Nanoscale Insight Into Lead‐Free BNT‐BT‐xKNN

Piezoresponse force microscopy (PFM) is used to afford insight into the nanoscale electromechanical behavior of lead‐free piezoceramics. Materials based on Bi_1/2Na_1/2TiO₃ exhibit high strains mediated by a field‐induced phase transition. Using the band excitation technique the initial domain morphology, the poling behavior, the switching behavior, and the time‐dependent phase stability in the pseudo‐ternary system (1–x)(0.94Bi_1/2Na_1/2TiO₃‐0.06BaTiO₃)‐xK_0.5Na_0.5NbO₃ (0 <= x <= 18 mol%) are revealed. In the base material (x = 0 mol%), macroscopic domains and ferroelectric switching can be induced from the initial relaxor state with sufficiently high electric field, yielding large macroscopic remanent strain and polarization. The addition of KNN increases the threshold field required to induce long range order and decreases the stability thereof. For x = 3 mol% the field‐induced domains relax completely, which is also reflected in zero macroscopic remanence. Eventually, no long range order can be induced for x >= 3 mol%. This PFM study provides a novel perspective on the interplay between macroscopic and nanoscopic material properties in bulk lead‐free piezoceramics.     

Diffused Phase Transition Boosts Thermal Stability of High‐Performance Lead‐Free Piezoelectrics

High piezoelectricity of (K,Na)NbO₃ (KNN) lead‐free materials benefits from a polymorphic phase transition (PPT) around room temperature, but its temperature sensitivity has been a bottleneck impeding their applications. It is found that good thermal stability can be achieved in CaZrO₃‐modified KNN lead‐free piezoceramics, in which the normalized strain d ₃₃* almost keeps constant from room temperature up to 140 °C. In situ synchrotron X‐ray diffraction experiments combined with permitivity measurements disclose the occurrence of a new phase transformation under an electrical field, which extends the transition range between tetragonal and orthorhombic phases. It is revealed that such an electrically enhanced diffused PPT contributed to the boosted thermal stability of KNN‐based lead‐free piezoceramics with high piezoelectricity. The present approach based on phase engineering should also be effective in endowing other lead‐free piezoelectrics with high piezoelectricity and good temperature stability.     

Temperature‐Insensitive (K,Na)NbO3‐Based Lead‐Free Piezoactuator Ceramics

The development of lead‐free piezoceramics has attracted great interest because of growing environmental concerns. A polymorphic phase transition (PPT) has been utilized in the past to tailor piezoelectric properties in lead‐free (K,Na)NbO₃ (KNN)‐based materials accepting the drawback of large temperature sensitivity. Here a material concept is reported, which yields an average piezoelectric coefficientd₃₃ of about 300 pC/N and a high level of unipolar strain up to 0.16% at room temperature. Most intriguingly, field‐induced strain varies less than 10% from room temperature to 175 °C. The temperature insensitivity of field‐induced strain is rationalized using an electrostrictive coupling to polarization amplitude while the temperature‐dependent piezoelectric coefficient is discussed using localized piezoresponse probed by piezoforce microscopy. This discovery opens a new development window for temperature‐insensitive piezoelectric actuators despite the presence of a polymorphic phase transition around room temperature.     

Wearable Energy Generating and Storing Textile Based on Carbon Nanotube Yarns

The challenges of textiles that can generate and store energy simultaneously for wearable devices are to fabricate yarns that generate electrical energy when stretched, yarns that store this electrical energy, and textile geometries that facilitate these functions. To address these challenges, this research incorporates highly stretchable electrochemical yarn harvesters, where available mechanical strains are large and electrochemical energy storing yarns are achieved by weaving. The solid‐state yarn harvester provides a peak power of 5.3 W kg^?1 for carbon nanotubes. The solid‐state yarn supercapacitor provides stable performance when dynamically deformed by bending and stretching, for example. A textile configuration that consists of harvesters, supercapacitors, and a Schottky diode is produced and stores as much electrical energy as is needed by a serial or parallel connection of the harvesters or supercapacitors. This textile can be applied as a power source for health care devices or other wearable devices and be self‐powered sensors for detecting human motion.     

