Editorial

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Open AccessEditorial

Editorial for the Special Issue on Micro-Manufacturing and Applications

by Atanas Ivanov

Micromachines 2021, 12(8), 851; https://doi.org/10.3390/mi12080851 - 21 Jul 2021

Viewed by 1133

This editorial is for collating the Special Issue on micro-manufacturing and applications, based on stringently selected papers presented to the editorial board of this Special Issue [...] Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

Research

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15 pages, 6990 KiB

Open AccessArticle

Experimental Study on Ultrasonic Vibration-Assisted WECDM of Glass Microstructures with a High Aspect Ratio

by Yan Chen, Xu Feng and Gongming Xin

Micromachines 2021, 12(2), 125; https://doi.org/10.3390/mi12020125 - 26 Jan 2021

Cited by 13 | Viewed by 2637

Abstract

With the rapid development of micro-electro-mechanical systems (MEMSs), the demand for glass microstructure is increasing. For the purpose of achieving high quality and stable machining of glass microstructures with a high aspect ratio, ultrasonic vibration is applied into the micro-wire electrochemical discharge machining [...] Read more.

With the rapid development of micro-electro-mechanical systems (MEMSs), the demand for glass microstructure is increasing. For the purpose of achieving high quality and stable machining of glass microstructures with a high aspect ratio, ultrasonic vibration is applied into the micro-wire electrochemical discharge machining (WECDM), which is proposed as ultrasonic vibration-assisted WECDM with a micro helical electrode. Firstly, the formation of a gas film on the surface of the helical electrode in WECDM machining is simulated, meaning the thickness of the gas film can be reduced by adding suitable ultrasonic amplitude, thus reducing the critical voltage, then the machining localization and stability were enhanced. Then, the micro helical electrode with a diameter of 100 μm is used to carry out sets of experiments that study the influence of ultrasonic amplitude, machining voltage, duty factor, pulse frequency, and feed rate on the slit width. The experimental results show that the machining stability and quality are significantly improved by adding suitable ultrasonic amplitude. When the amplitude was 5.25 μm, the average slit width was reduced to 128.63 μm with a decrease of 20.78%. Finally, with the optimized machining parameters, micro planar coil structure and microcantilever structure with a high aspect ratio were fabricated successfully on the glass plate. It is proved that ultrasonic vibration-assisted WECDM with the micro helical electrode method can meet the requirements of high aspect ratio microstructure machining for hard and brittle materials. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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13 pages, 5790 KiB

Open AccessArticle

Investigation of the Turbulent Drag Reduction Mechanism of a Kind of Microstructure on Riblet Surface

by Mingrui Ao, Miaocao Wang and Fulong Zhu

Micromachines 2021, 12(1), 59; https://doi.org/10.3390/mi12010059 - 06 Jan 2021

Cited by 15 | Viewed by 3197

Abstract

With the k-ε renormalization group turbulence model, the drag reduction mechanism of three- dimensional spherical crown microstructure of different protruding heights distributing on the groove surface was studied in this paper. These spherical crown microstructures were divided into two categories according to the [...] Read more.

With the k-ε renormalization group turbulence model, the drag reduction mechanism of three- dimensional spherical crown microstructure of different protruding heights distributing on the groove surface was studied in this paper. These spherical crown microstructures were divided into two categories according to the positive and negative of protruding height. The positive spherical crown micro-structures can destroy a large number of vortexes on the groove surface, which increases relative friction between water flow and the groove surface. With decreasing the vertical height of the spherical crown microstructure, the number of rupture vortexes gradually decreases. Due to the still water area causes by the blocking effect of the spherical crown microstructure, it was found that the shear stress on the groove surface can be reduced, which can form the entire drag reduction state. In another case, the spherical crown microstructures protrude in the negative direction, vortexes can be generated inside the spherical crown, it was found that these vortexes can effectively reduce the resistance in terms of pressure and friction. In a small volume, it was shown that the surface drag reduction rate of spherical crown microstructures protrudes in negative directions can be the same as high as 24.8%. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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17 pages, 5207 KiB

