Design of a low cross‐talk micro‐coil array for micro‐scale MRI

Design of magnetic resonance micro‐coil arrays with low cross‐talk among the coils can be the main challenge to improve the effectiveness of magnetic resonance micro‐imaging because the electrical cross‐talk which is mainly due to the inductive coupling perturbs the sensitivity profile of the array and causes image artifacts. In this work, a capacitive decoupling network with N(M ? 1) + (N ? 1)(M ? 2) capacitors is proposed to reduce the inductive coupling in an N × M array. A 3 × 3 array of optimized micro‐coils is designed using the finite element simulations and all the needed elements for the array equivalent circuit are extracted in order to evaluate the effectiveness of the proposed decoupling method by assessing the reduction of the coupled signals after employing the capacitive network on the circuit. The achieved results for the designed array show that the high cross‐talk level is reduced by the factor of 2.2–3.4 after employing the capacitive network. By employing this method of decoupling, the adjacent coils in each row and inner columns can be decoupled properly while the minimum decoupling belongs to the outer columns because of the lack of all necessary decoupling capacitances for these columns. The main advantages of the proposed decoupling method are its efficiency and design easiness which facilitates the design of dense arrays with the properly decoupled coils, especially the inner coils which are more coupled due to their neighbors. © 2013 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 23, 353–359, 2013     

Design of a pavement using piezoelectric materials

Pavement material is an important factor for creating a pedestrian and environmentally friendly walkway. Generally, kinetic energy of footstep during walking is mostly wasted, while, this energy can be harvested and converted to electrical power. This study aims to use piezoelectric materials within pavements in the form of tiles. The kinetic energy of walking is harvested through piezoelectric mechanism. The study proposed a pavement consisting of piezoelectric sensors. Flexible and green material are selected as the top layer of the pavement. The scaled prototype is fabricated according to the mechanism of walking. The pavement is tested in terms of voltage generation in different arrangements. The results show that in order to harvest the optimum energy of walking, the piezoelectric sensors need to be covered with a conductive layer such as a steel sheet. Also, it is found that covering the piezoelectric materials with a hard surface leads to load distribution over the sensors when stepping on it which subsequently, generates more voltage. Moreover, when the piezoelectric pieces are placed in an alternative arrangement, more voltage is generated. It can be concluded that the arrangement of the piezoelectric sensors and their connection to the conductive layer are important factors in harvesting the optimum walking energy. The study recommends that pavement equipped with piezoelectric material is a promising method to generate electricity when implemented in crowded areas.     

A Gibbs‐energy‐barrier‐based computational micro‐sphere model for the simulation of martensitic phase‐transformations

We introduce a material model for the simulation of polycrystalline materials undergoing solid‐to‐solid phase‐transformations. As a basis, we present a scalar‐valued phase‐transformation model where a Helmholtz free energy function depending on volumetric and deviatoric strain measures is assigned to each phase. The analysis of the related overall Gibbs energy density allows for the calculation of energy barriers. With these quantities at hand, we use a statistical‐physics‐based approach to determine the resulting evolution of volume fractions. Though the model facilitates to take into account an arbitrary number of solid phases of the underlying material, we restrict this work to the simulation of phase‐transformations between an austenitic parent phase and a martensitic tension and compression phase. The scalar model is embedded into a computational micro‐sphere formulation in view of the simulation of three‐dimensional boundary value problems. The final modelling approach necessary for macroscopic simulations is accomplished by a finite element formulation, where the local material behaviour at each integration point is governed by the response of the micro‐sphere model.Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of annealing on the fracture behavior of La0.58Sr0.4Co0.8Fe0.2O3‐δ, a potential energy material for oxygen separation

The perovskite material La_0.58Sr_0.4Co_0.8Fe_0.2O_3‐δ, offers high oxygen permeability at elevated temperature and is considered as a potential material for oxygen separation membranes. It can enhance the efficiency of oxy‐fuel combustion at high temperatures (> 800 °C) and hence due to the high reliability demands, required by the long term operation at elevated temperatures, it requires a thorough investigation from the view point of structural stability. Aiming towards long term stability, the present work is a detailed and systematic study on the effect of annealing on the mechanical behavior of dense La_0.58Sr_0.4Co_0.8Fe_0.2O_3‐δ. The study reveals that the indentation fracture toughness of the material increases with increase in annealing temperature. In most of the indentation loads, the subsurface crack profile was Palmqvist in nature with low value of the ratio of crack length versus indentation size (c/a). A consistent pattern of variation of c/a and indentation fracture toughness (K_IC) at all indentation loads was observed. Systematic drop in c/a and subsequent increase in fracture toughness in the as prepared test pieces has been attributed to residual stress accumulation during preparation.     

