Micromachines

41 pages, 14677 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Review of Spatter in Laser Powder Bed Fusion Additive Manufacturing: In Situ Detection, Generation, Effects, and Countermeasures

by Zheng Li, Hao Li, Jie Yin, Yan Li, Zhenguo Nie, Xiangyou Li, Deyong You, Kai Guan, Wei Duan, Longchao Cao, Dengzhi Wang, Linda Ke, Yang Liu, Ping Zhao, Lin Wang, Kunpeng Zhu, Zhengwen Zhang, Liang Gao and Liang Hao

Micromachines 2022, 13(8), 1366; https://doi.org/10.3390/mi13081366 - 22 Aug 2022

Cited by 91 | Viewed by 11913

Abstract

Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF) additive manufacturing. Spatter behavior has an intrinsic correlation with the forming quality in L-PBF because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes [...] Read more.

Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF) additive manufacturing. Spatter behavior has an intrinsic correlation with the forming quality in L-PBF because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes more severe in the fabrication of large-sized parts during the multi-laser L-PBF process. Therefore, investigations of spatter generation and countermeasures have become more urgent. Although much research has provided insights into the melt pool, microstructure, and mechanical property, reviews of spatter in L-PBF are still limited. This work reviews the literature on the in situ detection, generation, effects, and countermeasures of spatter in L-PBF. It is expected to pave the way towards a novel generation of highly efficient and intelligent L-PBF systems. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications)

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13 pages, 2696 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Acoustic Manipulation of Intraocular Particles

by Ari Leshno, Avraham Kenigsberg, Heli Peleg-Levy, Silvia Piperno, Alon Skaat and Hagay Shpaisman

Micromachines 2022, 13(8), 1362; https://doi.org/10.3390/mi13081362 - 21 Aug 2022

Cited by 5 | Viewed by 3396

Abstract

Various conditions cause dispersions of particulate matter to circulate inside the anterior chamber of a human eye. These dispersed particles might reduce visual acuity or promote elevation of intraocular pressure (IOP), causing secondary complications such as particle related glaucoma, which is a major [...] Read more.

Various conditions cause dispersions of particulate matter to circulate inside the anterior chamber of a human eye. These dispersed particles might reduce visual acuity or promote elevation of intraocular pressure (IOP), causing secondary complications such as particle related glaucoma, which is a major cause of blindness. Medical and surgical treatment options are available to manage these complications, yet preventive measures are not currently available. Conceptually, manipulating these dispersed particles in a way that reduces their negative impact could prevent these complications. However, as the eye is a closed system, manipulating dispersed particles in it is challenging. Standing acoustic waves have been previously shown to be a versatile tool for manipulation of bioparticles from nano-sized extracellular vesicles up to millimeter-sized organisms. Here we introduce for the first time a novel method utilizing standing acoustic waves to noninvasively manipulate intraocular particles inside the anterior chamber. Using a cylindrical acoustic resonator, we show ex vivo manipulation of pigmentary particles inside porcine eyes. We study the effect of wave intensity over time and rule out temperature changes that could damage tissues. Optical coherence tomography and histologic evaluations show no signs of damage or any other side effect that could be attributed to acoustic manipulation. Finally, we lay out a clear pathway to how this technique can be used as a non-invasive tool for preventing secondary glaucoma. This concept has the potential to control and arrange intraocular particles in specific locations without causing any damage to ocular tissue and allow aqueous humor normal outflow which is crucial for maintaining proper IOP levels. Full article

(This article belongs to the Special Issue Recent Advances in Acoustofluidics)

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16 pages, 5193 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Fabrication of Millimeter-Wave Frequency-Tunable Metamaterial Absorber Using MEMS Cantilever Actuators

by Myungjin Chung, Heijun Jeong, Yong-Kweon Kim, Sungjoon Lim and Chang-Wook Baek

Micromachines 2022, 13(8), 1354; https://doi.org/10.3390/mi13081354 - 20 Aug 2022

Cited by 11 | Viewed by 3525

Abstract

In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced [...] Read more.

In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced MEMS cantilever array having initial out-of-plane deflections, and the cantilevers were electrostatically actuated to generate a capacitance change. The dimensional parameters of the absorber were determined via impedance matching using a full electromagnetic simulation. The designed absorber was fabricated on a glass wafer with surface micromachining processes using a photoresist sacrificial layer and the oxygen-plasma-ashing process to release the cantilevers. The performance of the fabricated absorber was experimentally validated using a waveguide measurement setup. The absorption frequency shifted down according to the applied DC (direct current) bias voltage from 28 GHz in the initial off state to 25.5 GHz in the pull-down state with the applied voltage of 15 V. The measured reflection coefficients at those frequencies were −5.68 dB and −33.60 dB, corresponding to the peak absorptivity rates of 72.9 and 99.9%, respectively. Full article

(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)

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12 pages, 1822 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Integrated Amplitude and Phase Monitor for Micro-Actuators

by Sandra Nicole Manosalvas-Kjono, Ronald Quan and Olav Solgaard

Micromachines 2022, 13(8), 1360; https://doi.org/10.3390/mi13081360 - 20 Aug 2022

Cited by 3 | Viewed by 2471

Abstract

Micro-actuators driven on resonance maximize reach and speed; however, due to their sensitivity to environmental factors (e.g., temperature and air pressure), the amplitude and phase response must be monitored to achieve an accurate actuator position. We introduce an MEMS (microelectromechanical system) amplitude and [...] Read more.

Micro-actuators driven on resonance maximize reach and speed; however, due to their sensitivity to environmental factors (e.g., temperature and air pressure), the amplitude and phase response must be monitored to achieve an accurate actuator position. We introduce an MEMS (microelectromechanical system) amplitude and phase monitor (MAPM) with a signal-to-noise ratio of 51 dB and 11.0 kHz bandwidth, capable of simultaneously driving and sensing the movement of 1D and 2D electrostatically driven micro-actuators without modifying the chip or its packaging. The operational principle is to electromechanically modulate the amplitude of a high-frequency signal with the changing capacitance of the micro-actuator. MAPM operation is characterized and verified by simultaneously measuring the amplitude and phase frequency response of commercial micromirrors. We demonstrate that the MAPM circuitry is insensitive to complex relationships between capacitance and position of the MEMS actuators, and it is capable of giving real-time read-out of the micromirror motion. Our measurements also reveal and quantify observations of phase drift and crosstalk in 2D resonant operation. Measurements of phase changes over time under normal operation also verify the need for phase monitoring. The open-loop, high-sensitivity position sensor enables detailed characterization of dynamic micro-actuator behavior, leading to new insights and new types of operation, including improved control of nonlinear motion. Full article

(This article belongs to the Special Issue Optical MEMS, Volume III)

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11 pages, 3967 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Wide-Angle Mini-Light-Emitting Diodes without Optical Lens for an Ultrathin Flexible Light Source

by Yen-Lung Chen, Wen-Chung Chin, Chun-Wei Tsai, Chang-Che Chiu, Ching-Ho Tien, Zhi-Ting Ye and Pin Han

Micromachines 2022, 13(8), 1326; https://doi.org/10.3390/mi13081326 - 16 Aug 2022

Cited by 8 | Viewed by 2759

Abstract

This report outlines a proposed method of packaging wide-angle (WA) mini-light-emitting diode (mini-LED) devices without optical lenses to create a highly efficient, ultrathin, flexible planar backlight for portable quantum dot light-emitting diode (QLED) displays. Since the luminous intensity curve for mini-LEDs generally recommends [...] Read more.

This report outlines a proposed method of packaging wide-angle (WA) mini-light-emitting diode (mini-LED) devices without optical lenses to create a highly efficient, ultrathin, flexible planar backlight for portable quantum dot light-emitting diode (QLED) displays. Since the luminous intensity curve for mini-LEDs generally recommends a beam angle of 120°, numerous LEDs are necessary to achieve a uniform surface light source for a QLED backlight. The light-guide layer and diffusion layer were packaged together on a chip surface to create WA mini-LEDs with a viewing angle of 180°. These chips were then combined with a quantum dot (QD) film and an optical film to create a high-efficiency, ultrathin, flexible planar light source with excellent color purity that can be used as a QLED display backlight. A 6 in (14.4 cm) light source was used as an experimental sample. When 1.44 W was supplied to the sample, the 3200-piece WA mini-LED with a flexible planar QLED display had a beam angle of 180° on the luminous intensity curve, a planar backlight thickness of 0.98 mm, a luminance of 10,322 nits, and a luminance uniformity of 92%. Full article

(This article belongs to the Special Issue Advanced Technologies in Electronic Packaging)

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22 pages, 5778 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Oil Displacement in Calcite-Coated Microfluidic Chips via Waterflooding at Elevated Temperatures and Long Times

by Duy Le-Anh, Ashit Rao, Amy Z. Stetten, Subhash C. Ayirala, Mohammed B. Alotaibi, Michel H. G. Duits, Han Gardeniers, Ali A. AlYousef and Frieder Mugele

Micromachines 2022, 13(8), 1316; https://doi.org/10.3390/mi13081316 - 14 Aug 2022

Cited by 4 | Viewed by 3859

Abstract

In microfluidic studies of improved oil recovery, mostly pore networks with uniform depth and surface chemistry are used. To better mimic the multiple porosity length scales and surface heterogeneity of carbonate reservoirs, we coated a 2.5D glass microchannel with calcite particles. After aging [...] Read more.

In microfluidic studies of improved oil recovery, mostly pore networks with uniform depth and surface chemistry are used. To better mimic the multiple porosity length scales and surface heterogeneity of carbonate reservoirs, we coated a 2.5D glass microchannel with calcite particles. After aging with formation water and crude oil (CRO), high-salinity Water (HSW) was flooded at varying temperatures and durations. Time-resolved microscopy revealed the CRO displacements. Precise quantification of residual oil presented some challenges due to calcite-induced optical heterogeneity and brine–oil coexistence at (sub)micron length scales. Both issues were addressed using pixel-wise intensity calibration. During waterflooding, most of the ultimately produced oil gets liberated within the first pore volume (similar to glass micromodels). Increasing temperature from 22 °C to 60 °C and 90 °C produced some more oil. Waterflooding initiated directly at 90 °C produced significantly more oil than at 22 °C. Continuing HSW exposure at 90 °C for 8 days does not release additional oil; although, a spectacular growth of aqueous droplets is observed. The effect of calcite particles on CRO retention is weak on flat surfaces, where the coverage is ~20%. The calcite-rich pore edges retain significantly more oil suggesting that, in our micromodel wall roughness is a stronger determinant for oil retention than surface chemistry. Full article

(This article belongs to the Special Issue Design, Optimization, Fabrication and Applications of Microfluidic Devices)

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25 pages, 5499 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress in Development and Applications of Ionic Polymer–Metal Composite

by Si Won Park, Sang Jun Kim, Seong Hyun Park, Juyeon Lee, Hyungjun Kim and Min Ku Kim

Micromachines 2022, 13(8), 1290; https://doi.org/10.3390/mi13081290 - 11 Aug 2022

Cited by 21 | Viewed by 6113

Abstract

Electroactive polymer (EAP) is a polymer that reacts to electrical stimuli, such as voltage, and can be divided into electronic and ionic EAP by an electrical energy transfer mechanism within the polymer. The mechanism of ionic EAP is the movement of the positive [...] Read more.

