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Smart Materials for Soft Sensors and Actuators

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Smart Materials".

Deadline for manuscript submissions: closed (27 August 2018) | Viewed by 24583

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Prof. Dr. Youngsu Cha

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Guest Editor

Center for Intelligent & Interactive Robotics, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
Interests: smart materials; energy harvesting; flexible sensors and actuators; fluid-structure interactions; robotics
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Maurizio Porfiri

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Guest Editor

Department of Mechanical and Aerospace Engineering, Tandon School of Engineering, New York University, Brooklyn, NY 11201, USA
Interests: dynamical systems theory and applications; mechanics of advanced materials; multiphysics modeling; smart materials and structures

Special Issue Information

Dear Colleagues,

Soft active materials are emerging as a promising technology for sensing and actuation. These materials display physical coupling in two or more domains, such as electrostatics and mechanics in piezoelectrics, while offering the important benefit of flexibility. These propitious features constitute an empowering tool of for new applications in science and engineering, such as wearable devices, artificial skin, artificial muscles, biomimetic robots, and soft robots.

In this Special Issue, we are interested in smart materials for state of the art applications in soft sensors and actuators. We hope that this special issue will be a seed for the new ambitious insight into the science and engineering of smart materials. Exemplary material systems include electroactive polymers, ferroelectrics, ionic polymer metal composites (IPMCs), photovoltaics, piezoelectrics, shape memory alloys (SMAs), and thermoelectrics.

We invite your original research articles about recent technological advancements in smart materials for flexible sensors and actuators. Our scope includes experimental, theoretical, and computational approaches.

Dr. Youngsu Cha
Prof. Dr. Maurizio Porfiri
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

smart materials
soft active materials
multifunctional materials
electromechanical coupling
piezoelectrics
flexible sensors
flexible actuators
wearable devices
artificial muscles
artificial skin
biomimetics
soft robotics

Published Papers (6 papers)

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Research

13 pages, 1538 KiB

Open AccessArticle

Design of a 2 DOFs Mini Hollow Joint Actuated with SMA Wires

by Luigi Manfredi and Alfred Cuschieri

Materials 2018, 11(10), 2014; https://doi.org/10.3390/ma11102014 - 17 Oct 2018

Cited by 13 | Viewed by 5039

Abstract

Shape memory alloys (SMAs) are smart materials used in robotics because of its light weight and high force-to-weight ratio. The low energy efficiency, up to 5%, has limited their use for large actuators. However, they have shown advantages in the design of mini-robots because of the limited volume required for the actuation system. The present study reports the design and construction of a mini compliant joint (MCJ) with a 2 degrees of freedom (DOFs) intersecting axis. The MCJ prototype has a 20 mm external diameter surrounding a cavity of 8 mm, weighs 2 g, is 20 mm high and can perform an angle rotation of 30

^{\circ}

in less than 260 ms. It uses SMA NiTi wires in antagonistic configuration and springs to reduce the energy consumption and minimise heat production. The design methods and experimental results of the manufactured prototype are reported and discussed. Full article

(This article belongs to the Special Issue Smart Materials for Soft Sensors and Actuators)

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17 pages, 5252 KiB

Open AccessArticle

Corrugated Photoactive Thin Films for Flexible Strain Sensor

by Donghyeon Ryu and Alfred Mongare

Materials 2018, 11(10), 1970; https://doi.org/10.3390/ma11101970 - 13 Oct 2018

Cited by 19 | Viewed by 3486

Abstract

In this study, a flexible strain sensor is devised using corrugated bilayer thin films consisting of poly(3-hexylthiophene) (P3HT) and poly(3,4-ethylenedioxythiophene)-polystyrene(sulfonate) (PEDOT:PSS). In previous studies, the P3HT-based photoactive non-corrugated thin film was shown to generate direct current (DC) under broadband light, and the generated DC voltage varied with applied tensile strain. Yet, the mechanical resiliency and strain sensing range of the P3HT-based thin film strain sensor were limited due to brittle non-corrugated thin film constituents. To address this issue, it is aimed to design a mechanically resilient strain sensor using corrugated thin film constituents. Buckling is induced to form corrugation in the thin films by applying pre-strain to the substrate, where the thin films are deposited, and releasing the pre-strain afterwards. It is known that corrugated thin film constituents exhibit different optical and electronic properties from non-corrugated ones. Therefore, to design the flexible strain sensor, it was studied to understand how the applied pre-strain and thickness of the PEDOT:PSS conductive thin film affects the optical and electrical properties. In addition, strain effect was investigated on the optical and electrical properties of the corrugated thin film constituents. Finally, flexible strain sensors are fabricated by following the design guideline, which is suggested from the studies on the corrugated thin film constituents, and the DC voltage strain sensing capability of the flexible strain sensors was validated. As a result, the flexible strain sensor exhibited a tensile strain sensing range up to 5% at a frequency up to 15 Hz with a maximum gauge factor ~7. Full article

(This article belongs to the Special Issue Smart Materials for Soft Sensors and Actuators)