Field-Induced Multiscale Polarization Configuration Transitions of Mesentropic Lead-Free Piezoceramics Achieving Giant Energy Harvesting Performance

The development of high-performance (K,Na)NbO₃ (KNN)-based lead-free piezoceramics for next-generation electronic devices is crucial for achieving environmentally sustainable society. However, despite recent improvements in piezoelectric coefficients, correlating their properties to underlying multiscale structures remains a key issue for high-performance KNN-based ceramics with complex phase boundaries. Here, this study proposes a medium-entropy strategy to design “local polymorphic distortion” in conjunction with the construction of uniformly oversize grains in the newly developed KNN solid-solution, resulting in a novel large-size hierarchical domain architecture (≈0.7 µm wide). Such a structure not only facilitates polarization rotation but also ensures a large residual polarization, which significantly improves the piezoelectricity (≈3.2 times) and obtains a giant energy harvesting performance (W_out = 2.44 mW, P_D = 35.32 µW mm⁻³, outperforming most lead-free piezoceramics). This study confirms the coexistence of multiphase through the atomic-resolution polarization features and analyzes the domain/phase transition mechanisms using in situ electric field structural characterizations, revealing that the electric field induces highly effective multiscale polarization configuration transitions based on T–O–R sequential phase transitions. This study demonstrates a new strategy for designing high-performance piezoceramics and facilitates the development of lead-free piezoceramic materials in energy harvesting applications.     

HfO2含量对铌锑锆钛酸铅压电陶瓷性能的影响

针对Pb(Sb,Nb)O3-Pb(Zr,Ti)O3压电陶瓷制备过程中谐振反谐振频率差值Δf出现的波动现象,利用配料递减称量法,研究了HfO2含量对Pb(Sb0.5Nb0.5)0.08Zr0.50Ti0.42O3+1.5%(质量分数)MnO2三元系压电陶瓷的晶相结构、微观形貌和电性能的影响。同时分析了ZrO2原料中HfO2杂质的成因。结果表明:HfO2在该三元系压电陶瓷中属于无害但无用的杂质。通过调整ZrO2配料含量,可以使其Δf控制在合格范围内(7.0~8.0kHz),而且其他的电性能基本保持不变。     

Multiple access based on different lengths super orthogonal codes to support QoS of M2M communications in next generation networks

Global connectivity, low latency, and ready‐to‐use infrastructure of next generation wireless (NGW) networks provide a platform for machine‐to‐machine (M2M) communications on a large scale. However, M2M communications over NGW networks pose significant challenges because of different data rates, diverse applications, and a large number of connections. In this paper, we address M2M challenges over NGW networks, and in particular, we focus on random access overload issue and diverse quality‐of‐service (QoS) requirements to enable M2M communications in the context of NGW networks. To enable massive M2M access while QoS guarantees, we propose group‐based M2M communications on the basis of identical transmission protocols and QoS requirements. Furthermore, to guarantee low energy consumption for M2M devices in the same group, we propose a decentralized group‐head selection scheme. In addition, a solution is proposed by using an effective capacity concept to provide QoS guarantees for M2M devices with a strict time constraint. A new random access approach based on different lengths super orthogonal codes is proposed to ease massive random access challenges with provisioning diverse QoS requirements of M2M communications in heterogeneous NGW networks.     