Electroactive polymer (EAP) is a polymer that reacts to electrical stimuli, such as voltage, and can be divided into electronic and ionic EAP by an electrical energy transfer mechanism within the polymer. The mechanism of ionic EAP is the movement of the positive ions inducing voltage change in the polymer membrane. Among the ionic EAPs, an ionic polymer–metal composite (IPMC) is composed of a metal electrode on the surface of the polymer membrane. A common material for the polymer membrane of IPMC is Nafion containing hydrogen ions, and platinum, gold, and silver are commonly used for the electrode. As a result, IPMC has advantages, such as low voltage requirements, large bending displacement, and bidirectional actuation. Manufacturing of IPMC is composed of preparing the polymer membrane and plating electrode. Preparation methods for the membrane include solution casting, hot pressing, and 3D printing. Meanwhile, electrode formation methods include electroless plating, electroplating, direct assembly process, and sputtering deposition. The manufactured IPMC is widely demonstrated in applications such as grippers, micro-pumps, biomedical, biomimetics, bending sensors, flow sensors, energy harvesters, biosensors, and humidity sensors. This paper will review the overall field of IPMC by demonstrating the categorization, principle, materials, and manufacturing method of IPMC and its applications. Full article

(This article belongs to the Special Issue Hybrid Organic Electronics: Material, Structure and Application)

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16 pages, 5904 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Miniature Soft Sensor with Origami-Inspired Self-Folding Parallel Mechanism

by Yongqi Shi, Gang Wang, Wenguang Sun, Yunfeng Ya, Shuhan Liu, Jiongjie Fang, Feiyang Yuan, Youning Duo and Li Wen

Micromachines 2022, 13(8), 1188; https://doi.org/10.3390/mi13081188 - 28 Jul 2022

Cited by 6 | Viewed by 3521

Abstract

Miniature soft sensors are crucial for the perception of soft robots. Although centimeter-scale sensors have been well developed, very few works addressed millimeter-scale, three-dimensional-shaped soft sensors capable of measuring multi-axis forces. In this work, we developed a millimeter-scale (overall size of 6 mm [...] Read more.

Miniature soft sensors are crucial for the perception of soft robots. Although centimeter-scale sensors have been well developed, very few works addressed millimeter-scale, three-dimensional-shaped soft sensors capable of measuring multi-axis forces. In this work, we developed a millimeter-scale (overall size of 6 mm × 11 mm × 11 mm) soft sensor based on liquid metal printing technology and self-folding origami parallel mechanism. The origami design of the sensor enables the soft sensor to be manufactured within the plane and then fold into a three-dimensional shape. Furthermore, the parallel mechanism allows the sensor to rotate along two orthogonal axes. We showed that the soft sensor can be self-folded (took 17 s) using a shape-memory polymer and magnets. The results also showed that the sensor prototype can reach a deformation of up to 20 mm at the tip. The sensor can realize a measurement of external loads in six directions. We also showed that the soft sensor enables underwater sensing with a minimum sensitivity of 20 mm/s water flow. This work may provide a new manufacturing method and insight into future millimeter-scale soft sensors for bio-inspired robots. Full article

(This article belongs to the Special Issue Microrobotics: A Commemorative Issue in Honor of Professor Robert J. Wood)

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24 pages, 10600 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Study on Detection of a Small Magnetic Particle Using Thin Film Magneto-Impedance Sensor with Subjecting to Strong Normal Field

by Tomoo Nakai

Micromachines 2022, 13(8), 1199; https://doi.org/10.3390/mi13081199 - 28 Jul 2022

Cited by 3 | Viewed by 2180

Abstract

This paper deals with the detection of small magnetization using a thin film magneto-impedance sensor with subjecting to strong normal field. The sensor was made by soft magnetic amorphous thin-film with uniaxial magnetic anisotropy in the width direction of the element. It was [...] Read more.

This paper deals with the detection of small magnetization using a thin film magneto-impedance sensor with subjecting to strong normal field. The sensor was made by soft magnetic amorphous thin-film with uniaxial magnetic anisotropy in the width direction of the element. It was reported that the sensor has very high sensitivity, such as pico-tesla order, when it is driven by hundreds of MHz. In this paper, a sensitive measurement method aiming for detection of a small particle or a cluster of nano-particles, having low-remanence, is proposed. The point is the application of strong normal field in the measurement area including sensor element and particle. The normal strong field is applied in the normal direction of the sensor plane in the value almost hundreds of mT. Instead of such strong normal field, the sensor keeps high sensitivity, because of the demagnetizing force in the thickness direction. A theoretical estimation for clarifying an efficiency of the method, experimental results of sensor property and sensitivity with subjecting to the normal field, and also a confirmation of detection of a small particle using the proposed method is reported. As a special mention, detection fundamentals when a applied surface normal field has a distribution and also a particle would run through in the vicinity of sensor is discussed. Full article

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25 pages, 4369 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Engineering Organ-on-a-Chip to Accelerate Translational Research

by Jihoon Ko, Dohyun Park, Somin Lee, Burcu Gumuscu and Noo Li Jeon

Micromachines 2022, 13(8), 1200; https://doi.org/10.3390/mi13081200 - 28 Jul 2022

Cited by 31 | Viewed by 7399

Abstract

We guide the use of organ-on-chip technology in tissue engineering applications. Organ-on-chip technology is a form of microengineered cell culture platform that elaborates the in-vivo like organ or tissue microenvironments. The organ-on-chip platform consists of microfluidic channels, cell culture chambers, and stimulus sources [...] Read more.

We guide the use of organ-on-chip technology in tissue engineering applications. Organ-on-chip technology is a form of microengineered cell culture platform that elaborates the in-vivo like organ or tissue microenvironments. The organ-on-chip platform consists of microfluidic channels, cell culture chambers, and stimulus sources that emulate the in-vivo microenvironment. These platforms are typically engraved into an oxygen-permeable transparent material. Fabrication of these materials requires the use of microfabrication strategies, including soft lithography, 3D printing, and injection molding. Here we provide an overview of what is an organ-on-chip platform, where it can be used, what it is composed of, how it can be fabricated, and how it can be operated. In connection with this topic, we also introduce an overview of the recent applications, where different organs are modeled on the microscale using this technology. Full article

(This article belongs to the Special Issue Micro/Nanofluidic and Lab-on-a-Chip Devices for Biomedical Applications)

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14 pages, 3455 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Miniature Mobile Robot Using Only One Tilted Vibration Motor

by Renjie Zhu, Yifan Zhang and Hongqiang Wang

Micromachines 2022, 13(8), 1184; https://doi.org/10.3390/mi13081184 - 27 Jul 2022

Cited by 5 | Viewed by 3622

Abstract

In miniature mobile robots, reducing the number of actuators can effectively reduce the size and weight of the robot. However, it is challenging to design a robot with as few actuators as possible without losing good motion performance. This work presented a simple-structured [...] Read more.

In miniature mobile robots, reducing the number of actuators can effectively reduce the size and weight of the robot. However, it is challenging to design a robot with as few actuators as possible without losing good motion performance. This work presented a simple-structured low-cost miniature mobile robot. It is driven by only a single tilted motor and yet is fully capable of being controlled to move forward and turn left or right on the ground. Based on the stick–slip mechanism, the robot’s motion is achieved by interplaying between the centrifugal force generated by the vibration motor tilted on the robot and the friction force of the robot. The robot’s speed can be controlled by regulating the magnitude and the period of the applied voltage. Finally, the robot can translate and rotate on the ground and follow various arbitrary paths. The prototype weighs only 11.15 g, costs $6.35, and is 20 mm in diameter and 25 mm in height. The proposed system is experimentally verified and demonstrates the controllability of the robot by the movement along a straight line, a circle, and more arbitrary paths. Full article

(This article belongs to the Special Issue Microrobotics: A Commemorative Issue in Honor of Professor Robert J. Wood)

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13 pages, 5463 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Towards Robust Thermal MEMS: Demonstration of a Novel Approach for Solid Thermal Isolation by Substrate-Level Integrated Porous Microstructures

by Ole Behrmann, Thomas Lisec and Björn Gojdka

Micromachines 2022, 13(8), 1178; https://doi.org/10.3390/mi13081178 - 26 Jul 2022

Cited by 10 | Viewed by 3417

Abstract

Most current thermal MEMS use fragile structures such as thin-film membranes or microcantilevers for thermal isolation. To increase the robustness of these devices, solid thermal insulators that are compatible with MEMS cleanroom processing are needed. This work introduces a novel approach for microscale [...] Read more.

Most current thermal MEMS use fragile structures such as thin-film membranes or microcantilevers for thermal isolation. To increase the robustness of these devices, solid thermal insulators that are compatible with MEMS cleanroom processing are needed. This work introduces a novel approach for microscale thermal isolation using porous microstructures created with the recently developed PowderMEMS wafer-level process. MEMS devices consisting of heaters on a thin-film membrane were modified with porous microstructures made from three different materials. A thermal model for the estimation of the resulting thermal conductivity was developed, and measurements for porous structures in ambient air and under vacuum were performed. The PowderMEMS process was successfully used to create microscale thermal insulators in silicon cavities at the wafer level. Measurements indicate thermal conductivities of close to 0.1 W/mK in ambient air and close to 0.04 W/mK for porous structures under vacuum for the best-performing material. The obtained thermal conductivities are lower than those reported for both glass and porous silicon, making PowderMEMS a very interesting alternative for solid microscale thermal isolation. Full article

(This article belongs to the Special Issue The Fabrication of Microstructures from Powders and Their Applications in Microsystems)

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15 pages, 10380 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

THz Filters Made by Laser Ablation of Stainless Steel and Kapton Film

by Molong Han, Daniel Smith, Soon Hock Ng, Zoltan Vilagosh, Vijayakumar Anand, Tomas Katkus, Ignas Reklaitis, Haoran Mu, Meguya Ryu, Junko Morikawa, Jitraporn Vongsvivut, Dominique Appadoo and Saulius Juodkazis

Micromachines 2022, 13(8), 1170; https://doi.org/10.3390/mi13081170 - 25 Jul 2022

Cited by 4 | Viewed by 2653

Abstract

THz band-pass filters were fabricated by femtosecond-laser ablation of 25-

μ

m-thick micro-foils of stainless steel and Kapton film, which were subsequently metal coated with a ∼70 nm film, closely matching the skin depth at the used THz spectral window. Their spectral performance [...] Read more.