Open AccessArticle

Study on Flow Characteristics of Working Medium in Microchannel Simulated by Porous Media Model

by Yufan Xue, Chunsheng Guo, Xiaoxiao Gu, Yanfeng Xu, Lihong Xue and Han Lin

Micromachines 2021, 12(1), 18; https://doi.org/10.3390/mi12010018 - 26 Dec 2020

Cited by 4 | Viewed by 2163

Abstract

As a phase change evaporator, a microchannel array heat exchanger is of great significance in the field of microscale heat dissipation. The performance of which strongly depends on the flow resistance, capillary force, and other factors. In order to improve the heat dissipation [...] Read more.

As a phase change evaporator, a microchannel array heat exchanger is of great significance in the field of microscale heat dissipation. The performance of which strongly depends on the flow resistance, capillary force, and other factors. In order to improve the heat dissipation efficiency, it is necessary to perform an in-depth study of the characteristics of microchannel flow using numerical simulation. However, the current simulation model requires high computational cost and long simulation time. To solve this problem, this paper simplifies the numerical simulation of the rectangular parallel array microchannels by building the basic flow model based on the concept of porous media. In addition, we explore the effect of aspect-ratio (AR), hydraulic diameter, inlet velocity, and other parameters of fluid flow behavior inside the microchannels. Meanwhile, a user-defined function (UDF) is formulated to add the capillary force into the model to introduce capillary force into the porous media model. Through the above research, the paper establishes the porous media model for single-phase and gas-liquid two-phase flow, which acts as a simplification of microchannel array simulation without grossly affecting the results obtained. In addition, we designed and manufactured experiments using silicon-based microchannel heat exchangers with different-ratios, and combined with the visualization method to measure the performance of the device and compared them with simulation results. The theoretical model is verified through the suction experiment of array microchannel evaporator capillary core. The simplified model of microchannel array significantly saves the computational cost and time, and provides guidance for the related experimental researches. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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21 pages, 8536 KiB

Open AccessArticle

High Aspect Ratio Thin-Walled Structures in D2 Steel through Wire Electric Discharge Machining (EDM)

by Naveed Ahmed, Muhammad Ahmad Naeem, Ateekh Ur Rehman, Madiha Rafaqat, Usama Umer and Adham E. Ragab

Micromachines 2021, 12(1), 1; https://doi.org/10.3390/mi12010001 - 22 Dec 2020

Cited by 9 | Viewed by 2703

Abstract

Thin structures are often required for several engineering applications. Although thick sections are relatively easy to produce, the cutting of thin sections poses greater challenges, particularly in the case of thermal machining processes. The level of difficulty is increased if the thin sections [...] Read more.

Thin structures are often required for several engineering applications. Although thick sections are relatively easy to produce, the cutting of thin sections poses greater challenges, particularly in the case of thermal machining processes. The level of difficulty is increased if the thin sections are of larger lengths and heights. In this study, high-aspect-ratio thin structures of micrometer thickness (117–500 µm) were fabricated from D2 steel through wire electrical discharge machining. Machining conditions were kept constant, whereas the structure (fins) sizes were varied in terms of fin thickness (FT), fin height (FH), and fin length (FL). The effects of variation in FT, FH, and FL were assessed over the machining errors (FT and FL errors) and structure formation and its quality. Experiments were conducted in a phased manner (four phases) to determine the minimum possible FT and maximum possible FL that could be achieved without compromising the shape of the structure (straight and uniform cross-section). Thin structures of smaller lengths (1–2 mm long) can be fabricated easily, but, as the length exceeds 2 mm, the structure formation loses its shape integrity and the structure becomes broken, deflected, or deflected and merged at the apex point of the fins. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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8 pages, 2391 KiB

