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3 pages, 171 KiB

Open AccessEditorial

Editorial for the Special Issue on Structural Analyses and Designs for Flexible/Stretchable Electronics

by Rui Li

Micromachines 2023, 14(6), 1211; https://doi.org/10.3390/mi14061211 - 08 Jun 2023

Viewed by 865

Abstract

Flexible/stretchable electronics constitute a class of prospective technology incorporating stretchable/bendable/twistable components such that unprecedented properties superior to those of conventional rigid/brittle electronics are realized over [...] Full article

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

Research

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16 pages, 11434 KiB

Open AccessArticle

Island-Type Graphene-Nanotube Hybrid Structures for Flexible and Stretchable Electronics: In Silico Study

by Michael M. Slepchenkov, Pavel V. Barkov and Olga E. Glukhova

Micromachines 2023, 14(3), 671; https://doi.org/10.3390/mi14030671 - 17 Mar 2023

Cited by 2 | Viewed by 1307

Abstract

Using the self-consistent charge density functional tight-binding (SCC-DFTB) method, we study the behavior of graphene-carbon nanotube hybrid films with island topology under axial deformation. Hybrid films are formed by AB-stacked bilayer graphene and horizontally aligned chiral single-walled carbon nanotubes (SWCNTs) with chirality indices [...] Read more.

Using the self-consistent charge density functional tight-binding (SCC-DFTB) method, we study the behavior of graphene-carbon nanotube hybrid films with island topology under axial deformation. Hybrid films are formed by AB-stacked bilayer graphene and horizontally aligned chiral single-walled carbon nanotubes (SWCNTs) with chirality indices (12,6) and 1.2 nm in diameter. In hybrid films, bilayer graphene is located above the nanotube, forming the so-called “islands” of increased carbon density, which correspond to known experimental data on the synthesis of graphene-nanotube composites. Two types of axial deformation are considered: stretching and compression. It has been established that bilayer graphene-SWCNT (12,6) hybrid films are characterized by elastic deformation both in the case of axial stretching and axial compression. At the same time, the resistance of the atomic network of bilayer graphene-SWCNT (12,6) hybrid films to failure is higher in the case of axial compression. Within the framework of the Landauer-Buttiker formalism, the current-voltage characteristics of bilayer graphene-SWCNT (12,6) hybrid films are calculated. It is shown that the slope of the current-voltage characteristic and the maximum values of the current are sensitive to the topological features of the bilayer graphene in the composition of graphene-SWCNT (12,6) hybrid film. Based on the obtained results, the prospects for the use of island-type graphene-nanotube films in flexible and stretchable electronic devices are predicted. Full article

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

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21 pages, 8245 KiB

Open AccessArticle

Simulation and Printing of Microdroplets Using Straight Electrode-Based Electrohydrodynamic Jet for Flexible Substrate

by Dazhi Wang, Zeshan Abbas, Liangkun Lu, Chang Liu, Jie Zhang, Changchang Pu, Yikang Li, Penghe Yin, Xi Zhang and Junsheng Liang

Micromachines 2022, 13(10), 1727; https://doi.org/10.3390/mi13101727 - 12 Oct 2022

Cited by 2 | Viewed by 1501

Abstract

Electrohydrodynamic jet (e-jet) printing is a modern and decent fabrication method widely used to print high-resolution versatile microstructures with features down to 10 μm. It is currently difficult to break nanoscale resolution (<100 nm) due to limitations of fluid properties, voltage variations, and [...] Read more.