THz band-pass filters were fabricated by femtosecond-laser ablation of 25-

μ

m-thick micro-foils of stainless steel and Kapton film, which were subsequently metal coated with a ∼70 nm film, closely matching the skin depth at the used THz spectral window. Their spectral performance was tested in transmission and reflection modes at the Australian Synchrotron’s THz beamline. A 25-

μ

m-thick Kapton film performed as a Fabry–Pérot etalon with a free spectral range (

F S R

) of 119 cm

^{- 1}

, high finesse

F_{c} \approx 17

, and was tuneable over ∼

10 μ

m (at ∼5 THz band) with

β = 30^{\circ}

tilt. The structure of the THz beam focal region as extracted by the first mirror (slit) showed a complex dependence of polarisation, wavelength and position across the beam. This is important for polarisation-sensitive measurements (in both transmission and reflection) and requires normalisation at each orientation of linear polarisation. Full article

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10 pages, 2015 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design of Metal-Based Slippery Liquid-Infused Porous Surfaces (SLIPSs) with Effective Liquid Repellency Achieved with a Femtosecond Laser

by Zheng Fang, Yang Cheng, Qing Yang, Yu Lu, Chengjun Zhang, Minjing Li, Bing Du, Xun Hou and Feng Chen

Micromachines 2022, 13(8), 1160; https://doi.org/10.3390/mi13081160 - 22 Jul 2022

Cited by 7 | Viewed by 2799

Abstract

Slippery liquid-infused porous surfaces (SLIPSs) have become an effective method to provide materials with sliding performance and, thus, achieve liquid repellency, through the process of infusing lubricants into the microstructure of the surface. However, the construction of microstructures on high-strength metals is still [...] Read more.

Slippery liquid-infused porous surfaces (SLIPSs) have become an effective method to provide materials with sliding performance and, thus, achieve liquid repellency, through the process of infusing lubricants into the microstructure of the surface. However, the construction of microstructures on high-strength metals is still a significant challenge. Herein, we used a femtosecond laser with a temporally shaped Bessel beam to process NiTi alloy, and created uniform porous structures with a microhole diameter of around 4 µm, in order to store and lock lubricant. In addition, as the lubricant is an important factor that can influence the sliding properties, five different lubricants were selected to prepare the SLIPSs, and were further compared in terms of their sliding behavior. The temperature cycle test and the hydraulic pressure test were implemented to characterize the durability of the samples, and different liquids were used to investigate the possible failure under complex fluid conditions. In general, the prepared SLIPSs exhibited superior liquid repellency. We believe that, in combination with a femtosecond laser, slippery liquid-infused porous surfaces are promising for applications in a wide range of areas. Full article

(This article belongs to the Special Issue Laser Bionic Fabrication)

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9 pages, 3304 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Enzymatic and Cellular Degradation of Carbon-Based Biconcave Nanodisks

by Zhiyong Wei, Qingxin Mu, Hui Wang, Guanyou Lin and Miqin Zhang

Micromachines 2022, 13(7), 1144; https://doi.org/10.3390/mi13071144 - 19 Jul 2022

Cited by 1 | Viewed by 2027

Abstract

The assessment of the biodegradability of nanomaterials is of pragmatic importance for understanding the interactions between nanomaterials and biological systems and for the determination of ultimate fate of these materials as well as their potential use. We recently developed carbon-based biconcave nanodisks (CBBNs) [...] Read more.

The assessment of the biodegradability of nanomaterials is of pragmatic importance for understanding the interactions between nanomaterials and biological systems and for the determination of ultimate fate of these materials as well as their potential use. We recently developed carbon-based biconcave nanodisks (CBBNs) serving as a versatile nanocarrier for enhanced accumulation in tumors and combined photothermal-chemotherapy. Here, we investigate both the enzymatic and cellular degradation of CBBNs by monitoring their cellular response with electron microscopy, near-infrared absorbance spectroscopy, and cell viability and oxidative stress assessments. Our results show that CBBNs underwent significant degradation in solutions catalyzed by horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂), or in the presence of macrophage cells. The ability of CBBNs to be degraded in biological systems provides suitability for their future biomedical applications. Full article

(This article belongs to the Special Issue Nanoparticles in Biomedical Sciences)

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10 pages, 8561 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Toward Higher Integration Density in Femtosecond-Laser-Written Programmable Photonic Circuits

by Riccardo Albiero, Ciro Pentangelo, Marco Gardina, Simone Atzeni, Francesco Ceccarelli and Roberto Osellame

Micromachines 2022, 13(7), 1145; https://doi.org/10.3390/mi13071145 - 19 Jul 2022

Cited by 9 | Viewed by 3110

Abstract

Programmability in femtosecond-laser-written integrated circuits is commonly achieved with the implementation of thermal phase shifters. Recent work has shown how such phase shifters display significantly reduced power dissipation and thermal crosstalk with the implementation of thermal isolation structures. However, the aforementioned phase shifter [...] Read more.

Programmability in femtosecond-laser-written integrated circuits is commonly achieved with the implementation of thermal phase shifters. Recent work has shown how such phase shifters display significantly reduced power dissipation and thermal crosstalk with the implementation of thermal isolation structures. However, the aforementioned phase shifter technology is based on a single gold film, which poses severe limitations on integration density and circuit complexity due to intrinsic geometrical constraints. To increase the compactness, we propose two improvements to this technology. Firstly, we fabricated thermal phase shifters with a photolithography process based on two different metal films, namely (1) chromium for microheaters and (2) copper for contact pads and interconnections. Secondly, we developed a novel curved isolation trench design that, along with a state-of-the-art curvature radius, allows for a significant reduction in the optical length of integrated circuits. As a result, curved Cr-Cu phase shifters provide a compact footprint with low parasitic series resistance and no significant increase in power dissipation (∼38 mW) and thermal crosstalk (∼20%). These results pave the way toward the fabrication of femtosecond-laser-written photonic circuits with a steep increase in terms of layout complexity. Full article

(This article belongs to the Special Issue Programmable Integrated Photonic Devices: Design, Fabrication and Applications)

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14 pages, 4761 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Lasered Graphene Microheaters Modified with Phase-Change Composites: New Approach to Smart Patch Drug Delivery

by Victoria Gilpin, Deetchaya Surandhiran, Cameron Scott, Amy Devine, Jill H. Cundell, Chris I. R. Gill, L. Kirsty Pourshahidi and James Davis

Micromachines 2022, 13(7), 1132; https://doi.org/10.3390/mi13071132 - 18 Jul 2022

Cited by 12 | Viewed by 4129

Abstract

The combination of paraffin wax and O,O′-bis(2-aminopropyl) polypropylene glycol–block–polyethylene glycol–block–polypropylene glycol was used as a phase-change material (PCM) for the controlled delivery of curcumin. The PCM was combined with a graphene-based heater derived from the laser [...] Read more.

The combination of paraffin wax and O,O′-bis(2-aminopropyl) polypropylene glycol–block–polyethylene glycol–block–polypropylene glycol was used as a phase-change material (PCM) for the controlled delivery of curcumin. The PCM was combined with a graphene-based heater derived from the laser scribing of polyimide film. This assembly provides a new approach to a smart patch through which release can be electronically controlled, allowing repetitive dosing. Rather than relying on passive diffusion, delivery is induced and terminated through the controlled heating of the PCM with transfer only occurring when the PCM transitions from solid to liquid. The material properties of the device and release characteristics of the strategy under repetitive dosing are critically assessed. The delivery yield of curcumin was found to be 3.5 µg (4.5 µg/cm²) per 3 min thermal cycle. Full article

(This article belongs to the Special Issue Biohybrid Technologies: From Materials Manufacturing to Biomedical Application)

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21 pages, 4643 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Circuit-Based Design of Microfluidic Drop Networks

by Nassim Rousset, Christian Lohasz, Julia Alicia Boos, Patrick M. Misun, Fernando Cardes and Andreas Hierlemann

Micromachines 2022, 13(7), 1124; https://doi.org/10.3390/mi13071124 - 16 Jul 2022

Cited by 11 | Viewed by 3594

Abstract

Microfluidic-drop networks consist of several stable drops—interconnected through microfluidic channels—in which organ models can be cultured long-term. Drop networks feature a versatile configuration and an air–liquid interface (ALI). This ALI provides ample oxygenation, rapid liquid turnover, passive degassing, and liquid-phase stability through capillary [...] Read more.

Microfluidic-drop networks consist of several stable drops—interconnected through microfluidic channels—in which organ models can be cultured long-term. Drop networks feature a versatile configuration and an air–liquid interface (ALI). This ALI provides ample oxygenation, rapid liquid turnover, passive degassing, and liquid-phase stability through capillary pressure. Mathematical modeling, e.g., by using computational fluid dynamics (CFD), is a powerful tool to design drop-based microfluidic devices and to optimize their operation. Although CFD is the most rigorous technique to model flow, it falls short in terms of computational efficiency. Alternatively, the hydraulic–electric analogy is an efficient “first-pass” method to explore the design and operation parameter space of microfluidic-drop networks. However, there are no direct electric analogs to a drop, due to the nonlinear nature of the capillary pressure of the ALI. Here, we present a circuit-based model of hanging- and standing-drop compartments. We show a phase diagram describing the nonlinearity of the capillary pressure of a hanging drop. This diagram explains how to experimentally ensure drop stability. We present a methodology to find flow rates and pressures within drop networks. Finally, we review several applications, where the method, outlined in this paper, was instrumental in optimizing design and operation. Full article

(This article belongs to the Special Issue Micro and Smart Devices and Systems)

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11 pages, 2038 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Continuous Microfluidic Concentrator for High-Sensitivity Detection of Bacteria in Water Sources

by Seunghee Choo, Hyunjung Lim, Tae Eun Kim, Jion Park, Kyu Been Park, Chaewon Park, Chae Seung Lim and Jeonghun Nam

Micromachines 2022, 13(7), 1093; https://doi.org/10.3390/mi13071093 - 10 Jul 2022

Cited by 4 | Viewed by 2252

Abstract

Water contamination is a critical issue that threatens global public health. To enable the rapid and precise monitoring of pathogen contamination in drinking water, a concentration technique for bacterial cells is required to address the limitations of current detection methods, including the culture [...] Read more.

Water contamination is a critical issue that threatens global public health. To enable the rapid and precise monitoring of pathogen contamination in drinking water, a concentration technique for bacterial cells is required to address the limitations of current detection methods, including the culture method and polymerase chain reaction. Here we present a viscoelastic microfluidic device for the continuous concentration of bacterial cells. To validate the device performance for cell concentration, the flow characteristics of 2-μm particles were estimated in viscoelastic fluids at different concentrations and flow rates. Based on the particle flow distributions, the flow rate factor, which is defined as the ratio of the inlet flow rate to the outlet flow rate at the center outlet, was optimized to achieve highly concentrated bacterial cells by removal of the additional suspending medium. The flow characteristics of 0.5-, 0.7-, and 1.0-μm-diameter particles were evaluated to consider the effect of a wide spectrum of bacterial size distribution. Finally, the concentration factor of bacterial cells, Staphylococcus aureus, suspended in a 2000-ppm polyethylene oxide solution was found to be 20.6-fold at a flow rate of 20 μL/min and a flow rate factor of 40. Full article

(This article belongs to the Special Issue Micro/Nanofluidics for Cell and Particle Manipulation)

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36 pages, 6211 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Emerging Bioanalytical Devices and Platforms for Rapid Detection of Pathogens in Environmental Samples

by Lightson Ngashangva, Bahaa A. Hemdan, Mohamed Azab El-Liethy, Vinay Bachu, Shelley D. Minteer and Pranab Goswami

Micromachines 2022, 13(7), 1083; https://doi.org/10.3390/mi13071083 - 8 Jul 2022

Cited by 16 | Viewed by 5663

Abstract

The development of robust bioanalytical devices and biosensors for infectious pathogens is progressing well with the advent of new materials, concepts, and technology. The progress is also stepping towards developing high throughput screening technologies that can quickly identify, differentiate, and determine the concentration [...] Read more.

