Micromachines

20 pages, 547 KB

Open AccessFeature PaperReview

3D-Printed Chips: Compatibility of Additive Manufacturing Photopolymeric Substrata with Biological Applications

by Megan Carve and Donald Wlodkowic

Micromachines 2018, 9(2), 91; https://doi.org/10.3390/mi9020091 - 23 Feb 2018

Cited by 103 | Viewed by 9649

Additive manufacturing (AM) is ideal for building adaptable, structurally complex, three-dimensional, monolithic lab-on-chip (LOC) devices from only a computer design file. Consequently, it has potential to advance micro- to milllifluidic LOC design, prototyping, and production and further its application in areas of biomedical [...] Read more.

Additive manufacturing (AM) is ideal for building adaptable, structurally complex, three-dimensional, monolithic lab-on-chip (LOC) devices from only a computer design file. Consequently, it has potential to advance micro- to milllifluidic LOC design, prototyping, and production and further its application in areas of biomedical and biological research. However, its application in these areas has been hampered due to material biocompatibility concerns. In this review, we summarise commonly used AM techniques: vat polymerisation and material jetting. We discuss factors influencing material biocompatibility as well as methods to mitigate material toxicity and thus promote its application in these research fields. Full article

(This article belongs to the Special Issue 3D Printed Microfluidic Devices)

► Show Figures

Figure 1

10 pages, 2382 KB

Open AccessArticle

Wearable Pulse Wave Monitoring System Based on MEMS Sensors

by Yu Sun, Ying Dong, Ruyi Gao, Yao Chu, Min Zhang, Xiang Qian and Xiaohao Wang

Micromachines 2018, 9(2), 90; https://doi.org/10.3390/mi9020090 - 23 Feb 2018

Cited by 35 | Viewed by 8334

Abstract

Pulse wave monitoring is critical for the evaluation of human health. In this paper, a wearable multi-sensor pulse wave monitoring system is proposed and demonstrated. The monitoring system consists of a measuring unit and an analog circuit processing unit. The main part of [...] Read more.

Pulse wave monitoring is critical for the evaluation of human health. In this paper, a wearable multi-sensor pulse wave monitoring system is proposed and demonstrated. The monitoring system consists of a measuring unit and an analog circuit processing unit. The main part of the measuring unit is a flexible printed circuit board (PCB) with a thickness of 0.15 mm, which includes three micro-electromechanical system (MEMS) pressure sensors softly packaged by polydimethylsiloxane (PDMS), a blood oxygen detector and a MEMS three-axis accelerometer. The MEMS pressure sensors，the blood oxygen detector and the accelerometer are fixed on the expected locations of the flexible PCB. The analog circuit processing unit includes a power supply module, a filter and an amplifier. The pulse waves of two volunteers are detected by the monitoring system in this study. The output signals of the analog circuit processing module are processed and analyzed. In the preliminary test, the time delay of the three pressure pulse waves has been detected and the calculated pulse wave velocities (PWVs) are 12.50 and 11.36 m/s, respectively. The K value, related to the area of the pulse wave, can be obtained. Both the PWV and K value meet the health parameter standards. Full article

► Show Figures

Figure 1

19 pages, 2056 KB

Open AccessArticle

Monostable Dynamic Analysis of Microbeam-Based Resonators via an Improved One Degree of Freedom Model

by Lei Li, Qichang Zhang, Wei Wang and Jianxin Han

Micromachines 2018, 9(2), 89; https://doi.org/10.3390/mi9020089 - 22 Feb 2018

Cited by 4 | Viewed by 4215

Abstract

Monostable vibration can eliminate dynamic bifurcation and improve system stability, which is required in many microelectromechanical systems (MEMS) applications, such as microbeam-based and comb-driven resonators. This article aims to theoretically investigate the monostable vibration in size-effected MEMS via a low dimensional model. An [...] Read more.

Monostable vibration can eliminate dynamic bifurcation and improve system stability, which is required in many microelectromechanical systems (MEMS) applications, such as microbeam-based and comb-driven resonators. This article aims to theoretically investigate the monostable vibration in size-effected MEMS via a low dimensional model. An improved single degree of freedom model to describe electrically actuated microbeam-based resonators is obtained by using modified couple stress theory and Nonlinear Galerkin method. Static displacement, pull-in voltage, resonant frequency and especially the monostable dynamic behaviors of the resonators are investigated in detail. Through perturbation analysis, an approximate average equation is derived by the application of the method of Multiple Scales. Theoretical expressions about parameter space and maximum amplitude of monostable vibration are then deduced. Results show that this improved model can describe the static behavior more accurately than that of single degree of freedom model via traditional Galerkin Method. This desired monostable large amplitude vibration is significantly affected by the ratio of the gap width to mircobeam thickness. The optimization design results show that reasonable decrease of this ratio can be beneficial to monostable vibration. All these analytical results are verified by numerical results via Differential Quadrature method, which show excellent agreement with each other. This analysis has the potential of improving dynamic performance in MEMS. Full article

(This article belongs to the Special Issue Micro-Resonators: The Quest for Superior Performance)

► Show Figures

Figure 1

18 pages, 47693 KB

Open AccessReview

Light-Controlled Swarming and Assembly of Colloidal Particles

by Jianhua Zhang, Jingjing Guo, Fangzhi Mou and Jianguo Guan

Micromachines 2018, 9(2), 88; https://doi.org/10.3390/mi9020088 - 19 Feb 2018

Cited by 47 | Viewed by 8782

Abstract

Swarms and assemblies are ubiquitous in nature and they can perform complex collective behaviors and cooperative functions that they cannot accomplish individually. In response to light, some colloidal particles (CPs), including light active and passive CPs, can mimic their counterparts in nature and [...] Read more.

