaus, but also the area wetted by the liquid on the bonding regions. The precisely aligned chips were then directly bonded to the substrates at room temperature without thermal compression, resulting in a high shear bonding strength of more than 10 MPa. Micromachines 2011-02-18 2 1 Article 10.3390/mi2010049 49 68 2072-666X 2011-02-18 doi: 10.3390/mi2010049 Takafumi Fukushima Takayuki Konno Eiji Iwata Risato Kobayashi Toshiya Kojima Mariappan Murugesan Ji-Chel Bea Kang-Wook Lee Tetsu Tanaka Mitsumasa Koyanagi http://www.mdpi.com/2072-666X/2/1/17 Self-assembly in micro- and nanofluidic devices has been the focus of much attention in recent years. This is not only due to their advantages of self-assembling with fine temporal and spatial control in addition to continuous processing that is not easily accessible in conventional batch procedures, but they have evolved to become indispensable tools to localize and assimilate micro- and nanocomponents into numerous applications, such as bioelectronics, drug delivery, photonics, novel microelectronic architectures, building blocks for tissue engineering and metamaterials, and nanomedicine. This review aims to focus on the most recent advancements and characteristic investigations on the self-assembly of micro- and nanoscopic objects in micro- and nanofluidic devices. Emphasis is placed on the salient aspects of this technology in terms of the types of micro- and nanomaterials being assembled, the principles and methodologies, as well as their novel applications. Micromachines 2011-02-11 2 1 Review 10.3390/mi2010017 17 48 2072-666X 2011-02-11 doi: 10.3390/mi2010017 Hwa Seng Khoo Cheng Lin Shih-Hao Huang Fan-Gang Tseng http://www.mdpi.com/2072-666X/2/1/1 The relative adhesion of two genetically engineered polypeptides termed as H6-(YEHK)x21-H6 and C6-(YEHK)X21-H6 has been investigated following growth and self-assembly on highly oriented pyrolytic graphite (HOPG), SiO2, Ni, and Au substrates to study covalent surface attachment via histidine (H) and cysteine (C) groups incorporated in the polypeptides. Both polypeptides formed predominantly bilayer fibrils upon deposition, in agreement with previous studies. The relative adhesion of polypeptide fibrils to the substrate, as well as intra-fibril cohesion, was examined via a forced-scanning method employing contact mode atomic force microscopy (AFM). H6-(YEHK)x21-H6 polypeptide fibrils were observed to detach from Ni, Au, SiO2, and HOPG substrates at normal tip forces of 106 ± 10 nN, 21 ± 3 nN, 22 ± 3 nN, and 3 ± 1 nN, respectively. C6-(YEHK)x21-H6 polypeptide fibrils were seen to detach from Au substrates at a normal spring force of 90 ± 10 nN. It is concluded that the H6-(YEHK)x21-H6 and C6-(YEHK)x21-H6 polypeptide fibrils are covalently attached to, respectively, Ni and Au substrates, which has important implications for the use of these materials for NEMS fabrication. The structural stability of deposited polypeptide fibrils was also evaluated by using normal tip forces less than those required for fibril detachment. H6-(YEHK)x21-H6 polypeptide fibrils on Ni substrates were the most structurally stable compared to C6-(YEHK)x21-H6 polypeptide fibrils on Au substrates. Controlled delayering of bilayer fibrils was also detected for sub-detachment normal forces. Micromachines 2011-01-17 2 1 Article 10.3390/mi2010001 1 16 2072-666X 2011-01-17 doi: 10.3390/mi2010001 Narender Rana Christopher Kossow Eric T. Eisenbraun Robert E. Geer Alain E. Kaloyeros http://www.mdpi.com/2072-666X/1/3/129 Difficulties associated with testing and characterization of materials at microscale demands for new technologies and devices that are capable of measuring forces and strains at microscale. To address this issue, a novel electroactive-based micro-electro-mechanical machine is designed. The micromachine is comprised of two electroactive (piezoelectric) micro-elements mounted on a rigid frame. Electrical activation of one of the elements causes it to expand and induce a stress in the intervening micro-specimen. The response of the microspecimen to the stress is measured by the deformation and thereby voltage/resistance induced in the second electro-active element. The concept is theoretically proven using analytical modeling in conjunction with non-linear, three dimensional finite element analyses for the micromachine. Correlation of the output voltage to the specimen stiffness is shown. It is also demonstrated through finite element and analytical analysis that this technique is capable of detecting non-linear behavior of materials. A characteristic curve for an isotropic specimen exhibiting linear elastic behavior is developed. Application of the proposed device in measuring coefficient of thermal expansion is explored and analytical analysis is conducted. Micromachines 2010-12-14 1 3 Article 10.3390/microm1030129 129 152 2072-666X 2010-12-14 doi: 