The development of robust bioanalytical devices and biosensors for infectious pathogens is progressing well with the advent of new materials, concepts, and technology. The progress is also stepping towards developing high throughput screening technologies that can quickly identify, differentiate, and determine the concentration of harmful pathogens, facilitating the decision-making process for their elimination and therapeutic interventions in large-scale operations. Recently, much effort has been focused on upgrading these analytical devices to an intelligent technological platform by integrating them with modern communication systems, such as the internet of things (IoT) and machine learning (ML), to expand their application horizon. This review outlines the recent development and applications of bioanalytical devices and biosensors to detect pathogenic microbes in environmental samples. First, the nature of the recent outbreaks of pathogenic microbes such as foodborne, waterborne, and airborne pathogens and microbial toxins are discussed to understand the severity of the problems. Next, the discussion focuses on the detection systems chronologically, starting with the conventional methods, advanced techniques, and emerging technologies, such as biosensors and other portable devices and detection platforms for pathogens. Finally, the progress on multiplex assays, wearable devices, and integration of smartphone technologies to facilitate pathogen detection systems for wider applications are highlighted. Full article

(This article belongs to the Special Issue Microfluidics and Biosensors for Point-of-Care Applications)

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19 pages, 4367 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Femtosecond Laser Processing Technology for Anti-Reflection Surfaces of Hard Materials

by Xiaofan Xie, Yunfei Li, Gong Wang, Zhenxu Bai, Yu Yu, Yulei Wang, Yu Ding and Zhiwei Lu

Micromachines 2022, 13(7), 1084; https://doi.org/10.3390/mi13071084 - 8 Jul 2022

Cited by 16 | Viewed by 5470

Abstract

The anti-reflection properties of hard material surfaces are of great significance in the fields of infrared imaging, optoelectronic devices, and aerospace. Femtosecond laser processing has drawn a lot of attentions in the field of optics as an innovative, efficient, and green micro-nano processing [...] Read more.

The anti-reflection properties of hard material surfaces are of great significance in the fields of infrared imaging, optoelectronic devices, and aerospace. Femtosecond laser processing has drawn a lot of attentions in the field of optics as an innovative, efficient, and green micro-nano processing method. The anti-reflection surface prepared on hard materials by femtosecond laser processing technology has good anti-reflection properties under a broad spectrum with all angles, effectively suppresses reflection, and improves light transmittance/absorption. In this review, the recent advances on femtosecond laser processing of anti-reflection surfaces on hard materials are summarized. The principle of anti-reflection structure and the selection of anti-reflection materials in different applications are elaborated upon. Finally, the limitations and challenges of the current anti-reflection surface are discussed, and the future development trend of the anti-reflection surface are prospected. Full article

(This article belongs to the Special Issue Advanced (Citius, Minor, Simplicius) Laser Fabrication Technologies for Cross-Field Applications)

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31 pages, 5935 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Review of Bubble Applications in Microrobotics: Propulsion, Manipulation, and Assembly

by Yuting Zhou, Liguo Dai and Niandong Jiao

Micromachines 2022, 13(7), 1068; https://doi.org/10.3390/mi13071068 - 4 Jul 2022

Cited by 32 | Viewed by 7475

Abstract

In recent years, microbubbles have been widely used in the field of microrobots due to their unique properties. Microbubbles can be easily produced and used as power sources or tools of microrobots, and the bubbles can even serve as microrobots themselves. As a [...] Read more.

In recent years, microbubbles have been widely used in the field of microrobots due to their unique properties. Microbubbles can be easily produced and used as power sources or tools of microrobots, and the bubbles can even serve as microrobots themselves. As a power source, bubbles can propel microrobots to swim in liquid under low-Reynolds-number conditions. As a manipulation tool, microbubbles can act as the micromanipulators of microrobots, allowing them to operate upon particles, cells, and organisms. As a microrobot, microbubbles can operate and assemble complex microparts in two- or three-dimensional spaces. This review provides a comprehensive overview of bubble applications in microrobotics including propulsion, micromanipulation, and microassembly. First, we introduce the diverse bubble generation and control methods. Then, we review and discuss how bubbles can play a role in microrobotics via three functions: propulsion, manipulation, and assembly. Finally, by highlighting the advantages and current challenges of this progress, we discuss the prospects of microbubbles in microrobotics. Full article

(This article belongs to the Special Issue Micro- and Nano-Systems for Manipulation, Actuation and Sensing)

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12 pages, 7124 KiB

Open AccessEditor’s ChoiceArticle

Strain Rate Dependence of Compressive Mechanical Properties of Polyamide and Its Composite Fabricated Using Selective Laser Sintering under Saturated-Water Conditions

by Xiaodong Zheng, Jiahuan Meng and Yang Liu

Micromachines 2022, 13(7), 1041; https://doi.org/10.3390/mi13071041 - 30 Jun 2022

Cited by 9 | Viewed by 2314

Abstract

In this work, polyamide 12 (PA12) and carbon fiber reinforced polyamide 12 (CF/PA12) composites were fabricated using selective laser sintering (SLS), and the coupling effects of the strain rate and hygroscopicity on the compressive mechanical properties were investigated. The results showed that the [...] Read more.

In this work, polyamide 12 (PA12) and carbon fiber reinforced polyamide 12 (CF/PA12) composites were fabricated using selective laser sintering (SLS), and the coupling effects of the strain rate and hygroscopicity on the compressive mechanical properties were investigated. The results showed that the CF/PA12 had a shorter saturation time and lower saturated water absorption under the same conditions, indicating that the SLS of CF/PA12 had lower hydrophilia and higher water resistance when compared to the SLS of PA12. It was observed that as the strain rate increased, and the ultimate compression strength and the yield strength monotonically increased with almost the same slope, indicating that the strain rate had the same positive correlation with the compressive strength of the SLS of PA12 and CF/PA12. The water immersion results showed a significant reduction of 15% in the yield strength of SLS of PA12, but not very significant in CF/PA12. This indicated that the carbon fiber was favorable for maintaining the mechanical properties of polyamide 12 after absorbing water. The findings in this work provide a basic knowledge of the mechanical properties of SLS polyamide under different loading and saturated-water conditions and thus is helpful to widen the application of SLS products in harsh environments. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications)

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11 pages, 2485 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Fiber-Based SPR Aptasensor for the In Vitro Detection of Inflammation Biomarkers

by Yu Hua, Ridong Wang and Dachao Li

Micromachines 2022, 13(7), 1036; https://doi.org/10.3390/mi13071036 - 29 Jun 2022

Cited by 17 | Viewed by 3621

Abstract

It is widely accepted that the abnormal concentrations of different inflammation biomarkers can be used for the early diagnosis of cardiovascular disease (CVD). Currently, many reported strategies, which require extra report tags or bulky detection equipment, are not portable enough for onsite inflammation [...] Read more.

It is widely accepted that the abnormal concentrations of different inflammation biomarkers can be used for the early diagnosis of cardiovascular disease (CVD). Currently, many reported strategies, which require extra report tags or bulky detection equipment, are not portable enough for onsite inflammation biomarker detection. In this work, a fiber-based surface plasmon resonance (SPR) biosensor decorated with DNA aptamers, which were specific to two typical inflammation biomarkers, C-reactive protein (CRP) and cardiac troponin I (cTn-I), was developed. By optimizing the surface concentration of the DNA aptamer, the proposed sensor could achieve a limit of detection (LOD) of 1.7 nM (0.204 μg/mL) and 2.5 nM (57.5 ng/mL) to CRP and cTn-I, respectively. Additionally, this biosensor could also be used to detect other biomarkers by immobilizing corresponding specific DNA aptamers. Integrated with a miniaturized spectral analysis device, the proposed sensor could be applied for constructing a portable instrument to provide the point of care testing (POCT) for CVD patients. Full article

(This article belongs to the Special Issue Physics in Micro/Nano Devices: From Fundamental to Application)

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13 pages, 9121 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

From Microtiter Plates to Droplets—There and Back Again

by Thomas Henkel, Günter Mayer, Jörg Hampl, Jialan Cao, Linda Ehrhardt, Andreas Schober and Gregor Alexander Groß

Micromachines 2022, 13(7), 1022; https://doi.org/10.3390/mi13071022 - 28 Jun 2022

Cited by 4 | Viewed by 2903

Abstract

Droplet-based microfluidic screening techniques can benefit from interfacing established microtiter plate-based screening and sample management workflows. Interfacing tools are required both for loading preconfigured microtiter-plate (MTP)-based sample collections into droplets and for dispensing the used droplets samples back into MTPs for subsequent storage [...] Read more.

Droplet-based microfluidic screening techniques can benefit from interfacing established microtiter plate-based screening and sample management workflows. Interfacing tools are required both for loading preconfigured microtiter-plate (MTP)-based sample collections into droplets and for dispensing the used droplets samples back into MTPs for subsequent storage or further processing. Here, we present a collection of Digital Microfluidic Pipetting Tips (DMPTs) with integrated facilities for droplet generation and manipulation together with a robotic system for its operation. This combination serves as a bidirectional sampling interface for sample transfer from wells into droplets (w2d) and vice versa droplets into wells (d2w). The DMPT were designed to fit into 96-deep-well MTPs and prepared from glass by means of microsystems technology. The aspirated samples are converted into the channel-confined droplets’ sequences separated by an immiscible carrier medium. To comply with the demands of dose-response assays, up to three additional assay compound solutions can be added to the sample droplets. To enable different procedural assay protocols, four different DMPT variants were made. In this way, droplet series with gradually changing composition can be generated for, e.g., 2D screening purposes. The developed DMPT and their common fluidic connector are described here. To handle the opposite transfer d2w, a robotic transfer system was set up and is described briefly. Full article

(This article belongs to the Special Issue Droplet-Based Microfluidic Devices)

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18 pages, 12715 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Dielectrophoresis from the System’s Point of View: A Tale of Inhomogeneous Object Polarization, Mirror Charges, High Repelling and Snap-to-Surface Forces and Complex Trajectories Featuring Bifurcation Points and Watersheds

by Jan Gimsa and Michal M. Radai

Micromachines 2022, 13(7), 1002; https://doi.org/10.3390/mi13071002 - 26 Jun 2022

Cited by 5 | Viewed by 2272

Abstract

Microscopic objects change the apparent permittivity and conductivity of aqueous systems and thus their overall polarizability. In inhomogeneous fields, dielectrophoresis (DEP) increases the overall polarizability of the system by moving more highly polarizable objects or media to locations with a higher field. The [...] Read more.