Electrohydrodynamic jet (e-jet) printing is a modern and decent fabrication method widely used to print high-resolution versatile microstructures with features down to 10 μm. It is currently difficult to break nanoscale resolution (<100 nm) due to limitations of fluid properties, voltage variations, and needle shapes. This paper presents developments in drop-on-demand e-jet printing based on a phase-field method using a novel combined needle and straight electrode to print on a flexible PET substrate. Initially, the simulation was performed to form a stable cone jet by coupling an innovative straight electrode parallel to a combined needle that directs the generation of droplets at optimized parameters, such as f = 8.6 × 10⁻¹⁰ m³s⁻¹, Vn = 9.0 kV, and Vs = 4.5 kV. Subsequently, printing experiments were performed using optimized processing parameters and all similar simulation conditions. Microdroplets smaller than 13 μm were directly printed on PET substrate. The model is considered unique and powerful for printing versatile microstructures on polymeric substrates. The presented method is useful for MEMS technology to fabricate various devices, such as accelerometers, smartphones, gyroscopes, sensors, and actuators. Full article

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

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14 pages, 3028 KiB

Open AccessArticle

An Analytic Model of Transient Heat Conduction for Bi-Layered Flexible Electronic Heaters by Symplectic Superposition

by Dian Xu, Sijun Xiong, Fanxing Meng, Bo Wang and Rui Li

Micromachines 2022, 13(10), 1627; https://doi.org/10.3390/mi13101627 - 28 Sep 2022

Cited by 2 | Viewed by 1136

Abstract

In a flexible electronic heater (FEH), periodic metal wires are often encapsulated into the soft elastic substrate as heat sources. It is of great significance to develop analytic models on transient heat conduction of such an FEH in order to provide a rapid [...] Read more.

In a flexible electronic heater (FEH), periodic metal wires are often encapsulated into the soft elastic substrate as heat sources. It is of great significance to develop analytic models on transient heat conduction of such an FEH in order to provide a rapid analysis and preliminary designs based on a rapid parameter analysis. In this study, an analytic model of transient heat conduction for bi-layered FEHs is proposed, which is solved by a novel symplectic superposition method (SSM). In the Laplace transform domain, the Hamiltonian system-based governing equation for transient heat conduction is introduced, and the mathematical techniques incorporating the separation of variables and symplectic eigen expansion are manipulated to yield the temperature solutions of two subproblems, which is followed by superposition for the temperature solution of the general problem. The Laplace inversion gives the eventual temperature solution in the time domain. Comprehensive time-dependent temperatures by the SSM are presented in tables and figures for benchmark use, which agree well with their counterparts by the finite element method. A parameter analysis on the influence of the thermal conductivity ratio is also studied. The exceptional merit of the SSM is on a direct rigorous derivation without any assumption/predetermination of solution forms, and thus, the method may be extended to more heat conduction problems of FEHs with more complex structures. Full article

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

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9 pages, 2330 KiB

Open AccessArticle

Mathematical Model for Skin Pain Sensation under Local Distributed Mechanical Compression for Electronic Skin Applications

by Dongcan Ji, Yingli Shi, Jiayun Chen, Zhao Zhao and Guozhong Zhao

Micromachines 2022, 13(9), 1402; https://doi.org/10.3390/mi13091402 - 26 Aug 2022

Cited by 1 | Viewed by 1784

Abstract

Skin pain resulting from mechanical compression is one of the most common pains in daily life and the indispensable information for electronic skin to perceive external signals. The external mechanical stimuli are transduced into impulses and transmitted via nerve fiber, and finally, the [...] Read more.

Skin pain resulting from mechanical compression is one of the most common pains in daily life and the indispensable information for electronic skin to perceive external signals. The external mechanical stimuli are transduced into impulses and transmitted via nerve fiber, and finally, the sensation is perceived via the procession of the nerve system. However, the mathematical mechanism for pain sensation due to mechanical stimuli remains unclear. In this paper, a mathematical model for skin pain sensation under compression is established, in which the Flament solution, the revised Hodgkin–Huxley model, and the mathematical model gate control theory are considered simultaneously. The proposed model includes three parts: a mechanical model of skin compression, a model of transduction, and a model of modulation and perception. It is demonstrated that the pain sensation degree increases with the compression amplitude and decreases with deeper nociceptor location in the skin. With the help of the proposed model, the quantitative relationship between compression pain sensation and external mechanical stimuli is revealed, which has a significant benefit in promoting the design and mechanism research of electronic skin with pain perception function. Full article

