Strongly coupled piezoelectric energy harvesters: Finite element modelling and experimental validation

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordPiezoelectric energy harvesters (PEHs) are usually connected to a load resistor matching to the impedance of their internal capacitance to characterise the power generation during transducer design and optimisation. For strongly-coupled PEHs operating near resonance, this simple RC matching method underestimates the power output and fails to characterise the dual power peaks but are still often used in both simulation and experiment. This study analysed the internal impedance network and the power output characteristics of PEHs. Based on the analysis, a novel and efficient finite element model (FEM) for strongly coupled PEHs was developed and applied to a pre-stressed piezoelectric stack energy harvester (PSEH). A stationary analysis was first performed to simulate the pre-stressed state of the PSEH. The FEM then analysed the internal impedance of the pre-stressed PSEH, which was used as the optimal load resistance to simulate the electric power output. The simulated internal impedance and electric power output of the PSEH were validated by the experiment with good agreement. The FEM developed precisely predicted the electric power output, including the two identical power peaks, of the strongly coupled PSEH operating near resonance and outside resonance. In contrast, the FEM with the traditional RC matching showed only one power peak and significantly underestimated the power output near resonance, although it was still valid outside resonance. The developed FEM was also able to predict the effects of the static pre-stress and coupling efficiency figure of merit on the PSEH. The coupling efficiency figure of merit was found to increase the power output.Engineering and Physical Sciences Research Council (EPSRC

Self-powered and Self-configurable Active Rectifier Using Low Voltage Controller for Wide Output Range Energy Harvesters

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordData availability: All data are provided in full in the results section of this paper.This paper presents a self-configurable and selfpowered active rectifier that operates from 0.25–20 V for energy harvesting applications. The proposed circuit self-startups from a low voltage using a charge pump and amplifies the voltage with a voltage doubler (VD) topology to provide succeeding circuits such as boost converters with a higher voltage. When the voltage of the energy harvester reaches a high threshold, the circuit switches its topology to a full-wave rectifier (FR) that does not amplify the voltage. The start-up circuit can limit its voltage intake to prevent boosting the high voltage, which may damage the whole circuit. Comparators with a maximum operating voltage of 5.5 V used in the implementation of the rectifier are protected by a diode and resistor based circuit. A piezoelectric energy harvester (PEH) that has a wide open-circuit voltage of 0.4–15 V under the acceleration of 0.04–0.3 g was used to test the circuit. The experiment results showed the rectifier can startup from 0.25 V and switch its topology according to the PEH voltage. The voltage and power conversion efficiencies are over 90% in most cases.Engineering and Physical Sciences Research Council (EPSRC)Royal Societ

Development of an extrudable paste to build mycelium-bound composites

Mycelium-bound composites are promising materials for sustainable packaging, insulation, fashion, and architecture. However, moulding is the main fabrication process explored to date, strongly limiting the ability to design the complex shapes that could widen the range of applications. Extrusion is a facile and low energy-cost process that has not yet been explored for mycelium-bound composites with design freedom and structural properties. In this study, we combine cheap, easily and commonly available agricultural waste materials, bamboo microfibres, chitosan, and mycelium from Ganodermalucidum, to establish a composite mixture that is workable, extrudable and buildable. We study the impact of bamboo fibre size, chitosan concentration, pH and weight ratio of bamboo to chitosan to determine the optimum growth condition for the mycelium as well as high mechanical stiffness. The resulting materials have thus low energy costs, are sustainable and can be shaped easily. The developed composition is promising to further explore the use of mycelium-bound materials for structural applications using agricultural waste

Effect of calcination temperature on electrical properties of Nd0.7Ba0.3MnO3

In this work, Nd0.7Ba0.3MnO3 was synthesized via cryo-milling method to investigate the effect of calcination temperature on the structure, microstructure, magnetic and electrical properties. XRD analysis revealed all samples can be indexed to orthorhombic structure systems with Imma space group accompany with some minor phases of Mn2O4 and BaMnO3. FESEM analysis confirmed that a slight increase in the grain size from 117.4 nm (600°C), 119.5 nm (700°C), 121.0 nm (800°C), 123.1 nm (900°C) to 138.4 nm (1000°C) was observed when different calcination temperature was applied. Four Point Probe measurements showed that all samples are in paramagnetic insulating region and TMIT is lower than 20K. Resistivity increase when grain size reduces due to increase of effective grain boundary that weakens the electron hopping process via double exchange mechanism. Beside, a drastic increase of resistivity also observed due to present of minor secondary phase (BaMnO3) in sample C9

Magnetic Field Effect in Josephson tunneling between d-Wave Superconductors

The magnetic field effect in the Josephson tunneling between two d-wave superconductors are investigated. When the crystal orientation of one (or each) superconductor relative to the interface normal is such that midgap states exist at the interface, there is a component of the tunneling current due to the midgap states. For a junction with a flat {001}|{110} or {100}|{110} interface, this component is the predominant contribution to the current. The predicted current-field dependence differs entirely from the conventional Fraunhofer pattern, in agreement with a published measurement. This is because, apart from the Fraunhofer factor, the critical current depends on the magnetic field B through the current density also which is a linear function of B for weak B.Comment: 5 pages, 2 figure

A Study of Perturbations in Structure and Elastic Modulus of Bone Microconstituents Using Bimodal Amplitude Modulated-Frequency Modulated Atomic Force Microscopy

This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in ACS Biomaterials Science and Engineering , copyright © American Chemical Society after peer review. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acsbiomaterials.8b01087The authors thank the financial support by National University of Singapore through the Eng-Med Seed Grant (R-265-000-532- 112) and Ministry of Education, Singapore, through National University of Singapore on Academic Research Funding (AcRF) R-265-000-495-112. Y.S. thanks the support of research scholarship from National University of Singapore