Microscopic objects change the apparent permittivity and conductivity of aqueous systems and thus their overall polarizability. In inhomogeneous fields, dielectrophoresis (DEP) increases the overall polarizability of the system by moving more highly polarizable objects or media to locations with a higher field. The DEP force is usually calculated from the object’s point of view using the interaction of the object’s induced dipole or multipole moments with the inducing field. Recently, we were able to derive the DEP force from the work required to charge suspension volumes with a single object moving in an inhomogeneous field. The capacitance of the volumes was described using Maxwell–Wagner’s mixing equation. Here, we generalize this system’s-point-of-view approach describing the overall polarizability of the whole DEP system as a function of the position of the object with a numerical “conductance field”. As an example, we consider high- and low conductive 200 µm 2D spheres in a square 1 × 1 mm chamber with plain-versus-pointed electrode configuration. For given starting points, the trajectories of the sphere and the corresponding DEP forces were calculated from the conductance gradients. The model describes watersheds; saddle points; attractive and repulsive forces in front of the pointed electrode, increased by factors >600 compared to forces in the chamber volume where the classical dipole approach remains applicable; and DEP motions with and against the field gradient under “positive DEP” conditions. We believe that our approach can explain experimental findings such as the accumulation of viruses and proteins, where the dipole approach cannot account for sufficiently high holding forces to defeat Brownian motion. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, Volume II)

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20 pages, 7242 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Free-Space Applications of Silicon Photonics: A Review

by Chung-Yu Hsu, Gow-Zin Yiu and You-Chia Chang

Micromachines 2022, 13(7), 990; https://doi.org/10.3390/mi13070990 - 24 Jun 2022

Cited by 36 | Viewed by 8823

Abstract

Silicon photonics has recently expanded its applications to delivering free-space emissions for detecting or manipulating external objects. The most notable example is the silicon optical phased array, which can steer a free-space beam to achieve a chip-scale solid-state LiDAR. Other examples include free-space [...] Read more.

Silicon photonics has recently expanded its applications to delivering free-space emissions for detecting or manipulating external objects. The most notable example is the silicon optical phased array, which can steer a free-space beam to achieve a chip-scale solid-state LiDAR. Other examples include free-space optical communication, quantum photonics, imaging systems, and optogenetic probes. In contrast to the conventional optical system consisting of bulk optics, silicon photonics miniaturizes an optical system into a photonic chip with many functional waveguiding components. By leveraging the mature and monolithic CMOS process, silicon photonics enables high-volume production, scalability, reconfigurability, and parallelism. In this paper, we review the recent advances in beam steering technologies based on silicon photonics, including optical phased arrays, focal plane arrays, and dispersive grating diffraction. Various beam-shaping technologies for generating collimated, focused, Bessel, and vortex beams are also discussed. We conclude with an outlook of the promises and challenges for the free-space applications of silicon photonics. Full article

(This article belongs to the Special Issue Silicon Photonics and Other Integrated Photonic Platforms)

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11 pages, 2600 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel Fluidic Platform for Semi-Automated Cell Culture into Multiwell-like Bioreactors

by Francesca Maria Orecchio, Vito Tommaso, Tommaso Santaniello, Sara Castiglioni, Federico Pezzotta, Andrea Monti, Francesco Butera, Jeanette Anne Marie Maier and Paolo Milani

Micromachines 2022, 13(7), 994; https://doi.org/10.3390/mi13070994 - 24 Jun 2022

Cited by 3 | Viewed by 3219

Abstract

In this work, we developed and characterized a novel fluidic platform that enables long-term in vitro cell culture in a semi-automated fashion. The system is constituted by a control unit provided with a piezoelectric pump, miniaturized valves, and a microfluidic network for management [...] Read more.

In this work, we developed and characterized a novel fluidic platform that enables long-term in vitro cell culture in a semi-automated fashion. The system is constituted by a control unit provided with a piezoelectric pump, miniaturized valves, and a microfluidic network for management and fine control of reagents’ flow, connected to a disposable polymeric culture unit resembling the traditional multiwell-like design. As a proof of principle, Human Umbilical Vein Endothelial Cells (HUVEC) and Human Mesenchymal Stem Cells (hMSC) were seeded and cultured into the cell culture unit. The proliferation rate of HUVEC and the osteogenic differentiation of hMSC were assessed and compared to standard culture in Petri dishes. The results obtained demonstrated that our approach is suitable to perform semi-automated cell culture protocols, minimizing the contribution of human operators and allowing the standardization and reproducibility of the procedures. We believe that the proposed system constitutes a promising solution for the realization of user-friendly automated control systems that will favor the standardization of cell culture processes for cell factories, drug testing, and biomedical research. Full article

(This article belongs to the Special Issue Bioelectronics & Wearable Devices: Sensing, Signal Processing and Powering)

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18 pages, 4498 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Thickness and Structure of Dip-Coated Polymer Films in the Liquid and Solid States

by Zhao Zhang, Fei Peng and Konstantin G. Kornev

Micromachines 2022, 13(7), 982; https://doi.org/10.3390/mi13070982 - 22 Jun 2022

Cited by 14 | Viewed by 3550

Abstract

Films formed by dip coating brass wires with dilute and semi-dilute solutions of polyvinyl butyral in benzyl alcohol were studied in their liquid and solid states. While dilute and semi-dilute solutions behaved as Maxwell viscoelastic fluids, the thickness of the liquid films followed [...] Read more.

Films formed by dip coating brass wires with dilute and semi-dilute solutions of polyvinyl butyral in benzyl alcohol were studied in their liquid and solid states. While dilute and semi-dilute solutions behaved as Maxwell viscoelastic fluids, the thickness of the liquid films followed the Landau-Levich-Derjaguin prediction for Newtonian fluids. At a very slow rate of coating, the film thickness was difficult to evaluate. Therefore, the dynamic contact angle was studied in detail. We discovered that polymer additives preserve the advancing contact angle at its static value while the receding contact angle follows the Cox–Voinov theory. In contrast, the thickness of solid films does not correlate with the Landau-Levich-Derjaguin predictions. Only solutions of high-molecular-weight polymers form smooth solid films. Solutions of low-molecular-weight polymers may form either solid films with an inhomogeneous roughness or solid polymer domains separated by the dry substrate. In technological applications, very dilute polymer solutions of high-molecular-weight polymers can be used to avoid inhomogeneities in solid films. These solutions form smooth solid films, and the film thickness can be controlled by the experimental coating conditions. Full article

(This article belongs to the Special Issue Interfaces in Microfluidics)

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14 pages, 7042 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Analysis of a PDLC-Based Reconfigurable Hilbert Fractal Antenna for Large and Fine THz Frequency Tuning

by Prabir Garu and Wei-Chih Wang

Micromachines 2022, 13(6), 964; https://doi.org/10.3390/mi13060964 - 18 Jun 2022

Cited by 7 | Viewed by 3257

Abstract

The proposed reconfigurable radiating antenna design is based on the integration of a reconfigurable fractal antenna and electro-optic substrate material. This antenna can be adjusted to achieve either re-configurability or tunability in the desired frequency range for wireless systems. The electromagnetic characteristics of [...] Read more.

The proposed reconfigurable radiating antenna design is based on the integration of a reconfigurable fractal antenna and electro-optic substrate material. This antenna can be adjusted to achieve either re-configurability or tunability in the desired frequency range for wireless systems. The electromagnetic characteristics of the fractal antenna are manipulated at both the level of fractal geometry, electrical length and dielectric substrate. The designed antenna features multiband responses, in which the geometry and length change create a large frequency shift and the dielectric change using polymer dispersed liquid crystal (PDLC) creates fine and/or continuous tuning. The far field and scattering properties of the antenna are analyzed using the Computer Simulation Technology (CST) Microwave Studio Suite. The proposed approach has successfully demonstrated reconfigurable switching for up to four frequency bands between 0.2 and 0.6 THz. The dielectric constant change in the PDLC substrate shows fine and continuous frequency tuning with an 8% maximum frequency shift when operating around 0.54 THz and a high directivity of 7.35 dBi at 0.54 THz and 8.43 dBi at 0.504 THz. The antenna can also realize a peak gain of 4.29 dBi at 0.504 THz in the extraordinary polarization state of PDLC. The designed antenna can be readily integrated in the current communication devices, such as satellites, smart phones, laptops, and other portable electronic devices, due to its compact geometry and IC compatible design. In satellite applications, the proposed antenna can play a significant role in terms of security. The antenna could be extremely useful for satellites that want to keep their information secret; by constantly switching their operating frequency, spy satellites can evade detection and data collection from enemy ears. Full article

(This article belongs to the Section E：Engineering and Technology)

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15 pages, 8048 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High Performance Eight-Port Dual-Band MIMO Antenna System for 5G Devices

by Saad Hassan Kiani, Muhammad Abbas Khan, Umair Rafique, Mohamed Marey, Abdullah G. Alharbi, Hala Mostafa, Muhammad Amir Khan and Syed Muzahir Abbas

Micromachines 2022, 13(6), 959; https://doi.org/10.3390/mi13060959 - 17 Jun 2022

Cited by 14 | Viewed by 4306

Abstract

This study provides an eight-component multiple-input multiple-output (MIMO) antenna architecture for fifth-generation (5G) mobile communication systems. The single antenna element is comprised of an L-shaped radiating component, an L-shaped parasitic element, and a ground plane with a rectangular slot. The main element with [...] Read more.

This study provides an eight-component multiple-input multiple-output (MIMO) antenna architecture for fifth-generation (5G) mobile communication systems. The single antenna element is comprised of an L-shaped radiating component, an L-shaped parasitic element, and a ground plane with a rectangular slot. The main element with a slot-loaded ground plane helps to draw current from a coaxial feed from the other side of the board, while the parasitic element helps to elongate the current path and improve the impedance of the system. This enables the system to radiate at two different frequency ranges: 3.34–3.7 GHz and 4.67–5.08 GHz, with 360 MHz and 410 MHz bandwidths, respectively. For MIMO configuration, the radiating elements are designed on either side of a 0.8 mm thick FR-4 substrate, allowing space to accommodate a battery, radio frequency (RF) systems and subsystems, and camera and sensor modules. The corner and the middle elements are arranged in such a manner so that they can provide spatial and pattern diversity. Furthermore, at least 12 dB of isolation is established between any two radiating elements. Various MIMO performance parameters were evaluated, e.g., mean effective gain (MEG), channel capacity (CC), envelope correlation coefficient (ECC), realized gain, far-field characteristics, and efficiency. Single- and double-hand mode evaluations were performed to further demonstrate the capability of the proposed MIMO antenna. A prototype of the proposed MIMO antenna was manufactured and assessed to verify the simulated data. The measured and simulated results were found to be in good agreement. On the basis of its performance characteristics, the designed MIMO system could be used in 5G communication systems. Full article

(This article belongs to the Special Issue Microwave Antennas: From Fundamental Research to Applications)

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12 pages, 3968 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Dual-Wavelength Photoacoustic Computed Tomography with Piezoelectric Ring-Array Transducer for Imaging of Indocyanine Green Liposomes Aggregation in Tumors

by Xin Sun, Han Shan, Qibo Lin, Ziyan Chen, Dongxu Liu, Zhankai Liu, Kuan Peng and Zeyu Chen

Micromachines 2022, 13(6), 946; https://doi.org/10.3390/mi13060946 - 15 Jun 2022

Cited by 3 | Viewed by 2516

Abstract

Recently, indocyanine green (ICG), as an FDA-approved dye, has been widely used for phototherapy. It is essential to obtain information on the migration and aggregation of ICG in deep tissues. However, existing fluorescence imaging platforms are not able to obtain the structural information [...] Read more.