Swarms and assemblies are ubiquitous in nature and they can perform complex collective behaviors and cooperative functions that they cannot accomplish individually. In response to light, some colloidal particles (CPs), including light active and passive CPs, can mimic their counterparts in nature and organize into complex structures that exhibit collective functions with remote controllability and high temporospatial precision. In this review, we firstly analyze the structural characteristics of swarms and assemblies of CPs and point out that light-controlled swarming and assembly of CPs are generally achieved by constructing light-responsive interactions between CPs. Then, we summarize in detail the recent advances in light-controlled swarming and assembly of CPs based on the interactions arisen from optical forces, photochemical reactions, photothermal effects, and photoisomerizations, as well as their potential applications. In the end, we also envision some challenges and future prospects of light-controlled swarming and assembly of CPs. With the increasing innovations in mechanisms and control strategies with easy operation, low cost, and arbitrary applicability, light-controlled swarming and assembly of CPs may be employed to manufacture programmable materials and reconfigurable robots for cooperative grasping, collective cargo transportation, and micro- and nanoengineering. Full article

(This article belongs to the Special Issue Selected Papers from 2017 International Conference on Micro/Nanomachines)

► Show Figures

Figure 1

25 pages, 3534 KB

Open AccessArticle

Lattice Boltzmann Simulation of the Hydrodynamic Entrance Region of Rectangular Microchannels in the Slip Regime

by Niya Ma, Zhipeng Duan, Hao Ma, Liangbin Su, Peng Liang, Xiaoru Ning, Boshu He and Xin Zhang

Micromachines 2018, 9(2), 87; https://doi.org/10.3390/mi9020087 - 16 Feb 2018

Cited by 22 | Viewed by 5449

Abstract

Developing a three-dimensional laminar flow in the entrance region of rectangular microchannels has been investigated in this paper. When the hydrodynamic development length is the same magnitude as the microchannel length, entrance effects have to be taken into account, especially in relatively short [...] Read more.

Developing a three-dimensional laminar flow in the entrance region of rectangular microchannels has been investigated in this paper. When the hydrodynamic development length is the same magnitude as the microchannel length, entrance effects have to be taken into account, especially in relatively short ducts. Simultaneously, there are a variety of non-continuum or rarefaction effects, such as velocity slip and temperature jump. The available data in the literature appearing on this issue is quite limited, the available study is the semi-theoretical approximate model to predict pressure drop of developing slip flow in rectangular microchannels with different aspect ratios. In this paper, we apply the lattice Boltzmann equation method (LBE) to investigate the developing slip flow through a rectangular microchannel. The effects of the Reynolds number (1 < Re < 1000), channel aspect ratio (0 < ε < 1), and Knudsen number (0.001 < Kn < 0.1) on the dimensionless hydrodynamic entrance length, and the apparent friction factor, and Reynolds number product, are examined in detail. The numerical solution of LBM can recover excellent agreement with the available data in the literature, which proves its accuracy in capturing fundamental fluid characteristics in the slip-flow regime. Full article

(This article belongs to the Special Issue Microsystems for Power, Energy, and Actuation)

► Show Figures

Figure 1

11 pages, 1610 KB

Open AccessFeature PaperArticle

Microfluidics: A New Layer of Control for Extrusion-Based 3D Printing

by Ludovic Serex, Arnaud Bertsch and Philippe Renaud

Micromachines 2018, 9(2), 86; https://doi.org/10.3390/mi9020086 - 16 Feb 2018

Cited by 62 | Viewed by 9356

Abstract

Advances in 3D printing have enabled the use of this technology in a growing number of fields, and have started to spark the interest of biologists. Having the particularity of being cell friendly and allowing multimaterial deposition, extrusion-based 3D printing has been shown [...] Read more.

Advances in 3D printing have enabled the use of this technology in a growing number of fields, and have started to spark the interest of biologists. Having the particularity of being cell friendly and allowing multimaterial deposition, extrusion-based 3D printing has been shown to be the method of choice for bioprinting. However as biologically relevant constructs often need to be of high resolution and high complexity, new methods are needed, to provide an improved level of control on the deposited biomaterials. In this paper, we demonstrate how microfluidics can be used to add functions to extrusion 3D printers, which widens their field of application. Micromixers can be added to print heads to perform the last-second mixing of multiple components just before resin dispensing, which can be used for the deposition of new polymeric or composite materials, as well as for bioprinting new materials with tailored properties. The integration of micro-concentrators in the print heads allows a significant increase in cell concentration in bioprinting. The addition of rapid microfluidic switching as well as resolution increase through flow focusing are also demonstrated. Those elementary implementations of microfluidic functions for 3D printing pave the way for more complex applications enabling new prospects in 3D printing. Full article

(This article belongs to the Special Issue 3D Printed Microfluidic Devices)

► Show Figures

Figure 1

24 pages, 9806 KB

Open AccessArticle

On the Bipolar DC Flow Field-Effect-Transistor for Multifunctional Sample Handing in Microfluidics: A Theoretical Analysis under the Debye–Huckel Limit

by Weiyu Liu, Qisheng Wu, Yukun Ren, Peng Cui, Bobin Yao, Yanbo Li, Meng Hui, Tianyi Jiang and Lin Bai

Micromachines 2018, 9(2), 82; https://doi.org/10.3390/mi9020082 - 16 Feb 2018

Cited by 8 | Viewed by 4806

Abstract

We present herein a novel method of bipolar field-effect control on DC electroosmosis (DCEO) from a physical point of view, in the context of an intelligent and robust operation tool for stratified laminar streams in microscale systems. In this unique design of the [...] Read more.

We present herein a novel method of bipolar field-effect control on DC electroosmosis (DCEO) from a physical point of view, in the context of an intelligent and robust operation tool for stratified laminar streams in microscale systems. In this unique design of the DC flow field-effect-transistor (DC-FFET), a pair of face-to-face external gate terminals are imposed with opposite gate-voltage polarities. Diffuse-charge dynamics induces heteropolar Debye screening charge within the diffuse double layer adjacent to the face-to-face oppositely-polarized gates, respectively. A background electric field is applied across the source-drain terminal and forces the face-to-face counterionic charge of reversed polarities into induced-charge electroosmotic (ICEO) vortex flow in the lateral direction. The chaotic turbulence of the transverse ICEO whirlpool interacts actively with the conventional plug flow of DCEO, giving rise to twisted streamlines for simultaneous DCEO pumping and ICEO mixing of fluid samples along the channel length direction. A mathematical model in thin-layer approximation and the low-voltage limit is subsequently established to test the feasibility of the bipolar DC-FFET configuration in electrokinetic manipulation of fluids at the micrometer dimension. According to our simulation analysis, an integrated device design with two sets of side-by-side, but upside-down gate electrode pair exhibits outstanding performance in electroconvective pumping and mixing even without any externally-applied pressure difference. Moreover, a paradigm of a microdevice for fully electrokinetics-driven analyte treatment is established with an array of reversed bipolar gate-terminal pairs arranged on top of the dielectric membrane along the channel length direction, from which we can obtain almost a perfect liquid mixture by using a smaller magnitude of gate voltages for causing less detrimental effects at a small Dukhin number. Sustained by theoretical analysis, our physical demonstration on bipolar field-effect flow control for the microfluidic device of dual functionalities in simultaneous electroconvective pumping and mixing holds great potential in the development of fully-automated liquid-phase actuators in modern microfluidic systems. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)

► Show Figures

Figure 1

23 pages, 13869 KB

Open AccessArticle

3D Printing, Ink Casting and Micromachined Lamination (3D PICLμM): A Makerspace Approach to the Fabrication of Biological Microdevices

by Avra Kundu, Tariq Ausaf and Swaminathan Rajaraman

Micromachines 2018, 9(2), 85; https://doi.org/10.3390/mi9020085 - 15 Feb 2018

Cited by 53 | Viewed by 7554

Abstract

We present a novel benchtop-based microfabrication technology: 3D printing, ink casting, micromachined lamination (3D PICLμM) for rapid prototyping of lab-on-a-chip (LOC) and biological devices. The technology uses cost-effective, makerspace-type microfabrication processes, all of which are ideally suited for low resource settings, and utilizing [...] Read more.