High‐Density Microfluidic Particle‐Cluster‐Array Device for Parallel and Dynamic Study of Interaction between Engineered Particles

A high‐density and high‐performance microfluidic particle‐cluster‐array device utilizing a novel hydrodynamically tunable pneumatic valve (HTPV) is reported for parallel and dynamic monitoring of the interactions taking place in particle clusters. The key concept involves passive operation of the HTPV through elastic deformation of a thin membrane using only the hydrodynamic force inherent in microchannel flows. This unique feature allows the discrete and high‐density (≈30 HTPVs mm^?2) arrangement of numerous HTPVs in a microfluidic channel without any pneumatic connection. In addition, the HTPV achieves high‐performance clustering (≈92%) of three different particles in an array format through the optimization of key design and operating parameters. Finally, a contamination‐free, parallel, and dynamic biochemical analysis strategy is proposed, which employs a simple one‐inlet–one‐outlet device operated by the effective combination of several techniques, including particle clustering, the interactions between engineered particles, two‐phase partitioning and dehydration control of aqueous plugs, and shape/color‐based particle identification.     

Rational Design of Carbon‐Rich Materials for Energy Storage and Conversion

Carbon‐rich materials have drawn tremendous attention toward a wide spectrum of energy applications due to their superior electronic mobility, good mechanical strength, ultrahigh surface area, and more importantly, abundant diversity in structure and components. Herein, rationally designed and bottom‐up constructed carbon‐rich materials for energy storage and conversion are discussed. The fundamental design principles are itemized for the targeted preparation of carbon‐rich materials and the latest remarkable advances are summarized in terms of emerging dimensions including sp² carbon fragment manipulation, pore structure modulation, topological defect engineering, heteroatom incorporation, and edge chemical regulation. In this respect, the corresponding structure–property relationships of the resultant carbon‐rich materials are comprehensively discussed. Finally, critical perspectives on future challenges of carbon‐rich materials are presented. The progress highlighted here will provide meaningful guidance on the precise design and targeted synthesis of carbon‐rich materials, which are of critical importance for the achievement of performance characteristics highly desirable for urgent energy deployment.     

Design Principles of Functional Polymer Separators for High‐Energy,Metal‐Based Batteries

Next‐generation rechargeable batteries that offer high energy density, efficiency, and reversibility rely on cell configurations that enable synergistic operations of individual components. They must also address multiple emerging challenges,which include electrochemical stability, transport efficiency, safety, and active material loss. The perspective of this Review is that rational design of the polymeric separator, which is used widely in rechargeable batteries, provides a rich set of opportunities for new innovations that should enable batteries to meet many of these needs. This perspective is different from the conventional view of the polymer separator as an inert/passive unit in a battery, which has the sole function to prevent direct contact between electrically conductivecomponents that form the battery anode and cathode. Polymer separators, which serve as the core component in a battery, bridge the electrodes and the electrolyte with a large surface contact that can be utilized to apply desirable functions. This Review focuses specifically on recent advances in polymer separator systems, with a detailed analysis of several embedded functional agents that are incorporated to improve mechanical robustness, regulate ion and mass transport, and retard flammability. The discussion is also extended to new composite separator concepts that are designated traditionally as polymer/gel electrolytes.     

Conservation properties of a time FE method—part II: Time‐stepping schemes for non‐linear elastodynamics

In the present paper one‐step implicit integration algorithms for non‐linear elastodynamics are developed. The discretization process rests on Galerkin methods in space and time. In particular, the continuous Galerkin method applied to the Hamiltonian formulation of semidiscrete non‐linear elastodynamics lies at the heart of the time‐stepping schemes. Algorithmic conservation of energy and angular momentum are shown to be closely related to quadrature formulas that are required for the calculation of time integrals. We newly introduce the ‘assumed strain method in time’ which enables the design of energy–momentum conserving schemes and which can be interpreted as temporal counterpart of the well‐established assumed strain method for finite elements in space. The numerical examples deal with quasi‐rigid motion as well as large‐strain motion. Copyright © 2001 John Wiley & Sons, Ltd.     