一种用于求压电材料复参数的快速迭代算法

要精确地描述压电材料的性能,必须把压电材料的参数作为复数考虑。文章提出一种新的自动迭代算法,通过测量压电陶瓷的４种标准型振子谐振峰附近的阻抗（或导纳）,即可由程序自动求出压电陶瓷的全部材料系数。与常用的迭代法相比,本文迭代法巧妙的初值选取方法及选代频率点的选择,使得算法精度高,迭代次数少。     

Electrically Tunable Nanoporous Carbon Hybrid Actuators

A novel nanoporous carbon/electrolyte hybrid material is reported for use in actuation. The nanoporous carbon matrix provides a 3D network that combines mechanical strength, light weight, and low cost with an extremely high surface area. In contrast to lower dimensional nanomaterials, the nanoporous carbon matrix can be prepared in the form of macroscopic monolithic samples that can be loaded in compression. The hybrid material is formed by infiltrating the free internal pore volume of the carbon with an electrolyte. Actuation is prompted by polarizing the internal interfaces via an applied electric bias. It is found that the strain amplitude is proportional to the Brunauer‐Emmett‐Teller (BET) mass specific surface area, with reversible volume strain amplitudes up to the exceptionally high value of 6.6%. The mass‐specific strain energy density compares favorably to reported values for piezoceramics and for nanoporous metal actuators.     

Ensuring fairness among ECN and non‐ECN TCP over the Internet

Explicit Congestion Notification (ECN) has been proved to provide a fast indication of incipient congestion and thus better the performance of a TCP/IP network. In this work, we carry out investigations on gateway or router performance in providing fairnesss when both FIM ECN‐capable and non‐ECN‐capable connections are employed. We propose a new packet‐dropping scheme called Fair In‐time Dropping (FID) which drops packets from a connection upon detecting an incipient indication of congestion depending on its share of gateway or router buffer occupancy. We also show that a combination of FIM and FID offers the best fairness compared with a combination of FIM along with other dropping schemes. Copyright © 2003 John Wiley & Sons, Ltd.     

Engineering the Mechanics of Heterogeneous Soft Crystals

This work demonstrates how the geometric and topological characteristics of substructures within heterogeneous materials can be employed to tailor the mechanical responses of soft crystals under large strains. The large deformation mechanical behaviors of elastomeric composites possessing long‐range crystalline order are examined using both experiments on 3D‐printed prototype materials and precisely matched numerical simulations. The deformation mechanisms at small and large strains are elucidated for six sets of morphologies: dispersed particles on each of the simple cubic, body‐centered cubic or face‐centered cubic lattices, and their bi‐continuous counterparts. Comparison of results for the six types of morphologies reveals that the topological connectivity of dissimilar domains is of critical importance for tailoring the macroscopic mechanical properties and the mechanical anisotropy.     

On‐Body Bioelectronics: Wearable Biofuel Cells for Bioenergy Harvesting and Self‐Powered Biosensing

The growing power demands of wearable electronic devices have stimulated the development of on‐body energy‐harvesting strategies. This article reviews the recent progress on rapidly emerging wearable biofuel cells (BFCs), along with related challenges and prospects. Advanced on‐body BFCs in various wearable platforms, e.g., textiles, patches, temporary tattoo, or contact lenses, enable attractive advantages for bioenergy harnessing and self‐powered biosensing. These noninvasive BFCs open up unique opportunities for utilizing bioenergy or monitoring biomarkers present in biofluids, e.g., sweat, saliva, interstitial fluid, and tears, toward new biomedical, fitness, or defense applications. However, the realization of effective wearable BFC requires high‐quality enzyme‐electronic interface with efficient enzymatic and electrochemical processes and mechanical flexibility. Understanding the kinetics and mechanisms involved in the electron transfer process, as well as enzyme immobilization techniques, is essential for efficient and stable bioenergy harvesting under diverse mechanical strains and changing operational conditions expected in different biofluids and in a variety of outdoor activities. These key challenges of wearable BFCs are discussed along with potential solutions and future prospects. Understanding these obstacles and opportunities is crucial for transforming traditional bench‐top BFCs to effective and successful wearable BFCs.     