We present a novel benchtop-based microfabrication technology: 3D printing, ink casting, micromachined lamination (3D PICLμM) for rapid prototyping of lab-on-a-chip (LOC) and biological devices. The technology uses cost-effective, makerspace-type microfabrication processes, all of which are ideally suited for low resource settings, and utilizing a combination of these processes, we have demonstrated the following devices: (i) 2D microelectrode array (MEA) targeted at in vitro neural and cardiac electrophysiology, (ii) microneedle array targeted at drug delivery through a transdermal route and (iii) multi-layer microfluidic chip targeted at multiplexed assays for in vitro applications. The 3D printing process has been optimized for printing angle, temperature of the curing process and solvent polishing to address various biofunctional considerations of the three demonstrated devices. We have depicted that the 3D PICLμM process has the capability to fabricate 30 μm sized MEAs (average 1 kHz impedance of 140 kΩ with a double layer capacitance of 3 μF), robust and reliable microneedles having 30 μm radius of curvature and ~40 N mechanical fracture strength and microfluidic devices having 150 μm wide channels and 400 μm fluidic vias capable of fluid mixing and transmitted light microparticle visualization. We believe our 3D PICLμM is ideally suited for applications in areas such as electrophysiology, drug delivery, disease in a dish, organ on a chip, environmental monitoring, agricultural therapeutic delivery and genomic testing. Full article

(This article belongs to the Special Issue Polymer Based MEMS and Microfabrication)

► Show Figures

Figure 1

16 pages, 3366 KB

Open AccessArticle

Characterizing Sources of Small DC Motor Noise and Vibration

by Yong Thung Cho

Micromachines 2018, 9(2), 84; https://doi.org/10.3390/mi9020084 - 15 Feb 2018

Cited by 24 | Viewed by 9443

Abstract

Small direct current (DC) motors are widely used due to their low cost and compact structure. Small DC motors of various designs are available on the market in different sizes. The smaller the motor, the more closely it may be used by individuals. [...] Read more.

Small direct current (DC) motors are widely used due to their low cost and compact structure. Small DC motors of various designs are available on the market in different sizes. The smaller the motor, the more closely it may be used by individuals. Contrary to the size and simplicity of these motors in terms of structural design, sources of motor noise and vibration can be quite diverse and complicated. In this study, the source of motor noise and vibration was visualized over a very wide range of frequencies. The particle velocity of the motor was reconstructed from nearfield sound pressure measurements of motor noise. In addition to noncontact measurements conducted on a motor running at constant speed, the particle velocity of a stationary motor due to the impulse of an impact hammer was measured with an accelerometer. Furthermore, motor noise was measured under motor run-up conditions with different rotational speeds. As a result, by combination of these three methods, the sources of motor noise were accurately identified over a wide range of frequencies. Full article

(This article belongs to the Special Issue Micro/Nano Robotics, Volume II)

► Show Figures

Figure 1

10 pages, 2663 KB

Open AccessCommunication

Mini-EmulsionFabricated Magnetic and Fluorescent Hybrid Janus Micro-Motors

by Jiapu Jiao, Dandan Xu, Yuhuan Liu, Weiwei Zhao, Jiaheng Zhang, Tingting Zheng, Huanhuan Feng and Xing Ma

Micromachines 2018, 9(2), 83; https://doi.org/10.3390/mi9020083 - 15 Feb 2018

Cited by 12 | Viewed by 6892

Abstract

Self-propelling micro/nano-motors have attracted great attention due to their controllable active motion and various functional attributes. To date, a variety of technologies have been reported for the fabrication of micro/nano-motors. However, there are still several challenges that need to be addressed. One of [...] Read more.

Self-propelling micro/nano-motors have attracted great attention due to their controllable active motion and various functional attributes. To date, a variety of technologies have been reported for the fabrication of micro/nano-motors. However, there are still several challenges that need to be addressed. One of them is to endow micro/nano-motors with multi-functionalities by a facile fabrication process. Here, we present a universal approach, adopted from the emulsion templating method, for the fabrication of Janus micro-motors. With a one-step process, magnetic nanoparticles and fluorescent dyes are simultaneously embedded into the microparticles. The self-propelled motors can be used as an active label or fluorescent tracer through manipulation of their motion using magnetic guidance. Full article

(This article belongs to the Special Issue Selected Papers from 2017 International Conference on Micro/Nanomachines)

► Show Figures

Figure 1

8 pages, 1701 KB

Open AccessArticle

Design and Simulation of A Novel Piezoelectric AlN-Si Cantilever Gyroscope

by Jian Yang, Chaowei Si, Fan Yang, Guowei Han, Jin Ning, Fuhua Yang and Xiaodong Wang

Micromachines 2018, 9(2), 81; https://doi.org/10.3390/mi9020081 - 15 Feb 2018

Cited by 11 | Viewed by 5086

Abstract

A novel design of piezoelectric aluminum nitride (AlN)-Si composite cantilever gyroscope is proposed in this paper. The cantilever is stimulated to oscillate in plane by two inverse voltages which are applied on the two paralleled drive electrodes, respectively. The whole working principles are [...] Read more.