Recently, indocyanine green (ICG), as an FDA-approved dye, has been widely used for phototherapy. It is essential to obtain information on the migration and aggregation of ICG in deep tissues. However, existing fluorescence imaging platforms are not able to obtain the structural information of the tissues. Here, we prepared ICG liposomes (ICG-Lips) and built a dual-wavelength photoacoustic computed tomography (PACT) system with piezoelectric ring-array transducer to image the aggregation of ICG-Lips in tumors to guide phototherapy. Visible 780 nm light excited the photoacoustic (PA) effects of the ICG-Lips and near-infrared 1064 nm light provided the imaging of the surrounding tissues. The aggregation of ICG-Lips within the tumor and the surrounding tissues was visualized by PACT in real time. This work indicates that PACT with piezoelectric ring-array transducer has great potential in the real-time monitoring of in vivo drug distribution. Full article

(This article belongs to the Special Issue Piezoelectric Ultrasound Transducer for Biomedical Applications)

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21 pages, 5679 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Overview of the MEMS Pirani Sensors

by Shaohang Xu, Na Zhou, Meng Shi, Chenchen Zhang, Dapeng Chen and Haiyang Mao

Micromachines 2022, 13(6), 945; https://doi.org/10.3390/mi13060945 - 14 Jun 2022

Cited by 9 | Viewed by 4400

Abstract

Vacuum equipment has a wide range of applications, and vacuum monitoring in such equipment is necessary in order to meet practical applications. Pirani sensors work by using the effect of air density on the heat conduction of the gas to cause temperature changes [...] Read more.

Vacuum equipment has a wide range of applications, and vacuum monitoring in such equipment is necessary in order to meet practical applications. Pirani sensors work by using the effect of air density on the heat conduction of the gas to cause temperature changes in sensitive structures, thus detecting the pressure in the surrounding environment and thus vacuum monitoring. In past decades, MEMS Pirani sensors have received considerable attention and practical applications because of their advances in simple structures, long service life, wide measurement range and high sensitivity. This review systematically summarizes and compares different types of MEMS Pirani sensors. The configuration, material, mechanism, and performance of different types of MEMS Pirani sensors are discussed, including the ones based on thermistors, thermocouples, diodes and surface acoustic wave. Further, the development status of novel Pirani sensors based on functional materials such as nanoporous materials, carbon nanotubes and graphene are investigated, and the possible future development directions for MEMS Pirani sensors are discussed. This review is with the purpose to focus on a generalized knowledge of MEMS Pirani sensors, thus inspiring the investigations on their practical applications. Full article

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17 pages, 5572 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Wafer-Level Vacuum-Packaged Electric Field Microsensor: Structure Design, Theoretical Model, Microfabrication, and Characterization

by Jun Liu, Shanhong Xia, Chunrong Peng, Zhengwei Wu, Zhaozhi Chu, Zhouwei Zhang, Hucheng Lei, Fengjie Zheng and Wei Zhang

Micromachines 2022, 13(6), 928; https://doi.org/10.3390/mi13060928 - 11 Jun 2022

Cited by 6 | Viewed by 3189

Abstract

This paper proposes a novel wafer-level vacuum packaged electric field microsensor (EFM) featuring a high quality factor, low driving voltage, low noise, and low power consumption. The silicon-on-insulator (SOI) conductive handle layer was innovatively used as the sensing channel to transmit the external [...] Read more.

This paper proposes a novel wafer-level vacuum packaged electric field microsensor (EFM) featuring a high quality factor, low driving voltage, low noise, and low power consumption. The silicon-on-insulator (SOI) conductive handle layer was innovatively used as the sensing channel to transmit the external electric field to the surface of the sensitive structure, and the vacuum packaging was realized through anodic bonding between the SOI and glass-on-silicon (GOS). The fabrication process was designed and successfully realized, featured with a simplified process and highly efficient batch manufacturing, and the final chip size was only 5 × 5 mm. A theoretical model for the packaged device was set up. The influence of key parameters in the packaging structure on the output characteristics of the microsensor was analyzed on the basis of the proposed model. Experiments were conducted on the wafer-level vacuum-packaged EFM to characterize its performance. Experimental results show that, under the condition of applying 5 V DC driving voltage, the required AC driving voltage of the sensor was only 0.05 V_P, and the feedthrough was only 4.2 mV. The quality factor was higher than 5000 and was maintained with no drop in the 50-day test. The vacuum in the chamber of the sensor was about 10 Pa. A sensitivity of 0.16 mV/(kV/m) was achieved within the electrostatic field range of 0–50 kV/m. The linearity of the microsensor was 1.62%, and the uncertainty was 4.42%. Full article

(This article belongs to the Section A：Physics)

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14 pages, 1003 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optimizing Efficiency and Motility of a Polyvalent Molecular Motor

by Mark Rempel and Eldon Emberly

Micromachines 2022, 13(6), 914; https://doi.org/10.3390/mi13060914 - 9 Jun 2022

Viewed by 1707

Abstract

Molecular motors play a vital role in the transport of material within the cell. A family of motors of growing interest are burnt bridge ratchets (BBRs). BBRs rectify spatial fluctuations into directed motion by creating and destroying motor-substrate bonds. It has been shown [...] Read more.

Molecular motors play a vital role in the transport of material within the cell. A family of motors of growing interest are burnt bridge ratchets (BBRs). BBRs rectify spatial fluctuations into directed motion by creating and destroying motor-substrate bonds. It has been shown that the motility of a BBR can be optimized as a function of the system parameters. However, the amount of energy input required to generate such motion and the resulting efficiency has been less well characterized. Here, using a deterministic model, we calculate the efficiency of a particular type of BBR, namely a polyvalent hub interacting with a surface of substrate. We find that there is an optimal burn rate and substrate concentration that leads to optimal efficiency. Additionally, the substrate turnover rate has important implications on motor efficiency. We also consider the effects of force-dependent unbinding on the efficiency and find that under certain conditions the motor works more efficiently when bond breaking is included. Our results provide guidance for how to optimize the efficiency of BBRs. Full article

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23 pages, 7627 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermal Induced Interface Mechanical Response Analysis of SMT Lead-Free Solder Joint and Its Adaptive Optimization

by Shaoyi Liu, Yuefei Yan, Yijiang Zhou, Baoqing Han, Benben Wang, Daxing Zhang, Song Xue, Zhihai Wang, Kunpeng Yu, Yu Shi and Congsi Wang

Micromachines 2022, 13(6), 908; https://doi.org/10.3390/mi13060908 - 8 Jun 2022

Cited by 8 | Viewed by 5948

Abstract

Surface mount technology (SMT) plays an important role in integrated circuits, but due to thermal stress alternation caused by temperature cycling, it tends to have thermo-mechanical reliability problems. At the same time, considering the environmental and health problems of lead (Pb)-based solders, the [...] Read more.

Surface mount technology (SMT) plays an important role in integrated circuits, but due to thermal stress alternation caused by temperature cycling, it tends to have thermo-mechanical reliability problems. At the same time, considering the environmental and health problems of lead (Pb)-based solders, the electronics industry has turned to lead-free solders, such as ternary alloy Sn-3Ag-0.5Cu (SAC305). As lead-free solders exhibit visco-plastic mechanical properties significantly affected by temperature, their thermo-mechanical reliability has received considerable attention. In this study, the interface delamination of an SMT solder joint using a SAC305 alloy under temperature cycling has been analyzed by the nonlinear finite element method. The results indicate that the highest contact pressure at the four corners of the termination/solder horizontal interface means that delamination is most likely to occur, followed by the y-direction side region of the solder/land interface and the top arc region of the termination/solder vertical interface. It should be noted that in order to keep the shape of the solder joint in the finite element model consistent with the actual situation after the reflow process, a minimum energy-based morphology evolution method has been incorporated into the established finite element model. Eventually, an Improved Efficient Global Optimization (IEGO) method was used to optimize the geometry of the SMT solder joint in order to reduce the contact pressure at critical points and critical regions. The optimization result shows that the contact pressure at the critical points and at the critical regions decreases significantly, which also means that the probability of thermal-induced delamination decreases. Full article

(This article belongs to the Special Issue Advanced Packaging for Microsystem Applications)

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15 pages, 3859 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Contributions of Red Blood Cell Sedimentation in a Driving Syringe to Blood Flow in Capillary Channels

by Yang Jun Kang

Micromachines 2022, 13(6), 909; https://doi.org/10.3390/mi13060909 - 8 Jun 2022

Cited by 5 | Viewed by 3009

Abstract

The erythrocyte sedimentation rate (ESR), which has been commonly used to detect physiological and pathological diseases in clinical settings, has been quantified using an interface in a vertical tube. However, previous methods do not provide biophysical information on blood during the ESR test. [...] Read more.

The erythrocyte sedimentation rate (ESR), which has been commonly used to detect physiological and pathological diseases in clinical settings, has been quantified using an interface in a vertical tube. However, previous methods do not provide biophysical information on blood during the ESR test. Therefore, it is necessary to quantify the individual contributions in terms of viscosity and pressure. In this study, to quantify RBC sedimentation, the image intensity (I_b) and interface (β) were obtained by analyzing the blood flow in the microfluidic channels. Based on threshold image intensity, the corresponding interfaces of RBCs (I_b > 0.15) and diluent (I_b < 0.15) were employed to obtain the viscosities (µ_b, µ₀) and junction pressures (P_b, P₀). Two coefficients (CH₁, CH₂) obtained from the empirical formulas (µ_b = µ₀ [1 + CH₁], P_b = P₀ [1 + CH₂]) were calculated to quantify RBC sedimentation. The present method was then adopted to detect differences in RBC sedimentation for various suspended blood samples (healthy RBCs suspended in dextran solutions or plasma). Based on the experimental results, four parameters (µ₀, P₀, CH₁, and CH₂) are considered to be effective for quantifying the contributions of the hematocrit and diluent. Two coefficients exhibited more consistent trends than the conventional ESR method. In conclusion, the proposed method can effectively detect RBC sedimentation. Full article

(This article belongs to the Special Issue Interfaces in Microfluidics)

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11 pages, 2069 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Highly Accurate Method for Deformation Reconstruction of Smart Deformable Structures Based on Flexible Strain Sensors

by Chengguo Yu, Xinyu Gao, Wenlin Liao, Zhili Zhang and Guishan Wang

Micromachines 2022, 13(6), 910; https://doi.org/10.3390/mi13060910 - 8 Jun 2022

Cited by 2 | Viewed by 2201

Abstract

Smart deformable structures that integrate designing, sensing, and controlling technology have been widely applied in the fields of aerospace, robotics, and biomedical engineering due to their multi-functional requirements. The deformation reconstruction method essential for security monitoring and shape controlling, especially for the large [...] Read more.

