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13 pages, 5464 KiB

Open AccessArticle

Second-Order Vector Mode Propagation in Hollow-Core Antiresonant Fibers

by Lili Li and Limin Xiao

Micromachines 2019, 10(6), 381; https://doi.org/10.3390/mi10060381 - 07 Jun 2019

Cited by 2 | Viewed by 3056

Second-order vector modes, possessing doughnut-shaped intensity distribution with unique polarization, are widely utilized in material micromachining, optical tweezers, and high-resolution microscopy. Since the hollow-core fiber can act as a flexible and robust optical waveguide for ultra-short pulse delivery and manipulation, high-order vector modes [...] Read more.

Second-order vector modes, possessing doughnut-shaped intensity distribution with unique polarization, are widely utilized in material micromachining, optical tweezers, and high-resolution microscopy. Since the hollow-core fiber can act as a flexible and robust optical waveguide for ultra-short pulse delivery and manipulation, high-order vector modes guided in hollow-core fibers will have huge potential in many advanced applications. We firstly reveal that a second-order vector mode can be well guided in a hollow-core antiresonant fiber with the suppression of the fundamental mode and other second-order vector modes at the red side of transmission band. We interpret our observation through a phase-matched coupling mechanism between core modes and coupled cladding modes. A single second-order vector mode such as TE₀₁, TM₀₁, or HE₂₁ can be guided with low confinement loss at specific wavelengths with appropriate structure parameters. Our proposed hollow-core fibers have a modal engineering function which will open up a new avenue toward the single second-order vector mode propagation and its fiberized applications. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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14 pages, 3001 KiB

Open AccessArticle

A Novel Self-Activated Mechanism for Stable Liquid Transportation Capable of Continuous-Flow and Real-time Microfluidic PCRs

by Di Wu, Bing Shi, Bin Li and Wenming Wu

Micromachines 2019, 10(6), 350; https://doi.org/10.3390/mi10060350 - 28 May 2019

Cited by 4 | Viewed by 2550

Abstract

The self-activated micropump capable of velocity-stable transport for both single-phased plug and double-phased droplet through long flow distance inside 3D microchannel is one dream of microfluidic scientists. While several types of passive micropumps have been developed based on different actuation mechanisms, until today, [...] Read more.

The self-activated micropump capable of velocity-stable transport for both single-phased plug and double-phased droplet through long flow distance inside 3D microchannel is one dream of microfluidic scientists. While several types of passive micropumps have been developed based on different actuation mechanisms, until today, it is still one bottleneck to realize such a satisfied self-activated micropump for the stable delivery of both single and double-phased liquid inside long microchannel (e.g., several meters), due to the lack of innovative mechanism in previous methods. To solve this problem, in this article, we propose a new self-activated pumping mechanism. Herein, an end-opened gas-impermeable quartz capillary is utilized for passive transport. Mechanism of this micropump is systemically studied by both the mathematical modeling and the experimental verifications. Based on the flow assays, it totally confirmed a different pumping principle in this paper, as compared with our previous works. The

R^{2}

value of the overall flow rates inside the 3D microchannel is confirmed as high as 0.999, which is much more homogeneous than other passive pumping formats. Finally, this novel micropump is applied to continuous-flow real-time PCRs (both plug-type and microdroplet-type), with the amplification efficiency reaching 91.5% of the commercial PCR cycler instrument. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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13 pages, 4684 KiB

Open AccessArticle

Comparison of Micro-Mixing in Time Pulsed Newtonian Fluid and Viscoelastic Fluid

by Meng Zhang, Wu Zhang, Zhengwei Wu, Yinan Shen, Yicheng Chen, Chaofeng Lan, Fengchen Li and Weihua Cai

Micromachines 2019, 10(4), 262; https://doi.org/10.3390/mi10040262 - 18 Apr 2019

Cited by 16 | Viewed by 3139

Abstract

Fluid mixing plays an essential role in many microfluidic applications. Here, we compare the mixing in time pulsing flows for both a Newtonian fluid and a viscoelastic fluid at different pulsing frequencies. In general, the mixing degree in the viscoelastic fluid is higher [...] Read more.