Vertical Organic Field‐Effect Transistors

Field‐effect transistors are the fundamental building blocks for electronic circuits and processors. Compared with inorganic transistors, organic field‐effect transistors (OFETs), featuring low cost, low weight, and easy fabrication, are attractive for large‐area flexible electronic devices. At present, OFETs with planar structures are widely investigated device structures in organic electronics and optoelectronics; however, they face enormous challenges in realizing large current density, fast operation speed, and outstanding mechanical flexibility for advancing their potential commercialized applications. In this context, vertical organic field‐effect transistors (VOFETs), composed of vertically stacked source/drain electrodes, could provide an effective approach for solving these questions due to their inherent small channel length and unique working principles. Since the first report of VOFETs in 2004, impressive progress has been witnessed in this field with the improvement of device performance. The aim of this review is to give a systematical summary of VOFETs with a special focus on device structure optimization for improved performance and potential applications demonstrated by VOFETs. An overview of the development of VOFETs along with current challenges and perspectives is also discussed. It is hoped that this review is timely and valuable for the next step in the rapid development of VOFETs and their related research fields.     

Thermally Induced Flexo‐Type Effects in Nanopatterned Multiferroic Layers

The difficulty to generate and control large strain gradients in materials hinders the investigation and application of flexoelectricity and flexomagnetism. This work demonstrates that thermal expansion can be used to induce very large non‐uniform strains at the nanoscale, resulting in giant strain gradients at moderate temperatures. This is demonstrated in a nanopatterned multiferroic hybrid layer consisting of a regular array of ferromagnetic metallic nanocylinders embedded in a ferroelectric polymer matrix. The thermally‐induced strain gradients can fully depolarize the ferroelectric component, and modify the magnetization of the ferromagnetic component via flexoelectric and flexomagnetic effects, respectively. Finite‐element analysis provides a quantitative view on thermal expansion‐induced strains and strain gradients supporting the experimental findings. This work shows that nanoscale thermal strain engineering provides an additional degree of freedom to control electrical polarization and magnetization, which paves the way for the design and operation of novel functional devices and nanostructures.     

Microstructural Origins of High Piezoelectric Performance: A Pathway to Practical Lead‐Free Materials

Piezoelectric materials interconvert between electrical energy and mechanical strain and are widely used for electronic and electromechanical devices. Owing to growing environmental concerns, development of lead‐free piezoelectric materials with enhanced properties becomes of great interest. Key to the academic problem is a lack of fundamental understanding on the actual mechanisms involved at the microscopic (unit cell) level. While it is well known that giant responses occur near structural phase boundaries, and it has long been proposed that polarization rotation and nanodomains are major determinants, so far, atomistic understanding of the origin of the response has come mostly from theoretical simulations. Recently, notable breakthroughs have been achieved in improving the properties of piezoceramics and thin films. Precise mapping of atomic displacements by atomically resolved Z‐contrast imaging has demonstrated that gradual polarization rotation bridges the coexisting nanophases. These structural features, which take place on a length scale of just a few nanometers, now visible through aberration‐corrected microscopy, provide a new pivotal understanding on the outstanding piezoelectric behavior that has been obtained in all systems. They also provide key guiding principles for the development of lead‐free piezoelectrics, especially in the form of thin films, which remain far behind bulk ceramics at the time being. Coexistence of nanophases with flexible interconversion, introduced via phase boundary engineering, holds much promise for achieving high performance in other material systems with phase transitions.     

3D Printing of Interdigitated Dielectric Elastomer Actuators

Dielectric elastomer actuators (DEAs) are soft electromechanical devices that exhibit large energy densities and fast actuation rates. They are typically produced by planar methods and, thus, expand in‐plane when actuated. Here, reported is a method for fabricating 3D interdigitated DEAs that exhibit in‐plane contractile actuation modes. First, a conductive elastomer ink is created with the desired rheology needed for printing high‐fidelity, interdigitated electrodes. Upon curing, the electrodes are then encapsulated in a self‐healing dielectric matrix composed of a plasticized, chemically crosslinked polyurethane acrylate. 3D DEA devices are fabricated with tunable mechanical properties that exhibit breakdown fields of 25 V µm^?1 and actuation strains of up to 9%. As exemplars, printed are prestrain‐free rotational actuators and multi‐voxel DEAs with orthogonal actuation directions in large‐area, out‐of‐plane motifs.     