Open AccessArticle

High-Identical Numerical Aperture, Multifocal Microlens Array through Single-Step Multi-Sized Hole Patterning Photolithography

by Joong Hoon Lee, Sehui Chang, Min Seok Kim, Yeong Jae Kim, Hyun Myung Kim and Young Min Song

Micromachines 2020, 11(12), 1068; https://doi.org/10.3390/mi11121068 - 30 Nov 2020

Cited by 16 | Viewed by 3147

Abstract

Imaging applications based on microlens arrays (MLAs) have a great potential for the depth sensor, wide field-of-view camera and the reconstructed hologram. However, the narrow depth-of-field remains the challenge for accurate, reliable depth estimation. Multifocal microlens array (Mf-MLAs) is perceived as a major [...] Read more.

Imaging applications based on microlens arrays (MLAs) have a great potential for the depth sensor, wide field-of-view camera and the reconstructed hologram. However, the narrow depth-of-field remains the challenge for accurate, reliable depth estimation. Multifocal microlens array (Mf-MLAs) is perceived as a major breakthrough, but existing fabrication methods are still hindered by the expensive, low-throughput, and dissimilar numerical aperture (NA) of individual lenses due to the multiple steps in the photolithography process. This paper reports the fabrication method of high NA, Mf-MLAs for the extended depth-of-field using single-step photolithography assisted by chemical wet etching. The various lens parameters of Mf-MLAs are manipulated by the multi-sized hole photomask and the wet etch time. Theoretical and experimental results show that the Mf-MLAs have three types of lens with different focal lengths, while maintaining the uniform and high NA irrespective of the lens type. Additionally, we demonstrate the multi-focal plane image acquisition via Mf-MLAs integrated into a microscope. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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16 pages, 6998 KiB

Open AccessArticle

An Experimental Investigation of Steel Surface Topography Transfer by Cold Rolling

by Dong Xu, Quan Yang, Xiaochen Wang, Hainan He, Youzhao Sun and Wenpei Li

Micromachines 2020, 11(10), 916; https://doi.org/10.3390/mi11100916 - 30 Sep 2020

Cited by 6 | Viewed by 1989

Abstract

Automobile and household appliance panels require steel strips with extremely high-quality surfaces. Therefore, an in-depth study of the surface topography transfer of the steel strip during the rolling process is of considerable significance for improving product quality. In this study, the scale-invariant feature [...] Read more.

Automobile and household appliance panels require steel strips with extremely high-quality surfaces. Therefore, an in-depth study of the surface topography transfer of the steel strip during the rolling process is of considerable significance for improving product quality. In this study, the scale-invariant feature transform (SIFT) algorithm is used to realize the large-field stitching and the correspondence measurement of the surface topography of the roll and strip. The surface topography transfer mechanism and microconvex change law during cold rolling are revealed. Further analysis is conducted regarding the effects of different reduction rates and the initial surface topography of the roll on the formation of strip surface topography. Experimental results reveal that the furrow phenomenon occurs during the rolling process owing to the backward slip effect but is eliminated by the elastoplastic deformation of the matrix and the forward slip action. No furrow occurred along the width direction of the strip. With an increase in the rolling reduction rate, the transfer rate increases, and the strip surface topography is closer to the roll surface topography. Under the same rolling roughness condition and a small reduction rate (5%), the transfer degree increases remarkably with a rise in the reduction rate and increases slowly as the reduction rate continues to grow (from 7 to 10%). This study serves as a theoretical basis for the subsequent improvement of the surface quality of cold rolled strips. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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14 pages, 4415 KiB

Open AccessArticle

Monolithically Integrated Diffused Silicon Two-Zone Heaters for Silicon-Pyrex Glass Microreactors for Production of Nanoparticles: Heat Exchange Aspects

by Milena Rašljić Rafajilović, Katarina Radulović, Milče M. Smiljanić, Žarko Lazić, Zoran Jakšić, Dragomir Stanisavljev and Dana Vasiljević Radović

Micromachines 2020, 11(9), 818; https://doi.org/10.3390/mi11090818 - 28 Aug 2020

Cited by 4 | Viewed by 2485

Abstract

We present the design, simulation, fabrication and characterization of monolithically integrated high resistivity p-type boron-diffused silicon two-zone heaters in a model high temperature microreactor intended for nanoparticle fabrication. We used a finite element method for simulations of the heaters’ operation and performance. Our [...] Read more.