Fluid mixing plays an essential role in many microfluidic applications. Here, we compare the mixing in time pulsing flows for both a Newtonian fluid and a viscoelastic fluid at different pulsing frequencies. In general, the mixing degree in the viscoelastic fluid is higher than that in the Newtonian fluid. Particularly, the mixing in Newtonian fluid with time pulsing is decreased when the Reynolds number Re is between 0.002 and 0.01, while it is enhanced when Re is between 0.1 and 0.2 compared with that at a constant flow rate. In the viscoelastic fluid, on the other hand, the time pulsing does not change the mixing degree when the Weissenberg number Wi

\leq

20, while a larger mixing degree is realized at a higher pulsing frequency when Wi = 50. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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12 pages, 5344 KiB

Open AccessArticle

Higher-Order Mode Suppression in Antiresonant Nodeless Hollow-Core Fibers

by Aichen Ge, Fanchao Meng, Yanfeng Li, Bowen Liu and Minglie Hu

Micromachines 2019, 10(2), 128; https://doi.org/10.3390/mi10020128 - 15 Feb 2019

Cited by 15 | Viewed by 3785

Abstract

Negative curvature hollow-core fibers (NC-HCFs) are useful as gas sensors. We numerically analyze the single-mode performance of NC-HCFs. Both single-ring NC-HCFs and nested antiresonant fibers (NANFs) are investigated. When the size of the cladding tubes is properly designed, higher-order modes (HOMs) in the [...] Read more.

Negative curvature hollow-core fibers (NC-HCFs) are useful as gas sensors. We numerically analyze the single-mode performance of NC-HCFs. Both single-ring NC-HCFs and nested antiresonant fibers (NANFs) are investigated. When the size of the cladding tubes is properly designed, higher-order modes (HOMs) in the fiber core can be coupled with the cladding modes effectively and form high-loss supermodes. For the single-ring structure, we propose a novel NC-HCF with hybrid cladding tubes to enable suppression of the first two HOMs in the core simultaneously. For the nested structure, we find that cascaded coupling is necessary to maximize the loss of the HOMs in NANFs, and, as a result, NANFs with five nested tubes have an advantage in single-mode guidance performance. Moreover, a novel NANF with hybrid extended cladding tubes is proposed. In this kind of NANF, higher-order mode extinction ratios (HOMERs) of 10⁵ and even 10⁶ are obtained for the LP₁₁ and LP₂₁ modes, respectively, and a similar level of 10⁵ for the LP₀₂ modes. Good single-mode performance is maintained within a broad wavelength range. In addition, the loss of the LP₀₁ modes in this kind of NANF is as low as 3.90 × 10⁻⁴ dB/m. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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9 pages, 2345 KiB

Open AccessCommunication

Self-Healing Flexible Conductive Film by Repairing Defects via Flowable Liquid Metal Droplets

by Ruiwen Niu, Mingliang Jin, Jieping Cao, Zhibin Yan, Jinwei Gao, Hao Wu, Guofu Zhou and Lingling Shui

Micromachines 2019, 10(2), 113; https://doi.org/10.3390/mi10020113 - 11 Feb 2019

Cited by 7 | Viewed by 3466

Abstract

Self-healing flexible conductive films have been fabricated, evaluated, and applied. The film is composed of a fragile indium tin oxide (ITO) layer covered with sprayed liquid metal (LM) droplets. Self-healing of electrical conductivity is achieved via spontaneous capillary wicking of LM droplets into [...] Read more.

Self-healing flexible conductive films have been fabricated, evaluated, and applied. The film is composed of a fragile indium tin oxide (ITO) layer covered with sprayed liquid metal (LM) droplets. Self-healing of electrical conductivity is achieved via spontaneous capillary wicking of LM droplets into cracks/defects of the ITO film. The liquid metal adhering onto the ITO layer can also connect the ITO fragments during bending to keep the overall conductivity of the composite LM/ITO film stable. Stable and reversible electrowetting performance has been achieved with the composite LM/ITO as the conductive film, in either flat or curved states. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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9 pages, 3553 KiB

Open AccessArticle

High Sensitivity Photonic Crystal Fiber Refractive Index Sensor with Gold Coated Externally Based on Surface Plasmon Resonance

by Xudong Li, Shuguang Li, Xin Yan, Dongming Sun, Zheng Liu and Tonglei Cheng

Micromachines 2018, 9(12), 640; https://doi.org/10.3390/mi9120640 - 03 Dec 2018

Cited by 38 | Viewed by 4210

Abstract

In this paper we propose a gold-plated photonic crystal fiber (PCF) refractive index sensor based on surface plasmon resonance (SPR), in which gold is coated on the external surface of PCF for easy fabrication and practical detection. The finite element method (FEM) is [...] Read more.