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

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12 pages, 2983 KiB

Open AccessArticle

Transient Heat Conduction in the Orthotropic Model with Rectangular Heat Source

by Zeqing He, Yingli Shi, Yuqing Shen, Zhigang Shen, Taihua Zhang and Zhao Zhao

Micromachines 2022, 13(8), 1324; https://doi.org/10.3390/mi13081324 - 16 Aug 2022

Cited by 1 | Viewed by 1395

Abstract

Epidermal electronic systems (EESs) are a representative achievement for utilizing the full advantages of ultra-thin, stretchable and conformal attachment of flexible electronics, and are extremely suitable for integration with human physiological systems, especially in medical hyperthermia. The stretchable heater with stable electrical characteristics [...] Read more.

Epidermal electronic systems (EESs) are a representative achievement for utilizing the full advantages of ultra-thin, stretchable and conformal attachment of flexible electronics, and are extremely suitable for integration with human physiological systems, especially in medical hyperthermia. The stretchable heater with stable electrical characteristics and a uniform temperature field is an irreplaceable core component. The inorganic stretchable heater has the advantage of maintaining stable electrical characteristics under tensile deformation. However, the space between the patterned electrodes that provides tensile properties causes uneven distribution of the temperature field. Aiming at improving the temperature distribution uniformity of stretchable thermotherapy electrodes, an orthotropic heat transfer substrate for stretchable heaters is proposed in this paper. An analytical model for transient heat conduction of stretchable rectangular heaters based on orthotropic transfer characteristics is established, which is validated by finite element analysis (FEA). The homogenization effect of orthotropic heat transfer characteristics on temperature distribution and its evolutionary relationship with time are investigated based on this model. This study will provide beneficial help for the temperature distribution homogenization design of stretchable heaters and the exploration of its transient heat transfer mechanism. Full article

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

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12 pages, 5003 KiB

Open AccessArticle

Assembly of Surface-Mounted Devices on Flexible Substrates by Isotropic Conductive Adhesive and Solder and Lifetime Characterization

by Rafat Saleh, Sophie Schütt, Maximilian Barth, Thassilo Lang, Wolfgang Eberhardt and André Zimmermann

Micromachines 2022, 13(8), 1240; https://doi.org/10.3390/mi13081240 - 01 Aug 2022

Cited by 4 | Viewed by 1509

Abstract

The assembly of passive components on flexible electronics is essential for the functionalization of circuits. For this purpose, adhesive bonding technology by isotropic conductive adhesive (ICA) is increasingly used in addition to soldering processes. Nevertheless, a comparative study, especially for bending characterization, is [...] Read more.

The assembly of passive components on flexible electronics is essential for the functionalization of circuits. For this purpose, adhesive bonding technology by isotropic conductive adhesive (ICA) is increasingly used in addition to soldering processes. Nevertheless, a comparative study, especially for bending characterization, is not available. In this paper, soldering and conductive adhesive bonding of 0603 and 0402 components on flexible polyimide substrates is compared using the design of experiments methods (DoE), considering failure for shear strength and bending behavior. Various solder pastes and conductive adhesives are used. Process variation also includes curing and soldering profiles, respectively, amount of adhesive, and final surface metallization. Samples created with conductive adhesive H20E, a large amount of adhesive, and a faster curing profile could achieve the highest shear strength. In the bending characterization using adhesive bonding, samples on immersion silver surface finish withstood more cycles to failure than samples on bare copper surface. In comparison, the samples soldered to bare copper surface finish withstood more cycles to failure than the soldered samples on immersion silver surface finish. Full article