A novel design of piezoelectric aluminum nitride (AlN)-Si composite cantilever gyroscope is proposed in this paper. The cantilever is stimulated to oscillate in plane by two inverse voltages which are applied on the two paralleled drive electrodes, respectively. The whole working principles are deduced, which based on the piezoelectric equation and elastic vibration equation. In this work, a cantilever gyroscope has been simulated and optimized by COMSOL Multiphysics 5.2a. The drive mode frequency is 87.422 kHz, and the sense mode frequency is 87.414 kHz. The theoretical sensitivity of this gyroscope is 0.145 pm/◦/s. This gyroscope has a small size and simple structure. It will be a better choice for the consumer electronics. Full article

(This article belongs to the Special Issue Piezoelectric MEMS)

► Show Figures

Figure 1

15 pages, 9262 KB

Open AccessArticle

Active Control of a Small-Scale Wind Turbine Blade Containing Magnetorheological Fluid

by Fevzi Cakmak Bolat and Selim Sivrioglu

Micromachines 2018, 9(2), 80; https://doi.org/10.3390/mi9020080 - 14 Feb 2018

Cited by 20 | Viewed by 5626

Abstract

This research study proposes a new active control structure to suppress vibrations of a small-scale wind turbine blade filled with magnetorheological (MR) fluid and actuated by an electromagnet. The aluminum blade structure is manufactured using the SH3055 (Bergey Windpower Co. Inc., Norman, OK, [...] Read more.

This research study proposes a new active control structure to suppress vibrations of a small-scale wind turbine blade filled with magnetorheological (MR) fluid and actuated by an electromagnet. The aluminum blade structure is manufactured using the SH3055 (Bergey Windpower Co. Inc., Norman, OK, USA) code numbered airfoil which is designed for use on small wind turbines. A dynamic interaction model between the MR fluid and the electromagnetic actuator is constructed to obtain a force relation. A detailed characterization study is presented for the proposed actuator to understand the nonlinear behavior of the electromagnetic force. A norm based multi-objective H₂/H_∞ controller is designed using the model of the elastic blade element. The H₂/H_∞ controller is experimentally implemented under the impact and steady state aerodynamic load conditions. The results of experiments show that the MR fluid- electromagnetic actuator is effective for suppressing vibrations of the blade structure. Full article

(This article belongs to the Special Issue Selected Papers from ICMEAS 2017)

► Show Figures

Figure 1

11 pages, 8115 KB

Open AccessArticle

Perceptual Surgical Knife with Wavelet Denoising

by Tao Li, Yuta Sunami and Sheng Zhang

Micromachines 2018, 9(2), 79; https://doi.org/10.3390/mi9020079 - 13 Feb 2018

Cited by 2 | Viewed by 4444

Abstract

Robotic surgery is a new technology in medical applications and has been undergoing rapid development. The surgical knife, essential for robotic surgery, has the ability to determine the success of an operation. In this paper, on the basis of the principle of field-effect [...] Read more.

Robotic surgery is a new technology in medical applications and has been undergoing rapid development. The surgical knife, essential for robotic surgery, has the ability to determine the success of an operation. In this paper, on the basis of the principle of field-effect transistors (FETs), a perceptual surgical knife is proposed to detect the electrons or electric field of the human body with distinguishable signals. In addition, it is difficult to discriminate between the motions of surgical knives from the perceptual signals that are disturbed by high-frequency Gaussian white noise. Therefore, the wavelet denoising approach is chosen to reduce the high-frequency noise. The proposed perceptual surgical knife with the wavelet denoising method has the characteristics of high sensitivity, low cost, and good repeatability. Full article

► Show Figures

Graphical abstract

26 pages, 21059 KB

Open AccessReview

Tubular Micro/Nanomotors: Propulsion Mechanisms, Fabrication Techniques and Applications

by Fengjun Zha, Tingwei Wang, Ming Luo and Jianguo Guan

Micromachines 2018, 9(2), 78; https://doi.org/10.3390/mi9020078 - 13 Feb 2018

Cited by 64 | Viewed by 10147

Abstract

Micro/nanomotors are self-propelled machines that can convert various energy sources into autonomous movement. With the great advances of nanotechnology, Micro/Nanomotors of various geometries have been designed and fabricated over the past few decades. Among them, the tubular Micro/Nanomotors have a unique morphology of [...] Read more.

Micro/nanomotors are self-propelled machines that can convert various energy sources into autonomous movement. With the great advances of nanotechnology, Micro/Nanomotors of various geometries have been designed and fabricated over the past few decades. Among them, the tubular Micro/Nanomotors have a unique morphology of hollow structures, which enable them to possess a strong driving force and easy surface functionalization. They are promising for environmental and biomedical applications, ranging from water remediation, sensing to active drug delivery and precise surgery. This article gives a comprehensive and clear review of tubular Micro/Nanomotors, including propulsion mechanisms, fabrication techniques and applications. In the end, we also put forward some realistic problems and speculate about corresponding methods to improve existing tubular Micro/Nanomotors. Full article

(This article belongs to the Special Issue Selected Papers from 2017 International Conference on Micro/Nanomachines)

► Show Figures

Graphical abstract

11 pages, 3395 KB

Open AccessArticle

Ultrasonically Assisted Single Point Diamond Turning of Optical Mold of Tungsten Carbide

by Zhanjie Li, Gang Jin, Fengzhou Fang, Hu Gong and Haili Jia

Micromachines 2018, 9(2), 77; https://doi.org/10.3390/mi9020077 - 12 Feb 2018

Cited by 32 | Viewed by 7670

Abstract

To realize high efficiency, low/no damage and high precision machining of tungsten carbide used for lens mold, a high frequency ultrasonic vibration cutting system was developed at first. Then, tungsten carbide was precisely machined with a polycrystalline diamond (PCD) tool assisted by the [...] Read more.

To realize high efficiency, low/no damage and high precision machining of tungsten carbide used for lens mold, a high frequency ultrasonic vibration cutting system was developed at first. Then, tungsten carbide was precisely machined with a polycrystalline diamond (PCD) tool assisted by the self-developed high frequency ultrasonic vibration cutting system. Tool wear mechanism was investigated in ductile regime machining of tungsten carbide. The cutter back-off phenomenon in the process was analyzed. The subsequent experimental results of ultra-precision machining with a single crystal diamond tool showed that: under the condition of high frequency ultrasonic vibration cutting, nano-scale surface roughness can be obtained by the diamond tool with smaller tip radius and no defects like those of ground surface were found on the machined surface. Tool wear mechanisms of the single crystal diamond tool are mainly abrasive wear and micro-chipping. To solve the problem, a method of inclined ultrasonic vibration cutting with negative rake angle was put forward according to force analysis, which can further reduce tool wear and roughness of the machined surface. The investigation was important to high efficiency and quality ultra-precision machining of tungsten carbide. Full article

(This article belongs to the Special Issue Micro-Machining: Challenges and Opportunities)

► Show Figures

Figure 1

10 pages, 8667 KB

Open AccessArticle

Development of a Triple-Coaxial Flow Device for Fabricating a Hydrogel Microtube and Its Application to Bioremediation

by Kazuma Fujimoto, Kazuhiko Higashi, Hiroaki Onoe and Norihisa Miki

Micromachines 2018, 9(2), 76; https://doi.org/10.3390/mi9020076 - 12 Feb 2018

Cited by 10 | Viewed by 4743

Abstract

This paper demonstrates a triple-coaxial flow device to continuously produce a hydrogel microtube using a microfluidic technique. The hydrogel microtube can encapsulate a microbial suspension, while allowing the diffusion of oxygen and nutrients into the microtube and preventing microbes from passing into or [...] Read more.