In this paper we propose a gold-plated photonic crystal fiber (PCF) refractive index sensor based on surface plasmon resonance (SPR), in which gold is coated on the external surface of PCF for easy fabrication and practical detection. The finite element method (FEM) is used for the performance analysis, and the numerical results show that the thickness of the gold film, the refractive index of the analyte, the radius of the air hole in the first layer, the second layer, and the central air hole can affect the sensing properties of the sensor. By optimizing the sensor structure, the maximum wavelength sensitivity can reach 11000 nm/RIU and the maximum amplitude sensitivity can reach 641 RIU⁻¹. Due to its high sensitivity, the proposed sensor can be used for practical biological and chemical sensing. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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11 pages, 2466 KiB

Open AccessArticle

A Diffusion-Based pH Regulator in Laminar Flows with Smartphone-Based Colorimetric Analysis

by Wei Wang, Zhi Zeng, Wei Xu, Wenming Wu, Wenfeng Liang and Jia Zhou

Micromachines 2018, 9(12), 616; https://doi.org/10.3390/mi9120616 - 23 Nov 2018

Cited by 1 | Viewed by 2674

Abstract

A strategy for an on-chip pH regulator is demonstrated computationally and experimentally, based on the diffusion characteristics of aqueous ionic solutions. Micro-flows with specific pH values are formed based on the diffusion behaviors of hydrogen and hydroxide ions in laminar flows. The final [...] Read more.

A strategy for an on-chip pH regulator is demonstrated computationally and experimentally, based on the diffusion characteristics of aqueous ionic solutions. Micro-flows with specific pH values are formed based on the diffusion behaviors of hydrogen and hydroxide ions in laminar flows. The final achieved pH value and its gradient in the channel can be regulated by the amount of ions transported between laminar flows, and the experimental results can be further generalized based on the normalized Nernst-Planck equation. A smartphone was applied as an image capture and analysis instrument to quantify pH values of liquids in a colorimetric detection process, with monotonic response range of ~1–13. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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13 pages, 12809 KiB

Open AccessFeature PaperArticle

Cell Density Detector Based on Light Beam Focusing

by Aoqun Jian, Huiming Li, Yixia Zhang, Qianqian Duan, Qianwu Zhang and Shengbo Sang

Micromachines 2018, 9(11), 592; https://doi.org/10.3390/mi9110592 - 13 Nov 2018

Cited by 3 | Viewed by 2869

Abstract

Although the lab-on-a-chip system has been successfully applied in a wide variety of fields, the goal of achieving a cell counter with simple operation, low cost, and high accuracy still attracts continuous research efforts. In this paper, the authors explore a cell counter [...] Read more.

Although the lab-on-a-chip system has been successfully applied in a wide variety of fields, the goal of achieving a cell counter with simple operation, low cost, and high accuracy still attracts continuous research efforts. In this paper, the authors explore a cell counter based on light beam focusing to measure the density of adherent cells. In this sensor, the light emitted from the optical fibers is collimated by the collimating lens formed in polydimethylsiloxane (PDMS). The uniformly attached adherent cells act as a convex lens, focusing the collimated light propagated through them. The intensity of the focused light indicates the density of the adherent cells. For Hela cells, a detection limit of 8.3 × 10⁴ cells/mL with a detection range from 0.1 × 10⁶ cells/mL to 1.0 × 10⁶ cells/mL is achieved. This sensor is particularly useful for drug screening, cell pathology analysis, and cancer pre-diagnosis. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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Review

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19 pages, 3663 KiB

Open AccessReview

Wettability Manipulation by Interface-Localized Liquid Dielectrophoresis: Fundamentals and Applications

by Jitesh Barman, Wan Shao, Biao Tang, Dong Yuan, Jan Groenewold and Guofu Zhou

Micromachines 2019, 10(5), 329; https://doi.org/10.3390/mi10050329 - 16 May 2019

Cited by 18 | Viewed by 4213

Abstract

Electric field-based smart wetting manipulation is one of the extensively used techniques in modern surface science and engineering, especially in microfluidics and optofluidics applications. Liquid dielectrophoresis (LDEP) is a technique involving the manipulation of dielectric liquid motion via the polarization effect using a [...] Read more.