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

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10 pages, 2598 KiB

Open AccessArticle

Influence of Process Parameters on the Resistivity of 3D Printed Electrically Conductive Structures

by Kacper Dembek, Bartłomiej Podsiadły and Marcin Słoma

Micromachines 2022, 13(8), 1203; https://doi.org/10.3390/mi13081203 - 28 Jul 2022

Cited by 7 | Viewed by 1602

Abstract

With recent developments in conductive composites, new possibilities emerged for 3D printed conductive structures. Complementary to a vast number of publications on materials properties, here we investigate the influence of printing parameters on the resistance of 3D printed structures. The influence of printing [...] Read more.

With recent developments in conductive composites, new possibilities emerged for 3D printed conductive structures. Complementary to a vast number of publications on materials properties, here we investigate the influence of printing parameters on the resistance of 3D printed structures. The influence of printing temperature on the resistance is significant, with too low value (210 °C) leading to nozzle clogging, while increasing the temperature by 20 °C above the recommended printing settings decreases resistivity by 15%, but causing degradation of the polymer matrix. The limitations of the FDM technique, related to the dimension accuracy emerging from the layer-by-layer printing approach, greatly influence the samples’ cross-section, causing irregular resistivity values for different layer heights. For samples with layer thickness lower than 0.2 mm, regardless of the nozzle diameter (0.5–1 mm), high resistance is attributed to the quality of samples. But for a 1 mm nozzle, we observe stabilized values or resistance for 0.3 to 1 mm layer height. Comparing resistance values and layer height generated from the slicer software, we observe a direct correlation—for a larger height of the sample resistance value decrease. Presented modifications in printing parameters can affect the final resistance by 50%. Controlling several parameters simultaneously poses a great challenge for designing high-efficiency structural electronics. Full article

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

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12 pages, 4253 KiB

Open AccessArticle

An RBF Meshless Approach to Evaluate Strain Due to Large Displacements in Flexible Printed Circuit Boards

by Corrado Groth, Andrea Chiappa, Stefano Porziani, Pietro Salvini and Marco Evangelos Biancolini

Micromachines 2022, 13(8), 1163; https://doi.org/10.3390/mi13081163 - 22 Jul 2022

Cited by 2 | Viewed by 1265

Abstract

Thin plates are very often employed in a context of large displacements and rotations, for example, whenever the extreme flexibility of a body can replace the use of complicated kinematic pairs. This is the case of the flexible Printed Circuit Boards (PCBs) used, [...] Read more.

Thin plates are very often employed in a context of large displacements and rotations, for example, whenever the extreme flexibility of a body can replace the use of complicated kinematic pairs. This is the case of the flexible Printed Circuit Boards (PCBs) used, for example, within last-generation foldable laptops and consumer electronics products. In these applications, the range of motion is generally known in advance, and a simple strategy of stress assessment leaving out nonlinear numerical calculations appears feasible other than desirable. In this paper, Radial Basis Functions (RBFs) are used to represent a generic transformation of a bi-dimensional plate, with all the derivate fields being analytically achieved without the need for a numerical grid for large-displacement applications. Strains due to bending are easily retrieved with this method and satisfactorily compared to analytical and shell-based Finite Element Method (FEM) benchmarks. On the other hand, the computational costs of the juxtaposed methods appear far different; with the machine being equal, the orders of magnitude of the time elapsed in computation are seconds for the RBF-based strategy versus minutes for the FEM approach. Full article

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

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12 pages, 2868 KiB

Open AccessArticle

An Analytic Orthotropic Heat Conduction Model for the Stretchable Network Heaters

by Zeqing He, Yingli Shi, Jin Nan, Zhigang Shen, Taihua Zhang and Zhao Zhao

Micromachines 2022, 13(7), 1133; https://doi.org/10.3390/mi13071133 - 18 Jul 2022

Cited by 2 | Viewed by 1296

Abstract

Compared with other physiotherapy devices, epidermal electronic systems (EES) used in medical applications such as hyperthermia have obvious advantages of conformal attachment, lightness and high efficiency. The stretchable flexible electrode is an indispensable component. The structurally designed flexible inorganic stretchable electrode has the [...] Read more.