Smart deformable structures that integrate designing, sensing, and controlling technology have been widely applied in the fields of aerospace, robotics, and biomedical engineering due to their multi-functional requirements. The deformation reconstruction method essential for security monitoring and shape controlling, especially for the large deflection deformation, remains a challenge on accuracy and efficiency. This paper takes a wind tunnel’s fixed-flexible nozzle (FFN) plate as the research object to develop a highly accurate deformation reconstruction method based on sensing information from flexible strain sensors. The mechanical behaviors of the FFN plate with large deflection deformation, which is modeled as a cantilever beam, are studied to analyze the relationship of the strain and moment. Furthermore, the large deflection factor and shell bending theory are creatively utilized to derive and modify the strain–moment based reconstruction method (SMRM), where the contour of the FFN plate is solved by particular elliptic integrals. As a result, structural simulation based on ABAQUS further demonstrates that the reconstruction error of SMRM is 21.13% less than that of the classic Ko-based reconstruction method (KORM). An FFN prototype accompanied by customized flexible sensors is developed to evaluate the accuracy and efficiency of the SMRM, resulting in a maximum relative error of 3.97% that is acceptable for practical applications in smart deformable structures, not limited to the FFN plate. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics)

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14 pages, 15829 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of Different Surface Microstructures in the Thermally Induced Self-Propulsion Phenomenon

by Clint John Cortes Otic and Shigeru Yonemura

Micromachines 2022, 13(6), 871; https://doi.org/10.3390/mi13060871 - 31 May 2022

Cited by 5 | Viewed by 2735

Abstract

In micro/nano-scale systems where the characteristic length is in the order of or less than the mean free path for gas molecules, an object placed close to a heated substrate with a surface microstructure receives a propulsive force. In addition to the induced [...] Read more.

In micro/nano-scale systems where the characteristic length is in the order of or less than the mean free path for gas molecules, an object placed close to a heated substrate with a surface microstructure receives a propulsive force. In addition to the induced forces on the boundaries, thermally driven flows can also be induced in such conditions. As the force exerted on the object is caused by momentum brought by gas molecules impinging on and reflected at the surface of the object, reproducing molecular gas flows around the object is required to investigate the force on it. Using the direct simulation Monte Carlo (DSMC) method to resolve the flow, we found that by modifying the conventional ratchet-shaped microstructure into different configurations, a stronger propulsive force can be achieved. Specifically, the tip angle of the microstructure is an important parameter in optimizing the induced force. The increase in the propulsive force induced by the different microstructures was also found to depend on the Knudsen number, i.e., the ratio of the mean free path to the characteristic length and the temperature difference between the heated microstructure and the colder object. Furthermore, we explained how this force is formed and why this force is enhanced by the decreasing tip angle, considering the momentum brought onto the bottom surface of the object by incident molecules. Full article

(This article belongs to the Section A：Physics)

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18 pages, 16073 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Characterization of Fluidic-Barrier-Based Particle Generation in Centrifugal Microfluidics

by Masoud Madadelahi, Javid Azimi-Boulali, Marc Madou and Sergio Omar Martinez-Chapa

Micromachines 2022, 13(6), 881; https://doi.org/10.3390/mi13060881 - 31 May 2022

Cited by 8 | Viewed by 2971

Abstract

The fluidic barrier in centrifugal microfluidic platforms is a newly introduced concept for making multiple emulsions and microparticles. In this study, we focused on particle generation application to better characterize this method. Because the phenomenon is too fast to be captured experimentally, we [...] Read more.

The fluidic barrier in centrifugal microfluidic platforms is a newly introduced concept for making multiple emulsions and microparticles. In this study, we focused on particle generation application to better characterize this method. Because the phenomenon is too fast to be captured experimentally, we employ theoretical models to show how liquid polymeric droplets pass a fluidic barrier before crosslinking. We explain how secondary flows evolve and mix the fluids within the droplets. From an experimental point of view, the effect of different parameters, such as the barrier length, source channel width, and rotational speed, on the particles’ size and aspect ratio are investigated. It is demonstrated that the barrier length does not affect the particle’s ultimate velocity. Unlike conventional air gaps, the barrier length does not significantly affect the aspect ratio of the produced microparticles. Eventually, we broaden this concept to two source fluids and study the importance of source channel geometry, barrier length, and rotational speed in generating two-fluid droplets. Full article

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31 pages, 5679 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress in Physics-Based Modeling of Electromigration in Integrated Circuit Interconnects

by Wen-Sheng Zhao, Rui Zhang and Da-Wei Wang

Micromachines 2022, 13(6), 883; https://doi.org/10.3390/mi13060883 - 31 May 2022

Cited by 13 | Viewed by 5755

Abstract

The advance of semiconductor technology not only enables integrated circuits with higher density and better performance but also increases their vulnerability to various aging mechanisms which occur from front-end to back-end. Analysis on the impact of aging mechanisms on circuits’ reliability is crucial [...] Read more.

The advance of semiconductor technology not only enables integrated circuits with higher density and better performance but also increases their vulnerability to various aging mechanisms which occur from front-end to back-end. Analysis on the impact of aging mechanisms on circuits’ reliability is crucial for the design of reliable and sustainable electronic systems at advanced technology nodes. As one of the most crucial back-end aging mechanisms, electromigration deserves research efforts. This paper introduces recent studies on physics-based modeling of electromigration aging of on-chip interconnects. At first, the background of electromigration is introduced. The conventional method and physics-based modeling for electromigration are described. Then studies on how electromigration affects powers grids and signal interconnects are discussed in detail. Some of them focus on the comprehensiveness of modeling methodology, while others aim at the strategies for improving computation accuracy and speed and the strategies for accelerating/decelerating aging. Considering the importance of electromigration for circuit reliability, this paper is dedicated to providing a review on physics-based modeling methodologies on electromigration and their applications for integrated circuits interconnects. Full article

(This article belongs to the Special Issue Advanced Interconnect and Packaging)

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24 pages, 4537 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Atomic Layer Assembly Based on Sacrificial Templates for 3D Nanofabrication

by Guangzhou Geng, Zhongshan Zhang, Chensheng Li, Ruhao Pan, Yunlong Li, Haifang Yang and Junjie Li

Micromachines 2022, 13(6), 856; https://doi.org/10.3390/mi13060856 - 30 May 2022

Cited by 5 | Viewed by 3060

Abstract

Three-dimensional (3D) nanostructures have attracted widespread attention in physics, chemistry, engineering sciences, and biology devices due to excellent functionalities which planar nanostructures cannot achieve. However, the fabrication of 3D nanostructures is still challenging at present. Reliable fabrication, improved controllability, and multifunction integration are [...] Read more.

Three-dimensional (3D) nanostructures have attracted widespread attention in physics, chemistry, engineering sciences, and biology devices due to excellent functionalities which planar nanostructures cannot achieve. However, the fabrication of 3D nanostructures is still challenging at present. Reliable fabrication, improved controllability, and multifunction integration are desired for further applications in commercial devices. In this review, a powerful fabrication method to realize 3D nanostructures is introduced and reviewed thoroughly, which is based on atomic layer deposition assisted 3D assembly through various sacrificial templates. The aim of this review is to provide a comprehensive overview of 3D nanofabrication based on atomic layer assembly (ALA) in multifarious sacrificial templates for 3D nanostructures and to present recent advancements, with the ultimate aim to further unlock more potential of this method for nanodevice applications. Full article

(This article belongs to the Special Issue Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability)

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11 pages, 3810 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High-Performance Flexible Piezoresistive Sensor Based on Ti₃C₂T_x MXene with a Honeycomb-like Structure for Human Activity Monitoring

by Yue Su, Kainan Ma, Fang Yuan, Jun Tang, Ming Liu and Xu Zhang

Micromachines 2022, 13(6), 821; https://doi.org/10.3390/mi13060821 - 25 May 2022

Cited by 14 | Viewed by 4231

Abstract

Wearable and flexible pressure sensors have sparked great interest due to their unique capacity to conformally attach to the surface of the skin and quantify human activities into recordable electric signals. As a result, more and more research efforts are being devoted to [...] Read more.

Wearable and flexible pressure sensors have sparked great interest due to their unique capacity to conformally attach to the surface of the skin and quantify human activities into recordable electric signals. As a result, more and more research efforts are being devoted to developing high-sensitivity and cost-effective flexible sensors for monitoring an individual’s state of activity. Herein, a high-performance flexible piezoresistive sensor was designed and fabricated by combing 2D transition metal carbides, nitrides, and carbonitrides (MXene) with a honeycomb-like structure formed by femtosecond filamentating pulses. The sensing mechanism is attributed to the change of the connecting conductive paths between the top interdigital electrodes and the bottom microstructured films coated with MXene. The obtained sensing device demonstrates high sensitivity of 0.61 kPa⁻¹, relatively short response time, and excellent reliability and stability. Benefiting from the aforementioned extraordinary sensing performance, the sensor can be used with success to monitor tiny physiological signals, detect large deformations during human movement, and distinguish finger gestures, thus demonstrating its broad prospects in physiological analysis systems, health monitoring systems, and human–machine interaction. Full article

(This article belongs to the Special Issue Flexible and Wearable Sensors)

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12 pages, 2926 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Wireless Micro Soft Actuator without Payloads Using 3D Helical Coils

by Seonghyeon Lee, Woojun Jung, Kyungho Ko and Yongha Hwang

Micromachines 2022, 13(5), 799; https://doi.org/10.3390/mi13050799 - 20 May 2022

Cited by 3 | Viewed by 4065

Abstract

To receive a greater power and to demonstrate the soft bellows-shaped actuator’s wireless actuation, micro inductors were built for wireless power transfer and realized in a three-dimensional helical structure, which have previously been built in two-dimensional spiral structures. Although the three-dimensional helical inductor [...] Read more.

To receive a greater power and to demonstrate the soft bellows-shaped actuator’s wireless actuation, micro inductors were built for wireless power transfer and realized in a three-dimensional helical structure, which have previously been built in two-dimensional spiral structures. Although the three-dimensional helical inductor has the advantage of acquiring more magnetic flux linkage than the two-dimensional spiral inductor, the existing microfabrication technique produces a device on a two-dimensional plane, as it has a limit to building a complete three-dimensional structure. In this study, by using a three-dimensional printed soluble mold technique, a three-dimensional heater with helical coils, which have a larger heating area than a two-dimensional heater, was fabricated with three-dimensional receiving inductors for enhanced wireless power transfer. The three-dimensional heater connected to the three-dimensional helical inductor increased the temperature of the liquid and gas inside the bellows-shaped actuator while reaching 176.1% higher temperature than the heater connected to the two-dimensional spiral inductor. Thereby it enables a stroke of the actuator up to 522% longer than when it is connected to the spiral inductor. Therefore, three-dimensional micro coils can offer a significant approach to the development of wireless micro soft robots without incurring heavy and bulky parts such as batteries. Full article

(This article belongs to the Special Issue Integrated Fabrication Approaches for Soft Robotics)

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22 pages, 7568 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Wearable Near-Field Communication Sensors for Healthcare: Materials, Fabrication and Application

by Xidi Sun, Chengyan Zhao, Hao Li, Huiwen Yu, Jing Zhang, Hao Qiu, Junge Liang, Jing Wu, Mengrui Su, Yi Shi and Lijia Pan

Micromachines 2022, 13(5), 784; https://doi.org/10.3390/mi13050784 - 17 May 2022

Cited by 24 | Viewed by 4762

Abstract

The wearable device industry is on the rise, with technology applications ranging from wireless communication technologies to the Internet of Things. However, most of the wearable sensors currently on the market are expensive, rigid and bulky, leading to poor data accuracy and uncomfortable [...] Read more.