This paper demonstrates a triple-coaxial flow device to continuously produce a hydrogel microtube using a microfluidic technique. The hydrogel microtube can encapsulate a microbial suspension, while allowing the diffusion of oxygen and nutrients into the microtube and preventing microbes from passing into or out of the microtube. The microtubes also enable the collection of the microbes after task completion without contaminating the environment. In our previous study, we used a double-coaxial flow device to produce the microtubes, but continuous production was a challenge. In the present study, we developed a microfluidic device that fabricates a triple-coaxial flow to enable continuous production of the microtubes. Here, we characterize the production capacity of the microtubes along with their properties and demonstrate bioremediation using microtubes encapsulating a microbial suspension. Full article

(This article belongs to the Special Issue Selected Papers from the 8th Symposium on Micro-Nano Science and Technology on Micromachines)

► Show Figures

Figure 1

35 pages, 10324 KB

Open AccessFeature PaperReview

Geometry Design, Principles and Assembly of Micromotors

by Huanpo Ning, Yan Zhang, Hong Zhu, Andreas Ingham, Gaoshan Huang, Yongfeng Mei and Alexander A. Solovev

Micromachines 2018, 9(2), 75; https://doi.org/10.3390/mi9020075 - 11 Feb 2018

Cited by 55 | Viewed by 12358

Abstract

Discovery of bio-inspired, self-propelled and externally-powered nano-/micro-motors, rotors and engines (micromachines) is considered a potentially revolutionary paradigm in nanoscience. Nature knows how to combine different elements together in a fluidic state for intelligent design of nano-/micro-machines, which operate by pumping, stirring, and diffusion [...] Read more.

Discovery of bio-inspired, self-propelled and externally-powered nano-/micro-motors, rotors and engines (micromachines) is considered a potentially revolutionary paradigm in nanoscience. Nature knows how to combine different elements together in a fluidic state for intelligent design of nano-/micro-machines, which operate by pumping, stirring, and diffusion of their internal components. Taking inspirations from nature, scientists endeavor to develop the best materials, geometries, and conditions for self-propelled motion, and to better understand their mechanisms of motion and interactions. Today, microfluidic technology offers considerable advantages for the next generation of biomimetic particles, droplets and capsules. This review summarizes recent achievements in the field of nano-/micromotors, and methods of their external control and collective behaviors, which may stimulate new ideas for a broad range of applications. Full article

(This article belongs to the Special Issue Selected Papers from 2017 International Conference on Micro/Nanomachines)

► Show Figures

Graphical abstract

12 pages, 3340 KB

Open AccessArticle

Three-Dimensional Simulation of DRIE Process Based on the Narrow Band Level Set and Monte Carlo Method

by Jia-Cheng Yu, Zai-Fa Zhou, Jia-Le Su, Chang-Feng Xia, Xin-Wei Zhang, Zong-Ze Wu and Qing-An Huang

Micromachines 2018, 9(2), 74; https://doi.org/10.3390/mi9020074 - 9 Feb 2018

Cited by 7 | Viewed by 7303

Abstract

A three-dimensional topography simulation of deep reactive ion etching (DRIE) is developed based on the narrow band level set method for surface evolution and Monte Carlo method for flux distribution. The advanced level set method is implemented to simulate the time-related movements of [...] Read more.

A three-dimensional topography simulation of deep reactive ion etching (DRIE) is developed based on the narrow band level set method for surface evolution and Monte Carlo method for flux distribution. The advanced level set method is implemented to simulate the time-related movements of etched surface. In the meanwhile, accelerated by ray tracing algorithm, the Monte Carlo method incorporates all dominant physical and chemical mechanisms such as ion-enhanced etching, ballistic transport, ion scattering, and sidewall passivation. The modified models of charged particles and neutral particles are epitomized to determine the contributions of etching rate. The effects such as scalloping effect and lag effect are investigated in simulations and experiments. Besides, the quantitative analyses are conducted to measure the simulation error. Finally, this simulator will be served as an accurate prediction tool for some MEMS fabrications. Full article

► Show Figures

Figure 1

10 pages, 12114 KB

Open AccessArticle

Micro-Dosing of Fine Cohesive Powders Actuated by Pulse Inertia Force

by Hongcheng Wang, Ting Zhang, Miaomiao Zhao, Rangrang Chen and Liqun Wu

Micromachines 2018, 9(2), 73; https://doi.org/10.3390/mi9020073 - 7 Feb 2018

Cited by 5 | Viewed by 4787

Abstract

Micro-dosing of fine cohesive powders is the key technology in additive manufacturing and especially in high-potency active pharmaceutical ingredients (HPAPI). However, high accuracy micro-dosing (<5 mg) of fine cohesive powder is less trivial and still remains a challenge because it is difficult to [...] Read more.

Micro-dosing of fine cohesive powders is the key technology in additive manufacturing and especially in high-potency active pharmaceutical ingredients (HPAPI). However, high accuracy micro-dosing (<5 mg) of fine cohesive powder is less trivial and still remains a challenge because it is difficult to eliminate the aggregation phenomena caused by the strong interparticle cohesive forces (in small capillaries). This paper presents a novel micro-dose method of fine cohesive powders via a pulse inertia force system. A piezoelectric actuator is used to provide a high enough pulse inertia force for a tapered glass nozzle and drive powder particles in the nozzle to be discharged from the nozzle orifice with the help of particle self-gravity. The nozzles with outlet diameters in the range of 100–2000 µm were fabricated via a glass heating process. The α-lactose monohydrate powder is used as the micro-dosing powder. The influences of the tapered nozzle outlet diameter, amplitude of the applied pulse voltage, and angle of the nozzle axis on micro-dosing mass are researched. The minimum mean dose mass is 0.6 mg for a single pulse inertia force. The coefficient of variation of dose mass, which represents the micro-dosing stability, can be controlled below 5% when the dose mass is relatively small. Full article

(This article belongs to the Special Issue Additive Manufacturing for Medical Applications)

► Show Figures

Graphical abstract

7 pages, 2943 KB

Open AccessArticle

Controlling of Electrospray Deposition for Micropatterns

by Jiaxin Jiang, Gaofeng Zheng, Ping Zhu, Juan Liu, Yifang Liu, Xiang Wang, Wenwang Li and Shumin Guo

Micromachines 2018, 9(2), 72; https://doi.org/10.3390/mi9020072 - 6 Feb 2018

Cited by 10 | Viewed by 4692

Abstract

Based on the electrohydrodynamic (EHD) theory, a novel method of near-field electrospray is proposed to fabricate micropatterns with micro/nano-scale particles. Compared with conventional electrospray technology, the deposition area can be decreased to print a regular pattern according to the moving trajectory of the [...] Read more.