Compared with other physiotherapy devices, epidermal electronic systems (EES) used in medical applications such as hyperthermia have obvious advantages of conformal attachment, lightness and high efficiency. The stretchable flexible electrode is an indispensable component. The structurally designed flexible inorganic stretchable electrode has the advantage of stable electrical properties under tensile deformation and has received enough attention. However, the space between the patterned electrodes introduced to ensure the tensile properties will inevitably lead to the uneven temperature distribution of the thermotherapy electrodes and degrade the effect of thermotherapy. It is of great practical value to study the temperature uniformity of the stretchable patterned electrode. In order to improve the uniformity of temperature distribution in the heat transfer system with stretchable electrodes, a temperature distribution manipulation strategy for orthotropic substrates is proposed in this paper. A theoretical model of the orthotropic heat transfer system based on the horseshoe-shaped mesh electrode is established. Combined with finite element analysis, the effect of the orthotropic substrate on the uniformity of temperature distribution in three types of heat source heat transfer systems is studied based on this model. The influence of the thermal conductivity ratio in different directions on the temperature distribution is studied parametrically, which will help to guide the design and fabrication of the stretchable electrode that can produce a uniform temperature distribution. Full article

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

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10 pages, 2178 KiB

Open AccessArticle

Design and Thermal Analysis of Flexible Microheaters

by Dezhao Li, Yangtao Ruan, Chuangang Chen, Wenfeng He, Cheng Chi and Qiang Lin

Micromachines 2022, 13(7), 1037; https://doi.org/10.3390/mi13071037 - 29 Jun 2022

Cited by 10 | Viewed by 2190

Abstract

With the development of flexible electronics, flexible microheaters have been applied in many areas. Low power consumption and fast response microheaters have attracted much attention. In this work, systematic thermal and mechanical analyses were conducted for a kind of flexible microheater with two [...] Read more.

With the development of flexible electronics, flexible microheaters have been applied in many areas. Low power consumption and fast response microheaters have attracted much attention. In this work, systematic thermal and mechanical analyses were conducted for a kind of flexible microheater with two different wire structures. The microheater consisted of polyethylene terephthalate (PET) substrate and copper electric wire with graphene thin film as the middle layer. The steady-state average temperature and heating efficiency for the two structures were compared and it was shown that the S-shaped wire structure was better for voltage-controlled microheater other than circular-shaped structure. In addition, the maximum thermal stress for both structures was from the boundary of microheaters, which indicated that not only the wire structure but also the shape of micro heaters should be considered to reduce the damage caused by thermal stress. The influence resulting from the thickness of graphene thin film also has been discussed. In all, the heating efficiency for flexible microheaters can be up to 135 °C/W. With the proposed PID voltage control system, the response time for the designed microheater was less than 10 s. Moreover, a feasible fabrication process flow for these proposed structures combing thermal analysis results in this work can provide some clues for flexible microheaters design and fabrication in other application areas. Full article

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

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17 pages, 6144 KiB

Open AccessArticle

Design of a Morphing Skin with Shape Memory Alloy Based on Equivalent Thermal Stress Approach

by Wei Zhang, Yueyin Ma, Xinyu Gao, Wanhua Chen and Xutao Nie

Micromachines 2022, 13(6), 939; https://doi.org/10.3390/mi13060939 - 13 Jun 2022

Cited by 2 | Viewed by 1443

Abstract

Shape memory alloy (SMA) is one of the potential driving devices for morphing aircraft due to its advantages of pseudoelasticity, superelasticity, and shape memory effect. Precise and fast analysis of SMA has simultaneously become a key requirement for industrial applications. In this study, [...] Read more.