The wearable device industry is on the rise, with technology applications ranging from wireless communication technologies to the Internet of Things. However, most of the wearable sensors currently on the market are expensive, rigid and bulky, leading to poor data accuracy and uncomfortable wearing experiences. Near-field communication sensors are low-cost, easy-to-manufacture wireless communication technologies that are widely used in many fields, especially in the field of wearable electronic devices. The integration of wireless communication devices and sensors exhibits tremendous potential for these wearable applications by endowing sensors with new features of wireless signal transferring and conferring radio frequency identification or near-field communication devices with a sensing function. Likewise, the development of new materials and intensive research promotes the next generation of ultra-light and soft wearable devices for healthcare. This review begins with an introduction to the different components of near-field communication, with particular emphasis on the antenna design part of near-field communication. We summarize recent advances in different wearable areas of near-field communication sensors, including structural design, material selection, and the state of the art of scenario-based development. The challenges and opportunities relating to wearable near-field communication sensors for healthcare are also discussed. Full article

(This article belongs to the Special Issue Wearable Devices for Healthcare)

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8 pages, 2087 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Module-Fluidics: Building Blocks for Spatio-Temporal Microenvironment Control

by Bowen Ling and Ilenia Battiato

Micromachines 2022, 13(5), 774; https://doi.org/10.3390/mi13050774 - 14 May 2022

Cited by 1 | Viewed by 2508

Abstract

Generating the desired solute concentration signal in micro-environments is vital to many applications ranging from micromixing to analyzing cellular response to a dynamic microenvironment. We propose a new modular design to generate targeted temporally varying concentration signals in microfluidic systems while minimizing perturbations [...] Read more.

Generating the desired solute concentration signal in micro-environments is vital to many applications ranging from micromixing to analyzing cellular response to a dynamic microenvironment. We propose a new modular design to generate targeted temporally varying concentration signals in microfluidic systems while minimizing perturbations to the flow field. The modularized design, here referred to as module-fluidics, similar in principle to interlocking toy bricks, is constructed from a combination of two building blocks and allows one to achieve versatility and flexibility in dynamically controlling input concentration. The building blocks are an oscillator and an integrator, and their combination enables the creation of controlled and complex concentration signals, with different user-defined time-scales. We show two basic connection patterns, in-series and in-parallel, to test the generation, integration, sampling and superposition of temporally-varying signals. All such signals can be fully characterized by analytic functions, in analogy with electric circuits, and allow one to perform design and optimization before fabrication. Such modularization offers a versatile and promising platform that allows one to create highly customizable time-dependent concentration inputs which can be targeted to the specific application of interest. Full article

(This article belongs to the Special Issue Lab-on-a-Chip and Organ-on-a-Chip: Fabrications and Applications)

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19 pages, 4879 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Oscillation Characteristics of an Artificial Cochlear Sensory Epithelium Optimized for a Micrometer-Scale Curved Structure

by Hiroki Yamazaki, Yutaro Kohno and Satoyuki Kawano

Micromachines 2022, 13(5), 768; https://doi.org/10.3390/mi13050768 - 13 May 2022

Viewed by 2536

Abstract

Based on the modern microelectromechanical systems technology, we present a revolutionary miniaturized artificial cochlear sensory epithelium for future implantation tests on guinea pigs. The device was curved to fit the spiral structure of the cochlea and miniaturized to a maximum dimension of <1 [...] Read more.

Based on the modern microelectromechanical systems technology, we present a revolutionary miniaturized artificial cochlear sensory epithelium for future implantation tests on guinea pigs. The device was curved to fit the spiral structure of the cochlea and miniaturized to a maximum dimension of <1 mm to be implanted in the cochlea. First, the effect of the curved configuration on the oscillation characteristics of a trapezoidal membrane was evaluated using the relatively larger devices, which had a trapezoidal and a comparable curved shape designed for high-precision in vitro measurements. Both experimental and numerical analyses were used to determine the resonance frequencies and positions, and multiple oscillation modes were clearly observed. Because the maximum oscillation amplitude positions, i.e., the resonance positions, differed depending on the resonance frequencies in both trapezoidal and curved membrane devices, the sound frequency was determined based on the resonance position, thus reproducing the frequency selectivity of the basilar membrane in the organ of Corti. Furthermore, the resonance frequencies and positions of these two devices with different configurations were determined to be quantitatively consistent and similar in terms of mechanical dynamics. This result shows that despite a curved angle of 50–60°, the effect of the curved shape on oscillation characteristics was negligible. Second, the nanometer-scale oscillation of the miniaturized device was successfully measured, and the local resonance frequency in air was varied from 157 to 277 kHz using an experimental system that could measure the amplitude distribution in a two-dimensional (2D) plane with a high accuracy and reproducibility at a high speed. The miniaturized device developed in this study was shown to have frequency selectivity, and when the device was implanted in the cochlea, it was expected to discriminate frequencies in the same manner as the basilar membrane in the biological system. This study established methods for fabricating and evaluating the miniaturized device, and the proposed miniaturized device in a curved shape demonstrated the feasibility of next-generation cochlear implants. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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16 pages, 9432 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Magnetically Coupled Piezoelectric–Electromagnetic Low-Frequency Multidirection Hybrid Energy Harvester

by Yongqiang Zhu, Zhaoyang Zhang, Pingxia Zhang and Yurong Tan

Micromachines 2022, 13(5), 761; https://doi.org/10.3390/mi13050761 - 11 May 2022

Cited by 20 | Viewed by 5528

Abstract

The traditional single electromechanical conversion energy harvester can collect energy only in a single vibration direction. Moreover, it requires high environmental vibration frequency, and its output power is low. To solve these problems, a cross-shaped magnetically coupled piezoelectric–electromagnetic hybrid harvester is proposed. The [...] Read more.

The traditional single electromechanical conversion energy harvester can collect energy only in a single vibration direction. Moreover, it requires high environmental vibration frequency, and its output power is low. To solve these problems, a cross-shaped magnetically coupled piezoelectric–electromagnetic hybrid harvester is proposed. The harvester comprised a ring-shaped support frame, a piezoelectric generation structure, and an electromagnetic generation structure. The harvester could simultaneously generate energy piezoelectrically and electrically, in addition, it could generate electricity efficiently at a lower environmental vibration, and it can collect the energy in two vibration directions simultaneously. To verify the effectiveness of the device, we set up a vibration experiment system and conducted comparative experiments about non-magnetically coupled piezoelectric, magnetically coupled piezoelectric, and magnetically coupled piezoelectric–electromagnetic hybrid energy harvesters. The experimental results showed that the output power of the magnetically coupled piezoelectric–electromagnetic hybrid energy harvester was 2.13 mW for the piezoelectric structure and 1.76 mW for the electromagnetic structure under the vibration of single-direction resonant frequency. The total hybrid output power was 3.89 mW. The hybrid harvester could collect vibration energy parallel to the ring in any direction. Furthermore, compared with the non-magnetically coupled piezoelectric energy harvester and the magnetically coupled piezoelectric energy harvester, the output power was increased by 141.6% and 55.6%, respectively. Full article

(This article belongs to the Special Issue Piezoelectric Energy Harvesting: Analysis, Design and Fabrication)

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10 pages, 3311 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Laser Scanning Guided Localization Imaging with a Laser-Machined Two-Dimensional Flexible Ultrasonic Array

by Jianzhong Chen, Wei Liu, Dianbao Gu and Dawei Wu

Micromachines 2022, 13(5), 754; https://doi.org/10.3390/mi13050754 - 10 May 2022

Cited by 8 | Viewed by 2625

Abstract

Advances in flexible integrated circuit technology and piezoelectric materials allow high-quality stretchable piezoelectric transducers to be built in a form that is easy to integrate with the body’s soft, curved, and time-dynamic surfaces. The resulting capabilities create new opportunities for studying disease states, [...] Read more.

Advances in flexible integrated circuit technology and piezoelectric materials allow high-quality stretchable piezoelectric transducers to be built in a form that is easy to integrate with the body’s soft, curved, and time-dynamic surfaces. The resulting capabilities create new opportunities for studying disease states, monitoring health/wellness, building human–machine interfaces, and performing other operations. However, more widespread application scenarios are placing new demands on the high flexibility and small size of the array. This paper provides a 8 × 8 two-dimensional flexible ultrasonic array (2D-FUA) based on laser micromachining; a novel single-layer “island bridge” structure was used to design flexible array and piezoelectric array elements to improve the imaging capability on complex surfaces. The mechanical and acoustoelectric properties of the array are characterized, and a novel laser scanning and positioning method is introduced to solve the problem of array element displacement after deformation of the 2D-FUA. Finally, a multi-modal localization imaging experiment was carried out on the multi-target steel pin on the plane and curved surface based on the Verasonics system. The results show that the laser scanning method has the ability to assist the rapid imaging of flexible arrays on surfaces with complex shapes, and that 2D-FUA has wide application potential in medical-assisted localization imaging. Full article

(This article belongs to the Special Issue Piezoelectric Ultrasound Transducer for Biomedical Applications)

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10 pages, 3752 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Refractive Index Sensor Based on a Metal-Insulator-Metal Bus Waveguide Coupled with a U-Shaped Ring Resonator

by Xiaoyu Zhang, Shubin Yan, Jilai Liu, Yifeng Ren, Yi Zhang and Lifang Shen

Micromachines 2022, 13(5), 750; https://doi.org/10.3390/mi13050750 - 9 May 2022

Cited by 9 | Viewed by 2317

Abstract

In this study, a novel refractive index sensor structure was designed consisting of a metal-insulator-metal (MIM) waveguide with two rectangular baffles and a U-Shaped Ring Resonator (USRR). The finite element method was used to theoretically investigate the sensor’s transmission characteristics. The simulation results [...] Read more.

In this study, a novel refractive index sensor structure was designed consisting of a metal-insulator-metal (MIM) waveguide with two rectangular baffles and a U-Shaped Ring Resonator (USRR). The finite element method was used to theoretically investigate the sensor’s transmission characteristics. The simulation results show that Fano resonance is a sharp asymmetric resonance generated by the interaction between the discrete narrow-band mode and the successive wide-band mode. Next, the formation of broadband and narrowband is further studied, and finally the key factors affecting the performance of the sensor are obtained. The best sensitivity of this refractive-index sensor is 2020 nm/RIU and the figure of merit (FOM) is 53.16. The presented sensor has the potential to be useful in nanophotonic sensing applications. Full article

(This article belongs to the Special Issue Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability)

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