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Graphical abstract

9 pages, 4064 KiB

Open AccessArticle

Noninvasive Mechanochemical Imaging in Unconstrained Caenorhabditis elegans

by Takuma Sugi, Ryuji Igarashi and Masaki Nishimura

Materials 2018, 11(6), 1034; https://doi.org/10.3390/ma11061034 - 19 Jun 2018

Cited by 6 | Viewed by 3355

Abstract

Physical forces are transduced into chemical reactions, thereby ultimately making a large impact on the whole-animal level phenotypes such as homeostasis, development and behavior. To understand mechano-chemical transduction, mechanical input should be quantitatively delivered with controllable vibration properties–frequency, amplitude and duration, and its chemical output should be noninvasively quantified in an unconstrained animal. However, such an experimental system has not been established so far. Here, we develop a noninvasive and unconstrained mechanochemical imaging microscopy. This microscopy enables us to evoke nano-scale nonlocalized vibrations with controllable vibration properties using a piezoelectric acoustic transducer system and quantify calcium response of a freely moving C. elegans at a single cell resolution. Using this microscopy, we clearly detected the calcium response of a single interneuron during C. elegans escape response to nano-scale vibration. Thus, this microscopy will facilitate understanding of in vivo mechanochemical physiology in the future. Full article

(This article belongs to the Special Issue Smart Materials for Soft Sensors and Actuators)

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10 pages, 2426 KiB

Open AccessArticle

Fe₃O₄–Silicone Mixture as Flexible Actuator

by Kahye Song and Youngsu Cha

Materials 2018, 11(5), 753; https://doi.org/10.3390/ma11050753 - 08 May 2018

Cited by 10 | Viewed by 4247

Abstract

In this study, we introduce Fe₃O₄-silicone flexible composite actuators fabricated by combining silicone and iron oxide particles. The actuators exploit the flexibility of silicone and the electric conductivity of iron oxide particles. These actuators are activated by electrostatic force using the properties of the metal particles. Herein, we investigate the characteristic changes in actuation performance by increasing the concentration of iron oxide from 1% to 20%. The developed flexible actuators exhibit a resonant frequency near 3 Hz and their actuation amplitudes increase with increasing input voltage. We found that the actuator can move well at metal particle concentrations >2.5%. We also studied the changes in actuation behavior, depending on the portion of the Fe₃O₄-silicone in the length. Overall, we experimentally analyzed the characteristics of the newly proposed metal particle-silicone composite actuators. Full article

(This article belongs to the Special Issue Smart Materials for Soft Sensors and Actuators)

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12 pages, 7429 KiB

Open AccessArticle

Understanding the Thermal Properties of Precursor-Ionomers to Optimize Fabrication Processes for Ionic Polymer-Metal Composites (IPMCs)

by Sarah Trabia, Kisuk Choi, Zakai Olsen, Taeseon Hwang, Jae-Do Nam and Kwang J. Kim

Materials 2018, 11(5), 665; https://doi.org/10.3390/ma11050665 - 25 Apr 2018

Cited by 7 | Viewed by 4153

Abstract

Ionic polymer-metal composites (IPMCs) are one of many smart materials and have ionomer bases with a noble metal plated on the surface. The ionomer is usually Nafion, but recently Aquivion has been shown to be a promising alternative. Ionomers are available in the form of precursor pellets. This is an un-activated form that is able to melt, unlike the activated form. However, there is little study on the thermal characteristics of these precursor ionomers. This lack of knowledge causes issues when trying to fabricate ionomer shapes using methods such as extrusion, hot-pressing, and more recently, injection molding and 3D printing. To understand the two precursor-ionomers, a set of tests were conducted to measure the thermal degradation temperature, viscosity, melting temperature, and glass transition. The results have shown that the precursor Aquivion has a higher melting temperature (240 °C) than precursor Nafion (200 °C) and a larger glass transition range (32–65°C compared with 21–45 °C). The two have the same thermal degradation temperature (~400 °C). Precursor Aquivion is more viscous than precursor Nafion as temperature increases. Based on the results gathered, it seems that the precursor Aquivion is more stable as temperature increases, facilitating the manufacturing processes. This paper presents the data collected to assist researchers in thermal-based fabrication processes. Full article

(This article belongs to the Special Issue Smart Materials for Soft Sensors and Actuators)

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7 pages, 416 KiB

Open AccessArticle

Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites

by Boris Darinskii, Alexander Sidorkin, Alexander Sigov and Nadezhda Popravko

Materials 2018, 11(1), 85; https://doi.org/10.3390/ma11010085 - 06 Jan 2018

Cited by 9 | Viewed by 3135

Abstract

The temperature of the transition to the polar state in ferroelectric composites, representing spherical ferroelectric inclusions embedded in a dielectric matrix, under a depolarizing field effect is investigated. This temperature is determined both in the absence and presence of screening effects of the depolarizing field of the bound charges of spontaneous polarization at the inclusions surface. The absence case shows that the Curie point shift is determined by the ratio of the Curie constant of the ferroelectric inclusion to the permittivity of the matrix. Screening effects show that the transition temperature shift decreases through multiplying the value by a decreasing factor equal to the ratio of the screening length to the radius of the ferroelectric inclusion. Examples of the materials for the position of the Curie point on the temperature scale, largely determined by the tilting action of the depolarizing field and the compensating shielding effects, are given. Full article

(This article belongs to the Special Issue Smart Materials for Soft Sensors and Actuators)

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