Shape memory alloy (SMA) is one of the potential driving devices for morphing aircraft due to its advantages of pseudoelasticity, superelasticity, and shape memory effect. Precise and fast analysis of SMA has simultaneously become a key requirement for industrial applications. In this study, a user-defined material subroutine (UMAT) was implemented and successfully applied in a three-dimensional numerical simulation in ABAQUS based on the extended Boyd–Lagoudas model. In addition to the conventional detwinned martensite (M_d) and austenite (A), twinned martensite (M_t) was also considered to model the practical transformation accurately. Then, the equivalent thermal strain approach was adopted to simplify the simulation complexity with UMAT. By resetting the thermal expansion coefficient, the thermal strain equivalent to the original phase transformation strain was generated. The approach was validated in two cases, showing consistent results with the extended Boyd–Lagoudas model and reduction in time consumption by 89.1%. Lastly, an active morphing skin integrating the single-range SMA and a stainless-steel plate was designed to realize two-way morphing. The calculated arc height variation of the skin was 3.74 mm with a relative error of 1.84% compared to the experimental result of 3.81 mm. The coupled use of UMAT and the equivalent thermal stress approach helped to reduce the challenge in modeling SMA. Full article

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

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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 - 08 Jun 2022

Cited by 1 | Viewed by 1538

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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12 pages, 2821 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Mechanical Behaviors of the Origami-Inspired Horseshoe-Shaped Solar Arrays

by Zhi Li, Chengguo Yu, Luqiao Qi, Shichao Xing, Yan Shi and Cunfa Gao

Micromachines 2022, 13(5), 732; https://doi.org/10.3390/mi13050732 - 02 May 2022

Cited by 7 | Viewed by 1809

Abstract

The importance of flexibility has been widely noticed and concerned in the design and application of space solar arrays. Inspired by origami structures, we introduce an approach to realizing stretchable and bendable solar arrays via horseshoe-shaped substrate design. The structure has the ability [...] Read more.

The importance of flexibility has been widely noticed and concerned in the design and application of space solar arrays. Inspired by origami structures, we introduce an approach to realizing stretchable and bendable solar arrays via horseshoe-shaped substrate design. The structure has the ability to combine rigid solar cells and soft substrates skillfully, which can prevent damage during deformations. The finite deformation theory is adapted to find the analytic model of the horseshoe-shaped structure via simplified beam theory. In order to solve the mechanical model, the shooting method, a numerical method to solve ordinary differential equation (ODE) is employed. Finite element analyses (FEA) are also performed to verify the developed theoretical model. The influences of the geometric parameters on deformations and forces are analyzed to achieve the optimal design of the structures. The stretching tests of horseshoe-shaped samples manufactured by three-dimensional (3D) printing are implemented, whose results shows a good agreement with those from theoretical predictions. The developed models can serve as the guidelines for the design of flexible solar arrays in spacecraft. Full article

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

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9 pages, 2326 KiB

Open AccessArticle

Thermal Management of Serpentine Flexible Heater Based on the Orthotropic Heat Conduction Model

by Zhao Zhao, Jin Nan and Min Li

Micromachines 2022, 13(4), 622; https://doi.org/10.3390/mi13040622 - 15 Apr 2022

Cited by 4 | Viewed by 1583

Abstract

Flexible heaters can perfectly fit with undevelopable surfaces for heating in many practical applications such as thermotherapy, defogging/deicing systems and warming garments. Considering the requirement for stretchability in a flexible heater, certain spacing needs to be retained between serpentine heat sources for deformation [...] Read more.