We present the design, simulation, fabrication and characterization of monolithically integrated high resistivity p-type boron-diffused silicon two-zone heaters in a model high temperature microreactor intended for nanoparticle fabrication. We used a finite element method for simulations of the heaters’ operation and performance. Our experimental model reactor structure consisted of a silicon wafer anodically bonded to a Pyrex glass wafer with an isotropically etched serpentine microchannels network. We fabricated two separate spiral heaters with different temperatures, mutually thermally isolated by barrier apertures etched throughout the silicon wafer. The heaters were characterized by electric measurements and by infrared thermal vision. The obtained results show that our proposed procedure for the heater fabrication is robust, stable and controllable, with a decreased sensitivity to random variations of fabrication process parameters. Compared to metallic or polysilicon heaters typically integrated into microreactors, our approach offers improved control over heater characteristics through adjustment of the Boron doping level and profile. Our microreactor is intended to produce titanium dioxide nanoparticles, but it could be also used to fabricate nanoparticles in different materials as well, with various parameters and geometries. Our method can be generally applied to other high-temperature microsystems. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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15 pages, 6146 KiB

Open AccessArticle

Research on Voltage Waveform Fault Detection of Miniature Vibration Motor Based on Improved WP-LSTM

by Ruirui Wang, Zhan Feng, Sisi Huang, Xia Fang and Jie Wang

Micromachines 2020, 11(8), 753; https://doi.org/10.3390/mi11080753 - 31 Jul 2020

Cited by 10 | Viewed by 2692

Abstract

To solve the problem of vibration motor fault detection accuracy and inefficiency in smartphone components, this paper proposes a fault diagnosis method based on the wavelet packet and improves long and short-term memory network. First, the voltage signal of the vibration motor is [...] Read more.

To solve the problem of vibration motor fault detection accuracy and inefficiency in smartphone components, this paper proposes a fault diagnosis method based on the wavelet packet and improves long and short-term memory network. First, the voltage signal of the vibration motor is decomposed by a wavelet packet to reconstruct the signal. Secondly, the reconstructed signal is input into the improved three-layer LSTM network as a feature vector. The memory characteristics of the LSTM network are used to fully learn the time-series fault feature information in the unsteady state signal, and then, the model is used to diagnose the motor fault. Finally, the feasibility of the proposed method is verified through experiments and can be applied to engineering practice. Compared with the existing motor fault diagnosis method, the improved WP-LSTM diagnosis method has a better diagnosis effect and improves fault diagnosis. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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17 pages, 8852 KiB

Open AccessArticle

Deep Reactive Ion Etching of Z-Cut Alpha Quartz for MEMS Resonant Devices Fabrication

by Bo Li, Cun Li, Yulong Zhao, Chao Han and Quanwei Zhang

Micromachines 2020, 11(8), 724; https://doi.org/10.3390/mi11080724 - 26 Jul 2020

Cited by 8 | Viewed by 4311

Abstract

Quartz is widely used in microelectromechanical systems (MEMS). Especially, MEMS quartz resonators are applied to sensors and serve as sensitive elements. The capability of deep etching is a limitation for the application. Presented in this paper is a deep and high accuracy reactive [...] Read more.