10.3390/microm1030129 Leila Ladani Steven Nelson http://www.mdpi.com/2072-666X/1/3/112 This paper investigates the design optimization of an electrostatically actuated microcantilever resonator that operates in air. The nonlinear effects of electrostatic actuation and air damping make the structural dynamics modeling more complex. There is a need for an efficient way to simulate the system behavior so that the design can be more readily optimized. This paper describes an efficient analytical approach for determining the optimum design for a microcantilever resonant mass sensor. One simple case is described. The sensor design is a square plate that is coated with a functional polymer and attached to the substrate with folded leg springs. The plate has a square hole in the middle to reduce the effect of squeeze film damping. With the analytical approach, the optimum hole size for maximum sensitivity is found. Micromachines 2010-12-14 1 3 Article 10.3390/microm1010112 112 128 2072-666X 2010-12-14 doi: 10.3390/microm1010112 Chengzhang Li Michele H. Miller http://www.mdpi.com/2072-666X/1/3/82 Small-scale mixing is of uttermost importance in bio- and chemical analyses using micro TAS (total analysis systems) or lab-on-chips. Many microfluidic applications involve chemical reactions where, most often, the fluid diffusivity is very low so that without the help of chaotic advection the reaction time can be extremely long. In this article, we will review various kinds of mixers developed for use in microfluidic devices. Our review starts by defining the terminology necessary to understand the fundamental concept of mixing and by introducing quantities for evaluating the mixing performance, such as mixing index and residence time. In particular, we will review the concept of chaotic advection and the mathematical terms, Poincare section and Lyapunov exponent. Since these concepts are developed from nonlinear dynamical systems, they should play important roles in devising microfluidic devices with enhanced mixing performance. Following, we review the various designs of mixers that are employed in applications. We will classify the designs in terms of the driving forces, including mechanical, electrical and magnetic forces, used to control fluid flow upon mixing. The advantages and disadvantages of each design will also be addressed. Finally, we will briefly touch on the expected future development regarding mixer design and related issues for the further enhancement of mixing performance. Micromachines 2010-09-30 1 3 Review 10.3390/mi1030082 82 111 2072-666X 2010-09-30 doi: 10.3390/mi1030082 Yong Kweon Suh Sangmo Kang http://www.mdpi.com/2072-666X/1/2/68 A gap with variable geometry is presented for both cantilever beam and fixed-fixed beam actuators as a method to reduce the pull-in voltage while maintaining a required displacement. The method is applicable to beams oriented either in a plane parallel to or perpendicular to a substrate, but is most suitable for vertically oriented (lateral) beams fabricated with a high aspect ratio process where variable gap geometry can be implemented directly in the layout. Finite element simulations are used to determine the pull-in voltages of these modified structures. The simulator is verified against theoretical pull-in voltage equations as well as previously published finite element simulations. By simply varying the gap in a linear fashion the pull-in voltage can be reduced by 37.2% in the cantilever beam case and 29.6% in the fixed-fixed beam case over a structure with a constant gap. This can be reduced a further 4.8% by using a polynomial gap shape (n = 4/3) for the cantilever beam and 1.2% for the fixed-fixed beam by flattening the bottom of the linearly varying gap. Micromachines 2010-07-28 1 2 Article 10.3390/mi1020068 68 81 2072-666X 2010-07-28 doi: 10.3390/mi1020068 Darcy T. Haluzan David M. Klymyshyn Sven Achenbach Martin Börner http://www.mdpi.com/2072-666X/1/2/48 Shuffle motors are electrostatic stepper micromotors that employ a built-in mechanical leverage to produce large output forces as well as high resolution displacements. These motors can generally move only over predefined paths that served as driving electrodes. Here, we present the design, modeling and experimental characterization of a novel shuffle motor that moves over an unpatterned, electrically grounded surface. By combining the novel design with an innovative micromachining method based on vertical trench isolation, we have greatly simplified the fabrication of the shuffle motors and significantly improved their overall performance characteristics and reliability. Depending on the propulsion voltage, our motor with external dimensions of 290 μm × 410 mm displays two distinct operational modes with adjustable step sizes varying respectively from 0.6 to 7 nm and from 49 to 62 nm. The prototype was driven