Based on the electrohydrodynamic (EHD) theory, a novel method of near-field electrospray is proposed to fabricate micropatterns with micro/nano-scale particles. Compared with conventional electrospray technology, the deposition area can be decreased to print a regular pattern according to the moving trajectory of the substrate by shortening the distance between the nozzle and the collector to several millimeters in near-field electrospray. The controlling strategies in the near-field electrospray deposition process were investigated. The line width of printed pattern increased with the increase of applied voltage, deposition time, and flow rate of solution. However, it decreased with the increase of motion velocity of the substrate. By applying a suitable matching of electrospray parameters, the regular patterns with a line width under 500 μm were printed controllably on the substrate. Thereby, atomized particles from near-field electrospray were successfully deposited in specific patterns. Characters of ‘2’, ‘7’, and ‘9’ with uniform width and steady shape were patterned. This work provides an excellent way to promote the precision integrated manufacturing of electronic system. Full article

► Show Figures

Figure 1

12 pages, 8846 KB

Open AccessArticle

3D Printing Solutions for Microfluidic Chip-To-World Connections

by Sander Van den Driesche, Frieder Lucklum, Frank Bunge and Michael J. Vellekoop

Micromachines 2018, 9(2), 71; https://doi.org/10.3390/mi9020071 - 6 Feb 2018

Cited by 56 | Viewed by 11806

Abstract

The connection of microfluidic devices to the outer world by tubes and wires is an underestimated issue. We present methods based on 3D printing to realize microfluidic chip holders with reliable fluidic and electric connections. The chip holders are constructed by microstereolithography, an [...] Read more.

The connection of microfluidic devices to the outer world by tubes and wires is an underestimated issue. We present methods based on 3D printing to realize microfluidic chip holders with reliable fluidic and electric connections. The chip holders are constructed by microstereolithography, an additive manufacturing technique with sub-millimeter resolution. The fluidic sealing between the chip and holder is achieved by placing O-rings, partly integrated into the 3D-printed structure. The electric connection of bonding pads located on microfluidic chips is realized by spring-probes fitted within the printed holder. Because there is no gluing or wire bonding necessary, it is easy to change the chip in the measurement setup. The spring probes and O-rings are aligned automatically because of their fixed position within the holder. In the case of bioanalysis applications such as cells, a limitation of 3D-printed objects is the leakage of cytotoxic residues from the printing material, cured resin. This was solved by coating the 3D-printed structures with parylene-C. The combination of silicon/glass microfluidic chips fabricated with highly-reliable clean-room technology and 3D-printed chip holders for the chip-to-world connection is a promising solution for applications where biocompatibility, optical transparency and accurate sample handling must be assured. 3D printing technology for such applications will eventually arise, enabling the fabrication of complete microfluidic devices. Full article

(This article belongs to the Special Issue 3D Printed Microfluidic Devices)

► Show Figures

Figure 1

14 pages, 1635 KB

Open AccessArticle

Optimization of Wavy-Channel Micromixer Geometry Using Taguchi Method

by Nita Solehati, Joonsoo Bae and Agus P. Sasmito

Micromachines 2018, 9(2), 70; https://doi.org/10.3390/mi9020070 - 6 Feb 2018

Cited by 17 | Viewed by 7154

Abstract

The micro-mixer has been widely used in mixing processes for chemical and pharmaceutical industries. We introduced an improved and easy to manufacture micro-mixer design utilizing the wavy structure micro-channel T-junction which can be easily manufactured using a simple stamping method. Here, we aim [...] Read more.

The micro-mixer has been widely used in mixing processes for chemical and pharmaceutical industries. We introduced an improved and easy to manufacture micro-mixer design utilizing the wavy structure micro-channel T-junction which can be easily manufactured using a simple stamping method. Here, we aim to optimize the geometrical parameters, i.e., wavy frequency, wavy amplitude, and width and height of the micro channel by utilizing the robust Taguchi statistical method with regards to the mixing performance (mixing index), pumping power and figure of merit (FoM). The interaction of each design parameter is evaluated. The results indicate that high mixing performance is not always associated with high FoM due to higher pumping power. Higher wavy frequency and amplitude is required for good mixing performance; however, this is not the case for pumping power due to an increase in Darcy friction loss. Finally, the advantages and limitations of the designs and objective functions are discussed in the light of present numerical results. Full article

(This article belongs to the Special Issue Passive Micromixers)

► Show Figures

Figure 1

10 pages, 5757 KB

Open AccessArticle

High-Performance MIM Capacitors for a Secondary Power Supply Application

by Jiliang Mu, Xiujian Chou, Zongmin Ma, Jian He and Jijun Xiong

Micromachines 2018, 9(2), 69; https://doi.org/10.3390/mi9020069 - 4 Feb 2018

Cited by 30 | Viewed by 17636

Abstract

Microstructure is important to the development of energy devices with high performance. In this work, a three-dimensional Si-based metal-insulator-metal (MIM) capacitor has been reported, which is fabricated by microelectromechanical systems (MEMS) technology. Area enlargement is achieved by forming deep trenches in a silicon [...] Read more.