Flexible heaters can perfectly fit with undevelopable surfaces for heating in many practical applications such as thermotherapy, defogging/deicing systems and warming garments. Considering the requirement for stretchability in a flexible heater, certain spacing needs to be retained between serpentine heat sources for deformation which will inevitably bring critical challenges to the thermal uniformity. In order to reconcile these two conflicting aspects, a novel method is proposed by embedding the serpentine heat source in orthotropic layers to achieve comprehensive performance in stretchability and uniform heating. Such a scheme takes advantage of the ability of orthotropic material to control the heat flow distribution via orthotropic thermal conductivity. In this paper, an analytical heat conduction model with orthotropic substrate and encapsulation is calculated using Fourier cosine transform, which is validated by finite element analysis (FEA). Meanwhile, the effects of the orthotropic substrate or encapsulation with different ratios of thermal conductivity and the geometric spacing on the thermal properties are investigated, which can help guide the design and fabrication of flexible heaters to achieve the goal of uniform heating. Full article

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

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Review

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28 pages, 6240 KiB

Open AccessReview

Structural Flexibility in Triboelectric Nanogenerators: A Review on the Adaptive Design for Self-Powered Systems

by Zequan Zhao, Yin Lu, Yajun Mi, Jiajing Meng, Xia Cao and Ning Wang

Micromachines 2022, 13(10), 1586; https://doi.org/10.3390/mi13101586 - 23 Sep 2022

Cited by 22 | Viewed by 2144

Abstract

There is an increasing need for structural flexibility in self-powered wearable electronics and other Internet of Things (IoT), where adaptable triboelectric nanogenerators (TENGs) play a key role in realizing the true potential of IoT by endowing the latter with self-sustainability. Thus, in this [...] Read more.

There is an increasing need for structural flexibility in self-powered wearable electronics and other Internet of Things (IoT), where adaptable triboelectric nanogenerators (TENGs) play a key role in realizing the true potential of IoT by endowing the latter with self-sustainability. Thus, in this review, the topic was restricted to the adaptive design of TENGs with structural flexibility that aims to promote the sustainable operation of various smart electronics. This review begins with an emphatical discussion of the concept of flexible electronics and TENGs, and continues with the introduction of TENG-based self-powered intelligent systems while placing the emphasis on self-powered flexible intelligent devices. Self-powered healthcare sensors, e-skins, and other intelligent wearable electronics with enhanced intelligence and efficiency in practical applications due to the integration with TENGs are illustrated, along with an emphasis on the design strategy of structural flexibility of TENGs and the associated integration schemes. This review aims to cover recent achievements in the field of self-powered systems, and provides information on how flexibility or adaptability in TENGs can be adopted, their types, and why they are required in promoting advanced IoT applications with sustainability and intelligence algorithms. Full article

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

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27 pages, 8912 KiB

Open AccessReview

Recent Advances in Flexible RF MEMS

by Yingli Shi and Zhigang Shen

Micromachines 2022, 13(7), 1088; https://doi.org/10.3390/mi13071088 - 08 Jul 2022

Cited by 5 | Viewed by 3245

Abstract

Microelectromechanical systems (MEMS) that are based on flexible substrates are widely used in flexible, reconfigurable radio frequency (RF) systems, such as RF MEMS switches, phase shifters, reconfigurable antennas, phased array antennas and resonators, etc. When attempting to accommodate flexible deformation with the movable [...] Read more.

Microelectromechanical systems (MEMS) that are based on flexible substrates are widely used in flexible, reconfigurable radio frequency (RF) systems, such as RF MEMS switches, phase shifters, reconfigurable antennas, phased array antennas and resonators, etc. When attempting to accommodate flexible deformation with the movable structures of MEMS, flexible RF MEMS are far more difficult to structurally design and fabricate than rigid MEMS devices or other types of flexible electronics. In this review, we survey flexible RF MEMS with different functions, their flexible film materials and their fabrication process technologies. In addition, a fabrication process for reconfigurable three-dimensional (3D) RF devices based on mechanically guided assembly is introduced. The review is very helpful to understand the overall advances in flexible RF MEMS, and serves the purpose of providing a reference source for innovative researchers working in this field. Full article

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

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