up to a cycling frequency of 80 kHz, showing nearly linear dependence of its velocity with frequency and a maximum velocity of 3.6 mm/s. For driving voltages of 55 V, the device had a maximum travel range of ±70 μm and exhibited an output force of 1.7 mN, resulting in the highest force and power densities reported so far for an electrostatic micromotor. After five days of operation, it had traveled a cumulative distance of more than 1.5 km in 34 billion steps without noticeable deterioration in performance. Micromachines 2010-07-16 1 2 Article 10.3390/mi1020048 48 67 2072-666X 2010-07-16 doi: 10.3390/mi1020048 Sarajlic Yamahata Berenschot Tas Fujita Krijnen http://www.mdpi.com/2072-666X/1/2/36 The performance of micro-mixers is evaluated in terms of deviations from perfectly mixed state and mixing length (i.e., device length required to achieve perfect mixing). Different variations of T-mixer are reported for improved mixing performance, including geometric constrictions/obstacles embedded in the channel wall, heterogeneously charged walls, grooves on channel base, etc. Most of the reported designs provide improved mixing at the expense of reduced flow rate; there exists therefore a tradeoff between mixing and transport. The reduced flow rate, which affects species residence time, is unfortunately not taken into account in most micro-mixing performance analyses. This issue is addressed by the comparative mixing index (CMI), which evaluates mixing performance more appropriately by normalizing the effect of residence time among different designs. In this study, the performance of several mixing strategies are evaluated based on the CMI; these are mixer designs that incorporate (a) physical constrictions, (b) induced charge electro-osmotic (ICEO) effects, and (c) heterogeneously charged walls. The present analysis clearly identifies conditions under which a given mixer design is superior to a T-mixer. Micromachines 2010-07-12 1 2 Article 10.3390/mi1020036 36 47 2072-666X 2010-07-12 doi: 10.3390/mi1020036 Jain Yeung Nandakumar http://www.mdpi.com/2072-666X/1/2/34 When I joined a course on microsensors given by Steve Senturia, Martin Schmidt, and Roger Howe at MIT in 1988, I saw the first video of the earliest rotating silicon micromotor. It was the beginning of a high-time of microelectromechanical systems (MEMS): everything we did was new [1], and the MEMS community was sure that we not only reached a new frontier (which might be true), but that overcoming this boundary would lead to solutions for the most pressing problems of human kind [2] (which might not be true). With the demonstration of a rotating micromachine as a key element in MEMS, we had the impression that basically all problems in our young field could be solved. In the past 20 years, we saw the explosive development of the field. We now have a good idea of the value of MEMS, which is in many respects different to what we anticipated 20 years ago, and which includes many new developments. Micromachines 2010-06-30 1 2 Editorial 10.3390/mi1020034 34 35 2072-666X 2010-06-30 doi: 10.3390/mi1020034 Elwenspoek http://www.mdpi.com/2072-666X/1/1/19 We evaluated the dynamic micromixing performances in slanted groove micromixers (SGM) and staggered herringbone micromixers (SHM) and quantitatively compared their differences using concentration vs. channel length profiles obtained from numerical stimulations. It is found that faster and finer mixing took place in the SHM and the chaotic mixing was more effective at locations closer to the grooves; in comparison, slower and coarser mixing occurred throughout the whole channel of the SGM. Subsequently, the concentration profile-based characterization method was demonstrated in hybrid floor-grooved micromixers to study the interaction of SGM and SHM. Micromachines 2010-05-17 1 1 Article 10.3390/mi1010019 19 33 2072-666X 2010-05-17 doi: 10.3390/mi1010019 Du Zhang Yim Lin Cao http://www.mdpi.com/2072-666X/1/1/1 The continuous increase in capacity of non-volatile data storage systems will lead to bit densities of one bit per atom in 2020. Beyond this point, capacity can be increased by moving into the third dimension. We propose to use self-assembly of nanosized elements, either as a loosely organised associative network or into a cross-point architecture. When using principles requiring electrical connection, we show the need for transistor-based cross-talk isolation. Cross-talk can be avoided by reusing the coincident current magnetic ring core memory architecture invented in 1953. We demonstrate that self-assembly of three-dimensional ring core memories is in principle possible by combining corner lithography and anisotropic etching into single crystal silicon. Micromachines 2010-01-18 1 1 Article 10.3390/mi1010001 1 18 2072-666X 2010-01-18 doi: 10.3390/mi1010001 Leon Abelmann Niels Tas Erwin Berenschot Miko Elwenspoek