Microstructure is important to the development of energy devices with high performance. In this work, a three-dimensional Si-based metal-insulator-metal (MIM) capacitor has been reported, which is fabricated by microelectromechanical systems (MEMS) technology. Area enlargement is achieved by forming deep trenches in a silicon substrate using the deep reactive ion etching method. The results indicate that an area of 2.45 × 10³ mm² can be realized in the deep trench structure with a high aspect ratio of 30:1. Subsequently, a dielectric Al₂O₃ layer and electrode W/TiN layers are deposited by atomic layer deposition. The obtained capacitor has superior performance, such as a high breakdown voltage (34.1 V), a moderate energy density (≥1.23 mJ/cm²) per unit planar area, a high breakdown electric field (6.1 ± 0.1 MV/cm), a low leakage current (10⁻⁷ A/cm² at 22.5 V), and a low quadratic voltage coefficient of capacitance (VCC) (≤63.1 ppm/V²). In addition, the device’s performance has been theoretically examined. The results show that the high energy supply and small leakage current can be attributed to the Poole–Frenkel emission in the high-field region and the trap-assisted tunneling in the low-field region. The reported capacitor has potential application as a secondary power supply. Full article

► Show Figures

Figure 1

17 pages, 3292 KB

Open AccessArticle

Design of Microscale Magnetic Tumbling Robots for Locomotion in Multiple Environments and Complex Terrains

by Chenghao Bi, Maria Guix, Benjamin V. Johnson, Wuming Jing and David J. Cappelleri

Micromachines 2018, 9(2), 68; https://doi.org/10.3390/mi9020068 - 3 Feb 2018

Cited by 67 | Viewed by 16429

Abstract

This paper presents several variations of a microscale magnetic tumbling (

μ

TUM) robot capable of traversing complex terrains in dry and wet environments. The robot is fabricated by photolithography techniques and consists of a polymeric body with two sections with embedded magnetic [...] Read more.

This paper presents several variations of a microscale magnetic tumbling (

μ

TUM) robot capable of traversing complex terrains in dry and wet environments. The robot is fabricated by photolithography techniques and consists of a polymeric body with two sections with embedded magnetic particles aligned at the ends and a middle nonmagnetic bridge section. The robot’s footprint dimensions are 400

μ

m × 800

μ

m. Different end geometries are used to test the optimal conditions for low adhesion and increased dynamic response to an actuating external rotating magnetic field. When subjected to a magnetic field as low as 7 mT in dry conditions, this magnetic microrobot is able to operate with a tumbling locomotion mode and translate with speeds of over 60 body lengths/s (48 mm/s) in dry environments and up to 17 body lengths/s (13.6 mm/s) in wet environments. Two different tumbling modes were observed and depend on the alignment of the magnetic particles. A technique was devised to measure the magnetic particle alignment angle relative to the robot’s geometry. Rotational frequency limits were observed experimentally, becoming more prohibitive as environment viscosity increases. The

μ

TUM’s performance was studied when traversing inclined planes (up to 60°), showing promising climbing capabilities in both dry and wet conditions. Maximum open loop straight-line trajectory errors of less than 4% and 2% of the traversal distance in the vertical and horizontal directions, respectively, for the

μ

TUM were observed. Full directional control of

μ

TUM was demonstrated through the traversal of a P-shaped trajectory. Additionally, successful locomotion of the optimized

μ

TUM design over complex terrains was also achieved. By implementing machine vision control and/or embedding of payloads in the middle section of the robot, it is possible in the future to upgrade the current design with computer-optimized mobility through multiple environments and the ability to perform drug delivery tasks for biomedical applications. Full article

(This article belongs to the Special Issue Micro/Nano Robotics, Volume II)

► Show Figures

Figure 1

15 pages, 5160 KB

Open AccessFeature PaperReview

Investigation on Single-Molecule Junctions Based on Current–Voltage Characteristics

by Yuji Isshiki, Yuya Matsuzawa, Shintaro Fujii and Manabu Kiguchi

Micromachines 2018, 9(2), 67; https://doi.org/10.3390/mi9020067 - 2 Feb 2018

Cited by 20 | Viewed by 7898

Abstract

The relationship between the current through an electronic device and the voltage across its terminals is a current–voltage characteristic (I–V) that determine basic device performance. Currently, I–V measurement on a single-molecule scale can be performed using break [...] Read more.

The relationship between the current through an electronic device and the voltage across its terminals is a current–voltage characteristic (I–V) that determine basic device performance. Currently, I–V measurement on a single-molecule scale can be performed using break junction technique, where a single molecule junction can be prepared by trapping a single molecule into a nanogap between metal electrodes. The single-molecule I–Vs provide not only the device performance, but also reflect information on energy dispersion of the electronic state and the electron-molecular vibration coupling in the junction. This mini review focuses on recent representative studies on I–Vs of the single molecule junctions that cover investigation on the single-molecule diode property, the molecular vibration, and the electronic structure as a form of transmission probability, and electronic density of states, including the spin state of the single-molecule junctions. In addition, thermoelectronic measurements based on I–Vs and identification of the charged carriers (i.e., electrons or holes) are presented. The analysis in the single-molecule I–Vs provides fundamental and essential information for a better understanding of the single-molecule science, and puts the single molecule junction to more practical use in molecular devices. Full article

(This article belongs to the Special Issue Atomic and Molecular Junction for Molecular Electronic Devices)

► Show Figures

Graphical abstract

7 pages, 3380 KB

Open AccessArticle

Electrospray Deposition of ZnO Thin Films and Its Application to Gas Sensors

by Wenwang Li, Jinghua Lin, Xiang Wang, Jiaxin Jiang, Shumin Guo and Gaofeng Zheng

Micromachines 2018, 9(2), 66; https://doi.org/10.3390/mi9020066 - 2 Feb 2018

Cited by 29 | Viewed by 7201

Abstract

Electrospray is a simple and cost-effective method to fabricate micro-structured thin films. This work investigates the electrospray process of ZnO patterns. The effects of experimental parameters on jet characteristics and electrosprayed patterns are studied. The length of stable jets increases with increasing applied [...] Read more.

Electrospray is a simple and cost-effective method to fabricate micro-structured thin films. This work investigates the electrospray process of ZnO patterns. The effects of experimental parameters on jet characteristics and electrosprayed patterns are studied. The length of stable jets increases with increasing applied voltage and flow rate, and decreases with increasing nozzle-to-substrate distance, while electrospray angles exhibit an opposite trend with respect to the stable jet lengths. The diameter of electrosprayed particles decreases with increasing applied voltage, and increases with flow rate. Furthermore, an alcohol gas sensor is presented. The ZnAc is calcined into ZnO, which reveals good repeatability and stability of response in target gas. The sensing response, defined as the resistance ratio of R₀/R_g, where R₀ and R_g are resistance of ZnO in air and alcohol gas, increases with the concentration of alcohol vapors and electrospray deposition time. Full article

(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)

► Show Figures

Figure 1

14 pages, 3676 KB

Open AccessArticle

Strategy for Monitoring Cardiac Interventions with an Intelligent Robotic Ultrasound Device

by Shuangyi Wang, James Housden, Areeb Zar, Ruchi Gandecha, Davinder Singh and Kawal Rhode

Micromachines 2018, 9(2), 65; https://doi.org/10.3390/mi9020065 - 2 Feb 2018

Cited by 6 | Viewed by 4405

Abstract

In recent years, 3D trans-oesophageal echocardiography (TOE) has become widely used for monitoring cardiac interventions. The control of the TOE probe during the procedure is a manual task which is tedious and harmful for the operator when exposed to radiation. To improve this [...] Read more.