Quartz is widely used in microelectromechanical systems (MEMS). Especially, MEMS quartz resonators are applied to sensors and serve as sensitive elements. The capability of deep etching is a limitation for the application. Presented in this paper is a deep and high accuracy reactive ion etching method applied to a quartz resonator etching process with a Cr mask. In order to enhance the capability of deep etching and machining accuracy, three kinds of etching gas (C₄F₈/Ar, SF₆/Ar and SF₆/C4F₈/Ar), bias power, inductively coupled plasma (ICP) power and chamber pressure were studied in an industrial reactive ion etching machine (GDE C200). Results indicated that the SF₆/C₄F₈/Ar chemistry gas is the suitable and optimal choice. Experiment results indicate that Cr (chromium) mask can obtain a higher selectivity than aluminum and titanium mask. A “sandwich” structure composed of Al layer-Cr layer-Al layer-Cr layer was proposed. The Al (aluminum) film can play the role of releasing stress and protecting gold electrodes, which can enhance the thickness of metal mask. An optimized process using SF₆/C₄F₈/Ar plasmas showed the quartz etching rate of 450 nm/min. Meanwhile, a microchannel with a depth of 75.4 µm is fabricated, and a nearly vertical sidewall profile, smooth surface is achieved. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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Review

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27 pages, 4788 KiB

Open AccessReview

Application of Stereolithography Based 3D Printing Technology in Investment Casting

by Muslim Mukhtarkhanov, Asma Perveen and Didier Talamona

Micromachines 2020, 11(10), 946; https://doi.org/10.3390/mi11100946 - 19 Oct 2020

Cited by 74 | Viewed by 8738

Abstract

Advanced methods for manufacturing high quality parts should be used to ensure the production of competitive products for the world market. Investment casting (IC) is a process where a wax pattern is used as a sacrificial pattern to manufacture high precision casting of [...] Read more.

Advanced methods for manufacturing high quality parts should be used to ensure the production of competitive products for the world market. Investment casting (IC) is a process where a wax pattern is used as a sacrificial pattern to manufacture high precision casting of solid metal parts. Rapid casting is in turn, a technique that eases the IC process by combining additive manufacturing (AM) technologies with IC. The use of AM technologies to create patterns for new industrial products is a unique opportunity to develop cost-effective methods for producing investment casting parts in a timely manner. Particularly, stereolithography (SLA) based AM is of interest due to its high dimensional accuracy and the smooth surface quality of the printed parts. From the first appearance of commercially available SLA printers in the market, it took a few decades until desktop SLA printers became available to consumers at a reasonable price. Therefore, the aim of this review paper is to analyze the state-of-the-art and applicability of SLA based 3D printing technology in IC manufacturing, as SLA based AM technologies have been gaining enormous popularity in recent times. Other AM techniques in IC are also reviewed for comparison. Moreover, the SLA process parameters, material properties, and current issues are discussed. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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31 pages, 5104 KiB

Open AccessReview

Research Status and Development Trend of MEMS Switches: A Review

by Tongtong Cao, Tengjiang Hu and Yulong Zhao

Micromachines 2020, 11(7), 694; https://doi.org/10.3390/mi11070694 - 17 Jul 2020

Cited by 38 | Viewed by 6988

Abstract

MEMS switch is a movable device manufactured by means of semiconductor technology, possessing many incomparable advantages such as a small volume, low power consumption, high integration, etc. This paper reviews recent research of MEMS switches, pointing out the important performance indexes and systematically [...] Read more.

MEMS switch is a movable device manufactured by means of semiconductor technology, possessing many incomparable advantages such as a small volume, low power consumption, high integration, etc. This paper reviews recent research of MEMS switches, pointing out the important performance indexes and systematically summarizing the classification according to driving principles. Then, a comparative study of current MEMS switches stressing their strengths and drawbacks is presented, based on performance requirements such as driven voltage, power consumption, and reliability. The efforts of teams to optimize MEMS switches are introduced and the applications of switches with different driving principles are also briefly reviewed. Furthermore, the development trend of MEMS switch and the research gaps are discussed. Finally, a summary and forecast about MEMS switches is given with the aim of providing a reference for future research in this domain. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications)

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