Design and Fabrication of a Hierarchically Structured Scaffold for Tendon‐to‐Bone Repair

A hierarchically structured scaffold is designed and fabricated for facilitating tendon‐to‐bone repair. The scaffold is composed of three regions with distinct functions: (i) an array of channels to guide the in‐growth of cells and aligned deposition of collagen fibers, as well as integration of the scaffold with the tendon side, (ii) a region with a gradient in mineral composition to facilitate stress transfer between tendon and bone, and (iii) a mineralized inverse opal region to promote the integration of the scaffold with the underlying bone. Cell culture experiments confirm that adipose‐derived stromal cells are able to infiltrate and proliferate through the entire thickness of the scaffold without compromised cell viability. The seeded stem cells exhibit directed differentiation into tenocytes and osteoblasts along the mineral gradient as a response to the gradient in Young's modulus. This novel scaffold holds great promise to promote the formation of a functional tendon‐to‐bone attachment by offering a structurally and compositionally appropriate microenvironment for healing.     

Design of Architectures and Materials in In‐Plane Micro‐supercapacitors: Current Status and Future Challenges

The rapid development of integrated electronics and the boom in miniaturized and portable devices have increased the demand for miniaturized and on‐chip energy storage units. Currently thin‐film batteries or microsized batteries are commercially available for miniaturized devices. However, they still suffer from several limitations, such as short lifetime, low power density, and complex architecture, which limit their integration. Supercapacitors can surmount all these limitations. Particularly for micro‐supercapacitors with planar architectures, due to their unique design of the in‐plane electrode finger arrays, they possess the merits of easy fabrication and integration into on‐chip miniaturized electronics. Here, the focus is on the different strategies to design electrode finger arrays and the material engineering of in‐plane micro‐supercapacitors. It is expected that the advances in micro‐supercapacitors with in‐plane architectures will offer new opportunities for the miniaturization and integration of energy‐storage units for portable devices and on‐chip electronics.     

Oxygen‐Vacancy and Surface Modulation of Ultrathin Nickel Cobaltite Nanosheets as a High‐Energy Cathode for Advanced Zn‐Ion Batteries

The development of high‐capacity, Earth‐abundant, and stable cathode materials for robust aqueous Zn‐ion batteries is an ongoing challenge. Herein, ultrathin nickel cobaltite (NiCo₂O₄) nanosheets with enriched oxygen vacancies and surface phosphate ions (P–NiCo₂O_4‐x) are reported as a new high‐energy‐density cathode material for rechargeable Zn‐ion batteries. The oxygen‐vacancy and surface phosphate‐ion modulation are achieved by annealing the pristine NiCo₂O₄ nanosheets using a simple phosphating process. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized P–NiCo₂O_4‐x nanosheet electrode delivers remarkable capacity (309.2 mAh g^?1 at 6.0 A g^?1) and extraordinary rate performance (64% capacity retention at 60.4 A g^?1). Moreover, based on the P–NiCo₂O_4‐x cathode, our fabricated P–NiCo₂O_4‐x//Zn battery presents an impressive specific capacity of 361.3 mAh g^?1 at the high current density of 3.0 A g^?1 in an alkaline electrolyte. Furthermore, extremely high energy density (616.5 Wh kg^?1) and power density (30.2 kW kg^?1) are also achieved, which outperforms most of the previously reported aqueous Zn‐ion batteries. This ultrafast and high‐energy aqueous Zn‐ion battery is promising for widespread application to electric vehicles and intelligent devices.     

Temperature dependence of material length scale for strain gradient plasticity and its effect on near‐tip opening displacement

This paper investigates the temperature dependence of the material length scale in the conventional mechanism‐based strain gradient (CMSG) plasticity theory. The work reported here also examines the plastic strain gradient effect on the opening displacement near a sharp crack tip. The study examines the mechanical properties of two typical structural steels (S355 and S690) in onshore and offshore structures at two different temperatures (20 and 300 °C) through both the uniaxial tension test and the indentation test. The CMSG‐based finite element analysis then confirms a constant material length scale for these two steels at the two tested temperatures, despite the apparent temperature dependence of the macroscopic material parameters measured from the tension test. Using the calibrated material length scale, the subsequent numerical study demonstrates that the magnitude of the near‐tip crack opening displacement computed by the CMSG theory remains significantly lower than that computed from the classical plasticity.     

High‐Performance Al/PDMS TENG with Novel Complex Morphology of Two‐Height Microneedles Array for High‐Sensitivity Force‐Sensor and Self‐Powered Application

Triboelectric nanogenerators (TENGs) are widely applied to self‐powered devices and force sensors. TENGs consist of the electrode‐layer frequently made of high‐cost conductors (Ag, Au, ITO) and the tribo‐layer of rigid negative‐triboelectricity fluoropolymers (PTFE, FEP). The surface morpholoy is studied for enhancing performance. Here, a high‐performance Al/PDMS‐TENG is proposed with a complex morphology of overlapped deep two‐height microneedles (OL‐DTH‐MN) fabricated by the integrated process of low‐cost CO₂ laser ablation and PDMS casting for self‐powered devices and high‐sensitivity force/pressure sensors. The high open‐circuit voltage and short‐circuit current of the OL‐DTH‐MN‐TENG are 167 V and 129.3 µA. Also, the sensitivity of the force/pressure sensor of the OL‐DTH‐MN‐TENG is very high, 1.03 V N^?1 and about 3.11 V kPa^?1, at an area of 30 cm² that is much higher than the sensitivity of about 0.18–0.414 V N^?1 and 0.013–0.29 V kPa^?1 of conventional TENG sensors. Meanwhile, the high‐performance OL‐DTH‐MN‐TENG not only exhibits the energy storage capability of charging a 0.1 µF capacitor to 2.75 V at 1.19 s, to maximum 3.22 V, but also activates various self‐powered devices including lighting colorful 226 LEDs connected in series, the “2020‐ME‐NCKU” advertising board, a calculator and a temperature sensor. Numerical simulation is also performed to support the experiments.     

Suppressing Cation Migration and Reducing Particle Cracks in a Layered Fe‐Based Cathode for Advanced Sodium‐Ion Batteries

Sodium‐ion batteries have huge potential in large‐scale energy storage applications. Layered Fe‐based oxides are one of the desirable cathode materials due to abundance in the earth crust and high activity in electrochemical processes. However, Fe‐ion migration to Na layers is one of the major hurdles leading to irreversible structural degradation. Herein, it is revealed that distinct Fe‐ion migration in cycling NaFeO₂ (NFO) should be mainly responsible for the strong local lattice strain and resulting particle cracks, all of which results in the deterioration of electrochemical performance. More importantly, a strategy of Ru doping could effectively suppress the Fe‐ion migration and then reduce the local lattice strain and the particle cracks, finally to greatly enhance the sodium storage performance. Atomic‐scale characterization shows that NFO electrode after cycling presents the intense lattice strain locally, accompanied by the remarkable particle cracks. Whereas, Ru‐doped NFO electrode maintains the well‐ordered layered structure by inhibiting the Fe–O distortion, so as to eliminate the resulting side effect. As a result, Ru‐doped NFO could greatly improve the comprehensive electrochemical performance by delivering a reversible capacity of 120 mA h g^?1, about 80% capacity retention after 100 cycles. The findings provide new insights for designing high‐performance electrodes for sodium‐ion batteries.     

Strongly Coupled Interfaces between a Heterogeneous Carbon Host and a Sulfur‐Containing Guest for Highly Stable Lithium‐Sulfur Batteries: Mechanistic Insight into Capacity Degradation

The use of conductive frameworks as the host scaffold to obtain nanostructured sulfur cathodes is an efficient way to increase the sulfur utilization for redox reaction in Li‐S batteries with large discharge capacity and high energy density. However, due to dynamical interfaces driven by phase evolution between the conductive hosts and S‐containing guests during cycling, the cathode still faces poor stability. Herein, the use of O‐/N‐containing nanocarbon as the conductive host sheds a light on the role of the dynamic interface between the carbon host and S‐containing guest for a stable Li‐S cell. The outstanding reversibility and stability of N‐doped C/S cathodes are attributed to the favorable guest‐host interaction at the electron‐modified interface, manifesting as (i) a chemical gradient to adsorb polar polysulfides and (ii) ameliorative deposition and recharging of Li₂S on the region of electron‐rich pyridinic N and a graphene domain surrounding quaternary N. Highly reversible, efficient and stable Li storage properties such as mitigated polarization and charge barrier, high capacity of 1370 and 964 mAh g⁻¹ at 0.1 and 1.0 C, respectively, and 70% of capacity retention after 200 cycles are achieved. Mechanistic insight into the capacity fading inspires the rational design on electrodes for high‐performance electrochemical systems.