2D Percolation Design with Conductive Microparticles for Low‐Strain Detection in a Stretchable Sensor

Although a variety of stretchable strain sensors based on electrical percolation have been reported, stretchable sensors detecting low strains have been rarely demonstrated. This is because large stretchability of a strain sensor conflicts with high strain resolution at low strains. Here, the electrical percolation into 2D is confined and a strain sensor that is highly sensitive at low strains and simultaneously highly stretchable is presented. The 2D confinement of the electrical percolation is accomplished by a close‐packed monolayer assembly of conductive microparticles (MPs) on an elastomer substrate. The current profiles of the MP monolayer at low strains are in situ visualized using conductive atomic force microscopy. When the lattice of the MP monolayer is aligned vertically to the strain direction, the resistance is highly sensitive to low‐strain deformations (ε = 0 – 0.05), but the sensor has reasonable stretchability (ε = 0.3). The simultaneous achievement of the high sensitivity at low strains and the reasonable stretchability is explained by the relationship between the strain‐dependent current profile and the relative position changes of the MPs. A high‐precision pulse sensor clearly showing the representative peaks is demonstrated.     

A Matter of Size and Stress: Understanding the First‐Order Transition in Materials for Solid‐State Refrigeration

Solid‐state magnetic refrigeration is a high‐potential, resource‐efficient cooling technology. However, many challenges involving materials science and engineering need to be overcome to achieve an industry‐ready technology. Caloric materials with a first‐order transition—associated with a large volume expansion or contraction—appear to be the most promising because of their large adiabatic temperature and isothermal entropy changes. In this study, using experiment and simulation, it is demonstrated with the most promising magnetocaloric candidate materials, La–Fe–Si, Mn–Fe–P–Si, and Ni–Mn–In–Co, that the characteristics of the first‐order transition are fundamentally determined by the evolution of mechanical stresses. This phenomenon is referred to as the stress‐coupling mechanism. Furthermore, its applicability goes beyond magnetocaloric materials, since it describes the first‐order transitions in multicaloric materials as well.     

The intelligent multi‐domain service function chain deployment: Architecture,challenges and solutions

Network function virtualization (NFV) technology achieves flexible service deployment by replacing the middleboxes with virtual network functions (VNFs). In NFV, a set of VNFs are chained in a given order, called service function chain (SFC), and accordingly, data flow is steered to traverse all the VNFs in order to offer a service. With a large number of network devices and end users being connected into Internet, there is a growing demand for large‐scale multi‐domain networks to dynamically deploy the SFC across multiple network domains, in order to support efficient service provisioning. To this end, in this paper, we first investigate the state of the art of multi‐domain SFC deployment, and then propose an intelligent multi‐domain SFC deployment (IMSD) architecture by leveraging software‐defined networking (SDN), NFV, and deep learning technologies. Furthermore, we discuss the potential challenges to realize the IMSD and provide some promising solutions.     

Tailored Graphitic Carbon Nitride Nanostructures: Synthesis,Modification, and Sensing Applications

Various beneficial properties of graphitic carbon nitride (g‐CN) have been discovered during the promotion of its visible‐light‐driven photocatalytic activity for water splitting. These properties enable g‐CN working as a sensing signal transducer with multiple output modes. In this review, state‐of‐the‐art sensing applications of tailored g‐CN nanostructures in the recent years are presented. Initially, g‐CN nanoarchitectures featuring large surface areas, abundance of active sites, and high dispersity in water are presented along with their preparation methods. Then, sensing applications of these g‐CN nanoarchitectures are described in sequence of the immobilization of recognition elements; semiconductor and electron donating properties derive signaling transduction modes, and efficient approaches for improving sensing performances. The review is concluded with a summary and some perspectives on the challenges and future possibilities of this research field.