Electric field-based smart wetting manipulation is one of the extensively used techniques in modern surface science and engineering, especially in microfluidics and optofluidics applications. Liquid dielectrophoresis (LDEP) is a technique involving the manipulation of dielectric liquid motion via the polarization effect using a non-homogeneous electric field. The LDEP technique was mainly dedicated to the actuation of dielectric and aqueous liquids in microfluidics systems. Recently, a new concept called dielectrowetting was demonstrated by which the wettability of a dielectric liquid droplet can be reversibly manipulated via a highly localized LDEP force at the three-phase contact line of the droplet. Although dielectrowetting is principally very different from electrowetting on dielectrics (EWOD), it has the capability to spread a dielectric droplet into a thin liquid film with the application of sufficiently high voltage, overcoming the contact-angle saturation encountered in EWOD. The strength of dielectrowetting depends on the ratio of the penetration depth of the electric field inside the dielectric liquid and the difference between the dielectric constants of the liquid and its ambient medium. Since the introduction of the dielectrowetting technique, significant progress in the field encompassing various real-life applications was demonstrated in recent decades. In this paper, we review and discuss the governing forces and basic principles of LDEP, the mechanism of interface localization of LDEP for dielectrowetting, related phenomenon, and their recent applications, with an outlook on the future research. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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16 pages, 3122 KiB

Open AccessReview

Droplet-Based Microfluidic Thermal Management Methods for High Performance Electronic Devices

by Zhibin Yan, Mingliang Jin, Zhengguang Li, Guofu Zhou and Lingling Shui

Micromachines 2019, 10(2), 89; https://doi.org/10.3390/mi10020089 - 25 Jan 2019

Cited by 23 | Viewed by 4996

Abstract

Advanced thermal management methods have been the key issues for the rapid development of the electronic industry following Moore’s law. Droplet-based microfluidic cooling technologies are considered as promising solutions to conquer the major challenges of high heat flux removal and nonuniform temperature distribution [...] Read more.

Advanced thermal management methods have been the key issues for the rapid development of the electronic industry following Moore’s law. Droplet-based microfluidic cooling technologies are considered as promising solutions to conquer the major challenges of high heat flux removal and nonuniform temperature distribution in confined spaces for high performance electronic devices. In this paper, we review the state-of-the-art droplet-based microfluidic cooling methods in the literature, including the basic theory of electrocapillarity, cooling applications of continuous electrowetting (CEW), electrowetting (EW) and electrowetting-on-dielectric (EWOD), and jumping droplet microfluidic liquid handling methods. The droplet-based microfluidic cooling methods have shown an attractive capability of microscale liquid manipulation and a relatively high heat flux removal for hot spots. Recommendations are made for further research to develop advanced liquid coolant materials and the optimization of system operation parameters. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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23 pages, 3679 KiB

Open AccessFeature PaperReview

Recent Advances in Tunable and Reconfigurable Metamaterials

by Sanghun Bang, Jeonghyun Kim, Gwanho Yoon, Takuo Tanaka and Junsuk Rho

Micromachines 2018, 9(11), 560; https://doi.org/10.3390/mi9110560 - 31 Oct 2018

Cited by 57 | Viewed by 6971

Abstract

Metamaterials are composed of nanostructures, called artificial atoms, which can give metamaterials extraordinary properties that cannot be found in natural materials. The nanostructures themselves and their arrangements determine the metamaterials’ properties. However, a conventional metamaterial has fixed properties in general, which limit their [...] Read more.

Metamaterials are composed of nanostructures, called artificial atoms, which can give metamaterials extraordinary properties that cannot be found in natural materials. The nanostructures themselves and their arrangements determine the metamaterials’ properties. However, a conventional metamaterial has fixed properties in general, which limit their use. Thus, real-world applications of metamaterials require the development of tunability. This paper reviews studies that realized tunable and reconfigurable metamaterials that are categorized by the mechanisms that cause the change: inducing temperature changes, illuminating light, inducing mechanical deformation, and applying electromagnetic fields. We then provide the advantages and disadvantages of each mechanism and explain the results or effects of tuning. We also introduce studies that overcome the disadvantages or strengthen the advantages of each classified tunable metamaterial. Full article

(This article belongs to the Special Issue Optofluidics 2018)

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