In recent years, 3D trans-oesophageal echocardiography (TOE) has become widely used for monitoring cardiac interventions. The control of the TOE probe during the procedure is a manual task which is tedious and harmful for the operator when exposed to radiation. To improve this technique, an add-on robotic system has been developed for holding and manipulating a commercial TOE probe. This paper focuses on the probe adjustment strategy in order to accurately monitor the moving intra-operative catheters. The positioning strategy is divided into an initialization step based on a pre-planning method, and a localized adjustment step based on the robotic differential kinematics. A series of experiments was performed to evaluate the initialization and the localized adjustment steps. The results indicate a mean error less than 10 mm from the phantom experiments for the initialization step, and a median error less than 1.5 mm from the computer-based simulation experiments for the localized adjustment step. Compared to the much bigger image volume, it is concluded that the proposed methods are feasible for this application. Future work will focus on evaluating the method in a more realistic TOE scanning scenario. Full article

(This article belongs to the Special Issue Selected Papers from ICMEAS 2017)

► Show Figures

Figure 1

16 pages, 21236 KB

Open AccessArticle

Fundamental Study for a Graphite-Based Microelectromechanical System

by Junji Sone, Mutsuaki Murakami and Atsushi Tatami

Micromachines 2018, 9(2), 64; https://doi.org/10.3390/mi9020064 - 2 Feb 2018

Cited by 10 | Viewed by 5630

Abstract

We aimed to develop a process for constructing a carbon-based microelectromechanical system (MEMS). First, we prepared a highly oriented pyrolytic graphite (HOPG) crystal microsheet by exfoliation. We fabricated cantilevers and a double-clamped beam by controlling the thickness of the HOPG microsheet using a [...] Read more.

We aimed to develop a process for constructing a carbon-based microelectromechanical system (MEMS). First, we prepared a highly oriented pyrolytic graphite (HOPG) crystal microsheet by exfoliation. We fabricated cantilevers and a double-clamped beam by controlling the thickness of the HOPG microsheet using a MEMS process. Second, we used a graphite sheet with contour line adhesion by metal sputter deposition. Third, we used a highly accurate graphite sheet with face adhesion and laser cutting. The first resonance frequencies were evaluated. We confirmed improvement in Q values to 1/10 level of a quarts vibrator, high performance, and a simple structure. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

► Show Figures

Figure 1

11 pages, 1888 KB

Open AccessReview

The Fantastic Voyage of the Trypanosome: A Protean Micromachine Perfected during 500 Million Years of Engineering

by Timothy Krüger and Markus Engstler

Micromachines 2018, 9(2), 63; https://doi.org/10.3390/mi9020063 - 2 Feb 2018

Cited by 4 | Viewed by 7271

Abstract

The human body is constantly attacked by pathogens. Various lines of defence have evolved, among which the immune system is principal. In contrast to most pathogens, the African trypanosomes thrive freely in the blood circulation, where they escape immune destruction by antigenic variation [...] Read more.

The human body is constantly attacked by pathogens. Various lines of defence have evolved, among which the immune system is principal. In contrast to most pathogens, the African trypanosomes thrive freely in the blood circulation, where they escape immune destruction by antigenic variation and incessant motility. These unicellular parasites are flagellate microswimmers that also withstand the harsh mechanical forces prevailing in the bloodstream. They undergo complex developmental cycles in the bloodstream and organs of the mammalian host, as well as the disease-transmitting tsetse fly. Each life cycle stage has been shaped by evolution for manoeuvring in distinct microenvironments. Here, we introduce trypanosomes as blueprints for nature-inspired design of trypanobots, micromachines that, in the future, could explore the human body without affecting its physiology. We review cell biological and biophysical aspects of trypanosome motion. While this could provide a basis for the engineering of microbots, their actuation and control still appear more like fiction than science. Here, we discuss potentials and challenges of trypanosome-inspired microswimmer robots. Full article

(This article belongs to the Special Issue Locomotion at Small Scales: From Biology to Artificial Systems)

► Show Figures

Figure 1

12 pages, 9871 KB

Open AccessArticle

Micro-Electromechanical Acoustic Resonator Coated with Polyethyleneimine Nanofibers for the Detection of Formaldehyde Vapor

by Da Chen, Lei Yang, Wenhua Yu, Maozeng Wu, Wei Wang and Hongfei Wang

Micromachines 2018, 9(2), 62; https://doi.org/10.3390/mi9020062 - 1 Feb 2018

Cited by 26 | Viewed by 6809

Abstract

We demonstrate a promising strategy to combine the micro-electromechanical film bulk acoustic resonator and the nanostructured sensitive fibers for the detection of low-concentration formaldehyde vapor. The polyethyleneimine nanofibers were directly deposited on the resonator surface by a simple electrospinning method. The film bulk [...] Read more.

We demonstrate a promising strategy to combine the micro-electromechanical film bulk acoustic resonator and the nanostructured sensitive fibers for the detection of low-concentration formaldehyde vapor. The polyethyleneimine nanofibers were directly deposited on the resonator surface by a simple electrospinning method. The film bulk acoustic resonator working at 4.4 GHz acted as a sensitive mass loading platform and the three-dimensional structure of nanofibers provided a large specific surface area for vapor adsorption and diffusion. The ultra-small mass change induced by the absorption of formaldehyde molecules onto the amine groups in polyethyleneimine was detected by measuring the frequency downshift of the film bulk acoustic resonator. The proposed sensor exhibits a fast, reversible and linear response towards formaldehyde vapor with an excellent selectivity. The gas sensitivity and the detection limit were 1.216 kHz/ppb and 37 ppb, respectively. The study offers a great potential for developing sensitive, fast-response and portable sensors for the detection of indoor air pollutions. Full article

(This article belongs to the Special Issue Micro-Resonators: The Quest for Superior Performance)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Micromachines, Volume 9, Issue 2 (February 2018) – 51 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI