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In the past few years, different kinds of structural nonlinearities, such as external magnetic interaction and multistable structures, have been introduced into galloping energy harvesters to enhance energy harvesting efficiency. However, since the galloping-based piezoelectric energy harvester (GPEH) is a self-excited system, the conventional impedance matching method that is widely used in vibration energy harvesters is no longer valid for it. Therefore, the power characteristics of the nonlinear GPEH are still an open question to be solved. To this end, this paper is motivated to derive the approximate analytical solution of a monostable galloping-based piezoelectric energy harvester through the harmonic balance method and impedance matching theory. The analytical maximum power, power limit, and critical electromechanical coupling are studied from the perspective of the influence of structural nonlinearity on the power performance. Firstly, the approximate analytical solutions of output power, power limit, optimal resistance, and critical electromechanical coupling coefficient are derived. The accuracy of the analytical solution is verified by numerical simulation. It is found that the influence of structural nonlinearity on the power characteristics of the nonlinear GPEH is quite different under different wind speeds. After that, the power characteristics of the system under different wind speeds and different coupling conditions are investigated. The results showed that the maximum power of the system can be increased by introducing stiffness nonlinearity under low wind speed and weakly coupled configuration. Even more, the system can be shifted into a strongly coupled system when the nonlinearity is enhanced to a certain level. Reasonable design of stiffness nonlinearity can effectively reduce the critical electromechanical coupling, which indicates that stiffness nonlinearity is a feasible and effective way to improve the power performance of low-speed wind energy harvesting. [ABSTRACT FROM AUTHOR]

A series of Cu-doped layered P2-type Na0.67 Ni0.33-x CuxMn0.67O2 ( x = 0, 0. 05, 0. 10, 0. 15, 0. 20, 0. 25) with regular morphology and smooth surface were synthisized by sol-gel method. The morphology, structure and composition of those materials were characterized using SEM, XRD, EDS and XPS technologies, and their electrochemical properties were investigated by cyclic voltammetry and constant current charge-discharge methods through using them as cathode materials for sodium ion batteries. The optimum doping ratio was obtained. It is found that doping did not change the layered structure and morphology of the materials. Those materials exhibit good cycling stability and multiplicative performance due to the introduction of highly electrochemically active Cu2+ as a substituent and the increase of the surface active sodium storage sites. In the voltage range of 2. 0 V to 4. 3 V and a multiplicity of 0. 1 C, the initial discharge specific capacity of Na0.67Ni0.18Cu Ni0.15Mn Ni0.67O2(with Cu doped ratio of 0. 15) has an initial discharge specific capacity of 126. 74 mAh / g and a capacity retention rate of 79. 10% after 100 cycles, which is 50. 92% higher than that of the undoped material. The enhanced electrochemical properties of the material are attributed to the insertion of Cu2+ into the transition metal layer, and the radius of Cu2+(0. 73 Å) is larger than that of Ni2+(0. 69 Å), which widens the transition metal layer spacing and provides channels for Na+ diffusion, and in turn increases the Na+ diffusion rate. When charged to high voltage, the Na+ vacancy generation during Na+ de/embedding process is inhibited, thus the crystal structure of the material is stabilized, the P2-O2 phase transition is suppressed, and the cycling stability is improved. [ABSTRACT FROM AUTHOR]

During the past decade, metamaterial-based vibration energy harvesters (meta-VEHs) have been increasingly developed owing to the extraordinary characteristics of metamaterials, such as locally resonant bandgap, defect state, and wave focusing features. In this paper, the interface state, a feature recently found in topological metamaterials, is exploited for low-frequency vibration energy harvesting. The topological meta-VEH consists of two kinds of locally resonant metamaterials with different topological phases and a piezoelectric transducer being installed at the interface between these two metamaterials. First, the governing equations of the topological meta-VEH are established based on the mass–spring model. Subsequently, the dispersion relation of such a one-dimensional topological meta-VEH is obtained by applying Bloch's theorem. It is revealed that the interface mode can be attained in the low-frequency range through the band folding of the locally resonant metamaterial. Moreover, the finitely long model of this topological meta-VEH is built, and the transmittance response is calculated both analytically and numerically. Subsequently, the potential benefits of topological metamaterial, including wave localization and topological protection, are thoroughly investigated. It is found that the elastic energy in the interface state is localized at the interface position, resulting in a significant improvement in output power. Meanwhile, the topological protection property can significantly improve the robustness of the interface mode, thus achieving outstanding energy harvesting performance. Finally, to further enhance the energy harvesting performance, the stiffness tuning method and the defect enhancement method are proposed. It is found that integrating the defect mode and interface mode not only improves the output voltage but also achieves the capability of a highly robust energy harvesting. [ABSTRACT FROM AUTHOR]

Surface and lithium diffusion properties of Si(100) doped with B and P are studied using first‐principles plane wave pseudopotential method. The calculated results show that B‐doping has a greater effect on Si(100)‐7 than P‐doping. For 0.5 mol% P‐doping, the population difference between Si5─P bonds and Si5─Si3 bonds is 0.02. For 0.5 mol% B doping, the bond population of Si5─B is 1.8 times that of Si5─Si3 and the structure fluctuates greatly. The migration of a single Li atom from V and B sites on the structure's surface to an orthotetrahedral site inside the structure is simulated. Simulation results show that with the increase of P doping concentration from 0 to 1.0 mol%, the Li diffusion rate is ordered as 0.5 mol% < 0 mol% < 1.0 mol%. Furthermore, the ab initio molecular dynamics method is used to simulate the diffusion of multiple Li atoms in P‐doped Si(100)‐7. When the simulation time is longer than 0.09 ps, the Li diffusion rate is ordered as 0.5 mol% < 0 mol% < 1.0 mol%. Doping Si(100) surface with P could effectively reduce the diffusion barrier for Li atoms in it. [ABSTRACT FROM AUTHOR]

This article presents a theoretical study of a tunable metamaterial beam for low-frequency broadband vibration suppression. First, the mechanism of employing the shunt circuit technique to realize the internal coupling between two adjacent local resonators is introduced. The working principle of the proposed metamaterial beam by integrating the shunt circuit technique is demonstrated. The stability of the proposed metamaterial beam is then analysed, and the corresponding criterion is proposed. Subsequently, analytical models of the proposed metamaterial beam are developed. The band structures and the transmittances are calculated. The analytical study demonstrates the generation of multiple band gaps using a shunt negative capacitance circuit, which is equivalent to a coupling spring. A parametric study is conducted to investigate the effect of the equivalent coupling stiffness on the band gaps and the corresponding suppression regions. It is found that the band gaps are controllable by varying the equivalent coupling stiffness. Finally, to verify the analytical solutions, a finite-element model of the proposed metamaterial beam is developed. The simulation results confirm the existence of multiple band gaps, which are tunable through modification of the negative capacitance. The broadband vibration-suppression ability of the proposed metamaterial beam is thus confirmed. [ABSTRACT FROM AUTHOR]